From: Sky2high@aol.com
Message-ID: <0.93ddfbc4.255eebf6@aol.com>
Date: Sat, 13 Nov 1999 11:29:42 EST
Subject: Flaps
To: lancair.list@olsusa.com
Mime-Version: 1.0

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My original queries were:

On a Lancair 320/360 with the standard wings and original tail,

a)  What are the lift versus drag relationships at 10 (takeoff), 30 and 45 
(full) degrees of flaps?

b)  What is the significant purpose of takeoff flaps?

With respect to b):
My opinion (no data yet) is that in most airplanes (reflexed laminar flow or 
not) the flap takeoff position is used to get the airplane off the ground 
(highest drag, lowest acceleration) as soon as possible.  I believe that all 
flap positions induce drag, but the "takeoff" position provides less drag in 
the air than the plane has when rolling on the ground.  One component of the 
drag is a result from any added lift.  

At some speed during the airborne part of takeoff, the drag of the flap isn't 
worth the benefit, if any.  Of course, one retracts the high drag wheels as 
soon as you are unable to land back on the takeoff runway.  I retract the 
wheels before the flaps because I believe the wheels are contributing more 
drag.  If I was trimmed right for takeoff,  110 Kts is quickly achieved and 
raising the flaps produces a nice nose up pitch for the climb out.  I now use 
the Deakin technique (AVWEB columnist) of full throttle, 2600 rpm with either 
a steep climb attitude at 120 Kts or, more often, the high ground-speed 
covering 140 Kts, 500-900 fpm deck angle all the way to cruise altitude. CHTs 
are generally no more than 380 degrees regardless of the outside temperature. 
 I only take off from towered airports so I don't look out the window....  If 
there is any traffic, I step-climb.

So what......  So, is the flap takeoff position only useful in getting off 
the ground or controlling deck angle (for visibility) or helping with steep 
climb out rates or what?  Is speed better than altitude in a high performance 
airplane that, without power, becomes a lawn dart?

With respect to a):
It is my opinion that the flaps deployed beyond "out of reflex" contribute 
very little lift and a great deal of drag.  This is, of course, quite useful 
in an airplane that is hard to slow down when nearing the airport.  It is 
also quite useful in changing the trimmed pitch angle for visibility during 
the approach.  It seems that the greatest effect on lift is when you are in 
ground effect -- the downward blast of air from full flaps is impressive.

One example of the lift/drag relationship is the CAFE test of Fred's 320, 
where it was reported that there was only a few mph (3?) between clean and 
dirty stall speeds.  Of course, the angle of attack is quite different.

If the wing was at max performance at speed X when the flaps are "out of 
reflex," then should we not do this for the max power-off glide range at 
speed X?  What is speed X?  Another words, If the reflexed wing is best at 
180-200 knots, what is the best speed for the un-reflexed wing, if any? 

So What........  So, what is the best procedure for the go around?  Full 
throttle, then wheels up first or flaps up first?  Milk the flaps up and 
re-trim or just go to full up?  Should we stop the flaps at "out of reflex" 
or continue up?  How about the dramatic pitch force changes?  Are you 
prepared for right rudder application?

Any data out there?

Finally, Is the main drag component a product of horizontal stabilizer 
negative lift to counteract the flap-induced nose-down pitching moment?

Is everyone snoring by now? Does snoring contribute to drag?

Scott Krueger
N92EX
The EX stands for "experimental".


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