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 =
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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