Friday, 31 July 2009

July in review

July was another busy month with significant progress on numerous fronts. Much of the major work was associated with the engine management systems and avionics but in addition some major progress was made on the fuel system, wings and, equally importantly, documentation. The aircraft was also officially christened as G-JONL and I have a certificate from the CAA to prove it!

The grand plans to sort out the aircraft painting were frustrated by the unavailability of my Warrior for nearly three weeks due to a leaking nose wheel oleo seal, with the result that I have been unable to fly down to visit the paint shop. The good news is that the Warrior is back on line and the plan is to fly down to Sturgate on Monday 3rd August.

In a general sense, the project is slightly ahead of the original plan. I had intended to do the avionics whilst the aircraft was away being painted but in practice I've been able to more or less complete the work rather earlier. On Monday I hope to agree a list of jobs with the paint shop to be completed before the aircraft goes off for painting and will then have about a month to sort it all out.

Soon I shall have to start thinking about booking hangar space at Kirkbride and, of course, sorting out the transport to and from the paint shop. This really will signal the closing phase of the physical construction project as I start to prepare for final sign-offs, flight testing and so on.

I spent around 67 hours on G-JONL during July but that doesn't take account of all the hours spent at home working on the documentation, ordering parts and generally doing admin. I suspect one could easily double that figure!

Of swallows & the port wing

I've been wanting to finish off the port wing for a couple of weeks now but work has been temporarily suspended waiting for a nest full of swallows to fledge. Each time I went into the area where the wing is stored, four small pairs of beady eyes would watch my coming and going. A few days ago it became apparent that they would be fledging soon, for there was no longer room for mum or dad in the nest!

Well I went down to the workshop yesterday and the nest was empty! No signs of either the fledglings or their parents, so I am confident that they've fledged and it's unlikely at this late stage in the season that another brood will be started.

So it's game on for finishing the wing. I didn't have a lot of time yesterday but I did fix the pitot tube system and give the wing a final check out. I just need now to find out how the paint shop would like to receive the wing: with or without the pitot tube housing attached. Then I'll be able to rivet it up next week and that'll be another big job completed.

Avionics stack (3)

I've finished wiring the avionics! Well, more or less - there's still a bit of interconnection to do with the rest of the aircraft electronics but that's pretty trivial and can be left until later. I've also sorted out the instrument panel mounting and trial fitted the coaming and panels to the fuselage.

The instrument panels are attached to the coaming (glare shield for any Americans out there) and, in the middle, to the vertical central column. The central column needed to be fitted with shake-proof nut plates and then the instrument panel could be properly positioned and the mounting holes drilled. That completed, I decided to trial fit the whole ensemble into the fuselage. It certainly makes the cockpit area look a lot more full!

I've also completed the wiring of the avionics stack, comprising the following components
  • Mode-S Transponder
  • Altitude encoder
  • Com 1
  • Nav 1
  • Com 2
  • Intercom
  • Audio panel (home-brew)
  • Headset wiring
This was quite a big task but fortunately it could almost all be done at home on my workbench. It's one of those occasions where being a radio amateur is very helpful, with plenty of test equipment available.

Once the intercom and audio panel were built I was able to connect the headsets and confirm audio operation. Loud and clear! I'm particularly pleased that my simple audio panel, just a bunch of switches and a few resistors, works perfectly. A commercial audio panel would have cost around £1000 and is anyway too big to fit.

Next up was the two communications radios, Com 1 and Com 2. Firstly I confirmed that I was receiving audio from each Com receiver by listening to Carlisle Airport's ATIS, then it was time to attach a power meter and a dummy load to test the transmitters. Both transmitters produce around 10W, exactly to specification and the transmitted audio is just fine. Of course I also needed to check that the Com 1/Com 2 switching in the audio panel was properly routing both audio and Press To Talk (PTT) to the correct radio.

Finally I wanted to test the Nav radio. This is a bit more difficult as I can't hear any navigation beacons at home. So I retrieved my venerable signal generator from the loft and checked the VHF performance that way. I have no way to check the UHF Glide Slope receiver, so that'll have to wait until I can either borrow an ILS test set or, more likely, fly an approach on an ILS equipped runway.

