Slow delta wings?

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

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  1. Feb 21, 2010 #21

    deskpilot

    deskpilot

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    Like I said, I think I'll have to move the pilot back about 1ft. Problem is, I want to retain the lifting body roof line and a semi reclined seating position. If I go back much further than that, I loose one or the other. I don't think a fully reclined position will enhance long distance flying, unless you doze off. :zzz: = :dead:

    Yes, the fuse' sides could be slanted but that would take away valuable lifting surface off the wings and nothing gained except looks.

    Never heard of Yoda.

    Re the winglets, why do they put them on just about every new plane conceived these days? Look it up. I don't have span constraints, in fact, I want to make it narrower but need to do some sums first.

    Thanks for your comments guys.
     
  2. Feb 21, 2010 #22

    overlander

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    Doug
    Back to basics. Stall speed is a function of wing loading, barn door or delta. To reduce the stall speed you have to increase the wing area or reduce the MTOW - derate the aircraft. With a conventional layout you can adjust the wing camber to increase the lift - with flaps. This will increase the wing pitching moment. To counter this a tail plane or canard is used to apply a correcting moment. These are parasitic devices that add drag and weight. The delta avoids this. The aircraft is controlled in pitch by elevators acting as flaps. If you want extra lift you have add a tail plane which destroys the idea some what.
    The low aspect wing would be improved a little by the use of end plates or winglets this effectively increases the span for little extra weight.Could be combined with rudders as per long easy.
    Barry
     
  3. Feb 21, 2010 #23

    lr27

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    Compared to a sailplane, your pilot's position appears to be extremely upright. Just how deep is that fuselage?

    I think if you slanted the sides you would still get some lift from those areas, but that's just intuition. The canopy appears very wide where the pilot's head is and I bet you could slant it in on top instead of out on the bottom. I'll bet you would lose some lift from separated airflow on the sides of the canopy as is anyway. Even if they DID take away some "lift area", you would lose some of your intersection drag, wetted area, and possibly reduce separated airflow as well.

    Yoda Star Wars character is backwards who always talks. Ideal pilot is for lightest plane due to short stature.

    Winglets are fashion as much as anything, though for planes with span constraints they make sense. They would have to be VERY well engineered to do better than tip extensions. Unless you needed them for yaw stability as well. Or so I've always heard. The other thing is that they are probably optimized for a narrower range of speeds than extended tips would be.

    Also, I don't know what effect winglets would have on vortex lift, which could be very handy to have. For instance, I seem to recall that on the Facetmobile, vortex enables a very low airspeed, nose up descent at a reasonable rate. (I think it was suppposed to be comparable to that of a carrier landing.) Would be handy if in trouble in fog. Particularly since if I'm not mistaken it would also be spirally stable. If the wing was thin, conical camber could be used if there were not winglets.

    overlander:
    Stall speed is a bit more complicated with some deltas because they can take advantage of vortex lift, though this does involve a high angle of attack. Although it creates a lot of drag, vortex lift can enable high lift coefficients. I forget how high, but if you poke around the web you will find some old papers from the '50s on this.
     
  4. Feb 21, 2010 #24

    BDD

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    Ha! It is...yes...I think.
     
  5. Feb 22, 2010 #25

    deskpilot

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    I've copied this over from another post as it is associated with this thread.

    "Seb, I'm so glad you raised this question as I'm having the same problem with my Eagle-Ray design. I've been working out the Aspect Ratio and haven't been able to get it down from 8.1. The question arises as to how much of the plan view area does one use. On my current model, the stakes are pretty small but I am thinking of widening them by giving them a truncated delta leading edge. Why, well I want to decrease the overall width but maintain as much lifting area as possible.
    Another question arising is, does one take the plan view area of the winglets and fins into account, after all, they do provide some lift due to their angle.

    Sorry to patch into your thread but it's a very interesting one and somewhat 'outside the square' compared to conventional design work and theory."

    Now let me answer your question.

