If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.
While i was in poland, in the news, this aircraft appeared chashed into a hangar, i read the accident report, any thoughts??
I mean, how can the instructor stall the aircraft and the other pilots did nothing??
A Cessna 208B Grand Caravan skydiving plane crashed into a hangar while performing touch-and-goes as part of a training flight at Chrcynno Airfield (EPNC), Poland. One of the three pilots...
Everything that say is in my opinion, a screener might dissagree If you are dissapointed of yourself, look at me and feel better.
——————————————————————————
Considering that the instructor pilot was instructing them while turning into a 60deg bank at an altitude of about 40ft in a Grand Caravan just after liftoff, I think the lesson was how to commit suicide. Fortunately, his students failed to pass that test. Incredible.
I don't see anything here that relates to sane flight instruction.
Neither is a stall visible in the video, nor does the accident report mention it. I can't imagine that even the most stupid pilot would roll an airplane intentionally into a 60 or even 70° banked turn.
Looks more like a mechanical or medical issue to me.
Neither is a stall visible in the video, nor does the accident report mention it.
It is very possible that the plane was stalling. With such a bank angle a stall would be more of a horizontal motion rather than vertical. And one of the main effects of a stall is the loss of lateral (roll) damping, authority and control. In the video it seems that the angle of attack is high (the plane "dragging its tail" in the turn).
Plane crash in Chrcynno near Warsaw. The machine fell on a group of people, five people died. What do we know about the tragedy?On Monday evening, a small Ce...
If you look the video of that famous B-52 crash, it doesn't look like it is stalling either. But it is.
B-52 Crash at Fairchild Air Force Base in 1994.Patreon: https://www.patreon.com/user/membership
I can't imagine that even the most stupid pilot would roll an airplane intentionally into a 60 or even 70° banked turn.
First of all, you would be surprised how many "invincible" pilots do stupid reckless things intentionally, only to discover, just be fore they die, that they were not that invencible.
Second, it doesn't take an intentional 70° bank to bank 70°. Bank maybe 35 or 45° while going slow, pull back to try to keep the nose from lowering, and the stall will do the rest of the bank for you.
If you look at the video of the B-52, they were applying full right aileron but they were still banking to the left. The same happened in the ATR=72 crash in Nepal.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Gabriel. I don't agree with most things you wrote in your reply and if you compare the crash of the ATR with the 208 you should be able to notice an important and significant difference.
Anyway, since you apparently feel offended by my 'credentials' , experience tells me that this discussion with you leads nowhere and I'm leaving it.
It is very possible that the plane was stalling. With such a bank angle a stall would be more of a horizontal motion rather than vertical. And one of the main effects of a stall is the loss of lateral (roll) damping, authority and control.
I have to admit, I’m confused about this as well. With one wing at least partially stalled, and that amount of lift removed, wouldn’t there be a downward tendency? Also, wouldn’t this increase in (now uncontrolled) bank accelerate the stall? I have to reread the report but I thought it mentioned a wing strike, then continued flight before the crash.
EDIT: reread that.
At an angle of approximately 70 degrees, the left wing made contact with the grass surface of the runway, in close proximity to the airfield tower and a playground fence. Moments later, at 19:40, while reducing the bank angle, the aircraft collided with a parked off-road vehicle in front of a metal building, and then with the building itself.
If that 70 deg angle was caused by a wing stall, how does it continue to fly while reducing bank angle?
Gabriel
Anyway, since you apparently feel offended by my 'credentials' , experience tells me that this discussion with you leads nowhere and I'm leaving it.
I have to admit, I’m confused about this as well. With one wing at least partially stalled, and that amount of lift removed, wouldn’t there be a downward tendency? Also, wouldn’t this increase in (now uncontrolled) bank accelerate the stall? I have to reread the report but I thought it mentioned a wing strike, then continued flight before the crash.
If that 70 deg angle was caused by a wing stall, how does it continue to fly while reducing bank angle?
OMG, where to start. Let's make a list
I didn't say that the airplane stalled. I didn't even said that it likely stalled. I said that it is very possible that it did, as in what is seen in the video is not incompatible at all with a stall.
"One wing partially stalled" doesn't mean that "lift is removed". I mean, compared with the wing just not stalled and everything else being equal, yes. But you can be stalled and still have enough lift to sustain more than 1G.
Bank doesn't accelerate the stall. You stall ONLY when you pull up too mush, that is, when you increase the AoA too much. You can do an aileron roll, and bank 360 degrees and not stall. It is pulling back to try to keep your nose from dropping in a turn what puts you closer to (or into) the stall.
