full flying stab trim / wing AOA. any difference?

[dmc9014]

I have just enough knowledge to be dangerous so please be easy with me =)

As I understand it one of the things that effect the lift of a wing is its angle of attack. On some models I have seen an intentionally designed angle of incendence for the main wing relative to the fuselage. I am guessing this is done to help low speed lift performance without the use of flaps.

Assuming im not totally wrong, would placing a few degrees of up trim in a full flying stab have the exact same effect as setting incendence on the main wing?

Thanks in advance and if anybody wishes to write a long winded dissertation about the details of wing/tail/fuselage relative angles and how it performs and why it is done I would love to read it =)

[surfimp]

Assuming im not totally wrong, would placing a few degrees of up trim in a full flying stab have the exact same effect as setting incendence on the main wing?
Yes! Adding up trim to the flying stab would change the decalage, or the relationship between the AoA of the wing and the AoA of the stab. You can modify the decalage by shimming the wing or by trimming/shimming the stab.

Steve

[vintage1]

Not QUITE the same.

Adding +ve incidence to the wing will make the fuselage - and thrust line if it has power - point downwards relative to the main wing, whereas simply adding negative to the tailplane will not.

What difference this makes is dependant on whats sort of fuselage it is, and where the engine. if any, is mounted.

[fhhuber506771]

Sort of saying the same thing as Vintage...

The wing having a built-in positive incidence is designed to have the fuselage aligned for minimal drag at cruising airspeed. (or at maximum airspeed when discussing a racer)

All of the designer's chosen incidence angles and the thrust line angle are planned to coincide with a given speed, weight and CG location for the aircraft. Change speed. or CG or total weight and the incidences probably need adjustment... thats what elevator trim is for.

With the flying stab, you can alter the "decalage" angle (difference between horizontal stab and wing) at will. This is SLIGHTLY (very slightly) less draggy than trimming the model for level flight with an elevator deflection angle.

***********

Note.. I have seen an experimental model with "wingerons" and flying stab... The wings pivoted on the wing tubes to act as ailerons and it had adjustable "flaperon" mix to allow trimming the wing incidence AND the stab incidence simultaneously (in opposing directions, increasing or decreasing decalage). It worked... the setup was a bit off on that experimental model and the roll rate was abysmally slow.

[Ollie]

The incidence purpose is to help rigging how the plane set up.
Angle of attack is how the pitch attitude of the wing and horiz. tail change from moment to moment as the air flows changes during flying like looping, air speed, etc.

[dmc9014]

ok i think i understand a little better. the minimal cross section at cruise etc makes sense.

i guess the one part that continues to confuse me is why so many slow flyers have alot of incedence in the wing. i cant imagine it being for minimizing drag..... hmm it just occured to me that the positive incedence might be used to intentionally add drag to a slow flyer to slow the flight speed?

[vintage1]

No, its more that at the slow speeds they fly, that is the correct angle of attack to get the fuselage more or less horizontal.. they don't fly a great deal above stall speed anyway.

[Ollie]

The airfoil AOA adds to the induced AOA for the total wing AOA. For low aspect ratio wings, the AOA near stall is very high. For high aspect ratio wings, the AOA near stall is smaller. For high camber airfoils both the airfoil AOA and the induced AOA are both wing high total AOA. Delta wings (low aspect ratio) have such high AOA that it's wing seems never to stall.

Forget the fuselage for the flying function. You will accept the normal fuselage picture. Remember, the function of the fuselage is to hold together the wing and tail. Too bad the fuselage makes drag. The fuselage just over comes the drag with thrust.

[Sparky Paul]

No, its more that at the slow speeds they fly, that is the correct angle of attack to get the fuselage more or less horizontal.. they don't fly a great deal above stall speed anyway.
.
The horizontal fuselage is more a visual aid than anything else, which we need because we're not IN the airplane.
The fuselage is merely a joiner between the motor, wing and tail. These three determine how the plane flies.

[vintage1]

well it maybe on a 'stik' but on my models its often big enough to make a fair bit of difference, aerodynamically.