CG and spins

[moorea21]

Hi,

This question may not be in the right place, maybe even a different forum altogether would be better? If so, please advise.

I read in Jeremy Pratt's 'Private Pilots Licence Course' that
'A forward CG position makes an aircraft more reluctant to spin. A rearward CG makes the aircraft more likely to spin and the resulting spin will be flatter. A flatter spin i.e. one with a higher nose attitude is generally considered to prolong the recovery as well as making recovery more difficult..'

Why would aft CG make an aircraft more likely to spin?

Also, I was under the impression that aerobatic flight is often undertaken with max aft CG, for more control. If true, this seems to contradict the statement in quotes.

Can anyone help here?

Thanks

[Pilot DAR]

The more forward the C of G, the more aerodynamic effect is required from the horizontal stabilizer to maintain balanced flight (more nose up trim is required). Thus there is more down elevator available when you want to recover a spin at that C of G. At the aft C of G limit, the elevator is already trimmed down somewhat, so less range of elevator travel is available to apply nose down elevator control, and the airplane is balanced such that it is not so eager to lower the nose on its own (tail heavy), so more nose down elevator will be required.

In cruise flight, it is desirable to fly with a more aft C of G, as there will be less elevator deflection, and less drag - but the plane is also less spin tolerant.

While doing spin testing on a modified Cessna Caravan, I found the forward C of G spins were easily recovered, aft C of G spins were alarming. The plane recovered as required by regulation, but the spin was very flat, and full nose down elevator had to be held in for an extended period to get the nose below the horizon. If you spin behind the aft C of G limit, recovery from a spin is no longer assured for you, that really is the basis of the establishment of the aft limit.

[moorea21]

A very clear and comprehensive answer, thankyou. That makes it a lot clearer. So a forward CofG will point nose down in a spin, and there is plenty of elevator deflection left to recover because the elevator had to be trimmed upwards to push the tail down/nose up. Elevator for Aft CofG starts out trimmed down anyway, so you run out of deflection to recover from a spin, which will be flat because the aft CofG isn't weighing the nose down. Got it.

The Cessna sounds awful, did you have a parachute? I'm even more paranoid about weight and balance than I was now! Probably a good thing.

[cats_five]

At least some gliders will recover from a spin of their own if the CoG is far enough forwards. Apparently that happened with one of ours when someone pushing the weight limit spun it as part of a test flight. It was a single-seater.

[moorea21]

I have heard talk of a few planes that are allegedly impossible to spin; maybe some of these 'self recover' from the stall before hand, or just don't even drop a wing, ever? Never sure what to make of it when someone tells me something like that, I'm a total novice, so the fact that it sounds impossible to me doesn't mean much.

[bingofuel]

I believe the Beagle Pup had a large lump of metal ballast bolted to the tail or ventral to assist in spinning, clearly it would move the C of G rearwards when fitted.

[Maoraigh1]

"Also, I was under the impression that aerobatic flight is often undertaken with max aft CG, for more control."
For less stability, and more manoeuvrability?

[B2N2]

Easy explanation, consider a dart like used in the sport. Weight is in front to stabilize.
Visualize reversal, tail feathers in the back like normal but this time also the weight.
The weight is now after pushing the dart rather then forward and pulling it.
Destabilizing but increasing maneuverability which is pretty much defined as the ease of changing direction.
World class aerobatics pilots will know exactly where the sweet spot is for their aircraft.

As far as your fears about CG, consider that the aircraft has been designed and approved to be perfectly safe between the two CG limits.

[Genghis the Engineer]

"Also, I was under the impression that aerobatic flight is often undertaken with max aft CG, for more control."
For less stability, and more manoeuvrability?
Please don't use "less" "more" stability - it's meaningless without additional qualifiers.

Aft CG gives lower apparent static stability, lower manoeuver stability, generally less well damped short period longitudinal and lateral/directional static modes and Dutch Roll mode, it may well make the long period longitudinal mode better damped; the spiral mode is more complex because that is primarily dependent upon the RATIO of static lateral to directional stability.

It's the lower static and manoeuver stability values that tend to favour aerobatics, the reduced damping on the DR can be a nuisance, and the reduced SPO damping can interfere with accurate pitch control however.

A lot of that is trade jargon which most pilots don't need to know - but my important point is that to say something is "more" or "less" stable is generally over-simplistic and potentially misleading.

G

[B2N2]

G,

Not everyone is an engineer and you certainly don’t need that level of knowledge to enjoy flying as a private pilot.

Aft CG gives lower apparent static stability, lower manoeuver stability, generally less well damped short period longitudinal and lateral/directional static modes and Dutch Roll mode, it may well make the long period longitudinal mode better damped; the spiral mode is more complex because that is primarily dependent upon the RATIO of static lateral to directional stability.

This is certainly not an answer you should give an aspiring private pilot.
Its just meaningless gobblygook to them without any point of reference they can latch on to.

The instructor needs to teach to the level of the student.

[john_tullamarine]

This is certainly not an answer you should give an aspiring private pilot.

(Personal view, only)

Well, yes, and no.

One of the problems in this Industry is that pilots, in general, are trained to comparatively low levels of technical understanding. That's fine, so far as it goes as, the pilot's main thrust is to fly it rather than build, test and certify it. Unfortunately, the philosophy serves to encourage/perpetuate knowledge mediocrity, especially over recent decades where the whole thing at Industry training level has been dumbed down, in part due to cost minimisation desires.

Like many here, I know who G is and his background. One would expect that techo advice he gives will be both technically accurate and operationally pertinent. We are fortunate that we have a cadre of such folk in the PPRuNe sandpit for just those reasons.

