Achieving reliable short takeoff

[gyroo]

Hi guys,I thought I"d start this topic to see where it goes.It seems to me that most gyroplanes in our fleet are compromised because although most can be landed very short, almost all have to take off very long.While a powerful pre-rotator eliminates the need for taxying up and down milking the rotor up to speed, and also reduces the distance required to match the accelerating rotor with the increasing airspeed during the first part of the takeoff roll, a substantial distance is still nevertheless often necessary before the gyro flies itself off.I"m not talking here about jump-start gyros, because coming from the helicopter world where every pilot subconsciously levels the rotor before the skids finally lift off, the history of jump-starting in gyros is littered with accidents caused by the jump-start process occurring while the rotor wasn"t absolutely level, and where the jump start goes wrong by having a significant roll or pitch component, leading at best to an extremely untidy liftoff through to at worst a partial tipover and usual rotor strike.And, I write this fully aware that for gyroplanes, airspeed is life. In other words, our fixed pitch autorotating rotors just can"t perform like a powered helicopter rotor where more pitch with more power is pulled in to achieve better climb performance. A fixed pitch autorotating rotor achieves performance increases (ie, higher climb rates) solely by increased translational lift from increasing airspeed, with maximum climb rates obviously attained at airspeeds where the engine can maintain gyro airspeeds that allow the rotor to entrain more air per second without a lot of that engine power being robbed by airframe parasite drag.What I"m talking about with this thread is a prerotator configuration where the fixed-pitch gyro rotor can be taken to a 10% to 20% overspeed and the takeoff roll then commenced. The overspeed method has the benefit of having the rotor absolutely level, or at least the rotor attitude under the very precise control of the pilot (in contrast to a jump situation).A gyro with an oversped rotor will still need to roll sufficiently for it to acquire 25+ to 30+ knots airspeed before it begins to climb. And, to reliably climb at such risky low airspeeds will require about 8 pounds gross weight per installed horsepower. Even so, climbing at around 30 knots still has substantial risks in case of engine failure, where the emergency nose-down manoeuvre will further reduce rotor rpm, probably leaving not enough energy to flare reliably.So, what I"m inviting here is comment on this sort of concept1) Stationary into, say a 10 knot wind;(2) Rotor oversped by 20% (where flight rpm is say, 360, so we overspeed to 432);(3) Brakes off, takeoff roll commenced; (4) 30 knots indicated - hopefully gyro feels like it"s ready to fly itself off;(5) initial climbout to perhaps 50 feet with IAS holding at low to mid 30"s (mindful of the danger of having not enough rotor inertia to comfortably flare if engine quits); (6) less risky part 2 of the climbout where IAS is let go to mid 40s+ transitioning slowly up to 50; and(7) operations normal after that - 50 - 60 knots cruiseThe initial climbout I"m describing will be right on the boundary of the height-velocity curve, and very likely within the height velocity curve for a heavier gyro.The whole purpose of this concept is to balance the benefit of a short takeoff against the risk of being on the edge of, or behind the power curve for a number of seconds. It would be nice to be able to reliably undertake such a manoeuvre because if the technique was mastered on normal runways or open paddocks, then it would influence the types of landing areas that one could select in the knowledge that you could reliably do a short take off (STO) out of the site.Has anybody got any experience with "rotor overspeeding" from pre-rotation?Has anybody got any experience at transitioning an oversped rotor into normal autorotative flight?Has anybody got experience of engine failure during a steeper than normal initial climbout under full power?What effect does very high installed horsepower have, given that it is likely to tempt the pilot to climb out steeply (at risk if the donk quits?)Does anyone know how much a rotor will slow from normal cruise rpm during a high-power "hanging off the prop" steep attitude climb?Cheers,Mark ReganMelbourne

[birdy]

What I"m talking about with this thread is a prerotator configuration where the fixed-pitch gyro rotor can be taken to a 10% to 20% overspeed and the takeoff roll then commenced. The overspeed method has the benefit of having the rotor absolutely level, or at least the rotor attitude under the very precise control of the pilot (in contrast to a jump situation).Without sum form of anti torque ( tail rotor or coaxial) you can"t get past bout 90% flight rrpm without drifting off the ground, or at least getn dangerously giggly onit.

[birdy]

I"v only got a slightly improved version of the RAF prespiner on the ferel, and I prespin to bout 80% frpm with the stick full back ( as air breaks). Soons it reaches max rrpm, the stick is pushed full forward, throttle to the forward stop, 30 paces later ( bout 3 seconds) I"m at min level flight AS, the stick is back on or near the backstop and it"ll climb near virticaly until I dissengauge the spinner clutch.Any refinement of this system would see any single gyro off the deck inside 20 paces.NB; any prespin over 80% can be dun, but it means your ground breaks are usless, coz there"s no weight on the wheels.The stick on the backstop is Wots holdn you from Moven, but once you go past bout 80%, it"s a fine, giggley balance of disc attitude, power and holdn your mouth rite. You will get off shorter, but it"s not so easy.

