Building a 1/16 scale P39N Airacobra

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

  1. cecil_severs

    cecil_severs Member


    The wings were well worth waiting for, at least for us that is. Nice self portrait as well. It looks like you are contemplating the next logical step for an airplane this big,.... where to put the radio, control rods, etc. Just kidding really, I know I wouldn't want to see anything this precious crash and burn! More likely you're thinking of what museum to grace with this masterpiece.

  2. Bowdenja

    Bowdenja Active Member

    WOW Again! :shock: :shock:

    When are we going to see the prop spin!!! :D

    Truely a master piece, built by a master!
  3. bfam4t6

    bfam4t6 Member

    Congratulations on a perfect set of wings. You even gifted us with a great tutorial. I was really looking forward to seeing you start up this project again and it was well worth the wait. :D After seeing the picture that shows the size of the plane, I want, even more, to up scale one of my planes. You have done some very precise and inspiring work Leif. I look forward to your next update.
  4. gera

    gera Member

    Leif.............................Congratulations my friend, You did it again....
    Excelente Trabajo!!! :) ....I copy your tips to my hard disk for future Reference....I like how you take your time, think over how you are to proceed then jump into it...Carefully!!!!!!!!!!!!!!!! HA HA HA!!!!! Like watching in a microscope!!!! HA HA!!!! :shock: :shock: :shock: :shock:
  5. Leif Oh

    Leif Oh Member

    22. Adding the wing fairings

    22. Adding the wing fairings

    I was eager to finish off all the difficult stuff, so yesterday I added the wing root fairings. These are scary stuff, probably the parts with most compound (saddle-formed and therefore "impossible") curves of all on any aircraft. Here's how it turned out:


    1. First the easy part, the little covering plate at the front. Fitted beautifully, which was a consolation.

    2. Just showing off the two car-washing sponges purchased several months ago in anticipation of this moment. All building from now on will take place with the help of these universal supports. Three heights, depending which way you turn them!

    3. Preshaped main wing root fairings. Looking pretty good so far. Rolled over a coarse and a fine crochet needle. I am very impressed with the design of these parts. They really fitted most beautifully.

    4. Same basic idea as when covering the wings: Think ahead and do not place yourself in a position where you suddenly have to accomplish a lot of difficult positioning "before the glue dries". After dryfitting, I decided to start from the back/underside. Note the small area being glued.


    5. Repeat of the last image (sorry, my mistake, but I'll go ahead anyway).

    6. Both wing fairings glued in at the back, and the joint being touched upp with acrylic grey mixed with white glue.

    7. Now you can actually apply glue to the entire topside. Glue applied to the model, not the fairing to avoid smearing when positioning the part. Note folded-back wing fairing, already glued to the bottom.

    8. The fairing is glued all the way along the top, and only the final section at the front bottom remains. Here, it is massaged into place. At this point, glue was applied to the part, not the fuselage. Imagine, a single part stretching from the back underside, over and around the trailing edge, along the top of the wing, then around the leading edge and tucked in at the front bottom. Wonderful design.


    It was in fact necessary to add a small filler piece (made from a scrap copy of the fairing) to the back top side of the fairing on one side of the wing. This is most probably due to an earlier mistake in building, mentioned already when I mounted the stabilizer - and now it came back to haunt me again! You can sort of guess where it is in this picture, but the overall result is acceptable.

    All seams of the wing fairings have been touched up with a mixture of different shades of greys (from water-colour pencils) and white glue, but they are still quite protruding. I have suggested earlier that a thinner paper could be used for fairings to avoid this. I no longer think this would be possible, since the thinner paper would buckle too much when attempting to create those complicated shapes. A better idea, it now strikes me, would be to apply the technique suggested by Gil in winding the cylinders of the Wright 1820 engine, namely to sand down the edges of the fairings (and similar parts going on top of other parts). Pity I didn't remember that yesterday!

    What this picture also shows is a major mistake I made in varnishing. At this point I was unhappy with the matt varnish used so far, since it exhibited some clouding (probably because it had dried up too much over time, or because I hade used up too much of the clear part of it due to not shaking it enough earlier).

    I therefore decide to give the whole model a coat of semi-matt (20+ shine) clear varnish. This, however, is much too glossy, despite claims of being "satin" finish. This morning, on my way to work, I therefore hastened to buy a can of matt varnish, and hopefully the proper matt finish of the Airacobra will be restored tonight.

