Feb 20th

be careful what you wish for!

By monty stone

in a recent blog i had the temerity to forecast that in the future all trikes, as well as all other aircraft will be hooked up to a huge 'hal' like mainframe computor based in an underground silo in bumfuk , egypt, and thus allowing all FAA and all other 'official' requirements to be automatically carried out from afar. if your bi-ennial not current, your engine won't be allowed to start, etc. well, i recieved an e-mail from my local 'muni' that twelve cameras had been installed arround the airport in order ' day and night' to monitor all aircraft movements, in order, it says, to better serve all users. while i personally agree that all terrorists, and other wanna-be violent criminals should be strangled at birth, and 'inner cities' do need CCTV's on every street corner, in order to catch the bad guys, i don't wanna be a 'battery hen', or whatever they call domestic animals, locked in a cage , doomed only to poop and pay taxes. now i'm faced with the very real prospect of a take-off with my tire pressures below the FAA regulated PSI that it will be reported to the appropriate  authority, followed by the inevitable punitary action. this USA is one of the very few remaining 'bastions' of liberty left in this rapidly shrinking  'globalized' spinning rock we live on, and despised by many,( envy takes many forms,) and, with all it's many faults, our system WORKS!  one reason i emigrated to this USA in 1964 was it was becoming very obvious that in the UK pretty soon i would need a royal decree and pardon in order to fart. (the british royal court employed a 'royal farter' who's job it was to fart whenever the king felt the need, but didn't want to take the 'risk'.)   FTF ( freedom to fart) is a human 'right', and within obvious social 'mores' shouldn't be government regulated! now, where the hell was i? oh yeah, i don't think our local muni is unique with this 'red light tell-tale installation' but how far will it go? are our bedrooms soon to be installed with CCTV,s in order to forecast future population growth , like MEL GIBSON yelled while being eviscerated by the current king, FREEEEEEEEEDOM!                                                                                                                                                                                                               freezier nutszoff

Feb 19th

Development of a Simple, Compact, Efficient, and Strong Foot Launched Glider Paul Hamilton 1976

By Paul Hamilton


The following is a project I intensely focused on day and night throughout college. This was written over 40 years ago and the Razr variable camber wing is still an underdeveloped technology that could simply be incorporated very cost effective into modern trike, hang gliding and other types of wings.


I obtained a patent on this technology which has long ago expired and the technology in now public. Perhaps some would like to continue with this concept which has great potential.


It is a long report that describes the joy of flying hang gliders, aerodynamic basics as understood by me in 1976, but section six covers the Razr project with future possibilities. I did wind tunnel testing and actual flight testing of this wing. Some of the applicable pictures will be posted as pictures.


If we are seriously interested I will provide all the figures to the report. This is about a gliding wing which I never realized would be put on a trike undercarriage and a new sport born. Here is a journey back memory lane.


Well here it is scanned from the type written pages so there will be many errors so here you go:




Development of a Simple, Compact, Efficient, and Strong Foot Launched Glider



Paul Hamilton 1976





November 23, 1976

Table of Contents




I.   Introduction                             2


II.   History of Hang Gliding                 3


III.   What is Hang Gliding?                   4


IV.   The Wings of Today and How They

Developed Standard to High Performance  5


V.  Aspects to Consider in Glider Design Stability - Control ability -Wing Planform - Airfoils - Strength - Portability - Speed Range               7


VI.  RAZR Project

Theory - Design - Building -

Testing - Modifications                14


VII.  Future Plans for the Razr Project       18


VIII.  Conclusion                             19

You're standing on top of a 2,000 foot mountain with a smooth 22 mph wind blowing up in your face as you look into the valley below. You glider has been preflighted, the flying harness has been checked, and your driver

has been given instructions on where to pick you up five


miles away. Heart beat increases as you walk over to the edge and listen to the wind rip through the jagged rocks. Hooked in and ready to go, you give your launcher the signal to let go of the glider. With precise timing

your total physical and mental energy is used to thrust


out into the strong air current rising from 2,000 feet below. Rocketing straight up away from the mountain, you slow the glider up and start riding the smooth lift up. Looking north, you see the summit about 4 miles away

and a 16 mile ridge line that you can travel full length.


As you ride that ridge towards the bowl below the summit, you are now in the maximum lift area, free to climb above the summit and have a view of everything below you.

Freedom to relax and float around the sky, freedom


to point your nose at the ground and go into a high


speed dive, freedom to race around the sky and do endless circles, and the freedom to see how many miles your

skill and judgment can take you are all a part of flying.


For the reader to grasp total realization from this report, he would have to have flown freely out in the air and felt this excitement. It should be realized that this is more than a technical subject (even though

it is presented that way), it is a personal way for me to

express my feeling toward this awesome sport.






Since the beginning of time, man had looked up at the birds in wonder. Early in the l8th Century,

man left the ground and glided through the air with the wind in his face. These experiments with wind powered, quiet flight stopped when the Wright Brothers took off at Kitty Hawk. Foot launched gliding was reborn a few years ago and had progressed at a very fast rate since.

This is a technical story from the very beginning


of gliding, through their evolution, to future gliders. This class of nature powered aerospace vehicles can be taken to the top of any mountain and be launched for soaring flight. Man will someday be as good as the birds. This report is the next step to that goal,

Gliders and their characteristics will be fully discussed. Aerodynamic information to arrive at facts needed to understand a good glider are discussed. The authors work last summer was devoted to building an inflatable, double surface wing that can fly extremely well. This work will be discussed, for with additional work, it will surely fly better than any other glider in its class. The evolution of this Razr is told up to its present stage with future predictions also introduced.

This report is devoted to the development of this


double surface wing and to the advancement of "free flying".

II. Early History of Hang Gliding


Leonardo da Vinci is the recorded beginning of foot launched flight. His designs are in a log that ends abruptly when his flying machines are taken to the hill to fly.

No one really knew what happened.

Around 1eoo, a professor at Santa Clara College used engineering knowledge to design, construct, and

successfully launch a glider. With control surfaces on the trailing edge, turns, dives, and successful landings were made. Professor Montgomery's glider was then towed up to 4000 feet by one of his students. After cutting loose, the student made a successful 360 degree flight with a perfect landing in front of the crowd.

