Joseph's BV P.170

Discussion in 'Aircraft & Aviation' started by Darwin, Oct 10, 2005.

  1. Darwin

    Darwin Member

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    Here's hopes that Barry and Tim don't drum me out of the ship builder's forum, but I am now building an airplane. More specifically, Joseph entrusted me to a test build of his BV 170.P. To start with the start, the parts were provided in an 8 page pdf file. The pages are designed to be printed out on A4 paper, but Joseph listened well and kept the actual image section small enough to print out on letter size paper without either reducing the scale or cutting off the bottom of the parts....however, it was a close thing on my Epson. My recommendation here would be for Joseph to reduce his pages upper margin by about 5 mm. I think that would be all that is needed to guarantee no problems with printing here in North America.

    I chose not to use my top quality cardstock for the test build (the paper used resembles the cardstock used by Maly Modelarz in their mid- to late-90s kits. Well bleached, but not up to the finish of a good Bristol board. To appease the RPM, I started by using the cardboard from a Pizza Hut carton for the backing, but corregated cardboard has about zero bending strength across the corregations, so instead I used some of my rapidly dwindling primo stock from Lighthouse Model Art. My philosophy on a test build is if it can be built using just average materials, it can be built by just about anyone.

    The model is designed for butt-joined fuselage segments. Joseph suggested I might want to try using joining strips instead, but I prefer doing a test build using as closely as possible the designer's construction techniques (and just watch how quickly I violate that preference during the build). The model, as you will know from looking at Joseph's announcement, is three-engined, and has a central fuselage section with oversized nacelles at the wingtips. In nautical terms, would be classed a trimiran (and I can't spell work )&*$%& and am too pooped to figure out where the house hid the dictionary). The logical place for me to start was the forward section of the main fuselage. This is a pretty busy area....not only is the wheel-well box in this area, but it is where the wing spar penetrates the fuselage as well. The first subassy I built is the wheel well box. Photos follow (if I can make this new method of photo imbedding work). As an aside....I am doing the Burma Shave thing with this posting tonight....multiple postings. Please defer responses until I say I'm done for the night to keep the pieces together.

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  2. Darwin

    Darwin Member

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    Hmmm.....apparently, if my image size is too small, it doesn't create a thumbnail image. The first image above is the top view of the completed wheel well box. The second image is the bottom view of the assembly. A few deviations from Joseph's design. I chose to back the sides and top of the box with cardboard. Also, as designed, the inner side of the wheel doors is integral with the wheel well box. I chose to separate them from the box so they could be glued separately to the wheel doors. I'm glad I did, for the wheel well box is a few pixels too narrow, and a few pixels too short, to fit with the wheel well cutouts in the skin piece without a raw edge being visible. Joseph, please make to top of the wheel well boxes a few pixels wider and longer....I'm only talking about 0.5 mm here in either dimension....this probably could be left as is, and only a perfectionist will gripe. (How's that for self-incrimination?) I glued the ends of the box directly to the formers. With the adjustment I recommend, the box should fit perfectly into the space provided for it. Now the first real criticism of the design.....if you look at the three view in Joseph's string, you will notice that the wheel well box should extend back to nearly the trailing edge of the wing in order to accomodate both the strut and the wheel. The present design would shear off the wheels the first time the landing gear was retracted.

    Now the big deviation....Joseph designed the center part of the wing spar to be fitted through the central fuselage, then add the spar extensions to the resulting stubs. This requires the wings to be built integral to the main fuselage....a technique I find overly prone to severe wing warps, since it is near impossible to then build the wing on a flat surface. I decided to make a major modification to the design by adding a couple of extra formers that will snugly "box in" the wing spar. When I get to the wings, I will cut the center spar into two halves, allowing the wings to be build seperatefrom the body, and allowing me to build them against a flat surface to prevent warps. When completed, the stub ends of the spars into the boxed-in slot in the fuselage. Once again, my stick-and-tissue origins shine through. This series of pics show the wheel well box as modified by me.

