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Old 11-19-2012, 07:17 AM
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MJD
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Default RE: OS 91 VRDF experts wanted


ORIGINAL: freakingfast

I first discovered how well they ran is when I'd run the engine through at the end of the day with FAI fuel. I would do this for DF and Marine engines. If you don't do this, the bearings wont last. The engine was down on power a tad and you really had to lean it. I used a clip on rolling IV clamp so I didn't have to mess with my flight needle setting. One day I was out of 30% and too lazy and didn't want to spend the gas money to get some more so I pulled all the gaskets and hoped the piston wouldn't hit the head....what the heck, roll the dice. Well it ran fine, but it was visibly down on power and the engine easier to fall off the needle setting. Perhaps It would have ran better with the pipe re-tuned for the low nitro, but it doesn't matter any more as the plane flew away from home some weeks later.

As you know, you need a clean plane (dart) and flight time is limited by tank size, however before you even consider this, make sure you have a nice selection/candidates of CF props actually in your paws, not on order, not shown in stock and not promised, just in your hands and good luck with that. Cut down and thinned wood props work, but they are very fragile and time consuming.
Good practice, apparently this is SOP for the Euro speed cup fliers - run some FAI through the engine at the end of the day and pull the line at full tilt.

The Tettra 4060 and 4061 bubble free tanks are a reasonable 58x54mm in cross section and hold enough fuel for 2.5-3.25 minutes of full bore speed flying, more if you throttle back now and again. I use the 4060 on an OPS Speed .65 (~4 oz//minute) and so far the runs are long enough for the attention span of my remaining brain cells.

To the best of my knowledge the CF 9x10 APC rework/knockoff is a popular choice on 15cc DF engines in sport speed models overseas. By sport speed I mean the 190-210 mph stuff (Speed Cobra, other older speed designs, composite ME-163's etc) as opposed to the state of the art speed airframes that can make use of less diameter and more pitch. 20k on a 10" pitch prop has serious speed potential, and 9" diameter has the disc area to drag a little more airframe behind it.