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Thread: My Preposterous Fantasy Aircraft: The Luge

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    Moderator Topaz's Avatar
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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by Tiger Tim View Post
    I got the impression that's what was wanted. This stage:
    That's fine. Trouble is, those images are absolutely meaningless until you've done at least some minimal back-of-the-envelope calculations to determine some basic parameters of the airplane from the requirements. Without doing that, you might as well draw an SR-71 or 747 shape, since you have no more means of telling if those two shapes meet the needs of the requirements than any other, beyond statements including the words, "probably" and "I think...".

    This comes back to letting the requirements drive the design, not trying to draw an airplane separately from understanding the consequences of the requirements. All the latter gets you is pretty airplane pictures. The former gets you somewhere into reality. With not a ton of work, or by making comparisons to existing designs like Vigilant1 did above, you can get a pretty good notion of what wing loading, span, installed power, and MTOW will work with what you want for your design. Once you know those things, you can start doing some sketching of an airplane design that might actually work the way you want. Without that basic work, picking up a pencil and drawing is artwork, not engineering or even "design."
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

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    Registered User Himat's Avatar
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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by Topaz View Post
    ...
    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.
    Well, several airplanes have been designed to fit constrains set as hard limits at the start. The A4 Skyhawk should be able to carry one nuclear bomb and fit the carrier elevator without any wing fold. The Airbus A380 and probably several other airplanes have had span constrains. All soaring, racing and aerobatic competition planes are designed to fit the rules. Designing an airplane to fit the hangar is nothing new either, a jet fighter design pretty much have a hard limit (concrete) if they are to fit the standard NATO hardened shelters.

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    Moderator Topaz's Avatar
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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by Himat View Post
    Well, several airplanes have been designed to fit constrains set as hard limits at the start. The A4 Skyhawk should be able to carry one nuclear bomb and fit the carrier elevator without any wing fold. The Airbus A380 and probably several other airplanes have had span constrains. All soaring, racing and aerobatic competition planes are designed to fit the rules. Designing an airplane to fit the hangar is nothing new either, a jet fighter design pretty much have a hard limit (concrete) if they are to fit the standard NATO hardened shelters.
    Of course. But you can't say you have that hard constraint without also talking about the intended installed power, stall speed, projected aircraft weight, range, etc. All of those were considered in the design of, say, the A4, and the final chosen configuration, wing area, aspect ratio, maximum gross weight, etc. was selected to meet all the requirements for those parameters as well as others. Even the A4 had a minimum acceptable climb rate requirement, along with the others.

    Again, my point is that you can't just say you want a particular arbitrary airplane and fit it into some arbitrary constraint. A span, weight, or length constraint is just one more parameter for the requirements and specifications list that has to be developed before any airplane can be designed. Even a "I just need it to fly" ultralight has to have some kind of basic climb requirement, along with the requirements imposed by Part 103. Saying, "I want a one-piece wing monoplane with no more than 18' span and a 20hp motor" is fine, until you find out that perhaps that results in an airplane that can't climb adequately on a mid-summer day with a real-size human on board or even "climb very well at all" on any given day. It might be fine, or it might not be fine, but there's two ways to know: The expensive way of "build it and find out", or the not-expensive way of running some numbers first. You can't do any kind of rational structural design without those numbers (and more) anyway, so you might as well get started early and save a bunch of rework later.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

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    Re: My Preposterous Fantasy Aircraft: The Luge

    The constraints set here can't result in an airplane capable of performing the intended mission. 50 square feet of wing on 25 or 30 horsepower at 500 gross (almost certainly more given the requirements for industrial motor and real human pilot) just won't do it. A little math or looking at other similar aircraft makes this clear. But I think VB already knows this. After all he wants a preposterous fantasy aircraft.

    Rob

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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by RJW View Post
    The constraints set here can't result in an airplane capable of performing the intended mission. 50 square feet of wing on 25 or 30 horsepower at 500 gross (almost certainly more given the requirements for industrial motor and real human pilot) just won't do it. A little math or looking at other similar aircraft makes this clear. ...

    Rob
    Very likely true. On my own project, I get a projected 800fpm climb under sea-level, standard conditions with 22hp installed power, 63ft2 wing area, and 550 lbs design take-off weight. At a density altitude of ~4,700', that climb performance reduces to just over 500fpm. Of course, the wing area on my project is spread over 35' of span, which is a "sweet-spot" for a homebuilt three-panel wing in composites. Even then, my climb performance numbers are probably slightly optimistic because of the depressing realities of small wooden propellers. I tried to account for that, but still.

