Parlous State of Spin Knowledge and Training

[djpacro]

CASA's Part 61 MOS requires this as essential knowledge for all pilots:

"Differentiate between a spin and a spiral dive in a light aeroplane and describe the standard recovery technique for each manoeuvre."

Yet I regularly encounter pilots and students who do not know the "standard" recovery technique for a spin.

 

Worse, I regularly encounter flight instructors and trainee flight instructors who also do not know the correct recovery technique - either that "standard" one or, more importantly, the one described in the flight manual of the type they fly. They are required to have a spin flight activity endorsement so a greater underpinning knowledge and competency. Recently, a flight examiner failed two flight instructor candidates on the ground component of their test because they described dangerously incorrect spin recovery technique in their theory briefing.

 

CASA helped recently with their AC 61-16 Spin avoidance and stall recovery training

 

The FAA's Airplane Flying Handbook, Chapter 5: Maintaining Aircraft Control: Upset Prevention and Recovery Training has excellent information.

 

To go a bit deeper into the subject for much of the underpinning knowledge required by CASA for a spin endorsement I suggest starting with NASA TN D-6575 SUMMARY OF SPIN TECHNOLOGY AS RELATED TO LIGHT I GENERAL-AVIATION AIRPLANES by James Bowman (I worked with Jim for a while). It is engineering stuff however fairly light reading.

 

Edited January 25 by djpacro
minor typos

[djpacro]

19 hours ago, djpacro said:

To go a bit deeper into the subject for much of the underpinning knowledge required by CASA for a spin endorsement I suggest starting with NASA TN D-6575 SUMMARY OF SPIN TECHNOLOGY AS RELATED TO LIGHT I GENERAL-AVIATION AIRPLANES by James Bowman (I worked with Jim for a while). It is engineering stuff however fairly light reading.

 

"The way in which the mass of an airplane is distributed between the wing and fuselage is the most important single factor in spinning because it determines the way in which the airplane, while spinning, responds to control movements, especially to elevators and ailerons. An airplane rotating in a spin can be considered to be a large gyroscope. Since there are mass and angular rotation about all three axes, inertia moments are produced about all three axes."

 

Fig 3 shows the balance of pitching moments in a spin which basically determines the angle of attack in the fully developed spin. The nose down aerodynamic moments vs the nose up moments from inertia.

Worth repeating NASA's statement: "The way in which the mass of an airplane is distributed between the wing and fuselage is the most important single factor in spinning ..." NASA is not referring to CG there but to the moments of inertia.

 

"In order for the airplane to recover from the spin, the equilibrium must be broken, and this is normally accomplished by changing the aerodynamic moment by moving a control or combination of controls that can cause the greatest antispin moment. .......

The loading of the airplane dictates the control movements required for recovery. ..... Deflection of the rudder to oppose the spinning rotation directly is always recommended, but in many cases, it is not adequate to provide recovery. For the wing-heavy loadings, down elevator is the primary recovery control."

 

"Three factors are of almost overriding importance with regard to spin and recovery characteristics: (a) The relative distribution of the mass of the airplane between the wing and fuselage, which is commonly expressed in terms of the inertia yawing-moment parameter, a nondimensional factor relating the rolling and pitching moments of inertia (b) The tail configuration, which must provide damping for the spinning rotation and the rudder power for recovery and which is commonly evaluated in terms of an empirically determined tail-damping power factor (c) The density of the airplane relative to the density of the air, which is commonly expressed in terms of the relative-density factor"

 

We don't need to concern ourselves with effects of air density so just moments of inertia and tail design.

 

Some aircraft types have weak nose down pitching moments so the nose up inertia moments drive them towards a much higher angle of attack in the spin. NASA has shown this for the Grumman AA-1 

 

[facthunter]

Stabilised  spin pitch attitude. Not angle of attack.  You can just look at some designs and Know they will be bad in the spinning state. Small rudder often shielded made worse by fin and rudder sweepback and short rear moment arm. When I started ALL pilots did spins in spinnable planes. Now most people just speculate what it is and how it's managed best. One thing is for sure. At a normal circuit height, No spin will be recoverable so best Don't get into one  in those circumstances. Nev

[BrendAn]

With a rag and tube plane like my xair or a thruster is a spin even possible. With all the drag and lightweight.

