Analysing and modifying the AFX file with QBasic. - Page 11
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Thread: Analysing and modifying the AFX file with QBasic.

  1. #251
    Hello Ivan,
    Arenīt there three propellers that came out of your department? There was a wooden fixed-pitch propeller,
    I believe based on your Eindecker one, which I was whittling away at and sanding off with technical support
    from your workshop.

    Then, in my propeller department, there were two adaptations of the 2-pitch-position FW200 propeller, one
    for the Stearman and one for the Electra.

    This one is my first try at a CV propeller, with technical support from your department of course.
    Iīm sure that without your comments along the line, I would not have managed by any means. I admit I did not
    understand everything you said, and I have arrived at some results following a slightly different path, but
    everything does tie in with all you were saying.

    Although level flight performance is perfect at Critical Altitude and acceptable at 500 ft, the propeller is not
    by any means finished yet. The sustained climb test is still outstanding. I think Iīll do it with 50% fuel and full
    ammo ( as it is lighter without the wing guns).

    The other thing is trying to get the 316 mph down to 314. Here, there is a side-effect, (understandably):
    The more I manage to lower this, the slower the speed progresses from 290 to 314 mph, upto a "danger point"
    where it stops accellerating before getting there.

    Interesting too, I thought, and resulting from overcoming the interpolation "wall" between 290 and 314 mph,
    was that this
    required performance improvements also on the 30 deg. pitch graphs, but thinking about it,
    it seems logical I suppose.

    Another strange thing is the rather low 1083 Hp setting at S.L. that the sim seems to stubbornly be demanding
    for its 44.2 Hg Military Power. Iīd be much happier with at least 1100 hp (the take-off limitation I read on one
    source, seemingly for later models, although that wasnīt clear), and preferably 1150, which is in the specs.

    It also comes along with a side-effect: Full 1551 Hp WEP canīt be set with 60 Hg, because power goes wild,
    and WEP
    must be kept to 57.35 Hg. For the moment, adjustments on these two items donīt seem possible.

    Nevertheless, the differences lie within acceptable limits, and performance is behaving itself rather well, Iīd say.

    Incidentally, another improvement along the way: WEP at S.L., or rather 500 ft, is now giving a more logical
    speed: 134.5 mph, not the excessive 158 mph I was getting before!

    OK then, now for the sustained climb test!

    And here is the sustained climb test, without any additional adjustments as yet:
    I had to slew down to 1000 ft and let it travel to beyond 2500 ft several times, but finally, after the porpoising
    settled down (under Learjet Autopilot), at 2500 ft, it appears to be able to maintain 2700 fpm at 180 mph,
    with 1103 Hp and 23 degree. Pitch. Pitch and Hp are a bit lower than you had indicated, but seem OK to me.

    The question is whether this would be OK with your understanding too... I wonder!

    Last edited by aleatorylamp; August 3rd, 2018 at 06:25.
    "Why make it simple if you can also make it complicated?"

  2. #252

    Curtiss Electric Propellers

    Hello Ivan,
    On the War Department Performance Test page, it is apparent that, as I mentioned before,
    it mentions the P39-M model with the 1200 Hp -83 engine had a Curtiss Electric Propeller,
    reference number 614-1C-1-5-21, with a pitch range of 26-56 deg. and unknown radius,
    which for the moment I had placed at 10.4 ft, i.e. 10 ft 4.8 inches.

    The same page also mentions the -D Model with a -35 engine, and the propeller, although not
    mentioned as Curtiss Electric, has reference number 614-1C1.5-21, suspiciously similar to the
    previous one, but for the point instead of the hyphen in the number sequence, and gives pitch
    range as 21.5 to 51.5 degrees. Radius is also unknown.

    There is another document Iīve mentioned, P39DFlyingQualities.pdf, which has a rather broken
    typewriter type-face, making it quite difficult to read. It covers the P39D-1 model with its -35
    engine, and mentions it as being equipped with a Curtiss Electric propeller, but gives no further
    details on it, except for an airplane diagram showing propeller diameter at 10 ft 4.5 inches.

