[Carl Layden]

Hi Folks,

I've read several "how-to"s and seen a few videos. Some say couple ailerons to elevator so they go down like flaps when up elev is used. But others suggest the ailerons go up when up elev is used :

I've been using only elevator no coupling, about 45 deg of throw. I know I need to move my CG a little more aft (maybe 1/4"). I'd like to improve my harriers & elevators, ie slow them down and make the decent more vertical.

Suggestions on what may help?

[JimMcIntyre]

For harrier, I couple flap(erons) to elevator.

(in Homer Simpson style narrative)
elevator goes up, flap goes down
elevator goes down, flap goes up
...
:P

I have a seperate mix for spoilers for doing "the elevator"; up elevator, full spoiler (flaperons up) and a bit of throttle to keep the controls active.

[Carl Layden]

Jeez that took long, Jim you must live here on RCC :P

so to paraphase

flaperons for harrier
&
spoilers for elevator

guess that explains why I was getting confused it's opposite for each.

or as homer would say D'oH!

[sarawnty]

Hi Carl,
I think it depends on the kind of plane you're flying. I use about a 5/8" of UP deflection on my 40% Edge for both elevators and harriers. It helps to reduce, or in my case, eliminate wing rocking during these manuevers. Not sure about the science behind this but it works. However, too much deflection can make the problem worse.

[JimMoss]

Carl if your interested in tightening loops, what Jim Mc has described is the way to go (On my JR radio I have this switched with Elev-Flap switch).

For the Harrier and Elevator what Steve has described (IMHO) is the way to go (I use the Land switch for this).

Also as Steve has mentioned the more up flap you use the faster it will come down, to a point, If you use too much you loose your ailerons, just not enough movement anymore.

Jim Moss

[Carl Layden]

The plane I'm using is an Aeroworks Edge 540T 60/90 arf.

It's powered by a YS 1.20AC

It's beginning to sound like a little x'periment'n might be needed.

Thanks Jim and Stephen for the quick replies.

[Guest]

Having the ailerons go up with up elevator essentially lowers the angle of attack on the main wing (chord line is at less of an angle to the airflow) allowing less wing rock, and generally more stable elevators and harriers. Works best with ailerons that run most of the span and off the tip.

Using flaperons in these situations only increases the anlge of attack on the wing making things worse.

[JimMcIntyre]

Originally Posted by can773

Using flaperons in these situations only increases the anlge of attack on the wing making things worse.

While the effective angle of attack can easily be controlled by changing your pitch.... if all it did was change the angle of attack, full scale pilots would not likely find it very useful. :P


I like flaperon for harrier as it increases both effective lift and drag making for nice slow harriers. True, the same can be accomplished by increasing pitch angle of the aircraft but this results in something I call "falloff" (for lack of the technical term) where rudder movement results in amplified (due to increased pitch angle) CG vs CL (centre of gravity vs centre of lift) changes resulting in a "twitchy tail".

To each their own, and, as already mentioned, the design of the aircraft is important.

[Guest]

Sorry Jim but practical experience shows me otherwise.

Flaperons will serve to increase angle of attack vs no flaperons. When you are already at near or over the critical AOA of the airfoil using flaperons will only put you further into stall which does little to nothing for roll axis stability.

The drag on a model during harriers is already so high due to the wing area being presented to the airflow that whatever small amount of drag due to flaperons is essentially negligable.

Using a small amount of spoilerons during harriers or elevators can lower the wings AOA enough to bring the wing out of stall and significantly increase its stability, making for much more controlled flying in these manouvers.

I have never had any experience to lead me to believe that rudder becomes more sensitive with change in AOA, if anything I would say I have experienced the opposite effect where I find it to have less effectiveness in those situations.

[JimMcIntyre]

What I was eluding too is that a little down elevator will change effective AOA as well....

Yes, rudder may be less effective in a harrier (than in ordinary flight) due to reduced airflow but ... consider the affect effective AOA due to pitch angle and vector and you'll soon see the increased pitch angle required to sustain height (while keeping airspeed minim, which is the point) when deploying spoilers will result in increased roll coupling (picture hinge angle related to flightpath). Of course you have to picture the effective AOA to visualize the full effect of the coupling as the aircraft is not travelling along the normal thrust-line (now somewhere below the nose and above the turtledeck).

Again, much depends on the design as we haven't accounted for 'shadowing' of the flying surfaces at this extreme angle. A more closely coupled aircraft (eg. typical profile funfly) will behave radically different than a more 'square' design (longer relative fuse length)... to say nothing about higher aspect ratio designs.

... but I would be the last to claim to be an expert on this matter... IOW, use what works for you and your aircraft.