What's the purpose of the P-47's protruding barrel sleeves?

[trackend]

I cant believe they would interfere with an aircraft's armament for aesthetic reasons Dave, as they are called blast tubes I would have thought they are for blast IE hot gases. You have a point Dave regarding maintaining barrel alignment the M2's barrel being reciprocating would only be as accurate as the guides that the barrel moves on so supporting the barrel could be an answer but would not this increase the chances of a stoppage caused by the barrel seizing in the blast tube guides due to heat as to have any effect in maintaining the barrel alignment the tolerances would have to be fine. I believe the stagger is to off set the belt feeders within the wing.

 

[DAVIDICUS]

"I cant believe they would interfere with an aircraft's armament for aesthetic reasons Dave ..."

I was being sort of tongue in cheek and suppose I should have put a after that comment.

This whole issue, of course, is really about why they protrude so far. If the main spar was directly behind the number four gun and there wasn't that much room ahead of the spar, I could see how a staggered mounting would result in the number one, two and three guns protruding ahead of the leading edge of the wing.

What do you think?

 

[Matt308]

If I recall correctly the P-51 is not staggered. The P-40, F4U and F6F are.

My youngest son is 5. My older son is 10. Those are fun times at the airport. My grandfather used to take me to the Birmingham AL airport to watch the planes. This airport was shared with the Alabama Air National Guard and also had some sort of maintenance depot for C-135s. I remember seeing mostly F-4s and on occasions F-101 Voodoos (rare treat). I distinctly recall watching an airshow where the F-4s ligned up for a full throttle take-off and the poor crowd control resulted in hundreds of people literally running toward these huge planes roaring in full afterburner. Someone must have been on the ball, because they released brakes and got the hell out of there. I also recall that later in the show an F-101 buzzed the airfield perpendicular to the runway (and right over the crowd I might add). Scared the hell out of everyone with this 50ft pass from behind. Alas, those days are no more. This was about 1976, I think.

 

[Matt308]

It is interesting to take a look at the P-51 gun bay. You will note that the port bay innermost gun has a belt feed that takes a 30-40 turn forward to account for the non-staggered installation. I'll have to look, but this too may have been influenced by wing primary structure.

David, I'm still thinking that somehow the guns aligned parallel with the ground also plays into this somehow. I'm wondering if we are too focused upon a single rationale when in actuality the designers would be struggling with many design requirements that would have influenced their final choice. A common mounting block, coupled with wing spar location, belt feed complexity, maintenance, the need to maintain weapon accuracy, etc are all contributing to the Republic choice. I would bet that if you asked two different Republic engineers why the choice and depending upon their engineering discipline you would probably get two different answers.

 

[trackend]

Old subject but I spoke too a guy at Duxford today who is a specialist fitter on the P47 he said the Blast tubes act as heat shields to protect the wing skins and the leading edge they are staggered for belt feed configuration.
generally all blast tubes do the same job.

 

[DAVIDICUS]

Understood. The question really was why they protruded so far. If the P-47 had just six guns instead of eight (remove the inboard gun), it would appear that the outermost three guns still protrude much, much further than on the P-51, F-4, F-6, F4U, P-40, etc.

 

[Gemhorse]

A real interesting topic...I've always wondered why the P-47's guns were aligned as such, and find Trackend's friend at Duxford assertion a very balanced answer....I'm not sure, but firstly, are the barrels longer than the norm?

The P-47 was unique in having 8x .50's, and they indeed added to it's 'lethal-look', they were a great gun platform and perhaps the best strafer of the war, but wouldn't the whole gun and blast tube be adjustable for sighting, as there would be great advantage in adjustment if say they were being used for ground-suppression duties for say a week, and then re-adjusted for a reassigned week of escort duties...the alignment for these two duties that they were used for, would be useful, indeed critical, to their successful implementation respectively...
Also, as they were very fast and able craft, the barrels being extended wouldn't have had any real adverse effect on the aerodynamics, so perhaps one could conclude they were assisted in cooling by the extra airflow...on the other extreme, did they have any internal anti-freeze system?

Please bear in mind I'm an Artist, not an Armourer, and comment ask all this out of genuine interest in this fine aircraft.......

