What initially rolls the trike wing and what creates billow shift/washout/twist change. Five fundamental forces/moments

Published by: Paul Hamilton on 20th Jan 2017 | View all blogs by Paul Hamilton

 

There is plenty of speculation about what "initially" rolls the wing and creates billow shift/washout/twist change. We tend to focus on only a few and there are five fundamental forces. Three that help and two that do not. Note there are many more but here are the five  that are the greatest contributors.  We will look at these FORCES individually to get a basic understanding.  We are going to ignore the anhedral/dihedral and roll coupling because it complicates matters and we are looking at the FORCES and resultant MOMENTS that initially roll the wing.

 

 Forces helping us to roll:

 

1. As the weight is shifted to one side that weight shift moves the center of gravity to one side creating a moment rolling the wing. Gravity pulling down on the weight of the carriage and lift pulling up on the wing. As an example we will say the bar is moved 6 inches with a 1000 pound carriage to get 6000 inch pound rolling moment on the wing simply from weight shift. Let's call this "1 WEIGHT MOMENT" for short. This is the most straight forward and easiest to understand.

 

2. As the weight is moved over, it loads up the wing which creates uneven loading on the heavier wing side and the flexibility of the wing of the loaded side creates more billow shift/washout/twist change. Let's call this "2 WING LOADING ROLL" for short.

 

3. As we rotate the wing at an angle the weight can be broken down into two components, a component perpendicular to the wing and a side component . This can most easily be seen in this diagram. Let's call this "3 KEEL PULL" for short.

 

 

 

Note for this example the side load is 350 pounds pulling the keel to the side from basic gravity creating billow shift/washout/twist change. Note this force starts with any movement of the bar/shifting of the weight. One degree is 17 pounds and 30 degrees is 577 pounds. This is a huge force pulling that keel to the side starting billow shift/washout/twist change initially with the movement of the bar starting a turn.

 

We have all these factors helping us turn. The big question is how much does each of these three specific forces effect the turn. We will cover this later but they are different for every wing.

 

We have two specific forces working against us for rolling.  Both work against airplanes the same as trikes. We will number them consecutively since we are forces

 

Factors hurting is from rolling

 

4 MASS. Newton's laws of motion. Back to the basics for review:

 

Newton’s Basic Laws of Motion

 

Newton’s First Law: “Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.” This means that nothing starts or stops moving until some outside force causes it to do so. An aircraft at rest on the ramp remains at rest unless a force strong enough to overcome its inertia is applied. Once it is moving, its inertia keeps it moving, subject to the various other forces acting on it.

 

Newton’s Second Law: “Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.” When a body is acted upon by a constant force, its resulting acceleration is inversely proportional to the mass of the body and is directly proportional to the applied force. This takes into account the factors involved in overcoming Newton’s First Law. It covers both changes in direction and speed, including starting up from rest (positive acceleration) and coming to a stop (negative acceleration or deceleration).

 

Newton’s Third Law: “For every action, there is an equal and opposite reaction.”

 

In triking, we have this 100 pound (more or less), 32 feet (more or less) wing above us that must be moved. This is a pretty formidable force which many ignore. Take a 32 foot long pole weighing 100 pounds and try to roll it 30 degrees in 4 seconds. Takes allot of force/effort, more than you would think.

 

5 ROLL DAMPENING

 

Here is a new one for some. As we roll, the wing going down sees a greater angle of attack than the side going up which creates  a lower angle of attack, thus this slows down the rolling. However, the billow shift/washout/twist change relieves this roll dampening by reducing the angle of the airfoil on the down going tip and increasing the angle on the up going tip. Again how much billow shift/washout/twist change is a question which we will cover later. First an example to look at the actual roll dampening angle of attack increase for a rigid wing or trike with no billow shift/washout/twist change :

 

In a steady state start to finish, 50 MPH airspeed, 4 seconds to roll from level to 30 degree bank, with no billow shift (stiff wing), how many degrees is the angle of attack increased from the lowering wing with a 32 foot wingspan?

 

Lets use 50 MPH (70 FPS feet per second) for this. First we need to figure out how fast your tip is going down.
Your tip is 15 feet out and with a 30 degree bank it travels about 9 feet (8 in an arc) in an arc as it drops. So it is dropping at about 2 foot/sec.
So as it drops 2 FPS into 70 FPS air the change in angle is about 1.5 degrees. Again note this does not have any billow shift/washout/twist change. Stiff wing.

 

With a stiff wing and no billow shift/washout/twist change how much force out on that tip is that?

 

If we have a rigid wing with no twist and the desired roll rate adds 1.5 degrees of angle of attack on the wing about 15 feet out on the tip what is the force of 1.5 degrees additional angle of attack? Some basic math produces a force of 75 pounds. Calculating a moment for this we can compare to the weight shift moment we calculated above: 12 feet out for a moment of 10800 inch pounds. Note this is significantly more than the 6000 foot moment for the "1 weight moment" alone.

 

So we know that with no billow shift/washout/twist change, considering ONLY weight shift and roll dampening ONLY,  it is going to be much longer than 4 seconds. Almost twice as long. Note this is ONLY 2 of the 5 total forces for initial rolling. Add force "4 MASS" makes it harder/longer and "2 WING LOADING ROLL" and 3 KEEL PULL" make it easier with billow shift/washout/twist change.

 

To summarize,  we now have 3 forces helping is roll 1 WEIGHT MOMENT, 2 WING LOADING ROLL and 3 KEEL PULL. Note that 2 WING LOADING ROLL and 3 KEEL PULL BOTH create billow shift/washout/twist change.  We have both 1 MASS and 2 ROLL DAMPENING slowing/not helping roll.

 

Quite the mix of forces/factors. All of these forces come into play as the bar is moved to initiate a turn. Yes some believe that as the wing starts to drop and the rushing up air  helps billow shift/washout/twist change however this may or may not be is a secondary effect which is a result of the primary forces.

 

Which ones are more influential. Two of the four are pretty much the same for all similar wings, the 1 WEIGHT MOMENT help,  and the 4 MASS moment hurt. All others 2 WING LOADING ROLL, 3 KEEL PULL and 5 ROLL DAMPENING are effected by  billow shift/washout/twist change. It should be noted that the force from the 2 WING LOADING and 3 KEEL pull is the same but the effect with billow change/washout/twist change is different.

 

Why do some wings roll faster than others? Because the 2 WING LOADING ROLL , 3 KEEL PULL and "EFFECTIVE" 5 ROLL DAMPENING are effected by  billow shift/washout/twist change.

 

Faster rolling wings have more billow shift/washout/twist change. Slower rolling wings have less.

 

A rigid wing will not roll fast enough to be flown safely with 1 WEIGHT MOMENT force alone so billow shift/washout/twist change is needed. Again how much billow shift/washout/twist change is accomplished when the weight is shifted depends on the specific wing. Each wing is different.

 

So how much does the billow shift/washout/twist change in a turn, the following video shows plus and minus 6 degrees at the tip with one of the fastest rolling wings in the world.

 http://www.trikepilot.com/videos/view/washout-twist-change-test-verification_25106.html

 

 

So we know we only need 1.5 degrees to overcome the roll dampening to at least get the lift on each wing tip equal. We are getting 6 degrees in the above video for the fastest turning wing abruptly turning 45 to 45 degree turns. From this measured look at twist change for this wing that probable was one of the highest billow shift/washout/twist change, a good approximation for maximum twist change is 6 degrees plus and 6 degrees minus. Most other wings/situations will be probably be less. We can also see that it does not take much billow shift/washout/twist change to overcome the 1.5 of 6 degrees   "5 ROLL DAMPENING" force.

 

I would assume most wings are able to overcome this roll dampening force to provide less lift on the down going wing to roll fast enough to fly safely under the pilots control.  This is the magic of the FLEX wing.

 

This is a diagram showing the lift distribution of the wing in a turn with the twist greater than the 1.5 degrees needed to overcome the roll dampening

 

 

 

 

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Comments

102 Comments

  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    I'll bet this turns into another long one, Paul! There is much that could be discussed in what you've written above. To get the ball rolling:

    What about the effect of adverse yaw on roll?

    Do you consider the wing halves to be defined across at the geometric centre, or across the keel? In other words, is the upgoing wing bigger than the downgoing wing, or are they the same size?

    Three variables that come into play as the wing rolls are angle of incidence, angle of attack and lift. The same angle of attack at different angles of incidence will produce different lift and drag vectors on each wing, etc etc.

    Round two, folks...
  • Joe Hockman
    by Joe Hockman 10 months ago
    Paul this certainly does appear to be more of a holistic view looking at the 5 forces you mentioned and I agree all do play a role in the roll force decomposition. Thanks for your effort on this. During my first time reading through I seemed to have failed to follow your logic but then I reread it and thought I picked up on an incongruency.

    I think that there was a jump in your logic progression that did not add up. I did not check all your math on forces but in your example of a fixed wing rolling to 30 deg over 4 sec at 50mph you came to a conclusion that this resulted in an additional 1.5 deg in AoA at the tip.

