Electrify an ASK18 sailplane

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Terry Masters
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Electrify an ASK18 sailplane

Postby Terry Masters » February 25th, 2010, 12:18 pm

I have a Cliff Charlesworth ASK18 1/4 scale (4 metres) Sailplane and wish to add a pylon on top for electric power take-off and climb to height. It weighs 9lbs at present and adding the weight of power pod, battery etc I anticipate a total of about 10 lbs.
What motor esc combination should I fit? I'm not after wild performance.
Terry Masters 2888

Simon Wright
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Re: Electrify an ASK18 sailplane

Postby Simon Wright » February 26th, 2010, 8:34 pm

Hi Terry,

I assume that you are considering a fixed pylon approximately on the CG position with batteries in the fuselage. The critical feature on powerpack selection with a pylon will be prop type and diameter. It is generally considered best to use as large a diameter as possible with fairly course pitch turning at low rpm. At 1/4 scale the pylon would probably be 10" or so allowing reasonably large 18" diameter props on a geared inrunner or low Kv outrunner. Folding props are preferred for drag reduction but the concern would be of fouling on the pylon on start up.

A decision needs to be made on how you wish to fly your model too. Aiming for 50 w per lb of aircraft weight would give a reasonable climb to altitude (11 lbs =550watts) running on 4 Lipo cells would give (550/14.8=37.8Amps)a fairly low current. If you discharged at a maximum of 20c you could use a 1900mah pack (37.8/20=1.89a/h) to give 3 minutes of full power climb. On a model of that size I would probably fit 5000mah cells to give just under 8 minutes of full power climbout.

Selection is a trade off between cost, duration, power etc. It may be worthwhile to look at a few catalogues and brochures for similar size models with electric power to find a good starting point.

Several on line motor calcuators are available, Drivecalc.de is very good for producing thrust figures and power curves but you have to figure out how it will work on your model in flight. Motocalc is available as a free trial version and this can be fed with your aircraft data to give in flight estimates of performance.

hope this helps

Si
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Simon Wright
Posts: 75
Joined: December 5th, 2008, 8:40 pm
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Re: Electrify an ASK18 sailplane

Postby Simon Wright » February 26th, 2010, 9:37 pm

Done some research.

A bit of guesswork gves this as a start point for a Low cost set up ?

In drivecalc this gives 40A at 79% efficiency, 2981g thrust and 73kmh max.

TR 42-50-B 600kv Brushless Outrunner $19.99
http://www.hobbycity.com/hobbycity/stor ... _Outrunner

Turnigy 5000mAh 4S 20C Lipo Pack $29.99
http://www.hobbycity.com/hobbycity/stor ... oduct=9177

Hobbyking SS Series 60-70A ESC $16.13
http://www.hobbycity.com/hobbycity/stor ... 60-70A_ESC

Folding Propeller 14x10 W/ Alloy hub 50mm / 5.0mm shaft $ 10.88
http://www.hobbycity.com/hobbycity/stor ... .0mm_shaft

About $76 or £50 plus shipping

You could run a larger – say 17 x 10” prop if you reduced to 3s 11.1v. 3168g thrust, 47A 75% efficiency.

ZIPPY Flightmax 4400mAh 3S1P 15C $21.21
http://www.hobbycity.com/hobbycity/stor ... oduct=6504

Simon
LMA2345 now that should be easy to remember!

Terry Masters
Posts: 6
Joined: December 5th, 2008, 9:07 am
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Re: Electrify an ASK18 sailplane

Postby Terry Masters » February 26th, 2010, 9:49 pm

Hi Simon,
Many thanks for your detailed response. Gives me plenty to think about and I anticipate making positive progress within the next few weeks.
Regards,
Terry.

Simon Wright
Posts: 75
Joined: December 5th, 2008, 8:40 pm
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Re: Electrify an ASK18 sailplane

Postby Simon Wright » February 26th, 2010, 10:19 pm

No Problems Terry. Good luck with your project.

Ps- Fitting the motor as a pusher with folding blades rearwards gets rid of the fouling problem. A slow brain moment stopped me from mentioning this previously. Just need to check the blade roots and pivot bar-spinner allow full opening.
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