Its just meaningless gobblygook to them without any point of reference they can latch on to.

So, yes, the pilot might be able to get away with minimal knowledge for the great majority of routine operations and history supports such a view. It certainly follows that there is an effort involved and required to improve one's knowledge level.

The instructor needs to teach to the level of the student

Might I suggest, with respect, that a more useful statement might be along the lines of "to teach to the present level of understanding held by the student with a view to improving that level of understanding" ?

Might I suggest that sound basic knowledge is valuable in its own right (we don't all need to have the PhD level of knowledge and understanding) ? There is nothing stopping the motivated listener/reader from either asking for additional explanation or going off and doing a little personal research to find out a bit more about the discussion. While, for folks who have no background, it might take a few hours to locate and read up on the basics, there is nothing in his post which is not readily amenable to research via the net - one of the most valuable consequences of the net's development, in my view.

A suitable level of basic understanding doesn't require the maths which goes along with the subject. Just the basic results and ideas are the main value for the typical pilot.

[Pilot DAR]

I have heard talk of a few planes that are allegedly impossible to spin; maybe some of these 'self recover' from the stall before hand, or just don't even drop a wing, ever?

The only plane I have flown which is impossible to spin, and placarded so, is the Ercoupe. It has no rudder pedals, with the rudder being coordinated to the ailerons. And, the elevator is limited, so in most cases, you cannot pull it into a stall. If you do get it to stall or spin, and I have done both in it, you cannot hold it in, it just recovers on it's own. Other aircraft I have flown have control travels such that in some configurations, a pitch down in a stall is hard to achieve. But, as the aircraft can still be stalled in some configuration,s and still can be spun, they would not be classified as spin proof. Other types of modifications (like STOL kits) advertise that they improve stall spin resistance, and for my experience they do, but the aircraft can still be stalled and spun, and when you finally get it there, it can be a bit more sudden (it just held on to the bitter end longer).

A spin, in a suitable aircraft, is a benign maneuver, and well worth learning. A spin in a non spin approved aircraft may demand skill, and/or exceed limits during recovery. The Cessna Caravan upon which I did spin testing with an external load, recovered exactly as the design requirement states that it must. though in doing it, I came very close to both speed, and G limits during the recovery from the dive. The Cessna 206 is similarly unpleasant to spin.

Forward C of G spin in the Grand Caravan:

https://www.youtube.com/watch?v=zjB_q7AIvDo

[Genghis the Engineer]

BN2 had you read my post more carefully I said....

Please don't use "less" "more" stability - it's meaningless without additional qualifiers.

<SNIP>
A lot of that is trade jargon which most pilots don't need to know - but my important point is that to say something is "more" or "less" stable is generally over-simplistic and potentially misleading.

G


Re: unspinnable aeroplanes. I flew a programme years ago on the French HM1000 Balerit which was also unspinnable. I was not party to the testing, but was also assured by those involved that the same was true of the British CFM Shadow. Such aeroplanes do exist, they're just extremely rare.

G

[moorea21]

Thanks G, I understood some of your explanation, and will look up the rest. It basically fits with the analogy of the dart with nose/tail weight from B2N2, which works as an aid to visualisation, although obviously there is way more to it.

By coincidence it's a CFM Shadow pilot who most recently asssured me that his aircraft wouldn't spin, no matter what he did to it, and he couldn't get it to drop a wing either. I'd be happy to own one actually; apart from the 2 stroke engine I think it would suit me and my budget very well. The other aircraft I was told about with a reputation as being impossible to spin is the Cri-Cri, although I read an account of a test flight somewhere a while ago where the pilot inferred that he had acheived some kind of spin in it, but didn't comment further. I can't find the article now, unfortunately.

[Genghis the Engineer]

I would be surprised looking at the shape if the Cri-Cri is unspinnable, but I have been wrong before.

Re: the Shadow, I've flown most variants. I enjoy them, but will dissapoint you by saying that in my opinion the very best of them is the Rotax 503 engined Shadow CD. My biggest gripe would be the sheer number of materials and relative fragility which means it absolutely needs to be hangared.

But if you have a hangar and don't mind putting work into any maintenance tasks, which possibly includes developing some new skills - they're great little ships. Don't be afraid of 2 stroke engines, particularly the 503 which is a superb piece of engineering that just needs you to stay on top of the scheduled maintenance (but you should on any other engine too.)

G

[B2N2]

Be careful with claims like “this aircraft doesn’t spin” as a spin is an aerodynamic occurrence as the result of an asymmetric stall.
He may not be able to spin as the CG is too far forward.
I’ve flown at a flight school a lifetime ago where there was one 70’s Cessna 172 that simply wouldn’t spin no matter what you tried.
They had another one where every single stall led to a wing drop to the right.
Function of airplane and flight control rigging or lack thereof and tired old airplanes and probably bent.
I’ve also done hundreds of spins in the DIamond DA-20C1 Eclipse which is pretty spin resistant but when provoked will spin like the proverbial washing machine.
The only way you can make an aircraft impossible to spin is if you make it impossible to stall like with a canard design where the front wing stalls first and drops the nose and therefore prevents the main wing from stalling.
Now....people have been creative and have found other ways to hurt themselves in aircraft that “don’t spin”.

Might I suggest, with respect, that a more useful statement might be along the lines of "to teach to the present level of understanding held by the student with a view to improving that level of understanding" ?

@ Tullamarine and Genghis,
Quoted section is what I intended to say and whatever I put down came out different then intended.
Did not intend to but may have come across as insulting to G.

