Airplane's Behavior in flight:

In Flight without WVEs

In flight with sloted WVEs

The flight tests were conducted in same conditions; the same day, with equal weight. Results are:

1- Shorter takeoff distance

2- An 100 feet/minute better rate of climb

3- At equal weight, service ceiling increases by 1000 feet, from 15500 to 16500 feet.

4- 5 to 6 knots speed increase at 15500 feet*

5- Better glide distance at same speed

6- Different stall behavior, resistance to stall (effective angle of attack equivalent to an elliptical wing)

7- Better handling characteristics

8- Better mileage/gallon

*How to estimate the relation between induced-drag reduction and the speed gained:

Basically total drag can be divided into:

1- All friction drags, also referred as Cd minimum, or Cd0

2- Induced drag

The actual equation for power required to counteract the total drag can also be divided and expressed by:

Equation 1 : Thp for FrD = 1/550*.5*rho*S*V^3

(FrD for friction Drag)

Equation 2 : Thp for Di =
1/550*k*(2/P*rho*e)*(W/b)^2*(1/V)

where k = 1 for an elliptical wing, in
our tested case with WVEs k = 0.727

P = 3.1416

rho = density

e = the e accounts for profile drag variation and nonelliptical wing shapes
it also known as Oswald's efficiency factor

b = span

V = speed

Then we can say WVEs improve factor k that in the nominator. When it is decreased by 30%, Thp needed to counteract Di will be lowered by 30%: That extra power can then be used to increase the speed. Consequently it will contribute to increase the Thp needed in equation 1 for friction drag. Since V^3 is in nominator you can see that speed is a the main factor for the Thp demand. In addition the friction to induced drag is in the ball park of 2 to 1.

This is a kind of cybernetic behaviour: to appreciate the effect of decreasing by 30% the induced drag, you have to run some what-if's ? . This is out of the scope of these web pages: What I can say is that 30% lower induced drag contributes to increase the speed by 5 to 6 knots in my flight conditions at 155 kts. It sounds very low but it is what you can get by increasing the available Thp by 10%; in my Glasair that is the amount I would get if I fit my airplane with an 200 hp in place of my 180 hp. Surprising?

These numbers could be achieved because I was flying high, slow 155 kts, and usually close to or over gross-weight.

If you
have comments or suggestions, email me,** Henri
CHOROSZ**, at
*Hchorosz@aol.com*

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