Effect of prerotation on takeoff distance

Gyro_Kai

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Peter,

this needs to be managed carefully, in order to avoid blade-flapping. I would ease the rotor back, so it starts catching the wind and wind up (I love the English language) to even higher RRPMs to avoid a too high forward speed to RRPM ratio.

Kai
 

Vance

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I don't have a strong enough pre-rotator on The Predator to use this takeoff technique John and it is not something I have tried with any gyroplane I have flown so I wouldn't know how to teach you.
 

All_In

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I don't have a strong enough pre-rotator on The Predator to use this takeoff technique John and it is not something I have tried with any gyroplane I have flown so I wouldn't know how to teach you.
Oh that make perfect sense to me. It's not something I need for many many more hours so it can WAIT!
 

AirCommandPilot

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Bensen experimented with keeping the prerotator engaged. We've got more power to play with now days.
 

SandL

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Peter,

this needs to be managed carefully, in order to avoid blade-flapping. I would ease the rotor back, so it starts catching the wind and wind up (I love the English language) to even higher RRPMs to avoid a too high forward speed to RRPM ratio.

Kai
exactly what I said in my post lots could go wrong very quickly
instant high speed agressive flapping, or an instant leap off the ground at high nose attitude way behind the curve.
A high ground speed over a bumpy rough runway causing all sorts or wear and damage (wear..... another gem of the English language)
All these potentially catastrophic issues for the sake of a few feet of take off run.
 

ckurz7000

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Ok, next time conditions are right, meaning there's little to no wind, I'm going to do a series of test flights quantifying the benefit of that short fielf take off technique in a gyro some more. The maneuver is not a death trap and actually quite safe if you perform it correctly. But just reading how much can go wrong in a normal takeoff, I am definitely jumping onto the bandwagon warning people to try it out all by themselves.

My first impression is that it may shorten the takeoff distance over a 50' obstacle by about 10-20%.

-- Chris.
 

All_In

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Ok, next time conditions are right, meaning there's little to no wind, I'm going to do a series of test flights quantifying the benefit of that short fielf take off technique in a gyro some more. The maneuver is not a death trap and actually quite safe if you perform it correctly. But just reading how much can go wrong in a normal takeoff, I am definitely jumping onto the bandwagon warning people to try it out all by themselves.

My first impression is that it may shorten the takeoff distance over a 50' obstacle by about 10-20%.

-- Chris.
I'm realty looking forward to the results. Your testing ROCKS!
 

Vance

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Lift off distance?

Lift off distance?

Ok, next time conditions are right, meaning there's little to no wind, I'm going to do a series of test flights quantifying the benefit of that short fielf take off technique in a gyro some more. The maneuver is not a death trap and actually quite safe if you perform it correctly. But just reading how much can go wrong in a normal takeoff, I am definitely jumping onto the bandwagon warning people to try it out all by themselves.

My first impression is that it may shorten the takeoff distance over a 50' obstacle by about 10-20%.

-- Chris.
I would be most interested in the difference in lift off distance Chris as it seems like a rough field maneuver.

Thank you for doing the test.
 

Stan V

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1. pre spin to a high RRPM with a flat disk (stick forward)
2. release brakes and accelerate, with prespin engaged (with disk flat)
acceleration will be faster than normal due to less rotor drag
3. At a certain point at wide open throttle, release the pre spin, ease the stick back and leap into the air,
4. Then hold it down to gain air speed



Peter
I'd first like to say, if I felt that I needed to use these short take off technetics to clear a 50' obstacle from a short runway, I would trailer my machine out.

Vance had made a statement on another thread, saying something to the effect that "until you have both your air speed and RRPM up to flying speed you were going no where." I agreed.

Every gyro has different capabilities, some can't pre-rotate to anything close to flight RPM, or even an RPM that won't flap the blades if you go flat on the rotor while accelerating.

If you own a machine that can stand on its prop and climb at an (unsafe) low speed (if power is suddenly lost), and can pre-rotate to flight RPM, you will be able to make really short take offs, but they won't be safe and may be unnecessarily hard on your equipment.

For me, when I can achieve Flight speed and RRPM at the same time, I've made as short a take off as I can safely make.
 
