Sunday, 31 May 2009

May in review

May stated off with a distinct electrical flavour. There's a surprising number of cables that have to be pulled to the various extremities of the airframe, supporting various forms of lighting, trim and flap controls, fuel gauge senders and so on. In addition there's quite a lot of electrics in the cabin, associated with the control sticks. Of course there's also the instrument panel but that's for another day.

Anyway, May saw pretty well all of this work completed and a detailed cable and connector schedule was produced as I went along. I've also got a small pile of circuit diagrams sketched out in pencil that at some stage I'll want to make neat, preferably electronic copies of.

During May I also removed the Ballistic Recovery System, which is something that I should have done at the very beginning! It makes working in the confined space behind where the instrument panels will go so much easier.

After the electrics it was time to start on the engine and associated infrastructure. Firstly I laid the fuel pipes between the wing tanks and the fuel selector and on to the engine. I also fitted the gascolator and electrical fuel pump. Engineering the engine mounting bracket was next, with a few holes that had to be very accurately marked out and carefully drilled. At length, we were able to mount the engine but only after I had bought some mounting bolts of the correct length, those supplied by the factory being too long!

Finally, on the last day of the month I was able to fix the engine in place and install the oil and water distribution piping.

May has been a busy month, both with Sportcruiser building (45h 15m build time) and with other activities, so I am quite pleased with progress. June will be the month of the engine!

Engine-ering (2)

Today I started on the engine support systems. Firstly I had to find the correct mounting position for the water radiator and then shape and drill the brackets to fit. The system for mounting the radiator is a bit awkward and there have been various reports of the radiator corners rubbing up against the lower cowling, so I was careful to check it out. Yes, it's true, there really isn't much space between the radiator and the cowling. I'll have to keep an eye on this as the build progresses, though to be honest it's difficult to see how any real improvement can be achieved.

Next I started on the oil system. There are various hoses to be installed - essentially from the oil pump to the cooler, then on to the tank and finally to the sump, which is scavenged during operation. The only difficulty with this work is something that I should have foreseen! The engine is shipped with a small amount of inhibitor in the oil/water channels and I should have guessed that most of the inhibitor would have found its way to the bottom of the sump. So when I removed the blanking plug, inhibitor gushed out and I had to quickly improvise a channel to direct the fluid to a small container.

Whilst the engine was draining, I took the opportunity to start drilling out the rivet holes on the port wing. Large rivets are used almost exclusively on the wings but the holes are only drilled out to the very small temporary rivet size. So I carefully Cleckoed around a small area then drilled it out to the correct size before moving on the another section and repeating the procedure. It's a bit painstaking and, with some 400 rivets per wing to be installed, it's going to take some time!

Back at the engine compartment, the inhibitor had all drained out and I was able to complete the oil piping with the exception of the cooler to oil tank. I'm not quite sure what the best routing will be for this pipe, so I'm leaving the final installation until I've built a bit more of the engine infrastructure.

I also installed the complete water cooling system. This was a bit of a fiddle, with a mixture of large bore rubber pipes and pre-bent aluminium pipes. Unfortunately, installing these pipes seems to push the water radiator forwards a little, which will probably compromise the already tight clearance between the radiator and the lower cowling. Something to keep an eye on!

All in all quite an energetic day, so time for bed! Total project time is now 93h 15m

Thursday, 28 May 2009

Mounting the engine

Today, with the help of Chris, the engine was at last mounted and bolted into place. The correct bolts finally arrived, so there was nothing standing in the way of this major hurdle.

Firstly, I had to correctly position the engine on its mounting brackets. This is straightforward enough but I thought it would be worth while just checking that the proposed position would work with the cowling. So we carefully fitted first the lower cowling and then the removable upper cowling. These sections are held in place with Dzus clips, which attach the cowling to a flange on the firewall. Naturally, the position of the engine relative to the front of the cowling is critical - too far back and the propeller spinner could foul the front of the cowling. Too far forward and there would be a large gap 'twixt spinner and cowling.

After a bit of messing around we finally got the cowling assembled and the spacer, spinner and propeller hub all loosely attached to the engine. We even added one blade of the three blade propeller to get some idea what it would look like!

The results were spot on. About 6mm gap all round, between the back of the spinner and the front of the cowling, which is exactly what it should be. What a relief!

That done, the moment of truth when I needed to drill the holes for the engine mounting bolts. This isn't trivial, as there is no easy way to mark the positions for the holes. The build manual suggests using a cut off tip from a felt tip pen, so that's what we did. It was then time to remove the engine again and centre punch the mounting brackets for drilling.