    Then at the end your wrote: "So we know we only need 1.5 degrees to overcome the roll dampening to at least get the lift on each wing tip equal. We are getting 6 degrees in the above video for the fastest turning wing abruptly turning 45 to 45 degree turns. From this measured look at twist change for this wing that probable was one of the highest billow shift/washout/twist change, a good approximation for maximum twist change is 6 degrees plus and 6 degrees minus. Most other wings/situations will be probably be less. We can also see that it does not take much billow shift/washout/twist change to overcome the 1.5 of 6 degrees   "5 ROLL DAMPENING" force."

    I guess I would contend that the 1.5 deg for fixed wing example cannot be compared directly with your estimated 6deg in your video. More of an apples to oranges comparison. Why, your fixed wing example stated rolling to 30deg over 4 seconds and you basically rolled to 45deg in about 1 sec. Furthermore, my guess is your were traveling more than 50mph. I think if you were to do the equivalent math on the fixed wing an increase of more than 6deg in AoA at the tip would be calculated on the fixed wing. Yes I know this would be a hypothetical since you suggested that a fixed wing can't roll that fast (or at least safely). In any case, if the Rival S is only changing 6deg at the tip (due to increased washout) what would make up the difference? I think it is the decreased AoA all along the midspad due to billow to relieve the roll torque dampening. There is no question in my mind that Larry has indeed come up with the design changes needed to enable very fast roll response and certainly rapid changes in twist/washout/billow shift are an integral part of that.
  • Joe Hockman
    by Joe Hockman 10 months ago
    The other aspect I mentioned on your "gravity" graphic is that this "keel pull" seems to be more relevant in a static picture. According to Newton's 3rd law we will have an equal and opposite reaction. And in this case I think the centrifugal force and the lateral force from changed relative wind angle are likely the 2 forces at play. When I went back to view Larry's Blue Devil video he used the perfect camera angle to assess this. Even when he did some abrupt 90deg rolls the pendulum seemed to track squarely in the middle of the control A frame. Centrifugal force begins immediately when a bank is initiated. I guess upshot for me is that the "keel pull" force is not as great as we seem to be suggesting here. I'm guessing that the billow inflation and billow shift due to changed relative wing angle may be more of the driving force to pull the keel over than the pendulum weight associated with the "keel pull" force. Others may view this differently and there certainly is a chance that I could be wrong about that. I think we could creatively devised some controlled experiments to test role of contributing factors.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    If Paul would have twisted the bar (push forward with left hand and pulled back with right) after initiating the right bank, the roll rate would have increased as much as 50% faster with that wing. Abid mentioned Steve wrote you can't billow shift in a vacuum, but in fact you can billow shift without weight shift so long as the sail is "inflated" by twisting the bar and forcing the keel shift. in other words if we take an inverted wing and then we fix the leading edges from moving and then measure the lowest point of the trailing edge of the sail to the floor, if I push the keel to one side I can make the sail change elevation both higher on one side and lower on the other side. And this concept is what seems to me missing from Steve's theory. So if it will accelerate his already fast roll by twisting the bar, what can we determine from that? is it just reduced dampening? or is aerodynamic induced roll?
  • Larry  Mednick
    by Larry Mednick 10 months ago
    I fully agree with the first part of Joes last post the centrifugal force changes the dynamics completely. Only if it were hanging static would the side load due to gravity work as described. regarding the second part, I am waiting to see if someone thinks the numbers don't add up in Pauls video, because it seems to me AOA is decreased on the descending wing in the video based on the change of 6 degrees at the tip in Pauls video. that should be the discussion right now. Abid? Paul D? well??
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    You can also billow shift in zero g. It's sometimes used in a last-ditch effort to avoid a tumble if you stall inverted... but that's another story :-)
  • jeff trike
    by jeff trike 10 months ago
    Good to know Bryan. I suppose you tried that in a hangglider?
    I'll keep that in mind the next time I find myself in that situation.
  • Lucian Bartosik
    by Lucian Bartosik 10 months ago
    Larry, twisting the control bar as you describe above, creates a torque on your hang channel and hang bolt and trike mast (or pylon upright) and if you start telling people such things and they go out and try it and find it is increasing their roll rate, they may start doing that all the time, then possibly at some point in the future, something may fail up there at the connection point or on the trike mast. Notice I used the word "May".

    I bet you did not give any consideration to what might be going on up there, when you start "twisting" as you put it, but better stated, yawing the wing/control bar, all around. And if you are going to say that you did think about what might be happening up there, then why did you not bother to mention it when describing your twist suggestion, as something to take into consideration as a possible safety concern, if continued?
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Lucian, REALLY???
  • Ted  Bailey
    by Ted Bailey 10 months ago
    Centrifugal forces and twisting the bar in a spiral dive you change the turn radius track more on it's side so part of the turn path is now past negative like a 110-120 degree wang by roll control instead of a pitch maneuver with the pull-up and over part. Not as much fun but still gets you upside down while pulling positive G. for that past 90 on the horizon camera shot.
  • Gary Crayne
    by Gary Crayne 10 months ago
    Paul, the video link has the wrong path...need to drop "members".
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Yes Joe an apples to oranges comparison. I used my first example of 1.5 degrees as a baseline for a normal roll. I did the video to figure the MAXIMUM twist change I could get which was accomplished. For the baseline I feel the Revo/Rival S is greater than 1.5 degrees twist change but that becomes much more difficult to measure.

    Yes Joe correct again. As we transition from the INITIAL wing tilt into the bank and we go from the initial wing tilt/yaw, the carriage catches up with the wing roll centrifugal force will start to reduce the KEEL PULL force. At the completion of the turn initiation, yaw correction, and continued roll/turn to get to the stabilized/desired bank when the side pressure is released the KEEL PULL will be back to ZERO for the stabilized turn. Note that this is labeled INITIAL all over the place. Not transition, not secondary, not final, not stabilized. Thanks for your observations.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Lucian,
    I end up flying in allot of turbulence. That wing and undercarriage torque more than I am comfortable with. The momentum of the carriage is going forward and the wing violently torques to the side. Sometimes for hours a day. Much more torque on that bracket/mast/keel than I like or could possibly put by torquing the control bar myself. So I do not follow your logic that torquing the control bar as Larry said is bad. In fact I could have added this as a force to help move that keel to assist with billow shift,washout/twist change. I do not see any problem with it......
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Thanks Cary Crayne,
    try
    http://www.trikepilot.com/videos/view/washout-twist-change-test-verification_25106.html
    I had a bugger of a time trying to embed the video in the article. It can also be found in the videos.
  • Lucian Bartosik
    by Lucian Bartosik 10 months ago
    Larry and Paul H,

    There are all sorts of things you can do to a trike either on the ground or in the air that it was not meant to have done to it. Twisting the bar is just one of them. Since the design is meant to be operated by forward and backward and sideways movement, it would be best to leave your intentional inputs to those that the design was meant to operate under. The wing has operating parameters, which we have discussed on this list, and yes many of us have taken our wings outside those limits and for that matter well outside those limits and nothing has happened. However, common sense should tell you that it is best not to exceed or operate outside of what the machine is meant to do. Yes twisting or yawing happens in the air during flight but that can't be helped. Willfully and forceful twisting or yawing of the wing against the trike unit can be helped and may or may not cause wear over time that may or may not one day cause some sort of failure.

    It is simply against common sense to suggest that intentional twisting of a connection point that is not designed to be moved in that manner, is a sensible thing to do. Just like 30 degrees of pitch up and down and 60 degrees of bank is the max the wing should be subjected to, we can go well beyond those limits but is that a smart thing to do?

    You can do what ever you want in the air but I would strongly recommend that we do not suggest on here, that other pilots do any of the things the wing was not really meant to have done to it, because you have no idea who may be reading what has been written here. And they may well think that this is a good and safe thing to do because a few high and long time posters have been saying "this is what I do and I think it is perfectly safe to do it". Instructors should be setting examples to other pilots and not be suggesting doing things to a wing that even though they can force it into, it was not designed or meant to have intentionally done to it.
  • Gregg Ludwig
    by Gregg Ludwig 10 months ago
    I'm with Paul Hamilton with the technique to apply a yaw input via the control bar. The amount of force a pilot can apply with a yaw input is almost nothing as a percentage of the strength of the trike wing attachment. The yaw input works very well in some situations, especially with a trike that has insufficient engine thrust offset.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    gees Gregg I was just going to say that in a different way...

    More details later. Another dinner/date sorry
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Gregg, it sounds like you've flown my trike. At cruise rpm and above it flies banked to the right and yawing to the left. It prefers left turns to right ones. All that constant yawing hasn't produced a structural failure so far... ;-)
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Bryan:
    Very simple fix. If your trike has wheel pants with vertical fins/stabilizers, make a trim tab from 0.050" sheet metal, bend it outward and use industrial strength double sticky tape and attach that towards the top of your left fin. Angle it as needed so at cruise trike flies much more straight.
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Abid, thanks, but we've gone one better. We've used RC servo motors to trim the tab for inflight adjustability. It's our copy of the Revolution roll trim. XT912VO!
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Good. But once you find the right angle it usually works for different speeds as long as wing tuning does not change. Enjoy responsibly :)
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Thanks again. :-)
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Lucian and Gregg,
    Probably the biggest normal stress on the keel/hang block/mast is during a cross wind takeoff. Especially if you accelerate a little faster in bumpy crosswind air before you rotate. If any one thinks the keel/hang block/mast will get fatigued based on turning the pilot turning the bar, cross wing takeoffs or turbulence then the manufacturer should probably beef up those items. I have not seen any warnings/safety alerts that say there is a problem with this.

