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A340 undercarridge question.

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I was in hobbyco today.


I was looking at the models and finally realised which plane I had seen.


I knew one of the airbus planes had a "weird" set of wheels.




Now I know it is the 340.


But looking at the models, there are two kinds of that too!


One has a single set of wheels and the other has two sets of wheels.





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Guest Maj Millard

Heavy jets will often have a centre set of load carrying bogie undercarriage. The DC10-30 had one but didn't always use it so they must have been able to retract it independently ........Maj...



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I was in hobbyco today.One has a single set of wheels and the other has two sets of wheels.


There's a very straightforward reason for that.

The original design of the A340 - a sizeable long range airliner - required a 2 wheel centre bogie for structural reasons. As is usually the case, aircraft designs change size as airlines demand various extra levels of performance or load capability. This is why for any given airline jet you often see there is perhaps a -200 version, a -300, -400 and so on. Usually they "grow", but occasionally, such as in the case of the B747SP they can "shrink" too.


In the case of the A340, it grew, and grew quite a lot. The A340-600 was a much longer and somewhat heavier version, for which the 2 wheel centre bogie did not provide enough structural support. So Airbus engineers had to change it to a 4 wheel centre bogie to cope with this increased load. This was only one of many design changes it needed (including larger engines and so on).



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The 340-300 has a MTOW 45 tonnes heavier than an A330. At very light weights the 340 centre gear sometimes doesn't even touch the ground. You can operate the 340 without the centre gear, it stays retracted, but it reduces the MTOW to about 225 tonnes. The 340-600 was up in the 350T range for take off and 247ish for landing needing the extra bogie with brakes. The standard 340 centre gear has no brakes. Yes the 600 was a step too far in size and was a pain to taxi everywhere.



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