I was at Duxford recently, and spotted a Jet Provost Strikemaster that had a rough texture applied to a portion of the leading edge of the wing.

Jet Provost Strikemaster leading edge

Why was this applied?

  • $\begingroup$ Looks like part of the leading edge is missing and someone put in a rough patch awaiting the proper part, this is definitely not normal for any Strikemasters, and not for the Mk.80/80A in particular that were used by the Saudi air force. $\endgroup$ – jwenting Aug 15 '19 at 11:27
  • $\begingroup$ My guess: cheap attempt at a vortex generator. See answers to this question for the purpose. $\endgroup$ – DeltaLima Aug 15 '19 at 12:14
  • $\begingroup$ @DeltaLima: Almost - it's artificial roughness to trip a laminar boundary layer. $\endgroup$ – Peter Kämpf Aug 15 '19 at 16:51
  • $\begingroup$ Have you considered emailing Duxford to ask them? They'll likely know a lot about their planes. $\endgroup$ – David Richerby Aug 16 '19 at 8:19

The leading edges are roughened to improve the stall characteristics. Typically vortex generators are used for this purpose nowadays.

The 5 and the 5a were used by the RAF for pilot training and the nose strakes were fitted to improve the spinning characteristics - the leading edges of the wings had a roughened paint finish to improve the stall characteristics. The 5s with the tip tanks (I'm not sure if 5b is an official or 'unofficial' designation) were used by the RAF for nav training and didn't have the nose strakes (not sure about the roughened wing leading edges) I don't know if it was because the tip tanks themselves improved spin handling or if it was because they weren't flown by studes for spin training.

(source: User "Fritag" at www.britmodeller.com)

The rough grey coating on the wing of the aircraft was applied in order to break up the smooth airflow and give an early indication of the onset of a stall as the T5's original clean wing design gave the pilot little prior warning.

source: all-aero.com / RAF Museum

A great deal of work has been put into stalling, spinning and stall-warning over the years of Jet Provost and Strikemaster development. This has led to all sorts of devices, like inverted-aerofoil tailplane, fences under intakes, strakes round the nose, roughened outboard leading-edges and little "eyebrow slats" at the wing roots. Of all these devices, the Strikemaster requires only the "eyebrow slats" to give it that precious smooth spin, a tidy g break in the stall and a distinct stall warning.

source: Flight International 12 October 1972 500-501

At first it was forecast that the T.5 would take the place of the T.4 on certain roles such as high altitude training. Unfortunately the majority of T.4s had to be taken out of RAF service much earlier than anticipated so the T.5 had to take on more responsibilities. As a result, the RAF decided to update its fleet of Jet Provosts with new avionics suites, spin strakes, and roughened leading wing edges in 1973.

source: Jet provost heaven

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    $\begingroup$ Not sure you should use dudes posting on an aeromodeler forum as source data. Just sayin'... $\endgroup$ – John K Aug 15 '19 at 15:50
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    $\begingroup$ Still just anonymous people (like here) who may or may not know what they are talking about. You don't know they really are or what they know, or who wrote the All Aero bit. I've searched numerous pics of Mark 5a's and can't find any with that crazy leading edge treatment and can't find any OFFICIAL accounts that describe it, so I will default to skepticism, and my own knowledge of how dangerous that kind of LE contamination is. If that kind of surface treatment, equivalent to a heavy coating or rime ice, improves aileron effectiveness, well, there's a whole new paradigm. $\endgroup$ – John K Aug 15 '19 at 16:58
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    $\begingroup$ @JohnK I don't think it is increasing the aileron effectiveness, instead it increases the turbulence over the aileron close to stall. This gives an early indication of impeding stall, which is more friendly than the laminar flow suddenly stalling, especially in a training aircraft. $\endgroup$ – DeltaLima Aug 15 '19 at 17:05
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    $\begingroup$ No that kind of roughness will simply cause a full separation and complete loss of aileron control at an angle prior to the normal stall AOA. I could be wrong in all this, but I want to see an authoritative source because this is pretty bizarre, and like I said, all the pics of Provosts I can find all show normal clean LEs. $\endgroup$ – John K Aug 15 '19 at 17:13
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    $\begingroup$ Good find! I'm satisfied that the treatment was intended to modify stall behaviour and will delete my post. I still think tho that it was just done experimentally and may have not worked so well because I still can't find a picture of one in service with that treatment. $\endgroup$ – John K Sep 5 '19 at 15:19

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