Need advice on ultralight idea

Discussion in 'The light stuff area' started by GeneG, Jul 6, 2019.

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  1. Jul 6, 2019 #1

    GeneG

    GeneG

    GeneG

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    Hello all,
    Long time lurker, would like some guidance.

    I am interested in building an electric part 103 ultralight.
    My preferences are to build an aluminum aircraft similar in profile to the teenie two.
    My idea is to have it a mid wing, twin engine pusher plane.

    Some specific design info:
    the 2 motors would produce 15 horsepower at 11 kw and about 140? pounds thrust each.
    These would placed aft wing in the middle wing section which is permanantly attached to the fuselage. This section would be between 7 and 8 feet.
    Also located in the wing section would be the removable battery packs, the controllers and associated items.
    The outer wing sections would be removable like the teenie and would be approximatly 8 feet each producing a span of 23 to 24 feet, but can certainly be more. Construction similar to the Zenith CH750.
    I am thinking of a naca 4412 or similar airfoil, but welcome recommendations.
    I am not sure if I would need flaps or flaperons to meet the minimum stall speed.
    By moving all of the power system and weight to the wing area the wing can be moved rearward resulting in the spar carry through being aft of the pilot.
    I am open as to the tail feathers.

    The motors with props will weigh about 25 pounds each. I am considering ivo props, but would like recommendations.
    The controllers would weigh about 4.5 pounds each.
    The batteries will weigh in the area of 30 pounds each and can be installed in parallel as required. They will provide approx 60 amp hour at 92 volts each and measure about 20 inches by 16 inches by 3.5 inches.
    Additional batteries of 30 or 60 amp hours could be simply plugged in. I would argue that the 30 amp hour batteries at 30 pounds total would equal the 5 gallon fuel allowance. Since they are located just aft of the main spar, weight and balance is negligable.

    Adding up the minimum battery weights, the total power plant and fuel will weigh about 120 pounds.
    The power systems are completely separate and redundant. In case of a failure, the stopped drive can be prevented from freewheeling by shorting the stator.

    Thanks for your indulgence,
    Gene
     
  2. Jul 6, 2019 #2

    Tiger Tim

    Tiger Tim

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    From the sounds of things, it’s unlikely that you’ll be within the Part 103 limits. It seems like a decent analog for what you have in mind would be the Cri-Cri which is quite light due to its small size but also because of its size it’s much too fast (tiny wing has to go fast to make enough lift) to fit in the constraints of an ultralight.

    I can expand on some rough benchmarks I used to estimate this but it will have to wait for another time. It’s 2am here and I should get some sleep.
     
  3. Jul 6, 2019 #3

    Dana

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    Take a look at Advisory Circular AC103-7, I don't have a link handy but google will find it. In particular, the appendices to the AC contain tables intended to be used to determine whether an ultralight meets the legal limits... but they're also great for preliminary sizing of an ultralight intended to be legal.

    As for batteries, the FAA has said that battery weight can not be considered as "fuel" but must be included in the 254# empty weight limit.
     
  4. Jul 6, 2019 #4

    GeneG

    GeneG

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    I am familiar with the regs. I was unfamiliar with the fuel denial. I can however use the smaller packs and still be operable saving about 30 pounds. I can then add packs as baggage where needed.

    Thank you
     
  5. Jul 6, 2019 #5

    TFF

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    I would build a Hummel UL and test your motors. Once you know what the problems are, it will be easier to design in the fixes to your own design. Hummels have already paired down the T2, so they make a good place to start anyway instead of reinventing the wheel.
     
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  6. Jul 6, 2019 #6

    GeneG

    GeneG

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    The problem with that approach is that the redistribution of the drive train would necessarily move the wing.

    The original teenie weighed 306 pounds. A typical vw powerplant with prop etc without accessories is around 160 pounds. My total power train is fully 40 pounds lighter to start, bringing the total weight close to 265 pounds. II do have latitude in the powertrain to easily overcome this if needed.

    Lightening the ribs with holes saves about 3.5 pounds to go towards the additional length. Using a lighter spar assembly like the zenith one will also save weight.

    the wings will be almost equal to the ultracruiser so the l/d and flight performance are known.
     
  7. Jul 6, 2019 #7

    TFF

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    Like most turbine from piston conversions, the nose gets extended for CG. The relationship of motor forward, wing, and tail will be about the same no matter what shape you want. It’s going to have a long nose. I think the big design slowdown is going to be mid wing. It’s probably the heaviest way to mount a wing. Cool looking for sure. It’s also uses up more cockpit space. Wing, top or bottom, gets to piggyback on structure that already has to be there; automatic weight savings.

    I’m a fan of the T2. First plans I ever bought. I never built or flown one, but I did own a wrecked one in high school that I dissected. I was not going to save it, and it was probably one of the more crude ones built, which now actually gives me confidence in the design. The only elegance in the design is its simplicity. Even if you go T2 more than Hummel, knowing where the fat was cut would be a win.
     
  8. Jul 6, 2019 #8

    pictsidhe

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    If you move the pilot cg away from the plane cg, changing his/her weight will move the cg. These stressed skin tin planes are not easy to design or redesign. The Hummel is the evolved Teeny, a huge amount of work was done to get it to make weight. It doesn't really meet stall, but hasn't been called on that. It would be a much better starting point. By far the easiest option is to replace the 1/2VW with a single electric motor and battery pack. Once you start moving structural parts, the difficulty of the job will snowball. It may be possible to use a larger prop and gain a bit of propulsive efficiency over the 1/2 VW.

    Baggage battery packs would not be legal.
     
  9. Jul 6, 2019 #9

    GeneG

    GeneG

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    Since I am moving about 200 pounds from the very nose, to a small arm aft of the spar, a long nose is not the answer.
    The through spar is located between 2 angles embedded at that location. I believe that the structure can easily be engineered to accomplish this.