As for your last question.... can I do a list within the list?
The pilot might have reduced the AoA in response to a stall warning, partially regaining aileron control
One of the reasons why trying to correct for the bank close to the stall many times ends up increasing the bank is adverse yaw. Adverse yaw, the tendency of the plane to yaw in the opposite direction when applying aileron to one side (something that is perfectly normal in every airplane and one of the main reasons why the airplanes have rudders and the pilots practice a maneuver/exercise called "coordination"), is badly exacerbated close to or in a stall. If you apply right aileron and that causes the plane to yaw to the left, the yawing motion will cause the right wing to fly faster than the left one generating more lift, and will cause the plane to sideslip to the right causing the right wing to generate even more lift due to dihedral effect, effects that can overcome the now greatly reduced (if still existing at all) aileron authority so it makes the plane bank in the direction opposite to which you are applying aileron. That is why when the AoA is high (as indicated by buffeting or stall warning) you should reduce the AoA before attempting to do anything whatsoever with the ailerons. Anyway, the pilot might have realized of the uncoordinated state of the plane and applied right rudder. Heck, he might have kicked the right rudder just to try to point the nose away from the ground. That would reduce, eliminate or even reverse the yaw cause by the adverse yaw, helping the plane bank to the right.
You can see in the report (a part that you didn't quote) that they say that the plane was sliding to the left. That is consistent with the previous point and would also help roll right.
Finally, in the part of the report you quoted, they said that the left wing contacted the runway and moments later the plane crashed while it was still reducing its bank angle. Whatever was causing the plane to reduce its bank angle before the left wing contacted the ground could still be at play after it did.
And of course, the ground pushing up on the wingtip could also help reduce the bank angle.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Second, it doesn't take an intentional 70° bank to bank 70°. Bank maybe 35 or 45° while going slow, pull back to try to keep the nose from lowering, and the stall will do the rest of the bank for you.
I don’t see this aligning with the report at all. If a 45deg bank becomes a 70deg bank because ‘the stall does the rest’, how is that not stalled? And if one wing is stalled and touching the ground, how does one recover and continue to fly even momentarily? Not by lowering the nose with no altitude to give. Not by reducing bank angle with no aileron authority. Rudder and adverse yaw takes a moment that you don’t have. The rebound deflection from the wing strike is an interesting theory, I’ll give you that. But I think if it were forceful enough to reverse the roll, it would also cause enough drag on the wingtip to yaw you into the ground.
When I refer to accelerated stall, which is NOT what I think happened here, I refer to the fact that wing loading increases with bank angle, as does stall speed, more rapidly as the bank angle increases, and adding elevator, as one would do instinctively when striking trees, would further accelerate the stall. Whereas not increasing elevator would result in a continued descent into the ground. Either way, you’re not going to reduce the bank angle and continue flying before striking something else.
What I’m asking you here is how this 70deg bank could have not have been an intentional 70deg bank given the details of report (aside from incapacitation which has already been suggested)?
(And it should also be mentioned that even a 45deg bank at that altitude is fairly insane)
I suppose one could enter a climbing 35deg turn with insufficient power, experience a wing stall and the onset of uncommanded roll, then lower the nose, unstall the wing and arrest the roll around 70deg, but not before losing enough altitude to prevent a brief wingtip strike, then reduce the roll while not being able to gain altitude in time to avoid hitting the vehicles.
I think either that or, more likely, some classic rodeo flying gone wrong.
You wrote:
I don’t see this aligning with the report at all. If a 45deg bank becomes a 70deg bank because ‘the stall does the rest’, how is that not stalled?
My posts are already quite long without without going into the minute (but important) details, but stall is a complex phenomena starting with definitions. Yes, plural.
The word "stall" is used to refer to related but different aspects of a phenomenon.
1) Flow separation ("In this airfoil the stall progresses from the trailing edge", "The aileron is stalled").
2) Peak lift coefficient (the stall point in the airfoil's or wing's CL-vs--alpha graph).
3) FAA's definition (something like the speed at which the nose will pitch down regardless the application of up-elevator)
The point 2 is particularly tricky. It is very easy to see in a graph what is the AoA of maximum lift coefficient for an airfoil. But in a wing different sections of the wings will have different local AoAs (despite the wing having only one "official" global AoA) plus the flow is not 2D like in an airfoil (there is spanwise flow). So the wing will achieve the maximum lift coefficient after some sections of the wing have already been stalled for a while. Plus, sideslip, yaw rate and roll rate (but NOT bank by itself) , if present, not only affect the distribution of AoAs, lift, drag, and stalled / not stalled sections, but such distributions become asymmetrical inducing further roll and yaw.
