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Cynic
Picture of charlie12
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quote:
Originally posted by Sigfan Roy:


I know one of your pilots. He lives south of Memphis


_______________________________________________________
And no, junior not being able to hold still for 5 seconds is not a disability.



 
Posts: 13014 | Location: Pride, Louisiana | Registered: August 14, 2002Reply With QuoteReport This Post
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Originally posted by Xer0:
Another question for pilots. Does the fuel efficiency correlate directly in headwinds vs tailwinds? Like do you burn xx extra pounds of fuel flying 2 hours into a 100mph headwind, but would save the same xx pounds of fuel flying the 2 hours with the same 100 mph tailwind?


Yes, and no.

When most people think of fuel efficiency, they think of miles per gallon (or liters/km). Once you leave the ground, however, it becomes more complicated.

Specific fuel consumption is a measure of fuel efficiency per hour, for a given power output. It's the standard function of efficiency of an engine, and SFC doesn't change with a headwind or tailwind. The engine is burning the same amount of fuel per hour. The flight, however, takes longer to get there with a headwind, or gets there faster in the case of a tailwind. Consequently, more fuel is burned flying into the headwind, because the engine is burning fuel longer, due to a longer trip.

If you equate that to miles per gallon, then more fuel is burned for the same number of miles when flying into a headwind, than a tailwind. It could be said that the gallons per mile (more true in a turbojet airplane, whereas a car is miles per gallon) will show greater efficiency with a tailwind; less flight time, and less fuel burned.

Less fuel burned means that less fuel needs to be carried, which means the flight is lighter, which means that less power is needed in cruise, or the flight can climb higher, where fuel burn is more efficient, air is colder, true airspeed. higher, and the aircraft even more efficient at a given mach number.

For example, a 747 typically burns about 24,000 lbs of fuel per hour in cruise (4,000 gallons). For this it's doing .84 mach, which will indicate in the cockpit as about 280 knots at 36,000' of altitude with an outside air temperature of -54. and equates to a true airspeed of 415 knots. In still air, the airplane will have the same groundspeed, so figure a still air speed of 415 knot, or 477 mph.

Flying into a 100 knot headwind, that makes groundspeed 315 knots, and with a tailwind, 515 knots. Over a course of 3,600 miles, that's 7 hours with a tailwind. The same trip going westbound against the 100 knot headwind, however, takes 11.4 hours. That's a big difference. at 24,000 lbs/hr, the eastbound trip is 168,000 lbs of fuel, but the westbound trip is 273,000 lbs of fuel, and may require a fuel stop.

That's oversimplified, and at the heavier weight for the westbound flight, it's not going to reach a cruising altitude of 36,000' for some time, as it's too heavy. Therefore it will have to step-climb, meaning climb to an optimum altitude as fuel burns off; it's lower for longer, and thus even less fuel efficient.

A general rule of thumb is that for every 1000 lbs of extra fuel, 4% of that fuel will be burned to carry it, due to the weight increase.

The actual trip calculation is not nearly so simple for a host of reasons, but that's the gist of it.
 
Posts: 6650 | Registered: September 13, 2006Reply With QuoteReport This Post
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Fascinating thread. Thanks for taking the time to explain this stuff to laymen........


Remember, this is all supposed to be for fun...................
 
Posts: 4123 | Registered: April 06, 2007Reply With QuoteReport This Post
Dances With
Tornados
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801 MPH WINDS


Flight from L.A. to London reaches 801 mph as a furious jet stream packs record-breaking speeds.

