Horsepower is a way to measure how powerful an engine is. The higher the horsepower, the more work the engine can do, like going faster or pulling heavier loads.
Octane is a measure of how well gasoline can handle pressure in an engine without causing problems. Higher octane means the fuel can be compressed more before it explodes, which is better for performance.
Liquid cooled engines are engines that use a special liquid to keep them from getting too hot. This helps them run better and last longer, especially in powerful vehicles.
Centrifugal superchargers are machines that help engines get more air, which lets them burn more fuel and produce more power. This makes cars go faster and perform better.
Supercharging is a way to make an engine more powerful by pushing more air into it. This helps the engine burn more fuel and produce more power, making the car faster.
Car
Allison V-1710
The Allison V-1710 is an engine used in airplanes, especially during World War II. It was powerful but had some issues with how it performed in the air.
The Ford Mustang is a popular sports car that started being sold in the 1960s. It's known for its stylish look and powerful engine, making it a favorite among car lovers. People often talk about the Mustang because it's a classic car that represents freedom and fun driving.
A gearbox is a part of a vehicle that helps control how fast the engine's power is used. It can change the speed and strength of the power coming from the engine to make driving easier.
Efficiency is about how well an engine uses fuel to make power. If an engine is efficient, it means it can do more work with less fuel, which is better for performance and the environment.
Detonation is when the fuel in the engine explodes too early, which can cause knocking sounds and damage the engine. It can happen if the engine gets too hot, especially with parts like superchargers that increase heat.
A two-stage supercharger helps the engine get more air, which means it can produce more power. It's like having two helpers instead of one to push air into the engine.
An aftercooler cools down the hot air that comes from the supercharger before it goes into the engine. Cooler air helps the engine run better and produce more power.
A turbocharger helps an engine produce more power by using the hot air from the exhaust instead of using energy from the engine itself. This means the engine can work more efficiently and produce more horsepower.
Car
P-38 Lightning
The P-38 Lightning is a famous fighter plane from World War II. It had a unique design with two tails and was known for being fast and powerful.
An intercooler is a part that cools down the air that goes into the engine after it's been compressed. Cooler air helps the engine work better and produce more power.
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In so many ways as we have discussed on this channel before, World War II was a war of horsepower.
It was a war of octane, a war of boost, a war of durability, and a war of innovation.
Among the most fascinating parts of that war to examine are the elements surrounding piston
engines, especially the liquid cooled ones used in military aircraft. So many of the bedrock
principles of high performance engines that we know today were explored to incredible scientific
depth while trying to create airplanes to fly higher, faster, and more efficiently than those of
the enemy. While the massive air-cooled radial engines are in so many ways the most brutally
powerful units bolted into planes during the conflict, they don't quite spin my crank in ways
that the liquid cooled engines do. A few videos back when we went deep into the early history of
centrifugal superchargers in drag racing, I mentioned that I was going to be exploring
superchargers over the course of a few different pieces. Now consider this the second one of those.
Because this is such a big topic and because there's so much to cover, I'm going to use this video
as an introductory level look into the various different methods of supercharging used on the
most popular liquid cooled airplane engines of World War II. We're talking about the American
Allison V1710, the German DB600 series of engines, and of course the British designed and engineered
Rolls-Royce Merlin. In following videos down the road, I'm going to go deeper into the engines,
the people, and the performance that they yielded, but this is interesting nonetheless to examine.
Many of you are likely gearheads with the love of these historic machines and this may be stuff
you already know, but as I have learned, the audience that watches this stuff is often made of
younger enthusiasts who are learning the principles of engines and the history that surrounds the
horsepower we can make today. If you know all this stuff already, awesome. If you don't,
I hope you dig it. More depth will come in time as we dive into various different aspects of the
stuff we cover here. I used resources like A History of Aircraft Piston Engines by Herschel Smith,
Allison Power of Excellence, and Airplane Power from 1943, published by General Motors in the
making of this video. Now when it comes to supercharging, each country had its own idea of
the best method. They all have their pluses and minuses, and as we'll see, one country out of the
three chose a path that ended up being a pretty significant mistake. For starters, we should
probably examine why a piston aircraft engine needs a supercharger to be effective at high altitudes.