The combination of points 1 and 2 are important to understand the lateral-directional handling characteristics at low speed and high AoA's (which are 2 different things).
Low speed obviously affect the authority of the ailerons because the lift (including the change of lift do to a given aileron deflection) goes with speed squared.
However, the roll damping effect (caused by the down-going wing being under a higher AoA than the up-going wing) is affected in exactly the same way. So, if speed was the only variable, the same aileron deflection would generate the same spiral (same angle turned per unit of forward distance) at any speed. But the spiral will be much slower at slow speeds. Also the roll acceleration, and hence your "power" to initiate or stop a roll, will be much slower at low speeds.
The way high angle of attacks affects the lateral-directional handling quality is more complex. Adverse yaw happens at any speed and angle of attack (the down-going aileron always generate more induced and parasite drag than the up-going aileron), but it is exacerbated at high angle of attack because parasite drag is increased due to local airflow separation and induced drag increases at high lift coefficients. Another reason why it is exacerbated is that pilots are used to coordinate the aileron input with rudder input to cancel the normal adverse yaw, but no pilot (except maybe test pilots or aerobatic pilots) is used to apply large aileron inputs at low speeds and having to use much more rudder to keep the plane coordinated.
As explained earlier, adverse yaw will make the plane yaw in the opposite direction that your intended roll, which will make the wing you want to lower to fly faster and generate more lift and will create a sideslip that, combined with the dihedral effect, will increase the AoA and lift in the wing you want to lower. This many times results in an uncontrollable roll opposite to your input even if you are not fully stalled, which ends up in a spin when you pull up instinctively increasing the AOA and fully stalling the plane.
Finally, one of the most important things that happens at high angle of attacks is that the roll dampening greatly diminishes or disappears altogether. When an airplane rolls, the down-going wing sees a higher angle of attack (and higher towards the tip) than the up-going wing. Under normal circumstances this creates a rolling moment that opposed the roll, providing for stability and stopping the roll when you neutralize the ailerons. But at high angles of attack you will be approaching the stall region. Most airfoils don't have a linear behavior all the way to the stall where the lift just suddenly drops. They have a smoother behavior where the increase in lift with increasing angles of attack starts to flatten out and even starts to diminish some before you have the sudden drop. If you are in that region of the CL-alpha curve, the roll will not produce much roll damping if any which makes almost impossible to control the plane in roll (PIO will almost certainly ensue) even if the ailerons are still effective.
So yeah, you can have a condition where parts of the wing are stalled, the distribution of lift and drag is asymmetrical, the airplane behaves very different to what you are used to, it keeps rolling to the left even if you stop the aileron input and it rolls even more if you apply anti-roll aileron input, but you are not officially stalled.
That's why when the stall warning (or stall buffeting) goes off, you have to reduce AoA FIRST and stop the warning / buffeting BEFORE attempting to level the wings. with ailerons.
And if one wing is stalled and touching the ground, how does one recover and continue to fly even momentarily?
Who said that that happened? That's not what the report says. According to the report, the bank angle started to reduce a bit before the wing contacted the ground, and kept reducing afterwards but shortly after the plane crashed against different objects. I have the impression that the wing didn't stop sliding on the ground before the initial contact and the crash.
Not by lowering the nose with no altitude to give. Not by reducing bank angle with no aileron authority. Rudder and adverse yaw takes a moment that you don’t have.
All the roll authority you lose in the ailerons at a high angle of attack, you gain with the rudder. Rudder is much much more effective at controlling roll close to, at, or beyond the stall than in normal circumstances. Many instructors teach pilots to control yaw with the rudder as part of a stall entry and recovery. I am against that because wrong rudder or too much "correct" rudder can cause a spin. I prefer the concept of do nothing else until you reduce the AoA. Of course that will not help when you are 1 ft above the ground.
The rebound deflection from the wing strike is an interesting theory, I’ll give you that.
I never thought of a rebound. If the wingtip starts to slide on the ground while the plane is slowly descending, believe me the wingtip will not descend together with the plane. The ground will not let it. It will make as much up-force on that wingtip as necessary to keep it from penetrating the ground. So the bank will diminish*. That is what I meant. (*the other option is that the wingtip will be dragged back and the plane will start cartwheeling, which is what you said below)
But I think if it were forceful enough to reverse the roll, it would also cause enough drag on the wingtip to yaw you into the ground.
