1

General Science / Re: Why does faeces stick to some toilet bowls?

« on: Yesterday at 15:18:29 »

There is, or at least used to be,  a hangar on a factory estate near Thetford (Norfolk, UK) full of flushing toilets of various designs, where Jeyes tested their toilet cleaners. Probably worth enquiring of Jeyes if they have a "standard poo". In my days as a detergent chemist we had various standard stains and greases, so why not?

2

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: Yesterday at 15:07:50 »

Ledt's have a recap on the size, cruise speed and landing speed of your machine.

3

The Environment / Re: Media lies against nuclear power. What can I do to stop it?

« on: Yesterday at 08:41:26 »

If you like your present standard of living and don't believe in  magic, your grandchildren  are going to need liquid fuels. If their children are going to enjoy life too, they will need a sustainable human population (about one fifth of the present numbers) and either the means of using pure biofuel, or of synthesising heavier alkanes from atmospheric CO2.

This scenario is entirely feasible and desirable, but politically unacceptable at present. What can be done in the meantime is to make the UK economically independent of distasteful regimes.

4

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: Yesterday at 08:16:21 »

So far we have discussed a machine for carrying passengers backwards in an airway, or exposing its crew to enemy fire whilst attempting to remove scrap metal from a battlefield. There being little market interest for either, I don't see much point in  discussing the details until someone finds a bit of the atmosphere around 12,000 ft altitude, that doesn't move.

This afternoon I'll be passing over the Flying Bum en route from Cambridge to Oxford. It's a great landmark, but that isn't the primary function of an aircraft.

5

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 16/10/2018 17:23:20 »

Airlander is specified to 20,000 ft with a cruise speed of 80 kt.

It's generally preferable to fly above cloud for passenger comfort, so most non-jet traffic flies in the lower airways from 5,000 to 15,000 ft in the UK. Right now, the wind at Tingwall is 60 kt SW at 10,000 ft, Stornoway is 55 kt,  OK, it's a sea crossing so 2000 ft is safe (only 50 kt headwind all the way, but rough!)  but you'd get there quicker by boat! Fact is, if you regularly fly above 5000 ft, you need at least 150 kt cruise to make it worthwhile, and if you regularly fly below 5000 ft, you need rubber teeth. No way you can offer a service across mainland Europe below 10,000 ft.

The loiter speed for Airlander is 20 kt, so it can "hover" at 3000 ft or more on most days, but literally "falls short" of a zero-speed landing in anything less than a stiff breeze.

Worth noting that most licensed airfields are depicted on the charts with a "traffic zone". The Airlander base is marked "danger"!

6

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 16/10/2018 15:50:57 »

Recycling slight damage is done by field engineers, as the front line advances. Much quicker and easier to parachute in an engine - or even cannibalise one - than schlep the whole tank back to Detroit. If the front line is retreating, destroy anything that might be of use to the enemy, and regroup. Under no circumstances dangle your fighting vehicle from a dirigible, in sight of anyone with a decent rocket.

100 miles is about the minimum distance worth covering by air, unless there are special circumstances. The drive-on fast ferry across the Irish Sea (85 miles) runs at 45 kt and carries around 1500 passengers and 400 cars. Interestingly, it is likely to be replaced by a slower boat because it isn't economic - pity, because the breakfast is excellent! It's nearly always cheaper to fly and rent a car at the other end for business, and if you are going on holiday, another couple of hours on a regular ferry (a relaxing lunch!) is part of the fun.

I don't see the Flying Bum or any similar vehicle making a profit on a commuter route.

7

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 16/10/2018 12:49:45 »

Retrieving tanks is never urgent. If you win, you need to keep some armor alongside your occupying infantry. If you lose, the tank will be scrap metal and roasted soldiers. Using plastics instead of wood, we could make a tank-carrying glider capable of 300 mph or more.

Delivering civilian kit to remote locations is quite a different prospect  That's pretty much what the Flying Bum (US: Flying Ass) is designed for; slow, no landing strip.

Choose your question, then design the solution. More Cessna 172s have been built than any other aircraft, 'cos it's extremely adaptable and dead easy to fly, but there's a difference between  the regular, cargo, STOL, desert and float versions, the wing is in the wrong place for crop spraying, and Vs is too high for light glider towing.

8

Chemistry / Re: What is a Kjeldahl Bulb?

« on: 16/10/2018 12:35:18 »

Back to school! It should improve the smoothness of your poteen. Enjoy!

9

The Environment / Re: Media lies against nuclear power. What can I do to stop it?

« on: 15/10/2018 23:34:19 »

I worry about the anti-fracking lobby. Do they really want their lives to depend on the whims of Saudi Arabia and Russia?

