Hot and High variants

[killairbus 3]

For real world aircraft that have variants that are ceritified for hot and high operations above 10,000 feet. Will PMDG consider modeling these niche certifications for future releases if it's not too much for their developers? 

-Angelo Busato

Edited September 12, 2018 by killairbus

[mtrainer 136]

What is meant by a hot and high variant?  Every product they offer on their website can surpass 10,000 ft. without breaking a sweat.  Can you offer a more detailed explanation, perhaps with an example of a real plane to get an idea of what you're talking about?

Confused,

Mark Trainer

 

[thibodba57 462]

21 minutes ago, mtrainer said:

What is meant by a hot and high variant?  Every product they offer on their website can surpass 10,000 ft. without breaking a sweat.  Can you offer a more detailed explanation, perhaps with an example of a real plane to get an idea of what you're talking about?

Confused,

Mark Trainer

 

I think he's talking about operating at airfields that lie above 10,000' or atleast in density.  I don't think this is airframe specific because as far as I know there is no equipment modification needed to operate at these fields.  There are however Supplemental Procedures that usually address this though and this should all be includes in the current documentation.

[PopsBellNC 21]

He's talking about Hot/High airport operations. At high altitude airports, B757's are a common type for Bolivia, Peru, etc. for example. To my knowledge, more of a paperwork thing but, some models (like the 757) are inherently more capable at altitude.

"Hot" - really hot (45C) operations are are common in the Mideast. Carriers there purchase aircraft with that as a prime criteria. For a number of good reasons, Boeing (and those other guys in Europe 😉) certify all of their planes to work well in hot environments, often causing other carriers around the world (especially in the USA) to complain that they are paying extra for capabilities they do not need.

In the old days, we'd just use 747-200B's and takeoff from Riyadh at 2 AM.

[mtrainer 136]

Ahhh…I see, yes I die at airports over 7,000 ft. high more than anywhere else and I'm a pretty conservative dude.  As far as I know all you can do at high altitude airports is add a bit more flaps and increase your landing speed so you don't stall out.   And go around if it all doesn't look perfect.

Mark Trainer

[thibodba57 462]

1 hour ago, mtrainer said:

Ahhh…I see, yes I die at airports over 7,000 ft. high more than anywhere else and I'm a pretty conservative dude.  As far as I know all you can do at high altitude airports is add a bit more flaps and increase your landing speed so you don't stall out.   And go around if it all doesn't look perfect.

Mark Trainer

You don't add speed for high elevation.  In point of fact higher flap setting and a slower speed is what you want as the true airspeed is so much faster.  On the heavier equipment you could be moving so fast at higher weights I'd you don't use the slowest possible speed you could actually exceed the tire speed limit.

Edited September 12, 2018 by thibodba57

[killairbus 3]

Sorry with the "hot/high variants." I suck at terminology. 

Indeed I am asking about having future releases based on aircraft that are certified for airports above +10,000, like some 737s are for example. "Variant" is the wrong word for what I am describing. 

-Angelo Busato

Edited September 12, 2018 by killairbus

[Chock 17,769]

Unfortunately, the two classic hot and high Boeings, if one could consider such a thing, are the 727 and the 757, neither of which PMDG make (wish they would). The 757 is massively overpowered and creates a lot of lift too, both these features of it lend it to operating pretty well at high altitudes. Likewise, the 727, being a tri-jet but not an especially big one, could develop a lot of thrust and has massive full-span krueger flaps and slats which of course have no engines on them to cause detriment to the lift they generate, so they generate tons of lift. Additionally, the some 727 variants were indeed modified specifically for hot and high operations with the addition of an extra flaps setting, this is why 727s were popular in South America and Africa.

Having said that, the ability to create thrust alone is not the simple solution to hot and high operations which it would seem to be; an engine in hot and high operations will have two problems; the air it takes in is thinner, and it is warmer, so simply ramming the throttles forward would mean too much fuel for not enough air at a suitable temperature. You might even notice this phenomenon if you have a powerful car or motorcycle; it's likely you'll find it runs a lot better in colder temperatures than it does in hot ones, simply because it can suck in more air to mix better with the fuel. So ironically, with a powerful engine in hot and high operations, you might actually do a derated take-off to allow it to develop enough thrust in the thinner air; since it can normally create an excess amount of thrust, it'd still develop enough to get off to take off speed in a decent amount of runway length. This is the kind of thing your PMDG birds can simulate properly.