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    Before completing this substep, I drilled a hole in the top of the wheel well box for the landing gear strut. From the 3-view, the LG strut attaches at the front of the wheel well and somewhat off-center. All three main gear (yes, three!) are offset to the same side of the centerline.
  3. Darwin

    Darwin Member

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    After removing the wing spar section, it is now time to add the skin and finish up the first fuselage segment. My approach was to form the skin into a cylinder, then cut the ends of the landing gear doors free, score the seam between the fuselage proper and the landing gear doors, and fold the doors outward. As a note to Joseph, this may have built a bit easier had you designed it as three segments. However, with a longer wheel well box, this comment may go away. The easiest way I could see to assemble the section was to use a joiner strip to join the longinitudinal skin seam forward of the wheel well, then slide the wheel well box assembly into place (with glue applied to the joining surfaces only after extensive dryfitting...I had to build up one of my formers by gluing a thin strip of paper onto the former edge before I got a good fit. My problem, since I got a little overentheusiastic while sanding down the former edges. Note that the raw edges of the fuselage box need to be beveled down to fit the contour of the formers. after the wheel well box is in place, use a joiner strip to finish gluing the longitudinal seam. When dry, I then added the front and back formers, Note I cut the center of those formers out in order to have a means of positioning the former to exactly fit against the end edges of the fuselage skin. Joesph, please take note....beginners may be unaware of this little trick for easing the building process. Well, that's the end of tonight's entry. You can start throwing rocks now. (Non-casual observers will note that the wheel well box is installed backwards in the image showing the dry fit....the hole goes toward the nose, not the tail. It is installed properly in the final assy....trust me.)

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  4. Joseph

    Joseph Member

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    Thank you Darwin, I'm carefully noting all your comments in order to make it better next time.
    I was hoping you wouldn't notice the too short wheel wells...
    I made all the formers with a 0.2 mm offset from the skin, is the fit OK?
    Best regards,
  5. Darwin

    Darwin Member

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    Joseph, so far the former fit has been quite good. However, I'm not sure if you intended part MA to fit the front or the rear of cowling part 2. If at the front (where cowling parts 1 and 2 join), then former MA is sized correctly, but that leaves a gap between former MA and MB, and the butt joint is then a bit tricky. I recommend making former MA a bit larger in diameter and locating it toward the back of the cowl ring, with a joiner strip between cowl parts 1 and 2. That way, the two formers will make a snug butt joint. This will make sense to the rest of you when I manage to get a few pictures taken and posted.
  6. Joseph

    Joseph Member

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    Darwin, yes MA is intended to be slightly smaller than MB, and goes between parts 1 and 2. Maybe you can make a second MB former to make the butt joint between parts 2 and 3 (and chanfer it towards the front)
  7. Darwin

    Darwin Member

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    [​IMG]

    Hopefully, this image helps clarify the exchange between me and Joseph. The sequence I used was to join the ends of part 2, then glued piece MA in place at the front end of part 2. I then glued together the ends of piece 1. It was tricky, but I was able to glue part 1 to the cowl assembly without a joining strip and still have it look halfway decent, which speaks a lot for the fit accuracy of Joseph's design. This leaves a gap of about 1.5 mm or so between formers MA and MB when the cowl is joined to the fuselage. I trusted to Joseph's accuracy and butt-glued the back edge of part 2 directly to former MB without adding any filler. It worked, but if I had it to do over, I would have built up former MA by creating an additional former MB, then gluing MA to it (both on thick cardboard, of course) adn beveling the edge of the resulting assy. I would then join parts 1 and 2 using a joining strip, and finally gluing part 2 to the composite former. The remainder of the main fuselage was fairly straightforward until I got to the tail cone. Joseph designed this using two skin pieces that fit together like a clamshell.

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    This got a bit tricky. First, using a short piece of joining strip, I joined the upper edge of the two skin pieces from the former to about the end of the stabilizer/elevator locator, giving me a butterfly-shaped piece. When the join was dry, I formed the skin into a cylinder, and joined about the same distance of the bottom seam as I had the top. This left a piece that somewhat resembled a Bishop's Mitre. I then joined the very back tip of the tail cone. when that was dry, I used an embossing tool to finish shaping the tail cone, then carefully applied glue to the inside of the cone to complete the seam joins (without using joining strips). When this was dry, the former and triangular crutch piece assembly slipped into the tail cone skin just about perfectly. I think this would go a bit easier if the skin was redesigned as one piece, joined along the upper seam from the former to as far back as the two edges will fit together snugly (giving a butterfly shape rather than two clamshells). Just a thought, Joseph....it is buildable as it is.

