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IBob

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Everything posted by IBob

  1. IBob
    Hi Meglin, I am interested in what you have written here, but I am not understanding part of it. I am guessing by resource you mean working life? Also 'bends and tends to break...'? Can you check your translation? Thanks.
  2. IBob
    An aside regarding the charging and trigger coils that provide the energy and the timing for the ignition: off topic, and has been mentioned before, but this seems like a good place to revisit it. The gap between these coils and the trigger magnet cams on the flywheel is critical: too wide a gap has been seen to give poor starting, even with a well maintained engine and battery system. This gap is given as 0.4 - 0.5mm (16 - 20 thou) for old type coils, 0.3 - 0.4mm (12 - 16 thou) for new type coils. It is not hard to locate these fittings on the back of the engine, but the gotcha is this: Because the feeler gauge is between the strong magnet of the cam and the coil, it will stick tightly to the cam, and feel like a good snug fit, even if it is not. Furthermore, when 'feeling' from the side' the feeler gauge has to be flexed to fit the gap, which also gives the illusion of a snug fit. We found it easiest to use the brass feeler gauges which are part of some sets; also to remove (unscrew) the required gauge from the set to give better 'feel'. In the absence of brass feeler gauges, it would be essential to ensure the next size up gauge was 'no-go'.
  3. IBob
    Plus one for the cranking: There is no electrical connection on the 912 between the battery and the ignition systems. The electricity for the ignition is generated by coils in the stator as the engine rotates, and the engine must rotate at a sufficient speed for that to happen. So, to start well and reliably, the engine needs to rotate briskly.
  4. IBob
    That, and hold them still at the front while doing them up from the back...
  5. IBob
    https://www.theguardian.com/world/2021/aug/11/canada-helicopter-dairy-queen
  6. IBob

    Barber Snark

    IBob commented on red750's aircraft in Recreational (3 Axis)

    Apparently they are a great aircraft, and unusually enjoyable for the pax too, as they get to see over the top........)
  7. IBob
    Yep. Which is why I think something shifting back under the front-to-rear-stick torque tube with the initial acceleration and stick back takeoff, making it then impossible to get the stick forward, is a possibility: all the preflight checks would go just fine.
  8. IBob
    Indeed. And if your life depended on it? Furthermore, that aircraft never reached any great speed, so the principal force acting on the trim would be from the propwash...
  9. IBob
    I think he's barking up the wrong tree entirely here: while the dual trim tabs will provide a powerful trim, I would be surprised if they would overpower the pilot's ability to move elevator down, especially as it slowed in the climb. Here's an alternative possible scenario: Note the horizontal green tube that links the front stick to the rear stick, close to the floor, clearly visible at 2.00 in the above video. With stick back, that tube is raised, pushing the stick forward will lower it. And any solid object that has slid back during takeoff, lodging under that bar, will prevent the pilot moving the stick forward. Something like the fire extinguisher, visible at 0:33 would do it. And that's all it would take....
  10. IBob
    Yes, you did splendidly! Though several others here are a bit hot and cross...which invariably seems to be part of these little brain teasers too.........(
  11. IBob
    Incorrect angle of a attack on the wings would also do it....but that's pretty much the same as saying the empennage is incorrectly aligned with reference to the wings.
  12. IBob
    Skippy, your exceedingly large packed lunch has slid to the tail of the aircraft while you were executing that blinding climbout.......)
  13. IBob
    So, is the stick full forward...or is it forward as far as it will now go???
  14. IBob
    Yep, probably a bit on the light side. It's classed as a motorcycle battery. My 912 starts first pop, so the battery has never really been 'tested'.
  15. IBob
    Unibat CBTX20CH-BS 12V18AH lead acid came with the kit, I've emailed for the spec, including weight. Works fine. Located behind the pilot and could be further back as the Savannah S tends to run out of elevator authority on landing rollout. Poor starting risks expensive damage to the 912 and good starting requires the engine to turn over briskly. So I fitted a battery negative cable (rather than relying on the aircraft hull), as others have done.
  16. IBob
    Definitely put the battery behind you: it'll help with low speed elevator authority on rollout.
  17. IBob
    The battery + goes to one terminal of the starter solenoid. That's the fat red cable. The output of the voltage regulator (B on the regulator) that keeps the battery charged goes to the the same terminal on the starter solenoid. Make up a short cable with lugs on the ends, and connect the + side of the capacitor to that same terminal on the starter solenoid. Make up another short cable with lugs and connect the - side of the capacitor to your negative bus point. The usual place for the capacitor in the Sav is at the RH end of the front shelf that carries the throttle bar etc. Best wait until you have the throttle bar etc in place, on the Sav there's not much room there.
  18. IBob
    Breakers and switches? I added one more of each to split out my Radio and Transponder. And you'll need some sort of cap to go on the + terminal of that capacitor so it doesn't bite you. But that's easily made out of a piece of hose, if need be.
  19. IBob
    If fitting a battery isolator, you will then need to fit a the large electrolytic capacitor to the voltage regulator output. The reason for this is that during normal running, the battery acts as a load to smooth the output of the regulator. If the electrics are switched off (and the battery isolated) for some reason with the engine still running, there is a the possibility of a large spike in the regulator voltage and damage to avionics etc. I think that's right............? Can't remember capacitor spec, but mark Kyle has written about it here, he'll know.
  20. IBob
    That's the one. Works fine for me.
  21. IBob
    Hi Marty. Couldn't agree more. First. I changed the regular bulb supplied for a large flashing LED. Then I put another in parallel to that on the LH side of the panel. The RS part number for the flashing LED I used is 209-119. It comes with it's own bezel.
  22. IBob
    That's wonderful, Skippy! I, on the other hand, have a fat wing that develops so much lift, I must take off before lunch if I am to have any hope of being on the ground by tea-time...........)
  23. IBob
    Hi Perry, in short, no. I don't know what the return flow is, but it's through a very small orifice and certainly would not cause the RH tank level to go up when running on 2 tanks. As I recall, I set off with approx 20L in each tank, by the time I got close to your place (20min?) I had less than 10 in the L and about 25 in the R. So I went home. When I got back, there was fuel staining on the upper RH wing. So the cap was not properly sealed, I had low pressure there and hi pressure in the L tank resulting in fuel crossfeeding. The question then becomes what happens if you fly the L tank to empty. Some think the fuel from the R tank would somehow then make it's way down. But I'm not so sure.
  24. IBob
    Cross sectional area of 2mm vent pipe = 3.14 x .1 x .1 = .0314 sq cm Aircraft at 80kts = 41M/sec = 4100cm/sec So air arriving at face of pipe = .0314 x 4100 = 129cc per sec. Fuel leaving tank = 15L/hr = 15000/3600 = 4.2cc per sec And that's for a very small pipe, with fuel taken from only one tank. So there is a huge imbalance between air arriving at pipe and fuel leaving the tank, and the result will be pressurisation of the tank, even with a very small pipe, and the relatively small amount of fuel taken will not offset that.
  25. IBob
    Only if it's a very tiny aperture: do the maths.
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