View Full Version : What Folding prop and size to use?

02-24-2006, 11:25 PM
Having just jumped into the arena of motorized sailplanes, I have all kinds of questions. Right now my first.

I purchased a 6lb sailplane that came with a tin can 550 motor, it had a 9X5 prop. Since they are far and few between I bought a Power 25 with a 5mm shaft and stepped up to a 3s 2100mAh LIPO and yes a new charger. That first step is a doozy!

Of course I got no recommendation with the motor.

I can't seem to find any info on just how to figure what folding size prop to use and where to get it.

I'm sure someone knows, HELP! Please!

Thanks ahead of time.:rolleyes:

Jeremy Z
02-24-2006, 11:30 PM
Even though this is a beginner's question, it is a beginner's sailplane question. (not many of us use folding props on other than sailplanes)

You'd probably get better response if you posted it over in that forum.

Be more specific about which motor you bought. Is it the E-Flite Power 25? There should be data in the packaging with the motor, and if not, it should definitely be available through www.horizonhobby.com (http://www.horizonhobby.com). (or just give them a call) Make sure your battery will support the highest discharge that motor is capable of pulling. It may not be. (what's the max discharge rating of your LiPo? 6C? 8C? 10C? 15C? 20C? It makes a huge difference.)

Don Sims
02-25-2006, 01:21 AM
I'll drop it over in the sailplane forum for yea. Six lb sailplane with a 550 motor. You sure about your weight??

02-25-2006, 10:28 AM
Thanks guys, I thought I had pushed the "Beginers Buttin!":D

03-01-2006, 07:36 AM
How big is this sailplane? Is it made out of lead? On a power sailplane, you would be better off with Nicad or Nimh, cheaper and can push for a high drain capability, up to 30 C discharge.

Please restate the sailplane info and motor.

03-29-2006, 01:02 AM
The plane is a 2.5m mini Discus. I have a Power 25 eflite, 40A BEC, Power 20 3s Polyquest.

The box said it was 6 lbs.

Don Sims
03-29-2006, 01:31 AM
Highly improbable it's that heavy. If you have a food scale, try weighing it.

03-29-2006, 12:58 PM
With everything in and on the plane it weighs in at just a little over 4lbs.

Sky Sharkster
04-01-2006, 12:00 PM
To Catchinathermal, I checked the specs on the E-Flite 25 on the Horizon Hobby site Jeremy posted: http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLM4025A
They list the Kv as 870, the continuous current as 32A and max burst current as 44A for 30 seconds. Typically gliders are flown full power to climb, and with a 4 lb (plus) glider you will have to run it more than 30 seconds. That would put you over the max for both the ESC rating and likely the battery discharge rating. Result; Meltdown. My suggestion it to invest in an 8 cell (or two) 1500-2000 mAH NiMH. The climb may not be as fast, but you won't melt anything. Save the Lipo for a model that doesn't have those kinds of current-draw demands. This would be almost anything except a powered glider. I know it's a disappointment to hear this but if you cook the ESC you will have a very bad day. That Battery/ESC/Motor combo will be fine in an aerobatic or sport model that's "cruising" at one/half throttle with the occasional burst. Lipos are great in this kind of application but they are not happy with full-power, max-discharge runs. Not yet, anyway.
The recommended prop size range is 11" x 8" to 14" x 7". For 9.6v batteries (8 cell NiMH or NiCad) I'd try a 13" x 6" or 13" x 7". Just power up (full throttle) and let the glider start out slowly. It won't climb like a rocket at first but soon it will build up airspeed and begin to lift the nose. Don't let it stall, you will have to be ready to apply "down" elevator-GENTLY- to avoid this. About 30-40 degrees nose-up until it's high enough, then cut the power and enjoy! You should get a least a couple of climb-outs and still have plenty of reserve for thermalling and landing. If you're worried about the servo drain, disable the BEC and add a RX battery, on a plane this large it's probably a good idea.
Good luck!

04-01-2006, 08:49 PM
Thanks, as I haven't done much since the original post, I'll call the dealer and see what kind of a trade I can do. No more "Powered" Planes for me, from now on I will stick to Air "Current!"

Thanks again!