- #36
OCR
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A picture of a turboshaft engine... notice the "free power turbine".
A picture of a turboprop engine... no "free power turbine".
A picture of a turboprop engine... no "free power turbine".
OCR said:A picture of a turboshaft engine... notice the "free power turbine".
A picture of a turboprop engine... no "free power turbine".
Yeah, you're right...cjl said:Those are hardly technical drawings.
cjl said:What, exactly, is the difference between "proprotors" and "very large variable pitch propellers"?
E'lir Kramer said:Apparently my idea actually works in theory.
Carno Raar said:What is the actual difference between turboprop and turboshaft?
It's because a plane that is optimized for VTOL is not well optimized for speed or other performance.sophiecentaur said:Why do we not use VTOL these days? Harriers are being scrapped, as I understand.
Could it be because modern missiles can more easily deal with them?
I know nothing about this but it is an interesting topic.
sophiecentaur said:Harriers are being scrapped, as I understand.
Of course. But what is different now, from the situation when they were developed and used widely? I remember that, way back in the Falklands war, the Harriers could outmanoeuvre the Argentinian fighters by stopping dead in the sky and then the chase aircraft would have to fly past and become a target.russ_watters said:It's because a plane that is optimized for VTOL is not well optimized for speed or other performance.
OK. That answers the question. ThanksVanadium 50 said:Harriers are being replaced by the F-35B (at least for the USMC). One V/STOL airframe is being replaced by another.
Yup, lucky we aren't at war...Yetsophiecentaur said:Those danged politicians again.
Conservation of momentum tells us that what happens on board, stays on board. If the result of the internal 'wind tunnel' is not a net injection of downward momentum to some air then the lift can't be improved. We discussed the Bernoulli vs Newton III many times (I thought we had general agreement in the end) and, whatever the (important and highly relevant) local pressure situation happens to be, if there's no net down draught then there's no lift.E'lir Kramer said:Could an aircraft achieve lift by blowing a fast stream of air over an internal fixed wing? I.e., by having an onboard wind tunnel with a wing suspended inside?
Vanadium 50 said:A plane goes up when the sum of upward forces exceeds the sum of the downward forces.
To start climbing it must accelerate upwards.David Lewis said:This would violate Newton's First Law. When an airplane is climbing, the sum of upward forces is equal and opposite to the sum of downward forces. The net force on a free-body is zero unless it's accelerating.
Only the vertical component of acceleration is relevant to climbing. How long the acceleration period lasts depends entirely on the situation.David Lewis said:You are 100% correct that the aiplane will speed up, but this acceleration will be brief and transient, and mostly horizontal.
David Lewis said:When an airplane is in an ongoing climb, however, the sum of upward forces can be equal and opposite to the sum of downward forces.
You're right. Only the vertical component of acceleration is relevant when the plane initially begins to climb. However, the airplane can continue to go up when sum of all forces is zero.
davenn said:then it will hover, it won't climb
cjl said:No - when the airplane is climbing, steady state, it is not undergoing any acceleration, so the forces can indeed sum to zero. To initiate the climb, the vertical net force must exceed zero temporarily, but this is just a transient state.
cjl said:It's simple physics. F = ma. In a steady climb, acceleration = 0 so F_net = 0.
No, gravity is part of the F in F=ma.davenn said:if you were climbing in zero gravity ?
How about you explain what is wrong about it?davenn said:you are going to have to do a better job of explaining