PPL- Spin Training

[Pilot DAR]

I must say the both Pace and Pistons present compelling arguments, and I can easily agree with many aspects of both! Well done! I suppose that my aged flying heritage is just different enough from the present world of training, that I should probably take a step back, and let the pros do their job. That said, I do not automatically think "pro" and flying instructor in the same thought. With some exceptions, I have found myself alarmed with what some instructors do not know about flying - worse, they don't know they don't!

2 C 152's had bent horizontal tail spars as a result of botched spin recoveries.

However, can we go back to the bent spar on the 152 please? Being a 150 owner, this is of particular interest to me.... Something actually bent back there? There's not really much "spar" in the H stab, it's really mostly skins carrying the loads. Could it actually have been sloppy ground handling? That will bugger a Cessna H stab a lot faster than flying it poorly! To bend an H stab spar in flight, you'd have to pull considerably more than 4.4 G. That's a lot, and would have most PPL's shreaking, and fouling themselves. A few times we pulled 5+ in the Aerobat, just because we could, but soon sickened, and greyed ourselves out, so we quit it!

Honestly, are pilots acutally damaging 152 H stabs by poor flying? The Aerobat H stab has an extra spar, to carry the extra loads, and a beefed up fuselage mounting hardpoint. My 150M, and all 152's also have this beefed up fuselage, but I still inspect it thoroughly! I also have a G meter, and have never pulled as much as 3.5 G, nor passed red line in it. I have only once heard of a Cessna being bent in flight, and it was a 185 jump plane carelessly spiral dived through clouds by a scared pilot. It was the wings which bent, not the tail (though I know it is quite different from that of a 150).

Pistons, would you describe the 152 H stab damage in more detail, so I have some insight?

[Big Pistons Forever]

Both had diagonal span wise wrinkling of the skin and a straight edge placed along the after hat section showed both stabs had a permanent (albeit small) bend. Both stabs were deemed not worth repairing and were replaced. I should note that this occurred when spins were still required for the Canadian PPL. In one of the cases the pilot had told a friend that the airspeed was at least 10 knots over the redline and he pulled hard enough to grey out. The second is more ambiguous and the link between the damage and a botched spin recovery is not as clear. Contrary to their reputation, C 15O/152 will accelerate quite quickly at very steep nose down attitudes. A good example of this is the split S maneuver. Entered from 85 kts and level flight a 4.5 to 5 Gee pull is required to keep the airspeed in check. Any less and you will be right up against or over the redline

As you had pointed out the "aerobat" models of the C150/152 have most of their beefing up in the tail. I can see why....

[Pace]

Biig Pistons
To clarify to recover from a spin in the context of breaking an aeroplane is the point at which you stop the aircraft spinning. A dive or spiral dive are separate manoeuvres in their own right in which you can experience high speed high G in the recovery and where an aircraft can easily be broken. For the purpose off this discussion the two portions have to be separated.
You are unlikely to recover from a spiral dive or for that matter a dive at low level in the circuit but that is not an argument against students experiencing and learning how to deal with either?
How come spinning is different?
When you state that students don't realise that an aircraft is no longer spinning but has transitioned into a spiral dive that is very worrying concerning the quality of modern training methods ?
I am sure this argument between pro and anti spin training will go on for ever.
My advice to a late student or early PPL is take yourself off for a couple of sessions not so much as an aerobatic course but as an extreme handling course.

Pace

[mary meagher]

A spin being of PRACTICAL USE in the conduct of a flight in a glider? Ah, that is a different question, all right.

Firstly, let me make it plain that I agree, a spin is an aerobatic maneuver, and if you spin on your final turn, it is all too likely to be your final turn.

The point of glider flying altogether is to have fun. Not to get from A to B for a £50 cup of coffee, or to fly some rich owner to his stately hunting box.

And the reason for teaching glider pilots the difference between the spin and the spiral dive, which is useful as the recoveries are rather different, is that gliders soar in thermals, sometimes in numbers and very close together, as many as 20 in one thermal, 2 or 3 at one level, and hopefully all turning in the same direction. At speeds not very far from the stall, when a gust may suddenly tip you into that stall/incipient spin/ full spin.

I remember reading about a Lasham thermal, well populated, where the top glider actually did spin down through the gaggle, which scattered in all directions! no collision, nobody hurt, owing probably to the fact that we all have eyes on stalks while engaging in this bizarre behaviour.

Now let me ask one of our favorite trick questions.

Which is more likely to damage your aircraft? Flying faster than VNE? or
pulling excess G?

[Pace]

Mary
Are we going to delve into the realms of beyond VNE ? Beyond VNE will not normally break your plane it's what you do to slow your ship up that will brake it.
Intact in a retractable if you don't have the airspace for the most gentle of recoveries you are better off dropping the undercarriage way beyond it's operating speed than pulling back harder.

