Inaccurate airspeed

[jonstark]

In phase one and have been trying to check airspeed accuracy by averaging gps groundspeeds over a triangle course. Cruise is dead on. It’s been just a bit bumpy but just barely.

Here’s what I’m seeing...
Indicated vs gps
75 = 75
60 = 60
55 = 60
50 = 56
45 = 50
40 = 47

I have the standard 1/4” pitot tube about 4” below the wing and about even with the leading edge. Maybe a couple inches forward but I’d have to go look again.

The ASI is calibrated.
Static port in empennage as per mod.
Is there any way to improve pitot configuration?

Luckily the wing is honest and stalls are straight forward. Going into uncoordinated stalls tomorrow. Moose stalls! Good practice.

Jon

[PapuaPilot]

It looks like your numbers are fairly accurate. The slower you get the less accurate IAS will be and it will be less than TAS/GS due the increasing angle of attack.

I would suggest doing it again when it is smoother and you can get more accurate numbers.

[av8rps]

My Model 4 ASI was off 10 mph (reading slow) until I disconnected the static port located on the right rear side of fuselage. I now just run with the static port left open under instrument panel. If I open doors in flight it is not as accurate as with doors closed, but still better than when static on rear of fuselage reconnected. I have verified my ASI accurate many times over the years since I disconnected the static port line and know it reports 98+ % accurate, which is good enough for me.

I think if I had a static port on both sides of fuselage it might be more accurate? Many say the static port out on the wing located next to the pitot is best. But I like mine the way it is, so I'm leaving it disconnected.

And fwiw, my Highlander with a single static port mounted on boot cowl did the same thing. So I unhooked it like my Kitfox, and that one too now has airspeed accuracy within 2 mph overall.

Over the years I've heard Kitfox and Highlander owners complaining about how slow their planes are, and wonder if they just don't have ASI errors like I did? Many never take the time to verify the real numbers, which is pretty easy today with a GPS.

The fuselage is short for the length of the wing on this family of aircraft, and I believe that fact along with more adverse yaw than most other aircraft experience makes keeping the ball centered in flight difficult, ultimately making it difficult to get a static port to operate properly.

Your mileage may differ....:)

[Dorsal]

I get a similar result to av8rps with the static on the side of my aircraft (~8 mph low). Most of the time I have it ported under the IP which reads 3-5 high. I plan to do some experiments to see if I can get the side mount closer.