Concept for New (maybe) VTOL Craft

[Dave_Jackson]

The linked web page AeroVantage (http://www.unicopter.com/AeroVantage.html) is the preliminary evaluation of a configuration that could outperform the tilt-rotor and the tilt-wing.

It is submitted for consideration, critique, and to place it in the public domain.

Dave

[slowrotor]

Well, tilt props is not a new invention.
The Curtis-Wright X-19 had four tilt props.
Focke had a tilt prop STOL.

I think prop lift is the way to go, but I prefer the method of Focke and Dornier (DO29). That is, extreme STOL first, to be followed with VTOL.

slowrotor


Dornier DO 29 http://www.airliners.net/open.file?id=1179047&size=L

[Dave_Jackson]

slowrotor,

True, your slower approach may be the safest.
__________

The concept on the linked web page is that of providing a change in the disk area between hover and cruise. The result being a better Figure of Merit and a higher forward velocity.

It is the same objective as Sikorsky's extended blade patents are attempting to achieve.

The existing and currently proposed quad-rotors still put a downwash on the non-rotation wings during hover. However, more importantly IMO, it appears that their fore and aft rotors are not intending to take advantage of a higher induced velocity that is obtainable from coaxial rotors, which share the same stream tube.

In addition, all flight control, in both modes, might be obtainable from only; collective blade pitch and PropRotor tilt control.

Just an idea.

Dave
_______________

Addition:

slowrotor you may find this web page interesting; http://www.vstol.org/GermanVSTOLTransports.pdf

[maxtork]

Dave,

As I understand it you are trying to gain some effeciency by putting the rear rotors in the slipstream of the forward ones as a make shift coaxial set up. I think that when the prop rotors are rotated down into forward flight mode they will be a good distance apart. From what I have read the coaxial loses the performance gain as the rotors are set further apart. I have thought about this arrangement myself and one possible solution would be to use the forward rotors as pushers pointing down mounted on a high wing and then rotating aft which would put the prop closer to the rear rotor. The rear set could be tractors pointing up on a low wing and then rotating forward. I'm not a CAD whiz so I can't draw it up but I have played with the idea on paper a bit and it seems to work out.

I think one of the reasons the tiltrotors are not as effecient is due to the load they are trying to carry with it. For a military machine or one that is being used for revenue this is important but for a personal air vehicle maybe not so much. Take a V22 and cut down the gross weight to just empty plus fuel and crew and the required structure to carry the lesser load and the disc loading goes down a bunch. With lower disc loading you need less power and therefore smaller engines etc. Things might start to look a bit more promising at this point.

Just some random thoughts about your idea for what they are worth (not much at todays exchange rate!!!).

Max

[Dave_Jackson]

Max,

Yes, you are correct.

A very large gap between coaxial rotors is most efficient for vertical lift due to the large effective disk area and low induced velocity per sq-ft. Conversely, the same rotors with a very small gap will have a smaller effective disk area and a higher induced velocity per sq-ft., and this would be better for forward thrust.

As you probably already know, this is the main problem with the tiltrotor (and the tiltwing) configuration, such as the V-22. It is using the same disk area for vertical lift as it is for forward propulsion. It must therefore compromise between the two requirements.

Sikorsky has a number of patents for a Variable Diameter Proprotors (larger diameter for hover and smaller diameter for propulsion) and this is aerodynamically attractive. However, the mechanism for obtaining variable blade span creates its own set of problems.

Your desire to place the counter-rotating proprotors in close proximity to each other, for propulsion during forward flight, is ideal since this will halve the disk area from when the are two aerodynamically separate proprotors and are providing lift.

It may (or may not) be impractical to get the coaxial proprotors in close proximity to each other for propulsion, as you are suggesting. My thinking is to allow a reasonable distance between the fore and aft proprotors, but have the diameter of the aft proprotor equal the diameter of the front proprotor's streamtube at the location of the rear proprotor.

This also should/may result in an 'effective disk area' that is the average of the actual front and rear disk areas. And just as with your idea, the effective disk area of the proprotors in forward flight will be half the disk area of the proprotors in hover.


The essence of this idea is probably the application of separate electric motors at each proprotor. Your idea will probably involve four identical motors, whereas my idea will require smaller motors on the aft proprotors and larger motors on the forward proprotors.

