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Thread: Low aspect ratio ultralight

  1. #91
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    Re: Low aspect ratio ultralight

    Dana, the idea of shafts and gears is starting to look like a simplest of solutions after all. The shafts don't need a universal joint at the wing fold joint, they can be bellow the wing joint and simply plug into and unplug from a rubberized receptacle on the other shaft. Simple and easy, and reliable and cheap.

    This way one or two engines sit sideways behind the pilot and belts to a shaft running cross ways behind the spar. With two engines overrunning clutches can be used to automatically remove a failed engine from the drive system.

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    Re: Low aspect ratio ultralight

    Bruce, concerning the wing tip vortexes, I appeared to disagree with you earlier so let me explain.

    The propellers do eliminate the wing tip vortexes at the wings. Earlier I said that the system mainly moves the vortexes outboard, but this is way downstream from the plane. It seems to me that in spite of the local 'distortions' caused by the props that with anything creating lift the flow pattern will eventually resolve into the classic vortex pattern that you see in aircraft. With the XF5U system this takes a while to settle down. So you are right, at the aircraft the props eliminate the wing tip vortex.
    Last edited by Starman; February 6th, 2010 at 06:18 PM.

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    Re: Low aspect ratio ultralight

    ... at the aircraft the props eliminate the wing tip vortex.
    And at the aircraft is the important part

    Here is a front view with 8ft diameter props and 12ft between the prop centers.
    Attached Thumbnails Attached Thumbnails Low aspect ratio ultralight-ulf1.jpg  

  4. #94
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    Re: Low aspect ratio ultralight

    Re range, for sake of comparison the 35HP Cuyuna in my Kolb burns 3.3gph at cruise, so with the 5 gallon legal UL limit 2-3 hours is out of the question. Some planes burn less, of course, but I doubt a low AR design like yours would.

    Re driveshaft connections, good idea, a rubber spider coupling might be just the ticket... if you can find one that can handle the torque.


    Lots of torsional resonance issues, too.

    -Dana

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    Re: Low aspect ratio ultralight

    A coupling something like that, I don't know if they are made out of aluminum but it will be easy to make a couple out of aluminum with a water jet, which can also cut out the rubber spider.

    Yes, there will be a lot of torsional vibration potential with two single cylinder two strokes running on the same shaft and with an overall shaft length of 22 feet from one propeller flange to the other! But I have a surefire and easy plan to solve it, which will also allow the props to angle outwards and still use 90 bevel gears

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    Re: Low aspect ratio ultralight

    Here's a top view. Length is 19.5', width is 19.25', MAC is14.5' and wingspan is 15', for a wing area of about 220 sq.ft. and a 2lb/sq.ft. wing loading at 440lb gross weight.

    These are the possible engines:
    The MZ100 - 2 X 100cc - 2 X 18hp = 62lb
    The MZ34 - 2 X 313cc - 2 X 30hp = 84lb
    Attached Thumbnails Attached Thumbnails Low aspect ratio ultralight-ult1.jpg   Low aspect ratio ultralight-mz100.jpg   Low aspect ratio ultralight-mz34.jpg  

    Low aspect ratio ultralight-ulf1.jpg  
    Last edited by Starman; February 7th, 2010 at 04:02 AM. Reason: to update front view

  7. #97
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    Re: Low aspect ratio ultralight

    Quote Originally Posted by Dana View Post
    Re range, for sake of comparison the 35HP Cuyuna in my Kolb burns 3.3gph at cruise, so with the 5 gallon legal UL limit 2-3 hours is out of the question.
    About what percent of your full power are you using for that fuel consumption rate?

    This plane is so streamlined that it will take very little power once it gets up to the top UL speed and the induced drag becomes even less, so it could get very good range. With the wing tip props canceling the wing tip vortexes ideally the plane should have an infinite 'imaginary' span, and an infinitely large aspect ratio, or something.

    Drive train is a piece of cake
    Last edited by Starman; February 7th, 2010 at 01:22 AM.

  8. #98
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    Re: Low aspect ratio ultralight

    With your numbers above and the 440lb gross,

    How much of this is the engines, drivesystem to prop, tank and fuel weight allowances?

    Given a 5 gallon tank, your range is going to be fairly limited under the rules with twin engine setup. As Dana said 3.3gph with a single may give 60 minutes with a margin of safety, a twin engine setup with drives to wing tip props will come at a big weight disadvantage and have much greater frictional losses. This will cost power at the props and lead to a much shorter range and could even be as little as 45 mins to a empty tank.

