Crazy Pilot Flyby at 1m.

(With thanks to Gizmodo for providing the video) 

So this pilot with the Argentinian Air Force - damned Argentinians, who else is crazy enough to do this?! - flies low over trees and flies past his colleagues on the ground at an altitude of just 1m off the ground. If you thought the pilot’s POV was insane, just check the footage from his “friends” if you can call them that after what he did.

From a physics point of view, a jet fighter flying that low to the ground is subjected to ground effect. As the altitude of the plane decreases to 1-1.5 x its own wingspan, the air pressure below the wing increases. This results in an artificial reduction of aerodynamic drag causing greater speed and lift on the plane. This may make it more dangerous for a pilot to fly at low altitudes, since the greater speed calls for an even faster reaction time than normal. Add to that your usual barrage of obstacles such as buildings, pylons and yes, other people too. 

Edit: this is my 100th post! Finally made it to this nice achievement :)

Pendulum Waves

Exploiting the isochronous nature of pendulums in a really fun way. Simple harmonic motion is demonstrated here by the fact that each individual pendulum will sweep out an arc of a set frequency regardless of how much energy you put into it at the beginning. This is due to the relationship of: T (time period) = 2 pi x sqrt(l/g) where you can see that the frequency is entirely dependent on the length of the pendulum and the gravitational field strength.

It’s also weird to see that the pendulums move in and out of step of each other, sometimes going into chaotic patterns and then settling back in to a pattern of some sort. For that I have no reasonable explanation, apart from maybe the lengths of the pendulum strings are part of a mathematical progression or sequence to make these waves happen.

thisistheverge: Here’s the original article. nwkarchivist: Ten Years Ago Today, the iPod Enters the Market.  Presenting Steven Levy’s First Look. 10 years, wow. To say that technology has advanced by an incredible amount in 10 years is an understatement. To say we thought that this blocky, brick-like device was at the bleeding edge of consumer technology amazes me. Things can only get smaller, more flexible and faster from here on in.
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thisistheverge:

Here’s the original article.

nwkarchivist:

Ten Years Ago Today, the iPod Enters the Market.  Presenting Steven Levy’s First Look.

10 years, wow. To say that technology has advanced by an incredible amount in 10 years is an understatement. To say we thought that this blocky, brick-like device was at the bleeding edge of consumer technology amazes me.

Things can only get smaller, more flexible and faster from here on in.

Source: nwkarchivist

What does this fighter jet do that other fighter jets can’t? The picture you are seeing is that of a NASA-modified F-18 Hornet, the HARV (High Alpha Research Vehicle) High alpha is a property of certain types of fighter jets, and alpha itself is a shorthand form of saying the angle of attack of the wing. The angle of attack is defined as the angle between a line on a lifting body (such as an aerofoil) and the relative vector of the passing fluid (for simplicity’s sakes, we will presume it as the horizontal line of travel of the jet) As the AoA increases, the coefficient of lift increases, as shown by the graph below: (Image credit: http://www.allstar.fiu.edu/aero/lift_drag.htm) Basically, the more the aerofoil is tilted against the direction of travel, the greater the force of the lift…UNTIL a certain point, known as the critical angle of attack (original, I know) after which the coefficient of lift will decrease. This is described by the physical phenomena of flow separation, more specifically, the airflow going over the top of the wing becomes detached from the upper surface of the aerofoil and produces turbulence by eddy currents of air, reducing the lift force. High alpha planes have both advantages and disadvantages. A definite pro is the fact that a high alpha plane has more agility in the sky, a term being coined by the defence industry as “supermanoeuvrability” - it allows planes that have high alphas and the pre-requisite structural integrity to perform insane moves in midair such as Pugachev’s Cobra: (Image credit: Wikimedia) …which might just help turn the tide during a midair dogfight. A disadvantage of high alpha planes is that they have a massive induced drag which is self-afflicted - a compromise for such manoeuvrability.  So, to finish off, the HARV at the very start was an experimental NASA vehicle that achieved stable flight at 70 degrees AoA using thrust vectoring - the same technology that gave the Harrier its VTOL capabilities. To visualize this, draw an x-y graph, sketch a horizontal jet fighter. Tilt said jet fighter 70 degrees to the horizontal. At this point, the jet fighter would still be flying, stable, in the x direction. That is amazing. For anyone that wants to read up more on the subject, it seems NASA’s own papers have been declassified, and can be found here: http://www.google.co.uk/url?sa=t&rct=j&q=forebody%20strakes&source=web&cd=1&ved=0CBwQFjAA&url=http%3A%2F%2Fwww.nasa.gov%2Fcenters%2Fdryden%2Fpdf%2F88441main_H-2136.pdf&ei=vGW2TsqiJIHd8AOD1fDvBQ&usg=AFQjCNGbB773baTOrBrodoIhJzbydVLVPA
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What does this fighter jet do that other fighter jets can’t?

The picture you are seeing is that of a NASA-modified F-18 Hornet, the HARV (High Alpha Research Vehicle)

High alpha is a property of certain types of fighter jets, and alpha itself is a shorthand form of saying the angle of attack of the wing. The angle of attack is defined as the angle between a line on a lifting body (such as an aerofoil) and the relative vector of the passing fluid (for simplicity’s sakes, we will presume it as the horizontal line of travel of the jet)

As the AoA increases, the coefficient of lift increases, as shown by the graph below:

(Image credit: http://www.allstar.fiu.edu/aero/lift_drag.htm)

Basically, the more the aerofoil is tilted against the direction of travel, the greater the force of the lift…UNTIL a certain point, known as the critical angle of attack (original, I know) after which the coefficient of lift will decrease. This is described by the physical phenomena of flow separation, more specifically, the airflow going over the top of the wing becomes detached from the upper surface of the aerofoil and produces turbulence by eddy currents of air, reducing the lift force.

