Analysing and modifying the AFX file with QBasic.

[Ivan]

Hello Aleatorylamp,

It sounds like you have no shortage of computers.
How fast is the AMD K6 on this machine?

Last night I finished putting my computer together (details elsewhere) and did some basic animation with the MDL I had rebuilt earlier with the computer in pieces in my living room.
I had not actually played much with the EJ P-39D, but it appears it could use some work in a few places.
I will probably add a new Texture file and add a few Parts to address issues with the Flaps.
I don't think the Airacobra had Slotted Flaps!

- Ivan.

 

[aleatorylamp]

Hello Ivan,
It´s a Sempron 3000+ at 1.8 Ghz, similar to a Pentium 4 at 3000 Ghz. (More details on the other thread). I have so many old computers that I don´t know what to do with them, but to just throw them out seems like a lack of consideration and respect for their existence...

I´m just clearing the work-place to be able to do a couple of things with the P-39D. I agree, the flaps have to be made into split flaps. That´s on my list too!

The first thing I´ll do, however, is to correct the building-deviation on the right, i.e. try out and use the new non-distorting negative-decimal round-off formula you posted yesterday! The issue had me so mystified, you wouldn´t believe it!

What I thought I´d also give a try later on, just for fun, is to correct the rear-fuselage angle and height, and also correct the whole tail empenage cross-sections while I´m at it! I think it´s quite an interesting project - no hurry, no pressure!

OK, more later!
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

Salute to Gaius SEMPRONius Gracchus!

Using the old P-39D AIR file I worked on many years ago, I found that I had done some things pretty well, but there were a bunch of things that I did not address. Most probably it was because of a lack of knowledge at the time.

It is also obvious that this was derived from a FS98 AIR file because once I got the Sea Level power correct, I could not get the Supercharger to work.
Although it is certainly possible to add in the missing records, I will probably start over with a stock P51D AIR file just to make sure things are fairly consistent. There are many Tables / Records in the AIR file that I do not check and there may be something unexpected in one of those that would cause problems later.

This is a good time to test my instructions for creating a new AIR file for Combat Flight Simulator.

You seem to be seriously interested in fixing EJ's P-39D.
My goal with this project is just to fix the things that are most objectionable and the repair whatever damage my "fixes" may have caused.
This "Slotted Flaps" issue is one that would not have existed before I changed the Flaps from Plain Flaps to Split Flaps.

On your EJ P-39D, I would suggest you create a copy of the directory you have now and extract and Stretch the Parts again.
Although you know the two sides differ, your original code Truncated one side and really expanded the other.
I believe it is pretty likely that BOTH sides are actually different from what they should be mathematically.
That is why I basically re ran the StretchIt program on ALL the AFP Files.

- Ivan.

 

[aleatorylamp]

Hello Ivan,
So the Sempron was named after this man! He seems to have been quite a controversial innovator in those convulsive times.

As per your suggestion with the P-39D, I´ll perform a "redo from start" with the original AFX, stretching it with the correct formula. There´s really no other way around, but it´s OK, as the learning process here is one of the points of the exercise. Then I´ll move it into the correct null-point position, and copy over the improvements. The new parts are named differently anyway, so it won´t be very hard to do.

Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

Actually I doubt that AMD would name their new processor after one of the Gracchi.
It probably just sounded great to somebody. Inspiron, Sempron, Athlon, Moron, etc.

Last night I spent a couple hours going through my old P-39D AIR file and copying the changes to a new version from the stock P51D. It turns out that the one I had been modifying ALREADY WAS derived from the P51D. There was even still the Center1 Fuel Tank in place though it was set for Zero Gallons of fuel.
The Supercharger doesn't work on the new AIR file either nor does it work on OTHER AIR files.....

- Ivan.

 

[aleatorylamp]

Almost there again

Hello Ivan,
I skim-read about the Gracchis - they didn´t have a fortunate end,

Well! I´ve got the Airacobra to the point where it was before. The Move option worked as well as the Stretch option did, so the null point is once again at the correct Centre of Rotation. Everything is now correctly in place.

Screenshots will look the same, so there´s not much point in sending any.
More tomorrow! I´m off to bed.
Good night
Aleatorylamp.

 

[aleatorylamp]

Hello Ivan,
OK, I managed to get the model symmetrical, and with the correct length, span wheel locations and stance. Texture spread if fine too, and I also manually corrected my "nose-job".
The only thing is the null point, that is around ten inches below the centreline, and would have been better at 9.

