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OAT Probe

jwilbur

Well Known Member
Anyone install their OAT probe through the bottom of the RV10 fuse in the battery compartment bay or the bay just aft? Any reason not to?
 
Anyone install their OAT probe through the bottom of the RV10 fuse in the battery compartment bay or the bay just aft? Any reason not to?

You want to keep it out of the exhaust flow. Based on how much grime I clean off that location, I'm not sure I would put it there.

I have one adjacent to the first access panel on each wing. At that distance, I'm seeing a 1 degree difference in temps. I don't know if that reflects a real difference or just a calibration issue.
 
I did

I didn't get mine until it was shipped with my panel from Stien,then it was too late to put it into the wing. Put it as far back as I could.
People will say that the exhaust will effect it. I really don't think so. Exhaust is going to get blown away well before it hits the probe. So far high speed taxiing around shows it gives the same reading as my GRT probe which which is in my front Naca scoop. But that also gives me point of reference as well.
Made the install a lot easier that's for sure.
 
Agree with previous post not to put on bottom of fuselage. Exhaust and hot air from engine will cause a warmer than normal outside air temp. This elevated temp will affect TAS readings and thus affect wind direction and speed display. Recommend placement on wing access panel. Dan from Reno
 
I didn't get mine until it was shipped with my panel from Stien,then it was too late to put it into the wing. Put it as far back as I could.
People will say that the exhaust will effect it. I really don't think so. Exhaust is going to get blown away well before it hits the probe. So far high speed taxiing around shows it gives the same reading as my GRT probe which which is in my front Naca scoop. But that also gives me point of reference as well.
Made the install a lot easier that's for sure.

I moved mine from the NACA duct and moved it under the right wing near the first access panel. The new location shows 3-5 degree F lower temperature than the NACA duct. I think the NACA duct gets air that is heated by the engine/cowl and spillage from the inlets as well as the sun.

Just my observation.

TJ
 
Why was it too late?

It was already wired into our harness. Which meant fishing the actual probe itself out to the wing.
Once flying next month I'll do some testing and post if there's any discrepancies... I suspect that at the speeds the 10 goes, there won't be any issues, but I'll find out.

For what it's worth, I see ALOT of OAT probes installed in the NACA scoop.
Most certified planes they are on the windscreen about 6 inches for where mine is in the scoop.
 
Rear NACA scoop?

Many RV10s have NACA scoops in the back also (such as mine). Any thoughts about putting the probe in the rear scoops?
 
It was already wired into our harness. Which meant fishing the actual probe itself out to the wing.
Once flying next month I'll do some testing and post if there's any discrepancies... I suspect that at the speeds the 10 goes, there won't be any issues, but I'll find out.

For what it's worth, I see ALOT of OAT probes installed in the NACA scoop.
Most certified planes they are on the windscreen about 6 inches for where mine is in the scoop.

For what it's worth, there have been many, many reports here on VAF and other RV places that the NACA scoop will read high by a significant amount in flight.

Taxi testing isn't going to show this - nowhere near the amount of power or airflow. You might see a lot of OAT probes in NACA scoops on RV's, but that doesn't mean they are reading correctly. Those of us that have actually TESTED to location know that it doesn't work if you want accuracy.
 
... You might see a lot of OAT probes in NACA scoops on RV's, but that doesn't mean they are reading correctly. Those of us that have actually TESTED to location know that it doesn't work if you want accuracy.

Does this include tests on probes mounted in rear scoops? Any data on that location?
 
It was already wired into our harness. Which meant fishing the actual probe itself out to the wing.
Once flying next month I'll do some testing and post if there's any discrepancies... I suspect that at the speeds the 10 goes, there won't be any issues, but I'll find out.

Ok. I was in your situation and simply cut the harness, mounted the probe to the inboard most right wing access panel and spliced the harness back together--easy-peazy. No issues in a 100 hrs.
 
Ok. I was in your situation and simply cut the harness, mounted the probe to the inboard most right wing access panel and spliced the harness back together--easy-peazy. No issues in a 100 hrs.

Who knows. Maybe I'll do that. I've got a small window next month before its scheduled for paint. Might just run a new wire and leave the old one.
FWIW Paul, the one in my Naca is for my backup EFIS which I'll only refer to once in a while and won't be too concerned if it's TAS is off. If I'm staring at that screen, all I'll care about is altitude and indicated airspeed. 😜
 
Probe in rear NACA?

So let me ask one more time before just giving it a try. For those who installed AFT NACA scoops to feed an overhead console in an RV10, has anyone tried putting an OAT probe in a rear NACA scoop?
 
