Thrust or lift?
Guest
Posts: n/a
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.
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.
Last edited by puntosaurus; 14th October 2009 at 21:42.
Joined: Aug 2006
Posts: 418
Likes: 0
From: Below Escape Velocity
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.
Joined: Dec 2005
Posts: 1,693
Likes: 15
From: Wellington,NZ
Originally Posted by puntosaurus
Propellers autorotate; ever tried restarting an engine in a twin engined aeroplane ?
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.
Joined: Aug 2006
Posts: 418
Likes: 0
From: Below Escape Velocity
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.
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).
Guest
Posts: n/a
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.
.
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
Likes: 1,814
From: EGDC
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
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
Joined: Aug 2007
Posts: 122
Likes: 0
From: manchester
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?
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?
Joined: Apr 2003
Posts: 1,635
Likes: 1
From: Vancouver, BC, Canada
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
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
Joined: Jul 2003
Posts: 440
Likes: 0
From: Port Townsend,WA. USA
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.
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.
Joined: Jul 2003
Posts: 440
Likes: 0
From: Port Townsend,WA. USA
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?
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?
Joined: Apr 2003
Posts: 1,635
Likes: 1
From: Vancouver, BC, Canada
slowrotor,
Your not alone. This is typical throughout Rotorland.
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
All of my vertical flight ideas have been determined to be impractical. .................. But right now, the hope for vertical takeoff has dimmed.
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?
How about you, any projects?
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
