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center of lift

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by0ung(at)brigham.net
Guest

Posted: Tue Mar 28, 2006 8:02 am Post subject: center of lift

<<<<<<<<<<<<<



Mr. Ladd is correct;  our tail feathers hold the tail DOWN in flight since, 

on our wing, the center of lift is BEHIND the center of gravity.



 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>


	


Forget VG's    I have asked this before and not got  a good response that

helped me understand.



I have been told, and cant say from where, that the center of lift of a wing

will be around the 25% of the cord.  or around the thickest part of the

airfoil.  On our kolbs that would be near the front wing attach point.

If that is true and the rear cg is allowed to go to 35% of the wing cord or

about 6 to 7 inches behind the front wing attach point..   Then the

horizontal tail surface would have to be I LIFTING surface.  but we know

that the tail is designed to have negative lift to provide stability to the

aircraft.  So if Mr. Ladd is correct,,,   and the tail feathers hold the

tail down,,,,  then the center of lift on our wings is not at 25%,,,,  it

must be beyond 35% of the wing cord.



Am I missing something here?



Boyd

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n79rt(at)kilocharlie.us
Guest

Posted: Tue Mar 28, 2006 12:21 pm Post subject: center of lift

Yep...the "center of lift" being at 25% chord doesn't take into account

the "moment" that the airfoil produces...if it has been awhile since

physics class, "moment" is a rotation...in regards to an airplane the

rotation is considered positive when it tries to rotate leading edge

down.  So the combination of CG position AND the moment coefficient of

the airfoil determines how much downforce the tail has to produce...



Clear as mud?



Jeremy Casey



 



<snip>



I have been told, and cant say from where, that the center of lift of a

wing

will be around the 25% of the cord.  or around the thickest part of the

airfoil.  On our kolbs that would be near the front wing attach point.

If that is true and the rear cg is allowed to go to 35% of the wing cord

or

about 6 to 7 inches behind the front wing attach point..   Then the

horizontal tail surface would have to be I LIFTING surface.  but we know

that the tail is designed to have negative lift to provide stability to

the

aircraft.  So if Mr. Ladd is correct,,,   and the tail feathers hold the

tail down,,,,  then the center of lift on our wings is not at 25%,,,,

it

must be beyond 35% of the wing cord.



Am I missing something here?



Boyd

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Tue Mar 28, 2006 6:05 pm Post subject: center of lift

Yes - and it is easy to miss - although the center of lift can be at 25% 

or 35 % or where ever, the whole chord of the wing is still producing 

lift, and most of the wing is still going to be behind the CG. So 

regardless of where the wing produces the greatest lift, the sum total 

of lift produced will always be behind the CG. Unless you get the CG 

terribly wrong...

But with the sum total of lift behind the CG, the tail surfaces keep the 

wing from rotating around the CG, so they are stabilizing the airplane, 

or in effect, holding the tail down. Good question.



Richard Pike

MKIII N420P (420ldPoops)



boyd wrote:

 	  Quote: 	
		   



 <<<<<<<<<<<<<



 Mr. Ladd is correct;  our tail feathers hold the tail DOWN in flight since, 

 on our wing, the center of lift is BEHIND the center of gravity.



   



 Forget VG's    I have asked this before and not got  a good response that

 helped me understand.



 I have been told, and cant say from where, that the center of lift of a wing

 will be around the 25% of the cord.  or around the thickest part of the

 airfoil.  On our kolbs that would be near the front wing attach point.

 If that is true and the rear cg is allowed to go to 35% of the wing cord or

 about 6 to 7 inches behind the front wing attach point..   Then the

 horizontal tail surface would have to be I LIFTING surface.  but we know

 that the tail is designed to have negative lift to provide stability to the

 aircraft.  So if Mr. Ladd is correct,,,   and the tail feathers hold the

 tail down,,,,  then the center of lift on our wings is not at 25%,,,,  it

 must be beyond 35% of the wing cord.



 Am I missing something here?



 Boyd

- The Matronics Kolb-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Kolb-List

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

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