But, another problem (at least in the real world that is) and as Brian points out on this thread, is the tire speed limits in such conditions. This is something which can be altered for airliners to some extent, in fitting them with tires which are better rated for higher ground speeds, but there is only so much which can be done in this regard and in any case it wouldn't really be something which either FSX or P3D would normally model. So again, in your sim, you can simulate what the real aeroplanes do, which is fly at times when the temperature is cooler and limit the MTOW for certain routes.

At MMMX, Mexico City airport (Aeropuerto Internacional Benito Juárez to give it its proper name), which might be considered the classic hot and high airliner airport, there are two runways which are just shy of 13,000 feet long. They are 7,316 feet above sea level, which is pretty high up, in fact only about 700 feet lower than the point where you need to start pressurising aeroplanes to enable comfortable breathing, but in spite of the high altitude, you'd think that with runways which are well over two miles long, that'd give you enough tarmac to simply let your aeroplane roll along the ground gradually developing plenty of airspeed before you rotate, unfortunately doing that risks overheating the tires.

As you probably know, aeroplane tires are filled with nitrogen rather than air, which works better to keep the tires cool and also keeps them inflated better since nitrogen molecules are bigger than air molecules and don't seep out as much as air molecules can. But they're still at really high pressures, much more than in your car tires, for example, the tires in my MX5 car are at 26 psi, whereas the tires on a typical airliner are at 215 psi, i.e. those airliner tires are more than eight times the pressure in my car's tires. When something like that overheats, if it blows, especially if the gear is retracted at the time, the damage is quite likely to be catastrophic. This actually has occurred a few times and is one of the reasons why a walk around check by engineers, specifically testing the tire pressures on an airliner is really important, since if any tire is under-inflated, it means the other tires have to work harder to support the weight of the aeroplane and so they'll heat up quicker. This is exactly what caused the crash of Nigeria Airways Flight 2120 (a DC-8 flying out of Jeddah), which retracted its gear when it was overheated and which subsequently caught fire in the landing gear bay and caused an horrendous mid air fire. Another distrurbing example of this phenomenon was Mexicana Flight 940 (a 727 flying out of Mexico City), which had its nose gear erroneously inflated with air rather than nitrogen. This overheated tire on the take off roll and in combination with a brake which was binding a little bit, which also contributed to a fairly long ground roll, caused the overheated nose gear to set on fire and then explode in the nose gear bay. The explosion severed many of the control surface linkages and put the thing beyond the control of the crew.

All that grim stuff aside, one of the things you actually can do in your flight sim to simulate hot and high operations, is delay the gear retraction a bit if you have had a longer than normal ground roll for the take off; this will allow the airflow over the tires and brakes to cool them down somewhat. It is actually a not too uncommon a practice to do this, and on an aeroplane which PMDG does make (Boeing 747). You can find this procedure documented in the real 747's manuals.

Edited September 12, 2018 by Chock

[killairbus 3]

9 minutes ago, Chock said:

Unfortunately, the two classic hot and high Boeings, if one could consider such a thing, are the 727 and the 757, neither of which PMDG make (wish they would). The 757 is massively overpowered and creates a lot of lift too, both these features of it lend it to operating pretty well at high altitudes. Likewise, the 727, being a tri-jet but not an especially big one, could develop a lot of thrust and has massive full-span krueger flaps and slats which of course have no engines on them to cause detriment to the lift they generate, so they generate tons of lift. Additionally, the some 727 variants were indeed modified specifically for hot and high operations with the addition of an extra flaps setting, this is why 727s were popular in South America and Africa.

Having said that, the ability to create thrust alone is not the simple solution to hot and high operations which it would seem to be; an engine in hot and high operations will have two problems; the air it takes in is thinner, and it is warmer, so simply ramming the throttles forward would mean too much fuel for not enough air at a suitable temperature. You might even notice this phenomenon if you have a powerful car or motorcycle; it's likely you'll find it runs a lot better in colder temperatures than it does in hot ones, simply because it can suck in more air to mix better with the fuel. So ironically, with a powerful engine in hot and high operations, you might actually do a derated take-off to allow it to develop enough thrust in the thinner air; since it can normally create an excess amount of thrust, it'd still develop enough to get off to take off speed in a decent amount of runway length. This is the kind of thing your PMDG birds can simulate properly.

