The Gyro-Jet

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Bruno Ogorelec
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The Gyro-Jet

Post by Bruno Ogorelec » Fri Mar 24, 2006 1:34 am

Another product of my feverish brain. This time under the influence of secret technology of the Third Reich, no less.

But, this time I am fairly serious. Unlike the jet-powered flying belts and flying platforms, this one should fly easily. Wouldn't be too easy to build, but it would sure fly.

It is again powered by my Constant Flow engine pack (see http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2752 for details).

It is a gyrocopter, or an auto-gyro, whatever you care to call it. In other words, it does not have a powered rotor. Its rotor is spinning freely and serves the same function the wing does in the fixed-wing aircraft.

Note that the air blows through the gyrocopter rotor from below and exits above. Unlike the helicopter rotor, which is tilted slightly forward, the gyrocopter rotor is tilted slightly backwards.

Because the rotor is not powered, gyrocopter needs some kind of forward propulsion. This is usually provided by a motor situated behind the pilot and driving a pusher propeller.

In place of such a cumbersome device, my Gyro-Jet has the elegant ellipsoid of the Constant Flow engine pack sitting on top of an equally elegant V-tail. It provides thrust through two nozzles situated at the ends of the elliptical engine pack.

It also does another thing that any self-respecting gyrocopter does – rotor pre-rotation. And it does it in a more elegant way than gyros usually do.

Namely, the rotor will start spinning due to the air stream passing through it if you taxi the gyro along a runway. However, it takes some time and distance to get it to spin fast enough to provide sufficient lift for takeoff – especially in nil wind, or a wind in the wrong direction.

So, better gyrocopters have some means of pre-rotating the rotor, spooling it up to as high a speed as possible, so that the takeoff distance is as short as possible. Some manage a near-vertical takeoff. The problem with this is that it usually requires some kind of a transmission and a clutch that takes power from the propulsion motor to the rotary wing. It adds weight, cost and complexity to the other wise lightweight and simple machine.

The Gyro-Jet does away with all that. You sit in the cabin, pull the lever to turn the nozzles upward and wait for the jet exhaust to spin the rotor to a sufficient speed. Then you pull the lever back, the nozzles turn backward and start pushing the machine forward for takeoff. Neat, eh?

The rotor will be fairly expensive. To take advantage of jet-powered pre-rotation it must really be a multi-blade fan. For a number of reasons, I see it as a carbon-fiber fan with perhaps two dozen blades, with a fixed hub and rotor tips affixed to a perimeter ring of circular or elliptical section. But, a free fan will also work fine, as long as it has plenty of blades.

Imagine a tricycle landing gear, which I haven’t drawn (it can even be retractable) and this is it. Everyman’s flying machine.

OK, shoot me down now. Let me hear why it wouldn’t work.

(Before that, let me tell you that such a device did fly. Two were built at a secret BMW research and development facility near the end of the Second World War. The thing was powered by a BMW turbojet engine. The pilot was more or less sitting on the engine, as on a motor cycle. Scary. One of the two flew successfully, but the Allies were getting very close by then and the prototype was destroyed. The fate of the other one is unknown. It was probably also destroyed. It is not quite clear whether this other one was completed in the first place.)
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re: The Gyro-Jet

Post by Mike Everman » Fri Mar 24, 2006 4:40 am

Neat, yep. Not gonna shoot holes. Concerns over the very high inertia of large, ducted, many bladed rotors, but maybe it can be smaller in diameter than the average gyro-copter rotor.
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re: The Gyro-Jet

Post by Mike Everman » Fri Mar 24, 2006 4:43 am

I'd rather see you put the jet pack coaxial with the main rotor and turn the exhausts for tangential thrust, make the main more conventional, then put the brakes on the jet pack and rotate the nozzles to the rear. Just a thought.
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re: The Gyro-Jet

Post by Greg O'Bryant » Fri Mar 24, 2006 5:56 am

Bruno;
I have always wanted to make a gyro with a jet on it. Are you shure that it would need a multi-blade fan? I already have a good carbon fiber 2 blade picked out. Imagine how light a craft like that would be and don't gyro's get better MPG's than a conventional helicopter? I was thinking of a prop that was powered by tip jets or better yet develope the vortex thruster and have it be powered with valveless pulse jets. Anyway I do like your design is it one or two man?

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re: The Gyro-Jet

Post by Anders Troberg » Fri Mar 24, 2006 7:40 am

Once it starts spinning, a two bladed rotor will probably do the trick just fine, but it will probably be slower to start (especially if none of the blades are in the jet exhaust...).

