Telescopic gunsights

[Adrian Roberts]

This is one of those little things that has bothered me for a while...

Attached should be the well-known photo of Billy Bishop in his Nieuport 17.

Why is the telescopic gun-sight at an angle to the centre-line of the machine? It must be the sight to be used when firing directly forward as it is not at nearly enough of an angle to use with the Lewis in its upward mode.

I also attach a pic of an SE5a, albeit a drawing. This appears to show that the Vickers itself as well as the sight were at an upwards angle.

I know that when shooting you have to allow for the fall of the shot, and rifle sights are calibrated for this. If I was asked why these aircraft sights were angled I would be tempted to mutter about fall of shot rather than declare ignorance. But to me, the angle seems to be too exaggerated to be for that purpose. And if it was about fall of shot, could the angle be altered in flight or were they pre-set at an average angle?

I guess the anti-Bishop brigade would say that he never hit anything anyway so what did it matter where his sights pointed.....!

Adrian

[Adrian Roberts]

Just found a better picture of BB

(oh alright its the one I meant to use in the first place!)

Adrian

[Dolphin]

Adrian

I think that the Aldis sight on the Nieuport was located to take into account the trajectory of rounds from the overwing Lewis gun, ie if the centre line of the sight was extended, it would intersect the path of fire from the gun at the point where the pilot was aiming. Does that make sense?

The Vickers gun and Aldis sight (plus the Lewis gun on the Foster mounting) on the SE 5 and SE 5a were angled up at 5˚ from the centre line of the fuselage. I'm not sure why this was, and I can think of two possible reasons: the bullet paths from the weapons were set to intersect at a point in the pilot's best vision - the area above the fuselage, in between the centre section struts and below the upper wing; or the SEs normally flew slightly nose-down.

Other aircraft of the period had their machine guns mounted on the top of the fuselage (the Fokker and Sopwith designs) or incorporated into the fuselage (Albatroses and SPADs) and not half buried in it, like the SEs, so the Aldis, or other, gunsights were set level with the fuselage. Interestingly, the drawing below of the Martinsyde F.4 Buzzard, the machine that probably would have replaced the SE 5a in 1919, suggests that it might have had a pair of upwards angled Vickers guns (unless it's just the perspective of the drawing).

Best wishes

Gareth

[PhilB]

Two points:-

1/ The higher up the blades the bullet passes, the bigger the space for it to pass through.

2/ Is it possible that the attacker normally approached from behind and slightly below (so as not to be in the propwash and not visible to a rear firing gunner), so it would make sense to have your gun and sights angled up? It also gives you a bigger target.

And here`s an artist`s (?) impression! Phil B

[squirrel]

It may just be the way I am looking at the pics but...........

In the the pics of the SE5 and Martinsyde, the Aldis sights and the Vickers guns are paralell with the wings, suggesting that the angle of the sights/guns was to allow for the "attitude" of the aircraft in flight. Both apparently "nose down".

[Dolphin]

Squirrel

Your theory sounds most plausible to me, and I've been looking in reference books to find something to either confirm or deny it, but without luck. It's maddening when there's lots of information available on an aircraft type, but not the specific point that you're currently interested in!

Regards

Gareth

[squirrel]

Gareth,

I only caught on to this from something written about WW2 by Pierre Closterman in his book The Big Show and his description of the first time he saw a FW190 in flight. He said it looked nothing like the pictures he had seen with the shape apparently elongated and the nose down attitude.

I know the WW1 planes were smaller and slower but they certainly look different in the air to the way they appear on the ground, each with it's own characteristic in flight attitude.

Incidentally, my grandfather was RFC ground crew stationed at Farnborough.

If only I had his number I might be able to find out what units/squadrons he was with and what aircraft he worked on.

[NIGEL]

Normally the sight will point down below the barrel of a gun so that the gun shoots the bullet upwards to allow for loss of power of the bullet and for it to drop down on to its target.

On the aeroplane the wings are slopping backwards onthe fusilage for lift so the attached gun is already aiming high into the air. Therefore the sights are pointing upwards to accomadate all these angles but you will find that the sight is still pointing below the barrel of the gun at a set range to allow for bullet drop

[Howard]

Squirrel

Your theory sounds most plausible to me, and I've been looking in reference books to find something to either confirm or deny it, but without luck.  It's maddening when there's lots of information available on an aircraft type, but not the specific point that you're currently interested in!

Regards

Gareth

<{POST_SNAPBACK}>

It is indeed plausible. When an aircraft is in flight, the wings are at an angle to the on-coming air. This is the angle of attack. If the sight were parallel with the wing chord, it would in fact point up in level flight as the wings will have some positive angle to the horizontal. The slower it flies the larger this angle will be in level flight until it reaches one value when it will stall. In modern light aircraft this is roughly 14 degrees, I don't know what is was in the Great War types. The centre line of the fuselage is of little interest unless, like in some types, the fuselage adds a little lift of its own.

When an aircraft is in level flight at a normal speed, the centre line of the fuselage may be pointing up, be level or pointing down depending on type. In the aircraft I fly, it points up just a little, in sme Piper Cubs, it points down. 'tis the wings that matter most.

Howard

[NIGEL]

Squirrel my grandad in my avatar was also in the air corp on the ground his number was 103758 how do you find the info?

[PhilB]

But why does a gun need to be parallel to the top wing? Phil B

[squirrel]

Nigel,

Only have family "legend" on grandfather. As he was a tailor by trade I suppose he could have been stitching uniforms as opposed to stitching aircraft. All I have is photo of him in uniform with two of my uncles. One would have been about 3 and other about 8 years old.

Also have 2 propeller blade tips made in to photo frames with RFC badges; one has a photo of my grandmother and the other my great aunt.

Did a name search at Kew and and there are about 200 odd with his name but was unable to find anything.

[stan]

I can tell you by quite accurate scale models I've seen flown the SE5a certainly flys nose down!

[Adrian Roberts]

Thanks for your replies everyone. The answer may well be a combination of these things: the in-flight attitude of the aircraft fuselage dictated by the angle of attack, the need to be slightly below an enemy being chased, the fall of shot and the need to fire through a wider part of the propellor arc. Taken together, I think all these would have a cumulative effect.

I wonder if these ideas were arrived at at the design stage or "in the field"?

One other possibility: looking at the pictures of the SE5a and the Buzzard, is it possible that the the guns also needed to be angled up to avoid bullets striking the cylinder heads?

Adrian

[squirrel]

Having had a think about this overnight and tried to find a reference I am unable to.

But apart from the technicalities of mounting the guns and sights so that you don't shoot bits off your own arcraft, allowing for the in flight attitude of the aircraft, bullet drop etc., what about the prefered set up of the pilot?

Not all pilots would have the same converging point/distance or fire a wing mounted Lewis at the same time as a fuselage/nose mounted Vickers and may even have fired the twin vickers one at a time (?). This would mean that the angle of the guns/sights was probably diferent on each aircraft.

I have read of Ball, Mannock, McCudden, Bishop etc spending considerable time adjusting their guns set ups on the ground; I think Ball always did his himsef.

Albert Ball cetainly liked to get very close before firing so the converging point would be nearer his own plane compared to others. In this case there would be less allowance for bullet drop if I understand that correctly.

And don't forget that by pointing the aircraft at another you would have your nose gun(s) lined up anyway with the aiming coming when deciding which part of the opposing aircraft you wanted to hit.

Just some further thoughts on the subject.