    Perhaps it is possible from this information, to piece together the Curtiss Electric propeller for
    the D-2 model with its 1325 Hp -63 engine, with radius being 10 ft 4.5 inches, i.e. 10.3750 ft,
    and pitch range being 26-56 degrees.

    For the moment, itīs the closest I have managed to get, so I entered this data into the .air file,
    and was able to establish that at 500 ft, the slightly excessive speed further increased to 320 mph.

    Applying finer adjustments to the propeller graphs at J=1.6 and J=1.8 it has now been possible
    to curtail the excessive level speed to 314.1 mph, and it will not go above that under military power.

    The resulting fine-adjustment of the propeller radius has also increased sustained climb speed
    to 191 mph, which would also be plausible compared to the figures you were giving for your -F model.

    Slowly the picture seems to be getting more complete, which I find very satisfying!

    One drawback with cutting 0.025 ft off the propeller is that at high speeds went, as the sim only selected
    39 deg. pitch. So,
    S.L. WEP was 1.5 mph slower than before, and at 13000 ft, top speed was 22 mph
    However, tiny adjustments on the 40-degree propeller graphs at j=1.8 and J-2 fixed this very well.

    Now I can continue with the textures on the fuselage.
    Last edited by aleatorylamp; August 4th, 2018 at 03:04.
    "Why make it simple if you can also make it complicated?"

  3. #253
    Hello Aleatorylamp,

    Quote Originally Posted by Aleatorylamp
    Arenīt there three propellers that came out of your department? There was a wooden fixed-pitch propeller,
    I believe based on your Eindecker one, which I was whittling away at and sanding off with technical support
    from your workshop.
    The Eindecker Propeller really doesn't count. It is basically a modified Stock Propeller because I didn't know any better at the time.
    There actually have been a lot more adaptations than mentioned thus far. The Bombers you were working on from the Great War had a few Propellers that had some influence from my shop.

    Be careful about using specs for a Propeller from a different model Allison Engine. They tended to be significantly different in Diameter and Pitch Ranges and also in Reduction Gear Ratio.

    I fixed another minor bleed in the Tail section of the EJ P-39D last night. It was an easy fix.

    - Ivan.

  4. #254
    Hello Ivan,
    Well, as I commented before, without specific data one can only speculate, so thereīs room only for educated (or uneducated...) guesses.

    Unless you were to have a better suggestion for the Curtiss Electric Propeller, I would be inclined to use the 10.375 ft diameter propeller
    I have now, with its correspondingly
    fine-tuned Propeller Tables 511 and 512 to meet the conditions for the three test situations established.
    It also seems to work better in the problematic interpolation "wall" area around 300 mph for military power, so perhaps it is another reason
    to go for this diameter and 26 deg. minimum pitch.

    Summarizing possibilities:
    A) 10.375 ft is 10 ft 4.5 inches. Iīve seen this in other sources as well, not specifically for the D-2 version, but rather the D-1, or unspecified.
    The 26-56 deg. pitch range of the propeller for the -63 engine also seems more in line with the -83 engine I got the pitch data from,
    than the 21.5-51.5 deg. D-1 Propeller of the -45 engine, although it seems that the diameter was the same.

    B) 10.4 ft, which I was using for want of anything else. This is 10 ft 4.8 inches, nowhere to be seen, thus presumably less probable than A).
    C) The Aeroproducts Propellers on later versions produced shortly after these, I think were larger, so this size can be discarded.
    I believe that on -Q versions diameter could be over 11 ft.

    What size is the Aeroproducts Propeller on your version?

    Re: the model itself:
    Wings and wing-fillets now have a number of extra panels to make the surfaces less flat and angular - a bit more rounded - and also to
    triangulate further disappearing panels. Fuselage textures now also fit the area better. I think thereīs still one more disappearing panel
    in the nose area that needs triangulating, but should be easy.

