REFLECTOR: True airspeed issues fixed

[Geoff Gerhardt]

Guys,

If you remember, I recently realized that my static port was being
pressurized at higher speeds, resulting in erroneous altimeter and airspeed
indications.  At cruise, my altitude would be off by ~300' and I thought my
cruise TAS was ~160kts.

I have a pitot static tube and its mounted under the canard.  Based on your
tips, I attempted to counter this pressurization that occurs in that region
by wrapping foil tape around the pitot tube right before the static ports.
 Initially did a couple wraps - did nothing, so I wrapped quite a bit more
and saw a difference, wrapped a bunch more and saw a bigger difference.
 Now I was getting up to a ~1/6" of foil tape wrapped around the pitot
tube, but it was still off.

I was testing it by making sure the altimeter exactly matched the GPS
altitude on the ground (by adjusting the barometric pressure), then seeing
how much it was off at cruise.  I was still about 150' off at cruise, so
instead of wrapping more, I added a tee to my static system and had a vent
into the cabin that I could open/close in flight.  I got up to altitude
(9000') and opened the in-cabin static port and immediately my altitude
snapped to exactly what my GPS altitude was indicating and my airspeed
matched the GPS ground speed (after accounting for wind).

The best part of all of this is that I now realize that I've been flying a
whole lot faster than I thought.  If you remember, before I changed my
exhaust (from the normal, venting down out thru the cowl to venting inside
the cowling at the back towards the prop) I was seeing a TAS of ~150kts at
cruise, LOP.  After the exhaust mod, that jumped up to the high 150's,
usually seeing close to 160ktas.  Now that my airspeed is indicating
correctly, tho, I am cruising at 175-180ktas!  Even tho I'm going the same
speed as I always have, it feels like I'm going faster!

My normal hangar buddies that fly 172's and Warriors have no interest in me
telling them that I am cruising at 200mph, and give me the "yeah, whatever"
when I excitedly tell them how fast I'm cruising now.  They've grown tired
of me starting out 1/2hr after they do to go to our b'fast run.  I hope you
guys can appreciate that cruising at that speed while burning a measly
8.5gph is awesome!

Anyway, I now mounted my static port in a more permanent fashion on top of
the canard (dog house area).  I have that area blocked off quite well from
the nose area that would get pressurized when the gear doors open.  I
didn't see much fluctuations in the indications when I opened/closed cabin
vents, but I'll have to experiment a little more.

Geoff
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