Compound Helicopter

[brett s]

The autorotation issue could be fixed with asprague clutch on the output side so the transmission isn't being driven during autorotation, but the poor efficiency makes the whole idea impractical to begin with.

When your drivetrain friction losses alone are higher than tail rotor power requirements would be most of the time, it's a sign. And then there's dealing with all the heat generated, adding more weight...

 

[DennisFetters]

The autorotation issue could be fixed with asprague clutch on the output side so the transmission isn't being driven during autorotationQUOTE]

Yes, but now you need an extra set of gears to hook together the main rotor and tail rotor, or for an intermeshing system too.... so double the weight and expense, and more loss of efficiency.

It's all boiled down to the way it's done today is because that is the best way to do it, until other technologies come into play that go beyond the physics involved with the transmission of power through metal components currently used.

 

[quadrirotor]

Dennis, what do you think of the Touringcopter that i described in the thread on synchropters? It seems to me that the Touringcopter, with three small engines (Rotax 503, two for the rotors and one for the propulsion) is simple to make for the homebuilder and simple to fly for the sunday-pilot!!!.
Of course, if you need performances and if you don't bother with the construction: the Commanche set up is unbeatable!!!

 

[Rotor Rooter]

Dennis and Brett,

The concerns that you guys bring up are certainly important and they require serious consideration. The following is an attempt to address them in a satisfactory manner.

Low Efficiency due to High Friction:

Worm gears are not as efficient as a ring and pinion or standard beveled gears, because in a standard gear the metal of the teeth roll together without sliding, while the teeth in a worm gear strictly slide on each other creating friction between the metals and the viscosity tension drag of the oil.

The sliding friction of a worm & gear is definitely higher than the negligible sliding friction of other gearing arraignments. Basic efficiency tables show +/- 89% as the best that can be achieved. However, other information shows that the the optimal efficiency can be up in the high 90's. Low ratios, greater worm starts (multiple threads) and higher sliding speeds reduce this friction. The intended gearing for the SynchroLite is a 7.5:1 ratio with a quad worm.

Consider that the Robinson R-22 drives through an inefficient V-belt (not gear-belt) plus a gearbox. Then add the tail-rotor.


Lubrication:

The problem with this is the instant wearing of the teeth if you exceed the viscosity of the lubricant for only a moment, it shears metal.

Yes. The assurance of adequate lubrication is essential. I think (hope) that the use of an appropriate lubricant, combined with light-weight, low-cost lubrication duplicity and warning device should negate this problem.

Autorotation:

The autorotation issue could be fixed with a sprague clutch on the output side so the transmission isn't being driven during autorotation, but the poor efficiency makes the whole idea impractical to begin with.

This idea is only intended for intermeshing rotorcraft. The two gears and their common worm will provide the synchronization of the two rotors. The overrunning clutch will be centrifugal clutch that is located between the engine and the gearbox.

The other problem using a worm gear in a helicopter is when you need to autorotate, because when the larger driven gear becomes the driver to the smaller gear, the force needed to turn it is magnified by the ratio. So if it's a 5 to 1 reduction, it will take 6 times the force to turn the smaller gear, which can be devastating when trying to autorotate.

A Worm&Gear can back drive at ratios below 10:1. In addition, the freewheeling worm should offer negligible resistance to the combined driving of the 2 gears.

Weight and Complexity

Yes, but now you need an extra set of gears to hook together the main rotor and tail rotor, or for an intermeshing system too....

The total drive-train will consist of a single gear box with only three gears; plus the centrifugal clutch + flexible coupling between the engine and the gearbox. It should make for a; simple, lightweight and reliable unit.

Dave

 

[brett s]

Have to agree with Dennis - there's a reason you see the single main + tail rotor configuration on the vast majority of helicopters, it's the best compromise.

 

[DennisFetters]

Dennis, what do you think of the Touringcopter that i described in the thread on synchropters? It seems to me that the Touringcopter, with three small engines (Rotax 503, two for the rotors and one for the propulsion) is simple to make for the homebuilder and simple to fly for the sunday-pilot!!!.
Of course, if you need performances and if you don't bother with the construction: the Commanche set up is unbeatable!!!

Three times the chance of an engine failure, of which any one will bring you down. Three times the weight needed, and three times the fuel burn, and three times as expensive as one engine.


There are reasons they call them "compound" helicopters;

The designing is compounded with problem.

The manufacturing is compounded with complicity.

The test flying is compounded with multiple overlapping simultaneous problems.

Even normal flying compounds the normal workload of the pilot.

When things do go wrong in flight, the problems are compounded by the power of 3, and that's just when you need things to be really simple.....

 

[quadrirotor]

That's why a 747 has four engines!?!

On the Touringcopter, if one engine fails, you can persue your flight!!!
If two engines fail, you have a better choice of terrain to land!!!
If three engines fail, you are in the situation of having one unique engine failure!!!
Statistics show that, even with two strokes engines, the chances to have both engines failures at the same time are less than having one unique engine failure!!!

You said Dennis:"Three times the weight needed, and three times the fuel burn, and three times as expensive as one engine." Completly dishonest!!! the price and the weight of three new 503 are less than a new Lycoming 360 !!! The fuel burn, almost the same!!!

 

[DennisFetters]

That's why a 747 has four engines!?!
On the Touringcopter, if one engine fails, you can persue your flight!!!
If two engines fail, you have a better choice of terrain to land!!!
If three engines fail, you are in the situation of having one unique engine failure!!!!!!

A 747 is not a helicopter.

