13 posts • joined Saturday 24th July 2010 00:43 GMT
Book available again ....
Looks like the EFF have held Amazon's hand as they retraced their steps through the decision to take down the book.... http://www.bbc.co.uk/news/technology-21409490
Just the one bellywheel sir?
Only one belly wheel to be seen too, by the dead fatty as the perps shot their way through citizens in to the block.
For me it was astoundingly close to The Raid, which if you haven't seen I strongly suggest you do. I think the biggest hole for me was the lack of humour. Whatever else you say about the look / style /design of the film Dredd in 2000AD was always full of subtle jokes in the back ground they surely could have snuck a bunch in. Also as others have said Dredd one liners and funny crimes. Maybe I will see some that I missed on a second, 2D, viewing.(3D, while there are one or two pretty uses that are the now ordinary lots of fragments coming out the screen at you, pretty much leaves me cold and I have seen a lot of 3D films now).
The vehicles bugged me, not so much the Lawmaster which did, at least, appear to be rideable. Something that Dredd's comic square wheeled behemoth would and could never be. It was more the first chase taking place in a reasonably good condition Volkswagen T3 Transporter van that must surely be a collectors item by the time Dredd and co are doing their thing in Megacity One.
I will see it again and I will hope for sequels because any Judge Dredd is better than none (yes even Stallone Dredd) but I will wait in hope that someday someone does it right ... bring on a future Dredd reboot ;)
The main guy behind the Robin has moved on to hangliding these days. Others are aware of this but I am not sure that they are likely to be interested. The Reliant Robin Shuttle used 9 O class hybrid motors and a pile of L class solid motors in the two SRBs I believe. A tad bigger than a small hybrid or G class boost glider motor ;)
Is it turned on?
"...as it could sniff the roaring plasma gusts as they roll across its track using its coffee-tin sized Radiation Assessment Detector instrument."
I was going to ask if you knew if the Curiosity rover would be fully powered up during it's trip to Mars (called the Cruise Phase) as spacecraft are sometimes effectively dormant in transit. But a bit of digging here http://msl-scicorner.jpl.nasa.gov/Instruments/RAD/ found that :
"The RAD instrument will be used throughout the mission, including part of the cruise phase, to characterize the radiation environment of MSL. It is desirable for the instrument to be powered continuously while on the Martian surface. However, because of rover energy constraints, the present plan is to acquire roughly 15-minute observations every hour throughout each sol."
So it looks like there is a chance it may well be.
Copperheads are more commonly known as "Crapperheads". Essentially they are double sided copper clad filmwire cut in to narrow strips with one end stamped in to a zigzag crinkled shape for about 5 to 10mm and then dipped in a pyrogen. Which, I think, is mixed with carbon to make it slightly conductive/give it enough resistance. As mentioned they are notoriously unreliable.. Often fine copper whiskers from their being guillotined in to strips short the two copper layers out.
Look for e-matches like Davyfires or similar. These are the proper tool for the job.
Also there should'nt be any heat issue with the casing temp. Part of the US regs (NFPA 1127 iirc) which the motors must meet to be allow them to be sold define max external temp the motor casing can reach. Also remember that most hobby rockets of the size that take these motors use a cardboard or phenolic impregnated paper/card motor tube for the motor mount. They dont have any issues with the temperature that the casing reaches.
Might want to avoid epoxying the motor in to anything. The "RMS" bit of the Aetotech motor designation stands for "Reloadable Motor System" The reloadable motor bit is an aluminium motor casing with forward and aft closures (end caps) they dont come chea and are meant to be reuseable / reloadable. The reload is a bag of assorted cardboard tubes, washers, o-rings, propellant slugs or "grains" and a nozzle. These have to be assembled in the right order or the motor wont work as desired. Aerotech are the most open to failure due to operator error. I have done it. Forgot one o-ring, result rocket flambe.
"How about doing it the other way around by partially blocking the exhaust nozzle of the rocket motor?
In other words, raise the internal pressure of the motor rather than reducing the external pressure. If you can get the ratio of internal to external pressure the same as it would be at altitude then you should have a valid test."
The problem is that pressure drops with altitude. The pressure inside the unlit motor and outside the motor will be lower at altitude than ground level. For a rocket motor to work, for the chemical reaction to work fast enough for the motor to burn properly, the motor has to reach the correct operating pressure. This is achieved by careful design of the nozzle so that, among other things, it maintains a pressure differential between the inside burny bit and the outside. A pressure gradient. When the propellant ignites it creates huge volumes of combustion products / gas which raises the pressure in the combustion chamber, the inside of the motor. The rise in pressure increases the speed of the burning reaction, which increases the pressure which increases the rate of reaction... This depends on the geometry of the nozzle, a venturi, being correct for the designed burn characteristics of the propellant, the internal geometry of the propellant grain (a slot, star, "C", bates grain, etc..), motor casing materials and air pressure range through which the motor will operate. The nozzle geometry for commercial model rocket motors is designed for ground level launches up to a couple of 10's of thousands of feet. This is why Aerotech are being cautious. Raising the internal pressure of the motor for a ground level test by blocking the nozzle will lead to the motor over pressurizing and failing (going bang one way or another).