So far, so good. :ok:


Dave

[Graviman]

Dave, I've actually seen the Dornier Do-31 at the Munich Deutsches Museum

http://www.deutsches-museum.de/en/flugwerft/collections/vtol-aircraft/

The problem with all of these is high disk loading and complexity. High disk loading is bad because it reduces all up weight for a given power, complexity is bad because it reduces the percentage of the all up weight that is payload. There is also the cost of all those turbines, props, driveshafts, gearboxes etc. I notice you have not sketched in any structure for the rotors.

Separating lift and thrust is good, if only because it allows a streamlined cruise attitude, but for good hover capability you need as large an uninterrupted rotor area as possible. This needs to be as compact a configuration as possible or you limit where the machine can demonstrate its flexibility.

Later thought:

Hadn't we all agreed that, despite the assumption of incompressibility, having a puller prop ahead and below a rotor did in practice produce a measurable increase in pressure hence reduction in pitch?

Alternately put a pusher prop above and behind a rotor. Besides the rear rotor is best off being out of the streamtube of the front rotor. Like Chinook this reduces BVI vibration and increases the intake area. So you want that design to fly backwards. Still monstrously inefficient though...

[Dave_Jackson]

Mart,

The following are a bunch of obvious points, but they are being presented as logically comprehensible steps toward the essence of this concept.

The concept being; An Aerodynamically Variable-diameter PropRotor.

Helicopter rotors are efficient for lift because they have a large disk area and a low induced velocity per sq-ft.
Airplane propeller are efficient for propulsion because they have a small disk area and a high induced velocity per sq-ft.
The V-22 and the proposed V-44 have fixed diameter PropRotors. They are a compromise between a rotor and a propeller.
Sikorsky has considered a variable diameter rotor, however the mechanisms to vary the length of the blade's span are problematic.
The intention of the idea on this thread is that of using four proprotors that have physically fixed diameters. However, the pairing them allows for two different aerodynamically 'effective disk areas'. The larger area to satisfy the above #1 and the smaller area to satisfy #2.

For an elaboration on #5 consider;

Two rotors with given characteristics and arraigned in a side-by-side configuration will provide 'a large disk area and a low induced velocity per sq-ft.'. As wanted for #1.
Two rotors with the same characteristics and arraigned in a coaxial configuration will provide 'a smaller disk area and a higher induced velocity per sq-ft.'. As wanted for #2
In other words, if these two rotors are arraigned as side-by-side for hover, and then rotated 90-degrees and arraigned coaxially for propulsion, they will give a better figure of merit in hover AND a faster forward velocity in cruise, than current tilt-rotors do.


This is a large view of the initial workup of the craft. (http://www.unicopter.com/1471.jpg) It shows the PropRotors in their Hover configuration and in their Cruise configuration.

Dave

[slowrotor]

What is the point of designing a bit more efficient high speed VTOL..... there are no civilian VTOL's. The small civilian proprotor has not been invented yet.
I would focus on just getting off the ground and consider high speed efficiency in a future dream.

In addition, I would question your claim that streamtube contraction is significant at high forward speed.

[Dave_Jackson]

slowrotor;

Halftime at the Super bowl? :)

It appears that this could be significantly more efficient than the current design of tiltrotor; assuming that major problems don't crop up. Theoretically, an increase in the diameter of the rotors will improve the FoM at the expense of high forward speed.

Leishman (2006) says that the current V-22 looses 10% in Figure of Merit due to the downwash on the wing alone. He also says that the streamtube only contracts to 0.8, not the originally held belief that it contracted to 0.707. However he says that it is fully contracted within .25R below the rotor.

AERODYNAMIC OPTIMIZATION OF A COAXIAL PROPROTOR (http://www.baldwintechnology.com/MTR_AHS06.pdf)

Dave

[Deemar]

Dave Jackson said:

Airplane propeller are efficient for propulsion because they have a small disk area and a high induced velocity per sq-ft.

Actually, I thought that most airplane propellers were as large as practical given the size and weight of landing gear. I don't believe that there is an advantage to having a high disk loading, particularly when you've got a variable pitch prop that can cater for the differences between high speed cruise and low take-off speeds.

Daniel

[Heli-phile]

Hi,
had a look at the plans.
My instant concern would be there appears to be no reduntantcy for a engine failure (electric motor failure)
If each motor is independant with no shared drive the machine would very quckly loose control whilst in hover/transition (maybe even cruise)
What is the OEI proceedures??

