YACBL - yet another Corsair build log
I successfully (as in, back in one piece) maidened my GWS Corsair today.
LittleScreamers DeNovo motor
CC Thunderbird 9
GWS 8040x3 prop
3 HXT-900 servos
Covered with Coverite Microlite
No landing gear
I'll cover the more interesting aspects of the build.
I ended up trying two more power systems:
Castle Creations Thunderbird-18
KD-20-22L, APS SF11x7, GWS 1060x3 (3 blade)
HXT-28-30B, GWS 1060x3 (3 blade)
AUW is about 17.5 oz with either motor. It looks like this plane needs at least a 50g motor to balance properly (may be 40g + battery in the cowl)
- The motor has enough power for a scale flight, but not much more. I plan to try a 9050 when I get them. This will push the motor/ESC closer to the limit, but should still be ok. Long-term, I may replace the motor with a 150-180Wt low-kv motor from UH turning a scale prop.
- If you want to try keeping the model light, Hextronic 24g blue wonder is a better motor, and a much better deal.
- The model ended up somewhat tail-heavy. I guess I'll need to move the battery pretty much into the cowl. That did limit my flight time, as I didn't want to risk losing the plane.
- To the extent I tested them, the controls were responsive, and the model flew well - none of the scale behavior at lower speeds.
The build was reasonably close to stock. The major differences :
- Use of Gorilla glue where epoxy was recommended
- I used full sleeves for aileron rods. I did not bend the rods; just pressed them into the grooves, put in some Gorilla glue and covered by masking tape to keep the Gorilla foam from getting all over the wing.
- I set up tail servos before gluing the fuselage together. That made it a lot easier.
- I used Coverite Microlite (a British product, sold by Tower Hobbies) to cover the model. I didn't do too good a job - this was my first experiment with coverite on foam. I'm very pleased with the results. It added quite a bit of tensile strength to the foam at the cost of app. 15 g. total.
Found a design flaw when checking the operation of the ailerons. At about 1/2 of full deflection the torque rod head would hit the fuselage. Cut off some foam to let it move freely. Good thing I didn't have the fuselage glued together at that point.
- Full aileron rod sleeves and use of Gorilla glue to put them in. The glue foamed up and produced light and strong foam-like material around the rods. I believe the surrounding foam will fail before the glue does. There is absolutely no binding, the single HXT-900 servo has no problem moving the ailerons.
- Setting up tail servos before joining the fuselage. I was able to keep the control rods straight. I tilted the rudder servo to prevent the rod from bending. I think I could have used HXT-500 for tail surfaces.
- Use of Coverite.
What didn't work:
Mostly the motor - not enough power for me. The motor does look like the scale planetary transmission the real plane had. I was thinking of buying a scale radial engine model and sticking it behind the motor. That would look about right.
The weakest place for that model seems to be the tail and tail surfaces. I reinforced the elevators with pieces of 10x0.5 carbon strip. The tail itself flexed a bit too much before I covered it, feels ok now.
- As designed, torque rods don't have enough clearance to move freely
- Tail section feels weak, should be reinforced, esp. if no glassing/covering is intended.
- There isn't much clearance between the tail servo arms and the rods connecting the aileron servo to the torque rods, esp. if you use e-z connectors on servo arms. Next time I will set the aileron servo deeper into the wing, that should provide enough clearance.
Replaced the motor/ESC with a Thunderbird 18/KD 20-22L APS SF 11x7. This setup used app. 14 amp at WOT, app. 6500 rpm, lots of trust.
I liked that setup a lot more. For one,the CoG went where it should have been, the plane became a lot more stable. The extra power didn't hurt either. That etup was producing app. 6400 rpm at 14A (the numbers may be slightly off. I'm beta-testing a new wattmeter product for a friend)
The controls are effective, but not very quick. I have about 10mm deflection on ailerons and elevator; rudder is about 30 mm. The roll rate is about one roll per second. Full rudder does cause it to turn, sort of. Elevator is effective.
Unfortunately, on the third flight I failed to give it a hard enough toss. The Corsair took that opportunity to exhibit some scale-like behavior - dropped a wing and nosed into the ground. At about half throttle. Of course, this simply had to happen when my son (7) was watching.
Broke the motor mount stick, tore off the plastic squares the cowl screws go into. Glued the stick together (we'll see how it holds), used Gorilla glue to fill the holes left by the plastic squares. I didn't like these squares anyway.
Next to try is an HXT28-30B with a GWS 1060 3 blade. This looks almost scale. Static test shows app. 18A for 7400 rpm at full throttle. This is more or less what I want.
That's too bad about the crash. I haven't hit mine on the ground yet but I've oddly enough had about as many different combinations as you've had. I had three different aileron set-ups in the first 6 flights! :)
Thanks. Could have been worse. I credit the covering and possibly the weak motor mount.
Three different aileron setups have me intrigued. Two are obvious, what was the third one? What power systems did you try?
I also had a 400XT in it with an 8x6SF prop. Loved it. But I had a Unied Hobbies motor of some sort laying around, so I swapped it in. Didin't like it because I had to go with a 4" pitch to keep the amp draw in range. I went back to the 400Xt and 8x6 like I have in all my Alfa and GWS planes. Love it!!
Oh, that's right, you can put the servos on top of the wing, too..
I think I just found the setup I like a lot(nice part about working from home - I can grab a plane and go to the nearest township park, about 5 minutes, for a flying lunch)
HXT28-30B (1050kV), GWS1060x3. At full throttle the voltage is about 10V, 17A, 7000rpm. Motorcalc predicts static thrust of 27oz and it feels about right.
This is about 3 amp above the official rating for the motor, but I've been pushing 16-18A through it for a while now.
Total cost of the plane:
The kit is $27
Berg rx, $32
3 HXT-900, $12
CC Thunderbird 18 ESC, $25
LiPo, HXT-1000 (eventually.. waiting for the replacement) $16
Misc (prop, hinges, pvc tube, glue, Coverite) $20
App. $140 total, with about $90 of reusable parts. Not too bad. Could probably go just under $100 with GWS motor/ESC and a Corona receiver.
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