Sign in to follow this  
Guest Tom Goodrick

IMPROVED OAT GAUGE FOR JETS

Recommended Posts

As many know, the outside air temperature has a big effect on the performance of jets in high-altitude cruise. We really need a good temperature gauge to see what the true temperature is. I have used the Bell206 temp gauge for many years because it looked nice on the panel. But it is sensitive to airspeed and gives totally bogus values at high speed and high altitude.So I made a good OAT gauge the other day and have tested it. It works very well with no effect from airspeed. It shows the temp in C.Get it free from my web site at:http://home.hiwaay.net/~goodrick/Download.htmlFor anyone who is really concerned about the temperature effect, the following equation gives the ratio of thrust to nominal thrust at the standard temperature of -56.1C that exists in FS from 37,000 ft up. T/T0 = 1952 / (2457+9*C)Plug in C as measured by the AMB_TEMP_C.xml gauge. If C is 10 degrees warmer than standard, the thrust ratio is just under 5% less than unity. You would need to boost the thrust by 5% and take a penalty in fuel flow or let the speed stay low and keep the same fuel flow. If you fly with real weather instead of Clear Skies, there will be some effects.Tom Goodrick

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

'But it is sensitive to airspeed and gives totally bogus values at high speed and high altitude.'Technically speaking, the temperature reading given on the default temperature gauge is the correct total air temperature. The reason it's so high is that as the air at the probe is slowed and compressed, the temperature rises, thus you can have an inflight reading of the TAT at 37000 feet being in the range of -20-30 C or so. However, an Air Data Computer can take TAT and convert that to static air temperature, or the ambient temperature, which is what your gauge shows. (If I understand your post correctly)Of course, with FS, this is all accomplished through formulas and the sim engine, so the actual physics of total air temperature don't come into play.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this