Some design musings

Discussion in 'Hangar Flying' started by rtfm, Jan 14, 2014.

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  1. Feb 11, 2015 #361

    Head in the clouds

    Head in the clouds

    Head in the clouds

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    Well as Jay said, that all looks pretty sane, a clear sign that you're under pressure from the house move I suppose?

    Something like that would have good market potential I think but keeping the weight within limits will be your big challenge.

    A couple of points - you need to get familiar with Pt103 - you can't have a 75kt cruise so there's no point in designing for it, it will only be a weight hindrance. Your max S&L speed is 63mph/55kt/100kmhr, power-off stall speed must be less than 24kt/28mph/45kmhr (no mention that it has to be clean but I'm sure you're going to need about 20% more wing area unless you have an airfoil with exceptionally high CL), max empty weight of 254lb/115kg, max fuel 5gals/19lt - the fuel restriction benefits a series hybrid to get more endurance/range provided you can get down to the max empty weight which, with a 26.5hp MZ175 at 15kg, is possible but not easy.

    I'd stick with a 10hp electric motor, don't forget they have far more torque than an ICE and you can overload them for short bursts provided the cooling is effective.

    I would raise the electric motor to get the prop higher so as to avoid FOD from stones thrown up by the nosewheel - they do get thrown up even with the best wheelpants, mud flap or whatever device unless it's a flat plate under the prop, because the stones might get deflected down initially but they bounce back up again - guaranteed - and it doesn't take many prop strikes on full take-off power to wreck the prop.

    I would get rid of the cranks in the mainspar for structural and ease-of-fabrication reasons, particularly since you need the wings to be removable so they would presumably have plug-in stubs extending from the spars of the wing panels, those stubs would be most easily resolved into the wingbox if they slide in parallel to the wingbox spar.
     
  2. Feb 11, 2015 #362

    rtfm

    rtfm

    rtfm

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    Ha ha. I could put half a dozen small electric motors along the wing and have a 12-motor pure electric plane... and mount a small 2T motor in the back somewhere just to charge them That might be fun.

    My main concern is the wingspan. 28ft is (in my mind) very wide - I'd prefer half that.

    HITC
    Yes, I've read Part103 a few times, and understand the weight, speed and fuel limits. My first cut (above) exceed these limits, which s why I said I have more work to do on the weight and speed issues. But for now, they are a reasonable starting point.

    I have some packing to do today, but I'm sure I'll find some time to sit at the laptop and muse some more.

    Duncan
     
  3. Feb 11, 2015 #363

    Head in the clouds

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    Yes, there are a few threads about that too - this is a good one.

    Don't forget to familiarise yourself with AC103-7 as far as actual wing sizing is concerned, it provides formulae which avoids real-life testing to prove compliance.

    And there are a number of discussion threads about AC103 to search out on HBA including this current one.
     
  4. Feb 12, 2015 #364

    rtfm

    rtfm

    rtfm

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    Hi,Thanks Alan.
    Well, that used up my morning...

    So, sticking to what I have already spent months working on, here is my e-pt103 design proposal.

    Three electric motors sitting on each wing like eager birds on a wire...

    RTFM e-pt103 1.png RTFM e-pt103 2.png

    Looks like a smaller version of the Razorback, but with a small ICE and six (6) high-end RC electric motors. I put in a lot of work on the Razorback, and it doesn't make much sense to throw that all away just for the sake of novelty. Keep it in the family, I say... This is open cockpit, very small fuse (more like an extended cowl ending in a seat and a tail. It might even be fun to sit on it, rather than in it. Sort of like a sealed cockpit area, with built in Belite multi function panel, place for my iPad (also like the Belite) with legs on either side of the fuse shielded by mini-leg fairings. Very air-bike-like.

    I have only a slender grasp of the intricacies of electronics, so don't ask. HITC will (hopefully) help me with that side of things. In fact, one of the e-motors will run flat out for 6 minutes on two RC LiPo batteries. What's not to like about that? But I'll go with the safer LiFePO4 power packs HITC is using.

    Right now all I'm trying to do is to come up with a napkin design to get me started.

    Stall: 24kts
    Max level speed: 55kts
    MAUW: 240lbs

    ICE: 20hp (The small block Vanguard weighs only 23kg - it might be a contender. My figures use 30kg just in case)
    E-motors: 6x Hobby King Turnigy CA80-80 Brushless Outrunner (rated at 5hp ea) spinning 20x14 APC props.
    This gives 50hp (theoretical) for takeoff and emergencies, and (after charging duties have been undertaken, sufficient power to fly the plane at 55kts using only the ICE.

    Because I'm using six RC e-motors, a failure in any one motor will not be that significant. And they're cheap (about $200 ea). If this works, I can always upgrade to higher spec motors. Or not... Turnigy has a pretty good track record.

