Posts by David Haywood
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Rich of Observationz wrote:
I'm impressed by your knowledge...
Don't be! I'm not an expert on turbomachinery -- I only studied it at undergraduate/honours level (my doctoral/post-doctoral work was in thermo/fluids/energy engineering).
I thought this indicated that turbofans were state of the art for all supersonic propulsion
As you're probably aware the typical commercial aircraft engine is a high-bypass turbofan. If you're designing an engine optimized for supersonic travel then you end up using a much lower bypass ratio. What I meant was that by the time you're optimizing for continuous operation much past Mach 2, then you basically end up with a turbojet (or, at least, a turbofan which is essentially just a slightly leaky turbojet!).
My undergrad turbomachinery textbook has a nice diagram of aircraft engines showing speed vs. efficiency for various systems. ISSI have essentially the same diagram on their website -- with the addition of pulse detonation engines. This might illustrate the potential efficiency advantages of (pure) pulse detonation engines more clearly than radio does:
http://www.innssi.com/pde01.htm#Question3
Note the comparative performance with afterburning turbofans/turbojets...
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3410 wrote:
... it is quite possible to make (reasonably decent) much smaller versions [of MP3s]...
My phone extension at work used to be 3410. I used to have F3410 temperature transducers on one of my experimental rigs. At one stage I owned a Nokia 3410 cellphone.
This always seemed like a funny coincidence. And now you come along...
I've had quite a fiddle with the various MP3 compression parameters and seemed to get the 'Cylon effect' with any higher compression. Frankly, my voice already sounds bad enough without that as well. But thanks for the suggestions -- I'll go back and see if I can get any further improvement (without Cyloning).
3410 wrote:
You could perhaps remind them that, at offpeak times, a 56k dialup should take 6mb in only about 25 minutes.
One of the PA readers requesting this is aged 90. I'm not sure if he has that kind of time left to waste.
P.S. Is 3410 your real name?
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Riddley Walker wrote:
maybe pulse denotation runs cooler (although i can't think why it would).
Interesting comment...
If you're talking about rejected heat, then -- at supersonic speeds -- a pulse detonation engine will produce less rejected heat than either a turbofan/turbojet or pulsejet (of similar thrust) because it's more efficient. Thermal efficiency is the ratio of work output to heat input (and by 1LT: heat input = work output + heat output). Hence a more efficient engine will have greater work output for a given heat input, and therefore less rejected heat.
Theoretically speaking, in terms of efficiency, you always want to run the heat input process in an engine at as high a temperature as possible (see 2LT in any basic thermodynamics textbook). For many thermodynamic cycles (such as that enacted in the pulsejet or turbofan/turbojet) this also implies a high compression ratio. Reasons to reduce maximum temperature include materials limitations, a more optimal work ratio, and the avoidance of undesirable emissions (such as NOX) which can occur during high-temperature combustion.
All heat engines are subject to these limitations, and there is nothing special about the pulse detonation engine in terms of heat flow (other than its efficiency). At the time that the V1 pulsejet engine was developed there were high-temperature materials limitations that also affected the development of jet engines -- but these have (obviously) now been overcome. A more pertinent point-of-difference (in terms of material fatigue considerations) might be between cyclic and continuous combustion; however the team at the US Air Force Research Laboratory tell me that they have not experienced any problems with this.
The thermodynamic and fluiddynamic optimization of pulse detonation engines is, however, much more complicated than for turbofans/turbojets. It seems to me that it's only with the development of modern CFD methods that in-depth analysis and optimization has even been possible (I haven't personally done any modelling of pulse detonation engines -- but I have developed numerical models of pulse tube refrigerators, which contain several similar features).
[1LT = 1st Law of Thermodynamics; 2LT = 2nd Law of Thermodynamics].
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Plum wrote:
what was with the boosterism about biofuels? Sourcing truly sustainable biofuels is a very tricky problem.
We'll be running an article on biofuels in New Zealand sometime within the next six weeks.
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Thanks for your comments, Rich.
Hmmm... as Dr Hoke pointed out, it's still early days for the pulse detonation engine. But I guess it's worth pointing out that computer technology such as...
... holographic memory, massive parallelism or an optical processor...
