How to trim a free flight airplane?

Hello,

I am building my first free flight, balsa powered airplane. Once I am ready to fly the thing, how do you go about trimming the plane? I’m confused because since the wings, and rudder are glued in place, how do you make adjustments? Thanks in advance.

Well…I have built a handful of free flight planes before. What I have always done was make sure the wing and tail surfaces are as straight as possible. I then angle the rudder slightly to counter the torque from the rubber band/ prop. The instructions in most kits will tell you how much to angle the rudder.

Once everything is glued… I take two sewing needles and place them in the middle of each wing tip. Hang the model by the needles, and balance it by adding or removing weight in the nose.

Good luck!

Thanks TAdan. That was some very useful information. However, I have also read, that you can adjust the “thrust line” of the propellor shaft (down 3 degress, and either right or left 3 degrees) instead of angling the rudder. Have you had any experience adjust the propellor shaft? I like your idea of changing the rudder, but wanted to know which method you preferred more. Thanks again.

I have never tried adjusting the prop. I have always adjusted the rudder.

And as I think about it, after one or two hard landings whatever adjustments you made to the prop might not matter, hehe. They tend to go in nose first.

I always try and fly my models in tall grass and without the undercarriage. Ive had a few cartwheel after the undercarriage hits the ground.

Tadan, what you said makes sense. Thanks for the great inputs!

I would make the suggestion that the very first thing you want to do is to check that the models Center of Gravity (CG) is exactly where the plans say it should be. If it isn’t, try to get it there by adding weight to the light end of the model until it is (use old fashioned modeling clay) because if you don’t, 95% of the time no amount of fiddiling with the control surfaces will correct the problem.

Trimming a free flight model is a bit of an art-- more involved than I can cover here. Many free flighters use small tabs on the flying surfaces to allow for trimming. Others make the control surfaces moveable, and use small pieces of metal (i.e. soda can) as hinges- you can adjust the surface, and it will stay where you put it. Still others make the incidence of the stab adjustable. An adjustable thrust button is also a must in many cases-- it allows you to adjust the thrust line to get a decent climb without a stall.

I’d recommend checking out the Small Flying Arts website. (a google will find it.)

Also, the books on building and flying rubber powered models by Don Ross are very good.

I hope your model isn’t a Guillows kit-- they are notoriously bad fliers. Decent scale models, bad fliers. The wood is heavy, and there’s way too much structure.