TIPstalling & Flaperons
 

i am building a Patriot and was going to install 2 servos in the wing to setup for Flaperons... :)

then i read this post: :(
http://www.rcuniverse.com/showthread...98&forumid=162

i thought adding flaperons would help prevent tip-stalling!?

am i wrong on this? :confused:

any theory on tipstalling and flaperons/ flaps would be of a great help

THNXX

TIPstalling & Flaperons
 

When the angle of attack of a wing exceeds a critical value, about 12 deg, the flow across the top surface of the wing separates and lift drops a lot - the wing stalls. This separation doesn't happen uniformly along the span. On many tapered wings the wing is more ready to separate near the tips than near the root. In the real world one wing tip will go first, loses lift , drops and the fun begins. Dropping flaps on the root half of the span increases the camber of that section, increases the effective angle of attack relative to the tip section, and assure the root separates first - no tip stall. If strip ailerons are drooped the camber along the whole span increases so the wing is as likely to tip stall as without drooped ailerons.

TIPstalling & Flaperons
 

The problem with flaperons is that they go all the way out to the tips. So the higher lift works all the way out. Now the next problem is that if you try to use more than about 20 degrees of flap mixed in you get a lot of adverse yaw. The more flap the worse the problem is up to the 45 or so degree mark where the ailerons have NO effect and beyond that you actually have a reversal of the aileron action.

I did this on a 2 meter glider that had flaperons and elevator only with no rudder at all. Great experiment. I didn't notice any undue tip stallling but then I had a LOT of differential in my aileron control so that may have masked the effect.

If you're doing this for aerobatic reasons, as in coupled flaps and elevator, for snappy loops then just go ahead and do it. The tip stalling and reversal will only be an issue if you try to use too much flap on landings anyway. The rest of the time it'll make for some more interesting maneuvers.

TIPstalling & Flaperons
 

When a surface like a flaperons or an aileron is deflected down, the effect is to lower the angle at which the wing stalls.
If you are operating close to the maximum angle anyway, and add this deflection, you stall the wing in front of the surface.
That's where tip stalls come from.
Full-span flaperons then will require some care in flying, which avoiding tip-stalls demands anyway, so why make the process more difficult?
There's also the awesome adverse yaw a fully deflected flaperon generates, when the plane turns -opposite- the intended direction.
Flaps and ailerons are a much better choice than flaperons.

Advserve Yaw....
 

THis is Tony Frackowiak's "Hovering Cobra" showing the extreme effect of a fully deflected "flaperon" on the flight path...
The plane is slowly climbing to the RIGHT, despite the down deflection of the right aileron, which could be expected to roll the plane to the left. The left aileron is almost neutral..

thnx guys
 

so if i sum up all the info above, i could go for flaperons but keep the initial "flap position" deflection angle small and do some testing ...

i appreciate your help,
Vasek

TIPstalling & Flaperons
 

The Patriot has taper and sweep.

On this particular wing there is a good amount of taper and the aileron is of a contant chord length. When the aileron is deflected to make a flap, the outboard section will see a greater camber increase due to the aileron being a larger portion of the wing chord. This is bad news because a higher camgered - lower chord airfoil will stall way before a lower cambered - higher chord section on the same wing at the same angle off attack.

Swept wings will also have a tendency to tip stall unless you do things such as add washout (which would be hard to do with the patriot). If you do use flaperons you will make this tendency worse.

I'm not saying don't do it. I did like the fact that I had two servos on the ailerons rather than one. You may be able to slow the plane down slightly, but the stall will be much more sudden and uncontrollable. I think you will find that they are not pratical and will get you in more trouble if you didn't have them. I'll just say that landing the Patriot takes some practice just like any new plane that you have flown. If you have flown a low wing plane that is somewhat fast you should have no problem landing it.