Starman's plane

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Starman, Aug 27, 2009.

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  1. Aug 28, 2009 #21

    Starman

    Starman

    Starman

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    Good points. I haven't worked out the exact location of the wheels or the required rotation forces yet (but the anticipated force is one reason for the big horizontal tails).

    During rotation the main wheels will move forward towards the CG so at stall angle it will be close to balancing. One thing about the very long stroke gear is that as you rotate the craft will rise quite a bit and still be on the wheels, which moves the prop further from the ground. A hard landing would be a different case, life's a gamble.
     
  2. Aug 28, 2009 #22

    Starman

    Starman

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    Okayyy, don't anyone look up Sht on Google.

    I went to do some math and realized I'm missing some definitions.

    I understand Vht =volume or authority, Lht is distance between surfaces at the 25% point, MAC is mean chord, but what is Sht, Sw, and the b in (Sw*b)?

    Also, do you use feet or inches in these calculations? I'm guessing inches.

    Edit, i just realized S has to stand for surface area.

    Thanks.
     
    Last edited: Aug 28, 2009
  3. Aug 28, 2009 #23

    bmcj

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    :roll:
     
  4. Aug 28, 2009 #24

    BBerson

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    A couple thoughts:
    An engine placed some distance aft usually creates problems, such as spin problems.
    Check into the Prescott Pusher for some ideas and why it was not a success. Your design would be better than the Prescott, I think, if the engine is more in the center of the airplane instead of near the tail.

    Raymer advises to get the prop some distance behind the wing to reduce wing/prop interaction.

    If you put the engine just behind the CG and extend the double tail units far enough back, that might work. Then it would be more or less a conventional pusher with two separate tails.
    BB
     
  5. Aug 28, 2009 #25

    Jan Carlsson

    Jan Carlsson

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    Originally Posted by wsimpso1 [​IMG]
    On the general topic of being close coupled:

    Vht = Sht*Lht/(Sw*MAC) - Pazmany and Thurston talk about it in their books. Pazmany says that 0.30 appears to be absolute minimum, with .45 being typical and 0.70 being used on ships with big moments, big flaps, etc. Thurston recommemends a min of 0.55.

    Vvt is done two ways. Pazmany lists it as Vvt = Svt*Lvt/(Sw*b) and hints at 0.033 being a minimum, and is a check that you have enough vertical tail against adverse yaw and to yaw the airplane. Thurston uses Vvt = Svt*Lvt/(Sw*MAC) and recommends a min of 0.30, which is a check of the same type as is used in the horizontal tail.



    S is square = area surface
    h = horizontal
    t = tail
    v = vertical
    b = span
    L = length
    V = volume
    MAC = Mean aerodynamic Cord

    J = Jan
     
  6. Aug 29, 2009 #26

    wsimpso1

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    +1 on Jan.

    Volumn coefficients are normalized. All units cancel as long as the units are the same top and bottom.

    Billski
     
  7. Aug 29, 2009 #27

    Starman

    Starman

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    Good.

    Thanks J, there's one more piece I need to make this work, and that is, what does Sw mean?
     
  8. Aug 29, 2009 #28

    Starman

    Starman

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    Sorry, I forgot to answer this earlier.

    No, I wasn't thinking of a lifting tail on this one, it's just something I've toyed with mentally before. However, in the wing spar location thread one of the members said that the center of lift can go as far forward as the leading edge of the wing. Well if that happens, and most people put their CG at 10 - 20% chord, then the tail has to lift, doesn't it? I'm afraid this doesn't compute because I distinctly recall having to pull back while landing, or that may be due to ground effect.

    In addition, since I have a blended wing design, the fuselage will provide plenty of lift so at high angles of attack that would make the center of lift move even farther forward.

    IF the tail has to lift then I don't think an all moving surface will be stable, it would need a large fixed section with normal hinged surfaces.

    Does anyone here know of any person who likes to make X plane models for fun or profit?
     
    Last edited: Aug 29, 2009
  9. Aug 29, 2009 #29

    Starman

    Starman

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    I checked out the Prescott Pusher, being on this forum and getting these advises is a great help and I really appreciate it!