[Dave_Jackson]

Danial;Actually, I thought that most airplane propellers were as large as practical given the size and weight of landing gear. Thanks for mentioning your concern. I suspect that there is an optimal propeller diameter. However, what you say is correct because in most cases the diameter is physically limited before it can reach this optimal size.

IMHO, the very large helicopter rotor will probably have to be reduced to reach the optimal propeller diameter.

There are people on this forum that are much smarter than me on this subject. It would be appreciated if one of them would add to the discussion.


Heli-phile;

Another valid concern.

I hope that this is a viable answer.
So far, at least, I prefer the theoretical advantages of a single motor at each proprotor. However, it might have to be a custom motor. The reasons for this preference are;

Electric motors are very reliable.
A slow RPM motor will not require gearing.
The motor is brushless.
The only moving parts on an Outrunner style motor will be the permanent magnets and their outer encasement, plus bearings and stub shaft.
The coils, which are stationary, can be divided up among 2 or 3 independent power and control circuits. The idea is to include this redundancy, but put it within a single frame.Just thoughts for consideration.


Dave

[maxtork]

Dave,

Your idea on the redundant electric motor might work but could you also get all the props turning in synch with each other like a mechanical drivetrain would? I would suspect that having one or more get out of phase might cause some kind of vibration issues. I'm sure it could probably be done but how much complexity would it add? I guess if the props are balanced individually they shouldn't care what the other props are doing but I suspect that aerodynamically the interaction between props and airframe and prop to prop might cause some issues. Just a thought.

Max

[Dave_Jackson]

Max,

The following is presented as potential ideas to overcome valid concerns.
... but could you also get all the props turning in synch with each other like a mechanical drivetrain would?Each motor would be equipped with one, or more, encoders. These encoders, plus gyros and pilot inputs, will vary the power to each motor, as desired. If a motor starts getting too far ahead of the demanded requirement it can be temporarily made to act as brake by electronically turning it into a generator.

I suspect that aerodynamically the interaction between props and .... prop might cause some issues. This appears to be the biggest concern, to date. As the craft maneuvers during cruise, the streamtube from the forward proprotor may 'wander' about the plane of the disk of the aft proprotor. An idea is to try and have the fore & aft proprotors in close proximity during cruise and spaced apart during hover.


Please destroy any of the potential solutions if they are not valid.


Thanks,

Dave

[Deemar]

Dave said:


I suspect that there is an optimal propeller diameter. However, what you say is correct because in most cases the diameter is physically limited before it can reach this optimal size.



I think you'll find that momentum theory will tell you that larger is always better.

The limits that determine "optimal" are likely to be related to:

Tip speed and compressibility effects - however this is more of a limitation for helicopters as the advancing blade has a higher tip velocity in translational flight
Structural limitations - how heavy is the structure of the rotor/propellor.Daniel

[Dave_Jackson]

Daniel:

"I think you'll find that momentum theory will tell you that larger is always better." I totally agree, if you are talking about a hovering rotor.

If the helicopter only needs to hover, then the induced velocity can be 500 ft per second (through a minuscule rotor) or 0.5 ft per second (through a monstrous rotor), since the craft is not going anywhere.

If the craft is required to climb at, say, 50 ft per second, then the induced velocity must be at least 50 ft per second.

The same thing applies for forward flight and this is probably one reason why faster helicopters have a higher disk loading and a smaller rotors.

I speculate that this will also apply to propellers. If the intent is to have a fixed wing craft that will fly at 250 kts (422 fps) then the induced velocity through the propeller must be greater than 422 ft per sec. The designer will pick an optimal tip speed and an optimal pitch for this forward velocity. Then he will increase the size of the propeller until it is large enough to overcome the drag of the craft.


In the case of this thread's proprotor craft, the proprotors should be large for an efficient Figure of Merit in hover, but they will probably be quite a bit smaller when providing the desired forward velocity in cruise.

Dave

[maxtork]

Dave,

While thinking about your idea I came upon a variation on the same theme that you might like. Your initial idea comes from the basic fact that bigger rotors are better at a hover and smaller are better in foward flight (turned to act like a prop). Folowing those same lines what about using an intermeshing design? If you take a intermeshing rotor system with the rotors set at an angle to each other and then rotate them both forward for fast flight then each rotor would only "see" a portion of the oncoming airstream (think Kmax with short stiff rotors flying nose straight down). I guess it is a bit like a full size rotor flying edgewise through the air like a traditional helicopter just without the disymetry of lift or a need for a pusher prop. You would have a disymetry of thrust as the advancing blades would be either on the top or the bottom of the discs now but that may be useful depending on the design. I don't know how much of an angle to each other the rotor would have to be in order to get any bennefit in forward flight (or if the theory would work at all for that matter). Getting the whole ball of wax to rotate around a set of wings would be a bit of a trick as well but I originally thought of this as a tail sitter arrangement but I'm sure it could be made to fit another set up.

