Coffin Corner
- Thread starter hawkeye52
- Start date
The reason the high altitude envelope is called coffin corner is that the stall (which is fairly conventional) and mach limits begin to merge. The critical item here is the manners of the mach limit. Many aircraft experience a mach tuck, which causes the center of lift to migrate aft in the high transonic range, resulting in a strong nose down tendency. As this generally further increases the speed and mach number (with the nose pointed down) thye situation tends to become more and more divergent.
Not all aircraft experience such a mach behavior. The 747-400 which I fly does not experience such manners. Some of the Lear Jets were famous for having poor mach upset characteristics.
It is possible to model mach tuck in FS. To get it just right would take a fair bit of test and adjustment. Most flight models tend to ignore this aspect. For example a very popular recent WWII fighter offered in FSX which had bad high mach diving characteristics pretty much ignored this part of the flight envelope in it's FSX iteration.
Aircraft capable of reaching mach limit in level cruise tend to be jet powered and usually have flight controls that remain effective at such speeds. WWII fighters such as the one mentioned above also tended to have issues with flight controls becoming ineffective at high mach, which exabacerated the problem.
Cheers: Tom
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Not all aircraft experience such a mach behavior. The 747-400 which I fly does not experience such manners. Some of the Lear Jets were famous for having poor mach upset characteristics.
It is possible to model mach tuck in FS. To get it just right would take a fair bit of test and adjustment. Most flight models tend to ignore this aspect. For example a very popular recent WWII fighter offered in FSX which had bad high mach diving characteristics pretty much ignored this part of the flight envelope in it's FSX iteration.
Aircraft capable of reaching mach limit in level cruise tend to be jet powered and usually have flight controls that remain effective at such speeds. WWII fighters such as the one mentioned above also tended to have issues with flight controls becoming ineffective at high mach, which exabacerated the problem.
Cheers: Tom
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Thanks for the reply, F747.
In essence, you are telling me that flight sim aircraft ignore the coffin corner. If I were to push one to its extreme, nothing would happen.
Too bad.
I was hoping to encounter mach tuck in order to test myself in the recovery, which I have read is quite dicey.
- H52
In essence, you are telling me that flight sim aircraft ignore the coffin corner. If I were to push one to its extreme, nothing would happen.
Too bad.
I was hoping to encounter mach tuck in order to test myself in the recovery, which I have read is quite dicey.
- H52
H52:
It is certainly possible to model this as the tools are available in FS. One of the things that intervenes is that the MMO is usually set as a limit in the acft cfg file and the sime explodes the aircraft after 30 sec of overspeed. This is a certification limit and the actual plane usually will have some degree of structural integrity and controlability beyond this, but the safety margin has been removed... which keeps you out of coffin corner.
For example the 747 has a certified OPERATING MMO of M .92, but has been flight tested to something like M .997. In some inadvertent situations it sucessfully recovered from speeds well above M 1.0. In FS it will explode at 30 sec of M .921....
One aircraft that operates often in this environment is the U2.
It is an interesting discussion and it is not a universally ignored factor. If you do some testing, let us know what you find!
Cheers: T.
It is certainly possible to model this as the tools are available in FS. One of the things that intervenes is that the MMO is usually set as a limit in the acft cfg file and the sime explodes the aircraft after 30 sec of overspeed. This is a certification limit and the actual plane usually will have some degree of structural integrity and controlability beyond this, but the safety margin has been removed... which keeps you out of coffin corner.
For example the 747 has a certified OPERATING MMO of M .92, but has been flight tested to something like M .997. In some inadvertent situations it sucessfully recovered from speeds well above M 1.0. In FS it will explode at 30 sec of M .921....
One aircraft that operates often in this environment is the U2.
It is an interesting discussion and it is not a universally ignored factor. If you do some testing, let us know what you find!
Cheers: T.