 

[DAVIDICUS]

Perhaps the main wing spar was so far forward that the guns, when placed in a staggered arrangement, had to be located much further forward in the wing in order to accomodate their placement ahead of the wing spar.

 

[Gemhorse]

Yes, that's definately possible, they do have a healthy wing area.....I've always liked their 'ellipical-type' wing shape.....Perhaps someone has an exploded-plan drawing of the P-47, to study the guns placement abit more closer....

 

[lesofprimus]

The wing of the P-47 is a full cantilever type employing 2 main spars and stressed skin and multicellular construction. It has a span of 41', root chord of 109½", mean aerodynamic chord of 87.46"; a 5.61 aspect ratio; an angle of incidence of +1° and a top surface dihedral of 4° . Angle of incidence and amount of dihedral are fixed.

main spars which support attachment of the wing to the fuselage and three auxiliary spars, one each supporting the aileron and flap and the other supporting the landing gear.

Main spars are constructed of E-shaped cap strips riveted to webs of varying thickness from a minimum of .032" for the outboard web of both spars to a maximum of .250" thickness for the inboard web of the forward main spar. Both main spars are reinforced at suitable intervals by extruded angles which also serve as anchors for frame installations.

Inboard ends of the main spars of each wing are fitted with a pair of wing hinges which are pinned to the mating fuselage hinges by split bushings; tapered bolts expand these bushings to a tight fit, thus securing positive attachment.

The aft auxiliary spars support the movable surfaces and are constructed of angle cap strips and webs of .072" to .025" thickness. The landing gear auxiliary spar, since it is subjected to landing loads, is of somewhat heavier construction—namely, .091" web and is reinforced similar to the main spars.

Flanged ribs of alclad 24-ST are secured between spars at the angle stiffeners. Ribs vary from .051 to .032 with the exception of the root chord rib and gun bay partitioning ribs; the root chord rib is .064" and the gun bay partitioning ribs of .064".

Nose and trailing edge ribs are flanged and are also of Alclad 24-ST.

 

[Nonskimmer]

Ah, excellent. Especially the middle pic of the exposed bays.

 

[DAVIDICUS]

I wish we had similar illustrations of the internal structure of other aircraft's wings so that the locations of the main wing spar can be compared.

The P-51 didn't have staggered mountings. Perhaps the other American fighters didn't either. That would be one explaination as to why placement of the guns ahead of the main wing spar would not necessitate such an extreme protrusion of three of the four barrels ahead of the leading edge.

Nice pictures. That's a nice model. It appears to correctly display the position of the guns as parallel to the ground. Most P-47 models feature the guns aligned with the leading edge of the wing.

 

[Gemhorse]

Aw, really awesome!!...I thought they may have had more barrel length, but they're definately packed-in real tidy!...
Impressive compared to the P-51's, but is there a difference in barrel length?.....

 

[DAVIDICUS]

Ah, yes. See how far the guns sit back in the wing of the P-51? They are mounted much further forward in the P-47. The structure of the P-51 wing would appear not to have a main spar configured like the P-47.

 

[FLYBOYJ]

Excellent stuff Les! and a great description. Not that it matters but you even called out the right material and size and didn't call the sheet metal "gage material," as an aircraft maintainer, you bring tears to my eyes! "Someone else" said that once to me on this forum, hearing it was like scraping your fingernails on a blackboard! I told "them" that gage sheet metal is used in air conditioning construction, not aircraft! 8)

 

[DAVIDICUS]

If you think Les wrote that I have a box of magical rocks I'd like to sell you. It was cut and pasted from the website below.

http://rwebs.net/avhistory/history/p-47.htm

 

[the lancaster kicks ass]

If you think Les wrote that I have a box of magical rocks I'd like to sell you

 

[trackend]

Great Info Les but unfortunately you lost me at root chord . The P47 it appears directly to do with feeder configuration as looking at the pic the weapons could have been aligned in anyway as there seems to be plenty of room for the actions the P51 definately seems to be more constrained by space.

 

[Nonskimmer]

So DAVI, these rocks...how many colours do they come in, and will they make me pretty?

 

[lesofprimus]

Cut and paste...... But i did take the time to find it and do it, so ill take a partial credit, maybe 32%.......