    Currently the fuselage is 4ft deep and my pilot is reclined at ... Oh only 20*, that should have been nearer 30. Ah well, mistakes happen.

    Yes the canopy is wide so as too maintain the full lifting surface. Airflow could be controlled from spilling over the edge by a low dam at the edges, starting at the base of the windscreen. Fuselage to wing intersection would have a molded fillet, but not a large one. I accept that intersection drag will be present as well as the large wetted area.

    "Winglets are fashion as much as anything," I think not. Boeing wouldn't spend millions on fashion. In my case, yes, perhaps fashion comes into it, I like the look. Also bear in mind, I'm not going supersonic and the resultant drag will be minimal in comparison to the rest of the plane.

    Please don't compare to the Facetmobile. 2 totally different platforms with totally different flight characteristics. The delta has a much flatter AoA at slow speeds and doesn't stall per se. I very much doubt that the Dykes Delta (my base model) would be flying today as a safe 4 seater, if it landed like a carrier borne fighter.
    You have to remember that in delta design, a symmetrical wing profile is a must(FAR 23), not so in the Facetmobile which has a flat bottom.

    I'm not sure that I'll be getting into a lot of vortex lift conditions although, by adding the hard edge to the forward delta, this may come into play. I'm not a designer so have to rely on what I read and understand/remember.

    Thanks for your comments guys, I really appreciate them, and certainly don't just brush them aside. If I'm still making any big/dangerous mistakes, please say so.

    Yoda him I know not. My age showing I am. Starwar's fan not I.
     
  6. Feb 22, 2010 #26

    lr27

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    Fuselage depth: My car is only around 3'9" from the bottom to the roof on the outside. I'm sure you could be a bit lower than that and still be comfortable unless you are pretty tall. I'm 5'10" and there's plenty of room for me. More than plenty of room when I recline the seat a bit to ease my back. It's a '93 Saturn SL1.

    I know you don't want me mentioning the Facetmobile, but it has a canopy that blends in to the rest of the plane and appears to lift ok. In fact, Wainfan says that if the windshield glazing was lost it wouldn't fly. Note that almost all of the front surface slopes steeply:
    http://www.wainfan.com/FMX4G6.JPG
    It would NOT fly if that surface was not lifting.

    I've never heard of a part of FAR 23 where a symmetrical profile is required for a delta configuration. In that case, the Facetmobile is clearly not compliant. But I am VERY skeptical of this alleged requirement. Also, that would prohibit conical camber, which has been shown to be pretty useful.

    I don't see why symmetrical vs non symmetrical is so important here. Particularly since the Dyke isn't symmetrical either, with that canopy. The Facetmobile isn't QUITE flat on the bottom, although it does look like the Dyke has a bit more curve there. But neither one of them exactly bellies out.

    I've got nothing against the Dyke Delta, it appears to be fairly well designed. Note that a later mod to the strake area (if I recall correctly) is supposed to reduce stall speed by 15mph or something. I'll bet that results in a higher angle of attack and some vortex lift. Note that in this article, the aircraft's designer is quoted as discussing a reduced stall speed:
    http://ernest.isa-geek.org/Delta/Library/dyke_delta_0303.pdf

    Since the Dyke Delta does have a higher aspect ratio, I suppose it operates at a lower angle of attack.

    As far as winglets go you'll note that in my post I mentioned span constraints. Airliners have span constraints. Airliner manufacturers also have marketing departments. Don't forget that the primary purpose of the aircraft is to sell, and all other purposes have to be secondary. Airliner manufacturers also have enormous engineering departments who can make the VERY WELL engineered as I mentioned, in which case there can be a small advantage. Even then, they don't always use them, as I just confirmed by looking at some pics of recent Boeing products. I think they might be useful for tweaking existing wings for slightly different missions.

