RAF DH Chipmunk Smaller rudder fitted

[T-21]

This is not widely known that the RAF Chipmunk fleet had smaller pointed rudders fitted when delivered in the WB to WD serial range. From about 1951 onwards they were all fitted with the larger rudder that we know today. WD321 which may have been the test aircraft. I presume the bigger area was for more "bite" in controlling the yaw in spin recovery. No pictures but somebody might have diagrams from an early maintenance manual ?

[Dan Winterland]

It's a bit of a myth that the wide chord rudder was fitted to aid spin recovery. It's true there were a number of spinning accidents to the type on introduction, but the fix for this was the anti spin strakes and a change in the recovery technique. The wide chord rudder was principly fitted to give more rudder authority for aerobatics.

The myth is perpertrated by the fact that in the UK, spins are prohibited without the strakes and the new rudder. A mate owns a Chipmunk in Australia where no such restriction exists and spins his. He says there seems to be no difference between those which have both mods and those which don't.

[Dora-9]

Dan is (as usual) correct, the broad chord rudder had NOTHING to do with spin recovery. This was Mod H.104, published on 22.1.1951. The preamble states that this was to increase rudder authority during aerobatics and crosswind takeoffs & landings, as well as to reduce the required rudder input during protracted climbs - spin recovery is simply not mentioned. The "new" rudder was either fitted on the production line or retro-fitted to the RAF's active Chipmunk fleet. The large number already earmarked as non effective stock retained their narrow chord rudders, which explains why a large proportion of early Australian Chipmunks had this rudder.

However, given the distinct rumblings emanating from CASA, the situation regarding aerobatics being permitted in non-straked Chipmunks will soon change....

[Mandator]

However, given the distinct rumblings emanating from CASA, the situation regarding aerobatics being permitted in non-straked Chipmunks will soon change....

Dora 9 - Why?

[Brian Abraham]

The predecessor to CASA looked at the strake issue following a spin accident in the late 50s, early 60s, and came to the conclusion they were not needed. In some jurisdictions even the venerable Tiger suffered the indignity of strakes, thankfully not in Australia. That they make be readdressing the issue may be a reflection of the modern breed brought up on a Piper/Cessna diet, where the modern day aviator wouldn't know what a spin was.

[T-21]

Thanks chaps for all the feedback . At least we know the correct reason for the broader chord rudder.

[Mandator]

Brian: Interesting. In the UK strakes are mandatory on the Chipmunk, although under certain circumstances a Tiger can be flown without them.

[Flap40]

I used to fly G-APLO / WD379 in the early 1990's and that had strakes but with the small rudder and we regularly used to spin it.
There was nothing in the flight manual on board that aircraft which prohibited spins.

[bcgallacher]

When I did my PPL courtesy of a Flying Scholarship in the 1960's at Perth the RAF insisted that the only aircraft that could be flown by cadets had to have both anti-spin strakes and the broad chord rudder. As I recall the spin characteristics were variable - it never seemed to spin the same way twice and on one occasion it scared the hell out of me with an extremely slow response to the normal recovery action.Around about that time the school lost a Chipmunk - luckily without serious injury -when it spun in while flown by a very experienced instructor. In spite of this it was a lovely aircraft to fly.