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Old Nov 18, 2012, 08:57 AM
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Joined Dec 2002
302 Posts
Help!
flaps/camber?

Having just finished my 2.6m ASW28.
It has high loading of 27oz/ft2. (Ouch!)
I have just set up crow.
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I then upgraded my tx to a jr3810/8103 to additionally be able to set camber and flaps independantly of crow.
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I understand the advantages of crow for landing, including effectively introducing large washout to help avoiding tip stalling, but please can someone explain when I would use flaps and camber.
e.g., any use of flaps during launch?
How many degrees?
If lift drops, can I add touch of camber?
Do I then need to be careful about tipstalling because we are increasing angle of attack of whole wing including tips?
Or do I set camber to add slight washout by moving flaps slighly more than ailerons?
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(note, reflex will not be set as flaps have nil up movement)
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Above are all the issues spinning round my head.
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Please comment,
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Rgds, Steve
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Old Nov 18, 2012, 09:55 AM
Registered User
Joensuu, Finland
Joined Mar 2002
1,477 Posts
As an analogy, you could think of flap deflection as gears on a (manual shift) car - they will optimize wing profile for different speeds. A profile with lots of camber will provide lots of lift at low speeds, but if you try to fly faster, drag will increase rapidly. A low-camber or reflexed profile creates less drag even at high speed, but also less lift, so it needs to be flown faster. Normally only a little of camber is needed, typically 5-8. Any more than 10 will probably add more drag than lift.

Typically flaps are dropped when you are flying slowly and minimizing sink rate, such as in a thermal. While gliding between thermals, flaps are up to increase penetration. If thermal lift drops, I'd rather cover some ground with flaps up to increase probability of finding another thermal. But if it is quite sure that the weather is totally dead, flaps down would slightly decrease sink rate. Whether this sink rate reduction is significant or not, remains to be debated about. Flaps down certainly will restrict you to use only slow speed and you shouldn't expect to cover lots of ground or penetrate upwind in this configuration.

To use flaps during launch or not depends on the plane. Some planes are happy to climb at high speed and use the extra speed to zoom after line release. If you are having trouble at maintaining towline tension, flaps down should help. You just need to experiment and see what suits your plane and flying style. Same goes for washout - if the wing design is good, you shouldn't need it. But if you do experience tip stall issues, some washout as you describe could be useful. Again, try it and see what works for you.
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Old Nov 18, 2012, 11:10 AM
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Joined Dec 2002
302 Posts
Thanks for that....very informative.
This will be used for slope only.....it's obviously high aspect wing, will await good 15-20mph for maiden.
I suppose I am preparing myself if, for example, lift drops during flight, an want to minimise sink rate as much as possible.
I read somewhere, and have lost it now, of people tying their flap stick upwards with a rubber band for slope launch, suggesting any flap a big no no for launch for some reason
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Rgds, Steve
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Old Nov 18, 2012, 01:49 PM
Flagstaff, AZ
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USA, AZ, Flagstaff
Joined Mar 2003
3,853 Posts
I think the most common use of "flaps" on the slope is "snap flaps." This is a common "mix" that addd a bit of camber to the wing (5-10 depending on the air foil) when you pull elevator. The idea is to give your wings a bit of extra grip (lift) in hard banked turns. It also is useful for aerobatic gliders that spend time inverted or doing outside maneuvers... in that case when you push elevator the wing is reflexed. I fly mostly aerobatic gliders with symmetrical wings. I use snap flaps all the time.

For those times when the lift gets "iffy" I like to have a "Thermal" setting on my transmitter which cambers the wing slightly... just enough to give me a bit more float. I use a "flight phase" to set this.

I think it would be interesting to see if your glider respond to camber change... especially since it is a bit heavy in the wing loading. You could put camber on a slider or the throttle stick and see how she does. It can be useful to see how slow you glider will go and not be stalling.

Have fun!

Dawson
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Old Nov 18, 2012, 03:39 PM
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Bellevue WA,
Joined Dec 2003
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With the high wing loading I would not use much flaps or any crow during landing. The results will be allowing the air speed to get to low for the wing tips and a stall will occure. My best advice for flying scale (high wing loading) ships is to NEVER allow it to slow down ESPECIALLY during landing. On the slope your ground speed can be slower but don't allow the air speed to get to low even with crow and flaps or you will pay the price. I have a 4m ASW 28 that has a 26 to 28 oz wing loading so I know how they react to slower speeds.
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