skeeter_ca

I'm going to start building my BoT sailplane and was going to play with adding flaps, spoilers and ailerons. I know these aren't needed on a BoT but i thought it might be fun to experiment with them. However i really dislike seeing the control horns for the flaps and ailerons sticking way down under wing. I would perfer a flush control setup. Could i attach the pushrods down on the lower corner of the control surface while having the hinge on the top? What kind of problems should i look out for or is there a better method?

I would look something like this.

bogbeagle

I hope that the attached images are self-explanatory.

They show a flap mechanism on my sport model. The mechanism is concealed within the wing, driving the flap via a 3mm rod. However, the hinge line is below the wing' surface, so as to provide a crude Fowler mechanism. Very powerful flaps.

It should be possible to arrange your mechanism to suit ... full-size manage it ... but it will be require some accurate building work.

soarguy

Skeeter,

Go have a look at: www.geniebuild.com/g2_rds.html

Might be just what you are looking for!


soarguy

da Rock

Those hidden control shafts in pockets are really magic.

BMatthews

Skeeter, technically what you showed should work. But in reality it's a poor option due to the inevitable slop in any hinges and in the control rods to attachment points. In the method you show the lever arm is extremely short since it's based on the thickness of a very thin airfoil. This means that any play or misalingment becomes a very big percentage of the system. In actual practice we just can't build the system accurate enough or tight enough to not have the surfaces controlled in that way work well. Which is why the regular control horns is still the best method for us.

The angle drive rod in a slot shown in soarguy's link is one option that does work. But it's only good for ailerons as shown. For flaps you'd need to modify the setup to incorporate a 90 degree bend and then to angle the servo and torque rod to sit at 45 degrees to the flap so the activator arm in the slot is at 45 to the hinge line. Then it'll turn the flap through a full 90 degrees. However note that the elbow in this sort of system MUST be located right at the hinge line. If it isn't the whole arm and slotted pocket will lock up tight before it reaches a full 90 degrees of deflection. It may well be that adding a pivot to the slotted pocket so that it can pivot a little inside the contro surface will fix this. It's an idea that just occured to me while typiing this so you'd have to play with some mockups of this torque drive system to see if it works and makes the system more tolerant of slight misalignments.

But then doing something different always requires a bit of extra homework....

cutaway

If you're up for some brazing or silver soldering to make a custom mechanism, think nested torque tubes. You won't be able to use easy CA hinges though, the torque tubes would require inset bearings

skeeter_ca

The slop in the control system is what i was concerned with. I would not want to make a condition to allow flutter to develop. I do understand that it can get out of conrol very quickly. I was thinking maybe Du-Bro ball-links, like the ones listed below and build a twin blade control horn on the control surface to capture the link more solid and reduce the slop. The only thing is the servo arm would still be only bolted on one side. Those ball-links look like they would have zero play in them but i have never used them. What do you guys think? Is it worth experimenting with? Do i have any chance of success without buying and possible modifying some fancy control linkages?

http://shop.dubro.com/products/produ...3.0.0.0?pp=12&

skeeter