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Thread: Double delta wing design

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    Lightbulb Double delta wing design

    Other than my intro, this has been my only thread here. I am currently in the design stage of a double delta canard pusher. The original inspiration came from the wing design of the Dyke Delta. But where that plane is a 4-place tractor with the wing in the typical mid-fuselage position, I slid the wing back to the rear of the plane, widened the fuselage and lengthened it to accomodate six people, plus baggage. The canards are truncated in length and angled slightly downward to allow for better visibility. I slid the engine from the front to the rear and smoothed out the lines of the fuselage, blending them into the wing. I'm planning on using the inboard wing strake for fuel storage, similar to the Velocity. I want to use as much composite in the construction as possible. But this is the first time I've tried anything like this. The majority of my work is in sheet metal with the occassional composite repairs. I'm afraid that I've overbuilt the fuselage design as I'm concerned about the wing/fuselage interface will not be strong enough. Any suggestions?

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    Super Moderator orion's Avatar
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    There could potentially be a lot of suggestions but I would most likely have to discuss this in person. A few of the necessary questions to ask would be the following:

    The double delta canard design has several very unique flight and behavior characteristics, some of which are difficult to predict or analyze. The first question then is regarding your qualifications to actually design and configure an airplane. Aslo, what is your experience with this particular configuration and wing arrangement.

    Regarding structure, while you may have experience with metal, composites behave differently and the same design practices could result in an unsafe structure. For the most accurate analysis I would recommend that you have the design analyzed through finite element methods. Have you done this? Remember, ultimate strength is not your your only problem. You must also consider fatigue, stress concentrations and locallized loading, environmental and service considerations, etc.

    Basically, the questions that need to be asked will most likely address the entire airframe, not just small parts. This is not to scare you off nor criticize, it is just to make sure that whatever you fly will allow you to return to earth is a slow, predicatable and controllable manner.

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    My qualifications to design and build an airplane are probably the same as anyone else. I want to build an aircraft of my own design, provided that it can be determined to be safe and flyable. I know the differences between sheet metal and composites, I work with them everyday. Glass, Kevlar, Carbon Fiber, Refrasil, all of these are materials I deal with on a daily basis. I have full intention on having the design analyzed for feasibility, once it's completed. I have no intention on giving someone a partial plan and expect an answer. No, I don't have an engineering degree, and from what I've seen with a number of aeronautical engineers, I really wouldn't need one. I don't see myself as knowing everything there is to know about aircraft design, but I have to pick up something along the way, since my job is to perform maintenance, repairs, and modifications to multi-million dollar business jets, which have a combination of all kinds of materials, daily. I didn't jump into this project thinking that I knew it all. I didn't, I still don't, and I won't. But my interest in doing this kind of thing shouldn't be dictated by my credentials, or the lack of them

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    Smile

    Michael -
    GO FOR IT!!! The name of our game is "Experimental Aviation", not FAA TSO PMA etc.
    Your design does sound challenging, but probably nothing that some common sense can't help you with. Probably anyone with experience in structural engineering can help you with the fine points.

    You may wish to make a scale model of your design first, get some ideas for CG range, handling characteristics, etc.

    Or you may want to just jump into it - until it gets off the ground it's just money and time spent like on any other hobby. Do try to use a good, reliable power plant, and filch other design ideas and methods that may work so you don't have to totally reinvent the wheel.

    Good luck - keep us posted!
    Craig
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    Jupiter, FL

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    Cool

    Craig,
    Thanks for the support. In addition to using some analysis shareware that I've found on the Web, I am also planning to initially build an RC model, probably around 1/4 scale, to do some fundamental testing. By getting up to that size, I should be able to get a lot closer to actual flight characteristics. I know they won't be exact, but I should at least be able to determine if the design will fly.

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    Michael,

    Can you tell us a little more about what you want in the design and why? Why a "double delta" other than the delta Dyke had one, and why the canard? Are you trying to get vortex lift like the Viggen jet from Sweden?

    I am using a "double delta" of sorts on part of my design.

    I would suggest you go as large as possible, perhaps 1/3 or .4 scale. Why? With the delta and canard together you will have a large Reynolds number difference and the canard will be the driving issue on the low end. Many scale models have problems because the tail is flying below 100k-500K RE and separation (stall) occurs where it would not on the full size. Drag also changes (2x+) below 500k and it may have an effect.

