Postby Phil Clark » June 23rd, 2010, 8:33 am
Graham
I assume you know the guys in German building the B-25?........do you know if they are still using the same props as they show in the other video of the 400's on the test stand? They state 42" x 10" 3 blade..............
From past experience, that's no where near enough pitch, especially on a 180kg model. The 400 we ran in Ali's Skyraider (82kg's) ran on a 38" x 25" 2 BL prop, and even with that, performance was far from exciting. We were getting around 4,000rpm out of the 400 on that prop, even if they manage 4,000 on those huge 3 blade props, 10" of pitrch at 4,000 will not give any top end performance what so ever. No top end performance and well over double the weight of the Raider doesn't fill me with the joys of summer!!!!!
On the 1st flight of Al's Tigercat with the 150 radials, we made the mistake of try to fly with scale diameter 3 blade props, but to get the engines into a rpm range they were happy at (fullthrottle gave around 4,500), we were down at 12" of pitch. The test flight proved this to be much too low as Al had to fly ball's out just to keep the model in the air. He's since dropped the diameter by 2" and upped the pitch by 2" and the model is now flying well.
Phil
