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.

More on Floorboards

It's been a while since I made the mock up of the floorboards but at last I made the effort to get some qualaity birch plywood for the final product. Using the mocked up floorboards with I marked out the outline of the floorboards onto the birch ply paying attention so that there were no blemishes in the birch.

There were a couple of differences between the mock up and the final boards (go to to see details of the mocked up floorboards) to incorporate improvements, mainly around the cut out for the brake pedels.

Cutting was done with a band saw, fly cutter and fret saw to get the required shapes; one useful tip here is to score the underside of the ply along the proposed cut with a knife, this prevents the underside from ripping when sawn giving a clean edge to the ply.

The boards were drilled to take the self tapping screws that will fix them to the fuselage (tabs on the fuselage will have tinnerman nuts fitted).

The boards were then sanded and given a brush coat of varnish. Once this had gone off the varnish was sanded lightly to de-nib it and thre more layers of varnish were sprayed on. For spraying the varnish was thinned down with MEK in the ration 1 part varnish to 4 parts MEK.

Finally the bulkhead under the seats was cut and fitted. This is screwed into the crossmember under the front of the seat sling and will drop into a slot formed by two quater round strips of wood glued to the rear part of the floorboards. the battery box, which I have yet to make, will be positioned in the middle of the floorforward of the bulkhead.

I have still got to get a couple of extra tabas welded to the fuselage frame to provide additional anchor points for the floorboards but this should be done within the next couople of weeks as I write.