comfortcat
Well Known Member
Wow. a duplicate entry. I need to read more carefully.
Thanks Bruce.
CC
Thanks Bruce.
CC
Last edited:
Van's Air Force
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Where does OAT temp probe go?
- Thread starter comfortcat
- Start date
Neal@F14
Well Known Member
The builder of my RV-6 put the OAT probe in the NACA vent inlet on the right side of the fuselage just behind the engine cowl. Bad location totally. I can start the engine and watch the OAT gauge climb 10+ degrees as the engine warms up even before I let off the brakes to taxi. 
One of these days whenever I get a round tuit, I'm going to relocate the probe to the underside of the starboard wing next to the inspection cover.
One of these days whenever I get a round tuit, I'm going to relocate the probe to the underside of the starboard wing next to the inspection cover.
Greg Arehart
Well Known Member
Mine is under the horiz stab, right side.
Bob Ellis
Well Known Member
I placed mine in the wing NACA duct and works perfectly.
rleffler
Well Known Member
I put them on my RV-10 next to the first access panel under each wing. Yes, I have two. Even though they are about twenty inches away from the fuselage, they seldom agree on the temp. Usually there is a 1-2 degree difference. I'm assuming that is just exhaust heat migrating to one side of the other.\
mikehoover
Well Known Member
I had moved my pitot outboard a couple of bays so I used Vans original pitot predrilled hole in my left wing to mount the OAT probe. Seems to be working great.
TAS calculations
Putting hte temp probes anywhere in the fuselage flow will give higher than normal temps due to the heat coming off of the front of the airplane, not just the exhaust heat.
I get a kick out of the temp probes in the fuselage NACA ducts and the pilots talking about their TAS and how fast they are.
I put mine out on the outboard wing inspection panels. Much different readings, and more accurate TAS readings as confirmed by flying a GPS triangle.
Vic
Putting hte temp probes anywhere in the fuselage flow will give higher than normal temps due to the heat coming off of the front of the airplane, not just the exhaust heat.
I get a kick out of the temp probes in the fuselage NACA ducts and the pilots talking about their TAS and how fast they are.
I put mine out on the outboard wing inspection panels. Much different readings, and more accurate TAS readings as confirmed by flying a GPS triangle.
Vic
RV7AV8R
Well Known Member
Probe problem
I tested these probes and they are sensitive to the temperature of the mounting base as well as the probe tip. They basically integrate the average temperature of the whole probe and base. So if you put it in the NACA vent you need to insulate the base inside the aircraft so it is not warmed with cockpit heat. I did this with generous gobs of RTV and it seems to work ok.
I tested these probes and they are sensitive to the temperature of the mounting base as well as the probe tip. They basically integrate the average temperature of the whole probe and base. So if you put it in the NACA vent you need to insulate the base inside the aircraft so it is not warmed with cockpit heat. I did this with generous gobs of RTV and it seems to work ok.
I think real simple - an OAT shoudl be exposed to ambient outside air (uninfluenced by engine heat) and out of the. We've got one in the under-wing NACA scoop (RV-8), one just outboard of the underwing inspection panel (RV-3), and one on the tail inspection plate (RV-6), under the Horizontal tail. All work fine.
Bill Boyd
Well Known Member
OTOH
this goes to show what a terrible location the plans show for a cooling air inlet on the -6. Nothing like sucking air into the cockpit that's a good 10 degrees F warmer than what should be available at altitude for cooling occupants and avionics. If I'd known this 20 years ago, my OAT and NACA vents would BOTH be in a different location!
-Stormy
this goes to show what a terrible location the plans show for a cooling air inlet on the -6. Nothing like sucking air into the cockpit that's a good 10 degrees F warmer than what should be available at altitude
for cooling occupants and avionics. If I'd known this 20 years ago, my OAT and NACA vents would BOTH be in a different location!-Stormy
OAT probe
I put mine in the fairing between the left wing and fuse in front of the left main gear weldment. It's near the inside edge of the fairing. I put a narrow slot to the edge for the wires to pass through so I can remove the fairing without difficulty. The probe stays in the shade, and I think it's far enough away from the exhaust. Plus, the wiring run to the EFIS is simple.
John
I put mine in the fairing between the left wing and fuse in front of the left main gear weldment. It's near the inside edge of the fairing. I put a narrow slot to the edge for the wires to pass through so I can remove the fairing without difficulty. The probe stays in the shade, and I think it's far enough away from the exhaust. Plus, the wiring run to the EFIS is simple.
John
Cold Air
Interesting to note that around 1938 Benny Howard put the cold air inlets in the wing leading edge, well clear of the prop arc. Cessna reinvented this somewhere in the 172/182 production era.
Cessna vents were originally in the inboard leading edge, later models moved outboard, supposedly for noise reduction. Cessna OAT was mounted in the vent for many years.
Interesting to note that around 1938 Benny Howard put the cold air inlets in the wing leading edge, well clear of the prop arc. Cessna reinvented this somewhere in the 172/182 production era.
