cessna spin
 

I would be interested to hear from some one with technical knowledge in such matters their opinion on the following incident. Since it occurred several hind sight experts crawled out of the wood work to impart that yes it¡¦s common, always been a possibility, flaps and Cessna¡¦s recipe for disaster (in direct contravention of what I understood 10„a/lift flaps function to be). If this is the case why are the majority of pilots I¡¦ve spoken to since of all experience levels not readily familiar with such inherently dangerous characteristics? Why when these aircraft are, or used to be the workhorse of flying schools is it not disseminated that Stall/spins are commonly possible risk out side of the normal risk envelope and violent in nature.

The incident: -
Cessna 150 aerobat , 2 POB , half tanks, clear day, wx 15/20 kts, 800 ft amsl.
Right bank 35-40„a , Flaps 10 „a, 75 kts IAS, R/H window latched up.
No other A/C in the vicinity. Very small possibility that wind across escarpment near by could have generated a rotor wind of sorts,(highly unlikely but my explanation prior to the woodworms).
We were circling while taking pictures and had done so many times previously in the same configuration often with less speed more bank and less stable winds. Suddenly with out stall warning buffet or any other symptom the a/c flicked over in to a full left-hand spin. I didn¡¦t recover immediately
as in the circumstances I thought a control surface or cable had been lost. On completing spin recovery I did not apply full power for the same reason. Obviously given the height the whole incident was over fast and we levelled out at less that 200ft agl shaken not dead.
Understand that I make no claim to be the best, most proficient or faultless pilot and I am familiar as all should be with the risk of stall in varying configurations and am very conscious of its avoidance. On the day and in qualified hindsight I can say that there were no extenuating circumstances and this happened when it never had previously and was unforeseeable.
Opinions please.

Looking at the ground, steep turn slow in 20 kt winds. Seems to me configuration wouldn't matter much. When you turn from downwind to a crosswind and on to upwind, the drift over the ground causes people to instinctively tighten the turn. Pull too hard and you high speed stall.

Check c of g and flap rigging (symmetrical) if you want to try blame something else. As far as no stall warning, which wing is the stall warning device on and which wing had higher angle of attack?

Might you have hit your own slipstream?

Interesting.

With Flaps10, I wouldn't expect the normal Vs of about 40 kn to be significantly reduced.

With 40° bank, a quick back of envelope sum suggests a stall speed of about 52 kn, which gives a reasonably sensible margin below your chosen speed of 75 kn IAS.

But, heedm's suggestion makes sense. If you were flying initially into wind by attitude, and turned downwind continuing to fly by the picture out the window (and particularly ground references) and not by reference to instruments, then you could find yourself fairly rapidly below Vs due to the inertia of the aircraft. Combine that with a turn, where in an aircraft with moderate aileron drag like the C150, and a spin entry is not an unreasonable possibility.

Bear in mind that if you were that low, then the horizon is not a hugely useful attitude reference because it's position keeps changing due to surrounding landscape.


Considering your question about the use such aircraft are put to in a flying school, this aircraft would have been certified almost certainly to FAR-23. The worst case in there is a 3 kn/s decelerated case in turning flight. Let's look at your case...

At 75 kn / 40° bank, your turn rate will be 29s/per 360° [turn rate in rad/s = g.tan(bank angle)/V], so you could go through 180° in 15 seconds (rounding off). So you could change from 75 kn (into a 20 knot wind) to 75-(20*2)=35 kn airspeed in 15 seconds. The mean deceleration rate (it'll actually follow a sine function) will be 40 kn / 15 = 2.7 kn/s - which is getting into the right ballpark.

Working out the sine function is easy enough, at 29°/s, it comes out at an airspeed of 55+20cos(12.4t). [Note I'm making one major approximation here, that your aircraft's inertia is too high to allow the airspeed to match - this is obviously untrue, but bear with me]. To find the rate of change in airspeed at any point, differentiate this with respect to time.