Everything seems to work, to the extent that I am able to bench test it. That's very pleasing as it is a major part of the overall project and one that I have had to design entirely from scratch. Being an electronics engineer and a radio amateur to boot does have its advantages!

Further good news is that my Warrior is finally back on line, so I should be able to fly down to the paint shop on Monday next week to get that part of the project moving along. But that's next week. Today I am flying up to Glenforsa for the weekend. Needless to say, the weather is up to its usual tricks and I guess it'll be mostly IFR flying again.

Total project time is now 218h 05m.

Tuesday, 28 July 2009

Avionics stack (2)

After an enjoyable weekend with visitors from down south, it was back to building aeroplanes today as I got on with the avionics. One of the more complex aspects of the avionics stack is the radio navigation system. This provides two important functions
  • En-route bearings and tracking to known radio beacons, called VORs (VHF Omni-Range)
  • Instrument landing system (localiser and glide slope)
A specialist receiver is used to tune into these navigation systems and the results are then displayed on a Course Deviation Indicator (CDI) unit. The CDI has a manually rotated bearing dial that can be set to the desired track and the aircraft then flown to intercept it.

Necessarily there are rather a lot of wires between the receiver and the CDI and making all those connections was the challenge for today. In all some twenty connections had to be made to the radio and to the CDI, plus a fair number of other cables for power, control systems, etc.

Once that lot was completed, I then set about testing the completed system and fairly quickly came across a snag: the CDI would not calibrate! After a bit of diagnostic work I discovered two wires transposed at the CDI end. With that fixed, the calibration went smoothly and the system was soon as fully checked out as is possible on the workbench.

Ideally I would like to check the system against an actual VOR transmission but unfortunately I live too far away from any of the beacons to receive a signal at ground level. Perhaps I'll put the ensemble in the car and drive to a place where I can get a known signal. There's a few other items that I can usefully construct before I get to that stage, I think.

Friday, 24 July 2009

G-JONL it is

I just checked the G-INFO web site run by the licensing authority (the CAA) and was pleased to see that G-JONL is now registered! That was quick, considering that the paperwork only went in the post (second class) on Monday.

The good thing is that I now have an ICAO 24 bit aircraft address for my Mode-S transponder, so I can start setting that up (though of course I can't use it yet because I need an aircraft radio licence). And, of course, it's another step along the way to getting the Permit to Fly.

Thursday, 23 July 2009

Avionics stack (1)

After a few days of inactivity, I was able to spend several hours working on the project yesterday. The plan was to complete the mounting system for the main avionics stack, which comprises the GPS, two radios, the navigation/instrument landing system, an altitude encoder and the mode-S transponder.

This is a busy area, with a considerable amount of wiring and precious little space, due in part to the Ballistic Recovery System, which is mounted just forward. It makes a lot of sense to build these units up in a separate mounting so that the vast majority of the wiring can be completed away from the aircraft, in the relative comfort of home.

To achieve this, I constructed a pair of strong brackets to which the various equipment mounting frames are bolted. These brackets will, in turn, be the means of attaching the ensemble to the centre instrument panel, in due course. There isn't a great deal of room for error in either the dimensions or where the mounting holes are drilled, so a policy of measure twice, cut once was definitely in order.

I also had to fabricate a mounting plate for the altitude encoder, which is used by the mode-S transponder to send mode-C altitude information to radar controllers. This unit has a large number of connections to the transponder and also, of course, a static pressure input pipe. On balance I decided that it was best to have it close to the transponder and put up with a slightly longer static pressure pipe.

The finished article can be seen in the pictures. It took about six hours of metal bashing to get this far. Now for all the wiring!

Total project time is now 198h 35m.

Fitting the wheel spats (1)

This is a job I've been putting off for some time! The wheel spats are renowned for being awkward to fit and they certainly lived up to that reputation. In principle the task is simple enough - drill four holes for screws that are then use to attach the spat to some metal brackets either side of the wheel. The question is, where do the holes go?

The problem is this: the spats are a fairly close fit around the wheels, as one might expect, so it is not possible to "get inside" the spats while they are in position. Unfortunately, the mounting brackets are, of course, on the inside. It is therefore more or less impossible to determine where the holes in the brackets are.

