Question on AOT sensors with dual ADAHRS

[Janekom]

I have a few questions please. RV10 with dual Skyview and dual ADAHRS.

Will an OAT sensor installed inside a naca duct feeding the overhead ventilation, be accurate?
Secondly how will paint influence the accuracy of the OAT sensor?

 

[Dynon]

The OAT should remain unpainted.

It's hard to comment on a specific ducting, but the OAT really doesn't want to be anywhere near the engine, seeing sun, or in any other place where it might be heated.

 

[Rhino]

Not really a good idea. NACA ducts typically compress air, which affects temperature (raises it). How much depends on the duct type, airspeed, the location of the duct and the location of the sensor. Since the temperature can change with airflow, you'll likely see different temps when you open or close the ventilation too. The variations might be small, but then again, they might not. Generally it's a chance you wouldn't want to take if you can avoid it. Most people with RVs I've seen mount them to an underwing inspection panel, which makes them readily accessible. If connecting in the rear of the aircraft, some also use the bottom of the horizontal stab. This topic comes up fairly regularly in the Vans forums, and it's always cited as a bad idea.

 

[Janekom]

Thank you for the replies. I have looked at my logged flights using Savvy and saw that the OAT always goes to about zero degrees, or it tends to show more or less the right temperature. I am leaning toward a loose connection now.

 

[Janekom]

I have had a chance to go out to the aircraft. It was using the 201 as the OAT source. In other word not the Master, but the Slave ADAHRS. Then I also saw that someone has keyed in a 4 Degrees C offset - not sure why. I then measured the resistance of the OAT sensors installed as well as a brand new one I have spare. The new one as well as the one connected to the 200, was measuring close to 1.35KOhm, but the one one the slave measured about 1.9KOhm. This was on a 17 Degrees C day on the ground I therefore figured that the slave might be faulty. I have changed the Skyview so that it uses the 200 (Master) for the OAT source and went for a short local flight. The OAT indication seems to be correct now, butI will see on a long flight at higher altitudes.

I did not have time to replace the sensor with the higher reading and also did not have time to move them from the naca duct to a better position - will see. my question is if anyone out there knows what resistance to expect at what temperature on these sensors?

I assume is an (NTC) negative temperature coefficient sensor where the sensor's resistance decreases as the outside air temperature increases?

 

[rjones560]

I have a few questions please. RV10 with dual Skyview and dual ADAHRS.

Will an OAT sensor installed inside a naca duct feeding the overhead ventilation, be accurate?
Secondly how will paint influence the accuracy of the OAT sensor?

The probes should be mounted under the wing, (out of the sun) and far enough outboard that the exhaust stream does not have any impact on them. I mounted mine about 12” outboard of the wing root fairing on my RV10, but even further out would be fine.

 

[Janekom]

Thank you Rjones - will get there in time. at this stage trying to debug. But this is not what I was asking advice on in my last post

 

[Wheel_Nerd]

Dumb question. Building an S-21 now. Was looking at where on wing I was going to place OAT probe before I closed it up. I remembered I wanted to go with dual ADAHRS (200 + 201). Do I install 2 OAT probes too? Probably also need to buy these sooner than I thought I needed given the OAT probes come with the ADAHRS modules.

Also, the 10 ft won’t reach. OK to splice on more length to reach ADAHRS modules?

 

[rjones560]

So you are building a Rans S-21. The ADAHARS do not share OAT information so you need one for each ADAHARS. You can use any good aviation wire to extend the wire. I put the probes on he underside of the wings on my RV10, outboard far enough to be sure the engine exhaust would not effect them. Under the wing, out of the sun, would be fine for you as long as the doors can not hit them.

 

[Rhino]

Page 5-15 of the installation manual. Location is pretty much up to you as long as you avoid the things listed on that page.

 

[Wheel_Nerd]

So you are building a Rans S-21. The ADAHARS do not share OAT information so you need one for each ADAHARS. You can use any good aviation wire to extend the wire. I put the probes on he underside of the wings on my RV10, outboard far enough to be sure the engine exhaust would not effect them. Under the wing, out of the sun, would be fine for you as long as the doors can not hit them.

Thx! That’s what I thought given they both came with their own OAT probes. Nice to have someone that knows for sure to confirm.