[cats_five]

At least some gliders will recover from a spin of their own if the CoG is far enough forwards. Apparently that happened with one of ours when someone pushing the weight limit spun it as part of a test flight. It was a single-seater.

To add, I also know of a very serious competition pilot adding weight to the tail of their glider until they had a neutral elevator at 70 knots.

[Jim59]

My single glider is optimised for the lightest pilot in our syndicate by having lead weights (factory) fitted inside the tail wheel so as to reduce drag at normal cruise. In addition it has a water tank in the fin that allows us to add up to 8 litres of water in 1 litre increments. One has to do weight and balance calculations carefully. Spins well. Needs correct recovery. (It also has water ballast tanks in the wings with a total capacity of 200 litres.)

[Genghis the Engineer]

B2N2 - no offence taken, I just thought you'd somewhat missed the point of my post.

Re: spin resistance in individual airframes. There is experience that the range of control movement - particularly of the elevator and rudder can be significant. An aeroplane which is rigged down at the minimum available range of nose-up elevator and rudder in the direction you're trying to get it to spin can be very reluctant to spin. The big risk is that if the limited range is also the case in the opposite directions it can also be very reluctant to recover. One should be therefore very nervous of spin reluctant individual airframes.

G

[ShyTorque]

Genghis,

I have experienced the opposite problem. Asa 17 year old I flew a C150 which had come back from heavy maintenance after a landing accident and had been previously noted to markedly drop a wing on entry to the stall. It was my pre-FHT during my RAF Flying Scholarship course and we were required to enter and recover from a fully developed spin, which was still in the 35 hour PPL course back then. As far as I can recall, I entered the spin as per the book but the aircraft rolled very rapidly in the pro-spin direction. Something very strange then occurred and my instructor looked across at me and asked if I noticed anything unusual. I replied that we were upside down!

He agreed and asked me how I intended to recover. I said "I think I need to pull back on the stick!"

He nodded. I did so and the aircraft recovered quite quickly with opposite rudder, but at some stage the engine stopped. It restarted on the key. My instructor then said "Let's go back to the circuit and recover our composure". We did. I passed my FHT on the next trip. I don't know what subsequently happened to the aircraft but I think the wing rigging was found to be somewhat awry, hence the wing drop. Strangely, as a relatively ignorant young pilot, it didn't phase me nearly as much as it had done my instructor.

[Genghis the Engineer]

I'm not so sure about the aeroplane, but that's one hell of an instructor.

G

[moorea21]

So, Shy Torque, you were in an inverted spin, rather than just inverted? So pulling back on the stick while in an inverted spin would be the same idea as pushing the stick forward in a non inverted spin, yes?

G:- My objections to 2 strokes are really just noise and fuel burn. The Shadow CD seems the best to me too; narrower cockpit etc so more air for the prop, longer wings than some of the others, so slower stall and better glide angle. If the little rotax is actually a good engine, all the better. I'm encouraged by your opinion of the 503; all 2 stroke engines in any form are a mystery to me, I just remember being drenched in fuel by a seagull outboard in a rubber dingy years ago;- my only experience with 2 strokes, besides falling off the back of a GT750 in my teens.

A hangar would be obligatory at my local field, and I'm up for learning new maintenance skills. Plus a long standing member of the local club has owned one for many years, and loves it.

You mentioned the CFM's being fragile; one option for me to learn to fly is to buy one, and get the local instructor to teach me on it. He flies flexwings and 3 axis, but currently only owns a flex wing. Not sure if that level of financial commitment is quite called for; what if I decide to quit and want to sell it? Are they easy to sell, or do they 'stay on the shelf' for years?

Would you say the shadow is a good option for a novice student pilot to learn on? Or would the fragility be an issue?

Thanks for tolerating me veering off topic, let me know if I should just start a new thread....

[Genghis the Engineer]

I'll leave current admins like DAR to worry about thread discipline.

My impression is that Shadows I see on sale don't usually stay advertised for more than a month or two, so I'd hope that you can get rid of one if you want to quite easily.

There is a Shadow CD, G-MWVG (known to one and all as George) that was used for ab-initio PPL training from the Shadow Flight Centre at Old Sarum. Looking on G-INFO it is still there, with 4000hrs on it (although I don't think they're regularly teaching on it any more). I passed my microlight GFT on it in 1993! That probably tells you all you need to know about the robustness and suitability for student pilots, if well looked after.

The main thing with the 503 is that it needs regular maintenance - plugs at 25hrs (cost of a set about a tenner), every 50 hours for minor maintenance, monitor crankshaft wear from about 250hrs, and expect to decoke about every 150hrs and rebuild (actually about a 3 day job costing a few hundred pounds in parts, £700 if you're unlucky) about every 450hrs. I'd be very happy to own a 503 engined microlight again any time, having had a couple.

G

[dook]

One of the problems in this Industry is that pilots, in general, are trained to comparatively low levels of technical understanding.

My university ATPL students were trained and tested to very high levels of technical understanding. I accept this thread is at PPL level.

The static and dynamic stability lectures took me five hours in total and in terms of spinning I took them through the subject of B/A ratios also.

[B2N2]

My university ATPL students were trained and tested to very high levels of technical understanding. I accept this thread is at PPL level.

The static and dynamic stability lectures took me five hours in total and in terms of spinning I took them through the subject of B/A ratios also.

How much did they recall after taking the respective exams and how much of it do they need to know flying transport category aircraft?

0/0....
:rolleyes:

[Genghis the Engineer]

There's always an issue that all of the professional licences train and educate people for a plethora of professional pilot roles, not just any single one. Having recently added a US CP to my EASA CPL I was struck by the very different emphasis each places on different aspects of both theory and practice - yet in theory each qualifies me to do (almost) exactly the same things, just with a different registration painted on the side.