    I think Larry's point about rotating the control bar to create billow shift/washout/ twist change to roll the trike without weight shift is valid. Not speaking for Larry, but since he is a manufacturer perhaps he has designed the trike to do this (probably not he just gets lucky some times), or did he to the twist technique and that super strong keel/hang block/mast on the Revo get that way for other reasons? Another chicken or the egg question.
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    First we'll done Paul for leading the analysis on this and the video work - I am not aware of any similar studies - so it could enhance understanding of the science and art of wing design for everyone.

    To pick at some threads it has thrown up though - The example of rolling 30 degrees in four seconds producing 1.5 degrees of angle of attack change is quite a different roll rate to the video where it seems to roll 45to 45 in 2 seconds. The first is 7.5 degrees /sec ( a roll rate so slow as to be not teally typical of general handling) the second is 45 degrees a second. So 6 times the roll rate. I haven't done the complicated math but on the face of it that is 1.5 x 6 = 9 degrees increase in angle of attack at the tip - if the speed was the same. So a 6 degree twist change means that the billowshift (at the tip at least) is lagging behind the increase of angle of attack due to rolling. And this with a particularly high billowshift wing - so most other wings will have a higher differential still.

    I am not entirely convinced of the sideways force calculation in the keel. It ignores any centripetal forces and doesn't account for inertia relief of the rolling wing. It would be very interesting to stick a camera inside the wing on the keel looking at the cross tube junction so we can see what actual movement is occurring. I have spent some time idly wondering about the movement and spent some time staring upwards whilst rolling too and fro and not been able to detect movement by eye at that vantage point.

    The adverse yaw thing is interesting to speculate on its effects, as is twisting the trike to promote it. I have some thoughts on why it may be working;

    1. Simple anhedral - lots of wings are rigged so they have anhedral at cruising incidence - and they are the fastest rolling types generally. The response to adverse yaw then produces a rolling moment the way we are trying to roll.

    2. Being yawed produces 'out of balance ' flight. Adverse yaw produces a sideways force where we feel like we are leaning into the turn - perfect for producing / enhancing that sideways keel movement and creating greater billowshift.

    3. Larry's explanation that it produces greater drag on the forward wing and this flexes the leading edge and produces more billow / twist on that side is a new thing to think about which I hadn't heard before but if it us the case then it will add to the overall anhedral effect of adverse yaw producing roll towards the forwards wing.
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    PS the comment in the video about the tip twist increasing as speed is increased being due to extra lift isn't quite right. I wouldn't mention it as it's unecessary nit picking for an otherwise great piece of work, but what was actually happening is interesting and may have some relevance to how the wing works - if we are not pitching up then overall lift stays the same as speed is increased and as the angle of attack is reduced to speed up due to washout the tip should actually be proportionally generating less lift.. but it did seem to be the case that the twist did increase - maybe this is Larry's leading edge flex back due to increasing drag in action? - albeit symmetrically in this case.
  • Lucian Bartosik
    by Lucian Bartosik 10 months ago
    Paul H. you wrote: " Not speaking for Larry, but since he is a manufacturer perhaps he has designed the trike to do this (probably not he just gets lucky some times), or did he to the twist technique and that super strong keel/hang block/mast on the Revo get that way for other reasons?"

    I understand that Larry is the manufacturer but to my knowledge he has no formal training, nor degree in Aeronautics nor Aeronautical engineering nor mechanical engineering. Design of his trike and wing is then expected to have been created by someone other than Larry. If Larry has done all the designing himself what knowledge base has he drawn on for that design work? Sometimes we need to look beyond the surface when speaking about a manufacturer and the design of a trike and wing because one is not always both manufacturer and designer.
  • Lucian Bartosik
    by Lucian Bartosik 10 months ago
    Paul H. wrote: "
    Probably the biggest normal stress on the keel/hang block/mast is during a cross wind takeoff."

    Well since the trike takes off in a matter of seconds and the real stress exerted up at that junction is only a portion of that time until it leaves the ground, I'm sure you will agree that the forces acting up there are the least amount of time from an entire flight. Now on the other hand, the willful twisting by the pilot during an entire flight is far, far more time spent twisting that point up there at the attachment point.

    Therefore in your assumption of the biggest normal stress period, you seem to have failed to take that into account because if you had. you would have to agree the total amount of seconds/minutes of such twisting during a flight would have to come from pilot induced movement rather than the few seconds of take off possible stress.

    You also wrote: " I have not seen any warnings/safety alerts [from the manufacturer] that say there is a problem with this. I have not seen any written warning regarding this either. Neither have I seen any written warnings or safety alerts about holding the tip of you wing when fitted to the trike, sitting on the ground and walking it around or twisting/rotating it about its connection point at the hang block/hang channel. And this might be because the manufacturer never expected the pilot to be doing such a thing, since you can't possibly fill a book with every possible thing an owner might do to his trike, that would not be good to do to it.

    On the same line of thought, I have never seen any training syllabus from before sport pilot or after it, through the FAA course that teaches a pilot to twist or yaw the control bar during flight, or maybe you can point me to where it discusses that since you are probably more familiar than anyone here with the FAA training syllabus. If it is not brought up, discussed, written down or taught, it might be because the FAA do not expect a pilot to do that or fly that way. What are your thoughts on that point?
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Lucian, do you work for the Feds? ;-)

    One day Wilbur didn't say to Orville, "you know bro, it looks pretty fancy, but it's not certified, vehicle tested or registered - we'd better wheel it back in the shed".

    Personally, I'll take my cues to good practices from good pilots and doers, and ignore the rules and suits. Just like Wilbur.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Lucian said,
    "I understand that Larry is the manufacturer but to my knowledge he has no formal training, nor degree in Aeronautics nor Aeronautical engineering nor mechanical engineering. Design of his trike and wing is then expected to have been created by someone other than Larry. If Larry has done all the designing himself what knowledge base has he drawn on for that design work? Sometimes we need to look beyond the surface when speaking about a manufacturer and the design of a trike and wing because one is not always both manufacturer and designer"
    Well Lucian maybe Larry should go back and get a job which he is really qualified for. Perhaps sweeping floors or washing cars. All joking aside... I have found that common sense, logic, experience, and passion CAN be more important than any degree to producing a usable product.

    Yes the hang glider and trike designers, wing and undercarriage, do not know exactly all the details. In reality it is based on improving existing designs. Trial and error. This was incredibly frustrating trying to get specific answers from the industry leaders/experts TEN years ago trying to get specifics to write the FAA WSC Handbook aerodynamics section.

    Lucian, I am not going to debate this side torque issue any more. I have already said my opinions just go up and read them again for my response.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    OK Paul D, Joe H and Larry M,
    Yes the first example of 30 degree bank in 4 seconds does not match the video. Yea Yea I know. Why am i resisting trying to quantify this good question? I will get back to you on this it is not a simple answer. Stay tuned…
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Hi Guys:
    I thought we just went over a lot of the details of wing rolling conceptually in the other thread. So there are indeed people who have a fairly good idea of what is going on. But trust me when I say this, you could pick some of the largest wing manufacturers in the US and I can assure you from first hand experience they do not even have the idea that have been covered in the other thread. Just take it for what it is.
    Bill Brooks quite a few years back realizing that I was more than just throw stuff together and just make it work kind of guy, graciously handed me a Masters Thesis on flexwing that was presented in a UK university.
    So there are people but very few who approach the subject with a very disciplined rigor. Unfortunately the market size does not justify implementation of varied concepts. However, some of those concepts could be used also in tailless aircraft which are not pure weight shift flex wings. There may be a bigger market size there.
    I heard that Paul Dewhurst is working with Sergiy Drobyshev in Ukraine right now to try and develop some unique new trike wing. If so, my hats off to him. Hope you find a market for that product Paul and succeed.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    So Paul, how fast were you going in your video? 85 MPH? That's the only info we need since we can figure out roll rate from the video to know the AOA change that took place had the wing not changed 6 degrees AOI per side. This test should easily prove the truth at least in this particular case. Then I will strap on a go pro and force warp into the same wing and see if we get different results again.

    at this point I am fairly convinced it is the way Paul D and Abid have described for wings that roll maxed out in a constant roll rate while weight is applied to the down going wing. However if the roll is accelerating until its decelerating, then Steves theory that was posted here on TPS does not even apply in the first place. The mistake I see is thinking that acceleration in roll is limited to the first fraction of a second. So what does Paul Hamilton's video prove?
  • Joe Hockman
    by Joe Hockman 10 months ago
    Bryan, you are a hoot man. Wilbur chose not to tell Orville "she ain't certified yet, lets put her back in the shed". I had to laugh out load on that one.

