thestooges
Posts: 157
Joined: Sun Sep 02, 2001 4:46 pm

Effect Of Altitude /temperature On Aircraft Range

Thu Feb 12, 2004 6:42 pm

From reading various posts on A.net, it has become clear to me that an aircraft taking off on a very hot day from a high altitude airport (i.e. hot and high) will have its range considerably reduced and have other aspects of its performance affected.

Could somebody explain this phenomena for me,

Thanks
Nobody expects the Spanish Inquisition !!
 
707CMF
Posts: 4698
Joined: Thu Mar 14, 2002 5:39 pm

RE: Effect Of Altitude /temperature On Aircraft Ra

Thu Feb 12, 2004 6:53 pm

From reading various posts on A.net, it has become clear to me that an aircraft taking off on a very hot day from a high altitude airport (i.e. hot and high) will have its range considerably reduced and have other aspects of its performance affected.

Factually wrong and in the wrong forum (mods, please move this to tech/ops).

High Altitude and High temperature of airfield have no direct influence over the aircraft range.
However, the direct influence of both those phenomena is that air is less dense, which will have two consequences : thrust will be less efficient (be it a prop or a jet, the more dense the air is, the more efficient the thrust is), and the lift as well is less efficient for a given speed.
So an aircraft will need a greater speed to take off, and this added to the lessened acceleration, it results iin the need of either a longer runway or a lighter aircraft.

You can lighten an aircraft by putting less fuel in it, so indirectly, yes, it reduce the range of the aircraft.

Hope I've been clear enough,

cheers,

707
 
SlamClick
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RE: Effect Of Altitude /temperature On Aircraft Range

Fri Feb 13, 2004 2:05 am

TheStooges

I believe that the posts regarding hot/high ops shortening range refer to airliners and not small planes. It is probably a good idea to specify which you mean because there are differences in the way they are operated that are as great as the obvious difference in sizes.

Reply #1 is correct enough when speaking of light planes and normal full-size airports. But very misleading if we are talking about airliners.

A Cessna 152 has very little range of weights. One person or two people. Maybe a ten gallon difference between a light fuel load and a heavy load. Whereas, even the little Airbus I fly may have a twenty thousand pound range of possible fuel loads and a thirty thousand pound range of possible payloads. The Cessna can accelerate to terminal velocity on a runway too short for an airliner to use. So the considerations are very different.

Sorry but I have to speak from the reference point of US regulations and operational practices because that is my training and my experience.

The maximum allowable takeoff gross weight of an airliner, when it is less than the maximum certificated takeoff gross weight is a figure that will vary with density altitude (combined low pressure and high temperature being the worst) runway length available, obstacles in the departure corridor, runway slope, wind during takeoff, runway contamination, inoperative equipment or missing exterior pieces that affect airflow and that sort of thing as well as other factors.

All of these things can mean that we have to download the plane in order to have the required performance for this takeoff, be that accelerate-stop distance, climb gradient with an engine inoperative, gear/flaps down, gear up/flaps takeoff and finally gear/flaps up. There are other things too but you get the idea.

So if we can only lift X pounds on this takeoff and if the payload is fixed then we must reduce our weight in some way, and fuel is one variable. This would normally not be done on scheduled passenger flights. Normally the airline would opt to keep schedule and leave passengers/freight and for sure, the non-revs behind.

But where the load is a fixed quantity fuel must be reduced. I have done sports team charters that departed a hot/high airport, flew a hundred miles or so to a sea level airport, refueled and then continued to destination.

The most extreme example I have heard of this was a USAF cargo charter flight by a civilian DC-9-30F. It departed Hill AFB near Salt Lake City (4000+msl and hot) for Warner-Robbins AFB in Georgia. If takeoff performance had not been a factor they could have gone non-stop. But MGTOW was very limited by takeoff conditions and so this is what they did.

They put on a reduced fuel load and flew from Hill to Mountain Home AFB near Boise Idaho. (about 2500'msl but just as hot) Then from Mountain Home to Mather AFB near Sacramento California (sea level, hot but very long runway) From there they flew nonstop to Warner-Robbins, the original destination. If you have a map of the US handy you can see that this was a long way out of their way, but dictated by geography/topography. There was no fuel stop available to them going east from either HIF or MUO.

And that is how hot and high airports can affect aircraft range. It is limited by the required takeoff performance.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
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RE: Effect Of Altitude /temperature On Aircraft Range

Fri Feb 13, 2004 2:19 am

Actually the altitude and temperature have a very direct effect upon the amount of weight that an aircraft can takeoff with. It's the old density altitude thing - it affects jets just as it affects piston powered aircraft. 707 mentioned the reasons, however the net effect of this reduced capacity - in many cases - is a reduction in the fuel load that can be carried. There are also many other factors that influence the amount of weight (fuel) that can be carried - the big one is the 2nd segment climb requirements. Additonally, most, if not all, turbojet aircraft have limitations as to the maximum takeoff altitude (usually between 10,000' msl and 14,000' msl) and temperature (usually somewhere around ISA +30 C) at which they can operate. Bottom line is yes, field elevation and OAT can have a major impact on aircraft range.

Oops, I see that I was writing this while SlamClick was posting his "treatis".

Jetguy



[Edited 2004-02-12 18:27:50]
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Effect Of Altitude /temperature On Aircraft Range

Fri Feb 13, 2004 2:58 am

Jetguy

Hey man, jump aboard! As usual I was too long-winded to get my point across anyway.

Greetings to "America's finest city"

- "Biggest little city"
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
Guest

RE: Effect Of Altitude /temperature On Aircraft Range

Fri Feb 13, 2004 4:09 am

SlamClick...
Hey, I'm probably one of the most long-winded guys that hang out on this forum. Regarding America's finest city - sunny San Diego - what can I say? It's another perfect day in paradise - it's 72 F outside!

I just got off of the phone with our dispatcher and I've got a trip tomorrow that really illustrates the observation that Thestooges had. Tomorrow, I'm flying from Orange County (SNA/56' MSL) to Aspen (ASE/7820' MSL). The bizjet that I fly could depart SNA and fly to London or Paris with one stop on the East coast. Departing ASE, I can only carry enough fuel for a 1-hour leg plus reserves. That, my friends, shows the effect of takeoff field elevation, OAT and 2nd segment climb requirements on turbojet aircraft range.

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

RE: Effect Of Altitude /temperature On Aircraft Range

Fri Feb 13, 2004 5:54 am

Yeah, ASE is one of the places I think about when this topic comes up. Also, because of the runway slope there, any airline wishing to serve that place must get a waiver on the 2% slope limitation that most types have. The waiver comes at the expense of hefty performance limits.

- Outside RNO, 40o windy and sunny.
Happiness is not seeing another trite Ste. Maarten photo all week long.

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