Project-Ex

Discussion in 'Hangar Flying' started by DaveD, Jan 10, 2013.

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  1. Jan 10, 2013 #1

    DaveD

    DaveD

    DaveD

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    OK, I’ve finally managed to wean myself off constantly reading this forum, and managed to do some actual design work!!!

    Time to unveil “Project-Ex”, (reflecting the likely effect on my marriage)!!
    ProjEx Back.jpeg ProjEx Top Right.jpg ProjEx Bottom Right.jpg ProjEx Back Top Left.jpg ProjEx Top.jpeg ProjEx Left.jpeg ProjEx Front.jpeg

    It’s still early days so don’t be mislead by the shiny pictures, I’ve only really done some initial sizing. Next job is to do some more thorough weight estimations so I can get a better idea of the C of G.

    I’m looking at foam cored composite construction, strip plank “1-off” construction method for the fuselage. 2 spar wings (probably pultruded carbon fibre rod spar caps). Weight considerations will probably decide whether I go for a strut braced wing or not. I’m having a big internal debate about how to break down the parts, my current idea being a 3 piece wing, tail booms & rudders combined and a separate horizontal stabilizer...

    Seat: 2 (tandem)
    Span: 9.8m
    Length: 6.6m
    Main Aerofoil: GA37A315 (I’m undecided whether to stick with the rectangular wing for simplicity, or put in tapered outer panels)
    Tail: NACA0015 (the latest incarnation actually has some rudder area below the tail booms but it’s not in the 3D model yet, so not in the pictures)
    Engine: Mazda Renesis Rotary Conversion ~160Hp
    MAUW: 600kg (or less!!!)
    Stall: < 45Kt Cruise: Hopefully Around 120-130 Kt (lots of calcs still to do)

    Cheers
    Dave
     
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  2. Jan 10, 2013 #2

    flyvulcan

    flyvulcan

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    It's a neat looking project Dave. I'll look forward to watching its progress.

    Cheers,

    Dave

    PS I note that you have a spurious link at the end of your first sentence which connects with another website. This happened to me as well (same website) without my knowledge. You may want to remove the unwanted link to stop others going to that spurious website.
     
  3. Jan 10, 2013 #3

    Head in the clouds

    Head in the clouds

    Head in the clouds

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    That's good looking Dave.

    Just one consideration, have you a good plan for the pax entry and exit?

    Cheers,

    Alan
     
  4. Jan 10, 2013 #4

    DaveD

    DaveD

    DaveD

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    Good question, I thought I'd make the pilot seat fold forward, similar to a small car, and then make one of the side windows removable as an emergency exit. Possibly not ideal, but then a good 80% of my flying is with no pax.

    Cheers
    Dave

    P.s I can't see the dodgy link flyvulcan was talking about... Maybe it's gone?
     
  5. Jan 10, 2013 #5

    Jan Carlsson

    Jan Carlsson

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    With 160 HP, top speed will be about 153,90 Kts
    75% Cruise 139,00 kts
    Or there about.
     
  6. Jan 10, 2013 #6

    bmcj

    bmcj

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    Dave, nice looking design. I've often entertained a similar looking design, except mine has a stab across the top of the fins, ala OV-10 Bronco.

    Other Dave (flyvulcan), I don't see a link either. Do you still see it? If so, perhaps it's something specific to your computer?
     
  7. Jan 10, 2013 #7

    Jay Kempf

    Jay Kempf

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    Nice stuff. I think the vertical fin projecting below the tail boom is a good idea for a couple reasons. One is to neutralize the roll/yaw coupling and the other is to protect against prop strikes. The other thing I see is maybe to round out the belly a little bit which will give a little better flow over that area right where your gear attaches flowing into the prop and will give your PAX better foot room. I have worked on a ton of twin tailboom configs and consider it the best way to get a tail behind a single pusher prop. Take a look at your firewall rearward package and don't make it too tight. Cooling ducts are hard to plan for and really hard to do in the modeler but you will get to that eventually. I agree with you on the foam core one off method.
     
  8. Jan 10, 2013 #8

    autoreply

    autoreply

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    Ok. Pretty similar to my design too :)

    (Mine has an inverted v-tail, midwing, RG nose wheel and is side-by-side.)

    Some observations.
    Connections in flight surfaces, especially the tail booms are bad. Structural nightmare, flutter-prone. Detachable wing panels (which my design has) outwards of the booms are still fairly complex, but at least you can permanently fix the inner wing to the tail booms. In fact, I plan to do the whole airframe minus outer wings in only 2 molds... yes, really.

    As for cooling; have a good look at Jay's own design pics. Sloped lower firewall where the air inlet is, he's done it the right way. Also a great place to bolt a landing gear to, because that lower part of the firewall is an excellent bulkhead.


