Dynon D100 airspeed

I have two separate pitot systems. One is a standard ASI as my backup. My primary is the D100 Dynon EFIS. The EFIS is reading very low while the standard ASI is almost spot on. I've checked the EFIS lines and I find no kinks or loose fittings . When landing , the EFIS is indicating about 35kts so it's way to slow. The company thinks it's a line problem. Anybody got any expertise in this area with ideas?

Do you also have separate static ports or just separate pitot tubes with a common static port?

If they are both tee'd into the same static source and also the same pitot source, then it points to a calibration error.

That's easily checked by making a water manometer and connecting it to the pitot head with plastic tubing. It will also show up any leaks in the pitot lines.
(e.g. 20" head of water = 174 knots/199mph).

Have you also checked that you are plumbed into the correct ports? The Dynons have an additional port for the AOA line. If you have the pitot or static connected to that port you may well get a strange reading.

Dynon airspeed

They both use the same static source from Vans plans. Ive made sure it is plumbed to the correct line. The connections look good to me. Ive not tried any pressure test but how does that tell where a leak may be or does it just indicate there is one somewhere?
Thanks
Mike

Dynon airspeed

One other thing. I have seperate pitot tubes for the two but they share the same static port .

Manometer

Mark, can you explain the way to use and read the manometer in my situation? I think Id like to try it

Mike,

First you need a good length of softish clear plastic tube. Home Depot can usually oblige.
It should have an inner diameter that can slip over your pitot tube (if it's the bent tube variety) or can be attached to a joint in the pitot line.

A manometer shows the pressure in the line by the difference in vertical height of the two sides in a water column in a u-shaped tube. So you need to arrange about 4-5 ft of tube taped to a vertical surface in a U-shape.

Dying the water with ink or food dye makes it easier to read. When it's connected up, add water to the open end and watch the airspeed rise.

This is Kevin Horton's spread sheet for converting the manometer reading to IAS.

I'm sure, if you search, you could find a more pictorial guide to the process.

Mike Coady said:

One other thing. I have seperate pitot tubes for the two but they share the same static port .

Click to expand...

Then this would tend to indicate either the EFIS pitot tube is in an area of "low" pressure, the ASI pitot is in an area of "high" pressure or a combination of both. Do the manometer test on it as Mark posted and if OK you might have to check the actual pitot tube location. How are the pitot tubes physically installed? How different is the EFIS pitot tube installation as compared to the "steam" pitot tube?

This link helps with how to do the check

Have you tried swapping pitots from one instrument to the other for a comparison?

Pitot airspeed

Got a pressure test done today and I apparently have a leak. So, I swapped the lines and walllaaaa, sure enough, the Dynon reads faster now and my standard ASI is slower thus proving the leak. By the way, my installations are exactly as on plans so that was ok. Thanks for all the input. And, I think I'm gonna make that manometer anyway for fun.