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duncan_rtfm

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  1. duncan_rtfm
    Some years ago my wife and I visited Muriwai (on the coast near Auckland) and watched fascinated as hundreds of Gannets did great big circles out to sea and then back towards the rocks, skimming the cliffs by mere inches. And then off they'd go again for another circuit. I followed a single bird on his circuit, and he flew with amazing precision, time and time again. Truly amazing. Just having fun it looked like.
  2. duncan_rtfm

    Hi,

    Anyone know where I can get decals/stencils/wrap to apply to my white-painted fuselage and wings?  (I'm in Brisbane).

     

    Paint scheme.png

  3. duncan_rtfm
    Hi, I assume that the further aft the CG is from the main gear, the more difficult it will be to keep a tail dragger tracking straight down the runway, and vice-versa. Are there guidelines for this? Raymer suggests an angle of from 16 deg to 25 deg from the main gear to the CG. My undercarriage can be swapped left/right to convert the Fleabike from a tricycle to a tail dragger, so I'm looking for some real-world experience from guys who have flown well-behaved tail draggers. Any advice? Duncan
  4. duncan_rtfm
    Hi, So very sorry to hear of your health issues. It's a sad day - and one which is down the road for all of us eventually. Good luck with the sale.
  5. duncan_rtfm

    During SEQ's lockdown I've been champing at the bit, because I have been waiting for a wood delivery to carry on work on the Fleabike.  So, with nothing else to do, I have designed a new plane - this time a fully enclosed single seater.

     

    I've decided to build it with the cedar strip canoe method.  I have watched a huge number of Youtube videos of people building strip canoes, and it all looks reasonably straightforward.  However, all the online builders are working from plans, and don't have to make any design decisions. 

    My first design decision is how far to extend the front "keel".  It has to accommodate a 225mm diameter ring (to allow air into the engine compartment, and to provide for the prop shaft).  I don't actually know how to build this.

     

    This is what I've come up with so far...

     

    I'll build the fuselage in three sections.  The green section is a fairly straightforward "canoe".  The yellow section is a single piece cowl/engine covering.  And the orange section (as you can see) comprises the roof and the turtledeck

     

    Do I run a keel along the entire length of the green section?  And the yellow?  Or do I do this for all three sections?

     

    Are there any canoe builders on this forum who might be able to help with this?

    image.thumb.png.d3302e402814d8d149826724865d1663.png

    Regards,

    Duncan

  6. duncan_rtfm

    OK - the Fleabike fuselage is complete, windshield added and all sanded down.  Any suggestion regarding how to paint the Bike?

     

    I have some 117 fairing additive for West system, and I thought I might roll that on, sand it back and paint with West + pigment (white).  I'm leaving the control panels, seat, seatback (i.e. the upper central spine) natural wood, but painting the rest.

     

    Is there a better way?

     