A Virgin Atlantic Boeing 787-9, like the one seen here at Detroit Metropolitan Airport, reached 801 mph Feb. 18, 35,000 feet over Pennsylvania. (Tanya Moutzalias / Associated Press)
Tuesday is a nice day across the Northeast. Temperatures near 40 in New York, light winds out of the north at 5 mph to 10 mph, and wall-to-wall sunshine sound like a tranquil day — especially by February standards. But high up in the atmosphere, it's a different story.
The jet stream, the high-altitude air current along which storms travel, is furious. The river of air was clocked at more than 230 mph over Long Island on Monday. That measure comes from the 250-millibar pressure level, meaning it was at a height above 75% of the atmosphere's mass. It sets the record for the fastest 250-millibar wind speed ever recorded over New York and, probably, the country.
The 250-millibar level generally tends toward 30,000 feet to 35,000 feet. That's about the same height at which commercial planes fly. Unsurprisingly, the jet stream can have big implications on how quickly aircraft reach their destination.
With a speed max currently over central Pennsylvania, airplanes flying through the jet stream will either be sped up or slowed down big time, depending on their direction of travel. It's like the moving walkway at the airport. You have your own forward speed, but if you continue this velocity in an environment that is itself moving, it can propel you at an impressive rate.
A Virgin Atlantic flight from Los Angeles to London peaked at a whopping 801 mph Monday evening 35,000 feet over Pennsylvania. "[N]ever ever seen this kind of tailwind in my life as a commercial pilot," tweeted Peter James, a jet captain.
It appears that's a record for the Boeing 787-9 twin jet, which in the past has flown at speeds up to 776 mph. The ordinary cruising speed of a Dreamliner is 561 mph, with a maximum propulsion of 587 mph. Any speed gained on top of that is thanks to Mother Nature's helpful boost.
Although the plane didn't remain in the "jet streak" — the zone of maximum wind embedded within the jet stream — for long, it still arrived 48 minutes early. And you might notice something about the 801 mph reading — it's above the speed of sound (767 mph). Commercial aircraft ordinarily can't break the sound barrier, because they're not designed to handle the sudden increase in drag and other aerodynamic effects associated with those speeds. Despite a ground speed that high, the plane didn't come close to reaching that threshold because it was embedded in the swiftly moving air.
An LAX-JFK Delta flight overnight hit 678 mph at 39,000 feet over the Ohio Valley, while a 737 from Chicago to New York passed 700 mph at 8:43 Eastern this morning. Chicago to New York/Boston routes will be shortened to 1 hour, 24 minutes Wednesday instead of the usual nearly two-hour flight time.
Likewise, flight times from Dallas to Boston dipped below three hours, with an Embraer ERJ-190 twin jet achieving 739 mph in the jet streak.
Odds are that if you're flying west, you won't find the jet stream helpful. Departing flights out of New England and the New York area will probably incur 20 or 30 extra minutes of travel time, either slowed by the jet streak or forced to divert around it. But if you're traveling east, you might find yourself on the ground a bit sooner than normal.
For the jet stream to get cranking this much, there must be a big storm brewing somewhere, right? Surprisingly, it's the opposite (the closest developing storminess is in the western Gulf of Mexico on Tuesday). Storms cause the jet stream to bend, cresting and dipping into waves that ride across the Lower 48. Just like kinking a garden hose, it causes the flow speed to decline. In the absence of large-scale weather systems, a zonal west-to-east jet is free to gather considerable speed, much like how we reach our fastest highway speeds on straightaways.
The jet stream can usually get to speeds this high only in the winter because temperature differences between the north and south are maximized. Temperatures on Tuesday hovered around minus-10 to minus-20 in eastern Canada while soaring well into the 80s over Florida. Such large differences in temperature (and pressure) power the wind.
.
 
Posts: 11812 | Registered: October 26, 2009Reply With QuoteReport This Post
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Those are not 801 mph winds.

That equates, if the article numbers are accurate, to a 208 knot tailwind in normal cruise flight.

Far better to have it on the tail than on the nose.

The article's assertion that there was a 801 mph wind is in error.
 
Posts: 6650 | Registered: September 13, 2006Reply With QuoteReport This Post
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I read a article several years ago that I found interesting. I don't really know how factual it was but, it stated that during WW2 when US bombers were flying missions over Europe that when they had strong head winds they were sitting ducks.


 
Posts: 1101 | Location: Toano, Va.  | Registered: January 11, 2004Reply With QuoteReport This Post
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Picture of sourdough44
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I may fly my plane from WI to the Grand Canyon area the end of March, with the 15y/o Son. You can bet that winds aloft are a strong consideration, though route adjustments are somewhat limited.

When it comes to fuel, that’s a time equation. Even with onboard lav facilities(gator bottle), one needs a break after 3 hours.

If you see & hear that annoying plane while on the ‘bright angel’ trail, that may be us. Just kidding, there are flight restrictions.
 
Posts: 6132 | Location: WI | Registered: February 29, 2012Reply With QuoteReport This Post
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Picture of P250UA5
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quote:
Originally posted by sns3guppy:
Those are not 801 mph winds.

That equates, if the article numbers are accurate, to a 208 knot tailwind in normal cruise flight.