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  8. Darwin

    Darwin Member

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    [​IMG]

    One last point here. Joseph designed the cockpit section so that there is a straight-line profile between the two formers, rather than designing in a cockpit opening. The resulting cross-section in the center of the section was essentially an oval. When I looked at the top of the section, it became obvious that the canopy sides would bulge outward unless I did a bit of paper sculpting. I used my thumbnail to work in a crease along the line between the patterned part of the skin and the unpatterned canopy locator. I kept working in the crease until the join line went straight between the formers when viewed from the top. Hopefully, the picture of the top view will clarify this. This design technique works, but I recommend on Joseph's next design, you put a "step" in the fuselage at the end of the canopy, as if you were intending to use a cockpit tub and detailed interior. He is eventually going to want to go that detailed with his designs, and should develop the design techniques now, even if he is going to use an opaque canopy on the model.

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  9. Darwin

    Darwin Member

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    Finally got some pictures taken of the nacelle. The this section is very similar in construction to the main fuselage, so I won't go into too much detail, other than to detail a few problems I encountered. I tried building this cowl ring by joining parts 1 & 2 with a joiner, then doubling up the former and beveling the edge of the formers to fit the ring. the attempt using a joiner strip did not come out quite as well as simply butt-joining part 1 to part 2. The doubled-up formers worked quite well.

    I did get a bit of a surprise with the wheel-well assy. In the main fuselage, the skin piece extends beyond the wheel well in both in front and in back of the whell well. In the nacelles, the skin ends precisely at the end of the wheel well cutout. I didn't notice that at first, and just butted both of the formers up against the end of the well. That meant the skin was too short to go over the rear former. In order to get a fit, the rear former of this section (Former GD) has to fit over the back of the wheel well box.

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    The wheel well location portion of former GD need to be identified as needing to be cut out if the wheels down build option is taken. To help stabilize the assembly during the build, backing the sides and top of the wheel well box with thick cardboard is a real must, so I recommend enlarging the locators on the formers to account for 1 mm cardboard backings. After assembling the box, I added a couple extra formers to box in the wing spar stub, as with the main fuselage. One bonus this gives is an option to build the model so that it can be dissassembled for storage or transporting once built. This would really facilitate mailing the model for proxy display at model competitions (HINT HINT HINT).

    The second problem encountered was that former GE is undersize. It may "fit" at the very end of the second nacelle segment....however, because of the severely decreasing nacelle diameter in this area, the former needs to be made somewhat oversized so the edge can be chamfered and allow a good, snug "wedge" fit into the segment. Former GE' was a tiny bit undersize, but that may have been an artifact of imprecise joining of the skin piece bottom seam. To fit, that former also needed to have the edge chamfered. The rest of the nacelle build was pretty uneventful, and pieces fit nicely.

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    One last item needing a bit of correction. The unpatterned location indication for the lower half of the rudder extends too far up the nacelle end, and leaves a white gap after joining the rudder. The red line shows the edge of the rudder part....the blue line shows the boundary between the patterned and unpatterned portion of the skin.

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  10. Darwin

    Darwin Member

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    [​IMG]

    Plenty of practice building propellers with this model. I probably should have taken the time to build the blades around the tip of a round toothpick, but it works well enough even not taking that step. The spinner uses the conical sections approach. I prefer petals myself....once you learn the trick of gluing the petals to an appropriately sized and shaped wad of tissue paper rather than to each other, they become dead easy, and in my opinion give a more pleasing hemispherical shape than do the cone segments. Man, this beast must have been a handful to fly. Not only is there zero forward visibility for ground handling, but the gyroscopic forces must have been truly intense....however, I bet it whould have done one hell of a snap roll. Looking at the relative size of the spinner and the cowl opening, I have to wonder if it wouldn't have had cooling problems as well. One minor point, Joseph....as large as the spinners are, they fit completely over the crankcase end. Looking at the construction diagram, that was intentional, maybe?
  11. wunwinglow

    wunwinglow Active Member

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    No worries Darwin! Heck, I've got as many unstarted aircraft kits and projects as I have ships! I'm not proud, I'll not build ANYTHING!

