Prop Length VS Cowl/Fuse Width  
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All Forums >> RC Airplanes >> Questions and Answers >> Prop Length VS Cowl/Fuse Width
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Prop Length VS Cowl/Fuse Width - 5/13/2003 8:01:11 AM   
Spaceclam



Posts: 4640
Joined: 4/13/2003
From: chatsworth, CA, USA
Status: offline 		i don't think i used the word mount, if i did please excuse me. yes, i am farmilliar with angle of attack, and even if o weren't, the word is kinda self-explanatory. for some reason, my post was appearing and dissappearing, so i ended up puting on a douplicate. please ignore it, and his "whachamacall it" is known as the "thing" and has no aoa. here is an example. take a cube of wood, and put a ruler on top. i don't see any aoa, do you? the cube is just as square as the drainpipe, so obviously it can't fly, we just think it does. if you insist, i will get a picture by next week

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Prop Length VS Cowl/Fuse Width - 5/13/2003 8:03:32 AM   
Spaceclam



Posts: 4640
Joined: 4/13/2003
From: chatsworth, CA, USA
Status: offline 		i see now. what i meant by "mount" was you could not mount any wing or stabilizer on it with any aoa or incedence, because once again, reffering to the cube, it is square, and has no grooves, tilts, or cradles, so the stabilizers have the same aoas as the plane does

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Prop Length VS Cowl/Fuse Width - 5/13/2003 8:10:10 AM   
Spaceclam



Posts: 4640
Joined: 4/13/2003
From: chatsworth, CA, USA
Status: offline 		i did not meen to be rude or upsetting, and i apologise if i was

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Duct tape is like the force. It has a light side, a Dark side, and it holds the universe together.

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       Post #: 28

Prop Length VS Cowl/Fuse Width - 5/13/2003 8:20:53 AM   
Damnathius



Posts: 518
Joined: 9/28/2002
From: Lancaster, CA, USA
Status: offline 		As I said earlier, it is possible to watch a plane flying and not see any AOA, but this does not mean that it is not there. We are talking a few degrees. The plane in flight might "appear" to be level, but it isn't. If there is no AOA in flight, the plane will descend. Of course there are many, many planes with 0 degrees incedence built into the structure, but they cannot fly without AOA.

Pardon me, David. I should have stated that those that apply Bernouli's principal to airfoils and the creation of lift seem to rely only on these principals in their explanations, and it is my opinion that these principals have little or nothing to do with why planes really fly. Too often I get caught up in the piont I am trying to make and lose a sense of where I am at in my references.

There have been some studies on the type of airfoil that, when applying Bernouli's principal, would actually work at a given speed. It would have to be extremely FAT on the upper curve to actually cause enough of a low pressure to create lift without AOA. This is also not taking into account the weight being lifted. For all practical purposes, the principal is useless to flight. It looks good on paper and in science books, but it is hardly applicable in my opinion.

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       Post #: 29

Prop Length VS Cowl/Fuse Width - 5/13/2003 8:22:29 AM   
Damnathius



Posts: 518
Joined: 9/28/2002
From: Lancaster, CA, USA
Status: offline 		Thanks SpaceClam... I appreciate that. I also apologize for my retort.

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       Post #: 30

Prop Length VS Cowl/Fuse Width - 5/13/2003 8:36:32 AM   
LarryC


 

Posts: 405
Joined: 10/9/2002
From: Brookland, AR, USA
Status: offline 		Hey guys, you're all wrong, including Bernoulli about what makes an airplane fly. I learned the real truth a number of years ago while learning to fly full scale airplanes.
The truth is, money makes airplanes fly.
Quit throwing money at them, and pretty soon they're stuck on the ground.
This is also shown by the definition of airplane: A hole in the sky into which money is poured.

Have fun,
Larry

(in reply to herc75)
       Post #: 31

Prop Length VS Cowl/Fuse Width - 5/13/2003 8:45:41 AM   
David Cutler



Posts: 2163
Joined: 9/13/2002
From: Los Angeles, CA, USA
Status: offline 		Copied from a website about Bernoulli:-

The real details of how an object generates lift are very complex and do not lend themselves to simplification.

For a gas, we have to simultaneously conserve the mass, momentum, and energy in the flow. Newton's laws of motion are statements concerning the conservation of momentum. Bernoulli's equation is derived by considering conservation of energy. So both of these equations are satisfied in the generation of lift; both are correct.

The conservation of mass introduces a lot of complexity into the analysis and understanding of aerodynamic problems. For example, from the conservation of mass, a change in the velocity of a gas in one direction results in a change in the velocity of the gas in a direction perpendicular to the original change. This is very different from the motion of solids, on which we base most of our experiences in physics.

