The FAA would probably prefer to let such very old sleeping dogs lie.
One other small thing I learned from Barry is that the reported temperature at an airfield is not the temperature at the runway on the ground, but in the shadow at some height. So, if the temperature is say 32 degrees Celsius as reported it could be well over 40 on the runway that you selected for takeoff. That has an effect on the takeoff performance of course. Add to that that the performance figures in the POH probably is more marketing than exact science and you have something to watch out for. So what I do with every aircraft I start flying is figure out what these figures are with me flying that specific aircraft. So on a normal departure from a normal length paved runway I would look at where I would find the first intersection, how much runway there is to that intersection and see if I could takeoff before that intersection. Then I would later compare my performance with what is written in the POH. I think that at times we all do this, but I think this makes more sense than trying to stick with some numbers in the POH. The aircraft Barrty used in his test were not brand new but current and well maintained.
Well Barry certainly knows what he’s doing, but if he did not apply the atmospheric and weight corrections specified for the CIW PIW method, his data could be 20% out, and the aircraft much closer to it’s book values. This evaluation is not as straight forward as normal “pilot” math, but if you want to correctly evaluate the performance, you can;t overlook it!
Well … He did take care of that of course and takes the density altitude and the rest into account. He did everything to do it all conforming what was is the books :-)
Okay, though CIW PIW is more than just a density altitude calculation.
AeroPlus wrote:
One other small thing I learned from Barry is that the reported temperature at an airfield is not the temperature at the runway on the ground, but in the shadow at some height. So, if the temperature is say 32 degrees Celsius as reported it could be well over 40 on the runway that you selected for takeoff.
True! Having flown quite a bit in hot climes I can attest to that. I’ll never forget a t/o in Seville (LEZL) where the reported temp was 46C. It was probably well over 50C on the runway and my C172 behaved accordingly – t/o run more akin to a fully laden 747 than a Cessna……
AeroPlus wrote:
One other small thing I learned from Barry is that the reported temperature at an airfield is not the temperature at the runway on the ground, but in the shadow at some height.
Yes. Actually, that is how standard meteorological temperatures are reported, not only in Aviation. 2m over the terrain in a ventilated white enclosure, otherwise known as “Stevenson weather hut”.
That is what these used to look like, today they are electronic sensors mounted on a standardized plattform. Will try to take a picture of one of those when I get the chance.
Of course, over concrete you can get higher temps, however, they will not have a very high depth, maybe 50 cm or so. The measured air temperature at 2m over ground is quite representative for performance, at least from the moment of lift off it does not take that long to end up at above 2 meters.
However, a OAT of 32 degrees, let alone 46 C will have huge impact on engine performance even without the ground/2m difference.
The standard temperature is measured in the shade while on the runway temperatures could run much higher out in the sun.
The actual runway temps yes. But you will end up in the measured temps, which are measured in one of the devices I mentioned 2m over ground after a few meters above the runway. I’d think outside of the ground effect, the heat over the runway won’t mattter much, unless you are in an area where there is a high heat absorbing ground all over, in which case the 2m temperature also gets influenced.