    On the Prescott it looks like the high thrust line, marginal elevator authority and a blimpy fuselage did it in. I have a centered thrust line, non blimpy lifting fuselage, and I'll make sure it's got lots of elevator authority.

    Concerning engine location, due to the design I have many options available, the plan is to put a Mazda Rotary about a foot to a foot and a half back from the CG, it will be easy to adjust this location to balance things, and I can also move things like the battery and radiator for or aft for balancing. When I settled on this shape I wasn't sure about the engine so I made it adaptable. I can put three Honda V twin industrial engines further back, a Mazda rotary closer to the spar, or an inverted V8 right at the spar. I can put twin rotaries on it, this would require a different rear subframe with a conventional single tail ... or going to never never land, I can hang a couple of inverted big block cast iron V8s right under the spar center section, one reason I'm making it strong. All scenarios will be direct drive.

    Since the rotary is as inexpensive as the least costly and much less expensive than others and is also the most reliable I chose it. If I used piston engines I would prefer to use at least two of them for reliability, with close thrust lines (engines closer to center, drive shafts angled outwards).

    Concerning elevator authority: I think I figured out the main reason that a flying wing or delta is different than a short coupled design, and that is that the flying wing can't really stall. Does that sound reasonable?

    Any ideas what he means by some distance? Half the prop diameter?
     
    Last edited: Aug 29, 2009
  10. Aug 29, 2009 #30

    Topaz

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    Flying wings and deltas (which are just another form of tailless) are quite capable of stalling.
     
  11. Aug 29, 2009 #31

    orion

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    The problem here is that you're looking at all this in a very simplistic manner without really understanding how all these variables figure into the whole nor how they inter-relate in all the aspects of stability and control, and performance. Given the relatively complex nature of your configuration, it is unlikely that anything like X-Plane is going to give you any meaningful or useful information. We can go into a long and detail discussion of this (although its been discussed here before) but the simplest way of looking at this is just looking at the depth of analysis and the scope of the analysis package. Simply said, X-Plane costs something like fifty bucks; a moderate level panel based CFD analysis package (which still has significant limitations in looking at your configuration) costs at the very minimum about five hundred times that; a full 3D capable analysis package will double that again.

    Your discussion of lift vectors fails to account for the pitching moment generated by the wing nor does it address the vector direction of the lift and the attitude that airplane is at when this condition is achieved. Furthermore, your conclusion again fails to account for numerous variables that are involved in flight, control and stability requirements.

    The problem here is simply that we are unable to teach you what you're missing - that is waaaaaay beyond the scope of a typical discussion board. Most people going down this road (designing their own) commonly find that before they ever put pencil to paper they first have to make a rather sizable investment in proper references. Furthermore, they also find that no one (or even a small handful) reference covers the subject matter to a significant enough degree to be completely useful - this then means that you need several references for each subject, which leads to a sizable library. And that's for a normal airplane configuration.

    Now you introduce a configuration that will be strongly affected by interrelated flows and downwash fields, imposing control effects, high surface forces, complex control gradients, and on and on, and you'll find that this information will not be in any of them.

    We can help you here but that help can be only within the context of proper design practice - anything else will be no different than the typical "garbage in - garbage out" scenario of software. What you're doing is challenging at best so in order for it to make any sense will require a more in depth understanding of the physics, terminology, and design practices. A lack thereof will simply be a waste of your own time since what you'll come up with in the end will most likely be unsafe at best, downright deadly at worst.
     
  12. Aug 29, 2009 #32

    Starman

    Starman

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    I agree with all you say, we shall see how it works out. I think you'll find I've read more than you think but I just don't pay much attention to the terminology because I never discussed it with people before so that makes it look a little worse to you than it is. Couple that with my aptitude in physics and mechanics that I wrote about in the tortured aluminum fuselage thread (did you read that?) and there's hope :) Due to this I have a powerful seat of the pants understanding of the basics and the interrelations involved. I just don't have quantitative experience. I learn fast and I copy well.

    Another reason I'm making this 'adaptable' is so I can fine tune the parts that need fine tuning for safety, like the wings, after I make the fuselage structure. As I go on making and adding more parts I just have to work them out as I go and leave myself room for variations till the last minute.

