An official ‘hard landing’ is defined as landing with a vertical speed greater than 400 ft/min – wikipedia. I would imagine that is much harder than most passengers would describe as a ‘hard’ landing.
In the US check the NTSB database. It has info on all accidents and selected incidents since 1962. I am guessing a hard landing would be classified as an incident, but I don’t know.
ETA: after re-reading the wiki article that 400ft/min figure sounds more like an average decent and maybe is not used to determine hard landing v. regular landing. I will look for a better cite.
So after briefly searching around, I still do not have a great cite… As far as I can tell, the definition of a ‘hard landing’ is kind of subjective. It is somewhat defined in the commercial airliners maintenance manuals, and It varies greatly depending on model, roll, pitch, and yaw rates. But generally speaking, for a level landing, if the flight data recorder records a vertical acceleration greater than around 1.7-2.1g, then it requires the hard landing inspection. Additionally, the pilots can request the hard landing inspection if they feel it was a hard landing.
I’m not sure if I agree with the phrasing of that one. That’s like saying “Incisions are an essential part of surgery. If you could eliminate them, surgery wouldn’t happen.” It’s true, but misleading. Vortices, like incisions, are unwanted byproducts of a process. The thing is, you can’t eliminate vortices unless you have infinitely long wings. If you could get rid of the vortices (which you can’t), then there’s nothing to stop me from stipulating that lift would still be generated. The problem is that we’re in a magic fantasy land by that point, so I might as well say we all fly around on dragons and don’t need planes anyway.
Here’s my understanding of it: Wings work by hitting the air at an angle, not straight on. That’s called the angle of attack. This angle knocks air down, which according to Newton’s third, makes the plane go up. It’d be like slicing lengthwise through butter, but with your blade cocked up. The butter would push the blade up, right? Well air does the same thing to make a plane fly.
But since the wing is tilted up, it’s also tilted back. The lift vector doesn’t point straight up, but instead points a little bit backwards. That component is called “induced drag” since it’s part of the lift vector. That means that the more lift you generate, the more induced drag you have.
So what’s this have to do with vortices? Well when air from the high-pressure bottom of the wing “leaks” around the tip to the low-pressure top, it raises the pressure above the wing. That lowers the effectiveness of the wing, especially at the tip. If your wing isn’t generating as much lift, then you have to fly with a greater angle of attack to compensate. That creates more drag, as discussed above.
Vortex = less lift = higher angle of attack = more drag = more fuel = higher cost.
Heavier than air craft stay in the air by flinging air downward. You can fling a little bit of air quickly (short span, or a hilicopter) or a lot of air slowly (long span).
When you fling some air downward with a wing, it gets replaced by the surrounding air. This upward and downward air motion manifests as a vortex behind each wing tip.
Tip vortices may be an unavoidable consequence of generating lift, but given that winglets reduce the intensity of tip vortices AND result in more efficient flight, I don’t believe that tip vortices are a any kind of requirement.
End of cruise: Pilot reduces engine thrust, begins descent. You sense a little “whoops” negative g for an instant, and engine noise is reduced.
During descent, the flaps are extended. Whining noise, followed by increased air noise
Just before landing, the landing gear are extended. Some bumping noises, much increased air noise.
Landing. Thump as you hit the runway.
Immediately after landing, spoilers deploy (panels on top of the wing), reducing lift significantly, allowing the airplane to settle down on the landing gear and allowing braking to be effective. Braking starts. You sense heavy decelerative G-forces, increased air noise from spoilers.
About halfway down the runway, pilot deploys thrust reversers, helping to slow the airplane. You hear much more engine noise, may sense more deceleration.
(An aside: Most of the slowing of the airplane is done by the brakes. Thrust reversers and aerodynamic drag from the spoilers don’t have much of an effect, compared to the brakes.)
Near the end of the runway, thrust reversers become ineffective, and are stowed again. Reduced engine noise.
Airplane turns off runway. Increased noise inside cabin as passengers all rise and begin to rummage in the overheads for their luggage.
ISTM that Rocketeer is talking about commercial jets, or ‘heavies’, and Chessic Sense is talking about General Aviation aircraft.
‘Heavies’ do seem to use a lot of brake. How much of the deceleration is from the reverse thrust and how much is from the brakes, I can’t tell you.
When I was flying fixed-wing, I generally flew one of dad’s planes. I remember (before I got my license) hearing him talking about how much the brakes cost. So when I started flying, I habitually came in with 40° of flaps and set it right on the numbers. Never had to use the brakes. Actually, since it was in the ever-windy Mojave Desert, sometimes I had to add power to get to the turn-off. (It wasn’t entirely that I was trying to save dad’s brakes, of course. I just really like making that kind of landing.)
Though an 11.6 mile glide is not all that much at all to maneuver in.
Here’s another scary but successful one.
