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Location of OAT Probe

istrumit

istrumit

Well Known Member
I have noticed that my OAT, which is located in the fresh air scoop on the copilot side, never reads what the weather service forecasts. It always reads higher by several degrees.

I believe, but I am not sure, that the front air vents also seem let in warmer air than I expect based on my altitude. I will measure this to confirm.

But, I suspect my OAT is reading high because, unlike most RV-10s, I have two sets of cowling vents. I have the standard bottom ones, but also side ones on the bottom cowling, about 3 inches below where the top and bottom cowlings meet (9.5:1 pistons, so I am guessing the builder was trying to enhance cooling).

I think hot air from the cowling exit is mixing with outside air and entering the fresh air vents.

First - Does this seem like a reasonable suspicion ?
And Two - where to relocate the probe if needed ?

Thanks,

Scott
 
Data point..

If you do opt to relocate, I put mine on the bottom of the right wing just aft of the inboard access cover. Works fine in that location.
 
That's a known issue and your suspicions are correct. Underneath the wing or horizontal tail is where most seem to find the most accurate indication.

istrumit said:
I have noticed that my OAT, which is located in the fresh air scoop on the copilot side, never reads what the weather service forecasts. It always reads higher by several degrees.

I believe, but I am not sure, that the front air vents also seem let in warmer air than I expect based on my altitude. I will measure this to confirm.

But, I suspect my OAT is reading high because, unlike most RV-10s, I have two sets of cowling vents. I have the standard bottom ones, but also side ones on the bottom cowling, about 3 inches below where the top and bottom cowlings meet (9.5:1 pistons, so I am guessing the builder was trying to enhance cooling).

I think hot air from the cowling exit is mixing with outside air and entering the fresh air vents.

First - Does this seem like a reasonable suspicion ?
And Two - where to relocate the probe if needed ?

Thanks,

Scott
Click to expand...
 
I was at snf two years ago and was going to install my skyview system starting the day after SNF. I was looking at an RV-8 that had 2 OAT probes under the tail and another one up front. the owner was there and i asked him about it. come to find out, it was a test bed for dynon. he said that the best place in his option was under the horizontal on the fuse. so that is where mine is and reads almost exactly what the OAT is.

bob burns
 
I suppose I will relocate mine to the underside of the wing, sufficiently away from the fuselage.

Is special thermo-couple wiring required ?

What kind ? And where to source ?
 
istrumit said:
I suppose I will relocate mine to the underside of the wing, sufficiently away from the fuselage.

Is special thermo-couple wiring required ?

What kind ? And where to source ?
Click to expand...

No it's regular shielded tefzel. I don't remember off hand how many conductors but seem to recall it's 3.
 
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I tried under the stab, above the stab and halfway up the vertical, living in the hinge cove on the Rocket and never could get accurate free air temp. The 540 puts out too many BTU's. I bit the bullet and mounted it in the wing right in the wake of the pitot mast to keep the impact error out of it. Works great now.
 
I always get the best results under the HS, and usually on the right side. This location works great for systems that have the OAT probe plug into an ADAHRS or magnetometer that lives in the tail.
 
Jesse said:
I always get the best results under the HS, and usually on the right side. This location works great for systems that have the OAT probe plug into an ADAHRS or magnetometer that lives in the tail.
Click to expand...

Jesse,

Have you ever tried it on the Left side? I have mine under the HS on the left side. It was only after I installed it that I thought about the slip stream hitting the left side and bringing engine heat with it. I have a feeling I am reading a bit high, but don't have a way to prove it.

Larry
 
I put it under the empenage fairing just above the HS leading edge in the fuselage bulkhead.

I have watched the temp drop little by little while IFR and started picking up trace ice when it was reading 34 deg. F. so I consider it a fairly accarate location and with no drag penalty.

The air in this location is higher pressure outside than inside so any leakage at the fairing is migrating in to the probe.

This was also a convenient location due to the Dynon network using the AHARS for the conection point.
 
lr172 said:
Jesse,

Have you ever tried it on the Left side? I have mine under the HS on the left side. It was only after I installed it that I thought about the slip stream hitting the left side and bringing engine heat with it. I have a feeling I am reading a bit high, but don't have a way to prove it.

Larry
Click to expand...

When I put in dual ADAHRS I out one on each side usually. They do seem to agree. I don't think exhaust heat is getting to them, but if only one, I put it on the right side for the reason you stated.
 
I went with the heated pitot option, which requires a mast, and then I used the Vans-standard pitot tube hole (for the bent stainless) to put my OAT in. It reads accurately and I'm happy with it.
 
So it sounds like the left side is better for most folks ?

And, some folks are mounting it on an inspection plate (hate to put a hole in the wing skin).

And I need shielded tefzel, 3 conductor of sufficient length.

I am starting my IFR training now, and I don't want it to be 33F outside when my out says its 50F, so I'll be moving the probe.
 
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