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17. Ringing the Changes

11/04/2012

In chapter 12, we looked at how the Bristol Scout compared with the opposition – the Sopwith Pup, and later models, and it was truly remarkable how little the basics changed in front-line fighters.

There were exceptions, and Bristol’s designer, Frank Barnwell, produced two successful machines that were pretty much outside the standard layout. The Bristol M1C Monoplane was a very successful airframe, only marred by the unreliable 110hp Clerget engine with which it was fitted – and the War Department’s distrust of monoplanes. And the Bristol F2B Fighter was an unusual combination; many early machines had two occupants, one of whom was an observer armed with a gun, but the Bristol Fighter used the two-seat configuration and turned it into a very successful air-to-air machine, once the crews had adapted their tactics to make the most of its capabilities.

But the Scout must have taken up quite a bit of Frank Barnwell’s time in the early years of the war, since it was never designed for warfare in the first place, and it was continuously being tinkered with in order to make it more practical for front-line use.

Some of the details that were altered included:

Moving the oil tank. Rotary engines used prodigious amounts of oil – nearly as much as the petrol, and they used a lot of that. Can you imagine having to top your car up with as much oil as petrol? Originally the oil tank was fitted behind the pilot, but apparently it was possible, if you climbed steeply enough, to cause the engine to be starved of oil, because the tank wasn’t far enough above the engine. The solution was to move the oil tank in front of the pilot, between the instrument panel and the petrol tank which was right behind the engine. There are drawings showing the tiny baggage compartment they fitted in its place. I can’t believe it was much use, since it was only big enough for a spare pair of gloves or goggles, and you couldn’t reach it in flight – unless you were prepared to undo your strap, stand up and turn round! One of the effects this had was to move the centre of gravity – the point about which the aircraft balances. Today this is treated very seriously, and is calculated to fractions of a millimetre, but they didn’t bother much in those days. Nevertheless, it because the machine was now more nose heavy, you ran out of elevator control, and the aircraft tended to dive. They fixed this by adjusting the front of the tailplane ( the fixed horizontal tail surface) downwards a little bit.

This affected another odd thing about the Scout. When you look at a modern aircraft, you may not realise that the tail surfaces at the back are actually pulling downwards. It does this because it helps to make the aircraft stable, so that if the aircraft goes faster, the increased downforce on the tail will make it want to climb, and therefore reduce the speed. In aircraft before World War I they didn’t know this and the tail surfaces provided extra lift. By moving the centre of gravity forwards, and angling the tailplane down, it became a non-lifting tailplane, like modern aircraft. Unfortunately the all-important aerofoil section – the shape of the tailplane if you were to cut a slice through it from front to back – was now the wrong way up, but they don’t seem to have got around to altering that until a good deal later.

Tank size. As I said, the rotary engines consumed vast quantities of both petrol and oil, and there are drawings showing larger tanks – in fact so large that the gap between them has entirely disappeared, and they are made all in one. There was also a version with pressurised tanks (the earlier tanks relied on gravity to supply the petrol and oil to the engine, but this only worked when the aircraft was the right way up and flying without violent manoeuvring. Pressurised tanks were sealed and could be pumped up with a little air pump to ensure they’d keep feeding even if you were throwing the aircraft all over the sky). There’s also a drawing showing some armour plating to protect the petrol from gunfire.

The tailplane. They must have found that the aircraft wasn’t stable enough because they increased the size of the tailplane by adding another rib on each side to make it wider. Which are we building? The smaller one…

The rudder. And similarly with the rudder, except that they had at least three or four goes at increasing the rudder area. On many modern aircraft, the rudder is barely used in flight. To make a turn, you roll the aircraft (rock one wing up and the other down) using the ailerons (the control surfaces at the ends of the wings) using the stick, and the aircraft naturally goes into a turn. But on early aircraft the ailerons were not very effective, and so you needed to use the rudder much more. Not only that, but since there was no fixed vertical surface, you had to use your feet the whole time to keep the aircraft going where you wanted to, and obviously they decided they need a much larger rudder to get the control they needed. Oh, and one at least had a vestigial fixed fin. Which are we building? The smaller one…

The ailerons. The ailerons mentioned in the previous paragraph are the control surfaces at the ends of the wings. At the time the Scout was designed, most aircraft used wing warping to achieve roll control – you twisted the whole wing instead of having a separate bit. You’d think this would be really good, but it was awful. In fact, the Scout’s main competitor in early 1914, the Sopwith Tabloid, was rated poorly compared to the Scout for this reason. And the Scout was also unusual in having an aileron on each wing, where many others only put them on the upper or lower wings. Given that the control surfaces at the tail were all increased in size, it seems surprising that the later versions of the ailerons were made smaller. There are a number of possible reasons for this, but it’s one of the things we’ll need to investigate when we get the Scout airborne. Needless to say, ours will have the larger ailerons.

