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RFguy

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About RFguy

  • Birthday 27/12/1970

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  • Aircraft
    J230D, PA28-180A
  • Location
    YCWR
  • Country
    Australia

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  1. too many engineers have never been technicians dont put diodes in parallel, they DO NOT current share. but by all means put two in parallel for redundancy, just rate each diode at the full requirement Diode- use a diode with a Vr of around 40V. that will have a far lower Vd than a 150V diode. If you like Vishay, suggest https://www.vishay.com/en/product/97219/ https://www.vishay.com/docs/97219/vs-175bgq045hn4.pdf At Tj=125 and If of 20A, it will have a Vforward of about 0.3V, IE about 7Watts to dissipate. bolt to a chunk of aluminium, at least 20 sq inches surface area, 3mm thick. it will need a silicon washer and bush under the tab against the heatsink, since the tabs are live.
  2. From my rather critical POV, the UL twin problem indicates the these issues are ahead / beyond the UL staff and the buy is goign to need ot odo their own system design , and perhaps get advice .... My thoughts are , isnt this an obvious failure mode / system design problem that should be a well worn path by now for UL. Beware of twin of anything in electronics, same goes for everything else. Ultimately, the error though lies with the pilots not doing their checklist (check alternator contribution / battery voltage post start)
  3. Advice on idle : (documentation : ROTAX OM915, 912 "Section 2.1 " engine start : for iS engines -Section "3.4) After engine start" "Set linearized throttle position in a way that the engine runs at approx. 2000 rpm for approx. 2 minutes." then "Set linearized throttle position in a way that the engine runs at approx. 2500 rpm until oil temperature reaches 50 °C (120 ° F)." If you run a 912ULS at 1400rpm you'll foul up the plugs because the mixture between front and rear cylinders goes wild. (one end goes rich - front ? cant remember) .
  4. The FI rotax does not begin to charge the battery until 7 seconds or so over 2500 RPM. So after oil pressure is established, need to get RPM up to 2550 etc so the battery starts charging, this is obvious by looking at the ship battery voltage. Until that time, the ship battery is in discharge for internal ship loads (and not yet being charged by ALT-B) The ALT-A begins to run the ECU at about 1200-1300 RPM, approx. Very low RPM in flight (how ?) might cause some ECU confusion and require ECU to be powered by the ship battery if RPM too low to run the system from ALT-A/B Just discussing the rotax here because it's a good example of how it can be done. Putting aside miscellaneous annoyances and sensor issues of the FI rotax.
  5. take a good look at the fuel injection pump current requirements under various condix, they can pull a fair bit, and that you might have BOTH pumps on due to design (or error ?) Given that good quality, sealed non liquid electrolyte batteries generally do not have sudden failures, it's probably a good option as a power source. a strong schottky diode or MOSFET schottky implementation with some sort of current limit would be a simple and reliable option. A big schottky with say only 20V 30V reverse barrier will be pretty low voltage drop. maybe something like 12 or 14 gauge wire will serve as a current limit....maybe aim for wire resistance = diode drop under normal conditions, as a starting point. that will be fine as long as the charging system gets up to 14.4 , 14.6V region
  6. Mike I gather the UL system has one alternator and one ship battery. usually the single alternator is doing double duty and I think that's a bad idea, since the engine systems are not isolated from the troubles and switches and breakers and ge-finger trouble of the user.... The only way to really get away from it is a 2nd power source., or perhaps an independent feed from the battery with its own isolation relay (or a 2nd battery only for the UL so that buys you an hour etc, and some switch that you can cut over the Ul to main ship battery- but then you have a single failure point in the cabin maybe.... so, some thought required to escape the single power feed issue. The UL systems having its own feed from the battery and own isolation switch etc is probably the simplist.
  7. Mike On the UL electrical - I wonder how the dual ECU setup power is set up. Given the issue and what you;'ve told me, it might be worthwhile to consider modifications / additional systems. a recent story... I know a bit about the electricals of 915 rotax's these days. I had to find/fix a charging intermittant. The Rotax has two alternators - A and B (ALT A, ALT B) A is rated about 15A, B at 30A. "A" normally runs the ECUs (all rotax electrical) (thru their 'fusebox/switchbox"), B is routed to the ship to run systems and charge the ship battery. . In case of a failure of ALT A, the the system commenderes the B ALT and the ship is cut loose to run on ship battery. At start because there is no A or B, ship power is routed to the ECU C input until A(or B) gets going) then once running the ship power source is removed. and I can confirm it all works well. Everything including the dual injection fuel pumps are powered from the rotax control box, nothing can stop the rotax once it's going.... (except individual ECUs can be disabled- LANE A, LANE B) . I've demonstrated removing the battery terminals while the prop was going AND disconnected the output of ALT-A and it fails over onto ALT-B immediately cutting the ship lose.
  8. the way it is described in the part91 / FAR USA regs is suitable, I will look it out. It describes the result / protection required, but not how it is acheived, IE as long as the intention is achieved. good regulation
  9. dunno if I would use an SSR in that service The SSR must be rated at the stall current, which is probably 2 x the battery CCA !
  10. surely those rectangular square cornered windows are no good for high cycle count airframe pressurization cycles?
  11. FWIW https://www.airservicesaustralia.com/aip/current/dap/BUNAD01-175_30NOV2023.pdf accident report at 1445 local
  12. remarkable only for experienced on type, no doubt . There has to be more to this. No sane pilot goes off into full on type crosswinds with little time on type. ....
  13. This is the sort of crash where you want the battery to have a isolator at the battery, like GA aircraft. Maybe even double pole. and have non cracking insulated covers on exposed terminals
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