----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]---- Paul, weight and balance is simple math. If the propeller installed is 2 pounds heavier than the old one, you measure the distance from the datum (firewall) and multiply the weight times the arm (distance). Just for example, if an Ercoupe prop is 3 feet from the datum, the extra 2 pounds x 3 feet = a moment of 6 foot pounds.
This means that the new prop is exerting 6 foot pounds of rotational force on the center of gravity, trying to rotate the nose of the plane down. The cg has now moved forward- possibly out of the allowable range. Probably not with just 2 pounds. But to keep the cg at the exact same location as previous, you must produce an equal moment to push the tail back down. So- you need to somehow produce a 6 foot pound moment behind the cg. You can select any weight and any distance that produces that, providing there is a place to bolt it on to. The best thing is to use the least weight, farthest back. Then your empty weight isn't increased too much. 2 pounds placed at the tailcone (about 20 feet back) will produce 40 pounds of moment. That's more than 6 times the amount actually needed. We need to know the actual difference in weight of the 2 props, and then you can double-check the math and the weight. If you do have 2 to 3 pounds at about 20 feet from the datum, your moment is about 40 to 60 foot pounds. You could divide the moment by the distance of the prop to the datum and come up with a good estimate of the difference in weight. If the prop is 3 feet from the datum, and the moment of the weight in the tail is 60, then 60 divided by 3 is 20. There would have been a 20 pound difference between the 2 props. These numbers are all hypothetical, you'd have to measure actual distances (arm) and find the actual weight of your ballast. Jan Z Fresno, ca On Thu, 05 Oct 2000 17:46:57 -0700 Paul Anton <[EMAIL PROTECTED]> writes: > ----[Please read http://ercoupers.com/disclaimer.htm before following > any advice in this forum.]---- > Some time back there was a discussion concerning > one of the members Coupes that had permanent > ballast installed at the tail cone. > > Can anyone fill me in on the circumstances that required > this? > > We are covering Weight and Balance this week in my > A & P school and I am curious why this was done. > > Thanks > > Paul > N2273H > > __________________________________________________ > To unsubscribe from this list please send > mailto:[EMAIL PROTECTED] > ___________________________________________________________ > T O P I C A The Email You Want. http://www.topica.com/t/16 > Newsletters, Tips and Discussions on Your Favorite Topics > __________________________________________________ To unsubscribe from this list please send mailto:[EMAIL PROTECTED] ___________________________________________________________ T O P I C A The Email You Want. http://www.topica.com/t/16 Newsletters, Tips and Discussions on Your Favorite Topics
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