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12 Jan 1914. Monday.

12/01/2014

Frank got Sunday off, but was back at this desk on the Monday morning.

548 Empennage Stay Tube 12-1-14

His first sketch (548) was the final detail of the tail surfaces. These are the struts that go from the tailplane to the bottom of the fuselage to stop the tailplane wobbling sideways. They don’t do a great deal of work, and on many modern light aircraft of similar size and performance, you’d use cables or tubes of about 12mm (1/2in) diameter. But Frank was determined to keep the drag on these to a minimum and used commercially-available oval section tube. The brackets at each end need to be at right angles to each other, and so the ones at the top end look rather awkward fitting the ‘wrong’ way into the oval section. I’m also unclear why he chose to pin and braze the fitting; welding would seem to be a much simpler option, and one that we adopted on 1264. It’s also difficult to make final adjustments of the length of these struts on the job; I think they would have done this by adjusting the positions of the attachment brackets on the tailplane.

And while I’m picking Frank’s work apart, the tailplane, with its tiny, flimsy ribs, weighs far less than these four struts (there are two on each side). Having gone to all that trouble to save weight (and the tail is the area you would most like to save weight), why these big heavy tubes? It seems odd, that’s all.

Finally, I’ve noticed that the sketch refers to a later sketch, 875, which we don’t have. It would be interesting to see what changes he proposed.

549 Fuselage Clips for Attachment of Empennage

Sketch 549 is for the fuselage fittings for the tailplane; the top one is to attach the main spar and the lower one clips round the leading edge tube. On the C Scout they incorporated a method of adjusting the angle of incidence of the tailplane as a way of adjusting the hands-off trim, which meant altering the lower fitting so that the leading edge could be raised and lowered. They also introduced adjustable stays for the leading edge. But amazingly, they didn’t make the fittings for the spar adjustable, and there was no way of adjusting the rear spar, so I don’t know how they made adjustments in practice! We’ve modified the spar fittings to be able to adjust if necessary.

Having completed the empennage, Frank turned his attention to the rear fuselage, and the rounded decking that is there for looks more than any structural reason. The method of manufacture is absolutely standard and required no great thought on Frank’s part.

550 Fuselage Top Rear Covering Formers and Stringers 12-1-14

551 Fuselage Top Rear Covering - Detail of Formers 12-1-14

There are some interesting differences between this and the C Scout, however. If you look at the top left of the sketch at station H (marked as HT and HB) you can see that station H comes between the leading edge and the spar of the tailplane, and he added 16swg wires to stiffen things up there. This is really not good practice, since the tailplane and its struts would have been mounted on the longerons halfway between stations, and the longerons would have been prone to bending and eventual cracking. It’s difficult to see how this happened; I can only assume that he’d originally envisaged a smaller tailplane, and decided to change it after the fuselage was part-built. At any rate, by the time we get to the C Scout, the situation was resolved, with station H moved forward in line with the tailplane leading edge, and an extra station at the tailplane mainspar.

At this stage, they also reduced the number of stringers for the rear decking from 7 to 4. 

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  1. 18 Feb 1914. Wednesday | Bristol Scout

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