The up force on the wingtip doesn't need tp be much to stop the roll. And the drag force on that wingtip will be even less (up-force times mu. and the mu can be pretty low on a grass runway).
And, the plane might have started yawing to the left and maybe it would have cartwheeled had it not crashed against other objects shortly after the wing made the first contact.
When I refer to accelerated stall, which is NOT what I think happened here, I refer to the fact that wing loading increases with bank angle,
No it doesn't
as does stall speed, more rapidly as the bank angle increases,
No it doesn't.
The stall speed increases with load factor/loading, yes, but not with bank angle. You don't increase the load factor by banking. You increase the load factor by polling back on the yoke.
The graph that you see of load factor and stall speed increasing with bank angle is very misleading and done under the vertical speed is held constant, which is never mentioned and many pilots don't know, which causes a lot of bad understanding of the phenomena which ends up costing lives.
I almost give you the benefit of the doubt that maybe that's what you implied but:
a) Even if you did, it's a bad idea because it is as misleading as those graphs. I want better accuracy and clarity in things that are life-or-death.
b) You didn't imply that, as demonstrated by what you wrote immediately after.
and adding elevator, as one would do instinctively when striking trees, would further accelerate the stall.
Adding elevator will accelerate the stall, yes. But it will not FURTHER accelerate the stall (on top of the effect of the bank you mentioned previously, which doesn't exist). Adding elevator is THE ONLY THING that will increase the load factor and angle of attack and will accelerate the stall.
[CONTINUES BELOW]
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Whereas not increasing elevator would result in a continued descent into the ground. Either way, you’re not going to reduce the bank angle and continue flying before striking something else.
There was a way out (which obviously was not applied here, not in time anyway):
If you are going faster than the 1G stall speed, you can be stalled but still generating more lift than the airplane's weight. This seems to be the case here (IF the plane was stalled which, again, is just a possibility, not a high probability and even less a fact), judging by how the plane was almost keeping the altitude at a quite high bank angle. The problem is that most of that lift was pointing sideways, not up. If you roll the plane wings level (or just reduce the bank angle a bit) you will have good chunk of that sideways lift re-directed up.
Of course, the best way out is to never go in, which takes us to...
more likely, some classic rodeo flying gone wrong.
I agree. Regardless of the fine details of the mechanics of the accident, overall it pretty much looks like reckless behavior (although things like incapacitation, a mechanical issue or other unlikely events are off the table, so let's wait for the final report)
[THE END]
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
I have to find the time to read all of that (I will), but briefly:
Who said that that happened? That's not what the report says. According to the report, the bank angle started to reduce a bit before the wing contacted the ground, and kept reducing afterwards but shortly after the plane crashed against different objects.
Originally posted by ASN report
At an angle of approximately 70 degrees, the left wing made contact with the grass surface of the runway, in close proximity to the airfield tower and a playground fence. Moments later, at 19:40, while reducing the bank angle, the aircraft collided with a parked off-road vehicle in front of a metal building, and then with the building itself.
I get you. You suggest that the left wing made contact and remained there, while the rest of the plane 'reduced the bank angle' by descending toward the ground. I forgot about using immoveable-object-authority and gravity to reduce roll. But read this again: "reducing the bank angle" seems like an odd choice of words for, "the earth rose up to meet the airplane".
It sounds much more to me like the wingtip struck the grass during a deliberate maneuver (perhaps a bit of over-control, maybe) in an unstalled state, then right roll was commanded but the airplane could not climb to avoid the further obstacle in time.
I guess there's a video as well? I haven't seen it.
My first guess would be single engine failure with that remaining PT-6 at full power doing the rest. If you recall, there was a similar crash in a commuter t-prop with a pilot accustomed to engine failure in piston twins firewalling a turboprop and flipping it right over into the ground.
And it looks very similar to that KIng Air accident as well.
We process personal data about users of our site, through the use of cookies and other technologies, to deliver our services, personalize advertising, and to analyze site activity. We may share certain information about our users with our advertising and analytics partners. For additional details, refer to our Privacy Policy.
By clicking "I AGREE" below, you agree to our Privacy Policy and our personal data processing and cookie practices as described therein. You also acknowledge that this forum may be hosted outside your country and you consent to the collection, storage, and processing of your data in the country where this forum is hosted.
Tweet
Comment