Maybe not a good idea, as Tailspin Tom demonstrates using MS Flight Simulator.
I’ll run the same simulation tonight on XPlane, if I can figure out the A320 sim.
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Second Guessing Sully?By lex, on January 21st, 2009
38 comments to Second Guessing Sully? |
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Remember to leave the gear up…. I can’t tell if the image is supposed to be the ditching or not – since there is a runway in the near background…. ah, that’s supposed to be Teeterboro. I see.
I wonder how FlightSimX handled the actual ditching?
You may actually find Scully in X-Plane! And Mulder too!
I thought it amazing that the Naval Safety Center’s Jan-Feb Approach was focused on BASH – birdstrikes. Bet the ready rooms are paying a lot more attention these days. Send a freebie subscription to US AIR
http://www.safetycenter.navy.mil/media/approach/issues/JanFeb09/Jan-Feb09_Approach.pdf
And to top it off Brownshoes in Action Comix is back!!
With collision detection off in FSX, the aircraft just bounces back into the air with power and airspeed. With detection on, the plane quickly comes to a rest with some dust/smoke (spray, if you use your imagination) and the flight resets with a virtual rap on the knuckles.
I’ll fly it again tomorrow morning and get some pictures of the impact, maybe a movie.
Here’s an excellent summary page on this accident:
http://avherald.com/h?article=41370ebc/0005
Is it really true that the fly-by-wire system on this airplane will not let you go down to best glide speed? Any A320 pilots in the room?
Given how “Tailspin” ends his post, I don’t think he’s trying to second guess Sully. I”m sure he isn’t the first to try it on a Flightsim, nor will he be the last.
I seriously doubt the A320, loaded close to gross as it was would have made Teterboro. It was probably barely doable light. With all that fuel, and the people, probably wouldn’t have made it. The mess that would have made!
Sully done good. He made the right call.
Glide range doesn’t change with weight, but angle of attack required to achieve L over D max does. That’s not to say that Tailspin’s “testing” proves anything.
Reference: Aerodynamics For Naval Aviators, pg 371.
Really? I seem to recall that L/D Max occurs at the same AOA regardless of weight, but that the airspeed required to maintain that AOA increases with weight (so long as altitude remains constant).
Turns out I’m right! (See slide 17)
Better chuck that manual.
Never claimed my fun proved anything. But was interesting to be there in the front seat and imagine what it would have been like if I had to make the decisions. And no, I wasn’t in any way suggesting that Scully might have done otherwise. I say he done good.
As for the A320 limiting angle of attack (and thus speed power off) does anyone remebr the Airbus that went into the trees at the airshow when the systems wouldn’t let the crew pull harder?
And no, I wasn’t the first to try it in a sim. http://news.bbc.co.uk/2/hi/in_depth/7834499.stm
Lex, you are correct. What was I thinking?
Regardless, weight has no bearing on engine out glide range.
Umm, careful. Nose attitude controls airspeed. If a higher airspeed is required to maintain best glide AOA at higher gross weights, it’s hard to imagine that happening without trading potential energy (altitude) for kinetic (airspeed). Without pointing down towards more dirt (or river) rather than less.
Not an aero major. I just remember that engine out performance in the F-16 varied as a function of gross weight. I could do a flameout approach to NQX from 8,000 feet over head with 1000 pounds of gross weight and stores, adding 300′ for every 1000 pounds of weight above that.
And it’s true that sailplanes add water ballast to go faster. One of the things I’ve always liked about flying is you can always learn something new.
I can see what I’ll be doing when I wake up at zero dark thirty tomorrow! Assuming the sim has any basis in reality, of course.
David-
Best eng out glide (L/D max) is very closely approximated in the Airbus by “Green Dot” airspeed. Good guess for Green Dot for max grossed jet is about 220 or so. In normal flight control law, no problem getting there.
These guys ended up in Alternate law (dual eng fail=emergency electrical configuration=loss of 2 out of 3 inertials=loss of Normal Flight control law) so some of the protections were lost, but that would not affect ability to get to green dot.
