Colin: I spoke with Steve at GPAS and his comment was that the lowest rpm rduction of their PSRU would likely require to long of a prop to work with a KR2 for ground clearance reasons but my desire was to stick with the 3400 rpm max and not push the rpm up to 4400 rpm max. I do intend water cooled heads principly for a "Cabin Heat" source to get away from the time honored exhaust heat muff so as to reduce the opportunity for CO intrusion.
I still have no clean answer on the effects of the Thrust CL change but it is but 5 inches which still would leave the stabilizer in the prop wash. I learned long ago that the dumbest questions are the ones not ask! Don -------------------------------------------------------------------------------- ----- Original Message ----- From: "Colin Rainey" <brokerpi...@bellsouth.net> To: "KRnet" <kr...@mylist.net> Sent: Tuesday, February 20, 2007 12:07 AM Subject: KR> Thrust Line issues > Don and netters > Something else came to mind the other day when considering the effects of > raised or lowered thrust line. During flight training to become CFI's we > were always told that the reason the Piper Seminole was made with a high "T" > tail as compared to its sister plane the Piper Seneca which had a > traditional tail (and 2 more seats, but that is another story) is because > the Seminole was really ear marked for the training market, and so Piper > wanted the tail in "clean air". This was supposed to make it safer to flight > train in. I am told that the same designer, later worked for Beech and > designed the Duchess, which is why so much of the configuration resembles > the Seminole. > > My point for this post is this: while in most cases planes are designed with > the empennage "in the prop wash", some very successful designs are not. > These planes seem to experience less pitch change due to the change in the > amount of prop thrust over the elevator/stabilator, and the change is more a > function of airspeed/airflow. If by raising the thrust line, one lessens the > amount of prop wash over the elevator of a particular KR2 or S, that builder > may find a nice softening of the effectiveness, without becoming dangerous. > Then again it may favor one side only, causing good nose up authority, but > lose some nose down authority. > > I would also think that if the builder then used a longer prop taking > advantage of the greater ground clearance, he might not have any change in > the behavior of the plane to speak of at all. > > Just some ideas for thought. I was once considering a PSRU or re-drive as > some call them, for my 1915 cc VW original engine. Had I installed that, I > would have been 4 to 5 inches higher. This may be an issue many builders > have contemplated or evaluated. > > Colin Rainey > brokerpi...@bellsouth.net > > _______________________________________ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > Post photos, introductions, and For Sale items to <A > HREF=http://www.kr2forum.com/phpBB2/index.php > please see other KRnet info at http://www.krnet.org/info.html >
