Ultra low head speed Helicopter design- what will happen?

[leviterande]

Hi, let us say an ultralite helicopter is designed and yes it can lift its own weight and fly. THe rotor diameter is around 33ft or 10m and the head rpm is 60-100rpm

The rotorblades would have thicker chords I believe but other than that how will the characteristics be like? will it be unflyable?

 

[StanFoster]

In my opinion, the rotor rpm is way too low, and they would cone way up trying to lift the helicopter.

 

[choppergabor]

With that low RPM you won't get enough lift to pick that thing up. I doubt it. Stan is correct about coning. The more of the coning the less lift you get. Any weight on the machine so we have some idea what needs to be lifted?

 

[RotoPlane]

Hi, let us say an ultralite helicopter is designed and yes it can lift its own weight and fly. THe rotor diameter is around 33ft or 10m and the head rpm is 60-100rpm

The rotorblades would have thicker chords I believe but other than that how will the characteristics be like? will it be unflyable?

The main problem is a disk loading of .59 lb/sq.ft. (with 504 AUW) .The ideal is 1.3 lb.
The cone angle would be ~4° but could be reduced with tip weights.
The rotor rpm would be 228, if you had a 6" blade chord....the larger the chord, the lower the rrpm and the slower the tip speed.

You wouldn't want to fly this dude....with a .59 lb.sq.ft. disk loading, you would be at the mercy of a small wind gust.....that's if you could keep the blades rotating .

 

[PW_Plack]

To get a given amount of thrust/lift at lower RPM requires higher torque; that means moving the tail rotor onto a longer arm or giving it more thrust, both of which likely mean more weight.

Building very light 10m blades running at low RPM means low inertia, which brings its own set of issues.

I assume, being in Norway, your "ultralights" can weigh more than the 115 kg allowed here, so maybe the weight required to make this work would fit, but what need drives this compromise?

 

[RotoPlane]

Whoops, sorry….I've got a gyro mind-set right now! I still believe safe autorotation in this "helicopter" would be iffy.

 

[leviterande]

You are correct, the cyclic response would be very mushy.

I was thinking of having much larger chords than 6". Moe like 26"! I know it is extreme, but that is the concept I have in my head, a huigh torque low, head speed rotor that an lifts up at minimum head speed

 

[Jean Claude]

So, 100 rpm and 33 ft requires chord 30" ! 3° coning requires about 100 lbs /blade
Jean Claude

 

[BobK]

how low can it go? interference of rotational vector at the hub/root

how low can it go? interference of rotational vector at the hub/root

hwell: If the speed is way too low it won't autorotate?

Isn't it the angle of attack that takes foward vector of force into rotation? what about very very slow 16-40, max 60rrpm can't disk loading and coning become less of a tourque factor, but would require more blades, softer & self adjusting of the AoA reguardless of hub tilt?
A smart blade that gets control information from the hub (IR transeiver) and send back air flow data & presure? :flame:

Sorta a lot to mount on a few ultrsonically welded, CNC air knife cut pieces of Tyvek? at least if the electronics is distributed with more at the tip a weight for stability won't just be a dead weight.

O' to wish for a rich kite maker to show up at my door & the rotors would be near complete.

now
:focus:how low can rrpm be before near field fluid wake of previous blade in rotation interupt rotational forces. i've been looking at the vector drawing way too flat vectored?:noidea: does anyone have a rrpm counter to measure a maple seed pod? if blade shape is feathered on retreating blade vibration energies are ripest for collection to tuned load (ooopps)?

Where are the all my nerdy math friends with the slide rules now:wacko:?
The software flow charts & coding is easy, making the DSP completely light enough and the leading edge and inflation controls mechanically sound NOW THAT's a good trick!!!:rapture:
Always have fun & smile at yourself a little each day

 

[RotoPlane]

Kalle - Apparently you are hoping to use a light low hp, high rpm engine that is reduced to 100 rrpm (or using man-power). I surely am not going to say this cannot fly....but I do wonder if it can be done safely. As Jean Claude stated, for a 2-bladed rotor, it would take around a 30" chord and a high coning angle without heavy tip weights. It is very unlikely you are planning on using a gimbaled rotorhead....unless you have amazing arm strength. You can reduce the 30" chord by adding more blades. Whatever you're building....I do wish you success....

