Monday, 30 November 2009

November in review

Not a very productive month really.

A combination of truly awful weather and other commitments has meant that I've made far less progress than I had hoped for in November. There is no doubt that the 74 mile round trip to the airfield is a limiting factor, especially when the weather is bad but there really is no alternative - it's the nearest airfield with a long enough runway for meaningful flight trials and with suitable hangar space. Although the hangar has power and lighting, it's also true that the short days are limiting progress, as much as anything else because of the desire to avoid lots of travelling in the dark.

Not all is gloom and doom however. The hydraulics were completed and quite a bit of progress was made on the instrument panels. The seats were installed, various avionics problems were resolved and I was finally able to sort out the sticking rudder pedals problem.

Looking forward, I think the challenge is to complete the instrumentation during December. Then in the new year we'll be able to fit the wings and get the engine running. Could still be flying by Easter!

Tuesday, 24 November 2009

Emergency power

A Blog reader recently observed that the power circuitry to the flight instruments represented a single point of failure that would result in the loss of both roll indicators. When I came to think about it, the same argument applied to the radio communications system, which is arguably also an essential service.

Today, with the weather being, yet again, diabolical, I decided to stay at home and think about how best to provide some resilience. The problem is that there are several links along the way from battery to instrument/radio. Failure of any one of these links would result in the failure of that subsystem. Ouch!

In the end, I've decided to install a simple two pole emergency power switch, which takes power directly from the battery, via a fuse of course - I must still provide some protection. The switch applies this power to the flight instruments via one pole and to COM 1 via the other, bypassing the master solenoid, panel switches, relays, contact breakers and associated wiring. In this emergency circuit, there are virtually no points of failure.

Of course, by implementing this new circuitry, I am providing another route from the battery to some of the aircraft's systems and the master switch no longer acts as a total isolator. If the emergency power switch were to be left on with the engine stopped then the battery would eventually go flat. There's no easy way to fix this problem, other than to arrange the power take-off from the load side of the solenoid and accept the risk of the master solenoid failing.

I think I've decided to go straight to the battery in order to provide the most secure supply possible. I'll just have to overcome the flat battery risk by including a step in the shut down procedure to ensure that the emergency power switch hasn't been left on. I might also make it so the emergency switch powers the strobes or the landing light - that would make it more difficult to inadvertently walk away from the aircraft without noticing that something is amiss.

I need to decide where to physically locate this emergency power switch. Obviously not on the instrument panels - they are already cut and silk screened and there really isn't space, nor is it a good idea, in my opinion. Most likely I'll put it on the P1 side panel of the centre console. That way it is easily accessible in flight but is out of the way and unlikely to be inadvertently toggled. Next time I can get to Kirkbride it's something else to check out.

Instrument panel trestles

I had a go at making a trestle to support the P1 panel in the correct position without having to attach the coaming. The trestle sits on the fuselage floor and can be moved forward and aft slightly, to allow for easier access to the rear of the instrument panels.

I'm more of a metal basher than a woodworker, so the end result, whilst functional isn't especially well engineered. I can live with that, as the trestles will only be needed while I complete the panel wiring. Having proved the methodology on the P1 side, I now need another trip to B&Q - due to a miscalculation of the amount of wood required - then I'll be able to make the P2 trestle. There is no need for a trestle to support the avionics panel, as the centre console provides all the support that is needed.

I'm a little surprised that none of the other Sportcruiser builders seem to have come up with this solution. Maybe there is some dastardly defect in the idea that I will discover in a day or two? Or perhaps it's just that my panels are more complex than most and so the need for the trestles is self inflicted!

It's rotten weather again up here in Cumbria so I'm rather disinclined to make the pilgrimage to Kirkbride today. I'm away for a few days later this week, so I suspect it'll be next week before I can make further progress.

Saturday, 21 November 2009

Wiring up the instrument panels

With the awful weather and floods everywhere, I've not really been enthused to attempt the 74 mile round trip to Kirkbride, so I've spent a couple of days at home, wiring up the instrument panels.

The majority of the wiring is just power cables. With switches on the P1 panel and circuit breakers for each subsystem on the P2 panel there is quite a lot of to-ing and fro-ing of wires. As I am keen to be able to separately remove each panel, this has given rise to rather more connectors than I am entirely happy with. Hopefully there won't be any reliability problems!