Meanwhile in Germany, Otto Lilienthal was watching


the birds fly. After seeing how their feathers moved to turn and create more lift, Otto constructed a wing out of willow wands and waxed cloth (illustration #1). He was very hopeful for a negative drag airfoil which is impossible since energy can not be created.

An engineer for the New York railroad put the Pratt


Truss system into use for a stable, controlable glider


that even a beginner could fly. Octave Chanute also shared with the Wright Brothers his findings which were used by them as their beginning. With safety above all and wind

tunnel testing, the Brothers built many gliders (illustrations


#2, #3). These gliders flew extremely well and were very


safe. By putting an engine on one of these gliders, unpowered



foot launched flight was left dorment untill Francis Rogalla developed from N.A.S.A.'s multi-million dollar rocket

re-entry program, a simple and inexpensive manned kite.



r '-


This was made of bamboo and plastic which was safe enough to play with on sand dunes. From this point, a new sport

called Hang Gliding was born. (12)*


III. What is Hang Gliding?


Simply, foot launching a glider that has a slow flying speed.

·   To launch the glider, the pilot must get the glider moving through the air with a speed of at least

16 miles per hour. He does this by running hard with

very little wind, or lunging forward when there is a lot of wind, with a maximum wind speed of 35  mph.

He is hooked to the top of the control bar (triangle inderneath) by a harness and controls the glider by weight shift.

To go faster, he brings the nose of the glider down, pulling the bar back; push the bar forward to

slow up and go higher. For turns, move the body

over to the side you want to turn. Temporary loss of control will take place when the glider stalls or goes too slow. Control will be restored when speed

is regained. The pilot must develop a keen sense of airspeed, control, and awareness of conditions.

An experienced pilot stays up for hours, as long as his endurance holds and lift conditions persist.

The term lift is broken into ridge, thermal, and wave lift. Ridge lift is caused by air hitting'

a mountain and being deflected upward. The region

where air is moving up is called the lift band.

Thermal lift is rising air caused by the sun heating the earth. Soaring in thermals, the bird goes for the core of the thermal. This is located by feeling towards the maximum lift area, to make

concentric circles around an unseen drifting bulls eye.

Wave lift is caused by the air moving perpendicular over a series of parallel ridges. Getting thrown up against the first ridge, air rises the same as in ridge lift, but falls sharply to the ground

on the back side of that ridge. The air bounces in the valley, and goes up the next ridge. As it moves over this series of ridges, this wave becomes stronger until the edge of these ridges where the air splashes down strongly. The upward wave lift retaliation is

as wide as the valley.

*  See bibliography



The pilot's goal is to stay in these lift currents, then he is soaring free with the birds - the ultimate release of ones self.

The safety of the sport is determined primarily

by the hang gliding pilot. His skill and judgment, along with the quality of his glider, directly determine the accident rate. Pilot ignorance and inex­ perience are the primary causes of accidents. The gliders themselves are well engineered, soundly constructed machines. Almost all injuries result, directly or indirectly, from pilot error.

There are a number of different types and makes

of hang gliders, from fixed, ridged wings to the more popular Rogalla and high-performance Rogalla. The wings are made of aircraft quality hardware, tubing and Dacron sail cloth. (4)



IV. The Wings of Today and How They Developed


Only in the last two years have we had high performance gliders. In order to understand these high performance gliders, we must start with the standard. This is shown

as planform in illustration #4 as the solid lines. An


actual picture is shown in illustration #5.

The standard glider has an 82 degree nose angle. The billow (measured in degress of extra angle that the sail


:Iiese  a11 )


is sewn with in relation to the frame

is usually 4.0


degrees per side.  The L;D, sometimes called 'glide ratio'' (distance traveled horizontal in relation to distance traveled vertical) is around 4 to 1.

A high performance standard (illustration #5,dotted


lines) is a standard with less billow for less drag (il­ lustration #6 at, a wider nose angle, and a shorter keel (illustration #6 b). These aspects add performance but

as a result decrease stability which is graphed in


illustration #6 c for nose angle.


Looking at illustration #6 d, Case 1 shows the normal



keel camber for most standard gliders. Notice all the turbulent flow on top of the wing. This is because of the drastic

change in airflow direction and lack of surface area for this


air to flow along. If your keel were shaped as case 2, with negative reflex, it would perform better because of the lack of drag but would surely be a killer. It would have a negative moment (would want to dive).

A simple way to think about this is:  the aft section


of the keel acts as the elevator on an airplane. Elevator up - nose up. Elevator down - nose down.                                      Neutral reflex is fairly safe but in case of increased angle dives,

reflex should be put in so the glider will have some self­


righting ability. In the case of the  S keel, there will be a force up on the nose and a force down on the rear. This tends to cause a positive moment, depending upon

how much positive the aft section of the keel is.


The more it curves up in the back, to a point, the easier it will come out of a dive. (5)

Illustration #7 shows the evolution from the standard


to the high performance hang glider. The truncated tip is


a tube on the end of the leading edge spar with a couple of degrees negative angle of attack for washout. This design increased performance but was given to the roached batten tip for less weight on the tips for easy turning and a more

defined washout with good stability. With this washout (less angle of attack towards the tips) the billow would be de­ creased for higher performance. The radial batten tip is

now proven and tested to be the most efficient combination

between washout, sail billow and performance. If compared to illustration #1, it is seen that this resembles the end feathers of a bird. Two gliders using this principle are shown in illustration #8.

Further improvements such as an inflatable leading edge pocket are shown in illustration # 8 b. The conical wing design of the "Seagull" shown in illustration #9 has been evolving into a high performance glider since the beginning

of these machines. The unique cut conical design (with leading edges bent) shows excellent stability with increased performance as well as good handling characteristics. These new simple wings are now getting an 8 to 1 glide ratio.

The mono plane rigid wing (shown in illustration #10)


is controlled with rudders. This machine can reach speeds


up to 60 mph with extremely good stability and control. This glider will takedown to a very simple package. Because of

the complexity of launching1  this glide.r is usually left


to the expert. In this same performance area (10 to 1 glide ratio) is the biplane (illustration #11). This is better performance wise, but has the disadvantage of being not fully collapsible.