As we all know, engines need oxygen to properly combust fuel, and the higher we get above the
level of the sea, the less of it there is in the atmosphere. By using a supercharger to ram
massive quantities of air into the cylinders of an engine, as opposed to allowing it to get there
by the engine inhaling it naturally, the same engine that would be choking and failing at altitude
can now produce horsepower almost equal to what it would make on the ground.
If that seems like a weird principle, think of it this way. As the supercharger is cramming
all that additional volume of air into the cylinders, it allows the same amount of fuel
to be burned, or close to it, that would be burned at sea level, effectively tricking the
engine into thinking that it's down in better air. Of course, it's easy to understand the
basics here, but when we consider the timeframe of what we're talking about and all the constraints
the engineers are trying to work around, it's pretty amazing. For starters, there's the need
to somehow manage the boost that the supercharger is producing so you don't blow the engine up at
low altitudes. There's the fuel that the engine will burn, which in some cases could be 87 octane
and in others could be well over 100 octane, and finally you have to package it all in the
relatively tight confines of a 1930s or 40s fighter plane. In order to balance all these issues,
a whole slew of options were bandied about and ultimately created to properly quote
altitude supercharged aircraft engines in the war. You had engines with single-stage superchargers
geared to the engine, a single-stage supercharger with a two-speed mechanical clutch and transmission,
a single-stage supercharger with a variable speed hydraulic clutch,
a two-stage supercharger with a mechanical clutch, a two-stage unit with a hydraulic
variable clutch, a two-stage after-cooled variable speed clutch unit, and turbo exhaust-driven
superchargers with an intercooler. These different methods were employed by different countries,
sometimes multiple countries using the same setup, and they were done to create the best
high altitude aircraft possible, which also performed well and reliably at lower altitudes
without overworking the engine and blowing it up. Did they all work? To a degree, yes,
and that's what we need to explore now. Before we do that, let's define a few terms you'll
be hearing in this video. First off is absolute ceiling. This is, as it sounds, the maximum
altitude an aircraft can operate in. Not many factors contribute to these things, but safe
it to say, when this altitude is reached, the aircraft can no longer climb higher.
Service ceiling is defined as the maximum altitude an aircraft can operate at with a given load,
with normal responses from its controls and still being able to climb.
The last one to talk about is critical altitude. This is where the plane can achieve its top speed,
a place where the engine is making big power, the air is thin, and the performance envelope of the
craft can be reached. It's also the area that, once breached, sees the engine making less and less
power. Of course, all these numbers vary with an airplane's design, not simply the horsepower of
the engine or how it's boosted. Like all things in mechanical design, everything is a compromise
to some degree or another, especially with regard to airplanes. Okay, now that we have that defined,
let's go back to our methods of supercharging. The single stage one speed centrifugal supercharger
is where most everyone starts in this journey of warp boost. In one notable case, it's where a
well-known engine stayed in its majority form, leaving it with a slightly lame reputation.
Yes, as much as I love the Allison V-1710 airplane engine, it was not all that well handled during
World War II. Created in the 1920s originally as an airship engine, it was well designed,
rugged, and had the mechanical bones to stand in the ring with anything else the world threw at it.
Unfortunately, it was let down by its use of a single stage supercharger that was never really
improved upon due to reasons we'll get into in a little while. At the start of the war,
the Allison was making comparable power to rival engines and was capable of sending aircraft to
rival levels of altitude. But as time went on, supercharging improved everywhere else,
but the Allison was largely left behind. This is why the Mustang, Spitfire, and other truly war
changing aircraft used the mighty Merlin V-12 and the Allison was relegated to lower altitude,
ground attack style planes. As the rest of the world invested in much of the technology we're
going to go over here in the following minutes, the US left the V-1710 with its less than stellar
single speed single stage supercharger. This prevented the engine from being much good above
15,000 feet. While it may have made 1500 horsepower, that number would fall off steeply the higher it
climbed. The Allison had a really strong bottom end of its physical construction, had great cylinder
heads, but it was also hampered by a crummy intake manifold design that we'll also revisit later.
Long story short, in the grand scheme of things, the world never got to see the Allison perform
at its peak because the choices that were made in its usage and development really did hamper it.
