Automatic Boost Control

I have two basic questions

1. Why did so few USN & USAAF aircraft use this technology?
2. How exactly did this work?

1. They preferred their pilots to work for a living.
2. Magic.

1) they trained their pilots better and needed better off-design performance from their engines

2) cams, bellows, gears (many not circular) and levers, like any mechanical automatic control system.

Zipper730 said:

2. How exactly did this work?

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This is a good start:

TA152 and FW190-Series Aircraft Stabilisation and Engine Management Systems.......

swampyankee said:

1) they trained their pilots better and needed better off-design performance from their engines

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Like overboosting and things?

2) cams, bellows, gears (many not circular) and levers, like any mechanical automatic control system.

Click to expand...

Crimea_River said:

This is a good start:

TA152 and FW190-Series Aircraft Stabilisation and Engine Management Systems.......

Click to expand...

Thanks

I wouldn't say better training -- I'd say more training. Necessary due to a throttle setup that created extra work for the pilot.

Just like I wouldn't say a Spitfire pilot is better trained than a Fw190 pilot because the British pilot had to attend to separate controls for boost, mixture, ignition, prop pitch and throttle -- whereas the German pilot didn't.

By 1944, I'd certainly argue "better," especially as the Luftwaffe's training bases would be getting all sorts of noisy, destructive things dropped on then.

Little to do with US aircraft industry throttle decisions/technology in the late 30s/early 40s though, I'd say.

Greyman said:

Little to do with US aircraft industry throttle decisions/technology in the late 30s/early 40s though, I'd say.

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That would be prewar training.

Doesn't add up for me. The reason US manufacturers eschewed automatic boost control was that they wanted to give US pilots the option to accidentally override engine limitations?

"We train our pilots better -- so we'll give them some extra workload and require them to pay extra attention to a cockpit gauge."

Greyman said:

Doesn't add up for me. The reason US manufacturers eschewed automatic boost control was that they wanted to give US pilots the option to accidentally override engine limitations?

"We train our pilots better -- so we'll give them some extra workload and require them to pay extra attention to a cockpit gauge."

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I suspect it's because the fighter community didn't drive engine control issues; it's more likely to have been driven by commercial users and the military multi-engine community. Had the USAAC and USN paid for engine automation, they would have gotten it.

they did get it.

This is the trouble with making blanket statements about WW II. things changed from before the war (or at the beginning) to the end of the war.

There is also a lot of difference between an automatic boost control and a one lever "power" control.

The automatic boost control controlled one thing, the boost, it did not control the propeller at all and it did not control the mixture and it did not control RPM.

The automatic boost control was linked to the throttle and if the boost limit was being exceeded it automatically (and progressively) closed the throttle to limit the amount of air coming into the engine/supercharger. This limited the amount/pressure of the air/mixture leaving the supercharger and the pressure in the intake/manifold.

Now in some cases the levers that controlled one or more of these functions were interconnected to help prevent mistakes. Like linking the throttle lever to the mixture lever so if the throttle is rammed forward it takes the mixture control with it so the pilot isn't running at full throttle in lean condition. There were releases that did allow independent movement. but some were spring loaded so if the throttle was returned to a certain point in it's travel it linked back up to the mixture control without the piot having to engage and hooks or catches.

Many of the later fighters got much simplified throttle controls.

Hello Gentlemen,

I believe the reason why the separate manual controls was preferred was because they allowed a skilled pilot to get just a little more performance from his engine than the automatic controls would. Whether this was a likely thing in the middle of an aerial combat is debatable, and whether most pilots were skilled enough to be able to fine tune things is also debatable but the controls were there.

Here is part of a performance test of a P-39D that shows the slight differences that could result if a pilot took the time to adjust the mixture to get the best engine performance rather than relying on just "Auto-Rich" or "Auto-Lean". It isn't very much but it IS there.

- Ivan.

Wow, a whole 3mph at critical altitude.

Mixture control was separate for most Allied aircraft, even those fitted with automatic boost control.

Hello Wuzak,

Perhaps the best way to view this isn't the speed increase but the power increase.
25 HP at critical altitude is a bit over 2% and while that doesn't change speed by much, it won't hurt agility.
Note also the results at 25,300 feet. Auto-Rich and Auto-Lean didn't make much difference but tuning the mixture gave 30 HP to 45 HP increase which at that altitude was almost a 6.5% increase over the "Logical" setting of Auto-Rich for wide open throttle.

- Ivan.

swampyankee said:

1) they trained their pilots better and needed better off-design performance from their engines

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I have training hours for GAF/RAF/USAF from prewar period to 1945. When this stuff was being developed (late 30`s) there was no appreciable
difference in training hours.

If manual control of the engine allows more power, that means your automatic systems are either no good, or you have not
tested your fuel properly and dont know where the knock limit is.

