Factual Question about the Hudson Rvr Crash

Factual Questions
41

If this is considered too much of a hijack then please accept my apologies, but I didn’t want to start a new thread.

You might be interested in an aerodynamic aspect of the incident yesterday - namely, how much better at gliding a passenger jet is than a typical lightplane, as counterintuitive as this sounds.

The angle of glide is completely defined by the ratio of lift to drag (called the LD ratio) in an aircraft. Nothing else enters into this, not size, not weight, not speed, not anything. I have the figures for a 747, and for a Cessna 150, and the results are rather surprising. The ratio of lift to drag for a 747 is 17 to 1, while for a 150 it is 7 to 1. This directly means that a 747, from a given altitude, can glide almost two and a half times further than the 150 (17 divided by 7). Of course, the 747 will be going around 175 mph while so doing, while the Cessna will be around 50 mph, so the jet will arrive at ground level sooner than the Cessna, but will also, as noted above, go a lot further.

If we assume the LD ratio of the actual A320 was the same as a 747 (probably it was somewhat better) then for every foot it dropped the airliner would have gone 17 ft forward. I did the calculations on this,and without boring you with the details, the results are:

From the 3000’ altitude where the bird strike evidently occurred, the airliner would be expected to glide for 9.7 miles before hitting the ground (or water, in this case), and would take (at 175 mph) three and a half minutes to do it. The 150 could make only 4.0 miles from the same altitude, but would remain in the air, at 50 mph, for four and three quarters minutes.

Without measuring distances on the map, it looks like the 150 could not have glided far enough to miss crashing into the city, while the jet did it with relative ease.

All in all, the incident was an amazing thing to happen. How easily it could have become a huge disaster.

42

It would had been all kinds of awesome if the pilot landed the plane on the carrier deck. :wink:

Tour guide:

So that was the F-4 Phantom and follow me to the next exhibit. Here we see a Boeing 757 in the colors of… wait a minute, since when we have a 757 in display here??? :confused:

43

Thanks for all the answers and the other interesting questions.

That is very interesting Daylate and I am glad you came out of lurkdom to give us the information.

44

Thank you.

Lurkdom? I’ll have you know I’ve averaged 5.22 posts a year!

45

The captain of that airplane was a former F-4 pilot back in the seventies, i am just awaitin for the navy jocks to chime in about a missed approach on a carrier and having to ditch.

This will of course be after the amazement and admiration for a job well done in the circumstances.

I would nominate this captain as someone who should be entertained by obama on wednesday.

Declan

46

Ahem, see Cecil’s column about this…

47

Guess I was correct about turkeys as well as chickens used for tests, not sure why I thought they were frozen. Guess the cold weather made me think that. :slight_smile:

48

This is true. Up to a point. The speed difference may be only 4% but that does not mean the difference in friction and other effects are 4%. They are larger. Say the difference is 10%, well, it is still not huge but it may be enough to make a significant difference if that 10% difference results in some part being overstressed and breaking, etc.

I never quite understood why when in the straight of Gibraltar wind and current are in opposite directions it results in big waves and bad weather which is disproportionate to what you would expect comparing to when wind and current are going in the same direction. The difference in relative speed would not appear to cause such a big difference.

49

Keep that up, and you’ll blow your average. :slight_smile:

Serially, those computations were very interesting, and just what I hoped someone would supply.

50

Regarding aircraft bird strikes:

I was flying on an Ozark Airlines (remember them?) from Chicago to St. Louis back in the days when they still used DC-3s. It was night, and Illinois was going thru a lot of isolated thunderstorms - lightning, at night, in a DC-3, at about 2,000 feet, is impressive! Anyway, there were about six passengers on board plus the flight crew, and to keep from running directly thru the storms, we landed at at least three little airports during the trip. In this process everyone became quite well aquainted, and the aircraft captain began to regale us with stories of some of his flying experiences.

One of these was on a flight, same area, when the plane took a duck into the windscreen. The captain said this was one of the most exciting experiences in his entire career. The duck came all the way thru the windscreen and filled the cockpit with blood, feathers, duck meat, and duck shit. Both the pilot and the co-pilot were covered with this mixture. He said it was the most astounding odor he had ever smelled. Neither of them were injured, but when they landed the airport officials wanted to take both of them to the hospital because they looked like they had been almost killed.

BTE, commercial flying, in the 50’s was a LOT more enjoyable than it is now. Slower, but a heckofa lot more fun!

51

Ahem…that would be an Air Force F-4 pilot, so I expect NO Navy jocks to chime in at all.

