| General > General Technical Chat |
| Ignition systems |
| << < (3/12) > >> |
| james_s:
--- Quote from: NiHaoMike on October 01, 2021, 04:25:26 am ---Aircraft ignition systems are indeed mostly capacitive discharge, except for the few that use high frequency inverters direct to the spark plug. --- End quote --- Turbine engine ignitions, including those used in aircraft work like that. They are very similar to the spark igniters used on gas cook stoves. Aircraft piston engines almost exclusively use magneto ignition of the same basic design as used during the dawn of powered flight. |
| bdunham7:
--- Quote from: David Hess on October 01, 2021, 03:42:22 am ---Aren't modern electronic ignitions all capacitive discharge? That would be where a capacitor discharges into the primary with the secondary stepping the voltage up. The advantage over Kettering ignition is that with the energy stored in the capacitor instead of the coil is that much higher power can be achieved. --- End quote --- No, actually, coils and their driving transistors have evolved to pretty high energies and CDI really never was all that widespread among OEMs. The only OEM application I can remember were old Mercedes Benz V8s from the late 60's and early 70's. There were probably others, but with low-impedance primary coils and high current drivers, they can make very powerful multi-strike ignition systems using coil-per-plug arrangements. |
| David Hess:
--- Quote from: james_s on October 01, 2021, 04:33:12 am ---Aircraft piston engines almost exclusively use magneto ignition of the same basic design as used during the dawn of powered flight. --- End quote --- Do all piston aircraft still have dual magnetos with two spark plugs per cylinder for redundancy? As I recall, the test is to change the magneto selector from both to magneto 1 and then magneto 2 and the engine RPM is only suppose to drop by like 100 RPM or something. But I remember reading about US aircraft on Pacific island bases during World War 2 where they said maintenance was such a problem that aircraft often would not even run without both magnetos selected. |
| james_s:
--- Quote from: David Hess on October 01, 2021, 04:58:06 am ---Do all piston aircraft still have dual magnetos with two spark plugs per cylinder for redundancy? As I recall, the test is to change the magneto selector from both to magneto 1 and then magneto 2 and the engine RPM is only suppose to drop by like 100 RPM or something. But I remember reading about US aircraft on Pacific island bases during World War 2 where they said maintenance was such a problem that aircraft often would not even run without both magnetos selected. --- End quote --- All certified aircraft engines that I'm familiar with have dual ignition systems with two separate spark plugs per cylinder. I don't think there has been much development there in decades, most of the engines being made are still the same basic designs developed around the 1950s. There are some non-certified automotive engine based aircraft engines that do not, I'm not sure whether these use a magneto or conventional automotive ignition system. |
| bdunham7:
--- Quote from: David Hess on October 01, 2021, 04:58:06 am ---Do all piston aircraft still have dual magnetos with two spark plugs per cylinder for redundancy? As I recall, the test is to change the magneto selector from both to magneto 1 and then magneto 2 and the engine RPM is only suppose to drop by like 100 RPM or something. But I remember reading about US aircraft on Pacific island bases during World War 2 where they said maintenance was such a problem that aircraft often would not even run without both magnetos selected. --- End quote --- All conventional (old style) piston aero engines are like this, yes, but there are examples of newer systems out there flying around. But they aren't just for redundancy, you lose some power and the engine runs hotter with only one spark plug going. Some old rotary engines were spark plug fouling monsters, so having dual ignitions helps there too. |
| Navigation |
| Message Index |
| Next page |
| Previous page |