Owen said, "He had it pitched for high speed cruise. It was a pretty efficient combo but the high pitch seemed to be loading up the engine making quite hot."
I'm wondering if Owen means it was pitched to allow the engine to turn up at a very high RPM, thus causing the plane to go faster, thus "high speed cruise"? If so, then the resulting heat - the hot engine - would be the result of internal friction - parts turning against each other (friction) inside the engine. The faster the engine turns, the more friction is generated. More friction = more heat. If this is what Owen means, the prop was set to a flat pitch. Owen's second sentence refers to "loading up the engine" however. This would imply the prop was set to a sufficienty coarse pitch to limit the engine's ability to turn at its optimum RPM. In this case one could say the engine was "over propped" - the coarse pitch "loading up the engine". This would not cause the engine to get hot since at the lower RPM friction would be low. With such limited RPM however, the plane would not be capable of "high speed cruise.". Perhaps Owen would clarify which it was. What do you mean Owen with the phrase "loading up the engine"? Your two sentences seem to contradict each other in meaning. This is a very interesting subject with lots of variables and I'd like to comment, but to do so I'd need to presume what you meant and I'm a lousy mind reader. **************** Regarding my own plane, when I first got it I had a heck of a time keeping oil temps down and eventually learned I had a glitch in my electrical system that caused the gauge to read high. In the process of figuring things out however, and in the process of finding a prop to do just what I wanted - these two objectives running in parallel - I was enormously impressed with how easier it was to keep my oil temperature down by going to a coarser prop, one that allowed me to run at WOT at cruise altitudes (anything above 8 thousand feet) at the cruise RPM I wanted ( ±3100). Why 3100? Initially it was to keep my tip drag at an ideal speed but the immense improvement I got from reduced oil temperature as a result of lower engine RPM's was a very welcome secondary benefit. With my GP 2180 w/Ellison EF-2 and a Sterba 52 x 56, my engine operates right on the edge. That is to say, when starting the take-off roll the engine is slightly overpropped. I have to pull it back slightly since the engine cannot accept that last little bit of throttle. Once underway however, once the prop is unloaded and I am in the climb phase and especially once in the cruise phase, the engine can accept full throttle. At the higher altitudes I normally curise at on cross-country flights, the air is less dense and I've found a prop that turns 3100 WOT at 5 thousand feet will turn 3200 WOT at 12 thousand feet while using less fuel. I attribute this to the air being less dense, thus less drag. It's the same phenomenon that allows the plane to go faster for a given amount of thrust, the higher it goes. For my plane there is an optimum altitude where power and drag are at their respective optimum points. It's 12-13K for my KR-1½. One advantage of using the Lycomings and Continentals over the VW is their rated power RPM of 2700 is much lower than the VW's rated power RPM of 3500. Although props are longer for the certified engines, RPM is so much lower that mach tip speed limitations are of no consequence as far as I know. Mike KSEE ____________________________________________________________ How To Remove Eye Bags & Lip Lines Fast (Watch) Fit Mom Daily http://thirdpartyoffers.juno.com/TGL3141/5a3184b24d5294b216e8st02vuc _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/[email protected]/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to [email protected]
