jump gyro

Owly

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I'm new here, and I assume the topic of jump takeoff has been discussed extensively, and probably dismissed as impractical. But I believe that within limits it can work. In my case what I am talking about is jumping perhaps 5' off the ground and accelerating to flying speed. The purpose is to be able to operate out of hostile terrain where a roll is not practical. Here's the idea. The pre-rotation goes to well above operating RPM.... perhaps 25-30% with the blades in normal flight pitch. A collective designed to operated only during takeoff is linked to the pre-rotator linkage, and when the pitch is snapped in, the pre-rotator kicks out. At this point you are at full power with a fairly powerful machine, it leaps and begins to accelerate as the blade speed decays toward normal flight RPM or thereabouts, and hopefully the airspeed increases rapidly enough to drive the blades fairly quickly and little altitude is lost. The airspeed as it increases pulls off the jump takeoff pitch gradually until the blades are in normal flight pitch at which point there is NO PRESSURE on the collective mechanism. That mechanism might be a flex cable like the Scorpion II used such that it would not be bothered by rotor head tilt. A simple vane mechanism that reacted to airspeed would be the device that would pull off the pitch. The idea is that once the takeoff sequence reached the "leap point" the pilot would ONLY fly the aircraft and not worry about an extra function that he had to control. This could be a locked wheel takeoff, or even be done with skids, and the only object would to be to get into ground effect rapidly and clear of low ground obstacles such as sagebrush and rocks. It would NOT offer true vertical takeoff or give the ability to climb tall buildings or clear tall trees. It would offer access in and out of places such as sand bars in the Yukon River where willows are an obstacle or the desert country of the west where sage and lava rock make getting in the air with a ground run problematic at best. As I mentioned....I am well aware that there have been many experiments with jump gyros, and probably much discussion of them here in the past. I am not familiar with the methods used, but I have concluded that simplicity is critical, both in design and in pilot work load. It is also obvious that you cannot power the rotors after takeoff without ending up with a very complex machine, so stored energy in the form of rotor inertia is about the only practical option. It's also very obvious that lots of horsepower is critical if something like this is to work. The whole thing is contingent on the the stored energy in the rotor and rapid acceleration to flying speed. I personally think it could work. But what do I know
 

Heron

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I'm new here, and I assume the topic of jump takeoff has been discussed extensively, and probably dismissed as impractical.
But I believe that within limits it can work. In my case what I am talking about is jumping perhaps 5' off the ground and accelerating to flying speed.
The purpose is to be able to operate out of hostile terrain where a roll is not practical. Here's the idea.
The pre-rotation goes to well above operating RPM.... perhaps 25-30% with the blades in normal flight pitch. A collective designed to operated only during takeoff is linked to the pre-rotator linkage, and when the pitch is snapped in, the pre-rotator kicks out.
At this point you are at full power with a fairly powerful machine, it leaps and begins to accelerate as the blade speed decays toward normal flight RPM or thereabouts, and hopefully the airspeed increases rapidly enough to drive the blades fairly quickly and little altitude is lost.
The airspeed as it increases pulls off the jump takeoff pitch gradually until the blades are in normal flight pitch at which point there is NO PRESSURE on the collective mechanism. That mechanism might be a flex cable like the Scorpion II used such that it would not be bothered by rotor head tilt.
A simple vane mechanism that reacted to airspeed would be the device that would pull off the pitch. The idea is that once the takeoff sequence reached the "leap point" the pilot would ONLY fly the aircraft and not worry about an extra function that he had to control.
This could be a locked wheel takeoff, or even be done with skids, and the only object would to be to get into ground effect rapidly and clear of low ground obstacles such as sagebrush and rocks.
It would NOT offer true vertical takeoff or give the ability to climb tall buildings or clear tall trees. It would offer access in and out of places such as sand bars in the Yukon River where willows are an obstacle or the desert country of the west where sage and lava rock make getting in the air with a ground run problematic at best.
As I mentioned....I am well aware that there have been many experiments with jump gyros, and probably much discussion of them here in the past.
I am not familiar with the methods used, but I have concluded that simplicity is critical, both in design and in pilot work load. It is also obvious that you cannot power the rotors after takeoff without ending up with a very complex machine, so stored energy in the form of rotor inertia is about the only practical option.
It's also very obvious that lots of horsepower is critical if something like this is to work. The whole thing is contingent on the the stored energy in the rotor and rapid acceleration to flying speed.
I personally think it could work.
But what do I know?
I can read it better now, thanks.
Heron
 

