wrote in message
ups.com...
On Oct 10, 7:14 am, Scott wrote:
OK, I guess I can buy into that one, but I'm still confused a bit. If
one is limiting it (the O-320) to a given RPM that gives 100 HP out,
wouldn't that same RPM give less than 100 HP at high density altitude
just as an O-200 would?

Scott

They're not deliberately limiting it to 100 hp. The fixed-pitch
prop does that on any airplane. Your O-320 will make any O-200 look
sick. You need to fly a 150 with the O-200, and you won't complain
anymore. A 150 with the O-200 on takeoff won't generate anywhere near
100 hp. In fact, I have my suspicions that it never did, even at 2750
RPM. We had those engines in a couple of 150s, and I flew an Aircoupe
with a C-90, 10 less hp than the O-200, and it took off much shorter,
climbed and cruised much faster than the 150. It generated that 90 hp
at a lower RPM, which means that less hp was lost to drag. The
airplane weighed only 150 lb less than the 150.
A guy in the US did some testing on a 150. He did a static
thrust test, full RPM with the airplane pulling on a hefty spring
scale. Got around 230 lb, IIRC. Then he took that O-200 out and put in
a 100 hp Subaru conversion and did the static test again and got
almost 300 lb. That wasn't with a lower-pitched prop, either; the
airplane cruised as well as before at a similar RPM. Makes one wonder
about hp claims.

Dan

Don't confuse thrust with HP unless you're using the exact same prop and
prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust
because of gearing, disc area, etc? But, that thrust is only effective in a
narrow (vertical) speed range. The same engine, combined with an RV-style
cruise prop, would only generate (WAG coming) 250 lbs of static thrust.

HP claims on certified engines were +/- 5% back in the day when most "100
hp" 0-200's were built, meaning that a "bad" engine generated 95 HP when it
was built.

KB