    Only if you can ignore the rules will a reasonable range be possible, but if additional tanks can be considered luggage and you go on a serious diet of bread and water then maybe?

    So if in the rules a reasonable range would be 35-40 minutes max before playing engine out roulette.

    At such a range a all electric setup is very possible with a reasonable price and many benefits design wise. If your drag in cruise is very low then range might extend as far as 60 minutes using fuel burners. The electric however also gains not only by having very low frictional losses, but benefits from the very low cooling drag compared to a combustion engine.

    This brings up how are you going to cool your engines buried in the fuselage?

    So following this line of thinking ,we need a electric system that can give 40hp at takeoff and 20hp at cruise for 1 hour and have say a 10 minute safety.If a electric is far more efficent at creating thrust than a fuel burner and with no power sapping drivetrain, it should need less actual output in a real world situation. So lets assume only 35hp at takeoff and 17.5 for cruise for level flight.

    I reckon a decent all electric is quite feasable. It is at the low scale numbers and low range numbers for your design that electric works best at.

    Phil

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    Re: Low aspect ratio ultralight

    Here is the quick n' easy sure fire torsional vibrationless drive train layout for shaft drive, looking at it from above.

    1. propeller shaft - moderate stiffness
    2. 90 deg bevel gearbox
    3. drive shaft - high stiffness
    4. spider coupling @ hinge line - w. pliable rubber shock absorber
    5. soft torsion bar - rolls up 50 deg at max torque
    6. engine torque tube - very stiff
    7. two stroke engine
    8. belt drive with built in over running clutch
    9. middle Xsoft torsion bar - rolls up 85 deg at max torque

    The middle (extra soft) torsion bar #9 is curved to accommodate the prop shaft angles and might need a middle support bearing.

    Torsion bar #5 (soft) isolates the propeller gear boxes from the engine pulses, aided by the rubber spider coupling.

    The softer torsion bar #9 isolates the two engine pulses from each other and since it is softer it isolates shafts #5 from each other to prevent possibility of resonances between the two sides.

    Precision engine alignment with prop drive shaft #3 isn't needed because of the flexibility of torsion bar #5.
    Attached Thumbnails Attached Thumbnails Low aspect ratio ultralight-uldrive.jpg  
    Last edited by Starman; February 7th, 2010 at 06:57 AM.

  10. #100
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    Re: Low aspect ratio ultralight

    What are bars # 5 and 9 made from?

  11. #101
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    Re: Low aspect ratio ultralight

    Quote Originally Posted by Starman View Post
    About what percent of your full power are you using for that fuel consumption rate?
    I don't know; I've not seen HP curves for my engine (ULII-02). There are curves in the Cuyuna 430 brochure but I don't think it's quite the same. At any rate, that's cruising at 56-5800 rpm (static WOT is 6500).

    I don't know about your "extra soft" torsion bars. Some good engineering analysis is needed there.

    -Dana

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    Re: Low aspect ratio ultralight

    Quote Originally Posted by litespeed View Post
    So following this line of thinking ,we need a electric system that can give 40hp at takeoff and 20hp at cruise for 1 hour ...

    I reckon a decent all electric is quite feasable. It is at the low scale numbers and low range numbers for your design that electric works best at.
    Then how much would you guess, roughly what would it cost to buy batteries to supply one hour at 20hp? And about how much would that weigh? ball park is good.

  13. #103
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    Re: Low aspect ratio ultralight

    The Prius battery has an energy density of 45 Watts-hr/kg. I chose this one because the maker needed to balance weight vs cost. I expect you'd be willing to pay a little more for slightly less weight.

    20hp-hr is about 15000 W-hr.

    330kg, or about 730 lbs.

    Ouch.

    I'm sure you can find lighter, but's that's the ballpark you're looking for.

    Toyota Prius Battery - Information on the history, specifications, modifications and future development of the hybrid's battery pack.

  14. #104
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    Re: Low aspect ratio ultralight

    Quote Originally Posted by JimCovington View Post
    What are bars # 5 and 9 made from?
    I'm thinking spring steel solid bars would be best, also easiest to make and to tune. Concerning tuning, the torsional flexibilities I used in the first example is like maximums, it should be able to get by with a lot smaller amount of flexibility, like only ten degrees of windup at max torque but more is better.

    Front view with wings up
    Attached Thumbnails Attached Thumbnails Low aspect ratio ultralight-ulf1.jpg  

  15. #105
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    Re: Low aspect ratio ultralight

    Have you considered using articulated propellors like the V-173?

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