I picked up a used webra 40 blackhead a while back finally mounted it ln a 40 sized high wing trainer and fired it up. This engine seems faster than my webra 40 silverline. my question is to which propsize should I start with on the ground it seems to swing a 10-6 very fast but maby it should. I reailize this plane would be better off with a bushing 40 but this is is what I have and I do not want to spend any more money than I need to on it.

Thanks.

It sounds like the Webra .40 speed. It will work fine as is, you don't have to fly at full throttle. A 10X6 or and 11X4 will work fine.

Try a Master Aiscrew GF 11x5. The plane will like it (and you too!)>
Ciao
Beppe

 Thanks for the quick replys maby I can get by the hobby shop and get a 11-4 and 11-5 to try they may also slow the plane faster which will help a new piolet with landing approches.

Hi!
Use a 11x5 or 11x6 . APC or RAM!

The blackhead (AKA silverline) is cross scavenged and had a piston with baffle top. The Speed engines have a plain piston top, and finning right down to the crankcase.</p>

Most popular props for the .60 were 11x7.5 for screaming performance (speed) and good performance (silverline) </p>

The speed was no good at larger props as needed for more silence, but the Blackhead could use 12x7 props very well on standard mufflers. To persuade the speed engines to lower rpm than 16,000, long header tuned pipes were the way to go.</p>

APC 11 1/2" x 4 will make you happy!