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Old 05-11-2012, 11:28 PM   #21
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Eric?, you keep talking about speed and angle of attack. They are related but not always. Also wingtip vortices are most prevalent at high angles of attack on a CLEAN wing. Guess what you are doing in cruise??? One reason an airliner is more efficient at high altitude is we can operate at high speeds very near stall margins. The greatest efficiency of a wing(L/D Max) occurs basically right at stall(angle of attack). So when we are high and heavy, we are very near the stall speed and therefore very near L/D max and therefore benefitting greatly from winglets. I hope my logic came together there...kinda tired...
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Old 05-11-2012, 11:49 PM   #22
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John Baker have you encountered good data that shows airliners saving fuel at cruise?
Every single one of our(Continental) narrow body aircraft have winglets...that is proof enough. But, yes,they are the real deal. We even put them on our "classic" 737-500s which we knew would be retired by 2013...it was still worth it for just 3 years. Fuel is our number one cost and if you average 5% fuel saving over a year it is extremely significant. We spend BILLIONS a year on fuel....you do the math!!!!
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Old 05-12-2012, 12:02 AM   #23
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Thank you very much John and Marin.

It's very hard for me to visualize flying 500 mph in the vicinity of stall. FAR OUT!
It all makes sense and that's a plus plus for the winglets. Slower landing speeds in the "thick air" near the ground and high speed and angles of attack way up in the thin stuff. Ida never thunk.

How high could you go if you had no regs?
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Old 05-12-2012, 12:39 AM   #24
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The service ceiling is of a 737 NextGen which is the 737 model we make today is listed as 41,000 feet. This is the number given for all three versions we make currently, the -700, -800, and -900ER. I expect each model will have different individual figures. The -700 being the smallest and lightest would most likely have a service ceiling somewhat higher than the -900ER.

The service ceiling of the 787 is listed as 43,000 feet.

The service ceilings of our other models are in that same envelope.
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Old 05-12-2012, 12:52 AM   #25
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I know large AC landing can make very troublesome vortexes close to the runway and on approach.

Do you ever hear of any canard talk at Boeing? I think canards died out because they were sensitive to CG variations. One could make a really big canard with less wingspan.
Larger aircraft can make troublesome vortices in regular flight, not just on landing. We have footage of a 757 flying just off the top of a solid cloud layers. The camera plane was in front of the 757 with the camera looking back. It is the best illustration of lift in action I have ever seen, and anyone seeing this footage will realize instantly that lift is the product of Neuton's Third Law or whatever it is of action-reaction, not the Bernoulli Theory. You don't need Bernoulli at all to produce lift. What the wing does to the cloud layer is amazing and beautiful to see. It also shows the wingtip vortices very plainly as they are formed and remain in the wake of the plane.

Canards---- Well, I know Boeing has messed around with them as a design element from time to time but we've never put one on a production jetliner. The prototype 757, a plane I spent a lot of time in in the early 80s, was leased or sold to the government after we were done with it and it became a test bed for various military airplane development projects. One of them was for (I think) the F22.

In any event, whatever it was for, the 757 had a large canard installed on the top of the fuslelage just aft of the flight deck. But this was to test a proposed control system and had nothing to do with any jetliner design. The plane is still based on our military ramp at Boeing Field and it still sports its rooftop canard.

The proposed Sonic Cruiser would have had a canard but that plane, as much as everyone including the airlines liked it, was destined to never be as soon as oil prices started going up, so we focused our attention on the "backup" project which we code-named Yellowstone. Yellowstone became the 7E7 and then the 787.

The canard, by the way, I believe is a French invention. I may be wrong on that but "canard" is the French word for "duck." As in the bird, not avoiding being hit in the head.
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Old 05-12-2012, 05:54 AM   #26
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Today its in the computer , but all aircraft have tables that give the weight allowed at a particular density altitude.

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Old 05-12-2012, 09:46 PM   #27
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Indeed they must make money but I suspect that it must be to carry more weight or to have better aileron response at slow speeds or a wider CG envelope or to reduce the likelihood of tip stalling in high banked turns or to be able to operate at airports with wingspan limitations or any number or other performance advantages but I doubt they reduce fuel burn at cruise. John Baker have you encountered good data that shows airliners saving fuel at cruise?
Actually, you pay a weight penalty for them. I work at Boeing and can tell you they are VERY cost effective for longer haulers. Their performance gains are at cruise. No one who actually works for Boeing (or APB) would be able to share those numbers on a public forum, but APB's site gives some insight.

They are heavy though, so short-haulers don't care for them as much. With the cost of fuel as high as it is now, they're more attractive than ever.

