tend to generate span wise flow of the boundary layer, causing some of the airflow to move "sideways" along the wing. This occurs all along the wing, but as one moves towards the tip the sideways flow increases, as it includes both the contribution of the wing at that point, as well as span wise flow from points closer to the root. This effect takes time to build up, at higher speeds the span wise flow tends to be blown off the back of the wing before it has time to become serious. At lower speeds, however, this can lead to a considerable buildup of the boundary layer at the wing tip, adding to the problems noted above. Finally, while not directly related to the effects above, it was common during the early jet age to use T-tail designs in order to keep the aerodynamic surfaces well clear of the jet engine area. In this case it is possible for a pitch-up event to cause the turbulent air behind the wing to flow across the horizontal stabilizer, making it difficult or impossible to apply nose-down pressure to counteract the pitch-up. Aircraft with low-mounted tail surfaces did not suffer from this effect, and in fact improved their control authority as the wing's wake cleared the controls surfaces, flowing above it. This was not always enough to correct for the problem, however; the F-86 continued to suffer from pitch-up in spite of increasing nose-down pressure from the tail surfaces. Mitigation As the primary causes of the pitch-up problem are due to spanwise flow and more loading at the tips, measures to address these issues can eliminate the problem. In early designs these were typically "add-ons" to an otherwise conventional wing planform, but in modern designs this is part of the overall wing design and normally controlled via the existing high-lift devices. The first known attempt to address these problems took place on the platform where they were first noticed, the Douglas Skyrocket. This took the form of a series of vortex generators added to the outboard portions of the wing, breaking up the boundary layer. However, this was found to have almost no effect in practice. Nevertheless, a similar solution was attempted on the Boeing B-47 Stratojet where it proved considerably more effective. This may have been helped by the presence of the podded engines, whose vertical mountings acted as barriers to