Toasty tail plane batman
I suspect you may not have seen the kind of rocket motor that might be used in full effect. There isnt much that would withstand the rocket exhaust plume. Putting the rocket motor up front gives you a bunch of issues:
Assymetric thrust: as the motor has to be above or below the aircraft.
Drag as you need some kind of pod to contain the motor outside the airframe.
Thermal protection of the airframe which will add mass/complexity
A rear engined approach is probably wiser. Then you can get the thrust along the axis of the aircraft and have the motor contained within the fuselage.
The most succesful boost gliders I have seen have been rear engined (as flown by the UKs FIA R/C boost glider international gold meadlist Mike Francies and a Hybrid rocket motor powered R/C delta wing glider regularly flown by John Barber a member of the East Anglian Rocketry Society).
As to flipping, that is a risk that is inherent to Boost Gliders. Infact it is the usual flight failure mode ;). The aerodynamic requirements of a rocket and a plane are different. Rockets need neutral lift so that the fins / wings do not generate lift which would cause the rocket/plane to veer off course. Aircraft need lift so that they can fly. In boost configuration Vulture 2 has to be trimmed to give no lift. This has to be maintained until the craft reaches apogee at which point it will need to switch to plane/lift configuration so that it can fly back.
The change in the CofG of the craft needs to be addressed. Pre launch you have the full rocket motor mass at the rear fo the craft. As the motor burns it loses mass and the CofG moves forward. Providing the rocket phase of the design is good this change in CofG makes the craft more stable in rocket flight. For a rocket to be stable the Centre of Gravity needs to be infront of the Center of Pressure, CofP, (the point around which the aerodynamic foces balance). What makes for a stable rocket doesnt make for a stable plane. The plane needs to be trimmed to fly stably with a spent motor casing and fuel grain onboard not a live one. Many model rocket boost gliders eject the spent cardboard motor casing somewhere close to apogee. This shifts the CofG further forward still but probably isnt something you would want to do with a larger metal motor casing at a significant altitude
1) Weather balloons increase dramatically in size as they rise. As the air pressure drops the volume of the gas inside the balloon increase. Some folks don't seem to have accounted for this.
2) Weather balloons are far from rigid or stiff in any way. They are made from latex if I remember correctly. Having seen one or two launched they squidge around and change shape like a soap bubble in the wind. There's an awful lot of solid, round looking balloons in the designs. I doubt any kind of "shaped" balloon will work as you have to cater for the increase in volume with altitude and deal with the inherent lack of rigidity in the envelope.
3) The couple of weather balloons I have seen launched with weather measuring / camera payloads underneath have had the payloads swing around rather a lot. I suspect there will be a pendulum / oscillation thing going on that has to be damped out to get any platform stable. This could be difficult to damp out at altitude if there is little air to react against.
4) I have no idea what size or make of rocket motor you intend to use but a few things are worth bearing in mind:
4.1) It is illegal in the UK to make "explosives"* thanks to the 1875 Explosives Act**. Moving commercial rocket motors around (Aerotech, Cesaroni) which are bigger than 20Ns total impulse or made from propellant other than black powder (i.e. Ammonium Perchlorate Composite Propellant) requires paperwork from the HSE . Estes black powder motors aren't an issue. However I doubt they would give the kind of oooomph you are looking for.
4.2) Commercially available rocket motors have burn times in the order of a couple of seconds excepting Boost Glider rocket motors but these are difficult to obtain in the UK due to not necessarily being Classified and Authorised by the HSE or CE marked (See Placing on the Market, Storage and Transport of Explosives Regulations or POMSTER / HSE). Essentially if the motor isn't C&A'd and CE marked it cant be bought or moved in the UK. Every EU country has different rules on rocket motors and what goes for the UK probably wont be the same for other countries so watch out for designing in something you cant fly elsewhere in the EU. I suspect your best bet would be a trip to the US but the rules there are different again.
4.3) Rocket motors and explosive charges are much more difficult to light at higher altitudes. Igniting solid motors depends on there being air present to conduct heat between the igniter and the propellant. This isn't as big a problem, to some extent and depending on motor system selected, for motors as it is for any kind of loose black powder based ejection charge which can be very unreliable at altitude.
4.4) There are 3 main types of rocket motor:
Solid Rocket Motors use a solid oxidiser and a solid fuel. Probably, for ease of use, best in this case.
