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Spinning advice from 1936

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Spinning advice from 1936

Old 20th Jun 2020, 17:19
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Spinning advice from 1936

One of our former contributors on the Brevet thread which once enthralled so many Pruners filed away his 1936 notes on spinning, now his daughter has posted it for others. I understand spinning is no longer part of the PPL and that aircraft are much more predictable -- but most will spin and I think any pilot (or in my case very much EX-) pilot will find food for thought. Hals und Beinbruch!
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Old 20th Jun 2020, 17:48
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The spin recovery procedure taught on RAF Chipmunks in the 1960s closely follows the method in the 1936 notes except in one aspect: having applied full rudder against the spin, after a pause the stick is moved progressively (rather than abruptly) forwards until the spin stops. Perhaps the Chippie's spin characteristics are different from US pre-war trainers. The PN says max number of turns permitted was 8, but IIRC we were taught to recover after not more than 5 turns (presumably because the a/c would continue spinning for a turn or two before recovery took effect).

Pilot's Notes: Chipmunk T Mk.10
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Old 21st Jun 2020, 07:30
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Up to and during WW2, a 'Standard Spin Recovery' was used for all types. It was not long after WW2 that it was acknowledged the results were variable depending on type. And it was the Chipmunk's reluctance to come out of a spin which prompted one of the first variations on the standard recovery. The type acquired the spin strakes and wider chord rudder (and in the UK spinning is prohibited on the type without these) as well as the gradual movement of the control column after a brief pause, which was generally considered to be 2 seconds. And with the introduction of jets with swept wings and greater wing masses, the need for a type specific spin recovery was all the more apparent. It should be made clear that there is no standard spin recovery - the recovery you should use is the one from the types's Pilot Notes/POH/AFM. And no other!
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Old 21st Jun 2020, 10:22
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The Chippy's venerable ancestor the Tiger Moth had spin strakes added for the same reason, I think it was before it entered RAF service. I vaguely remember that one European country didn't require them, but another (Holland?) required even bigger strakes.
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Old 21st Jun 2020, 11:25
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Neither Canadian made Tiger Moths I have flown had any spin strakes, I understand it to be a national choice as to require them of not.

Yes, the optimum spin recovery technique will vary by type, and is usually published, even for some non spin approved types. I've never flown a Chipmunk, so have no comment on that type, but I can say that moving the controls forward progressively on some types will delay the recovery. I erred into doing this while spin testing a modified Cessna 206, and had a heck of a ride. For the next spin, after recalling the wording of the POH, I moved the control wheel "briskly" forward following rudder application, and it recovered nicely.
Take training, and read the applicable information for the type.
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Old 21st Jun 2020, 16:20
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Darrol Stinton, ‘Flying Qualities and Flight Testing of the Aeroplane’ writes:

“Attempting to make a general rule about spinning is like making a rule about a shark: there is no rule”. Darrol Stinton goes on to outline the recovery from a spin using the term;

Standard Recovery Drill or Procedure

(1) Throttle closed

(2) Ailerons neutral

(3) CHECK that you are in a spin, not a spiral, and also the DIRECTION of rotation.

(4) Stick BACK (i.e. conventional elevator-UP)

(5) Rudder FULL against the indicated direction of turn

(6) PAUSE (say long enough to count one hundred-two hundred-three hundred) allowing the rudder to bite and take effect. THEN:

(7) Move stick progressively FORWARD (elevator NOSE-DOWN) until rotation stops.

(8) EASE OUT of the ensuing dive.

The above is the technique applied when testing an aircraft for certification and for the most part there's little more than lip service to this published in the POH. It is a matter of required compliance on the part of the manufacturer.

I've been concerned for many years with regard to the language used, such as; "briskly", "pause" and "progressively" without any of these words being defined. Briskly could, in the heat of the moment, be applied too much and tip the aircraft inverted. A pause could be anything in a high adrenaline moment and delay the recovery too long similarly the term progressive. Stinton does offer some definitions but few manuals do so.
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Old 21st Jun 2020, 16:32
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Looks like he forgot a step:

(7.5) Centralise the rudder.


I also forgot that step in my first spin in a Slingsby Firefly, it very neatly transitioned into a spin in the opposite direction.
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Old 21st Jun 2020, 23:02
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Originally Posted by Fl1ingfrog View Post
Darrol Stinton, ‘Flying Qualities and Flight Testing of the Aeroplane’ writes: ....

(6) PAUSE (say long enough to count one hundred-two hundred-three hundred) allowing the rudder to bite and take effect. THEN:

(7) Move stick progressively FORWARD (elevator NOSE-DOWN) until rotation stops. ......

