P-38 Expended 20mm Cannon Cases

[ronl]

The P-38 Lightning had a compartment below the 20mm cannon which collected the expended 20mm cases and links. The cases and links were emptied through a panel/door on the starboard side of the nose which was often labeled "Shell Ejection". Does anyone have any detailed pictures showing this door that they could post? Better yet, does anyone have any pictures with the door open and showing the compartment where the case and links were collected?

Thanks in advance.

Ron

[51fixer]

The P-38 Lightning had a compartment below the 20mm cannon which collected the expended 20mm cases and links. The cases and links were emptied through a panel/door on the starboard side of the nose which was often labeled "Shell Ejection". Does anyone have any detailed pictures showing this door that they could post? Better yet, does anyone have any pictures with the door open and showing the compartment where the case and links were collected?

Thanks in advance.

Ron

I don't have a photo.
As I remember it is a cavity defined by the formers front and rear and the outer skin and the inner wall was along the Nose Landing Gear. Basically all existing components of the structure.
They added the exterior door and glued rubber to the alum surfaces to protect them from the brass.
I'm not sure they collected the links but I'm not sure on that. There is an ejection chute on the L/H side of the nose in the same position that might be for the links. Sorry it has been many years since I worked on a P-38.
A good book that covered the restoration of the POF P-38 is Motorbooks produced P-38 Lightning, Restoring a classic American Warbird by Jesse Alexander. It was published in 1990.

[ronl]

Thanks Rich,

I checked the Erection and Maintenance Manual for the P-38L and it indicates that both the expended cases and links from the 20mm were collected in this compartment. The cases and links from the four .50 cal guns were all ejected from the nose pod. The four slots for the .50 cal. cases and links are quite evident in pictures of the P-38.

Ron

[warbird1]

Thanks Rich,

I checked the Erection and Maintenance Manual for the P-38L and it indicates that both the expended cases and links from the 20mm were collected in this compartment. The cases and links from the four .50 cal guns were all ejected from the nose pod. The four slots for the .50 cal. cases and links are quite evident in pictures of the P-38.

Ron

Why would Lockheed design the plane to catch the 20 mm shells and links, but not the .50 cal ones?

[51fixer]

Thanks Rich,

I checked the Erection and Maintenance Manual for the P-38L and it indicates that both the expended cases and links from the 20mm were collected in this compartment. The cases and links from the four .50 cal guns were all ejected from the nose pod. The four slots for the .50 cal. cases and links are quite evident in pictures of the P-38.

Ron

Why would Lockheed design the plane to catch the 20 mm shells and links, but not the .50 cal ones?

I believe for weight and balance reasons.
A fighter with weapons in the wings carries that weight close to the center of gravity.
If they are in the nose the use of the ammo and the loss of weight will affect the balance of the A/C. By capturing the 20mm brass you retain some of that weight.

[shrike]

Thanks Rich,

I checked the Erection and Maintenance Manual for the P-38L and it indicates that both the expended cases and links from the 20mm were collected in this compartment. The cases and links from the four .50 cal guns were all ejected from the nose pod. The four slots for the .50 cal. cases and links are quite evident in pictures of the P-38.

Ron

Why would Lockheed design the plane to catch the 20 mm shells and links, but not the .50 cal ones?

One of the original armament options was a 37mm cannon which 're-racked' spent shells back into the feed mechanism, so originally there would have been no ejection slot. With the change to the definitive 20mm cannon, since there was room to catch the spent casings, there ws no need to redesign any more of the nose.
Keeping the spent shells on board may have helped a little with CG changes as well, but I doubt that would have been a major effect.

[51fixer]

Thanks Rich,

I checked the Erection and Maintenance Manual for the P-38L and it indicates that both the expended cases and links from the 20mm were collected in this compartment. The cases and links from the four .50 cal guns were all ejected from the nose pod. The four slots for the .50 cal. cases and links are quite evident in pictures of the P-38.

Ron

Why would Lockheed design the plane to catch the 20 mm shells and links, but not the .50 cal ones?

One of the original armament options was a 37mm cannon which 're-racked' spent shells back into the feed mechanism, so originally there would have been no ejection slot. With the change to the definitive 20mm cannon, since there was room to catch the spent casings, there ws no need to redesign any more of the nose.
Keeping the spent shells on board may have helped a little with CG changes as well, but I doubt that would have been a major effect.

Yea, probably not a major effect. A retired Lockheed engineer who visited Chino in the 80s told me that it was done to help with the CG.
Probably it was cheaper to do as well. Less parts and tooling to make.

[warbird1]

Wow, very interesting discussion. I learned something new. Thanks guys!

[51fixer]

Well, weight placed in the wings may be even farther from the center o gravity then the one placed in the nose.

