If you could go back to WW-2 with the knowledge you have now in engine design...what would you improve? No jets...

[XBe02Drvr]

My first thought is I would not place the superchargers in the nose case. The standard location behind the engine seems more durable and easier to plumb.

Numerous radials back in the day had a centrifugal blower in the nose case right behind the reduction gear.

 

[sotaro]

Numerous radials back in the day had a centrifugal blower in the nose case right behind the reduction gear.

I didn't know that. A two stroke with an open crankcase, i.e. not using crankcase compression, is significantly more dependent on boost than a 4 stroke, especially this one with it's diminished compression ratio. This would need a multistage turbo.

 

[XBe02Drvr]

I didn't know that. A two stroke with an open crankcase, i.e. not using crankcase compression, is significantly more dependent on boost than a 4 stroke, especially this one with it's diminished compression ratio. This would need a multistage turbo.

That's the beauty of the GM 2-stroke diesel concept. The crankcase has no connection to the mixture path as in a 2-stroke gas job. It's a regular oil bath crankcase with oil pump and galleries like a 4-stroke. Intake and exhaust are side ports, and their relative spacing, plus the boost from the blower accomplishes scavenging and intake simultaneously near the bottom of the downstroke. The only thing at the top of the cylinder is the injector. The ones we had were governed at 2150 RPM (2150 power strokes vs 1075 for a 4-stroke), but I'm sure with a little tweaking they could be run faster.
Cheers,
Wes

 

[Deleted member 68059]

That's the beauty of the GM 2-stroke diesel concept.

Yes, 2-Stroke diesels for aero use a pretty good, as the lower gas temperatures (due to diesel) mean the piston temperature changes are lower, and eases
cylinder lubrication, so they dont have the same constant tendancy to sieze which petrol-2 strokes do, I dont think the petrol
2-Stroke is at all suited to the duty cycle of an aero engine.

 

[XBe02Drvr]

I dont think the petrol
2-Stroke is at all suited to the duty cycle of an aero engine.

Back when I was a kid, the market was flooded with cheap 4 cylinder 2-stroke air cooled engines intended for WWII single-flight target drones. Some of the more poverty stricken EAA homebuilders tried to use them in their experimental aircraft, with disastrous results.
Cheers,
Wes

 

[PWR4360-59B]

Ah, things are not quite as simple as they appear.
granted they were not supercharged but did you know the First Porsche engine to exceed 1 hp per pound was the 4.5 liter 917 flat 12 engine of 1969? forged titanium connecting rods and other parts/materials not used in WW II. People keep wanting to compare modern engines and keep forgetting that the high performance aircraft engines of the day, on hp per pound basis took several decades for even race car engines to beat. And the race car engines were nowhere near as a reliable or durable as the aircraft engines. Your genesis theory needs a bit of work. The electronics in the proximity fuse consisted of a few vacuum tubes that were miniaturized. Want to try to build even a simple computer from a 1980s-90s car using vacuum tubes? reliability of said vacuum tube computer would be measured in minutes if not seconds simply due to the number of parts. BTW at the start of the proximity fuse program they would have been satisfied with a 20-25% dud rate if I remember correctly.
I would also note comparing lead content is a lousy way of comparing fuels. For example the post war Mil-F-5572 fuel specification allowed for 4.6cc of lead per US gallon for not only 115/145 but for 100/130 and even 91/96 fuel. You had to use better base stocks and other components for the higher grade fuel, not just more lead. The civilian ASTM D910-48T specification only allowed 4.6cc per gallon for commercial 115/145, both 100/130 and 108/135 were only allowed 3 CCs per gallon and civil 91/98 octane (yes, 2 points higher) was only allowed 2 CCs of lead.
Wright had to develop a brand new way of putting fins on cylinders for the above 1200hp R-1820s, also used on the 1900hp R-2600s and the R-3350s. They machined grooves into the cylinders that were larger at the bottom than at the top(surface) and formed sheet metal into a W configuration, very long outside arms and very short inside arms. This was "rolled" into the grooves so that the bottom of the W was swaged into the groove for mechanical interlock.
In a lot of cases you not only need the design of the new parts, you need the designs for the machines to make the new parts and in some cases you need the designs for machines that can make the machines that can make the parts you want.