    Well thanks Paul D. for picking up on the fixed wing to Rival S tip AoA change. Yes, I too thought that given different roll rates in the comparison we should have ~9 deg increase in AoA at the tip. So I have already come up with my hypothesis why Paul H. measured ~6deg increase in twist rather than a larger number but I am going to wait to hear his answer.
  • white eagle
    by white eagle 10 months ago
    Yes joe i got a goid laugh from that one too .
    My father was good friends with orville wright and lived near their bycicle shop in dayton as thats what got him into flying!
    So all this subject about 6 degrees or 9 degrees , tourqe the controll bar or not. Where is everyone going with this? I really dont see the productive quarrel. So many variables unless you all were in a nasa wind tunnel.
    To twist or not to twist that is the question? Thats a p floydian slip.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Joe,
    You get the award for best observation. There is no exact number. I estimated between 6 and 10 degrees but went with the lower range as a start hoping someone would provide some additional observations. Joe. You nailed it. I would feel comfortable with 8. Headed towards 9 and in the middle of my high/low estimates. Nice job.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    White Eagle,
    Another great observation and question. What does it really matter? Why are we bothering with these details? First there is a group where looking at the details challenges the mind since not everything is clearly understood. All these experts saying different things. Second, if you follow back to the last blog, Paul D said that he questioned the 2-24 diagram validity so I want to investigate this with the assistance of others.

    Additionally I have not seen any definitive information from a reliable source of how much twist the wing can achieve as it rolls. It appears that everyone is guessing and the video is to start some basis to provide a range of twist change. With the magic of the flew wing being able to WING WARP, I feel most would be better to understand HOW MUCH. I spend so much time explaining this wing warp to new and transitioning pilots, more more solid numbers would be helpful.

    My passion is to introduce people and train them to our great sport and this will help myself, others and maybe help designers understand more to evolve better wings in the future.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Ok for the numbers many have been bugging me about:
    To start a little background about NUMBERS.
    I had an intense 10 year job right out of college with brilliant aircraft designers. It was a small operation so I got to do aircraft design, test/measurement design, flight test planning, flight testing, data analysis, data evaluation, results and recommendations. COMMON SENSE to start is :
    If your assumptions and actual test results have LARGE variables, it is hard to make any definitive results. A little assumption/observation/nudge in one direction of this variable, a little assumption/observation/nudge in one direction of another variable, you simply add up all the variables and so on… So you start with what you think it is and then add on plus/minus to get a range of accuracy.
    So you try and provide a range of observations results that you think is reasonable. So here we go with a discussion of the range for each.
    The roll dampening for the claimed 45 to 45 degree turns in the video. This is a pretty simple calculation except we have acceleration and deceleration so any value will be an average.
    First variable: OK the roll is 45 to 45, 45 to 30, 45 to 60, or 40 to 40?. Our first variable we will stick with 45 to 45 since this is my best estimate but it is important to understand the variations.
    Second variable: the time it takes to roll 45 to 45. From start to finish I got 3 seconds plus or minus a second so 2 to 4. Our second variable we will use 3 seconds 45 to 45 or 1.5 seconds for a 0 to 45 degree bank. This would probably be 2 seconds for a 0 to 45. I did the video 45 to 45 here mainly to get the twist change angle only but it turns out we can get more here than I expected.
    OK now the math. At 15 feet out the tip travels about 11.8 feet with a 45 degree bank.
    With 80 MPH speed and 1.5 seconds for 45 degrees this is 4.5 degrees of roll dampening angle which is a reasonable number. This would be 3 degrees for 2 seconds and 6 degrees for 1 second.
    So if we use 4.5 degrees roll dampening at the tip and 8 degrees of twist at the tip to roll this is a healthy margin reduced lift on down going wing/increased lift on up going wing and to roll this fast which would be expected.

    Note this is with one of the fastest turning trike wings in the world. Why, because of its ability to change the twist with the least amount of effort. It is really pretty simple, the more twist you can get, the faster the wing will roll.
    Is this true for all wings? Probably but I cannot say that with assurance. Slower role rate means less roll dampening and less twist but from my experience you need significant twist to roll a wing safely.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Till you place calibrated angle of attack indicators at various stations along the span this is not going to really be of use much unfortunately.
    It is not a good thing if aerodynamic roll dampening is overcome completely and overtaken by forces acting against it. You do not desire that in a properly sorted out wing. That is like a F-16 that is inherently unstable and can only be safely flown because it has fly by wire controls being driven by a chip and not directly by the pilot.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Abid, you have flown the wing and so has bill brooks and Paul D. You like the wing. I like the wing. It doesn't do anything unpredictable at any speeds. It just flies great. I think we can all agree on that. You obviously do not like the finding here because it says that the diagram is right. At the end of the day I learned much from this debate, but clearly the wing AOI drives the turn in this case. How do I know? I can feel it. When I fly a BioniX I do not feel it. So I think it's possible both sides are very correct. If you look back at my original post, I said it was possible. And now I am quite convinced that it is. The RIVAL S is not primary weight shift for roll. Perhaps all the rules have been broken now :-)
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    No Abid we want the aerodynamic forces tip to overcome the roll dampening so we can roll as we wish. To stop the roll you relax the bar to stabelize at the desired bank angle.

    This is exactly what we want. Sorry you do not like the results.
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    From my point of view I think we need to be teaching theory in a way that's simple, truthful and useful. To get to the point of being able to make a simple but truthful explanation we first need to find out all about it, so our simplification doesn't throw out the truth.

    As for usefulness - that's a bit harder. Whilst being very interesting for some, and elevating appreciation for the sophistication of our machines, Is any of this useful in a safety way to a pilot to know?

    I guess at the most basic level an appreciation that the design is sophisticated may help prevent pilots from making changes to batten profiles, sail or structure before seeking advice from the manufacturer. It may also spin off to help us understand some handling techniques and what not to do.

    Paul
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Larry, what happens to roll rates and pressures at low entry speeds on this wing?
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Paul D, I'm greatly curious about the weight/billow shift debate because I was part of one of many teams back in the eighties who were trying to achieve the effect Larry is describing: lateral pilot movement causing billow shift to drive roll. There was a kind of race on to achieve this as a means to allow handling in low twist, high L/D wings, which of course lack sufficient billow to make it happen easily.

    I also think practical techniques can be derived from theory. Here's just one example of how knowledge of your trike's roll behavior could be useful: you're caught in cloud, and you know that the most common outcome from loss of horizon events is a spiral dive. I know that by flying slowly on a closed throttle and a constant heading gives me the best chance of getting out in one piece. A similar descent rate with throttle and speed is more likely to produce a loss of control in this situation. I can think of many other examples of how understanding roll helps pilots stay in control in real life situations.

    White Eagle, you have many amazing connections to aviation history!
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    Guys please don't let this descend into techiness with each other..

    Handling we desire to make the aircraft easy and precise to fly may bear some talking about. Conventional wisdom in certification codes and test flying is that we want proportional control such that response is proportional to both displacement and force of the control.

    A predictable and controllable response to a roll input should be that a given displacement produces a brief acceleration phase before stabilising at a steady rate of roll. A small displacement producing a small rate of roll and a larger displacement a proportionally faster rate of roll. A small but perceptible control force is desireable for small displacements, rising proportionally as displacement is increased. This gives tactile and predictable feedback to the pilot.

    We do not want an unstable condition where we need opposite control pressure to prevent rate increasing - that's normally a fail in all design codes flight requirements.


    Roll inertia is also important. The most desireable is a roll rate that very rapidly decays to zero as control input force is reduced to zero. Having to apply opposite control to reduce roll rate and aquire a target bank angle is not desireable and increases pilot workload and reduces precision achievable and increases the likelihood of loss of control at high bank angles and roll rates. We have been there and done that in the 80's with a design or two in the UK..

    So we need roll damping ( not dampening - that's to make something mildly wet..!) in its true sense of a force or 'frictional effect'that reduces an oscillation - in our case rolling, when we no longer command it. We don't want it to mean that our roll rates are too low and forces too high - or that reduces our controllability ( and pleasure) in another way,

    Personally when I flew the Rival S, through the manoeuvring that I did in it ( nothing overly close to the envelope limits) I felt that it obeyed all of the above - it was nice and light in roll but I didn't feel that roll rate kept accelerating - it felt like it rolled at the rate I commanded proportional to the input force and displacement.
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    Bryan - yes, good points. I use that in the same way for a coping strategy for an unavoidable descent through cloud - the lateral stability effects of climbing and descending flight we put in our syllabus quite early in and demonstrate it in the medium bank turning exercise. I am not sure how many folk correctly and fully understand the theory - but it's very useful for them to appreciate the effect in flight.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Hi Paul H:
    The way you are describing the handling you want I believe is non-compliance with ASTM standard and with BCAR Sec S for trikes in I understand you correctly. For example, if you are having to put opposite control input displacement in just to stop rolling in one way ..

    There is a simple sentence in ASTM standard and other standards that when interpreted correctly does this in

    4.3.3.2 Lateral control forces shall not reverse with increased displacement of the flight controls.

    BCAR Sec S is even stricter.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Yes Abid you are correct. What I should have said was "To stop the roll you relax the bar to stabelize at the desired bank angle" I edited my post above. Thanks for seeing this.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Thanks. I also just read Paul D comment above. Yes in almost all certification standards from ASTM design standard for trikes to airplanes to CS-VLA to Part 23 simplified criteria that I have some experience in using this reverse force is required because without that basically improper feedback or lack of feedback has historically resulted in tragic loss of control accidents.

    Leave it to Paul D to get my auto-correct iPhone use of Dampening. Haha. Hope everyone understood I have always meant Damping but my iPhone just does not like that word.