    Most of the fat was cut from lightening holes and lighter materials. Cal Parker did mention that the skins were 2 times the thickness required, and indeed were thicker than Cessna used in their smaller offerings.

    I offer the teeny for the fact that it is easier to construct, but am completely open to the final looks even though unlike others I don't find the looks unattractive:
     

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  10. Jul 6, 2019 #10

    BJC

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    A few things that you may already have considered:

    The original Teenie was modified by the developer into the improved Teenie 2, which, through additional modifications morphed into the Hummel series, one of which is advertised as being capable of meeting Part 103 criteria for an ultralight. Understanding all the mods from the original Teenie would be very instructive.

    Teenie sized wings, with minimal area and a relative short chord, operate at low Reynolds numbers, and getting assumed Cl max, for meeting the stall speed requirement, is challenging.

    With pusher propellers on the TE of a wing, it will be difficult to achieve the same propeller efficiency as a tractor configuration.

    Performance of batteries and controllers should be carefully assessed for actual, deliverable energy. Pay particular attention to the energy available for a go-around at the end of a flight.

    There have been some generously funded electric light aircraft development efforts. It would be instructive to research the reasons that most have been relegated to PR for the sponsors.

    None of this is intended to discourage you; it is intended as a reminder that the best way to learn is through mistakes - already made by others.


    BJC
     
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  11. Jul 6, 2019 #11

    GeneG

    GeneG

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    The pilot cg will be only slightly forward of the aircraft CG.
    I am uninterested in a front prop electric Hummelbird.
    I have provided a fairly comprehensive outline of the power system. It uses mostly off the shelf, commercially available proven technology save for thrust testing.
    The motors can easily be overloaded to make considerably higher thrust for a limited time. The only missing components are the hub mounts which I can initially fabricate myself.

    I could provide redrive units easily should that be necessary, but for now, I am looking at 48 inch 2 bladed ivoprops.

    Thank you for your input.
     
  12. Jul 6, 2019 #12

    GeneG

    GeneG

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    Teenie sized wings, with minimal area and a relative short chord, operate at low Reynolds numbers, and getting assumed Cl max, for meeting the stall speed requirement, is challenging.

    I did specify wings with an increased span and different airfoil. I also mentioned that I may need flaps or flaperons

    With pusher propellers on the TE of a wing, it will be difficult to achieve the same propeller efficiency as a tractor configuration.

    Cabin noise reduction is my goal here.

    Performance of batteries and controllers should be carefully assessed for actual, deliverable energy. Pay particular attention to the energy available for a go-around at the end of a flight.

    Commercial controllers are available and can provide the required power.
    The battery discharge rate is well within continuous drain specs of the manufacture. I need info from you guys on the required thrust requirements for climb and cruise to asses the true requirement. Aircraft design is not my strong point though I am somewhat conversant with the principals.

    Thanks for the reply.

    There have been some generously funded electric light aircraft development efforts. It would be instructive to research the reasons that most have been relegated to PR for the sponsors.

    None of this is intended to discourage you; it is intended as a reminder that the best way to learn is through mistakes - already made by others.


    BJC[/QUOTE]
     
  13. Jul 6, 2019 #13

    pictsidhe

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    If aircraft design is not your strong point, a monocoque is going to be very challenging. I doubt that the power system will be the hard part. Making the rest of the plane light yet strong enough to carry it will be.

    Without knowing span, wing area, excressances, we can't even guess at how much drag you'll have. The 103 appendices have calculations to estimate drag so that you can legally use X hp and skip top speed testing. They should give you a ballpark Cd0. Minimum power will be when Cd0=Cdi. You'll need to calculate the speed for that. Once you have some ballpark numbers, you can see if your idea will fly like an eagle, or a turkey.

    As an example, some ultralights use a calculated 40hp engine. My 103 project is currently looking at a calculated 15hp.
     
  14. Jul 6, 2019 #14

    BBerson

    BBerson

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    Morry Hummel's design was a modification of the very light Watson Windwagon, not Teenie Two.
     
  15. Jul 6, 2019 #15

    BJC

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  16. Jul 6, 2019 #16

    GeneG

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  17. Jul 6, 2019 #17

    TFF

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    I did not catch you were putting the motors at the wing. Fuselage component placements would be more like Sonex Jet or BD5 then, I would think. The skin may be thicker than a C150; I would have to check. I would say that without the skin being as thick as it is, it would be very fragile on the ground. I’m pretty sure that is the way the Hummel UL is. Fragile. I believe Morry Hummel built a T2 in the beginning. I think it’s still registered.
     
  18. Jul 6, 2019 #18

    GeneG

    GeneG

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    Putting the batteries and controller just behind the main spar and the motors attached to the rear spar, the cables are kept short and therefore light and efficient.

    I believe that the leading edge on a c150 is .032 as opposed to .040 while the skins are .016 instead of .020. I will however be using 6061 instead of 2024 so if I can, the thickness is fine.

    Thanks again
     
  19. Jul 6, 2019 #19

    TFF

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    I believe the C150 skins are either .025 or .020 depending on the year. T2 skins are I think .020. .040 skin is about bulletproof. Maybe a bonanza.
     
  20. Jul 6, 2019 #20

    GeneG

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    Just checked the manual. All skins are .020 2024t3
    All bulkheads and the main spar is .040 2024 t3
    The spar webs and longerons are 1.5 by 1.5 1/8" 6061 t6

    Total aluminum material
    3 sheets 4 x 12 2024 t3
    1 sheet 4 x 12 2024 t3
    75 feet of 1.5 x 1.5 x 1/8 inch 6061 t6
     

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