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Sport Planes (Formerly I/C & Gas Conversion) Discuss I/C or Gas Conversions, Aerobatic Planes and Sport Aircraft

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Old 02-05-2012, 01:10 AM   #1
spencer k
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Default GP Lancair 60 size electric conversion!!

Hi all, please help with some input.
Im doing extensive mods to this airframe, and would like to do this guy electric from the get-go.

Mods:
Shortened the wings to 68" (scale wingspan) and added nice scale winglets
Adding retracts
I glassed the wings, repaint fuse, and control surfaces
Obviously going electric here

At this time, i am estimating the AUW when completed to be 140-150oz, and 550-575sq in of wing area, yielding a 39.25 oz/ sq foot wing loading. I am looking for sport/scale flying with top speed in the 80 mph range. Keep in mind this airframe is slick, so im assuming it wont be too terribly power hungry.

I have plenty of 40C turnigy 6S 5000mah packs i would like to use (out of my trex 700e)

I think i can only get away with a 14" prop due to ground clearance.
Can you guys please give me a thrust value or watt value i should aim for?

Thanks in advance!!!
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Old 02-05-2012, 01:24 AM   #2
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Originally Posted by spencer k View Post
Hi all, please help with some input.
Im doing extensive mods to this airframe, and would like to do this guy electric from the get-go.

Mods:
Shortened the wings to 68" (scale wingspan) and added nice scale winglets
Adding retracts
I glassed the wings, repaint fuse, and control surfaces
Obviously going electric here

At this time, i am estimating the AUW when completed to be 140-150oz, and 550-575sq in of wing area, yielding a 39.25 oz/ sq foot wing loading. I am looking for sport/scale flying with top speed in the 80 mph range. Keep in mind this airframe is slick, so im assuming it wont be too terribly power hungry.

I have plenty of 40C turnigy 6S 5000mah packs i would like to use (out of my trex 700e)

I think i can only get away with a 14" prop due to ground clearance.
Can you guys please give me a thrust value or watt value i should aim for?

Thanks in advance!!!
Sure can, take a look:
Thread on 70 size glow engine conversion to electric
http://www.wattflyer.com/forums/showthread.php?t=45222

Hacker 6S2P A123 powered Models
http://www.wattflyer.com/forums/showthread.php?t=44686

Voltman Batteries (A123 Supplier in USA)
http://www.wattflyer.com/forums/showthread.php?t=62177

I've got two Hacker A50-12S motors swinging a 14X10 APC-E prop that put out about 1100 Watts or so. They turn that prop at 7950 RPM with a 6S2P A123 battery pack.

If you go to the Hacker motors, check out the A50-14S along with your 6S LiPo battery and a 14X12 APC-E prop. Motocalc predicts this setup will turn that prop at 7700 RPM, pulling about 1KW out of your LiPo. A Hacker A50-12L motor would be a little better, but that doesn't match with your 6S LiPo and prop diameter limitation. With the wing loading you've got, you don't want to underpower your model.

Check it out:
http://www.aero-model.com/MotorAppli...essAppChart301 (Scroll down to the A50 series motors)

Also, if you've not run across it yet, check out www.motocalc.com. This is a computer program where you select your motor/prop/battery/model wingspan, area and weight, and it gives you an idea on how it will fly.

Free for 30 days, then $39, and IMHO, worth every penny.

You'll likely find out from motocalc that this model has a very high stalling and flying speed, so you will need a motor that can turn a high pitch prop at a rather high RPM.

DennyV
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Old 02-05-2012, 01:28 AM   #3
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i agree, however motocalc said it could not give me any suggestions for my scenario.
first of all how many watts per pounds should i be aiming for?
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Old 02-05-2012, 01:43 AM   #4
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Originally Posted by spencer k View Post
i agree, however motocalc said it could not give me any suggestions for my scenario.
first of all how many watts per pounds should i be aiming for?
IMHO, for a model with a pretty heavy wing loading, you don't want to go much below 100 watts per pound, and it would be good to aim for 150 watts per pound. So for the worst case of a 10 pound model, that's 1500 watts.

That's only part of the project though. Also involved is the prop blade pitch speed in MPH, something that motocalc provides. You can have a model with 150 watts per pound, and a prop with such a low pitch that the pitch speed in miles per hour is less than the flying speed of your model. That's something motocalc will flag, and probably did for your setup.

For your model, you'd need a prop airblast blade pitch speed somewhere in the 80 MPH area, something a 14X12 prop turning at about 7700 RPM will provide.

Also with motocalc, look at the "Rate of Climb" figure for your setup. Anything over 2000 Feet per minute is a good figure.

Since you've apparently got motocalc, try plugging in these values for your power system:
Motor, Hacker A50-14S; Battery 6S 5000 Mah LiPo; Prop, a 14X12 APC-E prop. When you get into these higher powered models, IMHO quality components start to get important. Somewhere around 1/3 of the $$$ for the model, 1/3 for the power system, 1/3 for the radio is something close. Hacker motors are expensive, but they will perform per their specifications. (I've got 8 of them, from an A30, through two A60 sized 3KW units.)

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Old 02-06-2012, 04:50 PM   #5
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A fellow flyer here converted his Lancair to electric this past summer. He uses a Scorpion 4020-16 on 6S turning a 15/8/3 blade Emp prop for approx 1100 watts. The plane flies very nice, is slightly faster than it was with the original 4 stroke. He used a 12/6/3 Mas on the 4 st, took most of the field to get airborne. Now he uses less than half, his plane is right a 10 lbs if i remember right. FWIW flying barely
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