The above is the technique applied when testing an aircraft for certification and for the most part there's little more than lip service to this published in the POH. It is a matter of required compliance on the part of the manufacturer.
Back in 1936, NACA Tech Note 555 stated:
"The recommended operation of the controls for recovery from a spin, which presupposes that the ailerons are held in neutral throughout the recovery, is as follows:
1. Briskly move the rudder to a position full against the spin.
2. After the lapse of appreciable time, say after at least one-half additional turn has been made, briskly move the elevator to approximately the full down position.
3. Hold these positions of the controls until recovery is effected."

The latest NASA advice is in their TN D-6575 which states:
"It is important to note that when these results were obtained in 1935, the airplanes of that day probably were in the zero loading condition previously discussed and today this recovery technique would apply only for airplanes that have similar loadings. As previously pointed out, the control technique required for spin recovery is primarily dictated by the mass distribution in the airplane. Therefore, for airplanes of different loading conditions, this control technique recommended in 1935 would probably not apply.
....
The mass distribution and the relative density determine the tail configuration requirements and the control technique required for recovery.
....
The rudder is generally the principal recovery control, but for positive (wingheavy) loadings or for recovery during the incipient spin, the elevator can also be an important recovery control and can reduce the rudder power requirements.

Experience has shown, however, that relying on the elevator is dangerous because it might become ineffective for fully developed spins, flat spins, or cases in which the mass distribution has been changed or the center of gravity has been moved behind the normal rearward limit because of changes in loading of the airplane due to growth or operational factors."

I won't go back to the time when Stinton wrote his book but the current FAR 23 Flight Test Guide has: "Recoveries should consist of throttle reduced to idle, ailerons neutralized, full opposite rudder, followed by forward elevator control as required to get the wing out of stall and recover to level flight. For acrobatic category spins, the manufacturer may establish additional recovery procedures, provided they show compliance for those procedures with this section."

Originally Posted by Fl1ingfrog View Post
I've been concerned for many years with regard to the language used, such as; "briskly", "pause" and "progressively" without any of these words being defined. Briskly could, in the heat of the moment, be applied too much and tip the aircraft inverted. A pause could be anything in a high adrenaline moment and delay the recovery too long similarly the term progressive. Stinton does offer some definitions but few manuals do so.
As you can see, NACA explained the "pause"; "briskly" is about the rate of movement not the amount (which must also be specified) so that seems clear to me; "progressively" also seems clear to me. Pilots should know enough theory to understand why those words are used - Australia's CASA has such info required in their Manual of Standards for underpinning knowledge in the spin training.
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Old 21st Jun 2020, 23:13
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I had some great arguments with the late, very great Darrol Stinton about spinning from time to time.

Sadly his family last year blocked that book (and his other two) being revised and republished. Their reasoning completely escapes me.

G
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Old 21st Jun 2020, 23:37
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Spin strakes were not required on Oz Tigers or Chipmunks, never had issues spinning either myself. Some were of the opinion that the Chippy earned an unsavory reputation because of the length of time it took to recover, instead of waiting for the recovery action to take effect folk would become alarmed that recovery was taking too long and then start trying alternative methods - which would not work. The Tiger spin was rather benign I thought and used to enjoy it, anyone with an insight into why strakes were fitted?
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Old 22nd Jun 2020, 02:51
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Briskly could, in the heat of the moment, be applied too much and tip the aircraft inverted.
I have found the term very useful in understanding that being unenergetic about forcing the nose down promptly will delay the recovery, which could mean non compliance with the requirement that the single engined plane be recovered in not more than one additional turn. Yes, it is possible to get the nose too far down in some types, at some C of G positions. Too far down, will delay recovery a little, but more importantly, will result in a serious dive during recovery. If, at any point while flying a certified plane, you push the nose down so briskly as to end up unintentionally inverted, you need more basic flying practice.

The recovery of the Cessna Grand Caravan, for example, is vastly different at both C of G extremes, yet Cessna had to publish one procedure which works in all cases, hence "briskly". They condition the term with "... Far enough to break the stall.", and advise the pilot that "Full down elevator will be required at aft center of gravity loadings to assure optimum recoveries.". This, I can assure you is true! I had to briskly apply and then hold full nose down elevator, yet the nose would not go below the horizon for the first half a turn. But, using the Cessna procedure, the plane recovered compliantly, which was what I was testing to confirm.