Pace

[djpil]

Which is more likely to damage your aircraft? Flying faster than VNE? or
pulling excess G?

Not enough information.

pulling excess G?

In excess of the limit load factor?

Flying faster than VNE?

How much faster? 9%? 11%? Vne determined by fixed pitch propeller rpm or otherwise?

Its not just the likelihood of damage but the scope of damage if it does occur that is of interest when it comes to decide - pull harder or let airspeed go higher.

[Pace]

Its not just the likelihood of damage but the scope of damage if it does occur that is of interest when it comes to decide - pull harder or let airspeed go higher.

djpil

I would say the main concern is damage to oneself by doing anything which makes the aircraft unflyable. Anything else which doesnt make the aircraft unflyable is expendable.

It all depends on how much airspace you have to play with as well as the quality of the air you are diving through

Beyond VNE may be ok in smooth air but if you are beyonding VNE with a solid deck of cumulus fast approaching NOT GOOD Infact that might not be good sub VNE!!!
Undercarriage, airbrakes,overspeeding props is better than NO wings or tail.
Flying jets and it is quite common to descend high level near VNE and easy to exceed.
Low level its very easy to overspeed in level flight never mind descending.

Pace

[Mark1234]

I'm inclined to put the case for spinning gliders very, very simply. Gliders spend a lot of time turning close to the stall (aka thermalling), therefore, whilst they are spin resistant, there is far more likelyhood of entering a spin when gliding. If you carry extra speed as a margin, you simply don't climb as well.

BackPacker - the '21 is the most spin resistant thing I've ever flown - we don't spin them as they're reckoned to be unspinnable without tail-weights (for a more rearward CG), and yes, that's a factory thing, not simply someone's neat idea(!) There are other gliders that spin a whole lot more convincingly! Spinning gliders is also a wholly different ball game to powered, both in height loss, and violence.

To Mary's question, UK glider teaching is (or was, when I trained), firstly, think before you do it, and don't put yourself in a corner, BUT if in trouble/doubt PULL. The reasoning being that during certification VNE is set at 90% of the max demonstrated speed, whereas the structure has to demonstrate 150% of the max G load (usually 6G) and remain flyable. Doubly important as gliders tend to be very slippery and gain speed rapidly, and I suspect more flutter prone with long wings. Also, heaving a lot of 'G' tends to slow things up pretty quickly, leaving you unable to pull lots of G very soon.

We are also taught to recognise the difference between a spiral and a spin. One of the key ones being that a spiral shows rapidly increasing airspeed, whereas a spin is usually either unreliable (too much flow across the pitot), or steady.

And finally, to Abbey Road's point, pulling too hard (stalling) in a turn *should* not result in a flick, if the aircraft is in balance - being flown correctly - which is back to Pace's point about driving (ok, I'm being a bit flippant there..)

[Pace]

I dont think pulling hard would go down very well in GA aircraft beyond VNE.
Well it would go down very well but not in the way we are talking about.
Always thought you Glider pilots were an odd lot anyway

Pace

[Genghis the Engineer]

The logic is reasonable, except that it ignores that the combined high speed / g-loadings could potentially fail the aeroplane well within what would appear to be an OK speed, and an OK g-loading - but not together!

G

[Pace]

Which is more likely to damage your aircraft? Flying faster than VNE? or
pulling excess G?

Mark

Marys question was above! I stress her " Excess G" and flying " Faster than VNE".
Obviously in both Glider and powered aircraft the answer has to be its more dangerous to pull excess G because excess means higher G than the Gliders design limits.
Faster than VNE is wishy washy as that could be anything from 1 kt above to whatever?

Pace

[Mark1234]

Genghis: My immediate reaction is to say you're wrong, but I think I know something of your background, which suggests you know a lot more than me. Therefore, I'm going to ask why.

Just to make sure we're on the same page, I'm not talking about abrupt, full scale deflections, nor deflecting multiple controls - I entirely understand how they may cause bits to fall off. However, according to my understanding the Vn/Vg/whatever you call it diagram gives an envelope within which you can fly, in terms of G loading, and speed (confined to the pitch plane, but rolling gliders is kinda tedious anyway ). Anywhere in there you should be fairly sure bits will not drop off?

<sidenote>I have however seen Vg diagrams that 'taper' towards the right, defining lower load limits at higher speed. That seems reasonably intuitive, and is generally placarded / noted.