Plugging these into a spreadsheet (and differentiating numerically), it suggests that you hit the stalling speed of 52 knots at 7½ seconds (or roughly broadside to the wind) whilst decelerating about 4½ kn/s. This is right on the edge or possibly beyond what the aircraft is certified to have acceptable handling at.

I haven't taken into account the relatively low intertia of the aircraft, but equally I haven't taken into account that you may have inadvertently not increased power enough to hold the turn, pulled back on the stick slightly - or many other things. Analysis of that depth requires a lot more work, and I charge for it !

But basically, flying medium turns, at that speed, by reference to ground features, in a strong wind, does appear to give reasonable potential for an accelerated stall in the turn - which is quite likely in any aeroplane to cause a spin entry without prior stall warning, particularly when you may well have been decelerating at or beyond the certification limits for the aeroplane.

G

And, as John says, hitting your own slipstream is a fair possibility too.

G

Hi Genghis

That was some very good reading I thought and immediately tried the formula myself and this is what I came up with:

V = 75kn = 12.75Km/h = 38.5842m/s
g = 9.82
40° ba

9.82tan(40)/38.5842 = .4324

2pi / .4324 = 14.5309???

which is about half of what you got, I guess some difference in rounding, but where does the factor 2 come in? Did I miss something? :confused:
Cheers.

My calculator gives 9.82tan(40)/38.5842 = 0.2136, almost exactly a factor of 2 different from yours.

G

Ooops, somewhere deep inside the mysterious windings of my calculator, a sub-menu setting was of on another requirement. Thanx. :D

cessna spin
 

Thank you all for your responses. The gist seems to be high-speed stall due to careless flight. Obviously not impossible; the surprise being that as mentioned similar manoeuvres have been completed with more severe factors and no adverse response.I had considered slip stream as often I hit it. again circumstances as they were it could have been the clinch if so supprising now and not previously or since in more critical conditions.
This just leaves the woodworms. It seems to me that the figures could be crunched in the same way for all types of A/C arriving at differing values for different types in the same circumstances. Is the 150 inherently more unstable than other training types, is there validity to the theory, better off with out flaps.
Since the incident I now fly the turns flapless with slightly increased speed, the logic being recovery from spin being more straight forward as despite loosing the benefits of reduced stall speed there is the opinion that disturbed air from flap extension could hinder rudder efficiency in recovery? I am not happy with this really as I would have thought better to have the extra few kts to play with than ( so long as the wood worm theory is inaccurate) ease of recovery should the mistake happen again.

AIRBALL Hi, Cessna singles do have sometimes interesting stall spin characteristics. Power-On Landing Config stalls will invariably provoke wing drop and spin / spiral entry. This varies with model and marque within model. The most exciting model that I teach is the Cessna 210L thru N. Try this at a safe height ( only if you are spin training / spin recovery approved ). Set up the following configuration: Landing gear extended, flaps 40 degrees, RPM 2300, Manifold Pressure 17". Maintain level flight and altitude. As the speed decays, be ready to input full right rudder. When the stall is imminent, accelerate it by extra back pressure on the stick. The aircraft will suddenly ( usually promotes a quick " Oh F**K ) flick roll to the left and adopt a spiral or spin entry. Recovery is: IMMEDIATE (remember I said be ready) right rudder, ailerons neutral and stick forward to achieve horizon half way up the windscreen, introducing power as airspeed increases. Average CPL loses 750' feet at first attempt in recovery despite being fully briefed on what to expect, ( time wasted with uttering expletive ?), competency standard asked is 350 height loss and this is normally achieved on 2nd or 3rd attempt. This sequence is taught because the scenario of overshooting base to final ( left turn at about 500' AGL ! ), tightening the turn and a bit of nervous back stick would give similar results to that practiced at 3,500', i.e. 750' height loss or 250' below ground level in an inverted spin! ! ! . With proficiency training you might recover at about 150' if you did overshoot final and tightened up the turn, fixed it immediately and offered the expletive later. The Cessna 206 exhibits similar but more docile behaviour, as does the Cessna 182. I believe 172 and 150/152 are similar but have not provoked them personally. I think there was some reference to this Cessna characteristic in the Australian AOPA magazine some years ago by a contributor. So what you experienced was probably predictable ( you had power ON, Flaps extended). As for some explanation in aerodynamic terms, there are several parameters to consider. The flaps on all Cessna's are slotted Fowler and effective. With the 200 series there is sufficient power for torque induced counterclockwise roll ( maybe on the smaller ones too ? ) The propellor slipstream is spiralling clockwise and at high AoA P effect will contribute to extra lift on the right wing and reduced lift on the left wing, giving assymetric lift ( roll ) . So the torque roll coupled with the assymetric lift roll combine at the stall break. Please dont experiment with this unless qualified * * * :(

