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Design and build an 'Ultralight'

Discussion in 'General Discussion' started by Deskpilot, Feb 10, 2009.

  1. Deskpilot

    Deskpilot Well-Known Member

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    We've had several threads on the subject of designing and building an ultralight but nothing has ever come of them. I believe the main reason for those failures was due to an unstructured approach and too many people going off at tangents. What I have done here, is put forward a project, which may or may not be viable, but one to which anyone can have an input.

    Now, before you all go off with negative comments, let me say that this model is a design concept only, nothing is to scale. The model is incomplete for simplicity at this stage. Besides which, I'm only just coming to grips with GoogleSketchup (a free download if you want it)

    There are a few rules, love them or hate them but they're set in concrete.

    1. This project it to be treated with respect at all times.

    2. The aim is to, hopefully, produce a single seat aircraft that has appeal to the adventurous and perhaps younger flyers amongst us. A plane that is different from the rest.

    3. Only a few hand tools and no specialist skills needed to assemble the final design.

    4. Whilest cost is to be kept to a minimum, the engine, drive train and prop will always be the most expensive part of any build. To this end, only aircooled, auto, motorbike or aircraft engines are to be considered (80hp max). The availability of same being dependent on the builders powers of discovery. (The Prop housing and bearings are a specialized piece of engineering but need'nt be overly expensive if designed properly). I hope.


    Now, my preferred build method would be all Alloy tube, square and round, with plywood/foam sandwich ribs, plywood leading edge and rag skins. No welding

    Wing construction would be two tubes, leading edge and main spar with a full length aileron mounting spar and a suitable trailing edge. Foam sandwich ribs epoxied onto all spars and ply caps and bottoms to match leading edge thickness. I've chosen this method as, apart from being relatively easy, it will be quick enough to build and interest maintained. The plywood leading edge would provide additional stiffness and prevent the scalloping effect as seen on Thrusters etc.

    Now I realize some of you might think that I'm just after some free engineering advice, and you'd be right. I want to see my dream come to fulfillment. But at the same time, I want to give the same to any members of these forums who would like to share that dream.

    So, who's gunna start the ball rolling?
     

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  2. BLA82

    BLA82 Member

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    Love ya idea mate, lets hope we can get a roll on here.
    I have on simple question. How would you remove the prop? Would it have a removable tail section?
     
  3. Tomo

    Tomo "Young Enthusiast"

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    There pretty good drawings...

    I like the Idea.
     
  4. ozzie

    ozzie Well-Known Member

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    there was an eighties design from the states that was very similar to what you have here. The prop set up was complicated with the bearings that required practicatly complete dissasembly to work on. to stay within your budget it would be more practical to go with a more common belt or gear drive. ground clearance for the tail on rotation will be a problem as well. the wing itself is straight forward i would consider laid up glass for the ribs. foam is to fragile. use a larger dia for the forward spar tube and simple diagonal tube for the compression spar very simple like the wing design that steve cohen used in his early designs like the mosquito and advenger and still being used in his skydart. fabric covering to finish off.full span aileron with or without flap will also keep construction simple. if you keep an eye on the weight you will get ample performance with 40 hp. you are heading down the right track. avoid reinventing and keep it all simple.
     
  5. Deskpilot

    Deskpilot Well-Known Member

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    Wow, that's quick guys. So in reply:

    BLA82, prop is made up of individual, adjustable blades, something like Brolly props. Removal of an end plate allows for removal of prop. To remove the hub, yes, remove the emmpenage in one piece. I forsee, disconnect actuating cables/rods at the end of the boom tube, remove locking device that holds tail feathers and their own mounting tube, then slip the whole lot off.

    Ozzie, I would prefer belt drive but opted for the chain as it can be split and removed easily where as a belt can't be. In fact, I would probably go for twin chains for safety.
    Thanks for your input on wing construction. I was hoping to have a faster wing than what you're seeing. I will look at your suggestions though. As for fin and ground clearance, I thought a skid would suffice especially as the aircraft would be tail heavy when empty. That's why I included the lower fin.

    Tomo, a young man's acceptance of the idea is very uplifting, thanks for your support. Although I used to be a good artist/draftsman in my youth, these aren't drawings. ShetchUp is a 3D modelling program originally devised for making models to be included in/on GoogleEarth. I just printed the screen and copied into my picture files.
     
  6. pylon500

    pylon500 Active Member

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    What, no coaxial contra-rotating propellors? :ah_oh:
    Sorry Doug ;)
    I'm afraid that that layout is usually only done to prove a point (and has been done so a few times), I've just never figured what the point was. :raise_eyebrow:
    Maybe an exercise in problem solving?
    As concepts go, yep, pushers are OK, only have to deal with varying pilot weights.
    Tube/Boom rear fuselages are a simple solution to weight and manufacture times, but require careful attachment detail.
    Cruciform tails help alleviate adverse rudder roll and slipstream yaw, although there's always the problem of rotation and flare.
    My personal suggestions for a 'like' layout would tend more towards the vampire concept;
    IE build everything around a wing centre section, pilot hangs off front, engine sits in the middle, shorter wings hang off the ends of the centre section having less attaching load due to span load and twin booms surround and protect the prop while carrying the tail surfaces.
    My choice would be an inverted V tail.
    When it comes to foam and plywood ribs, the plywood usually makes the foam redundant.
    A thin layer of glass and epoxy would be plenty, or just use slightly thicker ply and cut out the centres.
    When you say two tubes for the wings, do you mean a large tube as a main spar and a smaller one set at the leading edge?
    Canter lever tube spars bend a lot and really mess up any wing sheeting (ask anyone with a BD-5)
    There is a lot of wasted material in a large tube spar, from a strength to weight ratio point of view, an I beam is usually lighter especially when combined with a D shell leading edge.
    If you have a D shell, what's the front tube for?

