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Old 09-22-2009, 08:59 PM
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Default RE: OS 10 & House of Balsa 1/2A P51

Try a 6x4 prop. If you want the most bang for the buck, run open exhaust with a crankcase pressure tap or just get some 3/16" thin wall latex tubing and run it on bladder. There might be a good selection of $3.95 pylon props over at APC for the .10 still. They used to carry odd sized props in this range, they still might.
A 7x4 is just too much for any kind of speed. These little engines can't swing the mass of heavy blades or too much diameter. If you were to spend 1/2 hour on a 7x4 MAS prop to shorten it and narrow the blades I'll bet you would be impressed. The next prop will take you less time, alsoonce you get your method down. It's a good skill to acquire if you want to go fast, because the .10 is kind of an oddball for speed prop availability. Finding the perfect prop off the shelf can be a long shot.
I would try to prop it for 18,000 rpm, at least. Use castor oil in your fuel!
OS might still sell a control line venturi, if you go to a high pressure bladder it might work better than the modified carb. The stock needle will work OK if you slip fuel tubing over it.
If this P-51 is small enough and clean enough, it will move out pretty good for ya.
Have fun!