Mainframe,

A quick read of the Type Certificate sheet indicates that the 210 models are not approved for spins (for this read = prohibited from intentionally doing).

I don't have a POH to hand for the models quoted but I suspect it will say something similar ... please do correct me if I am wrong ... ?

Very few aircraft are designed to handle the sort of flick manoeuvres which you are describing .. have you ever given any thought to the gyroscopic structural loads on the engine mounts and the forward fuselage .... or the empennage loads .. ?

I shudder to think what your little games have been doing to the particular aircraft fatigue lives ...

Really, I have to suggest that you give CASA an anonymous call on 131757 and have a talk to one of the structures or flight test certification guys in Canberra to discuss the ins and outs of what you are doing ... it might save your life ... or, more importantly, the lives of some unsuspecting crew who find an important bit fall off the aircraft ....

Or is your post just a tongue in cheek wind up ? If you are, indeed, serious it would be a great idea if you posted the registrations so that everyone else could carefully avoid flying in those particular aircraft ...

On a more general note, I support basic aerobatic and spin training quite strongly .. but it should only be done in aircraft for which the loads have been considered in design and for which such manoeuvres have been cleared by flight testing ....

Perhaps John Farley might offer some wise counsel to this chap ... ?

John_Tullamarine You are right, the Cessna 210 is NOT approved for spinning. Great care is taken in the demonstration to prevent progress beyond the incipient phase. The training manoeuvre described will possibly develop into a spin if IMMEDIATE corrective action is not taken as stated. As for the accident scenario, this is a very common cause of fatals in this country in Cessna 200 series, generally by young CPL's saying "watch this !" as they do a beat-up followed by a wingover, or even just a steep turn after takeoff. The reason for the training manoeuvre is to demonstrate the vicious response of the aircraft in those scenarios and is intended to prevent a future fatality. No pilot who has had this demonstrated will ever place themselves in a potential stall situation with power on. As for the stresses, the aircraft will break into the stall at around 45 to 50 kts IAS and the manoeuvre is controlled so as not to progress beyond 60 degrees AoB, this is far enough to instill respect. Sorry you took this the wrong way, it is not a windup, it is serious stuff and as stated, it is to prevent a future fatality. This is an aircraft characteristic and understanding the good and bad behaviour of the aircraft is important.

Rather you than me, my friend ...

I think that you are tempting fate with this one .... and I cannot see why the exercise need be done in this sort of aircraft when one could achieve the same sort of skill and caution with an acrobatic category aircraft .....

.. and how do you reconcile the flick loads on the structure ? .. these don't sit there waiting until a spin is established before they exert their influence on the airframe ....

spin
 

Again all good stuff, thanks for responses. One point of interest concerning spinning and my incident. Only two weeks before it happened I had a free hour in an Aerobat and took it up to play. First idea was to loop having had it demonstrated in another type a couple of weeks before. At about 70„a nose up I decided I wasn¡¦t ready for that and opted for stalls and spins. This was the first time in three years I had spun and first time solo. I completed three, the last being best, unsure of height loss but standard recovery for type being employed having revised it before take off. It was an alien environment when induced, If it had been more unfamiliar when it happened for real ¡K..who knows?
This is a happy story and the experience was invigorating. Spin familiarity was my saviour and in future I shall watch for inadvertent backpressure, increased AoA and speed stalls.

