RE: Best .21 engine
Hi!
A MVVS .3,5cc engine (.21) using 5% nitro, 20% castor oil and minipipe in a small (100-110cm wingspan airplane, pylonracer) at around 1,2-1,5kg will do fine on a 7x5 APC prop...expect speeds around 200-220km/h. Glowplug: Nova Rossi 4-6 or Rossi 4-6.
Regards!
Jan K
Airracing products
Sweden