    Tim P (remember, the P stands for Procrastinator...)

    Fascinating build by the way, project development in the raw.
  12. barry

    barry Active Member

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    drum head proceedings

    Darwin

    Would we do that to a nice guy like you I have been known to occasionally build an airplane only trouble is they take up so much space and as I prefer 1/33 and that's an issue.

    Great looking model tho and nice design from Joeseph

    barry
  13. Darwin

    Darwin Member

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    Well, Barry, they say confession is good for the soul. I prefer 1/32 myself, and as my arms become way too flippin' short, am starting to really like 1/24. I enlarged a PModlel F-104 to that scale. Storage was no problem....I have a grandson. :) Gone are the days of 1/144 scale plastic and 1-hair brushes, I'm afraid. :-(
  14. charliec

    charliec Active Member

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    The Luft 46 site says that the outer engines were handed (rotated in opposite directions) so it may not have been too bad. The engines the P.170 was designed for were BMW 801's - same as the Fw190. This engine had a cooling fan so overheating may not have been a problem. The view forward would have been truely awful - the Fw190s used one of the ground crew lying on the wing to direct the pilot while taxiing - and had good forward visibility compared to the P.170.

    Regards,

    Charlie
  15. Darwin

    Darwin Member

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    [​IMG]

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    A bit more progress. It hit me what this beast has been reminding me of. Make the wings about half the span, and this thing would fit into the racing sequence of Star Wars I. The fit of wing surfaces to fuselage and nacelles (why do I keep trying to use "pods") is just about perfect.

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    Maybe just a bit too perfect....when I took care to get a good join between wing and main fuselage, the wings got pulled back a bit and introduced a few degrees of sweep that shouldn't be there. Two ways to correct this. First, about one mm additional length could be added to the trailing edge, keeping the contour of the wing root as it is (rotate the tip contour around the tip-leading edge junction until about a 1-mm gap is introduced at the trailing edge). I'm just making an educated guess as the amount of correction needed, based on about five decades experience building stick and tissue models. The second (and most expedient way) is to provide some written instruction to glue the wing skin/main fuselage seam only between the leading edge and wing spar, and leave the trailing edge side "free-floating." The fillet would then be used to bridge the gap between the wing and fuselage and provide stability of the wing trailing edge half with respect to the fuselage location marking and straightness of the wing. The first approach is the hardest on the designer. The second is the hardest on the builder. As flexible as the spar is, the same distortion of the wing would have happened had I assembled the wing as a single piece as designed rather than splitting it into right- and left-hand panels. As precise as the parts fit have overall been with this design and as symmetrical as the distortion to the wing sweep is on the two sides of the fuselage, I don't think it was build imprecision that introduced it.
  16. Darwin

    Darwin Member

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    [​IMG]

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    Done. Joseph, the BV P.170 is ready for prime time. An enjoyable build, and a model that will make a nice addition to the display shelf. Stand by for the hits on your webside when you make it available.
  17. Joseph

    Joseph Member

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    Darwin,
    THANK-YOU! :grin:
    And here is the cover page - I've just realized that the propeller were supposed to be three-bladed. Oh well....
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  18. Joseph

    Joseph Member

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    Thomas Pleiner was kind enough to host the file on his site
    When you have logged in, the download appears in the left column
    Enjoy ! :smile:
  19. modelincard

    modelincard Member

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    You could just call it the P.170A[​IMG]
  20. charliec

    charliec Active Member

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    The Blohm und Voss looks even more bizarre in model form compared to images.
    I'm reminded of the French General who said "c'est magnifique, mais ce n'est pas la guerre" - one can only shake one's head. I wonder what RLM said when they were presented with this design.

    Regards,

    Charlie