A tool for JSBsim Airfoil Modelling

[IAHM-COL]

I can get the JSBSim property for TAT later if you want, its under /fdm/jsbsim somewhere!

Yeah thanks
If you can give me the specific pointer I can see if it's there
I tried my luck on the subtree jsbsim with no luck
IH-COL

[IAHM-COL]

True air temperature is the one you want because that is what a temperature sensor will measure. It accounts for heating effect of airspeed etc.

Temperature-degC is simple atmosphere temperature (SAT).

I have been thinking about this description. Currently, I am of the opinion the correct temperature here is the "SAT"; which is the temperature of the air that will be surrounding the aircraft. Normally a sensor would be applying sampling biases, which is not what I need to consider here.

What is your reasoning behind "TAT" being better?

[123apple]

Because, it is quite correct to speed up to increase temperature of the fuel (if you are flying in a region where external temperature is too cold).

I quote:
https://en.wikipedia.org/wiki/Total_air_temperature

total air temperature and is measured by a temperature probe mounted on the surface of the aircraft. The probe is designed to bring the air to rest relative to the aircraft. As the air is brought to rest, kinetic energy is converted to internal energy. The air is compressed and experiences an adiabatic increase in temperature. Therefore, total air temperature is higher than the static (or ambient) air temperature.

If you use SAT, then speeding up to increase fuel temperature wouldn't work correctly (unless you account for speed elsewhere in the system).

The probe is designed, so it takes into account the effect of airspeed on temperature.

[123apple]

The property is /fdm/jsbsim/propulsion/tat-c

[IAHM-COL]

Found the property. It is where you pointed it out,

However,
After reading the information on the wiki that you list:
https://en.wikipedia.org/wiki/Total_air_temperature

I can't figure out why you really think that the value in this sensor will be the correct temperature to use in the thermic transfer between the fuel tanks and the surrounding air of the wing?

See per example:

https://en.wikipedia.org/wiki/Total_air_temperature

The probe is designed to bring the air to rest relative to the aircraft. As the air is brought to rest, kinetic energy is converted to internal energy. The air is compressed and experiences an adiabatic increase in temperature. Therefore, total air temperature is higher than the static (or ambient) air temperature.

Clearly, this device is intended for a correction in the calculation of true airspeed. But the value of temperature it produces is higher than the temperature surrounding the wing at any given moment, since there is air compression going on within the sensor.

I suggest you rethink this and let me know if you still think the TAT is the temperature I should care about here.

In simple terms, imagine the thermodynamics phenomena taking place on the fuel-environment gradient through the tank surfaces.

Per example this quote in the same wiki page seems to provide correct synonyms, from what I can see

Static air temperature (SAT) is also called: outside air temperature (OAT) or true air temperature

[123apple]

In aviation terminology, the outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft, but unaffected by the passage of the aircraft through it

So there is a distinction between total and true air temperature. True air temperature is without the ram rise effect. Will look into this more tomorrow morning hopefully.

I also quote:
https://www.ctsys.com/blog/entry/oat-sa ... -what.html

TAT: Total Air Temperature. This is the SAT (Static Air Temperature) PLUS the temperature rise associated with high speed flight. So what exactly is the temperature (ram) rise and do we need to know what it is? Actually, yes we do….
The ram rise is the result of heating due to air friction and compression. Think of it as the temperature that the aircraft skin feels. Ram rise only becomes a factor at speeds above approximately 200 kts and is proportional to the aircraft speed, so the faster you’re flying, the higher the ram rise. At jet speeds of .80 Mach or higher, the pilot can expect a ram rise of about 30 degrees C, a significant increase when considering flight in icing conditions.
...

The total air temperature is what determines the formation of ice on your airframe, engine nacelles, generator inlet, interior fuel tank and any other aircraft critical surface.

If you think of it, you're sending a lump of metal through the sky at 250 knots + (indicated) -- air molecules bouncing off your airplane exert a force, imparting energy to your aircraft. So where does this energy go? The answer is, it increases the internal energy of the aircraft - that is, the aircraft experiences a temperature that is higher by the so-called "Ram Rise".

And this is why you speed up if your fuel tanks get too cold in flight.

Does this answer your question?

[IAHM-COL]

It does give me good guidance on what the assumptions are, that need to be taken in consideration.

It seems we are simply saying that as speed becomes really large then friction and compression coefficients play a non-negligible role.

I can see that.

On the other hand, that article you qoute above cites a delta of 30Celsius, and that is wild!!!

I'll do some test with (tat-c), produce plots and show them here. [Regular flying] Then we can discuss the differences I simulate.

***

There's already an important amount of heating that comes via airspeed with my code

Well, not airspeed, per se. But since to fly faster at any given condition, all else being equal, I would ask more power from the engine, then that means throttling up. Accelerated combustion means more heat (TIT). Most of the heat source of the engine oil in my workarounds come from there -- as the code I build causes the oil to sink some heat from that source and heat up consequently. This is, I push throtle and yes, all else equal, I'll gain speed. But also I'll get heat that will dissipate to oil -> to fuel -> to atmosphere in that order (if my FCOC is working).


Best,

[bomber]

How fast are you flying ?

I understand that at extreme speeds you'll get increase in temperature due to air friction.... take re-entry heat as an extreme example.
But...
What about wind chill factor ? .... "0 degrees feels like -5"
If you're flying high above the clouds what about the radiated heat from the sun, so surely there's a difference between times of day ?

Simon

[IAHM-COL]

@123


did the test flight
http://www.jafva.com/flight/1315/

I used now the tat-c as air temp parameter.

This is the data



If you are curious, I accelerated around the 1.0 timemark from 0.68 to 0.82 to see if there was any effect, and indeed there was. Tat responded and then fuel warmed.

I'm good either way. I'll leave the tat then

Thanks

IH-COL

[IAHM-COL]

How fast are you flying ?

I understand that at extreme speeds you'll get increase in temperature due to air friction.... take re-entry heat as an extreme example.
But...
What about wind chill factor ? .... "0 degrees feels like -5"
If you're flying high above the clouds what about the radiated heat from the sun, so surely there's a difference between times of day ?

Simon

1. At subsonic. This plane's reported max is around 0.82

2. Chill factor? I dont know. That's not the only think that came to mind on this exercise. What about viscosity? ie, the airspeed of the air lamina in contact with the wing is way slower than those farther away, due to viscosity of the fluid. Right? I would presume? And if speed plays this large effect, then my mind goes *kaboom*, as fundamentally, the molecular layer of air on the wing/air interaction must be virtually an static?

3. Yup. The sun. Praise the sun?! also I don't know how much this plays here.

But I've got some simulation that kind of has a decent profile, so I'm a happy camper for now, I guess.

Other areas of this craft systems itch more right now that I have at least some reasonable values here.