We do a demo in one of our Full Flight simulator periods for 320 initial qualification guys. We put you over SFO at about 20K feet and fail both engines. 280 (IIRC) is air start speed, but eats up Potential energy, so there is some trading: go fast to get a start, or go green dot for the range…
We let them restart one and go home to concrete. Contrary to what the NTSB lead said in her press conference, we don’t practice ditching.
Let me quote the tome (correctly, this time), which probably was written by aero majors.
“In order to obtain maximum glide ratio, the airplane must be operated at the angle of attack and lift coefficient which provide maximum lift-drag ratio. (reference to figure) …the maximum glide performance of a given airplane configuration will be unaffected by gross weight when the airplane is operated at L/D max.”
In your example, were you supposed to glide at L/D max, or did you have to maintain a higher airspeed for the engine to turn fast enough to supply hydraulic pressure for the controls?
An F-4 could (theoretically) perform a flameout approach if it started over the point of intended landing at some ridiculously high altitude that I don’t remember, but the speed required to power the controls was also very high. L/D max was not a concern in that case.
Graphs, I like: Macchi MB326H glide distance at different weights:
Tiny URL: http://tiny.cc/i7Bs2
Skyhawk A-4E/F/G/K glide graph from NATOPS: Tiny URL:
http://tiny.cc/VwqWF
A4G had to be 10,000 feet over intended runway facing landing direction. Less altitude for less heading change for final landing. FUN! to practice but banned later because too much ‘fun’ I guess. Tiny URL for the two parts means two URLs:
http://tiny.cc/xJq6u
&
http://tiny.cc/tu1Vc
F-4 glide ratio per NATOPS (no reference slide available): 1 mile for every 10K altitude. A frisbee could do better. Not exactly a 3deg glide slope…
Mongo – More like 12 nautical miles, not just “1 mile.”
Not as good as an A-4 at 18NM perhaps, but certainly 12 times better than only 1NM from 10k.
I still keep wunnerin if Flit is Lex’s alter ego.
Has anybody seem them both at the same time?
Flit, does it say anything about maintaining power control hydraulics with engines full of bird innerds and chunks of the first-stage rotors?
Because I’m thinking the hydraulics are being overlooked, and some enginerd who added accumulators might deserve a round of drinks over that decision.
There’s a big difference between no power and no control. Somebody added weight to keep that control, probably had to fight for it in the design phase. There’s a lot of souls who should be thanking him for a correct decision years before that behemoth first flew.
But then, I’m an engineer. When we design it right people live and nobody notices. When we’re over-ruled and, God forbid, people die, or businesses suffer outages and losses, we quietly get a bit of satisfaction in knowing we solved that problem earler and it’s not our burden to bear.
About the only way we can live with a failure that kills somebody. That can gnaw at a man.
The other way is to keep the e-mails/memos that over-ruled us and print them out at Staples then plaster them on the bathroom walls before the rest of the team comes into work.
Doesn’t give a lot of solace, but I can hold my head high when I go to work that day.
– Max
I am in no way an aerodynamiscist, but it would seem counter-intuitive to me that the weight of glider would have no effect on its glide ratio. Those wings will only generate a given amount of lift. What if we tried to glide 250,000lbs. 2.5mm lbs? 250mm lbs. I’m guessing the wings wouldn’t provide much glide for that much weight. That’s why bigger planes tend to have bigger wings.
Well, my post was about an F-4J. Your question I assume is about an Airbus A-320.
The A-320 has a Ram Air Turbine (RAT) that automatically deploys if both engines fail (among other things). Along with providing electronics, it is coupled to a hydraulic pump that allows one of the triple redundant hydraulic systems to function. Also, as you suggest there are system accumulators that help to maintain constant hydraulic pressure. Control should not be a problem, although perhaps slightly degraded.
Nevertheless, you concern is notable. Yet for a mostly French design, it seems to be fairly well designed.
Besides the downside prospects of deadsticking his gonna land machine over the heads of many hundreds of thousands of people, perhaps Sully had this crash on his mind.