In the last three years, hang gliding has doubled


its performance. An overall comparison is shown in illustration


#12. Notice the jump we are now getting on the birds.



V. Aspects to Consider in Glider Design


There are different types of stability. If an aircraft gets into an unstable position (steep dive or yawed sideways)

it will stay that way or oscillate back and forth. This is called static stability or static instability. In this case the straight and smooth aircraft will continue on its path unless disturbed by some force.

Dynamic instability is the worst type of instability. Once the aircraft starts to go off line, it will,                                          increase until you correct for its bad position or until the glider stalls, spins or dives.

Dynamic stability is the correction of this airship


to its safe, controllable flying position when disturbed or brought into a dangerous altitude or position. Therefore, dynamic stability is the desired condition in most cases. Smaller nose angles tend to dampen yaw for this increase in stability, the efficient area of the wing span is shortened and air does not hit it straight thus giving less performance

per unit length of leading edge. This is shown in illustration


#6 c by the larger stabilizing force and the greater difference between the angles alpha and beta in illustration #6 b.

The angle of attack is the angle of the wind hitting the wing (g illustration #6 d.) A wing stalls or looses lift when the angle of attack becomes too high. To keep the tip of the wing from falling off near a stall, the tip is put at a

lower angle of attack so the wing stalls (or looses its lifting force) near the center of the wing first. This characteristic

of the wing twist or washout is good for landing and taking off, but is less efficient at high speeds because the air hitting the wing at different angles of attack.

Positive pitching moment is the ability of the wing to




pull out of a high speed dive. NASA reports show that the standard glider has a negative pitching moment without reflex. With reflex, this value is brought up to around 0 or neutral.

Aspect ratio equals (wingspan squared over the area of


wing)G'more of a long thin wing.  Gliders with aspect ratios greater than 5 have more of a positive pitching moment, as long as the airfoil being used is not known to tuck under (vertical dive). (13)

Now we start to mix between the high aspect ratio. Kites and the tailless foot launched sailplane. This class we will call a foot launched glider (flg). These flg's have a pitch advantage of little weight shift to cause a large pitching moment. Also the tailless glider really does have a tail. The tail is the trailing edge of the wing itself. This is because that near this trailing edge, the airfoil is reflexed up

(bent up a little bit) which gives it an up elevator tendency as the speed increases. On·.a swept  wing  this reflex  should

be put on the tips for a better moment about the aerodynamic


center, (illustration #10 b). This reflex is measured as a percentage of the location where the chord line crosses the camber line. 100% is unstable and would have a negative moment to tuck under in a dive (illustration #14). (11)

For a stall condition the stability is a function of aspect ratio and sweepback as shown in illustration #13. In conclusion: pitch stability is a function of washout, sweepback, and reflex of the trailing edge.

Dihedral angle is the angle that the wings make with the


horizontal plane. In a calm air situation a glider would

dynamically stabilize from rolling with some dihedral angle (e.g. 10 degrees). Turns can be slower and the down wing tends to lift rather than drop. In more turbulent winds however, (since the center of mass is lower) the glider has a pendulum like oscillation. (7) Since we have the ability to correct

for these oscillations dihedral is usually put in for


cleaner turns.


Control ability is ideal if there is finger touch move- ments needed by the pilot to make the wing dive, turn, and climb. Control surfaces are the most efficient way to use pilot energy to turn the craft. The natural or free sensation is retained if these control cables are hooked to the body

so that only body movement is needed to act on the control surfaces. In turbulent conditions the pilot gets thrown around which activates these rudders. For this reason some pilots prefer a hand twist grip setup. Rudders (tip rudders) can then be deflected individually to turn, or both at the same time for dive brakes. Three dimensional control with a

stick is needed on large gliders where weight shift can't

,-.o1       n

contr6l:fpitch movements.


On the smaller gliders (wingspan 32 feet) weight shift has become a standard in all gliders except rigid wings. Simplification of glider as well as weight and drag elimination tend to make weight shift control a major design focus. Tip rudders tend to decrease overall performance because they disrupt the vortex flow of air from the bottoms high pressure

to the tops low pressure. Efficiency can be increased up to double, if a vertical fin is placed in the middle of the

glider. Other control surfaces should be kept away from the tips because they have less effect as control elements because they are in this turbulent vortex flow area. (11)

Wing planform is a top view of the wing as it lies in


a plane. Nose angleAchord taper outline the main shape of


this planform. The straight and square tip are both less efficient than a wing with a good taper. The tapering of a wing to a tip chord of less than one-fifth the root chord is considered a cut off point where the bad effects tend to be more pronounced. (14)

The tip at the end could have rake (which is positive


when the trailing edge is longer than the leading edge). Positive rake will increase the L;D (lift force over drag force) but is not as structurally strong. Shaping the tips smooth and sharp to the end also improves performance. (14)

The birds wings in illustration #15 show a thickness taper down to flat at the tip of their wings. This is the secret to good wing tip formation. This is most efficient for the bird who has spoilers and landing feathers, who also doesn't worry about dropping a wing tip near the

ground. For a more stable aircraft wing with maximum performance,


illustration #16 shows a wing that has a good stall pattern with no compromise in performance loss.

A long and slender wing is much better than a short,


fat one for performance. The lateral movement of the air down the wing is decreased as well as the vortex flow (drag) with

a higher aspect wing (illustration #17). A compromise between


a high and low aspect must be reached because of the support

loss of the high aspect. In formula: aspect ratio equals wingspan2Jarea of glider. For a standard glider this number is around 3,   where high performance hang gliders run between

6 and 7, and competition sail planes run around 18. For weight shift purposes as estimated aspect ratio of 7 or e will be


the limit. Performance increases as a function of angle of attack is shown for different aspect ratios in illustration



Since airfoil stability was discussed earlier, the focus will now be directed towards airfoil performance. To compare

the thick and thin airfoils, we will use NASA 0006 (illustration


#20), and NASA 23024 (illustration #21). We first notice that the thin 0006 stalls at 12 degree angle of attac,'this in itself is a disadvantage for takeoff and landing.


