p-factor

eg: stopmotion, new-york, street
take off with full throttle. Carriage yaws to the right while left wing drops

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21 Comments

  • Marc Habermann
    by Marc Habermann 1 year ago
    According to the p-factor comments, I like to put above video up for discussion. Some TPS members stated that p-factor issue is negligible, because the effect is limited to only some certain flight conditions means 99% of flight there is only marginal influence. Others, especially with slower or less horsepower trikes (or angled thrust line) cannot feel this phenomena or only at a non-annoying level. Also I had no issue going straight at full throttle with my former oldschool Cosmos 582, but max. speed was only about 50-55mph.

    As mentioned before, I am struggling with following points:

    High speed cruising, straight and level. By trial-and-error I found meanwhile a solution I can personally accept: Since I first adjust el. trim and afterwards increase power more and more to compensate descent rate, I`m able to get higher speed w/o significant carriage yaw and going straight.

    Second is the take off issue I try to illustrate with my video. Conditions were perfect, calm winds, exact headwind. Single seated the BMW punches the trike in the air like a blast. So I always reduce power and try to keep heading and gentle climb angle. Approx. climb 4m/s (790ft/min). Unfortunately the camera angle does not show left wing drop proper. Maybe it looks like it only takes an input to fly straight, but during climbout it feels nearly like slipping off the seat due to slant angle. Shortly after take off I dare not even to increase this bank by correction to the left.

    By the way heavy loaded take off procedure is easy as pie. A nice gentle climbout using full throttle is common. Also the wing flies great, straight and within a range of 40-85mph. There is a builing up much force while trying to stall the wing in flight, means ca. 2-3 inches before the bar touches the strut there is beginning a smooth stall with limited steering followed by a gentle nose drop. Therefore landing the trike is quite easy by just let it flare until the energy is gone and then push out.

    As being still a newbie in triking I always try to expand both knowledge and abilities, but regarding this issue I found no good solution so far (except putting some extra weight in the backseat maybe?) ;-)

    Some specs of my machine: max. climb: 5,6m/s (1100ft/min), Prop pitch: 15 deg., BMW engine approx. 95hp, wing: Profi TL, factory setting (sprogs and batten profile)

    Questions:
    Is yaw/wing drop and therefore not straight flight path seen in the vid normal for a slightly loaded, higher performance trike, means I have to improve skills to learn flying straight while take off by e.g. reducing power even much more?
    Have other similar machines same behavior or is even something wrong with my setup?
    Any hints to make my take offs look more professional?
    What do you think? What are your experiences?

    Thanks for reading and very sorry in case of bad/unclear spelling due to my limited language skills…
  • wexford air
    by wexford air 1 year ago
    Looks like it alright Marc, check that the trike pylon is not able to twist (yaw) relative to the wing keel, ensure the pylon is a good snug fit to the hang bracket and the hang bracket is not sloppy on the wing keel.
    If the wing is flying straight and the trike can easily twist left or right it makes it easy for this condition to occur and if it's tight then it's obviously harder for the wing and trike to be out of alignment. This is the easiest fix I can see without going into modifications, adjustments test flights etc etc. It's a bit of work to start making adjustments to the wing as you may start getting unwanted secondary affects.
    That looks like an aeros trike, have you been in Contact with the factory? Maybe it's normal for this trike-wing combo.
    One of the manufacturers may come along and add some input but in the meantime you try this and see what happens...
  • Marc Habermann
    by Marc Habermann 1 year ago
    Hi wexford air, thanks for your input. Indeed the hangpoint/pylon area I checked already. There is nearly no play/flex. Hangpoint is a massive alloy machined part. Your correct it`s an AEROS trike.
  • Mikael Markow
    by Mikael Markow 1 year ago
    My Profi TL/ Aeros2/ BMW1200 behaves similar except it has faster trim range.
  • Larry  Mednick
    by Larry Mednick 1 year ago
    Mark, you need to climb out in a left bank if you want to stay over the runway. I think we determined the Aeros/BMW had pretty bad P factor. We've already discussed how to eliminate P factor which is a proven method. However, if your P factor is not so bad when you have extra weights in the carriage, that sounds like a function of wing twist. Wing twist can be increased without increasing the weight by simply loosening or extending the hall back cable (3/4" maybe). I don't recall if the Profi TL has adjustment there. you can also shorten leading edges if there's adjustment there. If not you can rotate the tips higher and I do recall you have that adjustment.
  • Larry  Mednick
    by Larry Mednick 1 year ago
    Btw, the slow motion shows very well the yaw, or flat turn to the right caused by P factor. (912s go opposite). This is not torque, but P factor. Well done illustrating P factor.