After abortive attempts to shine a light through from behind the mounting brackets, I finally concluded that the only option was to remove the wheel and mounting brackets completely. This turned out to be quite a big job! It is necessary to remove the disc brakes, then the wheel and, finally, the hub, in order to get the brackets off the aircraft. it took about an hour to just work out how to do that.

With the brackets off, it was relatively simple to mark the correct positions for the holes, two on each side. Reassembly would have been simple had I not first put the hub back on the wrong way round! In the end though the work was complete and we were able to mount one wheel spat.

Rather than take the other main landing gear wheel off, I have made the assumption that the brackets are the same on the port side as on the starboard unit we worked on. No doubt in due course I will find out whether that strategy has worked! In all, this tedious task took all afternoon and Chris and I were definitely ready for a pint afterwards. The nose wheel spat will be looked into after a suitable period of time has elapsed and enthusiasm for such masochistic tasks returns.

Tuesday, 21 July 2009

Nature can be very cruel

I've been away rather a lot recently and this evening was the first chance I'd had for a while to check out the young aviators nesting in my summer house verandah. Imagine my sadness at finding the nest apparently unoccupied and three dead nestlings on the decking, obviously ejected from the nest above very recently. Of the fourth nestling there is no trace.

What happened here? The parents are still circling around, squawking and apparently aware when I approach the nest. Did some other bird invade the nest and kill the young swallows? Will the adults be able to start another family this year?

Nature can be very cruel.

Sunday, 19 July 2009

G-JONL

I have applied to the Civil Aviation Authority for the registration letters G-JONL. In the end there wasn't too much agonising over what call sign to go for - other options were either not available or sufficiently obscure as to be readily discounted. The registration is essentially the licence plate for my aircraft but it is also the call sign used on the radio and whenever the aircraft needs to be uniquely identified.

It's certainly a lot cheaper to have your own "cherished" call sign for an aircraft than it is for a car! I did at one time contemplate getting my amateur radio call sign, G3WGV for the Merc but the £500 price tag was too much for my Scrooge-like persona to bear. G-JONL cost me a mere £160 - perhaps the only example known to man where something in aviation is cheaper than in other walks of life.

Better not tell the CAA though... they have a pensions crisis of their own to manage you know!

Thursday, 16 July 2009

The LAA inspector visits

Today Tom, my LAA inspector came to the workshop to check out on some of my handiwork. he seems to have been quite pleased with what he saw and he signed off the following sections in the build log:

  • Fuel system
  • Starboard wing quality and attachments prior to disassembly
  • Starboard wing riveting quality after riveting complete
  • Electrical installation
  • Engine installation
  • Cowling installation
This means that I now have 13 of the 27 stage inspections signed off, so I guess I am officially half way!

Wednesday, 15 July 2009

Instrument panels

Slowly but surely I'm working myself up to doing the instrument panels. Big job!

A few days ago I obtained blank Flight and Engine instrumentation panels and I've been spending some time with Visio trying to decide on optimal layouts. You can see the way my thinking is going in the outline drawings.

A separate problem is the central avionic panel. One of the problems with fitting two radios is that there is insufficient room on this panel for all the radios and the intercom unit. Also, because there are now several sources - and destinations - for audio, some sort of audio switching panel is required. In larger aircraft this is provided by a separate panel. I neither have the room, nor the need for such complexity, so instead I have designed a very simple audio panel that I will build myself.

All this stuff has to go somewhere and the obvious place is in the centre console, just below the main avionics panel. The only trouble with this is that the panel is ultimately riveted in place and fairly inaccessible from behind. So I've spent a couple of days engineering a separate screw-in panel and fitting nut plates to the port side panel so both can be removed relatively easily.

The new centre panel can be seen in the picture. It holds the intercom unit (at the top) and below that you can see some holes for the switches that make up the audio panel. At the bottom is the flap control switch and associated position indicator. This small sub panel is attached to the centre console with four screws and will therefore be easy to remove should any engineering work become necessary later in the aircraft's life.

Getting this sorted out was a necessary precursor to starting on the avionics panel above. That will be somewhat of a larger task.

Tuesday, 14 July 2009

Fellow aviators

A few weeks ago I noticed that a small nest had appeared above one of the outside lights on the verandah of my summer house. For some time I wondered who the occupants might be, for I could never see any avians coming or going. Then about three weeks ago I noticed that there were four small eggs nestling amongst the feathers and moss bedding.