[facthunter]

I can't see why not. Older planes had no trouble spinning and spiralling and slipping as well if they had little Keel surface.   Your light draggy plane may well have a spin you could survive as it's Rate of Descent RoD will be a lot less but your seat design might injure you badly if it's lacking ability to absorb energy.  Nev

[BrendAn]

1 hour ago, facthunter said:

I can't see why not. Older planes had no trouble spinning and spiralling and slipping as well if they had little Keel surface.   Your light draggy plane may well have a spin you could survive as it's Rate of Descent RoD will be a lot less but your seat design might injure you badly if it's lacking ability to absorb energy.  Nev

I was told that Steve Cohen designed thrusters to be spin resistant. Does not mean it's true though.

Edited January 26 by BrendAn

[facthunter]

I would say that's right. Not enough back stick available. Makes them harder to get the 3 point landing right.  High wing is also pendulous. Nev

[djpacro]

2 minutes ago, BrendAn said:

I was told that Steve Cohen designed thrusters to be spin resistant. Does not mean it's true though.

Spin resistant does not mean that it won't spin nor that, if it does, it will recover.

A spin about 2 minutes into this video. Just because it recovered from this spin does not mean that it will recover from other spin modes.

J 

[facthunter]

It is said Spin resistant planes are hard to recover from spins. I haven't worked that one through yet.  Nev

[djpacro]

A spin resistance standard was added to the FAR 23 airworthiness design and testing requirements in 1991. The Columbia 300 was certified to this standard in 1998. It carries clear warnings in the POH "Do not attempt to spin the airplane under any circumstances ..... During the flight test phase of the airplane's certification, spins were not performed. It is not known if the airplane will recover from a spin."

 

The Cirrus was certified with an Equivalent Level of Safety by having the CAPS. Perhaps considered to have a spin resistant wing design as they followed some guidance from NASA with this. Anyway, the Cirrus spin certification and some spin testing done for EASA is a longer story for perhaps another day as it is slightly off topic.

[djpacro]

One of the gems is Cessna's booklet which was published back in the '70s to counter misinformation about spinning. About time that it was promoted again.

https://mikeklochcfi.files.wordpress.com/2018/03/cessna-spin-manual.pdf

 

It has much general information (obviously a lot of information speciific to the Cessna so be careful about generalising) too with information such as:

"For the purpose of this discussion, we will divide the spin into three distinct phases. ..... Here, in the entry phase, recovery from or prevention of the spin is as simple as normal stall recovery since, in fact, at this point that's all we are really faced with. .... 

During this incipient phase, spin recoveries in those airplanes approved for intentional spins are usually rapid, and, in some airplanes, may occur merely by relaxing the pro-spin rudder and elevator deflec- tions. However, positive spin recovery control inputs should be used regardless of the phase of the spin during which recovery is initiated. ....

 

Due to the attitude of the airplane in a spin the total motion is made up of roiling and usually pitching motions as well as the predominate yawing motions. Movement of the airplane flight controls affects the rate of motion about one of the axes. Because of the strong gyroscopic influences in the spin, improper aerodynamic control inputs can have an adverse affect on the spin motion. ....

 

Some of the additional factors which have (or may have) an effect on spin behavior and spin recovery characteristics are aircraft loading (distribution, center of gravity and weight), altitude, power, and rigging.

 

Distribution of the weight of the airplane can have a significant effect on spin behavior. The addition of weight at any distance from the center of gravity of the airplane will increase its moment of inertia about two axes. This increased inertia independent of the center of gravity location or weight will tend to promote a less steep spin attitude and more sluggish recoveries.

 

Forward location of the c. g. will usually make it more diffi- cult to obtain a pure spin due to the reduced elevator effectiveness."

 

I mentioned that effect of moment of inertia in another thread. Pilots get to determine weight and CG but, as Cessna stated above, the increased moment of inertia is independent of weight and CG. eg fuel in outboard wing tanks vs inboard wing tanks. However, we usually deal with small changes in weight and CG associated with a large change in moment of inertia. Pilots have been be caught out with small ballast weights added near the tail to adjust CG with no consideration given to the moment arm squared and the big increase in moment of inertia.

 

What some pilots (or the accident investigators) have observed to be the result of a small CG change was actually caused by a change in moment of inertia.

 

NB: the USA FAA supported this booklet with their bulletin to all flight instructors back then. 

 

Edited January 29 by djpacro
typos

[facthunter]

I'm not too happy with the full forward stick. On many planes you can end up spinning inverted that way and "centre controls without delay" once the desired result has been achieved, must be emphasised. Once you are unstalled you can't be spinning. The plane is controllable in the normal way but you might be in an attitude you have to do something positive about without delay.  Nev

[djpacro]

I noticed this site promoting CASA's Flight Instructor Manual. One would expect CASA’s Flight Instructor Manual to be a reputable source of correct information on spinning however ATSB Investigation AO-2017-096 of 22/5/2019 found otherwise.