Good post.
And some of what I was going to say as well.
First off, like mentioned above it took the automotive world many years to figure out what the aircraft engine designers did in WW2 days, no excuse for that since many automobile company's built aircraft engines in the big one. Secondly in the more modern day of engine design it was not so much "engineers" that is ones with a college degree, had anything to do with improving engine performance. It was smart uneducated know nothings like Smokey Yunick, Ed Iskenderian , Vic Edlebrock and a huge list of similar folks in the day.
As far as improvements ? I would not use any cast aluminum or magnesium, fuel would be diesel or kerosene, I'd increase the power density with something similar to this

or this,

And its not a "radical design" its very very old school stuff, there was even an aircraft engine built that way.
Turbo charging was used in WW2 so nothing new there, also I would use turbo compounding as well.
Electronics ? Like mentioned in shortround's post, and like seen right after WW2, the ECU's found in nowadays cars would have filled most of the house you live in, so that is not an option.

 

[swampyankee]

Yes, 2-Stroke diesels for aero use a pretty good, as the lower gas temperatures (due to diesel) mean the piston temperature changes are lower, and eases
cylinder lubrication, so they dont have the same constant tendancy to sieze which petrol-2 strokes do, I dont think the petrol
2-Stroke is at all suited to the duty cycle of an aero engine.

Whether an engine can manage an aircraft duty cycle is all down to design; certainly Fairbanks-Morse, MAN, and others build and built 2-stroke spark-ignition engines for continuous, heavy duty operation. The real problem is that an aircraft 2-stroke would have terrible sfc until direct fuel injection could be made to work.

 

[Deleted member 68059]

Whether an engine can manage an aircraft duty cycle is all down to design; certainly Fairbanks-Morse, MAN, and others build and built 2-stroke spark-ignition engines for continuous, heavy duty operation. The real problem is that an aircraft 2-stroke would have terrible sfc until direct fuel injection could be made to work.

Please list the 2-stroke petrol engines that you are referring to above.

You cannot compare marine/locomotive or static applications to aero, as the weight requirements are so different its impossible to event compare them (wall thicknesses etc).

 

[swampyankee]

Please list the 2-stroke petrol engines that you are referring to above.

You cannot compare marine/locomotive or static applications to aero, as the weight requirements are so different its impossible to event compare them (wall thicknesses etc).

No, you can't, but nor can you compare low-cost, light-duty engines to those designed for aviation use. There's nothing intrinsic to the two-stroke Otto cycle making it unsuitable for aviation use. One maker of two-stroke, spark-ignition engines was McCullough http://enginehistory.org/Piston/HOAE/McCulloch.html For others, see http://enginehistory.org/Piston/HOAE/SChron2S.html. Note this source is limited to horizontally-opposed engines, which are limited to low powers. Rolls-Royce, with the Crecy, was pretty sure it could be done: Rolls-Royce Crecy | Project Gutenberg Self-Publishing - eBooks | Read eBooks online

 

[wuzak]

As far as improvements ? I would not use any cast aluminum or magnesium

Magnesium was not commonly used in WW2, so it would be a non-starter.

Why not aluminium? What would you use? Cast steel?

fuel would be diesel or kerosene

So compression ignition?

I'd increase the power density with something similar to this

Not sure that the VW group 'W' engines would be a good option for an aircraft engine. To achieve the narrow angle between the paired banks the crankshaft needed an offset journal. This would be a weak point in the engine.

A broad arrow, like the Lion, or an X-type engine, would be better.

Turbo charging was used in WW2 so nothing new there, also I would use turbo compounding as well.

Turbocharging was used differently in WW2 than in cars. Modern control systems may not be able to be replicated in WW2.

Turbo-compound was experimented with in WW2, but the turbine materials were not up to the temperatures required, certainly in the case of the V-1710-E27.

 

[swampyankee]

Not sure why the lack of love for aluminum or magnesium.
Certainly, there were no good alternatives.

 

[Shortround6]

Magnesium was more of a country by country thing. The US certainly used magnesium in front covers (reduction gear cases) of some radials. ALos rear covers (supercharger housings?)
Germans used it in valve covers and crankcase covers, maybe more? It was most often used where there was little stress.

It is difficult with a modern perspective to see Aluminium and Magnesium from a 1930s perspective. Just before WW I (about 20-25 years before the period we are talking about) one engineer described Aluminium as "solidified dirt".
They were still learning how make good. high strength alloys and how to work it, (cast and/or forge),Wright had essentially given up and gone to steel crankcases on some of their engines. Allison actually located a small foundry doing work for some artists (who developed the process) for making thin section, high strength casting for sculptures. Using this process allowed them to make much stronger crankcases that were actually a few pounds lighter. Alcoa licenced the process and made the engine castings for Allison.

