Sunday, 16 May 2010

A New Instrument Panel

I had always planned to replace IH's instrument panel and with in mind had managed to purchase one through the Taylorcraft Foundation a couple of years before the start of the restoration. The new panel came complete with holes cut for the control yokes but all the instrument and mounting holes would need drilling.

The instrument centre positions were marked out on the new panel and 1/8th inch pilot holes drilled. The pilot holes were opened out to 16mm with a sheet metal step drill so that the main instrument holes could be cut out with a special hole cutter.

The cutter clamps either side of the metal sheet and as the nut/bolt are tightened up, the hole is bitten out of the metal. This leaves a perfectly sized, clean hole fo the instrument. The cutter is reversable for both 3.1/4" and 2.1/2" holes which covers the ASI, Tacho, Altimeter and mag switch but not the Oil Pressure and Temp gauges.

With the holes cut, the mounting holes are drilled using a drilling template.

The altimeter needs a cutout for the subscale setting knob. For this I made a template from an offcut of aluminium sheet, nibbling and filing the aluminium away until I got a good fit with the instrument. Once this was achieved, the template was used to mark out the area to cut away on the panel itself. The final result is shown above.
The two holes for the Oil Pressure and Temp gauges had to be cut using a fly cutter. This is a little more tricky because getting the right size hole is more fidley, or it is with the fly cutter I have, so plenty of trials were done on pieces of scrap before committing the the panel itself.

Monting holes were then cut with the panel in place in the cockpit. I still have holes to cut for the radio stack and Mic and Phone sockets but these will be left until I have finalised the radio equipment that will be carried.

Sunday, 28 March 2010

A new Battery Box

Mid February and the fuselage frame had one coat of epoxy primer applied. I would have liked to get to the stage of painting the acrylic top coat but have decided to wait until the warmer summer months as it will be easier to apply with the warmer, dryer weather. In the mean time I managed to give the frame a second epoxy coat, spray up some of the tail surfaces and start to fit out the cockpit area. This will be a first fit process allowing me to construct a new interior, fit it and make sure everything works before I finally top coat the fuselage. The sort of items that new working on are the new instrument panel, seats, baggage sling, parcel shelf, harnesses, stringers, trim system etc ... the list is endless.

To begin, I fitted the new floorboards and bulkhead forward of the seat. This is where the new battery box will be sited (previously it was under the seat sling which was difficult to access when changing batteries). I spent some time pondering various designs of battery box, most of which were prototyped in card prior to settling on the final design.

One of the earlier box designs; looks OK but how do you lift the batteries out?

The final criteria for the battery box was:
  • Should be lightweight.
  • Should be simple to construct.
  • Should protect the batteries and wiring from accidental damage from pilot & passenger.
  • Should take up minimal space in the cockpit.
  • Batteries should be easily replaced.
  • Machine screws/anchor nuts should be used to secure the battery box.

The final design consists of a simple tray made from aluminium angle which will be secured to the floorboards with machine screws. The underside of the floorboards will have an aluminium plate, with anchor nuts riveted on, bonded to the floor. The two batteries will sit in the tray and be enclosed by an aluminium cover fixed to the floor and bulkhead in a similar fashion to the tray.

The tray and cover sit over the centre join of the floorboards and will help secure them as there is no fuselage framework at this point to support the floor.

The tray will take two 12V, 7Ah batteries. The corners were simply cut at 45 degrees with a band saw.

The cover was marked out on a single sheet of 0.032 NS4 aluminium (equivalent to 5251 H22) using a fine permanent marker (not pencil), remembering to add between 1/16" and 1/8" for the bends. All fixing holes were pre-drilled prior to bending. The sheet was guillotined and the main bends made on a sheet metal folder. Some of the bends had to be done by hand later.

Two photo's showing the cover in place prior to final riveting

Inside the cover, two pieces of angle have been riveted in place. These clamp the batteries down preventing the positive/negative terminals from touching the case itself.

Wiring will pass through the bulkhead and be routed to the instrument panel along the port cockpit side. I have not made up the fixing plates yet but they should be ready to fix in place within the next week. After that the cover and tray will be painted.

The next task will be the construction of the parcel shelf. This should be fairly straightforward, I hope.

