My Preposterous Fantasy Aircraft: The Luge

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Victor Bravo, Mar 7, 2019.

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  1. Mar 7, 2019 #21

    BBerson

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    TINSFOS. (there is no substitute for span)

    The CriCri is 16 feet span. To suggest 14 feet with an engine three times heavier is....
    I would start with the Moni and work the span down some. No need for soaring. But for takeoff safety, an acceptable power off glide and low sink rate is still required for such unproven engines.

    The idea of a sleek but non-soaring sled (short span motorglider) is on my drawing board also. I envision a climb to 6000 feet, shut off the noisy vibrating engine and then do a Luge glide with wild maneuvering for about 20 minutes and land. No thermaling at all.
     
    Last edited: Mar 7, 2019
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  2. Mar 7, 2019 #22

    Victor Bravo

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    Monnett did that himself, there was a 16 foot "Mini-Moni", the original long wing prototype N107MX with the wings shortened later (now in the EAA museum) and they either built or were planning a 20 foot "Midi-Moni". They agreed that the 16 foot verison was a little bit of a handful with the tiny little KFM engine.

    You may be right, I may have to go up to 16 or 18 feet. But I'm not looking for a floater for this exercise, I really do want a modest amount of wing loading so the thing doesn't make me seasick in light turbulence. If I go with a narrow chord (18 span x 3 ft. chord) then balancing it becomes a little bit more complex. And I'm significantly limited in the storage footprint, the walls of my hangar are fairly well staked into the asphalt :)

    Mini-Moni EAA Museum Crop1.jpg

    Mini-Moni EAA Museum Crop2.jpg
     
  3. Mar 7, 2019 #23

    Himat

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    Reading the specification, I think minimalist single seat Sonex look alike as small as possible to fit one person. Then you have already mentioned the Monnet Moni, and that is very much what it would look like.

    Design wise, seeking inspiration from RC models is another option and a “full size” Shrike or similar could maybe be made to look the part.
    shrike.jpg
     
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  4. Mar 7, 2019 #24

    delta

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    This one would fit inside a 16ft square. Mostly flat plate.
     

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  5. Mar 7, 2019 #25

    Vigilant1

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    Go Shrike! It would have to be quite light to work at the HP VB wants to use (fabric covered wings, etc), but the layout looks like it fits the bill.
    Here's a preview video of the first flight (very lively handling!;)):[video=youtube;nSIM_-0uCkU]https://www.youtube.com/watch?v=nSIM_-0uCkU[/video]
     
    Last edited by a moderator: Mar 20, 2019
  6. Mar 7, 2019 #26

    Victor Bravo

    Victor Bravo

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    Guys, I'm really stoked about the fact that people are interested in this concept. In principle I welcome all the weird and oddball ideas (now I've asked for it).

    However, from a realistic aero standpoint, BBerson is 100% correct when he says that this type aircraft will need to be reasonably efficient with a reasonable wingspan and aspect ratio. In order for low aspect ratio to work with low power, it needs to be a very light wing loading, which will result in a "floater", which is not what I want at all.

    We got really good performance on low power (no power :) ) at 10 pounds per square foot in the gliders. This was only possible with high aspect ratio. What I'm talking about building here is of course nowhere near the efficiency of a glider, but aspect ratio really does work wonders.

    So I'm afraid that low aspect flying wings, Facetmobiles, deltas, etc. are not going to work for what I am try ing to accomplish in this particular design thread.
     
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  7. Mar 7, 2019 #27

    Himat

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    If I remember from studying the drawings, the Shrike have an aspect ratio around 3,4. There is no reason to not extend the span to what you would use on a Sonex/Moni lookalike. And at the same span loading the induced drag is no worse for a lower aspect ratio.;)

    Note that your suggested 14 feet span and 60 square feet area is an aspect ratio of 3,26.
     