I disagree in this sense.
The wing spar or the main structural beam in the wing is usually close to the CG in the fighters I'm aware of. If the weapons are in the wing they have to fire through the spar. The barrel usually extends through the spar so the receiver is on one side of the CG and the barrel on the other. The ammo is close to being in line with the receiver so it to is close to the spar and the CG.
So with say the P-51 or even a Spit that would be within a couple feet of the CG.
In a P-38 all this ammo is well forward of the leading edge of the wing and probably around 4 feet away from the CG for the cannon ammo and even further for the MG. In the P-38s I helped restore we put hundreds of pounds of lead up in the nose to replace the weight of the Weapons and ammo. Lefty Gardner used to carry extra radiators up in the nose of White Lightning.
Yes Spits bolt in weights but I suspect that has to do with the changes that took place with the evolving nature of increased engine horsepower and the larger size engines being squeezed into the same basic airframe.
The Mk XVIII here has weights bolted in the rear of the fus and in the vertical fin. With the monster of a powerplant up front they had to to maintain the CG. If you look close at air to air pics of the Griffon powered Spits you will see they have the elevator slightly below neutral (nose down) while straight and level. You rig the controls this way. What in everything else would have you diving toward the ground is level flight in the Spits. In later Mk 21-24s they made the horizontal longer to better carry the weight back there.
In service with the FR mk XVIII you added or subtracted weights bolted in based on whether you carried the recon camera, used the rear fuel tanks or any of several different operating schemes you could find yourself in. And they are still easy to get up on the nose on the ground.

[ronl]

GreatGonzo,

Actually, the expended cannon cases and links were ejected from the wings of the Spitfire. As a matter of fact, in all other aircraft that carried the Hispano 20mm (Hurricane, Typhoon, Tempest, Corsair, Hellcat, etc) , the cases and links were ejected from either the wing or fuselage (Mosquito, Beaufighter). The same was the case for expended cases and links from all aircraft carrying .50 cals. So, I am not really sure why they were collected in the P-38. Maybe to protect the fuselage pod from the cases possibly bouncing back up when they were ejected.

Ron

[warbird1]

GreatGonzo,

Actually, the expended cannon cases and links were ejected from the wings of the Spitfire. As a matter of fact, in all other aircraft that carried the Hispano 20mm (Hurricane, Typhoon, Tempest, Corsair, Hellcat, etc) , the cases and links were ejected from either the wing or fuselage (Mosquito, Beaufighter). The same was the case for expended cases and links from all aircraft carrying .50 cals. So, I am not really sure why they were collected in the P-38. Maybe to protect the fuselage pod from the cases possibly bouncing back up when they were ejected.

Ron

Is it possible that the designers were worried that the expended shells might be caught in the slipstream and possibly hit/nick the props?

[51fixer]

Oh, I should have been more precise. Spitfire did eject the 20mm shells snce the universal wing has been introduced. The B wing, however did have the boxes collecting them, right at the edge of the wheel well.

51fixer, You surely are right about Spit and her heavy nose problems. The other reason for wooden props would be the easiness of breaking by the contact with the ground, thus preventing the frame from rolling over her nose. I also agree with the problems of balancing the nose placed armour contrary to wing based. The later one is always in balance unless something doesn't work as the system operates in symmetry. Still the center of gravity is a point and the farther You go from it - the farther You are, no matter of the direction isn't it? Weight disposition in the wings does affect the manoeuvre abilty of the plane, or else?


I just wanted to show the example of wing mounted armamment ejecting shells int the boxes .

Aircraft have a basic center of gravity range, whether loaded or empty. The CG is a point at any moment but this point moves and so there is a range of movement allowed. Stay inside of the allowable range and it'll fly good or at least be controllable. Get the CG outside of the allowable limits and the A/C is less controllable and maybe even uncontrollable.
It starts with the empty weight CG. With minimum fuel, no external stores and expended ammo you could be on one extreme of the range. (Note that a T-6 with low fuel, a single pilot and no baggage can just exceed the fwd CG limit. Most have a little ballast (weight) bolted in the tail to counteract this situation.)
Fully loaded with fuel, bomb/drop tanks, ammo, rockets and the kitchen sink you could be on the other extreme. (A P-51 or Spit with rear fus fuel tank requires using fuel from the rear tank in a sequence. The A/C can be safely flown with a CG that is aft but only for climb and cruise. Use of that rear fuel moves the CG fwd into a range that allows the combat maneuvering when it is needed. Do those same maneuvers with the rear CG and you may fall out of the sky.)
Items on the A/C affect the CG because of weight and distance, this becomes a moment. A light weight item in the tail can have a large moment that is the same as a heavy item a foot away from the CG.
For military use there were charts and forms to calculate the CG and the Weight and Balance.
For civil ops of the P-51 and the T-6 the FAA has the CG range as part of the Type Certificate Data Sheet. This is specs for what the A/C has to meet to be legal to fly if it is registered in the US and flying in the Standard or Limited Category. At least with the P-51 both the gross weight and CG range are different than the Military specs.

[ronl]

Greatgonzo,

The expended cases from the 20mm cannon in the Sptifire Mk V were ejected from the wing also. However, they often jammed due the fact that the cannon was mounted on its side, and that the ejected cases had to be deflected 90 degrees to exit the wing. This was all corrected with the universal C wing which allowed for the cannon to be mounted upright, as well as using the smaller belt feed mechanism which was mounted on top of the cannon.

The 20 mm cannon used in the Lightning was the US built AN-M1 or AN-M2 which used a similar belt feed mechanism.

Ron