    It's gusting to 35 mph here and I am sitting at restaurant eating. This is pretty much the way I write these posts on this forum via my phone.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Yes "roger" Paul D and Abid. Control pressures are the basis for safety. I totally agree.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Next step for other wings data point. Please see photo/proposal.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Bryan, control pressure is pretty much the same at slow trim or fast trim. Roll rate is fastest from about 78-95 MPH. Keel shift gets triangulated at faster trim speeds because the rear wires tighten up. Extremely simple due to the downtubes moving towards perpendicular to the keel as the HB moves forward. I think slow trim will show an even greater billow shift per relative wind change due to roll and will still roll faster than most wings can. And I think "torque steering" will show even more billow shift.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Paul D, the wing wants to be symmetrical. It takes lateral force on the keel to make the wing asymmetrical. Release force on the control bar and the keel returns to center. You don't need roll damping to have static control force feed back. If the wing is turning due to asymmetrical AOI from each wing half, when you let go of the controls the AOI becomes symmetrical again and this removes roll rate. Roll damping is not the only way to get the same affect.

    So Paul's Video seems to support my original statement. Do you agree the "numbers" favor what I said they would?
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    It's a damn shame you can't get a camera view that shows the top surface, Larry. Lateral movement, then billow shift, higher AoA on the flattened upgoing wing, increased flow separation and therefore drag on the upgoing wing midspan feeding roll, roll rate increases until billow shift is fully developed, trike lateral swing lags wing roll...

    .. and I'd really like to fly that wing!
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Dah. Call me slow but... it's just dawned on me that moving the HB forward tweaks the anhedral at the same time... I guess that was your intention all along, huh?
  • Joe Hockman
    by Joe Hockman 10 months ago
    Paul, great job on the additional ball park calculations. I think they are reasonable. It sounds as though every one likes the numbers. Where I was going with my hypothesis is as follows. Since measured decrease AoA at the tip (6deg) at the 45 deg bank angle is not quite as much as your estimate of 8deg maybe 9deg of change in relative wing angle, that is OK and actually supports what I had expected. Remember the twist at the tip is not the only thing that is important. The entire trailing edge arc of the billow on the descending wing is also reducing the AoA due to excess lift again on descending wing. So a significant portion of the midspan and outboard toward the tip plays a big roll in dumping loads too, it is not just at the tip. So for me this finding makes a lot of sense and should make Larry happy too. Oh, BTW my guess is that if you did that same roll rate (45 to 45) at same speed with a 200+ lb passenger you are likely to get maybe another ~1deg at the tip and maybe another ~1deg to your mid span calculation of 3deg. Greater loads just means the wing will warp enough to handle the added load.

    Bryan, I agree with your comment of having a camera view on the top surface to see what is going on there. Not sure best way to do that. One thought I had is that Henry (the famous videographer) has some sort of a camera mount appendage that protrudes through the nose cone but curves down to give a nice frontal view of trike. Is it possible to take some thing like that and rotate it 180 so it curves up? If so that might give an ideal view of both upper surfaces.

    Yes my understanding is that Larry's VATS (Variable Anhedral Trim System) basically adds anhedral when trimmed faster and removes some anhedral when trimmed slower. It is actually a brilliant idea, big kudos to Larry. The importance of actual and effective anhedral in recent blogs on yaw/roll coupling and roll performance has been underscored in discussion on last couple "twist" blogs. Yes, I too would like to fly that Rival S wing some day. Sounds like an awesome performer.
  • wexford air
    by wexford air 10 months ago
    When you mention VATS Joe. It also has an extra influence on roll due to the movement at the top of the a-frame. Could you call it a Variable Geometry Roll System? The raven wing had the same setup and my Q2 (except that doesn't have the moveable hangpoint) basically it means the top of the a-frame is located at the hang block instead of further forward at the keel
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    I actually just read Paul H numbers post. I had not yet. I still stand by that till you put AOA measurement tools along the span you are guessing and thus your theories are not convincing at least me. Your experimental measurement is working on a pre conceived theory and you are trying to say that this is what happens. It was also clear that before the twist discussion Larry you and Paul both thought that up going wing in all trikes has greater AOA and I hope you understand that stuff looks ok in a student manual but it's not the real case. So if you want to conclude that this one wing is very different in its fundamental behavior that in it up going wing actually has greater AOA than down going wing??? Then please use AOA measuring devices. They are available and they read AOA reasonably well in real time almost. Paul H. Do you have an angle of attack gauge. I suggest 3. Inboard, mid span and at the tips.
    Personally I think Larry's wing has good billow shift and tons of anhedral effect designed specially at faster trim speeds and it aids in roll. Larry from 2002 when I first met him has been wanting fast roll rate wings with light pressures. If there was an aerobatic trike category Larry would be on it. Reflex 11 I believe still has higher or similar roll rate to Rival S without VATS and it was a regular wing. It simply has 27.5 foot wingspan compared to 28.5 of Rival S and it is 11 sq. m compared to 12.4 sq. m. It's tuned to a good profile along the span and it controls washout. On a rather heavy Revo it's landing speed suffers but on a standard 1040 pound gross weight trike it would be fine. Each extra 10 pounds on the Revo with that wing cuts its Vh by 1 mph.
    Larry's Rival S is designed and tuned and tweaked to be fast in roll because Larry likes it that way. Always has. I am a bit more conservative and I like slightly stiffer feel but still smooth because I know me or Larry in the end are not the ones flying these wings. It's an average pilot who's training is not necessarily done by recommended instructors only.
    But back to this interesting subject the wing span of 30 feet I do not think is correct and in any case the I think if we want to prove something we need to measure it reasonably and for that we need a measuring toll available that measures it as directly as it can. The measurements here are too vague for me to get convinced. Sorry guys. I see what Paul H. was saying yesterday to me that I do not like the result. Paul H I did not even read your result till this morning. My comment before and now though is still the same. Measure it properly. I like what is being done though but I am just not that loose with these things whil drawing conclusions. I'd like to know also but know a bit more correctly measured. May be Matt L can lend us some AOA sensors Paul.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Larry. I can feel it is good thing to say to your relatives but cmon man you think you are going to convince me with that. You know me better than that :).
    Let's see if we can talk to Matt and guilt him into lending us 5 or 6 AOA measuring devices and we can set them up and do some test runs while recording data. I'll help you. It's an interesting experiment.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Abid,
    If you do not like my numbers, test and/or make up yopur own. If you do not like my crude measurement technique, do it your self. If you do not like the diagram and think it does not apply to ALL trikes (which it MAY NOT) say it is relative to roll dampening. As I have said, this is a quick and dirty flight test to get a ball park result which was accomplished.

    Back in the days when I was working for Lear Fan, the fuel flow was not as expected. We were flight testing and every day was big bucks. In a meeting it was decided to get the manufacturer there to replace/calibrate the fuel flow meter but it would be a week. As a young engineer I jumped in and said “give me two hours I will calibrate and provide a result”.
    Went down to the airplane, pulled the fuel line, put it into a five gallon bucket and with a stop watch provided low, medium and high fuel flow rates which recalibrated our fuel flow meter. We were flying that afternoon. This was quick and dirty just like this measurement. We later got the fuel flow meter “calibrated properly” but the quick and dirty method was pretty darn close and did the job needed at the time.
    Again for this test on the trike wing, quick and dirty method close enough to do the job I wanted.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Abid,
    Please explain how 6 angle of attack sensors will measure wing twist?
  • white eagle
    by white eagle 10 months ago
    Bryan tuffnell. Thanks for the compliment. I dont mean to be such a name dropper but in truth i have been around and friends with many aviation pioneers and record setters scince i was a small boy. I think i inherited it from my dad flying pbys in ww11. And later working in the hang gliding ultralight industry and on to the flight line under a military contract.
    Interesting enough is this blog and just how much the conversation resembles conversations and discussions i listened too like dick and burt rutan. Or the sailplane designer george applebee.
    When i knew buzz aldrin he was the director of alb international airport .but the conversations i had with him was very acuetly listning to ufo stories.wouldnt you listen intently if buzz was telling you personally what he saw?
    Now in relation to the ambiguity of this blog i see the same hard thinking on different levels of discription by some really educated thought .Iam more simplistic in my view of things as i always like ruducing the fractions to the simplest form.
    I get confused easily but i can say that figure 2-24 by paul is good for the basic understanding of wing twist.
    But as well as abids view in his last posts are really getting to the point that you must really have absolute acurate measurement before really arguing the finer points of wing twist. It really could be suprizing how it deviates from theory in the end.
    IT just is so interesting and amazing the quality of itulectual abilitys and interpersonal communication between abid,yourself larry and my good friend joe hockman and many others posting here .
    In the end i hope it translates what matters most to me! That we have good stable efficient safe wings advancing are sport and those who love the closer to bird like flight original dream from folks no different than you or me like are dear friends otto , and wilbur . Its pilots getting together to hash out theorys and ideas and explainations athough may find disagreements that make pilots like me imagine what a hang glider or trike wing may look like in say 100 years. And after i take my anti ageing pill. Ill probably be in some blog somewhere saying yah i knew those guys abid paul larry bryan doug and of course my buddy joe when they were discovering those things?
    In order to imagine the futer you have to view the past
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Well what is it? Day 20? Finally it hits me. The whole equation reduced to a simple answer:

    If we have a wing X that doesn't billow then of course it is turned by weight shift and of course the descending wing is flying at a higher AOA we will call X. As we add billow shift the rules don't change, they reduce the effects though. So a non billow wing rolling at X roll rate has an increased AOA on the descending wing called AOA X. and wing that billows 5 degrees at the same roll rate of X has an angle of attack of X minus 5 degrees. And so on. The more the billow the more the AOA is reduced on the decsending wing.