I have to second what John.T has said. Deliberate spinning puts quite large, and often hard to predict stresses on the airframe (and especially the engine). This is taken into account during the design process but, unless you've had good sight of the certification reports, there are large risks associated with spinning an aircraft not designed for it, particularly with power selectied. They are not necessarily the relatively easy to understand risk of not recovering.

G

Spinning, my favourite subject!
Only last week I was out in a C150 with a photographer circling at 1000 ft with various combinations of bank and sideslip (flaps up) thinking that an unwary pilot could get a shock doing things like that.
I get to spend some time in Aerobats showing budding instructors the spin, including some inadvertent entries and they are invariably impressed with how quickly it can autorotate from a stall in a turn, given the right control actions from myself.
For more info on spinning Cessnas - here's a copy of a Flight article from 1978:
http://groups.yahoo.com/group/ozaero...%20Operations/

I am posting this at the risk of starting another war on airspeed vs. groundspeed...
There is one other thing to consider- what was the wind at the time? At the airspeeds you are at in slow speed flight, if the wind is more than 25% of your airspeed, you need to be concerned about the change in kinetic energy when you turn downwind.
The 25% is a rule of thumb I've found useful over the past years.

airball - any chance you had a bootfull of rudder in?
I remember touting photogs around in a 152 (ok., I ADMIT it) and you will nearly always finish up with rudder to counter the bank angle at some point. Any nudge into the spin regime then and you'll be away before you can say 'What.....?

Shawn, if you re-read airball's original question, he was flying about 75kn in 20kn wind, so about 25-30%, looks like your rule is good !

G

As I continually advertise my ignorance, let me proceed as usual and ask those erudite alumni of either Empire, or NTPS; To what rule or heuristic might the 25% KE pertain? Apparently we are talking about a change in the airspeed due to inertial effects. I would be very obliged if you could point me in the correct direction.

The 25% rule of thumb is just that. So far, no scientific evidence of it, just some personal experience. I also noticed that if you do the standard navigation planning exercise of flying between two points 100 nautical miles apart at 100 KIAS and start adding a wind that is directly along the track (to show how things don't always cancel out), that the effect really starts to show when you get to 25 knots of wind. Got me thinking and observing more closely and it appears to be a reasonable rule of thumb.
The folks who really know about this effect are ultra-light pilots - ask one of them what height he would climb to if taking off with a left cross wind of lets say 10 knots crosswind component and wants to do a right turn after takeoff. It's quite high, because when the right turn starts the aircraft will probably descend (their airspeeds are pretty low).
The folks who absolutely know and understand this are the model airplane folks. Their airspeeds are very low and even the slightest wind affects them when they turn.
Who knows, might be a good master's thesis subject...

Shawn,

Thanks for clearing that up, the visual of the ultra-light turning downwind from a crosswind really exemplified the problem, it doesn’t appear so vividly when using bigger airplanes as a model. A 25% loss of airspeed would be 44% degradation in lift. Another thing to put in my bag of tricks. That would be a fun thesis subject... (I thought it may have been Doolittle’s dissertation)

Loss of kinetic energy when you turn downwind, very interressant subject Shawn!

let's see the case of a downwind turn just after takeoff when the wind is more than 25% of your airspeed

I can found the following factors: (I maybe wrong!)

There is a variation of wind velocity and direction near the ground which affect lift, drag and moment of the aircraft. This horizontal gust or shear vary with altitude and are due to the friction of the air over the ground (sort of boundary layer).
In my view this ground boundary layer can have different profiles:
LAMINAR: low thickness, low velocity near the surface, gradual velocity change. (Mojave desert early in the morning!)
TURBULENT: greater thickness, higher velocity near the surface, sharp velocity change.

