Engine questions help

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BiffF15

Tech Sergeant
2,039
3,665
Aug 15, 2010
Florida
Okay, I have nephews (twins) who are first year engineering students and budding WW2 aircraft fans. They have asked me a few questions that are beyond my knowledge level hence my reaching out to you guys. Any help would be greatly appreciated. I'm working on getting them onto the forum. They are fans of War Thunder and I have given them Calum's book.

Here they are.

1. What led to the Brit use of sleeve valves?

2. Are the 23, 37, and 45mm cannons causing power plant problems from vibration?

3. Why the different types of con rods (Siamesed vs Fork & Blade vs unbalanced?

4. Why does the one of the three crankshafts on the Napier Deltic need to rotate in opposite directions to achieve the correct piston phasing?

Thanks in advance!

Cheers,
Biff
 
It was Ricardo who decided that sleeve valves were the way forward with the then available fuel from memory, the 20mm in the 109E caused the forward bulkhead to fail which is why the FF/M's were put in the wings, the Fiesla had the bulkhead redesigned for the better 151/20 cannon. The Deltic had one crank spin the opposite way for the simple reason if they all spun the same way the pistons would either be all at top dead center or all at BDC. There is a fantastic video on the Deltic on youtube.


View: https://www.youtube.com/watch?v=-vV-YaKsIGk
 
I will try on 3 of them.
BiffF15 said:
What led to the Brit use of sleeve valves?
Click to expand...
We can blame Harry Ricardo for this one. He was a noted engine designer in WW I and in the 1920s and in 1927 wrote a research paper advancing the Sleeve valve engine as way to overcome may of the faults of the poppet valve engines of the time. He was probably correct in 1927. Problems were that as other engine designers struggled to perfect the sleeve valve engine as production item, other designers were fixing most of the problems with poppet valves. Better steels for valves and valve seats, the sodium cooled exhaust valve, better valve springs (didn't break as often as 1920s springs) and so on.
full explanation could take a number of pages, large pages.
Not helped by some of the designers being related to each other (by marriage?) and a few (or one) being somewhat egotistical.
Clever design and theory ran into problems with materials and manufacturing processes.
BiffF15 said:
Why does the one of the three crankshafts on the Napier Deltic need to rotate in opposite directions to achieve the correct piston phasing?
Click to expand...
Might be trying to get the pistons phased correctly as you state. It was a two stroke diesel and needed to fire every time the pistons moved towards each other. Trying to get the desired piston motion with all three cranks turning the same way might have been very difficult. Each crank used 6 throws with two connecting rods on each throw. Perhaps you could have built an engine with all three cranks turning the same way but you may need to use 12 throws (each connecting rod on it's own throw) to get the piston motion correct. But that also means a long engine to fit in all the crank throws and the cylinders spaced further apart lengthwise.
BiffF15 said:
3. Why the different types of con rods (Siamesed vs Fork & Blade vs unbalanced?
Click to expand...
Siamesed seems to be new, or a modification of the old articulated connecting rod

Or are we referring to side by side rods, two rods sharing the same crank pin one behind the other.
In WW I or the 1920s with low cylinder pressures and low rpm they could get away with types of construction that they could not use in later, higher stress engines.
A lot depended on what each designer or team thought was bigger problem. Offsetting the cylinder banks from each other to use the side by side rods and introducing some twisting motions/vibrations or keeping the cylinders directly opposite each other and using more complicated connecting rods and rod bearings and lubrication. The Articulate rods also had the pistons on one side having a different stroke than the pistons on the other side.
In the 1920s it sort of pick your poison as some of this was faith and not quite good math. They were working on the math.
The 30s and 40s saw a lot of development in bearing materials and construction which allowed for smaller bearing area to carry the same load/s.
 
BiffF15 said:
2. Are the 23, 37, and 45mm cannons causing power plant problems from vibration?
Click to expand...
23mm - no problems, IMO. 37mm - it was still manageable. 45mm - this one might make problems.

FWIW - I served on a 30mm twin SP vehicle in 1990-91. Despite the vehicle weighting more than 10 tons ready for combat, the recoil of these two guns firing was still very much felt. We can just imagine a 45mm cannon recoiling & vibrating on a 3 ton fighter...
 
BiffF15 said:
Additional questions.

1. Why were motor driven cannons not explored during the war?
Click to expand...
We can approach this in several ways.
1. What did little know inventors do?
2. What needs do a motor driven cannon solve that conventional cannon could not?
3. What was needed to solve some of the motor driven cannon problems?
Faster firing needs a faster/more powerful ammo supply.