... is a little different from supersonic aircraft components. They make a few more computer processors per year than they do supersonic engines. Even at a prototype level a pulse detonation engine is cheaper than a supersonic turbofan (although typically you'd use turbojets for speeds above Mach 2). A pulse detonation engine has a huge advantage in terms of mechanical simplicity (and therefore cost) -- it's hardly more mechanically complicated than an afterburner!
I have unpleasant memories of doing brain-twisting exam questions on the intake design for supersonic turbomachinery -- they really are very complicated systems. I'm not as convinced as you are that they'll remain the dominant supersonic engine technology in the long term.
Unless, of course, you have insider knowledge on new supersonic turbofan/turbojet developments...? (In which case, please share!)
The really interesting question (to me, at any rate) is whether the pulse detonation engine-derived isochoric combustors will be taken up by the turbofan designers. It will be fascinating to see how Dr Hoke's research is received over the next few years.
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Will the Pulse Detonation Engine help to address New Zealand's 'air mile' issues? Find out in this week's episode of Public Address Science...
NOTE: A complete transcript of this episode is available here.
Further information:
-- Read more about Dr John Hoke's research work into Pulse Detonation Engines on the ISSI website (ISSI are civilian contractors to the United States Air Force Research Laboratory). Some interesting photographs of the prototype Pulse Detonation Engine can be seen in their image gallery.
-- Read more about the working principles of the United States Air Force Research Laboratory's Pulse Detonation Engine in the ISSI FAQ section.
-- Read more about Pulse Detonation Engines (in general) in Wikipedia.
-- Read more about Dr Hoke's test-bed aircraft: the Rutan Long-EZ.
-- Read about How Pulsejets Work on Bruce Simpson's excellent Pulsejet website. Bruce Simpson is a New Zealander who also runs the Aardvark Daily website, and is one of the leading figures in a worldwide resurgence of interest in pulsejets (the pulsejet flyby effect in this week's episode of Public Address Science is based on a short audio sample from one of his videos).
-- Read more about the V1 missile in Wikipedia.
This episode of Public Address Science was originally broadcast on Radio Live, 14th April 2007, 2 pm - 3 pm.
An archive of all Public Address Science episodes can be found here.
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Is Body Hacking as thoroughly distasteful as it sounds? Find out in this week's episode of Public Address Science...
Further information:
-- Read more about body hacking (and body modification in general) in the Body Modification Encyclopaedia.
-- Read more about Quinn Norton, a journalist and body hacking enthusiast, in her blog. Quinn has an interesting (and slightly disturbing) slide show on body hacking available here.
This episode of Public Address Science was originally broadcast on Radio Live, 7th April 2007, 2 pm - 3 pm.
An archive of all Public Address Science episodes can be found here.
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Another lovely post, Mr Slack...
And thanks so much for including Erica Lloyd's doco -- absolutely bloody brilliant!
As a lad, I used to climb the pylon in the park at Green Bay. I could get pretty high too -- looking down on the tiny ant-like people who walked beneath me, and who would sometimes shout up that they were going to call the police...
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Noizyboy & TroyHoward wrote:
where's the podcast/download then?
There's only one podcast up at the moment, but this (and all future podcasts) can be found under the heading 'Radio' at the top left of the PA system screen (immediately underneath 'search' and 'spotlit').
Or you can go directly here:
http://www.publicaddress.net/system/forum,6,public_address_radio.sm
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dc_red wrote:
Aren't university scientists compelled to pass on $1.15 overhead for every $1 of research funding?
To clarify: my estimation of $0.50 per $1.00 is before the money is delivered to the successful bidder, i.e. the cost of getting the money from MoRST to the research organization.
The research organization's overhead charge (i.e. the $1.15 per $1.00 of grant money) is an additional deduction from the delivered grant money. Of course, some of this money may be re-invested to pay for bidding on other grants.
Incidentally, the National Science Foundation (NSF) in the US tries to prevent this sort of thing by stipulating that the research grant can't be spent on overheads in other countries. As a consequence, a former colleague of mine at Canterbury was told that they couldn't accept grant money from the NSF, i.e. they weren't allowed to bring money into a university that was laying off staff for lack of funds. Go figure.