It was my gardener who first realised that I was landlord to a family of swallows (we initially thought they might be swifts but the type and location of the nest makes that highly unlikely). In the past week I've seen quite a lot of activity around the nest but they are very timorous and as soon as I get closer than about 10 yards the adults fly off.

This evening I got back from a few hours working on the Sportcruiser and thought I'd check up on the lodgers. Still no signs of mum and dad but the nest is now home to four tiny nestlings. They are quite hard to see as the nest is close to the roof line, so I've been using a small mirror to look inside the beautifully made mud and straw nest.

So I have a clutch of fellow aviators. Like the Sportcruiser, they are not yet ready to fly the nest but its only a matter of time. Somehow I have a feeling that the fledgeling swallows will be airborne first!

Friday, 10 July 2009

Painting

Aircraft painting is rapidly moving its way up the agenda. On Monday Chris and I intended to fly (in my Warrior) to a paint shop in the Midlands with a view to agreeing a deal for painting to start some time in September. Unfortunately that didn't happen due to the Warrior going tech - that is to say a (thankfully minor) technical fault has grounded it. Hopefully we can reschedule the visit for some time next week. I still have to agree a colour scheme but I think that will be easier after the visit.

Another thing to think about is that the paint shop can officially weigh and determine the balance characteristics of the aircraft after painting. That's a good idea but of course it's of no use if the aircraft isn't otherwise finished, including stuff like upholstery and instrument panels - jobs that I had previously thought might get left until after the aircraft has been painted.

If I do in fact manage to finish the aircraft to the point at which it can be weighed then it means that final assembly, post painting, to be done at Kirkbride airfield will be a pretty quick job. Essentially a case of attaching the flying surfaces and getting them all properly aligned, then doing all the various engine checks, etc. before applying to the LAA for a flight test authorisation.

That's not such a bad thing - it means that I'll be able to complete more of the work at my local workshop and have fewer long distance trips to Kirkbride, some 35 miles away. On the other hand, I'm unsure about the implications of having all the upholstery fitted prior to painting. Part of me feels that it's best to leave the finishing work until after all the mess of painting has been cleaned away.

So there's lots of things to discuss and sort out at the meeting.

Documenting the electrics

I wrote earlier about cabling and connector schedules. It is essential to properly document the electrics and the schedules are an important part of the package. For those, Excel provides an entirely suitable environment.

But the schedules only describe the individual wires and connectors, not the way they all connect up to make a working Sportcruiser. Or at least not in a way that can be readily comprehended. That's where circuit diagrams (schematics to our American friends) come in. At the moment, these are hand drawn but they really need to be transferred to a computer-based drawings package.

Although there are specialist computer applications for circuits, a more flexible approach is to use Visio, which is a graphics design package offered, these days, by Microsoft. Associated with Visio is a breathtaking array of predefined shapes and one can purchase stencils for specialist applications such as electronics. So that's what I did.

My SC will have something like 15 to 20 pages of circuit diagrams. Each one needs carefully laying out and must be drawn with certain standards in mind. For example, the connectors must cross reference into the connector schedule and each individual wire needs to be identified so it can be found in the cable schedule. Getting this lot set up has taken some time!

So far, I've only produced a couple of circuit sheets, which show the way the control sticks, elevator and aileron trims and so on work. Getting the rest of the circuits into Visio will take a while and I'll plod away at them on days when, for whatever reason, I can't make progress on the physical building work.

As I've said before, it's just as well I am an electronics engineer. I think I would have struggled with all this lot otherwise!

Tuesday, 7 July 2009

Finishing the starboard wing

Yesterday, Chris and I completed the riveting on the starboard wing. Although it seems like a big job, in the end it didn't take too long at all to insert the 250 or so rivets needed to fully finish the job. Not for the first time we were glad that we'd gone for a pneumatic riveter - trying to do that lot with a hand riveter would be nearly impossible!

Closing the wing was, however, a big step. Firstly, it marks the completion on a significant phase in overall construction. It was also the point at which we finally relinquished unfettered access, perhaps for ever to the wing internals.

That's not so important in the starboard wing, as it has relatively few services but the port wing, with its pitot/static pressure system, stall warner and vapour return piping is a somewhat more complex beast. So whilst it will soon be time to rivet up the port wing as well, there will necessarily be rather a lot of careful checks to be made before wielding the rivet gun. The picture on the right shows the final rivet being installed in the starboard wing.