    Because our "ailerons" are the wing the billow can act as an aileron IF it has enough billow to reduce the AOA more than the increase in AOA of the relative wind caused by the roll. Obviously the Aileron of an airplane has a LOWER AOA on the descending wing "driving" the wing down (more the other wing up I know...).

    So if we made our wing billow shift 30 degrees the. Without question the AOA would decrease on the descending wing.

    My conclusion is any wing that has lower billow than the AOA change due to roll rate is weight shift roll just as Abid and Paul D have described. But if the wing billows enough, you will get an aerodynamic roll just like an aileron driven 3 axis and weightshift is not needed.

    So there is no question in my mind that Abid and Paul D are correct. But does that only apply to wings with a billow shift < a certain amount per roll rate per air speed. Clearly there is a cross over and I realize this will cause the roll to ACCELERATE in roll WHEN the AOA is higher on the Ascending wing. In Paul's video he was accelerating in roll until the roll was decelerating. Since desceleration was quicker, we saw the higher AOA for most of the roll.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Paul:
    Its not a matter of liking or not liking. Its a matter of there is an established norm of design that is agreed upon most knowledgeable wing designers and for that matter airplane designers that angle of attack increases on downgoing wing. This is what happens when roll starts to happen. It immediately produces adverse yaw and airplanes try and curtail this by using differential ailerons and some other tricks to a point and flex wings try to curtail this by using billow shift for the most part. It is also accepted norm that some residual damping is still left in both types of winged aircraft. I am still working out exactly what is happening in a rotary wing in roll regarding this but it seems to be same with different blades loading differently depending on where they are.

    That is in a short simplified form what the accepted norm is. There are flight manuals both in airplane world and in trike world that say the opposite to simplify the discussion with students to convey a general working because students do not need to be designers. It serves its purpose well.

    But in case where we are now going to say that no that is not the case and angle of attack is greater on the upgoing wing, we have the onus to prove that by proper measurement. I am not closed to the idea. I think may be this one wing does do it that way, though I am skeptical. But to convince me of that I need to see measurements a bit better than what we have which I have to say are pretty ingenious on your part given what you had. I am suggesting AOA sensors calibrated on the wing like the ones from Dynon or the ones that actually measure pressure differential on top and bottom surfaces at 3 stations along the wing span so we can see the change from a normal 1 G smooth air flight to a turning flight of 45 degree angle of bank. The 3 stations should record a relative difference in angle of attack from S&L 1 G flight on both the downgoing wing and up going wing (total 6). That's just my suggestion. Do you think that will not yield results that are more precise? If so, how come?

    To be very honest, I could really give $0.02 arguing for or against this. It does not matter to me. I am simply curious and I simply came to the twist discussion to agree with and to make the case for what is accepted by Bill Brooks, Giles, me, Roy (UK) and it seems like Paul Dewhurst. To that end I can assure you that I did not know till recently that Giles Breau or Bill Brookes or Paul Dewhurst thought in similar lines to what I thought how roll process progresses in a flexwing. Hey but if that can be proven wrong, so be it. It does not hurt my ego one bit. There are tons of wing designers out there, that really can't agree on what is happening.
  • white eagle
    by white eagle 10 months ago
    I think that is a good analagy larry easy to conceptualize!
  • white eagle
    by white eagle 10 months ago
    Abid. Once again what is your background ! Didnt you tell me once that you have an aerodynamical engineering degree? I cant remember.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    WE: I have 3 engineering degrees but none in aerospace or aeronautical. Mechanical engineering, Microelectronics Engineering and Computer Science. I don't think I usually go around telling people my degrees or even what I have done in the past till conversation leads that way. I don't think I had a conversation like that with you but degrees IMO don't necessarily mean too much always. Any of us can be wrong and we should always be learning.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Abid,
    I have no idea why you are trying to explain to me something (roll dampening) you feel I do not understand. Have you even read it. I described in detail in this original blog. It appears you have not really read the basic forces I describe. What do you think I don’t understand about this basic aerodynamic concept? You are taking us in circles…..
    Here it is again.
    5 ROLL DAMPENING
    Here is a new one for some. As we roll, the wing going down sees a greater angle of attack than the side going up which creates a lower angle of attack, thus this slows down the rolling. However, the billow shift/washout/twist change relieves this roll dampening by reducing the angle of the airfoil on the down going tip and increasing the angle on the up going tip. Again how much billow shift/washout/twist change is a question which we will cover later. First an example to look at the actual roll dampening angle of attack increase for a rigid wing or trike with no billow shift/washout/twist change :
    In a steady state start to finish, 50 MPH airspeed, 4 seconds to roll from level to 30 degree bank, with no billow shift (stiff wing), how many degrees is the angle of attack increased from the lowering wing with a 32 foot wingspan?
    Lets use 50 MPH (70 FPS feet per second) for this. First we need to figure out how fast your tip is going down.
    Your tip is 15 feet out and with a 30 degree bank it travels about 9 feet (8 in an arc) in an arc as it drops. So it is dropping at about 2 foot/sec.
    So as it drops 2 FPS into 70 FPS air the change in angle is about 1.5 degrees. Again note this does not have any billow shift/washout/twist change. Stiff wing.
    With a stiff wing and no billow shift/washout/twist change how much force out on that tip is that?
    If we have a rigid wing with no twist and the desired roll rate adds 1.5 degrees of angle of attack on the wing about 15 feet out on the tip what is the force of 1.5 degrees additional angle of attack? Some basic math produces a force of 75 pounds. Calculating a moment for this we can compare to the weight shift moment we calculated above: 12 feet out for a moment of 10800 inch pounds. Note this is significantly more than the 6000 foot moment for the "1 weight moment" alone.
    So we know that with no billow shift/washout/twist change, considering ONLY weight shift and roll dampening ONLY, it is going to be much longer than 4 seconds. Almost twice as long. Note this is ONLY 2 of the 5 total forces for initial rolling. Add force "4 MASS" makes it harder/longer and "2 WING LOADING ROLL" and 3 KEEL PULL" make it easier with billow shift/washout/twist change.
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    Larry - do I think the video shows numbers that support billowshift being greater than alpha change from roll rate?

    I don't really want to start looking for evidence that supports what I previously theorised, or to be seen as some sort of argumentative sod for the sake of it. I am now open to the possibilty, and the video is a great start - but without more quantified info the error bands are too great to prove either way for me. I think we are seeing that it's a game of small angles of attack difference producing big control force differences and I don't see the video being a fine enough instrument just yet - if it's 45 to 45 in 2 secs then it's a big difference to 3 secs or plus or minus a few degrees of bank angles. And perceived thicknesses of green lines and bits of wood. And whether the speed is 95 or 65 makes a big difference to the real data too. I am conflicted whether the revo is a basis of defining theory for a training manual where we seem to all think 'most wings' don't have the same degree of twist change. I think we might have to carve the theory we teach up into steps.

    I have learnt for definite that roll dampening is what happens a lot flying in UKs often rainy weather..

    Seriously though I think this has been a really interesting thread and some good analysis of the elements of what is going on when we roll.
  • white eagle
    by white eagle 10 months ago
    Abid yah you told me when i asked you in a private message about a year ago or so. Not trying to be nosey just inquisitive. A degree dosent matter much unless you dont have one!
    But not having one doesnt mean you are not inteligent just harder to pay the bills and get along with the father in law?
    Where do you and paul agree! Its interesting conversation for thous of us absorbing from the background ? Certainly wing warping and twist is such a clean way to induce a turn. Less drag than ailerons. But gosh looking at billow and twist just think if we had a frame structured like the bones of a bird. And some different elastic fabric matierials and thin carbon graphite sections built in to a hang glider / trike wing? Being able to shorten and lengthen wingspan . Greatly increase billow ,diehedral , polyhiedral, ext.
    So the related question is a birds wing is simular to a trike wing in some aspects!
    They dont weightshift but boy can they turn ?
    How can that relate to the differnt opinions here or is it no relation to the subject?
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Paul D thanks for understanding the basics of the variables.