The four mounting bolts are 0.25" diameter, which does seem quite small considering the stresses that they will have to handle but so far there have been no reports of engines becoming separated from Sportcruisers, so I suppose they must be up to the task. Firstly I drilled small (2.5mm) pilot holes, trying hard to keep the drill perpendicular to the mounting bracket. That done, I drilled the pilot holes out to 0.25" using a slow drilling speed to avoid tearing at the aluminium mounting bracket.

Now the moment of truth! The engine was replaced on the mounting brackets and the four bolts were inserted. Well three of them were. The fourth required a bit of gentle persuasion by first drilling up through the mounting bracket and the engine bracket. I doubt the alignment was more than a few thou' out and soon all four bolts were in place and correctly torqued.

Thanks to Chris for his help today and to Jim for taking the pictures.

Total project time is now 88h 00m

Wednesday, 27 May 2009

Fuel system (2)

Well the fly in to Mull turned out to be something of a washout. On Saturday we had to wait until early evening to depart from Carlisle because the runway at Glenforsa was saturated with rainwater. Sunday was dull and overcast, with drizzle and low cloud, ruining any prospect of sightseeing flights. Finally, on Monday morning we gave up and flew back IFR, in IMC all the way until we got close to Prestwick and then, annoyingly, glorious, almost CAVOK weather back to Carlisle. Never mind, we were able to chat with the few other aviators who made it to the fly in and, of course, do some serious damage to the top shelf in the Glenforsa Hotel's bar!

Yesterday it was back to Sportcruiser building and several hours spent sorting out the fuel system. A few days ago I obtained the necessary Loctite compound (Loctite 572) for the fuel fittings so I was able to make up the brass fittings to the fuel selector, which mounts in the centre console between the two seats. Likewise I attached fittings to the gascolator and electric fuel pump.

I also installed my first piece of fuel pipe in the engine compartment. Fuel pipes forward of the firewall have to be protected with a fire resistant material and this comes in the form of a rubbery sleeve which slides over the fuel pipe. On the inside of this sleeve is a fibreglass-like material which acts as insulation.

This sleeving has a habit of shedding small flecks of the fibreglass insulation when it is flexed, so it's necessary to protect the ends of the fuel pipes whilst the sleeving is installed. It's also, of course, important to have as much of the fuel pipe as possible covered by the sleeving, though inevitably there is a small section at each end, where the jubilee clip goes, that cannot be fully covered.

Another area that got some attention yesterday was the routing of fuel lines inside the cabin. There is a small area in the centre forward area between the rudder pedals, which is where these fuel lines, together with brake lines and rudder control cables have to route. It's a bit congested down there! So I spent quite a bit of time trying to work out the best routing for the various services so they don't interfere with one-another and, especially, don't prevent the rudder pedals from achieving full movement. Soon I shall have to temporarily mount the rudder so I can see exactly where the rudder control wires will go and to gauge the precise rudder pedal deflections.

I also put some rubber protection around the various places where fuel pipes have to pass through or around metal edges. Even though the pipes will never move, it seems like a good plan to protect them as much as possible. Finally, with the assistance of my pal Chris and his daughter Lizzie, we adjusted the rudder pedal mountings and correctly greased them so they should be free moving yet secure.

Total project time is now 84h 00m

Friday, 22 May 2009

Engine-ering

This week I've made a bit of a start on the engine.

First, of course, the engine mount had to be found and attached. People are often quite surprised that such a seemingly lightweight, flimsy even, structure can hold the weight of the engine and handle the stresses from the thrust it produces. It's a steel tube construction, which is immensely strong, even if it doesn't look it! Steel welds very well and the welds are almost as strong as the original metal, so it's the obvious choice for the engine frame.

With the frame installed, it was time to attach some bits of engine! The oil cooler is the first item, as it sits below the engine. I also installed the oil reservoir (the engine has a dry sump, with engine oil pumped into the reservoir, which is also where the oil level dipstick is to be found).

Next it was time to remove the engine from its crate. The engine is bolted into a wooden crate and these bolts and associated mounting brackets have to be removed and new brackets designed for the Sportcruiser installed. Fortunately, I have access to a small hoist at the workshop so lifting the engine out of its crate was no problem at all.

With the engine suspended in fresh air it was easy to see how to remove the old brackets and fit the new ones. However, it soon became apparent that two water coolant pipes will snag on the engine mounting bracket. This is a problem that I won't be able to resolve until the engine is in place and I can see how to route the pipes, so for the meantime I have just removed them.

What I wasn't expecting was a load of preservative fluid in the cooling system. As the first pipe popped off the fluid ran out and created a rather large puddle on the workshop floor! Fortunately, it seems to have dried out, so I guess it wasn't oil based.

With those problems out of the way I could try positioning the engine on its mount and see how it fits. No problem! It seems to sit nice and square on the frame and it looks really good. I've not bolted it into place yet, as I am still waiting for the mounting frame bolts (the factory supplied bolts that are about an inch too long as you can see if you look at the pictures carefully).

