Unfastening of the OH-XTM Super Chug propeller and fitting a new one

Suomeksi

The propeller of the OH-XTM Super Chug (in Finnish Super Sytky), which was damaged in a landing accident and donated to Aviation Museum Society Finland, broke in the crash. A replacement in good condition is required. The wooden propeller on OH-XTM was manufactured in the United States and bears a manufacturing plaque reading “MARFA HEGY TEXAS.” The propeller is stamped with the dimensions 54x44, indicating its diameter and pitch. It is also stamped with the numbers 6-81, which presumably refer to the month and year of manufacture.

Fortunately, we were donated a suitable propeller for the OH-XTM Super Chug’s VW 1600 engine. Antti Laukkanen, restoration manager at the Finnish Aviation Museum, decided to part with a propeller he had for the benefit of our Super Chug’s engine. This propeller was manufactured by E. Pankkonen in the 1970s. Pankkonen produced propellers under official permit, including those for the Fournier RF-5 “Tuulia” aircraft. These were much needed in the 1970s: according to the 1975 damage summary in the Finnish Ilmailu (= Aviation) magazine, the Tuulia in Turku was already using its eleventh propeller in its history!

We were eager to test whether the bolt holes of the donated propeller would fit the propeller hub of the OH-XTM engine. For this reason, the original but damaged propeller, which was still attached to the Super Chug’s VW 1600 engine, needed to be removed.

The disassembly began with the propeller hub cover, i.e. the spinner. Once the numerous crosshead screws at the rear edge of the spinner were removed, the spinner could be pulled off with a bit of prying.

Now the broken propeller could be detached. The propeller hub bolts came loose easily, allowing both the bolts and the propeller's mounting flange to be removed. There was some speculation as to how tightly the propeller would still be stuck to the mating parts of the mounting bolts. However, after tapping the propeller lightly with a rubber mallet, it came off easily.

With the propeller removed, the mounting ring for the spinner’s screws underneath could also be taken off, leaving only the hub with the propeller mounting bolt mating sleeves (threaded inserts) attached. During the disassembly, all screws, bolts and washers were labelled and placed in a plastic bag to await the completion of the Super Chug’s restoration and the installation of the new propeller on the VW 1600 engine.

Once the broken propeller had been removed and the hub was free, the donated propeller was test-fitted to the Super Chug’s engine. The propeller bolt holes in the donated propeller matched perfectly with the threaded inserts in the hub. The new propeller’s holes were, however, slightly smaller in diameter than the mounting bolts. This means that when the propeller is eventually installed on the OH-XTM Super Chug’s engine, its bolt holes will need to be slightly enlarged.

Photos: Lassi Karivalo

Translation to English: Erja Reinikainen