Helicoptor whifs

[Weaver]

For helicopter what-ifs, the Helistat is, I think, the most special of them all.

Beyond that of a heavy lifter, what other role can it (or its successors) take?

It's a pity that that abortion gave the concept a bad name: it's failure was down to sheer bad engineering rather than anything to do with the fundamental idea. 

High-endurance radar platform is one use that immediately springs to mind. You could also use it for ocean patrol/ASW. On the one hand, it would have all the hovering advantages of a helo (dipping sonar, rescue winch) and the controlability neccessary to refuel from ships at sea. On the other hand, it would have almost the endurance/range of an airship.

[Sisko]

Check this one out.

Came from the Concept ships blog site, Very cool

Is there a side view of it sisko?  There seems to be something missing, for example, you can see four dust filters but only two engines, we should be able to see the long engine nacelles behind the top two in this view too.

Unfortunately no what you see is all there is.

As to whether it is feasable concept or not, it was drawn by an artist not an engineer

[dy031101]

High-endurance radar platform is one use that immediately springs to mind.

(It did right after I hit the "Post" button.)

On the one hand, it would have all the hovering advantages of a helo (dipping sonar, rescue winch) and the controlability neccessary to refuel from ships at sea. On the other hand, it would have almost the endurance/range of an airship.

How's the potential speed of such airships compared to those of helicopters?

[chrisonord]

For helicopter what-ifs, the Helistat is, I think, the most special of them all.

Beyond that of a heavy lifter, what other role can it (or its successors) take?

I saw a program of this thing setting off on its maiden flight, it destroyed itself big time, and killed one of the pilots also.
As soon as I saw it come out of its hanger I thought to myself, that thing is gonna kick the S*** out of itself, and it did so spectacularly.
It was on a Discovery channel program called Destroyed in seconds, and this thing did not disappoint!!!
Chris. 

[SSgt Baloo]

A couple of mine:

The Flying Gondola

Based on the Weserflug P.1003/1:

Der Schwebeflugfläche

(Or "Hoverplane" Auf English.)

[Stargazer]

Very nice! The Schwebeflugfläche actually reminds me of a mixture of some Hiller and McDonnell designs plus some really new elements... Very interesting!

[dy031101]

I saw a program of this thing setting off on its maiden flight, it destroyed itself big time, and killed one of the pilots also.

I don't think it crashed on its maiden flight.  Wikipedia recorded it as April 26th, 1986, and the crash as July 1st.

Well in any case, I think the entry's description as to the cause of the crash is pretty in line with Weaver's thought, a case of bad engineering rather than any flaw with the idea of the airship.

[chrisonord]

I saw a program of this thing setting off on its maiden flight, it destroyed itself big time, and killed one of the pilots also.

I don't think it crashed on its maiden flight.  Wikipedia recorded it as April 26th, 1986, and the crash as July 1st.

Well in any case, I think the entry's description as to the cause of the crash is pretty in line with Weaver's thought, a case of bad engineering rather than any flaw with the idea of the airship.

Well that is what the presenter of the program said so that is the info I have, another thing also is that it was built in the hanger of another ill fated US airship from a bygone era.
Chris.

[kitnut617]

Long time ago when Airwolf was on the TV I had this fanciful idea of building a large RC model of it.  Of course while researching certain aspects of it I got to realize it just wasn't going to work, Airwolf that is.  I had found a lot of info on propellers and rotors and got to learn about retreating blade stall and supersonic blade tip speeds and all that fun stuff when I got to thinking how could you make a helicopter go supersonic or to be more likely -- 4 or 5 hundred miles an hour.

After a lot of trial and error (lots of error) I came up with this below.  I found my old drawing I had done way before I ever had a computer, while un-packing some moving boxes.  The idea was to have all the blades the same length (about 2 feet IIRC) but keep the total blade area as on a UH-1, the inner ring of blades running counter rotating to the outer ring (to counter retreating blade stall) and also to have the inner ring of blades speed running the same as the outer ring (at the tips anyway)  These would be powered by a turbine buried in the center fusealge connected to two gearboxes with slightly different ratios.  High speed forward power would come from the two turbo-props in the tail nacelles.

[GTX]

Nice look - you should try scratchbuilding it!

Regards,

Greg

[Weaver]

Kitnut - couple of points:

1. Since your rotor is buried in the fuselage, it wouldn't suffer from retreating blade stall/advancing blade compressibility anyway since it's not exposed to the airflow from the craft's forward motion. You therefore wouldn't need the elaborate double blade ring: just some means of countering torque, say by having two contra-rotating layers or some side thrust at the tail.