Tuesday, 16 February 2010

Priming the fuselage

As soon as the fuselage is clean corrosion will begin so it is vital that the bare fuselage is painted as soon as possible to protect it from the atmosphere. I completed the cleaning one morning which left the rest of the day, about 7 hours, to prep for, and apply, one coat of primer on the fuselage. In total, the airframe will get three coats of paint:
  1. An acid etch primer (green)
  2. A 2 pack epoxy primer (white)
  3. A top coat of white two-pack

I'm using an HVLP (High Volume Low Pressure) spraying system to apply the paints which I'm told is easier for the beginner to get good results with. The system is self contained using a turbine unit to provide air for both the spay gun and a half face mask, essential when working with harmful paints. Details of the equipment can be found at although I did upgrade the gun to a gravity feed type at the time of purchase.

Prior to spraying the fuselage was mounted onto a rotating jig (courtesy of Rob Lees again) which makes the painting process much easier.

I started by spraying all the inside tubes first and gradually working outwards to reduce the chance that I would smudge areas that had already been painted but because of the complexity of a fuselage I did manage to paint myself into a corner on a couple of occasions. I ended up alternating from front to back to allow painted areas to go off before returning to those tricky areas that had been previously missed.

Several tips here - get used to your gun, how to change things like the amount of paint sprayed i.e. how wet it goes on as this does vary with the type of paint your using. Practice spraying left and right handed as you're sure to need to change hands at some point. Don't let your gun run dry before recharging with more paint as the paint may dry in the gun nozzle causing problems with delivery. Always clean your gun after use.

By the end of the day I had a green fuselage and in an ideal world I would apply the next coat (white epoxy) immediately but alas I had run out of time.

The following weekend was spent checking that everything had been sprayed, all those tabs, 'u' shaped channels, weld clusters etc and where necessary those areas were cleaned ready for retouching. Now because the epoxy hadn't gone on straight away I had two choices for the next stage.
  1. lightly scuff the surface to provide a key for the epoxy.
  2. spray a light flash coat of etch prime on then apply the epoxy.

I decided on the latter which would ensure a good key over the whole frame and anyway a second light coat wouldn't add much weight at the end of the day. Two hours later I was ready to apply the epoxy using the same techniques as for the etch prime. If I had any black epoxy, it would have been worth mixing a little in so that when it came to spraying the white top coat, I would be spraying onto an off-white colour making it easier to see what I was doing - problem was I didn't have any.

The epoxy took about 5 hours to apply with a lot of time spent again on all the tricky corners, tabs, clusters etc. The two photo's show the internal tubes painted white and the final complete airframe which I'm quite happy with. The top coat could just be applied to the cockpit area which will be visible after the fuselage is complete but I may decide to cover the whole frame with top coat as it will give added protection for very little increase in weight.

In the mean time I have a lot of other bits that are ready for grit blasting and painting up....

Thursday, 28 January 2010

Cleaning the fuselage

Christmas came and went, all the necessary welding work had been completed on the fuselage and so it was time to strip the fuselage frame of all it's paint. I had thought long and hard about how this should be done and had settled on grit blasting rather than paint stripping mainly because paint strippers are messy and toxic (in most cases). I had also decided to do the grit blasting myself rather than transport the fuselage to a professional because (a) I didn't have a means of transport and (b) because of the costs.

There were a number of prerequisites to the stripping process.
  1. Create a booth that would take the whole fuselage and keep the rest of the workshop free of dust. This would also serve as the paint spray booth later on.

  2. Make sure I had the appropriate blasting equipment including safety wear and consumables.

  3. Get some paint stripper just in case.

  4. Arrange for the AD inspection on the strut attachments at an early stage when the weld clusters had been cleaned up.

The booth was made from white tarpaulin sheet hung from the roof beams with the lights inside the booth. The dimensions were about 20 x 10 feet giving enough room to work around the fuselage. I also have a small extractor fan used to keep the dust down.

I bought a cheep hopper ( which holds a 25 Kg bag of grit/bead and utilises my compressor running at about 115 psi. In practice, this would last for about 30-40 minutes before having to be topped up. I also purchased a hood with spare lenses, gauntlets and disposable overalls to wear during the blasting.

I anticipated the blasting would take three days to complete followed by a day to paint the fuselage but as ever it took longer for several reasons. After three days I had completed the initial blasting but there was a lot of paint that just wouldn't come off mainly around the cockpit area.

There was a mixture of paints, what looked like powder coating and some rubberised coating which I decided might come off better if I applied paint stripper. Another day was spent applying the stripper. The paint stripper used was SV-35/PMA formulated specifically for aviation paints ( and non-toxic. I left the stripper overnight to be cleaned off the next day. The results looked pretty good. I can recomend this product as it's easy to work with, strips the paint quickly (I was working in neart freezing conditions over winter so it should work very quickly in the summer months) and is easy to dispose of afterwards.