Quote

Incorrect guidance

While the ATSB assessed that the instructor’s incipient spin recovery knowledge was consistent with established guidelines and did not contribute to the accident, the investigation identified incorrect incipient spin recovery guidance provided by CASA.

The CASA publication Flight Instructor Manual, provides the following guidance for incipient spin recovery:

---

RECOVERY FROM THE INCIPIENT STAGE

As soon as the aeroplane has stalled and commenced to yaw take the appropriate recovery action. Increase power, apply sufficient rudder to prevent further yaw and ease the control column forward sufficiently to un-stall the aeroplane. Point out that if power is to materially assist recovery action it must be applied before the nose of the aeroplane has pitched too far below the horizon otherwise its use will only increase the loss of height.

---

 

Increasing engine power prior to an application of sufficient rudder to prevent further yaw and applying sufficient nose-down elevator un-stall the wings as described is inconsistent with established guidelines and manufacturer guidance.

 

The United States Federal Aviation Administration publication Airplane Flying Handbook, Chapter 5: Maintaining Aircraft Control: Upset Prevention and Recovery Training provides the following guidance, consistent with established guidelines, regarding spin recovery:

To accomplish spin recovery, always follow the manufacturer’s recommended procedures. In the absence of the manufacturer’s recommended spin recovery procedures and techniques, use the spin recovery procedures in the spin recovery template. If the flaps and/or retractable landing gear are extended prior to the spin, they should be retracted as soon as practicable after spin entry.

 

Spin recovery template:

1. Reduce the Power (Throttle) to Idle
2. Position the Ailerons to Neutral
3. Apply Full Opposite Rudder against the Rotation
4. Apply Positive, Brisk, and Straight Forward Elevator (Forward of Neutral)
5. Neutralize the Rudder After Spin Rotation Stops
6. Apply Back Elevator Pressure to Return to Level Flight.

 

The handbook also provides further guidance regarding power use during spin recovery:

Reduce the Power (Throttle) to Idle. Power aggravates spin characteristics. It can result in a flatter spin attitude and usually increases the rate of rotation.

CASA advised the ATSB that this matter will be referred to Safety Education for review and correction as required.

When that ATSB report was issued “CASA has advised the ATSB that they have taken the following safety action …..” i.e. they reviewed the above text in the Flight Instructor Manual but took no action so they must believe it to be correct.

[LoonyBob]

On 26/01/2024 at 10:07 AM, BrendAn said:

With a rag and tube plane like my xair or a thruster is a spin even possible. With all the drag and lightweight.

Yes, Thrusters spin quite briskly...

[LoonyBob]

On 26/01/2024 at 12:09 PM, facthunter said:

It is said Spin resistant planes are hard to recover from spins. I haven't worked that one through yet.  Nev

The single engined tricycle Cessnas were an early form of spin-resistant aeroplane, although before that buzzphrase. BECAUSE they kept the CG so far fowards and used TE-stalling airfoils with stacks of washout, they don't have an adequate VS to recover from a developed spin, or even a steep incipient. The Cirrus is not designed with spins in mind, and was uncertifiable until political pressure was applied... from memory, BRS became a substitute for spin recovery...

[LoonyBob]

I consider the problem, in GA and RA, to be the lack of a spinnable trainer that is economically practicable. WTF do we not all do 3 hours with the GFA, where they have spinnable trainers and a great deal of currency on the manouvre??

[aro]

8 hours ago, LoonyBob said:

I consider the problem, in GA and RA, to be the lack of a spinnable trainer that is economically practicable.

Wasn't that the thinking behind the Tomahawk? Flying schools said we want a trainer we can teach spins in, so Piper built one.

 

Then the schools said "Oh! If you stall it it can spin, we don't like that" and didn't buy it.

[LoonyBob]

11 hours ago, aro said:

Wasn't that the thinking behind the Tomahawk? Flying schools said we want a trainer we can teach spins in, so Piper built one.

 

Then the schools said "Oh! If you stall it it can spin, we don't like that" and didn't buy it.

The Traumahawk empennage, in a spin, enters a non-destructive state of flutter (it's not true aeroelastic flutter; merely, excited by vortices shed from the fuselage, the top of the fin waves about 4" laterally, and the HS bends on it); which both scares the crap out of instructors, and causes cracking in the structure at the base of the fin (and who knows where else, if you keep it up?). Most won't do it in an incipient, and some allegedly won't do it at all; but several operators in SEQ have experienced it in the last 30 years, and taken spin training off their agendae.