    Now brace for a pretty wild idea. Change your design to a double T-tail (actually an inverted U-tail), like the Adam A500. Now make the wing+tail as one structural part and connect it with 4 bolts at the left and right trailing and leading edge root. Have a permanent bar that runs from your right rear bolt to the rightof the leading edge and bolts to the fuselage there. Now disconnect the two front bolts and the rear right one and replace the left rear bolt by a universal joint. Now move your tail downwards and to the left and bolt the middle of your H-stab to your right main gear.

    Yes, it took me a while to come up with this and it looks extremely complex. But dimensionally and structurally it works very well and my design (which needed a considerably bigger tail) fitted just fine in the stock container dimensions. A hell of a lot simpler in composites as all those complex joints..
     
  9. Jan 11, 2013 #9

    deskpilot

    deskpilot

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    My single seat design:

    Twin-boom pusher2.jpg Twin-boom pusher.jpg

    I intended for the outer wing panels to be removable. I went for mid wing so that the pilot could see over the wing when banked as in turning turning onto base. I like to see the field at all times if possible.

    BTW, what design package are you using?
     
  10. Jan 11, 2013 #10

    Joe Fisher

    Joe Fisher

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    The fuselage of the high wing would be easier to build if you use struts. I used to fly a brand new 1968 Cessna Cardinal the original with the thin wings. In turbulence the top of the cabin would pull away from the top of the doors. Some times I could see light through the gap. Just some thing to think about.
     
  11. Jan 11, 2013 #11

    Dan Thomas

    Dan Thomas

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  12. Jan 11, 2013 #12

    DaveD

    DaveD

    DaveD

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    Wow, thanks for all the feedback guys!

    I have to admit I’d come up with similar numbers but I really wanted to try and resist the urge to get carried away and make grand claims of how “fantastic” my design is going to be. I may be being excessively conservative, but I think reality will be:

    Engine isn’t really 160Hp (surely the marketing wouldn’t lie!!!!)
    Poor prop efficiency (fixed pitch, dirty air flow & 4 blades)
    Good old-fashioned drag – lets face it, it looks all slippery now but long unspatted undercarriage, aerials, pitot tubes, brackets, fixings, fairings, interference, cooling, leakage, less than perfect surfaces (surely not!!!) etc.etc.

    I guess what I’m saying is if I tell myself 120Kts and I get 135Kts I’ll be very happy. If I tell myself 140Kts and get 120Kts I’ll be annoyed, so I’m just managing my own expectations!

    Jay:-

    Interesting comment on rounding out the belly, I was subconsciously leaving space for the cooling inlet. although I haven’t decided whether it should be a single inlet underneath the belly or twin inlets tucked under the wings roughly level with the trailing edge (I’m currently having a good read of Hoerner’s books for some guidance on this one, but I’m certainly open to opinions). I must have had a telepathic moment regarding the sloping lower firewall as that was what I originally had in mind!

    Undercarriage/tail/prop-clearance compromise is a *%&#$ and has eaten hours of my time!!!! I actually hadn’t considered roll/yaw coupling to be much of an issue (don’t most aircraft have the majority of their rudder area above the CG?) but then I haven’t done the calcs yet! Main reason for the downward extension was to protect the Rudders, elevator and prop; but then to be able to achieve enough pitch up to stall... you need long, draggy undercarriage <sigh>.

    Auto:-

    When you say “connections in flight surfaces... Structural nightmare, flutter prone” do you mean just control surfaces and their associated control run linkages or do you mean the entire structure? I’d certainly want to make any structural connections at least as stiff as the structure they replace, which would clearly incur a weight penalty in dealing with concentrated loads at the hardpoints (a favourite subject of mine... see my previous posts!), but does that make them more flutter prone? And if so why? Or are you only referring to control run connections when you talk about flutter, which makes sense to me, as they will inevitably add some degree of slop to the system...

    I did consider a double T-tail (and a π tail) but high wing and T-tail looked like a scary “deep stall” waiting to happen, or really high aspect ratio rudders... I’m not sure how my current horizontal tail is going to go from a stability point of view. It’s nearly all in the prop wash which doesn’t leave much of it to “see” the real angle of attack of the aircraft (how I wish Orion was still around to give an opinion on this one. I never met, spoke to, or even exchanged an e-mail with Orion, but I really do miss his sage like presence on this forum).

    I Love the folding tail idea, and two-part construction would be great from a structural point of view...they’re not for me, but I’d love to see them, keep us posted!

