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  #46  
Old 02-12-2007, 01:39 AM
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neverquit neverquit is offline
G.Norman
 
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Yes, do tell!


Steve, stay on track here or start your own thread about your thingie please. : )
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  #47  
Old 02-12-2007, 02:03 AM
Marc Zeitlin Marc Zeitlin is offline
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Originally Posted by swinn View Post
So how much would you have to increase the wing area of a Cozy IV to reduce it's stall speed by, say 10 knots at gross weight?
If you assume that you operate at the same lift coefficient in both cases, then the areas will be related by the ratios of the square of the velocities:

A2 = V1^2/V2^2 * A1

Plug in the original velocity - V1, the new velocity - V2, which is SMALLER, and the original wing area - A1, and the new area will be the result. As an example, if A1 was 88 sq. ft., V1 was 80 mph, and V2 was 70 mph, A2 would be 115 sq. ft., or 30% more. Not surprising, given the 14% decrease in speed, and the squared relationship.

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How much would the induced drag increase?
Induced drag is linearly related to wing area. It would rise by 30%.

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How much slower would the cruise speed be, given the same power?
Harder to say exactly, but if we use a crude estimation of the power being linearly related to the area and related to the cube of the velocity, then:

V2 = (A1/A2 * V1^3)^1/3

If A1/A2 = 88/115 (from before) = 0.76, and V1 = 200 mph, then:

V2 = 182 mph.

So we lose about 10% of the top end, for the 30% increase in wing area.

All this is approximate, but it gives you the order of magnitude.

All these equations drop out of the simple relationships for lift and drag.

L = 1/2 * rho * V^2 * A * Cl

D = 1/2 * rho * V^2 * A * Cd
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  #48  
Old 02-12-2007, 07:29 AM
deuskid deuskid is offline
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Marc -

I SO appreciate your abilities and helpfulness...

thank you


is too feable and more would be less....


thank you


John
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  #49  
Old 02-12-2007, 02:51 PM
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G.Norman
 
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That's a good answer. Let's say you want to increase the canard length by 30% instead the total wing area. Or maintain the wing length and increase the canard width. How would this apply?


I know I can dig for this stuff on the Roncz canard design and other resources but its more fun to get a simple answer for all of us whom are curious.
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  #50  
Old 02-12-2007, 03:36 PM
Marc Zeitlin Marc Zeitlin is offline
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I know I can dig for this stuff on the Roncz canard design and other resources but its more fun to get a simple answer for all of us whom are curious.
More fun for whom? :-).

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Originally Posted by neverquit View Post
That's a good answer. Let's say you want to increase the canard length by 30% instead the total wing area. Or maintain the wing length and increase the canard width. How would this apply?
Changing the ratio of canard area to wing area (or canard moment arm to wing moment arm) will change your CG range, stability, and deep stall susceptibility.
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  #51  
Old 02-13-2007, 11:42 AM
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More fun for whom? :-).
Me : -) And hopefully others whom are curious. Aw c'mon, you know you like it. -Thanks

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Changing the ratio of canard area to wing area (or canard moment arm to wing moment arm) will change your CG range, stability, and deep stall susceptibility.
Understood. Just wondering if there is an applicable rough aeronautical formula to figure out say, enough length is enough for a certain application? Again, for curiosity. I'm not intending to add 6" to my canard to compensate for moving my main back. My plane's just fine.
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  #52  
Old 02-13-2007, 01:10 PM
Marc Zeitlin Marc Zeitlin is offline
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.... Just wondering if there is an applicable rough aeronautical formula to figure out say, enough length is enough for a certain application?
Not "an" applicable formula, but many. The process of changing things is iterative, as with any reasonably complex design. You change something, evaluate the effects on other areas, adjust things to compensate, and then re-evaluate both the original concern and the new areas, and keep doing that until everything is acceptable.

In the case of canard area/length/chord, there's an interaction between size and CG position, which then leads to issues of main gear placement for rotation, elevator trim position in cruise, and deep stall susceptibility. There are MANY formulae involved in determining these relationships and behaviors. All of which are available in introductory aerodynamics and stability/flight dynamics texts.
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