Owly

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swiss army knife

swiss army knife

Thanks for the Carter link.... These guys it seems have done a lot of work, and developed a pretty complex system that is designed to be all things to all people. Far beyond anything I envisioned. Inertia obviously is the fuel that makes it possible as I had imagined, but additional weighting of the rotor tips and doubling the flight RPM of the rotor for jump, and then leaping 150' into the air is way beyond what I'm seeking........ nor is a high speed / high efficiency cruise important. Active pilot control of pitch as I said before, simply adds to pilot workload when in fact the only time additional pitch is needed is during takeoff and presumably the vertical "no flare" landing. Somewhere between the sophisticated Swiss Army Knife Carter Copter and the typical gyro lies the technology that would meet the needs of many of us. My thinking is that pitch control (collective) is only needed for the first minutes of a jump start flight, and that the pilot does not need any direct control of pitch if as I mentioned the pitch bled off by itself to normal pitch as airspeed came up to flying speed..... A matter of seconds........... Compressed air pressure might even be a possible means of applying increased pitch for takeoff. Combining a full time pitch control with a tilting gyro rotor head seems a bit unreasonable........... I wonder what their method is? Any detailed photos of the rotor head out there?
Howard
 

PW_Plack

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Owly, mechanical complexity and pilot workload are not the big challenges. The sequence you describe puts the pilot at lethal risk on every jump takeoff due to extended time spent with neither airspeed nor altitude as resources if the engine quits.

The Carter system is actually quite simple. A mechanical governor using weights and springs tries to automatically hold the rotor at normal flight RPM. For jump take-off, a solenoid locks the governor in flat-pitch mode while the rotor is sped to 150% of flight RPM. (Not doubled.) When the solenoid is released, the governor tries to slow the blades by adding significantly more pitch than used in normal flight, gradually pulling it out as the blades reach normal speed.

Carter solves the problem with the height/velocity curve by building blades with so much inertia that they retain enough energy to complete the 150' jump even if the engine stops. From that altitude, you can achieve enough airspeed by the time you flare that the Carter suspension can avoid a catastrophic result.

One downside is all that inertia makes for more sluggish maneuvering. But then, the machine is not designed to be a sports car.
 

WaspAir

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Owly -- your description sounded very familiar to me.
Ever looked at an Air & Space 18A? Flight rpm about 240, pre-spin to 370 with heavy blades in flat pitch to store energy. Intended to jump to no more than about 15 feet vertically. No collective control -- just a "take-off" button on top of the throttle to pop in the pitch. In production back in 1965.

I can give you a demo in one if you're ever in my neck of the woods.
 

Owly

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I'm curious............ How does the system work? Paul's post mentioned a problem that had been in the back of my mind regarding rotor RPM decay and the need to drop the pitch down to flight pitch when the RPM decayed to a particular point. There basically are two "signals"..... air speed being enough to drive the rotor properly, and decaying RPM, both of which need to send the collective to the normal gyro pitch. I do not believe the pilot needs to be able to actively control the collective....... in fact it could result in doing stupid stuff. The no flare landing is not a huge asset as far as I'm concerned.... for example, and of course requires a heavy rotor to have enough energy to accomplish it, and offers a fairly narrow window. The simple leap off the ground to 15' or so is exactly what I am looking at. The carter is extreme as far as I'm concerned and of no interest to me........other than intellectually. What exactly does the take off button do on the Air and Space? And how does it operate? My vision of what it would do is that your rotors would be held in flat pitch, and centrifugal weights would result in the rotors snapping to somewhat more than normal pitch, and returning to flight pitch as the RPM decayed to normal flight RPM. I envision that you would "cock" the system on the ground.... (locking it into flat pitch), and the take off button would be a "trigger" that turned things loose so the governor would regulate pitch. Is this more or less how it works? I'd love to be able to crawl all over it and examine how it works.... I'm a guy that loves to design and build stuff, and nothing fascinates me more than examining other people's clever solutions. Howard
 

