OAT Location

[Ratman]

I've just ordered a D180 and have been pondering where to mount the OAT sensor. The install manual says "On the RV series, common locations include the wingtip and under the horizontal stabilizer."

Would this include "inside" an RV wingtip so I can hide it or does it have to be outside in the windstream? I was thinking the remote magnetic compass module would be in the wingtip as well so wiring would be short.

If it has to be outside, would a few inches behind the pitot work? The pitot will be one of your heated models but I'm not sure it would put off that much heat. What do you think? Just trying to put it somewhere that it won't be touched especially by a brush while washing the aircraft or near the tiedown rings.

 

[meljordan]

A word of caution about putting the EDC in the wingtip on an RV. I tried that on my 6 and ran into several problems. If you have any high current (nav lights, landing lights) in the wing tip and the wire to those runs anywhere close to the EDC (say within 12-18 inches) you will see a swing in the compass when you turn those lights on. The current in the wire induces a mag field and in my plane that caused the compass to swing 15 degrees. I tried moving the EDC back in the wingtip and then the big iron bar used in the aileron as a counterweight would effect the EDC so as you moved the aileron, the EDC would react. I gave up on the wingtip and put it in the fuselage tailcone where it works perfectly. Then it was a no brainer to put the temp probe below the horizontal stab (yes it needs to be out in the windstream) where it too works great. In that location it is not visable unless you get down on your knees and is out of direct sunlight, so it gives a nice constant reading.

Best Regards,
Mel Jordan

 

[dynonsupport]

As Mel mentions, the OAT does need to be in the free airstream. The OAT can only read the temp around it, and air is a great insulator, so all that air inside your wingtip will cause a lot of delay in measuring the real air temp.

 

[65xx]

On my RV-9A, I put my OAT probe in the first inspection panel outboard from the left wing root. I just dropped the panel, drilled the hole, installed the OAT and a shorter run for the wires to boot. Dan.

 

[Ratman]

 I gave up on the wingtip and put it in the fuselage tailcone where it works perfectly.  Then it was a no brainer to put the temp probe below the horizontal stab (yes it needs to be out in the windstream) where it too works great.  In that location it is not visable unless you get down on your knees and is out of direct sunlight, so it gives a nice constant reading.

Best Regards,
Mel Jordan

Thanks Mel, you just saved me a bunch of time. Do you think the ELT antenna will have any affect if it is back there? Not a lot of room in an -8 EMP fairng. If I have to I'll put it behind the rear baggage but that will be a pain.

 

[dynonsupport]

The ELT antenna will be fine as long as it's well secured and isn't moving around.

 

[Ratman]

Thanks Dynon Dude!

 

[Battson]

Sorry - dredging up old questions again - but:

Understand the gauge should be in free air, but out of direct sunlight?

Is the OAT gauge strong enough to take a few minor hits, like beetles / bugs in flight or small debris flicked up by the propwash or landing gear? Or does it need to be recessed into a pocket or vent channel of some kind?

I was going to use my air vent scat ducting, but might not have that kind of vent now...

 

[jakej]

The OAT 'Probe' is ok 'outside' out of sun

Jake J

 

[Battson]

Does the probe get affected by the wind factor, if placed in the slipstream?

 

[dynonsupport]

The probe is not corrected or calibrated for ram air rise, thus it is technically a TAT probe. So if it is in the free stream, it will read slightly hotter than actual OAT/SAT. This error is dependent on the recovery factor of the probe and the local airspeed, so it's really hard to correct for on an arbitrary install on an arbitrary aircraft.

Absolute worst case difference between TAT and SAT, assuming a .75 recovery factor, would be 1C at 100 knots TAS, 4C at 200 knots TAS, and 9C at 300 knots TAS, although the real world install difference is likely much lower.

 

[skysailor]

How sensitive is the rear of the probe? I plan to mount my probe in an inspection panel on the bottom of the wing which I think should be fine. The other possibility is in the skin of the wing in the wheel well area. It would be a bit harder to do here so I was hoping the inspection panel below the wing would be OK. Should I be concerned there will be no air movement inside the wing on the back of the probe?