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T-bird free flight conversion

Old 03-20-2011, 08:41 PM
  #1  
F7U
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Default T-bird free flight conversion

The concept was to build an old-school free flight and avoid the issues to fuel-drenching and chasing around for miles. The T-bird is an old favorite, known for stability and good performance. Also, my dad built one when I was about 7 years old and that plane really impressed me, as went OOS on its first flight.

Project started with a laser-cut semi-kit from BJModels.....great cut quality and good balsa. The motor is a 3000KV brushless, allowing use of a "scale" 6" prop (low drag at glide). Battery is a 2S, 370mA. Control is throttle and rudder, no elevator. Airframe modifications limited to stronger center wing joint (known weakness with the T-birds), widened pylon (to fit the battery), and modern covering (GOLDBERG lite). Measured thrust, static, is 4.5oz. Thus, strong climb but limited duration. Fuselage coated with a couple light sprays of laquer, with sanding in between coats. Weight, RTF, is 5.7 oz (the plan lists 5oz as free-flight weight) Suppose the savings in weight from .049, timer and two coats of dope almost made up for adding the micro rc unit and the battery. CG came out just right (lucky!).

Flown this plane twice. From glide test, added a .06" shim under the LE of the stab, as showed a slight stall. Low-power flight was a non-event....very stable (but still tried to give it elevator....old habit). Full-power climb really surprised me. Very quick acceleration and near-vertical. This plane really knows how to climb. Only correction from 1st flight was to add more movement to the rudder, as wanted the ability to spin it down in case of a thermal. So, flight plan is a gentle launch with about 1/4 throttle, roll on to full and it seems to know what to do. Only remaining trim issue is that after about 5 seconds the plane is almost vertical and may start turning on its back. Adding rudder just causes a wing-over. Suspect that is why the plans show the stab should be at a tilt? That may result in the spiral climb that the free-flighters trim to. For now, I can just roll the throttle off and the plane transitions well to a glide. Then just trim for a nice circle.

No in-fligh fotos yet, but during glide, there is plenty of time to set the transmitter down, get a sip of water and retireve the camera. Battery capacity good for 3 to 4 zooms to high altitude.

Would appreciate any input from some free-flighters about trimming for a spiral climb. That would really complete the project.
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Old 03-20-2011, 11:15 PM
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Forge
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F7U,

Really nice. I especially like the transparent yellow covering...very cool.

And I like the idea of being able to sip a cocktail while flying.

Good flying.

Forge

ps. what is the wing span on the plane?
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Old 03-20-2011, 11:36 PM
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kenchiroalpha
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Hi
Outstanding
Pleased to meet you
Thats quite a wonderful job you have done
Shes absolutely gorgeous
Some tips for trimming F/F aircraft
http://www.rc-airplane-advisor.com/r...ee-flight.html
Take care
Yours Hank
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Old 03-21-2011, 12:04 AM
  #4  
F7U
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Hank,
That is a great website you provided. Great info.
Appears "high thrust contest-type" free flights have some special trim requirements (been researching this subject on this very rainy Sunday)
Appears the climb requires a 3 degree left thrust to the motor, coupled with a washout on the right, outer wing panel. Supposed to give a right, climbing spiral. However, a thrust of 1:1 does not really qualify as "high thrust". Some hot 1/2As privide 12oz of thrust.
Free flighters are the real masters of model planes!

Interesting you mentioned the Pilatus Porter. I build a scratch one from 2X plans for a rubber-powered. Very light, 50" span. Really like both the real plane and the model.
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Old 03-21-2011, 12:10 AM
  #5  
kenchiroalpha
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Talking

Originally Posted by F7U View Post
Hank,
That is a great website you provided. Great info.
Appears "high thrust contest-type" free flights have some special trim requirements (been researching this subject on this very rainy Sunday)
Appears the climb requires a 3 degree left thrust to the motor, coupled with a washout on the right, outer wing panel. Supposed to give a right, climbing spiral. However, a thrust of 1:1 does not really qualify as "high thrust". Some hot 1/2As privide 12oz of thrust.
Free flighters are the real masters of model planes!

Interesting you mentioned the Pilatus Porter. I build a scratch one from 2X plans for a rubber-powered. Very light, 50" span. Really like both the real plane and the model.
Hi
Happy to be of help
My dad and i used to build and fly F/F aircraft, its what got me into the hobby in the first place
Still have many F/F's and they get much use with more to come in the future
Heres another wonderful site i think you may find of interest
http://www.ffscale.co.uk/
Take care
Yours Hank
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Old 03-29-2011, 06:18 AM
  #6  
F7U
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Thermal Flight!
Took the T-bird out Sunday morning, after making some recommended trim adjustments: left and down thrust and washout in the right, outer wing panel.
Under full throttle, makes a nice, steep spiral climb. Can easily adjust the rate of spiral with a bit of rudder trim.
Credit for the trim tips from a real free-flighter and some internet research.
On fourth buzz up to altitude, the ESC cutoff hit, so only got about 2/3s the altitude. This time, the plane seemed a bit unsettled on the glide. Then realized it was climbing. Wow, was really neat watching it "glide" back up to high altitude.
The entire flight control consisted of occasional rudder trims. Felt more like a spectator than a pilot. Even got out of the habit of giving elevator inputs. These old free-lights are aerodynamic oddities, but they sure are stable.
Anyway, a great diversion from my more typical park fliers.
Try one!

CORRECTION: Plans and laser-cut semi-kit form BH Plans. Check out the great selection.
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