Hybrid Rocket Motors use either a solid fuel and a liquid oxidise or a solid oxidiser and a liquid fuel. As far as I am aware nearly all hybrid rocket motors use the former.
Liquid Rocket Motors use Liquid Oxidiser (O2, N2O, HTP(H2O2)) and Liquid Fuel (H2, Kerosene Paraffin, Alcohol) or a Liquid Monopropellant (HTP(H2O2), Hydrazine (NH4))
While high altitude ignition of a hybrid is feasible I suspect the additional complexity and mass limits choice to a solid motor. Liquid Rocket Motors are fine for Space Shuttles and Saturn 5s but not for LOHAN. We have seen that LOHAN does not necessarily function well when alcohol is present.
5) Boost gliders are a bitch to design, build and get to work in the atmosphere at ground level (search YouTube for Boost Gliders i.e. http://www.youtube.com/watch?v=kbsafWNDiLo). They can and do work but they are challenging.
6) Issac Newton: An awful lot of the designs seem to assume that when your rocket motor lights and the rocket glider launches the platform some how stays put. That there is no drag between craft and launch guide and that for every action there isn't an equal and opposite reaction. As a lot of the platforms are dangling beneath the balloons and are necessarily going to have to be designed to be light even small amounts of drag between launch rail and craft will lead to the payload and launch guide being dragged around by the rocket plane. Icing on the launch guide could have to be accounted for. I have seen even small model rockets take the launch pad with them at lift off. Remember that commercial rocket motors are designed to give a fast hard kick in the trousers to a rocket. Not a glider. Not a long slow burn (a la Saturn 5 take off's and the TV show Salvage 1). On a 1m long launch rail a small rocket on a G Class motor (up to 160Ns total impulse) can be doing several hundred miles per hour before it leaves the launch rail. Obviously this depends some on motor selection, design of the craft, drag.....
7) Active stabilisation is tricky and vectored thrust is tricky too. Both are achievable http://www.rocketeers.co.uk/node/420 for example. But there is a significant mass penalty if you are considering it for a "Ballocket"
8) General rule of thumb at ground level is that a rocket has to be travelling at at least 30mph when it leaves the launch guide for air passing over the stabilising surfaces to be travelling fast enough to work. Below this speed the restoration forces on the fins/wings are insufficient for the flight to be stable. Quite how this translates to higher altitudes and lower air pressures I don't know. For passively stabilised rockets launched from the ground to this kind of altitude they will already have travelled a significant distance through the atmosphere during which time the fins will have worked to keep them going upwards and Newtons 1st law will keep it going in the direction the fins pointed it.
*Rocket motors, or rather solid rocket propellants, don't explode they deflagrate (burn very quickly) but for the purposes of the 1875 Explosives Act solid rocket propellants, regardless of their composition, are explosives.
** You can make small quantities for, I believe the wording is, "no useful purpose." This was included to allow the demonstration of compounds that may have vigorous reactions to students for educational purposes. I understand this to mean: mix up the constituent chemicals in the appropriate (small) quantities, tip out in to a loose unconstrained mound, ignite from a safe distance, watch it go WHOOOF, look suitably impressed. The moment you constrain it or use it to do something you are making it for a "useful purpose". You can make explosives if you have a licensed premises (not an easy licence to get) but then you still probably run in to C&A and CE marking to move anything from the point of manufacture.
Psion, Clie, N900....
I started out with a Psion 5 then went to a 5MX and have to agree with others on the functionality, the keyboard and the battery life. Yet to beaten I think. I really miss mine. I moved on to a Sony Clie peg-ux50 which was ok but never really replaced the 5MX in my affections. Now have an N900 which is great for what it is but still cant do a lot of what the 5MX did. I mean a calender that cant deal with events that recur on the Xth Weekday of a month or handle a reminder alarm more than 1 day before an event. Anyway the N900 and sucessors is sadly doomed now following the elopocalypse.
An androidy 5MX could be the dogs doodads though... where do I sign up..? As to the Conan seems a tad pricey. I wonder how much the Amstrad Pen Pad Prototype I have might be worth? 2p mebee?
H, V and C
Real3D uses left and right circular polarised filters. Older tech used horizontal and vertical plane polarised filters which were reputed to give more eye strain than circular polarisation. So as long as you take RC-LC and RC-LC make a pair of RC-RC and LC-LC or H-V and H-V to make H-H and V-V depending on cinema (IMAX Waterloo showed Avatar in H-V when I saw it) you will be able to enjoy your over priced 3D in 2D.
That'll be your RFID Membership Key......
You tried to register so you were trying to become a "member" To quote the TfL site "Membership key: £3 each to release the cycles easily and quickly. You will need to pay the £3 Membership key fee for each key you request (up to 4 keys)."
So pre pay one quid, pay for RFID key 3 quid, total 4 quid.
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