    Nice drawings though, I must play with sketchup some more.

    Arthur.
     
  7. ozzie

    ozzie Well-Known Member

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    Cohen Avenger

    Steve designed this in 1983 extremley simple, other than the tail it is all straight tube and plate. the seat was a simple hammock design. the wing is two tubes for spars and a third for the drag spar with glass ribs laid up from a simple mould. wing covering was painted fabric. if building this today i would use sewn up ultralam for covering. The fuse and tail took a weekend to build from scratch the ribs were laid up over the next week would have been faster if we had more moulds. the wing was built up and covered painted the following weekend. the powerplant was worked out during the following week and it was flown on the third weekend. two more were built next in the same time span.
    there were several engine setups. robyn 440cc direct drive and with cliff van pragg's belt redrive. 250cc robyn with redrive. or two 250cc direct drive engines. it was extremley robust. fun to fly, quick to set up and easy to trailer. simple and cheap to repair, this would be about as cheap as it can get without sacrifcing strength. great paddock basher. add a enclosed pod for those who get scared when outdoors.
    Ozzie
     

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  8. drifter_driver

    drifter_driver Member

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    mitchell p38 ultralight

    another design from eighties that looks similar to proposed concept.

    [​IMG]
     
  9. ozzie

    ozzie Well-Known Member

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    Ah the Mitchell P38 Lightning saw one of these at Mangalor 82 it did a stall turn and pancaked in.the fiberglass gear legs broke and it slid to a stop. six people picked it up, everyone grunted and complained about how heavy it was. tough bird tho. once again a straight forward and simple to build.
     
  10. sain

    sain Active Member

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    For a simple build process I've always been a fan of the skyranger aircraft. The whole "bolt everything together" concept is fantastic for fast build time with low-skill (no offense intended) workers.
     
  11. sain

    sain Active Member

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    Hmm.. interesting location on the prop - any thoughts on how to implement that? It looks like you've got it spinning around the tailboom, or did I misinterperet that? or is it just a very-early-concept-how-the-heck-do-i-work-this-software thing?

    Here are some links to some helpful-for-aircraft design software:
    http://aerodynamix.altervista.org/soft.htm list of a whole bunch of software
    http://gforge.katix.org/gf/project/zdesigner/ in-development aircraft design software
    http://xflr5.sourceforge.net/xflr5.htm free (open source) airfoil + wing analysis
    http://openfvm.sourceforge.net/ free (open source) CFD (fluid dynamics) sim
    http://http://www.calculix.de/ free FEM (finate element model) analysis (structural analysis tool)

    Hope some of that is helpful.
     
  12. Yenn

    Yenn Well-Known Member

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    I can't contribute to this as I am just going away for a month and by the way it is going it will be flying by then.
     
  13. Deskpilot

    Deskpilot Well-Known Member

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    Would have got back to you sooner guys but after spending a hour or so this morning, replying to your comments and questions, the missus interrupted my train of thought and, not thinking, I closed the wrong page. Lost the lot. All because of a bloody hair-do. :censored::censored::censored:

    So, back to the beginning.

    Sem, I know the Eastwood brothers vaguely and we have a Tyro in the hanger at Murray Bridge. I've seen Geoff demonstrate it and it fly's quite well, if you want a paddock basher. I think most builders would want something with a X-country ability and with more style. To my knowledge, the Tyro is still being produced, but don't quote me.
    The same goes for the Avenger, Mitchell Wing and any other 80's style pusher designs.
    Paddock bashers by today standards.

    Sain, please don't go side-tracking, this thread isn't about Kits you'd like to build.:closed:
    It's about taking a new design and making it work. The proposed model has been set in order to have everyone reading the same set of instructions instead of trying to convert it to what they want, if they were doing it. Now, what's the best way to go about it.
    Thanks for the links, I've had a quick look but need more time to look in detail. In answer to your question re prop position, yes, it revolves around the boom, read previous posts. Oh, and yes, there was, and will be, a lot of 'how-the-heck-do-I-work-this-software-thing' I'm not particularly pc and 3D modeling literate.

