Why the heck did they design it that way?

GrauGeist said:

Apart from a benefit of better visability over the cowl, an inverted engine has a lower center of gravity.

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Vertical C/G is not terribly important for aircraft. A higher thrust line permits a larger propeller or shorter landing gear, but thrust line in a geared engine isn't dictated by the location of the crankshaft. Indeed, it can't coincide with the crankshaft if the idea is to have a cannon firing through the hub.

An inverted engine probably adds more problems, especially oil scavenging, than it solves. Radials are notorious for getting oil in the cylinders below the crankcase; it's extremely unlikely that inverted v-12s would be better in this regard.

Two ways to look at that. When a P-51 etc, is upside down, its' Merlin is inverted. And all Radials have some inverted cylinders.

I don't see how an inverted engine would have an

swampyankee said:

Vertical C/G is not terribly important for aircraft. A higher thrust line permits a larger propeller or shorter landing gear, but thrust line in a geared engine isn't dictated by the location of the crankshaft. Indeed, it can't coincide with the crankshaft if the idea is to have a cannon firing through the hub.

An inverted engine probably adds more problems, especially oil scavenging, than it solves. Radials are notorious for getting oil in the cylinders below the crankcase; it's extremely unlikely that inverted v-12s would be better in this regard.

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Disagree - some equipment aboard an aircraft may or may not have much influence on flight characteristics outside of fuel cells), but an engine is a large portion of weight that can have a direct influence.

As far as inverted oil issues, several manufacturers were making inverted engines long before WWII, like Packard's V-1650 (L-12-A) and Allison's VG-1410, developed in the 1920's.

By the way, on a radial, you "push through" the engine before starting and that puts the oil back in the crancase and prevents hydro-lock.

And if an upright L or V was so critical, then the H or "boxer" would never have made it this far.

The two main ways engines lose oil to the combustion chamber is through the cylinder walls/ rings , and valve seals.

On a conventional V or inline engine the oil stays on the cylinder wall, but most is scraped off by the piston rings, and that is assisted by gravity in pulling that oil down. But the valves are facing down, oil trying to get past the valve seals into the combustion chamber will be assisted by gravity.

In a inverted engine the leakage past the rings may be assisted by gravity to get past the ring seal, but the leakage past the valve seals may be less than a conventional mounted engine, gravity isn't going to assist in the oil flowing up the valve stems.

So the conventional engine has better ring seal oil control, than the inverted engine, but the inverted engine has better valve seal oil control. So they might end up being close to the same overall in oil lost to the combustion chamber.

I think the 109's inverted engine gave a better view over the nose, but then again had the thrust line lower causing a bit longer landing gear.

It helps to see where they were coming from.



The huge BMW V-12 (46.93 L) was essentially two WW I six cylinder banks using a common crankshaft.

It was tall and wide.
Requirements for better vision are not hard to understand even if they didn't quite work out as planned.
Small cockpit with low roof tends to negate the advantages of the inverted engine, especially after they substituted teh DB series of engines for the smaller Jumo 210.

Shortround6 said:

There was a lot of contradictory thinking going on.

Like,

Lets use a fixed pitch prop on the interceptors so that will save around 200-250lbs on a 5500lb airplane and give us better climb..........

Of course because the pitch on a fixed pitch prop suitable for 350mph is so extreme it means we have to throttle our 3000rpm engine down to no more than 2200rpm (less?) for take-off and limit it to somewhere between 2200rpm and 2400rpm (depending on altitude) when climbing instead of the 2600rpm the engine is rated for max continuous (or at least 1/2 hour) but hey, the lighter weight will make up for the loss in power, right??????????

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Like "The bomber will always get through". Like 8.303's are better than 4-6 .50's. Like the "Big Wing", which Allen hates in his book, as did Leigh-Mallory and Dowding

Two other fabulous books.

David Fred said:

Like "The bomber will always get through". Like 8.303's are better than 4-6 .50's. Like the "Big Wing", which Allen hates in his book, as did Leigh-Mallory and Dowding

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We have a number of threads on the bolded part.

