Density altitude chart and interpolating numbers.
Alt. setting Pressure alt. conv. factor
29.92 ---------------------- 0
30.00 ---------------------- -73

What is the conversion factor for 29.97? For most, this would be easy, for me, my head starts to spin.

no worries...it's just the instructor in me coming out.

well, a thousand feet equals one inch of mercury

You're just splitting the difference between two numbers. The number you get has to be between them.

Yes, on a simple level I get this. But as I said, there is algebra involved to get the exact number and my algebra is nowhere near what it was in 8th grade anymore. It is a simple formula, I get that now. An hour ago, it eluded me. And instead of cheating, I tried to figure it out and understand.

It would be very easy for me to memorize all the answers and even recall them a year later, but I would not get anything out of that. None of the above even matters after you get a PPl anymore, but the FAA still wants everyone to understand the fundamentals and I am trying. :)

not too much algebra involved. remember...for each inch of mercury that changes, it results in a change of 1000 feet of altitude. 1/2" equals 500 feet. .25" results in 250 feet. .13" results in 125. .06" is 62.5' .03" is 31' etc

You are having the same issue in a round about way. Say "hi" and smile. Pretty simple concept, but sometimes one can over engineer it. :)

73/8*5= 45.625 or 45 in the case of the number needed to solve the rest of the question. 29.97 is 5/8 of the way to 30.0.

WTF, i ... i'm quittin my job!!
Where can i do this?!?

5/8 is 0.625.

29.92-current baro.=x
then take x*1000+Current field elevation=pressure altitude.


in the airplane...to find pressure altitude, you just dial 29.92 in the altimeter while sitting on the ground

I always like to find a better way to do things, even if it involves more complicated contraptions. :)

You've never even seen coke, or a cokehead, haven't ya..

give the hookers coke and they will be still.. LOL
That's like giving a 5 year old 1 gallon of coca cola and a kilo of sugar.. and then putting them to bed..expecting them to sleep..

I gave the formula above. Answer is 45. :)

Actually -45.

There is a lot of interpolation in Thermodynamics. There are pages and pages of basically spreadsheets for thermodynamic properties at different temps and pressures for different substances and you need to interpolate between the cells.

Sometimes you need to interpolate diagonally- that is, do it three times since you have to interpolate between pressures and temperatures.

I use it in other classes too but thermodynamics and heat transfer used it the most.

You would be right, my experience with coke and cokeheads is rather limited...

I was just curious how 29.97 is 5/8 of the way to 30.00

it's telling you the standard altimeter. if the pressure rises .08" of mercury, up to 30.00...it results in a decrease in altitude of 73 feet. if the pressure goes from 29.92 up to 29.97, it's going up .05" of mercury. based on our rule earlier...

1000/1" = x/.05" (1000 feet per 1 inch of mercury) = (x feet per .05" of mercury) should be 50'

(i did 50 feet with the rule of thumb method). 5 feet is not bad for a quick guesstimate

alright...gonna drive the 15 minutes home. cya