It was a takeoff weight miscalculation at TEB…
It is perhaps unfortunate that the flameout approach was removed from F-4 NATOPS, because it was the source of great mirth.
As far as what the actual glide ratio of the F-4 is, it’s mostly academic, since no one I knew had any intention of observing it, at least from inside the airplane.
Before Top Gun, there was a movie… Red Flag I think, about the USAF equivalent. To paraphrase one classic line: “The F-4 Phantom – proof that if you put big enough engines on a brick, it will fly.”
Sid-
Teterboro had a real bad string of luck for a couple of months around the time of that landing when the plane ended up in the building across the highway from the end of the runway. IIRC, it was almost one accident a month for 4 or 5 months.
I’m still amazed that the water in the Hudson was so calm that afternoon, because it had been pretty windy in the morning and a little choppy. Granted, I look across the bay up to the Hudson and the Verrazzano from the NJ side, but it was still pretty choppy in the morning.
I’m surprised that the “water” around New Yawk didn’t immediately eat away all metal parts of the airplane.
Flit is correct (ducking waiting for lightning strike). They would have had SOME Hyd and Some electric power. Flight controls would have been in Alternate law – which isn’t really too bad.
Nose
A-320 might even make a good USAF tanker…….
Not enough payload…
F-4 and “glide”- LOL. Same ratio as a rock tossed in the air. How strong’s your arm?
Nose-
Water in NYC corrosive- no that’s Naples harbor.
Flit describes B/U rat assist fine but is ‘alternate law’ assisted or is it powersteering without hyd pressure? Gotta be at least ‘lectric.
I guess it don’t matter. he must have had full authority to make that turn.
b2
Alternate law is still computerificated, just doesn’t have some of the refinements and protections.
Interestingly, Airbus didn’t want you to land in Alternate law due to a few idiosyncracies it has, so they designed the jet to go into “Direct Law” when the gear was lowered. Sully never lowered the gear, so he may be the first pilot to land a ‘Bus in Alternate law.
There is one last failure mode called “Mechanical Backup.” Comes from a loss of all 7 flight control computers. Intended to be used in flight while trying to regain the computers. Rudders and pitch trim only. Landed the sim in Mech once, not pretty. (Even “not prettier” than my normal landings.)
Late to answering BIOR’s question at #15, but the F-16 had a hydrazine driven emergency power unit which (theoretically) auto-started at flameout. That ran the flight control computers and hydraulics.
We never tested the EPU of course, hydrazine being a fatal biohazard.
Hydrazine. AKA “Rocket fuel.”
Just got some photos of the crane raising the Airbus. Rt engine intact but cowling all demo’d. Peeled back the skin behind wings on the belly. Guess cold water is harder than warm water, huh? In any event, a slick piece of fly by wire.
Updated info from a UK Airbus pilot. See bottom of http://tailspinstales.blogspot.com/2009/01/second-guessing-scully.html
Okay folks, has anyone heard of the “Glide Polar”
It may seem counter-intuitive, but in competition for the best time on a course, glider pilots take on water ballast to allow greater airspeed knowing that greater weight DOES NOT REDUCE THE L/D. It does, however, increase the both the sink rate and forward speed so that while the L/D doesn’t change, instead everything happens faster. Most power pilots fail to realize that there are two important speeds on the polar: (1) minimum sink and (2) best L/D. In order to glide further you must always fly faster than minimum sink speed by quite a few knots. There is another factor that changes the glide distance over the ground, tail wind vs. head wind. With a head wind you must fly faster than the best L/D. The rule of thumb adopted by glider pilots is “When in doubt, fly faster”.
Instantly after the bird strike at 3200′ Sully had to quickly make one of two choices: (1) make a down wind landing at Teteboro (the surface wind was light) or (2) ditch in the Hudson. His delay (heard on the cockpit recorder) committed him to ditch.
Contrary to common opinion, ditching can break up an aircraft and result in loss of lives.
Hats off to Sully. It was a bad situation.