Pace: I'm not sure as to your point - exceeding either limit could be by the tiniest percentage, or a large amount. Neither is recommended, the point that was made to me in training was that I have more 'room for error' in the loading sense than the velocity sense. To recap, the relevant certification requirements are:
1) That the aircraft is tested to Vd (max design speed), and VNE is set to 90% of that (so the prototype at least has been proved not to flutter/otherwise self destruct at 110% of VNE.
2) That the aircraft must sustain a loading of 1.5x the design limit (i.e. if it's placarded +6/-4, it must sustain +9/-6) without being compromised structurally for 3 seconds. Stuff may break, and you may need to throw it away afterwards, but it must remain flyable.

The sole point being, that you have more headroom in the loading dept than in the velocity dept. And frankly, at +9, you're going to really know you're pulling some.

Kinda sorry I chipped in now, but nevermind, I can always learn things. For the record, I've never gone over G or overspeed in a glider, or a powered a/c, and don't plan to!

[Pilot DAR]

BUT if in trouble/doubt PULL. The reasoning being that during certification VNE is set at 90% of the max demonstrated speed, whereas the structure has to demonstrate 150% of the max G load (usually 6G) and remain flyable.

Several reasons I disagree with this, and would rather slip past Vne, than a G limit if I've buggered up (and I have), assuming that I have the space (altitude).

The Vne/Vd relationship is indeed 100%/110% - with no damage at 110%. The 100% G limit load/150% G untimate load allows for permanent damage above 100% G, so in theory you could have bent the plane at 110% G (ask Pistons). You will not have bent the plane at 110% Vne, unless you're mixing a whole bunch of G in there too.

All aircraft are equipped with an airspeed indicator, few with a G meter. I'd very much know I'm 110% Vne, than guess at my G, while recovering from a buggered up maneuver, avoiding a secondary stall, and not greying out!

If you're pulling a whole bunch of G, you are much closer to a high speed stall or spin, which if you're just busy getting out of trouble, is the last thing you want.

If you're pulling a whole bunch of G, you are closer to greying out, if you're not the super G resistant pilot, you want to remain "all there" for your recovery.

All this being said, as Pace correctly points out, if, in a spin approved aircraft, you're getting into the high G and high speed corner of the envelope, you've not recovered the spin well. My recent spins in the Caravan at forward C of G showed that a one turn in spin required just less than one additional turn out, but the best I could do was to touch Vne, while pulling 2.8 G to get out of the resulting dive. The Cessna 185 and 206 are similar in this regard.

[BackPacker]

I have however seen Vg diagrams that 'taper' towards the right, defining lower load limits at higher speed.

I'm just speculating here, but if the Vg diagram "tapers" to the right, couldn't that be caused by the potential for flutter under high AoAs?

From what little I understand from wing design, is that the center of pressure/lift of a wing (in normal flight) deliberately coincides with the placement of the spar, to reduce/eliminate torque effects. Hence the reason that the spar is not in the middle of the wing, but placed at approximately 1/3rd from the leading edge.

At high AoA (caused, in this case, by high G loading at high speed) the center of pressure/lift moves forward and no longer coincides with the placement of the spar. This leads to a torque effect across the wing, and a slight warping of the wing across its length, which in turn increases the AoA of the outer portion of the wing. Until that portion of the wing stalls, and moves back to its original shape, after which the cycle starts again. AKA flutter.

Obviously this effect would be most pronounced when you have long slender wings.

So I can well imagine that gliders have (or rather - should theoretically have) lower G limits at high speeds than at lower speeds. (Of course other aspects of the construction may lead to a lower G limit overall than what the wings would be capable of, so this effect may not be relevant for the final Vg diagram.)

[Big Pistons Forever]

Originally Posted by mary meagher

And the reason for teaching glider pilots the difference between the spin and the spiral dive, which is useful as the recoveries are rather different, is that gliders soar in thermals, sometimes in numbers and very close together, as many as 20 in one thermal, 2 or 3 at one level, and hopefully all turning in the same direction. At speeds not very far from the stall, when a gust may suddenly tip you into that stall/incipient spin/ full spin.

You make an excellent point which on reflection seems pretty obvious Powered aircraft flown by recreational pilots don't spend most of their flights in slow flight and banked attitudes at altitude, gliders do, therefore I can see why spin training would be a good idea for glider pilots.....and why glider instructors are more likely to have the necessary experience to teach it properly and safely

I think spin training is a good idea for post PPL powered aircraft pilots. I just think it should not be treated as just another PPL air exercise...it is an aerobatic maneuver which should IMO be taught by an instructor qualified to teach aerobatics

[Mark1234]

Hmm. Very good point from PilotDAR there - rather a personal bias in my viewpoint; almost all the aircraft I fly are G-meter equipped, I mostly fly aeros, consequently have a decent G tolerance, and was thinking of things like a roll and pull through, etc. There's no earthly reason to be pushing VNE on a spin recovery I agree.