    Are you also doing a seaplane? Multiply the task many times if you catch the water bug.



    Holden
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    Holden,
    I don't have any particular reason for the double delta design, other than that I like it. If it doesn't seem to work out, I'll move to the single delta design. As for the canard, with the main wing pushed all the way back, I figured I'd need something to help hold the nose up.
    I appreciate the information regarding the aerodynamics numbers, but I have to admit that, not being an aeronautical engineer and this being my first practical airplane design, I don't have any idea what you're talking about. If you'd like to expound on this, or at least point me in the direction of literature or websites, I'd appreciate this as well.

    Michael

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    I've been wanting to design a six-seat airplane to be used simply for recreational flying. My own family is in Indiana, my wife's is mainly in Southern California and we live near Wichita, Kansas. I'd like to have something that will get us around quicker than land transportation. I'd ideally like to have something with around 180-210 knot cruise speed. Even if I went down to 120-150 knots, that's still a considerable time savings. The town I live in has a nice little municipal airport that is currently undergoing expansion(new runway, facilities, hopefully some more hangar space), and there is actually quite a bit of aerospace business here. Several companies that have contracts with my employer, Cessna Aircraft, as well as some smaller aircraft parts manufacturers. It's possible that I may be able to obtain much of what I will need right here at home! Back to the airplane, I'd like it to have about an 800 statute mile range, getting us to Indy on a single tank of fuel and to California on two to two-and-a-half tanks.

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    Micheael, as a fellow designer with out a degree I wish you the best of luck. Im currently working on a helicopter myself.
    With reguards to the double delta design I havent built any full sized aircraft but I have built 3 models with that plan form, just because it looks cool.
    I dont know the sweep your intending to use, mine were typically 72deg on the strake, and 45deg on the main wing. One thing to keep in mind is that if the strakes extend a long way forward, you will be surprized how far forward the CG is. What Im trying to say is that you may find the canard unecessary.
    One of the best layouts I found was a double delta with a V-tail arangement. This made the plane incredably stable and good balance.
    As far a building your aerodynamic knowledge there are a couple of sites, programs and books I can recomend.

    Mechanics of Flight, 10th edition, by AC Kermode. Very basic, yet increadably helpful book. One of my freinds lent it to me when I first started to design aircraft, still refer to it regularly. It has some basic formulae, with examples. Cant recomend it highly enough.

    This site , has some excellent info, mostly relating to RC but alot of good techncal info.

    Airplane PDQ , is a great program once you get the hang of it. It will give you a number of parameters very quickly. Infact, just put in what you want the aircraft to be able to do, and it will design it for you. (kinda takes all the fun out of it). You can also download a full working demo for free which expires after 15 days.

    DesignFoil , is a airfoil selection program. It has a virtual wind tunnel which shows the flow over the wing as well as giving Cl, Cd, Cm, and graphs all the data. There is also a wing crafter, flap bender, and various other features. You can download a demo but cannot print or import/export the data.

    One more thing I cannot recomend highly enough is a decent CAD program. I have been using Rhino CAD , it is a very easy CAD program to use. There is a free demo available, but you can only save 25 times. I tried using AutoCAD at first, but it takes ages to learn. RhinoCAD is like a windows program everything is point and click, with a good tutorial to get you started.
    When I first started designing I used to hand draw all my ideas. The thing that I found is that it is hard to draw acurately in 3d and some stuff that worked on paper didnt work in reality. Scince using CAD i have found the design process has been sped up ,assively. You can look at a peice from any angle, and see how every thing will fit before you make it.

    With the exception of AirplanePDQ, I have been using the others listed for over a year with great success, and recomend them all. Having to work on a limited budget the only thing you would have to purchase imediately is the book, everything else you can use the demo, (initially).

    Hope this helps you, and good luck with your design.

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    Michael, you also will need to remember that a delta wing is specifically designed to operate best at a high speed. With a sweep of 72 degrees, I think the best operating speed would be about 225 knots. You will need a big engine and that will guzzle your gas and reduce range. It will, hovever, increase speed. you also will need a longer takeoff run to gain enough speed (probably about 50-60 knots.) A solution would be to have non swept canards, which would bring the nose intothe air at about 30-45 knots. Then the large engine would have a semi verticle thrust direction, bringing the plane upwards.

