stevenmeyer2005
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L/D)max Value For Boeing 738 Or A320

Fri Feb 26, 2010 4:12 pm

Hi guys,

Does any one know Lift to Drag max values of the Boeing 737-800 or the Airbus A320?

Are the Lift to Drag max values different between the various Boeing 737 models?

Appreciate the input!

Stevenmeyer2005
Steven Meyer
 
tdscanuck
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RE: L/D)max Value For Boeing 738 Or A320

Sat Feb 27, 2010 2:17 am

Quoting stevenmeyer2005 (Thread starter):
Are the Lift to Drag max values different between the various Boeing 737 models?

I don't know what the actual L/D values are, but they should be different between different models because you've got different finess ratios on the fuselages and different wing loadings (same planform, different weights). Winglets and not-winglets will also make a difference.

Tom.
 
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Jetlagged
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RE: L/D)max Value For Boeing 738 Or A320

Sun Feb 28, 2010 4:26 pm

Quoting tdscanuck (Reply 1):
different wing loadings (same planform, different weights)

Surely L/D max is not affected by wing loading? The airspeed for L/D max is affected by weight though.
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tdscanuck
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RE: L/D)max Value For Boeing 738 Or A320

Sun Feb 28, 2010 5:12 pm

Quoting jetlagged (Reply 2):
Surely L/D max is not affected by wing loading?

Has to be, I think. Higher wing loading forces you to higher Cl at a given speed, which means lower L/D for that speed. Since this applies to all speeds, the whole L/D vs. speed curve moves down with increasing wing loading, so it can't have the same L/D max.

Tom.
 
FredT
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RE: L/D)max Value For Boeing 738 Or A320

Sun Feb 28, 2010 5:52 pm

Then L/D max would change with increasing gross weight as well... which it doesn't.  
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tdscanuck
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RE: L/D)max Value For Boeing 738 Or A320

Sun Feb 28, 2010 6:53 pm

Quoting FredT (Reply 4):
Then L/D max would change with increasing gross weight as well... which it doesn't.

Good point. I started realizing I'd done something funny after I posted...I think I was subconsciously imposing an equal payload constraint. With equal payloads, the gross weight between two derivatives is necessarily higher and the heavier one will always have lower L/D max *for that payload*. But if we're just talking max theoretically possible at any weight/speed then you're absolutely right, wing loading shouldn't play into it.

Tom.
 
keta
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RE: L/D)max Value For Boeing 738 Or A320

Sun Feb 28, 2010 7:12 pm

I know it's not what you're asking for, but it might give an idea, the average L/D in cruise for the A320-200 is about 16.3.
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prebennorholm
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RE: L/D)max Value For Boeing 738 Or A320

Tue Mar 02, 2010 2:21 am

Quoting stevenmeyer2005 (Thread starter):
Are the Lift to Drag max values different between the various Boeing 737 models?

The wings are identical on all 737NG versions (assuming identical winglet configuration). The wing produces all the lift.

Drag is produced by the whole plane. Therefore, the more fuselage, the more drag.

Consequently the 736 will have a slightly better L/D max than the 739.

But then the 736 has a larger tail which reduces that advantage. At the end of the day the differences among various 737NG models are very small.

As already stated the various weights don't affect best L/D. But it sure affects at which IAS you get the best L/D.
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