Possible to construct a Driggs Dart monoplane out of aluminum tubing?

Discussion in 'The light stuff area' started by AlistairL, Sep 17, 2017.

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  1. Dec 20, 2017 #41

    proppastie

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    Bruhn C4 there are column charts for steel tube and aluminum tube so that you can make an "as strong" assembly. Good Luck
     
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  2. Dec 20, 2017 #42

    Tiger Tim

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    [​IMG]

    It's certainly a competent looking little thing, isn't it? I foresee getting in and out to be a struggle so consider making a cockpit section from scrap wood first to see of some re-engineering of the door area is going to be needed in order to provide a bigger hole to climb through. As for the plywood covered wing, being cantilever it probably has to be skinned with something at least as far back as the spar. A set of Sky Pup plans might go a long way towards answering how to do it on a modern UL.
     
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  3. Dec 21, 2017 #43

    Bill-Higdon

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    As I remember there's a NACA report on a Aluminum wing for the Driggs Dart
     
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  4. Dec 21, 2017 #44

    AlistairL

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    Thanks again for the suggestions and feedback. Plywood paneling it is for the the design on the wing. As for the size of cockpit I've expected its size to be smaller than usual. For me I'm not too big in stature and believe it will be a close fit for me. I will run measurements and make a sort of test-rig to be sure. Overall the Driggs appears to offer a good potential for a modern variant.
     
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  5. Feb 5, 2018 #45

    AlistairL

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    After some thought I feel at the time being it would be a good start to build a modified J3 Kitten tail feather as suggested by Dew777. The design of it is similar to a Driggs and would be suitable for the task. For sake of storage and cost the wings will be 3-piece while constructed in original form. The Kitten tail feather will hopefully keep things busy until original issue of EAA Flying and Glider Manual 1931 can be procured. Hopefully in the reprint issue I have there will be enough information on the wing construction. A building log will be made to keep track of things. Overall around March should I be able to make a start.
     
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  6. Mar 3, 2018 #46

    dew777

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    AlistairL,
    Any new developments in your planned Dart build?

    Just curious . . .
     
  7. Mar 8, 2018 #47

    AlistairL

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    Should be ready to get things going in two or three weeks. At the moment doing a final run-down on the process of it all before beginning. Will provide an update shortly on here.
     
  8. Jun 20, 2018 #48

    dew777

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    AlistairL,

    Any time to make progress with your Dart project?
     
  9. Sep 25, 2018 #49

    AlistairL

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    Sorry for the late reply. After working on the job and such things have been more or less consuming, so I regret not gaining anything started. In the meantime I have put thought in how to start. I plan on the fuselage to be started initially with the jig described earlier in thread. I can probably to small bits to keep me occupied and brush up on techniques. Overall I have not discarded the project.
     
  10. Sep 26, 2018 #50

    lr27

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    If you're really going to make it part 103, I think you'll need to make it a bit larger, while still keeping it light. Let's say you're a real wizard and the whole thing comes out at 400 lbs gross. With 70 square feet of wing, that's 5.71 lbs per square foot. A 28 mph stall would require a Cl of around 2.9! The Air Corps added high lift devices that was supposed to have greatly improved the takeoff and landing distances, but it added 50 lbs. Info from Vintage Aircraft, September 2009, which can be found on line. Apparently the wood wing was tested and broke at around 6g, but a metal wing that was worked out made it to over 9g. The original wood wing weighed 94.5 lbs without the high lift devices, and the metal one weighed 104 lbs. Details in Air Corps Technical
    Report No. 3415, which I couldn't find in a quick web search. But maybe it can still be found someplace?

    You should also take a careful look at the size of the tail surfaces and so on, to be sure that the handling is reasonable. I think, on a lot of old planes, that it wasn't. A little bit of washout might be required, too, because of the taper of the wing. Apparently the original, without the high lift devices, landed at 55 mph, so some changes might be in order. With them, it was supposed to be 42 mph. It would be great to see one of these flying, but you'll have some engineering to do if you want it to be 103 legal.

    BTW, I noticed on the plans a splice in the longerons. So maybe you don't need very long steel tubing after all.
     
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  11. Sep 26, 2018 #51

    AlistairL

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    Thanks for the suggestions. Not much of an engineer but some alterations can be made to make it lighter would be a welcoming idea. As a novice it will take some little help in providing what needs to be done. I plan on having the wings be wood plus altered as a three-piece for sake of space if possible. With it being a relatively early design, some alterations would hopefully help.
     
