Building a 1/16 scale P39N Airacobra

Discussion in 'Aircraft & Aviation' started by Leif Oh, Sep 21, 2004.

  1. Bowdenja

    Bowdenja Active Member

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    Hey I think Raimund has something..........the reason Leif is so good he has FOUR hands!

    Man.............. I always over-look the obvious!

    Leif.............I gotta build me that wheel making thingy........either that or learn how to mold rubber.........those are the most realistic wheels I have ever seem on a model!

    What do you use to mount the rought wheel upon? Is it custom made?

    The only mandril(s) I have found will not fit a wheel that thick.

    Fantastic........amazing......... work!
  2. Leif Oh

    Leif Oh Member

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    Bowdenja - the mandrel is just an ordinary 2 mm bolt with washers and nuts. Had exactly the same problem as you, of finding a mandrel with enough capacity. This was the smallest gauge bolt I could find at the store.

    Dustin, Dimas - you're right, and I should have said so - the plastic tubing around the rest of the structure is really superfluous, and you should probably lose it in smaller scale builds. However, in this case it brings the diameter up to the correct measure for the rolled paper parts (equal to the scaled wire size of the design). And it was interesting to see whether it could be pushed on to a bent wire. Could be used for other applications.

    Raimund - a small tripod, and using the self-exposure setting of the camera is good for making demo pictures. Avoids blurred exposures as well.

    Leif
  3. bfam4t6

    bfam4t6 Member

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    Thank you for the clarification Leif.
  4. Bowdenja

    Bowdenja Active Member

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    Thanks Leif........... gotta go and get me a metric converter...........Dumb ole me did not even consider a bolt with washers and nuts. Again I always seem to overlook the obvious!

    Got to add that to my list for the Home Depot store.
    I've got a Dremel-want-to-be........Home Depot had a B&D model for 20 bucks around Christmas time, and I hated to pass up that kind of deal.

    Guess I could just make a mount on a board. Hmmmmm anybody already got plans for this?

    john
  5. Leif Oh

    Leif Oh Member

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    25. Oleo struts & main gear

    25. Oleo struts & main gear

    Continuing with the details of the front leg wheel well, one of the tasks was to roll the oleo strut governing the retraction and extenstion of the front landing gear. The result was disgusting, so I tried out a few variations:

    To the left you'll see three variants of the oleo strut. At the back is my failure of making a proper roll of paper. In the middle, a composite of plastic tubes, one inside the other, painted with green acrylic. At the front the real winner:

    [​IMG]

    The winner, without comparison, is made of one piece of 2 mm pianowire, a perfect representation of the stainless steel part of the oleo strut. The cylinder is made of the paper part from the kit, and some extra fittings of paper are added. The paper roll is much better, thanks to Gil Russel's tip of sanding down the last part of the paper to be rolled, which makes the joint nearly invisible.

    The good result with the pianowire inspired an attempt to do something better than the kit provided for the main gear legs. Ideally, I should have used aluminium tubes, but did not have any of the correct diameter. Instead I decided to try out two other tricks inspired by Gil's research in different threads on this site, namely aluminium foil and vellum paper (thin sketch paper):

    [​IMG]

    (Above left:) A piece of ordinary household aluminium foil was sprayed on the glossy side with 3M spray glue, and the piece pressed on to a sheet of vellum paper. This produced a very thin composite with a suitably matt aluminium surface, which cold be rolled and glued with ordinary white glue as a top layer representing the stainless steel section of the rolled part provided in the kit.

    (Above right:) The result is much better than another attempt, namely to paint the same part of the roll with Humbrol aluminium enamel. Despite polishing, the surface remained uneven, and not of the proper shine (the two on the right). The aluminium foil composite parts were deemed clear winners. And now I have a good piece of alu composite left for future builds - took me all of five minutes to make!

    [​IMG]

    (Above left:) Getting serious about paper modeling - the slots in the main gear are cut with a 1.8 mm router in the Proxxon hobby drill. A possible case of overkill, but it was good fun to use the proper tool!

    (Above right:) Inner plastic tube with 1 mm pianowire inserted, same procedure as front gear. Main axis oversize, to be trimmed later. Fork about to go on. Note small inner distance piece of plastic wire.

    [​IMG]

    (Above left:) Forks completed.

    (Above right:) Note VERY small second distance piece inserted into wheel cover. Axis length now trimmed. A VERY small part left protruding, to go into the small plastic bearing in the wheel cover.

    [​IMG]

    (Above left:) Final details added, main wheels completed with covers on. Note the VERY small tolerances on both sides.

    (Above right:) And yet, both wheels spin extraordinarily freely (although one slightly better than the other); very littel wobbling, and no touching covers, forks, or any other part.

    This is the most difficult subassembly I have ever managed, and I am happy that it worked out so well, although final mounting into the aircraft still remains of course, touch wood...

