Thrust or lift?

[puntosaurus]

Rotor blades are twisted, and for the same reason as propellers.

Propellers autorotate; ever tried restarting an engine in a twin engined aeroplane ?

The differences between propellers and rotors exist because they are optimised for different purposes, but their modus operandi and basic function are the same, ie chucking air from above the blade to below.

[Um... lifting...]

I was going to agree with puntosaurus... rotor blades are indeed twisted, aerodynamically as well as geometrically. One aspect of rotor blades that is a bit interesting is that the centripetal acceleration acting upon the mass of the blade provides tension along the blade axis... and stiffness. A blade rotating is much stiffer than one at rest.

[Tarq57]

Originally Posted by puntosaurus

Propellers autorotate; ever tried restarting an engine in a twin engined aeroplane ?

Of course they do. (No, I haven't. Only windmilled/zero-thrusted/feathered.)

But whether they'd store enough energy while autorotating to allow the helicopter fitted with such a lift source to successfully flare and land at a reasonably survivable speed might be another story.

[Um... lifting...]

But whether they'd store enough energy while autorotating to allow the helicopter fitted with such a lift source to successfully flare and land at a reasonably survivable speed might be another story.

And there again, you touch upon an issue in the V-22... though it does have wings. There are numerous hotheads over on the V-22 thread discussing this and other issues.
You can hover an airplane with enough power (Sean Tucker and other aerobatic pilots prove it often enough).
You can even hover a Harrier (though not for very long... you can see the fuel gauges moving).

[puntosaurus]

But whether they'd store enough energy while autorotating to allow the helicopter fitted with such a lift source to successfully flare and land at a reasonably survivable speed might be another story.

AhHa. Well I think that would be down to the certification authorities .

[[email protected]]

So Sainstman, you want to put a propeller on top of a helicopter - you will have to make it big enough to produce enough lift/thrust within the constraints of the engine power and then find a way of controlling the direction of that thrust.

Now you could either tilt the whole propeller/engine/gearbox combination (V22) or use a cunning method of adusting the pitch on each blade individually and hinging the blades so they can move - thus giving a means of tilting the thrust vector without moving the shaft/gearbox/engine.

If you get yourself a good book on helicopters (Shawn Coyle's for example) you will discover how a helicopter works - read it before posting here again pleas

[Davey Emcee]

Leave him alone, there's nothing on the telly.

[feathering tickles]

Seems to me that Saints' original post might not be suggesting any particular fundamental change to a "normal" helicopter layout. (please correct me if I'm wrong Saints').

Rather he might be grappling with the oft misused/misunderstood words LIFT and THRUST and what they actually mean within the context of a "rotating air movement propulsion system" (of whatever name it's given).

In essence does it "suck", "blow", both or neither? And whichever you decide it does, what do you want to call it?

[Dave_Jackson]

Saintsman,

I think that the words 'push' and 'pull' relate to the location of the thrust in respect to the object to which this thrust is being applied.

In this context these two rotorcraft would be construed as having push.
Hiller Flying Platform
de Lackner HZ-1 Aerocycle

__________________________

If you are talking about using propellers as an alternative to rotors, you may find this page of interest.


Dave

[slowrotor]

Saintsman,

A propeller is device that produces thrust to propel an aircraft forward and is designed for a particular forward speed.

A rotor is a propeller optimized to produce static thrust.
Other than that, the two are very similar.
Any propeller can be used to produce static thrust, but the larger rotor is more efficient for static thrust or lift (thrust is the same as lift, we often use either word when talking about rotors).

The early helicopters had large rotors and heavy engines. As engines get lighter, rotors get smaller. Eventually rotors will look like propellers.

[Dave_Jackson]

Hi slowrotor, Have you started any project?

[slowrotor]

Hello Dave,

All of my vertical flight ideas have been determined to be impractical.
Instead I am building an ultralight airplane. This aircraft might be used in the future as a testbed for some ideas. But right now, the hope for vertical takeoff has dimmed.

I check here once in a while, not much design stuff anymore.
How about you, any projects?

[Dave_Jackson]

slowrotor,

All of my vertical flight ideas have been determined to be impractical. .................. But right now, the hope for vertical takeoff has dimmed.

Your not alone. This is typical throughout Rotorland.

I check here once in a while, not much design stuff anymore.

Instead I am building an ultralight airplane. This aircraft might be used in the future as a testbed for some ideas.
How about you, any projects?

Yup. Two of us got tired of theorizing about concepts that also have limitations. One limitation being the lack of a few billion dollars.

We have started at the bottom and are building an extremely light electric rotorcraft. It is also intended to be the testbed for developing advances in electric VTOL propulsion.


Dave