[gyroo]

Thanks Birdy!I was wondering if or when you"d bite :-)I"ve read previously your posts on pre-spinning to above 80% flight rpm and getting jiggly on the wheels.I"ll keep the hook dangling in the water to see what other fish I hook on!Thanks again - your experience is invaluable.Cheers,Mark R

[MadMuz]

Can I bite too? Huh, can I, Can I

[gyroo]

Howdy again,OK, I"ll raise my head above the parapet enough to say that this thread is basically me exploring whether anyone out in Gyro-Land has any experience whatsoever with a powerful pre-rotator, that isn"t dependent on engine revs.In about 4 or 5 months time I"ll be push the start button (yes, electric start) on a 15hp 2-stroke Yamaha KT100 go kart engine as a pre-rotator, and I"m trawling around for anyone who"s had at least some actual experience with powerful pre-rotators that don"t need the gyro engine revving. I"ve carefully matched the ratios so that at 10,000 Yamaha rpm I"ll have 340 at the head. All the karting fraternity predict that the Yamaha will actually rev much higher if allowed to, despite the considerable rotor drag.From my piston helicopter days, using manifold pressure charts, I worked out that a Hughes 300 needed about 70hp to begin to feel noticeably "light and jittery on the skids", and needing positive directional control on the pedals. They needed about 120 to 130hp to hover IGE comfortably, with whatever of the "book" 180hp was actually left over because of density altitude could be used for a margin. Weights were usually roughly 1800 pounds.I"m figuring that the 15hp KT100 will allow me to push my 25 foot Patroneys up to 340 and that there"ll even be some reserve for overspeeding by maybe 15% or so. I anticipate that it"ll be jiggling on the wheels and the torque of the geared-down Yamaha at the head will be obviously trying to yaw the frame to the right. The advantage in having a completely separate 2-stroke as the pre-rotator means I can throttle the gyro engine and deflect the rudder to offset a fair bit of the yaw tendency, being prepared to do a double-shuffle on the rudder as the Yamaha is throttled back and the gyro engine throttled up. In fact I"m seriously considering rigging up the Yamaha throttle backwards, so that increasing throttle on the gyro engine will retard the Yamaha. My gross weight will be about 730 pounds. The Yamaha isn"t actually at the head - it sits within a chrome-moly frame behind my head, with a drive tube up to a plunging CV joint very close to the intersection of the pitch and roll pivots. 2 chain drives are at the head to provide 2 further speed stepdowns with an extremely expensive sprague bearing bolted on the front of the torque bar to provide freewheeling for the upper chain drive which is in constant contact with a conventional sprocket where an electric start ring gear would be. The Yamaha has a centrifugal clutch and the drive tube rpm up to the head is down to about 900 because of a 3rd chain drive that runs off the centrifugal clutch - it"s all competition Kart componentry (stuff that can stand up to a hell of a beating and constant heavy loads).This is the reason why I"m casting around for anyone at all who has the slightest actual experience with powerful pre-rotators. I know that absolutely everyone in Gyro-Land has an opinion, but what I"m after is anecdotes based on actual experience.If you go to You Tube and type in "Goped meets Autogyro" (a somewhat deceptive video because there was obviously a strong wind blowing), you"ll see that someone in the States has a similar, lower powered setup working.Any contributions?Mark R

[Tim]

G"day Mark, I"ll have a nibble. I didn"t have as much success as Birdy. My 27ft McCutchens used to fly S & L at 300 rpm but in calm air I could only successfully pre-rotate to 150 or 160 rpm (a bit over 50%) before the gyro used to start to screw around on the ground. You could squeeze a bit more rpm out of it if you had the gyro at angle to the centre line, then eased the stick forward a bit as it screwed itself to nearly aligned with the centre line. As it started to move forward you had to be prepared for the kick as you released the pre-rotator and gave it a tickle behind the ears with the whip. Once the pre-rotator was disengaged you could ease the stick back again as it accelerated and it would become airborne with the rotors at 250 to 260 rpm, but at a high angle of attack, levelling out as they reached full flying speed.This was by no means a pretty take off and I would not recommend it - needing a concerted and coordinated effort between three hands, two feet, a sphincter muscle and as Birdy said, holding your mouth just right.However, after seeing a video of such a take off, I was less than impressed with the coning angle as the slow blades lifted the machine off. After studying the video, my best guess would be something like 15 degrees, 12 degrees over the normal flying cone. I couldn"t help but wonder if this could have some bearing on hub bar problems because there are many "pilots" who continually horse their machines into the air well before the blades are up to full flying speed. Depending on the grade of hub bar material, this could easily stress it beyond its elastic limit which would obviously have a severe detrimental effect

[MadMuz]

;D Sorry about that Sounds like a great idea, there is a guy in the states with that, might be one of the butterflies? He starts the little motor and takes off with it running, then just reaches behind his head and switches it off. It is on youtube, but I am scared to look, I od"d on youtube last week and used $80 in prepaid credit in 8 days

[gyroo]

Thanks Tim!I"m glad you"re popping back on the forum regularly! I am carefully noting everyone"s various experiences, to better prepare me for the process of sorting this setup out and hopefully not tipping over the gyro in the process.Cheers,Mark R

[MadMuz]

This is that engine out in stills, a few more pics to come. Like I said, was not too scarey because no obsticals other than I didn"t want to go over the fence, I stopped about 20m short of fence. If I had gone over the fence and couldn"t restart the machine, it would have been a nightmare getting the car and trailer to get it. The most important thing was to not nose down until the climb stopped and the machine started dropping the nose itself with a neutral stick....If you save the pics then click thru them in a line, it is like a little movie, gives you the drift anyway

[MadMuz]

In the latter half of pics, you can see the nose down attitude.... enough rotor rpm to hold off in flare, seemed like ages (but not for Sambo )

[gyroo]

Jeez -Direct drive and the old V-tail!You must be REALLY old.MR

[MadMuz]

Whats that sonny?? eh? you young wiper snippers

[Echo]

..........

[Justin]

Unreal Echo !What will people think of next !