Sunday, 5 October 2008

New Door Hinges

Three pictures showing the manufacture of new door hinges. The original hinges were fixed with four small bolts to the wooden door frames. These had worked loose over time as the holes elongated so I've decided to replace the old hinges with a set that will be welded to the fuselage frame. This idea came originally from Rob Lees when he restored G-BREY.

The template was made from needlework template sheet which is a fairly stiff plastic sheet marked out with a grid pattern. I was able to bend it round the original hinges which gave an acurate measurement including the 90 degree bend which would need duplicating in the new hinges.

The hinges are made from 0.063" 4130 steel.

The hinges after adding the 90 degree bend.

Offering up the hinge to check alignment with the hinge on the door. The hinge was deliberately left 'long' because it will have to be fitted to the curve in the fuselage tubing. The door and frame will be used to get an exact fit when welding although I'll use the old door frames and not the new ones when tack welding the hinges in place.

New Door Frames

Mid September and I receive an 11 foot length of 2"x8" Ash wood which will be used to replace the old door and skylight frames. I've decided to go for the door frames first as they are in some respects easier to manufacture.

The first task was to cut a set of 1/2" deep blanks from which each new frame would be cut. After some head scratching we (myself and a good friend David who has an aladins cave of a workshop with all manner of equipment) managed to get 9 blanks from a single 4 foot length of Ash.

The original frames were used as templates for the new frames, in hindsight I should have spent more time studying the old frames as there were some defects which although not serious or problematic (after all the old doors fitted OK) have to some extent been copied onto the new frames.

The new frames were cut using a small band saw and jointed by hand. To provide the required strength and regidity, the frames were screwed and glued and left to cure in situ. Two pairs of hands make this job a lot easier, in this case my farther John spent two days helping.

The frames still need finishing off which will include a slot for the door catch, sanding down, varnishing and final fixing although this will be left until after the fuselage is beed blasted and primed.

The doors are slotted into the frames to check that all is well. I'm happy that the fit is snug and when finished the doors will not be draughty as long as some door seal is used.

Not much of a gap here.

I'm still working on the aileron and have started the metalwork for all the bits that will need welding onto the fuselage. This is because I would like to finish both ailerons (minus the covering), get various bits welded onto the fuselage and crack on with the interior before the end of the year. Next up, the door hinges.

Saturday, 6 September 2008

The Starboard Aileron - Part 2

In part 1 of renovating the starboard aileron I covered the disassembly of the aileron. Now I can cover the start of the reassembly.

Over the summer, progress was slow as I was waiting for delivery of much of the materials required for the restoration from the US. This took longer than I had originally anticipated (my advice to anyone restoring an aircraft would be to order at the earliest possible date, preferably before you start the restoration as long as you have a good idea of what will be needed). Now that everything is here I can start work again on the aileron.

The first job is to repair the crushing on the spars caused by over tightened bolts that hold the aileron hinge brackets on. You can see in this photograph how the spar has been crushed down around the bolt holes.

The approved repair method is to glue a plywood patch into the recess then sand it down so that it is flush with the spar. This provides a new flat surface on which to glue the plywood doublers for the hinges.

I arranged the plywood so that the visible grain is arranged along the length of the spar.

Simple G-clamps are used to force the plywood into the recess. Aerodux adhesive was used as it is easy to apply with a small paintbrush and any excess can be wiped off with a damp cloth.

Note: you cannot glue the doublers in place yet as this will prevent you from sliding the ribs back on.

All the aluminium parts were etch primed and then sprayed with an epoxy primer to provide a barrier against moisture. I have purchased a 4 stage HVLP turbine with a grvity feed gun for all the spraying. The turbine provides a separate air feed for a half face mask which is a must when spraying with most of the paint systems which can contain some very nasty chemicals. You must ensure that the turbine is located in a clean air source and that wherever you are spraying, the area is well ventilated. For most of the work at the moment I am sparying outside when conditions allow.

All the ribs laid out in order (thanks to them being stamped with a locating number) prior to being slid back on to the spar. I will not nail the ribs on until I have glued the doublers on and revarnished the spar. It all seems very awkward because the ribs have to be on the spar early in the process.

The ribs are slid on in order (and checked against the port aileron which is still assembled).

I then mount the aileron in a make shift jig; two axel stands, which will be used to support the aileron while I put it back together.

