snap rolls and other flick manoeuvres

[LeadSled]

---the AFM actually calls them "anti spinning strakes"

Dora -9,
Good one.
A case of a technically incorrect term becoming the norm, and used, not only by me, without further consideration.
Still on the Chipmunk, in the UK it never had the reputation for spin recovery problems, as it developed in Australia. As a matter of interest, the VH- Chipmunk I owned for some time did not have them fitted --- and I did plenty of spinning and aero's in said aircraft --- all in accordance with the DCA "Little Black Book", aka AFM.

At least one of the fatals was not the aircraft's fault, it was a coin jamming the controls, and doing to Arthur Kell what 4 years of efforts by the Luftwaffe and German AAA could not do.
Tootle pip!!

[roundsounds]

ATSB report on VH TSG makes specific comment on flick manoeuvres being prohibited in Tigers.
See page 48 of the report.
https://www.atsb.gov.au/media/575071...26%20final.pdf

[Centaurus]

Publicly-available video recordings showed that some Australian commercial Tiger Moth
operators conducted aerobatic flick (otherwise known as ‘snap’) and tailslide manoeuvres,
which were prohibited by the Type Design Organisation

That staggers me. In the mid 1950's I was involved as a flying instructor on Tiger Moths and Wirraways at RAAF No.1 Basic flying Training School at Uranquinty NSW.

Aerobatics were taught shortly after first solo on type. Certainly tail slides occurred inadvertently during aeros; but never on purpose. Not only were they a most uncomfortable manoeuvre, but an unnecessary one from the training point of view.

Flick rolls in level flight were demonstrated in the Wirraway as a means of entry into a high speed stall. This could happen if you pulled too hard during entry and recovery from a loop and that included if you pulled too hard during recovery from a dive bombing or air to ground gunnery.

But deliberate flick rolls in a Tiger Moth? No way was that ever a training sequence. A man would be a courageous idiot to deliberately try that in a Tiger.

[Sunfish]

Why the hell wouldn't the engineer in question automatically have gone for a rolled thread on the tie bar and perhaps shot peening of the surface to boot? A cut thread is only as good as the operator. I should know, I cannot cut a good thread to save my life. Also from memory, stainless has not as good a fatigue life as alloy steel (someone correct me). Also what is wrong with using a thread grinder?

As for an upper bolt with wrong (insufficient) grip length WTF?

I would have thought a Tiger today should be stronger than the 1930's version.

[CHAIRMAN]

Sunny, original 1930's rods I have seen were lathe cut - tool withdrawn in the last couple of threads to reduce stress points, and nice radius tool point. Problem with rolled threads is they increase the diameter of the material, so probably not suitable for manufacturing the rods in the 30's, which are a close tolerance in the fitting. Anyway the photos of the failed tie rods I've seen seem to indicate the thread as neither rolled or ground.
Surprise in the report was the use of shorter grip length bolts in the upper holes of the wing fitting - hadn't heard of that one before.

[actus reus]

Chipmunk spinning

As for the T10, it originally had a narrow chord rudder which meant that there was a strong possibility that the rudder would be 'blanked' during a fully developed spin.
My research (and I bow to Chipmunk owners/ experienced fliers of same both of which I am not), seems to show that the production version had a broad chord rudder fitted and anti spin strakes.
DORA-9 is correct for those I have spoken to unanimously agree that the stick force required (forward stick) to recover from a fully developed, upright spin is large. Darrol Stinton (the legendary test pilot/engineer) said that the stick force required was 28ftlbs which was nearly 3 times the force that the FAA allowed.
End result; FULL forward stick and hang on. Mind you, that is what I have used in a large number of spinning events in many different aeroplanes. I was taught that as the 'way' regardless of the aeroplane.
Delightful flight controls on the Chippy I will admit. Beautiful aeroplane.

[Dora-9]

actus reus:

As for the T10, it originally had a narrow chord rudder which meant that there was a strong possibility that the rudder would be 'blanked' during a fully developed spin.
My research (and I bow to Chipmunk owners/ experienced fliers of same both of which I am not), seems to show that the production version had a broad chord rudder fitted and anti spin strakes.

A quick Chipmunk history lesson, if I may.

All UK-built Chipmunks, be they T.10's, T.20's or Mk.21's, left the factory without strakes and with narrow chord rudders. A broader-chord replacement rudder (easily detectable by the distinct kink at the bottom of the trailing edge) was developed/approved in 1951 but it appears to have been retrofitted over the ensuing few years to the existing fleet commencing in 1953 (i.e. post production). It should be stressed that the larger rudder was intended to improve rudder authority during aerobatics and cross-wind take offs & landings, as well as reducing rudder load during protracted climbs. Despite that hoary old myth, it had NOTHING WHATSOEVER to do with improving spin recovery. The unintended consequence is that it may have made spin entry easier. Keep in mind that by 1953 a large number of RAF Chipmunks were already ear-marked for disposal (with the disbandment of RAF Reserve Command) and these aircraft never received the broad-chord rudder, which explains why all of the 60 odd ex RAF Chipmunks that initially came to Australia (deliveries commencing in 1956) still had the narrower rudder.

The strakes were fitted quite quickly to the existing RAF fleet in 1958, and certainly were intended to improve spin recovery.

With three exceptions (two Portuguese OGMA and one Canadian-built) all current Australian Chipmunks are UK-builds, and all four possible combinations of "tail; feathers" are present:
Narrow rudder/no strakes
Narrow rudder/strakes
Broad rudder/no strakes
Broad rudders/strakes.

I hope this clarifies the story.

Cheers.

[djpil]

......FULL forward stick and hang on. Mind you, that is what I have used in a large number of spinning events in many different aeroplanes.

that will result in a nasty surprise in some types.

I was taught that as the 'way' regardless of the aeroplane.

an example of the lack of adequate knowledge that I have observed over the years and, in my opinion, one of the potentially dangerous deficiencies in the standards for an instructor spin training endorsement.

As the subject is snaps - it can be fun to transition from a positive to a negative snap as one twirls around.

[roundsounds]

As djpil says, full forward stick and hang on is not a scientific or accepted method of spin recovery. Anyone who teaches that is playing Russian roulette with the lives of their trainees and anyone unfortunate enough to be a pax with them.
An understanding of what's going on aerodynamically is necessary, if you've got that knowledge you will understand why "full forward stick and hang on" is simply wrong! Recovery technique differs for aircraft types, you won't last long in a Pitts or Yak 50/52 using that method. You'll transition quite quickly from an upright to inverted spin in these types.
The NASA Spin Recovery technique is about as close as you can get to a "standard recovery" as and involves:
1. Power -- idle
2. Ailerons -- neutral
3. Rudder -- full opposite to yaw
4. Elevator -- forward as far as necessary to terminate rotation
Some spins may require relaxing back elevator pressure; others may require full forward elevator. If you reach the forward control limit, hold the above inputs until rotation stops, then:
5. Rudder -- neutral
6. Elevator -- return to straight and level