Backpack helicopter

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Bruno Ogorelec
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Backpack helicopter

Post by Bruno Ogorelec » Tue Feb 14, 2006 12:16 pm

The backpack helicopter has long been a dream of many. It has remained elusive, though, for a number of good reasons. I guess this is the best I have seen so far. The guy is obviously almost there. A little more tinkering and that will be it.

http://tinyurl.com/9ctmf

Warning for people with dialup connection: it's a fairly big video file; some 6 Mb

Veterans of backpack choppering will notice a crucial detail -- the designer has taken a leaf out of the hang gliders' book and separated the pilot from the craft. The pilot hangs from the chopper frame. This may well save his life and/or limb. Helicopters fixed to your back have a nasty habit of transmitting the torque to your spine when the blade is suddenly stopped, say in the event of the blade hitting the ground or something.

My personal opinion is that a backpack gyrocopter is a better bet than a helicopter, but that's definitely up for discussion. I also have ideas on powering it with a pulsejet, and those ideas have certainly been strengthened by this little movie.

Alas, I have no idea of the background to the machine featured here. I've been trying to track it down, so far with little success.

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re: Backpack helicopter

Post by Mike Everman » Tue Feb 14, 2006 3:04 pm

I'm going to watch that all day! You're a bad, bad man, Bruno! So simple. He's almost there. A little more diameter on his rotors, I think.
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re: Backpack helicopter

Post by Zippiot » Tue Feb 14, 2006 3:27 pm

do you know what kind/size engine is powering it?

if its a piston engine add a turbo and it should be able to squeeze some more power out of it. iff not then i cant give a suggestion.

how would you power it with a pulsejet? im not doubting just interested
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re: Backpack helicopter

Post by Zippiot » Tue Feb 14, 2006 3:32 pm

wait a second, i see an upper and lower blade. those things work great, but to the best of my knowledge have yet to be successfully applied to an aircraft. they tried it in WWII but itm often failed, resulting in a crash. but that was an airplane, not a helicopter...
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re: Backpack helicopter

Post by Mike Everman » Tue Feb 14, 2006 3:44 pm

counter-rotating rotors are done all the time. There's a big section in here somewhere about backpack jets, check it out.
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re: Backpack helicopter

Post by thecheat » Tue Feb 14, 2006 6:39 pm

I have a coaxial RC heli, flies great, better than my much larger one actually!

that's very interesting, I'm sure that if I sat in it (as I'm still yet a teen) would take off, I weigh only 140ish, though, if I ever got near one of those I'm sure my dad would promptly kill me (before the heli could).

the ONLY trouble with a co-axil heli is this: when in forward motion a circular traveling object (blades) produces MORE lift while on the part where it is moving against the wind than when with it, this causes the blades to bend on that side upward as heli blades are much more flexible than one might think. this is a problem on a co-axial (and single axial) heli BECAUSE once a certain speed is reached (moving forward) the blades try to occupy the same space at the same time and CRASH the blades hurtle off and you smash into the ground. YES, I've experienced this on my small heli before.

in this respect this heli is VERY impracticle as (i'd guess) once a speed of MAYBE 20 mph is reached the blades will contact. though, this is the best version I've seen as well, this one would actually work with a kid on it!
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Re: re: Backpack helicopter

Post by Bruno Ogorelec » Tue Feb 14, 2006 9:26 pm

Mike Everman wrote:I'm going to watch that all day! You're a bad, bad man, Bruno! So simple. He's almost there. A little more diameter on his rotors, I think.
Yeah, I know! :o) I've seen it about two dozen times so far. Can't stop returning to it.
Zippiot wrote:do you know what kind/size engine is powering it?
Nope. No idea. I have not found its provenance yet, except that it's a German homebuilt and that it was filmed flying last summer.
Zippiot wrote:how would you power it with a pulsejet? im not doubting just interested
At the moment, I'll just say “in the way Germans did it in World War 2“. (Only, they did it with a much bigger engine.) More about it as I explore the idea more thoroughly. It’s kind of crazy.
Zippiot wrote:wait a second, i see an upper and lower blade. those things work great, but to the best of my knowledge have yet to be successfully applied to an aircraft. they tried it in WWII but itm often failed, resulting in a crash. but that was an airplane, not a helicopter...
It’s been done successfully on a number of helicopters since.

