17
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 was pressurized to sea level pressure. But it's still within the limit of what passengers feel comfortable with.
This answer on aviation.SE contains a plot of ...
15
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 demanding and requires a lot of practice to master.
Hiller helicopters (which have been out of production for many years) were one of the rare examples of ...
14
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 impossible to control the airplane about its longitudinal axis.
When an aircraft stalls at the root first, it means there’s enough airflow over the
tips of your wings ...
11
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 technicians, the Boeing X-20 Dyna-Soar project was cancelled just after work had started on the actual spacecraft.
Here's an artist's impression of the X-20:
The ...
9
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 to lunar orbit - yes, but at 20%-25% of LEO payload
Air launch to Moon and back to LEO: Yes, but with about 5% of LEO payload
It is easy to overlook some ...
8
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:
$$C_d = C_{D0}+ \frac{{C_L}^2}{\pi e AR}$$
$C_D$ is is the aircraft drag coefficient
$C_{d0}$ is the aircraft zero-lift drag coefficient,
$C_L$ is the ...
7
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 traveling extremely fast). If the air goes too fast, it won't burn enough; if it goes too slow, it won't provide enough thrust.
Air goes in through gaps in the liner....
6
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 pressure side (see illustration from Wikipedia:
The key to understand the velocity distribution around an air foil is not to look at it independent from the ...
6
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 former has to carry around a lot of stuff at takeoff.
The only possible way to save you from the fundamental issue above is to throw the stuff out the back so ...
6
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 from thin airfoil theory by a small amount. $a_0$ is left in the above equation so one can predict the elliptical finite wing lift slope (effects of aspect ...
6
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 of the aerodynamic center. As Cl increases, it is desirable to have the center of lift shift aft. This produces speed stability by lowering the nose, thus ...
5
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 expansion (in a turbine)
Constant pressure heat rejection
And since efficiency is defined as Net output work / Heat input, Efficiency can be easily related to ...
5
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 forced to fly very low. Above around 50 feet (wingspan-dependent) you will not see much in the way of ground effect benefits.
The problem is that, even over ...
5
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't find any complete open source designs (i.e. high-quality, technical engineering drawings), but this is a good approximation.
5
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-flapping machine." It didn't use a propeller (or jet engine, of course!) but instead used a small engine weighing about 22 pounds when fully fueled. Its wingspan ...
5
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 supercomputers, and untrusted. It was quite common that a theorist or experimentalist would at best discount the results of the CFD, while others may totally disregard ...
5
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, satellites, or various space junk. The space shuttle, when it was in operation, reentered the atmosphere between Mach 10 to Mach 25, which would destroy both ...
5
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 nearest supermarket.
Source: from https://www.tesco.com/groceries/product/details/?id=254381873, "Tesco Everyday Value Milk Chocolate" provides 3840 kJ/kg, and the ...
4
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 jet engines on our rocket. The Falcon 9 puts out about 1.1m lbs of thrust, so we can use a GE-90 to add 120,000 lb, doubling the acceleration at sea level. ...
4
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 disappearance, gives a pretty good rundown of how planes are tracked currently.
The essence of it is that most air traffic control systems still rely on radar, whether ...
4
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 Aviation Maintenance Technician Handbook points out this advantage on page 16-5:
Sodium chlorate chemical oxygen generators also have a long shelf
life, ...
4
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 refuge systems are designed and installed, either underground, in mines or tunnelling projects or at industrial plants like oil refineries and chemical plants, ...
4
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 your departure terminal, then your ears would not pop on ascent, but they would have to pop at some point on the descent unless the elevation of the landing ...
4
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 and off.
A both liquid rockets and and jets need fuel but a rocket engine also needs oxygen, the jet engine pulls this from the air. So for the same amount of ...
4
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 where are you measuring):
Or:
And note that airplanes are designed to withstand thousands of those cycles.
So, as long as the turbulence is not catastrophic (...
3
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 the same time and due to the curvature the molecule on top has to travel faster before they meet again.
So what happens then?
When the airplane starts ...
3
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 manoeuvre well enough to avoid collisions with terrain or other aircraft in a variety of reasonably foreseeable weather conditions. It is the latter point which ...
2
I don't think there are any engineering issues with them, I just think there is no economic or operational niche for them.
They have the operational overhead of aircraft so why not just use a plane to begin with? They can only be used over relatively flat terrain or still water but is there anyplace in the world where the necessary terrain and economic ...
2
Superhydrophobic surfaces generally consist of a series of micro/nano scale pillars that increase the contact angle of water on the surface. Larger contact angle means water forms more spherical drops and can roll off more easily. Changing the chemical properties of the surface layer can also help change the contact angle.
These surfaces are optimized to ...
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