The simultaneous conservation of mass, momentum, and energy of a fluid (while neglecting the effects of air viscosity) is called the Euler Equations after Bernoulli's student, Leonard Euler. If we include the effects of viscosity, we have the Navier-Stokes Equations which are are named after two independent researchers in France and in England. To truly understand the details of the generation of lift, one has to have a good working knowledge of the Euler Equations.

Obvious really!

(argh!!)

-DC



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       Post #: 32

Prop Length VS Cowl/Fuse Width - 5/13/2003 9:00:44 AM   
maverick



Posts: 1575
Joined: 11/29/2001
From: Alameda, CA, USA
Status: offline 		[QUOTE]Originally posted by Spaceclam
what i meant by "mount" was you could not mount any wing or stabilizer on it with any aoa or incedence........[/QUOTE]
Well angle of attack and incidence are being used in this sentence as if they are interchangeable, when in fact they are not.

The incidence is the angle of the chord of the wing in relation to the centreline of the fuselage.

Now you can have a 0 degree incidence where the wing chord is perfectly in line with the fuselage, but this then brings in angle of attack whereby the fuselage centreline is slightly inclined when flying, thus producing an angle of the wing chord in relation to the oncoming airflow.

So a plane with zero degrees of incidence will still have an angle of attack when flying.

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Prop Length VS Cowl/Fuse Width - 5/13/2003 9:25:07 AM   
David Cutler



Posts: 2163
Joined: 9/13/2002
From: Los Angeles, CA, USA
Status: offline 		[QUOTE]Originally posted by maverick

The incidence is the angle of the chord of the wing in relation to the centreline of the fuselage.
[/QUOTE]

Actually it's not, as the 'centreline of the fuselage' implies the centre on the vertical plane, not the horizontal plane. As the fuselage isn't symmetrical about a horizontal plane, there cant' really be a centreline.

Also, strictly speaking, incidence is the relationship between the wing and the horizontal stabilizer. The fuselage can be almost any old shape, like a grand piano or a sausage, but it's the relationship between the wing it supports and the tail it also supports that creates incidence.

- probably!



-David C.

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       Post #: 34

Prop Length VS Cowl/Fuse Width - 5/13/2003 9:35:23 AM   
maverick



Posts: 1575
Joined: 11/29/2001
From: Alameda, CA, USA
Status: offline 		[QUOTE]Originally posted by David Cutler
Actually it's not, as the 'centreline of the fuselage' implies the centre on the vertical plane, not the horizontal plane. As the fuselage isn't symmetrical about a horizontal plane, there cant' really be a centreline.[/QUOTE]
Fair enough.....maybe I should have said the thrustline then.....but then as you go on to explain, this may not be correct either, as you say the incidence angle is in relation to the horizontal stab.

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Ack... - 5/13/2003 9:43:19 AM   
herc75



Posts: 37
Joined: 10/23/2002
From: Columbus
Status: offline 		What have I started...

"Sooo, if Bernoulli's full of crap...does this then mean its the AOA of the prop (pitch) that is really "pulling" the aircraft forward or was the other answer of pressurization correct." As I poke the bear with a stick!

Nick

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       Post #: 36

Prop Length VS Cowl/Fuse Width - 5/13/2003 9:46:49 AM   
sandal


 

Posts: 398
Joined: 12/9/2002
From: Dokka, NORWAY
Status: offline 		maverick;

You asked how a fully symmetrical wing creates lift. According to "the old" theory;

At 0 degrees AOA there is no lift. As AOA is increased, the point on the LE where air is split (up or down) will move down. This means that the air on top of the wing has to travel further.

Damnathius;

it is possible to say that the air is still and the wing moves through it, and that the air is lifted a few inches and comes down again when the wing passes through it. But relative to the wing, the air is moving.

According to Einstein there are no absolute coordinates in space, and no objects can be said to stand still or move without reference to another object's position and speed.

Am I way off track now?

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Re: Ack... - 5/13/2003 9:48:10 AM   
David Cutler



Posts: 2163
Joined: 9/13/2002
From: Los Angeles, CA, USA
Status: offline 		[QUOTE]Originally posted by herc75
What have I started...

"Sooo, if Bernoulli's full of crap...does this then mean its the AOA of the prop (pitch) that is really "pulling" the aircraft forward or was the other answer of pressurization correct." As I poke the bear with a stick!

Nick [/QUOTE]

There are two answers to this .

. . 42

and

. . Yes



-David C.

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       Post #: 38

Prop Length VS Cowl/Fuse Width - 5/13/2003 9:49:44 AM   
maverick



Posts: 1575
Joined: 11/29/2001
From: Alameda, CA, USA
Status: offline 		[QUOTE]Originally posted by sandal
maverick;

You asked how a fully symmetrical wing creates lift. According to "the old" theory;[/QUOTE]
No....I wasn't asking how it was done......it was a rhetorical question to get you thinking of other principals that may be in effect other than Bernoulli's theorem......and yes we are way off track!

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