Can airliners/large passenger jets make use of gliding to save fuel? Is such a thing feasable? I read that the airline carriers are havng a hard time with the cost of jet-fuel. What about flyng with fewer engines for part of the flight? or no engines at all???

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No; for every glide, there is a drop. For every drop, there has to be a corresponding climb to be there in the first place.
And; the fuel is all about the aerodynamics which exist whether gliding or thrusting.

I'm not sure how much can be gained by flying slower. I'm sure it would be considerable. But compared to ground costs, labor costs, congestion, depreciation, and a whole bunch of other factors...the more takeoffs and landings you can do to get the most passengers on and off, the more money you are going to make.

Slingshots...

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Passengers tend to get upset when the engines stop. Pilots, too.

There are things that can reduce fuel consumption. For example, UPS is working with the FAA to test a GPS-based technology (ADS-B) at their cental hub. This technology reduces air traffic contol delays and saves fuel.

Higher precision navigation is being used in some areas (Washington DC, IIRC) to again reduce delays. Jet engines are very fuel thirsty at low altitudes so reducing delays can save a lot of fuel.

Airlines are really being squeezed on fuel costs so you should believe me when I say they're investigating all sorts of ways to safely reduce fuel consumption.

I also find it ironic, that when Boeing decided not to compete with the A380 and instead go with the 787, there were plenty of people saying that was a bad move.

He who laughs last...

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Hi, What the airlines and manufacturers will do is sign up with John Northrop.
He designed and built the most efficient heavy lift flying wings ever concieved.
The Boeing blended wing design is a spin-off of this. Nothing is wasted, a truly elegant design. It also has advantages on the ground in that it will take up less
area in some ways. This remarkable design could be built to "Crab" sideways
to it's terminal gate ( just a possibility ).
Flying wings are superb examples of aeronautical design. Just fly them as they are supposed to be flown.
The only problems they had were the army's insistance on exploring slow ....
near stall speed envelopes with mis-placed CG. Asking for trouble .
When it comes to fuel, nothing beats a flying wing.
Best regards, Dan

Aye, Dan. During World War 2, the Germans worked on a project they called the "Amerika Bomber" that was essentially a flying wing, made mostly of wood. On paper, it would be able to bomb New York and return to Germany, without refueling. Once they were given money to develop it, they were stuck with a committee that had final say on the design. They decided to add all kinds of unnecessary parts, such as vertical stabilizers, ect, which killed its range and payload capacity, to the point where the designers gave up in disgust. It probably would have worked.

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Maybe The Hindenburg could be repaired.

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X-48B.

And; if fuel prices keep going the way they are, then the airlines won't give a hoot about the passengers being able to look out a window.

I didn't think that was a factor. The footprint at the gate seems like it would be about the same when it's nose in. And, as long as the main door was near the front, there wouldn't be much difference.
Yes; but if that's part of the design specs, then you're stuck with it.

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Flying wing designs are both beautiful and efficient. They do have a narrow center of gravity envelope and less pitch and yaw stability than conventional designs. Artificial stability technology (in the form of enhanced autopilots) wasn't all that good in the late 1940s when Northrup was testing their flying wing bombers. This not only reduced flight safety but also bombing accuracy. That isn't an issue any more, as seen with the success of the B-2. Artificial stability technology is very mature today.

Whether or not it would be accepted as a passenger plane is a matter of debate. It could make for an excellent freight hauler so long as it's loaded properly. Air freight is a large and growing market.

Can a jetliner use thermals to climb, or is it too heavy?

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How strong is the thermal?

Per wiki on gliders... a glider has a glide slope of between 30:1 and 70:1. The 767 has 12:1. So; given a pretty good gale or cyclone, I'm sure it can be done.

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Is it what they call 'free flight'?

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Can a jetliner use thermals to climb, or is it too heavy?

Way, way too heavy.

Airplanes are designed to meet specific mission objectives. Most airliners* are designed for efficient cruise performance. They use high-lift devices like flaps and sometimes leading edge slots to allow for slower/shorter take offs and landings. High speed cruise efficiency requires that the wings be sized to generate the required amount of lift with the lowest practical drag. That determines the size, sweep, and airfoil choice of the wings.