Great job overall, but the foundation was laid with those nice Air Force wings!

52

Lol okay

Declan

53

Bumping this to note that the NY Times has an article about the topic of putting screens over jet engines today.

54

I can think of at least three people who need a good kick where it hurts for this stupidity. “Lose lift”??? WTF ARRRRRRGGGGGGGHHHHHHHHHH

55

In defense of the associate professor, that was apparently NOT a direct quote. I suspect muddling in translation through the reporter.

56

Agree. Still … :wink:

57

Uhhh…as I explained to several non-aviation friends after this accident…

The biggest problem with any sort of screen is ICE.

In any sort of icing condition the screen would accumulate ice, unless you had some way to de-ice it. With engines and wings this is done with bleed air, but I suspect a screen mesh would be too thin to handle high pressure high temperature bleed air internally, so they might opt for an electrical solution. So you heat up this big screen in front of an engine, and hope that it heats up in time because if it heats up too late and just melts the ice off then you have chunks of ice thrown into the engine, which is much like…taking a bird down the engine.

Plus, as people have said - making the screen strong enough to withstand a goose or turkey buzzard impact would necessarily disrupt airflow into the engine. Have you seen the size of a GE90 engine on a 777? It would be like putting up a screen to prevent a 200-mph bird impact over your entire patio.

The problem has NOT been ignored by airlines or airplane manufacturers. Look at almost any high-bypass engine and you might see a spiral painted on the bullet nose. Here is an example on a GE-90. This has been proven to scare birds and force them out of the way before they can hear the aircraft.

Newer 737s also have a system that alternates landing lights when the gear is down until 500 feet. The lights flash on and off, creating a disorienting effect for birds and forcing them away. This is mostly useful in low visibility conditions but most 737s also have the spiral bullet nose (at least the -300 and beyond!)

In the end bird strikes are just a fact of life when flying aircraft. Rarely are they as catastrophic as what happened in NY, but they still happen every day.

58

In regards to all this math… what if the goat was on fire?:smiley:

I had a teacher in high school who flew B-52 Stratofortresses during the Cold War (anyone who has seen enough of my posts is probably bored stiff of this story now). He told of a story where they were flying maritime patrol over the Pacific Ocean (looking for that big Soviet invasion fleet, no doubt), a role for which the B-52 is rather well suited to.

On this particular occasion, the weather was pretty nasty, and as per standard operating procedure, their plan was to keep bulldogging through the storm until the tail gunner cried uncle (the tail gunner station in the B-52s that were old enough to have them were waaay off the plane’s center of gravity compared to the flight cabin, and tended to get knocked around a lot harder in bad weather. When the tail gunner wanted out of the storm, you got out of the storm as quickly as possible so you could see what injuries he’d picked up).

All of a sudden, the plane shuddered with a loud “WHAM!” Then nothing was working right. They were loosing speed, losing altitude, the plane was handling sluggishly, and they had lost the chin-mounted radar which they used to see where the surface of the ocean was compared to them (the plane was getting tossed around in the storm like a kite, and radar was the only instrument that would reliably tell them how high they were)

They turned the plane around, limped out of the storm and back over the California coastline, and followed some highways back to Castle AFB so they could land the plane and find out what happened. Their crew chief flagged my teacher down after he got out of the plane and showed him what used to be the bomber’s chin radome, now an inward gaping hole. Inside that hole, they could see what used to be the first bulkhead, now another hole, and behind that, another bulkhead with a hole.

Behind that hole? What, at one point in its life, was probably a duck. Which they hit at a closing speed of somewhere around 500 nautical miles per hour and nearly got killed by. Had the duck been flying six feet higher, he would have punched a feathery bloody hole through the flight deck, which would have been real nasty for a pressurized jet bomber at altitude even if it missed the pilot and co-pilot.

My teacher likes to think that his flying in Vietnam was so effective, that the communists employed a suicide duck to attempt to kill him, because he couldn’t figure out why a duck was flying all by itself in the middle of the ocean in such a big storm…:smiley:

59

I’d love to see a cite for that particular reasoning for the spiral. As I understand it, it’s more for ground crew to see that the engine is windmilling (when off) and stay clear of the blades. At operating speeds the engine’s fans are turning multiple thousand RPM (see here for some specs of the CFM 56-3 engine, used on the 737, (the -5 variant is used on several of the A320 variants.) At that speed it would be nothing but a blur, even at very high frame rates. I’d bet it would be a blur at anything more than a few hundred RMP.

60

At high speeds, wouldn’t the spiral look like a solid white dot? Kinda like a giant eye ball…