Slight thread deviation but oat related. I have an optional OAT sensor for my chronometer. I decided to mount it in one of the wing access panels per previous discussions here on VAF. I didn't like that it wouldn't have any support other than the RTV that is used to hold it in place so I found a small snap bushing that it would slide into. My question is how far should this thermocouple extend out into the airstream to be effective / accurate?
 
Slight thread deviation but oat related. I have an optional OAT sensor for my chronometer. I decided to mount it in one of the wing access panels per previous discussions here on VAF. I didn't like that it wouldn't have any support other than the RTV that is used to hold it in place so I found a small snap bushing that it would slide into. My question is how far should this thermocouple extend out into the airstream to be effective / accurate?

Which chronometer/OAT do you have?
 
I tried the front NACA and it will read high. It doesn't work there. I suspect you may find the same situation for the rear. There is a lot of heat flowing around the fuse in flight. The air coming out of my overhead vents, which is fed by the rear NACA vent, definitely "feels" warmer than ambient as does the front.
 
So let me ask one more time before just giving it a try. For those who installed AFT NACA scoops to feed an overhead console in an RV10, has anyone tried putting an OAT probe in a rear NACA scoop?

Decided to go straight to the source and ask the garmin guys. Answer I got was ANYWHERE on the fuse is a bad idea.
Looks like I have one PITA project to move mine before it flies to paint. Have some interior disassembling to do....🙁
 
back of the bus...

For what it is worth, on my RV7, I ran mine (Dynon set-up) back with the wires going to the tail and mounted in on the rear inspection panel under the HS. Seemed to give good numbers and not affected by exhaust (i.e. never saw change with power setting changes, attitude, etc..). Very small gage wire so weight etc is no factor. Always seemed to provide accurate true airspeeds as well, to me a very nice benefit of having an OAT hooked to a glass cockpit. Not sure if I could "spin the dial" and get a true airspeed anymore, clearly spoiled by Dynon.:) Plan on the same location for the 10 I'm building.
 
Just another data point. I put the OAT probe in the bulkhead under the rear tail fairing.

The tail area is an area of higher pressure and the small amount of air that leaks in around the elevator horn opening is migrating forward (past the temperature probe) in the fuselage towards the area of lower pressure (cockpit).

By testing multiple times I feel it is as accurate as I need it.


Flying a 3 way gps run with Kevin Horton's spreadsheet calculations shows my TAS within ~1 Knot of the calculated TAS on the efis which uses temperature.

Additionally when in the clouds and the OAT slowly drops to ~34-35 deg F I start picking up light ice on the wings and windshield which is what I would expect.
 
Rear NACA

With a dual Dynon set up I have 1 each installed in the left and right rear NACA.
An additional one is located inside the wing root mounted through the
fuselage wall serving my EI engine monitor.
For comparison, I see very little difference between any of the 3 probes in flight. 2 or 3 degrees difference showing up when flying north and the afternoon sun hits the one side of the airplane more than the other.
 
OAT Probe Location

For what it is worth, on my RV7, I ran mine (Dynon set-up) back with the wires going to the tail and mounted in on the rear inspection panel under the HS. Seemed to give good numbers and not affected by exhaust (i.e. never saw change with power setting changes, attitude, etc..). Very small gage wire so weight etc is no factor. Always seemed to provide accurate true airspeeds as well, to me a very nice benefit of having an OAT hooked to a glass cockpit. Not sure if I could "spin the dial" and get a true airspeed anymore, clearly spoiled by Dynon.:) Plan on the same location for the 10 I'm building.

Hi, please just to clarify your OAT probe location. I'm mounting mine now for Dynon D10. Are you saying you mounted it out of any air stream and inside the area under the vertical fin? I like it. Seems like this is a perfect location. It would measure air temperature with no affects from any wind warm or cold. Right? Is it a good location?
 
I mounted mine on the right fuse just inside the leading edge wing root cover. There seems to be enough gap to get airflow, and on the right side so on the downswing side of the propeller. Easy routing, it's protected and in the shade when parked. Seems to be consistent with all other available temperature information such as TAFs, AWIS and ATIS.

Martin
 
I had the same question during my build about where to mount the probe. By searching this forum, I learned that many people have found a variety of wrong places to place the OAT probe. For example, I learned that installing it in the NACA scoop may look cool, but reads hot. Garmin says put it on the underside of the wing. Get it away from the engine and air disturbed by the prop. It should be in the airstream. It is also in the shade on the bottom of the wing, unless you are upside down, which is not recommended in a RV10! Cut, then splice the cable after you have it mounted - not difficult. The Garmin manual says the cable can be extended up to 25 ft. I did not see any reason to reinvent the wheel, repeat mistakes made by others, or over-think it. However, they are experimental aircraft.
 