I can now begin to glue the plywood doublers back on to the spar. This will take a few days as the glue requires about 24 hours to cure. As each doubler is glued into place I will need to ensure that I drill the bolt holes otherwise I end up with all the doublers in place with no clue to where the holes should be (duh!).

I must say it feels good to see something coming back together at last although there is still a long way to go as I haven't started cleaning up the leading edge or the hinge hardware yet.

Another job looming are the door frames as I have just received some Ash timber so time permitting I should be very busy during september.

Sunday, 18 May 2008

Renovation of the Starboard Aileron

Well into May now and my shipment of hardware is only just being shipped from America mainly due to some bulky items including the new windscreen having to be back ordered. In the mean time I have sourced the etch prime and epoxy primer from Trimite in the UK so I can start to strip one of the ailerons and prep all the aluminium components so that when the American shipment is received I can put the aileron back together.

I started by taking numerous photographs of the aileron and all it's fittings and fixtures as a reference for when I have to reassemble the aileron. I will also use the other aileron as a pattern and the wing as a jig for aligning the brackets. Next, I removed the brackets and put them to one side. Because they are visible they will be painted in the red top coat which I don't have yet so I will bead blast and paint these at a later date.

The aluminium leading edge was carefully teased off and the nails removed with with a nail claw. I used a piece of aluminium sheet to protect the spar from being crushed during this delicate operation. Interestingly the aluminium was stamped as 016" 24S-T which according to a colleague of mine, was last used as a standard in
1929. The equivalent today is 2024T3.

The ribs are nailed to the spar so again each rib is teased off and the nails removed. As the ribs are removed they are stamped with a number (starting with the inboard rib) so that they will be reassembled in the same order.

With all the metal work removed from the spar, the plywood patches used to prevent the spar from splitting where the brackets are bolted through the spar, are removed. Although these were glued to the spar they came away very easily. The spar has been crushed by the bracket attachment bolts and will be repaired later.

The only visible damage to the aileron is a small split at the inboard end which will have no effect on the structural strength of the spar.

The spar is then rubbed down with wire wool to remove the old varnish. New plywood patches will be glued onto the spar where it has been crushed. The patches will then be sanded down flush with the spar thus filling the crushed areas. New plywood patches will then be glued on to prevent the spar wood splitting when the brackets are attached.

Most of the ribs needed to be stripped of old paint. This could be done by rubbing down with scotchbright or another soft non-ferrous material but I decided to do this chemically instead to save time. I'm using a paint stripper formulated specifically for removing epoxy and polyurethane paints (D23V). It came in a 25 ltr drum which I have converted into a dunk tank by removing the top then pouring water onto the surface to create a barrier as the fumes can be toxic. The ribs were then suspended in the stripper overnight.

Next day the ribs were removed from the dunk tank. The old paint literally ran off the aluminium and after washing in clean water the results are very impressive.

After washing the ribs were treated with alacrom (surface treatment) to protect them. The ribs will then be painted with an etch primer and epoxy before reassembly.

I should be receiving the wood ordered for the door and skylight frames and the floorboards soon so that will give me another job to be getting on with. At least I will soon be reassembling instead of just pulling the aircraft apart.

Sunday, 13 April 2008

The Harer STC

As part of the restoration project I will be implementing the Harer STC (Supplemental Type Certificate) which will have the benefit of allowing an increase in the aircrafts all up weight from 1200 lbs to 1280 lbs. Not a great increase but in addition to a target reduction of 50 lbs to the aircrafts current weight will bring a very useful increase of 130 lbs to the usable load.

In essence, the Harer STC calls for:
  • An 85 hp engine to be fitted.
  • The wing attachment fittings to be strengthened.
  • The lift strut attachments (at the wing) to be strengthened.
  • Additional cross bracing on the fuselage.
  • Provision for a larger baggage compartment.
I already have the 85 hp engine and don't intend to add the larger baggage compartment as this goes against the idea of keeping the aircraft as light as possible, but the other modifications will be implemented.

So while I await the delivery of all the hardware, paints and fabrics from the States, I decided to do as much of the airframe work, that will ultimately require welding, as soon as possible.