10

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 15/10/2018 23:27:30 »

Transporting tanks is easy. Way back in the 1940s, both sides built wooden gliders that could be towed by a conventional bomber and carry a tank. Cheap (cheaper than a tank, which in modern warfare has an expected front line service life of about 60 minutes), effective, fast (up to 180 mph even then), and with minimal radar profile. Release at 15,000 ft, dive and cokscrew at Vne, deploy the brakes, and skid to a halt next to your infantry, with the tank engine running. Eventually , somebody thought it would be more sensible to fit a couple of engines to the glider, and the Guppy was conceived, but only the unpowered versions saw action.

Like I said, choose your problem first, then design the solution. If you want to move tanks quickly to the front line, use a glider. If you are not in a hurry, use a ship and drive from the coast. The prospect of a damn great airship appearing over a battlefield and landing at  10 mph can only bring joy to the enemy.

11

Just Chat! / Re: Would it be wrong to try to get somebody kill themselves?

« on: 15/10/2018 18:03:46 »

Generally considered a Bad Thing to try to persuade anyone to kill himself, but I think it is equally indefensible to bully anyone into staying alive if he genuinely wants to die. This is where the law needs a serious review. Suicide and attempted suicide are not illegal in the UK if you are sufficiently fit and compos mentis to make all the arrangements yourself. The problem arises always and only if you are so sick, disabled, distressed  or mentally incompetent that you need help: it is a crime to assist a suicide.

So suicide is statutorily denied to those who need it most. In a marginal case, where someone seeks legal assistance (as with Dignitas) it has been argued that a third party purchasing your plane tickets or driving you to the airport, is guilty of assisting a suicide. Fortunately the Crown Prosecution Service has usually ruled that such prosecution would not be in the public interest thus establishing a sensible precedent that should be embodied in statute.

12

Physics, Astronomy & Cosmology / Re: Is acceleration downwards due to gravity less when the Moon is overhead?

« on: 15/10/2018 15:03:12 »

According to Kepler, orbits in free space do not circularise.

I think the answer to the original question is "yes".

13

Technology / Re: Are heavier-than-air hybrid airships a good idea?that weight doesn't influen

« on: 15/10/2018 09:03:28 »

It's a good exercise to calculate the minimum size of a beer can (0.15 mm aluminum) that can lift itself if filled with hydrogen, then extrapolate to a useful load carrier. Some years ago I sketched a rigidised aluminum blimp with aerodynamic (i.e. thin) wings that looked rather like a Beluga. Halfway through the calculations, my date walked out of the bar, but I still think it's an interesting idea.

Every aspect of every aircraft is a compromise, which is why there are so many different species of birds. We could talk round in circles unless someone specifies a primary mission: load lifting, VTOL, efficient cruise, whatever....

BC is right that weight doesn't influence drag for a near-buoyant craft, since W ≈ 0. You can maintain altitude as you burn fuel by displacing your lift gas with air, just like a Zeppelin, or by deriving some lift from hot air which you allow to cool as you lose weight.

14

The Environment / Re: Is there any hope of effective action on climate change?

« on: 14/10/2018 17:15:05 »

Religious leaders are responsible for most of the misery in the world, but fortunately humanity is beginning to show signs of growing up and ignoring such parasites.

My suggestion is to pay every woman £500 (or the locally-adjusted equivalent) every 6 months if she is not pregnant, and abolish all child benefit payments. The saving in health and education costs alone will outweigh the cost of the grant.

Strict immigration control and the prohibition of religious teaching in state schools (or even a curriculum change to ensure that religion is included along with sexually transmitted diseases and careless driving, under "things to avoid") will allow the UK to become a model of voluntary population control. If others wish to reproduce to starvation, it is up to them - there will be no handouts for famine relief in areas that cannot reasonably support their populations.

As for travel and transport I really don't see the point of most of it. Look around a city at lunchtime. Pretty well everyone wearing an office suit has no need to be there - anything you can do in an office, you can do on a computer at home, including "meetings" (what a waste of time). Travel for fun and adventure, and by all means transport goods around the place, but commuting and "business trips" really don't need to happen - as High Street shops are beginning to notice.

15

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 14/10/2018 14:26:06 »

Induced drag is not a function of weight.

Crosswind takeoff and landing is not a problem if you have  a vertical thrust vector - you just point the aircraft into wind and land vertically with zero groundspeed - i.e no crosswind.

16

Physics, Astronomy & Cosmology / Re: How did scientists measure the mass of the Earth and other planets?

« on: 14/10/2018 09:40:56 »

Cavendish's work refers to the process as measuring the density of, or weighing, the Earth.

