I've never seen one fail, but, as a bit of fun, here's an estimate of the energy in a flywheel at 6000 rpm, compared with the energy of a 1000 kg car.
Among the many possible criticisms that could be levelled at this "fag packet" type calc is that it over estimates the energy that a failing flywheel would deliver because you would still expect to see some parts or fragments of the failed flywheel attached to the crank. However, I think the calc is OK in an order of magnitude sense.
Units are metres, kilograms, seconds, except for the estimated speed of the 1000kg car, which is given in miles per hour.
ro=7850; dia=350e-3; thickness=15e-3; mass=ro*thickness*pi*(dia^2)/4; Inertia=mass*(dia^2)/8; rpm=6000; omega=2*pi*rpm/60; KE=Inertia*(omega^2)/2
KE =
3.4242e+004
mass
mass =
11.3289
% Equivalent speed of a 1000 kg car v_ms=sqrt(KE/1000); v_mph=3.6*v_ms/1.6093
v_mph =
13.0902
Number_Cruncher
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What's that in layman's numbers?
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Ah, sorry.
The idea of the calc was to compare the energy in a typical flywheel at 6000rpm against the energy of a 1000kg car. The last line of the calc shows that the car would have to be travelling at between 10 and 15 mph to have the same energy.
Number_Cruncher
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In plain English then...*bang*!
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Even more so, because I missed a factor of two in the equation for the KE of the car!
v_ms=sqrt(2*KE/1000); v_mph=3.6*v_ms/1.6093
v_mph =
18.5124
Number_Cruncher
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Number Cruncher you are the easiest of all the backroomers to put a face to. White lab coat, wild grey hair and thick black glasses. Probably holding something volatile in a test tube.
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"White lab coat"
With some alarming-looking stains, I bet...
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Number Cruncher you are the easiest of all the backroomers to put a face to. White lab coat, wild grey hair and thick black glasses. Probably holding something volatile in a test tube.
Professor Weeto?
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Remember prof Pat Pending from the Whacky Races?
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Oh dear - I dont think I fit in with this! Especially not the bit about stains JBJ!!
Think more on the lines of large tall Lancastrian seldom seen in anything other than blue denim - except when fairying around in a clean room with gown, gloves, face mask, and frilly shower cap!
I'll confess to keeping some pens and pencils in my shirt pocket, and sometimes taking blank A4 to the pub to enable sketches and equations to be discussed with other engineers over a pint as per Gareth's post.
Number_Cruncher
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"I'll confess to keeping some pens and pencils in my shirt pocket"
I nice neat row of different coloured pens in a shirt pocket is actually quite a bird-puller. Admittedly they start off by laughing at you, but at least it gets them talking. Has worked for me in the past.
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except when fairying around in a clean room with gown, gloves, face mask, and frilly shower cap!
Oh my God, you're that famous actor bloke in "Casualty"!
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"the energy in a typical flywheel at 6000rpm"
Make that 60,000 and you've got 100 times as much!
I recall an article in Scientific American in the 70's, suggesting the use of flywheels to store energy. I think they turned up in a few buses, helping them to re-use some of the braking energy to get going again, but never seemed to make it to cars, despite the square relationship with revs. Perhaps containing the energy in a collision was the problem!
The article also discussed ideal shapes, with some very surprising results, once you removed the need for streamlining, as they were intended to work in a near-vacuum. I don't remember gyroscopic effects being covered, though - could either make for a very even ride or stop you going round corners!
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The flywheel principle is in use as to power an experimental service on the Stourbridge branch line. See;
www.parrypeoplemovers.com/technology.htm
The quick calc I did above is the first time I've worked out how much energy there is in a typical car flywheel - I found the answer to be surprisingly large, and so I begin to find it more believable that it has a possible use in powering vehicles on short, repetitive routes, where recharging by spinning the flywheel up again can be easily accomodated.
Number_Cruncher
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as a bit of fun, here's an estimate of the energy in a flywheel at 6000 rpm, compared with the energy of a 1000 kg car.
This is the sort of thing that engineers do instead of going down the pub. Or while they're down the pub! Why, some of my best ideas.....
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Many years ago I used to work in the diamond trade and once visited a diamond polishing factory. The diamonds are polished on a scaife which is basically a cast iron disk of a similar size to a car engine flywheel. They had a seperate room where they would test new scaifes by spinning them up to 10,000 rpm (IIRC). The spinning scaife was surrounded by a couple of inches of heavy rubber set inside a block of concrete that was probably around 6 foot sqaure.
Unforunately I never got to see any of them tested but I was told that it was quite impressive when they broke.
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I remember visiting GEC in Rugby (where they make the steam turbines when I was at university. We were shown the building they use to overspeed test the turbines - it had a red-lead painted patch on the roof .
When asked we were told that a low pressure turbine blade had broken on the overspped test and had come through six inches of concrete and an inch of steel landing in the pond about 50 feet from the building.
The LP blades were up to 4 feet long and these normally run at 3000 rpm (50 Hz generator) and they test to a 10% overspeed.
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Erm. What's a dual mass flywheel?
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A flywheel with dual mass...
Fitted to most modern diesels to reduce jerkiness through the drivetrain.
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A dual mass flywheel (DMF) is a development of the standard flywheel that essentially adds a second flywheel (rotating mass) that is separated from the first by a pair of springs. The job of the springs is to hold the two masses in a fixed position relative to one another.
The assembly comes into its own when driven by an internal combustion engine. The rotation is engines is really far from smooth and this can be felt by the driver as vibration. With masses and spitngs selected carefully for a particular powertrain, the DMF is able to soak up a great deal of this vibration. The vibration excites the mass spring system in such a way as the unwanted vibration is absorbed.
They are increasingly common on high end diesels where smoothness and refinement of the vehicle is an important factor.
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Picture it as a flywheel within a ring gear, with springs linking them. It's to reduce vibration in the driveline
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There is more here if you are interested...
www.luk.com/content.luk.de/de/products/clutch_syst...p
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You will not only have to be interested but to read German...
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Forgot all my German, but I get the picture from the, er, picture.
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That's a good link to a helpful explanation, and there's also an equivalent English one;
www.luk.com/content.luk.de/en/products/dampers/zms...p
Number_Cruncher
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"quite impressive when they broke."
The J Samuel White's shipyard in Cowes (now defunct, but more here: en.wikipedia.org/wiki/J._Samuel_White ) had a huge static grinder that occasionally lost a wheel. When this happened, everyone just got out of the workshop as fast as they could...
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