Somebody hung an electric motor, a couple of pullies and a v belt on a Gatling gun before 1900 (?).
It is supposed to have fired at over 1000rpm. Problem was feeding it.
As an aircraft gun even a 5-6 barreled Gatling gun would be heavy and it either needed to fire through the prop, be geared to the engine/propeller, slowing down the rate of fire ? or you need to mount one in/under each wing.
In WW I there was the Fokker-Leimberger 7.9mm gun

But twelve barrels you need a large plane to carry it. Design was also flawed.

One reason it was so fast firing was that the ammo stayed in the belts and the two "spools" passed the belt between them and fired when the two 1/2 chambers met. The belt with the fired cases still in it pass out the other side of the gun. Big failing was that some of the cartridge cases split into the gap as the gun fired.
Powered guns can fall into two classes. One is using something like a power take-off from the engine to power the gun. Obviously this only works when the gun and the engine are in close proximity. The other is to use electric or hydraulic power to to drive the gun/s and the guns can be remote from the engines. Using the power take-off can mean that the gun fires in proportion to engine RPM. Electric and hydraulic don't have that restriction. Also means that the pilot/crew may be able to select different rates of fire.

Aircraft cannon were always a trade off between firepower and weight.
Another problem is that motor driven cannon sometimes take a while to get up to speed. Or in the case of guns driven by a power take-off, there is a clutch and gear train in the system and reliability may be a bit lacking in service. Some rather well known aircraft guns of WW II were a lot simpler and still took several years to get sorted out in cold atmospheres.

Hope that gives something to think about.
 
Gents,
Again thank you.

Tomo,
What I should have included in the build up to the question was would it no have been simpler to have a motor powered gun (not Gatling) to better the dependability over gas and recoil power?

Cheers,
Biff
 
Last edited:
BiffF15 said:
Tomo,
What I should have included in the build up to the question was would it no have been simpler to have a motor powered gun (not Gatling) to better the dependability over gas and recoil power?
Click to expand...
No, it would not. Making the Vulcans dependable was a major engineering effort at a time when technology was more advanced.

The advantage of the Vulcan is compactness compared to rate of fire. When the nose of the aircraft it occupied by a search radar, putting cannon there becomes more and more impractical. The F-8 could do it because its radar was relatively dinky and not the focus of the aircraft. The F-4 could not because it was a weapon system, not an aircraft, and a big radar was a key part of the system. When the wings are carrying relatively delicate missiles, wing-mounted guns are impractical. As guns become more and more secondary, having lots of guns makes less and less sense.

In addition, WWII fighters didn't have very powerful electrical systems because there weren't many systems that drew a lot of power. The spark plugs would have been drawing much of the power! (An F-4 was a flying power plant, by comparison.)

Finally, there's a weight and volume issue. An F-15 approaches the size of a B-17. Fitting a chunky 20mm Vulcan with a garbage can-sized magazine into the body isn't that hard. Even if you go down to .50 cal, where are you fitting this in the fuselage of a WWII fighter? Without ranging radars, how many seconds of fire do you need to keep the fighter effective? How do you synchronize an electrically-driven Gatling-type gun with the propeller? You would have to keep feeding ammo and be set up to eject unfired rounds because you can't suddenly stop the spinning barrels, and a clutch and brake to decouple the ammunition feed from the barrels and pause the ammunition feed several times a second would be insane.

Now stop and consider the development process for this gun and the aircraft to carry it. Seriously, no one chime in with answers on this. Biff and his nephews need to sit down and think through what this project looks like. Consider the entire setting and as many factors as you can think of. Map out a basic project plan. This would be a good theoretical case study for a project management class.
 
BiffF15 said:
Gents,
Again thank you.

Tomo,
What I should have included in the build up to the question was would it no have been simpler to have a motor powered gun (not Gatling) to better the dependability over gas and recoil power?

Cheers,
Biff
Click to expand...

Both gas and recoil-operated guns - at least majority of them - were very reliable with some thought invested in the way the installation is executed (ammo feed and heating work), and if people in the government-run facilities didn't screw up (like on the American Hispano). A motor-driven gun has a very few options wrt. where it is practical to be installed. The motor-cannon is an obvious location, but that does not work if the V12 engine is not set-up for that way of installation, and it will not work on the 2-row radials.
(1-row radial can do it with the spur reduction gear, but nobody was doing that beyond Pobjoy)
That means that there is no British, American or Japanese fighter that can take advantage of such an installation, unless it is a 2-engined type. The 2-engined fighters will need a lot of design, debugging and production effort to make the motor-driven guns work in what is now a remote installation.