So, I can continue on the transparent cockpit, but before that, I want to progress a bit on the CFS1 .air file I had started on some time ago, but I still have to decide on the type of engine I want to use.

I noticed your comment on the other the other thread relative to Automixture!
A very useful hint.

Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

My 9 inches below the Engine Thrust Line for CoG was also an estimate.
It may well be over 9 inches, but that is the number I am going with.
That small of a difference will probably not make any difference in flight models and if it does, you can easily shift one inch without any impact on the relationship between flight model and visual model. We are really not that precise with most models.

all engines used on the P-39 Airacobra were E series Allisons.
The E series was the only version with the remote reduction gear.

The version I am building is actually a P-39F or retrofitted P-39D-BE to start and if successful there will be a low level hotrod K version to follow. At this point, I really don't have any intention of building a military P-39Q, at least not yet.

I don't believe the P-39D-2-BE would have been any faster than the P-39D-BE or the P-39F. The extra War Emergency Power was only at about 2500 feet and I have a reference that suggests that was also being used on the regular P-39D series. I have already listed quite a few specifications in the new Airacobra thread.
To get a good idea of performance, you need to see the entire Power versus Altitude Graph. Take-Off power ratings really won't tell you much.

- Ivan.

 

[aleatorylamp]

Hello Ivan,
Thanks for your quick answer!

I had been trying to be more on-topic here once I noticed you had opened a new Airacobra thread, so I edited out some performance items from my previous post on this thread, adapted them for the new one and posted them there.

OK, so I can leave the 10 inches below the centre line for the moment, because changes here will involve repeating all the animations, as you also commented recently!

As regards performance, I see if I can find the performance chart you mention, and take it from there.
What I did notice very clearly from the P51D .air file adaptation I´m doing, is that Boost Gain has to go way down to about 2.47. Anyway, more technical details from now on would be for the new Airacobra thread!

Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

I believe you should keep your version of the Airacobra here as you had originally intended.
I believe I commented about this via email way before I started the Airacobra thread.
We are not really building the same aeroplane nor are we actually building by the same methods and I don't really want to confuse the issues and chase things that are not related to what I am actually trying to do with this project.
With the kinds of questions you have been asking, I am fairly certain you haven't actually done much research yet.

The information I am working from isn't terribly hard to find. It is just time consuming to put together in a way that is useable for building an aircraft project. There is also the issue of sorting through the contradictory information to determine what an "accurate" representation really should be.

- Ivan.

 

[aleatorylamp]

Hello Ivan,
OK, will do, no problem. I´ve just deleted my last post there. It appears I was
just in time. The last thing I want to do is interefere with your project.

You are totally correct in saying that the information isn´t terribly hard to find.
Actually, I had already seen all you posted on your Airacobra thread. That was
the reason behind my comment there:
"You have certainly put together a good summary of the different models."
I just thought my question would be more on topic on that thread, but don´t
worry, I´m just as happy to stick to this one.

So, as I fortunately don´t seem to be stepping on your feet, I´ll go for the
P-39D-D2, with its 1325 Hp engine, although whether I upload it or not will
depend on the success of my planned modifications.

Regarding progress with the model itself, once the negative decimal rounding
factor was solved, it looks like shifting the Centre of Rotation with AF99, or
by Modifying it with an external Moving Program, has the same effect all round,
i.e. texture mapping, landing gear locations in the .air file, and animations, as
was to be expected.

At the moment I´m working on the transparent canopy and checking the correct
height for the rear-fuselage and tail-empenage, to correct that shape.

Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Ivan,
I have just found an interesting performance test document, on the different
P-39 models, hand-written in blue pencil, which you may have come across too.
http://www.wwiiaircraftperformance.org/P-39/P-39_Aircraft_Performance_Characteristics.jpg

It is the last one on a list of links at the very end of this page:
http://www.wwiiaircraftperformance.org/P-39/P-39.html

It has extensive details - manifold pressures, RPM and speeds for different powers
at different altitudes. The first column corresponds to the P-39D-D2 with its 1325 Hp
engine, so there´s more than enough information I need for the .air file!

