Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: MK-84 on June 13, 2012, 08:16:00 PM
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What produces more drag?
A single engine prop with the prop windmilling or stopped (not feathered)
and why?
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Windmilling i would guess, as you are making the wind rotate the propeller and essentially power the engine as well, as the spinning prop will set the engine in motion. On the other hand, if the propeller is stopped, it only causes drag based on its surface are, not based on setting a heavy motor in motion. In game this is supported by your plane decelerating faster if you turn the engine off but keep rpms high than if you turn the engine off and lower the rpms.
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I've noticed that some props won't stop windmilling even when you're straight up and your airspeed is 11mph.
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Windmilling produces a significant amount of drag. The reason is that since the blade is turning,the air it is traveling faster over it's surface. And drag is related to the square of the air velocity. Also as the prop speeds up it produces lift, when it is driven by the engine the lift is due to the AOA is pulling the plane along. When the engine is not producing positive torque, the air is now driving the prop from the other side and producing a negative AOA on the prop blades, and hence it is producing lift opposing the direction of travel.
It is easiest just to think of in terms of total energy. It obviously takes energy to turn a prop, that energy comes from the air/momentum of the aircraft.
HiTech
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Windmilling produces a significant amount of drag. The reason is that since the blade is turning,the air it is traveling faster over it's surface. And drag is related to the square of the air velocity. Also as the prop speeds up it produces lift, when it is driven by the engine the lift is due to the AOA is pulling the plane along. When the engine is not producing positive torque, the air is now driving the prop from the other side and producing a negative AOA on the prop blades, and hence it is producing lift opposing the direction of travel.
It is easiest just to think of in terms of total energy. It obviously takes energy to turn a prop, that energy comes from the air/momentum of the aircraft.
HiTech
The lack of misspellings in this post is worrisome. I'm concerned something has happened to HiTech. Tonight I will play AH backwards to see if I can find out.
SOMEONE SAVE THE WALRUS!!!!!!!
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someone needs to check under hitechs bed for a seed pod
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Windmilling produces a significant amount of drag. The reason is that since the blade is turning,the air it is traveling faster over it's surface. And drag is related to the square of the air velocity. Also as the prop speeds up it produces lift, when it is driven by the engine the lift is due to the AOA is pulling the plane along. When the engine is not producing positive torque, the air is now driving the prop from the other side and producing a negative AOA on the prop blades, and hence it is producing lift opposing the direction of travel.
It is easiest just to think of in terms of total energy. It obviously takes energy to turn a prop, that energy comes from the air/momentum of the aircraft.
HiTech
If the engine has seized with the prop unfeathered wouldn't the prop just try to turn the whole plane and expend just as much energy generating torque?
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If the engine has seized with the prop unfeathered wouldn't the prop just try to turn the whole plane and expend just as much energy generating torque?
:headscratch: :rofl
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If the engine has seized with the prop unfeathered wouldn't the prop just try to turn the whole plane and expend just as much energy generating torque?
Actually it does. Of course with absolutely no success (you'll never see the plane rotate, too much lateral stability to overcome for such a small force). It ends up expending energy as drag.
After an engine seizure, with prop unfeathered though, you are pretty much out of options and are just going to have to live with the added drag (which will be significant). In the event of a oil/radiator hit, monitor affected parameter closely and feather then shutdown the engine before it seizes.
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A frozen prop. won't try to roll the plane because it is stalled.
It would probably impart more roll when fully feathered than at fine pitch.
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Do the props on the multiengines in game feather? Wait, what is the damage that lets your prop windmill other than running out of gas?
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A frozen prop. won't try to roll the plane because it is stalled.
It would probably impart more roll when fully feathered than at fine pitch.
Makes sense. Thanks :)
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A frozen prop(unfeathgered) does not create as much drag as a spinning one.
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A frozen prop(unfeathgered) does not create as much drag as a spinning one.
True, I was just saying that a frozen unfeathered prop will create more drag than a frozen feathered one.
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A frozen prop(unfeathgered) does not create as much drag as a spinning one.
I think prop drag depends largely on the AOA (angle of attack) of the prop. I really don't think the drag or torque would be significanltly different for a spinning vs. frozen prop. Whether or not the prop is spinning torque and drag will still exist (unless the prop is disengaged from the engine). If the prop is spinning all that means is some energy is being converted to heat inside the engine block (from piston rings rubbing against the engine block). If the prop is not spinning then ur basically converting energy into heat at the prop (and not in the engine). One can think of friction as converting some type of energy into heat, in this case that would be the forward momentum of an airplane.