    Now, a final remark before turning to the landing gears and wheels, with their myriad of nice details: You guys have been very kind, praising this model, and I'm very grateful. The truth is that is a rather mediocre model as far as craftmanship goes, and I'm increasingly ashamed of showing close-ups (you get very close at a scale of 1/16!).

    It has been a learning experience for me all the way, and still is. In the course of building so far, all the advice and experience available throughout this site has been invaluable. The main objective has been to demonstrate that each and everyone of us, even a comparative newcomer to the hobby like me, could get his or her own "museum-scale" model (at least as far as size and level of detail are concerned) by scaling up the high-quality paper models now available.

  6. cecil_severs

    cecil_severs Member


    I think that you are being much to hard on yourself. All of the praise and kind words that you have recieved for this project are well deserved. Believe it, it's true.

    Having said that I think that it's time for a new avatar for you, one that reflects this project and your intense devotion to it. So here it is. Use it if you like it. If not, oh well.

  7. Leif Oh

    Leif Oh Member

    Thanks for the suggestion, Cecil - excellent idea, and it is a done deed, for the duration of this build!

  8. bfam4t6

    bfam4t6 Member

    Cecil is right Leif. You deserve every bit of praise you have recieved during this build. I personally admire a man (or woman) who can acknowledge mistakes or things that could have been better and not try to cover them up. This I think is also what makes your build review so amazing. You seem to mention every slight mishap to us, and the best part is that you always explain how you corrected it. This allows all of us to learn. To be honest most of the "mistakes" that you mention are so slight that I probably would not mention them myself if it were my build thread. So, I thank you for teaching us. That is what makes watching you build this so wonderful. The pictures of the entire model to date are always very cool too :wink: Anyways, although you, being a anal man it seems, doubt the greatness of your build, I don't doubt it one bit! The model trule looks amazing, and I personally think that the scale makes it so much better becuase it DOES allow you to see all of the fine details. Keep up the great work. I am very excited to finally see this bird stand up on its own, so let us know how the gears go whenever you get the chance. Thanks for sharing this with all of us Leif.
  9. barry

    barry Active Member


    Leif it's a wonderful build and instruction manual I think you forget with closeup pics you move the perceived scale up to 1/5 and they still look brilliant.

  10. Leif Oh

    Leif Oh Member

    23. Making the wheels

    23. Making the wheels

    Reading Ron's article on how to make wheels was one of the very first and great revelations when I first came to this site. It led to the immediate purchase of an Olfa circle cutter. Now the time had come to practice what was taught there, and subsequently by others in various postings on the site.


    1. Each main wheel of the Airacobra is built up from no less than 13 parts, laminated on various thicknesses of cardstock, Bristol card, and ordinary thickness paper, all of which have to be cut out to fit inside each other in a most ingenious way to create a pile like the one in the middle.

    2. If the centre hole of your pieces has become too large - as a result of arduous work with the Olfa circle cutter, or because you have already drilled it for later fitting on a mandrel - cutting out the center section precisely becomes difficult. My way of solving that was to insert a small piece of 2 mm plastic tubing (later to be used as axis material over 1 mm piano wire) over the centre needle of the Olfa cutter. Cutting then becomes precise again.

    3. The inner rim of outer tyre parts is bevelled - tyres do have a slight inflection here, meeting the rim of the hub.

    4. Parts that are to fit inside other parts - such as brake, hub rims, and hub caps - are mounted on a 2 mm nut and bolt, with washers on each side, and sanded to correct outer diameter in a small hobby power drill. This may be an exotic tool, but any form of a simple small power drill, whether mounted or hand-held, really turns wheel-making into a pure pleasure.


    5. Now is the time to edgecolour really well, and more rather than less. The inner edge of tyre parts are painted with matt black acrylic, and preassembled hub parts with grey acrylic. Remember - you will not be able to get at these parts later on, so be sure not to leave any white area where it might be visible later.

    6. Here's the fun part - shaping the glued-up wheel. It's a breeze; easier and quicker than any other part of wheelmaking.

    7. Putting in the "safety pattern" specificed for the main wheels of the Airacobra. Just press down with a common brake-off knife blade, or a razor blade. Much easier than I imagined; two rounds of cuts crossing each other at 30-45 degrees. Note here: Do not do this until after the next step, painting. The paint will fill up the pattern so that it is almost invisible. I had to re-cut the pattern after initial painting.

    8. Paint the tyres while they are still mounted (but don't be tempted to do it with the motor running!). Start with diluted black acrylic, in order to let the paint soak into the rills created by the different layers making up the wheel. It is quite difficult to get thick paint to penetrate all the way into these rills, because they are so thin (0.25 mm at times); diluted paint penetrates but may still not adhere, because of, I imagine, glue remnants in the rills, so this step requires a lot of brush work. When you are satisfied, finish up by a coat of regular-thickness paint.