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  8. Mar 7, 2019 #28

    Hot Wings

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    This reminded me of another attempt to create a quick build Colomban like aircraft here on HBA:

    Gnat
     
  9. Mar 7, 2019 #29

    Vigilant1

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    If you have 54 sq ft of wing, how heavy do you want this plane to be (i.e. how fast do you want to stall?)? With an 18 ft span, it can't be very heavy if you want to climb on 25-40HP.
     
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  10. Mar 7, 2019 #30

    rtfm

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    Hi,
    The main function of any fuselage is to hold the flying surfaces in place. So I would design the flying surfaces first. Next, draw in your supine body and place the engine where it needs to go for CG purposes. Connecting the flying surfaces, body and engine is pure aesthetics from this point onwards, and no-one's going to be able to help you with that.
     
  11. Mar 7, 2019 #31

    12notes

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    If you're going to start with the flying surfaces, you could with the Hummelbird wing design, and modify the ribs to use your favorite airfoil. It's an 18' wingspan, 38" chord, made in 3 sections so no parts are over 6' long. Not very complex to build. Not sure if it meets all your design goals, but it seems to be what you're looking for, and an established wing design allows you to spend more time and effort on fuselage/tail design.
     
  12. Mar 7, 2019 #32

    lr27

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    Seems to me that a narrower chord won't mean balance problems unless you reduce the tail size to match it.

    Increasing the span and aspect ratio WILL make the ride a bit rougher, although you're probably used to that from sailplanes. A low aspect ratio plane won't ride as rough as the wing loading alone would suggest. A low aspect ratio could work with relatively low power, as long as you don't reduce the span too much. That's where the light wing loading would come from. One problem is that if you're lying down feet first, a low aspect ratio wing may block a lot of your view.

    Wondering if this mission couldn't be met by a lightened Formula 1/Goodyear or racing biplane design. The Davis Da-5 might also be a starting point, and apparently you can actually get plans for that, though of course it's too heavy, probably, for your smaller motor.

    If you need a bit more span than will fit under the Cessna, the simplest way may be to make the tips detachable. No need for control linkages or anything.
     
  13. Mar 8, 2019 #33

    BBerson

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    High aspect ratio requires extra span. The BD-5B is 21.5 feet span. Do you want something more dangerous than the BD-5?
    A large span might fit sideways in the hangar. We pushed 36' airplanes through a 28' factory door with some creative maneuvers.
     
  14. Mar 8, 2019 #34

    ScaleBirdsScott

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    The SD-1 Minisport seems like it's not far off from the proportions/size required. Total length is under 15 feet, and that includes the engine and rudder. The pilot is already fairly reclined, but lay the pilot back a bit more while you're switching everything to metal, and I feel you're basically there.

    IMG_0012-e1476007102841.jpg

    The SD-1 was behind our booth at Oshkosh last year so I got a good chance to look it over. I'm not 100% on the plywood construction methods for my own desires, but it seems like it could be directly swapped for metal with minimal fuss. The thing is minimalist and looks pretty good. And the kits seem reasonably priced.

    Fuselage Sample Drawing

    How they perform, I'm not the one to ask, but it's probably not too bad off.
     
    Last edited: Mar 8, 2019
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  15. Mar 8, 2019 #35

    Victor Bravo

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    I don't think the BD-5 is dangerous because of the 21 foot span. If that were true, the RV-3, Cassutt, KR series, and many other smaall single seat aircraft would be dangerous due to span alone.

    I'm looking for about 10 pounds per square foot wing loading, specifically to take the "floaty" out of it in normal summer conditions here in the southwest.

    The hangar door is not the prooblem in space. The problem is the shape of the hangar and all the stuff that has to share the hangar with the 172. I don't have room for 20 feet of span.
     
  16. Mar 8, 2019 #36

    BBerson

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    The BD-5 was dangerous because of frequent takeoff engine failures. Your preposterous proposal is apparently that because your space is small, somehow small span and small chord is somehow safe with an unknown engine. I don't agree. The CriCri has two engines near the the centerline and apparently handles single engine. The original CriCri was 138 pounds and probably flown by similar size pilots.
    I don't understand why large pilots are attracted to small airplanes.
     
