baxtrom

True, stagnation pressure is lower at higher altitude. Back to the drawing board.. perhaps vortex-induced vibration of a string or similar could indicate airspeed acoustically. Would be annoying on long distance flights though

Looks suspiciously close to [math]\pi + 1[/math]..

Thanks for your input Captain Panic! Actually, the device I imagine could be a small (decimeter scale) plate made from plastic or similar. It could be mounted to the fuselage in front of the cockpit window. With increasing airspeed, the stagnation pressure on the plate would bend it, producing a visual indication of airspeed. Depending on the material, the influence of temperature on the elastic modulus could be negligible. If it could work practically I have no idea. However, it's just a first draft of a preliminary embryo of an idea.

If real domain is considered then I guess [math]x \in [-1, 1][/math]? I would try numerically. Is [math]\int[/math] close to 3?

Perhaps a GPS based system is the best backup? But, like you say, it will give you ground speed. Also, I imagine something brutally low tech! Something that wouldn't stop working after power loss, thunderstorms, EMPs, mega solar flares et c

Ciao fellow engineers! With Air France flight 447 in mind (and assuming faulty pitot tubes caused the tragedy) could one imagine a robust, down-to-earth stone age backup technology which would give pilots rough indication of airspeed if all else fails? Perhaps a small membrane or similar in view of the cockpit window which would deform elastically from the air flow?

There, there, DrRocket!

Nah, I don't think Ptolemy would mind.

Because sin(90 deg) = 1?

Another one: if a guy throws a dart at a wall, the probability the dart will hit one predefined exact spot is P=0. Still, unless the guy is very poor at throwing darts and hits floor or foot or similar, he will hit an exact spot on the wall, so probability for apparent miracle (P=0) is P=1. It's not a paradox, just the wrong way of using statistics. I'll leave it to the math gurus to come up stringent formulations involving sets, measures, distributions, generalized functions et c for proving it.

sootydaz, are you sure the stress levels for material Z is not in MPa? From the data in the table it looks like a ductile material. If the data is in MPa it could perhaps be some polymer.

Right, so back to drawing board. Engineering approach: first of all, recognize relative complexity of egg geometry (egg shaped!) and imagine instead a spherical egg, as an approximation. Assume diameter of [math]d [/math] = 50 mm and wall thickness [math]t[/math] = 0.3 mm (from this article abstract). Now, from pressure vessel engineering, the hoop stress in a spherical shell is [math]\sigma = \frac{p d}{\mathbf{4} t}[/math], where [math]p[/math] is the applied pressure. This source gives a value for the tensile stress of egg shells as [math]\sigma_{\mathrm{max}}[/math] = 15.2 MPa. Assuming further the eggshell has similar strength in compression, and neglecting buckling, this gives [math]p_{\mathrm{max}}[/math] = 0.36 MPa or 3.6 bar. Would correspond roughly to the water pressure at a depth of 36 meters. However, presence of white & yolk will likely strengthen egg. A complicated question! (Edit: errors corrected! )

Hmmm.. if egg contains egg white + yolk, any external pressure evenly distributed over the egg would be balanced by hydrostatic counter-pressure from the near-incompressible (?) fluid inside, and the only resulting stress would be through-thickness compressive stress (not too effective for cracking the shell wall). If as by magic (or needle) egg is empty, it's a different question.

Hello all (non-truthers and truthers), the recent development on the al Qaida front (i.e. bin Laden killed) reminded me about the so-called 9/11 truth movement. Is trutherism expanding in the US and Europe? I guess it's big in the arab world (where everything is a conspiracy), but what about for example much talked-about "Architects and engineers for 9/11 truth", are they gaining ground? Is the truth movement much covered by media in the US nowadays?

JohnDoe, the torque required to drive the mechamism depends on what you attach to the other end of the worm gear. If, lets say, your mechanism is a wheelbarrow, where the wheel is driven by a motor through a worm gear. Say your worm gear has a gear ratio of 100:1, the wheel diameter is 0.5 m, and you want your wheelbarrow to be able to pull a load of 100 kg up a 10 degree slope. That means, friction losses aside, that the force required to push the wheelbarrow up the slope is 100 kg x 9.81 N/kg x sin(10 deg) ~ 171 N. In order to produce that force, the torque driving the wheel needs to be (force times radius) 171 N x 0.25 m ~ 43 Nm. Since the worm gear has a gear ratio of 100:1, the motor will need to produce just 0.43 Nm. Further, if you want to drive your wheelbarrow up the slope at say 5 km/h = 1.4 m/s, the wheel needs to rotate with a speed of 0.9 revolutions per second or 5.6 radians per second. This means your motor will need to produce 43 Nm x 5.6 rad/s ~ 240 Watts of power, or about 1/3 hp, at 90 revolutions per second or 5400 rpm.. (Edit2: corrected error, again..)

Hey, if you're an american redneck you can probably just go into walmart and buy an M16 or similar. At least it wouldn't risk exploding in your face. Don't point barrel at fellow rednecks and all will be ok!

"Normalizing" sounds like you divide the fourier transform with some constant in order to interpret the value on the vertical axis, are you sure don't mean something like that? Like, if you run a vector of 1's through your DFT routine, you'll get an output vector with nonzero first element. If you divide your DFT's with this number when plotting you have one common form of normalizing. Problem is that if you normalize you typically won't get back the original time domain vector if you do an inverse DFT so you need to be careful.. If you multiply your DFT with frequency you will get some sort of high pass filtering effect, since for [math]f \to 0[/math] the DFT will also approach zero. And if you do an inverse DFT you will get some weird results since multiplication in frequency domain means convolution in time domain..

Sounds like buckling!

One could imagine a scalar function [math] \phi(\mathbf{x}) [/math] which gives a perturbed position (i.e. displacement) as [math] \nabla \phi [/math]. Could be used as a math trick to reduce a system of equations to a single PDE under certain circumstances. Don't think [math] \phi [/math] would have any physical interpretation, though..

I was thinking outside the box!

Actually, a large-diameter pipe or pressure vessel can typically hold much greater internal overpressure than underpressure. This is because of elastic instability, which can arise when compressive forces become too large. It's similar to buckling of a slender column under axial compression. When a pipe or pressure vessel is subject to underpressure, compressive hoop stresses build up in the wall of the vessel. If they become too large..

A related topic is crushing of piping due to underpressure, i.e. a buckling phenomenon. In some cases, pipes collapse due to underpressure, for example when steam condensates into water. Theoretically, a similar mechanism could cause large compressive hoop stresses in a pipe when the water is contracting.. Otherwise, I agree. Thermodynamic properties of water = good for frogs!

sounds like he's doing a random walk