The first job requires welding a diagonal bracing tube across the bottom of one of the fuselage bays. In fact two tubes are required so that they will form an X with an existing bracing tube. The first job was to work out how I could accurately cut the tube ends so that they would fit into the tube clusters and the existing bracing tube. Luckily I found a very useful web site some time ago and remembered to bookmark it for later use. provides a tube coping calculator that will give you a cutting template for joining two tubes. For the tubes I have there are various intersecting angles from 40 to 90 degrees. I've had a look at a couple of other programs for doing the same job but this one is very simple and straight forward to use.

Here's a sample template, downloaded in PDF format then printed and cut out ready to be wrapped around a tube.

The Template is wrapped around the tube, which can then be cut and ground to shape. I used a dremmel for grinding.

A finished 90 degree intersection.

The final join in the center of the X. This was straight forward as the intersecting angle is 90 degrees.

The rear tube cluster showing the new bracing tube in place. Cutting this pattern is slightly more complicated as there are two horizontal tubes which intersect at different angles. I used a mashup of two templates to get the basic cutting template and then had to finish the grinding by eye plus a lot of trial fitting until I was satisfied with the result.

The forward tube cluster was even trickier because there are two tube sizes and different angles. Again I used two templates to get the general shape.

The tubes will be welded in place once I have prepared all the other fittings such as door hinges, harness attachments and repairs to the rudder and horizontal stabilizers.

Sunday, 27 January 2008

A new interior - Floorboards

I've been sidetracked so far this year with three other projects, a new car, an AD on Taylorcraft lift struts and the small matter of someone trying to build a new town on our airfield but I have at last managed to make time to start work on the aircrafts interior. The old interior was not unattractive or particularly tatty, but I feel that it could be better in a number of ways. The floor was the original aluminium which had been modified over the years and then covered with carpet. This will be replaced with a 6mm birch plywood flooring and aluminium kick plates.

Working on the principal that everything will have to be done at least twice before it works I set about creating a template floor in cheap 5.5 mm plywood first. This will then be used as the template for the final floor. First the shape of the current floorboards was transferred onto the onto the plywood.

I used a hole cutter and fly cutter to get the shape around the heel brakes. The rest of the cutting required is just straight lines at various angles.

I used a jigsaw to cut the straight lines which meant setting up a straight edge to help guide the saw. The calipers have been set to the distance between the edge of the jigsaw footplate and the saw blade. Once set this is used for all cutting.

Once cut, the floorboards (which are in two halves so that they can be removed) are laid out. I will have to make some fine adjustments before I am happy with the fit, mainly because the old aluminium boards overlapped and the new plywood boards have to but up to each other. This photograph shows the two floorboards in situ with work still required.

The bulkhead will slot into a grove formed by two quarter round strips of wood that will be glued in place. A battery box holding two sealed dry cell batteries will be fixed in the center of the bulkhead where it shouldn't take up too much space and will be easily accessible. It will also help fix the floor and bulkhead in place.

I still have to manufacture the kick plates and battery box before I'm confident that I can finally make the floorboards.

Tuesday, 1 January 2008

A new year and the first sign of trouble

January 1st begins pretty much as 2007 ended - foggy - so I'm back in the workshop to finish off removing fabric. All that remains are the rudder, horizontal stabilizers, elevators and undercarriage legs which shouldn't take too long.

The undercarriage legs had been recovered a few years ago when I discovered some corrosion and had to have sleeves welded over the corrosion so I don't expect any serious issues here.

Unfortunately as I began to strip the various components it soon became clear that there is serious corrosion in all the tail feathers and that these will all require time and effort to sort out.

The rudder was the only area where there was a visible hole in the tubing although I have not carried out a punch test on any of the other sections of corroded tubing yet. It appears that moisture must have been getting through the fabric for some considerable time but because of the thickness of the Razorback fabric it was not obvious during any of the previous 9 annual inspections.

Horizontal Stabilizers
The horizontal stabilizers are mainly corroded around the fuselage attachments which means they cannot have an internal sleeve welded inside. Note that in the second photograph the repair is to a curved tube which will be more difficult to achieve.

Similarly, there is a lot of corrosion around the weld clusters which will be much more difficult to repair and will probably require new U channel pieces and tube.

With so much work to do, I will have to get approval from Carl, my inspector, for each repair method. The repairs must also conform to AC43.13-1B to ensure that structural integrity is maintained. For the moment I will try to reduce the opportunity for the corrosion to get worse while I try to figure out how to repair the damage.

Strangely, this has not depressed me but has confirmed the need to renovate the aircraft in the first place as I now know that in places it did need it after all.