The fire trucks I used to drive were powered by GMC two-stroke Diesels. GM used to rate these diesels according the expected duty, Firetrucks were allowed to make more power than an over road truck and both were allowed higher powers than stationary power plants (generators or pumps). However even 1990s the GMC 2-stroke (they were banned from new construction in the mid 90s. My department got one of the last Pierce fire trucks with one of these engines) had a miserable power to weight ratio compared to aircraft engines, however good they may have compared to other diesels. The 8V-92T in the truck weighed as much as a small car for it's 450hp.

You are going to need unobtainium to get a 700hp 12V-92 of about 4000lbs down to 1500lbs or less even if you mount twin turbos on each cylinder bank and accept only a few hundred hours of engine life and get the engine up to about 1000hp.

The problem with a lot of these high powered engines is keeping the cylinder cool, Whether you fire the cylinder once every revolution or once every two revolutions you have to keep it cool or the oil breaks down on the cylinder walls and then the piston rings pack it in and then the whole engine fails.

 

[Deleted member 68059]

No, you can't, but nor can you compare low-cost, light-duty engines to those designed for aviation use. There's nothing intrinsic to the two-stroke Otto cycle making it unsuitable for aviation use. One maker of two-stroke, spark-ignition engines was McCullough http://enginehistory.org/Piston/HOAE/McCulloch.html For others, see http://enginehistory.org/Piston/HOAE/SChron2S.html. Note this source is limited to horizontally-opposed engines, which are limited to low powers. Rolls-Royce, with the Crecy, was pretty sure it could be done: Rolls-Royce Crecy | Project Gutenberg Self-Publishing - eBooks | Read eBooks online

Hi,
You suggested I was wrong because MAN and Fairbanks-Morse made 2-stroke spark ignition high duty engines, I asked which they were.

None of the engines in that list from AEHS are from MAN or Fairbanks.

There IS something absolutely intrinsic about the 2-stroke Otto cycle which makes it unsuitable for aero engines, which is that it DOUBLES the thermal load on the engine for a given size, which is prescisely why they are so hard to develop into reliable high-duty cycle units in light weight modes. These problems all vanish with 2-stroke diesel, as the combustion temperatures are much lower.

With regards to the Crecy book, I`m not sure from where in the pages you find evidence that it didnt suffer from prolific piston siezures - flicking through my copy here I cant see that being suggested.

In fact (if you visit the Rolls-Royce archives) and request file "RRHT - HIVES 3019", you`ll find a letter from Hives himself to Bulman (Bulman was in charge of aero engine development at the Air Ministry) - dated 19th October 1942.

===============================

"Dear Bulman
Replying to your letter of the 5th, we are not short of instructions and contracts to build 2-stroke engines.

We have only one slight hitch, and that is to get them to run, and continue to run!

Yours Sincerely

Hives"

===============================

(the exclamation mark was not added in by me).

 

[TheMadPenguin]

ASSUMING that I walk through a wall into 1937...
1: Fix the damned torpedoes. Their flaws were easy to prove, BuTorp was slow to listen to anybody but themselves.
They ran 11 +/- 1 feet too deep because the depth sensor was on the outer hull, and Mr Venturi lowered the pressure causing the torp to run deeper until the pressure was "as required". Move the sensor into an internal cavity open to the sea, but not to rushing water.
The Mag Detonator DOES NOT WORK. Remove it, stick to contact.
The Gyroscope which allows off-bore firing can jam, causing a circular run. Strengthen the mounting so it can't jam on the acceleration of launch
The firing pin will bend on a direct (perpendicular) impact, but works at 45 degree impacts: Mount 2 pins, each at 45 degrees from run-line, let EITHER one trigger the warhead.
2: Describe the magnetron-based radar and VT fuse theory to people who can turn theory into working wonders. Put VT fuzes as proximity detonators in air-to-air rockets.
3: BTEXXTEL (Benzene, Toluene (which is Methyl Benzene), Ethel Benzene, Xylene (which is dimethyl benzene), Xylidine (which is dimethyl benzamine) and Tetra Ethyl Lead (with dichloro ethane or dibromo ethane) to convert 87 -> 150 octane fuel.
4: Revolver and Gatling cannons, allowing short bursts to convey crushing damage. .50, 20mm and 30mm Gatling, at least, 75mm & 90mm revolver for AAA as well.
5: The RPG as a substitute for the bazooka. The Hedgehog using RPG-like rockets rather than spigot mortars.

