Title says it all. I am about to put in a large order to Hobby King and want to know what engine from their extensive selection (I'm suffering from overchoice) is best for this plane. I'm looking for light; don't want or need "vertical". So if you are flying a converted Olympic II and are happy let me know. I did find quite a few older threads, buy HK has certainly changed/added to their lineup. Plane is 100 inch span with a wing area of about 928 sq. inches. Not sure of the all/up weight but I'm sure it's in line with other 100 inch gas bags.

You need to measure the inside diameter of the fuselage, to see what size motor will fit. A lot of sailplanes have about a 40mm inside diameter, allowing up to a 35mm diameter motor.

Then, decide how many pounds of thrust you want.

A 35-42 will give you about 595 watts or about 4 pounds of thrust (4S). How heavy is your plane?
The NTM PropDrive 35-42 is $16.00 and will put out 450 watts (3 pounds of thrust) with a 3S LiPo. Battery would have to be about 2200 mAh 30C with a 55A speed controller. A 4S LiPo will give you about 700 watts (4.6 pounds of thrust).

I chose to go with a smaller motor for my Cularis (foamie, I know, but it's also a 2.6m span). Airplane should weigh about 1500g when finished, and I chose the RCTimer 3536-8. 1000kv should put out 32 amps swinging a 12x6 folder on 3S. 62oz of static torque.

Best of all, the motor only weighs 102 grams.

30 year old Oly II I gave to a friend which he converted with a 35-42 and is setup for ALES with a CAM switch. Nice climb but not silly.

Ray's Oly II (0 min 23 sec)