Hey guys!

I have an old Thunder Tiger Gull 1900 powered sailplane I'm hoping to set up just for fun flying, and for aerial photography.

Here is the plane in question:


Since that photo, I have re-covered the wing in Monokote transparent, it looks pretty awesome with orange on the top, blue on the bottom, and when the sun shines through the wing, it looks awesome sea-green color!

I have 2 brushless motors I was thinking of using. I also have differnet batteries. Can you guys help me pick which setup is best?

My plane has a 66" wingspan, average chord of 7.5".

I will list them from lightest to heaviest. This is not counting the camera, which is an additional 4.8 ounces.

Light setup:
This motor:
https://www.unitedhobbies.com/UNITE...?idProduct=2106
With 30 amp ESC and 1300 mAh 3S 15C lipo
AUW: 30 ounces
Stall speed: 14.8 MPH
With 10x5 prop, approx. 20 Amp draw yields 32 oz. thrust, for about a 1:1 thrust to weight ratio.

Medium setup:
This motor (same as previous one):
https://www.unitedhobbies.com/UNITE...?idProduct=2106
With 30 amp ESC and 2200 mAh 3S 20C lipo
AUW: 34 ounces
Stall speed: 15.8 MPH
With 10x5 prop, approx. 20 Amp draw yields 32 oz. thrust, for about a 0.94:1 thrust to weight ratio.

Heavy setup:
This motor:
https://www.unitedhobbies.com/UNITE...?idProduct=2128
With 40 amp ESC, 3 amp UBEC, and 2200 mAh 3S 20C lipo
AUW: 38 ounces
Stall speed: 16.7 MPH
With 11x7 APC-TE prop, approx. 25 Amp draw yields 41.7 oz. thrust, for about a 1.1:1 thrust to weight ratio.

Now, with the camera's weight included:
Light setup: AUW 34.8 oz, stall speed 16 MPH, thrust to weight 0.92:1
Medium setup: AUW 38.8 oz, stall speed 17 MPH, thrust to weight 0.82:1
Heavy setup: AUW 42.8 oz, stall speed 18 MPH, thrust to weight 0.97:1

So which setup do you guys think is the best compromise for photography use?

I kind of like the sound of the medium setup, even though the thrust to weight ratio is the worst, I like the long runtime I would get with that smaller motor and larger battery, plus I'm not too worried about the thrust, this isn't a 3D plane or anything!

I don't really know much about sailplanes, what's your advice?

For what it's worth: This plane was originally heavier, this plane originally used a Speed 600 sized brushed motor, a rather heavy AM receiver, a clunky old speed SWITCH (it was on/off only), and... NICAD BATTERY PACK! You know, those 7.2 volt long packs.
The plane was close to 60 ounces in its original form... Yuk... I don't know how it even flew, it practically needed a headwind just to be able to launch. It is pretty amazing to think that if I use my lightest possible setup, I could have this plane weigh about half what it originally weighed!

Your light setup is pushing the limits of your battery.
Either prop down to get the amps down, or go with the medium setup.

Also, I predict that your light setup will not even deliver 20 amps. Even if it does, the voltage will lag behind, giving you less wattage than the medium setup.

In other words, the larger battery with the higher C-rating, will be more powerful and last longer than the smaller battery with lower C-rating.

Hmm thanks for the warning on the battery. I was afraid the smaller battery wouldn't be practical. Ah well I can use the larger one, it's not THAT much heavier.

What do you think about the 2 different motors?

Hey, I just realized I got the working current rating wrong on that motor, it is rated 22 amps not 20.

So, here is revised figures for the "medium" setup:

Without camera:
AUW 34oz, Stall speed 15.8 MPH, reccommended prop APC-TE 11x5.5, pitch speed 40.6 MPH, thrust 36 oz, thrust to weight ratio 1.06:1

With camera:
AUW 38.8oz, stall speed 16.9 MPH, with same prop the pitch speed and thrust are the same, thrust to weight ratio is 0.93:1

Doesn't that look pretty decent, good enough to climb to altitude then glide as much as possible?

I figure if I was drawing 22 amps continuously, that would only give 6 minutes of motor runtime with the 2200 mAh battery. I am guessing that should be enough for at least 15 minutes of flight, if I can glide more than half the time. What do you guys think?

Whatever setup I use, it is darn sure going to fly better than before, when it was so heavy I could not get it to climb at more than a 15 degree angle or so.

In fact, last time I tried to fly this plane in its previous setup, AUW was 44oz, with brushed motor and gearbox, an AM radio and 8.4v NIMH battery, it was a calm cool afternoon and I actually couldn't get the plane to climb. I fought with it, trying to get altitude, but it just kept wanting to stall, and it maintainted about the same altitude (only about 30 feet above ground) for a while until the batteries went dead and I had to bring it down in the bushes! That was an unpleasant experience that I hope to never do again. And yes the CG was set as per the instructions. I was able to gain altitude the first time I flew it, but I think that is because there was WIND to help me. This plane just sucked so bad in its previous setup.

I couldn't view the link.

And, yes. Your setup sounds much better than before.

You may want to test fly it without the camera first. Just to get some idea of how much more you can load the plane up with.