Yeah yeah I know...I should quit thinking and drink more right!

Max

[Dave_Jackson]

Max,

The basic idea is to have two independent streamtubes for lift get combined into one streamtube for propulsion.
Your second sentence is correct.

However. it appears that your idea is not changing the 'effective' disk area from when the rotors are facing up (lift) to when they are facing forward (propulsion).

Is this a one rotor version of your idea?
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,382,556.PN.&OS=PN/6,382,556&RS=PN/6,382,556

or ~ if the above does not work

This patent number 6,382,556 to go in this page http://patft.uspto.gov/netahtml/PTO/srchnum.htm


Dave

[Deemar]

Dave said:

If the helicopter only needs to hover, then the induced velocity can be 500 ft per second (through a minuscule rotor) or 0.5 ft per second (through a monstrous rotor), since the craft is not going anywhere.

If the craft is required to climb at, say, 50 ft per second, then the induced velocity must be at least 50 ft per second.

The same thing applies for forward flight and this is probably one reason why faster helicopters have a higher disk loading and a smaller rotors.

Not quite right.

The induced velocity is the vector difference between the inflow velocity and the outflow velocity. It can be small compared to these velocities. For example, a helicopter that has a 10 ft/sec downwash hovering will have something like (but not exactly) a 50 ft/sec inflow and a 60 ft/sec outflow while climbing at 50 ft/sec. It's the change in momentum that matters. I believe you have a copy of Stepniewski's "Rotary-Wing Aerodynamics", it is explained in the early chapters of that book.

I'm not quite sure why higher disk loadings are favoured for faster helicopters. I'm sure Nick Lappos has posted about it in the past. Maybe I'll check Stepniewski tonight.

[slowrotor]

Dave,
The prop size for hover and forward flight are so different that I would consider using a small prop for forward flight and just shut down the lift props after wing borne lift is achieved.
The electric lift fans cannot operate for long anyway with limited battery.

1) large electric lift fans for hover and slow flight.(1% of flight)
2) small prop on heat engine for forward flight (99% of flight)

slowrotor

[Graviman]

I'm not quite sure why higher disk loadings are favoured for faster helicopters. I'm sure Nick Lappos has posted about it in the past. Maybe I'll check Stepniewski tonight.


Daniel, it's because a more powerful engine is already required for higher speeds. So there is less of a compromise in requiring more power for hover. If you take the power vs speed curve the higher disk loading has advantages at speed, due to less parasitic drag, so increasing disk loading just pushes the min power Vy to a higher speed. Ultimately retreating rotor stall limits how far you can push the effect though.

Like everything it's a compromise. It is probably why Nick commented about variable radius being all gravy, since you could increase the disk loading with speed and reduce it for hover. But mechanical complexity and poor transient performance limit its practicality.

Later thought: Increasing disc loading also reduces rotor mass (as you comment), but variable radius would still have you carrying around unecessary mass. This likely is another good reason why variable radius has never got beyond concept testing.

Dave, i'm amazed Leishman find's time to write all this stuff. Paper printed off for a quiet evening...

[Dave_Jackson]

Deemar,

An interesting argument. We are probably talking about the same thing, but from slightly different perspectives

Let's forget the vectors since; the proprotor's thrust and the craft's motion will be vertical during vertical climb, and the proprotor's thrust and the craft's motion will be horizontal during forward flight.

As you say "It's the change in momentum that matters." Momentum is the quantity of motion of a moving object, equal to the product of its mass and its velocity. In other word; the mass can be large and the velocity low, or the mass be small and the velocity large.

As you have said, large rotor is more efficient for hover, but as Mart has said "a more powerful engine is already required for higher speeds".

The 'geometric pitch' of the propeller must be high enough to provide the desired velocity of the craft during forward flight, however as you say, the diameter of the disk should be large to provide efficient lift during hover.

The idea of this thread is to change the 'effective' disk area between hover and cruise so that it is closer to the optimum diameters for both requirements.

