Big day today.
The petrol tank, which is the most complex fabrication on the aircraft, was offered up to the fuselage for the first time.
Ian Harris and Rick have been sweating blood over this for the past month, and so it was a very nervous moment for us. Thankfully, it all went pretty well according to plan, though until you’ve tried it you don’t realise how many things there are for it to bump into.
Designer Frank Barnwell was obviously aware that he needed to fit as much petrol on board as possible, and made the tank as BIG as he possibly could. The result is that it’s a very close fit at the front, bottom and back, and we had to spend ages making sure it wasn’t going to contact anything.
But after a bit of jiggery pokery we convinced ourselves that actually it’s a d*** good fit, and when it’s finally in place it will look perfect.
I visited Ian Harris yesterday where he and Rick were hard at work on the petrol tank.
One of the oddest features of the design is the back edge of the top cover. The picture below shows it more or less straightened out and you can see two things.
First, because the tank is more or less semicircular in cross section, and the back is sloping to match the slope of the cabane struts, the back edge is curved.
Second, the edge has been doubled over onto itself.
We don’t know why it’s been doubled over like that, but we’d spent weeks worrying about how to make that doubled-over edge, and considered abandoning it altogether, making the flange of the rear end stick outwards instead of inwards, and making it out of a separate curved strip of steel that would be soldered to the top cover.
In the end, Ian decided to do what it said on the instructions, and folded it over our wooden former to get the initial fold in the right place, then continued tapping it all the way over, and finally running it through the rolls to even it up. The result is absolutely perfect, and only took about half an hour, apparently! It’s also much easier to form around the back end than we feared.
So now we just need to find out what it’s for…
By the end of the day, the tank was as you can see. The sump and mounting channels are permanently riveted and soldered to the bottom, and the top and bottom are permanently riveted to the back.
So what’s left to do – in order – is:
Rivet the rear baffle plate to the top and bottom.
Rivet the front baffle plate to the top and bottom.
Rivet the front plate to top and bottom .
Solder the filler neck in place (it’s just loose at the moment).
Easy. Except that each rivet has to be fiddled into place from the inside using a pair of tiny pliers. Then you hold it in place using a magnet while you move the tank over a specially-built anvil, consisting of a long piece of steel bar, about 30mm x 75mm, clamped to a very solid post on the floor and a machine tool, to leave sufficient overhang to reach the full length of the tank. On the end of it is mounted a ‘set’ – a tool like a punch with a hollow nose which the head of the rivet sits in. Once you’ve got that all in place without dropping the rivet, pop a copper washer over it and rivet it in place using a hammer and a LOT of skill, as one false move will send the rivet crooked and it will have to be very carefully drilled out before starting again.
It probably only takes about three good taps using another set on the top to complete the process.
Now take a look at the number of rivets in each seam, and you begin to get an idea of the time and effort involved in making the b***dy thing.
But it, along with the propeller, will be the piece de resistance of the build, and we think that we’re looking at another two or three days to completion.
A month ago I made a list of outstanding jobs which went into as much detail as I possibly could. It ran to three pages of closely-packed words, and I sacred everybody with threats that it had to be completed and we mustn’t lose focus.
Since then, Theo’s been up for a day, taken some work back with him and got it all completed. This means that for the first time since 2009 there are no Bristol Scout parts in his house.
And today I actually came home at 1530, since there was nothing more I could do in the short term.
It’s a very strange feeling; for the last five or six years, we’ve been climbing the hill, with no sight of the summit. We’ve said vaguely that we hoped to have it finished by the end of a particular year (2012 was the first one, I note!) Suddenly, we’ve come over a ridge and there is the summit, and the idea that it will be ready to fly in May seems entirely practical. Of course it’s nice, but it’s also a rather unsettling feeling.
Theo has made up the cable connections for the shoulder straps for the modern harness. I’ve cut the slots in the back of the cockpit for them to fit through, and they are now fitted and complete.
The ply cover is now covered in fabric, and awaiting completion of the petrol tank before it’s finally fitted. I’ve started sewing the leather cockpit surround to the ply cover with copper wire.
Rick and his partner Marian are well on with a protective sock for the propeller, and is ordering a HUGE socket with a torque wrench for bolting the propeller boss to the engine.
He’s also making progress with the instrument panel. It had developed a bit of mould, but it’s all come off with a light sanding, and we’ve got the captive nuts to go on the back.
The next big event is to fill the oil system and see if it leaks, and I’ve got castor oil on order. The tank is about 32lt capacity, but at about £10/lt I’ve only ordered a part tankful!
Of course the most important work is the petrol tank, and Rick and Ian got two days at it last week, some of which was filmed. They’re working on it again on Thursday, and I’m told there’s a possibility it might be finished, though I think that’s a bit optimistic. Nevertheless, it’s certainly getting close.