We also have to think about the effect of leaving ground effect:
— increase in induced drag and thrust required
— increase in angle of attack to maintain the same lift
— reduction in climbing performance (more drag with the same thrust)


I have experienced this problem while towing big gliders in summer: (180 Hp tug with a 750+ Kg glider), we had to do a turn just after takeoff (200 feet max) to avoid some house (noise). We always used to turn upwind and One day I decide to turn downwind towards a great cumulus and I never made it......As I was turning , I lost around 10 Kt of airspeed and start to descent.....unable to recover.......I had to release the glider in a crop field (pilot and glider OK). Wind speed was around 30% of towing speed and turbulent.


stardust

I'm not sure I totally agree with you Shawn about ultralights.

Microlights tend to have very little inertia and huge amounts of wing, so steep turns tend almost entirely to remain in the wind axes, rather than intertia keeping them in earth axes.

But, ultralights tend to operate not much above the stall. Typically at a cruise speed of 40-50 kn, compared to a typical Vs on a US FAR-103 ultralight of 20-24 kn, or 30-35kn for a European Microlight or ULM. They also don't generally have much excess power to balance the turn with.

So, standard practice is to do steep turns in a shallow descent, providing energy to keep the speed on in the turn.

Still a valid handling issue, but I think not entirely related to this Cessna case - where the ratio of inertia to wing area will be much higher.

However, ultralights have another issue - in a 60° banked turn at ultralight speeds, a 360° turn can be done in about 8 seconds - so the risk of flying through your own wake turbulence is very real. For which reason, such turns are (or should be) flown climbing or descending - and not level.

G

Sideslip?
 

Sorry for being so late to this topic (I've just now read it), but it seems to me we are talking about the airspeed drop that occurs when you turn downwind from a sideslip.

GTE, I think the discussion that Shawne brought up may be valid for the Cessna spin that was the original subject of this thread.

Look at what airball posted regarding his incident:

Then look at what djpil posted:

What both incidents have in common is using a C150 to take pictures. What djpil points out is that he had to use bank and sideslip while taking the pictures. One would assume the reason for this was driven by the need to place the aircraft on the proper ground track in order the get the desired photo.

When an aircraft is sitting at the end of the runway ready for takeoff with a 20kn crosswind, it is already in a 20 kn sideslip when it leaves the runway. When you land in a 20 kn crosswind, you are sidesliping 20 kn just to keep the aircraft on the centerline.

Rule of thumb (Shawne or GTE check me on this)

If you're sideslipping into the wind and then quickly turn downwind, expect a temporary loss of IAS roughly equal to your sideslip speed.

Remember, you are flying the aircraft with IAS speeds relative to a moving airmass. It's usually when you are referencing a fixed point on the ground (whether taking pictures, taking off, or landing) that you enter a sideslip relative to the moving airmass you are flying in, because you are concentrating on a fixed point on the ground.

The 2 Cessna C150 photo examples, the glider tug example, and the ultralight examples all seem to demonstrate this. Inertia comes into play when you consider how long it takes for the aircraft to recover the airspeed downwind that you gave up during the sideslip.

Without deep thought, I'm inclined to believe that anybody making a habit of initiating a turn from sideslip is likely to spend a certain amount of their life spinning. Turns in a FW aircraft need to be entered from balanced flight, and continue to be balanced.

A tiny amount of sideslip is inevitable in entering a turn, but I mean tiny.

G

Is it possible that the extra noise produced by the open window
fooled the brain into thinking you were going faster than you really were?

Genghis, the sideslipping finals turn (top rudder) is much in favour in long-nosed tail draggers; you get a better view of the landing environment and the degree of sideslip acts as a variable extra drag inducer.

The pilot must know his(her) vehicle, of course, and be comfortable with the margins over the stall/departure to avoid the scenario you hint at!

The sideslip has to be got rid of before arrival, of course, and there is some satisfaction in the co-ordinated elimination of sideslip and bank as the threshold is reached at the button speed.

[Edit to spell Genghis properly; sorry!]

I agree, but it's flown at approach speed (1.3Vs or higher) and manoeuvring turns (as opposed to a controlled descending finals turn) would not be initiated at these conditions without first returning to balanced flight. The poster discussed use of sideslip in aerial photography at relatively low levels, which if reported correctly, certainly sounds to me a little foolhardy.