There is no doubt that 4-6 .50 cal guns from 1943 firing 1943 ammunition are much better than eight .303s from 1940 firing 1939/40 ammunition.
BUT that was not the choice faced by the British in the mid and late 30s or even in 1940.
They had choice of eight .303s or basicly four late 1930s .50 cal guns (six were too heavy for the engines avialable).

The .50 cal was under 600rpm when tested by the British and did not go to the 750-850rpm numbers until very late 1940 or early 1941.
so it is 150-160 .303 bullets per second vs 36-40 . 50 cal bullet per second not the 52-56 bullets per second of the later war US fighters with 4 guns.

Then we have the ammo problem/s.
When tested by the British the .50 cal had a MV of about 2500fps. about 60fps more than the .303.
The US changed the type of powder used as propellent and got the MV over 2800fps but not until after 1940.
so striking power was much less than later ammo, about 20%.
The US didn't seem to have any incendiary ammunition for the .50cal or at least not very effective incendiary ammo. The M1 Incendiary is pretty much an enlarged
de Wilde bullet as developed by the British. This does not show up until well after the BoB. By 1943 the US is phasing that out and switching to the M8 API round in which every AP round has a small charge of incendiary material in the nose and not using mixed belts of different types of ammo.
Thinking you could get 1943 P-51/FM-2 gun power in a British fighter in 1940 without a time machine is just wrong.

Shortround6 said:

We have a number of threads on the bolded part.

There is no doubt that 4-6 .50 cal guns from 1943 firing 1943 ammunition are much better than eight .303s from 1940 firing 1939/40 ammunition.
BUT that was not the choice faced by the British in the mid and late 30s or even in 1940.
They had choice of eight .303s or basicly four late 1930s .50 cal guns (six were too heavy for the engines avialable).

The .50 cal was under 600rpm when tested by the British and did not go to the 750-850rpm numbers until very late 1940 or early 1941.
so it is 150-160 .303 bullets per second vs 36-40 . 50 cal bullet per second not the 52-56 bullets per second of the later war US fighters with 4 guns.

Then we have the ammo problem/s.
When tested by the British the .50 cal had a MV of about 2500fps. about 60fps more than the .303.
The US changed the type of powder used as propellent and got the MV over 2800fps but not until after 1940.
so striking power was much less than later ammo, about 20%.
The US didn't seem to have any incendiary ammunition for the .50cal or at least not very effective incendiary ammo. The M1 Incendiary is pretty much an enlarged
de Wilde bullet as developed by the British. This does not show up until well after the BoB. By 1943 the US is phasing that out and switching to the M8 API round in which every AP round has a small charge of incendiary material in the nose and not using mixed belts of different types of ammo.
Thinking you could get 1943 P-51/FM-2 gun power in a British fighter in 1940 without a time machine is just wrong.

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Well, Wing Commander, H.R. Allen, DFC in his book "Who Won the Battle of Britain" (ph. 79-80) disagrees. And "Flying Guns Of World War II" says the AP. 303 used at that time had no explosive content. The cartridge was a 7.7x56R. The incendiary version had 1/2 gram. It also had a slightly lower muzzle velocity (747 meters/sec. (Pages 330 and 331) of the Flying Guns book I have uploaded in other posts. And the incendiary round was NOT armor piercings

David Fred said:

Like "The bomber will always get through". Like 8.303's are better than 4-6 .50's. Like the "Big Wing", which Allen hates in his book, as did Leigh-Mallory and Dowding

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..or like 6 - 0.5 in are better than 4 - 20 mm?

The choice of 0.303 in was actually the result of testing in the 1930s, which showed that the effect of individual 0.5 in was not proportionately greater than that of 0.303 in.

The "bomber will always get through" was the result of two simultaneous logical errors: first, that the defensive armament of bombers would be devastating against interceptors and, second, that civilian populations would collapse into anti-government revolution when a couple of bombs dropped someplace in the neighborhood.

The .303 AP had no explosive content but the .303 De Wilde was loaded in at least one gun of the eight and each .303 incendiary bullet held 7 grains of material. Which is just under 1/2 gram. But one gun was firing 19-20 bullets a second. Tests showed this bullet was about twice as likely to set a fuel tank on fire as the .303 incendiary/tracer. There were not enough to supply more than two guns per plane.