Automatic controls are pivotally connected to the use of fuel injection, therefore if you are not flying aircraft with injection,
you will not develop the same level of automation as someone who IS (i.e. Germans). Sadly for the USA, this also applies
to a large extent to turbocharger controls.... whoops. This was responsible for many of the problems with the Lightning.

Ivan1GFP said:

Hello Gentlemen,

I believe the reason why the separate manual controls was preferred was because they allowed a skilled pilot to get just a little more performance from his engine than the automatic controls would. Whether this was a likely thing in the middle of an aerial combat is debatable, and whether most pilots were skilled enough to be able to fine tune things is also debatable but the controls were there.

Here is part of a performance test of a P-39D that shows the slight differences that could result if a pilot took the time to adjust the mixture to get the best engine performance rather than relying on just "Auto-Rich" or "Auto-Lean". It isn't very much but it IS there.

- Ivan.

View attachment 567400

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I don't believe this D model -35 had autoboost yet. I believe the automatic boost control came with the slightly later -63 and -73 in the P-40K and P-39K/L.

Snowygrouch said:

Automatic controls are pivotally connected to the use of fuel injection, therefore if you are not flying aircraft with injection,
you will not develop the same level of automation as someone who IS (i.e. Germans).

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I am not so sure about that. The Hurricane I and Spit I both had automatic boost control with carburetor equipped Merlin IIIs. The Hurricane II with the, still carbureted, Merlin XX had very advanced engine management with a Constant speed prop, automatic boost control and automatic fuel mixture, all in 1940.

slaterat said:

I am not so sure about that. The Hurricane I and Spit I both had automatic boost control with carburetor equipped Merlin IIIs. The Hurricane II with the, still carbureted, Merlin XX had very advanced engine management with a Constant speed prop, automatic boost control and automatic fuel mixture, all in 1940.

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Sorry I seem to have idiotically mixed this thread up with the one which is concurrently running on the Kommandogerät, although the two are not THAT dissimilar topics..hah.

I would point out that "automatic mixture control" is still a switch, its just once you have SET rich or lean... it then ensures that is maintained. German controls integrated that as they realised that if you have the throttle full foward you`ll be wanting max power and so it decides for you to go rich. The German controls also do the supercharger gearing for you (admittedly thats a simple one in the Merlin until the XX !).

If you were in a P51 you had (depending on the version) up to 4 positions to choose from, Idle cutoff, auto lean, auto rich & "emergency full rich".

The P-38 didn't suffer from bad turbocharger controls. The P-38 had 4 real issues at the start of its service life.

1) It didn't have a good cockpit heater. An electric heater fixed this, but was a BIG issue until it was fixed. Early P-38 pilots were FREEZING, literally.

2) The British gasoline had much different aromatics than US gasoline, resulting in poor mixture from the factory when early British fuel was used. This took about 9 months to detect and correct, and was not an issue after it was discovered and corrected.

3) The Allison initially had a very smooth intake manifold setup that was broken up into four sets of 3-cylinder manifolds. It was so smooth that the flow to the cylinders had the center cylinder running lean and the two end cylinders running rich. It was not cured for about 9 months. Today, all flying Allisons run intakes with turbulators in them. Nobody runs the original smooth intakes, though they do make a good static display engine. Likewise, but unconnected to these faults, nobody runs the early wrist pins either, because they crack at the taper. Late wrist pins do not taper. Late valve lifters are also sought for flying engines. All the "late" parts are better than the "early" parts. Finally, nobody is running backfire screens either, because once you learn to operate the Allison, you don't need them. I actually have one of the backfire screens in my collection, courtesy of Joe Yancey, who just opened a new facility for overhauling Allisons at the Chino, CA airport.

Items 2 and 3 made for the "Allison Time Bomb" monicker in service but, once fixed, the engine started and operated just fine. Once the faults were eliminated, the Allison had the longest TBO of any V-12 in US service and held a tune a long time. That said, the Merlin was a superb engine and ran well during normal squadron use, too. This is NOT a knock on the Merlin. You can't really knock the Merlin and be credible doing so.

4) The biggest problem early on was VERY poor pilot training. We did not have combat veterans at first, and we were ill-prepared for entering the combat area in bad formations and with the engines not set for rapid combat changes. Once they started setting the engines for higher power when entering combat areas, there were a LOT fewer losses due to being attacked while setting the throttles and mixture/props for combat. We lost a lot of P-38's while the pilots were turning on gunsights and setting throttle, mixture and prop for the fight ... during the first firing pass. Once we entered the combat area ready for a fight, these losses dropped way off. You may have good training, but combat veterans do not magically pop up until they go through combat and survive multiple times to pass on what they know. The Germans developed combat veterans in the Spanish Civil War. We didn't. The British developed combat veterans during the early phases of WWII, when we were neutral. It took a while for the USA to have combat veterans to change the way things were done at first.