    Here are some screenshots with a kind of Siberian ambience, although it is really the Danish Station Nord in Greenland.

    Attached Thumbnails Attached Thumbnails Russia1.jpg   Russia3.jpg   Russia5.jpg  
    "Why make it simple if you can also make it complicated?"

  5. #255

    Flaps, and Curtiss Electric Propeller.

    Hello Ivan,
    I see you are making headway with the first phases of your new Airacobra Models.

    A while back you were asking about how Iīd solved the flaps-bleed problems, and Iīd answered that wheel-wells were still bleeding through the extended flaps seen from behind.

    Well, fortunately Iīve just managed to fix this by taking the wheel-wells out of Gear-Centre, eliminating the wheel-door glue there, and placing the wheelwells into Wing-Low left/right, together with a duplication of the animated flaps, and including a vertical glue template between them. Now it all works perfectly!

    Only moving the flaps out of Gear left/right into Wing Low left/right is not enough, as they will allow the landing gear in Gear left/right to bleed through.

    Another thing on the flaps: The inner flap section will perhaps have to be corrected, as long as it doesnīt interfere with the wing-root.
    It seems not to be square, but should be more angular, nearing the fuselage centre on the flap trailing edge.

    Re: Curtiss Electric Propeller, contīd:
    After finding the 10 ft 4 in. (10.375 ft) diameter of the Curtiss Electric Propeller used on early Airacobras, I noticed it was the same as indicated on several diagrams in documents on the airplane with Aeroprotucts Propeller. You had also had mentioned it in one of your posts a few days ago.

    So both propellers were the same diameter, with differt mechanisms as can be seen on an exploded-view drawing showing both propellers simultaneously. The inner part near the hub can be seen as built differently.

    I noticed that the same reference number is indicated for the blade design of the Curtiss Electric Propeller for different aircraft models, but the pitch range varies. Nevertheless, the movement is always a total of 30 degrees: 26-56, 21.5-51.5 or 21-51.

    This would lead me to believe that the Curtiss Electric Propeller used on early models was always the same one, same diameter, same blades, but with a mechanism that allowed pitch-range to be set depending on the engine, so that the 30-degree movement could be made to start between 21 and at least 26 degrees.

    The Aeroproducts Propeller on a -Q version had a range of 28-63 degrees, and I know -Q versions had larger diameters, and possibly -N versions as well.

    In my last post I asked about the diameter of the Aeroproducts Propeller you were using, meaning the one on your planned P-39Q version, as you had already mentioned the diameter for your earlier P-39F version, but I forgot to mention the -Q version specifically!


    Last edited by aleatorylamp; August 6th, 2018 at 05:09.

  6. #256

    Flaps and radio

    Hello Ivan,
    The small correction in the shape of the inboard flap edge unfortunately (and expectedly) interacts with the wing-fillet,
    so itīs not worth fixing and best left alone! I will, however, correct the inboard flap-line on the wing-texture underneath.

    Unless of course, one were to modify the wing-fillet shape, bringing the outer edge of the component inwards,
    along the red line on the screenshot, at that part parallel to the fuselage. Then the inboard flap edge would be flush with
    it, and the inner part of the wing would
    have to have a wedge shape added. ...All much too complicated, perhaps...
    Update2: The best way is maybe an in-between correction: Make the flap-edge parallel without adding a wedge fillet to
    the wing as per the screenshot with the red circle.
    It isnīt a very obviously visible correction on the model, ...only a small
    but at least I know itīs better and itīs there!

    Incidentally, I noticed that on earlier versions, the radio was placed inside a small compartment in the aft-fuselage.
    Unfortunately, I havenīt been able to find out as of which later model it was moved to the aft-cabin.

    Slowly the model is getting to a finished state, although Iīm still checking for possible flaws, glitches and bugs.

