Slow delta wings?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by deskpilot, Jul 21, 2009.

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  1. Jun 7, 2010 #81

    deskpilot

    deskpilot

    deskpilot

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    Just wondering, would a dog tooth l.e. or vortilons help with my slow speed handling?

    Further to my C.G. calcs, I ignored the forward sweep of the t.e. as I didn't know how to take it into account. I believe, how-ever, it would have moved the CG back a bit more. This is a problem I think, as, with the current figures, the CG is in line with the pilots head so, to me, it looks as though the weights and balances will be out of wack. ie, to nose heavy. My gut feeling is that it should be about 12inches further forward.
     

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  2. Jun 7, 2010 #82

    BDD

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    For what it's worth I remember going over some plans for a free flight delta wing model designed in the 50's and it's c.g. was at about 50% of the root chord (on the wing's longitudinal centerline in this case). This was a 45 degree swept wing delta with a straight trailing edge. I built a small balsa wood model in the early 80's to see how deltas flew and balanced. It seemed to balance at about 50% chord, had 45 degree sweep too. I used a symmetrical airfoil section and angled the elevons up a bit. It glided pretty well but not with a great glide ratio, of course, and really went a long way in ground effect. The results were pretty good so I have a scaled up version that I was going to fly as an R.C. plane but haven't finished it. I was interested in this as a possible ultralight or light plane like your concept. I didn't have any front strake but would have had a tractor engine arrangement in a full sized plane.
     
    Last edited: Jun 7, 2010
  3. Jun 7, 2010 #83

    orion

    orion

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    I think there is a problem of terminology here or simply how the design process is being handled. You talk about CG (center of gravity) but you seem to be referring to geometry - it's really confusing trying to follow what you're trying to do. For instance, looking at the side view of your plane, most of your wing mass is probably just aft of he pilot but hen you have two concentrated masses (pilot and engine) well forward of that point. If we just look at the basics and guesstimate masses for wing and landing gear, I'd estimate that the balance point is probably at the pilot's knees, or thereabouts.

    But knowing that doesn't help you any since the balance must be within the allowable envelope, which is set by the static stability criteria and elevator (or elevon) control authority. As such, you first need to set your configuration and then do the stability analysis, determining the neutral points and the forward-most CG point based on being able to bring the airplane to full stall in ground effect. Once you have those fore and aft limits and some up front analysis of the mass distribution in your plane, can you see whether the pieces make sense and whether the configuration will fly.

    Some of this has been discussed herein in many forms - use the search function for stability and allowable CG range.
     
  4. Jun 7, 2010 #84

    Starman

    Starman

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    That original spar design of yours bothered me a bit and I didn't stop to think why but someone pointed it out, this one is better but ... Basically you have to deal with two main forces, the lift force and the twisting force ... and you need some kind of rear spar to attach the control surfaces to .. sooo ...

    Before we get started a little observation on terminology: by center of gravity I assume you mean the term I like, which is center of lift (more or less) which is an old fashioned term, but these engineers here don't like that and prefer the term center of pressure, whatever that means :). For you I'll use center of lift.

    So the two main forces on the wing are lift and twist. You can deal with the lift forces with a single spar and the twist forces just need an anchor point not too close to the spar OR use a spar that is very torsionaly stiff.. What you have drawn as front and rear spars may work better as the front and rear shear webs of the main spar which could be torsionaly stiff. But it is safer and easier for us beginners to use an anchor point and the ideal place for that is at the rear spar, where the rear spar attaches to the center section, and the rear spar is normally at the front of the control surfaces..

    So now it gets more fun. Since the outer part of the wing causes the greatest bending force on the spar and since it can be easier to design and make a straight spar then it can be ideal for your rear spar to take the main lift forces if it is straight. Then you don't have to worry about designing the more complex angled spar joint of front swept spars where they come together at the fuselage. I hope that makes sense, the rear spar goes straight out to the main outboard center of lift of the wing so it carries the bending forces and the lift of the inboard part of the delta, since it is so close to the center section, mainly needs a strong anti torsional connection. The problem here is that the front spar can be thicker so lighter but it needs to be longer so heavier :) The rear spar is normally too low on most wings but on a delta like yours it can get pretty thick towards the center, due to the geometry of your trailing edge, and due to the short wing span it can be plenty strong enough without being too heavy.

    I hope I didn't say too much :roll:
     
    Last edited: Jun 7, 2010
  5. Jun 7, 2010 #85

    Starman

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    I can draw a sketch of that idea if it will help.

    Also, you can average out the two deltas (fore delta (strakes) and main delta) in your design into a single delta of the same area with a straight leading edge. I had to use a strake on my design due to the construction method, but you don't.
     
  6. Jun 8, 2010 #86

    deskpilot

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    Thanks for your replies guys. I've certainly got a few things to muse over in the coming day. I would appreciate the sketch Starman. Strange that no-one jumped on the dog-tooth and vortilons post. I thought I'd be shot down as these suggestions are 'too far outside the box' or not workable at my slow speeds. For what it's worth, another idea I have is for the addition of under-wing cargo pods, big enough to carry camping gear. The attachment pylons in this scenario would over rule the vortilons. You can say if you want to, I'm a dreamer :nervous:
     
  7. Jun 8, 2010 #87

    Starman

    Starman

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    Since your center of lift is too far back you can move it forward by filling in the space between the front of the strake to the tip of the leading edge. Red is the main spar, green is the front spars and blue is the front stub spar. If the main (rear) spar is carrying all the bending lifting loads then all that is needed at the front is a single bolt on each side for the torsional connection
     

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  8. Jun 8, 2010 #88

    BDD

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    I wouldn't think that that rear spar would be receiving or therefore carrying much of the loads from lifting forces. It wouldn't be the main spar.

