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Dec 07, 2019, 02:06 PM
AMA 179-CD
According to BP Hobbies, Cheeta motors are made by Suppo according to their specifications. Note, all our Cheetah motors include engravings so you can easily identify your motor.
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Dec 07, 2019, 08:35 PM
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The empty weight of the Windfree is 28oz (800g), wo/Rx batt. Well within the design weight.

From looking at examples of motorized TD sailplanes it looks like a 22xx or a 28xx outrunner will do. Along with a sub-1000mAh 2- or 3s lipo flight battery. I can save a little weight and space by converting over to a Spectrum Rx from the old 27mHz Rx. I've got a copy of Motocalc and I'll crunch the numbers to see which motor and lipo combo gives the best performance w/ the longest run time (my usual approach to e-planes).
Dec 08, 2019, 07:48 AM
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This indeed will be a light woodie. I wonder what the wing loading will come in at? I like the idea of a sub 1000 mah battery. That’ll keep her light and still give you 3+ launches to ‘400’ ft.
Dec 08, 2019, 09:58 PM
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With a wing area of 555 in2 (3.85 ft2) and a weight of 32 oz the wing loading is some 8.31 oz/ft2. The Rx nicads weigh 100 gm (3.3 oz) and I don't see the outrunner/lipo combo weighing much more than that, so that all be close to the electrified weight.
I'm a big proponent of building as light as possible, extra ballast weight can always be added for wind penetration.
I'm toying with the idea of putting the flight lipo over the CG so that different battery weight won't affect balance.
After I get the Windfree project done, I have a vintage Oly99 that I want to electrifly...
Last edited by oly99; Dec 08, 2019 at 10:13 PM.
Dec 09, 2019, 08:41 AM
Registered User
The higher aspect ratio really cuts down on the wing area resulting in a larger than expected loading. The Oly99 you’re planning on building next will have nearly twice the wing area.

I like to give myself plenty of cg adjustment and preferably behind the stated cg, which is typically conservative.
Dec 09, 2019, 08:47 AM
Registered User
I wonder if there are any Windfree flyers who would share the cg location of their ships. This will help us position our components in our builds.
Dec 09, 2019, 06:02 PM
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I've got a 1970's vintage Oly99, ready to get a motor. I'm going to do the Windfree first.

On the Windfree: wing chord at root is 181mm. Distance back from the LE is 58mm (32%) for the center balance point, +/- 6mm. I usually mark my "best balance point" with tape or a scrap of Monokote.
Dec 13, 2019, 10:36 PM
Registered User
I got Motocalc and crunched the numbers, and it looks like the AXI 22xx 950 kV outrunner on a 1350 mAh 3s lipo wil give good performance and good flight times. I'll look at other motor/prop combos and see if I can get better run times.

As an aside, I've looked at the Oly99 and as it sits now, it's a porker. The wing area is a respectable 780 in2, but the weight is 1440 gm (50 oz). It uses full-size servos, a full size Rx and a big Rx battery, along with 6+oz of lead in the nose. It can lose a lot of weight. Motocalc suggests that it might need something like an AXI 28xx with an 11" prop-- heavier plane with more drag, especially with the undercambered airfoil.
Dec 14, 2019, 07:20 AM
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I wouldnít concern myself with run time. As long as your motor is rated for sufficient current to create a minimum of 100 watts/lb, youíll get at least 4 launches to thermal height. Probably more launches due to the light airframe. Iíd guess you could expect flight times approaching 20 minutes in dead air with the 1350 battery using multiple launches. You may even find that a smaller battery gives sufficient performance, such as an 3s 850 mah. I have used an 850 in my 48 oz Oly II and get at least 2 launches. Using the smaller capacity battery I need to monitor voltage closely since the battery voltage decline is rapid once the voltage begins to drop. Iím unsure if itís the particular battery or the lower capacity.

I wondered what the differences between an Oly99 and an OlyII were. I believe my OlyII has close to 1000 in**2 wing area , which would improve the wing loading over the 99. Iíve scratch built a second wing with the same selig airfoil Skybench uses on their OlyIIs with flaps. The ship flys well in calm weather with either standard or modified wing.
Dec 14, 2019, 10:14 AM
Registered User
Having flown RC aerial photography starting in the days of brushed motors and Nicads, I fret over run times more than I need to. And having the motor simulation program, it's fun to optimize things. Realistically, an 850-1350 mAh Lipo will work with the limited run times needed.

The Oly99 is a classic design and the OlyII is an improvement on it. I still use rubber bands to secure the tailfeathers on my Oly99.
Dec 14, 2019, 02:54 PM
Registered User
So your Oly99 is already built? Well saw the nose off it and install something like this in it. You’ll be happy! Easy peasy

That’s my OlyII winch
Last edited by Left Hand Slicer; Dec 14, 2019 at 02:55 PM. Reason: Addition
Dec 15, 2019, 11:04 AM
Registered User
I've posted this picture before, but it's my Oly 99 scratch built for electric. The other is my original kit built Oly 99 together with my dad and his Windfree. Picture from about 1975.

Dec 15, 2019, 07:18 PM
Registered User
LHS-- that 28xx motor is the ticket. For some reason, my Oly99 needed 4-5 oz of lead in the nose for balance. In addition to using heavy full-size servos, full-size Rx, and a large Rx batt pack. This was done at the time where I used lead buckshot epoxied in for noseweight. So I'm going to need to hack the lead out of the nose, and if I can't figure where the excess tail weight is, I'll need to lengthen the nose a little.
The Windfree looks to be a simple bolt-on conversion.

Jim-- those are two sweet Olys. Mine is finished in transparent Yellow, too.

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