I've also installed the static pressure air pipes. Static pressure is used by four instruments:
  • Altimeter
  • Vertical speed Indicator
  • Mode-C altitude encoder
  • Air speed indicator (this instrument also uses pitot pressure)
We're only dealing with what is, effectively, normal air pressure, although it is usual for the cabin to be slightly higher in pressure than the outside air (due to ram air effects), so a separate static pressure source is taken from outside.

Soon I'll be at the stage where I need to marry up the panel wiring and the multitude of wires that converge on the instrument panels from all corners of the fuselage and from the engine compartment.

This produces something of a problem, as there is nothing to physically support the panels until the instrument coaming is installed but I can't really install the coaming until I have finished the bulk of the interconnection work. So I'm planning to build a pair of trestles out of wood, which will sit in the foot-well on each side of the centre console and provide a solid table to lay the panels on. This should also make it a lot easier to complete the installation, when the time comes to screw the panels to the coaming.

I feel a trip to B&Q coming on tomorrow!

Monday, 16 November 2009

Instrumentation again

With the hydraulics out of the way, it is time at last to focus on the instrumentation.

First I mounted the fuel selector valve to the centre console panel and then fixed the panel roughly in place. I could then add the flap control switch and position indicator. It was good to connect that up to some power and see that the flap server and indicator system still works OK. I even managed to get the wiring the right way round first time, so that flaps up was with the switch up and showed up on the indicator. The wonders of a comprehensive documentation system!

Next I installed the home-brew audio panel above the flap controls. The audio panel lets the pilot select which radio(s) he is listening to and which one is used for transmission. There are commercial units available but they all have far too many functions for my little Sportcruiser and, more to the point, are too big to fit in the available space. It is not usual to need to fit an audio panel in such a small aircraft!

Finally I mounted the intercom at the top of the centre panel and connected it up to the headsets, power and PTT lines from the control sticks. It all worked! I am particularly pleased with the way the centre console panel has worked out. It was a bit of a challenge to work out the best layout but I think the result looks very neat and professional.

Next I turned my attention to the P1 instrument panel. I mounted all the instruments and switches and was delighted with the appearance of the completed panel. In particular, I am pleased that I went for small rocker switches, which I think are far more in keeping with the modern look of the aircraft than the old fashioned toggle switches that are more usually fitted. I also fitted the avionics into the centre panel and did a little work on the P2 panel (not pictured) as well. No time today to wire everything up - that's a job to do at home over the next week or two.

Finishing the hydraulics

Yesterday I was able to spend a full day at the airfield working on JONL. Firstly Mike and I filled the port brake system - a job that took less than 15 minutes, which just goes to show how much more quickly you can do a job when you know how!

I fixed the problem with the leaking bleed nipple by temporarily wrapping some plumber's thread seal tape around the thread and tightening the nipple up to the seal tape. This provided a fluid tight seal, whilst leaving the bleed nipple wide open to force fluid up into the system. As a result the job was both quicker and much less messy. And there was almost no wasted fluid, which at 14 quid a litre is no bad thing! Mike's impressive brass syringe, pictured, made short work of the job once we worked out how to do it.

With the brakes now completed, I clambered into the cockpit and checked that each wheel does indeed brake and that under hard braking there were no visible leaks. I also checked the correct operation of the parking brake valve. All seems fine, though, of course, I'll have to wait until the taxiing trails before I can really test the brakes out properly.

As we were filling the system, Tom, my LAA inspector came along to check out my work on the rudder control system and to provide some helpful hints and tips. The result is that with the brakes now finished and the rudder system "signed off" the foot well area is more or less finished and I can get on with the instrumentation, which is the last big job before we put the wings on.

All in all a successful first part to the day. Some more stuff happened as well!

Friday, 13 November 2009

Instrument panels

Hurrah! The instrument panels have returned from painting and silk screening and are, at last, good enough to install in G-JONL.

I've already made a start on the P1 panel, fitting the six-pack of flight instruments and the various power switches. Quite a lot of the materials I need are up at the airport and I won't get there until Sunday, so there's a limit to what I can achieve right now.

There is no doubt that the silk screening makes a really good professional job and I'm really looking forward to seeing the instrument panels in place very soon now! Quite a lot of work to do to get to that stage and the small matter of the Ballistic Recovery System, which needs to be fitted before the instrument panels can be finished but which isn't yet approved in the UK. I'm working on that...!

Thursday, 12 November 2009

Other things

In between doing heroic battle with brakes and hydraulic fluid, I fixed a couple of other things during the past couple of visits.

