No bounce landing

[the-minister31]

And keep in mind that they did not land on the asphalt...

[photofly]

They did have an gear problem, allegedly. So maybe 600-700fpm with an unlocked gear is enough to rip it off, but it might not if it had been locked down.

[PilotDAR]

Maybe pilotDAR can chime in here. What is the minimum vertical speed a landing gear needs to be able to withstand upon touchdown for certification?

Off to family Christmas...

In the mean time, here's the standard:

Sec. 23.473

Ground load conditions and assumptions.

(a) The ground load requirements of this subpart must be complied with at the design maximum weight except that Secs. 23.479, 23.481, and 23.483 may be complied with at a design landing weight (the highest weight for landing conditions at the maximum descent velocity) allowed under paragraphs (b) and (c) of this section.
(b) The design landing weight may be as low as--
(1) 95 percent of the maximum weight if the minimum fuel capacity is enough for at least one-half hour of operation at maximum continuous power plus a capacity equal to a fuel weight which is the difference between the design maximum weight and the design landing weight; or
(2) The design maximum weight less the weight of 25 percent of the total fuel capacity.
(c) The design landing weight of a multiengine airplane may be less than that allowed under paragraph (b) of this section if--
[(1) The airplane meets the one-engine-inoperative climb requirements of Sec. 23.67(b)(1) or (c); and]
(2) Compliance is shown with the fuel jettisoning system requirements of Sec. 23.1001.
(d) The selected limit vertical inertia load factor at the center of gravity of the airplane for the ground load conditions prescribed in this subpart may not be less than that which would be obtained when landing with a descent velocity (V), in feet per second, equal to 4.4 (W/S) except that this velocity need not be more than 10 feet per second and may not be less than seven feet per second.
(e) Wing lift not exceeding two-thirds of the weight of the airplane may be assumed to exist throughout the landing impact and to act through the center of gravity. The ground reaction load factor may be equal to the inertia load factor minus the ratio of the above assumed wing lift to the airplane weight.
[(f) If energy absorption tests are made to determine the limit load factor corresponding to the required limit descent velocities, these tests must be made under Sec. 23.723(a).]
(g) No inertia load factor used for design purposes may be less than 2.67, nor may the limit ground reaction load factor be less than 2.0 at design maximum weight, unless these lower values will not be exceeded in taxiing at speeds up to takeoff speed over terrain as rough as that expected in service.

[corethatthermal]

a mush attitude

When we say that, i believe we are implying that there is no stall BREAK or sudden loss of lift, but rather a gradual reduction of lift with lowering airspeed. Perhaps someone can come up with a proper definition of a stall or exactly at what point in the lift curve does this A/C qualify as being in the stall ?

[AuxBatOn]

a mush attitude

When we say that, i believe we are implying that there is no stall BREAK or sudden loss of lift, but rather a gradual reduction of lift with lowering airspeed. Perhaps someone can come up with a proper definition of a stall or exactly at what point in the lift curve does this A/C qualify as being in the stall ?

In flight test, the definition must be well defined as to remove subjectivity. Common definitions include full aft controls, uncommanded wing drop or uncommanded nose pitch.

[photofly]

a mush attitude

When we say that, i believe we are implying that there is no stall BREAK or sudden loss of lift, but rather a gradual reduction of lift with lowering airspeed. Perhaps someone can come up with a proper definition of a stall or exactly at what point in the lift curve does this A/C qualify as being in the stall ?

Proper definition of stall is when the AoA exceeds the critical AoA.

I think there’s an error in my arithmetic. I’m going to go for an angle of approach about 15 degrees (which is 1 in 4!) and a rate of descent somewhat higher than 600fpm. I’ll go through it all in more detail tonight.

[AuxBatOn]

a mush attitude

When we say that, i believe we are implying that there is no stall BREAK or sudden loss of lift, but rather a gradual reduction of lift with lowering airspeed. Perhaps someone can come up with a proper definition of a stall or exactly at what point in the lift curve does this A/C qualify as being in the stall ?

Proper definition of stall is when the AoA exceeds the critical AoA.

I think there’s an error in my arithmetic. I’m going to go for an angle of approach about 15 degrees (which is 1 in 4!) and a rate of descent somewhat higher than 600fpm. I’ll go through it all in more detail tonight.