thecheat wrote:the ONLY trouble with a co-axil heli is this: when in forward motion a circular traveling object (blades) produces MORE lift while on the part where it is moving against the wind than when with it, this causes the blades to bend on that side upward as heli blades are much more flexible than one might think. this is a problem on a co-axial (and single axial) heli BECAUSE once a certain speed is reached (moving forward) the blades try to occupy the same space at the same time and CRASH the blades hurtle off and you smash into the ground. YES, I've experienced this on my small heli before.
in this respect this heli is VERY impracticle as (i'd guess) once a speed of MAYBE 20 mph is reached the blades will contact. though, this is the best version I've seen as well, this one would actually work with a kid on it!
You are right but only if the rotor does not have collective cyclical pitch control. It is the detail that makes helicopter rotors pricey. It is a complex set of actuators that change the pitch of the blade as it makes the circle, so that it uses greater pitch going downwind than going upwind. That equalizes the lift of the advancing blade with that of the retreating blade and they remain roughly level.

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re: Backpack helicopter

Post by Bruno Ogorelec » Tue Feb 14, 2006 11:24 pm

Can anyone help me identify things on this machine? It looks incredibly simple.

What I see is a single horizontal cylinder protruding forward. To the man's left on the cylinder is a carb, which sucks from a big bright blue bottle, which is presumably an air filter cum intake silencer. The snaking black thing on the opposite side is obviously a tuned 2-stroke exhaust. The dirty cannister on the right is obviously the fuel tank. And that's about it. Nothing else.

The reductor/drive split must be remarkably compact. I don't really see any details that would indicate collective pitch control.

The guy sits on something that looks like bicycle seat, doesn't he?. It's affixed to that back downtube, which looks like some kind of a spine of the assembly. I don't see any means for him to move the rear stabilizer, unless he does it with a twistgrip.

Why are the front two legs tied together at the ends with that loose strap? He'll just trip on the damn thing.

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re: Backpack helicopter

Post by Greg O'Bryant » Wed Feb 15, 2006 5:18 am

Yikes when the ride is over don't stand up too fast!! I like the idea of a gyro plane with a jet tip prop for thrust. It would be very light weight.

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re: Backpack helicopter

Post by Mike Everman » Wed Feb 15, 2006 6:36 am

Well, Bruno, I've certainly studied the video enough!

Starting with what we know, two shafts, one within the other. Most likely transmission is a bevel gear set, which don't really come with concentric shafts, so he's had to home grow it, which isn't super difficult, but I'd expect he does bearings and such for a living. One would expect him to have two cylinders on that motor, but it's hard to see.
I think you've ID'd most everything else. I see no evidence of pitch changing gear, so he's just on the throttle for altitude. The handlebars have me stumped too, unless he's turning them for his control of throttle and rudder, then a cross-bar would complicate things. I like the seperate poles the more I look at it, might make it easier to get one out to stop a fall.

This guy is great... ;-)
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re: Backpack helicopter

Post by Anders Troberg » Wed Feb 15, 2006 7:42 am

I think he could have flown for real, he just choose not to (and I sure understand him, espicially if this was the first test flight). A couple of times in the video, he is hovering, so he should be able fly gor real.

My main concerns are:

* Landing. If he should tip over, things get ugly.
* Can it autorotate or will it become a brick in the event of a power failure?
* The rotor is awfully close to the pilot.
* It must be awfully windy to fly, definately not for cold weather.

I think safety could be improved a lot by ducting the rotors and put some wire mesh or vanes below the rotors. Vanes could also be used to control it by directing the air stream.

Either way, I want one!!!
Why are the front two legs tied together at the ends with that loose strap? He'll just trip on the damn thing.
Probably to stop one pole from bending outwards in the event of a bad landing. Could be solved in a nicer way.
It’s been done successfully on a number of helicopters since.
The Soviets did it, very succesfully, on a number of Kamov helicopters.

