Analysing and modifying the AFX file with QBasic.

[Ivan]

Hello Aleatorylamp,

Here is why I think when I post a reply, you interpret it strangely and you go off on yet another weird direction:

Or better: I´ll foget the whole WEP/non-WEP issue, which seems not to have a decent solution anyway. There are too many contradictory pieces of information, and there are not enough possibilities offered by CFS to do it well.

Everything will go into the normal throttle lever travel: This way the pilot can do what he needs, set whatever power he needs, whenever he needs. All he has to do is wathc the Manifold Pressure gauge, and pay attention to the altitude. Of course, all kinds of abuse will also be tolerated, so that will depend on the criteria of the pilot. The engine won´t blow up anyway.

I am really not sure how you arrived at that solution but one day later you are back to doing something else.

Another matter is the Manifold Pressure for Military Power. It seems to be more correct at 44.2 (from the pencilled-in-blue chart) instead of 42 (from the Allison Engins Operations and Maintenance Manual .pdf. Even though CA is now at 12500 ft, MP is still not so high there, so maybe I´ll have to push it up further.

This is also a strange sequence to choose to do things.
How did you select 12,500 feet as the Critical Altitude?
I am not saying this is correct or incorrect because I don't really know, but if you are finding the Manifold Pressure to be too low at 12,500 feet and need to raise it, then either you really raising the Sea Level Manifold Pressure.... Or you are raising the Critical Altitude so the 12,500 feet value you have listed is just a particular test altitude and not really the Critical Altitude.

You mention a certificate which I do not know about. If it is a modern Type Certificate, just keep in mind that modern operating conditions are not the same as they were during war time.

The other performance report I mentioned as giving yet another two manifold pressure values of 45.4 and 45.9, is for a test with a manifold type with "T" Screens on a P-39D-1 with the -35 engine, reported on the Performance Test Page, where all the other graphs are on.

It is the 5th. test down from the top, in case you are interested. I´ve already posted the link before,http://www.wwiiaircraftperformance.org/P-39/P-39.html , but I know you are not working on the same aspects as I am yet, although it does have to do with the engine you have on the version you were starting out from, although it isn´t your -F version.

Why did you choose to reference a report on a P-39D-1 which does not have the same version engine as the one you are building? Why did you pick a report on an engine with an experimental intake manifold? Power outputs, Manifold Pressures and even Critical Altitudes would be pretty useless information for a standard production aircraft. You are wasting your time with this report unless you are just trying to get some extra historical perspective and you would have to come to your own conclusion as to how this report is useful.
I believe it is entertaining but not useful.

Updated paragraph: Incidentally, the 3rd. report down on this page also refers to a -35 engine on a P-39D model, and quotes CA for Normal Power is at 13100 ft, and Military, at 13800ft.
What fun! CA seems to be a very flexible parameter, to be put wherever looks convenient by anyone interested! It also seems to vary whether you are rating for climb or for level flight... How nice...

This is a more useful report but still not representative of a service configuration P-39D.
From your summary of a summary, it appears things do not make sense, but if you read the actual report, the numbers make perfect sense.
Read the last line of the "Purpose" section of this report.
It says "Individual intake port backfire screens not installed in engine."
Now you would have to ask: What does this mean and does it alter the data I am looking for?
Simple answer is yes. It significantly changes the numbers and was probably the reason for conducting this test.

If it is specifically listed then it probably was not the normal configuration of this engine.
It would also be the removal of an obstruction from the intake system and without the obstruction, it makes sense that there would be better air flow and Critical Altitude would increase.

Now if you look at the table for Critical Altitude for Normal Power and Military Power, you will see that Normal Power is 2600 RPM while Military Power is achieved with 3000 RPM.

THAT was the difference, so it all makes sense if you read the information in the report.

- Ivan.