Jul 8th

More on turns....

By Bryan Tuffnell

ABOUT a hundred and seventeen years ago, an obstreperous bicycle mechanic with the very United Brethren name of Wilbur was busy concerning himself aircraft control. He figured that to turn an aircraft, yaw - which at the time most people thought held the key to turns - wasn't enough; a turn had to consist of the appropriate amount of roll, pitch and yaw. The Wright's lingering contribution to aviation is the concept that a turn is not a bend in an otherwise straight line but a three dimensional carved curve, and is why to this day we have control surfaces that operate in pitch, roll, and - usually, and it's important for us to understand that as trikers we have a degree of control of this - yaw.

A hundred and seventeen years later, it seems many of us trikers have forgotten Wilbur Wright's epiphany. We insult our wings in turns by rolling at trim speed and keeping it there, counting on the wing's inherent roll-yaw coupling to convert roll into some semblence of a turn. It works - kind of - and around we go, trike wings being generally forgiving of our lack of technique. Any lack of skill tends to go unpunished until a bit of load comes on... which it does when banked and turning... and this gets exacerbated by billow shift... which means that any absence of skill is most likely felt when trying to roll the wings level. In other words, you're more likely to have trouble rolling out of a turn than rolling into a turn, which is a bad time to discover you don't know something.

If you are flying straight and level and add bank, you have commanded the wing to fly straight with bank on - nothing more. The fact that the wing cannot do that is not incidental; the wing will fall off into an uncoordinated turn. But - here's the rub - while as trike pilots we have little direct control of yaw, we absolutely do have a measure of indirect control. To convert a slipping, banked flight into a coordinated turn we must add pitch. So, some rules:

  • ROLL gives BANK and SLIP
  • BANK and SLIP both cause a bit of YAW.

Okay, if that's as far as you go, you'll get a 'turn' of sorts. But it's like shifting your weight on a bicycle while steering straight ahead: your wing is out of balance.

  • ROLL and PITCH UP (pushing out) gives a BALANCED (COORDINATED) TURN.

Now, let's add finesse at the start of the turn: 

  • PITCH DOWN (pulling in) aids ROLL

There's sound aerodynamic reasons for this. You sometimes hear that pulling in a touch increases airflow over the wings and makes billow shift more effective, but that's not all. Who can give the correct reason?

And how do we translate this into real flying? We should have our hands fixed on the bar, a fair bit more than shoulder width apart (if your hands move, I recommend a couple of wraps of electrical tape on the bar to mark where they should stay. I also vastly prefer gloves to bar mitts, which encourage you to grab the bar the way a wino holds a bottle of Chardonnay - I like to have my thumbs either on top of the bar or pointing to each other along the back of the bar, never wrapped below the bar). Try this for an experiment:

  • Take your right hand off the bar altogether. Sit on it.
  • Roll to the left with your left hand.
  • Watch what happens.

You probably pulled the bar back a little as you rolled. No? Then try doing so. By pulling into the turn with just your inside arm, it's easy to simultaneously pull the bar back. Great! Now... when you're getting close to the desired bank angle,

  • PUSH FORWARD with the heel of both hands (not the crook between your thumbs and forefinger) until

If you've done this correcdtly, you'll whizz around and around in cirlces with no change in airspeed or bank. You'll lose altitude - unless you ADD THROTTLE - the final factor.

Rolling level should be the reverse:

  • REDUCE POWER while

I used to preach that any time you lost control in roll, reducing power and pulling in would always allow you to roll level. I don't say that now, because there are now trike wings that require you to have a basic grasp of turns, and such wings are not necessarily bad, they just won't take an insult: if you're slipping badly, you must correct for that before you're back in control (more on that later). This is may sound challenging, but is uttely fundamental to every form of flying, and every 3 axis pilot knows and comes to grips with this.

We're not riding bicycles here, we're pilots; we kid ourselves if we think that all we need to do to turn is to roll. If we do that, we're relinquishing our control from us as pilots and relying on factors such as sweep, dihedral, airfoil section, washout, midspan twist and a whole host of factors - down to the angle of struts and the size of our windscreens - to provide the control that we do not. You know how some wings have winglets? They exist because the designer couldn't achieve the roll-yaw coupling she wanted without compromising other aspects of her design. 