    I would consider these climb numbers about the minimum realistic values one should set for specifications on a real-world airplane. You wouldn't get this performance with an 18' span wing, probably regardless of area. Certainly not on 50 ft2 area wing. If an 18' span one-panel wing (or anything close to it) is a requirement, then one seriously needs to start thinking about a more-powerful engine. That's not a shot against anyone. It's just physics.

    You can do these calculations without ever drawing more than a broad, roughly-scale "napkin" sketch of an overall configuration. Going farther than that without doing them is probably a waste of time, IMHO, if you're really trying to design an airplane.
    Last edited by Topaz; March 8th, 2019 at 07:14 PM.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by Victor Bravo View Post
    I am already aware of most of the small single seat aircraft out there that are known to the public. I have seen a Hummel Ultra Cruiser in person, and waatched it fly, and without disparaging anyone the aircraft is not what I want to be flying around in. It's the op posite of what I am trying to create with this concept.
    The Ultra Cruiser (this is the first mention in this thread) and the Hummelbird (mentioned several times) are different aircraft. The Ultra Cruiser was designed to fit part 103, has almost twice the wing area and a bit over half the wing loading, has a 95 mph VNE, which is slower than the cruise speed of the Hummelbird, and is designed for a completely different mission. The Hummelbird is E-AB only, has a VNE of 145mph, and misses all of the part 103 targets by a good margin. Judging one by looking at the other isn't a fair comparison.

    I suggested the Hummelbird wing because the aircraft meets most of your design criteria.The wing is 18' long. It has a wing loading of 10 lbs/sq.ft. It cruises between 100-120mph, on 30-45hp. It has a reclined, but not quite laid back seating position. The fuselage is not built on a jig, it's built on two 2x4s bolted together in a T shape, slightly less than 10' long. Before you bolt the spar in, it's less than 30" wide. If you don't have room to build that fuselage, I'm not sure you'd have room to build any fuselage.

    I'm not trying to change your mind on what you want, just clearing up what seems to be a misconception of the construction method. I understand you'd like a different seating position and fuselage construction method.

    You mentioned wanting to keep the fuselage parts to 12 foot lengths, but for an 18 foot wingspan, the one piece wing requirement means you need 18 foot lengths for the spar. Or at 12' spar and two 3' wing extensions, which is really a 3 piece wing at that point.

    What exactly is the wingspan limit that you can fit without disassembly?

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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by BBerson View Post
    I don't understand why large pilots are attracted to small airplanes.
    We're perverts?

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    Re: My Preposterous Fantasy Aircraft: The Luge

    Quote Originally Posted by Himat View Post
    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.
    Attachment 78903
    Rans did a similar lifting body design....the S-11 Pursuit. It didn't seem to be a success for whatever reason. https://en.wikipedia.org/wiki/Rans_S-11_Pursuit

    https://doc8643.com/aircraft/PURS

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    Registered User Victor Bravo's Avatar
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    Re: My Preposterous Fantasy Aircraft: The Luge

    If I remember correctly, Randy Schlitter damn near got killed and burned to a crisp in the S-11. "Not a success" is kind of an understatement. I do not know the details of that accident but I do remember reading that it was really serious.
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    Re: My Preposterous Fantasy Aircraft: The Luge

    There has been lots of threads on the S-11 on HBA. Was Schlitter’s fire after it hit the ground? It was the 2 stroke I think that he crashed. The 912 ones did better. It had a funky stall where the fuselage would keep flying when the wings stopped. I don’t think he wanted to sell something like that to the general population.

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    Re: My Preposterous Fantasy Aircraft: The Luge

    The "Kelly" Johnson sketch posted by Tiger Tim had assumptions built in, specifically, the Allison engine and a thousand hp per engine.

    The results of that sketch, with half a century of hindsight, had several problems, some could have been fixed with little ( relative ) effort, like the poor cockpit layout. Others would have needed a lot more work, like the thick airfoil that limited Mach performance. Still others needed developing, and failed to get it, like the cooling system that turned oil to treacle and intake air so cold the lead fell out of the fuel.

    Enormous money and time was wasted on designing a second generation successor to the P-38, which had silly design requirements like a powered turret, ( based on a romantic notion that was disproved in blood by the British Boulton Paul Defiant ) and engines never available, or never developed.

    In hindsight, a laminar flow wing, redesigned cockpit, cooling system and dive brakes would have been a faster, better, and actually shipped before the war was over airplane.

    But that is not what the customer ordered.

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    Registered User Himat's Avatar
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    Re: My Preposterous Fantasy Aircraft: The Luge

    A configuration that might work for a very small airplane. Joined tandem/biplane wings, engine up front, V or T tail. The pilot is to sit between the wings with his but at the rear lover wing leading edge and feet under the front high wing. To keep weight down, junk that industrial engine and fit a two stroke or Wankel.
    Click image for larger version. 

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