Question of the day

[Erik Brouwer 8]

OK, let's give it a try.

EDITED TO SHARPEN THINGS UP A BIT

From the 'common gas law'(algemene gaswet in Dutch, don't know English translation), and the law of Boyle-Gay-Lussac, we can deduct that when temperature rises, density decreases.

When density decreases, following Bernouilli's principle and the formula for lifting force

we can conlude we need much, much more airspeed to gain the same amounts of lift. That makes operating from a normal runway (+/- 3000m) very difficult.

Add to that that such hot air decreases the engines performance notably. When density decreases, less air can be compressed in the combustion chamber. This results in the following conclusion, that when ignited hot air doesn't expand as much, , as cold air does. This reduces thrust very, very much.

So concluding we have:

- High airspeeds needed to gain sufficient lift (and lóóóng runways needed)

- Low engine performance to gain this high airspeeds.

rgds,

Erik

[hero93 27]

Because there is a Sand-Storm.

[Rónán O Cadhain 71]

Give us a hint.

[Rónán O Cadhain 71]

More fuel is needed due to inefficiencys which makes the plane even heavier.

Pilots can't opperate normally due to the heat. #

The heat causes haze and mirages on the runways which affects visibility rules.

The heat causes haze and mirages on the runways which reflects into the pilots eyes, and alters his dept perception.

[Alp 1]

In case of rejected take off, at that temperature the brakes will overheat more rapidly and the aircraft would not stop on the runway

[tcarmona 0]

In my Jeppesen flight computer (manual, a beautiful piece of art), 54º at sea level assuming that PRESSURE ALTITUDE is at ISA MSL of 1013Hpa(29,92in for our fellow Americans) make DENSITY ALTITUDE of more or less 4500Ft(1.372mts).

It means that one is at an atmosphere equivalent at this altidude but at sea level. ISA (international Standart Atmosphere) is 15º, and 1013Hpa. at sea level.

One can say its high or not, depending on the lenght of the runway vs weight and thrust.

L= 1/2Cl x Ró x V2 x S (LIFT = 1/2 Coeficent of Lift(flaps change this for e.g., angle of attack...etc) x Ró(air density) x Square Velocity x Wing Surface area)

Less Density, more Velocity..., more velocity, more runway, full TOW, more runway to achive V1 and VR speeds.

So I have the same conclusions as Erik with one more, maybe its possible to do it with the plane almost empty (weight and balance), but airliners are made to take people and cargo... so lets stay down...

Antonio CS.

Lisboa.

[ChrisB 11]

I see folk still fly according to Bernoulli here It looks like people need to read Eberhart and Anderson "How Planes Fly". Bernoulli works (but he only invented formulae that wrapped around the Newtonian facts), but Newton rules...

"To every action, there is an equal and opposite REaction. "

So while Bernoulli Sucks , good old Isaac pushes

"Hot and heavy" don't work (See mine a page or so back)

[bionicCrab 7]

Interesting .... however I don't think those two guys came up with that theory... you'd think it would be evident to any child that has stuck his hand outside of a car window that bernoulli is kind of "weak" theory

[Erik Brouwer 8]

I see folk still fly according to Bernoulli here It looks like people need to read Eberhart and Anderson "How Planes Fly". Bernoulli works (but he only invented formulae that wrapped around the Newtonian facts), but Newton rules...

"To every action, there is an equal and opposite REaction. "

So while Bernoulli Sucks , good old Isaac pushes

"Hot and heavy" don't work (See mine a page or so back)

Well, Bernouilli's law is indeed easy to deduct from other laws of physics. But that doesn't make it 'suck'. Point is, the conditions needed to make Bernouilli's law work, are sort of unrealistic.

Still, if you take Bernouilli's law out of my story, it still works. I see you come with the same conclusion as I have (you can't take anything with you), but it would be interesting if you explained the story behind it!

[Klemm-35 13]

I stick on it that the 54 C is almost the limit. The temperature of the air just above the runway will be higher, cause the asphalt is heating it up. I don't know how much it will affect on airliners, but it gave me some interesting experiences with small planes. You get airborn, but the plane is hardly climbing as long as you are over the runway.