Sure but from a pilot point of view, it’s not always obvious where and when that is, hence using subjective criteria to define stall. This is normally documented in the AFM.

[Capt. Underpants]

I don’t agree. The aircraft pitch was pretty much level, which, combined with a reasonable flight path angle, gives a moderate (not high) angle of attack. They were in steady flight a long way from the stall- they had plenty of energy. There was simply no attempt to raise the nose.

Even if the aircraft was close to the stall the pilot had plenty of time on approach to add power and lower the nose, given that this was a gear problem and not an engine problem.

In the BA crash you referenced the pilots lowered the nose to maintain airspeed and entered ground effect prior to the threshold, which is not what happened here.

So now that you took the time to analyze it in more detail, I assume you do agree?

[photofly]

Yes, as I wrote earlier, I did some analysis of the video, and it looks like the aircraft was pretty much stalled on final approach.

I've just been looking at the second camera angle from the video, which shows the approach from a little earlier - about 3.5 seconds before impact, but I'm unable to get much out of it.

We still don't know why the pilot didn't lower the nose to maintain (or increase) airspeed, like the BA pilot did.

[GoinVertical]

Regarding the definition of stall for airplanes that are controllable well into the stall, I always taught it as the aircraft is "stalled" when the wing has exceeded the critical angle of attack AND is producing less lift than gravity is exerting on the aircraft.

A lot of GA aircraft just mush or wobble down in a descent while being perfectly controllable. Some of them show no buffet or nose drop at all, unless it's an accelerated stall.

I recall a technique an old-timey pilot examiner used to teach to C150 students, if you're in a situation where you lose your engine and can't see good anything to land on (night, IMC) trim full back, keep the wings level with rudder, and you should be able to walk away from the impact. Never tried it or taught it that way, but it probably works similar to the "landing" shown here.

Looks like the aircraft was on the back side of the lift curve, but still controllable the whole way down. I suspect, as others said, even if they did try to flare, it would have had the opposite effect than desired.

[photofly]

Regarding the definition of stall for airplanes that are controllable well into the stall, I always taught it as the aircraft is "stalled" when the wing has exceeded the critical angle of attack AND is producing less lift than gravity is exerting on the aircraft.

That’s not a helpful criterion.

Oftentimes the wing produces less lift than the weight of the aircraft, when the aircraft is far from stalled. Any time the aircraft is in a climb, for example, when there is a vertical component of thrust.

And when the airplane is a steady non-stalled descent, there is a significant upward vertical component of drag, so the lift, again, is less than the weight.

I believe that what you mean to say is that the forces on the aircraft are unbalanced when the airplane stalls, but even that is not true: for as long as the vertical speed and airspeed remain steady, all forces are balanced and constant. It is possible for this to be so even if the AoA is beyond the critical AoA and the aircraft is “stalled”.

As you note, controllability, stability, and stall are three different things.

[GoinVertical]

Regarding the definition of stall for airplanes that are controllable well into the stall, I always taught it as the aircraft is "stalled" when the wing has exceeded the critical angle of attack AND is producing less lift than gravity is exerting on the aircraft.

That’s not a helpful criterion.

Oftentimes the wing produces less lift than the weight of the aircraft, when the aircraft is far from stalled. Any time the aircraft is in a climb, for example, when there is a significant vertical component of thrust.

And when the airplane is a steady non-stalled descent, there is a significant upward vertical component of drag, so the lift, again, is less than the weight.

I believe that what you mean to say is that the forces on the aircraft are unbalanced when the airplane stalls, but even that is not true: for as long as the vertical speed and airspeed remain steady, all forces are balanced and constant. It is possible for this to be so even if the AoA is beyond the critical AoA and the aircraft is “stalled”.

When the wing is no longer producing enough lift to meet or exceed the force of gravity AND has exceeded the critical angle of attack.

[photofly]

But The conjunctive clause is simply wrong. When the wing exceeds the critical angle of attack it is stalled, regardless of the amount of lift it produces.

It is not “unstalled” if it exceeds the critical angle of attack but somehow does produce more lift than the weight of the aircraft. Which it could, under some unusual circumstances.

[digits_]

I was about to write the same thing, but I have some trouble coming up with a clear example where lift would exceed weight in a stalled airplane.