2. You'd have a huge problem with intake momentum drag. That is to say, your rotor is effectively taking a cylinder of air that's moving over the aircraft horizontally and re-directing it to the vertical. In drag terms, that's exactly the same as having a solid, circular air brake the diameter of your rotor sticking up from the craft at 90 deg. you could recover some of this the way that the F-35/Yak-38/Yak-141 do by having cascade vanes under the rotor that can turn the downwards flow partially backwards again. however, on those aircraft, that's a transitional phase used at relatively low airspeeds, not in the cruise at 500 mph.

I've always thought the best way to get a high speed rotor was an extension of the Sikorsky ABC concept, i.e. two very rigid, co-axial, contra-rotating rotors. You can deal with the supersonic tip of the advancing blade by good blade design, and you just eat the retreating blade stall: it's even on both sides so it doesn't roll the helo over, and by the time it's producing significant losses, you're going fast enough for the machine's conventional wings to unload the rotor anyway.

[Mossie]

1. Since your rotor is buried in the fuselage, it wouldn't suffer from retreating blade stall/advancing blade compressibility anyway since it's not exposed to the airflow from the craft's forward motion. You therefore wouldn't need the elaborate double blade ring: just some means of countering torque, say by having two contra-rotating layers or some side thrust at the tail.

Wouldn't the two props on the tail be able to provide counter torque?

[kitnut617]

Kitnut - couple of points:

1. Since your rotor is buried in the fuselage, it wouldn't suffer from retreating blade stall/advancing blade compressibility anyway since it's not exposed to the airflow from the craft's forward motion. You therefore wouldn't need the elaborate double blade ring: just some means of countering torque, say by having two contra-rotating layers or some side thrust at the tail.

I had worked out the blade speeds at different diameters all the way down a regular rotor blade at their traditional RPM at one foot increments and found that the blade tips went supersonic very close to what the max forward speed of a helicopter really is, about 250 mph.  The idea of all those small blades was to have them all travelling at the same speed which meant that the inner ring of blades would have to operate at a different rpm to the outer ring to have the blade tips travelling at the same speed.  Of course there was a slight difference in the speed of the other end of the blades but not much to notice (all to do with diameters and rpm).

But I don't pretend to be an aircraft engineer and to be honest I had no idea that by having the blades buried in the wing I wouldn't have the stall or compressibility problem.  Having the two rings of blades counter-rotating seemed to me a way to counter torque and also somewhat the gyroscopic effect of each ring (being a motorcycle rider I thought this would be quite important)

2. You'd have a huge problem with intake momentum drag. That is to say, your rotor is effectively taking a cylinder of air that's moving over the aircraft horizontally and re-directing it to the vertical. In drag terms, that's exactly the same as having a solid, circular air brake the diameter of your rotor sticking up from the craft at 90 deg. you could recover some of this the way that the F-35/Yak-38/Yak-141 do by having cascade vanes under the rotor that can turn the downwards flow partially backwards again. however, on those aircraft, that's a transitional phase used at relatively low airspeeds, not in the cruise at 500 mph.

My thinking was that in fast forward motion the blades wouldn't be doing any lifting at all, they would still be spinning but set in a neutral position, the lift would be provided by the wing shape but this was as far as I got with it.  The forward power idea of two engines in the fin nacelles was also a bit different to the normal, the idea was that the whole assemble, fin, nacelle, prop, would work as a rudder much like the directional jet nozzles that are all in vogue.  But then as this would have been another new innovation not proved, I went off in another direction with this system on a more conventional aircraft, see below

[jcf]

Evidently the Skyhook project is still going forward:
http://en.wikipedia.org/wiki/SkyHook_JHL-40

... and of course there is the Cyclocrane which is neither fish-nor-fowl:
http://www.uh.edu/engines/epi311.htm

http://www.youtube.com/watch?v=cWLhH3wsxUo

[Weaver]

I had worked out the blade speeds at different diameters all the way down a regular rotor blade at their traditional RPM at one foot increments and found that the blade tips went supersonic very close to what the max forward speed of a helicopter really is, about 250 mph.  The idea of all those small blades was to have them all travelling at the same speed which meant that the inner ring of blades would have to operate at a different rpm to the outer ring to have the blade tips travelling at the same speed.  Of course there was a slight difference in the speed of the other end of the blades but not much to notice (all to do with diameters and rpm).