For me, working in the technical side of aviation, the theoretical aspects of my EASA CPL are vastly more useful than the extremely minimal and light-GA centric FAA CPL written syllabus. On the other hand the greater emphasis on handling in the FAA CPL checkride is more useful to me as a test pilot than the "let's pretend we're 1960s airline pilots" content of the EASA skill test: but having done that I've found myself very well equipped to do bits of ferrying around Europe in minimally equipped aeroplanes.

Basically, I am saying that any licence course, or education course (and these combined ATPL degree programmes are both) should NOT be really narrowly focused one specific job is. That is, in my opinion, a deeply flawed view.

G

[blind pew]

Having done 3 atpls, plus light aircraft, microlight,glider and paraglider qualifications on four continents, the knowledge base is impossible for one small brain to comprehend. It stems from old systems, accidents and the flying environment modified to the lowest common denominator by those who lack the ability of sky gods. There will never be a consenus even in a relatively small gliding club in one of the british isles and especially in a frog one. Add regulators, many of which dream of flying a jet, and the system is well and truely up the creek.
The best one can hope for is to write,read and talk then disagree.
From someone who nearly didn't get out of a spin, whose pupil then didn't 30 years later, and did his first open cockpit spin of a single seat vintage glider 2 years ago..when the CFI wouldn't. In the right aircraft, with a proper preflight check..great fun!

[double_barrel]

I imagine that this is something that those who fly plane loads of sky divers are acutely aware of?

[ZeBedie]

I've been told that spin characteristics are defined not just by CofG location, but by weight distribution, such as a lump of lead added in the tail. Is there any validity in this comment, or is weight distribution totally taken into account by knowing CofG location?

[lederhosen]

Some years ago I did a gliding instructor course here in Germany which involved a lot of spinning. It was interesting that with a rather large instructor trainer in the front that one of the two types of gliders would not stay in a spin, we were using K13 and K21s. We did days and days of spinning and the result was always the same on the K13 half a turn and despite full crossed controls it was out. So my practical experience backs up the CG theory at least on some machines. With light trainees I have found the K13 spins to your heart’s content.

[Maoraigh1]

The Bolkow Junior Flight Manual has different spin entry instructions for 2 different C of G ranges.

[Pilot DAR]

Correct. C of G is a very important factor, and spin recovery characteristics will drive C of G limits. But the moment of inertia can have an effect too. If you put a small mass wayyyy back, yet remain within C of G limits overall, the spin recovery could be affected, as there was more inertia to overcome for recovery. I think of a few engine change STC's which include a few pounds of lead in the tail to balance a heavier engine. That said, I expect that for spin approved GA types, you couldn't get enough mass far enough back, yet within C of G limits, to become a problem, but I would be considering it during flight testing. Happily (for maintaining spin recovery characteristics, most of the things I've tested hanging off the back of a GA plane were also big enough to have aerodynamic stabilizing characteristics to overcome any mass destabilizing characteristics.

I have spun these, they all remained compliant:


https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/800x600/b185a2_4ee13f619311eb6734ac552b8c32f45fe477e769.jpg


https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/800x548/c206_boom_2_c4c82d69a2b352d9ef8d8d9c593a18f7d69b9824.jpg

The booms are light

And:


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/800x533/copy_of_img_4778001_50f3d11e1759003984917dcb2b607ff8c3be5e61 .jpg

Ugly at aft C of G, but compliant, there's quite a stabilizing effect from the stowed towed survey bird. Video here:

https://www.youtube.com/watch?v=zjB_q7AIvDo

[Big Pistons Forever]

The Cessna 150 with the Lycoming 150 hp engine mod is not certified for spinning. The heavier engine required the battery to be moved to the tail. The heavier bits at both ends created addition polar inertia such that the airplane no longer had acceptable spin recovery characteristics

in any case spin training has no place in ab initio flight training. Instead all of the emphasis should be on spin recognition and recovery. A deliberately entered spin with pro spin controls maintained after the aircraft departs is an aerobatic maneuver and should be thought by an aerobatic instructor as part of a basic aerobatic course.

[pasta]

Some years ago I did a gliding instructor course here in Germany which involved a lot of spinning. It was interesting that with a rather large instructor trainer in the front that one of the two types of gliders would not stay in a spin, we were using K13 and K21s. We did days and days of spinning and the result was always the same on the K13 half a turn and despite full crossed controls it was out. So my practical experience backs up the CG theory at least on some machines. With light trainees I have found the K13 spins to your heart’s content.
There's actually a spinning kit for the K21, which consists of a bunch of weights bolted onto the bottom of the fin. It's pretty much unspinnable without that.

[lederhosen]

I think fairly obviously that is what we were using. I agree with a previous post that more than incipient spin recognition training on light powered aircraft is overkill (excuse the pun). On the other hand after nearly half a century of gliding, and an initial instructor course under the tutelage of Andy Gough, I believe there is definitely a place for spin training in flying sailplanes. Not least we spend a lot of time in tight turns, low and slow when thermalling down in the weeds.

[CISTRS]

I agree.
Best not to trim into the turn pressure on the stick.
Be aware of the first signs of buffet, and release some back pressure.

[ShyTorque]

The RAF’s Bulldogs always had a reputation for being tricky with regard to spin recovery. During my time instructing on them I did a little research into weight and balance, which wasn’t routinely calculated in detail for every flight. It appeared that with two average to heavy occupants the fuel level needed to be watched because many airframes were right on the aft C of G limit and they could be put outside. Which of course might explain the very rapid roll rate that could be experienced. Being built like racing snake back then had its advantage.