Cheers,
Aleatorylamp

 

[aleatorylamp]

Interesting V-1710-63 performance details

Hello folks,
In order to produce a more or less usable .air file for the moment,
for the P-39D-D2 Airacobra and its 1325 Hp Allison V1710-63 engine,
there is some interesting information in the 2 performance documents
I have found, i.e. the Allison Operations and Maintenance Manual .pdf
and the site with test results and links I posted before. The following
would appear to be appear quite useful:

5-minute powers, 3000 RPM:
--------------------------
Take-off: 1325 Hp, 51.0 "Hg MP, done at 104 mph.
WEP S.L.: 1550 Hp, 60.0 "Hg MP, giving 306 mph.
Standard Emergency: 1450 Hp, 55.0 "Hg MP.

15-minute powers, 3000 RPM:
---------------------------
Military Power at S.L.: 1050 hp, 44.2 "Hg MP.)
Military Power 12000 ft: 1150 Hp, 44.2 "Hg MP, giving 362 mph.
(Another source states 42.0 2Hg MP.

Normal rated Power:
-------------------
at S.L. : 910 Hp, 2600 RPM, 37.8 "Hg MP.
(Another source states 880 Hp, but no MP).

10800 ft: 1000 Hp, 2600 RPM, 37.2 "Hg MP.

Critical altitude is 11200, or 12000 ft (also named military
rated altitute), depending on the source.

Landing speeds 89 mph, with flaps and gear down.

There are several cruise powers mentioned, but I´ll see to that
later on, once the basis for the .air file is established.

My thoughts as to the distribution of powers, i.e. normal
throttle lever travel and WEP (type 2 methanol-water), would
be to include the 15 minute powers in normal power, and have
the 5 minute powers as F10-WEP.

The problem here would be that 1550 Hp WEP is rather more than the
1325 Full take-off power. Were this to be included in WEP, then we´d
all take off with 1550 Hp, which doesn´t sound reasonable. But, how
to prevent prolongued use of 1325 take-off Hp would be the question.

A different matter is how accurately I´ll be able to put allo this into
the .air file, but it will be fun to try.

Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

I am somewhat curious as to where you got the designation P-39D-D2.
Other than your posts, I have never seen this designation.
I believe that with the V-1710-63 engine that you specified, you are really referring to the P-39D-2-BE.

If this is true, then I believe you need to recalculate the Center of Gravity.
My calculations were based on an aeroplane (P-39Q-1) equipped with a 37 mm cannon.
The 20 mm Hispano that was standard on the P-39D-2 would have been quite a bit lighter and changed the balance of the aeroplane.
That 20 mm Hispano cannon was also the reason I did not choose to build the D-2 version even though it met the requirements in other respects. The 20 mm cannon was not well thought of by US forces operating the P-39.
The P-39K is basically the same as the P-39D-2 but with a 37 mm gun which is why I thought it would be a good follow-on build after the P-39D/F was done.

If you graph the data you have collected about engine power and settings, you will probably find that it will be contradictory in certain areas.
To actually build something, you will need to sort through the data to have some consistent values. I had to do the same with the V-1710-35 but there were some choices about who and what to believe.

You also need to be careful about anecdotal data. Your "20 MPH Faster" quote from the post you deleted is a good example of such a comment that I find to be not very plausible.

The table of data that you have linked is pretty good. It is actually the same place where I am finding data on other models of the P-39.
The problem as usual is that some of this data contradicts other data that I have, one has to choose what to believe.
There is also no data on the exact model that I am attempting to build.

I have actually been messing around with the EJ P-39D. Last night I finished reworking the Flaps so that they are no longer "Slotted Flaps".
I have been doing my best not to alter the shapes even though I know that they are incorrect. Proper shapes would have made things easier. My objective is to do a general cleanup and corrections without altering the general shapes and appearance of the original model.
This model uses "Retracted Flaps". I generally use "Deployed Flaps".
Both have their advantages and limitations, but I believe my standard method of Deployed Flaps is better overall if Aircraft Animator is used.
Aircraft Animator also does not remember Deployed Flaps from one execution to the next.
The problem is that the tool is so simple to use that it omits some very useful features.

I also reworked the Main Landing Gear Wells so that they would no longer disappear from certain angles.

I was also tempted to build a Transparent Canopy as well in order to test the required Assembly sequence for when I build the actual Project.
It looks to be pretty easy because of all the resources that are still remaining.

- Ivan.

 

[Ivan]

Hello Aleatorylamp,

You are totally correct in saying that the information isn´t terribly hard to find.
Actually, I had already seen all you posted on your Airacobra thread. That was
the reason behind my comment there:
"You have certainly put together a good summary of the different models."