So after spin testing a dozen or so types, the thing I have learned the most, is to read what the manufacturer published in the flight manual, and do that.
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Old 22nd Jun 2020, 06:39
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Spin strakes were not required on Oz Tigers or Chipmunks, never had issues spinning either myself. Some were of the opinion that the Chippy earned an unsavory reputation because of the length of time it took to recover, instead of waiting for the recovery action to take effect folk would become alarmed that recovery was taking too long and then start trying alternative methods - which would not work. The Tiger spin was rather benign I thought and used to enjoy it, anyone with an insight into why strakes were fitted?
They were fitted soon after the type's introduction after a number of accidents. The issue was determined to be the blanking of the rudder by the tailplane at high angle of attack. The strakes create a vortex which flows over the rudder re-energising the airflow to make it more effective. Other types such as the Tiger and Miles Magister had them. At about the same time, a wide chord rudder was fitted. This was not to improved spin recovery, but to improve handling during aerobatics. But somehow the two got included together in the restriction.

The entry to the spin in those days was usually from the stall, whereas when I was instructing on the RAF's Chippys, we entered from a positively entered semi-flick manoeuvre with full rudder shortly followed by full up elevator applied at 50 knots. This led to a very stable nose down spin which recovered quite rapidly. I flew a number of spin entries from the stall (not all intentional!) which led to a slower, flatter spin which took far longer to recover. I suspect this flatter spin prompted the introduction of the strakes.
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Old 22nd Jun 2020, 06:57
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And as for elevator movement, it really depends on the type. When the Bulldog entered RAF service, it used the Beagle Pup's recovery (Similar to the Chipmunk's) which was reasonable considering it the Bulldog was designed from the Pup. However, they were very different types. the Bulldog was heavier, had more span and that enormous canopy. And several were lost in spinning accidents quite soon after it entered service. It was only after one recovered after the canopy was jettisoned that it was realised that the huge canopy was blanking the rudder. From then, the recovery was changed to a very positive elevator input described as "move the control column firmly forward until the spin stops" which was almost akin to a bunt. This fixed the issue by forcing the rudder into the clear slipstream.

The danger of using the wrong techniques is highlighted by the accident report into a Slingsby Firefly being flown by two current Tucano students where it was postulated they failed to recover from a spin by the application of a technique which wasn't the one recommended in the Firefly POH.
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Old 22nd Jun 2020, 11:56
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Fl1ingfrog wrote:
Briskly could, in the heat of the moment, be applied too much and tip the aircraft inverted. A pause could be anything in a high adrenaline moment and delay the recovery too long
Too true! I found my first spin a high adrenaline moment even with a highly experienced ex-CFS instructor beside me (Victa Airtourer, 1965). Of course I knew what was coming but it was still a shock when the aircraft seemed to stop in a gentle turn, lurched sideways and downwards and began spinning. Anyone without spin training has no chance, as seen a couple of years ago when an ex-airline captain with ten times my number of hours spun his C152 off a steep turn with fatal result. About that time, following a fatal stall-spin in a Tiger Moth, someone even suggested in this forum that Tiger Moth aircraft might be inherently dangerous ... too right they are, unless their pilots had been taught to recognise the incipient spin and of course to recover from it. Like Megan I found the TM a docile beast and a superb teacher, as was her successor the Chipmunk.

I remember that individual aircraft can also be different. Tiger Moth DP would recover from a developed spin in three-quarters of a turn, but IT needed seven-eighths. Maybe because DP was rigged to 4.5 degrees incidence, while IT was rigged to the minimum 4 degrees in the hope it would go faster (it didn't). Maybe because DP was built by DH in 1940, while IT was built by Morris Motors in 1941. Of course the old warhorse had so many bits and pieces that inconsistencies were inevitable, a tradition nobly followed by the Tucano according to the rueful engineers on the Mil Aviation forum.

Interesting that Canadian TMs had no strakes, maybe unnecessary because they had canopies over the fiendishly cold open cockpits, increasing the side area?
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Old 22nd Jun 2020, 13:47
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Anyone without spin training has no chance, as seen a couple of years ago when an ex-airline captain with ten times my number of hours spun his C152 off a steep turn with fatal result.
Well, honestly, for a C152, letting go after doing whatever you did to enter a spin, and it will probably find it's way out on its own, with enough altitude. It is noteworthy that aerodynamically, the C152 is identical to the Aerobat versions, which can be recovered from a six turn spin (not as much fun as it sounds). I am aware of fatal spins in C150/152's from altitude, I have never understood how the fatal part was accomplished.