Can I sneak a few books along with me in this wonderful fantasy? Like the schematics for the P-47N?

 

[Shortround6]

Somethings, like the torpedo stuff, are easy to fix.

Other things are not so easy. Just because you know what Xylidine is you have to know what it actually does (how it works, not just that it does it) and you have to know how to make it in quantity. A change in refining processes or additives saved tens of thousands of tons of high grade steel, supposedly enough for around 20 destroyer hulls.

Same with the VT fuse, theory was easy, manufacturing the things was a major industrial effort.

Gatling cannon weren't exactly unknown, somebody had put an electric motor, a couple of pulleys and v-belt on a gatling gun back in the 1890s, rate of fire was astounding, so was the weight, feeding it for more than few seconds was a problem. Sticking any sort of gatling gun in a wing was a problem due to the size.

RPGs depend on propellent technology that didn't exist at the time. Some rpgs are two stage, a fast burning charge blows the rocket out of the tube with a low (cough cough) signature (back blast) and the main engine ignites several yards out to avoid barbecuing the firer. The German Panzerschreck and American bazooka used the long tubes to try to consume all the rocket propellent in that first few feet of travel. Firers still needed some sort of shield and face/eye protection. Panzerfaust was actually a recoilless gun. Powder Charge and inert material went out the backend to counter the projectile leaving the front end. Russian RPG employs the 2nd method to get the rocket far enough away from the firer for the rocket to ignite.

Idea is easy, getting the rocket to ignite reliably and on time is a bit of a problem. Rocket backblast onboard ship might be a bit of a problem.

 

[TheMadPenguin]

Somethings, like the torpedo stuff, are easy to fix.
Other things are not so easy. Just because you know what Xylidine is you have to know what it actually does (how it works, not just that it does it) and you have to know how to make it in quantity.

You only need to know that it works, and how to make it in quantity.
Every element I mentioned was used in WWII, just not early WWII.

Same with the VT fuse, theory was easy, manufacturing the things was a major industrial effort.

I didn't want to write a book.

Gatling cannon weren't exactly unknown, somebody had put an electric motor, a couple of pulleys and v-belt on a gatling gun back in the 1890s, rate of fire was astounding, so was the weight, feeding it for more than few seconds was a problem. Sticking any sort of gatling gun in a wing was a problem due to the size.

So what's needed is to apply a few years of engineering smarts. The real problem with the Gatling cannon is nobody realized how much it could affect air combat. 6-8-12-16 machine guns were the stream of thought, not two that put out the fire of 6. The idea was overlooked, therefore, how to implement the idea in a smaller volume and mass wasn't addressed.

RPGs depend on propellent technology that didn't exist at the time.

The rocket fuel for RPGs is good old smokeless powder followed by good old ammonium (or Potassium) perchorlate. 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane co-crystal with cyclo tetramethylene tetranitramine isn't needed. We had the rocket propellant then. Bazooka, Panzerschreck and Panzerfaust come together with (then-known) shaped charge warhead.

Idea is easy, getting the rocket to ignite reliably and on time is a bit of a problem. Rocket backblast onboard ship might be a bit of a problem.

We had rockets. We had them on ships. We had them on planes. We had them on men's shoulders.

Speaking of destroyer hulls, putting the Gearing class into production instead of the Fletcher class would have saves a few lives. Gearings survived "kamikaze" hits better than the Fletchers did.

 

[XBe02Drvr]

The idea was overlooked, therefore, how to implement the idea in a smaller volume and mass wasn't addressed.

