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56 votes
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Why do all airliners have life jackets?

The plane would be lighter. Not by much. It cannot be hard to dedicate different planes to different routes. This adds to the logistics difficulties in scheduling the airframes. It's MUCH easier ...
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  • 4,362
54 votes

Why are airlines so concerned with checked baggage weight?

Airlines do care about your carry-on weight and even your weight. Many have carry-on weight limits, which low-cost carriers usually enforce, weighing the carry-on and tagging it as cabin luggage. Full-...
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  • 17.6k
38 votes

How large are the banners that are trailed behind small planes for advertising?

Pre-911 I towed banners, and towed them with a C172 and a C182. Parasitic drag of the banner is the limiting factor. We had different letters, and for the C-172, the letters were about 1.5 meter ...
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  • 17.4k
35 votes
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Can the removal of a duty-free sales trolley result in a measurable reduction in emissions?

Yes, the removal of payload will result in a measurable reduction in emissions. First, I have to correct some math: the engines don't run at 150 kN in cruise - that would indicate a L/D ratio of only ...
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  • 17.6k
32 votes

How can lift be less than thrust that is less than weight?

Your misunderstanding lies in your thought that lift is smaller than thrust, while in fact, lift is much larger than thrust. The lift is provided by the wings. Their purpose is exactly to create a ...
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  • 12k
30 votes
Accepted

What is the reasoning behind using depleted uranium as counterweights in the 747?

Boeing Boeing would have used DU because it had the right combination of physical characteristics and cost. Their tests showed that the radiation exposure for workers was low (2.6% of the statutory "...
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30 votes

Why are "counterweights" used in aircraft production?

In the context of aircraft design and maintenance, the terms counterweight and ballast generally have separate and different meanings. Both concepts involve mass used to balance, dampen, or adjust ...
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  • 16.1k
25 votes

Can the removal of a duty-free sales trolley result in a measurable reduction in emissions?

Well, any reduction in Basic Operating Weight, which eliminating the trolley achieves, is an increase in efficiency, because anything not humans and their bags paying money, or kerosene, and not ...
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  • 103k
20 votes

What is the reasoning behind using depleted uranium as counterweights in the 747?

[W]hy did Boeing (and McDonnell Douglas) decide to use such a hazardous (and potentially dangerous from a military perspective) material? Because it's not particularly hazardous and it's not very ...
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20 votes
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What are the concerns and consequences of an overweight landing?

Two things: Loads on the landing gear. This can be alleviated by carefully touching down, but you never know what exactly will happen in the next landing, so better don't count on it to be smooth ...
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20 votes

How large are the banners that are trailed behind small planes for advertising?

The letters and spaces can be made of a soft nylon type material that is extremely light. (there are different materials available, but all are made of durable, light-weight material). The number ...
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  • 16.8k
19 votes

Why do all airliners have life jackets?

Why do airlines not remove the life jackets from planes that fly over land? They do, at least some of them. I fly on intra-European routes regularly (mainly Eurowings) and have never seen life ...
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17 votes
Accepted

Which part of aircraft is contributing the most weight of airplane?

Aerospace Engineering e-Mega Reference shows the following table for two aircraft (the large commercial jet, the B747-100, and the military jet, the C-5A). You can see that it differs quite a lot ...
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17 votes
Accepted

How heavy are the Boeing 747 landing gear?

It seems I misspoke in my comment in which I gave the moments for 747-400BCF gear retraction. I didn't realize the component weights were further on in the document I referenced. The weights for the ...
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  • 38.7k
17 votes

Why do all airliners have life jackets?

Because this can still happen. That’s US Airways Flight 1549 on the Hudson River. They made a movie about it starring Tom Hanks. There’s no way to predict disasters, and had the plane been “...
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17 votes
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Is it possible for an airplane to enter another airplane?

Clearly the plane must enter and exit through the belly of the larger plane Why so? If you drop this condition, things become much easier, because you could attach the smaller planes externally and ...
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  • 8,565
16 votes
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Why are "counterweights" used in aircraft production?

The counterweights in the original question were from a Boeing 747 rudder, so I will explain what their purpose is. John Walter's answer covers all applications of balances and ballast well enough, so ...
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14 votes

How does aircraft weight affect landing distance?

If you discount aerodynamic effects, and assume the same landing speed, on a theoretical level mass makes no difference. The additional kinetic energy to be dissipated is exactly cancelled by the ...
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  • 27.5k
11 votes

Why do all airliners have life jackets?

Why do airlines not remove the life jackets from planes that fly over land? The plane would be lighter and the safety demonstration shorter. Some do. As a specific example, if you fly Delta from ...
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11 votes

Can the removal of a duty-free sales trolley result in a measurable reduction in emissions?

When American Airlines switched from paper to iPad for the pilots, they saved 40 lbs (18 kg). This translated to "\$1.2 million of fuel annually". (forbes.com; 2013) Of course this is across AA's ...
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  • 120k
10 votes

What is the weight of the fuselage (only) of the Boeing 747?

The fuselage weight for 3/4 of a 747-300 Combi minus engines, fuel tanks, seats, catering, cargo handling, navigation gear, control surfaces, pumps, hose is 70,000 lbs, according to Big Imagination, ...
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  • 2,308
9 votes

What are the physical laws for upscaling an RC model to 1:1?

This is not a full answer: much is mentioned by Michel Touw, but I'd like to correct a common misconception. The mass growing as the third power of linear dimensions applies only to solid objects. ...
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  • 8,565
9 votes

What are the concerns and consequences of an overweight landing?

The major issue with landing a plane that is overweight is over-running the runway. If you are trying to land a plane that is over it's rated landing weight, you will need to be going faster to keep ...
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  • 91
9 votes

How large are the banners that are trailed behind small planes for advertising?

To add to mongo's and 757toga's answers, during my time towing in Central Florida in the late 00's, in addition to the 5' letter banners, we also had 8' letters that we often used when towing over ...
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  • 2,862
9 votes

Why aren't there V-tail airliners?

Controllability and redundancy. Airliners are certified according CFR 14 Part 25, which specifies that upon engine fail the aircraft must still be able to fly and climb: it must have more than one ...
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  • 57.7k
9 votes
Accepted

What is the average weight difference between composite and metal airliners?

(Own work via boeing.com) Overlayed scaled drawings. Above you see similar sized planes with the same 3-class seating (± 1 seat). The newer-more-composite 787 is 16 tonnes heavier, yet delivers up to ...
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  • 120k
9 votes
Accepted

Are there any airliners capable of vertical climb with engine thrust only by pointing the nose up?

No, there are few planes that can do this at all. In order to be able to climb out straight up you need a thrust-to-weight ratio greater than 1. In other words you need enough thrust to propel the ...
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  • 95.9k
8 votes

What is the reasoning behind using depleted uranium as counterweights in the 747?

Depleted Uranium is 68% denser than lead and costs much much less as DU is a discarded material. Therefore, there were both space requirement considerations as well as cost considerations when using ...
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  • 269
8 votes

Is an aircraft's maximum landing weight really weight, or is it mass?

On Planet Earth, 1kg of mass exerts 9.81 Newtons of force (weight). Because this is true anywhere on planet Earth to within a tiny fraction of a percent, we use kg as a convenient measure of weight, ...
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  • 28.3k

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