Electric help required

[Dougie Swan 1]

Hi

I have just started a build of a Porterfield Collegiate, it was designed for a brushed motor with a reducer but I want to fit a brushless motor but as I am a returning modeler with no experience of these motors can anyone offer some advice and /or recommend a suitable motor, speed controller and battery size I would need

The model is 69" span, its an old astro flight kit

Thanks

Dougie

[Bruce Collinson]

Dougie,

Welcome back to the fold!

You could do much worse than speak to George Worley who is 4Max, who will be able to specify and supply the entire power train and all of the accessories needed to hook it up. My experience of his equipment is that although presumably mainly Chinese, it is robust and I particularly like his LiPos. He is a helpful fount of advice and information.

You could probably undercut him at somewhere like Hobbyking but penny wise ....

BTC

[kc]

4Max have several sections of their website showing recommended setups. Worth looking for a similar type model with comparable size and weight. Note that similar sorts of model there have similar span but very different weight and therefore different sizes of Lipo and motor. Lots of useful info on that site.

[Andrew Calcutt]

1000 watt motor and 4 cells turning a 14 inch prop should do nicely,overlander have good range of motors.

[Simon Chaddock]

Dougie

Outerzone have a plan and a 'period' review of the Astro Flight Porterfield Collegiate.

The original kit came in at 63 oz although it was suggested that a heat shrink film would save up to 8 oz over the cloth and dope used.

A Brushless motor and LiPo instead of a geared brushed and NiCd would save some more weight so my guess is it would be realistic to assume it might be near to 48 oz or 3 lbs particularly with modern lightweight RC gear..

At that weight a 450 Watt motor would give it a 'lively' performance with a power loading of 150 Watts/lb. It would cruise 'sedately' with a corresponding increase in flight duration on less than half of that figure.

I hope this helps.

Edited By Simon Chaddock on 04/06/2020 22:18:32

[PatMc]

Posted by Andrew Calcutt on 04/06/2020 21:30:40:

1000 watt motor and 4 cells turning a 14 inch prop should do nicely,overlander have good range of motors.

That's about 8 or 9 times the power of the Astro geared motor the model was designed around.

A motor that will pull about 200 - 300W at full throttle when using a 12" -14" prop should give a scale like performance.

When looking for a motor ignore the power stated in the specification.
I'd suggest a motor weighing between 150g & 200g; this is heavier than necessary but will help with the cg, has a greater range of kv available than a lighter motor and will run cooler as it will be less stressed than a lighter motor. The motor kv will depend on the number of cells in the battery used, my choice on 3s would be 750 - 850kv & on 4s 550 - 650k, prop size between 12" & 14".

You can download two articles from OZ with build notes etc as well as two versions of the original plan via this link.

 

Edited By PatMc on 04/06/2020 23:15:41

[Dougie Swan 1]

Thanks for all the replies, they are really helpful

I have emailed 4max to ask for a setup that I can use

Dougie

[Richard Clark 2]

Posted by Dougie Swan 1 on 05/06/2020 16:52:52:

Thanks for all the replies, they are really helpful

I have emailed 4max to ask for a setup that I can use

Dougie

I agree with Simon Chaddock and PatMc on the power though I think Simon's weight may be a little optimistic. 450 watts will be more than ample but it's not grossly over powering it. And such a motor running at well under maximum power is more efficient than a smaller one working harder.

An advantage of electric over glow is that you can experiment on the ground with a wide range of propeller sizes, even without a 'wattmeter' (though they are useful). Just stop the motor after a minute or so and check it is not 'too hot' with a couple of fingers. 'Warm' is ok.