But the .50 cal ball and AP of the 30s and 1940 also had no explosive content. The US may not have had an incendiary round yet approved. The British didn't like the samples they got and designed their own. This leaves the .50 cal tracer as the only .50 cal projectile at the time with any hope of setting fire to anything.

The incendiary bullet may very well have had a velocity of 2370fps but the ball was 2440 and the AP was about 2500fps. This difference is pretty trivial compared to the 2500fps to 2800fps difference in the .50 cal ammo. ALL of the early .50 cal ammo was about 2500fps. The bullets were slightly heavier than the later ammo.

To make a difference in the BoB you would have needed a factory tool up to make the .50 cal guns by the thousands per year (US could barely supply their own and a few exports in 1939/40) and factories making millions of rounds of ammo before the BoB. The British had given Remington a large contract for ball, tracer, armour piercing and drill ammunition for RAF use in American aircraft purchased in 1940. They also got ammo from US government contracts VIA the US Steel Company contracts. US Steel was used to buy "surplus" US military equipment and supplies and then resell it to the British in order to keep up the facade that the US government was neutral.

The plain facts are that the early .50s didn't fire as fast in rounds per minute (or second) their muzzle velocity was lower and the ammo was deficient in the quantity of incendiary material fired per unit of time compared to the same number of guns in 1943.
Now the quartet of early .50s may have been better than eight .303s but by nowhere near the margin the later guns and ammo would have.

Now let's put six .50s and 235 rounds per gun (807lbs) in a Hurricane with a 2 pitch prop and see what happens to climb and ceiling?
The eight .303s and 334 rounds per gun went about 433lbs.
Four .50s with 250rpg is going to go around 556lbs.

Might as well post my message from this thread again;

Greyman said:

I gotta say, "the bomber will always get through" has to be one of the most misunderstood quotations.

The idea wasn't that bombers would always get through to their targets no matter what the enemy did to defend - it was that no matter how much effort you put into defense, your cities wouldn't escape being bombed.

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Greyman said:

Might as well post my message from this thread again;

I gotta say, "the bomber will always get through" has to be one of the most misunderstood quotations.

The idea wasn't that bombers would always get through to their targets no matter what the enemy did to defend - it was that no matter how much effort you put into defense, your cities wouldn't escape being bombed.

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Yes, but in many cases the cost of bombing was greater than the cost of being bombed, the effect of being bombed was grossly overestimated. Germany had to call off its bombing offensives against UK in daylight and then at night. Italy's assault n UK never got started. The British attacks on Germany had little effect until 1942/3 when the war was half way through.

A Wing Commander as I mentioned already goes through everything you say in detail, and disagrees. So believe what you wish.
And 4 Hispano II were not available in the BoB, and two bladed props were not used.

But have it your way.

David Fred said:

A Wing Commander as I mentioned already goes through everything you say in detail, and disagrees. So believe what you wish.
And 4 Hispano II were not available in the BoB, and two bladed props were not used.

But have it your way.

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I have the book but haven't read it yet.

I did not mention two bladed props, I said two pitch props which were a totally different thing.

David Fred said:

And the incendiary round was NOT armor piercings

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The M8 API most certainly was. API: Armor Piercing Incendiary.

Perhaps you're confusing that with the M23 Incendiary ammunition, which was solely incendiary?

The results of the air fighting show that the .303-inch Browning was certainly effective enough. Better tactics, more training, and at least some gunnery training would have helped far, far more than a tiny (at best) upgrade to .5-inch guns.

David Fred said:

A Wing Commander as I mentioned already goes through everything you say in detail, and disagrees. So believe what you wish.

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OK I have read the first 4 pages in the chapter on armement and he not only makes the same mistakes others do on what the the cycle rate of the Browning .50 cal was and when but also falls into the same trap of using the 1941-42 ammo for his ballistic comparisons rather than using the 1930s/1940 ammo. In fact he may be using too high a velocity for the .50 cal.
You will find many sources claiming the .50 cal has a muzzle velocity of 2900fps, which is what the author uses. This may very well be correct for some guns.
However the ground guns as Used by the US army in WW II and the water cooled AA guns used by the Army and Navy used 45 in barrels. The Aircraft guns used 36 in barrels. Either the ground guns are carting around 9 in of barrel too much or one can expect some sort of velocity loss for the aircraft guns.
The loss of some initial velocity is not that important to aircraft guns as due to the thinner air they are fired in (at much above sea level) they don't slow down as much as bullets fired at sea level and so have shorter times of flight and hit while still moving at a higher velocity.

