if the f-20 is a cressline kit,the c/g is way off!!!!! i may have been the only guy to get one to fly..it did fly great!! os dynamax. i made the ducting myself. stock ones sucked..it weight 12 lbs. flew 155 mph..if you use the c/g they tell you,it sits to heavy on the nose. will not rotate!! the fying c/g is also wrong.. i had to fill the, pre cut, gear holes and start from scratch. figure c/g before you start your build.. i know 4 guys who built the kit,,none flew...they were very fast ,on the ground.. its worth building.. i wish i had another.. sold mine.. rd c/g was off two inches by the way....do not include the leading edge exstention in your c/g calc.....