[ItsonlyMeagain]

“in any case spin training has no place in ab initio flight training.”

Try telling that to the family of the 26 year old who crashed a C150 out of Jerez in Feb.

Looking at the video, he was in a fully developed spin and there was no attempt to recover. Did he know how to?

Like ShyT, I did a 35hr PPL where spinning was taught, the to the Bulldog where it was taught and repeated constantly. A career in the RAF and airlines and a private Bulldog and now gliders. I have never accidentally spun, but I sure know how to get out of one if I have a bad day.

Me

[The Ancient Geek]

Spin training is a compromise.
Records show that more people have died during spin training than from accidental spins so the decision was made to limit PPL training to incipient spins. This leads us to the effectiveness of the training which IMHO is probably inadequate.
We all (hopefully) occasionally practice engine failures and emergency landings but how many practice recovery from incipient spins with any regularity ?.

[ShyTorque]

I’m sure that after so many decades of “spin awareness/avoidance” training, many civilian flying instructors now have far less spin experience than the majority of those in the job years ago. It’s understandable that some might actually even shy away from the subject as much as possible.

Being RAF BFTS jet trained, I’m grateful that spinning was seen as nothing unusual. We needed that experience because we were expected to fly to the limits of the airframe (and aerobatics put students potentially closer to spinning when we reached the limits of our ability). Without that ingrained early full spin recovery training I certainly would have accidentally killed myself, at least on one occasion in a JP3A that I’ll never forget.

[ShyTorque]

We all (hopefully) occasionally practice engine failures and emergency landings but how many practice recovery from incipient spins with any regularity ?.

I wonder how many would recognise when a spin has developed beyond the incipient stage and understand the differences in the required recovery actions?

[Big Pistons Forever]

Most real world stall spin accidents occur at such low altitudes that if the airplane IS ALLOWED to enter far enough into a spin that spin recovery techniques must be used as opposed to a stall recovery, then they would not have enough altitude to recover.

If the pilot is not good enough to recognize when the airplane is departing controlled flight I highly doubt that he/she will be actually be able to use training on recovery from a spin.

Personally I think most spin training outside of aerobatic training is negative training because pilots have to hold into spin control inputs through at least 1 turn before classic spin recovery control inputs should be used. Instead training should emphasize control of yaw in the event of a unintended stall. No airplane will spin if yaw is controlled at the point the wing stalls

[EXDAC]

I wonder how many would recognise when a spin has developed beyond the incipient stage and understand the differences in the required recovery actions?

Unless being done for fun or training, if the recovery is not started as soon as a wing drops, the pilot needs more training. I did over 20 turns in a Schweizer 1-26 but it was just for fun. When a student stalled a Blanik L-13 in a thermal and the rotation started I took over without debating where we were in spin development.

I had intentionally spun gliders several times before I started my SEL training. Shortly after solo I asked my instructor if we could do some spins. He said no, went and got some spin training, then said yes.

My ASW-19b took full rudder and full opposite aileron to provoke a spin entry. Never could keep it rotating. I never could get the ASW-28 to even start to spin. Neither allowed spins with ballast so could not explore what either did where it really mattered (trying to scratch away without dumping). Both were really well behaved and I never came close to an inadvertent spin entry in either. A fellow club member had a scare when his LS-4 snapped into spin entry during a low altitude save. Another club member died recently after stalling his Standard Cirrus in a low altitude save.

I was against the elimination of spin training. I don't think anyone who has not experienced that first half turn really understands how quickly it can happen.

[ShyTorque]

It’s been many years since I instructed on RAF fixed wing SEP aircraft but my recollection is that RAF CFS teaching was that anything beyond 360 degrees of undemanded roll or 180 degrees of undemanded yaw was no longer considered “incipient” and required full spin recovery actions. But maybe that was just the Bulldog.

[B2N2]

Awareness, understanding and recognition of the conditions under which a spin will occur
will make spin training obsolete.
Similar to driving a car, literally millions of people have never gotten into a skid without having done any slip/skid pad training.
Understand that an airplane will NEVER spin unless stalled first.
Avoid the stall, avoid the spin.
I used to ask my students what the way was to avoid a bar fight……don’t enter a bar.

[megan]

I've been told that spin characteristics are defined not just by CofG location, but by weight distribution, such as a lump of lead added in the tail. Is there any validity in this comment, or is weight distribution totally taken into account by knowing CofG locationAs mentioned by DAR it certainly does, think of a skater doing a spin with arms outstretched who then brings the arms in close to the body, the centre of gravity is unchanged but the rate of rotation increases, angular momentum at work. DAR and Genghis would be able to give an explanation into angular momentum control/stability issues.

[David J Pilkington]

Correct. C of G is a very important factor, and spin recovery characteristics will drive C of G limits. But the moment of inertia can have an effect too. If you put a small mass wayyyy back, yet remain within C of G limits overall, the spin recovery could be affected, as there was more inertia to overcome for recovery.Indeed. M.Sc Thesis by P. Kefalas at Cranfield University, Aircraft Spin Dynamics Model Design, 2001 has some good info including this summary.

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/862x705/spindynamics_def85a491f6f94d2ee509e8937aafb54a6c62c8e.png

I think of a few engine change STC's which include a few pounds of lead in the tail to balance a heavier engine.Yes. I've seen some fairly significant amounts of ballast added to fix the CG with nil consideration of moments of inertia effects on spinning etc.

[Pilot DAR]

Another club member died recently after stalling his Standard Cirrus in a low altitude save.

I'm going to guess that the "save" was not entirely successful, if the outcome was fatal...