Owly

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Blown Disk

Blown Disk

More on the ST or jump gyro......... A tractor gyro offers many advantages....and some disadvantages..... obviously. One potential advantage I can see is the blown disk. Suppose you have a pretty powerful engine..... 2.5 Soob of O-320 Lyc for example.... tractor mounted....... At full throttle, it's going to throw a huge blast of air through the rotor when the rotor is tipped back for takeoff. This slip stream will decrease in velocity the farther it gets from the rotor of course, but it still should be a significant "wind". I don't know anybody with a tractor gyro........... And I am curious as to how much benefit this prop blast provides........ and there is the possibility of designing to maximize this effect. It would be interesting to see how much difference if any there is in the take off performance between two extremely similar gyros........ tractor & pusher. Same weight, same power, same disk. Has anybody done any serious examination of this?
Howard
 

brett s

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Your brakes or tires will only allow a certain amount amount of thrust before you start moving, depending on where the gear is in relationship to the CG you also might have to watch out for nosing over.

The propwash stream contracts & accelerates rather then expanding & slow down as it gets further away from the prop. At least for the distance we're talking about...
 

Alan_Cheatham

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While the performance of the Carter system is on the extreme side the mechanical complexity necessary to jump a gyro 15 feet vs 100 is the same except for rotor mass. You would still need collective pitch (usually designed to work without pilot input), ability to power the rotor to above flight rpm during prerotation, ability to pull that prerotation power from the main engine and not have the main propeller rob it (Carter uses a device to automatically de-pitch the prop during prerotation).

As for the tractor configuration, early Autogiros of 1930's tried to use prop blast as a means of prerotating the rotor by having horizontal tail surfaces that could direct the prop blast up into the rotor, but the method was ineffective and the mechanical prerotator became standard practice.

Over the years there has been much discussion about jump takeoff, search the forum and you should find information about it.

.
 

Owly

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Alan:
Using the prop blast to try to spin up the rotor is a far different thing than using it to provide airflow through the disk for lift.......... An oversped rotor reacting on the artificial wind should create lift. The Carter obviously allows full pilot control of collective.... or it wouldn't be possible to make the zero forward speed landing without a flare........ Complexity is never a good thing, but many things cannot be done without some complexity. A rotor head that allows the blades to twist for pitch control is not a particularly complex thing compared to a 3 blade head with pitch, flap, and lead/lag, and swash plates that allow collective and cyclic. As I mentioned before I think.... the very short term pitch application could be done with something as simple as an air can / cylinder. The other very simple control system would be to have a centrifugal weight system that when spun fast, forced the blades to be pitched more than usual, and as the blade RPM dropped, brought the blades back to normal pitch. Imagine a trigger as I mentioned before. The blades are locked into zero pitch for spin up, the spin up goes to 50% more than normal RPM, the trigger is pulled, and the latch is released.... the blades go the the max pitch allowed, and as RPM drops, return to "normal" flight pitch. At full throttle with quite a bit of horsepower, the whole process is going to take seconds. The initial jump, rapid acceleration to flying speed as the pitch decreases. If designed properly it would be a seamless process.
 

WaspAir

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... What exactly does the take off button do on the Air and Space? And how does it operate? My vision of what it would do is that your rotors would be held in flat pitch, and centrifugal weights would result in the rotors snapping to somewhat more than normal pitch, and returning to flight pitch as the RPM decayed to normal flight RPM. I envision that you would "cock" the system on the ground.... (locking it into flat pitch), and the take off button would be a "trigger" that turned things loose so the governor would regulate pitch. Is this more or less how it works?
You're close.
There is a small hand-operated hydraulic pump in the cockpit and a system with solenoids/valves to direct the pressure. You select one button to "de-pitch", pump a few strokes with the handle, and the blades go flat, working against a spring load. That's the "cocked" status you were thinking of. You select another button to clutch in the engine, pump away on the same handle, and it starts the blades spinning. Throttling up gets the blades spinning in the 150% rpm range. The take-off button (it is a "trigger") releases all the hydraulic pressure and the springs take over; the clutch disengages the engine and the blades pop up about 8 degrees in initial collective pitch. Pitch-flap coupling in the feathering and flapping hinge linkage automatically takes care of the pitch reduction needed to transition to autorotation, without any pilot intervention.
 