And then we have to connect up the last bits of petrol piping, and we can take it outside and see if we can start the engine…
All civilian aircraft are required to have registration letters so that they can be easily identified. That’s why they all have the BIG letters on the underside of the wing, on the side of the fuselage and / or on the tail fin. The requirements are all in CAP 523, if you want to check it out.
So if you want to apply military markings – and that includes every warbird on the display circuit – you have to apply to the relevant arm of the military for special dispensation to use their markings, and they check carefully to see that you aren’t planning to surreptitiously start an uprising by impersonating the real thing.
Thus our aircraft will have a civilian registration applied to it – G-FDHB, using Granddad’s initial – but we want to use exactly the original markings from 1916, and this week we got permission from the Deputy Assistant Chief of Staff (Air Engineering) at Whale Island in Portsmouth officially giving that permission. It officially allocates serial number 1264 to our aircraft, which is great news. I’ve sent the letter off to the CAA, but it means that we are officially allowed to apply the exact original markings, and the only place the civilian registration will appear is on a small metal plate which has to be attached to the airframe somewhere.
No-one has ever offered a satisfactory explanation for this form of identification; it’s not as permanent as the serial numbers on cars, for example, which are welded permanently in place or etched into the engine block. These can be bolted to the airframe, and thus can be easily removed. I understand they were originally intended to aid identification when the thing crashed and caught on fire, and everything including the occupants were fried to a crisp and completely unidentifiable, and it occurs to me to wonder how many times they have actually proved useful…
But not in the hangar. This was the view outside the hangar on Sunday morning when I started work on the Scout.
It’s been a while since I wrote on the blog. This is partly because there hasn’t been as much progress as I’d have liked and partly because what progress we have made hasn’t been very photogenic.
The need for progress is becoming urgent if we are to keep on schedule for the first flight in the spring. Essentially we have two major items waiting to be made, and a long list of little jobs, some of which have to wait on the large ones.
We are still waiting for the petrol tank, and the cowlings and side shields.
The side shields and tanks were going to be made by Steve Moon in Southampton, who is said to be the go-to man for these items. Since the side shields are attached to the petrol tank, this meant that the tank had to be fitted first. Poor Steve had had a heart attack in the autumn which had slowed him up a bit, but he said that he could get onto our project in March. This meant that we had to have the tanks completed and installed by the end of February.
Then a couple of weeks ago, Ian Harris picked up the work on the tanks again and we were able to get them away for tinning, which has to be done before assembly. The results of the tinning were frankly disappointing; the plates were distorted by the heat, and the finish was decidedly patchy. But Ian felt it was possible to carry on and we could rectify the situation later on.
What he also said was that the tanks would now take top priority, and that if we wanted he would take on the manufacture of the side shields.
This was a big help, since it meant that Steve Moon could make the cowlings without needing the aircraft in this works. This meant that the manufacture of cowlings and side shields could take place in parallel, and we shouldn’t need the trailer to be complete until a good deal later.
In the meantime, there is a long list of relatively minor parts we can be getting on with, and progress on these has been slowed by the fact that Rick had an argument with a circular saw – and lost – and while his hand is strapped up I’ve had to help out with some other urgent work of his. That’s now done, and I’ve been able to get back to the Scout. We’ve now got engine controls in place and working; the oil pipework is complete, and the petrol pipe from the Tampier valve to the bloc-tube carburettor is all in place.
The ply cover has been covered in fabric and doped, and we’ve made a rebate in the front engine former for the petrol tank when it arrives.
Rick and Ian have one good hand each, and so are able to do the riveting on the tank (!), and are expecting to get a good chunk of it done in about a week’s time.
Theo has taken a list of jobs away with him to do in sunny Dorset, and we have done much of the work to install modern seat belts (a requirement if we’re going to be allowed to fly it). I have some old seat belts off another aircraft (in fact I’ve got four!) but we’ve decided that all of them are a bit too tatty to go on the Scout so I need to order new ones…
So progress is being made, but my detailed list of jobs to be done before we can go flying runs ot five pages, closely typed, and there are a good few sleepless nights wondering if we’ll make it to the next centenary if we miss this one…
I’ve spent a satisfactory day getting various bits installed – at least temporarily – on the fuselage.
The engine controls and mixture valve are mounted now, though they’ll all have to come off again for painting, and the pushrods haven’t been fitted. The picture shows them both with strings showing where the pushrods will be.
I’ve also had a fun day routing the oil piping.
The pipe from the tank to the oil pump is enormous – 35mm diameter. I assume this is because the castor oil is very high viscosity, and although the flowrate isn’t huge – 5 lt/hr – you need to be sure the oil pump suction doesn’t dry out. In fact the actual oil pump suction connection itself is only 28mm dia., so it’s been fairly straightforward to use copper pipe and fittings for domestic water. We’ve included a lever valve in the system so that we can leave the aircraft stored for long periods without worrying that all the oil will work its way past the pump and onto the hangar floor! It was an option on the original drawings, so we’re making sure it’s included. The rubber hose connections at each end should ensure that any vibrations or movement of the engine are isolated from the pipework. They also make access for maintenance and repair easier.