More on that later. Lastly, as the Allison powered airplanes are often used in lower
altitude applications, pilots had to be very careful not to over boost the engine. In American
airplanes, they were responsible for doing that themselves with various controls in the cockpit.
Of course, there were loads of opportunities for mistakes, but like this formerly confidential World
War II memo tells us, guys would also use the max power settings to simply make more speed.
Note that the author here is saying that with 66 inches of boost, the engine will likely be near
1800 horsepower at 3000 rpm. This is in 1942, a few revisions and a few years into the conflict.
This was highly discouraged behavior because it would inevitably lead to someone
melting down a perfectly good engine. But as they say, boys will be boys.
Next up, we move from the simple single speed single stage supercharger to a single stage
two speed supercharger. Effectively, we have the same unit as before, but with a clutch and a simple
gearbox to step the speed of the supercharger up when we get our airplane to higher altitudes.
Of course, the benefit to this system is that by spinning the supercharger faster and moving
more air, we should make more horsepower at higher altitudes. All this is well and good,
but the reality is that there are limits to these things, and one of them is the efficiency
of the supercharger themselves when it is in theoretical high gear. At this time in history,
meaning the 1930s and 40s, the relatively rudimentary impeller wheels in these superchargers would
start to have real trouble when the outer tip speed passed over 1300 feet per second or about
886 miles per hour. Not to mention that at some point the supercharger becomes so inefficient
that the heat generated by the discharged air to the engine can have a drastically negative effect
on detonation and other issues and simply cause a loss of power. So even this two speed system
has its drawbacks. Pilots would have to be conscious of their engine RPM when in high gears to not
overspeed the supercharger and cause any number of issues, the least of which was likely a loss in
power, the worst of which was a supercharger killing an impeller and sending its guts through the engine.
The two speed single stage system was largely an early war stop gap in many ways and wasn't
the favored method to make the most efficient and maximum power on a warplane. Interestingly,
the clutch to engage the second speed in this arrangement could be engaged in a couple of
different ways. Engaging the clutch manually had to be a very violent experience for both the airplane
and the pilot, but there was another way this worked as well. Some of them had an altitude control
unit that would automatically engage the second speed at around 7 to 9,000 feet when the aneroid
control kicked in. The power and performance curve in this style of two speed supercharger looks
almost like the teeth on a saw blade. There are radical jumps when the second stage was instantly
engaged. It was hard on equipment, but there are other ways and better ways. Now it was German
engineers who favored the next approach and in many respects did it the best. This is a single
stage supercharger with a variable speed hydraulic clutch. Now the major benefits of this system
should be kind of obvious. Removing the human element from the equation by using a hydraulic
clutch that would apply itself relative to the altitude of the aircraft meant that the engine
was in theory always seeing the optimal supercharger speed for where it was in relation to sea level.
It drastically smooths out the power curve and allows the pilot to concentrate on his job
of attacking the enemy, not worrying about trimming fuel, adjusting throttle position,
or having to study his altimeter in order to engage high speed gear for the supercharger at
the right time. The interroid controller did all of that for the pilot. Now the airplane itself does
not see a drastic fall off in power and then a spike when the blower speeds up. Now this hydraulic
engagement style of clutch doesn't necessarily improve the maximum output of an engine,
but like a dyno curve that gets improved when power is picked up through the rpm range before
getting to peak, this makes the plane a better performer in the middle range of its altitude
before reaching critical altitude where power and performance begin to drastically drop off.
The German DB engines had their superchargers mounted not in the rear of the mill like an
Allison or a Merlin, they were mounted on the side. They were run by bevel gears in a jack shaft
and the fluid coupling was installed on the jack shaft which would control the speed of the supercharger.
Now the mounting seems curious, but it does allow the supercharger to ingest the air
and throw it more smoothly toward the intake manifold. It eliminates one of the bends that
the other design has when the air has to turn sharply to get into the blower and then sharply
out of the blower to get to the intake manifold. Next up is the two-stage centrifugal supercharger.
This is where the Merlin engine outshone all others of its era. A brilliant mathematician named Sir
Stanley Hooker began working at Rolls Royce in the late 1930s. He was an expert in studying what
we'd now call fluid dynamics or theoretical aerodynamics and this guy could basically see air.