The approved method for removing the crud is by pressure washing with water which I don't have the equipment to do so instead it was brushed off with water, a messy and time consuming job. I then had to bead blast the whole fuselage again to clean up the remaining paint.

There were still odd spots of paint which hadn't been removed so another day was spent getting these off by using a craft knife blade followed by further bead blasting.

The finished product was cleaned with an air hose and tack cloths prior to painting.

In all the process took about 10 days spread over 4 weeks, but I did loose a week because the weather over here was so bad I couldn't get to the workshop. In hindsight I should have spent more time paint stripping and left the bead blasting just for the final finish but that's what this blog is about, helping you save time through my experiences. I think a realistic timetable for the job would have been 2 days to paint strip, 1 day to clean and 3 days to blast, still a lot of work but very satisfying once completed.

Next time, priming the fuselage.

Tuesday, 26 January 2010

Welding Work

During December I begun the preparation of the fuselage for it's eventual bead blasting and painting. There was no repair work necessary as the aircraft has never been crashed and there is no evidence of major corrosion but there are a number of other jobs that need to be completed.

The job list included:
  1. Adding structural harness attachment points.

  2. Welding on additional tabs to support the baggage sling, 'D' windows, hat shelf, floor boards and skylight.
  3. Welding up and re drill the rear horizontal stabiliser mounting holes (to be re drilled).
  4. Have my inspector sign of AD.2008-09-18 (Wing strut attachment bracket).

The plan was that if these jobs could be completed by Christmas, then I would grit blast and paint the fuselage in the period between Christmas and the New Year. Of course things don't always go as planned, but more of that later.

The first problem encountered was that the harness brackets that had been made ( were flawed, the bolt couldn't be fitted because the fabric would interfere, so I had to make new ones to fit (see below). They were manufactured in the same way with the same spec material but now weld at an angle to give better clearance.

My friend David made four post supports from 4130 rod with an internal M6 thread. These were welded to the fuselage to provide additional support for the skylight.

The additional tabs were all welded on over a couple of evenings and I begun to plan the cleaning and painting of the fuselage frame.

The AD inspection was scheduled to be done once the fuselage had been bead blasted as this was purely a one off inspection for corrosion or cracks around the strut attachment fittings and it would mean I wouldn't have to remove paint at a later date.

I'll discuss stripping and repainting the fuselage in the next posting soon.

Sunday, 8 November 2009

Harness Brackets

When I bought IH back in 1998, the aircraft was fitted with a 4-point harness where the shoulder straps were attached to the cross tube that supports the top a the seat sling. This was totally unacceptable as in a crash this can lead to compression of the spine and severe back injuries. Later I moved the attachment position to one of the top cross members further back in the fuselage using a U-bracket around the cross tube. This was better but not perfect, so now I'm taking the oppotunity to weld some permanent brackets into the airframe.

Two brackets were cut from .090" 4130 steel plate and drilled to take an AN4 bolt. After welding, the holes will be reamed out to size.

Port and Starboard fittings

Saturday, 7 November 2009

Refurbishing the Fuel Tanks

IH has three fuel tanks, one in each wing plus the header tank in the nose, and these need some refurbishment and pressure testing before they are refitted. For now I only need to have the nose tank sorted but I'll work on all the tanks as they will all need the same treatment.

Firstly, I bought new fittings for each tank to enable me to fit all new AN fittings throughout the aircraft. The tanks still have their original heavy fittings and also showed some signs of mistreatment around the filler where the pipe has been used unsupported when fueling. So the plan is to weld in new fittings and filler necks and reinforce the area around the filler necks.

The tanks were sent away to a local CAA welding company; the tanks were labelled with the fitting part numbers next to the appropriate existing fittings. The results of the welding are shown below.

Main Tank

Wing Tank
The tanks were also pressure tested by the welding company and all pin holes and cracks welded, so I now have a good set of tanks.
The paint was then stripped from the outside of the tanks using proprietory paint stripper and scotchbright to produce tanks ready for priming.
The tanks were first painted with an acid etch primer and then painted in a white epoxy primer. The nose tank will eventually get a white top coat as well as this is visible within the cockpit. Note that when painting the fitting holes were blanked off to prevent paint getting either inside the tanks or into the fittings threads.

The finished epoxy primed tanks.