F10 Posted October 12, 2021 Posted October 12, 2021 The Gazelle flight manual states that with an alternator failure, switch it off and then “land as soon as practicable”. This means, you can fly to a field, where technical help may be available. In context. “Land as soon as possible”, means basically land at or on the first suitable surface. “Land immediately”, means, get it on the ground right now, even if it results in damage. So it seems the alternator failure is not too serious. However, in the manual, it also says it’s important to keep the alternator on at all times. So, what is the problem switching it off? Of course your battery will run down, but as far as I know, the engine will still run? After all, if you pass a magnet rapidly over or through, a copper coil, it will induce a current? So the engine should still generate a spark, even with a run down battery. The manual certainly has no warning about the battery running down with regards engine operation. Any opinions?
Hongie Posted October 12, 2021 Posted October 12, 2021 afaik, rotax don't have a magneto to generate the power to create a spark (like a traditional aircraft engine al la Lyc/conti etc), they have a coil. The coil needs power from battery/alternator/generator to send to plug to make said spark.
facthunter Posted October 12, 2021 Posted October 12, 2021 (edited) Tt's not a normal alternator and I think you just disconnect it from the system for safety. Your battery will supply the rest. Ignition? I don't know. Radio etc for 'whatever" charge state and condition it has. Permanent magnet alternators are weird. I have no idea how they are regulated. Some ignition systems can use a separate winding in the alternator to power the coils. In a normal alternator the output is regulated but the current in the rotor and sometimes won't excite if the battery is dead. Nev Edited October 12, 2021 by facthunter
F10 Posted October 12, 2021 Author Posted October 12, 2021 34 minutes ago, Hongie said: afaik, rotax don't have a magneto to generate the power to create a spark (like a traditional aircraft engine al la Lyc/conti etc), they have a coil. The coil needs power from battery/alternator/generator to send to plug to make said spark. Now I have heard that…which makes sense…but like I said, I still thought a current would still be induced. It seems very strange to me that the manual doesn’t give a “warning” or “caution” about this because it means if the alternator (yes I know it’s a different type part of the ignition at the back of the engine) fails and the battery runs flat, the engine will fail. You would think that’s a rather important detail! I think I will have to look at this. Even my Rotax maintenance manual doesn’t even mention the need for constant battery power?
F10 Posted October 12, 2021 Author Posted October 12, 2021 44 minutes ago, Hongie said: afaik, rotax don't have a magneto to generate the power to create a spark (like a traditional aircraft engine al la Lyc/conti etc), they have a coil. The coil needs power from battery/alternator/generator to send to plug to make said spark. Now I have heard that…which makes sense…but like I said, I still thought a current would still be induced. It seems very strange to me that the manual doesn’t give a “warning” or “caution” about this because it means if the alternator (yes I know it’s a different type part of the ignition at the back of the engine) fails and the battery runs flat, the engine will fail. You would think that’s a rather important detail! I think I will have to look at this. Even my Rotax maintenance manual doesn’t even mention the need for constant battery power?
Thruster88 Posted October 12, 2021 Posted October 12, 2021 The alternator windings are separate from the ignition windings although they are in the same stator part. Normally the alternator cannot be switched off in a 912. Casa obviously wanted the VH gazelle to have this feature like other VH aircraft in the event of smoke in the cockpit etc. It would be interesting to see how it was done electrically.
F10 Posted October 12, 2021 Author Posted October 12, 2021 45 minutes ago, facthunter said: Tt's not a normal alternator and I think you just disconnect it from the system for safety. Your battery will supply the rest. Ignition? I don't know. Radio etc for 'whatever" charge state and condition it has. Permanent magnet alternators are weird. I have no idea how they are regulated. Some ignition systems can use a separate winding in the alternator to power the coils. In a normal alternator the output is regulated but the current in the rotor and sometimes won't excite if the battery is dead. Nev Well truth be told, flying back from Leongatha, I noticed when checking T’s and P’s, that the voltmeter needle was fluctuating quite a lot. Soooo, I decided to switch off the alternator which did steady it up. However, I noticed the battery voltage was slowly dropping even after switching off all other services. This seems to confirm the engine ignition system is drawing power…I think you would hit 10 Volts pretty darn quickly! Precautionary landing time with an actual alternator failure! All good when I switched the alternator on again. I think on the next bad Wx day, I might just clean up or roughen with some sand paper, the earths and some other electrical contacts……
F10 Posted October 12, 2021 Author Posted October 12, 2021 (edited) 13 minutes ago, Thruster88 said: The alternator windings are separate from the ignition windings although they are in the same stator part. Normally the alternator cannot be switched off in a 912. Casa obviously wanted the VH gazelle to have this feature like other VH aircraft in the event of smoke in the cockpit etc. It would be interesting to see how it was done electrically. Yes good point! You are correct, it was a CASA requirement for VH. Yes…I will have to try figure out how it was done. I think it may just isolate the battery from the alternator to battery charge input, but the battery can still power other systems? The Gazelle has an alternator switch, and an alternator out warning light…which is quite handy! Edited October 12, 2021 by F10
pluessy Posted October 12, 2021 Posted October 12, 2021 self-energised CDI, power is only required for the soft-start modules (ignition retard during cranking): 1 1
F10 Posted October 12, 2021 Author Posted October 12, 2021 (edited) Ok, so no external power required. Seems to confirm why no issue is made in manuals about external power. I have always found this system complex, being an old magneto/distributor/coil/contact breaker man! Edited October 12, 2021 by F10
Hongie Posted October 12, 2021 Posted October 12, 2021 3 hours ago, Hongie said: afaik, rotax don't have a magneto to generate the power to create a spark (like a traditional aircraft engine al la Lyc/conti etc), they have a coil. The coil needs power from battery/alternator/generator to send to plug to make said spark. 1 hour ago, pluessy said: self-energised CDI, power is only required for the soft-start modules (ignition retard during cranking): Live and Learn 👌 1
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