He was an unbelievably brilliant man and he was able to look at, having never seen an aeronautical
engine or a centrifugal supercharger, what needed to be fixed to make them better. He was tasked
with making what amounts to a glorified air pump work more efficiently. Now after improving the
company's single-stage blowers drastically enough to raise output by 30% of the Merlin,
he had the concept of mounting a pair of superchargers together, one feeding the next.
Taking a supercharger off of one of the company's larger engines and combining it
with the Merlin's unit, he created the finest blower of the war and it allowed the company
to effectively double the output of the engine by the time the conflict had ended. Hooker knew
the bones of the Merlin were sound. It didn't need to be expanded in size or drastically reworked,
it just had to do its job more efficiently. And the two-stage, two-speed supercharger was the
ticket to doing just that. With this improvement, the engine was capable of much more altitude.
Its compact packaging meant that it would fit into existing applications with little rework
and its performance was improved in breathtaking fashion. As we can see here, the critical altitude
was stretched out by a bunch and while it gave up some performance at lower altitude,
it was of little concern. Flying higher and faster was always the goal. These units allowed
the smaller supercharger to work at lower altitudes without overboosting the engine,
but the clutch would be engaged at higher altitudes to deliver the extra horsepower punch
needed to out-climb the enemy and attack from above. Combining all the above with the fluid
coupling we spoke about earlier has an even more positive effect because this allows for the same
benefits as it did with the single-stage clutch, but in an even more dramatic fashion.
There was no dramatic drop in performance before an aircraft got to the proper altitude to engage
the second blower because it would all happen smoothly and perfectly matching the conditions
the plane was in. Effectively, this was getting close to the best of both worlds.
The next evolution was the use of the two-stage supercharger with the fluid coupling with the
addition of an aftercooler. This again was a large performance enhancement because of the job
the aftercooler did. Remember that we mentioned fuel types and characteristics earlier in this
discussion. As gearheads know, the higher the octane rating of fuel, the more resistant it is
to detonation or spontaneous ignition happening before it should inside a cylinder. An aftercooler
was a massive improvement in power making at altitude because it was placed behind the second
stage of the blower. It cooled the air charge as it entered the engine. Now as air is compressed,
of course it gets hot. Hot air entering a cylinder can lead to detonation and detonation can lead to
engines failing, especially when they are being worked hard, very high up in the sky. Higher octane
fuels like the 100 plus octane gasoline being developed in the United States during the war
helped to stave off detonation, but cooling the intake charge made this even better. By cooling
the charge, engines could run higher compression ratios. And again as gearheads know, high compression
engines plus crummy fuel can lead to detonation, which is why you don't put 87 octane in your
high performance high compression engine, but if you're able to manage that with a better fuel,
a cooler intake charge and more compression, you're going to make a lot more power.
As we can see here, there's a drastic improvement in the critical altitude and power throughout
the whole operating range of the aircraft. The downside is you have to find a place for
the after cooler and adding stuff to a plane can make it heavier and less aerodynamic.
Engineers got creative with their placement of the after coolers,
preventing a loss of aerodynamic performance and allowing for the additional horsepower to be used
rather than wasted trying to push the airplane through the sky.
Lastly and perhaps most interestingly, we get to turbo charging, or as it was known at the time,
turbo supercharging. If you remember at the beginning of this exercise, I mentioned that
one country seemed to make a large scale mistake when it came to their chosen method of World War
II era supercharging. That country? The United States. The United States decided very early
on that turbocharging was going to be their root of two stage boost making in aircraft.
They did this for good reason. A turbocharger is the most efficient method of making boost
and it did things that the gear driven centrifugals could not dream of doing.
As the turbocharger doesn't use the engine's power to be turned, but rather the heat energy
and the exhaust to do its work, it's a vastly superior way to make power versus a mechanically
driven blower. In fact, the turbo supercharge combination has the most amazing power curve
of all we have seen so far. It raises the critical altitude many thousands of feet
while producing virtually the exact same amount of horsepower at that height as the engine does
at sea level. So what was the mistake? Packaging. Sanford Moss of the General Electric Company
was the man who developed these systems for the military at the time when the United States
committed to this method, all work on improving gear driven centrifugal superchargers basically
came to a halt. The Allison was hampered severely by this in almost all applications outside of
a handful of legendary ones, most famously the P38 Lightning. A large plane, there was plenty of
room for all the associated plumbing, the intercooler and the monstrous turbochargers.