One downside is that the long bit slopes upwards when the aircraft’s on the ground, making it possible to get an airlock in the system. There doesn’t seem to be any way around this, and I think we’ll just have to lift the tail into a flying position when we fill the tank for the first time to make sure no air bubbles get in.
The output from the pump is in an awkward position at the bottom of the pump facing inwards. I’ve had to use a combination of rubber hose and 8mm copper pipe and fittings to get a sensible run.
The pump outlet has a rubber hose connection to reduce vibration, then there’s an elbow and a tee, all in 8mm. The pipe that curves upwards goes to the engine inlet; the other one goes to the oil pulsator.
I’ve tried to route it as straight as possible so as to get as few airlocks as possible, but once again it’s impossible to eliminate then when the aircraft’s on the ground.
The location of the pulsator makes connecting to it rather difficult; we were going to make a hole in the plywood gusset plat underneath, but this would (a) weaken the fuselage structure and (b) make it difficult to remove the pipe, so I’ve come up with another solution as you can see.
(You may remember that the pulsator is an open-ended pipe covered up by the glass dome. The idea is that the strokes of the oil pump will show as pulsations in the surface of the little bit of oil inside the dome. In practice, I’m told, it never works, and it’s much easier to go by the smell of castor oil and the film of it on your goggles. If either stops, start worrying!)
Finally, Rick and I spent much of the day in Hereford A&E yesterday, after he came very close to losing the tip of his middle finger in a circular saw. It’s looking as if the damage may be relatively limited, as all the tendons appear to be intact, though probably damaged. But part of his index finger was sliced off, and the top joint of his middle finger is dislocated and broken. Thankfully it’s his left hand (he’s right-handed) so it’s not as disabling as it might have been, but it was a very shocking and unpleasant experience, and the result of just a moment’s inattention. Rick’s a professional, and uses the saw all the time for his work. He is very, very careful at all times, and it’s hard to see how he could have done more to protect himself. Let’s hope he makes a quick recovery and can get back to work without too much delay.
I’ve been puzzling over how to fit the fuel system into the aircraft for a week or so.
The only drawings we have are for the Gnôme engine installation, and the carburetion seems to have been significantly different. The throttle lever was fitted on the right hand side of the cockpit above the top longitudinal, so that the lever would have stuck out above the cockpit coaming. The mixture was operated by a knob which you twisted underneath the instrument panel, also on the right hand side.
It’s conventional to fit the engine controls on the left side, since most people are right handed and would prefer to have the control column in their right hand. It’s possible that’s how the Gnôme installation worked on the Scout, since the cockpit is so tiny that it was probably easier to reach across with your left hand to reach the controls!
But the throttle lever operated a Bowden wire, and it didn’t seem to be compatible with the bloc-tube (carburettor) for the le Rhône engine which is a reasonably stiff sliding motion. All the other le Rhône installations we’ve seen use standard parts made by Tampier, including the levers and mixture valve as well as the bloc-tube, and we’ve decided to go with these in order to make things as simple as possible when it comes to flying it. It also means putting them on the left side, since they can’t easily be handed, and this will be in line with all the other installations, making it easier to transition from one type to another.
The controls are operated by pushrod, rather than cable, and we need to make sure there’s a sensible run for them, clear of feet and so on.
The first lash-up looked like this, with the mixture valve mounted on the rear engine mount on the left side, where it would be accessible from the inspection panel. The inlet would run just outside the line of the fuselage frame (but inside the side shield), and the outlet would run straight through to the bloc-tube inlet. One downside was that the pushrod would be contacted by the pilot’s left foot.
The throttle lever bellcrank is mounted just above it. This photo shows the pushrod runs, which looked to be reasonably clear of the pilot’s feet. There was one major flaw in this arrangement, however; the throttle was operating the wrong way round!
This wasn’t a major problem, however, as we found it wouldn’t be too much of a problem to raise the bellcrank up to the top of the opening in the engine mount and move the pivot inboard. This kept the pushrod well above the toes of the pilot and was a pretty simple and solid mount.
But we weren’t happy about the mixture valve, and on a trip to the Shuttleworth Collection it was apparent that their Sopwith Camel had the mixture valve mounted aft of the levers, which would mean that there were no pushrods in the way of the pilot’s feet.
And we’ve come up with this location, which has the benefit of being reasonably easy to mount and a sensible run for the pushrod. There’s a strainer in the top, and this location makes it reasonably accessible from the cockpit too. The bits are on order, and we’ll be looking to get it installed – along with the oil pipework – in the first couple of weeks of 2015…