Jack--
I commonly cruise at 105 mph. I have a 71-48 McCauley prop on my
Ercoupe. I can easily hit 125 mph in a dive. There are several things
you can check:
1. Your airspeed indicator--when I lead the flight of Ercoupes in
to
the EAA convention each year, someone always asks about airspeeds. We
each call off our airspeeds on the radio. We are flying in trail, so
you know we are actually doing the same speed. One pilot says he is
going 115, someone else says 85, etc. The called out speeds are all
over the place. Checking the airspeed indicator with a GPS will be
affected by winds. In order to do an accurate check you must fly north
for a few miles, east for a few miles, south for a few miles, west for a
few miles, and average the speed shown on the GPS and compare that
average with your airspeed reading.
2. The surface of your airplane--when I bought my plane the paint
was
peeling in quite a few places. I stripped it off and polished the plane
and picked up about 4 mph.
3. Your prop--you say you have a climb prop. What is the pitch?
I
have seen some props stamped incorrectly, so you can't always go by the
numbers stamped on the prop. A prop shop will give you an accurate
pitch. Also, if your prop leading edge is rough your airspeed will be
lower.
4. Your rigging--if the plane is out of rig you are getting more
drag,
lowering your airspeed.
5. Your RPM--tachometers also can be off quite a bit. There is a
device called a TachCheck that some A & P's have that accuratly measures
your actual rpms. Also--low rpms are not good for your engine. You
don't get adequate cooling or oil circulation. The green arc on the D
model starts at 2400 rpm and goes to 2575. My mechanic says I should
run at about 2450, and I do. Babying an engine does it harm, not good.
6. How many venturi's and other drag causing things do you have
hanging out? This will also slow you down.Hope I helped you. Syd Cohen NC94196 Ser. No. 1519
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