  12. Sep 27, 2018 #52

    lr27

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    I'm a mechnical engineer, more or less, but not an aeronautical one, so keep that in mind. I have had a fair amount of engineering education.

    I wonder if weighing and sorting the wood does anywhere near as much good for full scale projects as it does with models. Probably not quite as much, since balsa is more variable. I suspect whatever engine you pick will be lighter than the original used. So you might pay special attention to the tail surfaces. I'll bet you could make very light but usable tail surfaces with foam ribs, spar web, etc. capped with thin wood or carbon fiber. But you'd have to do some engineering. If you're aiming for part 103, you could extrapolate from the Skypup, at least for the wing and tail surfaces. If you enlarge the design enough to be good for part 103, your wing will be longer than a Skypup's, but the Skypup's wing has much less taper. It's in 3 pieces, made of wood and foam. Anyway, one problem with extrapolation is that you'll end up extrapolating from some parts that are overbuilt, perhaps to use a standard size of material. The nominal weight for the whole aircraft is 190 lbs. Apparently they tend to come out heavier, but legal. You might consider a somewhat thicker airfoil if you don't think it will ruin the appearance. The fuselage structure would probably be a lot harder to extrapolate, I imagine. Come to think of it, another problem is that the Skypup has no ailerons. So maybe you need to extrapolate from a MiniMax or something. Any extrapolation must be done with engineering principles in mind. Your intuition may or may not be valid, and it not something to trust your life to.

    One general principle is to weigh EVERYTHING that goes into the aircraft and think about whether that's the lightest option, or whether you need it at all.
     
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  13. Sep 27, 2018 #53

    lr27

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    oops, duplicate post somehow
     
  14. Sep 27, 2018 #54

    lr27

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    Had the thought the other day that perhaps a semi-monocoque fuselage out of okuome might work, though perhaps it wouldn't be as crashworthy. Or maybe just the rear fuselage. Seems like it would be less complicated, but that may just be because I'm looking at it from far away.
     
  15. Sep 27, 2018 #55

    AlistairL

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    Very valid observations and input, very much appreciate it. Aero materials have come quite away since the time on the Driggs conception. Foam would offer more opportunities and freedom to make the craft light with ease of construction. I've looked into the Sky Pup in the past and there are a few key parts from it that will come of some inspiration for a 103-type Driggs. Foam rib wings, if possible, in cantilever form will be of welcome. It would make working from the EAA 'Flying and Glider Manual' rib plans more straightforward with my abilities. Same in regards to tail feathers. Of course such drastic deviation from from original design will need some input from more experienced builders in what and how to do it.
     
  16. Sep 27, 2018 #56

    addicted2climbing

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    Hello AlistarL,

    I sell plans for the Raceair Skylite and it would not be too tough to modify the deign to give a stand off scale looking Driggs dart. Or consider using the Texas Parasol fuselage layout as the basis as well. The hard part will be the cantilever wing that still meets part 103. For this possibly look at the Hummel designs... If you did not have an aversion to struts than the skylite plans could get you 75% of the way there I think.

    Another similar fuselage option would be the Legal eagle.

    I am in the midst of launching a new website for the Skylite but for now you can find more info on the old site. http://www.raceairdesigns.com/skylite.html

    Here is the fuselage in Solidworks.

    Skylite Fuselage - Tube Frame, Single Tail Tube crop.jpg

    I may one day try and design a version of the skylite using the Texas Parasol aluminum angle or the tube and gusset style as used on the Graham Lee / Airdrome aircraft.

    Marc
     
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  17. Sep 28, 2018 #57

    AlistairL

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    That's another few routes to consider overall. Those designs feature some similar attributes to the Dart. Main goal at this point is to maintain much of its original form with implementing some modern materials. If it comes at least close being 103 than that is fine. Would any major redesigning be required if wing ribs were replaced with foam or will it not be of too much effect in its design?
     
  18. Sep 28, 2018 #58

    addicted2climbing

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    If you want to keep the cantilevered wing than metal ribs may be your only option as I dont think you can get there in Part 103 with a wood built wing. But I could be wrong.

    Marc
     
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  19. Sep 28, 2018 #59

    AlistairL

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    Metal would be very new territory for me but there was a metal rib variant. Through my lack of metal working, I reckon aluminum sheeting is the natural option for that. Its different but I would consider it.
     
  20. Sep 28, 2018 #60

    proppastie

    proppastie

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    probably best to work with materials you know, because to design even a copy is a somewhat big elephant to swallow.
     
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