    I will be happy to redo the variables to one side to look at a different perspective. What do you want?
    2 degrees 45 to 45, how much less twist change and how much less airspeed do you want to get a different answer.
    Am willing to go to the lower end for you. Give me the numbers you want to change that you feel are reasonable. I am completly open to this...
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    WE, I am putting together a look at the differences and the agreements to try and simplify this.
    Stay tuned....
  • Lucian Bartosik
    by Lucian Bartosik 10 months ago
    wexford Air

    The Raven was a great wing with innovations not found on any other wing from the variable geometry A-Frame connection to the vortex generators to the wing tip tuning and elasticated connection of the wing surfaces at the trailing edges. There were many other things not readily apparent to the eye like the internal design and function of the top fin's king post and what it would do in the event of an inverted negative G-loading to assist the wing in coming back around. It was a pleasure to fly. I also Loved the Pegasus Bandit wing, especially when fitted to a Rossi Trike, another superb wing to fly.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Paul H:
    I think you are taking this waaaaay too personally. Honestly I do not think you do not understand roll damping.
    I will bow out of this discussion. This tiny market of trikes is not worth it for me. I would simply point to Paul Dewhurst's post above. That is exactly the point I was trying to make. Your measurement method is too crude to prove anything one way or another even though it is a good start.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Paul D. I think many big single surface wings such as the Polaris 19m also react aerodynamically in roll. But as i said before, if you are "hanging" on the wing waiting for it to drop, I'm quite convinced it is in fact weight shift in roll and billow is not "driving" the roll. It seems to me that traditional high performance stiff, low twist double surface wings are the ones that can't billow shift enough, especially at slow speed. But we all already knew that.
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    The old joke was 'shift, wait' was 'weight shift'.
  • Lucian Bartosik
    by Lucian Bartosik 10 months ago
    Larry, I suppose it all depends on what you perceive as not being able to billow shift enough. I believe all flex wing trike wings have a billow shift in them when rolling left or right. If we go way back to the first, I believe, real tight as a drum trike wing, the Raven, design by Roy Venton Walters, which they did their debut flight at Popham, sort of our British Sun n fun in an extremely tiny way, it was quite an innovation as far as wing design was concerned back then. Also it was an extremely agile wing with a very fast roll rate, in fact it was proving a little too fast in its first version, for many pilots and the feeling of the manufacturer was that in the hands of the inexperienced, it might prove to be too much wing in that state, so they re-tuned or dampened it down somewhat, to make it a bit more docile and therefore a safer wing in the hands of the more novice or lower time pilots who would probably make up the largest portion of the customer base for this new wing. Paul D. may remember the first version of that wing or may have gotten to fly it at that time.

    I am sure that several wings out there can be re-tuned to be more agile with fast lighter roll rates but the question is how much of that is really needed by the average pilot flying trikes today. Sure you and I and I'm sure the Pauls would love flying them but the majority of trike pilots out there may well find that a little too much wing to handle and could find themselves getting in over their heads too quickly in the control of the wing from simply thrashing it around the sky to getting caught out in nasty turbulence at some point. That is why there are strict rulings or parameters laid out in BCAR-Section S and the D-ULV and ASTM standards for flight handling, to make sure we have predictable wings that won't possibly rise up and bite and unsuspecting flyer.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Liciian, not billowing enough was with reference to IF there is a cross over point from weight shift roll to dynamic roll as Paul's video seems to show the RIVAL S is. As I have said I also believe many single surface wings are and clearly many wings are not and in fact are weight shift.

    The problem we have with "dangerous wings" is when they go from heavy damping and very easy to fly, but cross over at a high speed in a high slip situation to "pro roll" and if that pro roll is over powering all of the sudden when it happens.

    Regarding "hot wings" there is a version of the RIVAL S that is unbelievable that we do not offer to the public and quite honestly ots been a while since I have flown that version. But understanding how to coordinate turns when flying the RIVAL S is critical. This side to side bar movement is not going to work well at all with this wing. we offer "standard flying" wings as well. Great for pilots that don't want to do any transition training. But if you learn on a RIVAL S, that skill will transfer down to fly all other trike combos. The problem is these new trike pilots don't realize they fly differently from many self taught trike pilots with lots of experience and over estimate that a CFI can jump in their REVO with that wing and just go fly as easily they do themselves. People like Paul dewhurst get in and are told nothing and just fly the heck out of it. It others will need to re learn the proper way to turn a trike if they want to be successful with it. Otherwise they wind up flying it around high siding it the whole time in a PIO.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Just had a long and detailed phone conversation with Bill Brooks, the P&M designer who is highly respected by all and has all the academic and practical credentials as a flex wing designer. I can’t say how much I appreciate Bill talking with me for 30 minutes of his valuable time.
    I have learned to get the story DIRECTLY and not hearsay through others. We talked about a number of subjects/concepts relating to billow shift/washout/twist change.
    We covered the roll dampening concept in detail since this is the basis of this discussion and his interpretation is EXACTLY as I first described in the main blog above as force 5 ROLL DAMPENING. Again, not sure what Abid does not think I understand.
    Yes he did say that HIS wings do not billow shift/washout/twist change more than the roll dampening angles of attack. I pressed him for a number of billow shift that he gets in his wing and he said he does not know for sure. I pressed harder and did get a number but it was significantly lower that what I measured in my test. Since I forced it out of him I do not want to publish it here since it was a guess and I respect the confidentiality of my conversations with others.
    Then we got to the subject of OTHER wings, not his, twist angle being greater than the roll dampening angle. Much discussion of stability and ability of different wings being able to achieve this higher level of billow shift/washout/twist change.
    After verifying all the basics, I popped the BIG question which I guess is the controversy. “Do you think that other production trikes can produce twist more than the roll dampening?”. After much discussion deliberation his answer was “It’s hard to tell”.
    So if his conversations with others were interpreted that “wings cannot, do not achieve billow shift/washout/twist change greater than the roll dampening”, this SIMPLY IS NOT TRUE. Yes it would be easy to interpret this differently based on talking about his wing and what he feels about it.
    Happy to set the record straight on this.
    Grateful that Bill spent the time and shared his expertise on a multitude of design issues including his brilliant STARS system VG.
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Paul H:
    I will bite since you talked to Bill.
    The question is not about twist. Every flexwing that has a floating keel twists and billow shifts.
    Every wing turns and utilizes billow shifts today. That is what makes the effect of roll damping lower and makes roll forces and roll rate effective. That is not the point of contention.

    The point to develop this theory properly is:
    Is roll damping completely overtaken by billow shift and if so what is the effect of it and how can a wing with this unbalance of forces have spiral mode/roll/lateral stability desired by design standards like BCAR Sec S and F2317?

    What is the balancing method that stops the acceleration due to billow shift overtaking roll damping besides pilot's input in opposite direction or pilot having to push the bar out to get higher AOA and stop the rolling acceleration. These last two are not acceptable methods to comply with lateral control stability requirements as best as I understand though the second is a highly advised action in roll in general for flex wing pilots in training.

    Third the point is that if the claim is that Rival S or large single surface wings overcome roll damping AOA difference completely and overtake it, there need to be proper measurements done to prove that to the claim as I understand it that upgoing wing while rolling has developed due to excessive billow shift higher angle of attack and downgoing wing has lower angle of attack. Simple angle of attack measurement along the span in level and during rolling is what is needed and averaged. We need not be concerned with twist change which is delta of angle of attacks between root to tip and everything in between.

    I am not saying you or anyone else does not understand roll damping. I am saying that you are saying something different than Bill, me, Giles. Siebel experiments and if so lets try and measure it in at least as much detail and carefulness as Siebel did. I believe Paul Dewhurst has said the same thing.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    OK Abid I will tell you what you do not understand. All this is based on the phase 1 of the turn. Look at the second word in the title of this blog. It sez initially. I have tried to say is in so many ways but at least you have not picked up on it. Initially means:
    of, relating to, or occurring at the beginning; first:
    the initial step in a process.

    Yes I am familiar with what you just said.

    OK give me some time and I will explain to you the next step on the roll process AFTER THE INITIAL step and answer your questions on control pressures.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Abid, the point is that it IS possible and most likely demonstrated on the video. That is worth stopping and taking a breath to realize and concede. Let us take a moment to digest this.
  • Rizwan Bukhari
    by Rizwan Bukhari 10 months ago
    Pau H, I think you took Abid's contribution the wrong way. To me it seems like he was just trying to help, he makes some good points about the raw nature of your experiment. I will say the same thing to you that you tell everyone else. "Take a chill pill". Just be open to learning, you don't know everything, nobody does. But through this forum we get to share and learn and sometimes I feel you let your ego get in the way. I don't really have a dog in this debate but I feel your last few posts are counter productive and not contributing much to your own blog. Peace out!
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Well Riz you are predictable about being the judge of what I do. Yes take a chill pill :-)
  • white eagle
    by white eagle 10 months ago
    The great riz wan speaks. When are you availible for flying lessons?
  • white eagle
    by white eagle 10 months ago
    Paul , abid just hash it out. No ones getting their pc feelings hurt here. THE DISCUSSION is a rather difficult one to concieve. So far iam trying to think of down hill snow plowing.yaw in the waist, weight bering shift on the inside ski,uphill ski speeds up , .degrees of twist in the tips. It gets complicated. You both have some really good points. So help the slightly confused (me) up the ladder?
    The theory of relativity suggest that two positions viewing the same object may have different discriptions based on the angles there viewing it from.
    Paul is discribing the initial first phase of the turn , abid is discribing complete phase of twist,billow,washout roll dampening!
    You both have alot to say. Iam doing my best to learn something i dont know!
  • Joe Hockman
    by Joe Hockman 10 months ago
    Well it seems the discussion here has taken a bit of a turn or twist (pun intended). FWIIW, I don't believe any relationship has been conclusively established other than greater billow shift helps to alleviate roll damping forces and perhaps the Rival S wing has enough billow shift to overcome a large portion of those forces. I do understand that overcoming ALL of the roll damping force would create an unstable roll condition and be an unsafe wing in the hands of a pilot that has did not understand and anticipate its behavior. Even though all modern flex wings to have washout, billow and billow shift, it appears the magnitude of billow shift and twist may be rather critical in not only providing the desired spiral dive / roll performance rates but also in determining the safety margins needed for the average Joe pilot.