Firstly, I've completed the fixing of the seat backs. In the end, the simplest solution was the best, using a pair of hooks per seat back fashioned out of 1.5mm aluminium sheet, which hook onto sections of aluminium angle mounted to the airframe. These hold the seats in the correct position, preventing them from slipping down and locating them laterally. With no-one sitting in the seat, the back can be pulled forward and then removed entirely, making for very easy access to the area behind the seats. Once someone is sitting and strapped into the seat no movement of the seat back is possible.

As far as I can see this is an entirely satisfactory system but I will discuss it with the LAA inspector when he visits on Sunday just to be sure.

I also fixed the problem with the Com 2 antenna. Once the SWR meter was in the circuit it soon became apparent that the antenna wasn't working at all and investigation soon revealed that the BNC plug at the radio end of the antenna lead wasn't properly attached, with the result that the inner conductor pin was too far back to make reliable contact. I remade the connection and obtained an SWR reading of 1.4:1, which is certainly very satisfactory.

As far as I can see, the avionics are now fully functional and awaiting the arrival of the instrument panels so I can complete the job. This evening I got the good news that the panels are finished and in the post to me, so with a bit of luck I will have them some time tomorrow. Other jobs mean that the next time I will be able to get to the airport will be this coming Sunday but I can make a start on the instrument panels at home.

Hydraulics (2)

After a couple of rather frustrating and very messy days at the airfield, I'm glad to be able to report that I've filled the starboard braking system with hydraulic fluid and confirmed that the brakes work well. But earlier today I wasn't so sure that things were going to end up so successfully!

Yesterday I rigged up piping to let me inject hydraulic fluid into the brake pipes. Try as I might, I couldn't get any fluid at all into the brake calliper using the squirty oil can I'd procured for the task. Hydraulic fluid everywhere, except where I wanted it! Mike, our local LAA strut guy offered to bring in a large, powerful syringe this morning and I decided to get on with other things in the meantime.

Today, heavy duty brass syringe in hand, I was disappointed to find that I could still get hydraulic fluid everywhere apart from into the braking system. Eventually I removed the disc brake callipers and discovered that the pistons on both sides were fully retracted and, apparently, seized, as shown in the picture. In that position, no hydraulic fluid could get into the calliper via the bleed nipple to ease the piston out. Much head scratching later, I discovered that a sharp tap on the piston unseized it enough to force fluid into the slave cylinder via the normal hydraulic pipe. Just as well - there is no way to prise the piston out and for a while I was convinced that I was going to have to replace the units at considerable cost.

Once the pistons moved out from their fully retracted position, it was possible to get hydraulic fluid to pass through the calliper and on up into the rest of the system. Unfortunately, another problem quickly made itself apparent, as the parking brake valve, pictured right, started leaking fluid, even before any significant pressure was applied.

An hour or two later, having removed the parking brake valve I could see that the problem was a badly seated olive on the pipe out to the starboard brake pedals. With that fixed I was able to fill the entire starboard brake system, in the process spilling rather a lot of fluid. The problem is that the bleeder nipple isn't really designed to have fluid forced into it and when you try to do that quite a lot of fluid seeps around the screw thread that is necessarily loose. I can't really see a solution to that problem other than to have a tray underneath that catches the escaping fluid!

Eventually the job was done and after tidying up I carefully checked for leaks (none found) and then experimented with both the P1 and P2 brakes. Both were firm, with no sponginess and I was able to demonstrate that the wheel was indeed being braked. I also confirmed that the parking brake functions as expected.

So, a very messy but, in the end successful day. On my next visit I will fill the port side brake system and hope that the experience gained today makes for a somewhat swifter and less messy conclusion!

Tuesday, 10 November 2009

Hydraulics (1)

As it turned out I didn't get to Kirkbride today. Instead I spent half a day at Carlisle Airport, where I contract as the Senior Air Traffic Engineer, sorting out a few problems and attending to a pile of administrative stuff. Mustn't complain - it helps to pay for expensive hobbies like flying!

Just as I got home the doorbell rang and there was a courier with a delivery from Airworld. Amongst other things the delivery included a litre of Aeroshell 41 hydraulic fluid (far far more than I shall ever need I hope). So I now have all the materials I need to complete the braking system and there is no further excuse for not completing the job. The plan is to go to Kirkbride tomorrow mid morning and make a start.

I also received a tube of Copaslip, which is recommended for the exhaust system joints to prevent them seizing up and then causing fatigue cracks in the muffler. I think I'll leave that until I'm ready to start on the engine again in a few weeks' time.

