17 votes
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If aircraft are pressurised, why do our ears pop during liftoff and landing?

Because the cabin isn't pressurized to sea level pressure instead it to about 8k ft equivalent. (while the plane is 4.5 times higher) This means there is less differential pressure than if the cabin ...
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15 votes
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How does a helicopter hover

Most helicopters of modern manufacture are dynamically unstable while hovering- they require constant, "hands-on" control inputs from the pilot to keep things in balance. This task is very ...
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14 votes
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In case a plane stalls, what should stall first, the tip or the root of the Wing? Why?

It is preferable for the wing root to stall first. If the wingtip stalls before the root, the disrupted airflow near the wingtip can reduce aileron effectiveness to such a extent that it may be ...
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  • 432
11 votes
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Could air-launched space planes reach escape velocities?

Believe it or not, we could have done this 50 years ago, if government funding hadn't been pulled from a project at the last minute. Frustratingly, after years of work by scientists, engineers and ...
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  • 2,485
9 votes

Could air-launched space planes reach escape velocities?

Now, I wonder if an air-launched spacecraft in the next 20 years realistically could really fly us to the moon - that is, could they reach escape velocities? Air launch to LEO: Done now Air launch ...
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8 votes
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Is a wing that runs the length of an aircraft viable?

You mean very low aspect ratio (span to longitudinal length) wings? Low aspect ratio has larger induced drag and glide very poorly. The total drag coefficient of an aircraft can be expressed as: $$...
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7 votes
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How is fuel mixed with air in a jet engine?

The place where air and fuel are mixed is the combustor, also known as the flame holder: The diffuser takes in the compressed air and slows it down (remember that aircraft with jet engines are ...
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  • 2,485
6 votes

How are wind tunnel models used when designing supersonic aircraft?

In the Fluid Dynamics community about 40 years ago, the group was primarily divided into experimentalists and theorists. However, at that time CFD was quite new, had to be run on expensive ...
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  • 493
6 votes

How an airfoil works

It is true that the air on the "top" (suction side) is faster than on the "bottom" (pressure side). The interesting thing is that the air on the suction side is so fast, it overtakes the air on the ...
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  • 1,202
6 votes

Are rocket engines practical for commercial aircraft?

At a fundamental level, it should be clear that throwing stuff out the back is going to be less economical than sucking in stuff in the front and throwing it out the back faster. For one thing, the ...
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  • 11.3k
6 votes
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Do all airfoils have a lift curve slope of $2\pi$?

In general, most airfoils only approximately display the $2\pi$ lift slope as predicted by thin airfoil theory. That is because airfoils are not actually infinitely thin in practice, and will deviate ...
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  • 251
6 votes
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What technologies prevent drones from being as efficient as birds?

Somebody needs to design a chocolate-powered drone. Yes, seriously. The total energy stored in a 40AH 12V battery is about the same as the calorific value of five 100g chocolate bars from your ...
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  • 12.5k
6 votes

In case a plane stalls, what should stall first, the tip or the root of the Wing? Why?

It depends on wing geometry. You need to look at the aerodynamic center of the wing, which is the center of effort for perturbation forces. The center of lift (unstalled) will usually be well forward ...
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  • 3,590
5 votes
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Efficiency in a gas turbine or aircraft engine

Gas turbines are modeled using Brayton cycle which in the simplest case consits of: Isentropic compression (in a compressor) Constant-pressure heat addition (combustion chamber) Isentropic ...
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  • 2,149
5 votes

What are the engineering challenges in WIG craft development?

This is mostly an issue of safety trade-offs and not necessarily technical shortcomings. While a WIG vehicle, often referred to as a Ground Effect Vehicle (GEV), has improved efficiency it is also ...
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5 votes

Detailed dimensions of an aircraft engine compressor blade

The ESA has a page on compressor blades. They give a good dimensioned diagram of an approximate shape; here are some basic dimensions: Length: 300 mm Width: 30 mm Height: 70 mm Thickness: 5 mm I can'...
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  • 2,485
5 votes
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Did Otto Lilienthal ever experiment with non-human-powered aircraft?

I'm going to answer my own question because just before posting it I found an answer. The Otto Lilienthal Museum has a comprehensive list of Lilienthal's designs. One is listed as the "small wing-...
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  • 2,485
5 votes

Can a blimp enter Mar's atmosphere as a glider?

I assume that the person you are referring to is Felix Baumgartner, who achieved a maximum speed of Mach 1.25. While this speed is very fast, this is nowhere near the speeds achieved by meteorites, ...
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4 votes

Could air-launched space planes reach escape velocities?

Start your mental model by assuming a rocket flight path. A velocity/altitude vs time chart for the Space Shuttle: (source: aerospaceweb.org) Jet engines have better $Isp$ than rockets. Let's put ...
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4 votes
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Possible Hazards of Software Controlled Systems (Ex. Airline GPS/Elevator)?

Commercial air traffic is in pretty constant contact with air traffic control, and GPS is not the primary method of tracking aircraft position. This article, written in the wake of the MH370 ...
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4 votes
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What are the advantages of chemical oxygen generation over compressed tank storage?

One advantage these chemical systems may have over compressed tanks is how well they are suited for intermittent use and long-term storage (as opposed to regular, continuous operation). The US FAA ...
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  • 3,211
4 votes

What are the advantages of chemical oxygen generation over compressed tank storage?

From personal experience of refuge systems, oxygen generating systems are preferred over medical oxygen gas tanks because of space requirements, portability and the ease of relocation. When emergency ...
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  • 9,517
4 votes

If aircraft are pressurised, why do our ears pop during liftoff and landing?

There's a difference between being pressurized to an absolute value and being pressurized to a relative value. For instance, if the cabin immediately pressurized to the same atmospheric pressure as ...
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  • 3,525
4 votes

Are rocket engines practical for commercial aircraft?

Economically a rocket engine will always lose out to a jet engine. We'll ignore solid fuel rockets, they are impractical for commercial air travel due to their fixed thrust and inability to turn on ...
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  • 766
4 votes
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For how long could a plane handle turbulences?

You may want to look for aircraft fatigue loads, which are the typical loads that an airplane may experience during a fly (some sets include data for harsh conditions). They look like this (depending ...
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4 votes
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Will a lift force be created by the Coanda effect if high velocity air flows under a half-toroid shaped saucer?

It is important to realize any airborne device will go in the direction of the sum of all force vectors (including gravity). We have our centrifugal impeller drawing air in from the bottom. The device ...
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4 votes

Why does the air in a jet engine not flow out of the front?

Well, it can, and sometimes it does. That is called a compressor stall. https://www.youtube.com/watch?v=7MYh2KtEUQk So if you waded through the video, let me explain a little bit more if I can. The ...
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  • 3,590
3 votes

How an airfoil works

You are partially right. The air does move faster on the top of the wing than at the bottom. This is true, however as you pointed out the reason for that is not that 2 air molecules enter the wing at ...
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  • 1,704
3 votes

Lift Requirements for Hybrid Airship

As with any aircraft an airship need to be able to generate lift equal to its weight to remain airborne and also some additional lift to be able to gain height. Equally important is the ability to ...
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