Lockheed AC-130 & M102 105mm Howitzer Engineering question please?

[M.A.D]

Would anyone know or care to estimate the dimension of the space that the modified M102 105mm howitzer (including its special recoil obsorbing mount) takes up in the Lockheed AC-130 gunship?  Especially width-wise in terms of the C-130's 3.13m (10ft 3in) width cargo compartment!

Thanks in advance!

M.A.D

[Rickshaw]

Going by these photos, I'd say about 2-3 metres.

[Jeffry Fontaine]

The rather old and OOP 1:72nd scale AC-130 kit from AMT Ertl/ESCI contained an almost complete 105mm weapon plus some other interesting bits.

[M.A.D]

Much appreciate your feed back and cool pictures/drawings Rickshaw and Jeffry Fontaine!!

So the prospects of mounting and employing this ‘modified’ M102 howitzer in an aircraft with a cargo compartment/cabin width of 2.67m (8ft 9in) might be stretching the friendship.

Talking about stretching friendships, does anyone know the technical term for the ‘recoil travel’ of a gun/howitzer on firing? Saying this does anyone know the recoil travel distance of the M102 on firing?

I wonder if the OTO-Melara Mod 56 105 mm pack howitzer would have a smaller dimensional (static and on firing) footprint than the M102, which would allow it to be operational in that cargo compartment/cabin width of 2.67m (8ft 9in)?

P.S. Looking at the topographical cutaway drawing of the AC-130 you've provided, the C-130's internal cargo compartment/cabin width is 3m (10ft) by my recollection, and if the drawing is to scale, then it looks as if at minimum the M102 takes up an estimated ~2m, with an allowance of an additional ~1m for recoil and working space.......

M.A.D

[kitnut617]

When I was designing a bit of drilling equipment, I was told it had to be able to go inside a C-130 and that the absolute max it could be was 10 feet wide. That was so it could go through the rear door opening. hth

[M.A.D]

When I was designing a bit of drilling equipment, I was told it had to be able to go inside a C-130 and that the absolute max it could be was 10 feet wide. That was so it could go through the rear door opening. hth

😮😋 makes sense!!

Thank you for your valued input and real-world experiance kitnut617

M.A.D

[kitnut617]

When I was designing a bit of drilling equipment, I was told it had to be able to go inside a C-130 and that the absolute max it could be was 10 feet wide. That was so it could go through the rear door opening. hth

😮😋 makes sense!!

Thank you for your valued input and real-world experiance kitnut617

M.A.D

I should have said that I hope knowing that, you could scale the pics Brian posted ---

[M.A.D]

When I was designing a bit of drilling equipment, I was told it had to be able to go inside a C-130 and that the absolute max it could be was 10 feet wide. That was so it could go through the rear door opening. hth

😮😋 makes sense!!

Thank you for your valued input and real-world experiance kitnut617

M.A.D

I should have said that I hope knowing that, you could scale the pics Brian posted ---

Acknowledge your last kitnut617 👍

M.A.D

[Rickshaw]

As it is inside you could claim that they have beefed up the recoil recuperaters so that it could absorb sufficient recoil to only recoil a metre or less.  From the pictures I supplied that looks about the distance it recoils in the AC-130 (going from the yellow recoil guard at the rear of the weapon).  You could remove the recoil recuperater (the tube over the barrel) and replace it with a slightly thicker tube to take that into account, if you wanted to be truly accurate.

[M.A.D]

As it is inside you could claim that they have beefed up the recoil recuperaters so that it could absorb sufficient recoil to only recoil a metre or less.  From the pictures I supplied that looks about the distance it recoils in the AC-130 (going from the yellow recoil guard at the rear of the weapon).  You could remove the recoil recuperater (the tube over the barrel) and replace it with a slightly thicker tube to take that into account, if you wanted to be truly accurate.

I like the way you think Rickshaw!! 😮👍


M.A.D

[tankmodeler]

P.S. Looking at the topographical cutaway drawing of the AC-130 you've provided, the C-130's internal cargo compartment/cabin width is 3m (10ft) by my recollection, and if the drawing is to scale, then it looks as if at minimum the M102 takes up an estimated ~2m, with an allowance of an additional ~1m for recoil and working space.......

If you look at the photos of the 105 inside the Spectre you can see that the gun, plus recoil length fits within the approx. 2 1/3 m from the fuselage interior wall to the back of the yellow recoil guard. That's about the same as the width of the interior of the Friendship so if you could add a small blister to the side of the Friendship fuselage the carriage could be mounted a bit outboard of the actual fuselage wall, which would provide some interior space, just a little, behind the recoil cage. It would still be a tight fit requiring some interesting ammo storage given how the loaders have to service the piece. But it might work.

Shortening the recoil stroke is a very bad idea as it increases the recoil impulse to the fuselage increasing loads on the airframe.

Just sayin'...

Paul

[Rickshaw]

Shortening the recoil stroke is a very bad idea as it increases the recoil impulse to the fuselage increasing loads on the airframe.

If the recoil recuperators are designed properly, there should be little impulse imparted to the fuselage.   There is little if any imparted to the ground, on the ground mount.   The aim is ensure the weapon remains stationary and doesn't need relaying.   If you increase the amount of recoil that is absorbed by the recuperator and decrease the recoil travel, it should all even out.

[M.A.D]

tankmodeler / Paul, the notion of a fuselage blister to facilitate the recoil of the 105mm howitzer makes perfect sense!! 
As a simple grunt, I see what you are saying with your analogy:

Shortening the recoil stroke is a very bad idea as it increases the recoil impulse to the fuselage increasing loads on the airframe.

But then Rickshaw's counter comment also seems valid 😮😜

Thank you for your input!!


