I'm trying to add a motor to my old 3m gas bag but don't have a lot of room to play with in the nose. It looks like a 28mm outrunner will be about the max and still fit inside once I chop the nose. Also it looks like the servos will have to be moved back toward the bulkhead which is no issue. My question is will a 200W outrunner with an 11X6 folder work decent enough? Also it looks like battery room will be very limited. I have some 800mah 3cell batts but would that be sufficient or should I figure out a way to cram in my 1500mah lipo? Thanks for the input in advance

What is the weight of the model and what are your plans for it? (ALES? just sport flying?)

That's a whole lot of glider for a 28mm motor and 200watts would be marginal at the very best. Your best bet would probably be a geared inrunner but then you might have to lengthen the nose to make everything fit. Another option would be to bulge the nose for a 35mm motor. One of the most powerful 28mm outrunner motors for a low price is the HobbyKing 2834. I have one on a 3D plane, plus two I just ordered yesterday, and I'm swinging a 11" slo-fly prop and pulling 375watts with a 11.1volt battery.

https://www.hobbyking.com/hobbyking/...dproduct=17600

Another option is to consider mounting the motor in front of the firewall.

It is often possible to make it pretty by placing a removeable balsa cowl around the motor (if the motor can is a small enough diameter).

You probably will have to reverse the shaft of the motor for this mounting.

As for motor size you might need something bigger. My 3 meter plane only weighs 40 oz and my motor generates 250 watts.

Craig

Weight in it's current form is 40oz RTF. I'm just looking to get it up to 200-300ft in a reasonable climb. Need a lazy day sailplane for when I don't want to drag out the high start

Hmmmm. At 40oz. I think it's doable with a 28mm motor. My 2834 generates over 4 pounds calculated thrust. I like power so I would go with something in the 300watt, 30amp, range. You might want to go with a lower kv, 900-1000?, in order to be able to swing a bigger prop.

250 to 300 watts should be plenty.

you can figure out battery/speed control/prop/motor combinations here:
http://www.ecalc.ch/motorcalc_e.htm?castle
Very helpful.

Thanks for the help guys. After playing with that calculator I think an elfite park 480 will be the ticket. A 35mm can I know but it seems like it will be better in the long run according to the calculator. I'm going to do some major surgery on the nose and put some 1/16" ply in there once I thin out the balsa walls.

Hi jwhitacre.
Just a little more info... I think you will be happier witha 35mm motor and larger pack than 800 mah. Keep in mind that you will need some weight in nose, so why not make it functional? This 2m project has been fun, but I still have some nose weight, and I'm using most of the 1000 mah pack on longer flights. Here's a link
http://www.rcgroups.com/forums/member.php?u=90147

I suggest a test assembly of the system on the glider before you finalize the motor or location. Check the CG and adjust from there. Have fun! Jeff

Ok I have tried motocalc this program (e-calc)and others and they always say "unrealistic set up, prop will stall or maybe flying speed = 250 Mph " none of which will make me happy. Is there not a program that will let me enter flying weight, model type (3D, sailplane etc) wing area Desired motor run time at full throttle and desired watts per pound and bang it will suggest a battery size including volts and charge rate and a motor in KV plus suggest prop size and pitch.

Seems to me these programs require you buy the motor first then check it out to see if it will work. Being retired I need the program that does what I mentioned.

I just finished an E-Bubble Dancer that came out at 43 ounces all up. Its powered by a Hacker 28mm A20-22L with an 11x6 prop. A quality 800 mahr pack would do just fine. peak watts is only about 220 or so.

That setup will get the 43 oz BD to ALES launch height - 200 meters or 652 ft - in almost exactly 30 seconds, so a lazy launch to 200-300 feet will be a breeze.

No need for a larger, heavier setup. Why have permanent ballast you cant remove on light days?

MrE, thats a very nice e-conversion! The Bubble Dancer is a very clean low drag airframe as well. Do you need much nose weight to make CG? Im familiar with the Hacker A20-22, is a very efficient motor. Ive not used one in a glider conversion though. Not intending this to be a thread jack...
Jeff

I didnt have to add any extra nose weight. In fact, I had to move things around to get the CG back far enough with the 1500 mahr pack Im using now. Thats my only decent small pack at the moment.

Im planning to use an 850 TP 65C pack down the road with a slightly larger hacker A20-12XL. I want a tad more power for ALES contests on windy days and the 12XL will give me an extra 75 watts or so easily for a slight weight gain - offset by the smaller pack. I like to get to altitude in ALES contests with about 5 seconds to spare or so.

Thanks for the reply.
Jeff

Thanks for all the info guys. I ended up piking up a Rimfire 35-30-950 outrunner for cheap. I put smaller HS-81s in there to save weight and to free up room. With the new layout I can stuff a 1500mah lipo in it so that should work out fine. Once the LHS gets my 11X6 folder in Thursday I can try the setup out.