Th ASiiP 2 1                   Th                             AAf & l

g =  8        Q  =  12                 Q  =  8        Q =  12

cr, =

.8     cL =

.8                cL =





L =   1.1





D =   001


=   .011

c   =   .012   c



D                                                       D                            D =








Q   =  Angle of Attack





L =  Coefficient of Lift


D  = Coefficient  of Drag

Speed is a function of angle of attack. At e degress  the wing is going faster than at 12 degress. When the thin airfoil

is going fast, it has the same CL as the thick airfoil but not as much drag. Therefore this thin section would be more efficient and go faster than the thick section at small angles of attack. At slow speeds with high angles of attack the CL

of the small airfoil stays the same while the CL of the thick




section goes way up. Also the thick section will not stall until 16 degrees where the thin will stall at 12 degrees. To summarize: the thin airfoil is better at high speeds and the thick airfoil is better at low speeds.

Strength is of great importance to an air machine. If


the wing fails in some way, the pilot's life is in great danger. In building a glider if one sticks with the saying "It's only

as _strong as the weakest part," and is sure to analyze every small part and stress point, the glider will be airworthy. Force in aircraft is rated in G's. This is defined as the force there is in one G. If the glider started free falling

there would be no G's on it. To stay in a turn, there are more G's applied as shown illustration #22. Gusts and high speed turbulence flying as well as acrobatics cause high G loadings that must be taken into account.

Special aircraft hardware must be used to insure the light­


est and strongest possible glider.


Wing loading is measured as the (total weight in pounds of flying machine and man) I (total area, square feet) of the' wing. Generally, the larger the wing loading, the faster the glider will fly as well as the faster it will sink. This

wing loading principal can change ofcourse with the character- istics of the wing planform and airfoil shape. General values are given in illustration #19 for wing loading and forward

speed. Wing loadings for foot launched gliders run between

o.e and 1.2 lbs/ft2. The larger values are for the higher per­


formance gliders. A safe wing loading and therefore speed must be chosen for safety and performance to match with the

gliders purpose.


Portability is one aspect that makes hang gliding possible for most people. An important advantage to the standard frame

is that it can be folded up into a 17' to 21' long tube with a diameter of about eight inches. This is done by taking out bolts at the point K (figure #23) and folding the crossmember H along the keel B. The leading edges C are then dropped back

parallel to the keel. Rolling the sail up with wires and control


bar packed inside, the pilot can easily take this tube on his car. With a weight of 3e lbs. this glider can be packed on the shoulder for almost unlimited access to any mountain top.

Most can be reached with a four wheel drive. Another practical advantage is the ease in storage. It's easy to put up in a garage on hangers or suspended from the ceiling by ropes.

Rigid wings do not have this portability advantage. They must' be hauled in a box on top of the car or in a trailer and they are not comfortable.

A high speed range of a glider is the main criterea most


designers are striving for. A slow speed is needed in a glider for easier launches and establishing a minimum sink rate for floating up in a lift (vertical wing current) situation. High speed landings on foot are dangerous. With slow speed foot launched gliders, landings are as soft as a feather.

High speeds are needed to get quickly away from down air currents. Longer distances sometimes must be covered with

ease and altitude. A glider designed for higher speeds flys


more horizontal and therefore loses less altitude per unit distance (better glide angle).

The needs of soaring, gaining altitude, and going long distances, is therefore a good speed range. The pilot would

then be able to change his flying speed to different atmospheric conditions ( such as an increase or decrease in wind velocity).

VI. RAZR Project


In the last two years, hang gliders have evolved extremely fast. There have been a lot of new radical designs out. Many people have died test flying these prototypes also. We

have now got some good safe designs. The gliders now are small


enough to be turned by weight shift and have a single surface at a high aspect and maximum area. A double surface that would change its thickness with speed (higher speed thinner airfoil; lower speed thicker airfoil) is a major step in increasing performance while not sacrificing weight shift control.

The development of a changeable double surface started


around Christmas of 1975. The planform first looked like illustration 24 a. Evolving on paper to figure 24 c, the aspect ratio was increased as well as the area of the double surface with relation to the total area of wing. The ribs were hooked onto the leading edge to make a more rigid structure and avoid wing changes at extreme angles of attack or odd positions.

The single surface tended to stabilize the wing while the performance is achieved in the double surface.


The theory of the Razr is a changing airfoil as a


function of angle of attack and therefore speed. If the double


surface at the nose is cut away (shown very well on the cover of this report) then air is allowed to flow into this double surface. With more vertical air (high angle of attack) there



is more projected area of this ram air, thus causing a high pressure inside the wing in relation to the outside top surface pressure which is lower any way because of the angle of attack. Thus with both pressures working with each other, they tend

to find the most comfortable airfoil profile which tends to fill in the vacuum or drag area to a smooth laminar flow situation giving the most efficient airfoil for low speed (figure #25). For a low angle of attack the opposite is true.

Less projected area causes a lower pressure inside with relation to the upper surface and therefore gives a more sleek airfoil

for higher speeds." The air goes in the ram air, pressurizes


the inside and then flows out at the tips.


This changing shape of the Razr can be compared to the changing shape of the dolphin. For the energy put into locomotion for the dolphin, his speed is outstandingly fast. A dense elastic membrane covering a viscous fluid enable the dolphin skin to compress under pressure to eliminate that impact drag. In low pressure or vacuum areas, this skin can expand and fill in that vacuum area to allow smooth flow

and eliminate a separation of the fluid into a turbulent area. When the Navy used this principle on a submarine, the speed doubled for the same conditions.

The inside and outside pressures of the Razr airfoil


allow total freedom for the surface to form to the most efficient shape for the immediate condition.

Vortex drag, which is air flowing from the high


pressure on the bottom of the wing to the low pressure from


the top via the tips, (illustration #26), is reduced by  this




smooth flow out the end of tips. Using this theory concerning the elimination of tip drag and high efficiency of the airfoil, it was time to start construction and find out how this would really work.

