Geodetics

[seafuryfan]

Inputs welcome to this interesting thread, or on here if you'd prefer.

Geodetics - good or bad? - Key Publishing Ltd Aviation Forums (http://forum.keypublishing.co.uk/showthread.php?t=89443)

[John Farley]

I have read through the other thread and can say that Ralph Hooper (father of P1127/Kestrel/Harrier family) agrees with all the anti-geodetic views expressed there. He cannot understand why the designers that used geodetics did not go the conventional stressed skin way - which was by then well established in for example flying boats.

He views geodetics as a rather pointless half way house between the well past it's sell by date Hurricane type of structure and the Spitfire for example.

[old-timer]

Very good points about geodetics John, I was always impressed by geodetics but they must have been very complex to manufacture & assemble, I wonder if they used less raw al' alloy material compared to stressed skin construction ? - maybe the folks at Brooklands would have some more data ?

[astir 8]

They were certainly cheating in that wartime "bomber in a weekend" film - those big sections of pre-assembled geodetic panels would have taken a good while to put togther but that wasn't counted.

As I understand it, the RAF had a policy pre-war that aircraft structure had to be as far as possible repairable by RAF groundcrew (with their existing skills) on the airfield. Hence the Hurricane (and the preceding Fury, Hart etc) had the fuselage frame made out of dozens of tubes rivetted and fishplated together and individual tubes could be relatively easily replaced. The Wellington's geodetics fall under the same heading - an enormous production problem but easily repairable.

Whereas the not much later Me 109 had a fuselage made out of about 6 big sheet alloy pressings with another 6 or so stringers inserted and rivetted. I believe that the 109 took half the manhours to build compared with a Spitfire - I've never seen a comparison with the Hurricane!

[Been Accounting]

Could it be used with carbon-fibre?

[stressmerchant]

Although it may be viewed as a pointless halfway stage, it must be remembered that much of the work on allowable buckling of stressed skin panels post-dated the design of aircraft such as the Wellington. Although initial research was done in the late 1920s, research by people such as Leggett (ARC report 2430, 1940) and Kuhn (NACA TN 2661 / 2662 1952) only appeared later. The choice of geodetics would also have been influenced by the background of the designers - Barnes Wallis was a former airship designer, and would have had extensive experience with the geodetics. As far as I know there was only one true stressed skin airship (the ZMC-2?), the rest were effectively geodetics.

In the early 1990s I did some minor work on the Super Airbus Transporter (Beluga) design, and had to dig back though the early research on large shell frames. I was suprised how much influence airship design had on aircraft fuselage design - in the proceedings of one post-WWII conference one of the comments (I think from prof Puglsey) on a paper even went so far as to suggest that a monococque fueslage was nothing more that a scaled down airship frame!

[old-timer]

Airships - those were the days- shades of Nevil Shute's book 'slide rule'
no 3D mega-wizz computers in those days, just lots of clever mathematicians & engineers. (still plenty of clever folk around but those slide rule skills must be a dying art these days)

I imagine that geodetics had a greater battle damage tolerance than stresed skin construction ?

Was the earliest use of stressed skin al' alloy for fixed wing the supermarine S6B schneider trophy racer ?

Interesting thread - keep those replies going :ok:

[lotusexige]

The last person I saw use a slide rule was Frank Costin who had worked on the Mosqueto and the Vampire. I was quite surprised to see him produce a slide rule from his pocket to work something out. This was in the mid 1980s.

[biscuit74]

Part of the point about the system of construction by Hawker at then time of the Hurricane design is that it was specified by the authorities - not by Hawker, since they wanted structures that could easily be maintained and repaired throughout the Empire, possibly well away from 'advanced' servicing facilities.

That was the point and it worked well, It is also worthy of note that the result was that the Hurricane could be repaired after battle damage in a fraction of the time, and at a fraction of the cost of the Spitfire.
This, combined with the fact that there were significantly more Hurricanes than Spitfires available at the time is why the Hurricane was vital in the Battle of Britain. (There is a lot of nonsense spoken about Hurri vs Spit. We needed both. To have been without either of thsie superb aircraft would have meant a very much closer run thing. )

As for geodetics. The R100 designed on geodetics principles was a resounding success. It was only removed from service after the ridiculous R101 shambles. A very light and extremely strong construction, if you get it right.

Ralph Hooper was, I suspect talking many years later and when stressed skin construction was much better understood and executed. Very easy to be clever in hindsight, of course. I recall that the stresed skin of the early Kestrel series wasn't so smart. Some examples of oil canning and rear fuselage damage before they got that right, because they were looking for maximum lightness and rigidity to get VTOL.

For the Wellington, geodetics prodcued a light and very strong structure for its day. Highly flexible yes. Any old style balsa modeller will tell you about the benefits of geodetic construction, popular at one time for rubber power endurance models. A right pig to make !

And I still have my slide rule. I occasionally threaten our students that I will make them use one, when they demonstrate a lack of understanding of the difference between precision, accuracy and significance.

[old-timer]

Thanks for those details megan, it always fascinates me how quickly aero engineering developed , wright bros' to space flight in one generation almost :D