    As I say - no details, just a basic napkin sketch.

    Regards,
    Duncan
     
    Last edited: Feb 12, 2015
  5. Feb 15, 2015 #365

    autoreply

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    I like this one a lot.

    Ditch the cranked wing. Why bother focussing on a 24 kts stall speed? Unless you are legally forced to have it (FAR103, which is irrelevant to you right?), I wouldn't bother having it below 35 kts or so. Makes it a lot less marginal in more then minimum turbulence, lighter airframe etc.


    ICE at the back? Way quieter cockpit, but a bit harder to do the cooling well. ICE would favor a smaller prop, electric needs as big a prop as possible.
     
  6. Feb 15, 2015 #366

    rtfm

    rtfm

    rtfm

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    Hi,
    The consensus seems to be that the cranked wing has to go. Oh well. So much for aesthetics :)

    The idea at the moment IS to try a Pt103 plane. There are probably only two niches in the homebuilding market which have any promise of marketability: STOL and Pt103. My heart lies with fast glass (ie the Razorback), but if I ever hope to sell a few kits, it will probably be better to go with Pt103.

    The difficult thing is (of course) keeping the weight down, and then keeping the speed down. I can keep the speed down OK, but the weight is a bit of an issue (surprise surprise...) Anyway, it is a nice challenge.

    Duncan
     
  7. Feb 15, 2015 #367

    autoreply

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    I don't think so... at all. There is a niche for affordable single-seaters. Few people would put up with the 24 kts stall if they wouldn't have to.

    By constraining yourself to FAR103, you're enormously compromising the design and most truly legal FAR103 designs are pretty marginal.

    IMHO much better to go in the direction of the Luciole or Spacek SD1.
     
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  8. Feb 26, 2015 #368

    rtfm

    rtfm

    rtfm

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    Hi again,
    It seems that a joined biplane design (as I conceived it) will be too heavy, and quite difficult to construct. Besides, the plane just goes too fast even with minimal power to fit into Pt103

    I am still pondering both a single and a side-by-side design. But in the meantime...

    I have come up with a "modular" design for a Pt103 plane.

    Basically, the wing inner section, undercarriage, and tail boom will be a single integral unit.
    The wings are removable (sliding into the central section). And the "fuse" or pod is bolted on afterwards. Once the wings are removed, the basic superstructure of wing stubs, boom, and tail feathers, can be wheeled onto a trailer. Or into your garage or hangar.

    I will probably go with a tail-dragger undercarriage, but for the moment, it is tricycle. The pod can be enclosed, open, motorcycle-style, or simply a seat with the pilot out in the breeze. It doesn't matter. It just attaches to the main superstructure afterwards as a bolt-on extra. Wings are swept forward, allowing the pilot almost completely unobstructed views.

    The Pod:
    Glass/2mm cork sandwich. Reinforced at the rear engine mount, of course.

    Wings:
    Glass/2mm cork sandwich for the D-Tube. Fabric rear of the spar. Junkers flaps/ailerons. Junkers surfaces = foam core. The reason for using Junkers are many. First, there is no worry about the extra drag they create in cruise. Second, they are extremely effective. And third, they allow the wing to be built as an integral unit, with no worries about having to cut out flaps and ailerons. Junkers are a bit heavier, but I think there is room for that.

    The engine will be something like the Bailey Aviation 5V which is a 195cc 2 valve SOHC 4-stroke producing 20-odd HP, and weighing 17kg (just on 37lbs) - but probably detuned to produce about 12hp or so. Or I could go for the Polini Thor 200 or one of the other small PPG engines.

    The reason I can afford to use such tiny engines is that there will be six 8hp electric motors (3 on each wing) fed by a single 36Ah LiFePo4 battery. The engine will charge the battery at the same rate as it discharges,which is possible with the LiFePo4 battery available here in Aus. Even if the on-plane charging fails, the battery will power the motors for 8 minutes.

    So take-off power = 10 +6x8 = 58hp Whoo-hoo! Cruise power = 10hp + charging requirements

    Weight of the 6x electric motors = 10.8kg (23.75lbs). Weight of battery = (under 2 kg)

    I could opt for even smaller RC motors (something in the 5hp range) which might be cheaper, lighter and would still run off the 36Ah battery. There are a lot of possibilities, and they cost peanuts.

    The last pic is just the basic structure. The pod just bolts on.

    This has been a lot of fun.

    Using a combination of a small ICE and multiple electric motors takes Pt103 out of the "marginal" territory, and adds some real emergency power and reliability to the design.

    Regards,
    Duncan
    PS Please excuse the crude rendering. It is not my long suite, and besides, the X-Plane rendering engine for planes really sucks. But you get the idea.

