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OAT RV4

There are a lot of options.
Probably the worst two places are in the NACA vent and just behind the firewall.

I put both of mine in the last bulkhead, under the leading edge of the VS. as soon as air starts moving through that area, the temps stabilize after sitting in the hot sun.


(Click to enlarge)
 
There are a lot of options.
Probably the worst two places are in the NACA vent and just behind the firewall.


(Click to enlarge)

I initially installed my Dynon OAT probe there as well. It was always a few degrees out when flying. I was told that Dynon has compensation for ram effect so the probe is supposed to be exposed to the airstream. I relocated it to the side of the fuselage about 4" under the stab and it has always been accurate since (when compared to a few others in flight).

Might depend on your probe/EFIS manufacturer.
 
I mounted mine on my RV4 on the bottom of the right wing, just inboard of the inspection opening. It?s easy to get to for mounting and inspection if you ever need to.
 
Outside air temp

Where is the best place to mount an OAT on an RV4?

My OAT probe on my RV-4, is under the horizontal stab, about 10-12 inches aft of the leading edge of the stab, just below the split line where the turtle deck skin and bottom skin overlap.

I have very accurate readings and my True Airspeed reflects that accuracy.

And, say hi to John Howroyd if you see him.

Jake
 
I initially installed my Dynon OAT probe there as well. It was always a few degrees out when flying. I was told that Dynon has compensation for ram effect so the probe is supposed to be exposed to the airstream. I relocated it to the side of the fuselage about 4" under the stab and it has always been accurate since (when compared to a few others in flight).

Might depend on your probe/EFIS manufacturer.

I've never heard that and I was a Dynon beta tester when I installed it. I am within a degree +/-, with others I have flown with. Close enough not to worry. Also the GPS speeds match the TAS, less any wind component.
 
There are a lot of options.
Probably the worst two places are in the NACA vent and just behind the firewall.

I put both of mine in the last bulkhead, under the leading edge of the VS. as soon as air starts moving through that area, the temps stabilize after sitting in the hot sun.


(Click to enlarge)

Why is it not ideal to mount it in the vent?
 
On my -6, I put it one bay ahead of the inspection cover under the horizontal stab. Had good access to it with the stab fairing removed, and backup access through the inspection cover if needed. Keeps it out of the sun on hot days.
 
On my -6, I put it one bay ahead of the inspection cover under the horizontal stab. Had good access to it with the stab fairing removed, and backup access through the inspection cover if needed. Keeps it out of the sun on hot days.
Rob, do you have a photo of your oat sensor installation?

Hammy
 
I tried multiple locations around the tail on the Rocket and always got a 5-6 degree rise in flight due to the big thermal generator on the nose. Ultimately, I installed it in the wake of the pitot mast on the wing and its now rock solid.
 
The oat probe on my RV4, which is the GRT aluminum vane, is mounted under my right wing, just inboard of the inspection opening on the bottom of the wing. This is well clear of any engine/exhaust heat, and out of the sun always. It reads 5* too warm all the time, and it doesn’t make a difference if you have selected Fahrenheit or Celsius. It’s 5 degrees too warm. There is no adjustment for this. I have it talking to my EIS, and may try connecting it directly to my Horizon EFIS to see if that makes a difference. It was grounded locally out in the wing, and the GRT tech suggested trying to ground it where the EIS is grounded (main ground bus - forest of tabs) - which I did. No difference. If the EFIS direct connection doesn’t change anything, then I have a bad probe. The consequences of an erroneous OAT indication on an EFIS equipped airplane with an air data computer integrated is unreliable data related to TAS, density altitude, percent power calculations, on screen winds aloft indications, and any performance related fuel to destination calculations. It might not be a big difference, but it definitely affects my confidence in what I’m reading. I check the indicated winds during approach to land frequently to get an idea on what to expect as related to reported surface winds. These indications are based on TAS, heading, and WAAS generated GPS ground speed. Maybe an erroneous TAS (based on inaccurate OAT) doesn’t make that much difference, but I’m not sure. A relatively accurate OAT (within a degree or two) should be a pretty simple thing to accomplish. We’ve been measuring temperature this way for decades. An inaccurate probe is a miss by whoever made it, and they should replace it.
 
I'm mounting it on the inspection plate in line with and just in front of the pitot tube.

Edit: The inspection place is behind the pitot tube. So I mounted it on the other side (forward) of the main spar. Slighter shorter distance between pitot tube and OAT that way (compared to mounting it on the inspection plate) and the OAT gets air undisturbed by the pitot tube.

Note that I'm using Van's bent 1/4" tube pitot. Have the idea in the back of my mind to 3D print a streamline starting with the OAT and including the pitot.

Finn
 
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Oat

I mounted mine on the bottom of the wing to fuselage fairing. Easy to get to, not much wire, and it always matches the awos.
 
I mounted mine on the bottom of the wing to fuselage fairing. Easy to get to, not much wire, and it always matches the awos.

Did you feed it fresh air? That is where i ended up putting mine and unless it is in the hangar for the first flight of the day it is way off. Outside, in flight it reads 20F high...I will likely move it to the aileron bell crank inspection panel when I get around to it.
 
Rob, do you have a photo of your oat sensor installation?
I don't think so, but I could take one. It's essentially the same place as the photo of the Red RV earlier in the thread. Below and behind the leading edge of the HS.
 
Did you feed it fresh air? That is where i ended up putting mine and unless it is in the hangar for the first flight of the day it is way off. Outside, in flight it reads 20F high...I will likely move it to the aileron bell crank inspection panel when I get around to it.

No, just prop blast. It does hang out in the wind. It sounds like something else might be happening with yours, like it might be picking up exhaust temperature or something? Maybe a wrong setting for type of sensor in your EFIS? Mine just seems to like it there.
 
The most non-sensical yet wonderful option that I went with was from Stein! They said mount it under the wing root fairing, that plenty of air gets in there and it's protected from sunlight, and it works great! Short cable run and nothing to bump into, I went right out of the bay in front of the spar where the fuel tank line comes into the fuselage. YMMV, but it works great for Stein and me too!

Fitz
 
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The most non-sensical yet wonderful option that I went with was from Stein! They said mount it under the wing root fairing, that plenty of air gets in there and it's protected from sunlight, and it works great! Short cable run and nothing to bump into, I went right out of the bay in front of the spar where the fuel tank line comes into the fuselage. YMMV, but it works great for Stein and me too!

Fitz

Maybe the group can help me with this issue. I also mounted my probe out of the air stream (under emp cover, far aft). Due to a different thread, I became concerned about the fact that Garmin, and likely the others, corrects the sensed temp to account for heat generated from the pressure of the air stream on the probe (sorry, forgot the technical name). I asked Garmin if there was a way to turn off that correction and they said no, the probe MUST be out in the air stream.

Does anyone know how low we are reading from actual due to having our probe in relatively still air? I am kind of surprised Stein suggested this now that I have seen the guidance in the Garmin manual (not surprising that I missed it-manual is up to 700 pages). Hoping they may know how big or little of an error this creates for us.

Larry
 
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Some rough calculations... At 200mph, the stagnation pressure is about 0.6psi over ambient of about 14.7psi. That's about a 4% increase in pressure. That corresponds to a 4% increase in temperature as well, but remember this is absolute temperature, so that's 4% of 273K (~10C) or 491R (~20F).

That assumes that your temperature probe measures temperature right at the stagnation point though, which isn't the case. It measures the average temperature of the aluminum probe stuck into the airflow, and I expect the moving air all around that probe overwhelms any effect of the temperature increase due to the air hitting it. I would be very surprised if the actual error is more than about 1C, or 2F.
 
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