OAT Location

Flybuddy2 · #1 09-13-2010, 12:19 PM

Currently have my Dynon OAT probe in my NACA vent and getting a higher temp reading than actual there. Looking to move it onto the left wing inspection plate just behind the pitot tube. I've got a stock Van's ss pitot tube. Even though the OAT is wider than the pitot will it suffer any inaccuracies mounted there due to the turbulent airflow from the stem of the pitot. If so, how far should I offset it?? thx Tom

f1rocket · #2 09-13-2010, 12:45 PM

You might try mounting it to the bottom wing fairing cover. That get's it out of the exhaust and/or cowl airflow. No need to go all the way out into the wing. If you do put it out there, I don't think the airflow around the pitot will bother it.

Flybuddy2 · #3 09-13-2010, 02:05 PM

Quote:

Originally Posted by f1rocket

You might try mounting it to the bottom wing fairing cover. That get's it out of the exhaust and/or cowl airflow. No need to go all the way out into the wing. If you do put it out there, I don't think the airflow around the pitot will bother it.

Is yours there?? if so, does it read accurately? Seems like it might get some limited exhaust flow there. Heck of a lot easier to mount it there though. Pierre did a super job on grommets and sealing and I'm having a tough time routing wires through the wing. Ground a small hole in the pvc tube that houses the strobe/nav/landing light wires and fishing 041 wire through there but it keeps hitting something before it makes it to the fuselage. Sounds like the bottom wing fairing is worth looking at.

RickWoodall · #4 09-13-2010, 02:10 PM

When i did my research on this, I was led to believe that mounting it on the back emp deck of the fues, under the emp fairings was as good a location as any. It is out of the weather, but also out of turbulent air, exhaust etc.

Made sense to me at the time. I dont think you want it in the "wind" do you?

At the back there should be no ill effects from cabin heat etc that would effect it. Further, for the skyview it now plugs into the back side of the adahrs so the wire run is very simple in that location.

mike newall · #5 09-13-2010, 02:13 PM

Mounted ours front right of the lower fuselage - bottom skin by the fuel vent.

Outside where the exhaust can't touch it - easy to wire in, haven't flown yet but got that position from the forums ages ago.

Brantel · #6 09-13-2010, 02:16 PM

That is where I have mine. It works in the air when there is a bunch of air movement around in there. On the ground, it will read high if the Sun is beaming on the airplane.

It is a little slower to respond to changes in that location but it works good enough.

I am not sure there is a perfect place for these things. Also, I don't think many if any of the affordable EFIS makers dynamically adjust for all the variables that can impact a OAT probe.....

Quote:

Originally Posted by RickWoodall

When i did my research on this, I was led to believe that mounting it on the back emp deck of the fues, under the emp fairings was as good a location as any. It is out of the weather, but also out of turbulent air, exhaust etc.

Made sense to me at the time. I dont think you want it in the "wind" do you?

At the back there should be no ill effects from cabin heat etc that would effect it. Further, for the skyview it now plugs into the back side of the adahrs so the wire run is very simple in that location.

elippse · #7 09-13-2010, 02:51 PM

In the cabin NACA duct, it gets air warmed by the engine that flows out of the inlets and down the side of the fuselage and into the cabin. That is why it indicates a higher temperature. On one airplane I tested it hardly dropped in going from 2000' to 10,000'. It is subject to stagnation heating if out in the airstream, which is 7.2F maximum at 200 mph. If you mount it in the tailcone just above and behind the elevator spar cutout you will get reasonably fast response and true OAT.

roee · #8 09-13-2010, 03:05 PM

The OAT probe should ideally be in the air stream in clean flow, away from the prop wash and away from structures that may otherwise affect the local air flow, out of direct sunlight, and away from any other sources of heat (engine, exhaust, cabin).

Underneath the wing is probably about as good as it gets. But why choose a spot right behind the pitot? There are plenty of other convenient spots (other under wing inspection panels) away from the pitot.

N8RV · #9 09-13-2010, 03:16 PM

I had originally mounted mine in the NACA vent, only because I had recalled seeing others mounted there. Then I read the installation instructions (Duh).

"It is important that the OAT probe be mounted somewhere on the skin of the aircraft where it will not be affected by heat sources (sun, engine, aircraft interior, etc). It is acceptable to extend the length of the included wiring for the OAT. The ideal location would receive no heat from the aircraft engine or any other source in the aircraft body. While this may be impractical, it is a good idea to mount the probe as far away from heat sources as possible. On the RV series, common locations include the wingtip and under the horizontal stabilizer." (Dynon D-100 installation manual, Appendix B)

I remounted mine beneath the horizontal stab. I've had no troubles with it there.

Hope that helps.

f1rocket · #10 09-13-2010, 04:12 PM

Quote:

Originally Posted by Flybuddy2

Is yours there?? if so, does it read accurately? Seems like it might get some limited exhaust flow there. Heck of a lot easier to mount it there though. Pierre did a super job on grommets and sealing and I'm having a tough time routing wires through the wing. Ground a small hole in the pvc tube that houses the strobe/nav/landing light wires and fishing 041 wire through there but it keeps hitting something before it makes it to the fuselage. Sounds like the bottom wing fairing is worth looking at.

Yep, and it reads fine. I mounted mine forward of the spar to make the wiring easier. The oil pattern from the exhaust indicates that the exhaust flow doesn't (can't) get that far forward on the bottom of the wing.