Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by leviterande, Oct 14, 2008.
If I read correctly, the precession issues killed it.
The counter-rotation neutralizes the precession.
Forward speed is limited because the inflow tends to tilt the disc backward opposing forward flight. This limits forward speed.
Looks like fun though... I'm surprised nobody's duplicated it since then.
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I don't understand all the fail-safe modes. If an engine quits, you can always throw a parachute (BRS), or make a gliding landing (with small wings). A couple of big airbags on the underside might also help. I'm sure all those redundant engines, props and such are way more complex.
And just a sidenote, virtually every helicopter also has a no-go zone, where an engine failure is likely to seriously hurt you:
Precession isn't canceled by contra-rotating rotors; rather the contrary. If your left top rotor goes down and your left bottom rotor goes up, they'll touch. There's a reason the discs on the Kamov are so far apart.
The Hiller platform had rigid counter-rotating propellers, not rotors. I chose the word "neutralize" carefully. I did not say canceled. Precession is not cancelled, but it is neutral with respect to the pilot in that he can tilt the machine forward to get a forward tilt.
If the machine had only a single propeller, in this case, the pilot would need to tilt the machine 90 degrees ahead to allow for precession, I think. (lean right to go forward)
In any case, precession does not seem to be an issue with the counter-rotating Hiller platform. So Dan's comment about precession killing the platform is incorrect, as far as I know.
My VTOL book says the platforms had some advantages over helicopters, such as flying close to obstacles, but suffered from high fuel consumption.
That Hiller platform sounds like a very good idea to persue, and easy! To increase fuel economy and use a smaller engine make the prop diameter bigger, like just going from five to ten feet would make a huge difference. Something like an 8 ft diameter seems practical, and evidently it's pretty easy to make as far as the control system works, there isn't one, only the throttle. For safety all you need is a ballistic parachute on your back
Neither would help you if you're hovering at 100'
They made a helicopter of similar configuration (pilot standing on top) around the same time.
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Any system that uses a rotor or prop so close to the ground will be limited in its choice of surfaces. The wind created would kick vast quantities of any loose materials like dust or sand or leaves or grass; some of those would obscure vision and/or incapacitate a pilot, and others could clog the fan or its cage. Ordinary helicopters have a time of it already, even with rotors eight feet or more off the ground.
We have a Cirrus with the ballistic 'chute. Below 1000' it's pretty much useless, as it does take some time to rocket out, expand and fill before it can contribute to any deceleration, and that's after the pilot's reaction and deployment times are figured in. On anything with open fans or rotors it would probably get tangled up in the machinery.
What I meant instead of a ballistic chute, actually, was a rocket powered escape pod ... plus a parachute. A Gemini type rocket on top as used in the first space capsules. You would be wanting to be sitting down for that part Something like that wouldn't help much though if you were sideways when you triggered it
You could make this platform using a seated position and just lean the upper body, or stand if you wanted to.
And for the important part ... to make the power source fail safe use at least two engines, fuel supplies, etc, each one of which can lift the machine by itself. In that case the engines would normally be running at bellow 50% unless you were climbing fast.
Sorry, then I misunderstood you.
Nope, not at zero knots. but neither would a helicopter (see the above graph). That was my point; it's unrealistic to except a "totally" safe design. No aircraft is and neither is a helo, since both have "dead zones" where escape isn't always possible.
I like the Russian approach (just blow the rotor head off)
Apart from that; there's a big difference between a fast Cirrus and a much slower aircraft/helo; the latter don't drop that fast and parachute forces are much lower.
3-4 seconds to stationary descent? That'd be 250 ft of freefall.
As for the wings; helo's come in with forward speed as well, mainly to make an autorotation possible. Who not do the same with a VTOL design?
@ Starman; you're referring to something like the Russians used for their tanks? They dropped a complete tank, hung it on parachutes and a 100 ft long line, hanging beneath it, ignited a rocket motor above the tank, slowing it down. Yes, the crew remained inside during the drop :gig:
Here's a long vid, action around 31:15:
Considering curing the issue of precession, has anybody considered using the simplest rotor head there is for control... Why not usea small 10 ft teetering prop/rotor for a small VTOL.
How about a ligth one manned 200kg VTOL with a 10 ft teetering rotor for control? I know some helicopters used direct tilt hubs like gyrocopters.(B.J Schramm Scorpion helicopter for instance). Sure they are not as good as true swashplates but teetering hinges are way simpler and we are not looking for best performance here in a first prototype VTOL. Seriously, why hasn't anyone thought about using the mechanism of a gyrocopter head to both neutralize and control a small 10ft rotor VTOL?
I believe the Scorpion had a true rotor head. The link rods from the swash plate were hidden inside the mast instead of along the outside, but they're there.
Dan, I know some versions of this helicopter had an ordinary swashplate and some hade direct hub tilt control. It is very confusing to know the exact name but yes some B.J helicopter had direct control. One can see the collective-wire indicating that the collective is seperate from the direct control. Early helicopters used direct hub tilt. heck, even the advanced V-22 uses direct hub tilt control!
The helicopter is either shramm scorpion I or II. You can see the picture here. It is a fixed swashplate with a seperate collective mechanism. A closeup:
Rotorway "Scorpion Too" helicopter - development history, photos, technical data
Rotorway "Scorpion" helicopter - development history, photos, technical data
My point is, what about having a teetering 10ft propeller/ rotor for control and elimination of the precession
OK. I can see that direct-tilt control there. Thanks
If one goes to a ten-foot prop he might as well build a helicopter, I'd think. The power requirements for small, highly-loaded disks might make it a heavy, poorly-performing machine. But it sure would be fun.
My idea of a fun machine would be a really light fixed-wing ultralight, electric motor driving a big, slow, quiet propeller for cruising over the countryside at low level at something like 30 mph.
I can definitely see the low level cruising, what a joy. A fixed wing ultralite may be the last resort to any vtol. By keeping the wing loading low and the prop big and engine power small, a low slow level flight on a quiet calm day isnt too wrong for sure
Hi guys, i'm currently building a flying platform (similar to hillers but not exactly the same) 5 foot duct, 1 set of ivoprops (three blades) with 50hp engine and im getting enough lift for a 10 and a half stone person but i'm not 10 and a half stone, so, what do i do? do i 1; go on a diet, 2; get another set of blades on there spinning the opposite direction, 3; use a bigger engine, 4; use 2 engines, each turning its own set of blades? or use fan blades instead of ivoprops? any suggestions most welcome.
Someone had a look at the hillers blade tip clearence from the duct and its 1cm or so which i thought was too much of a gap, everywere i'm reading that it has to be really close, i mean, really really close without touching when spinning, i read elsewere that they glued a peace of carpet to the duct to close the gap and it made a great difference, i know the one in the museum hasn't got carpet glued to it but the bigger gap is there so i made mine with the gap, if i close this gap will it really make that much of a difference to lift?
the efficiency of a ducted propeller is lower than "slightly larger free propeller"
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