We also decided to fit the canopy, albeit only on a temporary basis. The open canopy needs more height than is readily available in the workshop, with the result that the fuselage has to be moved slightly whenever we want to open it. It was nice, though, to see the canopy fitted and to recall the sleek lines of the completed fuselage - something that we haven't seen for three months.

Fitting the gas struts to the canopy required a certain amount of drilling out and cleaning of threads. The manufacturing process resulted in quite a lot of composite material bunging up the mounting holes and all this surplus material had to be carefully removed.

Finally, to get a better impression of what the completed aircraft will look like as much as anything else, we fitted the engine cowling. This also enabled me to check clearances for various engine components now that the engine installation is essentially completed.

As expected, the water radiator is very close to the lower cowling. This seems to be a general problem with Sportcruisers and there's probably not a lot that can be done as there are very limited options for moving the radiator due to other components in the vicinity. If it turns out to be a problem then I'll have to place some rubber rubbing strips in appropriate places, or perhaps even consider putting a small bulge in the cowling at the appropriate places. Let's hope that turns out to be unnecessary.

In the evening, the local Air Cadets, where I am a Civilian Instructor, came to look at the project. Lots of interesting questions and I think most were somewhat surprised that one could build one's own aircraft. It was certainly interesting and educational for them to see how an aircraft is put together and fits in well with the theory that I try to teach them on parade nights! One of the older ones has even asked if he can help with the project. Of course, said I!

Monday, 6 July 2009

Fuel tank selector

With the engine fuel system completed, my attention turned to the small matter of getting fuel from the wing tanks into the engine. The Sportcruiser has a 57 litre fuel tank in each wing. A fuel selector switch, located in the central console area lets the pilot select which tank is supplying fuel to the engine. All this, together with the vapour return line, means that there is a fair bit of fuel piping to be installed in and around the cockpit.

The area around the central console is rather crowded! in addition to fuel lines, there are rudder and elevator controls, many electrical connections and brake pipes all vying for the rather limited space available! So finding the best routing for the fuel pipes has proved to be a bit of a challenge. A key consideration is that nothing gets close to the moving parts that make up the elevator and rudder controls. Quite apart from the risk of compromising control effectiveness, there is also the very small but nonetheless important risk of rupturing a fuel line. We definitely don't want to go there!

In the end it turned out to be a fiddly job but not too difficult. The fuel system is now completed and another significant phase of the project is ready for sign off.

Total project time is now 172h 50m.

Sunday, 5 July 2009

Engine fuel system

Yesterday was another busy day, with significant progress on several fronts. Having completed the engine instrumentation the day before, all the necessary sensors were now installed, so it was at last possible to connect up the various parts of the fuel distribution system.

The fuel system on an aircraft can seem rather complex. Firstly there are two fuel tanks, then there are both mechanical and electric fuel pumps (for resilience mainly) and the Rotax engine has two separate carburettors, one on each side of the engine. Another pipe goes to the fuel pressure sensor mounted on the firewall Finally, there is a low volume fuel return to the port fuel tank, designed to minimise the possibility of vapour locks.

Within the engine bay (known as Firewall Forward) all fuel pipes have to be protected against extremes of heat and, potentially, fire. Each fuel pipe is therefore shrouded in firehose, which is quite chunky and bright red in colour, making the fuel lines really stand out.

I decided to fit a fuel flow transducer and that is located between the mechanical pump and the carburettor distribution section. The flow transducer will enable the Engine Management System, in conjunction with positional data from the GPS, to compute endurance, fuel reserve, fuel economy and so on. The fuel flow transducer is shown on the right.

Other work completed includes installing all the mounting nut plates for the inspection covers on each wing. These nut plates rivet onto the aluminium skin and provide a tapped nut for the inspection cover screws. I also attached the starboard wingtip to the wing. With this work completed, I can now rivet up the wings and complete another major phase in the build programme.

Inside the cockpit I started tidying up the vast collection of wires by tie-wrapping them to appropriate cross members. Most of this work will have to wait until the instrument panels are completed but it was worthwhile jut to reduce the general clutter in the cockpit.

