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prkaye

Well Known Member
I've been working on rigging, and when I tested my flap travel I got to wondering why Vans designed the flaps to have so little downward travel? The max is between 30 and 40 degrees (I forget the exact number offhand). In rental planes I have flown flaps can be deployed by as much as 45 or 60 degrees.
Is there a reason for Vans' small flap angle?
 
Paul - the flap on the -9 is really big. You're gonna find that full flaps of 35 degrees or so is plenty.
 
apkp777 said:
Older Cessnas have 40, but the newer ones 30. On a go around your up a creek with 40 degrees
Click to expand...

I had a C150 once upon a time and never used 40 flaps for that reason. If the cb tripped on a go around, you weren't going anywhere. That airplane had a performance problem (compared to an RV) with no flaps. :)

Seriously, Phil, these airplanes do not need more than 40 flaps - especially with a CS prop which will act like a barn door at idle power. Even with a FP prop, 40 flaps is most adequate and at that, only needed on very short runways.
 
flap travel

Phil, nice registration eh? :) C-FUNC... I thought they were all taken!!

I thought the Glastar flaps were cool, with the long, fowler-like flap travel.
I wanted to add drooping ailerons, but some Beaver floatplane guys that had them said that they compromised roll control when you needed it most.

I find in my -9a that the last 10 degrees require more pitch trim force to compensate, but not much steeper approach, ( unscientific opinion only). I seem to be able to steepen the approach much more by bleeding off another 5 knots; it really sinks at 62 KIAS! compared to 68.
It may be a characteristic of the airfoil as well. If best lift is at about 15 degrees, and going from 20 to 30 only lowers the stall one knot or so, I have to ask what the real benefit is. 40 degrees may indeed be a great speed brake, but cause some directional control with the tail in all that dirty air.
The big low wing ( no flap) on our Jodel effectively blanked the rudder in the flare, causing some fun when crosswind or gusts were present!
 
flaps

The statement that ailerons can overcome a split flap situation is incorrect. Ailerons can overcome a split flap at a partial flap setting, but not in most cases with one flap up and the other all the way down. The Piper Navajo is but one example of this, there has been at least one fatal in a Navajo caused by split flap. There is still a current AD on this depending on the mod status of the airplane. The larger and more complex the airplane the more complex the flap assymetry protection.
 
Phil:

In addition to what others have said keep in mind the purpose of the flaps. Van's flaps are "drag" flaps. They help you slow down and lose altitude by creating drag. Once you start flying your RV you'll notice how much easier it is to slow your RV down once you extend 10 degrees of flaps. Without them you'd have to plan a lot further ahead to get your airspeed down. By the time you put Van's out to 40 degrees, you've got plenty of drag to help you get into whatever spot you want to alight.

Cessna flaps on its singles are mostly "lift" flaps -- technically called single-slotted-fowler-flaps. They add lift to the wing and enable the aircraft to fly at considerably slower airspeeds than without the flaps. They don't produce drag as much as they add lift. Just add five knots to the landing speed of a Cessna high wing and see how much farther you float down the runway even with full flaps -- it's a lot.

On either case I don't recall many airplanes, especially current models, that exceed 40 degrees of flap. If 40 degrees won't do it, you might want to go around ;)

Chris
 
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