Sight and gun alignment

[MikB]

Tube gunsights and (especially) top-wing mounted MGs on WW1 fighters always look as it they're aligned to shoot a few degrees above the apparent centreline of the aircraft.

Given the close ranges of most successful WW1dogfight engagements, there's no way this could be for trajectory compensation. And because top-wing guns are mounted some distance above the line of sight, you'd expect there to be a convergent downward line of gun-aim, with some kind of visual measure to bracket enemy wingtips for correct range - although such would obviously work only in ideal circumstances.

Is the upward aligment an illusion of some sort, or did the aircraft typically have some sort of nose-down trim?

[Buffnut453]

Not sure I've noticed the issue you're identifying...but here are a couple of thoughts to consider.

Firstly, the centreline of the aircraft is irrelevant.  The angle of the fuselage when flying straight and level is dependent on the wing's installed angle of attack and the aerofoil section rather than an arbitrary line drawn on the fuselage.  Here's a rather extreme example from WW2 but the Whitley's wing had a rather large built-in angle of attack which resulted in a pronounced "nose down" appearance in straight and level flight (although, admittedly, this appearance was exacerbated by the Whitley's rather large "Bruce Forsythe" chin).

 

The second issue is that the pilot needs to see the aircraft he's aiming at and with the guns will be aligned to converge on that sighting point.  Aligning the guns straight forward may put the sighting point below the level of the cowling which would make it impossible for the pilot to maintain visual sight of his quarry, particularly at the short engagement ranges that were common during the Great War.  

Edited 14 May , 2023 by Buffnut453

[charlie962]

5 hours ago, MikB said:

Is the upward aligment an illusion of some sort, or did the aircraft typically have some sort of nose-down trim?

Could it have been to clear the prop?

[MikB]

16 hours ago, charlie962 said:

Could it have been to clear the prop?

I never heard that top-wing guns were ever synchronised, and I always understood they were in use before Allied synchronisation gear beame available, so yes, the intention was to clear the prop arc to allow forward firing.

The disadvantage was that the pilot's line of sight or aim was not closely aligned to the line of bullet flight so that aiming without exact ranging was very much more difficult than for a pilot aiming more-or-less along the barrel. The top-wing gunner in a tailchase has to get to - or near - a specific range where he knows the gun trajectory will cross the sightline at an angle. Even if he uses tracers, these are very hard to follow at close ranges.

Of course, this issue doesn't include the well-publicised cases of shooting up from below at an unaware enemy, when the gun is taken out of the default alignment.

Buffnut 453, thanks, I take your point that the centreline of the aircraft or the apparent axisline of the engine probably doesn't represent line-of-flight. I can't really imagine any other explanation for the apparent upward angle of guns and sights.

 

[alex revell]

Hi, 

Pilots set up their guns - Vickers and Lewis -  to their personal liking at their squadon's firing butts.

On this subject, here is an extract from my biography of McCudden, The Happy Warrior.  In June 1918  McCudden was visiting 56 Squadron after delivering a Snipe for testing by the pilots of  No.1 Aeroplane Supply Depot  

 Quote: 'To the delight of James and Gerald Maxwell, the morning of 13 June was again fine and warm and they both took off at 6.05AM, James flying William Irwin’s Viper-powered SE5a (B179) which he had flown for a short test-flight before taking off, commenting that it was a ‘very nice machine’. This time it seemed as if their luck was in. Maxwell’s diary reads: ‘Did a topping show in morning. Self and McCudden attacked four different two-seaters which we filled with lead but did not get down.’ James did not take the failure to down these two-seaters as philosophically as Maxwell. On the evidence of the accuracy of his shooting with a camera gun while instructing at Turnberry, he knew that his marksmanship was as good as ever. Back at Valheureux, testing the guns of Irwin’s SE at the firing butts confirmed his suspicions – they were hopelessly misaligned. James was both furious and disappointed that one of the fundamental rules of his teaching while in the squadron had been so soon forgotten. Eugene Macdonald remembered that he was ‘hopping mad’ and angrily tore into Irwin for not having his guns properly sighted, pointing out that not only did his own life depend on his guns being accurate but, more importantly, the lives of his comrades. EOQ

Hope this clears up the question.