In today's world, turbos fit comfortably, most of the time, under the hood of an automobile.
In the 1940s and on engines this size, they required multiple people to actually lift them
and move them. Turbochargers in their entire systems were too hopelessly massive to fit
in any aircraft like the P51, the Spitfire, really anything of that class. And there were other
problems as well. In the European theater at high altitudes and freezing air, the turbos and
associated parts would fail and cause severe mechanical issues. When the P38 was brought to
warmer climates like the South Pacific, they really did stand out in combat. Their power,
altitude capability and performance were awesome. But unfortunately, this technology was so far
ahead of its time in terms of pure bulk, it wasn't adopted widely and was very much more
problematic than the other more proven methods. Had the Allison gotten the Sir Stanley Hooker
treatment in volume and in different applications, its reputation and legacy would be vastly different.
Turbos were successful on radial engines as well, most famously the large by huge P47,
which was basically an engine with a plane built around it. Again, breathtaking and
awe-inspiring performance for the time, but the bulk they brought was just too much to overcome in
so many other places. In turbo supercharged applications, an intercooler was used. Note
the difference here. The aftercooler we spoke of before would cool the charge after the second
stage of the supercharger as the air was heading into the engine. In these planes, the charge would
be cooled heading out of the turbo and then into the gear driven blower attached to the engine.
Hence the inter part of the intercooler word, it was happening during the middle of the intake
process. In many ways, intercooling is not as efficient as aftercooling because as the air
went through the gear driven supercharger, it would get heated up and compressed on the way into the
engine, but it still worked very, very well. When it worked. In period literature, it was claimed
that the turbo supercharger could deliver sea level power up to 30,000 feet. Unfortunately,
the size and heft of the whole package was really only suitable in large bombers or
the large fighters that would fly high in the sky to attack the enemy's bombers,
but for the live fighter planes like we mentioned, it just wasn't an option.
Consider this the first step into what will be a much deeper walk into the world of World War
II supercharge liquid cooled aircraft engines. As I mentioned, there is an incredible depth
to this subject and it is one that employed the best mechanical engineers in all of the
warring countries to refine and make better. Perhaps much of this is common knowledge to
historic airplane buffs, but I am talking gear heads here, some of which may not have known
the extent to which boost, mechanical supercharging and turbo supercharging played a major role in
the outcome of the air war that gripped the entire world in the late 1930s into the middle 1940s.
Next time you revisit this topic, we will take a look at the fascinating life and times of
Sir Stanley Hooker, the man who could see air, a brilliant mathematician who had perhaps the
most dramatic impact of any single man on the mechanical fronts of World War II.
I am Brian Loans, thanks for watching. Like and subscribe for more historical,
mechanical and altitude busting content.
About this episode
Exploring the pivotal role of supercharging in WWII aircraft engines, this episode delves into the engineering innovations that allowed planes to perform at high altitudes. The discussion covers the American Allison V1710, German DB600 series, and British Rolls-Royce Merlin engines, highlighting their unique supercharging methods. Notable insights include the advantages and drawbacks of various supercharger designs, including single-stage and two-stage systems, as well as turbocharging. The episode emphasizes the impact of these technologies on aircraft performance and the war's outcome, setting the stage for deeper dives into specific engines and their engineers in future episodes.
There's nothing like upping the horsepower of an engine with boost. Multiple methods of supercharging exist today and have been brought to an incredible level of efficiency.
While these methods were not invented in WWII, their use was vastly studied, tweaked, and tested to their limits back then. This video is the next in a series about the history of centrifugal superchargers and their use on piston engines.
Consider this your 101 level course in WWII supercharging. Here we go over the various methods and systems used on aircraft from the USA, Germany, and Great Britain. Which countries did it best? Which country made a mistake in their method? Who ruled the horsepower roost and why?
It was a war of horsepower and boost was a huge factor in making more of it than the other guys
