A dumb idea

[lucien]

I was thinking, since a helicopter's spinning rotors have the drag coefficient of a parachute, could you funnel the heat produced by the engine upward onto the bottom of the rotors to create an effect similar to hot air balloons, or would the rotor wash make this completely impossible in the first place

[sobek]

No that would not work.

[VAOZoky]

[PeterP]

Is it really such a dump idea?!.... I don't want to judge about it ....

:P

 

But to use this effect that you describe most effectively it would be sure wiser to remove the rotors completely and install a Balloon hull that is able to lift the remaining parts and also install tubes that lead the hot gas directly into the Ballon.

 

BTW: Thanks for making me laugh by questioning things like this!

+1!:smilewink:

[Weta43]

If you just turned the raw exhaust gasses upwards, the downward thrust from the upwards directed gasses would outweigh any lift you got from the hot air flowing over the rotors - unless you mounted a device to remove all the kinetic energy from the gas before it left the system.

 

As PeterP said, removing the rotors and directing all the hot gas into a large ballon would do it :-)

[PeterP]

*Sorry*

Remember:

There aren't any dump questions - there are only dump answers that let the question look dump...

... and here comes a very dump answer: ;)

 

 

Don't remove the rotors!

 

Install a balloon that collects the kinetic energy that is provided by the turbines and lead the surpluses of this hot air (that is also providing extra lift) back again to the tip of the rotors - so it is used for disburden the engines.

 

A picture comes to my mind:

 

 

The outcome would be a Green-ECO-Hybrid-Rotorkraft that is using the normally unused exhaust for extra lift and rotor momentum that leads much less fuel consumption.

 

 

So : we only need a system that is able to funnel the exhaust of the engines back through the spinning rotor-mast into the hot-air-balloon and also to the tips of the rotor-blades.

Edited November 29, 2012 by PeterP

[Meatwod]

Guys, Rotors don't push against the air. Forcing air up through the rotors does nothing for lift. Lift is generated by air flowing at a faster speed underneath each rotor blade.

 

The volume of air needed to generate thrust (not lift) is massive. The lift fan on the F-35 is an example of the amonut of mass flow need to generate thrust (it should be called and thrust fan!). Having a vectored exhaust would be ideal since the exaust gas could be pointed opposite of the desired direction of travel. However, a helo engine can't produce enough thrust justify enormous expensive of a veectored thrust system.

[Weta43]

You could run a second turbine (providing even more hot air !) to run a cooling system to chill the skin of the balloon to remove the heat signature from the hot air, and make the balloon faceted, RAM coated, and encompasing the whole helicopter (I still say skip the rotors :-) ...

Stealthy and efficient !!! :)

That balloon might make deck landings in a stiff wind interesting :/

 

Forcing air up through the rotors does nothing for lift.

 

Remembering that there's no such thing as a priviliged reference frame, please use that statement to explain vortex ring state.

Edited November 29, 2012 by Weta43

[PeterP]

Meatwod - please don't be such a grinch, don't you realise that we have a promising concept here?!

 

...and I bet if others provide some more input like Weta43 , we will end up with a machine that not only can fly - ... it will sure produce more energy as we have put in it at the beginning.

 

:) and all energy and transport problems of the humankind are solved at once !

 

...I'm in the tower at my drawing board. ... doing some conceptual blue-prints.

 

...would be nice if someone can give me meantime a hint how I establish the Bose-Einstein superfluid around the balloon.

Edited November 29, 2012 by PeterP

[pbishop]

I was thinking, since a helicopter's spinning rotors have the drag coefficient of a parachute

 

Where is this comming from? Why did you post something you have no idea about? Cd values for rotor blades are lower than some airfoils for airplanes. Why, just why?

[Weta43]

Where is this comming from? Why did you post something you have no idea about? Cd values for rotor blades are lower than some airfoils for airplanes. Why, just why?

 

You missed the thrust (!) of his post because of the way he phrased it.

 

Think rotor in autorotation = parachute in free fall.

 

(no offence meant Lucien - & if you have a question you ask it :) )

[VincentLaw]

Guys, Rotors don't push against the air. Forcing air up through the rotors does nothing for lift. Lift is generated by air flowing at a faster speed underneath each rotor blade.

 

Air actually has a higher speed over the top of an airfoil, not underneath. You are right though, directing air upwards would create negative lift and increase drag on the rotors.

 

@OP Transferring thermal energy from the lower surfaces of the blades to cooler air would technically generate thrust, but it would be balanced out by absorbing the energy from the exhaust flow in the first place.

Edited November 29, 2012 by VincentLaw

[pbishop]

I meant no offense either, but it is important that people reading this know that the drag coefficient is not related to thrust but rather the speed of the blades.

 

Now if I understand the question properly, the best way to explain it would be to imagine the rotors as wings spining from some fixed point. Any changes you make to a wing should in theory have the same effect on the rotor blade (in simplistic scenario) or vs versa. So therefore, adding heat under a wing does not have any effect nor would it affect a rotor blade. The only thing pointing the exhaust at rotor blades does is reduce the aircrafts heat signature.

 

When we fly gliders, and sometimes planes, thermals are a good way to increase altitude. The difference between thermals and the exhaust are many. But the main one that we need for this example is mass air flow. When thermals occur, they create an upward airflow effectively changing the buoyancy of the aircraft (based on bernoulli) if the amount of air pushing upwards is great enough to have an effect. Now if we apply this to helicopters, the air the rotors would need to produce the same effect would have to cover the entire area the rotors travel in. They would also require that enough air be able to pass through the path of the rotor downwash undisturbed to have any effect (which is not exactly accurate, but it serves the purpose here). Because of the small area of the exhaust, it would only change one small area of the blades and not the entire path of the blades, which in comparison is negligeable. It would be like putting a puddle under a boat expecting it to float. But thats not all, because the airflow from the downwash created by the rotors is much greater than the exhaust, it effectively destroys it before it reaches the rotors. It therefore has no notable effect on lift or drag created by the rotors themselves, only the airflow around the helicopter, which is also negligeable (in terms of lift and drag of the rotors). There simply is not enough mass airflow from the exhaust to have any effect on the rotors.

 

Now all this wasnt very scientific (and some parts were even simplified to server the purposes here), but it should give a general idea. There are so many things that effect helicopter flight that it is almost impossible to explain every little detail.

 

As far as creating thrust, thermal differences like balloons change buoyancy and do not create thrust. Therefore, the idea that pointing hot air up like a balloon would only work if my (very general) explination for thermals above is satisfied. Thermal differences in the surroundings of an aircraft do not create, nor are they ever defined as thrust.

 

On a side note, it is important to note that drag and lift are not the same as drag and lift coefficients, even if they are related. In the case of a helicopter falling like a parachute, it is not the drag, but the lift that allows it to stay afloat.

 

I hope this explains something.

Edited November 29, 2012 by pbishop