I'm very interested in how the 7148 will work with my Don's Dream Machines C-85/O-200 STC engine. I'm expecting slightly better cruise speed since the engine can put out around 93 HP at the 2575 RPM limit. Even cruising at 2400 RPM, I should be putting out more HP than a C-85 at the same RPM, while 2400 is the equivalent of 75% economy cruise on the O-200. But where I really expect to see a difference is climb performance. Not only will the engine be producing more torque, but I should be able to climb at a higher RPM than the 2100-2200 I normally saw with my old C-85.
Even though the 'coupe has a reputation as a "clean" design, I really think our big fat wing is what limits the speed potential of the airframe. (That and the Vno and Va limits!) Dave --- In [email protected], "Donald" <dongen...@...> wrote: > > > > Where I get lost in all that, is the figures get skewered by available > horsepower, drag, and such. In theory one could get some high number pitch, > and cruise 150 mph in a coupe. I wonder if someone has ever made a chart, > listing takeoff distance, climb rate, and top speeds, perhaps on a chart so > one could make better choices. > For instance I am told that I will be quite disappointed with my McCauley 71 > by 51 on the C85 engine, but I hope it will cruise with the big boys. > > . > --- In [email protected], "Ed Burkhead" <ed@> wrote: > > > > > > Larry, > > > > I presume you have an O-200 in your Coupe? The STC for putting the > > O-200 in Coupes calls for the regular C-150 prop to be used. (Many > > installations on LSA eligible 415-C and 415-CD planes used that STC as > > "accepted data" even though they didn't actually use the STC to > > authorize the installation.) > > > > On a Coupe, the pitch called for makes it a climb prop with a cruise of > > only about 108 mph but with quite good climb. Sorry I can't remember > > which pitch is called for in the STC. > > > > The first number is the length of the prop. The second number is how > > many inches forward the plane would move (with no slippage) on each turn > > of the prop. (Slippage usually runs around 5%. > > http://edburkhead.com/Ercoupe/enginepropeller_efficiency.htm ) > > > > Thus, a pitch of 50" goes forward farther than would a 48." The flatter > > 48" is better for the low speeds of a climb so it gives you greater > > climb. > > > > Ed > > >
