alan0899, exactly which model do you have and how much does it weigh? I would guess that your Skyraider is one of the smaller light models. If not, I may have to do some more testing. From taking tach readings and watching performance I found with a 11" prop on a 46 size engine, the prop better be turning at least 12,000 rpm or you will be lucky to get off our grass run way. This is with planes that are rated for 40\46 size engines. Do you know what rpm your are getting with your combo?? [8D]