We are evolving into a stage in GA where modifications are more common, and multiple modifications a factor too. It is a sad oversight that mod upon mod(s) are stacked up on airplanes, perhaps in the effort to modernize legacy types, and the inter relationship is overlooked, or poorly considered. Sure, the gross weight increase is STC'd, but was it considered for compliance (spin characteristics) when combined with other mods - like tip fuel tanks (Flint) or extra wing tanks (Monarch)? The now longer range plane, with the gross weight increase, will probably say that the weight above a certain weight must be carried as fuel (for landing weight considerations), but has anyone properly evaluated the changed handling characteristics (spin recovery) at a higher weight, and with fuel weight further away from the C of G (by span, rather than fuselage station)? Might you be flying a multi mod plane, and not be entirely aware of the compliance of the combined mods? The first clue would be: If there is not a flight manual supplement which relates all of the aerodynamic/weight/power mods to the airplane in ONE flight manual supplement, it's likely that you're flying a plane which has not had the combination correctly reviewed together. Each STC tells the installer to consider the relation of each mod to the others, but it is often not done, and if done, not completely done. Your Cessna 210 gets several mods installed together, does the installation shop require that the plane be test spun for confirmation of compliance following multi mods? Rarely, though I have done it for shops following major mods.

When you get in an unmodified certified single engine plane, you know that it has compliant spin recovery characteristics, whether spin approved or not. Once you install more than one mod on it, that assurity of handling characteristic compliance goes way down. The flight manual supplement will be your clue - if it does not describe the compliance of the modified configuration you're flying, beware!

So, though BPF and I do not entirely agree about spin training, I will certainly agree that it should be taught by an aerobatic or spin competent instructor, and treated as a practiced emergency procedure, not something which is "fun", unless aerobatics is your fun, in which case, get trained properly, and go for it. But I do feel that every pilot should be exposed to an incipient spin entry and recovery, just to bring understanding. After that, yes, train avoidance, as long as that training promotes stall recovery by application of nose down elevator (as opposed to adding power) and highlights the need to keep the ball in the middle all the time.

No airplane will spin if yaw is controlled at the point the wing stalls

No modern certified and properly rigged airplane will spin if yaw is controlled......

I've flown a few homebuilt types which had a pretty unforgiving stall, I've flown a couple of horribly rigged planes, that would rather spin than stall, no matter how centered the ball is maintained, and I've flown a few antique types with no washout in the wing (DC-3) who have an unforgiving stall. But, yes, generally, keeping the ball in the middle is the best step toward preventing a spin entry. Thereafter, don't accidentally stall it! And, be aware, is the type of flying you're about to do a higher risk? Turns during aerial photography or ground observation at slower speeds, tightening a turn to base or final, or low speed parachute jump runs, where jumpers are going to gang up on the outside of the plane before departing...

[ShyTorque]

Strange how the brain can begin to dust off some of its old pages. I recall that the old Jet Provost 3 wasn’t allowed to be aerobatted or spun if there was any fuel in the tip tanks and if that was part of the sortie profile it was normal to take off with “half tips” so they would be empty by the time you climbed to minimum entry altitude. One of the pre spinning checks was to confirm that the main gauge reading had begun to decrease. At least I think that’s correct…..it’s 44 years since I last flew one and a year longer since I nearly killed myself by inadvertently flick rolling then spinning one inverted from a badly botched aerobatic manoeuvre (had I not previously recovered from one in a C150 as mentioned earlier I might not be here writing about it).

A similar cockup in a JP (Strikemaster in fact) may well have been a factor in the sad demise of an ex Harrier display pilot of my acquaintance, quite some years later.

[megan]

The moment of inertia was demonstrated by famed test pilot Janusz Żurakowski in the Meteor, vertical climb to zero airspeed, close one throttle, allow the aircraft to rotate in yaw through 540° back into a vertical dive and recover, the maneuver required a load of under wing rockets to give it the necessary angular momentum to get through the 540°. Earned the name "Zurabatic Cartwheel".


https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/297x800/5878464_orig_d8b68fbaa5deaea553ddf70aadb02ee1936804a2.jpg

A not very good video starting at 2:20

https://www.youtube.com/watch?v=tjhOnB2AgOs

[Big Pistons Forever]

I'm going to guess that the "save" was not entirely successful, if the outcome was fatal...

We are evolving into a stage in GA where modifications are more common, and multiple modifications a factor too. It is a sad oversight that mod upon mod(s) are stacked up on airplanes, perhaps in the effort to modernize legacy types, and the inter relationship is overlooked, or poorly considered. Sure, the gross weight increase is STC'd, but was it considered for compliance (spin characteristics) when combined with other mods - like tip fuel tanks (Flint) or extra wing tanks (Monarch)? The now longer range plane, with the gross weight increase, will probably say that the weight above a certain weight must be carried as fuel (for landing weight considerations), but has anyone properly evaluated the changed handling characteristics (spin recovery) at a higher weight, and with fuel weight further away from the C of G (by span, rather than fuselage station)? Might you be flying a multi mod plane, and not be entirely aware of the compliance of the combined mods? The first clue would be: If there is not a flight manual supplement which relates all of the aerodynamic/weight/power mods to the airplane in ONE flight manual supplement, it's likely that you're flying a plane which has not had the combination correctly reviewed together. Each STC tells the installer to consider the relation of each mod to the others, but it is often not done, and if done, not completely done. Your Cessna 210 gets several mods installed together, does the installation shop require that the plane be test spun for confirmation of compliance following multi mods? Rarely, though I have done it for shops following major mods.