In addition and as you have previously said, the proprotor will have to have collective pitch, and the pitch will be much higher during cruise.


slowrotor,

You are probable correct if the intent of this tread was that of conceiving an economical, safe and simple VTOL craft.

Perhaps I should have mentioned at the beginning that the object of this thread's concept is to consider a craft that improves on the shortcomings of the V-22.

The Advancing Blade Concept is a beautiful 'Rotor & Propulsor concept', as a contrast to the tiltrotor's 'PropRotor & Wing concept'. However, it is appearing that the ABC concept may only be able to provide cruise speeds of 250 knots and higher if a reverse velocity blade can be conceived. At the present time, to my knowledge, any improvement to reverse flow through the blade will create a greater dis-improvement to the forward flow through the blade.

The idea on this thread is just another attempt to get a 'Free Lunch' out of Nick.


Mart,Dave, i'm amazed Leishman find's time to write all this stuff. Paper printed off for a quiet evening... It is a very interesting article. Maybe his students do the 'grunt work'.

At the risk of winding Nick up ~ again :O, this report could have been done, and should have been done, many, many decades ago if America had not been redirected away from twin main rotors.

Dave

[IFMU]

At the risk of winding Nick up ~ again , this report could have been done, and should have been done, many, many decades ago if America had not been redirected away from twin main rotors.
That's the problem with America. No free thinking, no innovation. Everything we do is just because somebody from some other country, like Russia or England or France told us to do it. :ugh:

-- IFMU

[Graviman]

Dave, the problem here is the classic one for new concepts - they do not go into details until too late. To convince skeptics you need to take a concept, stick with it, and flesh out the details to the point where there is a counterarguement for every concern.

If that concept was symmetrical then no problem. But there would need to be detailed calculations showing the performance of the design. Everytime a concern is raised there needs to be another calculation to quantify the concern. Ignoring cost, that needs to be at least power vs speed performance, range, component mass (including structure), and handling.

Your spreadsheets are a good start. To provide a compelling arguement you have to show quantitatively that symmetrical will outperform conventional. If the numbers added up even i would be convinced. My strong suspicion is that the benefits do not make themselves present until high cruise speeds.

[Dave_Jackson]

IFMU,

Don't get depressed.

Igor Beaver over-hyped the single rotor. A number of American gurus, in the 1940's, said that the single rotor was not the way to go.


Mart;But there would need to be detailed calculations showing the performance of the design.This is the very point that I was trying to make in the previous posting; in respect to disk area.

The disk area (http://www.unicopter.com/0949.html) is the cornerstone in building rotorcraft algorithms. Yet no rotorcraft Aerodynamicist has ever developed the calculations that mathematically and comparatively interrelate the disk areas of all the various rotor configurations. It was never done in Momentum Theory. It was never done in Blade Element Theory. It was tunnel vision on the single rotor.

Leishman's article is a step in right direction.


Dave

[Graviman]

Dave, looking at your idea for this week:

http://www.unicopter.com/AeroVantage.html

I notice that the machine magically appears from hover to cruise state - perhaps with the same post edit "ping" that masked so many cheap effects on 60's TV Sci-Fi series... :)

I still think that if you want the best transition performance you need a low front rotor and high rear rotor, to avoid interference effects. Keeping the rotor/prop hubs at the same position in space will also simplify the drivetrain. Even so, the penalty of carrying those wings around in hover will be high.

But i see what you are trying to do, take fixed wing performance and give it limited VTOL capability for short duration hover. If a seperate engine drives each diagonal rotor pair you also maintain some failsafe capability.

But the verdict still has to be: Too complicated...

[Dave_Jackson]

Mart,
The concept definitely has pros and cons, but so far - so good.

Some quick replies.
the machine magically appears from hover to cruise state.Yes, transition is currently the primary concern. Here are Seven preliminary ideas for effecting the transition. (http://www.unicopter.com/AV_Methods.html)

I still think that if you want the best transition performance you need a low front rotor and high rear rotor, to avoid interference effects. .... Even so, the penalty of carrying those wings around in hover will be high.
The V-22 looses 10% of its thrust in hover due to its downwash on the wings (Leishman and one other). This 2x4 PropRotor only places a downwash on the wings during transition and the downwash will not be normal to the flat-plate surface of the wings.

