Hi all:

I am in the process of building a HOB 2 X 4 sailplane. I need some advice on a power unit to get it up. I was thinking on using a GWS Speed 400 motor. Will this produce enough thrust for lift and/or sustain vertical lift? Also what prop would you recommend? Should I use a gear box? I know this is a lot of questions, yet any help on this I can use for sure.

SPECS:
Wingspan: 49.5"
Wing Area: 409 sq in
Wing Loading: 9.8 oz/sq ft
Weight With Standard Radio: 28 ounces
Fuselage Length: 38.5"
Airfoil: Flat-Bottom, Polyhedral

Heres my 2X4. Its a old kit(maybe 15-16yo) I made it to slope off the earthen dams around here in lite lift. I replaced all the light ply fuse parts with balsa and extended the nose 1 inch (should have been farther) so wouldnt have to add lead. I use a Gws 300 with the "D" gear, the slow stick motor. Its on a power pod and run it with 3s Li-ion cells propped down to draw about 8 amps. It climbs at I guess you would call a leisurely rate but gets there. I have a 400 with a D gear on another plane and should try it sometime. Weight is 29 ounces ready to fly includeing battery and everthing. I think a 400 would work good esp. with a nose mount. Maybe the 3 to 1 ratio with a 10X47 prop. Folder would be a plus. I also use the 400xt Hobbby Lobby brushless on other planes and it would be a good cheap choice also. Build it as light as you can and its a pretty decent little sailplane and thermals really quite well but it is really an excellent light lift sloper or tree line rider. With 2500ma batteries I can fly for 45 to 60 minutes hunting bubbles and still come down with power to spare

Good Luck
Bob

Thanks Bob;

I think I shall try the nose mount GWS 400. I have the fuse built with the stock lite ply. Might try drilling some holes in the side to reduce the weight factor. Had even considered a OS .15 on the front with a lite landing gear as a tail dragger for TOG. I might be pushing this little bird hard. I do like the way you have yours set up. HOB says I can use standard size servos but I have installed the H-55's because of the weight factor again. I thank you for your help and if you could post some pics of the servo and battery compartment I sure would be interested in seeing them and just how you did that part.

Heres a couple of pics of the nose. When I fly powered I put the battery pack first then ESC and then the servos. I run full size servos as I need the weight any way. The RX is placed under the LE of the wing bay. When I dont use power I put the battery first then the RX and the servos stay the same. Have to add about a 1/2 ounce I think.

I think that your idea of cuttting some holes in the fuse behind the wing is a good one. And with the motor plus the batteries and if you can fit the "55s" and or the RX all in the nose maybe you will balance OK. Have found that this plane is not touchy in the CG kocation and mine flys better a little tail heavy esp. on the slope when you need quick turns and shows lift better too. The plan CG is set pretty far foward because Im sure it is mostly appealing to soaring starters, because nowdays the big boys want all the whistles and bells.
Post back if I can help you or when you get it up!!!!!!!!!!!!
Good Luck
Bob

Thanks for the pics Bob. I will be sure to post you the pics of the finished 2 X 4 when I get it done. I like your idea of the pod mount motor, for then I could remove it when I fly it power free. There is a guy in my club that has a stick build sky hauler that takes sailplanes up piggyback and release them at about 1K feet. Thank you for all your help.