    Note here: Now is the time to make the criss-cross pattern. Doing that will make a lot of white reappear in the cuts. Repaint with diluted matt black, soaking into the cuts. Since the paint now is diluted, it will not clog up the pattern, and yet the full black is retained, since you've already painted it once. This is learning by doing; no way to figure out these things beforehand.


    The front wheel is similar in construction, but simpler. Incidentally, it shouldn't have a criss-cross "safety" pattern, but I just couldn't stop myself - it was such fun.

    The last step is to varnish the center metal parts (brake drum, hub and rims) with matt clear varnish. I haven't varnished the rubber tyre parts, in order to keep them as matt as possible to simulate rubber, and to make a difference in shine against the hub.

    What I would do differently: Originally, I had in mind to make correctly revolving wheels, that is wheels where the hub, the tyre, and the tyre caps revolve, while the brake drum is fixed to the landing gear. This is entirely possible to accomplish with a good wheel design such as this, at least in a scale of 1/16. But I simply couldn't figure out how the wheels came together until I had actually built them. Now I know, and will attempt such a set in some other future project.

    It would have required mounting inner parts, such as brake drum and hub caps last, after securing them to the landing gear, and also various intricate small pieces of plastic tubing acting as stoppers and distance pieces inside the hub cap and brake drum. But I think it is doable.

    Even if you mount the wheels rigidly, as I intend to in this instance, it would be a preferable sequence of doing things, since the inner and outer parts then will not be as deformed by screwing them tightly on to the mandrel as they now are. (This sequence of work was actually outlined in Ron's original article, which I didn't notice until re-reading it now...)

    But I'm quite happy with the wheels as they turned out, and it wasn't as difficult as I thought it would be.

  11. cecil_severs

    cecil_severs Member


    Wonderful build thread as usual. I don't remember seeing the tire tread pattern done this way before. Who needs aftermarket wheels now? I think that your methods can be used pretty well at 1/32 scale or even 1/50 or so with some success. Definitely something I'll try though not on my current airplane build ( 1/144 scale flying flea).

  12. dhanners

    dhanners Member

    Not to sound like a broken record, but I just wanted to express what a joy it has been -- not to mention learning experience -- to watch your work on this plane. Despite your self-depracation, every piece has been exquisite and you pack more detail into a "simple" wheel than most of us do in an entire model.

    It has truly been a pleasure to watch a master at work, and have him share his techniques and insights with the rest of us.
    David Hanners
    St. Paul, MN
  13. wunwinglow

    wunwinglow Active Member

    You know how some models look like, well, models. And some look like the real thing...

    I think you can see where I am going with this! Leif, this is a magnificent model. And I wouldn't worry too much about not having a dead-flat finish, most aircraft acquire an oily sheen even if they are painted originally with matt paints. And a slight gloss makes it look like a metal surface rather than paper.

    Whatever, wonderful job. Thanks for sharing it with us all.

    Tim P
  14. Leif Oh

    Leif Oh Member

    Thanks, guys, for the comfort. I'm beginning to feel better about the old Airacobra already. The flat varnish has gone on (although it's difficult to get rid of the gloss, once it's there; lesson for the future).

    I'm actually having a good time with the landing gear details now. Wonderful design, so intricate, and all those tiny little details fit together marvellously well (so far; touch wood!). I'm taking it slow and enjoying myself.

    Glad you liked the tyre treads. I'm sure I've picked it up on the site; just happy it worked and that I could replicate it. A razor blade would be my tip for smaller scale tyre treads.

    Best to all, Leif

    PS. Cecil, if you need any info on the Flying Flea, I've saved a replica of an original 1930 "How to build it...", two-part, article from an British 1930s magazine. It's on the web somewhere, and I'll dig it out when you need it (although I think you'll get along fine without it for your current, truly flea-like scale - looking forward to see that!).
  15. dimas Karabas

    dimas Karabas Member

    Simply stunning! Amazing job on the wheels! Love it! Way to go. Please more close up pictures.
  16. Ron

    Ron Member

    My tutorial and even my builds look like child's play when put beside your magnificent work. Thanks for the mention! It makes me feel all warm and fuzzy inside :p I'm going to follow your tutorial on the next one

    Thanks for sharing this with us in such detail!
  17. Leif Oh

    Leif Oh Member

    24. The front gear

    24. The front gear

    I've made the front gear leg, trying out a method of making axes and wheel legs I've been thinking about for a long time, and it turned out really well. Here's the report, which I hope some of you will find useful:


    The idea is to use 1 mm pianowire, with plastic tubing of 1 mm inner diameter going on outside. The wheel will have one small piece of this plastic tubing glued in as a bearing (fitting quite nicely into the 2 mm hole necessitated for sanding it in the hobby drill; see previous installment), and small additional pieces of tubing on each side fixed to the axis in order to center the wheel within the wheel fork. The plastic tubing used is the kind you buy in hobby shops for inner RC control rods.

