Feathered vs Windmilling Prop

[Crism]

I put together an animated power point that makes visualizing the whole aerodynamic process a lot easier. If you do download it make sure you actually view the slide show and not just look at the slides individually in the editing mode, as they won't make any sense.

http://www.mediafire.com/?ndmdmrgjmzq

Ok guys lets quit the complaining....back to the regular topic.

NICE job on this from what I can see. Is the pitch of the blades changing at all from regular flying to a windmilling prop though? I've got a Seminole as a mental image here. Also, you might want to add-in the negative AOA angle in there when you show that as you did with the positive.

Pictures make sense now. I had to dig back to basic aero and angles and math because I continuously forgot about the 2 relative winds averaging out.

I also remember back to working on CFI when my friend and I were trying to figure out why you need left rudder in a nose-down descent in a fixed-pitch single-engine prop. It was due to p-factor reversing depending on the AOA created as the airplane was pitched down with the relative forward velocity and prop RPM. Some relatively deep and interesting stuff.

 

[tgrayson]

It was due to p-factor reversing depending on the AOA created as the airplane was pitched down with the relative forward velocity and prop RPM.

Actually, the vector diagrams don't support this. When generating the negative AoA, the descending blade will be less negative and the ascending blade will be more negative. This still creates a left yawing tendency.

 

[tgrayson]

potential is indeed changed to kinetic and back, and the managing the driving region of the rotor system is key to an auto.

You're not reading what he wrote:

ENERGY is being produced also...unlike a windmilling prop on an airplane.

This is a false statement, or rather, two false statements.

 

[shdw]

BTW...nice website...did you borrow any of that information from the FARs without saying so????????

To be honest, I don't even know. I don't think so, but it is 200 pages of info so I am sure I missed something. I can tell you that when I do locate anything I need to give credit to I can assure you it will be done.

Nowhere in my post did I take credit for that

No, credit was implied by the method of the post. Here is what you did: "You are correct except that drag..." Then went on to copy/paste. The method readily used here would have been to say that first two sentances as you had, then go on to say something like, "From the <source> it says..."

HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA.....you are WHACKED!!!!!

Calm down, I was only telling you why it received that remark. No need to get all bent out of shape over it.

 

[MikeD]

You're not reading what he wrote:

This is a false statement, or rather, two false statements.

Ah yes. I glossed over that one that he wrote there.......was probably auto-filtered by me for accuracy.

Agree. Not being produced, but rather, its being changed in form/type.

 

[shdw]

Pictures make sense now. I had to dig back to basic aero and angles and math because I continuously forgot about the 2 relative winds averaging out.

That is what I was attempting to convey with my downdraft scenario. I guess it wasn't as clear cut as I had hoped. These were the words I was looking for, "two forces (relative winds) have a percentage effect on the actual RW experienced by the wing." Then explaining a known experience of a downdraft reducing AOA...

 

[Mike H]

Windmilling props generate reverse thrust. The faster they windmill, the greater the reverse thrust.

So on turboprops with a beta setting on the prop control, the prop is really just windmilling? :hugerolleyes:

and drag is really just reverse thrust? :evenbigger rolleyes:

You're trolling, aren't you?

 

[tgrayson]

So on turboprops with a beta setting on the prop control, the prop is really just windmilling? :hugerolleyes:
and drag is really just reverse thrust? :evenbigger rolleyes:
You're trolling, aren't you?

I hope you're joking; I'd hate to think that any pilot (or any human being) is so dismissive of new knowledge.

 

[Matt13C]

I am not an ME pilot just yet, so please forgive me if what I say is incorrect, I am just trying to better understand the topic.

In feathered position, the prop is set perpendicular to the relative wind and locked.

If the prop is windmilling it will cause more drag not just because there is more surface area, due to it not being feathered perpendicular, but also because the prop will develop lift/thrust counter to the direction of flight, negative thrust due to the shift in relative wind the prop is experiencing with no engine driving it.