When you get in an unmodified certified single engine plane, you know that it has compliant spin recovery characteristics, whether spin approved or not. Once you install more than one mod on it, that assurity of handling characteristic compliance goes way down. The flight manual supplement will be your clue - if it does not describe the compliance of the modified configuration you're flying, beware!

So, though BPF and I do not entirely agree about spin training, I will certainly agree that it should be taught by an aerobatic or spin competent instructor, and treated as a practiced emergency procedure, not something which is "fun", unless aerobatics is your fun, in which case, get trained properly, and go for it. But I do feel that every pilot should be exposed to an incipient spin entry and recovery, just to bring understanding. After that, yes, train avoidance, as long as that training promotes stall recovery by application of nose down elevator (as opposed to adding power) and highlights the need to keep the ball in the middle all the time.



No modern certified and properly rigged airplane will spin if yaw is controlled......

I've flown a few homebuilt types which had a pretty unforgiving stall, I've flown a couple of horribly rigged planes, that would rather spin than stall, no matter how centered the ball is maintained, and I've flown a few antique types with no washout in the wing (DC-3) who have an unforgiving stall. But, yes, generally, keeping the ball in the middle is the best step toward preventing a spin entry. Thereafter, don't accidentally stall it! And, be aware, is the type of flying you're about to do a higher risk? Turns during aerial photography or ground observation at slower speeds, tightening a turn to base or final, or low speed parachute jump runs, where jumpers are going to gang up on the outside of the plane before departing...

Yes obviously keeping the ball centred is good practice at all times but that is not what I was getting at. What is important is that Yaw is controlled after the airplane stalls, which will often require an immediate full rudder input. This is where pilots get into trouble. The airplane unexpectedly stalls and starts to yaw and the pilot freezes. By the time they wake up it is too late as they are probably too close to the ground to recover from the inadvertent spin.

What training has to emphasize is developing the muscle memory so that if the airplane starts to depart controlled flight there is the instinctive push forward on the stick and application of rudder opposing the yaw. I stand by my contention that there are no airplanes that a reader of this forum is likely to fly where this technique will not always avoid a spin entry. However some unforgiving airplanes will give you very little time to intervene so the stall recognition and recovery is especially important.

Finally I would suggest a practical definition of a “spin” is where classic stall recovery control inputs will not recover the airplane and indeed will exacerbate the situation. Only spin recovery inputs will recover the airplane. However I have never seen an airplane that will not recover with a conventional stall recovery technique if the stall recovery inputs are correctly and forcefully applied before the airplane has completed more than 180 degrees of yaw after departing controlled flight.

[ShyTorque]

But some aircraft may initially produce undemanded roll, rather than yaw at the incipient stage. Hence the RAF teaching, which was that if there was any autorotation with buffet, immediately centralise the controls, which should stop it developing. If the yaw subsequently continued beyond 180 degrees, or the aircraft continued to roll in excess of 360 degrees, the full spin recovery technique should be used.

Having said that, during formation “tailchasing”, we found that it was easy to manoeuvre the Bulldog very rapidly by briefly inducing autorotation…but of course that wasn’t officially taught because we weren’t supposed to flick roll that aircraft.

I did once experience an inadvertent high rotational spin when my student messed up a roll off the top manoeuvre. He was slow to sort it out and so I took control and applied full pro spin control followed by the normal spin recovery technique and it recovered very rapidly (to the extent that the rugby playing student was so alarmed that he squeaked)!

[Fl1ingfrog]

I would suggest a practical definition of a “spin” is where classic stall recovery control inputs will not recover the airplane and indeed will exacerbate the situation.

I don't think such a definition can cut the mustard. The characteristics of some aeroplanes could put a lie to that one. Think of the Tomahawk losses during its early days.

However I have never seen an airplane that will not recover with a conventional stall recovery technique if the stall recovery inputs are correctly and forcefully applied before the airplane has completed more than 180 degrees of yaw after departing controlled flight.

Following a discussion with a number of competition pilots: it was common to use pitch alone to recover from a spin during the first two to three rotations (still incipient). Keen to try this I used the club Robin 2160. This technique worked perfectly, recovering precisely onto per-determined headings, as promised. I then tried the same holding in the spin for 6 rotations (a fully developed spin is said to take place after 4-6). On recovery it was impossible to shift the stick; fully aft it was as if set in concrete. Only after a conventional recovery using max opposite rudder was it possible to shift the stick but only when the rotation slowed. Recovery was then conventional.

[Big Pistons Forever]

I think it is important to note this thread started with “ in the Private Pilot Course” . My comments are in relation to that. When I teach aerobatics the instruction is much more nuanced as there are many ways to depart controlled flight that would not apply to PPL training. Aerobatic airplanes also have high control authorities that add extra complexity ( eg into vs out of spin aileron inputs).

I believe that “spin training” in the PPL is negative training as pro spin controls have to held in for at least a full turn before the spin recovery is initiated. There are no times in non aerobatic flight that pilots should deliberately apply and hold pro spin control inputs.

In addition a lot of stall and spin training is very artificial. In the real world you don’t get into a stall by first doing a HASEL check and then slowly pitching up until the airplane stalls. Personally I like to present stall spin avoidance with scenario’s that emulate real world accidents, like the base to final skidded turn or the panic turning pitch up when you think you are not going to clear the trees on a short field takeoff.

[Fl1ingfrog]

a lot of stall and spin training is very artificial. In the real world you don’t get into a stall by first doing a HASEL check and then slowly pitching up until the airplane stalls. Personally I like to present stall spin avoidance with scenario’s that emulate real world accidents, like the base to final skidded turn or the panic turning pitch up when you think you are not going to clear the trees on a short field takeoff.

