Compound Helicopter

CrazyEgg

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I was on break at work eating a sandwich when suddenly an idea struck me it was this:
why can't you have a helicopter with a propellor for forward thrust instead of using the main rotor

i wrote some ideas down, came home and did some research and found out they actually exist and are called compound helicopters
i also did some initial drawings when i was on my break, but after doing research i found something which looked exactly like what i had drawn
http://en.wikipedia.org/wiki/Piasecki_X-49

so i just have a couple questions:
1. why dont more if not most helicopters use this technology?
2. can an alternative be found to power the main rotor instead of an engine?
3. can current helicopters be simply modified to have a propellor on the back?

well im not an engineer so i cant answer the first and third question (i hope some of you can though)

but i have an idea for the the second question:
you could use tips jets - compressed air from a compressor / small jet producing thrust bled through to the end of the rotors

i say this because then hopefully the torque which the tail rotor compensates for is not there, and it could be lighter without all the 'technical stuff' going from engine to rotor(wouldnt it?)

i thought an autogiro would make a good base if the compound helicopter was being powered by tip jets, or a small helicopter like a mosquito xe could be used and the tail rotor would be taken away and a prop will be added.
Both aircraft will need a set of wings

advice will be very much appreciated

thank-you
 
Simple economics are why you don't see them everywhere - adding any sort of auxiliary propulsion also adds weight & cost. More weight = less payload capacity...

Bottom line, in the commercial market going a little faster isn't worth the loss in payload or extra expense to the vast majority of paying customers. There might be a niche market for such a thing, Sikorsky is testing the waters again with their X2 concept - but it'll never replace a conventional design for 99% of operators.

Tip jet powered rotors aren't a new idea either, they've come & gone for the exact same reasons. Less efficient, and also noisy to boot!
 
Hello Emmanuel

There are a few heli manufacturers even kit heli companies which are experimenting
with this concept of compound Heli's.

Even the heli cycle was tested by its creator in compound form and the top speed did
increase. But this was the same heli in which its creator crashed and died. Nothing to do with the compound thing.

Do some more brain storming, might come up with some better and new idea.

Best Regards.
 
i understand that adding extra weight reduces payload, but all you need to do is replace the tail rotor and just install a propellor on the same shaft that the tail rotor was driven from, unless im mistaken.
it should weigh less than 100kg wouldnt it and depending on the helicopter it could even weigh less

rehan the heli cycle's top speed increased by around 20mph didnt it?
what kit manufacturers are experimentung with compund helicopters (can see to find too much info about compounds on the net)

one idea i really like is to use a smaller scale version of the f35 engine for vtol
http://upload.wikimedia.org/wikipedia/commons/0/0e/Engine_of_F-35.jpg

smaller versions of that setup could be very useful couldnt it?
also using that setup means you have no rotors, so could travel at much higher speeds
 
You're not just replacing the tail rotor - you still need anti-torque control, you're adding an additional source of fwd thrust.

Adding any weight at all means the payload goes down by that amount. So you're either reducing the range or leaving passengers behind.

Remember that everything is a tradeoff, and for most operators this one isn't worth it. As you discovered these aren't new ideas, they were tested & rejected.

Btw, a VTOL jet is the most inefficient method of vertical lift ever invented - taking an insane amount of power & fuel burn compared to anything else. Once again, there's a niche mission for a very specialized aircraft of this type - in this case military only, because it'll never be worth it to a civilian operator.
 
but if you take the rotor offline you wouldnt have the torque would you?
like say you use the rotor only to take off and land and during transitions (where a rudder could be used to deflect air in the direction which will compensate for the torque)
so during normal flight only the prop will be powered (so the heli will need some wings)

i do get what you are saying though about having tradeoffs especially in this case where you will have to add a prop a rudder mechanism and wings

if a vtol jet is the most inefficient way, what would you say is the most efficient way of ahieving vtol (if there are any)
 
but if you take the rotor offline you wouldnt have the torque would you?
like say you use the rotor only to take off and land and during transitions (where a rudder could be used to deflect air in the direction which will compensate for the torque)
so during normal flight only the prop will be powered (so the heli will need some wings)

So then the pusher prop that's blowing air over the rudder in a hover needs to be even larger & uses more power than a tail rotor would require, since that's less efficient at countering the torque - and it's heavier too.

TNSTAAFL...

There's some video on YouTube of a UH-60 that Piasecki's testing using that basic setup - watch it & note that it's barely got enough yaw control margin to hover (look at the rudder deflection). In a slight dive it hit 177 kts, which a regular UH-60 will also do - sure, they'll eventually get this one up a bit faster, but again at a huge weight penalty. Giving up a significant fraction of your payload just doesn't work most of the time.
 
Compound helicopter or advanced gyrocopter?

Compound helicopter or advanced gyrocopter?

Here is and old concept by Anton Flettner that two of us are playing with.


1509-C.gif


It is an intermeshing helicopter that only requires three gears.