It's a neat solution, but it would probably be more effective if the engine was closer to the center of the rotor, somewhat like the traditional engine placement on most autogyros.

Come to think of it, this would probably work nicely with a propeller too, but instead of tilting the entire engine/prop assembly, one would use control surfaces directing the airflow at an upward angle through the rotor.

An elegant side effect of this design is that the engine will actually push the aircraft down while the rotor is spinning up, making it more stable against wind and making the brakes work better so that it's less prone to start rolling before it's really up to speed.

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re: The Gyro-Jet

Post by Bruno Ogorelec » Fri Mar 24, 2006 8:50 am

Mike Everman wrote:Neat, yep. Not gonna shoot holes. Concerns over the very high inertia of large, ducted, many bladed rotors, but maybe it can be smaller in diameter than the average gyro-copter rotor.
Among the reasons I wanted a ducted prop (though this one isn't really ducted, it just has a rim) is the smaller diameter needed. I also wanted to avoid using collective pitch adjustment. With smaller diameter rotor and even vestigial ducting, the problem of retreating blade lift can be reduced to the point where it does not have to addressed at all. You just tolerate it.

Why would inertia be bad in a rotor that doesn't have to change its rotational speed quickly? Frankly, I can see good points in some inertia there. But, make it unducted if you like.
Mike Everman wrote:I'd rather see you put the jet pack coaxial with the main rotor and turn the exhausts for tangential thrust, make the main more conventional, then put the brakes on the jet pack and rotate the nozzles to the rear. Just a thought.
Of course, this can be done – and has been proposed by Pegg and Makowski for a pulsejet-powered helicopter, but it is mechanically more complex and puts the bulk of the engine pack where it would interfere with clean airflow into the rotor disk. My solution is lighter and aerodynamically sounder. It also avoids the need to make the various conduits to the engine able to work during the rotation of the engine pack…
Greg O'Bryant wrote:Bruno;
I have always wanted to make a gyro with a jet on it. Are you shure that it would need a multi-blade fan? I already have a good carbon fiber 2 blade picked out. Imagine how light a craft like that would be and don't gyro's get better MPG's than a conventional helicopter? I was thinking of a prop that was powered by tip jets or better yet develope the vortex thruster and have it be powered with valveless pulse jets. Anyway I do like your design is it one or two man?
Well, no; it doesn’t really need a multi-bladed fan, but pre-rotation would sure as hell be kind of ridiculous with a two-bladed rotor. You’d need to pre-pre-rotate it in order to start pre-rotation…

Yes, I love gyrocopters for the reasons you mention and for the simple reason that I like things simple. I hate great complexity in mechanical devices. That’s why I ruled out tipjets very early on. The ones that really worked well (like the small Dornier helicopter; one of my all-time favorites) were relatively complex and expensive.
Anders Troberg wrote:Once it starts spinning, a two bladed rotor will probably do the trick just fine, but it will probably be slower to start (especially if none of the blades are in the jet exhaust...).
As I told Greg; if you need pre-pre-rotation to start pre-rotation to be able to take off neatly, it’s getting a bit ridiculous. What I have in mind is a vehicle with a character of a water-scooter or a snowmobile. You sit down, strap yourself in, turn the key, wait a bit and take off.
Anders Troberg wrote:It's a neat solution, but it would probably be more effective if the engine was closer to the center of the rotor, somewhat like the traditional engine placement on most autogyros.
More effective? In what way? As I said responding to Mike, the tail placement ensures a cleaner airflow into the rotor disk.
Anders Troberg wrote:Come to think of it, this would probably work nicely with a propeller too, but instead of tilting the entire engine/prop assembly, one would use control surfaces directing the airflow at an upward angle through the rotor.
Yes, that has occurred to me, too. I wonder why no one seems to have thought of it (as far as I know). The closest idea I have seen was the Bensen compound gyro-helicopter, which had a conventional helicopter rotor coaxial with a gyroplane rotor. The unpowered rotor was driven by the air stream generated by the powered rotor. Weir but it worked. Don’t know how well, though.
Anders Troberg wrote:An elegant side effect of this design is that the engine will actually push the aircraft down while the rotor is spinning up, making it more stable against wind and making the brakes work better so that it's less prone to start rolling before it's really up to speed.
Yes.