I agree but of course you cannot omit HASEL from training scenarios. The entry to the spin that I teach to the non aerobatic pilot is an incorrectly applied turn: smoothly apply maximum rudder, then progressive hand control to fully aft (no need to consider pitch up) and roll in the direction of the intended turn. On some types the spin entry is after a slight pause but not immediate, on others it can take second or too and be unexpected. I don't introduce the term 'pitch up' because the horizon is irrelevant. The vast majority of students and pilots generally confuse pitching movement with the horizon.

Scenario teaching is the way we should be going in my view, in all things. However I encounter a very strong, even a dismissive attitude to it in working groups.

[Pilot DAR]

What training has to emphasize is developing the muscle memory so that if the airplane starts to depart controlled flight there is the instinctive push forward on the stick and application of rudder opposing the yaw. I stand by my contention that there are no airplanes that a reader of this forum is likely to fly where this technique will not always avoid a spin entry. However some unforgiving airplanes will give you very little time to intervene so the stall recognition and recovery is especially important.

I 100% agree with this.

[Fl1ingfrog]

I have never seen or witnessed any evidence supporting 'muscle memory' in response to an unexpected stall or spin. There are a number of signs for the pilot to learn that indicate that the conditions for a stall are imminent and require avoidance action. Ex 10a in the UK and EASA syllabus is meant to deal with this but unfortunately has never been standardised and is poorly understood.

Somatosensory information and instinct should be treated with care. In regard to the stall and spinning Beggs and Mueller are a valuable read.

[Big Pistons Forever]

FLingfrog

I have certainly used muscle memory in gliders. Last year I was flying the club PW5 and trying to core a very narrow thermal. To do that I was flying at minimum speed and high bank angle to minimize my turning circle. I was momentarily distracted by a radio call and inadvertently let the airspeed drop a few knots which caused the glider to stall. The stick went forward without conscious thought and then stepping on the rudder stopped the yaw. I flew out of the thermal under control after losing less than 100 feet.

I do believe that the instinctive pitch down if the airplane surprised you with an inadvertent stall can be taught. Finally most airplanes will talk to you when they are getting slow and at high AOA. I make a point of demonstrating the so called “soft stick” and get pilots to maneuver in slow flight so that they recognize the change in control forces.


I guess I have hijacked the thread so back to the OP’s question. As a previous poster noted the effect of aft C of G can be significant in gliders but less so in your typical powered trainer. However most trainers that are cleared for spinning have a more restrictive C of G envelope for spins. This will result in the aft C of G limit being moved farther forward in order to eliminate undesirable or even dangerous spin characteristics.

[EXDAC]

I flew out of the thermal under control after losing less than 100 feet. .

I'm going to guess that you are not in the habit of flying in pre-start contest gaggles. 100 ft altitude loss would take out several other gliders in some thermals I have shared.

[Big Pistons Forever]

I'm going to guess that you are not in the habit of flying in pre-start contest gaggles. 100 ft altitude loss would take out several other gliders in some thermals I have shared.

That would be because I would not be flying at 40 kts and 55 degrees of bank, which was the minimum that would keep me in up air; in a "prestart gaggle contest". But thanks for your "contribution" to this thread :hmm:

[Fl1ingfrog]

'Muscle Memory', as it is known but in reality is actually a memory of the brain, enables the efficient repetition of a physical skill or a task but that is all. I do not know of any evidence that supports the idea proposed. The stall and the spin are only predictable following a particular form when it is deliberately induced. Glider pilots of course spend much of their time close to the stall particularly when thermalling. This stall will be of no surprise therefore and is repetitively practiced. Non of this is the experience of the vast majority of powered pilots.

[EXDAC]

Glider pilots of course spend much of their time close to the stall particularly when thermalling. This stall will be of no surprise therefore and is repetitively practiced.

No, experienced contest pilots do not stall in thermals and do not practice stalls in thermals. Most know that even a small relaxation in stick back pressure will avoid the stall with no altitude loss. 55 deg bank with full ballast is routine flying in the desert SouthWest of USA. Anyone who could not thermal in those conditions without stalling would have few friends.

[Fl1ingfrog]

No, experienced contest pilots do not stall in thermals and do not practice stalls in thermals. Most know that even a small relaxation in stick back pressure will avoid the stall with no altitude loss. 55 deg bank with full ballast is routine flying in the desert SouthWest of USA. Anyone who could not thermal in those conditions without stalling would have few friends.


Exactly, you confirm my point.

[[email protected]]

Strange how the brain can begin to dust off some of its old pages. I recall that the old Jet Provost 3 wasn’t allowed to be aerobatted or spun if there was any fuel in the tip tanks and if that was part of the sortie profile it was normal to take off with “half tips” so they would be empty by the time you climbed to minimum entry altitude. One of the pre spinning checks was to confirm that the main gauge reading had begun to decrease. At least I think that’s correct…..it’s 44 years since I last flew one and a year longer since I nearly killed myself by inadvertently flick rolling then spinning one inverted from a badly botched aerobatic manoeuvre (had I not previously recovered from one in a C150 as mentioned earlier I might not be here writing about it).

A similar cockup in a JP (Strikemaster in fact) may well have been a factor in the sad demise of an ex Harrier display pilot of my acquaintance, quite some years later.
Shy, my recollection of the JP 3A is the same as yours but ISTR no fuel in the tip tanks was allowed for spinning.

Ah, the memories of watching North Yorkshire spin quickly one way and then the other as I tried to stop the high rotational spin..

I have recently passed GST on an Ikarus C42 microlight which you are not allowed to spin - the recovery was talked about during the training but I feel my 40-year old experience of actual spinning is more valuable.