    Iīll also probably darken the grey landing-gear struts, to increase the contrast with the under-wing light-grey.

    Attached Thumbnails Attached Thumbnails Top-view.jpg   Newflap.jpg   NewFlap2.jpg  
    Last edited by aleatorylamp; August 6th, 2018 at 09:40.

  7. #257

    Virtual Cockpit

    Hello Folks,
    Thanks to help from Ivanīs Workshop on different issues, everything seems to have come out pretty well,
    better that Iīd expected.

    This applies to all aspects of the work involved in extensively upgrading and updating this model
    from the original 1998 Eric Johnson AF5 AFX files:

    - More accurate dimensions according the most recently found more accurate documentation.
    - More correct positioning of the modelīs centre of rotation.
    - More rounded shapes all around.
    - Corrected height of aft-fuselage and tail-empenage, belly-curve and nose-gear.
    - More correct shapes for leading edge, wing, wing-root, and tailplane.
    - More efficient glue-sequences to keep bleeds at an absolute minimum.
    - Transparent Cockpit with pilot.
    - Improved engine and propeller tuning in the .air file.
    - SCASM-corrected Virtual Cockpit Chase-Mode View.

    Then, the panel Iīm going to use for the upload is a CFS panel by Dan Griffin, which was included with one of
    the Airacobra uploads in 2005.
    In my opinion it looks quite good and does the job.

    Here are some screenshots, also including two Virtual Cockpit views.

    Now comes checking that everything is OK in the Dp files, writing the checklists and the readme texts,
    and then the model will hopefully be ready for upload!

    Attached Thumbnails Attached Thumbnails Screenshot.jpg   VC-view2.jpg   VCview1.jpg   V-panel.jpg  
    Last edited by aleatorylamp; August 7th, 2018 at 16:26. Reason: spelling and wording

  8. #258

    Not quite there yet!

    Good morning!

    As often happens, last minute adjustments were required.
    Ivanīs latest post on his Airacobra thread mentions a more accurate fuselage width than the one I had,
    which came in very handy indeed! Thank you once more, Ivan!

    I had already corrected the original AFXīs fuselage width as per data obtained from the previous drawings
    I was using, and it turns out that my fuselage was still just under 2 inches too narrow. This also led me to
    check the tailplane span on the new drawings, and mine was still short by 3 inches per side!

    Thus, I made a copy of my AF99 build, took out everything except the nose, fuselage, cockpit, and tail empenage,
    packed it into an AFX file, and ran it through my QBasic Modifier with a multiplier to get the fuselage width exact.

    Then I unpacked the new parts into my regular build, adjusted the front nose panels to be flush the spinner,
    manually fine-adjusted the tailplane span and re-compiled the build.

    Admittedly, the corrections on the visual model are not noticeable, but I know theyīre there, which is satisfying,
    as one of my main aims with this model is to get shapes and dimensions as accurate as possible.

    Now the only thing remaining is to re-SCASM the model for the virtual cockpit. This should be straight forward,
    ecause expectedly, parts order will not have changed.

    It turns out that the QBasic Modifier is certainly worth its weight in gold!

    I was even dreaming of writing a QBasic Program to make custom-made Propeller Tables 511 and 512, so that this
    will automatically and instantly create these tables accurately, instead of having to go through manual adjustments
    on individual points on the different graph lines. ...No harm in wishful thinking, I suppose!

    "Why make it simple if you can also make it complicated?"

  9. #259
    Hello Aleatorylamp,

    Quote Originally Posted by Aleatorylamp
    As often happens, last minute adjustments were required.
    Ivanīs latest post on his Airacobra thread mentions a more accurate fuselage width than the one I had,
    which came in very handy indeed! Thank you once more, Ivan!
    "You're Welcome" for the data. I was pretty sure you already had the data though because you posted a link to a PDF from the "Legends in Their Own Time" site in a much earlier post which I quoted in the Airacobra thread.

