Tuck and Tumbles

[Abid]

Just as gyroplanes usually end up killing their occupants if they get to zero G, so do trikes. Generally in a parabolic arc of a flight, gyroplanes or any aircraft will reach 0G while still on its way upwards to the apex. Now at 0 G gyroplane rotor RPM slow down very quickly and blades start hitting the tail and prop and you find generally propeller blade tips at some distance from the debris field (usually still within 200 to 300 feet of main debris field). The main giveaway is that you will find propeller blades cut and the rotor blades having the color of the propeller blade marks on it somewhere and the propeller blades cut have no dirt or grime in them where they are cut. Meaning they did not get cut by impact damage. In gyroplanes if the pilot did not reduce power to idle (which he should) you will also find that gyroplane banked in zero G after cutting the tail and prop blades. This we usually refer to as torque induced bank or torque roll. This is a symptom of gyroplane having reach very low to zero G but it isn't the cause of it. We want to avoid designing machines that without pilot action can get into these low G situations and train pilots not to do things that will put the aircraft in low G situations. It isn't one or the other. It is both that produces chances of a safe result.


This problem is also present in trikes (weightshift control) and has killed it share of trike pilots. It was much more prevalent in 1980's and 1990's but through studying the problem they came up with tests to show that the machines are resistent on their own to get into these situations and mainly through changes to training curriculum these accidents today in trikes are very rare. Still one or two happen somewhere in the world every year. Like this one.

| | its_amazing_video · Original audio

. its_amazing_video · Original audio

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One paper that was done on this subject in trikes and presented some tests to show that trike designs were reasonably resistant to entering these tuck and tumbles inadvertently is attached below. The fudamentals remain the same in gyroplanes. Given the presence of a horizontal stabilizer, the same results can be expected from a gyroplane.

https://bura.brunel.ac.uk/bitstream/2438/733/1/Tumble%20where%20Test%20Pilots%20fear%20to%20tread.pdf

 

[rancherman]

Help me understand what I just seen here- The tree kinda obscured the climb out, but got just enough right at the end. It appeared to me there was a nose lowering input (or was that the beginning of a stall?) like half second before the massive tumble

When near zero g, balance (along with weight shifting control) means nothing? and the only thing I can figure is a prompt pushover from the engine thrust.
Right? Wrong?
Then the tumble quickly folds up the wing.

 

[Abid]

Help me understand what I just seen here- The tree kinda obscured the climb out, but got just enough right at the end. It appeared to me there was a nose lowering input (or was that the beginning of a stall?) like half second before the massive tumble

When near zero g, balance (along with weight shifting control) means nothing? and the only thing I can figure is a prompt pushover from the engine thrust.
Right? Wrong?
Then the tumble quickly folds up the wing.

It's not near zero G. You get to 0 G in the apex of a parabolic arc climb and your control inputs don't do anything. No weight = no weightshift control and pitch is completely dependent on that. So you are just along for the ride. Then it usually tucks and many times the pitch stability of the trike will let you recover but sometimes the tuck introduces a rotational inertia that overcomes pitch stability and dampening and it will start to tumble and once that happens the wing tips actually accelerate the tumble more and more with each rotation via aerodynamic forces. You get -3 G's in one full rotation. High thrust lines can add to this but this happens even when your thrustline is not that high. A trike having 2 people will have its CG lower versus a trike with one person as explained in that paper.

The idea that at the apex of a parabolic arc you are at low G and not zero G is not quite right. You certainly can be very likely to be at zero G

How zero-gravity parabolic flights work

The parabolic flight recreates a state of weightlessness during a zero-gravity aircraft flight to conduct scientific research without going into space.

www.airzerog.com

 

[Resasi]

Good post with valuable knowledge Abid.

Noticed it came from UK.

 

[Abid]

Good post with valuable knowledge Abid.

Noticed it came from UK.

Trikes became popular there in the 80’s even though they were invented in the US and given that a lot of them were flown from farm fields there whereas in the US people flew from airports it’s not surprising. Dr. Bill Brooks who is a friend designed Pegasus trikes another friend engineer designed Mainair models. Later they were combined to make P&M. These guys were very helpful to me in understanding the black magic that is the trike wing and how to optimize its design.

 

[wolfy]

I thought they were first conceived in Europe.
I have an old flying mate who started hang gliding when moyes first did by getting towed behind boats he also started building trikes well before they were available to buy. I was sure he told me years ago (when he started me in trikes) that he first heard of them coming from Europe. It may be my miss understanding though.

wolfy

 

[Abid]

I thought they were first conceived in Europe.
I have an old flying mate who started hang gliding when moyes first did by getting towed behind boats he also started building trikes well before they were available to buy. I was sure he told me years ago (when he started me in trikes) that he first heard of them coming from Europe. It may be my miss understanding though.

wolfy

Both hang gliding and trikes were invented in the US first starting with Dr. Rogallo from NASA. I guess you could consider Otto Lilienthal inventor of hang gliding originally. He was from Germany but Rogallo wing is the main ancestor of modern designs.

 

[j4flyer]

The bottom line is that there a few machines in the world that won’t / can’t kill you if operated outside of their intended envelope. Only training and the use of common sense can avert an accident.
Having said this, I am still finding after all these years (and now YouTube videos) , people who still ignore history and believe they can succeed without proper training. These folks are becoming stats that harm the sport and bring devastation to their families.

 

[Aerofoam]

The first ultralight I know of was an "Icarus hang glider with a little 2 stroke on the back that would be enough to maintain flight.
The quicksilver was turned into a weight shift trike-ish aircraft about the same time as the
Pterodactyl with an undercarriage and was basically a hang glider with a tricycle frame underneath.
They added the canard to make it 2 axis joystick controlled instead of weight shift. It had a 30hp. 2stk. Cuyuna.
The climb rate was so good they actually were careful to conceal it at shows where the FCC might take notice.
This was when the ultralight rules were being considered and people thought that the limits may include foot launched, or max. climb rate.
I think the climb rate was around 1200fpm., it blew away everything else.....

 

[Sv.grainne]

FCc? Please explain

 

[wolfy]

Both hang gliding and trikes were invented in the US first starting with Dr. Rogallo from NASA. I guess you could consider Otto Lilienthal inventor of hang gliding originally. He was from Germany but Rogallo wing is the main ancestor of modern designs.

Of course the rogallo wing was conceived over there but it was John dickenson and Bill moyes who bought them to the world as a hangglider.

wolfy

 

[Abid]

Of course the rogallo wing was conceived over there but it was John dickenson and Bill moyes who bought them to the world as a hangglider.

wolfy

Yes certainly all these guys were pioneers but Barry Palmer an American aeronautical engineer in California was attributed with first control frame hangglider and first powered trike that was also FAA registered. His second trike was in fact much more like what we would consider a trike today. None of the pioneers ever made any money from their inventions.