Given your specific requirements for a very light and powerful drive suitable for small fuselages, particularly for F5J and RES gliders, you’ll want to focus on specialized components that are optimized for such applications.

The Tenshock VIPER 1020-12T 4pole 5200KV with Micro Edition 5:1NL gives you all you need from a small and very powerfull motor.

Size and Weight: Since you mentioned narrow installation conditions, the motor should be compact and lightweight. Brushless motors are often preferred for their high power-to-weight ratio.

Power: The motor should provide enough power to meet your requirements. Brushless motors are known for their efficiency and power output.

The high quality Reisenauer  5:1 gearbox ensure that the motor  is durable and trustable solution for your model

Data:
Weight 77g
Diameter 22mm
Length withour shaft 59mm
1085 rpm/V
4 poles
Hole circle 14mm, 3xM2,5
For 2-3 lipos
Current max 50 amp.
max. power on 2s 300 watts
max. power on 3s 500 watts
Timing 6-10°
8khz
Gear shaft: 6mm