SonexBuilders.net

Greetings,

Has anyone else suspected interference between the wheel pants and the stock pitot static tube location? My wheel pants are 1" wider, and that's all to the outboard side, so it's a bit closer than the stock wheel pants would be. The tube appears completely stock, and in the correct location.

There are times when the airspeed seems erratic, and it looks like it could be affected by the wheel pants. It doesn't always seem that way though. Sometimes I'll be sure it's a problem, then it will be completely smooth. I've tried to cause problems by yawing to the right, but I can't say I've ever been able to make it happen. I've thought of trying to make a new pitot static tube that is bent outboard and maybe extended farther forward to see if it makes any difference. Just curious.

Thanks,
Rusty

A tool to help verify static port location: https://jasflyer.com/FAQ/AN4.aspx

Thanks, but neither of those articles does much for me. One says don't put the pitot tube where it can be affected by an aircraft structure. That's exactly my question- is the stock location on a Onex too close to the wheel pants? It's pretty darn close.

Rusty

SURE the lines and tube are clear? The slightest drop of water (or mud dauber) affects that pitot if it is sitting in the bend. I sit in tie downs and am subject to weather. Even with a pitot cover on - sometimes I get a tiny drop of water in the tubes and readings are erratic. I actually keep a spare pitot - dry in a bag - ready to swap out and then take the other home to run a pipe cleaner and airline through to get it absolutely dry. Maybe once every 8 months or so.

I also blow out the lines from inside the aircraft to out. (NEVER blow into the lines when connected to instruments - you will destroy the instruments.)

I've certainly never seen anything in the tubes, but it won't hurt to take a closer look. They're covered, and in a private hangar, so no particular risk of contamination.

Rusty

Well,

If it is any comfort, you´re not alone!

Ages ago I had a chat with Kerry about this. He mentioned that on the factory prototypes they often just terminated the static port line under the instrument panel. Hm…….

I decided to give it a try- so far my own attempts had not met with any success. The result was that the asi closely corresponded with the one in a RV4 flying on my wing. Low down it was also comfortably close to the groundspeed indicated by the gps.

The only issue I could observe was that when in the pattern and raising the nose to bleed off airspeed for flap deployment, the asi pointer would for a short while not immediately slow down- before it again decided to behave.

Better than constantly indicating too much, I thought. So it has been like this for the last 5-6 years or so.

Interesting thought about the static port. That would be easy to test, and I might even be able to do it in flight since I have quick connects that I could make reachable for the test. Leaving it open to the cockpit seems like it would change when you open or close air vents though?

I'm still not 100% sure it's a problem. There's no such thing as a smooth day in the summer afternoons when I fly, so it could all simply be turbulence related. I do notice it only in climb, which would cause more potential interference with the wheel pants. On the othe rhand, a careful look at the Dynon logs often do show a correlation between pitch and speed, so maybe it's all normal. The good news is that it's not significant enough to be a hazard, though it makes climb speed testing imprecise.

Rusty

Don't forget instrument error from slipping. Depending on which way you slip the static side is pressurized or not and false readings will occur. Probably similar to Kai's point about flap deployment.

One of the things I plan to look at today is the hole placement on the static probe. I can't recall if there's one, or two, or even where it's located on the probe. Van's static port was similar to most certified planes, where there was a port on each side of the aft fuselage that were connected together by a Tee. That might be better, but maybe not enough to notice.

On my Panther build I installed static ports on each side of fuselage. After flying a 3 leg speed course found it to be reading 8 mph low. Installed a T in the static line to the ports and flew the speed course again with the Bottom of the T open. Now reads 1 mph slow, been flying it that way for 260+ hours. Opening a vent causes a little bump in IAS and then settles to previous reading. Cabin heat has no effect.