So I'm at the start of the next significant phase of the build. Unfortunately I won't make any further progress for a few days as I'm away at the Mull fly-in for the Bank Holiday weekend.

Total project time is now 79h 30m

Fuel system (1)

Whilst I am waiting for the LAA inspector to come along and take a look at my handiwork on the wings and fuselage, my attention has turned to the engine and associated systems.

This is a big part of the overall build and needs to be carefully thought through. Unlike with the electrical systems, there is quite a lot of information in the build manual, albeit some material has been rendered partially out of date by changes in the kit.

So this week I started with the fuel system. Fuel is stored in tanks in each wing and fuel lines are routed via the wing root (where it connects into the fuselage) to a fuel selector valve, which lets the pilot select which tank fuel will be drawn from. The fuel line then routes forward, past the rudder pedals on through the firewall to a strange device called a gascolator. Really the gascolator is merely a fine filter and a water trap combined into a single unit which is deliberately at the lowest point in the fuel system. As water is heavier than fuel, it sinks to the lowest point and can be drawn off via a small valve at the bottom of the gascolator.

From here, fuel routes via an electrical pump and a mechanical pump (belts and braces!) to a complex array of pipes that deliver fuel to the two carburettors and a fuel pressure gauge. There is also a vapour lock relief system which ensures that there is always a small flow of fuel back to one tank. This simple system means that should the fuel vaporise in the fuel lines then the gas will be harmlessly returned to the fuel tank and a constant supply of liquid fuel is maintained at all times.

So far I have only laid the fuel lines from the wings to the selector valve. There's lots more to do yet!

Friday, 15 May 2009

Avionics - initial musings

I've been used to having plenty of good avionics in my Warrior aircraft, which is fully equipped for instrument flying. Of course, at least for now, kit build aircraft are limited to day visual flight rules (VFR) only, so there is no need for the same level of instrumentation.

But old habits die hard! I've been used, for example, to having two communications radios (the units used to talk to ATC) and it's certainly handy being able to occasionally work two units at once, or listen out on one frequency whilst working another one. So two comms it is then!

Similarly I've been used to having VOR capabilities (VHF Omni Range is the traditional and still primary method of navigating en-route). Whilst it is certainly true that the GPS provides far better situational awareness, it suffers from the not inconsiderable disadvantage that it relies for its operation on tiny signals from satellites that can be turned off at a whim by the US DoD. It's not likely to happen but it's the risk that keeps 50-year old technology like VOR and the like in use to this day. So it looks like I'll be wanting a nav radio as well then.

These days pretty well all aircraft are fitted with a transponder. This is the unit that responds to secondary radar interrogations and provides position and altitude information to the air traffic controller. A squawk code also enables the controller to uniquely identify each aircraft on his screen if necessary. These days, Mode-S is the way to go and that is what I will specify.

Finally, of course, I shall want to install a GPS. For the time being, a VFR only GPS such as my Garmin 296 is perfectly adequate, so that's what I'll use.

The whole ensemble is a bit of a tight fit! Unfortunately the Ballistic Recovery System parachute housing also gets in the way limiting the depth behind the panel unacceptably. Happily it seems that the aircraft manufacturer has come up with a solution to the problem, so I shall be working on this over the next few weeks.

Avionics is a critical part of the overall design of the aircraft, so I'm spending plenty of time thinking about it before I make any decisions that I might later regret.

Testing the electrics

I've spent the last week completing the general electrics, which broadly comprises the following sub assemblies:
  • Strobe lighting to wingtips and optionally, tail fin and/or fuselage tail cap
  • Navigation lighting to the same locations
  • Flap deployment servo and position display logic
  • Elevator and aileron trim servos and position display logic
  • Control column wiring
  • Fuel level sender wiring
In addition, I have laid coaxial cables for the following avionics, not all of which will necessarily be installed, at least to begin with:
  • Comms transceiver 1 antenna
  • Comms transceiver 2 antenna
  • Navigation receiver antenna
  • Transponder antenna
All these wiring systems have been made up into harnesses and every cable/connector is uniquely identified, so it should be relatively simple to make any changes to the electrics at a later date, should that be necessary.

Gradually the spaghetti has been tidied up as more and more subsystems are completed, tested and finalised. The picture to the left shows the wiring on the port side of the aircraft, behind the P1 (pilot's) seat. In the main cable run are three separate looms: strobe/nav lighting to the wingtip and to the tail fin, plus control wiring to the flap deployment servo. The loom also contains the coaxial cable to the navigation receiver antenna. Separately, you can also see the cable for the transponder antenna, which will be installed on the underside of the fuselage.