Also, think of the maneuverability of the thing, as it has vectored thrust through two independent nozzles, which are positioned at quite some distance from each other, providing good leverage. You would be able to do a number of things a Harrier fighter pilot would recognize. With a rotor sturdy enough, I guess you could perform some weird aerobatic feats with this thing. It would not be your common or garden variety gyro.

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Re: re: The Gyro-Jet

Post by Bruno Ogorelec » Fri Mar 24, 2006 9:16 am

Anders Troberg wrote:It's a neat solution, but it would probably be more effective if the engine was closer to the center of the rotor, somewhat like the traditional engine placement on most autogyros.
It has just occurred to me that you may be thinking in terms of mass distribution. My layout would have a relatively high polar moment of inertia, compared to a gyro with its engine closer to the center of gravity.
That would mean a higher initial resistance to pitch and yaw oscillations, but a greater difficulty in stopping them if and when they do start.

What I'm counting on is the flat surface of the engine pack on a relatively long arm acting as a horizontal stabilizer, damping pitch oscillations. As for yaw oscillations, I am not aware that they have ever been a big problem with gyros. Correct me if I'm wrong.

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re: The Gyro-Jet

Post by Anders Troberg » Fri Mar 24, 2006 9:45 am

No, my thought was simply that the closer to the centre of the rotor disc you have the exhaust, the more you will have a rotor blade in the exhaust stream (time percentage-wise) as the exhaust will cover a larger part of the circumference of the smaller circle.

Of course, it will get a worse leverage, so it may just even out in the end.
Why would inertia be bad in a rotor that doesn't have to change its rotational speed quickly?
I agree, inertia is more or less what keeps an autogyro flying, especially if you have to do an autorotation.

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re: The Gyro-Jet

Post by Bruno Ogorelec » Fri Mar 24, 2006 10:34 am

Just another small sketch -- Gyro-Jet in flight. I love that little machine. I want to fly it very badly.
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re: The Gyro-Jet

Post by Dave » Fri Mar 24, 2006 12:07 pm

Very nice Bruno!
Need another passenger to help balance the load?
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re: The Gyro-Jet

Post by larry cottrill » Fri Mar 24, 2006 2:36 pm

I like the basic concept very much. Except for a case like the Hindenburg, I do NOT like powerplants attached to an airframe via some kind of thin struts - it's just asking for fatigue and mechanical resonance problems. I would move the engine to the rear of the wide part of the fuselage, and achieve your pre-rotation by having the nozzles slanted upward toward the rear of the rotor disk (rather than firing vertically through the central zone.

I just wouldn't trust any powerplant setup that's way off the centerline and attached through a pair of thin struts that impose bending moment during both roll and yaw maneuvers.

L Cottrill

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Re: re: The Gyro-Jet

Post by Bruno Ogorelec » Sun Mar 26, 2006 8:28 am

Larry Cottrill wrote:I like the basic concept very much. Except for a case like the Hindenburg, I do NOT like powerplants attached to an airframe via some kind of thin struts - it's just asking for fatigue and mechanical resonance problems. I would move the engine to the rear of the wide part of the fuselage, and achieve your pre-rotation by having the nozzles slanted upward toward the rear of the rotor disk (rather than firing vertically through the central zone.

I just wouldn't trust any powerplant setup that's way off the centerline and attached through a pair of thin struts that impose bending moment during both roll and yaw maneuvers.

L Cottrill
Larry, such engine locations have been used in practice with quite some success in a number of cases. Several successful aircraft carry their engines on the single vertical tail fin.

In fact, look at the engine location in quite a number of airliners and bombers -- engine pods hung on thin vertical foils that themselves hang from thin wings...

I think the (relatively lightweight) engine pack is well supported by the V-tail. The important structural consideration will be the torsion on the tail boom, but it is relatively easy to make such a cylindrical/conical structure resistant to torsion.

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re: The Gyro-Jet

Post by Bruno Ogorelec » Sun Mar 26, 2006 9:18 am

OK, here's a structurally easier layout. A shorter boom, the engine pod used as a structural member, shorter load paths etc.
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re: The Gyro-Jet

Post by Bruno Ogorelec » Sun Mar 26, 2006 12:12 pm

The same thing stationary, with the tricycle undercarriage.
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re: The Gyro-Jet

Post by Anders Troberg » Mon Mar 27, 2006 8:14 am

I'd still prefer the engines just behind the rotor mast. If nothing else, it would give a better airflow over the rudders. Also, autogyros, like helicopters, like to have the weight close to the rotor mast. Remember, every kg you put back there needs to be balanced with maybe 4 or 5 kg in front due to the longer leverage.

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