    For information content, this is the same as the "Design Analysis" article I am using but just in a less pretty and more readable format. The "Design Analysis" article is where I found the data I just posted and you clearly had that if you were posting a link to the PDF.

    - Ivan.

  10. #260
    Hello Rami,
    In view of recent developments, it may be a good idea to delete this thread.
    Thank you very much,
    "Why make it simple if you can also make it complicated?"

  11. #261
    Hello Aleatorylamp,

    Shouldn't we leave it in place as evidence for all to see?
    At times I wasn't particularly nice, but I believe this thread contains a lot of evidence to justify my conclusions.
    Then again, other design threads have plenty of evidence as well.

    - Ivan.

  12. #262
    Hello Ivan,
    Whatever. We can leave it if you want.
    As I am no longer uploading the P39D-2, I thought there wouldnīt be any point in keeping the thread, but as you wish.

    What I still canīt understand is why you didnīt make it clear from the very beginning,
    that you werenīt quite happy if we both worked on the same AFX, even if our reasons were different.
    You actually seemed to welcome the idea, which makes it even stranger.

    Hello Rami,
    Well, then it wonīt be necessary to delete this thread after all.
    Thanks for your attention anyway.

    "Why make it simple if you can also make it complicated?"

  13. #263
    Hello Aleatorylamp,

    Quote Originally Posted by Aleatorylamp
    What I still canīt understand is why you didnīt make it clear from the very beginning,
    that you werenīt quite happy if we both worked on the same AFX, even if our reasons were different.
    You actually seemed to welcome the idea, which makes it even stranger.
    I really don't have any objection to you working on the same AFX. If I did, I would not have attempted to help you at all.
    What you may not remember is that well before I started the "Airacobra" Thread, I contacted you via Email and asked you not to bring discussions of editing this AFX into the new thread.

    It didn't take you very long before you forgot our agreement and did that anyway. That was really rather annoying....

    I also told you back on this post what my intent was regarding this project.

    Go back and read through this thread and see how many "Oh Dear!" and "That is Not what I stated" comments there are.
    As I see it, you are quite careless and unobservant when reading and working with that gets to be quite frustrating which is something I have tried to avoid saying directly for a very long time.

    - Ivan.

  14. #264

    Change in plans.

    Hello all!
    Yesterday, I found a backup file of my improved 1998 Airacobra AFX by Eric Johnson, on an old fall-back
    computer Iīd forgotten about, dated 4th August, and thought that it seemed a pity to waste all the time
    and effort, not only my own at that, that this work had entailed.

    Thus, I changed my mind about not uploading the model, and proceeded to repeat the numerous minor
    improvements and corrections Iīd undertaken after that
    date, with the exception of the fuselage-width
    correction, which not only proved unnecessary, but also
    counter-productive, as the fuselage width dimensions
    at the fore and aft cabin were indeed correct.

    the slight bulge in the centre was 0.8 inches short on each side, because I had chosen, for building reasons,
    to maintain the sides straight, so as to avoid errors with the wing-root and some glue templates.

    Despite my bad memory, I think I completed all the necessary corrections, mostly on flaps/wheel-wells, propeller/nose
    and some hairline cracks at the aft wing-root and the tail fin.

    I even eliminated one bad bleed that I hadnīt managed before, involving the canopy-glass and the cabin-floor, which
    was corrected
    by increasing the slant on the canopy glass/frame inclined glue-template. Then, there is now a small
    fin-fillet, at the fin-base on the fuselage back, and the pilot moves his head with
    the rudder.

    So, fortunately, after re-SCASMing for the Virtual Cockpit View correction, the model has come out quite nicely, and
    I have just uploaded it. Once approved, it will be available at:

    Attached Thumbnails Attached Thumbnails Screenshot1.jpg   Screenshot2.jpg   Screenshot3.jpg   Screenshot4.jpg  
    "Why make it simple if you can also make it complicated?"

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