Van's Air Force
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Temp probe
- Thread starter togaflyer
- Start date
tommylewis
Well Known Member
wing
Under side of the wing in an inspection plate, mine is on the right side.
Under side of the wing in an inspection plate, mine is on the right side.
Auburntsts
Well Known Member
Bottom right wing, inboard-most inspection panel.
koupster
Well Known Member
Mine is mounted inside of the flap hinge stiffener (my terminology). It doesn't produce any drag there, and is much slower to respond to hot ramp temperatures. For clarification, a link to a picture of the flap hinge stiffener follows (Thanks, Jason).
http://www.jasonbeaver.com/rv7/wings/2009/11/
Cheers, David
http://www.jasonbeaver.com/rv7/wings/2009/11/
Cheers, David
The temperature probes of these designs (JPI, DYNON, etc...."stinger" type probes) are best mounted on the underside of the wing like most guys are posting here. It's because the probe needs to reside OUTSIDE the boundary layer to pick up a ram rise effect when inflight. It allows for a more accurate and consistent temperature reading. At our speeds (<200 knots), the ram rise correction isn't that high (maybe only +2 deg C) but consistency is the name of the game. A probe inside the structure to avoid the airstream might not give consistent readings and drift around too much to be reliable. I guess it depends on how accurate you want to measure it (performance calculations, etc.).
aturner
Well Known Member
Could someone educate me regarding the ram rise effect and true airspeed calculation? Is this factored out by the EFIS? Or does the true airspeed require that the ram rise be left in? In other words, does an accurate true airspeed need the warmer temp in the freestream, or the static air temp?
BillL
Well Known Member
Maybe the picture was taken in a mirror? An optical seclusion.
Temp probe ram rise
Could someone educate me regarding the ram rise effect and true airspeed calculation? Is this factored out by the EFIS? Or does the true airspeed require that the ram rise be left in? In other words, does an accurate true airspeed need the warmer temp in the freestream, or the static air temp?
Aturner.....
Well, that's a good question. I'm not sure the EFIS systems we use account for the "K" factor ram rise, because if it did during the calibration setup routine, then yes you would have a more accurate true airspeed calculation. But to tell you the truth, I think with these probes and the relatively lower airspeeds we fly, the K factor might not be significant enough to make that much of a difference, (1 or 2 degrees of correction) so it would just use the "total" temp and call it even.
TAT=total air temp, what you see in flight without any correction. Also sometimes called RAT, ram air temp. Some (most?) EFIS systems we use just stick with "OAT" cause it's easier due to the relatively low correction factor.
SAT=static air temp, TAT or RAT temp corrected for K factor--or ram rise increment.
OAT=Officially, outside air temp, more accurately observed on the ground and not moving, but susceptible to radiation effects and possibly inaccurate, especially in the summer.
The ram rise is always positive and the correction to SAT would be to subtract a few degrees to get it. K factor can vary a bit depending on the speed. The higher the speed, usually the more subtraction to get SAT. The probe located inside the NACA scoop is ok because it's just outside the thin boundary layer that exists on that NACA ramp. Boundary layers are small, depending on where they are on the airframe, but can be as little as 1/8" to 1/4" thick in the areas of interest where the probes are located beneath the wing (measured in wind tunnels and/or with hot-wire anemometers-----a different chapter). Temp probes inside the boundary layer (like some old flush bulbs) aren't that accurate and are troublesome because there's too much random drift of the reading. They're not used much any more. That's why you see modern aircraft with temp probes sticking out in the airstream. Especially Boeings, Airbus, military fighters----(Rosemount, etc.) pretty much everything nowadays. It gets more complicated when the probes are heated for anti-ice protection (more sophisticated probes like the Rosemount).....but I won't open that Pandora's box, cause that's the domain of the big guys with lots of speed. Look at Beech, Piper, Cessna, etc...their probes "stick out" into the airstream to get outside the boundary layer.
Hope this helps. My dad always said I give a dollars worth of answer to a nickel question. (Heehee).
Could someone educate me regarding the ram rise effect and true airspeed calculation? Is this factored out by the EFIS? Or does the true airspeed require that the ram rise be left in? In other words, does an accurate true airspeed need the warmer temp in the freestream, or the static air temp?
Aturner.....
Well, that's a good question. I'm not sure the EFIS systems we use account for the "K" factor ram rise, because if it did during the calibration setup routine, then yes you would have a more accurate true airspeed calculation. But to tell you the truth, I think with these probes and the relatively lower airspeeds we fly, the K factor might not be significant enough to make that much of a difference, (1 or 2 degrees of correction) so it would just use the "total" temp and call it even.
TAT=total air temp, what you see in flight without any correction. Also sometimes called RAT, ram air temp. Some (most?) EFIS systems we use just stick with "OAT" cause it's easier due to the relatively low correction factor.
SAT=static air temp, TAT or RAT temp corrected for K factor--or ram rise increment.
OAT=Officially, outside air temp, more accurately observed on the ground and not moving, but susceptible to radiation effects and possibly inaccurate, especially in the summer.
The ram rise is always positive and the correction to SAT would be to subtract a few degrees to get it. K factor can vary a bit depending on the speed. The higher the speed, usually the more subtraction to get SAT. The probe located inside the NACA scoop is ok because it's just outside the thin boundary layer that exists on that NACA ramp. Boundary layers are small, depending on where they are on the airframe, but can be as little as 1/8" to 1/4" thick in the areas of interest where the probes are located beneath the wing (measured in wind tunnels and/or with hot-wire anemometers-----a different chapter). Temp probes inside the boundary layer (like some old flush bulbs) aren't that accurate and are troublesome because there's too much random drift of the reading. They're not used much any more. That's why you see modern aircraft with temp probes sticking out in the airstream. Especially Boeings, Airbus, military fighters----(Rosemount, etc.) pretty much everything nowadays. It gets more complicated when the probes are heated for anti-ice protection (more sophisticated probes like the Rosemount).....but I won't open that Pandora's box, cause that's the domain of the big guys with lots of speed. Look at Beech, Piper, Cessna, etc...their probes "stick out" into the airstream to get outside the boundary layer.
Hope this helps. My dad always said I give a dollars worth of answer to a nickel question. (Heehee).