Cessna vents were originally in the inboard leading edge, later models moved outboard, supposedly for noise reduction. Cessna OAT was mounted in the vent for many years.
Neal@F14
Well Known Member
this goes to show what a terrible location the plans show for a cooling air inlet on the -6. Nothing like sucking air into the cockpit that's a good 10 degrees F warmer than what should be available at altitude
Hammer meets nail head!
In the summertime, I can definitely tell it. The warmer air coming out of the vents was no issue last week when I was up in Idaho, but of course this airplane was designed in Oregon, not Texas where we have triple digit heat all summer long.
Pictures of OAT install
Sorry for the crumby pictures. I had my wing fairing off so I thought I'd add photos of my OAT probe install. I think it's easier than putting it under the horizontal stab and more protected than probes mounted in the NACA scoop.
The keyhole makes removing the fairing easy. Just locate the probe so that the slot is covered by the rubber seal.
John
Sorry for the crumby pictures. I had my wing fairing off so I thought I'd add photos of my OAT probe install. I think it's easier than putting it under the horizontal stab and more protected than probes mounted in the NACA scoop.
The keyhole makes removing the fairing easy. Just locate the probe so that the slot is covered by the rubber seal.
John
N941WR
Legacy Member
I mounted my OAT in the last bulkhead, under the empennage fairing, in the tooling hole. It does read high on the ground but by the time I'm at pattern altitude it is within one or two degrees of everyone else I have flown beside. One advantage to this location is that you don't have to worry about hitting it when cleaning the plane.
(Click to enlarge)
(Try using the search function, I just copied this from a prior thread on the same topic.)
(Click to enlarge)
(Try using the search function, I just copied this from a prior thread on the same topic.)
I mounted my OAT in the last bulkhead, under the empennage fairing, in the tooling hole. It does read high on the ground but by the time I'm at pattern altitude it is within one or two degrees of everyone else I have flown beside. One advantage to this location is that you don't have to worry about hitting it when cleaning the plane.
(Click to enlarge)
(Try using the search function, I just copied this from a prior thread on the same topic.)
I put mine there, and it reads 5-8 degrees higher than everyone else (RVs, Long-EZ, etc.). Thinking of moving it at annual.
left wing, middle inspection cover.
In the shade, out of the prop slipstream. Easy access, turn the cover 90 degrees and set it up inside the wing, no need to disconnect. Thought about placing it downstream of the pitot mast to minimize drag, but took the easy way out.
- Roger
In the shade, out of the prop slipstream. Easy access, turn the cover 90 degrees and set it up inside the wing, no need to disconnect. Thought about placing it downstream of the pitot mast to minimize drag, but took the easy way out.
- Roger
N941WR
Legacy Member
Are you sure your probe is accurate?
OAT calibration
Easy to check. Just compare OAT to CHTs first thing in the morning in the hanger (or some other long time period of constant temperature soak)... Usually mine are within a degree or two. Close enough for the purpose, I suppose. When the temps get close to 32F it is nice to have an accurate OAT. Perhaps one could soak the probe in a cup of ice slurry to verify accuracy at this critical point.
-Roger
Easy to check. Just compare OAT to CHTs first thing in the morning in the hanger (or some other long time period of constant temperature soak)... Usually mine are within a degree or two. Close enough for the purpose, I suppose. When the temps get close to 32F it is nice to have an accurate OAT. Perhaps one could soak the probe in a cup of ice slurry to verify accuracy at this critical point.
-Roger
Four probes
Dual Dynon probes are located in the rear NACA inlets behind the baggage bulkhead right near the ADHARS installation.
EI engine monitor Temp probe is located inside the right wing bay out of the slip stream.
Fast response temp probe located in the engine compartment between and about 5 inches above exhaust pipes.
All agree when the airplane is hangared within a degree.
When the airplane is parked in the sun they are all different for obvious reasons.
In flight however all are within a degree or 2 with the one in the wing root
showing lower than the Dynons in the NACA.
The NACA probes are the most accurate as long as they are not up front near the engine heat such as the RV under wing ducts and the rear NACAs for the RV-10.
My firewall probe is first and foremost a fire indication system and generally gives me rear engine temp indications usually in the 150F range.
Dual Dynon probes are located in the rear NACA inlets behind the baggage bulkhead right near the ADHARS installation.
EI engine monitor Temp probe is located inside the right wing bay out of the slip stream.
Fast response temp probe located in the engine compartment between and about 5 inches above exhaust pipes.
All agree when the airplane is hangared within a degree.
When the airplane is parked in the sun they are all different for obvious reasons.
In flight however all are within a degree or 2 with the one in the wing root
showing lower than the Dynons in the NACA.
The NACA probes are the most accurate as long as they are not up front near the engine heat such as the RV under wing ducts and the rear NACAs for the RV-10.
My firewall probe is first and foremost a fire indication system and generally gives me rear engine temp indications usually in the 150F range.
As described here, in the hangar whenever I've checked it before flight, it does, in fact, match EGT, CHT, and even the outside temperature that my car reports
. So I'm pretty sure it's accurate.
