open bolt vs closed bolt ~ the Ki-44 tojo (Full Version)

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WO Katsuki -> open bolt vs closed bolt ~ the Ki-44 tojo (8/16/2012 7:57:52 PM)


we all know you cannot synchronize an open bolt gun to fire through the propeller

can anyone tell me about the Ho-3, and if it's an open or closed bolt gun?

want to confirm that as a reason why it wasn't used on the Ki-44-IIc (that 4x Ho-3 version that was proposed but never built)



Commander Stormwolf -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/16/2012 10:42:32 PM)


http://pwencycl.kgbudge.com/J/a/Japanese_20mm_Type_97_gun.html

Ho-3 was an open bolt system, same with the Type 99



Gregg -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/17/2012 12:28:25 AM)

I do not know about you basic premise there.
Almost all machine guns fire from an open bolt.
The reason is not to have a live round end up in a hot chamber.
To do so is asking for a round to cook off on you.
Gregg



WO Katsuki -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/17/2012 1:03:52 AM)


but an open bolt can't be synchronized through the propeller

WW1 lewis guns fired on the top deck of the S.E.5 for example


Vickers or Browning could be synchronized

most 20mm guns (Hispano, Oerlikon based) couldn't fire through the propeller, so they were mounted either in the engine hub or in the wings

some 20mm guns (ShVak or Ho-5) could fire through the propeller


I wonder about the Ho-155, a 30mm gun, based on the Ho-5 (based on a closed bolt browning design)
could you fire a 30mm closed bolt through a propeller?



PaxMondo -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/17/2012 4:33:31 AM)

Browning 50 cal is not a very good example of a gun to fire through a prop ... looses something like +60% of it ROF to be synchronized ... which is partly why the US mounted the guns on the wings ...

German MG/151 20mm is better example of gun well enabled to fire through a prop....



Commander Stormwolf -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/17/2012 10:40:03 PM)


I'd say ROF is not the right measure of gun accuracy,

pilots will tell you that

1) muzzle velocity (projectiles reach the target quickly will less lead time) and

2) ammo quantity (longer firing time, more ability to make corrections,
and simply more chances to hit if you miss the first time)

are more important

increasing ROF will lower reliability (more jamming and overheating), and reduce the stability of the gun platform

for example the A6M2 and N1K2 have about the same accuracy on their 20mm guns -

in truth, the N1K2 carried a lot more ammo (200 vs 60) and had about 30% more velocity (2500ft/s vs 1900ft/s)






Itdepends -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/18/2012 4:43:13 AM)


quote:

ORIGINAL: Commander Stormwolf
I'd say ROF is not the right measure of gun accuracy,

Nobody asked or made comment on it.



PaxMondo -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/18/2012 5:33:21 AM)


quote:

ORIGINAL: Itdepends


quote:

ORIGINAL: Commander Stormwolf
I'd say ROF is not the right measure of gun accuracy,

Nobody asked or made comment on it.

+1



Sakai007 -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/18/2012 4:12:42 PM)

The P-40B&C, P-39, and P-63 all had .50 cal brownings that fired through the prop disc. I wonder why they continued to mount them as such on the P-63 knowing the they would be half as effective as the podded .50s mounted under the wings? I have read about P-38 pilots commenting on the hard hitting nature of the closely grouped 4x .50s & single 20mm mounted in the nose. Many of these pilots, in the Pacific at least, had come from flying P-39s and P-40s. I wonder if having the full ROF in their nose mounted guns had something to do with their opinions.



LoBaron -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/18/2012 4:28:38 PM)

Wing mounted guns did not only have advantages. The added weight makes fighters less responsive and nimble on roll and influence
the aerodynamics of the airfoil, usually in a negative way.

The main customer for the P63s was the SU, and they became experts in making the P39 airframes competitive against the Germans.

One of the main reasons they accomplished this, was that they stripped the wing mounted guns for improved rollrate and stall characteristics.
On the P63 they stuck to that method.



Commander Stormwolf -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/18/2012 11:26:14 PM)


centerline armament was obvious to luftwaffe and vvs

as someone mentioned, wing guns increase angular moment of inertia and reduce roll rate

every single soviet fighter for example had a large caliber gun in the propeller and 2 on the engine,

centerline armament means more accuracy (and so you can carry fewer guns, and less weight),

so it helped the soviet fighters to carry fewer guns and compensate for the weight of the poor materials , and allow decent performance (La-5 for example)

they also modified the lend lease aircobras (sometimes replacing the 37mm with 20mm hispano to save weight), removed the wing guns, and removed some fuel tanks as well

usaaf and raf had big engines will good fuel, so they could afford the extra weight of their armament,
though the spitfire with a 20mm hispano in the nose would have seemed logical..



Sakai007 -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/19/2012 2:19:18 AM)

Excellent answers, I appreciate being educated. :D The comment on the adverse effect on airfoils made me think of the P-51B and the way the 4x .50s were slanted in the wing to fit with that laminer flow design which was quite thin for the era. They fit, but it caused other issues, such as jamming under high g load. This is a serious fault for a fighter aircraft IMO.

The air battle over the eastern front almost seems tailor made to the P-39 IMO. This aircraft was most effective at low - med altitudes where it's Allison made the most power. Getting rid of those useless .30 cals in the wings must have made a real performer out of the earlier model Airacobra's, with the improvement to roll rate that you all mentioned here, and improved climb with every pound shaved off.



Commander Stormwolf -> RE: open bolt vs closed bolt ~ the Ki-44 tojo (8/19/2012 11:38:52 PM)


actually you probably could synchronize the Type-99-1 on a propeller, they did it with the D3Y Myojo

the key is to have a constant-speed propeller --> Zero with the 20mm on the nose would have been deadly



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