    If you want to make your takeoffs more "professional" try pinning the bar forward to the front strut at slower than lift off speed (you left a few inches in the video). Then the carriage will swing through slower which will smooth out the lift off and allow the carriage to actually not "swing" forward on lift off. Don't forget to hold the trike in ground effect for a few seconds before climbing out since you will take off at a slower speed this way.
  • Doug Boyle
    by Doug Boyle 1 year ago
    A student had a trike that, when test flown, had a carriage that would swing out to the right on takeoff, or, uncorrected, would turn left. This setup utilized a Suzuki Geo motor swinging a 72" prop. We used a simple check of the thrust line, utilizing two pieces of 10' conduit clamped to the mast and compression strut appropriately spaced to remain parallel, and hung a plumb bob from the center. This revealed a 1 3/4" discrepancy when compared to the center of the spinner. Further investigation suggested a bend/twist in a motor mount support. Replacing/rewelding and realigning the offending pieces restored its sweet flying nature.
  • white eagle
    by white eagle 1 year ago
    So let me see larry. P factor,is more like the thrust getting out of balance with the foward motion causing a yaw. Do i get that right.Then engine tourqe is caused by the turning of the propeller. They both must efect each other. So if i look at one of those long drag racing cars is this why they are so long with those monster engines? So when configuring a trike tri gear how does tourqe and p factor come in to play with length and width of the gear. That providing anything ive said makes any sense. Iam just trying to grasp a better understanding of both?
  • Doug Boyle
    by Doug Boyle 1 year ago
    White Eagle, The propeller produces more thrust on one side compared to the other; said another way, the blade going down produces more thrust than the blade going up. This effect is amplified during high angles of attack, such as in takeoff (high power, low speed). It's effect is countered with rudder in conventional aircraft and other ways in Trikes.
  • Doug Boyle
    by Doug Boyle 1 year ago
    Oops, I forgot to address the second part of your question: torque. If Godzilla reached out and stopped your prop in flight, it's the direction you would spin (opposite the prop rotation). All of the turning forces in flight are usually addressed by the manufacturer through various means. In conventional aircraft these would include engine offset (side-to-side), engine angle (top-to-bottom), differential aeileron deflection, angled (offset) vertical stabilizers, trim tabs (rudder and aeileron), and different wing washouts. Some of these you can spot by looking at a Cessna from the rear and sighting the trailing edge of the wing; also, by carefully examining the position of the vertical stabilizer.
  • Marc Habermann
    by Marc Habermann 1 year ago
    Thanks for feedback.
    Definetely with extra weight (sorry dad) it is very easy to handle, e.g no wing drop and therefore only some small corrections to the left are needed.
    Larry. Don't know, if I get you right. Means "hall back cable" main crossbar tensioner, clipped at rear end of the keeltube? If yes there is no adjustment. Same with length of LE (fixed). I only can rotate the tips little up and down some deg. (3 positions) I thought this adjustment is only to compensate a built in turn tendency of the wing. So would it be worth to try both e.g. one step up?
    p.s. the homemade wheelpant rudder is still in progress.
    @Mikael: your combo should have even more p-factor due to more hp of your BMW?
  • TL Triker
    by TL Triker 1 year ago
    Hi Mark,

    My Aeros does the same thing, it has a Suzuki G13BB engine. I have lots of nose right on takeoff, but it got better after adding some weight in the nose area. I did this because when I performed a hang check the trike was butt heavy, the nose wheel was about 13 inches high, now is around 7-8. I am also on the light side so 1 up the p-factor is more noticeable than 2 up. Keep in mind that the Aeros has a big frontal nose area and this doesnt help with the situation. Recently I bit the bullet and purchased an earthX battery to replace the big heavy 24Ah battery that is currently installed. The battery was installed under the pilot seat so with the earthX battery my nose might go back up some, we'll see how it behave once I take it back up.
  • TL Triker
    by TL Triker 1 year ago
    Forgot to mention that offsetting the engine helps a lot. This is on my to-do list. I trained in a Revo and it really spoiled me, it flies straight as an arrow at any speed. Mine took some time to get used to it with the p- factor deal.
  • white eagle
    by white eagle 1 year ago
    Doug thanks. I understand , i use to have a biz designing rc powered slope soaring sailplanes. Even with those little engines i had to offset the thrustline usually 2 - 3 degrees. I like hearing the different ways people explain things like a gorilla grabbing the prop. Just a great way to percieve an aerodymamical subject.
  • Mikael Markow
    by Mikael Markow 1 year ago
    Marc, for this reason I have adjusted the foot throttle stop so I don´t get full power!
  • Frank Dempsey
    by Frank Dempsey 1 year ago
    That sounds crazy Mikael. What if you really need full power sometime such as climbing over an obstacle? I would seek another solution.
  • Joe Hockman
    by Joe Hockman 1 year ago
    I agree with Frank. Personally I would never want to limit my thrust. Some day you may need every bit of it.
  • Larry  Mednick
    by Larry Mednick 1 year ago
    I 3rd that comment. That is putting a bandaid over the symptom. Treat the cause.
  • Abid Farooqui
    by Abid Farooqui 1 year ago
    This is clear p-factor. Your prop disc is badly misaligned to relative wind. Its needs to be at 90 degrees to relative wind. Aeros trikes have this flaw for many years.
  • TL Triker
    by TL Triker 1 year ago
    I think the design back then worked/was meant for the less powerful engines like the 503 and 582, but now the design needs to be updated according to the hp of the engine installed. They produce engine mounts for BMW, Rotax 912, HKS, Suzuki, 582, but they dont compensate for each engine p-factor. Too bad, I fly an Aeros trike myself and I consider the p-factor issue anoying, perhaps the factory is used to it across the board or they dont think it is a big deal "since it is mostly noticeable on takeoff". I love my trike, I just need to start figuring out a design of a new engine mount to get rid of the propeller factor. Then, I would love it even more.
  • Marc Habermann
    by Marc Habermann 1 year ago
    OK, so I`d like to resume for my person:
    With my trike in general is nothing “wrong”. I was not sure about that as I rebuilt the trike from scratch. Now I have the needed convincement that my setup is according to factory standard. It seems that Aeros sees no need to change construction to reduce p-factor. Maybe because most customer do not complain/are used to this phenomena or use engine with less hp. As any changes regarding engine mount are nearly impossible for me, I will concentrate on:

    - Use of throttle more cautiously, especially during takeoff
    - Going on to experiment with an operated rudder at the wheel spat to reduce carriage yaw

    I will share any outcome
    Finally I thank you all for your valuable input. As there is unfortunately only a negligible market left for higher performance trikes in my country, it is hard to talk in person to somebody with real own experience. Unfortunately it seems that only 3-axis and gyros are interesting nowadays…
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