The glider was built in the summer of 1976, funded by Steve Sheehan and Ken (Zulu) Kuklewski of Sierra Wind Sports in Reno. The best hardware from the leading manufactures was used to produce a high quality frame of good structure..The sail was cut out and brought to a seamstress who we worked with. The glider is shown soaring (figure #27) after its 15th test flight.

The main problem in test flying was learning how to fly


a glider with such high performance characteristics. The first few flights were uncontrollable over-corrections. It was hard

to say if it was the glider or the pilot. Testing moved immediately  from the rocky mountains of Reno to the softer sand  and consistent sea breezes of San Francisco. After much trial and error, it was getting excellent performance as well as carring heavy pilots.

Different leading edge cambers were tried for ease in


turning. The tips turned down worked best and gave the most desirable flying characteristics. After flying the Razr for about 2 weeks, we realized that modifications must be made. It was noticed from figure #2e that there was too much material on the bottom and not enough on top. Shifting more material to the top (figure #29), a rotor area is taken away and a more efficient airfoil is established. Since no air

was flowing through the nozzles (nozzles at tip of wing on

trailing edge. Figure #27), they were also removed. The stability of the pitch was so positive that the trailing edge was cut linear for ease of turning and elimination of that positive camber at the tips. This positive camber was pitch stability from dives but also adds drag. This new profile as well as the closing of the ram air is shown by the dotted lines in figure #24 c.

The new Razr is shown flying in illustrations 30-36.


Illustration #32 shows a smooth wing twist out to tips. In illustration #34, notice the flat transitions of the double surface to the single surface. An abrupt transition would cause drag.

The speed range is what had been expected. It doesn't


take much running to get it off the ground. Top speeds were tested by climbing all the way foreward on the control bar (illustration #35), notice the arm position in relation to

the other pictures. The arched body is for streamlining. Esti­


mated speeds of up to 55 mph were achieved with the glider always having a positive moment (tendency to pull out) when the bar was released. Flying next to other high performance gliders the minimum sink was as good even though the wing loading was greater. At moderate speeds (25 mph) the glide is extremely flat, estimated to be 8 or 10 to 1.

Turning was a matter of learning how to turn this new wing. Improvement is still needed for roll but future testing and experimenting will tell. Pitch control is very sensitive with only a 7 foot keel and is always positive at higher speeds.

In quest for the perfect air flow and most efficient flow through the inflateable pocket, the escape opening was modified several times. From figure #30 it is noticed that the air re­

lease    tip of glideirs) very small and fat in comparison'


to the large skinny opening in figure #31. At higher speeds the pressure inside the wing was too small that the bottom collapsed when the escape nozzle was too big. Also, minimum sink efficiency was decreased.

With the estimated air f   low through the nozzles more exact, another modification was done. The ram air was closed and supported from collapsing by an aluminum rib. The bottom

surface out on the tips was slightly cut out and a more efficient


escape nozzle was sewn in. The wrinkles and negative cup shown in illustration #30 was taken out by scalloping the trailing edge to look like the yellow outline of illustration #24 c.

Shape of the inflatable double surface is of main concern. Illustration #33 shows the bottom of this surface while in flight. This is before the air escape nozzle was opened up.

When it was opened up too much this surface was concave instead of convex as shown here. Illustration #36 is most interesting

if the leading edge is observed closely. The camber at the nose is small and it increases toward the middle and then tapers

ever so slightly towards the tips. Also, the high camber is what was expected with the slow speed (noted by body position).

VII. Future Plans for RAZR Project


A project already being considered is shown in illustration


#37. The double surface has more percentage area in the wing and the crossmember will be inside the double surface.

A fully cantilevered wing with control surfaces is also being considered. It would be a foot launched sailplane similas to illustration #38 (which is now being built in Lake Tahoe), but smaller. The wings fully collapse and would use the inflatable double surface idea.

A patent on this changeable double surface airfoil is now' in the making. Hopefully, the design will be sold to a leading manufacturer and thus be developed to its full potential.

VIII. Conclusion


Hang gliders have progressed to a stage where the single surface airfoil is giving its maximum performance. The in­ flateable double surface is a major breakthrough in their evolution. This is shown by the performance of the Razr. It flys faster, sinks at the same rate, and is stable or more stable than the high performance gliders on the market. With all these good characteristics, it also has less area than

is recommended for single surface gliders of today.


These conclusions are not drawn from theory only, but from actual flying and testing. This is the break though that has been needed for about a year. The future of foot launched gliders will soon be using this idea to increase the perfor-

mance of these flying machines to a maximum. With full development


of this idea, we will soon equal the birds, not in ability, but in flying apparatus. This alone has been a goal of man since the beginning of time.











1.     Abbott, Ira H. and Von Doenhoff, A. E. Theory of Wing Sections, pp. 452-453, 506-507. New York, Dover Publica­ tions, 1959.


2.     Boone, Dick Evolutioof the Radial Tip Glider.       Ground

Skimmer Magazine. No. 4):21-2). August 1976


3.    Hall, StPn Stnbility of Tailless Gliders. Ground

Skimmer. No. 42:22-26. July 1976.


4.      Hamilton, Paul What is Hang Gliding, p. 1.  Program for

2nd Annual Reno Fly In. June 12-13


5.    Hamilton, Paul Pilots Workshop••Glider Aerodynamics.

Glide Path Magazine.  No. 2:18-19. May 1976


6.     Hayward, Charles B. Practical Aeronautics, pp. 12-15.

Chicago, A erican School of Correspondence.  1912.


7.    Lougheed, Viator Aeroplane Designing for Amateurs,

pp. 43, 58-59. Chicago. The reilly and Britton Co.                     1912.


8.      Mac Cready, Paul B. Hang Gljder Performance: Compar­ isons, FP damentals, and Potentials.   Ground Skimmer Maga­ zine.      Nr. 38:22-25.   March 1976.


Me KinJ.ey, James L. and Bent, Ralph D. Basic Science for Aerospe Vehicles, 4th ed.,      pp. o8, 89.                      New York

Me Graw-Hill Book Company. 1976.





