    I too am designing a plane using canards, only they are only to support lots of battery and motor weight(it is electric), and to slow the plane on landings. The conventional tail in the back does all the manuevering. If you used the same principles and used elevons to change pitch and roll, then stress in the nose would be reduced due to lack of pressure created by control surfaces. I hope this helps, and good luck!
    Thomas Schneider

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    This is a fairly late post for this thread, but to those joining still, it's all good info
    I also was/am toying with a double delta configuration based on a BD-5 kit I have!
    I wanted to fit it into the Australian 'Ultralight' catagory, below 1000 odd lb A.U.W., and below 45kt stall.
    To do this I needed to add a lot more wing area, but making the wing longer or wider, or both, just wouldn't work on the BD-5 for various structural and/or moment arm reasons.
    My only answer was to go delta, I even found that this has been tried before.
    A picture appears on page 13 of EAA's SPORT AVIATION October 1975, referred to as the 'Crater Dart!'
    Anybody know any more about it?
    My idea was to try to use a double delta to create a high 'aoa' vortex off the inner strake to help with the low speed end, but I never got around to investigating how this vortex is controlled, IE Do you need a high wing loading to generate it?, can you generate it with a low wing loading and a sharp leading edge?, With a low wing will it still run out along the leading edge or will it try to stick to the side of the fuselage?
    Apart from this , there was a lot of 'serendipidous' gains to the delta layout, because the root chord wouyld be in the order of 9 to 10 feet, I could use an 8 to 9% wing section that would still be around a foot thick at the spar, which on a wing of only 16 foot span would give me a very light weight spar if ANY!.
    Also with the double delta I could build a 7 foot wide centre section (safely within legal trailer width) giving me wide track undercarriage, a thick wing to retract it into, lots of space near the centre of gravity for fuel, and fairly lightweight outer wing panels.
    My attached photo shows a bit of PhotoShop work that I didn't change the exhaust on, if I build it, it will more than likely be a turbo-fan (I have an APU that I hope to use) not a straight jet.
    Meanwhile I have too many other projects in the way trying to earn a living, before I can get back to it.
    Arthur.
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    perhaps I shouldn't warm up this old thread, but I couldn't help remembering something I read about double delta's:

    in NASA CR-512 ("An experimental investigation of the flow fields about delta and double-delta wings at low speeds" - 1966) a comparison was made between a 62 delta and a 75/62 double delta.

    The double delta had a higher Cl (appr. 0.15 - 0.2 higher), also the moments of the double delta were a bit different.

    since the PDF file size is 24 MB, I didn't try to include it with this post...

    By the way, Pylon500: I like your BD5 based double delta. I'd love to learn how to analyze such a planform. Would digital DATCOM fit the bill?
    Last edited by h_zwakenberg; May 8th, 2006 at 10:19 AM.

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    Super Moderator orion's Avatar
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    In my view, one of the most attractive double-delta designs was the series from Sweden, the Draken. A short tme ago I worked a bit at cofiguring a smaller version of the Lil' Draken, which was the scale technology demostrator prior to the initiation of the full scale Draken program. The new variant was to be powered with a more conventional engine and a pusher prop. I got a bit busy to continue for now but may return to it in the future.

    The double deltas are interesting and relatively efficient, especially considering the low aspect ratio. But as was indicted earlier, they really are optimized for higher speed flight and as such, for general aviation, might be rather inefficient as compared to more conventional layouts.

    In configuring an aircraft around this layout, it is important to understand that the configuration derives its lift not only from conventional low pressure fields, but also from the phenomenon known as "vortex lift". This is one reason the double deltas can achieve a higher clmax than just a plain delta - the highly swept fore surface at high angle of attack generates a vortex flow, sort of like a strake on a more modern fighter. This high energy flow creates a very low pressure field, thus providing the aircraft with more maneuverability at high speed and a somewhat higher lift coefficient at low speed.

    But when combining this configuration with a canard, some of these characteristics may be compromised due to the disturbance and downwash field created by the lifting canard. I would guess there might be some non-linear effects that may provide the airplane with some rather surprising characteristics - something I'm sure most pilots would not want in their airplane.
    Last edited by orion; May 8th, 2006 at 11:43 AM.

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    Lille Draken ("small dragon") is indeed a very nice aircraft. If I only knew how to analyze double delta's. I've collected a sizeable collection of information on delta's, alas, double-deltas don't seem to be covered by those reports, with the exception of the one I referred to above.

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