-5 flaps

Loupark

Loupark

Filing Flight Plan
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Lou
Has anyone built their plane with the flaps
retracting an extra 5 degrees for more cruise speed?
Since my plane is a plans built, I'm highly considering this
but would like to know if anyone has been successful.
Lou
 
what are you building? ive never flown an airplane with reflex flaps but have flown a glider with them. its pretty sweet, you can really feel the acceleration when you reflex them.
 
ive heard theyre good on the Flight Design CT

i dont really understand the aerodynamics about HOW it makes it faster thoough... can someone explain that to me?
 
lift = 1/2*rho*V^2*S*Cl

reflexing the flaps lowers the angle of attack of that wing section, which lowers the coefficient of lift (Cl)

to maintain the same amount of lift the wing can either go faster, or increase the angle off attack back to the previous value with the same speed. we choose to go faster.
 
The obvious question would be: Why doesn't every aircraft, with flaps, have negative flap ability?
 
mdreger said:
The obvious question would be: Why doesn't every aircraft, with flaps, have negative flap ability?
Click to expand...

That's my question! Here's where an engineer chimes in with another equation I don't understand to explain the drawbacks ___________

:skeptical:
 
I think some Maules do and I know someone who mod'd their Viking to do so
 
mdreger said:
The obvious question would be: Why doesn't every aircraft, with flaps, have negative flap ability?
Click to expand...
The Zodiac 601XL could have negative flaps: there's an upstop to keep them from going up past the 0-degree position at the outboard end. I'm told that the upstop is there for a very good reason: without it, the likelihood of aileron flutter is increased pretty dramatically, as reported by builders who've left it out.
 
tonycondon said:
what are you building? ive never flown an airplane with reflex flaps but have flown a glider with them. its pretty sweet, you can really feel the acceleration when you reflex them.
Click to expand...

Well, you asked.
http://www.homebuilt.org/kits/littner/champion.html

This is a whole lot more popular in Europe, than the US.
If you look up Pioneer 300, it's the same plane but with a
composite skin.
Lou
 
mdreger said:
The obvious question would be: Why doesn't every aircraft, with flaps, have negative flap ability?
Click to expand...

Because the Aeronautical Engineers that designed the plane optimized the plane for max gross flight. The heavier the plane is, the less helpful the reflex flap is. I'd bet there is a certification issue in here somewhere, too - but I don't know enough about the certification requirements for new designs to say for sure.

What would be the downside of flying with a negative flap setting during maneuvers, takeoff, landing? Less lift. Anything else? These potential negatives are probably why most (all?) certificated aircraft don't have them.

If you routinely fly under gross it does seem like a reflex flap would give you more speed in cruise flight. Build your experimental that way and have a ball.

-Skip
 
Last edited:
jmaynard said:
The Zodiac 601XL could have negative flaps: there's an upstop to keep them from going up past the 0-degree position at the outboard end. I'm told that the upstop is there for a very good reason: without it, the likelihood of aileron flutter is increased pretty dramatically, as reported by builders who've left it out.
Click to expand...

It could be done on the 601XL by just changing the bends when you make the flap. The stop would still need to be there because the outboard end needs to be under some tension because all of the pressure holding it in place is on the inboard in.

P.S. If the flap is fluttering it is "Flap Flutter" not Aileron flutter. Still flutter and still bad.
 
GigG601XL said:
P.S. If the flap is fluttering it is "Flap Flutter" not Aileron flutter. Still flutter and still bad.
Click to expand...
The message I remember reading on the Zenith list mentioned aileron flutter...but your explanation is as good as any.
 
Let'sgoflying! said:
I think some Maules do and I know someone who mod'd their Viking to do so
Click to expand...


Some Maules do indeed have them.
I had a State Trooper friend in Florida whose patrol plane was a Maule which had them. He only used them when traveling to and from his "hunting zone" or on cross country flights. He thought they worked quite well.
 
Loupark said:
Has anyone built their plane with the flaps
retracting an extra 5 degrees for more cruise speed?
Since my plane is a plans built, I'm highly considering this
but would like to know if anyone has been successful.
Lou
Click to expand...


The high wing Murphy Rebel has them the last I knew. Yield was about 3-4 knots in cruise with reflex deployed, perhaps a higher aspect wing could get more.
 
Skip Miller said:
Because the Aeronautical Engineers that designed the plane optimized the plane for max gross flight. The heavier the plane is, the less helpful the reflex flap is. I'd bet there is a certification issue in here somewhere, too - but I don't know enough about the certification requirements for new designs to say for sure.

What would be the downside of flying with a negative flap setting during maneuvers, takeoff, landing? Less lift. Anything else? These potential negatives are probably why most (all?) certificated aircraft don't have them.

If you routinely fly under gross it does seem like a reflex flap would give you more speed in cruise flight. Build your experimental that way and have a ball.

-Skip
Click to expand...

It seems like this wouldn't affect takeoffs or landings because you wouldn't use that setting for those phases of flight,
 
Dave Krall CFII said:
The high wing Murphy Rebel has them the last I knew. Yield was about 3-4 knots in cruise with reflex deployed, perhaps a higher aspect wing could get more.
Click to expand...



3 knots here, 4knots there. It seems worth it for just thinking ahead of time.
Lou
 
Loupark said:
3 knots here, 4knots there. It seems worth it for just thinking ahead of time.
Lou
Click to expand...

Yes, it's usually fairly easy to do if done from the ground up. Probably the fuel savings would pay for the alterations if flown for long enough.
 
IIRC, the RV-10 has the 'negative' flap setting. It'll be fun to play with it. :)
 
Teller1900 said:
That's my question! Here's where an engineer chimes in with another equation I don't understand to explain the drawbacks ___________

:skeptical:
Click to expand...

I think the main reason most aircraft don't have negative flaps is due to the maximum flap speed and weight. One advantage of stopping the flaps at the 0 degree position is that the stops now carry much of the flap load instead of the flap linkage. If the flaps don't hit the stop then you need a stronger (heavier) linkage and drive system for the flaps.

My glider goes from -10 to +90 degrees of flaps. It has no restrictions on speeds at which the flaps can be extended.

Brian
CFIIG/ASEL
Schreder HP16T
 
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