singel09
Posts: 135
Joined: Thu Jan 20, 2005 12:32 pm

High Air Temp Affecting Aircraft Performance?

Wed Aug 02, 2006 6:36 pm

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
 
FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: High Air Temp Affecting Aircraft Performance?

Wed Aug 02, 2006 8:28 pm

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.
 
Barbro
Posts: 47
Joined: Tue Jun 21, 2005 4:40 am

RE: High Air Temp Affecting Aircraft Performance?

Wed Aug 02, 2006 8:30 pm

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.
 
boeingfixer
Posts: 573
Joined: Fri Jul 29, 2005 2:02 am

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 12:01 am

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
 
EssentialPowr
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Joined: Wed Sep 06, 2000 10:30 pm

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 12:07 am

FredT, nice explanation.
 
bri2k1
Posts: 952
Joined: Sun Dec 19, 2004 4:13 am

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 12:12 am

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
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 12:57 am

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.
 
boeingfixer
Posts: 573
Joined: Fri Jul 29, 2005 2:02 am

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 1:15 am

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
 
singel09
Posts: 135
Joined: Thu Jan 20, 2005 12:32 pm

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 10:46 am

All,

thanks for the clarification!

Mause
 
HT
Posts: 5857
Joined: Sat May 07, 2005 6:20 am

RE: High Air Temp Affecting Aircraft Performance?

Thu Aug 03, 2006 4:06 pm

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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