RhinoDrvr
Pre-takeoff checklist
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- Nov 7, 2013
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RhinoDrvr
Hi all,
My friend owns a 1999 Lancair 320 Mk. II that he's been flying for the past 3 years. I recently bought into a share of the airplane, and we've been slowly working out some of the kinks in the plane.
A recurring problem for us is that the alternator will begin to overcharge (~15 - 16 volts) on flight longer than about twenty minutes. The alternator itself is off a Suzuki Samurai and is rated at 50 amps. Our max amp draw in the airplane is 40 amps with the landing light, pitot heat and strobes all on. Typical draw is around 12-15 amps.
Start/Taxi/Takeoff/Climb usually have the alternator doing fine, then once we level off in cruise the alternator will begin to overcharge, and once it begins it will continue for the rest of the flight. Today we sat on the ground at our destination for ~45 minutes, then took off again, and the alternator was overcharging from takeoff.
My guess is that the alternator is not receiving ample (any) airflow for cooling due to the plenum that is fitted to the top of the engine. Therefore, the internal voltage regulator is overheating and ceasing function. Once it is allowed to cool sufficiently (overnight, or a couple hours) it has no problem functioning again. We also usually toast an alternator annually.
We cleaned off all the electrical connections in the airplane, and bench tested the alternator, getting a good test (although only loaded from 20 amps to 50 amps, not down to 10 amps).
Does it sound logical then, that cooling would be causing the voltage regulator to fail, and allow the alternator to overcharge the system? What types of schemes have y`all got running in order to keep the alternator cool. It seems that cooling is an issue in this airframe for everything except the cylinder heads, which the plenum does a good job of keeping cool.
Would an external voltage regulator mounted somewhere in the cabin work better than an internal regulator? A ram air scoop directed at the back of the alternator? A heat shield between the cylinder 1/2 exhaust an the alternator? Ideas?
Thanks!!
Rhino
My friend owns a 1999 Lancair 320 Mk. II that he's been flying for the past 3 years. I recently bought into a share of the airplane, and we've been slowly working out some of the kinks in the plane.
A recurring problem for us is that the alternator will begin to overcharge (~15 - 16 volts) on flight longer than about twenty minutes. The alternator itself is off a Suzuki Samurai and is rated at 50 amps. Our max amp draw in the airplane is 40 amps with the landing light, pitot heat and strobes all on. Typical draw is around 12-15 amps.
Start/Taxi/Takeoff/Climb usually have the alternator doing fine, then once we level off in cruise the alternator will begin to overcharge, and once it begins it will continue for the rest of the flight. Today we sat on the ground at our destination for ~45 minutes, then took off again, and the alternator was overcharging from takeoff.
My guess is that the alternator is not receiving ample (any) airflow for cooling due to the plenum that is fitted to the top of the engine. Therefore, the internal voltage regulator is overheating and ceasing function. Once it is allowed to cool sufficiently (overnight, or a couple hours) it has no problem functioning again. We also usually toast an alternator annually.
We cleaned off all the electrical connections in the airplane, and bench tested the alternator, getting a good test (although only loaded from 20 amps to 50 amps, not down to 10 amps).
Does it sound logical then, that cooling would be causing the voltage regulator to fail, and allow the alternator to overcharge the system? What types of schemes have y`all got running in order to keep the alternator cool. It seems that cooling is an issue in this airframe for everything except the cylinder heads, which the plenum does a good job of keeping cool.
Would an external voltage regulator mounted somewhere in the cabin work better than an internal regulator? A ram air scoop directed at the back of the alternator? A heat shield between the cylinder 1/2 exhaust an the alternator? Ideas?
Thanks!!
Rhino