    image.thumb.png.810e537c88f48de330472b300a7d77df.png

  7. duncan_rtfm
    Hi, Plenty of maths involved in the optimal placement of CG, wing articulation (front and optionally also the rear) and so on (in fact I wrote a whole 30-page paper on this), but as kasper says, a lot of the rest draws heavily from existing designs (for example, the HM293 on which the Fleabike is firmly based) and others. As far as the undercarriage is concerned, after some initial thought experiments (quickly shot down by experienced and knowledgeable forum members, both here and elsewhere), it is now essentially the undercarriage of the HM293 prettied up a bit. Same for the wing masts and braces. Regards, Duncan
  8. duncan_rtfm
    Interesting. Well, certainly cheaper than 4130... Me? Whack the ground? 😄
  9. duncan_rtfm
    I've just checked my HM293 plans, and it seems that they specify 25mm OD, 22mm ID. Am I reading this correctly?
  10. duncan_rtfm
    I concur. 25mm it is. I'll keep my box of 20mm foam riblets for another project perhaps. Ha ha - I have so many let overs from this project "perhaps for a future project" that I need a separate shed to house them all!
  11. duncan_rtfm
    Hi again, I am equipping the Fleabike with 18-inch tundra tyres, and no spring damping at all. I am relying on the big soft tyres to do all the damping for me. But yes, a study of the HM293 is certainly on the cards today. Duncan
  12. duncan_rtfm
    Hi, See post above/below. Various lengths. My only concern is whether I need to go with 25mm tube vs 20mm OD Duncan
  13. duncan_rtfm
    Hi, Good to hear that our methods are identical, if not the means of getting the riblets cut. I also intend to cut end plates out of ply, and a straight sanding block to tidy up any bits and pieces. Mine are now cut and in a box. The only trouble is I made the steel strut hole 20mm OD - I'm thinking I should have made it 25mm? Thoughts? The carbon rods are just for alignment - they get removed when the foam has been bonded. a one metre length of 4mm CF rod is about $8 from hobby shops. Similar aluminium/brass etc is a bit cheaper, but this is a tool, not part of the strut. Buy once, use many times. It just depends on the most convenient purchase. I also checked on the price of streamlined 4130 steel tube - but at over $80/metre, that's not going to happen. I need this for two front wing masts (650mm each) Four rear wing struts (460mm and 520mm) Six main gear legs (1000mm each) Regards, Duncan
  14. duncan_rtfm
    Hi there, All options are on the table at the moment. I'll probably end up giving a few of them a go, and seeing which one works best. But the folded AL sheet idea is a good contender. Might be the subject of a nice photo-post for all to see. Duncan
  15. duncan_rtfm
    Hi guys, Thanks for your suggestions, but I've given this some more thought, and because I don't have any of the kit needed to hotwire foam, this is what I've decided to do. Materials required: 2x 25mm steel (or aluminium) tubes 1x sheet XPS foam (local hardware store, $12.50) 2x steel/aluminium/brass/carbon fibre rods (4mm diameter) Method: Chop the foam sheet (1200mm x 600mm x 30mm) into a zillion 100mm chord "riblets" Grease up the tube and the big hole in the riblets with West epoxy Thread required number of the riblets onto the steel pole, bonding each new one to the preceding with some West Thread the two brass/aluminium/ carbon fibre rods through the 4mm diam alignment holes Wait for it all to set Rinse and repeat All that's left to do is to affix the attachment hardware to the ends of the steel/aluminium tubes, and to coat the foam with a layer or two of epoxy and possibly a layer of glass fibre. There are enough little riblets in a single sheet of XPS from from Bunnings to make several struts for several planes. Just sit back and watch the router do its magic. Of course, hotwiring things would be easier, but as I say, I don't have the kit.
  16. duncan_rtfm
    Thanks for your help gents.
  17. duncan_rtfm
    Hi, Yes, I came across that one, but no tensile strength listed. I'm wanting to carve wing struts out of hoop pine, and need to know if the wings will fly off on their own at 1000 feet...
  18. duncan_rtfm
    Hi folks, Does anyone know the tensile strength of Hoop Pine? I've looked everywhere, and can't find it. Thanks, Duncan
  19. duncan_rtfm

    Question:
    After wasting about an hour (and two cups of coffee) on the laptop searching for suitable fuel drain plugs, not a single manufacturer/distributor cares to specify the diameter of the thread going into the fuel tank. It seems I am looking for a 1/8" NPT, but I need to know what size hole I need to cut into my tank to accommodate this. Any ideas?

    Duncan

  20. duncan_rtfm

    Hi,

    Is this the sort of fuel pump I should be looking at fitting (Aircraft Spruce)?  If not, what do other people use?

     

    Regards,

    Duncan

    image.thumb.png.279e88f47d185111ee2a74256623ac73.png

  21. duncan_rtfm

    My fuel tank is a weird shape

    image.png.fc2e47ab5fd3108c98a63e318bc5c42e.png


    Constructing this was proving to be a nightmare, so I created a flat-pack, which looks like this.

    image.png.4e1dd4c8d67af6882abe760b7711dae2.png

    Sketchup can't do this, so I had to do it by hand. I'll cut it tomorrow. Basically, I'll epoxy tape along all folding seams on the inside (red lines), seal the reast of the MDF with epoxy and bend everything together when the epoxy is still in the green stage. The top is a separate piece, which will allow me to reach inside and apply the fillets. Then I'll bond the top on. If this works, I'll commit to 9mm ply.

     

    This will also allow me to accurately measure the tank's capacity.