    Arthur. OK, tongue in cheek re contra-props but have you seen the new Hummingbird. Same principle but hugely more expensive
    http://esotec.co.nz/hb/HTML/HomePage2_F.html
    I first became away of this setup when I saw a Fantrainer photo. It was different from the norm and I liked the set-up. It obviously works albeit with the emmpenage secured by going round the prop instead of through it. I'm guessing, but I suspect the positives about it is that there is no 'shadowing' of the tail assy, more direct airflow on the tail control surfaces resulting in a more responsive aircraft. Rather like the thrust effect from the trail edge of a birds wing. It's power doesn't come from it's beak :laugh:

    Weights and balances: Yes, a problem. So how do we overcome it. A sliding cockpit for example, but that's a bit complicated. How about a set of coordinates for build mods dependent on proposed pilots weight. Ah, don't forget, we have a choice of engines, all of different weights. How do we come up with a simple solution that fits the majority if not all potential builder/fliers?

    Boom design: I know that there are some difficulties to over come particularly around the inlet side of the prop hub. Localized stresses need to be dissipated, but how. An inner tube riveted through the outer? Rivets = stress points? Any other way? Also, the tail feathers. Dependent on the style you choose, fixing them to the tube.....a lot more rivets. Would a slip on tube work as stated in a previous post. What torsional problems would there be?

    Tail Feathers: I have considered H, Y and Cruciform. V's and inverted V's don't appeal to me. Why do you choose that option?

    Vampire: I to, like the Vampire. Great little plane. But I don't want to re-invent the wheel. There are a lot of twin boom pusher types out there. Now, if we could take the Vampire pod, wings and engine, with a single boom where I'd like it to be, that would be quite near the ultimate design I'm after. Just got to find a way to build it easily and cheaply. Hey, we could have our own Squadron :thumb_up: You with me?

    Wing design: I opted for the foam sandwich as it's simple and fast. Duplicating the ribs wouldn't put anyone off. Fiberglass is messy and quite daunting for the inexperienced but I take on board what you've suggested. Same goes for just using thicker plywood. The right power tools would made the easier. I forgot to mention in my preamble that detachable wings is a design requirement (more complications) because we can't afford our own hangers, can we guys? So, Spar design = tubes, not 'I' beams or wooden boxes (too heavy?) 3 are stronger than one so, can we get two tubes to slip one over the other without excessive play? What sizes are available, can we achieve a sliding fit? I do propose the large one for the main spar and a smaller one for the leading edge. Is there a problem with that? The plywood over the L/edge is not to create a D box per say. It's just to eliminate the scalloping effect with the rag skins. I don't know the history of the DB5 so what gives? Can we design around it as I don't want struts and wires, they're so ugly.

    Right, time for the news, or lack of. Keep the questions coming guys, but don't forget, we need answers/suggestions as well.
     

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  14. Deskpilot

    Deskpilot Well-Known Member

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    Now that's what I like, a really positive outlook. Good onya Yenn :clap::clap::clap:
     
  15. sain

    sain Active Member

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    Deskpilot, the skyranger reference was more along the lines of a suggestion as to how the plane could go together to fullfill your
    "3. Only a few hand tools and no specialist skills needed to assemble the final design."
    requirement.
    Your design seems to support the "bolt it all together" concept quite well, at least to my eye.

    It was not intended as a build-this-instead suggestion. Sorry about that.:blush:
     
  16. hihosland

    hihosland Active Member

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    While mentioning the Skyranger it would be worth while looking at that "rib free" wing construction system.

    If one is to build the minimum/minimum-cost aircraft I do not understand the aversion to the scolloped wing surface. To avoid it is going to add complexity, cost and weight.
    'dems my thoughts
    Davidh
     
  17. Deskpilot

    Deskpilot Well-Known Member

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    Point taken Sain, no offense meant.

    DavidH, whilst I refer to this project as an ultralight, it's not meant to be recreating something of the 80's. Sure I want to use those simple skills, but update the design to modern standards. I've attached a hand modded picture of what I'm aiming for but it doesn't have to have the 'molded pod' look. Just some form of 'stream-lining'. A performance approaching 80knots would be desirable. Is it too much to ask? Do you think I expecting too much?
     

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  18. hihosland

    hihosland Active Member

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    Deskpilot did ask "Do you think I expecting too much?"

    No not at all. I wholeheartedly endorse your project.

    All I was suggesting is that there is a lot of designs out there that would meet many of your desires. The Skyranger wing, the Tyro, the Back Yard flyer, the Bantam all having attributes that are worth serious consideration.

    Although none of them have you preferred propeller configuration.

    When it crashes there is some merit in having the heavy bits arrive first and the floppy bits arriving later. In a light weight pusher config there is the risk of the pilot being sandwiched between stationary mother earth and a still flying engine.

    Davidh
     
  19. ozzie

    ozzie Well-Known Member

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    Ron Wheeler and i were watching a Hovey Wing Ding (a bi plane pusher with the pilot way out in front) flying around. He said that it looked a bit like going into a fight leading with your chin.:laugh:
     
  20. Deskpilot

    Deskpilot Well-Known Member

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    Crashes, CRASHES. Who'd dare suggest such a thing ;) :laugh: If you're gunna go, go quickly, I say.

    Being serious for a bit, whats the correct definition of the compression tube in a wing. Damned if I can find a decent explanation. Same goes for compression rib. Any one have a good drawing of all wing components?
     

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