Ma.ltby, R.  L. Flow Visualiza.tion in Wind Tunnels Using IndieatorB. AGARD ograph 70, pp. 108-109. North Atlantic Treaty Organization Advisory Group for Aeronautical Re­ search and Development.   Royal Aircraft Establishment, Bedford, .England. April 1962.


M8rske, Jim Experiment in Flying Wing Sailplanes,

pp. 44-45, 14-15. Jim Marske, 130 Crestwood Drive, Michi­

gan City, Indiana. 1970.


Pointer, Dan Hang Gliding the Basic Hangbook of Sky­ surfing, 6th ed., pp. 39-60, 63.  Santa Barbara, California. Daniel F. Pointer. 1975.


Valle, Gary Gliders Pitch, Stability, and Control. Ground  Skiru.ner, No. 42:44-46. July 1976.



Warner, Edward P. Airplane Design: Performance, 2nd ed., pp. 30. 240-246. New York. Me Graw-Hill Book Company.


Bibliography (Cont.)






15.      Manta Wings, 1647 East 4th Street, Oakland, California.


Product Pamphlet.




16.      Seagull Aircraft, 3021 Airport Avenue, Santa Monica, California 90405.    Product Pamphlet.




17.      Delta Wing Kites And Gliders, Inc. 13620 Saticoy,


Van Nuys, California 91408. Product Pamphlet.




18.      Ultra Light Flying Machines, Box 59, Cuperino, California.  Product Pamphlet.




19.      Bede Aircraft, Inc. 355 Richmond Road, Cleveland, Ohio.       Product Pamphlet, p. 12.


Feb 16th

Weight-Shift Control Trike Aerodynamics- Wing tip angle of attack (AOA) in turns test demonstration Part 2

By Paul Hamilton


There has been a question about the basics of angle of attack of the tip in a turn for the weight-shift control trike wing considering wing twist and roll dampening. Here is a simple test with airflow and angle of attack clearly shown for a turn.


We saw in the last video that the twist in the wing tip could vary as much as 6 to 9 degrees up and down from neutral in extreme turns side to side in the Revo Rival S trike. This was a simple test, but the measurements were simple, reliable and repeatable with error bands providing a reliable 6 to 8 degrees twist change. We calculated the roll dampening factor. Here we are actually able to look and see it.


Here, with this visualization of actual airflow and wing twist in relation to the airflow, we are able to see the angle of attack of the tips for the phases for a turn. We went 60 degrees to 60 degrees bank to be able to detect the airflow and angle of attack of the wing. Any smaller is just too hard to see a significant enough change to provide reliable conclusions.




So based on our visualization of this video, we will break the side to side (60 degrees left to 60 degrees right) turn down into six distinct phases. We have not considered the adverse yaw which is a completely different topic. Phases of the turn:


Phase 1 Initial weight shift/billow shift, washout/twist change.


This is where the weight is shifted, side pressure applied and the tip twists to reduce lift to start the roll.


Phase 2 Start of the roll.


This is where the wing starts dropping and starting the rolling momentum of the heavy wing above. The wing is just starting to accelerate down. Side control pressure is present to provide maximum twist in the wing to continue to roll/accelerate the wing down. Here we have a significant reduction in angle of attack of the wing from the billow shift/washout/twist change to provide enough tip roll moments to roll the wing.


Phase 3 Mid roll acceleration.


This is where the wing has gained some roll momentum, shown here as the “wing level” rolling side to side, and still gaining roll momentum. Here we see the angle of attack on the wing start to increase as the roll dampening (change of airflow to the wing as the wing drops increasing the angle of attack of the wing). Here we see the roll dampening start to increase. Here roll pressure is still applied to provide as low as angle of attack on the tip as possible to continue the roll.




Phase 4 Max roll acceleration.


This is where the roll momentum has built and the wing is dropping at the maximum roll velocity. Here the roll dampening is at its greatest and the angle of attack on the tip is the greatest because of the roll dampening. Here we are past level and the turn is initiating in the other direction. This is where adverse yaw is probable the greatest and trying to catch up with the turn.


Phase 5 Roll deceleration.


Now we have some centrifugal force and we can release the control pressure to let the centrifugal force bring the undercarriage out directly under the wing and stabilize the turn in the opposite direction.


Phase 6 Stabilized turn.


Once the control pressure is released we are in a stabilized turn and the angle of attack on the tips is equal as in level flight except we have greater g loading in the higher banked turn.


It should be noted that in a WSC roll the weight of the undercarriage provides substantial rolling moment. However, the percentage of actual weight shift verses aerodynamic billow shift/washout/twist change  rolling moments is largely dependent on the specific trike design and the ability of it to provide the twist change from the weight shift, wristed keel or roll assist (which is used with the P&M STARS system). Based on calculations, I estimate the percentage of weight shift rolling moment to twist change aerodynamic rolling moments to range between 25 to 75 percent of the total rolling moment for the trike depending on the specific design.


 We have a large range of trike designs out there with different design characteristics…


Feb 6th

Cross Country (Long Distance) Flying Prep & Gear

By Rizwan Bukhari

Hi all,

I wanted to start a blog about cross country flying. For new pilots who are exploring long cross country flying, what considerations should they take?

Jeff trike made an awesome recommendation "Delorme Inreach" a PLB (Personal Locator Beacon) GPS tracker that allows two way text messaging.

How about a tent, tie downs, thermal blanket, knife etc?


How do you prepare for a cross country trip? What would you take to your cross country trip? Any brand recommendations that have worked well for you?









Jan 31st

....cont.... the sound of silence, second bit.....