    Leif
  6. Gil

    Gil Active Member

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    Leif,

    Absolutely beautiful! Glad the Aluminum Foil Paper series had a positive effect and outcome. The oleos have the "look" which is what counts.

    Best regards, Gil

    P.S. Currently writing the tube tutorial. Should be done in a day or two.
  7. Leif Oh

    Leif Oh Member

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    26. Front gear well completed

    26. Front gear well completed

    [​IMG]

    [Above:] Here are all the subassemblies and remaining parts which are going into the bottom recesses and wells of the aircraft. Just for fun, I tried to make a count of the parts making up these subassemblies, and arrived at the respectable figure of 161 parts assembled or lying around in this picture.

    [​IMG]

    [Above:] Starting to glue in the parts that were to go into the front gear well, it became immediately evident that preassembling parts to this degree was a mistake in some cases. The preassembled bulkhead with four struts proved to be too wide, and trimming the sides of it of course destroyed the whole assembly. Reverting to a fortunate extra copy printed of all these small parts, a new bulkhead was assembled, trimmed, and fitted into the well. Mounting the front gear proper was not a problem, although at this stage it is still vulnerable and apt to sway.

    [​IMG]

    [Above:] Assembling the intricate system of folding (in the full-size aircraft) struts supporting the front gear proved to be quite a challenge. It was virtually impossible to find a good starting point; something you could qlue down and fix in a correct position, in order to proceed from there. Every part instead hung on to, and dependended on other parts for its correct positioning. I finally decided to start by glueing the hydraulic cylinder to the main strut at what I guessed would be a reasonably proper angle.

    [​IMG]

    [Above:] From there on in it was a matter of adding no less than six other small struts, and join them all to each other and to the ends of the main strut, all of it hanging in thin air, so to speak. Everything sort of swayed back and forth at this stage, and it was a sweaty business until the glue started to set and everything still held together in a reasonably proper position.

    What a difference when the glue had dried completely an hour or so later - everything was rock solid; no sway in the tall gear, nothing flimsy. I am really impressed both by the strength of the model design (the struts really are both functional and indispensable), as well as by the intricacy of the full size design. Still quite can't figure out how these struts were supposed to fold up when the gear retracted, but is interesting to think about. You can learn a lot from a really detailed model; things you can't possibly deduce from a drawing.

    [​IMG]

    [Above:] Finally the preassembled gear well doors were added. I now think it was a mistake to mount the hinges to the doors before glueing the assembly to the wheel well. All of the hinges needed trimming, and the mounting is far from perfect. But at least they're in place, and quite firmly so, even if they are only glued to the tiny little hinges. Good job again, Halinski!

    Leif
  8. Leif Oh

    Leif Oh Member

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    27. Main gear wells completed

    27. Main gear wells completed

    [​IMG]

    The main gear is not as firmly fixed to any framework part as the front gear. Rigidity stems from the fact that the wheel well covers on the outside are glued to each other and the wing (in the real aircraft the two parts slid on top of each other). The covers thus act as structural support for the main gear, which otherwise is just butt glued to the wheel well. It works OK though.

    [​IMG]

    Attaching the inner wheel well cover, with its struts, went OK. I still quite can't figure out how the struts folded or slid, but it is clear that the retracting gear itself triggered or pushed the retraction of the inner gear door, by actuating the small green part on the black strut. Cooling air outlets added.

    These were all the remaining parts and subassemblies going into the wells and recesses on the bottom part of the aircraft. Time to turn it onto its wheels!

    [​IMG]

    And it works just fine. Focus here is on one of the few remaining details, namely the pitot tube. The pitot head was not supplied in the kit and was made from scratch.

    Next on the agenda is the radio antenna, where I'm eager to try out a small tool I've made specially for this (and future builds).

    Leif
  9. bfam4t6

    bfam4t6 Member

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    This is very exciting Leif. As I'm sure you know, everything looks amazing. Those are much better then any gear I've ever made. Mine either sprawl under the planes weight or you can see a little mountain of glue going 1/4 of the way down the gear to give it enough support. I look forward to see what you've come up with for making the antenna. Great work!
  10. Leif Oh

    Leif Oh Member

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    28. The radio antenna

    28. The radio antenna

    [​IMG]

    Above is the little tool I wanted to try. It is a machine sewing needle, which has been filed down (with an abrasive disk in the hobby drill) on one side, to serve both as a needle, and a "hook", pushing a thread into a small hole in the model.

    [​IMG]

    The mounting of the antenna is started with an ordinary needle, tying a small loop of ordinary thick sewing thread to the fin.

    [​IMG]

    The antenna proper has been started by tying a knot with a small loop at one end. This is pushed down into the canopy frame by the little tool above. Worked pretty well, although you have to make the hole first with an ordinary needle.

    [​IMG]

    The hole is injected with white glue and tension is applied to the antenna. The knot inside acts as a stopper. The loose protruding end is cut off.

