Making a look-alike ILS-antenna on the DO-5 nose

Last spring the missing lower part of the nose cone was made of glass fibre to the C-47 (DO-5), owned by Aviation Museum Society Finland. To make the nose appear real, it should include an Instrument Landing System glidepath antenna. It consists of the antenna arch, made of 10 mm thick aluminium tube, a vertical support in the middle of the arch, the antenna stem shields, a base plate, a wedgelike form plate and a rubber seal. With the aid of the form plate it’s possible to fasten the antenna tightly and at the right angle on the curved surface of the nose cone. Both ends of the antenna arch penetrate the stem shields, reaching the underside of the base plate, where at both ends of the antenna tube there’s a connector for the antenna’s electric wire.

We don’t have this antenna to fit on the DO-5. So we decided to make a look-alike copy of the antenna, because the DO-5 will not be made airworthy. We were lucky to get an original antenna for making the look-alike copy, although it is without the form plate made of cork and the rubber seal belonging to the antenna. At the same time, however, we got a broken base of the antenna to be used as model, on which to make the look-alike copy. The base still had the form plate and the rubber seal in place. We are obliged to return the form plate, so it, too, has to be done.

Picture by Reijo Siirtola.

To make a look-alike copy we made a model drawing, which is on the outside looks like the original antenna. The difference from the original antenna is that we replace the original antenna made of aluminium tube with a solid 10 mm thick aluminium bar. The fastening of the antenna arch to the base plate also differs. Because our antenna will not be functional, we’ll fasten the antenna arch to the base plate with nuts. For that purpose the ends of the antenna arch will be pushed with their shields 10 mm past the underside of the base plate and the ends will be threaded for the nuts. We’ll have to make a new form plate, too. We’ll make it out of mass plate that can be reshaped, instead of cork.

Photo by Reijo Siirtola.

We started making the look-alike antenna by dismantling the antenna base we had. The antenna end shields, made of hard plastic, which were attached to the base plate with small screws, were broken. They were mended with epoxy putty. After the putty had dried, the shields were formed to their original shape and painted black. At the same time holes were opened through the shields, to enable the ends of the aluminium rods, modelling the antenna arch, to be pushed through the shields.

Photo by Juha Veijalainen.

To make the antenna arch, we cut an overlong piece of 10 mm thick round aluminium rod.  To bend the antenna to its original form, we built a bending device. With it we bent the aluminium rod to the exact arched form of the original antenna. We pushed the overlong ends of the antenna arch through the antenna shields to cut them to exact length. For that purpose we measured from the original antenna the distance from the top of the arch to the surface of the base plate and added the necessary 10 mm, the distance that the antenna ends reached below the base plate. We cut off the extra bits from the antenna arch ends, after which the ends were threaded for the fastening nuts.

To make the vertical support in the middle of the antenna arch, we cut off from 10 mm aluminium rod an also overlong piece for the centre support. We shaped the top end of the rod as concave, for it to press tightly against the top of the antenna arch. We measured the necessary length for the centre support and marked the lower end of the rod accordingly and cut off the extra. The centre support is fastened at the top with a small bolt through the antenna arch and at the bottom end with a small bolt through the base plate.

Then we marked the attachment point for the centre support on the antenna arch and drilled a hole for the top fastening bolt. There’s already a hole in the original base plate for the bottom end bolt. After the holes have been drilled in the top and bottom ends of the vertical support, inside threads were made with a threaded pin, and the vertical support for the antenna arch was ready for fitting in.

A new form plate to replace the original one made of cork had to be made. We made this form plate out of easily workable mass plate. The mass plate was ground wedgelike from the sides. The side against the base plate was left straight, but the side against the nose cone was worked as concave, according to the original model. Finally holes were drilled in the new form plate for the antenna arch nuts.

It was time to assemble the antenna. We pushed the ends of the antenna arch in their shields in such a manner that the vertical support in the middle of the arch settled nicely between the antenna arch and the base plate. We turned into place the bolts to the ends of the vertical support. Then we fastened the antenna shields to the base plate with four small screws through the base plate. That done we tightened the antenna arch into place with the nuts at the arch ends. The vertical support worked as a stiffener when fitting the antenna arch into place. When the form plate with its rubber seal was fitted, the glidepath antenna look-alike copy of the DO-5 instrument landing system (ILS) was finished.

The next thing to do will be to go to Turku and install the antenna look-alike copy onto the upper edge of the DO-5 nose cone’s lower part made of glass fibre. The DO-5 is situated by the Turku Airport Terminal, beside the Caravelle “Bluebird”. We can measure the exact position of the antenna from the original “DAK” nose cone, so according to that we’ll drill the necessary holes into the upper edge of the lower half of the DO-5 nose cone made of glass fibre and install there the ILS-antenna look-alike copy we made. We’ll go and install the antenna still before the winter sets in.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.