The cowl position is better, all engines might be suitable for this. It will limit the number of guns, though.

After all is said and done, once people started installing 8-12 LMGs, 6-8 HMGs, or 4 cannons on the fighters, all the perceived benefits of the motor-driven cannon hit the brick wall of the much more complicated installation than if these guns were self-sufficient since most if not all of these guns will not fit around the engine, and must go to the wing.

The motor-driven guns on the bombers - in the turrets, or in the pintle mounts; single, twin and quad mounts - will make even more problems.

Hope this helps.
 
Regarding sleeve valves....

The main author to criticize the traditional valve system was indeed Ricardo, but his comments must be placed in their context, that is, the early 1920s. At that time, valve technology was far from the advancements that would be seen in the 1930s and 1940s—sodium cooling, new metals, new alloys to protect valve seats.

Furthermore, Ricardo was well aware of the successes achieved before the Great War by the Argyll company, which had produced a fairly high-performance valveless engine (Burt & Mc Collum system). This success could be contrasted with the difficulties encountered by renowned engines of the time, such as the Hispano V8 or the Bristol Jupiter, two engines which, despite their advanced design, still experienced problems with their exhaust valves.

In this context, the recommendation to use a sleeve valve system was logical, especially since it was accompanied by other considerations concerning volumetric efficiency and turbulence, as well as the size of the upper cylinder, which Ricardo considered too complex for multi-cylinder valve engines, specially for aircrafts where dimensions are a significant factor.

One hundred years later, we see that all these arguments have been swept aside by technological and metallurgical advances that have allowed tulip valves to persist !

Furthermore, the debate on volumetric efficiency and turbulence has never truly been settled—it seems that the results depend primarily on the specific construction of different engines, and not on their fundamental principle.

As for size, it turned out that the requirement to ensure a tight seal at the top of the moving sleeve prevented a truly significant reduction in diameter of air-cooled radial engines – however, the liquid-cooled cylinder heads of the Napier Sabre did reduce the width considerably, owing to the absence of finning.

Ultimately, the Bristol Hercules and Centaurus line, like the Napier Sabre, are fabulous machines - and among the most powerful engines of WW II !
 
There are motor driven guns, usually in APCs or helicopters.
These are single barrel guns and not particular high rate of fire. Like the gun in the Bradley fighting vehicle.
The 25mm Bradley gun used a 1.5hp motor to start with.
Basically they replace the gas system (gas tube, piston, piston rod and main spring) with a motor and chain drive to cycle the bolt back and forth.
It has been used on at least on 7.62mm gun.
There are advantages if the operators are looking for variable rate of fire (not usually needed in WW II aircraft) and in cannon the gun doesn't care about different ammo type that either have different recoil (heavier or lighter bullets) or different gas pressures in the barrel (different propellent) for different ammo, like HE shells or modern AP rounds for a gas operated weapon. APC cannon often use 2 different belt feeds on the gun that can be changes by flipping a switch/lever.
In an APC with a slow rate of fire (200-300rpm) the Chain guns may be timed to release less propellent gases out of the breech into the interior of the vehicle.
Most of the advantages don't seem to apply to a WW II aircraft gun.
A high rate of fire chain gun is going to need larger electric motor than a low rate of fire gun. Electric motors and generators in WW II were heavy.
 
elbmc1969 said:
When the wings are carrying relatively delicate missiles, wing-mounted guns are impractical.
Click to expand...

Also turns out that for supersonic flight you want really thin wings. Not sure autocannons would fit. And no, you absolutely don't want bulges either.
 
For the engineering students, try having them think about trying to come up with a power driven gun.
Forget about all the "gun" stuff, like extractors and ejectors and even firing pins.
A single barrel, single chamber (non-revolver, non-rotary) gun is a liner mechanism. Bolt (breech block) reciprocated back and forth (wait a while before you introduce the Madsen gun) and does so at around 8-20time per second depending on size of the gun/ammunition.
How does an electric motor or hydraulic motor turn the rotary motion into the reciprocating liner motion?
And why would it be better than normal machine gun actions.
 
4. File:Napier Deltic Animation.gif - Wikipedia
 
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