I do like this sentence:
page 81 second sentence of the first paragraph:
" The Colt was, in effect, a minor quick-firing cannon and it's bullets could contain warheads designed for explosion on impact, incendiary purposes or the piercing of armor; naturally, with it's greater muzzle velocity , the Colts armour-piercing ability would be considerably more effective than that of a Browning bullet, and to this consideration must be added the bullet weight which is was over four times greater in the former than in the latter."

Sounds like a Colt salesman.
Let's be clear here, the .50 cal Colt NEVER had a bullet that exploded on impact issued for service use in WW II, let alone in time for the BoB.
It is highly doubtful that ANY SORT OF INCENDIARY ammunition (aside from tracer) was available in time for the BoB although it did become available later.
Even at 2500fps the .50 will penetrate more much more armour than the .303 in large part due to it's greater weight per unit of frontal area.

His nice little table has some mistaken assumptions. Like the 2240fps mv for the .303 MK VII. an easy typo but he use that to figure out his muzzle energy figures, if you use the correct velocity of 2440 fps the muzzle energy goes up 18% for the .303 and if you use the correct bullet weight and velocity for the .50 cal ammo as it existed in 1940 it's muzzle energy goes down a bit over 21%. Once you correct the rate of fire to 600rpm for the Colt .50 (which is being generous for 1940) and also change the .303 Browning down from 1350 to 1150rom the Colts energy advantage shrinks from over double to about 18.7% which is nice but not an overwhelming blow them out of the sky advantage that the author claims.

The author also makes a few other leaps of faith or judgement. Like relating the story of Group Captain Peter Townsend and an engagement where he fired at and damaged a german bomber that made it back to base with 220 hits from the .303 which is very good shooting indeed. The author then asks what would would have happened if the German had been hit by 220 .50 cal rounds. Interesting question but it rather glosses right by a few facts. One, Group Captain Townsend may have fired his entire load of 2400 rounds (if a Spitfire I, more if a Hurricane or SPitfire II) and with equal accuracy a load of 2400 rounds of .50 cal ammo weighs 720 lbs and not the 160lbs that 2400 rounds of .303 ammo weighs. Two, Group Captain Townsend had about 17 seconds of firing time. it would have take 60 seconds to fire 2400 rounds of .50 cal ammo from four 1940 Colt .50s.
The author then goes on to say "after ten such strikes, the bomber would have exploded with such ferocity as to have put Townsend's life in danger from the resulting flying debris."

Really?? no HE ammo, no incendiary ammo, tracers make up what percentage of the belt, 20%? if used at all?

I am not sure 10 20mm strikes would have destroyed a German twin engine bomber in such a fashion unless the bombs in the bombay blew up. The chances of ten .50 strikes blowing up a bomber in such a fashion are slim and none and slim has already left town.

Please note I am not saying that it was impossible to shoot down a bomber with 10 .50cal hits. Just that the likelihood of the bomber blowing up with such ferocity that the fighter pilot is in serous danger from flying debris is a more than bit much.

During 1941 trials vs. a He 111, the British figured 10 rounds of .5-inch Winchester AP had a 23.2% chance of downing the bomber in a stern attack. This was entirely due to damage in the engine area (immediate lethal damage to the supercharger, fuel system, oil system or coolant system).

If the .5-inch AP round managed a leak in one of the self-sealing tanks it was not considered lethal. No .5-inch incendiary round was used in the trial. I suspect for the reason Shortround mentioned; none available until sometime in '42.

To get about the same percentage, the .303 Mk.VI incendiary needed about 22 strikes and the .303 Mk.I AP needed about 24. Hispano HE/I needed 4.

Sholto Douglas thought the results/conclusions of the trial were rather optimistic.