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Autogyros


The_Rocketeer
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So everybody knows that helicopters are incredibly difficult to make in KSP because of the lack of rotor parts, and also because there's no simple way to make a collective control.

However, in a conversation with Claw in another subforum, I realised that autogyros are possible in game as an alternative to fixed-wing flight. For the unknowing, these use a freewheeling rotor to generate lift by airflow going through the rotor from below. It turns out that KSP's lift/drag model is absolutely up to the task of making one of these work.

What is required is a slightly backward-raked helicopter rotor that will begin to turn due to the force of air hitting the blades. They need to be angled such that the forward-moving side is producing conventional aerodynamic lift, i.e. is near level, while the rear-ward moving side is pitched to generate greater drag, like a pitched-down elevator, which provides some lift as well as the drag force that drives the rotor around.

I tried a long time today to make a stock autogyro, and in the end I failed because my skills with making stock roller bearings are, well, not. However, I know that others have made stock bearings that are perfectly adequate to operate a lifting rotor - all stock choppers have one!

So, here's a showcase/proof of concept using mod parts from the KAX mod to make up for my lack of bearing ability. I also challenge the community, to build an all-stock autogyro and share it with us.

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Made this a while ago:

http://i.imgur.com/NjY3u4t.png

http://i.imgur.com/B6VRKGg.png

http://i.imgur.com/XRStK4p.png

Fully equipped with rockets, machine guns, and missiles, and flame thrower. Required tweak scale, firespitter, KAX, and BDA.

It's cool but not an auto giro. I would love to see one built and working in stock.

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Oh, I see! An autogiro doesn't have a powered rotor. Oh well, it was still fun.

Yeh, this is the fundamental principle.

Still, if u take that model, rake the rotor back one notch, and try flying with just the thrust-prop, you'll probably find it works out.

Watch out on takeoff tho, cos the lift-rotor gives really uneven lift while spooling up to speed, and that takes a little while. From what I've seen, autogyros tend to take off fast and steep, and go straight into a smooth bank to let it balance out.

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Thank you for now giving me the autogyro bug....

I can't see how to solve the issue of asymmetric lift. It never reared its head in stock helicopters. So far, I can either have rotation and crashes shortly after take off. Or zero rotation but a completely decoupled rotor disc and a very pleasant little outing.

I suppose the way forward will have to be reaction wheel/rcs spam to overcome the roll moment that is induced. I think Bob and Bill's expressions capture the moment perfectly, they know that if I pitch up there's a good chance they'll be brown bread...

Currently the craft is setup with:

Rotor disc currently has around 10 degrees of pitch (blades).

I tried angling the mast rearwards but I think I ran into movement problems, so to emulate that the rotor assembly mounting point has been angled back 4 degrees relative to the mast.

I also tried with the rotor disc at 5 degrees pitch, as well as completely flat and adding fins to the tips at 35 degrees to induce rotation.

As it stands I can see one two ways of kludging it: rotor disc flat. But add aerodynamic surfaces somewhere around the rotor blades or the actual mast itself. Something that will induce rotation, without causing the asymmetrical lift.

How could you make the retreating blade flap? I can't see a stock solution to that. You could give each rotor blade its bearing between it and the hub and create some sort of track whereby the retreating blade's angle is forcefully changed by a "bump" - imagine a camshaft and its lobes. Seems overly-complicated, but you could[?] get away with a wheelless bearing for the blades... Hmmm.

I should really learn to stop thinking by typing. Sorry. I ought to know how to write briefly and concisely...

EqxONko.jpg

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Thank you for now giving me the autogyro bug....

I can't see how to solve the issue of asymmetric lift. It never reared its head in stock helicopters. So far, I can either have rotation and crashes shortly after take off. Or zero rotation but a completely decoupled rotor disc and a very pleasant little outing.

I suppose the way forward will have to be reaction wheel/rcs spam to overcome the roll moment that is induced. I think Bob and Bill's expressions capture the moment perfectly, they know that if I pitch up there's a good chance they'll be brown bread...

Currently the craft is setup with:

Rotor disc currently has around 10 degrees of pitch (blades).

I tried angling the mast rearwards but I think I ran into movement problems, so to emulate that the rotor assembly mounting point has been angled back 4 degrees relative to the mast.

I also tried with the rotor disc at 5 degrees pitch, as well as completely flat and adding fins to the tips at 35 degrees to induce rotation.

