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#11
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On Fri, 25 Jul 2003 11:57:53 GMT, Terry Spragg
wrote: For the simplest possible reason: An auto gyro is always flown in autorotation, with fixed plade pitch set for 'gliding'. If you apply torque to an auto rotor, you do not get lift, you get propelled groundward. G'day Terry, Are you saying that autogyro's have negative pitch on their rotor blades? If so, you are wrong. If that's not what your saying, I apologise. I have misunderstood your meaning. Could you please explain this statement? Cheers, Phil I was wondering about that myself! Fly Safe, Steve R. |
#12
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#13
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"Rod Buck" wrote in message ... In message , Terry Spragg writes An auto gyro is always flown in autorotation, with fixed plade pitch set for 'gliding'. If you apply torque to an auto rotor, you do not get lift, you get propelled groundward. Alas, not true - an autorotating rotor does NOT normally have negative blade pitch - it has positive pitch of 1-3 degrees, and therefore generates lift by rotation. Therefore, if you powered it by a torque from the hub, it would lift off perfectly well. It would NOT try to screw it's way into the ground, as it would if the blade pitch was neggy. Pitcairn gyros used jumpstart, where the blades are spun up to well above normal RPM, in zero pitch, then the usual autorotational pitch of 1-3 degrees is applied (either by collective or by delta-three hinges, which increase the pitch angle when hub torque disappears.) You must, of course, declutch the hub drive as soon as you increase pitch and take off - with no tail rotor or other countertorque means, you'd spin real fine.... The delta-3 hinge is a ferocious beast - once you get above flight rpm, you MUST take off, there is no way out - bit like lighting those Shuttle SRB's - it's not a question of whether you go or not, it's just which direction.... As soon as you declutch the motor, or reduce motor RPM, the hinges increase the pitch, and off you go..... The gyro leaps 1-200 ft in the air, and then the prop drive provides forward motion to start normal autorotational gyro flight - the rotor pitch is NOT reduced again to do this - it stays at the normal 1-3 deg. If you apply power, you are flying a helicopter, which must have some manual control over pitch if both powered flight and autorotation is to be possible. Wrong again, friend. It's perfectly possible to have a helo with a fixed pitch rotor, set to the small positive angle for autorotation, and alter lift by changing engine power, and thus rpm. (You can then use head gimbal as in gyro to alter pitch cyclically for directional control). (The rotor rpm would be quite a bit higher than normal for the same lift) However, the rotor momentum (flywheel effect) makes the control extremely sluggish and impractical, compared to collective pitch control. However, one safety improvement would be that, as the rotor is always in the low-angle suitable for autorotation, if the engine quits, a freewheel device in the rotor drive chain would ensure you entered auto painlessly. -- Rod Buck Rod, You just answered soooo many of my questions. THANK YOU! Would you mind if we talked a bit via e-mail? Again, thanks Phil Williamson Oregon City, Or. |
#14
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In message , Charlie+
writes On Wed, 30 Jul 2003 21:06:07 +0100, Rod Buck wrote as underneath my scribble : Rod, as a matter of interest have you personally done one of these takeoff jumps? Sounds exciting/scary! Not done it personally - seen it in the flesh once, and on film lots of times. Scared me sh*tless to WATCH it - never mind fly it! Presumably the change over to propdrive is immediate on initiation so there is some element of forward drive from the start of the leap? Yup, dead right. My impression is that there is some sort of changeover mechanism, whereby the motor drives either the rotor hub, to spin-up the rotor to well above flight RPM, or the normal propeller to provide inflight thrust as in a normal gyro. So, when you get up to 150% flight RPM, you pull the lever, the hub is declutched, and the prop engaged.... Is the direction of the leap unpredictable / local wind etc causing major imbalances? Also is there some drop in initial altitude until full gyro level flight and control can be achieved? if so - how much swoop do you estimate? Charlie+ From what I've seen, you obviously line the gyro's nose into wind, (and as in all aviation, a decent wind helps no end). Got to be careful to get the cyclic central, so the thing leaps up vertically (but with some forward thrust from the prop during the