Far better to have it on the tail than on the nose.

The article's assertion that there was a 801 mph wind is in error.


My understanding of the article was that it was an estimated 800mph ground speed




The Enemy's gate is down.
 
Posts: 15154 | Location: Spring, TX | Registered: July 11, 2011Reply With QuoteReport This Post
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Originally posted by sourdough44:

If you see & hear that annoying plane while on the ‘bright angel’ trail, that may be us. Just kidding, there are flight restrictions.


There are; one side of the Grand Canyon chart is for tour operators, the other for the public. It's really wise to land away from the canyon and get briefed by someone who is familiar with the SFAR 50-2 airspace, communication procedures, altitudes, routes, position reports, etc.

South Rim is a very busy airport at times. I've landed there when there are eight traffic patterns in use for fixed wing, to one runway, and aircraft holding a three holding points in VFR holds, getting cleared into those patterns, with no radar, and everyone else coming and going doing broadcasts in the blind with position reports. Very busy. When it gets busy, the one runway can have upper and lower inner and outer traffic patterns, both right and left traffic going at the same time, and I've seen all of them full. Busy.

Other times, it's much quieter. Always carry plenty of extra fuel in that part of the country. FAA minimums are not adequate.

quote:
Originally posted by P250UA5:

My understanding of the article was that it was an estimated 800mph ground speed


It did. I was referring to the opening line of the post, the link, which stated that it was 801 mph winds.
 
Posts: 6650 | Registered: September 13, 2006Reply With QuoteReport This Post
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quote:
Originally posted by charlie12:
quote:
Originally posted by Sigfan Roy:


I know one of your pilots. He lives south of Memphis


There are over 5000 of us now, and many live in the Memphis area, but prob not as many as you might think. I believe about 70% of those 5000 commute from somewhere else.
 
Posts: 1121 | Registered: July 23, 2014Reply With QuoteReport This Post
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New personal wind record for me Tues night. Had 208 knots of wind in the face going from Portland, Maine to Memphis. Previous high for me was about 174 knots. Ended up having to divert to Indianapolis when our weather radar quit and didn't want to fly into the thunderstorms that were all around the Memphis area that night. Heard that 7 other flights ended up diverting due to those storms.
 
Posts: 1121 | Registered: July 23, 2014Reply With QuoteReport This Post
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Picture of Suppressed
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When I worked for America West Airlines at BWI, there was a flight that arrived from Phoenix way too early because of high tailwinds. It was the first flight of the morning and none of the ground employees had arrived at the airport. Since there was nobody to greet the plane, a 737, the pilot stopped short of the jetway and deployed the airstairs so that the passengers could deplane.
 
Posts: 3229 | Location: MD | Registered: March 23, 2003Reply With QuoteReport This Post
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A 737 doesn't have air stairs.
 
Posts: 6650 | Registered: September 13, 2006Reply With QuoteReport This Post
Dances With
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quote:
Originally posted by sns3guppy:
A 737 doesn't have air stairs.


Actually some do.

There is a 737 variant called a 737-200 Combi which is still used in Canada because it is configured as, more or less, half passengers and half freight. This variant is perfect for Canada's desolate areas. Not enough passengers for a full flight, not enough freight for a full flight, perfect airplane solves that! These airports may not have a jetway or a truck with stairs. This is a very very old series, no longer made, and the Canadian airlines who operate them have to scrounge around world wide to find others to buy.

Ryan Air is Europe operates 737-800's with airstairs.

I'm not sure exactly the definition of air stairs, but these planes have stairs built into the airplane, self contained, that do not require outside equipment or a jetway.

And if I'm not mistaken, the Boeing Business Jet has built in air stairs.





Link to original video: https://youtu.be/p3-kWnIqHc0




Link to original video: https://youtu.be/p_dvRTIWHQY

This last video is interesting, notice the air stairs at the 4:20 mark. Passengers plane/deplane at the rear, the cargo loads/unloads and rides in the front half.




Link to original video: https://youtu.be/7O5WHFBmuKs

.
 
Posts: 11812 | Registered: October 26, 2009Reply With QuoteReport This Post
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Boeing offered it as an option, and it's still an option, but it's not standard equipment; even many combi's didn't have them.

Many operators removed the air stairs for the weight savings, and because the air stairs, when installed, could ground airplane. The stairs use sequence microswitches, which require one switch to be closed before the next sequence begins, and a failure at any point locked up the system. They were primarily installed at customer request in old classics, mostly discontinued, and are rarely seen in any of the 737's today.