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I think prop drag depends largely on the AOA (angle of attack) of the prop. I really don't think the drag or torque would be significanltly different for a spinning vs. frozen prop. Whether or not the prop is spinning torque and drag will still exist (unless the prop is disengaged from the engine). If the prop is spinning all that means is some energy is being converted to heat inside the engine block (from piston rings rubbing against the engine block). If the prop is not spinning then ur basically converting energy into heat at the prop (and not in the engine). One can think of friction as converting some type of energy into heat, in this case that would be the forward momentum of an airplane.
Don't forget about the compression of the engine.
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In either case, the area of the props represent pretty close to flat plate drag from stagnation pressure on the blades themselves. That is why multi engine SOP was to feather the prop immediately.
For a single engine a/c (like a Mustang) the flat plate drag of that big Hamilton Standard prop is purty near as much as the Total Drag on the airframe.
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smoe, you are missing the increased air flow over the prop do to it's rotation. This is causing most of the drag on the prop as it spins, not the engine.
HiTech
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And that drag is caused by aoa of the blades. Faster spining prop has more of the blade area presented to the wind than feathered. But if pitch is the same for both stationary and stopped, the stopped prop would have more drag because the blades would be stalled.
You dont get something for nothing. The only thing driving that prop is airflow.
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A frozen prop(unfeathgered) does not create as much drag as a spinning one.
:airplane: You sir, are correct! A wind milling prop presents a drag coefienct equal to the diameter of the prop. A prop which is not wind milling only presents the phyiscal width and length of the blade for drag. Guess there is not much use in trying to explain "beta" range in turbo-prop driven aircraft, who have to make a emergency decent. (like the Beech Kingair).
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And that drag is caused by aoa of the blades. Faster spining prop has more of the blade area presented to the wind than feathered. But if pitch is the same for both stationary and stopped, the stopped prop would have more drag because the blades would be stalled.
You dont get something for nothing. The only thing driving that prop is airflow.
This is NOT correct Zeagle.
HiTech
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Yeah i think you are correct ht. ... The lift from the moving blades makes the difference.
I stand corrected :salute
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When the engine quits I just set RPMS down to 0.
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Try gliding the typhoon with a windmilling prop. and with it stopped.
That said, it's pretty hard to get some props stopped in game with some windmilling down to 30mph.
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I have fond in the P-51D by hitting the minus key 3 times once you are at about 400+ mph in a dive that the pony picks up speed and stays fast for a long way. Even if you are being chased by another 51 with wep on you will still out pace it and have all your wep if you need it later. Does that count as feathering the prop ?
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I have fond in the P-51D by hitting the minus key 3 times once you are at about 400+ mph in a dive that the pony picks up speed and stays fast for a long way. Even if you are being chased by another 51 with wep on you will still out pace it and have all your wep if you need it later. Does that count as feathering the prop ?
No that counts as making no logical sense. And engine running at less than full power is not going to to provide as great an acceleration as one that is.
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Makes total sense.
The prop speed and angle are not condusive to propelling the plane over a speed of 500mph but a feathered prop. will allow a plane to exceed that speed in a dive.
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Wow what a cool post. My brain hurts though a bit.
Just to clarify for my small brain, is this true or false: Leaving engines on and at idle produces more drag than an idle prop so the plane will slow down faster than having the engine off.
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Makes total sense.
The prop speed and angle are not condusive to propelling the plane over a speed of 500mph but a feathered prop. will allow a plane to exceed that speed in a dive.
You'll need power to reach 500 mph even in a dive so feathering the prop would slow you down -- real world.
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(http://i1211.photobucket.com/albums/cc426/Coogan11/4565686470_acb9e58ee71.jpg)
Ever see one of these fall out of a tree?
If it doesn't spin, it falls fast. (no drag) When it spins if falls slowly. (drag)
Coogan
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Ever see one of these fall out of a tree?
If it doesn't spin, it falls fast. (no drag) When it spins if falls slowly. (drag)
Coogan
There is drag in either case. When it spins it creates lift.
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I think a real life P51 will dive faster at 30,000 feet with the prop. feathered than under power but the reverse is true at lower altitudes.
It would have to fully feather.
The reno guys run as coase a pitch as you can run and the props are good to only a few mph over 500 with 4000hp.
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Ever see one of these fall out of a tree?
Thanks for explaining it in a way that the flight math aerodynamics inhibited like me can understand. :salute