That is the same thing Eagle's Perch said with their twin-engine 503 powered helicopter...... just before they tried shutting off one engine and balled it up, and that terrain was flat and clear. If that little helicopter could not maintain flight and make a safe landing with one person, a helicopter with a 503 will certainly not do so carrying 3 engines, (one for pushing and two for lifting), let alone an extra person.

Most people can't keep one engine running right, let alone 3.

Statistics show that, even with two strokes engines, the chances to have both engines failures at the same time are less than having one unique engine failure!!!!!!

So do you have 3 separate tanks for fuel, and buy your fuel at 3 different places? Engine failure is not the only things that bring you down....

You don't need to have both engines fail at the same time. If one fails you will be coming down. 99% of the twin engine aircraft don't have two engines for security. It's because they need both for the power to fly.

You said Dennis:"Three times the weight needed, and three times the fuel burn, and three times as expensive as one engine." Completly dishonest!!! the price and the weight of three new 503 are less than a new Lycoming 360 !!! The fuel burn, almost the same!!!

Where do you come off calling me dishonest? Comparing a Rotax to a Lycoming is apples and oranges.

You could make a conventional helicopter fly on one 503, that's all I was saying. There is nothing dishonest about it.

You know André, dreaming and contemplating and tinkering about how a helicopter should be, or could be, is great. The fact of the matter is when you actually have some experience in the matter, things start to take on a little different shape. Reality tends to have that effect. But, until you have accomplished designing, building and flying one of your own, you will not understand the reality of it, and no one can tell you different.

You asked. Sorry you didn't like my answer.

 

[Rotor Rooter]

Have to agree with Dennis - there's a reason you see the single main + tail rotor configuration on the vast majority of helicopters, it's the best compromise.

Coincidently, I just posted the following on PPRuNe.

Sikorsky's Dilemma is Rotorcraft's Problem

The Problem;

At the birth of rotorcraft in the US, Igor's simple VS-300 single-rotor helicopter was in competition with the more technologically advanced Platt-LePage XR-1 symmetrical twin-rotor helicopter. The simpler craft won the contract, due to the government's desire for fast deliver.

The single-rotor thereby became the predominant configuration.


The Dilemma;

How can anyone hope that the predominant Sikorsky will ever produce the superior symmetrical twin-rotor configuration?

To do so would be an admission that they were wrong in the late 30's, and, that they continued to perpetuated the error for 70 years.

The new moderator then shut the thread down. Perhaps he is having problems walking in the footsteps of his predecessor.


Dave

 

[gyromike]

Coincidently, I just posted the following on PPRuNe.



The new moderator then shut the thread down. Perhaps he is having problems walking in the footsteps of his predecessor.


Dave

Maybe they were tired of seeing your theories repeatedly shot full of holes by Nick Lappos.

 

[Rotor Rooter]

gyromike.

Maybe they were tired of seeing your theories repeatedly shot full of holes by Nick Lappos.

He won a few.

Yes, it was fun having technical arguments with Nick. It looks like that has ended now that he's gone to Bell.

Dave

 

[karlbamforth]

I think that is the whole point.

A theory is put forward for others to comment on. Once all reviews are put forward the theory can be modified or discarded.

We need theories in order to move forward and improve technology.

Thats how it works.

Often on here we hear ppl say "yeah well that been tried many times and everyone failed so you are wasting your time."

Lots of ppl tried to fly and failed before "The Brothers" got it right if they had listened to the Nay sayers where would we be now.

 

[Rotor Rooter]

CrazyEgg's 'Compound helicopter' and karlbamforth's 'discussion of theories'

CrazyEgg's 'Compound helicopter' and karlbamforth's 'discussion of theories'

I believe that the following is an example of a compound helicopter, which has resulted from the critiquing of an initial idea.

The picture at the top of this web page shows a single-rotor concept that was presented at the AHS International 2002 Annual Forum.

The conceptualist was then made aware that it was extremely unlikely that the craft would be able to transition from cruise to slow-speed flight if there was no power. This is because the retreating blades must return from reverse velocity airflow to conventional airflow during the transition.

The picture at the bottom of the page shows the much later addition of compounding wings, which are required to support the retreating side during this transition.


Dave

 

[CrazyEgg]

can someone explain to me about why it is difficult to transition from hover to forward flight in a compound?
will it still be difficult even if you add a set of wings?

 

[brett s]

Don't recall anyone saying it was difficult.

Adding wings brings up another set of compromises - they'll definitely hurt hover performance (not just the added weight, also from rotor downwash on them) & can potentially cause issues in autorotation.

 

[Rotor Rooter]

can someone explain to me about why it is difficult to transition from hover to forward flight in a compound?
will it still be difficult even if you add a set of wings?

The later compounding (addition of wings) on Sikorsky's Reverse Velocity Rotorcraft Proposal is is not the problem. This addition of wings is an attempt at providing a solution.

The problem has to do with the craft's high speed and the reverse direction airflow over the retreating blades during cruise.

• To make the transition from cruise to autorotation may be impossible. The retreating blades must make the transition from 100% reverse velocity to 100% conventional velocity. At some point during the transition, the positive lift on the retreating side will be offset by an equal amount of negative lift on the same side. Since there must be bilateral symmetry of lift, all lift must be removed from the advancing side. During this time, only the front and rear quadrants will be contributing to the lift and to the autorotation of the rotor. In addition, the speed of the rotor must be increased from 50% NR to 100% NR.
• The rotor will probably be unable to support the craft from only two quadrants, while at the same increasing its rotational speed.

Dave