    [​IMG]

    The same procedure has been carried out for the downlead to the radio in the aft fuselage.

    [​IMG]

    The antenna - still only attached at the canopy - is varnished with clear acrylic. The idea is for the thread to swell before tying it to the fin. Tying it still wet, it will tighten even further when drying.

    [​IMG]

    The same procedure has been carried out for the downlead. When the acrylic has dried, the varnished thread is carefully sanded with very fine sandpaper to remove fluff.

    I'd like to thank Rob (jrts), Chuck (CMartin) and PB (Bugbrains) for valuable advice on the subject, offered in another thread on the site.

    Leif
  11. barry

    barry Active Member

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    How to do it

    Leif

    Always, alway, always a good read full of info and great pics wonderful job

    barry
  12. shrike

    shrike Guest

    I came across something inthe bead section of the local craft store the other day that may be useful for antennae and such.
    I found spools of .012in (0.3mm) clear nylon coated stainless steel cable. Stretch or sag in the relatively short lengths we'd use would be nil.
  13. Leif Oh

    Leif Oh Member

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    29. Finished!

    29. Finished!

    I don't know if you remember, but I actually started the build of the Airacobra exactly eight months ago by building the propeller. That was an interesting task, and you can read about it in a thread of its own.

    [​IMG]

    So, when the antenna was in its place (thanks, Shrike, for the tip on 0.3 mm plastic coated wire; wished I'd had that!), it was just a matter of pushing that huge fan on to the electric motor axis, and charge up the battery.

    [​IMG]

    Pushing the button (situated under the "21") let the engine loose for its first warm-up run.

    [​IMG]

    Ready and waiting to take up its permanent place, just around the corner:

    [​IMG]

    ... where it is now hanging from the roof.

    The Airacobra in 1/16 scale is hereby officially declared FINISHED!

    Leif
  14. Swinger

    Swinger Member

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    Congratulations Leif, that was a fantastic build with a great result! :) However... Could you take some more photos of your Airacobra - in daylight? :lol:
  15. yaniv

    yaniv Active Member

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    out stending work g8 resolt
    the models look lime 1 thet need jest to texi the runway open engens and tack off :)
    reale enjoy to see a models fimsh thet way in this reasolt
    kip doing a g8 work

    b.a
    what is the next project?
  16. rkelterer

    rkelterer Member

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    leif , congratiulations

    you built an impressive model - in size as well as in workmanship - the construction photos are excellent - and you finished it :D

    best wishes from austria
    raimund
  17. Gil

    Gil Active Member

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    Leif,

    Congratulations on an exemplary job excellently done!

    You are truly one of the people that attract viewers to this site. It's hoped that some of your very capable modeling expertise has rubbed off on us all and that, in turn, we'll all be contributing better built models.

    Warmest regards, Gil
  18. Leif Oh

    Leif Oh Member

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    30. Epilogue: The Airacobra airborne

    30. Epilogue: The Airacobra airborne

    Many, many thanks to all of you, for your support, enthusiasm, and kind prodding during this build!

    Swinger is right, though - daylight makes a difference. Luckily I was able to get a few shots today of the Airacobra getting a first taste of air under its wings; a couple more shots from the hangar apron; and there was even an opportunity when it was parked over the maintenance pit to catch a rare view of its intricate underbelly. Here's what I got:

    [​IMG]

    The Airacobra clearing the building on the opposite side of the street (and just barely the flower pots in our living room window), turning final from left base over the street (you can have a closer look of what the approach looks like here).

    [​IMG]

    On final, a critical passage through our living room window, to set up for a landing on runway 01, our hallway carpet. Field well in hand; engine on idle. Flaps about to be lowered.

    [​IMG]

    On the hangar apron (our kitchen table). For a comparison of finish, go have a look at this surviving Russian Airacobra (no. 26 as compared with my 21), on exhibit at the Tikkakoski museum in Finland.

    [​IMG]

    For a similar view of the Tikkakoski Airacobra, go here.

    [​IMG]

    A bottom up view, from the maintenance pit in the hangar. Have a look also at the landing gear of no. 26. Note particularly how nothing but alu foil would reproduce that shine of the main leg!

    [​IMG]

    A final quick daylight peek into the cockpit to end this mini "Airacobra walk-around" - and the entire tale of this 1/16 scale Airacobra build.

    Leif
  19. gera

    gera Member

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    Hi Leif:
    First let me congratulate you for your patience and fortitude in this great build. Second, I congratulate you on your beautiful workmanship. Your P-39 is an example of the excellent work that can be done with a paper model.
    Third, thank you for the excellent photos of the build, I surely learned a lot from them as well as your explanations.
    OK.........what´s Next????????? :D :D :D

    Gera
  20. Ashrunner

    Ashrunner Member

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    Lief

    Magnificent build on the P-39. It looks fantastic!