Hartmut, I think we've come to a consensus here. I've just wanted some good tech data to justify the change to my checklist. I'm going to use 1800 RPM for the run-up, which is high enough to get a good mag check, and also the recommended RPM for check the Stromberg mixture control. Checking full throttle can be done at first application of power on takeoff roll.
Thanks to Bill for contributing his information. I sometimes agree that the C-85 is "all steak and no sizzle" when I compare the performance numbers. I'm hoping to change to the O-200 crankshaft in a couple years to get some of that sizzle. Even though the RPM limits are unchanged because it's still a C-85, torque at a given RPM is increased and the engine doesn't work as hard and produces more power at a given RPM from everything I've read on the conversion. The performance numbers Bill cites pretty much bear out what I typically see. Thanks, Dave --- In [email protected], Hartmut Beil <hb...@...> wrote: > > > 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. > 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_5:092010 >
