Spitfire undercarriage question

[jonesy]

OK, at the airshow on Sunday late in the afternoon, and wondering why the Spitfires hadnt started up yet.

Then the announcer piped up and said because of the strong crosswinds ( and yep they were almost a quarter Wellington strength!) the Spits would not be taking off. This was, he said, due to the closeness together of the u/c legs making the aircraft unstable on the ground and hence a bit risky.

I'm interested-any substance to that statement? Seems like a real design flaw to me

If so, why so close together unlike other similar-era machines?

Oh yeah, then the bloody things did take off so now even more confused!!

[lumpy]

Definitely some substance to that statement . The ME109 was famous ( infamous ) for exactly that problem , killing many pilots in landing accidents . Its about maximising performance in the air , and making the best of whats left - ground handling ( remember the guns take up a fair bit space in the wing , so it wasnt just a case of being able to put the UC further out ) . I think a lot of the fields that were used in wartime also had a bit more flexibility in terms of being able to takeoff and land into wind , whichever direction that was .

[Bruce]

I wouldnt describe the the Spitfire undercarriage as a design flaw, but it was indeed a design compromise.
When deciding where to put the undercarriage legs, the designers were faced with a dilemma. They could be placed outboard and retract inwards as on the hurricane, but as they are attached to the spar structure, this has to be stiffened up so that the inboard spars dont distort with landing and takeoff loads. the problem then is such a spar becomes heavy and by necessity, quite thick, which creates a thicker wing. At the same time the wing guns also need to be fitted in around them. On the Hurricane this gave it a thick, strong wing, but performance was reduced by the extra drag, weight and aerodynamic compromise.
On the Spitfire, RJ mitchell and his team wanted a thin, aerodynamicly ideal wing, which needed a much thinner spar. Putting the UC outboard on this was impractical, so the legs were attached inboard, very close to the fittings where the wings attached to the fuselage, taking the landing gear loads off most of the wing structure. The ME109 went even further and attached the UC legs to the fuselage, separate from the wings, which enable the fuselage to be moved when the wings were off.
The drawback is of course the narrow track of the gear, which was addressed on later versions to a small degree by bending the legs outwards at more of an angle - the Spit legs however always had a very narrow track which wasnt ideal for field operations. It is worth remembering however that in the 1930s, the aircraft that proceded the Spitfire were Biplanes, which had fuselage mounted, narrow track undercarriages so it wasnt seen as a major issue. Airfields at the time were also just large open spaces, so takeoff and landing could be made into wind, reducing the crosswind trickiness.
Aircraft design is full of compromises, (I know this from experience!) and in this case the narrow gear allowed the amazing wing which gave the Spit its performance edge - an acceptable compromise that was worth making!

[jonesy]

Well thats good to know! I'm quite staggered by the developments over a 30-odd year period where aircraft design was incredibly experimental and thinking outside the square, particularly the Brits.
As it is, I owe my existance to the design skills of de Havilland and co, for if their Mossie hadnt have been such a good performer during WW2 then my old man may well have been in some trouble!!

[corsair67]

Don't have that problem with a Corsair - it just tries to kill you in other ways! ;D

[jonesy]

Also wonder how much was trial and error-"whoops, best we move that undercarriage outwards a bit and probably get another test pilot"

[Bruce]

Feb 1, 2012 20:58:47 GMT 12 jonesy said:

Also wonder how much was trial and error-"whoops, best we move that undercarriage outwards a bit and probably get another test pilot"

Not a lot probably. By the late 1930s aircraft design was a refined art, with serious science and precision behind it. Although RJ Mitchell is credited with the spitfire, it wasnt a case of him sitting down at a drawing boards and producing all the plans for the Spitfire. the Vickers Design office (the Spit was a vickers design, but built by the parent companies Supermarine division) probably numbered several hundred skilled engineers at the time, with teams working on systems, stress analysis, aerodynamics, armaments etc, so that by the time the prototype flew it was largely how the production machines would appear. In fact test Pilot Mutt Summers' first comment after the prototypes first flight was "Dont touch a thing". Of course through service experience changes were implemented and the design refined, but there was no point in the process that it was "oops maybe we need to do this, or this...". As an example of the systematic and scientific approach, the first Spitfire was completely flush riveted, which was a new thing at the time. The air ministry wanted to reduce the build time by changing back to conventional round head rivets. In order to prove the performance losses that would come from going back to round head rivets, Supermarine glued split peas (as used in soups) on top of all the rivets to study how many could be changed before performance suffered!