    I'm also going to be going for a little more in person help when I identify the correct helper(s). Who knows? Please PM me and tell me what you would charge.

    In the meantime, I've got the inner fuselage tub mockup made out of plywood so that I can figure out the patterns for the outer fuselage pieces. The only thing I need to decide before cutting metal for the fuselage tub is where the main spar will go, I think it might be good to move it back a bit and increase my length.

    Anyway, this is going ahead on schedule, and I don't need luck, I just needed to get my resistance out of the way, which I did.
     
  13. Aug 29, 2009 #33

    GESchwarz

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    Starman, we are all trying to help you. Orion put it well by describing your concept as unsafe, even deadly, so there's no point in even discussing performance potential.

    By informing us of you decision to proceed with construction based on a three view that has been judged by several very highly qualified experts in this forum to be un sound, indicates to me that you are not listening.

    Building first and designing later...there is just no surer way to make scrap than that. There is a lot more we could say, but again, like Orion said, that's waaaay beyond the scope of this discussion board.
     
    Last edited: Aug 29, 2009
  14. Aug 29, 2009 #34

    Starman

    Starman

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    I listen to constructive criticism, and if you don't have any then go away. and don't judge me! you have no idea.

    I've already made changes thanks to the help I've gotten here.
     
  15. Aug 29, 2009 #35

    GESchwarz

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    What we are trying to say is that you have a tremendous amount of learning and design work to do before you can begin building. To do otherwise is to all but insure that you will be making a lot of scrap. I’ve been designing and fabricating all my life, and I can tell you that you are jumping the gun.

    Don’t make the mistake of taking my criticism as being personal. I am sincerely trying to help you.
     
  16. Aug 29, 2009 #36

    Topaz

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    That's always seemed to be the case with this board in general. Certainly is the case for myself.
     
  17. Aug 29, 2009 #37

    Starman

    Starman

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    Listen Gary, I know you are trying to be helpful and I do appreciate it, but your listening ability leaves a bit to be desired, since you analyzed mine. I know what motivates you and how you feel and how you think. You don't know me or what I've built or my abilities and I don't blame you for assuming the worst but now is the time to drop it!
     
  18. Aug 29, 2009 #38

    GESchwarz

    GESchwarz

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    Starman, let's keep that animated cartoon between you, Topaz and me. :speechles

    Ya, I don't believe I've ever been accused of beating around the bush. I for one, and I believe my feelings are shared by many in the aviation community, believe that we are our brother’s keeper. I therefore have a genuine interest in your welfare and success as a designer and homebuilder. As members of the EAA we all have an interest and a stake in the success of each member. The criticism that flies in this forum is kid’s stuff compared to the beating we can get from Mother Nature, the laws of physics, the FAA, litigants, and the ground pounding, voting masses. :ermm:
     
    Last edited: Aug 29, 2009
  19. Aug 29, 2009 #39

    Dana

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    You still don't get it, do you?

    The problem (and you're far from the first person who's been told this on this board) is that you don't know what you don't know. I don't know if it's us or yourself that you're trying to convince that you know more than you obiously do. Tooting your own horn about how smart you are (or think you are) in the manner of a petulant child means nothing, especially when it's obvious from the things you say that you don't have any "understanding of the basics and the interrelations involved".

    We're not trying to citicize but to help... but as Orion says, the basics of what you need to know are way beyond what you can learn on a forum like this.

    Take a step back, drop the "I'm so smart" attitude, buy, read, and understand even a basic book on aircraft design (because it's obvious you haven't), and you'll have a much better handle on what works and what doesn't... and what questions to ask.

    -Dana

    They say that people who don't read history are condemmed to repeat it. Unfortunately, people who DO read history are condemned to watch it replayed by don't..
     
  20. Aug 29, 2009 #40

    Starman

    Starman

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    Obvious? Listen carefully, (removed by Moderator), I've read quite a few of those books. I've said that many times here already so obviously you think I'm a liar. I understand those books very well (removed by Moderator).


    Mod Note: Disagreements and criticisms are fine. Name calling will not be tolerated.
     
    Last edited by a moderator: Aug 29, 2009

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