With regards to mounting the temperature sensor in the NACA inlet. My first reaction is that by design the inlet has some compress-ability in the throat or slightly forward of that area. As we know the gas law tells us that increased pressure comes with increased temperature.

It would be interesting to block the outlet of the scoop and see what the temperature differential is compared to a wide open outlet. Low speed - small variance, high speed - probably increased temperature relative to the OAT.

Just a thought on other factors that may be causing the errors besides engine thermal sources.

-larosta
 
On my -9 I mounted both on the rear bulkhead, under the empanage fairing. It reads high o the ground but once air starts moving through that area, it is always within a degree, high or low, of people I fly with.

The reason I mounted it there was to keep me from hitting it when I wash the plane.
 
Ok. I was in your situation and simply cut the harness, mounted the probe to the inboard most right wing access panel and spliced the harness back together--easy-peazy. No issues in a 100 hrs.

I called Dynon about cutting my OAT cable and splicing a piece into it because I mine is too short. They haven?t returned my call yet. Now that?s it?s been a few years since you did it, is it still a good idea to cut and splice it?
 
Mine is on the inboard inspection panel of L wing. Installed after wing attach with no problem. Works great...
 
I called Dynon about cutting my OAT cable and splicing a piece into it because I mine is too short. They haven’t returned my call yet. Now that’s it’s been a few years since you did it, is it still a good idea to cut and splice it?

Just fine except for the fear of cutting a $400 RTD wire. I think best to solder the wires (Being an RTD, the resistance is critical to an accurate reading) and did so with a stagger cut, not all in the same axial location. I pulled back the shield and pulled it back over the splices to solder it back together and shrink wrapped the shield.

I had the fear but it worked out just fine. I tested both locations with thermocouples and watched the temperature deviations, with the under wing location as the winner.

IMO: It slowed the plane 3 kts, but had to be done. :p
 
Just fine except for the fear of cutting a $400 RTD wire. I think best to solder the wires (Being an RTD, the resistance is critical to an accurate reading) and did so with a stagger cut, not all in the same axial location. I pulled back the shield and pulled it back over the splices to solder it back together and shrink wrapped the shield.

I had the fear but it worked out just fine. I tested both locations with thermocouples and watched the temperature deviations, with the under wing location as the winner.

IMO: It slowed the plane 3 kts, but had to be done. :p

How can the wire cost $400 when the entire assembly costs $35?

50' of RTD wire costs $23 https://www.automationdirect.com/ad.../thermocouple_-a-_rtd_extension_wire/rtd_wire

Anyway what's the difference between splicing it in and adding to it? There's still a resistance in the extra wire. Then I'd also have to go find those little connectors and install those.
 
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UPDATE :

I thought I had to route the OAT probe to the EFIS but I have the 3 wire probe and that one goes to the D10A Remote Compass, so I might not have to cut the wires after all. I also had a doubt about the length resistance possibly affecting the readings but I found this in the D180 installation manual, in an appendix :

You may lengthen or shorten the connections between the OAT and EDC-D10A. Use the provided crimp connectors on the new wire leads.

and

Before calibration or adjustment, it is possible for the OAT sensor to read as much as 5 degrees Celsius off the actual value. Therefore, it may be necessary to adjust the displayed air temperature value to compensate for this. To make this adjustment, you must enter the menu system and press the following sequence of buttons: MORE > SETUP > MORE > OAT. This will display the OAT adjustment menu. Press INC or DEC to increase or decrease the currently displayed OAT value.

It is important to make this adjustment when the air surrounding the OAT probe is at a known temperature. This can be achieved with a standard thermometer. Adjust the displayed OAT until it agrees with your independent temperature reference.



So BAMM ! My troubles seem to be gone for now.
 
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Agree with PD. I?ve mounted several OAT probes in the wing bottom skin close to an inboard inspection cover. That?s outside the exhaust flow, and out of the sun. It is an easy install and results in accurate readings, which enhance air data that directly affect performance and efficiency.
 
How can the wire cost $400 when the entire assembly costs $35?

50' of RTD wire costs $23 https://www.automationdirect.com/ad.../thermocouple_-a-_rtd_extension_wire/rtd_wire

Anyway what's the difference between splicing it in and adding to it? There's still a resistance in the extra wire. Then I'd also have to go find those little connectors and install those.

1. Garmin Probe -$513 @ Spruce
2. wire is cheap
3. soldered to eliminate issue with resistance.
4. splice vs extension -irrelevant
What is your point?
 
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