I understand the concept with respect to blade speeds and it's theoretically sound. However the engineering problems in building it would be quite severe. Am I right in thinking that the outer blades are attached to an outer ring? In that case, that ring must be very big and to be strong enough to take the induced forces, pretty heavy too. The inner blades' mounting ring must also be pretty big and heavy, and if there's a "guide ring" between the two sets of blades then so must that be. That's a lot of rotating mass that's creating a lot of gyroscopic inertia but not contributing to lift.

Also, the middle "guide ring" has to absorb the friction from BOTH sets of blades travelling in opposite directions. Even if it's not intended to take the major lift loads, the blades will still flex from their roots, applying some force to it.

But I don't pretend to be an aircraft engineer and to be honest I had no idea that by having the blades buried in the wing I wouldn't have the stall or compressibility problem.

Just to be crystal clear, I'm not an aircraft engineer either, nor am I pretending to be one. These are purely my thoughts based on aircraft engineering/design books I've read.

As I understand it, the advancing/retreating blade problem only becomes critical when the air flow due to the forward motion of the helicopter is added to the airflow over the blades caused by their rotation. Put it another way: when the helicopter is hovering, there is no advancing or retreating blade because they all have the same relative airspeed wherever they are in the circle. it's only when the helo starts to move that one side of the disc becomes "advancing" and the other side "retreating".

Let's say the hovering air speed over the blades is R, the helo's forward speed is V, and the local air speed over a section of blade at any given moment is L.

On the advancing side, the L=R+V. This can rapidly approach supersonic speed, which is precisely why helo top speeds are about 250mph.

On the retreating side, the L=R-V. Since the amount of lift generated by a blade is proportionate to L and it's angle of attack, the ever reducing value of L as the helo accelerates forces the blade to adopt a higher and higher angle of attack to maintain lift, until eventually, the airflow breaks away and the blade stalls. However before you got to this point, there'd be such a large migration of lift from the retreating side to the advancing side that the helo would probably enter an uncontrolled roll anyway.

You can see from this that if the blades arn't exposed to the helo's forward airspeed (as in your design) then V is zero (for the blade) and L is therefore constant.

Fixed wings can help with this problem by providing additional lift as the helo accelerates so that the total lift required from the rotor is smaller and angles of attack can therefore be lower right across the disc. They can also help with roll control using ailerons. However the downside is that they're dead weight in the hover, thus reducing lift capacity.

Having the two rings of blades counter-rotating seemed to me a way to counter torque and also somewhat the gyroscopic effect of each ring (being a motorcycle rider I thought this would be quite important)

The two rings would indeed counter torque reactions, just as co-axial contra-rotating blades do on Kamov helicopters.

They wouldn't do anything to counter gyroscopic effects though, because gyroscopic inertia is independent of the direction in which the mass is rotating: all that matters is the size of the mass and the speed of rotation. Two small, contra-rotating gyroscopes have the same gyroscopic inertia as one large one of twice the mass, rotation at the same speed.

2. You'd have a huge problem with intake momentum drag. That is to say, your rotor is effectively taking a cylinder of air that's moving over the aircraft horizontally and re-directing it to the vertical. In drag terms, that's exactly the same as having a solid, circular air brake the diameter of your rotor sticking up from the craft at 90 deg. you could recover some of this the way that the F-35/Yak-38/Yak-141 do by having cascade vanes under the rotor that can turn the downwards flow partially backwards again. however, on those aircraft, that's a transitional phase used at relatively low airspeeds, not in the cruise at 500 mph.

My thinking was that in fast forward motion the blades wouldn't be doing any lifting at all, they would still be spinning but set in a neutral position, the lift would be provided by the wing shape but this was as far as I got with it.  The forward power idea of two engines in the fin nacelles was also a bit different to the normal, the idea was that the whole assemble, fin, nacelle, prop, would work as a rudder much like the directional jet nozzles that are all in vogue.  But then as this would have been another new innovation not proved, I went off in another direction with this system on a more conventional aircraft, see below

That's fair enough: the rotors are effectively "feathered" and the craft behaves like a circular-winged aeroplane. You might want to incorporate shutters over and under the rotor disc to make a smooth wing surface though, otherwise the lift from your body/wing will be seriously compromised.

Swivelling the fins and nacelles would certainly work, although as you say, it's be an engineering complication.

If you had a single blade ring and therefore needed to counteract torque, you could do it with differential pitch on the two pusher props, switching to rudder trim at high speed to avoid the loss of propulsive efficency from non-optimised prop pitches.