2 position collective for a LW - Jump Take-off

[magilla]

Think it's doable to put a direct drive cable (wunderlich type) prerotator and incorporate a 2 position collective on a tractor gyro??

Looking to develop a jump take-off for the LW type tractor gyro.

I figure with the increased length of the tail boom, the moment arm is pretty long to counter the torque from the rotation, so thrust from the prop against rudder should be sufficient to keep the airframe fairly stable.

Also, Bensen noted that 25hp on the Bensen Gyro was sufficient to hover.

With a LW weighing about 200 pounds more, I wonder what the HP to the rotor system would have to be?

And could a Wunderlich drive it?

Is it feasible to incorporate a collective pitch adjustment to the DW head?

Does someone have any plans for a collective pitch adjustment??

[Ga6riel]

magilla
If I am right, what you mean is, to engage prerotor puts a positive pitch into the rotor, and when you disengage, it automaticly returns to autorotative pitch.

I did see a model that accomplished this in a very simple way, I have little doubt some mechanical genius has done the same in full scale. I shall have a look around for the file.

[Screw]

Screw-In

What you are speaking of is called a "Jump Gyro." They tried this with the Kellett KD-1s or YG-1B in the mid 1930s. I believe six were destroyed through pilot error.

Although the concept has been proven through this and a few other gyros, the engineering involved, weight, power, and risk of pilot error just has been worth it to catch on.

Screw-Out

[pwendell]

Jump-takeoff sounds really good on paper, but can be a risky maneuver even under ideal conditions. I personally think it makes a lot more sense to develop a pre-rotator powerful enough to bring the rotors to flight speed -- 300 RPM or so -- reliably. This will allow the pilot to safely apply full power immediately and to place the disk at a relatively shallow AOA during the takeoff roll, allowing for rapid acceleration to minimum power required speed. Using this technique, very short takeoffs should be possible with much greater safety and simplicity than a jump takeoff. Such a pre-rotator may or may not require that the blades be depitched. I know that Larry Neal is working on this kind of pre-rotator.

I also think its worth asking if there are very many situations where Jump-takeoff is actually necessary as opposed to a very short take-off, say well under 100'. Remember that you can't count on a jump take-off to do much more than keep you off the ground long enough to build sufficient airspeed for flight. It certainly won't allow you to clear any objects and may actually result in more distance to clear an object than a good, short take-off. The more I've thought and read about this, the more I've come to think that jump-takeoff might be more of a 'gee-whiz', marketing kind of feature, than a practical and safe flight regime for a gyroplane.

Flame suit on.

[magilla]

Hmmmm.

Pete: OK. I agree - effective short take-off is what I am seeking far more than an actual hovering type jump take-off. I completely agree that the risk involved is far too much for the novelty.

However, would still like to work a "tube within a tube" concept to increase collective pitch for a short take-off, and to cushion for landing.

Having performed numerous autorotations to the ground (with engine at idle) in a helicopter, the idea of having a little collective cushion at the bottom is a safety feature worth a little additional engineering complexity.

Collective allows you to trade rotor RPM for lift directly...

Ga6riel - I was looking at more of two separate items combined - the prerotator accelerating the rotors to say 150% of normal flight, and then a two position collective to convert that to lift -and in doing so, be able to take off within one's own rotor diameter (at max thrust).

Not necessarily straight up, but rolling 10-15 feet and then climbing like a raped ape...

The difficulty comes in somehow converting a non-rotating movement into a rotating movement, and doing it without the typical helicopter swashplate. Maybe a flexible tube inside of the mast that is attached to each blade with push-pull tubes - a little movement either way adds or removes pitch from the blade.

Anyway, if the pre-rotator alone can generate lift by accelerating the rotor system, then that would be the best way to go - just need to figure how many horses required to turn the rotors to 150%.

[KenSandyEggo]

" (If) I am right, what you mean is, to engage prerotor puts a positive pitch into the rotor, and when you disengage, it automaticly returns to autorotative pitch."

The way it works, at least on my J-2 and the Air & Space, is you flatten the pitch during prerotation and then add full pitch and throttle on take-off. Mine doesn't have enough power except to get her "light on her toes." I got a heck of a jump take-off ride in an A & S with John Potter a few years ago. She shot straight up to way above the roof of a big hangar. However, it was about 20 degrees out.

I also got a ride with Jim Mayfield in the Groen Hawk a few years ago. She also shot up quite a bit before transitioning into forward flight.

[Ga6riel]

so whats the story Ken, would you go for better STOL ability rather than jump take-off, given the complexity ???

[MechFx]

Hi, sorry to interrupt the flow.

This machine was at Mentone 04, I dont have any info but I believe it was an attempt at a dual pitch adjustable head. I seem to remember an electric slip ring and some solenoids/elctromagnets involved.

could be way off track,

cheers

Art

[Dick Illyes]

Dick DeGraw had his jump takeoff machine at Mentone in 2005 and made repeated takeoffs from a standing start. He also had his LFINO (Leap Flight In Normal Operation) machine at Bensen Days in 2005.

I think in the next few years we will see much more robust pre-rotators and a number of solutions providing jump takeoff or very short run takeoffs.

I expect to see kits for most of the popular machines. This technology should also allow directing some horsepower to the rotor in flight for reduced rotor angle and higher forward speed.

[larry]

Iv been lookin at a lot of different gyros. I was looking at the dominater and they say they have a hydrolic pre rotor that will run the blades to 300 rpm. Is this true or just a marketing item?

[Biggles]

I had on show an electrically variable collective rotor head on show at Mentone in 2000. It was specifically designed to be a bolt on to Benson type gyros.

It was stressed to 2.5 times the spin up centrifugal loads and extremely strong in other ways with both mechanical and electrical stops, it weighed only 10 pounds more than a normal Benson rotor head. It needed to be manufactured totally by NC machine in volume so there were no accumulative errors and the cost would be OK.

It just had a 3 position switch sprung loaded to the center position on the control stick, the time taken to travel the 3 degrees was 2.5 seconds. The collective could be stopped in any setting in flight, I have some pictures if I can work out how to post them on this web site.

This would improve both T/O to about 20 feet with a normal hydralic spin up and skilled landing distances to 15 feet in a no wind condition.
Kind Regards - Robert Kelsall

[rtfm]

Hi,
I'd be EXTREMELY interested in finding out more about this. Any info at all wouod be welcome.

Regards,
Duncan

[KenSandyEggo]

A consistent jump-take-off capability could put the gyro into favorable competition with helis. I believe the Groen Hawk hoped to do this, and still may, but we're talking a big-ticket item in the Hawk.

As mentioned earlier, I went down to Kentucky to see John Potter for a ride in the A&S, and he showed me a 2-blade variable pitch head that I guess he and Don Farrington developed but never did anything with. I think someone here mentioned who owns it now. I don't even know if they tested it on a gyro. It looked like the one posted here a few threads back. That almost looks like the top of John Potter's head in the photo. Didn't he always wear straw hats?

I think the big drawback is consistent prerotation to beyond flying rpm. I can easily spin my blades to over 400 rpm depitched and that still doesn't give me a jump take-off when I pitch them and add full throttle. The A&S does, but I heard that it's not that impressive on warm days. I doubt if a Wunderlich prerotator will ever do the job. I believe it will take some sort of transmission like in the J-2 and A&S.......which means more money and weight.

[Ga6riel]

I think the increase in complexity is the inverse to a decrease in safety.