And, recall that the certification standard for single engine planes also requires that it be impossible to create an unrecoverable spin with any use of the controls. So, with enough altitude, and any attempt to either let go, or recover, a 152 should come out.

Though I am a strong proponent of spin training for every pilot, I reluctantly agree that most accidental spins are entered at altitudes too low for a recovery anyway. That fact that a few pilots carelessly spin and die in an unrecoverable situation does not mean that is should not be trained - at least to an awareness level.

I only spun the Canadian Moth a couple of times, about 40 years ago, but nothing stuck in my memory as being unusual, other than we did it on skis rather than wheels. The Moth I check flew a few years ago handled delightfully, though as they were maintenance check flights, post rebuild, I only stalled it, no spins.
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Old 22nd Jun 2020, 15:05
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it will probably find it's way out on its own, with enough altitude.
Agreed, but not from 400ft it won't, which was the estimated height from which the 152 was doing photography. I'm well past it now but I still think the benefit of spin training is to raise the awareness level, as you say -- to recognise the situations in which it can occur, and the wing-drop before the spin itself. From fading memory, with full power, lowered nose and rudder an alert pilot might have caught the earlier 150 just in time from that situation but it would have been a close thing.

Our Aerobat frightened its owners one day, fortunately from 4000ft. I thought it seemed reluctant to recover after four turns so we filed a report with the CAA. Darrol Stinton duly arrived complete with parachute and passed it as normal as long as the manufacturer's procedures were followed. A great guy who gave me great encouragement ... he didn't disagree when I said I thought it was a horrible thing anyway, how can you do aerobatics with a steering wheel
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Old 22nd Jun 2020, 15:17
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I think another advantage of having done spin training is to help a pilot to be more tolerant of the 'startle effect'. It is one of the few PPL manouevres (as it used to be) that feel genuinely alarming the first time you experience it.
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Old 22nd Jun 2020, 21:17
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"I'm well past it now but I still think the benefit of spin training is to raise the awareness level, as you say -- to recognise the situations in which it can occur, and the wing-drop before the spin itself.! (Geriavaitor)

I entirely agree. Spinning itself is fine as a demonstration, but the main point is to get pilots to recognise when the aircraft is about to bite you and spin if you don't do something to sort it !
In sailplanes we fly close to the stall much more frequently than power pilots, so I spent a lot of time with gliding pupils flying near the stall, feeling the buffet and general sloppiness of controls so an almost automatic recovery to normal was likely even when distracted.

(When at height in wave, playing around like that, sometimes letting a wing drop and then picking it up with rudder was a good exercise to help develop confidence and some finesse. Some two seaters can do a fair 'falling leaf' that way. I know picking the wing up with rudder is no longer taught routinely, but at height, in the right conditions, it's still a useful exercise.)
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Old 22nd Jun 2020, 21:46
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Originally Posted by Pilot DAR View Post
..... I am aware of fatal spins in C150/152's from altitude, I have never understood . ....
Everyone who spins Cessnas should read this
https://www.kevincfi.com/files/pdf/m...%20Cessnas.pdf
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Old 22nd Jun 2020, 23:58
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Cessna probably more than any other manufacturer has sought to inform as the above link shared by djpil demonstrates.

In truth very few pilots spin aeroplanes, many do not want to and physiologically find it insufferable. Those of us who spin a lot either as part of aerobatics or as instructors can take things too much for granted and slip into debating the science of it all. This is why pilots such as Gene Beggs and Eric Muller sought to give the ordinary Joe the get out of trouble technique: shove hard against the peddle giving the most resistance and let go of everything else. This works whether your upright or inverted. They never advocated this as a primary technique although many accuse them of doing so.

The Language used in many POH in my view is important. Words in the ear of those experienced pilots who are used to recoveries from unusual attitudes can have a very different meaning in the ear of the pilot not so experienced in all this. The aeroplane does not stall by itself in fact it will not. It is the pilot who stalls and spins not the aeroplane. The "startle" factor followed by disorientation can cause the human to do all sorts of strange things whatever enforced training they may previously have been given. The mandatory PPL spin training given to me for pre 1st solo was probably worthless. At a speed above the stall the pro-spin rudder pedal was jammed hard against the floor followed by the hand control then being yanked back hard against the stop. The nose pitched up pointing vertically towards Mars before going seemingly inverted before the nose dropped and we entered the spin. It was usually necessary to keep pushing the rudder hard to maintain the spin. For me this was all fun and increased my confidence in the aeroplane immensely. For others it was the last time they would fly.

Last edited by Fl1ingfrog; 23rd Jun 2020 at 00:14.
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