    The descent at the rate of a carrier born fighter idea was as an alternative to descending in a spin and smashing into the ground, as would normally happen in a fog to a disoriented pilot, not for normal flight operations. I suspect the Dyke Delta could do it too, but faster since it's heavier. I think in this condition vortex lift could be very useful as a way to keep things slow.
     
  7. Feb 22, 2010 #27

    Starman

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    Hellooo... the only delta in the Dyke is in the name, it is NOT a delta winged airplane and neither is this design here, just so you know. :)

    Also, the previous reclining seating arrangement looks much nicer, and the canopy does lift no matter what the slope of the canopy sides is.
     
  8. Feb 22, 2010 #28

    ultralajt

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    English is not my native language. So, often I improvize.....
    Pardon me, please.
     
  9. Feb 23, 2010 #29

    deskpilot

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    Really? If not, what would you call it? I assume your thinking is that a delta has to be triangular in shape.

    I believe the correct description is 'a double delta with a forward swept trailing edge'.
     
    Last edited: Feb 23, 2010
  10. Feb 23, 2010 #30

    autoreply

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    You just have a low aspect ratio tapered wing, with a more or less blended fuselage.

    A "real" delta would involve vortex lift and all kind of complex stuff that most likely causes your head to explode. At least it would cause mine, but that might be related to brain size and capabilities...
     
  11. Feb 23, 2010 #31

    Starman

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    I promise, I didn't make it up, I read about it somewhere :) :ponder:

    Of course names don't need to matter, particularly in our society, and the Dyke is still called a delta even though it isn't.

    I think the Dyke Delta is technically a low AR highly tapered flying wing with moderate wing sweep, yours is a low AR moderately tapered flying wing with slight sweep. Still, it looks good, and that's what counts.
     
  12. Feb 23, 2010 #32

    deskpilot

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    Not going to get into a fight over a name guys but my understanding is that vortex generation is involved so.....................!

    lr27, you're right about FAR 23, I saw it somewhere else. I'll post it when I find it. Whist looking it up, I realized that there appears to no specific rules relating to delta's or other 'exotic' wing platforms under FAR, not at least that I could find. Perhaps you can point me in the right direction.

    I agree with what you say about the Facetmobile, fairly obvious really. As for the DD not being a symmetrical wing, the fuselage does come into the equation. The wing itself is symmetrical, a modified NACA 0012 I think, but don't quote me. The latest mod to the wing is the addition of what they refer to as a 'cuff'. This effectively is another leading edge that bridges the existing 2 edges, making a double cranked LE. I haven't read anything that suggests a higher AoA at slow speed (landing). I don't know what AR the DD has so if you know, I'd appreciate you letting me know.

    I found that my current AR is 8.1, which is way too high I think. The only way I can reduce it is by taking the fuselage top out of the calculation, when I get 6.5. A new fuse' design is possibly needed and if so, it will be more streamlined.
     
  13. Feb 23, 2010 #33

    lr27

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    I'm afraid I can't point you to any legal stuff about weird configurations.

    It's funny, from your picture the AR looks much less than 8:1.

    When I do a web search on Dyke Delta specifications, the first page has the span and area. By those specs it's 2.76:1. (span squared divided by area)

    Part of the higher angle of attack is for low aspect ratios in general. The lower the AR, the less lift change you get per degree of change in angle of attack (often aka alpha). On delta configurations with sharp edges, vortex lift comes in and allows the wing to hang on at even higher angles with more lift. I recall Wainfan says that with the Facetmobile, when it was flying slow enough, he was looking through the extra windows in the floor.

    Probably there are other places in the video, but check out the takeoff at 4:45 and the landing at 6:45 for extreme examples of a delta going to a higher angle of attack:

    Or check out any video of the Space Shuttle landing.
    more fun stuff:
    F-106 Delta Dart - Video Vault see landing video upper right

    ----------------- warning: diverges from thread below:
    This one's not quite relevant, but it's very entertaining. I heard about this program from a guy who worked on it. Was a test to see about towing lauch vehicles to give them a bit of speed and get them above the atmosphere. Feasible to loft more weight this way than under a wing:

    if you're really curious:
    Reuseable Launch Vehicle - KST's Rocket Testing and Jet Engine Testing
     
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  14. Feb 23, 2010 #34

    deskpilot

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    Oh Hell, another mistake. I forgot to square the span.
     