All in all another long and productive day. Total project time is now 168h 20m.

Friday, 3 July 2009

Paint schemes

I'm starting to think about getting my Sportcruiser painted. The plan is to complete as much of the build at the workshop as I can, up to the point at which the flying surfaces are ready to be fitted. At that stage, I'll have the aircraft painted and when that's completed it will go to Kirkbride airfield to have its wings attached, etc. leading up to flight testing.

One of the problems with living here in Cumbria is that aircraft paint shops are few and far away. I've started making a few enquiries and it seems that I'll have to head down to the midlands to find something suitable, which is a nuisance but, apparently, unavoidable. As the engine is now fitted, I no longer have the option of using a 7.5 ton box truck - it's now too long to fit! So I have to arrange transport. Fortunately, suitable local transport does exist, so that is unlikely to be a problem other than the inevitable cost.

So what sort of colour scheme shall I go for?

The Sportcruiser seems to look best with curves rather than straight lines. This is probably mostly because of the huge sweeping canopy, together with the fact that the tail plane is significantly higher than the wings. Quite apart from aesthetics, it is necessary to consider visibility issues - after all, this is a day VFR aircraft, so it's a good idea if it can be seem against the blue (or more usually in the UK grey) sky. Furthermore consideration has to be given to heating effects and this tends to preclude the use of dark colours on the upper surfaces.

So my thinking at the moment is that I'll go for a simple two tone scheme, with a darkish colour underneath and white on top. Something like the picture, perhaps.

But first I have to select the paint shop. That'll involve a visit and I hope to fly down to one potential supplier in the next week or two.

Engine management

My Dynon D120 Engine Management System (EMS) arrived a couple of days ago so I've been busy getting to understand how it works and, today, installing it in my Sportcruiser. It really is a nice piece of kit but it is also quite complicated and, apart from roughly setting it up so I can test the various sensors, I've not yet got into any sort of optimisation yet.

So the last couple of days have been occupied with getting the EMS installed. Firstly, I had to make up a bracket to mount the fuel pressure sensor on the firewall. A neat job can be achieved with some 1.2mm thick aluminium sheet and a piece of heat-shrink tubing. I also mounted the ammeter shunt on the firewall, immediately above the main fuse box, which makes for a tidy implementation with nice short wires, which is important given that some fairly high currents are involved.

Each sensor has its own set of wires and, of course, there are plenty of other connections to be made. This has forced me to put some considerable effort into the instrument panel area. Where hitherto there were lots of connectors that didn't actually connect to anything, now quite a lot of the interfaces have been completed, albeit I still haven't "dressed" the cables, so it still looks like a huge bunch of spaghetti.

The first task was to get a properly wired source of 12V and to implement the master power switch, albeit in temporary incarnation until I can start wiring the panel itself. The master switch energises the master solenoid, which in turn provides power to the aircraft electrical systems. I was then able to provide power to the EMS and start connecting up the various sensors.

The first sensor was the Outside Air Temperature (OAT). OAT is important for aviators because of potential icing and to provide early warning of significant changes in the weather. The OAT probe is mounted on the underside of the fuselage, next to the transponder antenna. I connected it up to the EMS and sure enough, the ambient temperature was displayed on the EMS. A good start!

I continued with the installation, progressively wiring up and then testing each of the various engine sensors:
  • Ammeter, showing battery charge/discharge
  • Oil temperature
  • Oil pressure
  • Fuel levels in both wing tanks
  • Fuel pressure
  • Fuel flow, enabling economy/endurance calculations
  • Tachometer
  • Cylinder head temperature in two cylinders
  • Exhaust gas temperature in two cylinders
That's a lot of sensors! I'm pleased to be able to report that all sensors function correctly, to the extent that I am able to test them without running the engine and without fuel in the tanks in the wings that are still not attached.

In addition, I've wired connectors for various other aircraft systems that interface with the EMS:
  • The GPS, which provides positional information for range and fuel consumption calculations
  • The stall warner
  • RS232 interface for firmware updates and for configuration management
  • External tachometer
Apart from a few tidying up actions, I have now completed the installation of the D120 EMS. This completes a major item of work and it moves me considerably closer to finishing the engine installation. It also means that more or less all of the aircraft's electrical engineering is now completed.

Total project time is now 161h 50m