    I have yet to find anything definitive regarding West Systems epoxy and fuel tanks (I don't plan to use ethanol-fuel). Vinyl ester worries me, because it looks like I'll have to do the complete layup on the inside in one go (including the fillets) because VE doesn't stick to VE very well.

    However, I've discovered that 747 Polyester is about as gas, ethanol, diesel etc proof as one can get, and it isn't expensive. If I can find some locally, I'll go with that.

    Duncan
  22. duncan_rtfm

    Question:  Does anyone know where I can get Polyester 747 resin?  Apparently it is completely gasoline proof.

     

    Alternatively, does anyone have any experience using Vinyl ester resin for fuel tanks?

     

    And lastly, how does West System stand up to fuel?

     

    Regards,

    Duncan

  23. duncan_rtfm

    Questions:

    I have built the first rough prototype of the gas tank out of 3mm MDF held together with masking tape, and it fits!  Ta-Daaa!  Well, it's a bit snug, to be honest, so today I'm going to cut prototype #2 out of 9mm MDF, and screw it together.  If that is OK, I'll commit to 9mm ply.

     

    Question #1:  What hardware do I need to include?  I've been to the marine supply stores (online) and there are so many filler caps, it's hard to choose.  I will have a transparent tube on the outside of the fuselage to show fuel depth, but what about fuel pumps?  Is it as simple as fitting a pipe and running it to an external pump (there's plenty of space behind the engine)

     

    Question #2: What do I seal the tank with?  I've seen videos online of a guy building a fuel tank for his boat, and he seals the inside with epoxy (West).  However, I've also read that I need to use vinyl ester resin.  The problem with vinyl ester is that (apparently) it doesn't bind well to vinyl ester.  My plan is to cut the individual sheets, glass the inside surfaces, wait for them to cure, clean up the edges, and then bond/screw all sides together, and apply a fillet.  Thoughts?

     

    Regards,

    Duncan

  24. duncan_rtfm

    I was going to have rigid main gear struts (triangulated with two struts attached to the base of the fuselage, and one up just under the seat), and rely on the 18 inch tundra tyres for damping, but I'm thinking I may find it more comfortable to include some form of damping.

     

    I was looking at rear shocks for bikes, and they offer 60-70mm travel, with a max loading of about 250kg each.  Larger are available, of course.  They are also quite reasonably priced.

     

    Would this work?

    image.thumb.png.9f0328a2a4038f3af51624e26d690af3.png

    1. facthunter

      facthunter

      You don't want it too rubbery (Travel) It will only get more x wind sensitive on the ground and I think it will be pretty limited already. Nev

  25. duncan_rtfm
    Hi,
    Things have gone silent on my end for a while - some minor medical issues, but mostly a lot of head-scratching over the design of the wings.  I had NO IDEA how difficult designing a wing would be.  And a Flea wing especially, because it is made up of separate panels, with hinges and pivot points.  Sourcing the correct hinges has been a nightmare - found some some this morning which I think will do nicely.  (Naturally) I opted for a swept wing rather than a rectangular one, so first I had to calculate the centre of pressure before I could position the spar to which the pivot is attached, and then I had to update the spreadsheet to check on the optimum CG.
     
    image.png?u=af344176&access_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiI0OTM4YThhMmFmNGQ1ODM1Y2JhODNmZmQ0MjU4YmQ4NyIsInN1YiI6ImhyWE1jWGp5Zkw4R0ZsdlRYYzFfT2paMVB4VmJScl9rTzVFQzFYLVNZWGciLCJpYXQiOjE2MjYxNjY4MDB9.eApiCI1iKGKTpCZR2zkaPEbOYiMik1HmjKBI9SzIg30&accept=image%2Fpng
    That done, I had to calculate the size of each rib, and the position of the cut-outs for the two spars.  Cutting the ribs was easy, of course.  Next up was cutting the cradles for each of the wing sections, so that the ribs would be perfectly spaced, and vertical, with the required 4 deg dihedral.
    image.png?u=af344176&access_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiI0OTM4YThhMmFmNGQ1ODM1Y2JhODNmZmQ0MjU4YmQ4NyIsInN1YiI6IllGbU5JZ3RwLXZXWll4MllfSEZ5b3NhN0dPcUpXWks1dExsM1pEVlBPRjgiLCJpYXQiOjE2MjYxNjY4MDB9.cb_9nT7wrqpnhQEM-BWd-NvD4JnCo9oHfLLDhyfNpms&accept=image%2Fpng
    I trial fitted everything, and when satisfied that it all fitted together nicely, bonded the spar caps (blue in the screenshot above).  I checked that the trailing edge (4mm glass fibre rod) was straight (it was).  I then threaded the 16mm Tassie Oak dowel for the leading edge.  Also straight, and a nice fit.  I then bonded the LE in.
     
