The Cessna 120-140 Association Forum

So I was reading in the February EAA Sport Aviation about the fellow with the rat rod Cub and the Verner radial engine. He discussed that he adjusted his ground adjustable prop for some sort of max static RPM and was not happy with the performance. He re-adjusted to max torque RPM and had much better performance at a lower RPM.

On our small Continentals the overhaul manual states max horsepower as a measure of RPM (2750+100hp on my 0-200A for instance) but does not list a max torque RPM like the Verner engine website does http://www.vernermotor.com/page1.html The 2 limits are different on the Verner engines apparently.

Just a curiousity question for the coffee crowd. Is there such a thing as a max torque RPM on our Continentals or is it just the max rated RPM for max horsepower?

The C90 lists a max continuous RPM of 2450 and a 5 minute max RPM of 2625. A max continuous RPM and a 5 minute limited RPM I believe is unique to the C90 among the 3 main engines powering the fleet. I assume best torque RPM would also depend on which prop the engine is turning. Typically my C90 turning my cruise prop turns 2300 RPM at the beginning of a takeoff roll and increases in RPM with airspeed. Not at all a scientific observation, but 2300 RPM always feels in the seat of my pants like it could be the best torque RPM for the C90.

Get your HP vs RPM chart for the O200 out. Torque=(5252*HP)/RPM

Ah, yes, HP=lb-ft x rpm / 5252 or Torque=(5252*HP)/RPM

John, my overhaul and engine TC docs don't have a hp/rpm chart unless I look at the fuel flow charts and extrapolate (or I'm just not seeing the obvious).

I found this chart on the Supercub forum with various engines and pistons. Curiously the high static rpm on my 0-200A with the 337'd prop is 2400 which is near the top of the torque curve on this chart. Someone in the distant past was doing some homework.

This is what I came up with:
Note that the C90 is the only one where the torque and HP don't peak at the same (rated) RPM.

[Edit] Actually, these numbers are a lot like the charts in the previous post.

Well! The seat of my pants is definitely wrong on this one. I will say that i never turn my C90 as fast as it can go, but I do like the C90 numbers.

(Puts on his professor's cap)

2475 is the maximum RPM allowed unless you have the Flottorp-Beech adjustable prop, in which case 2625 is authorized with a 5 minute limit.