    On the picture above, the smaller (bent) piece of plastic tubing was pushed on to the right hand pre-bent wheel fork required by the design, before the final 90 degree bend creating the wheel axis was made. The axis part was made overlong, to be trimmed down later to the exact length required to team up with the left hand wheel fork. The axis will be longer than specified in the design. (Watch out for this in your own builds. Designs are often made for fixed wheels, i.e. only half an axis.)


    1. The slightly prebent part to be rolled into the front leg is sanded thin at the initial stretch, and - most importantly - at the end section. This is an absolute gem of a tip, for which I am very grateful to Gil on this site. It will make the final seams A LOT less protruding than mine have been so far. It also makes it easier to start the roll (which otherwise is quite difficult, using 0.25 mm thick 225 g paper).

    2. The roll is made over a 2 mm pianowire, to enable the plastic tubing & wire leg to go inside without sticking. Glue is not applied until after a few layers of rolling.

    3. Rolled front leg, plus inside plastic tubing & 1 mm wire. First distance piece in place. White glue is used throught, nothing exotic required (although anyone fond of cyano acrylate could use it to an advantage, particularly when glueing in the small part of plastic tubing making up the wheel bearing).

    4. Preassembled fork parts. The one going on over the wire part has to be mounted open, the opposite one can be closed beforehand.


    1. Front leg has gone on; plastic tubing painted with acrylic grey.

    2. Fork over fixed part goes on open. At this point some adjustments had to be made to the bend in the plastic tube/wire fork. It is important that the paper part goes on without force and fits well.

    3. The fork is closed. The distance piece of plastic tubing was shortened in order for the wheel to remain centered.

    4. The distance piece, and the wire, on the opposite side was trimmed several times before mounting the already closed opposite fork part. Don't force anything, and keep sighting the whole gear from all directions in order to keep it aligned and straight. The assembly is still possible to adjust by twisting the wire carefully, as long as the glue has not dried completely.


    The finished front wheel assembly. It spins quite freely, and with almost no wobbling (right).

    I am very happy that this method to make revolving wheels worked out so well, and I'm going to use it on the main gear as well.

    Best, Leif

    PS. For prospective builders of the Halinski P39N Airacobra, I can now say with certainty that part no. 58a should be doubled on to one layer of Bristol board or similar (and the whole lamination folded up on itself) if you build in the original scale 1/33. If you, like me, should build at double that scale you probably need to double it on to two layers of Bristol.

    The part is one of the middle sections of the tyre, and from the 3D instructional sketches it is clear that it should be thicker than just doubled up on itself, as indicated on the parts sheet. However, I wished to finish mounting the wheel before remarking on it, in order to be absolutely sure.

    (I doubled the folded part on to 1 mm cardstock, since I didn't discover this until about to assemble the wheel. Two layers of Bristol or just 0.25 mm paper, and then folding the whole composite on itself should yield the same outcome.)

    This is the ONLY major mistake I've found in the whole kit so far. The fit is really marvellous throughout. - L.

    PPS. I've just found out, when replenishing my stock of piano wire and plastic tubing, that the correct gauge of the piano wire used is 0.75 mm, and not 1 mm as the text above says. Anyway, if you employ the method, you will be sure to measure the fit when you're in the shop getting the stuff. But it needs pointing out - whenever it says 1 mm pianowire in this or some subsequent post in this thread, you should read 0.75 mm piano wire.
  18. dimas Karabas

    dimas Karabas Member

    Awesome build. One question, why plastic tubing around wire? Could you not just use the wire iteslf?
  19. rkelterer

    rkelterer Member

    hi leif,

    where is your third(holding the camera) and fourth hand (pressing the button) :eek: ? for the pictures - excellent - there is nothing else to say.

    cheers from austria
  20. bfam4t6

    bfam4t6 Member

    Amazing job Leif. I am also curious about the plastic tubing. I understand the section that you are using as a bearing on the axle. It's a great idea. Is the rest of the gear put into tubing just for extra support?

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