I want to stress that pilots are dying because they don't have a basic grasp of this. Henry and Ken's video is a great lesson: they are alive in all likelihood because Henry knew that pulling in (and reducing power) makes roll more effective, and under the loads they were experiencing was absolutely necessary. Several Arrow pilots have discovered that you cannot overcome billow shift in turns on that wing by rolling with weight shift, and pitching up to remove billow shift is needed before you can roll out of a slipped turn; knowing that has saved lives (my own included). 

I apologise to the majority of you who know all this... but I believe this stuff, and not pilot age or refresher training or lack of maintenance, is the biggest single cause of pilots losing control of their trikes. 

So, for a pop quizz:

  • What happens to billow shift in an unbalanced turn? In a coordinated turn?
  • Where is your weight in a coordinated turn?
  • Why does pulling in increase roll rate?
Jun 23rd

Finned wheel coverings?

By roger larson

Curious of thoughts about the finned wheel pants that are used on the trikes.  Has anyone flown with and without them on the same trike and noticed a difference?

The revolt doesn't have wheel pants.  What will be the good, or the bad of not having them?

Jun 6th

Trike Maintenance Kit

By Anton van Wyk

I have the following items for sale. It is brand new and I bought it after doing the maintenance course, but sold the trike soon after.


New - Sidchrome SCMT26922 - TORQUE WRENCH 10-160Nm 10-120ft.lb. - $250


New – 4 x NGK Spark Plug - BR8ES - $16

New – 6 x ROTAX 125 EXHAUST SPRING - 66mm - NON EVO Rotax Part No: 938795 - $20


New – Anti Static refuelling kit - $35

Wire Twist Pliers - $30

New – iPad knee dock - $35

May 7th

How to find Trike Pilots and Instructors near you and/or finding a place to get trained, transitioned or updated.

By Paul Hamilton


This has been an incredible start to the flying season. I have never gotten so many calls asking “where can I find a trike instructor near me?”


Good news and bad news. The good news is that most of the qualified trike instructors and many pilots are listed at:




This is the most comprehensive, up to date site to find pilots and instructors. This is where I send everybody. Pilots and instructors, please look at this and let me know if it is up to date for your area. I personally maintain this and try to be as accurate and comprehensive as I can.


The bad news is that there may not be a qualified trike instructor close to you. Many times it is better to travel and concentrate on flying with a full time established school and get it done. Your program is listed at http://sportpilottraining.sportaviationcenter.com/sport-pilot-applicant/sport-pilot-applicant-start/ We have two and sometimes THREE FULL TIME trike instructors ready to train you. I can give you your checkride. One stop shop.


Other trike instructors please feel free to list your web site here and MAKE SURE YOU ARE ON THE TRIKE LOCATOR http://lsapilot.sportaviationcenter.com/sport-pilot-locator/




Paul Hamilton, CFI, DPE LSRM-trike


Apr 28th

Rotax 912 float warning. Check yours. It can happen to you. It has happened to me.

By Paul Hamilton


Recently, I have had numerous problems with the Rotax Carb Floats. Luckily I was able to avoid an engine failure, just loss of power but enough to land safely. This has been for new and old floats. They absorb fuel and can sink.


Some say that the newer floats are OK, Wrong. Some say that the older floats are OK, Wrong. I have seen sinking floats in all ages.


It is really simple, run the engine or the electric fuel pump and fill the carb bowls. Pull the bowls and see if the fuel level is equal below the top of the bowl. See if the floats all look like they are floating at the same level and lastly take the floats out, let them dry and weigh them. If a float is more than 3.1 grams it is no good. Rotax sez 7 grams for both, but in my opinion, this does not  leave much room for error.


This is a simple safety check for all 912 carb owners


Check your floats.


Apr 11th

Initial Flight Review Airborne new M3-Sport trike with XRS wing

By Paul Hamilton


Just had my first test flight on the new Airborne M3-Sport trike with XRS wing. It was everything I expected. Note this has just myself (140 pounds) and one flight so these are my first impressions.


Nice improvements. What stuck out most has how straight it tracked. We would expect this with the huge wheel stabilizer area plus the winglets providing significant vertical stabilizer/rudder. Because of this, there is very little adverse yaw in the turns. No uncomfortable/odd slipping hard/scary to get out of turns. This lack of adverse yaw appeared to slow down the turn response slightly but the turn pressure is similar to the other high performance Airborne wings and maybe better.