Just over 100 of the combi's had aft airstairs. Alaska Airlines had a few combis until a few years ago. Air Stairs still exist, but few operators use them or have them on board, or have retained them on aircraft that had them installed, and most that did are long retired and gone.
 
Posts: 6650 | Registered: September 13, 2006Reply With QuoteReport This Post
Ammoholic
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quote:
Originally posted by jeffxjet:
quote:
Originally posted by Xer0:
Another question for pilots. Does the fuel efficiency correlate directly in headwinds vs tailwinds? Like do you burn xx extra pounds of fuel flying 2 hours into a 100mph headwind, but would save the same xx pounds of fuel flying the 2 hours with the same 100 mph tailwind?


Winds aloft have no bearing on fuel efficiency. The fuel burn is a function of altitude and power setting. The only affect is has is that flying a 400 mile trip with a 100 knot headwind means you effectively fly 500 miles. Flying the same trip in reverse with a 100knot tailwind means you really fly 300 miles. Obviously flying 500 miles uses more fuel than flying 300 miles and this is where your extra fuel burn comes in.

The first half is correct, the second half is an oversimplification. The effect of a headwind or tailwind depends on your airspeed. The 100 knot headwind that would be a annoying inconvenience for a jet doing 500 knots would have a J-3 Cub going backwards big time.

If the headwind and the tailwind are the same magnitude, the headwind hurts you more than the tailwind helps you. This is because you will be effected by the headwind for more time than you are effected by the tailwind. For example, say you are flying 400 nautical miles at a true airspeed of 300 knots and you have a 100 knot headwind going one way and a 100 knot tailwind going the other way. With the headwind, your ground speed will be 200kts and the trip will take two hours. With the tailwind, your ground speed will be 400kts and the trip will take one hour. With zero wind, the ground speed will be 300kts and the trip will take 1 1/3 hours. The headwind added two thirds of an hour to the trip, but the tailwind only saved you one third of an hour. I picked these numbers to keep the math easy so I didn’t have to take my socks off, but pick whatever numbers you like and do the math and you’ll see that with the same velocity a headwind costs you more time than a tailwind saves you.
 
Posts: 6872 | Location: Lost, but making time. | Registered: February 23, 2011Reply With QuoteReport This Post
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Picture of Suppressed
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Originally posted by sns3guppy:
A 737 doesn't have air stairs.


Back in 1990 this one did. Otherwise, that first step would have been a Duesy.
 
Posts: 3229 | Location: MD | Registered: March 23, 2003Reply With QuoteReport This Post
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Picture of erj_pilot
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Originally posted by Suppressed:
...that first step would have been a Duesy.




"If you’re a leader, you lead the way. Not just on the easy ones; you take the tough ones too…” – MAJ Richard D. Winters (1918-2011), E Company, 2nd Battalion, 506th Parachute Infantry Regiment, 101st Airborne

"Woe to those who call evil good, and good evil... Therefore, as tongues of fire lick up straw and as dry grass sinks down in the flames, so their roots will decay and their flowers blow away like dust; for they have rejected the law of the Lord Almighty and spurned the word of the Holy One of Israel." - Isaiah 5:20,24
 
Posts: 11054 | Location: NW Houston | Registered: April 04, 2012Reply With QuoteReport This Post
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quote:
Originally posted by slosig:
The 100 knot headwind that would be a annoying inconvenience for a jet doing 500 knots would have a J-3 Cub going backwards big time.


We used to do that a lot in the J3. Not in a 100 knot headwind, of course, but The J3 can easily be flown slowly enough that with some headwind, it tracks backward over the ground.

I've done vertical takeoffs in the J3 where, from the end of the runway, the climb was up over the numbers and back to the numbers, thanks to the wind. Also approaches to a landing in the tiedown in the J3 and a Cessna 150 in Kansas, where lack of wind was something to talk about.

It doesn't take a lot of headwind to fly some of those light airplanes backward over the ground.

Conversely, with a tailwind on final, and thus higher groundspeed, I've had touchdown speeds in excess of 200 knots in large airplanes at higher altitude airports (Kabul and Bagram, for example).

Makes for hot brakes.
 
Posts: 6650 | Registered: September 13, 2006Reply With QuoteReport This Post
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