[GoinVertical]

But The conjunctive clause is simply wrong. When the wing exceeds the critical angle of attack it is stalled, regardless of the amount of lift it produces.

It is not “unstalled” if it exceeds the critical angle of attack but somehow does produce more lift than the weight of the aircraft. Which it could, under some unusual circumstances.

I was responding to corethatthermal and AuxBatOn's discussion about stalling vs mushing vs technical definition in "Hershey bar wing" aircraft. Some students, and even some pilots with experience, have trouble identifying a stall when there is no obvious nose drop, wing drop, buffet, etc, especially if they've got a few dozen hours in airplanes that have a prompt nose drop at stall.

I'm not arguing with the technical, aerodynamic, definition of a stall.

[photofly]

I was about to write the same thing, but I have some trouble coming up with a clear example where lift would exceed weight in a stalled airplane.

Lift depends on angle of attack but also airspeed. If you can push a plane fast enough you can develop as much lift as you want, even though the wing is stalled.

Typically there would be stability issues with maintaining flight like that, but that would be a separate matter.

It’s also worth noting that other than transiently, you don’t get a free choice of how much lift a wing creates. If you push a plane faster so the lift increases, it will accelerate upwards so reducing the angle of attack, until the lift decreases, the forces come back into equilibrium and a new steady state is assumed.

I was just reading a NASA online book (it’s free) about the X31 which was designed to experiment with manoeuvring a post stall aircraft.

[photofly]

I was responding to corethatthermal and AuxBatOn's discussion about stalling vs mushing vs technical definition in "Hershey bar wing" aircraft. Some students, and even some pilots with experience, have trouble identifying a stall when there is no obvious nose drop, wing drop, buffet, etc, especially if they've got a few dozen hours in airplanes that have a prompt nose drop at stall.

I agree. I think the best way though the difficulty is to teach an appreciation of angle of attack, so pilots can discern when it’s clearly too high. Pitch and/or roll instability is a symptom of a stalled wing, but not determinative; high AoA is determinative. Why not teach that?

[AuxBatOn]

Where’s the AoA gauge in most aircraft?

The important part is understanding that yes, AoA is what theoratically defines stalls and for flight with more than 1g (like in a turn) the aircraft will stall at higher airspeed than published.

What’s most important is knowing what defines stall in your aircraft. We, test pilots, go at great lengths to characterize this and publish it in the AFM in pilot speak. During initial type training, this should be at least demonstrated under various conditions.

[photofly]

Where’s the AoA gauge in most aircraft?

Angle of Attack is very simple: it's the difference between the direction the aircraft is pointing and the direction the aircraft is moving through the air (in the vertical plane as the pilot sees it. In the horizontal plane the difference between the same things is the sideslip angle, which is also important).

You can tell which way the aircraft is pointing by looking out of the window. You can tell which way the aircraft is travelling by combining what the ASI, altimeter and VSI are telling you. You don't need an AoA gauge to tell what your AoA is.

If you want to sum up the technical skill of piloting an airplane in a few lines, that's it.

In point of fact, you can read your AoA directly off the ASI if you know (or are willing to estimate) what your g force is.

[AuxBatOn]

Where’s the AoA gauge in most aircraft?

Angle of Attack is very simple: it's the difference between the direction the aircraft is pointing and the direction the aircraft is moving through the air (in the vertical plane as the pilot sees it. In the horizontal plane the difference between the same things is the sideslip angle, which is also important).

You can tell which way the aircraft is pointing by looking out of the window. You can tell which way the aircraft is travelling by combining what the ASI, altimeter and VSI are telling you. You don't need an AoA gauge to tell what your AoA is.

If you want to sum up the technical skill of piloting an airplane in a few lines, that's it.

In point of fact, you can read your AoA directly off the ASI if you know (or are willing to estimate) what your g force is.

What's the critical AoA on your aircraft? What about a 777? Sure you can estimate AoA but you can’t for every type, determine with precision where the aircraft is in relation to the critical AoA, hence the importance of learning individual aircraft’ behaviour during stalls (both unaccelerated and accelerated). Do you think that if they had recognized the symptoms of a stall on their aircraft, the Air France pilots over the Atlantic would have stalled and maintain pro-stall inputs for more than 35,000 ft to their death?