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Motocalc Recommendation

Old 10-31-2003, 01:50 PM
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viper6
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Default Motocalc Recommendation

I have a hand launch glider that I am converting to electric glider. I used motocalc to figure out the powertrain. It recommended a GWS 280 geared 5:1 with an 11X9 prop on 8 NIMH 720mah batteries.
I have a GWS 280 geared 5.33:1 and an 11X8 Graupner CAM folding prop.
I am wondering...
Are motocalc recommendations reliable?(Do they work)
Is the prop too large for this configuration?
Is 8 cells too much?

The all up weight should be approx. 14 oz
The wing is an Eppler 205 w/ 288 sq.in.

Thanks
Old 10-31-2003, 03:32 PM
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Matt Kirsch
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Default RE: Motocalc Recommendation

I punched up the numbers. Looks good to me. 2.5 Amps is no problem for the 280 motor. 5.8 ounces of thrust in a 14oz plane is a little light, but you should be able to manage a reasonable climb. The runtime is phenomenal!

You can get a better thrust-to-weight ratio by using an 8-cell pack of 300 or 370 mAh NiMH cells. They're 2/3 AAA, but are closer to half the size and weight of the 720's. The cells I'm talking about are like the Gold Peak GP37AAAM cells sold at dynamoelectrics.com. I bet you can get a custom pack made at cheapbatterypacks.com.
Old 10-31-2003, 05:36 PM
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Dr Kiwi
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Default RE: Motocalc Recommendation

Hi Viper and Matt - It is possible that the thrust might actually be better than that calculated by MotoCalc. I haven't used an 11x8 folder, but in my crude but 'real world' testing, my 280 geared 5:1, on 8-cells:

with an 11x5.5, 3810 rpm, produced 230g (8.1oz) static thrust @ 2.8A (29W)

with an 11x4.7, 3480 rpm, 256g (9.0oz) static thrust @ 3.2A (33W)

with a 10x4.7, 3780 rpm, 220g (7.7oz) static thrust @ 2.7A (27W)

on 7-cells, with the 11x4.7, 3210 rpm, 214g (7.5oz) static thrust @ 2.7A (24W)


Cheers, Phil
Old 11-02-2003, 07:36 PM
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viper6
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Default RE: Motocalc Recommendation

Thanks for the confirmations. I am rebuilding the fuse to accomodate the larger battery speed controller and motor mount. Hopefully I can arrange the gear so that I can use the battery to balance the CG so I don't have to add weight to balance.
Thanks,

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