That was his ultimate objective, but what his torsion balance experiment actually did was to measure G in terms of the force between known test masses.


Apologies for placing my note after BC's reply! Editorial cockup, not a wormhole in spacetime..

17

Physics, Astronomy & Cosmology / Re: How did scientists measure the mass of the Earth and other planets?

« on: 14/10/2018 09:37:33 »

from: alancalverd on 12/10/2018 09:49:23Using F = GmM/r2 you can calculate the force on a falling object of mass m in terms of M, the mass of the earth, and G, which we assume to be a universal constant.

That doesn’t work.  We’re trying to compute at least a rough G and M here.  We don’t know either of them yet.  We do know force F is 9.8 newtons for a 1KG mass.  We can assume we know r.  We therefore know the product of G and M, but not either separately.

We don't "know" F = 9.8 N/kg. We define the newton as1 kg.m.s^-2, and have a measured value of g = F/m

We don't "assume" r: it is a measured value - see below.

As I said, Cavendish (1797) measured G directly. 

Maskeleyne estimated the density of the planet from an experiment in 1774 at Schiehallion, measuring the deflection of a plumb bob on two sides of the mountain. In fact, that was a measure of G rather than ρ_earth since the assumption that the mountain was homogeneous was more defensible. Newton had considered the possibility but rejected the experiment as too difficult.

As F = ma, we can measure the acceleration of a falling object or the period of a pendulum to get a value for F/m

F=ma works (F 9.8 = 1 (mass) * 9.8 m/sec acceleration), but that doesn’t yield either mass of Earth M nor G, which are the two things we’re trying to determine here.
The pendulum thing is a function of acceleration (9., not of the mass of Earth.  Put a pendulum in a rocket accelerating at that rate and it will have the same period as here on Earth.  It tells you nothing about the mass of the Earth under you.

You have missed the point. If we know F/m we know GM/r², and we have known r since 200 BC (Eratosthenes), so all that was required for an accurate estimate of M was Cavendish's determination of G. The reason for using a pendulum  is that we know the period T = 2π√(Lm/F) for small oscillations, which is a simpler experiment than measuring the acceleration of an object in free fall.

The most amazing fact in all this, hundreds of years and thousands of experiments later,  is that the gravitational masses of all bodies are identical to their inertial masses. Why?

Interestingly, Hipparchus estimated the radius of the moon's orbit around 130 BC, though his assumptions regarding the earth's orbit of the sun were somewhat wild.

18

Technology / Re: Are heavier-than-air hybrid airships a good idea?

« on: 14/10/2018 09:25:39 »

A disk-shaped craft is not as subject to side-winds as a slab-side , like an airship or a tube .

All aircraft are equally susceptible to crosswind in flight. You fly through a "box of air", and if the box is moving sideways or backwards in relation to your intended track, you have to go faster and change course to compensate. It's not the same as crosswind on the ground, which has the same effect as on a car or boat - you weathercock into wind depending on the shape of the vehicle and the position of its wheels or keel.

Obviously the effect is less significant at higher airspeeds, but the increase of windspeed with altitude means that even at 500 kt you need to correct for wind drift and going backwards at 150 kt and 30,000 ft is one of the joys of propeller aircraft.

19

Physics, Astronomy & Cosmology / Re: How did scientists measure the mass of the Earth and other planets?

« on: 12/10/2018 09:49:23 »

Using F = GmM/r² you can calculate the force on a falling object of mass m in terms of M, the mass of the earth, and G, which we assume to be a universal constant.

As F = ma, we can measure the acceleration of a falling object or the period of a pendulum to get a value for F/m

Cavendish's experiment is a classic procedure for measuring G.

Hence M.

The Inverse Square Law is "obvious" if you think of gravity like llight, propagating in straight lines, so it's a good starting guess. Using the ISL, you can show that the orbit of a planet around a star is necessarily elliptical. Observation shows this to be correct, and you can preedict the orbit of a comet to a very pleasing degree of accuracy . Deviations from the idealised ellipse will be caused by the presence of other massive bodies, so we gradually accumulate "corrections" to our astronomical observations that give us estimates of the mass of these other objects.

Like Einstein and indeed every other scientist worthy of the name, Newton made some predictions which were tested by observation, and thus he (or his successors) demonstrated the validity of the mathematics. This is what distinguishes science from computer modelling, economics, philosophy, politics, or religion.

20

Technology / Re: How much efficiency will increase if a three layer magnetic circuit is used?

« on: 12/10/2018 09:35:03 »

What is your definition of efficiency? It looks to me as though you are measuring linear pull. Rotating magnets are a clever but entirely conventional way of switching a strong pull at a short range with very little input torque.