  15. Feb 23, 2010 #35

    LittleBird

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  16. Feb 23, 2010 #36

    bmcj

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    While I would not technically call it a delta, I have no issues naming it a delta. After all, it is somewhat similar in appearance to the typical delta winged fighter, and it is only a name, not a technical description.

    I would disagree that a plane must be able to take advantage of vortex lift to be considered a delta. The description "delta" comes from the triangular shape of the Greek letter Delta. Vortex lift just happens to be a useful result of the planform.

    The F-102 was a true delta wing configuration, while the F-106 was considered to be a clipped delta. The Verhees might also be considered a clipped delta.

    Bruce :)
     
  17. Feb 24, 2010 #37

    deskpilot

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    I concur your statements Bruce. In my earlier post re delta's being triangular, I should have said delta wings. Of course, a true delta is triangular, but our wings are all modified delta's.

    Kevin, yes and no. I'm looking for the same concept but a lot prettier.

    Re my 8.1 AR. Boy did I get my knickers in a twist. Did everything wrong. I'm now looking at figures down in the 2.0 - 2.5 range, depending on what I use as a lifting surface. Working on my twin fin model, I can divide the airframe into:
    Main wings
    Strakes
    Fuselage upper surface
    Winglets and fins.(because they're angled and will provide lift)
    Now as to what area's I should or shouldn't be using, Any suggestions?
    By the way, I've been asked several times why the winglets. Lets just say that I like the look, even if it's slightly detrimental.
     
  18. Feb 24, 2010 #38

    lr27

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    I think it's customary to omit the winglets and deal with any associated reduction of induced drag by calling it higher span efficiency. Of course, this means you can get the span efficiency above 1.

    I think it's customary to assume that the wing continues across the fuselage at the same chord, but I'm not sure how to account for the strakes.

    I like the vortex lift thing because it may reduce the speed at which the aircraft smacks into the ground if the engine goes out or if it's stuck on top and needs to descend through cloud. Most airplanes won't do the latter becasue they are not spirally stable. A delta wing probably could, though I don't know if it's still spirally stable when the vortex lift is going on. I suppose some careful testing with a model I have would answer the question at least partly, but I'm sure there's some better testing out there already done and reported on..
     
  19. Feb 24, 2010 #39

    autoreply

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    The aoa correction for short span aircraft isn't too complicated:

    dCl / dalpha = 2pi *(Ar/(Ar+2))

    dCl/dalpha is the slope of the liftcurve in radians. In other words, for an infinite aspect ratio it's 2PI, so for each tenth of a radian (5.3 degrees) you increase your angle of attack the lift coefficient (Cl) goes up by 0.63. For an aspect ratio of 2 that same 5.3 degrees increase in angle of attack yields only a 0.315 higher Cl :)

    As such an aspect ratio of 2 gives you only half the dcl/dalpha. That's good for turbulence (only half the gust strength), but for a normal profile that means your angle of attack for stall is in the 30 to 40 degrees angle of attack region. That's a biggie for the landing gear design. Making the aspect ratio a bit higher is the easiest solution.

    The above part doesn't include vortex lift, but on your design I doubt it'll play any role ;)
     
  20. Feb 24, 2010 #40

    bmcj

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    Yes, for a small, lightweight plane like this, I would ignore vortex lift in your planning and calculations. Just go with the conventional formulae. It may be able to develop vortex lift, but you might never see that benefit except in situations where you pull some hard g's or inadvertently raise the nose too high on landing. The delta wing fighters have heavily loaded wings and need that extra AOA to bring their landing speeds down. Your lighter wing loading will allow you to land at a more comfortable AOA (much like the Dyke Delta).
     

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