Ironically, you mention low-speed handling and that's an issue they've had to watch carefully. Many smaller carriers fly in areas that have the FAA watching the challenges they will be presenting. They do save fuel though. I can assure you that.
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Old 05-12-2012, 09:55 PM   #28
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In any event, whatever it was for, the 757 had a large canard installed on the top of the fuslelage just aft of the flight deck. But this was to test a proposed control system and had nothing to do with any jetliner design. The plane is still based on our military ramp at Boeing Field and it still sports its rooftop canard.
Yep. The FTB was brought back online a few years back to test the latest block of F-22 improvements. Now if they could get pilots that would agree to fly the F-22.

It also has the F-22 nose on it.

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Old 05-12-2012, 11:25 PM   #29
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Thank you very much John and Marin.

It's very hard for me to visualize flying 500 mph in the vicinity of stall. FAR OUT!
It all makes sense and that's a plus plus for the winglets. Slower landing speeds in the "thick air" near the ground and high speed and angles of attack way up in the thin stuff. Ida never thunk.

How high could you go if you had no regs?
Just depends how light you are. A light 767-200 has tons of power to spare since it has the same engines as the other 767s and much lighter. And like Marin said, the737-700 is the hot rod of that fleet for the same reason as the 767-200...same engines as it's bigger brothers but lighter.

Another consideration in high altitude flight is that you are also going transonic. So not only are you very close to the low speed stall buffet margin but you are also very close to the high speed buffet margin. This has been referred to as "coffin corner" because you can't go any slower or you will stall....or go any faster and you get into high speed mach buffet. I don't push it that far. Even though the computer says you can go that high, it is not really a good idea to go to the max altitude displayed on the cruise page of the flight management computer. We have had more than one airplane go into a high altitude stall. If you hit turbulence and/or your airspeed begins to decay, the engines are barely breathing and there just isn't enough power to power out of it. A high altitude stall usually results in 4000-10000 feet of lost altitude. I have only done it in the simulator and it is quite sobering.

Probably more than you wanted to know....
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Old 05-12-2012, 11:40 PM   #30
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Well it is a bit of an ugly duckling is'nt it.

Most of my ultralights were flying wings. One was very stable and one was very unstable. Once one learned to fly it the unstable one was more capable and in many ways safer. I had two ULs that were flying wings w a fwd mounted elevator. Most called them canards but they could only be considered such below trim speed as then the elevator then became a wing....producing considerable lift. They were very efficient. I could fly over 100 miles w less than 5 gallons of gas and climb 1400 fpm at 40mph. At a 60 degree banked turn I could still climb about 500fpm. That was a very fun maneuver. Crank it over ....point the wing at a point on the ground about 200' below and just revolve around it. I'm gett'in excited just think'in about it.

OMAC is for Old Man Airplane Company and they were working on a canard about the size of a Cessna Citation. Had a fairly large canard wing. But in commercial aviation I think the stability of the tail is required for flexibility in payload position ...CG. With a canard flying slowly it's pitch control surface is providing lift. That's why they are so efficient. With a tailed AC flying slowly the tail is creating tremendous drag. But flying fast the tail could be providing lift. Does anybody know or think that could/would happen? If so the tailed AC (it would seem) could be as efficient as a canard but then no AC flying fast can be efficient. But that seems to be so w airliners flying fast at high altitude.

Marin what I asked about was how high CAN they fly .....not how high they should fly w passengers ect. What if you just opened the throttles and observed at what altitude you could'nt go any higher at any angle of attack?


We were posting at the same time. Thanks very much John .....no not too much info at all. Very interesting stuff we UL pilots are totally unaware of for obvious reasons. So you use power to recover from a stall Hmmmmm. With ULs we just dive our way out ....w enough altitude or die if not. I've never died. Thanks John.
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Old 05-13-2012, 12:24 AM   #31
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Well it is a bit of an ugly duckling is'nt it.

Most of my ultralights were flying wings. One was very stable and one was very unstable. Once one learned to fly it the unstable one was more capable and in many ways safer. I had two ULs that were flying wings w a fwd mounted elevator. Most called them canards but they could only be considered such below trim speed as then the elevator then became a wing....producing considerable lift. They were very efficient. I could fly over 100 miles w less than 5 gallons of gas and climb 1400 fpm at 40mph. At a 60 degree banked turn I could still climb about 500fpm. That was a very fun maneuver. Crank it over ....point the wing at a point on the ground about 200' below and just revolve around it. I'm gett'in excited just think'in about it.

OMAC is for Old Man Airplane Company and they were working on a canard about the size of a Cessna Citation. Had a fairly large canard wing. But in commercial aviation I think the stability of the tail is required for flexibility in payload position ...CG. With a canard flying slowly it's pitch control surface is providing lift. That's why they are so efficient. With a tailed AC flying slowly the tail is creating tremendous drag. But flying fast the tail could be providing lift. Does anybody know or think that could/would happen? If so the tailed AC (it would seem) could be as efficient as a canard but then no AC flying fast can be efficient. But that seems to be so w airliners flying fast at high altitude.

Marin what I asked about was how high CAN they fly .....not how high they should fly w passengers ect. What if you just opened the throttles and observed at what altitude you could'nt go any higher at any angle of attack?