 

[FRENCHCORSAIR]

Hi everybody.
I think that's just a matter of profile, to have the correct thrust with a low rotor's speed.
I speak about profile in the news about the VTOL giroplane.
Christian

 

[Rotor Rooter]

This will provide you with some information. It does not address the other pros and cons which have been mentioned by others above.


Disk - Large Chord & Low Tip Speed

 

[leviterande]

i am intending to use low horspower engine, not my feet thanx, but maybe if I am on a diet ?


Anyway I remember there was a blackwhite videoclip of a 10m coaxial early helicopter that not only flew with control but with amazingly slow blades that you could track them by your eyes, it wasnt a video effect. the blades were slow and huge. aah if I only could find this video again


Kalle

 

[Rotor Rooter]

On topic, but perhaps off track.

On topic, but perhaps off track.

This may have been the world's most efficient helicopter.
This may have been the world's first helicopter (to fly).

A modern high-tech version of this helicopter may (or may not) be of interest.

OTHER: Helicopter - Outside - Side-by-Side - Cornu, Paul, 1907 - First flight


Dave

 

[leviterande]

This may have been the world's most efficient helicopter.
This may have been the world's first helicopter (to fly).

A modern high-tech version of this helicopter may (or may not) be of interest.

OTHER: Helicopter - Outside - Side-by-Side - Cornu, Paul, 1907 - First flight


Dave

Yea, That was along my lines of thinking, an ultra low head speed craft with high solidity ratio around 30inch a chord

 

[RotoPlane]

Kalle - If you didn't need to keep this an UL (which is doubtful with a 33' rotor anyway), you could go with a coaxial design you mentioned in the above post. No tailrotor needed and the blade chord could go from 30" to a little above 15", unless you still want a high solidarity per disk. I assume you will be using semi-rigid rotorheads and some form of swashplate. Just a thought……

 

[leviterande]

One of many ideas I have to eliminate the torque is the idea of driving the huge 30" chord rotor by some kind of "cage-fans". No, no the typical propeller as it brings problems.

I have been thinking about installing "cage-fans" longitudinally, along the length of the rotorblade.

the cage-fan produces an additional force upwards on the rotorblades. The positive up force together with the wide chord should make the heli lift up at a low rrpm

I was thinking of this STOL design:
http://www.fanwing.com/

What do you think about that.

The heli would lift at much lower rrpm from that design compared to traditionally driven rotorblades, since the rollcage-fans induce an upward momentum on the blades as well: check the takeoff runs of the FANWING STOLs

 

[bmoore2156]

Have you considered retreating blade stall? It might hover but you might not want to fly in any direction very fast.

 

[RotoPlane]

After an engine failure, the descent rate on a fanwing would be fatal I think. I believe those fans with power loss, would have so much drag that the rotor would slow quickly and fold. I really think you would be better off using the props at the root ends. If you plan on humans flying with this helicopter, crash landing is not an option......but then, I want to live . I like the fact that you are thinking out of the normal box.

 

[leviterande]

Ed.
That is correct, the Fan will drag insanely UNLESS: the cage-fan rotates freely and a clutch is needed, but thats way too complicated so a fast High rpm motor should let the fan rotate freely even after the motor stopped perhaps?

bmoore, if it aint gonna go anywhere, why the hassle.
Lets se here : as a blade is advancing or rotating it has an airspeed, say in my case

around 30mps minimum. As the blade retreats in a forward flight of 30ms or 100kmh the retreating blade will definitetaly stall as the airspeed will be zero. but I wont be zipping at 100kmh ..

I belive you are concerned about the characteristics of "roll-cage" in a retreating blade.
I want to know that as well..