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SGK

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Your right on the money Jean.:)
Iv found that, for the shortest possable ground roll, you need to;
Prespin to max. rrpm, useing ground breaks and RTV to arrest any forward roll
Simutainiously stick full forward and hit WOT.
Acceleration is rapid, and wen at min lift off speed, ease back, all with the prespinner engauged.

Startn the roll with a virtical RTV means liftoff speed is reached much earlier, and wen you do pull back, the rotor gets clean air.

NB, i dont think theres a VRS, but theres definatly a time lag between startn the roll and the rotor getn clean air if the roll starts with backstick, which costs ground distance.

NB.2, if you plan on usen this method, think about it, hard, coz theres sum unexpected feed back thats a real attention getter.
I'd rather not to advocate such tecnique to be used on most modern gyros. With flat disc you can reach rather high forward speed and blades still flapping within limits. When pulling back in such situation, the stalled area of the disc just explodes and pang!
Depending on how much energy you have accumulated, it can end in nose-up and roll to the left without lifting and loop/roll ending in an ugly barbecue.
I would say: Prerotate to max. rrpm, stick back as much as the the wind allows, full power, nose high in the beginning and lowering before pulling back again for lift off.
If you think that risky techniques can help you to make shorter take off, you better find a longer strip.
 
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Brent Drake

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I'm very surprised at some of the comments. This is a short field or soft field takeoff. Your instructor should have driven this into you in training. It goes with rotor blade management.
 

AirCommandPilot

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Birdy, is there a video of you taking off using this method? It would show that it's not an issue if done correctly.
Sure blade flap would be an issue if you don't know what you're doing, but so is flying in general. He's not saying to "yank" back on the cyclic at high speeds. He's saying to "ease" back when the rotor gets enough RPM.
 

birdy

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At least you read wots rit Bobby, not many here can. :(
So no, sorry, i wont be postn anymore on this topic, certainly no vidio, untill these morons learn to read.
 

Jean Claude

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What's left to do now is to write some computer code or try some simple theoretical calculation to prove my conjecture.
Most pilots believe that the shortest is obtained by nose up of the rotor from the start of rolling. This is wrong. The static rotor thrust tilted back harming to the rapid acceleration of the autogyro. Other hand, as long as the forward speed is too low, the induced velocity by the pre-launched rotor prevents flow through the disc in the direction "autorotation" and the rotor slows down faster than if it were horizontal.
So, better hold the horizontal rotor, or even negative A.o.A until an adequate forward speed. Only now the stick to back may rapidly accelerate the rotor, when the compound the general flow and induced speed allows the air to flow through the rotor from bottom side to top side.

When pre launch is powerful, it is particularly favorable to start with negative AoA of disc.
This just is my result of simulation.

 

EI-GYRO

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It depends;

It depends;

Cant wait for all the budding Chuck Yeagers to start trying this.

Are there not enough people screwing up takeoffs as it is ?

A guy asked me recently how much runway a gyro needs.

I told him it depends.
 

ckurz7000

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The rotor in my gyro loses 30 rrpm over the time it takes me to accelerate to 75 km/h. If I accelerate the rotor to 240 rrpm, I have a sufficient margin of error to pull it off safly. It still is not something a fledgling pilot should try but it isn't a death trap either.

-- Chris.
 

Jean Claude

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Chris, If you give me chord, diameter, max disc A.o.A on ground, aircraft weight, prop thrust about 30 mph, then I can find the forward speed when pull the stick.
 

ckurz7000

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Chord: 20 cm
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prop thrust: 2,5 kN (a guess)

Greetings, -- Chris.
 
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swilliams

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John I think the one Nick makes for the Aviomania is a great pre spinner but I think it has a blade length and wide limit. I like how it runs off the engine not the battery. I think something like that that could handle bigger blades would be great.

Sincerely SWilliams
 

All_In

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The rotor in my gyro loses 30 rrpm over the time it takes me to accelerate to 75 km/h. If I accelerate the rotor to 240 rrpm, I have a sufficient margin of error to pull it off safly. It still is not something a fledgling pilot should try but it isn't a death trap either.

-- Chris.
This is great information.

And great post guys... learning!
 
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