    I have decided to start another blog on how to experiment effectively to develop understanding and improve characteristics of interest. It seems to me that many contributing here may not fully understand importance of how an experiment is conducted will determine what can be learned and how important the measurement system is in the process of developing fundamental understanding on cause and effect relationship. I do, however, believe there may be a few here that do understand the importance of this.
  • John Glynn
    by John Glynn 10 months ago
    I do not want to create more controversy but I have been fascinated by flexwings and how they each individually accomplish turns etc. I know that everything in aerodynamics is a compromise. Some wings do certain things better than others. What I find especially intriguing about the Rival S wing on the Revo is that the roll pressures are pleasantly light. I have (not on my own but with Larry or Wes in the back seat) been allowed to initiate and perform steep turns at a fast roll rate (all within placarded limits). What I find amazing is how and the world can you make something start rolling so fast, and also make it stop rolling with so little force. When you do the math, I imagine all that weight out on the wings rolling very quickly, and then stopping the roll on a dime. The wings are like long levers with weight that is moving about the longitudinal axis. How in the world can our weight shift aircraft achieve such quick handling with so little bar pressure to initiate or stop the rolling force? I am glad that things progressed so far over the years. My first hang glider trike was poor handling, glided like a brick, and unknowingly we attached trikes back then to the wing with a heim joint, which allows you to literally yaw the trike. It was a horrible idea but we think we needed that for crosswind landings. We then had to hold the darn trike straight while flying, like we didn't have enough to do. Handling has come such a long way. After my last flight in a Revo I previously always believed that someday when I physically could fly a trike anymore I would switch to a bush plane...not anymore. When I am too old or not in shape to fly the modern latest trike, I will be too old to fly, and probably drive as well. Keep up the great work designers.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    It turns out the weather has gotten better for the next couple of days. No global warming here. 30 feet snow in the mountains and students/pilots have me booked solid for the next week.

    I plan on providing a complete discussion of phase 2 in the roll process after the initial bar movement but it will have to wait. Simply, after the initial bar/movement, the next phase has all the 5 forces described changing completly and the centrifical force RELIEVING the control forces for this again alleged scary/unstrable/non certifidable/unsafe contriol pressures next step. For those who want to dispute, there is your hint to what is my next blog. Again, hint/focus centrifical force after initial roll input for csafe ontrol forces. Hopefully i can get back on this in a coulpe of weeks. Best. Paul Hamilton
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    Rival S as roll is initiated and billow shift starts also uses dihedral effect (more like anhedral effect actually) which is rolling moment due to side slip. The first thing that happens as soon as rolling accelerates a wing down, the adverse yaw creates a slip and the anhedral effect in it is quite strong and it adds a rolling moment in addition to billow shift alleviating roll damping. That is my observation. In such a design it is of utmost importance that if roll is initiated with force that you push the bar out to coordinate the turn. Technically it's really not coordination but that is what flex wing guys keep calling it so the term sticks. If you do not do that and you started the roll with a good whack to the side, it wouldn't surprise me if it kept rolling. Larry has put a damper in a few months back to help novice non-transitioned pilots.
    This strong rolling moment due to slip especially at above 80 mph IAS is significant. This was simply my observation from flying it on the Revo. I liked it but I told Larry it's an advanced wing which will require transition training.
  • John Glynn
    by John Glynn 10 months ago
    My real question is how can you stop all that mass moving about the longitudinal axis with a light input pressure on the bar. It instantly rolls into a turn and then just as instantly stops rolling at the desired bank, all without mush input pressures. Makes a person wonder what is actually stoping all the rotational mass in the quick rolling turn? If I have the long "lever" of a wing with mass extending outward in both directions to each side, and get it all moving so quickly in roll, it would be hundreds of pounds of rotational mass and resultant force all stopped with a light touch. Heck even in my trike I have amazed airplane pilots with the quick handling and mine is nothing at all like a Rival S/ Revo combo. Simply amazing. OK not simply amazing, complicatedly amazing.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    And to bring anyone up to speed that doesn't know the RIVAL S. In the link below in the opening scene 10 seconds in shows the RIVAL S rolling and then abruptly stopping the roll and locking in a bank angle. How does it stop all that rotating mass as John points out?

    http://www.youtube.com/watch?v=ZAMPRmqhjCI -
  • John Glynn
    by John Glynn 10 months ago
    While dreaming of flying in my sleep I believe I have a theory. Most of the lift on a Rival S must be created in the center of the wind near the Keel and not toward the wing tips. The annehedral, twist, etc all contribute to this. Thank of the wing as a v-bottom boat cutting through the waves in the air. But if you lean to the side it will tip easier than a large flat bottom boat. The quick turn is like leaning quickly in a canoe or Kayak, banking easily. Hundreds of pounds of rotational mass is set in motion, rotating along the longitudinal axis (the keel). The small outward pitching of the control bar causes a higher angle of attack at the tip and the wingtip can instantly create the additional needed hundreds of pounds of lift required to counteract the hundreds of pounds of rotational mass this immediately stopping the roll. So much fun with so little effort. Everything is a compromise in flying. After waking up and dreaming of flying, it will take hundreds of pounds of force to remove the smile from my face. We sure a lucky to live in an age where you no longer have to carry a flexwing up a sand dune and run like hell and hope for a 20 second flight. Maneuverability like we now have in avaiation typically only comes with a 4 - 8 year commitment, a hair cut, and a uniform.
  • Tom Currier
    by Tom Currier 10 months ago
    Paul, I've been lurking on this and the other technical threads. Very important to these discussions (which are very definitely holding my interest and really making me think about my flying) are pilots in training to fly these damn contraptions. I'm very glad to hear that you're taking a sabbatical from these threads to go teach your students. The bottom line for this industry is more buyers/pilots are needed and the busier the industry leaders such as yourself are the better for all of us involved.
  • Paul Dewhurst
    by Paul Dewhurst 10 months ago
    Hi Paul

    It's good speaking directly with the designers isn't it - Bill changed the way we think about and teach billowshift in the UK - the direct contact was useful for us. Helps refine onwards transmission of our 'hearsay'....

    Going right back to my original post that kicked all this off, it does seem that Bill confirmed his experience of billowshift and roll damping is that the lift envelope is the opposite of that in the manual - at least until development in design changes that norm...
  • Abid Farooqui
    by Abid Farooqui 10 months ago
    John Glynn: you got it. I could put it in more technical conceptual terms of what is happening with AOA change as you push the bar out and roll stops but you have the concept. But it's not hundreds of pounds of lift at the tips. It's much less pounds than that but it creates a big moment arm to re introduce more roll damping. This is also what happens in wings like the original Wizard wing by Airborne. This is why some people who are not taught to push the bar put in roll much would have difficulty and PIO in rolling Wizard wing hard IMO.
    Paul D. Ditto.
    Back to Sebring Expo where people are few but serious. Two sales for our gyroplanes in first two days of the show.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Paul D,
    Once you guys in the UK get more billow shift/washout/twist change the diagram will be back in vogue :-)
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    John Glynn,
    Great boat analogy.
    You asked what helps stop the wing momentum in a snappy turn? A little more technical based on this blog subject.
    Pretty much the same in all trikes.
    After the initial roll, after the adverse yaw, and you are ROLLING and TURNING, you release the side pressure and let the centrifical force put the CG of the trike carriage back under the middle of the wing. This immediatly reduces the the billow shift/washout/twist back to nuetral, or there abouts. Now you have have enhanced roll dampening on the dropping inside wing because it's angle of attack is much greater slowing/stopping the roll into a coordinated turn (of course with the proper pitch pressure for the specific wing).
    Another "magic" of our flex wing and seperate under carriage.
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    Paul, I think it's important to note that centrifugal force develops only as roll becomes turn. It's only because most trike wings are so forgiving that any centrifugal effect occurs as a result of roll alone. Many aircraft fly straight, or nearly so, with bank applied, with no centrifugal effect or turn, until pitch is added. In trikes, centrifugal effect doesn't fully develop until the pilot pitches up to turn bank into a balanced turn, and I feel that's a point to hammer home.

    I know many pilots don't add pitch to turns, and many trikes forgive this error, at least most of the time. I accept that my views on this are agreed with by some and not many, but I firmly believe that this failing (lack of correct use of pitch, and to a lesser extent throttle, in turns) is ultimately the greatest single cause of loss of control in trikes, and that's why I'm so keen to see this addressed.
  • Larry  Mednick
    by Larry Mednick 10 months ago
    Amen, Bryan
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Yes Bryan,
    You must be turning to use centrifical force. That is what I ment and it was not clear so I changed it to read correctly as I intended.
  • Paul Hamilton
    by Paul Hamilton 10 months ago
    Yes it now reads correctly ROLLING and TURNING. Good catch again.

    As far as pitching for turns, I have been teaching this "j" turn (in over out) for yerars . In fact it is in my trike training video (over 10 years now) and part of the training program with a specific test question. Yes but many lower performance wings do not need it much and can get away with sloppy pitch coordination....
  • Bryan Tuffnell
    by Bryan Tuffnell 10 months ago
    I like the term 'J turn'. I first heard it used on this site. It's a good description of the right actions to turn, and follows the rules:
    Pitch down aids roll.
    Roll provides bank.
    Bank plus pitch up makes a turn.
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