G

Indeed; but it can be safe if the general rule is always applied:

Never do something at low level that you have not thoroughly practised and understood at a safe height.

I've seen it go wrong, and it was the photog who paid the price for too low/late an ejection.

> The folks who absolutely know and understand this are the
> model airplane folks. Their airspeeds are very low and even the
> slightest wind affects them when they turn. Who knows, might
> be a good master's thesis subject...

As a model flyer...

I don't think many model pilots do understand the 'downwind turn' issue. The debate surfaces regularly in the magazines and newsgroups. Usually we're too worried about the effect a downwind turn has on ground speed to notice if the sink rate is any higher/lower. The downwind turn has a bad reputation because the high ground speed fools the pilot into thinking he's going too fast. Pilot tries to slow up which causes a higher sink rate or worse a stall and spin in.

As a early solo glider pilot (lapsed)..

I never noticed the wind while circling in a thermal drifting downwind. Sure if you look down you can see your track isn't a circle on the ground but I can't say I noticed any "up's and downs" are you go round and round. Not even when you are sharing a thermal with another glider.

However it's clear that gliders have innertia or wind shear wouldn't be a problem, the plane would instantly accelerate to maintain it's flying speed.

Jury still out.

Cwatters illustrates the stall/spin problem with model flyers who focus on ground speed instead of airspeed. Imagine what would happen to the glider if the pilot DID try to make the ground track circular? If there was a good wind, he might stall/spin on the downwind-to-upwind turn in the thermal.

The glider tug pilot who wants to make a left downwind turn after taking off with a right crosswind, should first turn right to negate the sideslip, then perform a balanced turn to the left. It will take longer to get to the desired heading, but at least you'd arrive at the final heading with normal airspeed. However, if the tug pilot insists on maintaining a ground track (AND heading) along the extended centerline of the runway, he will be in a right sideslip due to the crosswind just prior to making the left turn. If he turns left now, he will experience a loss of airspeed because the turn is not balanced.

A long time since I played at being a tug pilot.... (and I say that with not the slightest flicker of a wry smile on my face)

A glider does its very best to drive the tug and pull it into line with the result that the tug pilot has two options .. either

(a) slip (which I had never thought anyone would permit due to the reduced climb performance ... nobody like a glider pilot to keep an eye on which tug pilot gets to height quickest ... and crucify the pilot who costs him/her an extra dollar or two) or

(b) use the leg to make it fly nicely and properly.


.. or am I just being old fashioned ?

(c) Request the glider pilot to fly a half wing span (tug) out to the side opposite to the leg you are using and which is gradually beginning to get the shakes. On a long tow that's worth a beer in the bar afterwards.

Nothing to do with the thread, of course, but a happy thought on a glorious soaring week-end.

Of course, the 150 WAS designed for it. And spin vs. no spin training has always been a big debate. I've always found it interesting how easy it is to spin a 150, especially with power applied. I did my flight training in Canada where spin training is still mandatory, and the 1974 vintage 150 training aircraft I flew probably had more spins in its history than I could ever count. My instructor liked doing spin entry with power, since that would likely be the scenario in an approach gone wrong. The stall horn rarely got a chance to go off and there was very little buffet before the aircraft would roll over into a very well developed spin (very pretty over the fall colors of the Ottawa Valley). Also, it's no wonder you didn't get horn. If memory serves, the stall horn is on the left leading edge, and you were likely making a turn to the right. so your right wing would have stalled first. Worst "almost incident" we had was when a student did the preflight and filled the tanks prior to his lesson. The student was 230lbs + and the instructor was at least 200 (putting the little 150 over gross.) The instructor had been flying spins all day (the class was all at that point in the training) and so the instructor was a bit tired to notice the over gross situation. The instructor entered a demonstration spin and the aircraft would not recover using the standard method. Faced with no other choice the instructor threw in power - knowing the results could go either way. We suspect a combination of the yaw input from the prop and the increased airflow over the tail allowed them to recover from the spin. Stupid thing to get in to. Good thing he was familiar enough with spins to know his options.