Perhaps it should be "Mostly Correct".
There were two pieces of data that I had to estimate based on fragmentary evidence:
The .30 Caliber ammunition load of the P-39C and
The .50 Caliber ammunition load of he P-39Q.
I wasn't building either version yet, so it wasn't crucial that I get the numbers entirely correct but if you were actually able to find a good reference for these, I would be interested to know where. I am thinking the P-39Q information should be fairly easy to find if I look hard enough but the data for P-39C would probably be a bit harder.

I just finished the first pass at Engine Power and Level Speed tuning for the P-39D/F model.
Speed at Sea Level (500 feet)
309 MPH - Actual but this number was probably corrected to Sea Level
310 MPH - Model

12,000 feet
368 MPH - Actual
368 MPH - Model

Some sources put the altitude a bit higher for maximum speed.
Now it is time to tune some of the other bugs out of the AIR file.

- Ivan.

 

[aleatorylamp]

Further Progress

Hello Ivan,
First things first! Here are 2 links to the Allison "E"-type Engine Operations and Maintenance handbook, all 26.9 Mb of it! It takes quite a while to download, but it is something I´m sure you will enjoy. The second seems faster:

http://tradecoastcentralheritagepark...dbook_1944.pdf

http://www.avialogs.com/index.php/en...allations.html

I misinterpreted the -D2 nomenclature from somewhere, where they said the -D version had -D1, -D2, -D3 and -D4 subtypes, and mistakenly added the "D" as well, instead of only the number.

I corrected the fin/rudder and the canopy last night.
The fin was placed 0.33 ft too high and the lower part had to be extended another 0.22 ft.
The canopy, although the top and base-line seem OK, had the front and back 0.2 ft too low. These corrections will make the nose and aft fuselage slant correctly.
Then, the spinner is too small, and be about 0.28 ft fatter.
The worst is the "slim" belly - it has to go down another 0.8 ft. I still have to check the width.

These will be the reference points for the fuselage correction.
First I´ll do with the 8 sides it has, and then skillfully insert an extra 4...

I still have to do the flaps on my version. Personally I prefer putting in retracted flaps tagged with Speed below 195, because of AA missing things with deployed ones, as you said too.
Updated comment: With flaps built as retracted, I only need to delete the 4 deployed-flap parts, untag the old retracted flap parts, leaving them as normal wing parts, and repeat the undersurface of the retracted flap, tagging it with Speed Below 195.

Well, it´s coming along. Here´s a blueprint screenshot, showing the cabin and fin shape changes (which don´t fit the old fuselage properly!), as well as the centre of rotation.
The CoG is set a little aft of what I had before, but perhaps not enough. Would think it is still too far forwards? Perhaps the best place to correct the still-needing-attention CoG would be with the 2 places that offer offsets in the .air file.

Regarding the .air file, I´m not sure what to do:
I wonder if it would be better to eliminate the 1550 Hp max. 60 "Hg WEP, keeping it as the 1450 Hp standard 55 "Hg WEP. This would, however, include Take-Off power, which should really only be 1325 Hp with 51 "Hg.
I wonder if you would like to suggest something...

Well, it´s slowly progressing... It´s actually a lot of fun too!

Updated comment:
I´ve just changed the new screenshot - again! It now shows the bright-orange (thickened to be more visibile) outline of the planned, improved, more pot-bellied fuselage, but not as much as I had it a while ago! The air intake also has been moved upwards by 0.1 ft, and the spinner is fatter now too. Of course, as always, I value your views and/or opinions should you like to comment.
I´ve also checked the main landing gear. It seems to have the correct position, which is a relief.

Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Folks,
A lengthy part of the job, but not difficult: The fuselage, still 8-sided, to make dimensioning of all the parts in the three components easier, is now more pot-bellied.
I still have to adapt the wing roots to the new fuselage belly, which may be a bit more difficult,
and position the forward landing-gear parts accordingly. You can see in the blueprint that they are still not done yet.
Here´s 2 screenshots. The look is a bit more realistic.
I still have to get the texture mapping a bit better overall.
Cheers,
Aleatorylamp

 

[Ivan]

Hello Aleatorylamp,

I had to do a couple more revisions to the flight model I was working on.
I had originally planned to do the P-39K with the V-1710-63 engine and had left a couple parameters unchanged when I switched to the P-39F.
About three hours of editing and testing and now the numbers for mine are:
314 MPH @ 500 feet and
368 MPH @ 12,500 feet.

