second Outside Air Temperture probe?

[Pilottonny]

I already purchased and installed an OAT-Probe in the left wing for my Dynon D100, so it can show TAS. Now that I received the D120 Engine-probes, I found a second OAT-probe in the set! I was wondering what I could use this second Temp-probe for? Does anybody have a (useful!) idea of what temp. to show on the D120 ?

The first things that came to mind:

• Cabin temp.: well, I can feel for myself if it is hot or cold, right? Let?s not waste weight on a gadget like this!
• Engine compartment temp.: What does that tell me? OK, if it gets really hot, there is probably a fire, but that will be pretty obvious because of the flames and smoke, right?
• Exiting air temp. from engine compartment: What does that tell me? It will vary with OAT, engine temp. , power setting, climb, decent, etc. No real use , is there?
• Fuel system temp.? Strapped to the fuel pump, or a critical fuel line (insulated by the fire sleeve) , it may give me a pre-warning for vapor lock? (I will be running Mogas!)

Anybody got a useful suggestion? Or should I just not use it at all?
To me, the Fuel temp. setup sounds like a good idea, especially because I will be running Mogas. But than the question arises of where to install it, to get some useful reading.

Now I am wondering what you creative minds com up with!

Regards, Tonny.

[elippse]

Originally Posted by Pilottonny

I already purchased and installed an OAT-Probe in the left wing for my Dynon D100, so it can show TAS. Regards, Tonny.

Where in your left wing did you install the probe? My original OAT sensor used with my RMI I installed in my right wing behind the rear spar but ahead of the flap to keep it out of the flow field, and so get no stagnation rise. When I got my Dynon I put its sensor in the tail cone above and behind the elevator spar pass-through hole. Both sensors agree with each other within 1C and both agree with forecast temperatures aloft, so that I know my TAS is correct. I recommended to Dick Shapley that he install his Dynon sensor in the tail cone of his -9A, which he did. I had him fly his plane at slow speed and see what his OAT was, then get up to max speed and again look at his OAT. They were the same, indicating no stagnation rise. This rise is a maximum of 7.2F at 200 mph TAS. If your OAT recovers +5F error from it, that will give a +1.8 mph TAS error.

[Pilottonny]

Elippse,

Mine is in the middle of the underside of the wing, about 30" from the fuselage side. It's sticking out about half-way, to avoid to much additional drag. It does not see any sun and is out of the way of anything hot (cabin air, exhaust, cooling air). I am not flying yet, but I guess it will indicate accurate enough.

Regards, Tonny.

[elippse]

Originally Posted by Pilottonny

Elippse,

I am not flying yet, but I guess it will indicate accurate enough.

Regards, Tonny.

Not really! Sticking out in the free-stream subjects it to the temperature rise, so your OAT will probably indicate 3F to 5F high!

[terrykohler]

You didn't say if your engine is injected or carb. If it's the latter, you can use the second probe to help detect carb ice. As to location of the OAT probe, the important thing is to not have it mounted where exhaust gas will affect reading. Mine is mounted in the NACA vent and I really don't care if sunlight gives me a slightly off reading when I'm flying in clear air. My interest in temperature is when I'm IMC and I'm watching for temperatures slightly above to about 10 degrees below freezing. Otherwise, the slight deviation in temp really has little impact on my TAS value.
Terry

[jrvssgl]

Myself, I am adding a temp probe in my fresh air box. This will enable me to watch the temperature for ice, and also allow me to see how well me carb heat works. Just a thought.

[flybill7]

Originally Posted by elippse

Not really! Sticking out in the free-stream subjects it to the temperature rise, so your OAT will probably indicate 3F to 5F high!

I'm trying to decide where to put my OAT sensor. Regarding putting the sensor into the free-stream, the Dynon folks say: We don't take into account ram air rise, because below 200ish knots, the effect is fairly small. Also, small errors in OAT will not affect TAS tremendously.

It would be easier to simply mount in the the wing bottom, in the air-stream. But I don't want to get inaccurate readings.

Not sure what people mean when they say put it in the tailcone area. Does that mean it's not sticking into the airstream there?

... Bill

[Pilottonny]

Terry, please look at my signature!