Owly

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A bit more on info on the 18A...... It sounds like almost exactly what I envisioned....except for my misguided notion that airspeed would be the "signal" that flattened blade pitch to normal. What is not clear here is exactly what draws the blades back to normal flight pitch. I am assuming (logically) that we have something akin to a governor with fly weights that actually pull the blades to the 8 deg jump pitch and as the rotor RPM decays they lose their "authority", and the spring loaded system draws the blades to normal flight pitch. Your description suggests that the spin up pitch is flatter than normal flight pitch.... which introduces another complexity in that they obviously shouldn't be drawn back to zero....... or is zero the normal flight pitch? It is clear to me now after giving it some thought that RPM needs to govern the pitch if only for safety reasons, and that the higher RPM will bleed off fairly quickly bringing the "governed" blade pitch to normal. A simple mechanical latch with a pin that trips it would work fine I think.... If the blades latched at flat pitch automatically once the centrifugal weights allowed them to go back to flat pitch, and the trip would release that latch via a cable or whatever, the whole thing would be simple and reliable. My issue with these jump machines is the fact that they all seem to have the incredibly complex 3 blade heads, and I see no reason at all why an ordinary two blade gyro with the tilting head couldn't incorporate such a system. It is very little additional complexity.... a pitch system, springs & fly weights, latch, and trip. The important thing is that the blades naturally fall into flat (normal gyro) pitch.

Howard
 

WaspAir

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No, no weights, and no separate governor device.

Spin up collective pitch is flat, zero degrees, to minimize the power demands on the engine (you don't want the engine to be really screaming, because you're also driving the prop at the same time). Flat pitch also helps keep the aircraft firmly planted on the ground, ensuring that the friction of the tires on the ground provides adequate anti-torque effect during the pre-spin. The springs pull in the direction to add pitch (normal flight pitch is positive).

The blades are hinged. By appropriate arrangement of the linkage and hinge angles, you can get feather and flap coupling so that the interaction will cause it to seek the desired flight pitch on its own.
 

Owly

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What is a mystery to me about the Air and Space... still....Is what forces the blades briefly into the full 8 degree pitch. I can see how the blades can be mounted such that they want to find their normal flight pitch of 0-1 deg or whatever it is, but at the moment of release the pitch must snap to 8 deg for the jump, and then over a brief time period return to normal. I've considered a number of ways to do this...... but I am very curious about how it is done here. From your description, the pump pulls the blades to flat pitch for spin up, and presumably spring tension must snap the blades to full pitch, and they then must return to normal pitch. My thinking at the moment is that for a jump takeoff the time period at which the blades must be at full pitch would be somewhere from about 3 to 10 seconds only. this could be accomplished in a number of ways. My favorite of the ideas I have had is a diaphragm operated by air pressure or vacuum. The actuator (diaphragm) would be mounted right to the head, the air or vacuum would be applied, and bleed off at a fixed rate..... or by a governor operated bleed valve along with a fixed orifice. Governor sounds complex...but can be extremely simple and reliable. Just a pair of small hinged weights operating a disk covering a bleed orifice that as the RPM decreases release the pressure on that disk. I'm thinking that a system with a fixed (adjustable) bleed orifice could be tuned on a tethered machine so the pitch bled back to normal in the same time the rotor bled off speed to flying RPM approximately. It would be a really simple system that would probably be highly reliable. Simple is good!! Howard
 

WaspAir

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Yes, springs pull in the full pitch when you punch the take-off button.
The whole jump process from punching to climbing away is very brief, since you're hopping no more than 15 feet, and nowhere near 10 seconds. One of these days I'll get somebody to video me so you can see it.
 

Alan_Cheatham

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What is a mystery to me about the Air and Space... still....Is what forces the blades briefly into the full 8 degree pitch. I can see how the blades can be mounted such that they want to find their normal flight pitch of 0-1 deg or whatever it is, but at the moment of release the pitch must snap to 8 deg for the jump, and then over a brief time period return to normal. I've considered a number of ways to do this...... but I am very curious about how it is done here.
Maybe this picture of an 18A will help you to understand.

The blades are mounted on flap hinges, the blade pitch control arm is arranged with an offset to the flap hinge line so as the blade flaps there is also a pitch change to the blade, in this case as the blade flaps up blade pitch is reduced.

To initiate a jump hydraulic pressure is released and spring pressure pushes the blades to jump pitch. The 150% rotor rpm at the beginning of the jump causes an increase in centrifugal force on the blades and keeps them pulled flatter out (less cone angle), but as the rotor looses energy and slows down to normal flight rpm centrifugal force is reduced and the blades increase in flap (more cone angle). The increase in flap angle causes a decrease in blade pitch because of the offset in the flap hinge line and pitch control arm.

.
 

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