|Jul 12, 2004, 01:59 AM|
Take Didier's Funtana Foam Plans and Balsa ..
And build with wood over the plans, following them very loosely ..
Then I scrounged whatever was lying around -
MP Jet 25-35/20, CC PH 25, 2x Pico + & 1x HS-60 for aileron.
Plan on trying a 10cell NiMh as it looks like I need weight in front to balance.
If it flies at all I might put LG on and try a Lipo ..
I've got it finished just enough to see if it will fly .. this should be interesting.
|Jul 12, 2004, 12:31 PM|
Yes the wing ribs seem weak but no problems yet.
It is based on the Tom Hunt modelairtech.com "built only from sticks" method.
I just flew it and it flies great, although on first flight it went through a cartwheel because of my cowardly 1/2 power launch the first time.
A few cracks in various places in the fuse resulted - CA'd and 2nd flight got it all trimmed out.
12.8 oz w/o batt.
Hovers at only *full throttle* ( haha ) on a 10 cell NiMh, 10x7 on the MP Jet 25/35-20
Was really a science experiment to see if slapping some wood together would produce anything resembling a 3D plane.
I'd like to do another but with flat plate wing and see how it does.
|Jul 12, 2004, 11:37 PM|
I think I'll need to get a lipo for it; nimh makes it too heavy to throw around the sky.
I had to change the impedance of the 1050 mah HeCells to match the performance I see.
MotOpinion - My 3D Plane NiMh
5669ft above Sea Level, 30.17inHg, 80°F
Motor: MP Jet AC 25/35-20 3850 .05; 3850rpm/V; 1.34A no-load; 0.1 Ohms.
Battery: Hecell 1050 .02 imped. .75 oz; 10 cells; 1050mAh @ 1.2V; 0.02 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: APC 10x7 3:1; 10x7 (Pconst=1.11; Tconst=1) geared 3:1 (Eff=95%).
Airframe: My 3D; 365sq.in; 20.1oz; 7.9oz/sq.ft; Cd=0.039; Cl=0.16; Clopt=0.35; Clmax=0.81.
Stats: 123 W/lb in; 77 W/lb out; 18mph stall; 27mph opt @ 48% (22:09, 94°F); 40mph level @ 67% (11:24, 103°F); 1521ft/min @ 39.9°; -374ft/min @ -9.1°.
Possible Power System Problems:
The estimated steady-state still-air battery temperature at the hands-off cruise airspeed and throttle setting (greater than 200°F) is higher than the suggested maximum temperature for this cell type (140°F). This could result in battery pack damage unless adequate cooling airflow is provided and/or run times are kept short. A lower current would also decrease the battery temperature.
Current can be decreased by using fewer cells, a smaller diameter or lower pitched propeller, a higher gear ratio, or some combination of these methods.
Power System Notes:
The full-throttle motor current at the best lift-to-drag ratio airspeed (18.8A) falls between the motor's maximum efficiency current (9.4A) and its current at theoretical maximum output (33.6A), thus making effective use of the motor.
The static pitch speed (49mph) is within the range of approximately 2.5 to 3 times the model's stall speed (18mph), which is considered ideal for good performance.
With a wing loading of 7.9oz/sq.ft, a model of this size will have very sedate flying characteristics. It will be suitable for relaxed flying, in calm or very light wind conditions.
The static thrust (21.4oz) to weight (20.1oz) ratio is 1.07:1, which will result in extremely short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and vertical climb-outs. This model will probably be able to perform a hover or torque roll.
At the best lift-to-drag ratio airspeed, the excess-thrust (13.1oz) to weight (20.1oz) ratio is 0.65:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.
This analysis is based on calculations that take motor heating effects into account.
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