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  17. Mar 8, 2019 #37

    jedi

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    For reference: I have a C 175, Twister and UL WSC trike in a 40 foot door T hanger. Also an old hang glider and typical other accumulations (15-20 old radios and 20 years of old publications, no unreasonable offers refused). No lift or other tricks. Rollers under the Twister (Span 24' 7") to slide to the side.
     
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  18. Mar 8, 2019 #38

    Topaz

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    It wasn't. Whatever wing-related danger lay in the BD-5 was due to an entirely inappropriate airfoil choice for the low Reynold's number conditions of that wing near the stall. The fact that the engine and driveline tended to break a lot and that the airplane was very short-coupled didn't help.

    Before you go setting wing parameters, recognize that you've chosen a very small, fairly heavy motor (and before anyone thinks that's a criticism, I've chosen a very similar motor for my project), and that unless this airplane is the sort of "light" that drove the Cri Cri to such a complicated structure, you're going to be scratching for ways to optimize climb in the sort of hot-and-high conditions we see in our area nearly every single summer.

    If you have a hard 20' span constraint and insist upon a one-piece wing that doesn't remove or fold, then you may well be looking at a biplane, tandem wing, or Pou configuration, none of which you want, I know. I chose a different route, with a 35' span high aspect ratio wing, and have a very good climb rate even "hot-and-high", but "pay the price" for that performance with a three-piece wing.

    My point here being that you can't cram an arbitrary design into an arbitrary space, with an arbitrary engine, and have things work out "just fine." Choosing span, wing loading, and even the basic configuration at this point is putting the cart way before the horse. It's time to stop for a moment, look at not only your storage requirements but your climb, stall, and range requirements. Confirm your choice of engine. Those parameters, nailed down, are going to drive your wing loading and span values through a process of calculation, and from there you'll see if you can have a one-piece wing or not. If not, and a one-piece wing is a hard requirement, then you can look at alternative configurations that allow you to have a one-piece wing by having more than one wing.

    Without any of this being done, all you're going to get out of this thread is some nice drawings of airplane-like shapes. There won't be any basis in reality.
     
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  19. Mar 8, 2019 #39

    Hot Wings

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    Would those be red lines drawn with blue ink? :roll:
     
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  20. Mar 8, 2019 #40

    Victor Bravo

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    If I took all the other junk out of my hangar (workbenches, shelves, a friend's Volkswagen, tools, misc. stuff) I might be able to get as much int here as Jedi has done. That would be a bigger project than building the Luge.

    One of the hard constraints on this is that I want the build to be simpler than the other siimilar airplanes. I'm definitely NOT as good with sheet metal as most of the RV builders, and I'm definitely NOT up for the 5+ year building process that most RV's take. So the Luge concept is by specific intent 2 orders of magnitude less complicated than a miniaturized RV would be. The single place Davis airplanes have a big fiddly weldment at the tail that I can do without. The Teenie has a 3 piece wing and is severely cosmetically challenged, plus it uses a different engine than I want. The Hummel airplanes are jig-built conical fuselages and round formers, and too large to fit in the space I have.

    If any of you remember the old original Quickie 500 model airplane, that's kind of what I'm trying to achieve here with me riding in it.

    A one-piece wing is definitely a preference, just so I don't have to do an assembly procedure before and after each quick fun flight. I have a lot of experience putting together and taking apart sailplanes, and I am really really hoping to not have to do that kind of thing. Yes they do have one-person rigging stuff for sailplanes, but it's still a bunch of effort.

    My fall-back position if it is necessary is to have short 3 or 4 foot tip panels that I can plug on without help from anyone else, or that fold down like the Sonex One-X. But the extra build time, weight, effort, and formal engineering that goes into that is unattractive to me.
     

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