We were posting at the same time. Thanks very much John .....no not too much info at all. Very interesting stuff we UL pilots are totally unaware of for obvious reasons. So you use power to recover from a stall Hmmmmm. With ULs we just dive our way out ....w enough altitude or die if not. I've never died. Thanks John.
You still use pitch to recover from a stall....you have to...but at lower altitudes you have a vast amount of power and if you are not fully stalled(imminent stall) you can power out of it and that is usually the way it is taught al though that line of thinking is changing. There is an increased stall awareness(and training) due to Air France over the Atlantic and the Q400 in Buffalo...both events where the pilots lost control.

Eric, one of my sim instructors got the airplane(767-400 sim) to stall with the nose pointed straight at the ground!!! We were in the low 20s and he had to do some serious maneuvers to get it into that state...basically a split S. But there we were pointed straight at the ground with a windshield full of Earth and the wing was not flying. Do you know how hard it is to push the nose over in that case. Every fiber in your body says to raise the nose because the ground is rising up right in your face. Anyway, it was a wild ride. We recovered below 10000ft with the structural integrity of the airplane in question....it was a sim!!!
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Old 05-13-2012, 02:03 AM   #32
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Old 05-13-2012, 02:36 AM   #33
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Eric-- From an aircraft manual I have.....

"One factor that most people overlook when talking about this subject is aircraft pressurisation.* Most civilian large aircraft won’t pressurize the cabin to more than 6 or 8,000 ft.* If the cabin pressure remains at, say 8,000 ft, as the the aircraft climbs, the pressure differential becomes greater and greater.* If the structure is not strong enough to whithstand these pressurs, it will catostrophically fail.* The 737 has a service celing of 41,000 ft.* Theoretically, the engines have plenty of power to create lift and climb higher, but due to the cabin pressure limitations, it it were to go much higher, the structure would catastrophically fail.* This is true for most larger narrow- and wide-bodied aircraft."
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Old 05-13-2012, 06:37 AM   #34
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"Theoretically, the engines have plenty of power to create lift and climb higher, but due to the cabin pressure limitations, it it were to go much higher, the structure would catastrophically fail.* This is true for most larger narrow- and wide-bodied aircraft.""

The various saftys will prevent the cabin from overpressure, and many ferry flights used to be done by accepting a higher cabin altitude by the crew.

No pax on board.

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Old 05-13-2012, 07:16 AM   #35
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The various saftys will prevent the cabin from overpressure, and many ferry flights used to be done by accepting a higher cabin altitude by the crew.

No pax on board.

FF
^^^^^^^^^^^^THIS^^^^^^^^^^^^^^^^

And FAA certification states a max cabin altitude of 8000ft at max certified service ceiling. That gives a differential pressure of about 8.5 PSI. I think the 737NGs pressure relief is at 9.1...if my memory serves me...which it generally doesn't!!!
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Old 05-13-2012, 01:32 PM   #36
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On our 787 the max is 9.4 psid, holding the cabin altitude at only 6000 feet at a max cruise of 43,000 feet.

Don't try that with an aluminum airplane.
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Old 05-16-2012, 11:12 PM   #37
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Baker what a high strung stall sim.
That's a rush in a hang glider too.

What I want to know about the airplanes is how high will they fly given just the airframe and engines? All that other stuff aside. 60000'?

I went to 12500' in one of my ultralights and know it could have gone much higher but it's just too cold. A friend of mine went 21000' in an UL that had a ho-hum climb rate compared to mine but he set a world record. Obviously I could have broken it but he was in the business and needed the notoriety much more than I.
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Old 05-17-2012, 12:41 AM   #38
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Baker what a high strung stall sim.
That's a rush in a hang glider too.

What I want to know about the airplanes is how high will they fly given just the airframe and engines? All that other stuff aside. 60000'?.
No telling...are you asking totally stripped down??? Again, no telling. The 767-200 is the hotrod of our fleet. But if I said a number it would be total speculation. An empty 762 with minimal fuel could likely make 50,000....dunno about 60...
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Old 05-17-2012, 12:42 AM   #39
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How high can they fly, or high will they fly. Two slightly different questions. One of the more challenging aspects of flying the 787 high was actually the ability to meet regulations. An aircraft flying at FL400 must be able to descend to FL250 within 2 and half minutes in an emergency. This was very problematic for the 787. The wing is so efficient, it was tough doing that without exceeding speeds.

Boeing (and Airbus for the A380) had to pursue exemptions to present rules to get the cruise altitude they have now. I suppose theoretically something up at FL450 would be possible if you could talk the computers into it.
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Old 05-17-2012, 01:12 AM   #40
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Here ya go Eric. I was thinking about you and our conversation as I was flying to Cancun the other day. As you can see, there is a 30 knot window between the highspeed buffet and the low speed buffet. That sounds like a lot but that is only 15 knots wither side. We were within 1000ft of the computed max altitude with a true airspeed of 445 knots.
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