Crap is really easy to trap. You just fall into it. I overheard a gentleman talking at a recent race about how the Russians go thru this elaborate alignment process to compensate for the deflection of the journal pin under load. Duke Fox used to do this on some of his engines. All was well until he said they picked up 1500 RPM!!! Crap Trap!!!!!!!!!! Crap Trap!!!!!!!!!! Remember that that is a whole bunch of HP, maybe 25% or more. You can’t do it with an incremental change, only a fundamental one. (tuned pipes, turbo-charger, etc.) If he had said 200 RPM he might have been close, but perhaps not even that.

Letters, I get letters. A customer called. He was a man of Klingon type honor, a former member of the High Counsel. Now his stature is diminished, and he is without honor. It seems that he had measured a BDC of .896 on his Jett, which yields at TDC of about .189 (remember top dead center plus stroke equals bottom dead center). He then measured TDC using his crap trap type methods and got .182. He was confused. The reason he was confused is because he had no faith. Dammit. Top dead center is Bottom Dead Center minus the Stroke. God made it that way. You cannot change it. Einstein can’t change it. It’s simple math. At any rate, I told him that if it did not come out to be what I said, then I would feature either him or me next time around. Sorry.

Sometimes I talk about things I don’t know much about. This is one time. There are many others who could do it better, but the message is not getting out. It really needs to.

I watch people fly and try to stay on the course with airplanes that Chip Hyde couldn’t fly. Our ability to trim a racer for a circular course is terrible. It’s a shame, too, because it is really so easy.

Rules for trimming a racer:

1. Call the manufacturer and find out the best c.g. and throws and use them!!!!!!. If you don’t balance the airplane, then please skip to the next page. (maybe later I will do a crap trap on balancing)
2. Set the low rate throws at slightly less than recommended and the high rate at 20% more. That’s 20% more than the low rate! E.g., if the low rate is “40”, then the high rate should be “48”, not “60”. (1.2 times the low rate). Take the time to do this. It will save you a crash later.
3. Fly the first flight rich, very rich, so you can get the centers of the trims without crashing. Center the elevator and ailerons first, obviously. Then try to fly the course.
4. When you make your first few turns around the course take note of several things: How are the rates? Try the high rates (remember they are 20% higher) You can get two shots at the throws this way and use this info to set your final throws. Second, watch the airplane thru the turns. Is it yawing? Is the nose high or low? A few clicks of the rudder will take the yaw out. (do not watch the smoke trail, it will confuse you)
5. With all three trimmed, there is one important thing left, which is really the subject of the Crap Trap. What are the wings doing during the turn? Think of the fuse as an arrow. When you enter the turn at pylon 1 it is pointed directly away from, regardless of the bank of the wings, right? When it finishes the turn, it should be point directly back to you, regardless of the bank of the wings. If not, then the airplane is either rolling up, or down. If up, then add weight to the left wing. If down (seldom needed), then add to the right tip. Do not change the Rudder!!!!!!!! Do not change the rudder!!!!!! Do not change the rudder!!!!! Get the message? You have already trimmed the rudder for zero yaw, then why would you want to race a yawed aircraft? It doesn’t matter if you under roll, or over roll, the “arrow” will always return to you, if you have the wing weight right. If not, it will never return to you, and you will continue to fight it around the course. Sometimes you have to add a bunch of weight, like ¾ oz. It depends. Sometimes I add some aileron mixing, but that causes adverse yaw in the turns, so be careful.
   
   This is essentially a balance problem. The engine is on the outside. When you pull g’s, you are multiplying your imbalance by 25-50 times. This causes the airplane to roll right or left during the high-g turn. A little weight on the tip goes a long way. Watch the spinner. It should be point right back to you every time!!!

In summary. Balance the airplane to specs. Trim the airplane, and set the rates. Add weight to the wing tip until the airplane does not roll out or into the turn. Don’t use rudder to control a balance problem.

Dub

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