As it stands I can see one two ways of kludging it: rotor disc flat. But add aerodynamic surfaces somewhere around the rotor blades or the actual mast itself. Something that will induce rotation, without causing the asymmetrical lift.

How could you make the retreating blade flap? I can't see a stock solution to that. You could give each rotor blade its bearing between it and the hub and create some sort of track whereby the retreating blade's angle is forcefully changed by a "bump" - imagine a camshaft and its lobes. Seems overly-complicated, but you could[?] get away with a wheelless bearing for the blades... Hmmm.

I should really learn to stop thinking by typing. Sorry. I ought to know how to write briefly and concisely...

http://i.imgur.com/EqxONko.jpg

That's because your travel speed is much greater than the rotation speed of the rotor. That can't be if you are emulating an autogyro. Make bigger rotors wit better weight/lift ratio, so they spin up a slower speeds and the tips move faster.

Edit: I thought about it for a minute, and I think I remember the trick, and it could be done in principle in KSP. You have to angle the whole rotor and the blades so that the blades see a positive AoA relative to the direction of travel, but negative relative to their plane of spin. Something like the rotor inclined 30º, and the blades having 15º negative AoA. That way aerodynamics forces accelerate the rotor, like a windmill, and they still provide lift.... but I'm still not sure you won't need a functional swashplate to have cyclic pitch control. After all, De La Cierva is the guy that invented modern helicopter rotor mechanisms, and he did it to solve the autogyro problem.

Rune. Aerogyros exploit aerodynamic effects that I'm not sure you can replicate in KSP. I would have to pick up pen and paper to remind myself this stuff...

Edited by Rune
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That's because your travel speed is much greater than the rotation speed of the rotor. That can't be if you are emulating an autogyro. Make bigger rotors wit better weight/lift ratio, so they spin up a slower speeds and the tips move faster.

Edit: I thought about it for a minute, and I think I remember the trick, and it could be done in principle in KSP. You have to angle the whole rotor and the blades so that the blades see a positive AoA relative to the direction of travel, but negative relative to their plane of spin. Something like the rotor inclined 30º, and the blades having 15º negative AoA. That way aerodynamics forces accelerate the rotor, like a windmill, and they still provide lift.... but I'm still not sure you won't need a functional swashplate to have cyclic pitch control. After all, De La Cierva is the guy that invented modern helicopter rotor mechanisms, and he did it to solve the autogyro problem.

Rune. Aerogyros exploit aerodynamic effects that I'm not sure you can replicate in KSP. I would have to pick up pen and paper to remind myself this stuff...

Hmm interesting points to ponder. I hadn't thought to try the bigger rotors, but the mass adds up quite quickly and you soon end up having too much mass to be spun through errordynamics?

So I gave your idea a go, thank you no offset limit mod for making it easy. Offset the cargo bay bearing box up, added 30 degrees of rotation to the mast, -15 degrees to the blades. And yes, holy crap, it works a dream while you're on the ground. Beautiful. But of course, once airborne... Wants to backflip. But thinking about, I suppose it just involves experimentation to find the angles that give you enough airflow to spin, yet don't lead to asymmetric lift and don't induce massive backflips. This is definitively cleaner than the road I was going down. And I would never have gone to such "extreme" angles on the mast.

However... Before I'd read your reply and tried it, I did manage to kludge one into being by going down the "camshaft lobe" style route that would allow a flapping rotor blade. I only got as far as adding freewheeling bearings to the rotor blades, but it works. There is a lot of flap in the blades and it ain't pretty (to be fair, I don't think helicopter flight when you see the blades flap can ever be described as pretty...), nor optimal... But she flies, and is relatively stable. Although disc needs more spin. I suppose this is a cheating autogyro... More tinkering to be done.

A4dKrfb.gif

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I'm really glad someone else is taking this up, and without a doubt you're having more success than me so far.

I also started with the Mk II parts, tho part of me is disapproving of their lifting-body aerodynamics. Then again, at these speeds I doubt there's much of a contribution...

I'm still experimenting for now...

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I've tested it and I must be a very bad pilot, but I haven't been able to have controlled flight. Most of the time there were blades hitting the ground, uncontrollable rolling or pitching while accelerating ... I think decreasing blade angle would help for spinning up. Coaxial would certainly help. I made a version with a long tail with a reaction wheel, and placed wide side wheels. Still no success. It has potential, in the mean time I think I'll stick with normal helicopters :-)

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