leap, so the leap is actually forward, even if the rotor is horizontal) Then, at the top of the leap, the rotor must be angled back to the normal gyro angle to ensure upward airflow through the rotor (and drag to balance the prop thrust) as you move into wind. Where there is a wind of, say, 15mph or more, I saw no evidence of drop or swoop at the top of the leap - it just flew off. In nil-wind, I would anticipate there must be some drop, maybe 50ft. Depends on the engine thrust, and how quickly it accelerates the gyro to normal forward flightspeed. This is why a wind prevents drop, of course. A 15mph wind means you've got at least 20mph airspeed at the top of the leap - you must gain at least 5mph forward speed in the leap if the prop is running. This is enough to maintain level flight. -- Rod Buck |
#15
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#16
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Let me jump in here a little. I got to ride with John Potter at
Paducah, KY last winter in an Air & Space. The prop is constantly engaged. There is no transition from the engine powering the rotor and then switching to the prop after the jump in this craft. The Lycoming turns the prop just like any other prop in a pusher configuration. The rotor is engaged via a multi-belt driven geared transmission. The rotor spins up to somewhere over 300 rpm (while depitched)if my memory isn't letting me too far down. The tires alone keep the gyro from counter-rotating. One wheel was on a piece of ice during one of the spinups and John had to move it onto a dry patch. Once the proper rotor rpm was reached, John reached to the panel and pressed a button. The blades instantly repitched and we shot straight up like a rocket. I'm sure that the transmission disengages simultaneously. The ship reaches maybe 30-40 feet and smoothly transitions into forward flight and a climb mode. There is no loss of altitude during the transition. Now I suppose someone could screw it up and not have enough throttle on during the jump start, but the engine rpm seemed to up there some to get the blades going, and the jump happens very quickly. As I recall, full throttle is applied as soon as she jumps. It's a very, very fast sequence. You're at the top of that jump before you can blink. We took off on the runway and then from the tarmac perpendicular to the wind, and there didn't seem to be any problems.....no more than a plane taking off in a crosswind. I felt no yawing or unsteadiness from the crosswind jump and never experienced any dropping. Now I'm going strictly by memory on the mechanics, but I believe I have the basics correct. Ken J. - Sandy Eggo Rod Buck wrote in message ... In message , Charlie+ writes On Wed, 30 Jul 2003 21:06:07 +0100, Rod Buck wrote as underneath my scribble : Rod, as a matter of interest have you personally done one of these takeoff jumps? Sounds exciting/scary! Not done it personally - seen it in the flesh once, and on film lots of times. Scared me sh*tless to WATCH it - never mind fly it! Presumably the change over to propdrive is immediate on initiation so there is some element of forward drive from the start of the leap? Yup, dead right. My impression is that there is some sort of changeover mechanism, whereby the motor drives either the rotor hub, to spin-up the rotor to well above flight RPM, or the normal propeller to provide inflight thrust as in a normal gyro. So, when you get up to 150% flight RPM, you pull the lever, the hub is declutched, and the prop engaged.... Is the direction of the leap unpredictable / local wind etc causing major imbalances? Also is there some drop in initial altitude until full gyro level flight and control can be achieved? if so - how much swoop do you estimate? Charlie+ From what I've seen, you obviously line the gyro's nose into wind, (and as in all aviation, a decent wind helps no end). Got to be careful to get the cyclic central, so the thing leaps up vertically (but with some forward thrust from the prop during the leap, so the leap is actually forward, even if the rotor is horizontal) Then, at the top of the leap, the rotor must be angled back to the normal gyro angle to ensure upward airflow through the rotor (and drag to balance the prop thrust) as you move into wind. Where there is a wind of, say, 15mph or more, I saw no evidence of drop or swoop at the top of the leap - it just flew off. In nil-wind, I would anticipate there must be some drop, maybe 50ft. Depends on the engine thrust, and how quickly it accelerates the gyro to normal forward flightspeed. This is why a wind prevents drop, of course. A 15mph wind means you've got at least 20mph airspeed at the top of the leap - you must gain at least 5mph forward speed in the leap if the prop is running. This is enough to maintain level flight. |