I've arranged for my LAA inspector to visit the airfield this coming Sunday to check through the work to date. In particular I want him to check out the rudder and braking system, with a view to signing those items off before I start building up the instrument panels, making the rudder pedal area rather less accessible.

Speaking of which, I must remember to chase up the instrument panels again tomorrow...

Monday, 9 November 2009

Of radios and things

I'm still waiting for my instrument panels to come back from painting and silk screening - it's a long and frustrating story that I won't bore you with, suffice to say that I should have them back later this week.

On a more positive note, the Aircraft Radio Licence for G-JONL arrived today so I am now able to test the transmitters properly, on air and into the antennas. Unable to progress the general instrumentation, I therefore decided to check out the radio systems.

G-JONL has two communications radios (Com 1 and Com 2) plus a navigation radio (Nav 1) used for tracking en-route nav aids and for instrument landing approaches. One way and another there's quite a lot of cabling and many interconnections. Most of these had been tested in isolation but today was the first time that I connected everything together and performed an end-to-end test. The picture shows the avionics stack propped up on a box for the tests.

The result was a qualified success. Com 1 works just fine on both transmit and receive, from both the P1 and P2 seats and Nav 1 picks up the Dean Cross VOR and provides a sensible bearing, even with the aircraft in the hangar. Unfortunately, Com 2 is seriously deaf and as yet I can't really determine why. The antenna appears to be OK when I check it with an antenna analyser but both transmit and receive are significantly worse than the Com 1 performance.

I'll take an SWR meter up to the airport tomorrow and see if that sheds any light on the matter. Certainly the symptoms seem to indicate an antenna problem, even though the analyser gives it a clean bill of health. Lobbing a few watts at it and checking the SWR seems to be the next logical check to do.

I did a few other things today. Firstly, I aligned the rudder by adjusting the turnbuckles so that the rudder pedals are in line when the rudder is in its neutral position. I also made a start on fixing the seat backs - I've decided to try using Velcro and that has necessitated attaching aluminium strips to the back of the seats for the Velcro stick on to. I did the P2 seat today and it seems to be fine, so I'll have a go at the P1 seat tomorrow.

Friday, 6 November 2009

Braking system

The Sportcruiser has hydraulic brakes and, in common with most aeroplanes, has differential braking (separate right and left wheel brake pedals) to permit directional control, turning, etc. Furthermore, both seating positions have brake pedals, so it is possible to control the aircraft from either position.

All this means that the braking system is somewhat complex! There are hydraulic pipes running back and forth between the pedals, a brake lock mechanism for parking and, of course, pipes to the brake disc callipers on each wheel.

Yesterday, I spent a few hours checking all this lot out, prior to filling the system with hydraulic fluid, hopefully some time next week. I had to replace a length of pipe, from the brake lock to the right (starboard) wheel, as it was inadvertently damaged during transport to the paint shop. I also connected the hydraulic pipes up to the brake callipers and secured the pipe to the landing gear legs using ty-wraps.

In the picture you can also see the temperature monitoring labels, which are required by the LAA because the main landing gear is painted a dark colour. Apparently they are concerned that the gear may get too hot in bright sunlight but as I am not in the habit of landing upside down, I would have thought that the wings would provide the requisite shade!

As far as I can see, the brake system is now ready for filling. I have to get some special brake fluid, AeroShell 41, which complies with the necessary MIL-PRF-5606H specification. That's on order today.

Monday, 2 November 2009

Sticky rudder pedals

Yesterday Mike and I had a go at a problem that's been bugging me for a while. The rudder pedals are mounted in nylon bushes that are meant to hold the pedal system firmly in place yet permit free movement. Well they didn't. Although the pedals moved OK, they were quite stiff, so the springs that are supposed to centralise the pedals in the absence of any input were ineffective.

Well we fixed that yesterday. Taking the nylon bushes out it became apparent that they are in fact not round but are, instead, slightly oval. This means that it's not possible to fully tighten the bushes and that was my first mistake. The bushes were also rather dry and looked like they needed some lubrication - my second mistake.

So Mike and I put some silicone grease into each bush and very gently tightened up the bush halves until we could just detect the pedals stiffening up. About a half a turn back from that position for each of the nine bolts seems to be the sweet spot and the pedals are now much more free-moving. We attached the turn-buckles to the rudder control cables and checked the whole system out. Altogether much better!

There is obviously a natural tendency to over tighten these bolts that must be resisted.