On the Starboard side, things are a bit more complex! The ducts for both communications antennas and for the elevator area all converge here, as do the other starboard side wiring looms. This is also the logical place to put the trimmer relay box, which is needed to control the inputs from the two control sticks and send the correct sense signals to the trimmer servos. Finally, all the strobe and navigation lighting looms converge here and you can clearly see the blue crimp terminals used to connect all these wires together.

Eventually it was time to test all these systems, so I rigged up a somewhat Heath Robinson test rig, as you can see in the picture! Eventually, of course, all these wires will terminate in the instrument panel, with switches and indicators to control each subsystem. For now, spaghetti is once again the order of the day. I'm pleased to say that end to end tests of all subsystems was successful.

So the electrics are now, more or less, completed, until such time as I come to the instrument panel wiring. Before that the engine and firewall forward beckons as the next major project.

Total project time is now 73h 00m

Friday, 8 May 2009

More spaghetti

After a couple of days working at Carlisle Airport, I was able to spend a few hours today doing, you've guessed it, yet more wiring. Today I completed the circuitry around the control sticks, including the aileron and elevator trim logic. Although simple enough in principle, there's actually quite a lot of wires back and forth between the control column area and the increasingly busy area to the rear of the seats.

I chose the area behind the seats as it is a natural focal point for much of the control wiring and it's a large, unobstructed area that is reasonably accessible. Strobe lighting circuits, all the trimmer controls, all the coaxial cables to the various antennas and various other wires all converge on this central point. It's also where the box containing the trimmer control relays will live. Fairly soon I shall have to start connecting all the various wire ends together and I think I'll make a small platform out of aluminium to mount all these connections and keep them tidy.

I'm at the stage now where I can test some of the subsystems. Today I tested the trimmer relay logic, from the control sticks all the way through to the actual servos. I'm pleased to say that everything worked first time, so it looks like all my preparatory work on the cable and connector schedules is paying off.

I reckon I have another dozen or so hours more work to do on the fuselage wiring, then the next stage will be to start on the engine compartment, or possibly the instrument panel.

Total project time is now 65h 00m

Monday, 4 May 2009

Even more wires

After an excellent weekend staying with my pal Tim near Oxford and flying in to the Abingdon Air and Country Show, I was raring to go with a bit more aircraft construction today.

More electrical wiring was on the agenda and the plan was to finish the wing electrics and test as much as possible. With that work completed, I can consider getting the LAA inspector down again to inspect the wing innards and check on my electrical handiwork therein. I'll then be able to rivet up the wings and that will be the first major task completed.

One of the problems with the wings is that they need to be able to be removed without damaging the electrical systems (and the fuel systems, come to that). So I've put quite a lot of thought into the sort of connectors to use and where they should go. In the end I've standardised on Molex 1625 series crimp terminal connectors, which are sturdy and have a good locking action without being too large. Whilst the connectors themselves are quite reasonably priced, the cost of the essential crimping tool is enough to make your eyes water! Anyway, I've used three way connectors for the fuel senders, four way for the strobe/navigation lights and six way for the aileron trim servo (on the starboard wing only).

I also had to think how I would connect the strobes at the wingtips. It's not really possible to drill a hole big enough to let a four-way Molex connector through, so something smaller was needed. In the end I found some tiny round locking connectors which, whilst fiddly to solder are just the job and fit easily through the 10mm hole in the wingtip edge. This means that if ever needed it will be easy to remove the strobe light without having to dismantle the wingtips (umpteen rivets to drill out and risk of damage to the paint job).

So I've achieved today's objective. The wing electrics are completed and tested as much as can be. Meanwhile, the fuselage is rapidly taking on the appearance of a large plate of spaghetti... just as well every wire is labelled and catalogued!

Total project time is now 57h 00m

Friday, 1 May 2009

Wires everywhere!

I finally got all the stuff I need to make a proper start on the electrical wiring, so I spent four hours today pulling cables through pipes and attaching plugs and sockets where feasible. It takes a surprising amount of time but at least there is some evidence of progress to show for it now.

Included in the wiring is the coaxial cables for the Com1, Com2 and Nav antennas. The connections to these antennas will be much more difficult to get to when the fuselage has been fully riveted, so it makes sense to do this work early on. Whilst I was at it, I laid cables to the fin tip and to the tail cap to permit me to install a strobe in one or other position at some stage in the future. At the moment I don't feel it's necessary to do so but that would change if there were ever any prospect of the aircraft being certified for night operation. For the sake of running a few wires, I decided it was worthwhile future proofing the design.

I feel as if I have made good progress today. Tomorrow I'm flying my Warrior, G-JLIN down to the Abingdon Air Show and staying with a pal of mine near Oxford for the night. So the next opportunity to work on my Sportcruiser will be bank holiday Monday.

Total project time is now 52h 00m