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High Air Temp Affecting Aircraft Performance?  
User currently offlineSingel09 From Netherlands, joined Jan 2005, 151 posts, RR: 0
Posted (8 years 4 months 3 weeks 1 day 4 hours ago) and read 6523 times:
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The last weeks, Europe suffered from extreme high temperatures.

Does this have any effect on aircraft performance, like more thrust is needed on take-off, or longer take-off runs to achieve the same (take off  Smile ) as with lower outside temperatures.

It got me thinking as I saw a few A430 models take off at Heathrow, and I had the idea they were slowly climbing.

Any insight would be nice.

Mause

9 replies: All unread, jump to last
 
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 1, posted (8 years 4 months 3 weeks 1 day 2 hours ago) and read 6511 times:

When it is hot (or at high altitudes), the density of the air goes down. This means that for each volume of air, less oxygen is available.

To get power, we burn fuel to heat the air and make it expand. With less oxygen, less heat (fuel) can be added and the possible power outtake is smaller.

Further, there is often a limit on how much you can heat the air. In turbojet engines, the limiting factor is typically the temperature of the air which goes into the turbine. Hotter air in means you cannot add as much heat before exceeding this limit as you could when the air going in was cooler.

The less dense air also affects the amount of lift the wings can generate, meaning higher unstick speeds, stall speeds etc.

The thrust needed is the same, but the maximum power (and thus thrust) available is reduced, resulting in lower performance. This translates to either lower take-off weights, or longer runways needed and slower climbs for the same weights.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineBarbro From Finland, joined Jun 2005, 60 posts, RR: 0
Reply 2, posted (8 years 4 months 3 weeks 1 day 2 hours ago) and read 6508 times:

Yes, high temperature effects flying. The air is thinner (normal laws of pysics, everything expands when heated..) and thus the wings have to compensate by having more speed.
Also engine thrust is affected, although I don't know exactly how. Has got something to do with the temp-difference between the core and by-pass air.
A given aircraft may need more runway to drag a mass up, if that runway is not available --> TOW should be limited.


User currently offlineBoeingFixer From Canada, joined Jul 2005, 534 posts, RR: 0
Reply 3, posted (8 years 4 months 3 weeks 23 hours ago) and read 6475 times:

One of our 727-200's out of CYYZ last night heading west bound was climbing to FL320 but ran into a very warm band at FL270. The TAT was +17 C and they had to use engine anti-ice as they were going through some cloud layers. The combination of high TAT and engine anti-ice reduced their rate of climb at FL280 to 200 fpm. The total time to climb to FL320 from CYYZ was a grueling 43 minutes which normally takes only 22-25 minutes.

So, in short, yes high OAT effects performance.

Cheers,

John



Cheers, John YYC
User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 4, posted (8 years 4 months 3 weeks 23 hours ago) and read 6471 times:

FredT, nice explanation.

User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 5, posted (8 years 4 months 3 weeks 22 hours ago) and read 6470 times:

Quoting FredT (Reply 1):
The less dense air also affects the amount of lift the wings can generate, meaning higher unstick speeds, stall speeds etc.

The true airspeeds are higher. Fortunately, the indicated airspeeds don't change. That makes it simple to remember things like stall speed, rotation speed, etc. It may take longer (a LOT longer) to reach them at high density altitude.

A pilot like myself who trained at a 5,800 foot MSL airport and then transitions to flying near sea level has a huge surprise on that first landing approach. The much lower density altitude also translates to a lower groundspeed, so even at the correct Vref, it feels like you're going to stall. Hard to describe.



Position and hold
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 6, posted (8 years 4 months 3 weeks 22 hours ago) and read 6460 times:

Quoting BoeingFixer (Reply 3):
One of our 727-200's out of CYYZ last night heading west bound was climbing to FL320 but ran into a very warm band at FL270. The TAT was +17 C and they had to use engine anti-ice as they were going through some cloud layers. The combination of high TAT and engine anti-ice reduced their rate of climb at FL280 to 200 fpm. The total time to climb to FL320 from CYYZ was a grueling 43 minutes which normally takes only 22-25 minutes.

Which engines did it have? The -7s were never exactly a powerhouse to begin with.

Quoting Bri2k1 (Reply 5):
A pilot like myself who trained at a 5,800 foot MSL airport and then transitions to flying near sea level has a huge surprise on that first landing approach

Also some seemingly very short takeoff rolls!



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineBoeingFixer From Canada, joined Jul 2005, 534 posts, RR: 0
Reply 7, posted (8 years 4 months 3 weeks 21 hours ago) and read 6456 times:

Quoting SlamClick (Reply 6):
Which engines did it have? The -7s were never exactly a powerhouse to begin with.

Ours have -15 pods and -15A centre. At normal climb EPR for that TAT, they were having a rough time with the warm thin air. Especially having to use Inlet AI. Payload was 35,000 lbs with 50,000 lbs of fuel giving a gross weight at T/O of 180,000 lbs. The departure was at 2AM local and the OAT was still +28 C.

Cheers,

John



Cheers, John YYC
User currently offlineSingel09 From Netherlands, joined Jan 2005, 151 posts, RR: 0
Reply 8, posted (8 years 4 months 3 weeks 12 hours ago) and read 6409 times:
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All,

thanks for the clarification!

Mause


User currently offlineHT From Germany, joined May 2005, 6525 posts, RR: 23
Reply 9, posted (8 years 4 months 3 weeks 7 hours ago) and read 6383 times:

Quoting Singel09 (Thread starter):
The last weeks, Europe suffered from extreme high temperatures.

Does this have any effect on aircraft performance, like more thrust is needed on take-off, or longer take-off runs to achieve the same (take off ) as with lower outside temperatures.

A collegue of mine was scheduled to fly on a KL F50 LCY to AMS last week.
At first she was denied check-in due to load retrictions at LCY.
After a while her check-in was processed, but her luggage didn't make it onto that flight - IMO, it apparently was not loaded onto the a/c intentionally as there is no real way luggage can get lost or being processed too slowly at LCY !
-HT



Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
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