When I worked at GE Armament Division in '69-'70, they had been addressing the "volume and mass" issue since just after WWII, and the Vulcan, Mini, and Micro were the best the technology could produce over 20+ years of development.
They built them smaller and lighter and had reliability, recoil, and accuracy problems, not to mention the occasional ammo explosion. They built them bigger and heavier and the problems went away. Shorter barrels resulted in airframe burn damage. Lighter weight construction led to catastrophic failures in feed mechanisms and jams in ammo drums, with drastic consequences to the aircraft. Not like a belt feed jam in a wing mounted .50 cal. Feed line breakage often led to ruptured cartridge casings and the spillage of loose propellant powder into the breech mechanism with predictable results. The test range techs used to bring back all sorts of mangled and burned scrap metal for R&D to analyze.
It stands to reason, a .45 cal 1873 Single Action Army is going to have more bulk and mass than a single shot .45 cal percussion Derringer.
So, no, rotary cannons in WWII fighters were not a practical proposition, except MAYBE in a Lightning, Mosquito, Black Widow, or Beafighter. (Let's not forget the skip bombing Mitchells!)

 

[TheMadPenguin]

"So, no, rotary cannons in WWII fighters were not a practical proposition, except MAYBE in a Lightning, Mosquito, Black Widow, or Beafighter. (Let's not forget the skip bombing Mitchells!)"

Mitchell B25, Douglas A26, Martin B-26, de Havilland Mosquito/Hornet , P-38, Any bomber with a tail turret, and that's just a few needing the 20mm
The .50 gatling would strengthen the defensive fire of any bomber with twin .50s mounted anywhere.
Put 2 of each in an F7F, add 2 .50 Gatlings to the 20mm Gatling in strafing light bombers.
But the .50 Gatling development started in 1982, yes?
So (as I said) the idea was overlooked.

 

[XBe02Drvr]

"So, no, rotary cannons in WWII fighters were not a practical proposition, except MAYBE in a Lightning, Mosquito, Black Widow, or Beafighter. (Let's not forget the skip bombing Mitchells!)"

Mitchell B25, Douglas A26, Martin B-26, de Havilland Mosquito/Hornet , P-38, Any bomber with a tail turret, and that's just a few needing the 20mm
The .50 gatling would strengthen the defensive fire of any bomber with twin .50s mounted anywhere.
Put 2 of each in an F7F, add 2 .50 Gatlings to the 20mm Gatling in strafing light bombers.
But the .50 Gatling development started in 1982, yes?
So (as I said) the idea was overlooked.

No, the .50 Gatling was looked at in late '40s, but then the push was "bigger and better" and the interest was .60 cal and 20MM. Turret mounted Vulcans would have been impractical in WWII bombers, as they take up so much space and weight. The M113 APC-mounted VADS (Vulcan Air Defense System) fills the interior of an armored personnel carrier with ammo drum and feed mechanism. And has less than half a minute of firing time. The only airborne turret mounted Vulcan was the three barrel, slow turning version installed in some Hueycobras and Apaches, and that took up a lot of space, could only carry a few seconds worth of ammo, and was hard to keep on target due to recoil effect when fired off axis. Not the sort of thing to defend you to Berlin and back.
Dream on, Penguin.
Cheers,
Wes

 

[Shortround6]

GAU-19/A (GECAL 50) 12.7 mm Gun (United States) - Jane's Air-Launched Weapons

"A single three-barrel GAU-19/A system ready to fire on a Black Hawk pintle mounting weighs 144 kg empty and 250 kg with 750 rounds.On the three-barrelled version a 4 hp AC/DC electric motor is mounted on the lower starboard front of the rotor housing. This provides a firing rate up to 2,000 rds/min."

3 .50 cal M2 guns weigh 110 kg (heaviest weight I could find in "AHT" for 6 guns divided by 2)
very little electricity needed,
firing rate of approximately 2400 rds/min.

I will grant you that the GAU-19/A is much more reliable and has a much longer gun life. it is also about 50 years newer than the M2 aircraft gun.

a major problem with high rate of fire guns in WW II was feeding them, conventional belts don't work well without some sort of delinking system, adds weight and bulk.
You also need some way of moving the belt, just pulling from the gun itself can lead to jams and broken links/belts. Some bomber turrets used electric motors to move the belts but the motors had to feed the belts at the proper rate (servo controlled) too fast and the belt bunched up and jammed, too slow and the belt started to stretch. No two guns fired at exactly the same rate and even the same gun could fire at different rates on the same flight (cold vs warm oil in the gun/air temperature).

The devil is often in the details.
The problem with solid rocket propellent for the first anti-tank rockets was not the chemical composition but the physical composition. Burn rate is affected by grain size/structure, especially in a cast rocket motor. Cracks/voids can also really affect the burn rate/accuracy. In some cases (post WW II?) there were rockets for use at different temperatures (climate conditions).