Original Posted By: "jarheadpilot82"
Chris,Congratulations on getting your bird flying. I just read over your notes and wouldlike to share some thoughts. Forgive me in advance if I missed anything yousaid, but here are some thoughts:15.9" is not having the CG too far forward. I have plenty of time flying in thatrange, and as Mike G pointed out, the plane has normal handling there. As theplans note, the acceptable range is 15" to 20". If you are in this range andthe plane does not have normal behavior, it is likely something else. If you have a good electronic scale W&B, it is a very easy matter to do an exactcalculation to know exactly where the CG will be with a 205 pound pilot. Ifyou have any trouble with this, send me the data privately, and I will do itfor you. The whole point to our previous work is so people can do a calculation,and not guess nor estimate. I can not say for sure without numbers, but thereis a very good chance that a 15.9"/150lb pilot plane will still be in CG witha 205 pound pilot.If you load up the plane and move the CG back and it flies better at say 19.8",this doesn't mean that the 'problem' has been corrected. It is possible in riggingto have the illusion that the condition is 'fixed', when it has just beenmasked. If the incidence is not correct, but this is less noticeable with theCG aft, that doesn't constitute a solution, just a mask.If your plane has a different airfoil, than the best advice is going to come froma guy who not only has time with your airfoil, but also the standard one. Youneed to contact PF Beck and Don Harper. Both their planes fly well, they havemotors in your weight category, PF would box as a welterweight, Don as a superWelterweight. (147 and 154 lbs) PF's has the Std. airfoil, Don the Ribblett.Get on the phone with them and ask about their CG, and also the rigging onDon's plane, including the incidence and the position of the horizontal stab.Get a smart level, and measure the stuff in degrees, and listen to the man flyingthe combination, not the theory of what it should be.A few guys mentioned 'twisted' stabilizers. Am I reading the correctly? or is thecomment really about the incidence of the stabilizer? Twist to me implies washin or wash out on a wing, I am not used to calling anything in the tail twisted.I bring this up because other people may also not be getting the comment.A little work on calculation and direct research with people flying the same airfoilin a similar plane is a whole lot less work than following any suggestionto move the wing some random amount. If, after investigation, it turns out thatthe wing does need to be moved, I can also show you the exact calculationto hit your new target CG right on. That is more complicated than a normal calculation,but the CG articles we did, available from Doc Mosher, walk you throughit step by step.My neighbors 200HP Glasair only did 160mph with full aft stick on its first flight;3 people from the EAA chapter all claimed the CG was wrong. Actual issue?LE of the stabilizer was off by 5/8". Corrected, the plane does 240 mph. 601XLcame to our hangar 2007, aircraft could not be effectively trimmed. Builderwas told it was a CG issue by several people. In reality, stabilizer was off by1.5 or 2 degrees. Corrected the plane flew very well. I have a lot of storieslike this, do some research and your plane will get squared away shortly. Followsomeone's guess and go on a wild goose chase. Take your pick.Hope to see many of you at Brodhead.William WynneRead this topic online here:
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