    If it works with the pilot location etc, you could extend the front (main) spars to their intersection point and use the cross spar as a drag support brace (blue spar optional). It would also act very well as an additional spar which is very stiff which would also help support the front spar for lift loads as well as drag loads. If extending the green spars forward can't be done, just make the joints between blue and green spars moment connections. Actually, the triangular, in plan view, spar system would be stable against drag loads by it's configuration. The spars would just need the ribs to brace the spars for drag loads. Some diagonal braces or drag and anti-drag wires could be used too and it would be like a truss structure for drag loads when viewed from above.
     
    Last edited: Jun 8, 2010
  9. Jun 8, 2010 #89

    Starman

    Starman

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    I'm just responding to the first part of your post because I saw it and went and changed my drawing before I saw what you added to it. You are right, I got carried away with the idea of the rear spar being at the control surfaces. It could still work if the green had a single bolt holding it to the blue, making it a pivot point, which was the idea. That forces the lift loads to go into the end of the red spar. Also, since so much of the lift forces are inboard the bending forces would be rather small anyway. I used this style of spar on my delta design, which is in the drawing below. It works out great for a pusher because the engine goes in between the two spars.

    Yes, that was the idea, I just didn't explain it well enough in my other post.
     

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    Last edited: Jun 8, 2010
  10. Jun 8, 2010 #90

    Starman

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  11. Jun 8, 2010 #91

    BDD

    BDD

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    Is that a lifting body or a delta wing. Either way, I like it.
     
  12. Jun 9, 2010 #92

    Starman

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    Neither one, it's a delta lifting body. :)
     
  13. Aug 7, 2010 #93

    gtex09

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    Hello dear All,
    I'm really pleased to see that you're on the same way... the design of J.Dyke's delta and the one of B.Wainfan's Facetmobile are really beautyfull, I'm convinced you have to get all the basics that are included inside if you want to design your own machine.
    Did you have a look to the PAV report ?

    After all prototyped versions form cardboard model to the 2.4m one, I'm also convinced that we can achieve a very safe and simple machine based one those basics.

    But my designed model, which was very close to the one of Deskpilot, crashed for unstability reasons (see GTx9-06, various videos).
    YouTube - ‪gtex09's Channel‬‎

    I kept finally the GTx9-05 model to prototype the last model, the GTx9-07, and validated it afetr several strong tests (You can have a look at all videos on my youtube channel)
    YouTube - ‪gtex09's Channel‬‎
    YouTube - ‪gtex09's Channel‬‎

    I'm currently building the GTx9-08 version, scale 1:1, span 6m, sandwich skin (PET foam/fiberglass) as an ultralight machine
    Target is to have something visible by the end of this year...

    Any question just feel free to ask.
    Regards.
     

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  14. Aug 8, 2010 #94

    steveair2

    steveair2

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    Very cool project! My questions are what engine do you plan to use? Is it one or two place and what will the empty weight be? Also, could you post pictures of your progress?
     
  15. Aug 8, 2010 #95

    gtex09

    gtex09

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    Hi steveair2,
    The engine is a BMW flat twin 66kW (90hp) motocycle engine, adapted to aircraft...
    The full weight is (will be) 450kg, with 2 persons and 70kg of fuel.
    You will get a lot of answers to your questions in the thread : https://www.homebuiltairplanes.com/fo...html#post71057
    Cheers.
    GT
     
  16. Aug 8, 2010 #96

    gtex09

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  17. Aug 11, 2010 #97

    danF

    danF

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    So far no luck for light weight engine/psru/prop designs. My goal is for 130hp and 140lbs wet engine and PSRU. Anyone know of an assembly fitting this requirement? I think possible using (mostly) existing parts. Comments?
    Dan
     
  18. Aug 13, 2010 #98

    gtex09

    gtex09

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    Hi Dan,
    So far I just know the BMW R-1200-RT which gives you an excellent power/weight ratio.
    This newest version gives 110hp at 7750rpm, and when adapted to an aircraft, the weight should be under 80kg, but the previous versions, which are accepted in Europe on ultralights, are very close to those figures.
    The main advantage you'll by using this kind of engine, except the fact that vibration keep at a very low level due to the flat twin concept, is the result of the long experience acquired by BMW on this machine for motorcycles, since they produce it and improve it step by step..... Reliability keeps a very important point for a flying machine, isn't it ?
    Cheers.
    :)
     
  19. Aug 14, 2010 #99

    Rienk

    Rienk

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    My recommendation would be the Yamaha 150 out of their snowmobiles.

    150 hp, turbocharged, in-line 4, 1000cc
    Four stroke, liquid cooled, fuel injection, altitude compensation.
    No built in gear box (lighter weight).

    All up weight (with gearbox, radiator, oil cooler) will probably be around 160-180 lbs.
    I don't think you're going to be able to get a higher power to weight ratio than that, with a reliable and proven engine - with relatively inexpensive parts.
     
  20. Aug 14, 2010 #100

    gtex09

    gtex09

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    Yes, you 're right, but it's just a pitty that we are not allowed to use it in an ultralight class airplane....:ermm:
     

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