Sailplanes are designed to have a high lift to drag (L/D) ratio with a low sink rate. Training sailplanes commonly have L/D ratios in the 20 range while high performance competition sailplanes have L/D ratios of well over 50. L/D is also known as the glide ratio. A sailplane with an L/D ratio of 30 can glide for 30 feet (or meters) forward for every foot (or meter) of altitude lost in calm air. They're probably the most efficient aircraft anywhere. Their wings tend to be long and thin in both thickness and chord (distance from leading edge to trailing edge). Depending on the design, some sailplanes can exceed 150 MPH to race from one thermal to another and slow to a low descent rate while circling in a thermal.

Airliners are clean aerodynamically because higher drag means higher fuel consumption for a given airspeed. I've read that some airliners have L/D ratios well over 20**. However, that's at speeds far too fast to use for thermals. Besides, to take advantage of a thermal, you need to circle in it to gain altitude. To an airliner, a thermal is little more than a source of turbulence. Thermals rarely reach up to airliner cruising altitudes anyway.

*There are some special purpose airliners that are designed for short takeoff and landing performance more than for cruise efficiency. There are several excellent Canadian designs that fall into this category.

**By comparison, I doubt the L/D ratio of my Piper Cherokee light plane is more than 8 or 9. My plane just doesn't glide all that far if the throttle is cut. I sometimes wonder if Piper engineers skipped drag class.

It's been almost 3 decades since my aviation classes, but IIRC, a Cessna 172 was around 7...so you're lucky.

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Is it what they call 'free flight'?

Yes, I believe it is or is similar. Standard airline routes tend to bunch planes into airways that go from one ground-based navigation station to another. This increases the distance between points because airways go between the navigation stations instead of the airports. It also tends to bunch planes together.

The free flight concept allows planes to fly more direct routes between takeoffs and landings, reducing both distance flown and congestion. ADS-B reverses how air traffic control (ATC) is done. Currently, ATC uses ground-based radars to track planes and determine their position. It also uses a device called a transponder to positively identify the planes (via an assigned identifier code) and to determine the plane's altitude. These ATC radars cost a lot of money to install and operate. I've heard the cost could be over a million dollars a year per radar.

Instead of radars, ADS-B uses GPS data. The planes transmit their altitude and position (and maybe course info) on a regular basis to simple and inexpensive ground receivers. Planes with advanced equipment can also receive the ADS-B transmissions from other planes, allowing the planes to work out their own separation. It may sound like chaos but it works very well. The ADS-B ground receivers can be located in places that wouldn't be suitable for ATC radars, such as the tops of mountains. This can greatly improve coverage in mountainous terrain. I've also read that properly equipped planes can receive additional data via an uplink for things such as weather information.

The FAA is moving to require ADS-B equipment in nearly all planes by 2016 or so. There is a concern about how much the equipment will cost. If it's $1000-2000 per plane, it'll be rapidly adopted. The last number I heard was over $6000 per plane and that may not even count installation costs. That's a lot harder for people like me who fly older planes that might not be cost effective to upgrade.

ADS-B is a wonderful invention. It's already in use in some places and is well on it's way to becoming the new international standard for ATC. However, like everything else involving aircraft, it isn't cheap. The only thing cheap about an airplane is the air in the tires. I paid almost $30 this week for a [profanity deleted] air filter and $16 each for spark plugs.

ADS-B: Will It Be Filled In?


UPS Pioneers ADS-B

Airport radar soon a blip in history

how long would it take a larger plane to fall/glide down from say 30,000 feet?

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I have a few hundred hours in Cessnas, mostly in 172s. They glided quite a bit better than my Cherokee. The worst plane in regards to glide ratio that I ever flew was a 1969 Yankee. It was a fun little plane but it had the glide ratio of the Space Shuttle (pre-flare). In that plane, you'd better be high or very close to a good landing spot if you had to glide. Otherwise, you aren't going to make it.

Will an answer from 39000 suffice?

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how long would it take a larger plane to fall/glide down from say 30,000 feet?


Based on this article about a real incident, I'd guess about 15 minutes. Following a miscalculation in determining how much fuel to load, they ran out of fuel. Using excellent airmanship (the Captain flew sailplanes for recreation), they managed to land the plane without injuries at a closed airport. It's a great story. The plane suffered some damage but was repaired and returned to service. I recall reading recently that it was retired recently.