Keeping the rotor/prop hubs at the same position in space will also simplify the drive-train.The drive-train consists of four independant PropRotor+Motor, with a liberal sprinkling of electronic SAS.


Theoretically the 2x4 Effective Aerodynamic Disk Area (http://www.unicopter.com/1612.html) should give a better hover AND a faster cruise than the current V-22.

A testimonial; "This is actually a very good idea. It is one of the most cleaver solutions I have seen yet. You have actually had me looking at your idea for about 20 minutes now." ~ Dennis Fetters.

Mart, Any ideas for a good transition mechanism?

Dave

[Graviman]

Dave,

I understand that in the laminar flow environment of a university wind tunnel critical spacing of the propellers ensures perfect reversal of the induced swirl.
(unless i found a way to break the tunnel by not securing the turbulence generator boards :uhoh:) In the real world of turbulence, gusts, manouvres, tired pilots, etc without ducting to force this you will need to use a large amount of tip washout to at least minimise BVI.

In practice, i just don't see the advantage. Leishman comments that it is only really applicable for high disk loading, which we aim to avoid in helicopters - right? Even so similar diameter disks have the advantage of the rear rotor drawing in clean (laminar) air from outside of the front rotor. For your concept I just don't get what the benefit is.

If we are agreed that critical spacing is of interest only to PhD students trying to expand the capabilities of CFD software modelling, then forget trying to cram in the prop-rotors ahead and astern the wing. Space them out nicely so that you can have a nice simple vectoring system - consisting of sprockets and chains (like Harrier). Trust me simple solutions work - every time! (I'm used to having to justify why i want to redesign castings and repackage layouts to the money men).

What i mean by "transition" is that at some point your concept must go from its very power hungry, hence time limited, hover to its real comfort zone of high speed cruise. It is designed for >300mph high speed, right? Otherwise, why not just put down an order for "son of X2"? Your nice pictures of laminar flow stream tubes will become a jumble of lines where that wing is partly stalled and our PhD students have a field day seeing whose CFD code gets the closest to right answer. You could eat even more payload with a wing swivel mechanism. You could provide a self stowing helium balloon...

The point is that the Chinook development team faced similar problems and opted to put the rear rotor up out of the way of the messy front rotor outwash. If you want to see a 21st century bi-plane, look up the Quickie Q2 then see whether the rear wing is the low or high wing.

Perhaps i have laboured my points too strongly for your tastes. But my honest opinion just has to be that this concept is just too complex to be competetive... :)

[Dave_Jackson]

Mart,... from its very power hungry..hover to its real comfort zone of high speed cruise.


Cruise is the 'comfort zone'?
Look at some Russian aircraft with counter-rotating propellers. Then look at their speeds; which are up to 570 mph.

'When the going gets tough, the tough get going.'

[Cyclic Hotline]

http://news.xinhuanet.com/english/2008-02/29/content_7693921.htm

Maybe Dave in action again? :)

[Dave_Jackson]

Cyclic Hotline,

Notice the decal. :)

[Sikorsky X2-1/2]

Dave

[Graviman]

Dave,

Do you have any thoughts about this concept? It is perhaps an overly complicated approach, for a cargo machine. The basic principle of combining the tilt rotors to one large low disk loaded assembly is an interesting idea though. The down-side is still how the machine can be made to respond in the event of Cat A double engine failure during transition.

http://www.baldwintechnology.com/

http://www.baldwintechnology.com/Airplane_Mode_r02.png

[Dave_Jackson]

Graviman,

It's an unusual, but interesting, concept.

I believe that it is being considered as an entrant for the US 'Joint Heavy Lift' (JHL), along with a large Boeing tandem and a Bell V-44. Sikorsky had submitted two coaxial rotorcraft, but it appears that one or both were recently rejected.


Dave

Now, if they are able to separate the rotors for hover and combine them for cruise ......:)

[Dave_Jackson]

Graviman,

Baldwin's Mono Tiltrotor is not a contender for the JHL. They only mention the JHL program from an evaluative perspective.

These were the original five contenders.
--Sikorsky X2C, X2 Technology Crane - coaxial rotor (165 knots);
--Boeing ATRH, Advanced Tandem Rotor Helicopter (165 knots);
--Sikorsky X2HSL, X2 Technology High Speed Lifter - advancing blade compound (245 knots);
--Bell Boeing QTR, Quad Tilt Rotor (275 knots); and
--Frontier Aircraft OSTR, Optimum Speed Tilt Rotor (310 knots).

