Caudron C.59's horizontal stabilizer is straightened
Tiistai 19.11.2019 - Member of Tuesday Club
During the 90 years of storage, the Caudron’s horizontal stabilizer has bent badly and it is also otherwise in such poor condition that it had to be dismantled for the restoration work. During the dismantling it became clear that the reason for the bending was the batten on the leading edge. The batten on the trailing edge was also slightly bent. Both battens had to be straightened before re-installing the stabilizer parts and the fabric covering. The team decided to try and straighten the battens by making them thoroughly wet and then fastening them on a level table top to dry and straighten.
Some flexible ventilation duct was found in the storage of the Finnish Aviation Museum and this duct was used to make a container for soaking the leading and trailing edge battens. A four meters long piece of duct was needed for the battens which are nearly three meters long. When the battens had been placed inside the duct, the ends of the duct were bent upwards and the duct “tub” was filled with water. The team estimated that it would take about a week for the battens to get thoroughly soaked when they were submerged in water.
The battens were taken out from their bath after a week, and it seemed that both battens had already straightened by themselves. Obviously wood returns to its original shape when it is thoroughly soaked, in this case to the shape which had been made for the horizontal stabilizer. However, the leading edge and trailing edge battens were fastened on a heavy table surface using clamps. There the battens could dry and hopefully regain their correct shape.
After another week the clamps were unfastened, and the team found out that the battens were dry and almost straight. The thinner trailing edge batten was completely dry but the leading edge batten felt damp and it was still a little bent. The team re-fastened the leading edge batten on the table with the damp side upwards.
In the following week the batten was unfastened and the whole horizontal stablizer frame (leading and trailing edge battens and the end battens) was assembled and placed on the table. The team noticed that the leading edge batten was still slightly bent and the whole frame rose 3 cm up from the table top at its starboard rear corner instead of being flat against the table top.
The team decided to soak the leading and trailing edge battens for another week. Also the end battens were placed in the tub because they were a couple of centimeters bent inwards. After a week the battens were taken from the tub and this time they were fastened on the table as a frame. In the assembly work the leading edge batten was pushed straight using wedges. The aim was that when the leading edge batten dries when assembled in the frame, it would not bend back into its previous shape.
Another week went by and the frame was unfastened. The team noticed that again the frame was not flat but the rear corner of the frame rose slightly from the table top. The leading edge batten was still damp on the side which had been against the table. Therefore the leading edge batten was fastened on the table once more and left to dry for two weeks.
After two weeks the horizontal stablizer’s leading edge batten was unfastened and the trailing edge batten and the end battens were assembled. The team was delighted to see that the frame rested flat on the table – the leading edge batten wasn’t bent any more. Now the repaired ribs could be preliminarily tested between the leading and trailing edge battens. The Tuesday Club team had worked hard to return the battens to their original shape and succeeded.
Photos: Lassi Karivalo
Translation: Erja Reinikainen.