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The Caravelle has two wing fences on each wing, so as to limit the spanwise airflow (and associated tip-stall problems) that would otherwise occur due to its rearward-swept wings.

On most Caravelles, such as this VI-R, this takes the form of a large inboard fence which wraps around the leading edge of the wing, and a smaller outboard fence which starts significantly behind the leading edge and rises only about half as far from the wing's surface as the inboard fence does:

VI-R fencing

(Image by Lars Söderström at Airliners.net, via Dura-Ace at Wikimedia Commons, cropped by Dura-Ace at Wikimedia Commons.)

On most 10Bs and all 12s, in contrast, the outboard fence is larger (although still not quite as large as the inboard fence) and wraps around the leading edge in the same manner as the inboard fence, as can be seen on this 10B:

10B fencing

(Image by Aldo Bidini at Airliners.net, via Russavia at Wikimedia Commons.)

However, some 10Bs, such as this one, have the older, smaller design of outboard fence:

10B with VI-R fencing

(Image by Felix Goetting at Airliners.net, via Fæ at Wikimedia Commons, cropped by Fæ at Wikimedia Commons.)

Why the two different styles of outboard Caravelle wing fences? I'm wondering if it might be related to the modified wing used on the 10B and 12, but, if so, then why do some 10Bs have the older style of outboard fence?

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Every square inch of skin surface adds to induced drag, so nothing is going to be bigger than it absolutely needs to be. Whether through math or empirical testing (or some of both), it was determined that the outboard fence could be as small as it is. Therefore making it larger was detrimental to range, fuel economy, speed and cargo/pax capacity.

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    $\begingroup$ Then why do some 10Bs have the smaller outboard fence, while most 10Bs have the larger outboard fence? If the 10B doesn't need the larger outboard fence, then all 10Bs should have the smaller one; if the 10B does need the larger outboard fence, then all 10Bs should have it. $\endgroup$
    – Vikki
    Mar 21 at 21:27
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    $\begingroup$ "Every square inch of skin surface adds to induced drag" - I'm sure you meant to say friction drag, right? $\endgroup$
    – Peter Kämpf
    Mar 21 at 21:42

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