The Dihedral. The dihedral is the amount the wings slope up from the middle to the tips, and that seems to have been increased fairly early on. Its effect will have been to increase roll stability, and may have been related to the change in aileron size, though until we can get more examples built and try the differences, it will be difficult to say exactly what difference it made.

PS. At the time the Scout was built, the terminology still hadn’t settled down. What we call the wings are referred to as ‘planes’. And the undercarriage – the wheels, and the structure that held them in place – was called the ‘chassis’.

The engine. The original pre-war prototype was fitted with the 80hp Gnome rotary engine, since that was the most powerful engine available at that time. The RNAS ordered their first batch of machines with the Gnome, since it was supposed to be more reliable, while the RFC wanted the 80hp le Rhone. the two were pretty much interchangeable, and Grandad did just that on 1264, since the le Rhone was actually much more powerful. Later versions were fitted with a wide variety of engines; the 80hp Clerget, the 100hp Gnome, and the 110hp Clerget. These needed a slightly bigger cowl, revised engine mounting plates and different rigging.

Wing cutouts. Being able to see is absolutely crucial in air combat, and the two sets of wings interrupted one’s view quite a bit. Later versions had strips cut out at the inner ends of the lower wings, and of the centre section of the top wing too.

Windscreen. Later models were fitted with a rudimentary windscreen. Does 1264 have one? Of course not.

Armament. The Scout wasn’t originally intended as a war plane, and in any case, no-one envisaged they’d need to actually shoot at each other at the outset of the war, so the Scout had a huge variety of armament fitted. Although much of it started out as a sort of DIY effort at the front line, there are Bristol drawings showing some of the solutions adopted. The problem was that any fixed machine gun mount had to be close enough to the pilot to enable him to reach the trigger and change the ammunition drum, but not shoot through the propeller, since the propeller is the most highly stressed piece of equipment on the aircraft and even a tiny bit of damage could cause a bit of it to fly off, and the resulting vibration would destroy the aircraft in a matter of seconds. The most radical solution was adopted by pioneer Lanoe Hawker, which involved fitting a Lewis gun to the side of the fuselage but firing at an angle out sideways. With this very strange contraption he won a VC for downing three Germans in one flight. There is a Bristol drawing showing this arrangement. There’s also a drawing showing a more conventional arrangement mounted on the top wing firing over the top of the propeller. In Grandad’s case, there were two simply mounted on the side of the fuselage firing straight forwards through the propeller, and never mind the risk. As some sort of sop to Health and Safety, the propeller blades had fabric tape wound round them to stop the splinters coming off in your face!

In fact there were some experiments with interrupter mechanisms (which stopped the machine gun firing as the propeller blade was in line). There’s even a story that one of these was sent to the front line but maladjusted so that every bullet ended up hitting the propeller…

In addition, many were fitted with home-made bomb racks. Grandad did quite a bit of bombing with his, though was never very accurate. The bomb racks were fitted underneath the engine, and Grandad discovered that if you released them when you were going too slowly, the bombs caught on the undercarriage axle.

Internal wire bracing. In the early days, they used wire cable at at the heavily stressed areas (front of the fuselage and the wings inboard) and piano wire elsewhere. Each one required a bottlescrew for adjustment – 133 in total – and later on they changed to threaded rod; 2BA and 4BA. This must have been a lot easier and cheaper to manufacture – not least because each end of the wire cable had to be spliced. If you’ve ever tried splicing a rope, you’ll know how tricky and time consuming it is, and doing it with wire is even trickier! There’s a good description of it on the Vintage Aviator’s website.

External wire bracing. All the bits of wire that you can see from the outside were originally made in wire cable, similar to that on the inside. Later on they changed to things called RAFwires, which were solid rods in a thin aerofoil shape which reduced the drag greatly. They have to be specially made to the length you need, and are therefore very expensive; thank goodness we don’t need them on 1264!

All in all, it seems a fair bet that no two of the 400-odd Scouts that were built were the same, and even designer Frank Barnwell couldn’t tell precisely the difference between a Scout model C and a Scout model D. The model Ds obviously incorporated more of the later changes than the Cs, but there was no clear dividing line that enables one to identify one model from the other.

And with all that tinkering, it seems surprising that Grandad’s main complaint – that the cockpit was too small and he could only fit in by removing the cushions. I’m the same height as him and these days I’m a good deal thicker round the middle. Will I fit in? Only time will tell.

 

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From → Research, Technical

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