    Deskpilot:-

    Unless I’ve totally stuffed the initial C of G estimate (entirely possible!) the pilot’s head is in front of the leading edge so visibility should be pretty good... hopefully!

    The design package is AutoCAD 2010... It’s a horror to do 3D design on (by all accounts Solidworks and Rhino are both much better) but I already had it on my PC at home (I’m an Engineering consultant) and use it extensively for 2D stuff (which it is very good at)... So don’t buy it, but if you already have it, it’ll do the job (slowly and in a frustrating manner!!!)

    Joe:-

    Struts...structurally good, aerodynamically bad; So for me, the jury is still out, I’ll keep you posted...

    Dan:-

    Love the pic’s... looks like massive amounts of dihedral, any idea why ?

    Phew... that was an epic post, did anyone make it to the end?
     
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  13. Jan 11, 2013 #13

    fly2kads

    fly2kads

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    I did, but I'm kind of a masochist that way.

    BTW, I like where you're going with this. Looks like the pilot's view will be fantastic.
     
  14. Jan 11, 2013 #14

    flyvulcan

    flyvulcan

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    Re the dodgy link, it's now gone. When I first viewed the first post, the word "work" was a hyperlink. It isn't any more so it seems that perhaps my computer has a glitch... So please disregard.
     
  15. Jan 11, 2013 #15

    StarJar

    StarJar

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    With hotwired foam cores, a tapered wing will be about as simple as a non-tapered wing.
    With a foam core, I would suggest to try and use an airfoil on the thinner side, which would keep the weight down. There's probably a 'sweet spot' where the spar material weight, and the weight of the foam, will create the lightest wing. You probably already know that. One cool trick is to use different airfoils on the root and tip templates, to give the tips a more delayed stall.
    Looks cool!
     
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  16. Jan 12, 2013 #16

    autoreply

    autoreply

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    Those are actually pretty low numbers. I'd expect a lot more speed from such a composite design (using wheel pants). Even my own design (80-100HP) should be a lot faster as that.
    Inlets are a difficult trade-off. Low is best for cooling during climb, but prone to ingestion. Under the wing are also fine there but cause pretty large drag.
    Will it fall on it's tail if you get out?
    Both. Try thinking up a connection of your tail. Your tail will take up to over half a tonne of force. Now try to react that into two detachable joints.
    Most T-tails are perfectly fine and the issue is a tad overstated by some. Anyway, by the time you have tall enough fins for stability, your T-tail will be far above the wing wash. Nót above the prop wash though. My design (inverted V-tail) comes pretty close to the propwash just before stall. No need for a stick shaker anymore...
    Just for clarity, what did you mean by "breaking down the parts"?

    Like trailer-able, or just for during construction? If it's just for construction, I'd build the whole wing (Rutan-style), then layup the tailbooms over the wing, they lay up another wing skin, from the boom inboard. That solves a lot of the structural complexities of the boom/wing connection.

    As for visibility, shoulder wings are best for visibility, you can look over them and under them backwards.
     
  17. Jan 12, 2013 #17

    BBerson

    BBerson

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    Small booms are flexible and flutter prone, especially in fiberglass. Make them tall, like a Cessna 337.
     
  18. Feb 7, 2013 #18

    DaveD

    DaveD

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    OK I'll come clean, my calcs show a top speed of 163kts and a 75% power cruise of 123kts, but I'm not making any promises!

    Low is still winning... at the moment!

    Now that is an excellent question! The current main gear placement was a "quick and dirty" guestimate but I'll certainly have a look at this later!

    For trailering, but only to get it to the airfield initially from my workshop, not on a daily basis. I like the idea of making the booms and wing centre section a single piece, certainly the additional weight involved in making them removable looks bad. The plan for the wings is Graphlite rod type spars and foam sandwich skins rather than Rutan style, to leave room for fuel.

    Unless I opt for a strutted wing the spars are going straight through the fuse unbroken, hence the high wing (so the spars don't pass through the passenger!). Anyway, at 160kts I'll only need the visibility to see who I'm rapidly leaving behind :roll:!!!

    I figured the booms were on the small side, but having not done any calcs yet I thought I'd stick with the usual internet apporach: Slim and sexy in the pictures but wide and heavy in reality :gig:!
     
    Last edited: Feb 7, 2013
  19. Feb 8, 2013 #19

    craig saxon

    craig saxon

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  20. Feb 12, 2013 #20

    DaveD

    DaveD

    DaveD

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    Thanks for that link Craig, I'd never heard of this ultralight before. It looks a lot like what I sketched when I first started the Project-Ex design, before I decided to go for a tandem configuration.

    I'm reworking the booms/tail and have tweaked the fuselage slightly since the pics at the start of this thread, should have some more pics up in the next few days.
     

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