Adding flaps
 

I have started on a rebuild of a plane I have rebuilt five times already. I'm currently wondering if I can add flaps on this go around. As it turns out I'm having to reattach the strip ailerons the wings are currently equipped with, so I will now have the option of adding flaps.

My question is how to drive the flaps. The torque rods currently in use will be covered over by flap torque rods. I have the option of putting servos in the wings, or copying JHH's design and using two nested brass tubes. One will leave horns hanging down which I don't have now. The other is kind of finicky to build and takes up a lot of space at the input ( servo) side.

Any other ideas on how to set up flaps where there were none before? Also how much of the strip aileron should be flap? The ailerons are 17" long right now.

John

You’re going to get a lot of differing opinions here, but here are mine:

I am not a fan of torque rods, so my suggestion is to put aileron and flap servos in the wing. Simple, effective, sturdy, reliable. You didn’t mention what type airplane you have or what type flying it’s for, but since you’ve gone this long without them I will assume that the flaps will be more of a want than need, and as such I’d use somewhere between 1/3 and 1/2 of the available hingeable span for flaps.

Best wishes, enjoy!

Not sure why you want to do this? Adding flaps to an IMAC type model isn't going to do much for you on landing if you are already setting up correctly.

If you set 'em up correctly on landing, with a slow flight condition, an IMAC type or a Turbine model will land about as short as you could ask for from any model. Not worth the hassle/expense of setting up separate flaps.

Did I miss something? I didn’t see any description of the model. Either way, I just assumed he wanted flaps because…he wanted flaps.

No reason to mess with flaps if there is no advantage to be gained.....

This is a case of wanting to try a bit of different engineering, and because the opportunity is there. The plane is an old ducted fan model which I had extensive experience with landing deadstick. It will slow down to a crawl if you are not careful to keep the airspeed up. I wouldn't be considering it but the hinges needed to be changed so the opportunity presented itself.
As a side note I have worked really hard to NOT have protruding parts like horns, hence the torque rods, and because the surfaces are all less than 17 square inches torque rods work quite effectively.
I can't think of any other solutions than servos in the wings or nested brass torque rods ( which work very well ).
The reason of why-- because I wanted to, not because I needed to.
John

AH, the reason we buy RC stuff; because we want it...... lol

If you are redoing the hinging anyway consider hinging the ailerons from the top & connecting the
linkages from two, wing mounted servos to the bottom of the ailerons.

The thickness of the aileron in effect becomes the length of the control horn the difference being no
horn hanging down. Linkages have to be very precise with no slop.

That is an excellent suggestion. That is the approach I have used in several larger models such as Ziroli the F9F Panther.
Unfortunately in this case the aileron is only .25" at its thickest. I used 1/4" square stock for the trailing edge when I built the wing. They really are strip ailerons.
I have been toying with the idea of a split flap as I have enough wing thickness to fit in the servo and I can get a horn on top of the flap if I move the hinge line further towards the center of the wing. If I move the flap hinge line forward by 2.5-3" I have enough room for a 5/8" tall horn on top of the flap ( hidden).
John

If you are going to move the hinge line forward for the flaps you may as well move the entire hinge line forward & widen the ailerons as well.
You are going to reduce your aileron area anyway when you make half the length flap & wider ailerons at smaller angles will be more effective
than thin ailerons at large angles. Then top hinge/bottom drive them.

Or, easier still, fit a second aileron servo & drive the strip ailerons individually. Then use the smarts in the transmitter to drive them both down
as flaps when landing. Or drive them both up & use them to kill lift. Some elevator mixing will probably be needed as well.

If they are just strip ailerons and only 17" long and 1" deep already cutting them in half to add flaps isn't going to add that effective of a flap to begin with. If it were me and I wanted to add flaps I'd just use 2 servos and mix them as flaperons. If you want to keep the torque rod set up just run 2 servos side by side in the wing center. 1 on each torque rod and as I said mix them to operate as flaperons. I've had a few jets including my old bvm viper that use flaperons. You won't lose any effectiveness on your ailerons in flight that way.