By monty stone

back at the hanger the engine, a 377 rotax, sc, si, was disected, the engine, had been fitted with a 'rebuilt ' crank, but the main bearings had steel ball cages, instead of delrin, and one cage had broken up, and had locked up the crank. on reflection my choice of a field was obviously very wrong, i don't think i panic'd, but certainly 'target fixed' on that field. what has all this to do with trikes? well, the older ultralights and 'unsophistacated ' trikes' both feel similar when flying, you 'fly' the wing, how you 'get there' is a little different , but speeds, climb rate, landing speeds are similar, (naked, older trikes!). the main difference, apart from the 'obvious' reversal' is the rudder. the rudder  is VERY dominant in ul's, neglect it and you'll be slipping and sliding all over with adverse yaw that'll keep you awake at night! we trikers are SO spoilled, due to some 'fancy wing design features, that we ' wingliterates' have been eagerly absorbing of late,  we ALMOST don't have to ko-ordinate our turns! (i did say almost!). and 'we don't need no stinking rudder! but we do need to make better 'landing field choices.' in my 'defence' this was my first emergency landing, though not my last!                                                               no damage, scratches only so i'll pretend i planned it.                                                                                                                                                                                                                                                                                               ps, this plane had a second chance chute, but it never entered my head to use it, i still had control and a triangular field in view! plus the 'boss' woulda 'reamed me a new arsehole over the repack cost!                                                 pps, to newbies only, when that big fan stops during a glide at idle  you will pick up a bit of speed and distance  due to getting rid of that big 'disc umbrella'.                                                                                                             ppps. 'cross-control' to increase drag doesn't have much effect with a 3inch boom tube.                                                                                                                                                                                                                                                                                                                      ..................freazier nutszoff

Jan 31st

the sound of silence part one!

By monty stone

the flight was routine. i was flying one of  five beaver ul's that our flying club had. it had a recent engine overhaul and i flew it, to check it out, for free, avoiding the $20 per hour rental. i was over our local training area we refered to as the 'valley of death', we named it due to several ' failed arrivals'. the asi started to slow, so i gave it more gas whereupon it seized,  and my world got 'silent'.   i set up a decent glide angle, i was at about 900ft with abundant grassy fields, so, ignoring the REALLY suitable field directly under me i 'fixated' on a triangular field, WAY smaller, and had numerous obstructions around it, the right side had a long row of tall poplars and buildings, the left side had a barbed wire fence with many black and white cows munching away on the other side. the 'base' side had power lines and a small river with houses and a road. we had always tried to 'arrange' unexpected landings close to a road to facilitate retreval. by the time i had second thoughts about my choice it was too late to 'start again'. most things get bigger, the closer you get, this triangle shrunk! i cleared the power lines, my chief concern, and started my 'round out' at about thirty feet, prior to flareing but as soon as i got in ground effect the plane would'nt sink, it just floated and floated! the 'sharp'corner' of my 'trigon' was getting closer, quickly. i figured at this rate i'd be in the 'tidal swamp' that waited for me at the end of my 'field', though at the time i didn't know  what was there. any how, i decided to 'wheelbarrow' it in, trying to break the nose-gear off and hope the 'jagged bits' would stop me. well, i hit on the nose wheel very hard, but it only bounced me up. by now i was running out of everything, altitude, airspeed and ability! this particular planes nose wheel was fixed, didn't steer, so was REALLY rudder dependant, i had full left rudder and swerved into the barbed wire, and stopped. i got out and walked the six feet to the end of the field. there was a five foot drop into 'ooze' that flooded twice a day with the tide. i turned my attention to the engine. the prop was now free, a common feature of two stroke seizures, the float bowl was full of clean gas, no water or debris, WTF! i saw a barn in the cow field and saw phone lines going to it (this was before cell-phones, a world without them!), i explained to the farmer i had a 'emergency' landing and could i use his phone to call the 'boss' of the club. while waiting for help to come the farmer told me that a few years before 18 skydivers had perished in his field when their plane nosed in. the boss and his mechanic arrived, we held on to the wing while the 'boss' fire-walled it, till it seized again. his mechanic took one of the other engines off another beaver and fitted it, we held on to the wing while the boss rev'd it, when he nodded we let go and he took off, clearing the power lines by a few feet! cont......

Jan 29th

Trike flying is so much fun

By Rizwan Bukhari

In the recent past, we have discussed a lot about accidents, In the end if you train well, take care of your aircraft and fly in safe conditions then there is nothing like trike flying :D Aviation is only as safe as you make it.


Here is a beautiful video of pure joy of trike flying.





Jan 25th

Experimentation to develop understanding of aerodynamic phenomena.

By Joe Hockman

I am going to start this blog by saying something that might ruffle a few feathers.  If you think about where we have come since Francis Rogallo days we can reflect on a rather consistent evolution and many may argue we have come a long way.  I can easily defend an argument that states we are still in the dinosaur era.  One factor at a time experimentation, tweaking and copying another manufacturers design improvements have led us to the slow evolution and state where we are today.  But if I think of where we could be today given the time span, availability of new materials, etc and using more efficient methods to extract fundamental understanding of flex wing phenomena, quantified understanding of what specific design alterations and materials yield, gee we could be light years ahead of where we are right now. Ok so I may have caught your attention. If so read on.  If not then feel free to exit now from this blog and move on.

I keep hearing this oft repeated phrase, through "trial and error" improvements are made.  That my friends is the most often used form of experimentation to discover or understand complex systems because there is very little fundamental understanding on certain attributes or phenomena. But that is the most inefficient method of developing needed understanding and design improvements.  That is why I occasionally toss in the idea of controlled experiments.  But so far no one seems to have picked up on that.

So if you don't mind I will jump on my soap box for a moment.  In my 25+ years working in R&D at DuPont and previously many years in academia I have had the wonderful opportunity of working closely with many brilliant minds.  Chemists, chemical engineers, engineers with many other specialties, etc almost all with Phd degrees and some with 2.  I taught experimental design for more than 2 decades to these highly educated colleagues.  Almost without fail, all believed the only way to develop understanding of a "black box" system is to do 1 factor at a time experimentation.  This has been drilled into their heads through course and lab work in academia at both the undergraduate and graduate level.  Then I teach them statistical methods of experimental design which can be described as objective driven experimentation within an experimental framework that manipulates multiple variables simultaneously yet is able to quantify individual variable effects and variable interaction effects in a mathematical model.  OK off soap box.