A quad worm will result in an efficiency of greater than 89%. In addition new materials and lubricants may improve this efficiency. The possibility of a ball worm & gear would be even more efficient.

The fan in the picture would be replaced with a straight through propeller from the worm, for use during forward flight. This will basically result in no friction to the propeller and a halving of the the power (and friction) to the two rotors.


More stuff for the interested;
http://www.unicopter.com/1645.html
http://www.unicopter.com/1514.html
http://www.unicopter.com/1509.html

Dave
 
I would hope it's much better than 89% - a CH-47D only loses approximately 4% total, including losses from hydraulics, generators, and drivetrain friction.

Most of the standard engineering texts I've seen list a single gear mesh at around 99% efficiency - the exception I've seen is worm gears which can vary a lot.
 
another option

another option

but if you take the rotor offline you wouldnt have the torque would you?
like say you use the rotor only to take off and land and during transitions (where a rudder could be used to deflect air in the direction which will compensate for the torque)
so during normal flight only the prop will be powered (so the heli will need some wings)

If you're curious about prior work on related ideas, take a peek at this thing:

http://en.wikipedia.org/wiki/Fairey_FB-1_Gyrodyne

The anti-torque rotor was brought 'round 90 degrees to the right side of the cabin so that it provided thrust as well, looking a bit like one of the propellers on a twin engine airplane. I've seen some nice film of this thing flying and it looked terrific.
The follow-on "jet gyrodyne" used compressor driven tip-jets for the main rotor. Eventually they built the Rotodyne with twin turboprops.
 

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Brett,

You are correct in that 89% efficiency is poor. Our belief is that this high power loss will be offset by, no tail-rotor power loss and a lighter gearbox; plus the advantage of having a simpler drive-train.


The future might offer additional advantages such as buckyballs as a lubricant,

or ball tracks.
1509-A.gif




Dave
 
Today MV 22 Osprey tilt rotor tookoff for its first US marine mission from Al Asad Base. Iraq after a month long trails in desert.

MV 22 is the military version of the V 22 or the CV 22.
Gunship versions are also in action.

The British Navy is also goin thru trails of a V22 version for aircraft carrier.

Check out Fox news. VOA or You tube

Bet USMC are havin fun with it. Looks stable and its rock solid performance.
The only draw back is that it cannot make an emergency auto landing.
 
Looked at that and thought Wow, somebody was thinking about that concept way back in the 50's. Then suddenly remembered who began putting ideas to paper about vertical flight... De Vinci!

Widely considered to be one of the greatest painters of all time and perhaps the most diversely talented person ever to have lived. As an engineer, he conceived ideas vastly ahead of his own time, conceptualising a helicopter, a tank, concentrated solar power, a calculator, the double hull, and outlining a rudimentary theory of plate tectonics. Few of his designs were constructed or even feasible during his lifetime, but some of his smaller inventions, such as an automated bobbin winder and a machine for testing the tensile strength of wire, entered the world of manufacturing unheralded. As a scientist, he greatly advanced the state of knowledge in the fields of anatomy, civil engineering, optics, and hydrodynamics.

Pity he's not around to give us some pointers on Gyros.
 
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The idea of compound helicopters is to have a very fast helicopter. To do it they use fixed wings in order to relieve the rotor in fast forward flight. The rotors, especially the powered rotors, have a big limitation in lifting the helicopter at high speeds.

The rotor is needed for take off, but is not useful in forward fast flight. Of course, the efficiency of this kind of helicopters in the hover is bad (because the fixed wings drag).

Ferran
 
Here is and old concept by Anton Flettner that two of us are playing with.
It is an intermeshing helicopter that only requires three gears.

A quad worm will result in an efficiency of greater than 89%. In addition new materials and lubricants may improve this efficiency. The possibility of a ball worm & gear would be even more efficient.

The fan in the picture would be replaced with a straight through propeller from the worm, for use during forward flight. This will basically result in no friction to the propeller and a halving of the the power (and friction) to the two rotors.


More stuff for the interested;
http://www.unicopter.com/1645.html
http://www.unicopter.com/1514.html
http://www.unicopter.com/1509.html

Dave

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 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. On a standard bevel gear the metal touches and creates heat, but will not instantly fail .

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.
 
Devil.gif
Due to a strong bias against the tail-rotor
Devil.gif


Resesi, Your comment about Leonardo da Vinci ~ the engineer;

"........ perhaps the most diversely talented person ever to have lived. As an engineer, he conceived ideas vastly ahead of his own time, conceptualising a helicopter ......"


Comments about Igor Sikorsky ~ the promoter;

"Sikorsky studied at the Russian Naval War College in St. Petersburg from 1903 through 1909, but did not finish formal studies. For a short time, during late 1906 and early 1907, he studied engineering in Paris. In 1914, Saint Petersburg Polytechnic Institute awarded him an honorary degree in engineering."


I wonder where rotorcraft would be today if Igor had stayed with his airplanes and let others develop the rotorcraft.


Dave
 
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