The Air Transat guys were losing 2,000 ft./min. altitude after final engine flameout. Although they still had enough altitude to spare that they had to fly some circles at the Azores to get down to landing altitude.
Thank you. I’ve never given this much consideration, but that explanation makes it very clear and immediately a duh moment for consequences of the pressure differential.
Chessic Sense said:
I chased my way through a string of wikipedia pages.
Aerodynamic drag is drag due to the cross section of the object, skin friction, and interference drag, which is an effect in transonic flight i.e. crossing from below sonic to supersonic speeds.
Induced drag is caused by additional airflow not from airspeed. The wing has an airflow from airspeed that runs from front to back across the top of the wing. The wingtip vortex pulls air across the top of the wing, which (a) adds air pressure, and (b) changes the airflow direction slightly (vector combination). More pressure above the wing means less pressure difference, which means in order to keep the same lift, the plane has to increase angle of attack. Increasing angle of attack puts more wing profile into cross section, increasing drag. That increased drag is the “induced drag”, induced by the act of how the cross flow affects wing performance.
The airflow moving sideways is work being done by the airplane, and therefore fuel being spent by the engines. That work is being done in a manner that does reduces lift and increases drag, ergo it is inefficient. Remove the vortex and that work is spent on lift, not drag.
Whack-a-Mole said:
Aerated concrete. Autoclaved aerated concrete - Wikipedia The chemistry makes hydrogen bubbles in the material. That and lighter weight aggregate make it lighter and crushable.
Kevbo said:
There’s no reason the surrounding air must come from the air below the wing. In theory, one could eliminate air wrapping around the wingtip, thus preventing vortex formation, but still deflect air by the pressure differential from top and bottom of wing. In practice, eliminating wing wraparound is difficult. Reduction is possible, but reducing it is a trade off in wingspan or winglet size/weight vs performance improvement. As a practical matter, the air wants to wrap around the wing rather than move in from above the plane. That’s because the air under the wing is higher pressure than the air above the plane. That air pressure wants to equalize.
Chessic Sense said:
A better analogy is “Pain is an essential part of surgery.” Pain is a natural outcome of cutting tissue, and tissue trying to heal. It isn’t the point of surgery, and theoretically isn’t required, but eliminating it is difficult because of the inherent nature of pain. Meds only go so far. Same thing with winglets etc. We can reduce wingtip vortices, and vortices aren’t required for flight, but are a natural consequence of the mechanism of flight and are nearly impossible to completely eliminate because of that.
Leaving San Diego a couple weeks ago, our pilot told us we’d be delayed because they had re-configured the runways and now we were too heavy to take off with the wind behind us. He said to wait for further word from him. My question was, don’t they always take off into the wind anyway? At least when they can? Or at least with a cross wind?
I know what you mean, and don’t disagree with the physics of what you’ve said, but the fact is, the A320 has one engine type that has a whine that is somewhat more distinct than the others, so much so that it is specifically recorded and simulated for that aircraft type in full-flight sims. The absence of the whine makes the test pilots antsy.
Yes, but I’ve always found it to be less organized and useful. I think thisis it (though I seem to remember another database from the last time I looked!). I didn’t see anything for this past weekend about a hard landing in Las Vegas, but I don’t know the details of your flight. Unofficial and less thorough, avherald.com also doesn’t report a hard landing.
Assuming the FAA uses only the ICAO Annex 13 definitions (most countries add additional criteria), a hard landing is an incident requiring a hard landing structural check. If the aircraft is substantially damaged, it may be classified as a Serious Incident or an Accident. An accident is defined as:
Most countries have additional regulations about what is a reportable incident to the airline and to the aviation authority for trend/SMS/informational purposes.
Maybe they got instructions to taxi to one end of the runway and then the wind changed directions.
I was practicing touch-and-gos once when that happened. The tower told me to land and do a long roll-out to the far end of the runway, then turn around and take off again.
The preferred runway in SAN is 27 for arrivals and departures. However, if the visibility was low they might have switched to landing on runway 9 which has lower visibility minimums than runway 27; that is, they can land at a lower visibility than if they were landing on 27.
Switching to landing on runway 9 would also require departing on 9 even if there was a tailwind unless the tower approved an opposite runway departure (27) but that would most likely result in a departure delays waiting for a break in the arriving traffic.
There are lower maximum takeoff weights departing on 9 anyway due to the obstacle near the end (parking garage I believe.)
No they don’t always take-off into wind. There are many things that go into the decision to use a particular runway. In some places that have several airports near each other, a change in the duty runway at one airport means the other nearby airports have to change their duty runway as well so the traffic flow works in the local airspace. The upshot of this is that sometimes an airport is operating off a non-preferred runway.
There are also occasions when the maximum weight taking off from one runway with a tail wind will be higher than the maximum weight allowed taking off into wind. This would be due to terrain or other obstacles infringing the take-off path on one runway only. This obviously wasn’t the case for you though.
