Tom
What you are referring to is the test for performance. Will the engine perform under load. I agree that this should be tested at higher speeds, where the load happens, best crank up to the published numbers for static speed of the engine - propeller combination A test at a lower speed does not represent the full power load onto a spark plug. Only a full run-up will. Like I previously said, you test for general function of the parts in question: left magneto, right magneto, carburetor heat. Then you test for performance. The parts tested here are piston, cylinder, valve train and yes spark plugs. That test you want to do briefly at the published static rpm. I am pointing this out because I was struggling for a while with an engine that would run perfectly up to 1900 rpm. But it would not always develop full power. It basically got stuck at 1900 rm where it should make at least 2050. With that low of a static rpm it was not airworthy. Your suggested test speed would not detect the problem and depending on severity you would find out after the crash. No. Out of own experience I disagree. Do all the tests for function at the 1700 rpm, but make sure the engine has enough power before take off. Hartmut Date: Fri, 20 Nov 2009 19:47:33 -0800 From: [email protected] Subject: RE: [ercoupe-tech] run up To: [email protected] CC: [email protected] One more reason for a "mag check" is to check for a spark plug breaking down under heavier load conditions ,at higher pressure and higher RPM. You can check a magneto for firing at 600-900 rpm and misfires will be evident at that rpm, but plugs will fail at higher speeds. I agree with RB that 1700 is adequate to run these checks. Tom --- On Fri, 11/20/09, Hartmut Beil <[email protected]> wrote: From: Hartmut Beil <[email protected]> Subject: RE: [ercoupe-tech] run up To: "Techlist Ercoupe" <[email protected]> Date: Friday, November 20, 2009, 4:18 AM Guys We have to look at the purpose of the run up to come to a usable solution. Two reasons come to my mind: 1. we test for function of all crucial parts. Magnetos and Carburetor heat . 2. we test for take off performance. For the first test we don't need a full throttle run up. We have to notice a drop during the magneto test to verify that both are working and can be switched off. And the carburetor heat is tested also by noticing the drop in rpm. The magneto drop should not be excessive, a drop of more than 100 rpm would indicate a non firing or barely firing spark plug. That's why you do the run-up. Not to satisfy some numbers. Since the Ercoupe brakes are suited for slowing the plane down, but not so much for holding the plane at full throttle in a static position, it is common sense to do this kind of run up at a lower rpm. I am using 1600 rpm and I am seeing magneto rpm drops between 25 and 75 rpm. Anything more and I have to look deeper into the issue. Think about it, you don't do a full throttle run up in a tail dragger either. As for the performance test, I do briefly a full power test where and when applicable before take off to be sure to reach the recommended static rpm. That rpm value differs between the allowable engine propeller combinations. For the latter reason, I am also inclined to say that the experienced drop in rpm when doing the magneto test also depends prop pitch. So in result, there is no strict rpm to do the run up with. Nor is there a rpm number of magneto drop that you should or should not see. Rather than requiring a certain rpm number, I would recommend using always the same number when doing the run up. Learn what the drop usually is and be alert when it is different from the usual. Hartmut Keep your friends updated— even when you’re not signed in. _________________________________________________________________ Windows Live: Make it easier for your friends to see what you’re up to on Facebook. http://www.microsoft.com/middleeast/windows/windowslive/see-it-in-action/social-network-basics.aspx?ocid=PID23461::T:WLMTAGL:ON:WL:en-xm:SI_SB_2:092009