Recent information;
Lockheed Martin and Karem Aircraft Team to Support Department of Defense Joint Heavy Lift Program (http://www.lockheedmartin.com/news/press_releases/2008/0229ae_horizontallift.html)

Dave

[Dave_Jackson]

DESIGN: AeroVantage - Transition Mechanism - Proposed Methods - Forward and Aft Moving Elbows (http://www.unicopter.com/1642.html)

DESIGN: AeroVantage - Transition Mechanism - Proposed Methods - Upper and Lower Arms (http://www.unicopter.com/1655.html)

[Overdrive]

Very complex transition methods. Why not pivot the cabin/compartment in the centre of a frame with engines left & right or fore & aft, and have the transition of rotor alignment to cruise achieved aerodynamically by the changes in rotor cyclic & collective, rather than physically? This would mean a much simpler hanging/bearing arrangement for suspending the cabin.

The transition of the cabin position could be partly achieved by a controlled/damped/assisted use of its own CofG, in hand with small wings/canards for returning from cruise at speed.

This would of course mean siting the whole power and transmission system remotely from the cabin area, maybe in a separate enclosed aerodynamic compartment.

[Dave_Jackson]

Overdrive

You are correct. All of the proposed mechanisms under consideration (http://www.unicopter.com/AV_Methods.html) may be complex, and therefore relatively heavy.

Mechanically it is unattractive, but it appears to be very attractive aerodynamically. Hopefully, some method may provide the 'free lunch'. Your idea of using cyclic control to transition the PropRotors will be considered. Thanks.


Dave

[Graviman]

Dave, no comprendo. What is so aerodynamically attractive about operating with high disk loading in hover, then making one rotor sit in the turbulent air of another during cruise?

[Dave_Jackson]

MartDave, no comprendo. What is so aerodynamically attractive about operating with high disk loading in hover, then making one rotor sit in the turbulent air of another during cruise? Attractiveness is a relative thing. In this case it relates to the tasks that are being requested of future VTOL aircraft and their ability satisfy these tasks.

Current helicopters satisfy a very small portion of the continuum between the balloon (100% hovering) and the supersonic airplane (100% fast-forward). The objective is to have an aircraft that can expand its portion of the aircraft continuum by offering more than current VTOL craft. One market that has been mention is that of commercial traffic over distances of approximately 250 miles or less.



cattletruck.

You maybe referring to this craft - Igor's VS-300-C
The three tail rotors were intended as substitutes for the rudder and two elevators that are used on airplanes. This was necessary for the control of the helicopter during hover.

http://avia.russian.ee/foto/gallery/sikorsky/sik_vs-300_8.jpg

A possible solution to faster forward moving VTOL craft is not in tilting rotors but in producing faster spinning (and thus shorter) main rotors. Sikorsky is working on this, except that they are slowing the main rotors. ;)


Dave

[Graviman]

Dave, what i'm confused by is that you were championing seperate lift and thrust rotors. Why the change of view to what to me appears less ideal? :confused:

CattleTruck, the multi tail rotor was a short term compromise introduced only while the dynamics of cyclic control were being investigated. The ~90 degrees lead angle that we all take for granted was not then understood - and why would it be, since it is not an issue for smaller diam stiffer propellers.

[Dave_Jackson]

Mart, Dave, what I'm confused by is that you were championing separate lift and thrust rotors. Why the change of view to what to me appears less ideal? Your confused? So am I.
It's all Nick's fault. He threw down the gauntlet many years ago when he said that there's no such thing as a free lunch. :ok:

With a little more seriousness; every concept (configuration) has its pros and cons. Some improvements may be worthy of a free coffee-brake, but none are worthy of Nick's free lunch.

Sikorsky held off further development of the ABC concept for 30 years. Waiting for outside entities to develop new materials and devices cannot be the only reason. The X2-ABC (http://www.unicopter.com/1465.html) will have incremental improvements over the XH-59A ABC (http://www.unicopter.com/0891.html). In addition, I sincerely think that the Intermeshing and Interleaving configurations will be better than the Coaxial.

However, in any future battle for the high-speed VTOL market both the ABC-Rotorcraft and the Tilt-Rotor will have their pros and cons.

