"Tell me about split gun trails" Topic

Tell me about guns that have the back part of the carriage as 2 parts that move apart. For example a PAK 40 rather than a 25 pounder. The 2 parts of the trail move together and are affixed to the tow. However when deployed the 2 parts move apart stabilising the gun platform. Mathematically the best angle between the 2 parts when deployed would be 90 degrees. Is this always the case? Would a lesser or greater angle be used where that would make a more stable platform? Indeed is it possible to change the angle between the shafts/trails or do they lock out at a set angle?

US 105mm locks at a set angle. not sure what it is, but less than 90.

Most split trails are designed to lock at a certain angle.

I've never seen a gun with a 90 degree trail. Might make sense in math but not physics: recoil goes straight back so you want to resist that force more directly.

Some of the AT guns had a significant ability to traverse the gun. So the recoil would not always be going straight back in relation to where the trials were placed.

Yes, generally trail legs lock into place, and the tube itself had/has limited traverse when legs & spades are positioned. For indirect weapons especially of large calibers digging in the trail legs & spades in very important. As the tubes in the gun platoon are declinated to all fires on a single target based on sheaf, i.e., Open, Closed, etc.

And the recoil is usually large after each shot. So you want to dig in the spades so after the recoil you may have to fire more rounds on the same target, etc.

For AT guns which were direct fire weapons, digging the spades are important as well. However, I've seen in videos, etc. that an AT crew can literally pick up the legs, etc. and traverse the entire gun to fire at another target which is currently out of the LOS/FOF on the AT gun.

example a PAK 40 rather than a 25 pounder.

Note the PAK 40 is an AT gun and fired directly at a target. The 25lber was usually fired indirectly i.e. indirect fire support with HE rds. generally. AT guns usually fire "Tank Killer" rds, i.e. Armor Piercing, HEAT, etc.

"The canon de 75 mm mle 1897 modifié 1933 was a modified version with a new split-trail carriage that entered service in 1935. It was intended for the anti-tank role with a split trail carriage designed by the Atelier de Bourges. This gave it a much wide traverse (58° instead of 6°) as well as an improved elevation (-6° to +50° instead of -11° to +18°)."

"In 1935 the Arbel platform was introduced; this was a simple circular grooved base that gave the gun a 360° field of fire, at the cost of increased time to limber and unlimber. It was not unlike the method used by the British on the 25pdr."

"The Russians on the other hand had a great WW2 122 mm howitzer … Its one exceptional element is the three-legged carriage. … Three points are necessary to define a plane in math, and three are necessary to give a gun a stable position. Three relatively equal trails allowed for an unlimited traverse – unlike with the ancient box or the early 20th century split trail designs. A four-legged trail would be one more than necessary, and lead to issues during emplacement as the fourth could float in the air (have you ever seen a three-legged stool to wobble? How about a four-legged one?).

Unlimited traverse is important because it enables a quick reaction to all calls for fire (not just in a 60° arc) – and to a sudden demand for self-defence fires, as against tanks.
…

Some anti-tank guns with a 360° traverse feature were employed as well, albeit it was quite unnecessary for up to 76.2 mm calibre because such AT guns were 'light' enough to be traversed by their crew. The French had a 47 mm SA modèle 39 TAZ prototype on three legs and the British 40 mm two-pounder AT gun had a different three-trail design, too. Both were essentially over-engineered, as much heavier AT guns were very well man-handled during WW2 (the limit for this was somewhere in the 1,000 – 1,200 kg range). The French gun can be considered to be the first one with such a system as later employed in the 2A18, though. The same three-trail concept was also used in a French 75 mm AT gun prototype before the French armaments industry quitted WW2 involuntarily."

And don't forget the German 88mm AA/AT gun had 4 legs and a 360 degree traverse. But later in the war there was a an "improved" 88mm AT gun again with 4 legs. But were not produced in the numbers of the older 4 legged version. link Of course the original designs were for AA and then AT.

Why is 90 degrees the mathematically best angle? What assumptions went into that?
Physics IS math.

The 2-pounder had a three-legged trail with two different angles between the legs, i.e. they didn't point to 0, 120 and 240 degrees.