I am not suggesting that any wing designer (P&M, AC, Airborne, NW, Evolution, etc) should go out and willy nilly throw together a bunch of experiments that involve changes to many wing variables without giving very serious thought to many implications including safety, feasibility, etc. To the contrary, all aspects should be considered.  With regard to flexwing design and developing quantitative understanding we could initially take some baby steps focusing in on one variable in a way that not only enables development of a mathematical model on how that variable adjusted at various levels impacts any aerodynamic or other performance criteria that can be quantitatively measured, but also develop good estimates of uncertainty about that model. Only through careful and disciplined experimentation can true cause and effect relationships be established.

A very important word on measurement systems. Only through the use of capable measurement systems can one reliably establish true cause and effect relationships.  A capable measurement system must be both accurate and precise, otherwise either biased and/or uncertain results are obtained.  Additionally, a measurement system should be both repeatable and reproducible.  Repeatability implies replicated tests or trials will give consistent results with low error.  Reproducibility relates to different operators (in our case pilots) being able to reproduce the results of other operators. To tie this concept into recent discussion, using thick reference lines and pieces of 2x4s to give approximate guesses on amount of twist is a very crude measurement system.  It is slightly better than a WAG but it does not have the required accuracy or precision to be a useful measurement system. It is also likely not adequately repeatable or reproducible.  For this type of investigation one would want to use the best available yet practical measurement technique. Abid suggested the use of AoA sensors mounted in selected locations.  If such sensors provide accurate and precise measurements and would yield both repeatable and reproducible results then this would be by far the preferred measurement system if it is indeed relatively simple and safe to implement.  Only by using capable measurement systems can we be confident that the results and models developed truly reflect reality.  Most every one has likely heard the term "garbage in garbage out" which is extremely important any time experimentation is conducted. I am not suggesting the crude measurement Paul H used to assess twist AoA was garbage as I already indicated my view is it was better than a WAG.  In a modeling context, you can have the best most sophisticated and beautiful empirical model in the world but if all the Xs and Ys are noisy and based on questionable measurement systems then the model is likely not useful.

The experimental methods I am advocating have proven to be effective, efficient and do accelerate the discovery and developmental cycle times of any program where experimentation is needed to develop true cause and effect relationships.  I am 100% convinced that if we have specific "improvement" goals for flexwings (and for what hangs below the HB for that matter) then a simple statistically designed experimental approach will help achieve such goals quickly. Through intently observing many discussions of a technical nature on this and other forums I am amazed at what is actually "known" or "unknown" about how flexwings work or perform under certain scenarios.  I contend there is a significant in the unknown category that should actually be in the known category. I also believe that when more fundamental understanding is available to designers, instructors and advanced pilots the more we can advance the sport for the benefit of our community and make the participants and equipment safer for all.

Lastly, even though I am not a designer or manufacturer of wings, I would certainly contemplate developing the needed relationship with one (or maybe more than one) to help them pursue their innovation and improvement goals in a very efficient manner.  I have already thought about approaching Kamron at NW on this.

Feel free to add your thoughts related to both experimental methods and potential goals that specific designers or the community could pursue.

Jan 20th

.....the wing's the thing!

By monty stone

a trike,  is  basically a wing, and a bunch of 'other stuff' hung under it. during flight at altitude, to me it is an object of 'adulation' and awe! (with a tinge of 'don't fail me now!). however many air mollecules hit it they are ignored!, but, UV will attack it. we in washington state run screaming for our 'moms' when the sun DOES come out. we don't 'TAN' we 'RUST', one month it came out TWICE! we all stayed indoors both days!  until recently when the trike wing 'gurus' finally began to blurt out the TRUTH about THE  WING! we sure had to squeeze them! , we, average trike drivers were abyssmally ignorant of the 'true nature of 'flex wing flight, now we are ALL eggspurts, more or less, and each of us could convert a stack of tubing and a roll of bedsheet into a wing, that somebody else should be willing to test-fly! !. we are completely at peace with them little engine pishkins hurrying to and fro 80 times a SECOND, just behind our heads. no problem, but that wing is our personal magic carpet, enableing us to enjoy the SECOND most pleasureable experience known to mankind, next only  , of course to sugar coated cream-filled do-nuts. the alluminum parts start to die as soon as they are born, though slowly. the plated fasteners pretty gold stuff starts to 'go somewhere else ' in a few months, but doesn't leave the fitting degraded, only 'unprotected' till the ensuing rust film will then protect from corrosion  . the wire bits get 'longer' but, unless kinked or cut, would probably outlast the other stuff, though mfrs, and wire co's reccommend replacement periodically. the 'jesus' bolt, the most feared and respected bolt in history, is also replaced, periodically, though a 'used' bolt has already been 'tested' and works, whereas a 'new' bolt is an 'unknown' quantity, to each his own. if replacing a 7$ bolt takes your mind off a 'looming' mega $$ wing fabric replacent cost then it works! so, how can we extend the life of our wing. don't ding the leading edge, (or any other wing tubeing), ONLY fly at night, i tried this, using a hand held flash light to help with the landings, and though fun, it has it's limitations.  but if you INSIST on flying in daylight then, realizing the insideos nature of UV degradation we cover, when possible, though it often 'aint possible all the time. i seem to remember some magic 'potion-lotion' that mega$$ yacht sails use to repel uv rays?? i paint my leading edges and outer two panels with a secret latex paint i get from my local hardware store, i tell 'em it's to paint my dogs kennel, i lied, i don't even have a dog, if i told them it was for my wing they would double the price and make me sign a 12page 'waiver', plus a seven day 'waiting' period, credit ck and homeland insecurity interview  . this 'secret' paint seems to accept being frequently rolled up by not cracking or peeling. this is on my 'lowly' northwing, my chronos repels it and looks like a 'molting python'. the french 'trilam' is slightly shiney and doesn't like being painted. when 'observers' point to the 'flakes' i put my finger to my lips and whisper ' prototype boundery layer test'. i recently sent a test patch from my morthwing to the factory and they said i had 10% of life left.  i took this as a  'kind' gesture, but at 82 they are being 'optimistic!,  for the wing also! . kamron said they usually 'retire' the wing fabric at 50% but the frame lives on! so, anyone out there in 'flexwingflyingthingamyland' got any ideas to prolong my life, i meant my wing's life let's have it,.............freazier nutszoff


Jan 20th

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

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.




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.




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