High alpha planes have both advantages and disadvantages. A definite pro is the fact that a high alpha plane has more agility in the sky, a term being coined by the defence industry as “supermanoeuvrability” - it allows planes that have high alphas and the pre-requisite structural integrity to perform insane moves in midair such as Pugachev’s Cobra:

(Image credit: Wikimedia)

…which might just help turn the tide during a midair dogfight.

A disadvantage of high alpha planes is that they have a massive induced drag which is self-afflicted - a compromise for such manoeuvrability. 

So, to finish off, the HARV at the very start was an experimental NASA vehicle that achieved stable flight at 70 degrees AoA using thrust vectoring - the same technology that gave the Harrier its VTOL capabilities.

To visualize this, draw an x-y graph, sketch a horizontal jet fighter. Tilt said jet fighter 70 degrees to the horizontal. At this point, the jet fighter would still be flying, stable, in the x direction. That is amazing.

For anyone that wants to read up more on the subject, it seems NASA’s own papers have been declassified, and can be found here:

http://www.google.co.uk/url?sa=t&rct=j&q=forebody%20strakes&source=web&cd=1&ved=0CBwQFjAA&url=http%3A%2F%2Fwww.nasa.gov%2Fcenters%2Fdryden%2Fpdf%2F88441main_H-2136.pdf&ei=vGW2TsqiJIHd8AOD1fDvBQ&usg=AFQjCNGbB773baTOrBrodoIhJzbydVLVPA

How a Differential Works - or, My Continued Attempt to Understand What Really Happens In a Car. (Image credit: http://www.motorera.com/dictionary/pics/d/differential.jpg) A differential in your car is probably one of the most ingenious yet the most taken-for-granted thing. Probably. This clever system of gears helps the car turn the corner without having to make one of the tyres slip against the tarmac.  Turning your car may entail you turning the steering wheel, but on the mechanical level, so much more is going on. The wheels that are being driven by the engine need to turn at different velocities seeing as though they trace out slightly different routes through a corner (the inside wheel to a corner has less distance to travel and hence can corner with less speed than the outer wheel) To do this with an OPEN differential, the input pinion coming out of the engine turns the massive ring gear which houses pinion gears within it. If the car is on a straight, it has no need at all to have wheels turning at different speeds, and so the pinion gears are effectively locked against the ring gear, turning the axle shaft of both left and right wheels at the same speed. If the car turns right (for example) you will find the right wheel is on the inside of the curve and the left wheel is on the outside. Then you have a speed differential between left and right wheels (where it gets its name from) where the right wheel needs to go slower than the left wheel in order to turn the car right.  The pinion gears then work - 2 of them effectively top and bottom connected to the axle shafts of the left and right wheel - turning within their housings so that the left wheel turns a lot quicker than the right wheel. Limited slip differentials work on the same principle but employ clutches and springs within the pinion gears. They work as an open differential when the car is going straight during normal conditions, but if you are driving on ice and find that one wheel is on ice and the other isn’t, the limited slip diff will help you keep control of the car. As the icy wheel slips, wanting to turn at a faster speed than the normal wheel, the clutch tries to react by keeping both wheels spinning at the same speed until the torque (turning moment) of the icy wheel overpowers the clutch. 
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How a Differential Works - or, My Continued Attempt to Understand What Really Happens In a Car.

(Image credit: http://www.motorera.com/dictionary/pics/d/differential.jpg)

A differential in your car is probably one of the most ingenious yet the most taken-for-granted thing. Probably. This clever system of gears helps the car turn the corner without having to make one of the tyres slip against the tarmac. 

Turning your car may entail you turning the steering wheel, but on the mechanical level, so much more is going on. The wheels that are being driven by the engine need to turn at different velocities seeing as though they trace out slightly different routes through a corner (the inside wheel to a corner has less distance to travel and hence can corner with less speed than the outer wheel)

To do this with an OPEN differential, the input pinion coming out of the engine turns the massive ring gear which houses pinion gears within it. If the car is on a straight, it has no need at all to have wheels turning at different speeds, and so the pinion gears are effectively locked against the ring gear, turning the axle shaft of both left and right wheels at the same speed.

If the car turns right (for example) you will find the right wheel is on the inside of the curve and the left wheel is on the outside. Then you have a speed differential between left and right wheels (where it gets its name from) where the right wheel needs to go slower than the left wheel in order to turn the car right. 

The pinion gears then work - 2 of them effectively top and bottom connected to the axle shafts of the left and right wheel - turning within their housings so that the left wheel turns a lot quicker than the right wheel.

Limited slip differentials work on the same principle but employ clutches and springs within the pinion gears. They work as an open differential when the car is going straight during normal conditions, but if you are driving on ice and find that one wheel is on ice and the other isn’t, the limited slip diff will help you keep control of the car. As the icy wheel slips, wanting to turn at a faster speed than the normal wheel, the clutch tries to react by keeping both wheels spinning at the same speed until the torque (turning moment) of the icy wheel overpowers the clutch. 

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