[KAPTEJNLN1 0]

WELL IT COULD BE BAD CLIMB PROFORMANCE AND BECAUS OF YOU ARE TO CLOSE TO THE LIMIT AND A GOOD PILOT WOULD therefore NOT TAKE OFF.

because the aircraft is tested at 60 degres c. so it must be something at the airport or infligh

It could be something whit the runway as far as i know from an test where they used a 747 where they got an car driving behind and blow it away then they say they must only have the enginge at full power for 2 min els the runway would be blown away to.

[Arnaud 5]

Yes but that is for asphalt runways, lets take that the runway in the question is concrete.

I'd say that the limitation would come from the exhaust gas temperature. I know the old A310-200 had issues with OATL, and need to lower the maxi takeoff weight limitation due to the OAT and the exaust gas temperature. At 54, I believe any airliners would suffer such problem with engines at full thrust or even idle.

There could also be problems with jetA1 unable to pressurize and at unsuitable temperature.

[KAPTEJNLN1 0]

Yes but that is for asphalt runways, lets take that the runway in the question is concrete.

I'd say that the limitation would come from the exhaust gas temperature. I know the old A310-200 had issues with OATL, and need to lower the maxi takeoff weight limitation due to the OAT and the exaust gas temperature. At 54, I believe any airliners would suffer such problem with engines at full thrust or even idle.

There could also be problems with jetA1 unable to pressurize and at unsuitable temperature.

weel year, i am also talking about boeing that is tested at 60 degrees. but the new airbus are also tested at 60 and -45 degrees as far as i know. but if it was whit lower fuel i dont know.

and about the JetA1 fuel it could be an danger whit fire if there is a leak then you tank the airplane i dont know how flame able it is.

[Aerosoft Team [Inactive Account] 51558]

It's my guess that airlines will not let their aircraft takeoff, simply because it's no good operating temperature for the pilots themselves. You can't possibly demand people to perform intensive work at that temperature, and even with air conditioning, as I said, you'd be burning too much fuel to make the flight affordable (let alone the detrimental effects on the distance you can fly!).

I just looked it up to be sure: it seems people can not survive temperatures above 45 degrees for too long.

And yet there are people living in areas that have those temperatures regular! And an aircraft does does not fly loose a lot more money then an aircraft that burns some fuel (as aircraft are rather well insulated the fuel use to cool or heat the aircraft from the APU is not very high btw.

So while complicating factors, it does not prevent an aircraft from taking off.

[Aerosoft Team [Inactive Account] 51558]

Viewing A330 performance out of DXB wjere conditions could happen..the only reason i could suggest is that full thrust take-off is required, as temp is higher than Tref.. so i would guess the ones that can't take off are too heavy, which at DXB would be A330 that weight more than 200 tonnes

steve

Sure, you will not get the same performance as Schiphol airport at -8 feet and minus 10 degrees Celcius. But I assure you that if the runway is long enough a modern airliner will still be able to take-off with a good load. Many airliners will be even be able to fly at close to max operational weight. Something they do not do often. See we are talking density altitude! If you take it rather simple it does not matter if the aircraft is at sealevel and at 54 degrees or at an airport at 4200 feet! And we all know aircraft take-off from airports like that. MD11's operate at Quito airport that is at 9000 feet without any problem. And they do so at high temperatures as it can get pretty warm there. Now all systems on board of an airliner are certified to higher temperature (most to 60 degrees). So the aircraft should be fine.

[Aerosoft Team [Inactive Account] 51558]

Maybe the lack of correct aircraft performance charts for temperatures like that?

Bingo, this was the winner of the day.

In almost every performance chart the limit is at 50 degrees so performance, runway length and even important things like V1 are not documented. Basically it also means the aircraft is not certified as the pilot does not know what will happen. This happened a few years back in the USA at major airport with runways more then long enough to use under those conditions. But after a short discussion with the FAA the airliners could not take off.

In countries where these conditions are more common it does not stop flights. I have seen a Australian flight manual where the performance charts where manually extended. Marginally legal but being done as it would otherwise make life hard.

[Delta777 272]

Bingo, this was the winner of the day.

Again?? Looks like Shaun has to contact me twice now.

[Thralni 24]

And yet there are people living in areas that have those temperatures regular! And an aircraft does does not fly loose a lot more money then an aircraft that burns some fuel (as aircraft are rather well insulated the fuel use to cool or heat the aircraft from the APU is not very high btw.

So while complicating factors, it does not prevent an aircraft from taking off.

There actually are countries where the regular temperature is 54 degrees? Wow. Tell me what these places are, please? Then I know where not to go!