By George is absolutely correct; they are NOT anti-spinning strakes! (PM sent, btw).
But there are some in the UK who claim that fitting the strakes was a pure “political fix” (the story involves a prominent MP’s son being killed in an RAF spinning accident) and further that the strakes are of limited effectiveness. Certainly the Canadians were unimpressed for the need to equip their Chipmunks with these. Is it significant that following their exhaustive investigation into Chipmunk spinning, the Australian DCA published a report in June 1960 (i.e. two years after the RAF fitted their strakes) which never mentions the effectiveness or otherwise of this item?
As fitted, the UK strakes were distinctly crude, not even matching up to the tailplane leading edge. In contrast, the tapering Sassin/Aerostructures strakes are a very elegant solution:
There have been volumes written about Chipmunk spinning. I’m not really qualified to further comment, other than to point out the Chipmunk has several incipient “gotchas” lurking around:
- Any brake selection limits rudder travel.
- Failure to use the published entry technique can result in nasty surprises.
- The aircraft won’t simply recover by letting go (unlike some types); the correct recovery technique is essential.
- One quirk of Chipmunk aerodynamics is that while control forces are normally quite light the elevators can really firm up in a spin, with the result that the pilot thinks because of the push force involved that he has full forward stick when he hasn’t. At least one Aero Club had witness marks painted on the control box and taught students to push the stick until the marks aligned.
- Sometimes the first indication that the aircraft is recovering (i.e. the correct technique has been employed) is that the spin “tightens up” with an increasing spin rate initially – this one still gets me!
In 1967 at Bunbury WA I did something really stupid in a Chipmunk (see item 2); the ensuing manouvres and spin frightened me witless. It was 28 years before I got in a Chipmunk again!!!