    Ready for takeoff2.png Ready for takeoff3.png Ready for takeoff.png Over water.png Basic structure.png
     
    Last edited: Feb 26, 2015
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  9. Feb 26, 2015 #369

    autoreply

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    Why FAR103 when you live down under?
     
  10. Feb 26, 2015 #370

    rtfm

    rtfm

    rtfm

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    How many non-Aussie guys know about Civil Aviation Order 95.10?

    Duncan
     
  11. Feb 26, 2015 #371

    autoreply

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    I do (or thought I did) fairly intimately. Anything I missed that relates to FAR103?
     
  12. Feb 26, 2015 #372

    Hot Wings

    Hot Wings

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    I too am aware of it and it appears that you are allowed 300Kg and limited to 30Kg/M wing loading. Other than that you are pretty much free to do as you please - unless there is some fine print that we are missing?

    Unless you plan to move here, or want to sell a bunch of planes with no certification problems, why limit yourself to US part 103?
     
  13. Feb 26, 2015 #373

    Head in the clouds

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    Unfortunately 95.10 isn't as good for us from a manufacturing viewpoint as it might appear to be. Sure the design limitations are not at all onerous and a great little plane can be built within them, multi-engine, jet, whatever, but the problem is that it's no longer an unlicenced category. The planes have to be registered with all the cost and hassle that entails and the pilot must be an Association member with a Pilot Certificate. And - the planes cannot be factory built, they have to be homebuilt under the 51% rule.

    Given those constraints the market for a kit here is miniscule, so I think Duncan's thinking is that Pt103 provides a fairly large potential market in the USA for a factory built airframe due to the lack of registration and licencing requirements there.

    I have a bit of a Pt103 concept churning away in the back of my head too. I think that USA is probably ripe for a revival of the ultralight when something cheap, slow and easy to fly presents itself, but it has to be kindly enough for people to teach themselves to fly from a manual without ending up in the news. I think it can be done, time will tell.
     
  14. Feb 26, 2015 #374

    rtfm

    rtfm

    rtfm

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    Hi guys,
    The market for 95.10 (only in Aussie) is extremely small. Pt103 would be far larger. My idea is to aim to satisfy Pt103, and satisfy the local market as well by so doing. Possibly the weight limitations of part 103 will be too restrictive and difficult to meet. In which case, I can slide up to the 300kg allowed by 95.10, enjoy my personal fun machine, and (if the plane flies well, see if there are any local takers). It's a moving target...

    I will only know which design spec I can realistically aim for once I have built some test pieces to verify their weights. At the moment it is all on paper, based on some early test strips I made last year.

    Regards,
    Duncan
     
  15. Feb 26, 2015 #375

    Hot Wings

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    That does have some logic to it.

    Part 103 weights are restrictive, but it's also one of the reasons I find the group so interesting. Designing for part 103 is kind of like racing with a set of rules rather than in the unlimited class.
     
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  16. Feb 27, 2015 #376

    pictsidhe

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    I like the diamond biplane. If it's too fast, you can use a smaller and cheaper motor...
    As long as the wing area and power match the calculations in ac103.7, you should be fine.
     
    Last edited: Feb 27, 2015
  17. Feb 27, 2015 #377

    rtfm

    rtfm

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    Hi,
    I like the diamond biplane too. A lot. My reasoning behind going for a single wing for my Pt103/95.10 design, is that the monoplane is far easier to construct, is lighter and is more customisable (with respect to the pod which you decide to bolt onto the basic airframe. With the diamond biplane (I like that name for it, thanks) you are pretty well stuck with the fuse as it is, and putting it together is going to be more complex.

    However, it is my preferred design both for a single seat and a side-by-side design which I have been working on for months now. But they are significantly quicker planes...

    Regards,
    Duncan
     
  18. Feb 27, 2015 #378

    autoreply

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    So you're designing a plane for a category on the other side of the world with the remote option that you might ever be able to sell it. Look how many companies making enough money off FAR103's to earn a reasonable living, 2?

    Design and build something YOU want. Unless you do so, you will never finish a build or design.
     
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  19. Feb 27, 2015 #379

    WonderousMountain

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    Unless, you do. Then you'll have done it!...

    LuPi
     
  20. Feb 27, 2015 #380

    TFF

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    I would not waste your time on 103. It is a tinker class of aircraft. Some kits for sure, but its really a home grown class. Spend money on LSA or fast; they are the only thing that sells; kit wise. 103 builders dont want to spend any of thier money; a kit coming half way across the world will not be profitable. If you need to make money in the venture, make it simple and make it not glass. Both are problems you want. If you want glass, it better be a Glas/Lanc-air at half the price.
     

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