OK, so in the interest of accurateness, I went up this morning when it was
relatively
calm and did 3 and 4 leg runs and used the very handy National Test Pilot
School (NTPS) GPS Pitot-Static-Error spreadsheet to calculate Vtrue and the
results are not quite as optimistic as my previous quick estimate but not too
bad anyway. I include the output from the spreadsheet so you can look at it
there.
As a summary, I normally plan for 130 knots true at 5100 RPM at 4500-5500 feet
as I mentioned. The check this morning shows that at 5100 I get 127 knots at
3000'
and 128 knots at 4500' (MP 23.5 and 22.5 respectively). At 5200 RPM the speeds
do go up to 129 knots at 3000' and 130 knots at 4500' (MP 24 and 23
respectively).
I looked at measurements I took in 2021 with the same prop with a little more
pitch
and the speed kit (which I still have to paint and re-install) and I was
getting 135 knots true at 4200' and 5100-5200 rpm. I reduced the pitch slightly
which did make me loose some of this speed, but I like the takeoff performance
better now, although it wasn't that bad before. I could get about the same
climb with both finer and coarser pitch but the transition from 60 knots to 110
knots used to be a little sluggish and the RPM would drop to max torque at 4900
RPM. Now it stays at 5100+ RPM, the ground run is much shorter and no longer
do I experience sluggishness when I retract the flaps and accelerate to cruise
climb speed. It just feels better.
Overall, I am very pleased with this engine/prop combination and the current
setup.
Chris
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