#17
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Let me jump in here a little. I got to ride with John Potter at
Paducah, KY last winter in an Air & Space. I think the key word there is winter. Low density altitude is key. Once the proper rotor rpm was reached, John reached to the panel and pressed a button. Hmm, well, the button on the panel is to engage the prerotator clutch. If you'll remember, once that button is pushed the throttle is increased so the engine is about 1500 RPM. At that point you begin pumping the hydraulic lever to engage the clutch. You slowly pump the handle to maintain continous pressure while at the same time working the throttle to maintain 800 RPM. It is very much like engaging the clutch on an Enstrom. Once rotor RPM and engine RPM marry the handle is quickly pumped until the engage button on the panel pops out. This indicates the system is fully engaged. From then the RPM is increased to 370 RPM. The blades instantly repitched and we shot straight up like a rocket. I'm sure that the transmission disengages simultaneously. The blades are depitched by pushing a button on the top of the throttle. Hehe, it all happens so quickly that it is easy to lose track of what happens when. That's why the depitch button is on the throttle. It would take too long to push a button on the panel and then have to bring your hand back to the throttle. The ship reaches maybe 30-40 feet and smoothly transitions into forward flight and a climb mode. There is no loss of altitude during the transition. Winter had a lot to do with that. Jump takeoff is unlikely above a 2000' DA. No doubt pilot skill, gross weight, wind, etc. play a major part. But I do know that when I've flown the 18A it was in the summer. Max jump height was about fifteen feet and after the jump we sunk to about five feet before we got ahead of the power curve and established a climb. I do remember also that if, after the jump, the aircraft settles to the ground, power must be reduced and the sequence started all over again. BTW, for a jump, the rotor is spun to 370 RPM. Operating RPM green arc is from 200-320 RPM. It's all a bit tricky but quickly becomes second nature. Regardless the 18A is a great flying ship. Stephen Austin Austin Ag Aviation Charleston, Missouri |
#18
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The only problem with the A&S was a severe limitation on the operation at the local field because of noise restrictions - it sure was a loud bird. Hmm, at Farrington Airpark? I think someone was pulling your leg. I've never heard of any noise restrictions there. It's kind of in the boondocks anyway. And, for that matter, there is a stock car track about one hundred yards from the strip (the strip actually began life as a drag strip until Don bought it). Anyway all those cars are one heck of a lot louder than an 18A. Stephen Austin Austin Ag Aviation Charleston, Missouri |
#19
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"Stephen Austin" wrote in message
... The only problem with the A&S was a severe limitation on the operation at the local field because of noise restrictions - it sure was a loud bird. Hmm, at Farrington Airpark? I think someone was pulling your leg. I've never heard of any noise restrictions there. It's kind of in the boondocks anyway. And, for that matter, there is a stock car track about one hundred yards from the strip (the strip actually began life as a drag strip until Don bought it). Anyway all those cars are one heck of a lot louder than an 18A. Stephen Austin Austin Ag Aviation Charleston, Missouri Nope. My A&S 18A lesson was in NJ, but I forget the town. Even though the airstrip was in the Western (less populated portion of the state - rural, actually), the local residents were the highly paid, city-commuter types (NYC) and, apparently both vocal and influential. The 18A clearly was louder than the other planes (typical spam can range, plus a goodly amount of low-powered Cubs, Champs, etc.) - it definitely stood out during ops. Michael Pilla |
#20
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NJ, but I forget the town. Even though the
airstrip was in the Western (less populated portion of the state - rural, actually), the local residents were the highly paid, city-commuter types (NYC) and, apparently both vocal and influential. The 18A clearly was louder than the other planes (typical spam can range, plus a goodly amount of low-powered Cubs, Champs, etc.) - it definitely stood out during ops. Michael Pilla Man, don't you hate that? Was it one of those deals where the airport was there long before any of the homes? Stephen Austin Austin Ag Aviation Charleston, Missouri |
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