M.A.D

[Jeffry Fontaine]

Something to also consider is the fact that the ammunition used with the 105mm Howitzer aboard the AC-130 is not being fired with a full powder/propellant charge.  There is no need to fire a full charge 105mm round for what is basically a direct fire support mission from an aerial platform.  Reduced charge means that the recoil forces transmitted to the airframe will not be as severe as that of a howitzer on the ground firing a full charge round against indirect fire targets. 

[M.A.D]

Yes, great and valid point

Jeffry Fontaine

, more about the amount/volume of explosive delivered by a round the size and weight of the 105mm, which is what I need and I'm looking for! Which brings me back to the question of employing the  OTO-Melara Mod 56 105 mm pack howitzer in place of the in place of the M102 105mm howitzer, as I assume the actual gun -especially the breech block area would be somewhat smaller/shorter in dimensions 


M.A.D

[Rickshaw]

The difference between the two weapons (M101/M102 and M56) is slight, as far as muzzle velocity goes:

M56 - Muzzle velocity   416.0 m/s (1,360 ft/s)
M101 - Muzzle velocity   1,550 ft/s (472 m/s)
M102 - Muzzle velocity 494 metres per second (1,620 ft/s).

Essentially, where the M56 wins over the M101/M102 is in it's lightweight construction and ease of disassembly and reassembly for pack duties.   Where it loses in in it's durability, which is why the Australian Army replaced it's M56s in RVN after about two years use with M101s.   While not a worry for airborne use, it's lack of wheel bearings on the ground mount prevent it being towed anywhere far or fast.

The M56 would require modification for extended use.  It's mount and it's tube would require "beefing up" and so would it's breech assembly.

Interesting discussion here, BTW, about the 105mm's recoil on the AC-130.

[M.A.D]

Thank you once again Rickshaw.
I was aware of the OTO-Melara Mod 56 105 mm pack howitzer shortcomings, in terms of solidness and wear due to its lightweight principle and construction, but envisaged it firing far less in its airborne application.
Perhaps, ideally, I need a variant of the XM204 105mm Soft Recoil Howitzer!!😮😜
https://youtu.be/yDQDJnUJyl8, which would eleviate much of the concerns of recoil and stress loads on the aircraft!

P.S. that article re the employment of rails to guide and obsorb the M102's recoil in the AC-130 was very interesting!!



M.A.D

[tankmodeler]

Rickshaw's points are very valid, I was just imagining you didn't want to redesign the recuperator system for this use. If that's on the table., then yeah, it could certainly work. And, yeah, the Spectre 105s are certainly not firing on anything like full charge. I'm pretty sure the targets are seldom more than 4-5 km away and a 105 could probably hit that, firing downhill as it is, with the primer charge alone.

Paul

[Old Wombat]

I'm pretty sure the targets are seldom more than 4-5 km away and a 105 could probably hit that, firing downhill as it is, with the primer charge alone.

Most targets would be in 20mm range, so all weapons could be brought to bear (or 25mm for AC-130U Spooky II, or 30mm for AC-130W Stinger II & AC-130J Ghostrider variants).

The Wikipedia article is pretty good:
https://en.wikipedia.org/wiki/Lockheed_AC-130

This The Drive/The Warzone article is pretty good too but has the bonus of having a 40sec clip of the 105mm being charge tested, including an internal shot of the recoil, about half-way down the page:
http://www.thedrive.com/the-war-zone/9940/the-usaf-finally-gives-its-ac-130w-gunship-the-big-gun-it-desperately-needs

[tankmodeler]

I thought that one of the reasons that the 105 and 40mm guns were carried is the ability to get a tad further away from MANPADs on the ground. Yes, they provide a much bigger punch than the Vulcans or miniguns, but I had read somewhere (lost in the mists of time, unfortunately) that the reason to step up to the 40 and then 105 was to be able to step back from targets that might be better defended.

Could be wrong, of course. Frequently am.

Paul

[Rickshaw]

One of the problems with using aircraft "gunships" is that with the invention of MANPADS, the targets are able to defend themselves from the attacking aircraft much more easily.   The reason why the calibre of weapons has increased over the decades is because of their increased range, rather than necessarily their increased effectiveness.  The use of initially 7.62mm miniguns, then 20mm Vulcans, 25mm Rotary Cannon, 40mm Bofors and then 105mm guns was to put the aircraft at much greater range from their targets.   

With the need to switch to night operations a final way of preventing them from being shot down.   The operational limits on their use has meant that you need near total dominance of aerial superiority and usually night operations to make them effective.   Only the USAF attacking insurgents in Afghanistan/Iraq/Syria can guarantee both conditions, which is why they tend to be rather limited in their utility.

So, unless your user can guarantee near total air dominance and/or only night operations, your gunship isn't going to be of much use.   The day of the gunship is nearly over.   Soon, we will see transport aircraft armed completely with longer ranged missiles.  Roll on the "Arsenal Ship". 

[Volkodav]

All this talk of gunships has me Imagineering a Blackburn Beverly with a 25pdr, a 6pdr Molins gun and either a Vickers 40mm or 2pdr pom pom.

Then of course there would be the follow on Argosy and maybe Belfast 

[Old Wombat]

The AC-130W came out with a 30mm auto-cannon & missiles, the 105mm has been re-introduced to improve the effectiveness of the aircraft.

So, the AC-130W now has a 30mm auto-cannon, a 105mm M102 howitzer and missiles.

[M.A.D]

Could be wrong, of course. Frequently am.

Paul

Takes a real man to admit it! Good on ya mate 👍

M.A.D

[Jeffry Fontaine]

@ M.A.D. - Have you given any consideration to a smaller caliber weapon?  Say something like the 6pdr/57mm gun?  If they could fit one in a Mosquito MkXVIII then I see no reason why it could not be made to fit inside of your project aircraft.