Straiga, why you keep writing a dissertation to folks who know this stuff is beyond me. But since you asked about props, here's a quickie lesson...
The correct answer is a Curtiss Electric propellor. It had no mechanical stop at all since any blade angle change was done with an electric motor in the prop dome. Without a mechanical stop the blade can swing through a greater degree of angles than otherwise possible. Most (if I remember correctly) P-38 models used a Curtiss prop because it allowed full feathering without any oil loss. Plus the prop could swing through a much larger range of angles which would prevent over-speeding. Once you set a given RPM, the electric motor would rotate through a series of planetary gears at a ratio of 7,500:1 to change prop pitch. This pitch was held by a friction brake inside the motor. Given that the wiring and electrical motors back then weren't exactly great, a small short could cause all sorts of trouble. Unless the Curtiss was well taken care of by a very picky mechanic, the prop could run wild when the wiring or motor had a problem. When it worked, the Curtiss was probably the best prop on any WW2 aircraft. There was no wait time or lag when you throttled up; you had 2,700 RPM right now and it held that RPM setting regardless of what the engine did. Another good thing was the lack of any oil dependency. You could have the engine oil system full of holes, generators shot to bits, and the Curtiss would keep working as long as you had battery power. Once set, the Curtiss could hold a given RPM without any electrical draw at all. If you needed to change RPM all you had to do was kick the battery on for a moment, change RPM, and kick the battery back off.
Hamilton Standards and Aeroproducts props used oil, not only limiting them to a given pitch range, but also causing a rather severe problem if damaged. Later models of Hamilton had a provision to dump oil out from behind the prop dome to feather it in an emergency. B-29's were fitted with 14-foot Hamiltons that had a provision to dump oil in case you had to feather an engine.
Hamiltons were tied into the engine oil system, which meant that if you (somehow) dumped too much oil overboard the prop governor couldn't function at all. With no control over prop pitch the prop would run wild and damage or blow the engine. You also had to exercise the prop to make sure you got the oil sludge out of the prop dome before flight. Although most pilots didn't mind, the Hamilton had a throttle-up lag of a second or two between when you advanced the throttle for takeoff and when the prop responded by changing pitch to maintain RPM. On average, pilots liked the Hamilton because it was simple, had very few frills, and nearly always worked to perfection. Mechanics also loved the simplicity of how it was built. Oil simply pushed a control plate, attached to a bevel-geared cam, forward or backward to set a given RPM.
Aeroproducts also used oil, but didn't tap it off the engine oil system. They were completely self-contained so any engine damage wouldn't screw up the prop's operation. The regulator, oil, governor, oil lines, and valves were all contained in the engine nose. Only a direct hit on the prop itself would cause loss of operation. Unfortunately, if you look at a cut-away of any Aeroproducts unit, you'll find a horrifically complex nightmare of gears, cams, hydraulic pistons, and splined drives that would give the average mechanic migraines. Like the Hamilton, it had a mechanical stop the blades couldn't rotate past. But since it wasn't dependant on engine oil, crews tended to think it would be a bit more survivable in any event of oil loss.
You can get a LOT more info from America's Hundred Thousand on all three prop types, along with a cut-away view of what they looked like on the inside.
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Flakbait [Delta6]
Delta Six's Flight SchoolPut the P-61B in Aces High
