This forum is superb for exchanging ideas, problems,
and solutions, but we seem to be very short on hard data. Maybe that is
because it is hard to get, or because some people don’t know how to
calibrate and test carefully, or some don’t want to know. As a
result we have a lot of anecdotal evidence, much of which is clearly
wrong. Example: one LIV-P owner proudly announced at the Lancair dinner
he was getting 305 knots at 70%. I had flown in that the airplane, and
knew the airspeed indicator was not calibrated, and the owner’s
calculation was based on an E6B which meant it had a built in 20 knot error
based on OAT and compressibility effects. Put that in, and you get about 285
knots pretty much like everyone else. And he really had no clue about the
exact power setting, just a guess.
Maybe we just prefer rumors and BS to facts. Perhaps
that is why rumors are so popular. Facts are such nasty things.
They just won’t go away.
I propose we make a concerted effort to gather and
exchange reproducible, defensible data, and share it with the group. Not
the swing of the needle in an updraft or satisfying GPS reading while screaming
downwind, but data that is good enough for us to compare the relative
performance of props, modifications, etc.
With the new Chelton (and other) instrumentation,
factory calibrated far better than your steam gauges, good GPS data, and
careful data recording (OAT, Altitude, fuel flow, etc.) we can get excellent
data without a long and painful calibration process. The new Electronics
International MVP-50 is also a superb instrument, built to good standards with
reasonably accurate sensors and ability to record and regurgitate vast amounts
of data. When I was ordering mine, I found that some of their customers
have used the extra channels to monitor things like engine cooling air delta P,
firewall temperature (how hot is that epoxy REALLY getting?), and other nuggets
of information useful to the rest of us.
This rant is motivated by last night’s rereading
Kent Paser’s excellent book, Speed with Economy (1994, possibly
available through EAA). It documents Kent’s 20+ years of modifications with
his 160 HP Mustang II. Kent is an aeronautical engineer, and took the
time to calibrate his instruments and conduct careful experiments making
changes one at a time to isolate what worked and what didn’t. Net
result: an increase of 64 MPH in top speed and 59 MPH in cruise
speed. Slowed to his old economy cruise speed, fuel flow was cut IN
HALF.
Our Lancairs already incorporate a lot of the
features that Kent explored and adopted, but most of us have failed to learn
his (and other) lessons about exhaust systems, engine air cooling, exhaust air
leakage in low pressure areas, where we should lavish our attention to detail
and such.
If we can collect and disseminate GOOD data in a
format that another can study, digest, and learn, then we can advance our aviation
interests even better than we are now doing.
Moreno’s challenge: produce and publish
(here, of course) “test reports” documenting what you measured, how
you measured it, if and how you checked your instruments, and any helpful
comments. I promise that if I ever get my Lancair IV finished (early next
year?) I will keep testing and recording and share the news, good or bad,
because it should not be an ego thing, but a sharing of information thing to
help advance our “state-of-the-art.”
I recall one year that Brent Regan and I walked around Oshkosh trying to capture the
essence of the place in a few short words. The Greeks thought the world
consisted of Earth, Air, Fire, and Water. We concluded that Oshkosh consisted of Hope, Denial
(of the laws of physics), Money, and Bullshit.
It need not be that way. Advancement comes from
knowledge, and knowledge comes (in part) from testing, experiments, and real data.
Fred Moreno, Thirsting for Data