So, what about a feathered, unlocked prop, if it is even possible to feather but not lock. Will that create more or equal drag as a locked feathered prop? Once it starts moving the relative wind would shift slightly towards the direction of rotation, but in the feathered position it would then create lift perpendicular to the direction of travel correct?

 

[Mike H]

I hope you're joking; I'd hate to think that any pilot (or any human being) is so dismissive of new knowledge.

Not dismissive of new knowledge, but that pegged the needle on my BS meter

 

[Matt13C]

I found this explanation and accompanying graphics/animations to explain it. Still curious about the unlocked feathered prop though.

http://home.scarlet.be/comicstrip/Drag prop/Drag From Prop.htm

 

[PFGiardino]

So on turboprops with a beta setting on the prop control, the prop is really just windmilling?

The beta setting changes the angle of attack by changing blade angle.
Windmilling changes the angle of attack by changing the relative wind.
Doesn't seem like BS.

Same result, different means. Beta, I'm assuming, would create a more efficient reverse.

-The guy who was wrong on page one.

 

[matman]

The beta setting changes the angle of attack by changing blade angle.
Windmilling changes the angle of attack by changing the relative wind.
Doesn't seem like BS.

Same result, different means. Beta, I'm assuming, would create a more efficient reverse.

-The guy who was wrong on page one.

wow, where did you go to flight school?

 

[Mike H]

The argument that drag is reverse thrust means that the C-172 you fly has thrust reversers. Clearly that's not the case, now, is it?

 

[SteveC]

Not dismissive of new knowledge, but that pegged the needle on my BS meter

I have never seen tgrayson post BS.

It might be worth your time and effort to go back through the thread and review what he is saying. This: "The argument that drag is reverse thrust means that the C-172 you fly has thrust reversers." ...tells me that you're not really tuned in to what he's getting at.

Just a friendly suggestion.

 

[chuckles1225]

In feathered position, the prop is set perpendicular to the relative wind and locked.

If the prop is windmilling it will cause more drag not just because there is more surface area, due to it not being feathered perpendicular, but also because the prop will develop lift/thrust counter to the direction of flight, negative thrust due to the shift in relative wind the prop is experiencing with no engine driving it.

So, what about a feathered, unlocked prop, if it is even possible to feather but not lock. Will that create more or equal drag as a locked feathered prop? Once it starts moving the relative wind would shift slightly towards the direction of rotation, but in the feathered position it would then create lift perpendicular to the direction of travel correct?

Matt, there is nothing that physically locks a feathered prop to prevent it from rotating...the fact that it is aligned with the oncoming air means that the blades will remain stationary. In order to get the prop spinning again all you need to do is twist the blades slightly so they start windmilling. This process can also be explained using tgrayson's theory.

 

[chuckles1225]

The beta setting changes the angle of attack by changing blade angle.
Windmilling changes the angle of attack by changing the relative wind.
Doesn't seem like BS.

Same result, different means. Beta, I'm assuming, would create a more efficient reverse.

Seems logical to me

 

[matman]

Matt, there is nothing that physically locks a feathered prop to prevent it from rotating...the fact that it is aligned with the oncoming air means that the blades will remain stationary. In order to get the prop spinning again all you need to do is twist the blades slightly so they start windmilling. This process can also be explained using tgrayson's theory.

But there are centrifugal stop pins that prevent it from feathering below a certain RPM.

 

[tgrayson]

"The argument that drag is reverse thrust means that the C-172 you fly has thrust reversers." ...tells me that you're not really tuned in to what he's getting at.

Yes, thank you.

Drag isn't reverse thrust, reverse thrust is drag. By definition. Any force that acts parallel and opposite the flight path is drag.

 

[tgrayson]

Matt, there is nothing that physically locks a feathered prop to prevent it from rotating...the fact that it is aligned with the oncoming air means that the blades will remain stationary.

Agreed...once the blades stop generating aerodynamic force, the resistance of the engine will bring it to a halt.