WTF they used a T tail on a "spinnable" aircraft, I cannot begin to guess...

[facthunter]

 Fashion?  It just stresses the fin, Traumahawk?  Nev

[LoonyBob]

So described by student pilots, I am told!

 

[facthunter]

Too aeroelastic for ME. I only flew one once. It just didn't feel right. On T tails. the venerable B 727 T tail had 5 FIVE times the load in the tail that was expected when it was test flown with strain gauges fitted..   Nev

[djpacro]

If one believes CASA's Flight Instructor Manual one would believe that the recovery method from an incipient spin is different from a fully developed spin. Identify when one is no longer in an incipient spin and suddenly the recovery action is different. See my extract from Cessna's Spin Booklet above, repeated here:

"During this incipient phase, spin recoveries in those airplanes approved for intentional spins are usually rapid, and, in some airplanes, may occur merely by relaxing the pro-spin rudder and elevator deflections. However, positive spin recovery control inputs should be used regardless of the phase of the spin during which recovery is initiated."

 

The test pilots and engineers who write the bits ablout spinning in flight manuals follow FAA AC 23-8C FLIGHT TEST GUIDE FOR CERTIFICATION OF PART 23 AIRPLANES which defines the spin:

Quote

A spin is a sustained autorotation at angles-of-attack above stall. The rotary motions of the spin may have oscillations in pitch, roll, and yaw superimposed upon them. The fully developed spin is attained when the trajectory has become vertical and the spin characteristics are approximately repeatable from turn to turn. Some airplanes can autorotate for several turns, repeating the body motions at some interval, and never stabilize. Most airplanes will not attain a fully developed spin in one turn.

No mention of the word "incipient" at all in that document.

 

When the word "spin" or "spinning" is used in the AFM or POH then it simply means "a sustained autorotation" and use the method in that AFM/POH for spin recovery.

 

That is especially important for types not approved for intentional spinning as they have only been tested for recoveries from a spin of up to one turn.

 

Picking up that Cessna statement again: "During this incipient phase, spin recoveries in those airplanes approved for intentional spins are usually rapid, and, in some airplanes, may occur merely by relaxing the pro-spin rudder and elevator deflections." "may occur" ... well, of course, the spin behaviour is changing all throughout the incipient spin phase so don't expect that to work at the instant just prior to the established fully developed spin.

 

However, it is a good technique for aerobatic pilots, in a type approved for intentional spins, at the onset of autorotation to centralise the controls and close the throttle.

[LoonyBob]

The FAA flight test guide rests largely on RAeS/ARL and German data from pre-WW2; again, the FAA FTG is not a comprehensive first-principles study, but a guide for flight testing.

 

It is just this failure to distinguish between an incipient and full spin, that eroded the original Certification requirement to recover from a developed spin.

 

The Empire Air Training Scheme training material on spins and how to feed them, is much more comprehensive, but very hard to find! I repeat, I strongly recommend all RAAus pilots who have not practices deliberate spinning yet, to get the experience from a gliding club with an appropriate aircraft.

[Roundsounds]

On 30/1/2024 at 11:54 PM, LoonyBob said:

I consider the problem, in GA and RA, to be the lack of a spinnable trainer that is economically practicable. WTF do we not all do 3 hours with the GFA, where they have spinnable trainers and a great deal of currency on the manouvre??

There are airplanes like Citabrias, Decathlons, Cessna Aerobats, Robins and others available for spin training. The main issue I have with gliders being used for power pilot training is the lack of a throttle, I often find during spin training pilots miss setting  idle during recovery. It’s highly likely an unintentional spin will be in a situation with power applied.

 

It’s one thing to verbalise it during a briefing, but the proof is in the application. I usually arm the speed brake during stalling sequences in jet simulator training, following the recovery manoeuvre it’s often still armed. Stowing the speed brake is part of the standard Boeing stall recovery manoeuvre. The trainees might have recited the actions during the briefing or immediately prior to the exercise but often omit the step during the practice sequence. As a human factors consideration I fear power pilots would omit setting idle power if spin training was only conducted in a glider. 

Edited February 22 by Roundsounds

[facthunter]

That's a valid point, and gliders have very high  aspect ratio wings but you have to use what is available. While spins don't load airframes much a mucked up effort at recovery CAN so I'd rather have stronger planes to do that training in. A well executed recovery will pull 2.5 G but if you hit a gust at the same time you might double that on that occasion.  Nev