But, another problem (at least in the real world that is) and as Brian points out on this thread, is the tire speed limits in such conditions. This is something which can be altered for airliners to some extent, in fitting them with tires which are better rated for higher ground speeds, but there is only so much which can be done in this regard and in any case it wouldn't really be something which either FSX or P3D would normally model.

At MMMX, Mexico City airport (Aeropuerto Internacional Benito Juárez to give it its proper name), which might be considered the classic hot and high airliner airport, there are two runways which are just shy of 13,000 feet long. They are 7,316 feet above sea level, which is pretty high up, in fact only about 700 feet lower than the point where you need to start pressurising aeroplanes to enable comfortable breathing, but in spite of the high altitude, you'd think that with runways which are well over two miles long, that'd give you enough tarmac to simply let your aeroplane roll along the ground gradually developing plenty of airspeed before you rotate, unfortunately doing that risks overheating the tires.

As you probably know, aeroplane tires are filled with nitrogen rather than air, which works better to keep the tires cool and also keeps them inflated better since nitrogen molecules are bigger than air molecules and don't seep out as much as air molecules can. But they're still at really high pressures, much more than in your car tires, for example, the tires in my MX5 car are at 26 psi, whereas the tires on a typical airliner are at 215 psi, i.e. those airliner tires are more than eight times the pressure in my car's tires. When something like that overheats, if it blows, especially if the gear is retracted at the time, the damage is quite likely to be catastrophic. This actually has occurred a few times and is one of the reasons why a walk around check by engineers, specifically testing the tire pressures on an airliner is really important, since if any tire is under-inflated, it means the other tires have to work harder to support the weight of the aeroplane and so they'll heat up quicker. This is exactly what caused the crash of Nigeria Airways Flight 2120 (a DC-8 flying out of Jeddah), which retracted its gear when it was overheated and which subsequently caught fire in the landing gear bay and caused an horrendous mid air fire. Another distrurbing example of this phenomenon was Mexicana Flight 940 (a 727 flying out of Mexico City), which had its nose gear erroneously inflated with air rather than nitrogen. This overheated tire on the take off roll and in combination with a brake which was binding a little bit, which also contributed to a fairly long ground roll, caused the overheated nose gear to set on fire and then explode in the nose gear bay. The explosion severed many of the control surface linkages and put the thing beyond the control of the crew.

All that grim stuff aside, one of the things you actually can do in your flight sim to simulate hot and high operations, is delay the gear retraction a bit if you have had a longer than normal ground roll for the take off; this will allow the airflow over the tires and brakes to cool them down somewhat. It is actually a not too uncommon a practice to do this, and on an aeroplane which PMDG does make (Boeing 747). You can find this procedure documented in the real 747's manuals.

That was an awesome read. thanks!

-Angelo Busato

[kevinh 409]

There is in fact a specific option for 737-700 hot and high operations. Boeing call it the High-Altitude/High-Temperature Airport Operations Feature Package.

http://boeing.mediaroom.com/2011-08-01-Boeing-Delivers-Milestone-737-with-High-Altitude-High-Temperature-Operation-Features

It’s basically a higher thrust rating with extended passenger oxygen capacity. The engine rating is CFM56-7B26/B2. It is the same TO/GA thrust as the -7B26 at sea level but equivalent to the -7B27 engine at high altitude. As the -7B27 engine is intended for the heavier 737-800/900 aircraft, using that thrust limit in a 737-700 increases the thrust to weight ratio.

Edited September 14, 2018 by kevinh

[harrry 322]

35 minutes ago, kevinh said:

There is in fact a specific option for 737-700 hot and high operations. Boeing call it the High-Altitude/High-Temperature Airport Operations Feature Package.

http://boeing.mediaroom.com/2011-08-01-Boeing-Delivers-Milestone-737-with-High-Altitude-High-Temperature-Operation-Features

It’s basically a higher thrust rating with extended passenger oxygen capacity. The engine rating is CFM56-7B26/B2. It is the same TO/GA thrust as the -7B26 at sea level but equivalent to the -7B27 engine at high altitude. As the -7B27 engine is intended for the heavier 737-800/900 aircraft, using that thrust limit in a 737-700 increases the thrust to weight ratio.

