The future in an aircraft charging system

Discussion in 'Hangar Flying' started by Pops, Jun 18, 2019.

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  1. Jun 20, 2019 #21

    Hephaestus

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    I'd imagine you'd run 5 in series - 15v and then regulate down to 14.4 as you'd see on a normal auto style system. Smaller buck converter would drop the extra efficiently versus trying to boost.
     
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  2. Jun 20, 2019 #22

    Sockmonkey

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    I'm thinking use a little stirling engine as your coolant pump. It's saved HP as long as it doesn't weight more than a normal coolant pump, and will self-adjust match coolant flow to engine temp.

    One other thing you could do for an engine that uses a turbo is to drive the intake turbo with a belt like a supercharger and use an unconnected exhaust turbine to drive the alternator.
     
  3. Jun 20, 2019 #23

    Pops

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    On the above post #19, I was looking at one of my 40HP heads, it has more room than the angled single port and dual port heads. But a plate could be welded on the later heads to enlarge the area.

    Never a starter, I try to save as much weight as possible. Percentage wise its a huge increase in weight. For dual ignition, drill the heads for the spark plugs, use the GP's simple mag mount and the surplus Slick 4330 mag on the flywheel end and hand prop. Nothing is easier to hand prop than a VW.
    Easy to make a simple controller for the 12 volts.
     
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  4. Jun 20, 2019 #24

    Pops

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    Yep. Just pick out the voltage regulator that will handle the amps.
     
  5. Aug 20, 2019 #25

    12notes

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    I'm thinking of using these for my Hummelbird. Since the cylinders stick out of the cowl, my thought was to put this on an appropriately spaced plate on the bottom of the exhaust pipe, with the heat sink in the breeze/prop wash. I can position/adjust to get 300C on the hot side reliably, but I'm at a loss how to calculate cool side heat sink size with 100+mph of wind across it. The heat sink datasheet charts tend to stop at 800cfm, and I'll be using 9,000cfm.
     
  6. Aug 21, 2019 #26

    pictsidhe

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    If there is no data, you'll have to test. Unless you want to get into heat transfer mathematics. Testing will be quicker! There are many variables in a heat sink, so each one will follow a different curve as airspeed increases.
     
  7. Aug 21, 2019 #27

    AdrianS

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    Stirling engine sounds too complicated to me.

    The magnetic reduction gearbox I'm building is a prototype PTO/starter for a turbocharger-based gas turbine. We plan to drive it from the compresser side on an extension of the shaft.
    If it works, you could probably drive it off a normal turbocharger, although I have no idea what that would do to the boost profile.
    It probably won't be light, but neither is an alternator.

    Having started playing around with the latest magnets, I think the magneto generator could do with a re-think.
    I reckon you should be able to get 100 watts or so from magnets on the flywheel and coils facing them. There's a lot of homebuilt wind turbines doing that, at much lower RPM.
     
  8. Aug 21, 2019 #28

    pictsidhe

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    I suspect that a direct drive motor-generator would work better on a turbo-turbine. If you want mechanical work out, options are wider. But all will need work.
     
  9. Aug 21, 2019 #29

    Sockmonkey

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    They're actually pretty simple. People build working models out of junk around the house all the time. Naturally, for practical applications you want something properly made.
     
  10. Aug 22, 2019 #30

    Derswede

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    Wander around a ham radio flea market (i.e. a hamfest) and you will find lots of light AL heatsinks. My 1.2KW amp's cooling fin deck is about 2-3 lbs. The idea of a directed air blast would work well. I do have some surplus CPU heat sinks I'd pass to someone who would like to test the idea out and let us know the data generated.

    Derswede
     
  11. Aug 22, 2019 #31

    mm4440

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    TECs are just not practical for energy recovery. A turbo alternator makes more sense especially if integrated into a turbocharger,
     
  12. Aug 22, 2019 #32

    Vigilant1

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    Why? If we don't care about efficiency (because we have plenty of waste heat), and we have nearby/convenient flowing cool ambient air? Are these reverse Peltier chips unreliable or otherwise impractical for small wattage reqmts?
     
  13. Aug 22, 2019 #33

    12notes

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    Cooling air is about as convenient as you can get in the Hummelbird.

    I ordered two to play with. I'm also probably going to using a buck/boost converter so it will always provide the same voltage, rather than regulating down when up to temp and having low voltage at lower temperature differentials.
    [​IMG]
     

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    Last edited: Aug 22, 2019
  14. Aug 22, 2019 #34

    Derswede

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    If you want to try a heat sink, 12 Notes, let me know. Will probably be back in Princeton, KY in the next few weeks.

    Derswede
     
  15. Aug 22, 2019 #35

    12notes

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    Thanks for the offer, but I just found two of these 4 lb. monsters at work, from a project long since dead. 1/4 of this on each TEG should probably do it.

    I'm at least a month out from testing this, the engine needs assembling, and it'll take some tweaking to make a consistent 300C plate attached to the exhaust.
     

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  16. Aug 22, 2019 #36

    Aesquire

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  17. Aug 23, 2019 #37

    litespeed

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    It sounds good in theory. But I agree all the cooling drag could make it quite inefficient even with free heat.

    I would just use a small propped generator to get some watts.
    Simple and reliable.
     
  18. Aug 23, 2019 #38

    12notes

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    If I orient the heat sink into the airflow, and round the leading edges/taper the trailing edge, I would think it shouldn't be much more draggy than the cooling fins on the cylinders. That's just a guess, though.
    I have a propped generator I can mount, and I intend to make the heat sink/TEG/plate sandwich removable, so when I finish my plane (hopefully by the end of the year), I can test which has more drag.

    It can't really be an experimental without experiments, after all.
     
  19. Aug 23, 2019 #39

    Vigilant1

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    So, if you determine that the exhaust pipe at your mounting location is too hot for the TEG's, will you put a heat sink with fins between the pipe and the TEG plate, then much more generous fin area on the "cool" side of the TEG?
    I think the wild card will be operation across varying airflow rates (taxi, climb, cruise, post-flight shutdown/heat soaking). At the temps you are talking about, the difference across ambient air temps will be less important than the differences due to airflow rates. You might find you need some sort of shutter, maybe controlled by a bimetallic strip (like the vents on a greenhouse). It should be very interesting project, I think a benchtop rig with a fan/blower and a hotplate/burner plate will save you a lot of time.
     
  20. Aug 23, 2019 #40

    12notes

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    I plan on mounting the plate to a standoff (I have a few designs in mind) attached to the exhaust, controlling the heat transfer with the standoff contact area and an airgap. 300C at cruise would be nice, the TEG can stand up to 400C intermittently, but I'd like some safety margin so would probably set the cruise target at 280C, and full power should be ok if it's a bit over 300C. I'll have to research what the manufacturer means by "intermittently". With the buck/boost converter, the voltage will stay at 14.4, with the amperage of charging would dip while taxiing and peak while cilmbing. Since no flight system will be dependent on the charge, this is just a "nice to have" feature, and I plan on a LiFePO4 battery that will run everything else (radio, lights, etc.) for at least a couple of hours anyway. If I ever decide to upgrade the engine, I'll have capacity to run EFI. If not, I'll have the capability to do a long cross country at night, not that I'm planning on ever doing so.

    I was talking with my boss yesterday about testing this with a hotplate and a leaf blower, so we're thinking along the same lines.
     
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