IMHO, the primary limitation with the ABC craft is its speed limitation. Prouty has said "What is good for high speed flight is bad for hover and what is good for hover is bad for high speed flight." The same might be said about reverse velocity and forward velocity. At this point in time, it appears to me that anything that is done to the blade to minimize or utilize the effect of reverse airflow will create a greater impediment to conventional airflow.

Perhaps this section on Reverse Velocity Utilization (http://www.unicopter.com/B473.html) will help inspire someone to come up with a solution, get a patent, and make a zillion dollars.

Just my two cents.

Dave.


PS. The UniCopter ain't dead. Far from it. It's just that one should have 'a number of irons in the fire'.

[verticalairborne]

Just came up with an old but really simple design.

Great idea.

YouTube - Custer Channelwing in Flight (http://www.youtube.com/watch?v=-Sn5JL9t_C4)
Welcome to the Custer Channelwing Website. (http://www.custerchannelwing.com/)

That Extra Little Lift | History of Flight | Air & Space Magazine (http://www.airspacemag.com/history-of-flight/custer_channel_wing.html)


should be enforced by nasa and some companies.
Great future and probably the highest amount of power to lift ratio.

[Graviman]

Interesting concept, but would suffer from mildly poor autorotational characteristics... :ooh:

The same is true of any design using engine power to drive airflow over the wing. If electric motors and batteries were used as backup power until normal gliding could be established - but this eats significantly into payload. Best for any design to just be capable of powerless descent.

[Dave_Jackson]

This non-technical paper may be of interest; Recent Development of Rotorcraft Configuration (http://www.bentham.org/eng/samples/eng1-1/Cao.pdf)

Mart,
The above paper relates to our previous discussion on this thread.
Going a little deeper into the subject, this page has information on Sikorsky's Variable Diameter Tilt Rotor (http://www.unicopter.com/1621.html).
In the past, link #2 provided the article for free. Currently, there are numerous links to it on Goggle, but all, or most, want money.

Dave

[slowrotor]

Interesting paper about the variable diameter tilt rotor. Sounds more complex than the V-22 if that is possible.

I saw the V-22 fly at Oshkosh earlier this month.
And the Martin jetpack was demonstrated for its first public display. The jetpack was really two ducted fans with a piston engine for power. It managed to climb about 4 feet. The designer said flights of 6 feet have been accomplished. It seemed to require two assistants for stability.
slowrotor

[Graviman]

Dave, some interesting papers there - a lot to go through...

I'm still not convinced the complexity of variable diam is justified when variable rpm is also considered. Those centrifugal forces are not to be easilly dismissed. Even then most of these configs still struggle to achieve a low disk loading. And the mass of all those complicated mechanisms nibbles into payload. And as for modes of failsafe...

I'm still rootin' for X2, since to me it is the best way to get a helicopter to perform at speed.

[Dave_Jackson]

Graviman & Slowrotor

Mart, there might be reasons to worry about the X2's future.

Initially, five proposed configurations were funded for 'Joint Heavy Lift' program evaluation. It then got reduced to following three. Heavy quad-tilt-rotor from Bell-Boeing
Optimum Speed Tilt-Rotor technology pursued by Karem and Lockheed Martin
JHL - Sikorsky's X2 technology
.
There is an article in the new issue of AHS's Vertiflite on the JHL program. This article says that the door has been opened for Sikorsky's Variable Diameter Tilt Rotor to now be included in the ongoing configuration evaluations.


Dave

[Dave_Jackson]

http://www.crprogroup.com/eventnotebook/Aviation%20Symposium%2009/Friday/Evolving%20Future%20Technology%20Panel/Mr%20Bruce%20Tenney.pdf

[rotate1953]

I have been on this site before and I'm wondering why the Industry has Lost interest in it? It is a (Super) efficiante Lifter and My prototype works well powerd by Electric Motors with props.see it at twitter charles Glazebrook or r/cuniverse?

[msmfi]

Dave,
Have You ever consider idea of Variable Solidity Rotor, ... instead of Variable Diameter Rotor ? :)

Regards,
Mirek

[Dave_Jackson]

Dave,
Have You ever consider idea of Variable Solidity Rotor, ... instead of Variable Diameter Rotor ?

Mirek,

No meaningful consideration about variable solidity.
My closest consideration has been that of high solidity and variable tip speed, such as; DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed (http://www.synchrolite.com/1090.html).

We are both posting on the new thread 'A New Rotorcraft Called a Tiltplane' on another rotarywing forum. I will post a response to Variable Solidity there.


Dave