Interestiing.  They have a lot of routes in China with very high altitudes and it seems this package is very much needed, in particular the Oxygen extension which with the MSA well over 14000 ft in the area they operate will enable descent then diversion time on Oxygen.

[swood721 28]

American Airlines has an extra button on the overhead for a high altitude airport. No idea what it actually does as I don’t fly for AA, my airline just uses their sims. The 757/767 has a limitation to 8400ft PRESSURE altitude for takeoff and landing. That’ll get you in and out of BOG but not much higher unless you have some kind of modification/performance data from Boeing.

[JRBarrett 3,070]

27 minutes ago, swood721 said:

American Airlines has an extra button on the overhead for a high altitude airport. No idea what it actually does as I don’t fly for AA, my airline just uses their sims. The 757/767 has a limitation to 8400ft PRESSURE altitude for takeoff and landing. That’ll get you in and out of BOG but not much higher unless you have some kind of modification/performance data from Boeing.

One system whose behavior has to be modified for high altitude airport operations is the pressurization system.

Ordinarily the cabin altitude will slowly increase during climb - beginning at the ambient pressure altitude of the departure airport and ending up at a final altitude of between 7000 and 8000 feet, giving a pressure differential of typically 8 to 9 psi (airframe-specific) between the inside and outside of the aircraft at typical cruise altitudes.

This becomes a problem for a standard pressurization controller at a high altitude (8000 foot +) airport where the ambient pressure altitude in the cabin (on the ground) may already be well above the maximum altitude the controller would normally maintain in cruise before pressurization even begins.

In essence, the controller will have to work in reverse of its normal schedule in climb, actually decreasing the cabin altitude once the doors are closed and pressurization starts upon takeoff.

The opposite problem occurs in descent. The normal descent pressurization schedule is to decrease cabin altitude in descent from the normal 7000-8000 foot altitude found in cruise at higher flight levels, ending up at the ambient pressure altitude outside of the aircraft on landing. With a high-altitude destination, the controller will have to increase cabin altitude above it’s normal maximum, just to insure that the cabin is unpressurized once the aircraft is on the ground.

When there is a “high altitude” switch in the cockpit, it will normally be used to put the pressurization controller in the alternate climb / descent schedule required for airports located at higher altitudes than the normal max cabin altitude when fully pressurized.

[Ralgh 43]

American Airlines Sharklet A319s have the night altitude button too. The button also increases the altitude for the high cabin altitude warning and the altitude the oxygen masks will automatically deploy. 

[swood721 28]

On 9/15/2018 at 8:41 AM, JRBarrett said:

One system whose behavior has to be modified for high altitude airport operations is the pressurization system.

Ordinarily the cabin altitude will slowly increase during climb - beginning at the ambient pressure altitude of the departure airport and ending up at a final altitude of between 7000 and 8000 feet, giving a pressure differential of typically 8 to 9 psi (airframe-specific) between the inside and outside of the aircraft at typical cruise altitudes.

This becomes a problem for a standard pressurization controller at a high altitude (8000 foot +) airport where the ambient pressure altitude in the cabin (on the ground) may already be well above the maximum altitude the controller would normally maintain in cruise before pressurization even begins.

In essence, the controller will have to work in reverse of its normal schedule in climb, actually decreasing the cabin altitude once the doors are closed and pressurization starts upon takeoff.

The opposite problem occurs in descent. The normal descent pressurization schedule is to decrease cabin altitude in descent from the normal 7000-8000 foot altitude found in cruise at higher flight levels, ending up at the ambient pressure altitude outside of the aircraft on landing. With a high-altitude destination, the controller will have to increase cabin altitude above it’s normal maximum, just to insure that the cabin is unpressurized once the aircraft is on the ground.

When there is a “high altitude” switch in the cockpit, it will normally be used to put the pressurization controller in the alternate climb / descent schedule required for airports located at higher altitudes than the normal max cabin altitude when fully pressurized.

I should have guessed. That’s the procedure we have in our books about flying into BOG  and other high elevation airports. So basically, AA has the ability to do automatically what we have to perform manually.