With the minimum twist wing design, it performs surprisingly well with the 80 HP 912. Quite the glide for landing round out.


Again with just me, I could push the bar all the way to the front strut and it would not stall. When I brought it up quickly into a mild whip stall, the whole wing broke lift and pitched down quickly. Yahoooooo. When it stalls it stalls. No roll to either side and a clean straight break. We would expect this for a low twist high performance wing.


The trim system is about as effective as the other Airborne wings. Not a huge speed difference but I did not crank it to tight until I review this system better. From the factory trim was full throttle 75 MPH and glide at 65 MPH. Slightly faster than I like but I need to fly double with extra weight before I move the trim position on the keel.


What I really liked and thought was a big improvement was the offset engine angles providing minimum torque AND P factor effect throughout the engine and speed ranges. That high speed/full throttle irritating right turn of the older models drove me crazy. The combination of the engine offset with the vertical stabilizer area solves this problem.


Overall I think it is a winner and a great improvement. Make no mistake, this XRS is a high performance wing. You can get a lower performance wing on the updated/upgraded M3-Sport undercarriage and these should be options also.


This is a great option for the top of the line mid range priced trikes.


I will have this here for a while for demos as I train Warren the owner. Call me 775:772-8232 or e mail paul@SportAviationCenter.com  if you want more details for pricing and availability. 


Mar 29th

For sale Transmitter+intercom+headsets

By Jozinko Sajan

For sale:

- ICOM IC A5 (channel spacing 25kHz) with ICOM powered cable from board network what includes a voltage stabiliser and interference suppressor

- Intercom Pilot PA-200 with VOX, powered by 9V battery (without an interference from alternator) + velcro PTT

- 2pcs headset Pilot P51 with volume control, gel ear pads, microphones to a noisy background

All was flying on my trike.

Video link: https://youtu.be/C-QubOJcipU?list=PLCB48D3B4F688E77B

Why I cant give here photos? :) I will send you by email...


Mar 28th

Heated Clothing for trike pilots

By Paul Hamilton

Flying in ther winter can be warm and comfy. Everyone has their own ideas about this. I have tried to simply bundle up and use those heated pads. This helps but does not cut it for a professional trike operation in the winter. I need to stay warm all day and keep my customers warm all day. The only solution I have found the only thing that works for me is heated clothing. Simple.

Here is an excert that I have on my web site for winter flying:

It may seem that it is cold flying in an open cockpit when it is freezing out there. It may appear that winter is not the time to go triking, microlighting, ultralighting powered hang gliding. Let me dispel these misconceptions.


OLYMPUS DIGITAL CAMERA Yes it is cold out there but you can use a modern state of the art heating system used my the military. It is simply heated clothing. I now use heated gloves, boots and vests. Gloves are 22 watts. Boots are 22 watts. Vests are 44 watts. HeatedInsoles That totals 88 watts of heating right near your skin to keep you warm and toasty. heatedVest Imagine trying to hold an 88 watt light bulb, it would burn your hands. This 88 watts is efficiently put where you need it to stay warm.

HeatingCoils We have the technology and can use it. Have looked and tried other systems and chose the Gerbing heated clothing mainly because of the technology plus it is available at the local motorcycle shop so it is easy to get, add or replace as necessary. Other brands probably do a good job also.  Gerbings developed Microwire™ in response to a Department of Defense contract for heated clothing for Special Ops Forces. You will use this to stay warm while you fly. Enough said. Here we show you how we suit up with all the heating clothing to keep you warm.

Check out what you see while flying in the winter. Snow, cold/crisp air - warm and tosty. 

For those do it your selfers how to design your own system.

Mar 11th

Importing trikes from the US to the UK

By Paul Hamilton

Hey trike pilots in the UK. If I want to import a new trike or a used N Numbered trike to the UK from the USA, does any one know how or if this has been done?

There are four possibilities:

Ultralight 103, new S-LSA ASTM complienent, used S-LSA and used E-LSA. Any ideas, suggestions or contacts are welcome and helpful.

Now that the UK has left the EU, is this helpful for importing US trikes to the UK?

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.











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Bibliography (Cont.)






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