Change of engine thrust line. A rigging tip.
Having converted my RV-6 to an RV-6A, I found that the new engine mount moved out the engine by about 1/8? and swung the engine a tad to the left, from the pilot's view.
After the change ?Rough Red? didn't fly nearly as well. It required more right boot and the RH wing had become heavy.
I added rudder tab and bashed the appropriate aileron edge but despite being trimmed OK the plane didn't feel like its old self. With the ball centered, and no compas swing, it seemed to be out of level when flying straight and level.
I spoke to a few people about changing the thrust line and the opinion was clearly that I was out of my tree. ?These engine mountings are precision things that the designer has worked over to perfect the design?. You know the drum.
After putting up with this for about 70 hours I put a couple of washers between the engine and the two Left Hand engine mounts in much the same way as the droop washers are used. The change in the thrust line, though very slight now centered the prop cone with the cowl as it originally was.
I have now flown ?Rough Red? for several hours with the changed thrust line and can say that this has gone a long way towards correcting what one could call ?a rigging condition?. Because the change was slight, the tab is still needed to centre the ball though I don't need so much right boot on take off. The plane feels better, the right wing which became heavy is now lighter, and that nagging feeling that the plane is not level in level flight has disappeared.
I am only conveying this because it may solve someone else's problem with trying to trim out errors with trim tabs and bashing ailerons when the problem could be an engine mount which is on the edge of manufacturing tolerances.
For the cost of a couple of washers and a little time it can always be put back if it doesn't work.
After all ?Rough Red? is Experimental.
Ted
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