>, >I am almost in the position to order my gearbox. The gearbox is in >direct link with the proppelor and rpm, so I need to make a >dissision for the diameter. Now is my question wat is the max >diameter I can use on the KR2-s. I do not mean the ground clearance, >but I am affraid that the giroscopic force wil brake off the fire >all if you use for example a 65 inch dimeter prop. >stef ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Stef, The firewall will handle the longest prop you want to run based on ground clearance. But, it's not as simple as all that. You'll want no less than 8 inches of ground clearance but you must also consider the rpm that your engine will turn the prop and keep tip speed at less than 85% the speed of sound or it will loose efficiency. Also, when you determine the diameter, there will be a given pitch that your engine can handle (load) to allow the engine to turn the rpm needed to obtain best power. On my 0-200 for example, Ed Sterba recommends a 60 inch diameter with a 68 inch pitch. A larger diameter prop would require less pitch to allow the engine to reach the same rpm. Talk to several prop makers, tell them what you have and see what they recommend. Start by determining the longest propeller you can handle while giving you the required ground clearance and work it in steps from there. Larry Flesner
