Pitot Replacement

[n38139]

I have an RV-4 that has a Piper Pitot mast on my airplane. I am having problems with airspeed indications on the "fast" end of the scale 10 to 15 knots. I don't know that the mast is the problem but I have put two different airspeed indicators and they both have the same indications. I have flown with others and checked my speed so I know it is an indication problem.

I know I could have a leak but since I have rebuilt every thing else on the airplane I am going to start at the pitot input and go all the way to the indicator as well as the static ports. My question is what type of pitot probe should be used, I am leaning towards an AN style probe but open for inputs.

thanks

[David Paule]

Is it reading high or low? Is it accurate at low speeds?

Also, could you describe the static port, shape and location? Generally, errors are with the static port.

And with the holiday, there might not be a good discussion developing, but you could search the archives for similar issues.

Dave

[Norman CYYJ]

More than likely a static problem. Check that the static source is in the proper location and that there are no leaks in the system. Open and close the air vents does cause a momentary change in air speed if so you have static leaks.

[n38139]

It reads low on the high end of the speed scale. All of my static instruments are reading correctly.

[curtis]

I have the Piper blade style pitot-static probe on my -6A, but it was never accurate. I got the system to be accurate by not using the static portion of the probe and installing the standard Vans static ports.

[Norman CYYJ]

It is next to impossible to tell if your static instruments are working properly, they will work with just cabin air and appear to be working well. The air speed needs a proper static source to work properly.

[curtis]

For approx a year I flew with just static system open to ambient cabin pressure and all of my airspeeds while in flight were almost spot on. I added the static ports when I upgraded the plane by installing an autopilot. The issue with using cabin air is the pressure bumps in the static system when opening and closing any air vents.

[rvbuilder2002]

Originally Posted by curtis

I have the Piper blade style pitot-static probe on my -6A, but it was never accurate. I got the system to be accurate by not using the static portion of the probe and installing the standard Vans static ports.

This likey explains your problem exactly, if your airplane is using the static port on the pitot tube. Most RV builders are unaware that here are a bunch of different part numbers of Piper blade style pitot tubes. Many of the variations are different angles on the bottom surface (where the static port is located).
Take a look at the line connections to the pitot. If there are two lines then the static is being sourced from there also.
Installing standard static ports and re-plumbing the static system to them would likely totally solve your problem.

[Ironflight]

I'll echo what Scott said - using the PITOT part of the Piper blade is just fine, but forget about the static being accurate if you use the ports on the blade. We have the blade on two RV's, and use the standard Van's static ports on both - and they are very accurate.

Paul