    Next job is to bond in the shear webs.  They are already cut, so it will be just a matter of slapping on the West System epoxy, and clamping.  There are also two 19mm x 19mm drag/anti-drag spars which, although the router cut the holes in the ribs in the correct places, it can only cut at 90 deg, so I have to "angle" the holes so that the spars will fit.  And then bond them in place. By this time, the wing should be pretty rigid.
     
    I also had to design the wing attachment hardware.  The rear wing consists of two halves, separated by the width of the aft fuselage (about 135mm).  The inner rib is reinforced, and bolted to a metal attachment on the fuselage.  The outer attach point is at the first hinge point.  This hardware has been drawn, but not cut yet.
     
    Next came the drawing of the wing sheeting.  Not as easy as it might sound because of the swept wing.  But I've completed that now also.  The rear wing will require three full sheets of 1.5mm ply.
     
    As you can see - a lot of time at the computer.
     
    So much for the wing.
     
    I have decided (based on the astute comments here on the forum) that placing the gas tank in front of the firewall - while convenient, because I could use a regular 20 litre gas tank from Bunnings and some fittings from boat shops, this was a terrible position not only because of the proximity to the hot engine, but also in terms of the change in CG as the gas gets used.  So I've moved it to inside the fuselage directly on the CG.
     
    image.png?u=af344176&access_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiI0OTM4YThhMmFmNGQ1ODM1Y2JhODNmZmQ0MjU4YmQ4NyIsInN1YiI6InJJd0tuMVZUanVHMHE3SkV2bW1kcndDSmpWNmVxUUJvYVVYaDJoV3FKRjgiLCJpYXQiOjE2MjYxNjY4MDB9.xW2zxffCn5yK36chvd4qMGKL2zpO6wDoryROH1QGobs&accept=image%2Fpng
    The grey area inside the fuselage in the screenshot above is the new position for the gas tank, with a filler cap jutting through the side just under the pilot's knees, out of the way.  About 18 litres (about three hours flight time).  I'll have to fabricate it.  I thought of plywood sealed with vinylester, but it strikes me that I have a whole box of 3D Core foam, which looks like this:
    image.png?u=af344176&access_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiI0OTM4YThhMmFmNGQ1ODM1Y2JhODNmZmQ0MjU4YmQ4NyIsInN1YiI6IklxOHNTZ3FIM3RsdUNWZjczRU9Sb0o4TVVnYzgwbVd5TnV5MWVweDdOTlkiLCJpYXQiOjE2MjYxNjY4MDB9.gRgERKcSFoWKtxhC898zn3fefW7w050XTG3SxH5reoo&accept=image%2Fpng
     
    Extremely light, very easy to cut on the router, and simple to laminate with a layer or two of vinylester and glassfibre.  I'll prototype the tank out of cardboard, and then Bunnings plywood before I commit to the actual tank.
     
    So that's what I've been up to since last time I wrote.  As usual, comments welcome.
     
    Regards,
    Duncan
    1. duncan_rtfm

      duncan_rtfm

      For some reason, none of the pictures in the above post are showing.  Here they are in sequential order.

       

      Wing plan:

      1781854664_WingwithCP.thumb.png.66f6eae4a8b163a5b71ab863e2064d97.png

      Wing with internals and cradles:

      41877074_Wingwithinternalsandcradle.thumb.png.d7306d81b2cc411037d8b1168ad3e5e7.png

      Side view showing new gas tank position:

      1678110000_Sideviewwithnewgastank.thumb.png.4b306d5ccfff08c3190cc37cc3802474.png

      3D core foam:

      2036985391_3Dcore.png.c2d3b6258762b45ac13972eba9f02e53.png

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