I am a bit surprised you had such a simple time with doing the Flaps.
Mine was much more involved and took the better part of a day to finally get working the way I wanted.
First I tried the method you described, but could not get rid of the bleeds of the Wing Roots from outboard.

Thanks for the link to the V-1710 E series manual. I am not sure if I already have a copy of the one for the E series but I know I have the equivalent for the F series engines. The folks naming the PDFs don't make it obvious from the name of the file, so I can't tell without going through a bunch of files. Be very careful when using this for reference material though.
This manual is from 1944 and everything is fine if you are building a P-39Q but the earlier models may not have had the same engine power ratings and limitations. Production quality improved as time went on AND fuel quality improved so that often the same nominal model of engine would be making more power in 1944 than 1942.
My subject is the Airacobra from 1942 when it was an important fighter aircraft of the US Army.

Whose drawings are you using for your corrections? It isn't clear where you are getting the reference numbers for your changes.

Be careful about references you find. It seems there is a LOT of incorrect information even from people who should know better.
I have seen one "source" with access to an actual P-39 that didn't know that the 4 guns IN the wings were actually .30 caliber instead of .50 caliber. I have an actual printed book on my shelf that has lots of cool pictures but the assertions and conclusions in the written text are simply incorrect. I have a report that was written about the Allison engines that has aircraft performance curves that I know are incorrect because there are actual flight tests that contradict them.....

Gotta Run.
- Ivan.

 

[aleatorylamp]

Hello Ivan,
My version would also tie in with an early model performance, so following your recommendations, I expect the good table to go by is the one which is hand-pencilled in blue.

Yours had a stronger turbosupercharger, tuned more for "high-altitude" speed. The numbers for mine have to be slightly lower (306 and 362 mph), but I haven´t done any further adjustments to the .air file yet. At the moment they are at 334 and 380 mph, much too fast!

Then, following your original suggestions, I looked for and found a huge set of nine Paul Matt drawings at The Blueprints.com, with top, bottom, front, back, side-flying, side on ground, with nothing under-fuselage, with extra tank, and with bomb views.

They are different Q-models, with a 4-bladed prop, but that shouldn´t affect the basic shape, I suppose. The shape is the same as on the 2 before and after stretching overlay drawings you posted a while back. At least it hasn´t got the straight edged fin of the pink pinball!

Re. flaps: I hadn´t tried out my planned "easy" flap modification until just now, and I hadn´t dealt with the wing-root or any other bleeds yet, and these are quite apparent.
The results are like you said, so I´ll re-think that after wing-roots and wings are correctly placed.

I´ve dropped all wing-root parts to the new belly-line by 0.46 ft (I didn´t shift the components - this goes against my principles!), and now the wing parts will follow. However, wing-tips must drop only 0.24 ft, so that will take some doing!
All top parts of the landing-gear struts will need adjusting too.

Actually, the only components I shifted down a bit were the tailplanes, because they were already shifted, so it would have been too laborious to un-shift them first... anyway, no matter!

The model´s getting the look more and more - it had already started doing so with your main modifications a while back, and now it´s doing more so!

More later, as we´re off to the farmer´s market.
It´s finally sunny, not dull rainy and cloudy any longer, since yeasterday afternoon.
About time summer came too! They say it´s the old government´s fault - they did so many cut-backs that they also cut back on spring and summer!!
Cheers,
Aleatorylamp​

"Why make it simple if you can al
​

 

[Ivan]

Hello Aleatorylamp,

I hadn't actually gotten to the point of copying down the values from the image in the link you posted.
As it stands, it is so faint that the numbers don't really stand out very well on a quick read.
I didn't see a reason for doing that because it doesn't include the version that I am interested in.

In reality, the P-39D/F that I am building didn't have a Turbocharger. Only a few of the prototype Airacobras had a Turbocharger.
In fact, the Supercharger on my version and your version were probably identical.
As with any Flight Simulator model, if you give the same specifications to two authors, the method of implementation may be a bit different because we all have slightly different priorities in what we want to show in the flight model.

If the Wing Root and Wing Tip move different amounts, it is actually pretty easy to address.
Pick one side to move the Wing Panels with (I would probably go with the Wing Tip because the joints are a bit more confusing there), and then just snap the Wing Root ends of each panel to match the corresponding Wing Root vertex.

By the way, your "Pink Pinball" manned target was actually a P-63 King Cobra and I believe it was actually painted Orange and not Pink.

- Ivan.