I'm still interested to know if I'm missing something on Genghis's point however. For the tapering of the Vg plot, I'd always assumed it was simply that you're putting a whole load of stress on the spar in the rearward sense, leaving it less capacity in the vertical sense - the loading upon it being vector sum, rather than neatly resolved parallel and perpendicular. Quite probably more complicated than that.

[Genghis the Engineer]

Originally Posted by Mark1234

Genghis: My immediate reaction is to say you're wrong, but I think I know something of your background, which suggests you know a lot more than me. Therefore, I'm going to ask why.

Just to make sure we're on the same page, I'm not talking about abrupt, full scale deflections, nor deflecting multiple controls - I entirely understand how they may cause bits to fall off. However, according to my understanding the Vn/Vg/whatever you call it diagram gives an envelope within which you can fly, in terms of G loading, and speed (confined to the pitch plane, but rolling gliders is kinda tedious anyway ). Anywhere in there you should be fairly sure bits will not drop off?

It's known as the V-N diagram, and looks like this...



This diagram's quite a good one, because it shows two different diagrams - the manoeuvre envelope (what you can do in still air), and the gust envelope (what turbulence can potentially do to the aeroplane).

The tapering in the top right, and bottom right, corners, when you combine these two flight envelopes, covers the risks of gust induced overload at high speeds. It's not to do with combined high speed / high g manoeuvring.


In flight, the main loads in the wing are in most designs taken in what's called the "D-box", comprising the leading edge and the mainspar. Manoeuvering loads (g force if you like) mostly bends this, so everthing's trying to bed tip-upwards. Flight loads - those related to airspeed - tend primarily to twist the whole wing, normally in the sense nose-up at the tip (one of the design parameters not often talked about in flying circles is the torsional divergence speed - where the whole wing twists off at high speed), although include bending and also drag loads.

So, at high speed and high g, there will be bits of the wing - most likely somewhere on the leading edge, which is taking simultaneously loads due to g, loads due to speed related drag, and loads due to torsion. These may all add up in the same bit of structure, and cause it to fail.

Now, if the design and certification team did their jobs right, at Vne and N1, it shouldn't, because that combination should have been accounted for, as the loads have at Vdf and 1g. But, I doubt that at Vdf and N1 + safety factors, the same will be true and I'd reckon on a significant risk of structural failure.

Safety factors incidentally do vary a bit, but they should never be less than 40% on structural limits, and 10% on speed limits - they may often be rather more, particularly with composite aeroplanes.

Many years ago, I won a sweatshirt in the Flyer's "that worst day" competition with pretty much this explanation!

G

[Mark1234]

Fascinating, thanks. Never seen the separate envelopes before, makes more sense that way. I was thinking of Vne & N1, not Vdf & N1+safety factors, can entirely understand why that might break! (I'm assuming N1 is shorthand for normal 'placarded' load limit).

[tinpilot]

The shape of the pitch plane flight envelope is due to the different design gust loads at Vb & Vne. The airframe should be capable of withstanding the limit load at any speed but the fact that it will be able to withstand higher loads at slower speeds is rarely placarded. The K21 is one exception.

Modern gliders are very slippery; one certification standard is that the glider should not exceed Vne in a 30 degree dive with the airbrakes extended. In a steep nose down attitude with the airbrakes in, the only way to stop the glider whistling past Vne in a few seconds is to load the wings - high AoA=lots of induced drag & helpfully pulls the glider out of the dive.

Pulling 130% of the limit load will damage the wings, but at least the wings should stay attached. Fly at 130% of Vne & there's no guarantee that the elevator will stay on. In a steep nose down attitude a slick glider will shoot way past 130% Vne unless you pull some g.

The utility category minimum limit load for sailplanes is 5.3g, add in the inherent slipperyness of modern gliders & you can see how glider pilots are more concerned with Vne than pulling too much g. In practice, nobody pulls anywhere near 5g in spin recoveries but hesitant students sometimes get uncomfortably close to the redline. The de-brief may include the "excess g is safer than excess speed" line just to encourage them to pull more than 1.1 g in the recovery.

[Pace]

This is all very interesting and a very different approach to powered flying.
One question I have is concerning air brakes!

Are those speed limited or are they good to VNE and beyond. In the Citation I fly the speed brakes are good throughout the speed range.

Is that the same in a glider and would use of speedbrakes be more comfortable for the pilot rather than using high G pulls to slow down.
That of course also depends on how effective the speed brakes are?

On the Citation they are effective and brakes out huge descent rates can be achieved while remaining within the speed constraints.
Even a Citation with fairly straight wings is slippery and takes a long time to slow down. Flying STARS with speed requests means they are a useful tool for bleeding speed off quickly.

Pace