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Re: re: Backpack helicopter

Post by Bruno Ogorelec » Wed Feb 15, 2006 12:08 pm

Mike Everman wrote:two shafts, one within the other. Most likely transmission is a bevel gear set, which don't really come with concentric shafts, so he's had to home grow it, which isn't super difficult, but I'd expect he does bearings and such for a living.
Mike, have you seen the counter-rotating prop drive used on some of the big outboard boat engines? Maybe it could be adapted. If so, there's your complex component off-the shelf. Well, almost. You'd have to modify it extensively, I guess, but it would still be easer than doing it from scratch. Maybe you could buy internals and just cast a new housing for your purpose.
One would expect him to have two cylinders on that motor, but it's hard to see.
So would I. Power is everything here. With a flat twin, he'd get a 95 percent increase in power for, say, a 30-percent increase in mass. But, if it's possible to do it with a single pot, why not?
I like the seperate poles the more I look at it, might make it easier to get one out to stop a fall.
Yes, that's occurred to me, too. But, I'd still put some kind of a curved ski-style extensions on tips, to avoid pitch-poling.

Mike, you're an engineer -- what would you say to a Kaman-style separate intermeshing rotors as opposed to Hiller-sytle (or Kamov-style) stacked coaxial ones. You'd need a double bevel drive for both, but somehow I like the Kaman layout better. I don't like packing too many mechanical components together and having every single loading transmitted to every single component. It's asking for trouble unless you have the development resources of Toyota. I'd feel more confident with separate rotors and they may even prove cheaper in the end. Unless you buy a ready made set, like the outboard assembly I mentioned.

Also, I like the broader loaded disc that the Kaman layout offers. Looks more like a wing to me. Not very scientific, but there you are...

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Re: re: Backpack helicopter

Post by Bruno Ogorelec » Wed Feb 15, 2006 12:25 pm

Anders Troberg wrote:I think he could have flown for real, he just choose not to (and I sure understand him, espicially if this was the first test flight). A couple of times in the video, he is hovering, so he should be able fly gor real.
Anders, you could be right. Maybe it was the very first flight and he was just not confident enough.
* Landing. If he should tip over, things get ugly.
Right. I'd put ski-extensions on tips to avoid the tips digging in.
* Can it autorotate or will it become a brick in the event of a power failure?
Brick would be my guess. I think you need a larger prop than that for autorotation to work well. But, I could be wrong. Ballistic chute is what you need. However, if you are flying low, it will not do you much good either. And low flying would be exactly the point of this machine as far as I'm concerned. I think the answer is simply in quality engineering.
* The rotor is awfully close to the pilot.
Right again. I'd really add perhaps a foot to the distance.
I think safety could be improved a lot by ducting the rotors
Yes. Modern carbon fiber technology makes this a viable (if expensive) option. I'd certainly think about it. Besides, it helps lift a great deal. A ducted rotor also lets you engineer the coaxial shaft differently, easing the bending loads. I'd really, really hate to have to design a lightweight coaxial counterrotating shaft assembly exposed to strong bending loads.
Vanes could also be used to control it by directing the air stream
With such a small mass of the machine, compared to the pilot, I'd say that weight shift is preferrable. It's responsive enough, it's more intuitive and cuts down enormously on mass and complexity.

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re: Backpack helicopter

Post by skyfrog » Wed Feb 15, 2006 3:06 pm

Hi Bruno,

I enjoy this video very much, thank you. Here's another instance of contra-rotating coaxial rotors :

http://www.gyrodynehelicopters.com/qh-50e.htm

You can find a drawing of the transmission system in that link. This is no more a secret as it has been 40 years old, or more. I am more interested in this one because it was powered by a turbo-shaft engine, the Allison.
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re: Backpack helicopter

Post by Mike Everman » Wed Feb 15, 2006 3:10 pm

Brick is right! I think the rule of this thing is, "don't fly higher than you are willing to fall, under a motor and shrapnel bomb"
As to ducting, even advanced materials wouldn't be practical. The weight is one issue, but the main killer is that the tips need to be so close to the inside of the duct for it to be worth doing, it would have to be unreasonably round for it's size, and stay that way under all conditions.
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