As Tzenntech said it, we need speed, no acceleration! You have to find the perfect mixture between acceleration and speed for every plane! Big props give us huge Amps-drawings which kill our cells, as we have 10s runs and not only 2-3s for a complete speedrun! If you have batteries for us which can deliver 450A for 10s and thats for about 5-6 Speedruns in one flight, iīll be pleased to try a 18x21 on my speeder but it will end with about 350km/h and not more, so really boooooorrrrriiiiing speeds
! Donīt forget, we are running much larger pitches up to 27 on our speed props at much higher rpm!
The maximum we run on competitions are 3-folded props, when we need the thrust, which 2-blade could not give us, but we try to avoid more than 2 blades as efficiency goes down, when itīs possible! The only thing we are playing with 4-, 5- or 8-bladed props is show and the amount of sound! Unfortunately itīs not like in the US or Australia and noise is a big problem! We have large restrictions on noise production for combustion engines here in Germany which are mostly 78db, excluding elektro! But if you have a 5x5 screamer at 45000 rpm which is much louder than that, a lot of clubs get problems with surrounding inhabitants and speed planes are not allowed to fly! So the only thing you can do is getting noise down, using such high-blade props or stop flying! What is better?: Loosing a few km/h speed due to less efficiency or complete stop flying such planes
and do some F3A, F3K or gliders
These props are more for Hotliner style flying as they are producing a lot of thrust! Ralph has broken the 100 m/s vertical averaged for 2 s (about 98m/s averaged for 4s) about one year ago i think with the Chimera, so much more than the best F5B-ship is doing at the moment and this not only for 2s runs but for much longer times, if you have good eyes
! So they are perfect for fun-flying and very silent speedtrainig on every club even with noise restrictions, thats all!
Yes an F5B ship could get much faster than 350 km/h but not much faster than 400-420, when its special biult for it without 4 flaps and thats the end! You never could build an F5B ship FAI legal as sturdy as you need it above 420 km/h! Donīt ask me how i know! Even our special modified F5B ships found their end at these speeds as torsion is to much for these high aspect ratio thin wings! The plane is still flying but isnīt going in the direction you want to fly! Not really funny for the pilot i can tell you! Kai Koppenburg, Erwin Schamburger, myself and a few others learned this lesson about 3 years ago and started then building special F3S-designed planes! The first real F3S designed plane was Michael Jakobs Eagle, for which i built the molds and planes in 2007! All others started about 1-2 years later!