In brief- I've got a 1/4 scale Ryson ST-100 Cloudster motor glider (scratch-built composite) 15' span & 28.5 oz./sq.ft. wing loading.
I also have a Plettenberg 370/40 A3, a NiCd pack consisting of 24 2000 mah cells & a future-30.40K ESC.
The scale prop should be 17.5" in dia. APC makes a 17/13. 18" is about all that clearence will allow.
I'm flying at 4700 ft. ASL.
Question - Will it fly on what I have????
How well?? Climb rate????
Is there a better prop size (other than 17/13) that will fit.
Should I trash it and start another project???

It'll fly. Assuming its got about 2400sq.in. of wing and weighs 430oz and using the 17x13. The motors pulling 40A and the batteries are good for 2.5 minutes. With these numbers it'll fly like a trainer with slow climbs. Could get a better picture with more specs.

Mike

How do you launch this thing? It's almost as big as a Cessna 152.

What more do you need?
I will try to provide any info that you need to better understand the situation.
Thanks for the reply.

Actual wing area, all up weight without the motor and natteries. How do you want it to fly? How long? Limiting factor's going to be the batteries, do you want to spring for different cells?

Mike

Thanks for the interest Mike!
The wing area is 2070 sq. in. (14.375 sq.ft.)
Weight w/o motor and batteries is estimated at 21 lbs.
This is a scale motor glider so it should fly slowly. It will be launched under its own power (ROG). I would like to reach +-600 feet AGL and shut down to look for lift. A couple of restarts from 100 ft. back up to 600 would be nice.

Different cells would be OK if it realy makes a biiiiig difference. I guess I'd rather see how it does with the cells I have before investing in more cash. It may turn out to be a dog!!!

Mike,
There is a picture of the plane in the Warbirds forum.
It is was made on 1/5/2004, Post #10. That's not Judy in the picture

That's some piece of work, looks good. Guess it is a little smaller than a Cessna. Below are some setups. The batteries are not going to be real happy (hot, be sure to provide some cooilng air) with any of them. I'd start with the 15x12 to give the batteries a break. Also, if I'm not mistaken the speed control has a maximum rating of 40A.

Prop Climb Curr Dur

15x12 414fpm 30A 4min

16x12 477fpm 34A 3.5min.

17x13 527fpm 39A 3min.

Have fun!

Mike

Mike,
The ESC is a Schulze Elektronik gmbh Future-32.40 (6 to 32 cells NiCd-NiMH 40/53A).
You are right! The ESC can handle 40 amps.
It looks like any of the props will get me to altitide +-600 ft. on launch and return from +-150 ft. about 2 more times.
I guess I'll use the 15/12 for flight and the 17/13 for show.
The cowl has three forward facing vents of 4 sq. in. each and two exits of 6 sq.in. each. Do you think that is adequate? I could add one more (non-scale) exit in the bottom of the cowl if absolutely necessary.
Would LiPo cells work in this application? Can you give me some indication of performance improvement?

You have restored my desire to finish the project.
Thanks a bunch,

Jim

Exit area for cooling should be a minimum of 1.5 times the size of the intake area. You're right on the bubble. Unless things are really out of whack, you won't hurt the motor in one run. Take it up once and see how hot things get. Sailplanes generally spend most of their time motor-off, so I wouldn't worry.

The only thing stopping you from using LiPolys is your wallet. Nowadays, we have high-current LiPolys so not only can you double the duration, you can cut the battery weight in half. For the same weight as NiCds, you can have four times the duration, perhaps five. You can run the bigger prop for a faster climb rate, and still make multiple climbs.

IMHO, the best deal in high-current LiPolys is the Kokam 1500 from Bishop Power Products. Each pack is capable of 12 Amps continuous, so three in parallel will easily run the 15x12 prop or the 16x12 prop. 4500mAh means more than double the run time. Reduced weight means a quicker climb rate. Add a fourth pack in parallel, and you can run that 17x13 prop for nearly three times as long as you could on NiCds.

But... They're expensive, and there are new, more capable cells coming out all the time. You might want to wait. To get the same voltage as 24 NiCds, you need at least 7 cells in series, maybe 8. Then you need three or four of these packs in parallel. At $17 per cell, 21-32 cells (depending on what you decide) is a pretty hefty chunk o' change

Matt,
Thanks for the help. I'll post some pictures as things near completion.
The big race is getting close so I'm going to be out of touch for awhile. Judy is making drops for some of the Iditerod mushers and we always help with our local "Race To the Sky" which starts in two weeks. Take Ironman, the Boston marathon and the Indy 500, add 'em up, and you still have 455 miles to go in the Iditerod.

Thanks again,

Jim

Not concerned with cooling the motor, it's the batteries that are going to get hot, got to get a load of air to them and don't put them near anything thats heat sensitive.

Mush!

Mike

Mike,
The batteries are under the cowl. One eight cell pack centered behind each cheek opening and one centered behind the opening straight below the prop. Eack pack (roughly 7" x 2" x 1") is held in a ventilated 60/61 T-6 Aluminum battery tray that is attached to the fire wall. The trays stick into the cowl 6.5 inches and the barreies can be loaded and unloaded from behind the firewall through the cockpit. The trays are designed to be heat sinks and are attacked to the 1/2" fire wall (glass over ply). I could put insulators between the tray flanges and the fire wall if you think that might be wise. The trays will touch nothing but air except at the firewall.
The motor is housed in a machined 60/61 T6 aluminum heat sink and supported on three 1/2" aluminum pedistals of the same alloy which attaches to a back plate at the fire wall. It also touches nothing but air except at the fire wall.

You know where mushers got the name? Its the sound you here when you step in doggie do do.
With seventeen siberians, I do a lot of mushing!!!

Thanks again,

Jim

Sounds like you've got it more than covered. Post some results after you fly it.

Good luck with them huskies

Mike