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Flight/Trim Questions

Posted: March 9th, 2016, 4:45 pm
by freeflyer
Need some help on flight. I've got the Freedom Flight model. Built 2 of them up and they behave differently.

1st plane will not circle and will only glide in a straight line. The center of gravity seems good as it does not descend quicky, just slowly glides to the ground. The horizontal wing at the tail is tilted with the left side up and the rudder is angled on the fueselage per the instructions.

2nd plan won't transition at all. When launched it will simply climb and then do a big arc into its descent. When hand tossed at shoulder level it seems to glide as it should without a rapid descent or a stall.

Any suggestions on trim or other changes are greatly appreciated.

Re: Flight/Trim Questions

Posted: March 10th, 2016, 5:17 am
by bjt4888
Congrats on building a couple of nice gliders. For glider one, check to see if the fllaps are bent down exacltly the same. One mm difference at any point alongthe flap will affect turn. Also check to see that the right wing and left wing are equal in weight (balance the fuselage on a finger of each hand to see if one wing hangs down). Sandthe heavier wing till corrected. A small 1/16" ball of clay on the wingtip can aid turn.

The second glider sounds like it needs some wing incidence. This can be accomplished by adding a 1/32"shim between the fuselage and the wing mount forward of the wing leading edge (remove front tape, install shim of hard balsa or the like, apply a newpiece of tape) .

Give more details and i can provide better help (ex. Amount of flap deflection, wing incidence, center of gravity location, bank angle and inclination angle of launch, weight of gliders) .

Brian T.
AMA since 1972

Re: Flight/Trim Questions

Posted: March 10th, 2016, 9:08 am
by bjt4888

Sorry, I wasn't very clear in my previous reply. If wings are unbalanced in weight with the heavier wing outboard of your turn direction you can possibly sand that wing a little to improve turn. If the wing that is heavier is already the side that you are turning, you can leave things as is. Sanding the wing would work if you can sand in such a manner as to not impact the wing airfoil too much. I'm guessing that it is most likely that the issue is difference between the left and right wing flap deflection or some other misalignment.

Good luck and supply more data as I requested in my previous post if you would like better assistance.

Brian T.

Re: Flight/Trim Questions

Posted: March 10th, 2016, 11:01 am
by freeflyer
Thanks for the reply.

After more tests flights I also learned how fragile these plans are. Some repair work needs to be done along with probably building the other two plans sill in the box. I'll post up with more questions on the trim when I have a chance to get some more flight time.

Re: Flight/Trim Questions

Posted: March 14th, 2016, 9:53 pm
by fifty_missions
The Freedom Flight glider has one major inherent flaw, the fuselage is too short aft the trailing edge of the wing to the leading edge of the stabilizer. The fuselage needs to always be longer than the wingspan!

Build a new fuselage and lengthen it by 20%. Divide the overall length into 1/3's. At the first 1/3, make a mark, that is where the leading edge of the wing should be placed.

With the glider that is diving on launch, the trailing edges of the wings are too thick and do not flex straight for the high speed launch envelope. You could
1) thin those wings more to their trailing edges to allow them to flex.
2) Add some up elevator to the trailing edges of the stabilizer. Just pinch the material as you bend. Just a degree per test. This may require adding more ballast to the nose to remove any stall tendencies.
3)Add a degree incidence under the front of the wing.
4) A bit of both steps 2 & 3 may work.

Good Luck

Re: Flight/Trim Questions

Posted: April 16th, 2016, 6:43 am
by P2P
We have a glider that nosedives after it gets to a peak height. I'm pretty sure it is due to the transition because it never seems to slow down at the top. We tried adding incidence and adding/taking off clay but it never seemed to work at high speeds. We use a design related to the Modified Upsweep.

Re: Flight/Trim Questions

Posted: April 16th, 2016, 1:36 pm
by fifty_missions
Post a good side view and to view picture. The glider does not have enough positive incidence in flight. Transition is tricky. In the end it will be a combination of turn, pitch, and roll axis that allows the glider to transition at the apex. There are many factors here that will not allow the transition-

1) Nose length is too long
2) Fin is too big or too much area (controls the glider like n arrow)
3) Glider does not have enough positive incidence on the wing in flight
4) Trailing edge of the stabilizer is bent down (sometimes almost imperceptibly!)
5) There is no inducement of turn (Fin, stab tilt or wash-in on a wing)
6) Launches are made without any tilt.

Tell in a test launch which way does the glider want to orbit?

Thanks, Tom