Tuesday, January 31, 2012

Scientist debunks flying myth. (Cambridge, UK)

One of the most common myths in science, why aircraft fly, has been debunked by a Cambridge University scientist, Prof Holger Babinsky.


By David Millward, and Nick Collins

 Aeroplanes can fly because their wings cause the air pressure underneath to be greater than that above, lifting them into the air.

But engineers have for years been frustrated by a theory which wrongly explains what causes the change in pressure to occur.

The myth is commonly found in school textbooks and aeroplane flight manuals, and is so widely believed that even Einstein was rumoured to subscribe to it.

Now a Cambridge scientist has become so fed up with the bogus explanation that he has created a minute-long video to lay it to rest once and for all.

The video, published on YouTube by Prof Holger Babinsky of the university’s engineering department, seeks to explain in simple terms why the myth goes against the laws of physics.

According to conventional wisdom the pressure change happens because the air on the curved upper surface of the wing has further to travel than that below the flat underneath surface, meaning it must travel faster to arrive at the other side of the wing at the same time.

In fact the real explanation is nothing to do with the distance the air has to travel. The curvature of the wing causes the change in air pressure because it pushes some of the air upwards, which reduces pressure, and forces the rest beneath it, creating higher pressure.

A law known as the Bernoulli equation means that when pressure is lower, air moves faster – so the air stream above the wing does move more quickly than the one below, but this is not what causes the difference in pressure.

Prof Babinsky proved his theory by filming smoke passing across a wing.

If traditional wisdom had been correct the smoke above and below the wing should have reached the front edge at the same time.

The video demonstrates that the explanation is fundamentally flawed because the plume above the wing reached the edge much sooner than the plume below.

If the distance the air had to travel was causing the pressure to change, then a boat's sail – where the air travels the same distance on the inside and outside of the curve – would not work, Prof Babinsky said.

He added: "I don’t know when the explanation first surfaced but it’s been around for decades. You find it taught in textbooks, explained on television and even described in aircraft manuals for pilots.

"There is no law in physics which states when streams of particles start at the leading edge of the wing they should reach the tailing edge at the same time.

"I've even heard a story that Einstein drew a design for an aircraft wing with a long, squiggly line on top of an aerofoil to make the distance for the air to travel greater, but this would not work."

Friday, August 26, 2011

Status of General Aviation: Some Notes/Links

Harry R. Clements, The Rise and Fall of General Aviation — An Economists View with Focus on Single Engine Aircraft and the Impact of Airline Deregulation (2000 conference paper)

Matt Thurber, Free Fall: The Unexpected Decline of the Billion Dollar General Aviation Industry (Tab Book, 1995).  Seems to be out of print (Amazon link) Author indicates it was never published.

Janet R. Daly Bednarek and Michael H. Bednarek, Dreams of Flight: General Aviation in the United States.  College Station, Tex.: Texas A&M University Press, 2003. Pp. xviii+191   (Reviewed in Technology and Culture, Volume 45, Number 3, July 2004, pp. 629-630).  "Overexpansion and increased federal regulation precipitated a steep and apparently permanent decline in sales of general aircraft [...] commercial and military aviation interests have largely succeeded in limiting general avia- tion’s influence. [...] Faced with declining numbers of pilots and increasing costs for flight training, aircraft, and maintenance, American general aviation enters its second century facing an uncertain future. Still, interest and enthusiasm among America’s general aviators remain strong, and new technologies such as ultralight aircraft continue to fuel a fascination with powered flight."  (TL 721.4.B38)  Also see Bednarek's bibliography in General Aviation: An Overview.

Joseph J. Corn, The Winged Gospel (OUP, 1983) [TL 521.C643]. 

Dominick Pisano, "The Social and Cultural History of Aviation and Spaceflight" 2003

J.G. Wensveen, Air Transportation: A Management Perspective (6th ed, 2007, link), see section 4, The General Aviation Industry, pp 111ff, for a useful overview.

General Aviation Statistics (AOPA)
FAA Aviation Statistics

James Lardner and Robert Kuttner, Flying Blind: Airline Deregulation Reconsidered (Demos, June 24, 2009).

GAO:  AIRLINE DEREGULATION: Reregulating the Airline Industry Would Likely Reverse Consumer Benefits and Not Save Airline Pensions (2006).

Matt Thurber, Can general aviation reverse its decline (Blog: 03-2011)

Robert Goyer, Is Flying really that Expensive?  (Blog: 03-2011) References an APA whitepaper: "Role of Prices in the Decline and Renewal of General Aviation" (2009).  Both make case that expenses apart from A/C have tracked inflation.  A/C have been 2.5-4x rate of inflation, hourly cost of operation now far exceeds rental rates for most users.  Goyer has another blog post Part 23 Do Over where he mentions a number of experimentals which he would never fly again, but does not list them.  One comment:  "Come on Robert! First you dangle your list of scariest homebuilts right in front of our noses; Then you yank it away again [...] Be a man and fess up the list. Informing the public about designs which you believe top be really scary to fly would be a valuable public service. Perhaps your bosses are more worried about the flood of lawsuits such an admission might cause,"

Kerry Kovarik, A Good Idea Stretched Too Far: Amending the General Aviation Revitalization Act to Mitigate Unintended Inequities (article, 2008) 

Eric A. Helland, Alexander T. Tabarrok, Product Liability and Moral Hazard: Evidence from General Aviation (article, 2008)

Eric Helland and Alex Tabarrok, Crash and Learn: Consumption Externalities and the Reduction of Aircraft Accidents (working paper, 2007)

Phillip J. Kolczynski, GARA: A Status Report (Blog, 2001)

Scott Tarry, "Issue Definition, Conflict Expansion, and Tort Reform: Lessons from the American General Aviation Industry" (article, 2001)

William Keith Stockman, The Crash of General Aviation: A Public Choice Perspective (PhD Dissertation, George Mason University, 1996).  Argues that "rent seekers" are the primary cause of the decline of general aviation.  "The industry and its users have fallen victim to the successful rentseeking of of others and have only recently had any success in reversing this trend.  {MVO notes passage of GARA} Though durable good's models do offer some explanations for the industries woes, the majority of the evidence points to a public choice explanation.  Thus, the industry should look toward public choice solutions if it desires to reverse the current trend"  (p. 8)

Lawrence J. Truitt, Scott E. Tarry, The Rise and Fall of General Aviation: Product Liability, Market Structure, and Technological Innovation (article, 1995)

GARA: The General Aviation Revitalization Act of 1994 (Public Law 103-298)
The complete text of the 1994 law.

United States Airline Deregulation Act (1978):  Alfred Kahn Overview.  

Tuesday, December 21, 2010

CGS Hawk Arrow

Notes to self:  took at look at a used single seat CGS Hawk Arrow for sale (ad link).  This one is registered as an ELSA (N4209F), powered by a Rotax 503 DCDI 50HP 2 stroke engine with electric start.  The engine was rebuilt in 2004 and has about 50 hours on it.  TBO for this engine is listed at 300 hours or 5 years, which ever comes first.  It is a simple engine and could be rebuilt for parts cost (link) or by a rebuilder for considerably more.  It has pretty complete VFR instruments, with a hand held radio, but no transponder, electric fuel pump in addition to mechanical fuel pump, an anti-collision strobe, full flaps and in flight elevator trim.  The sails are probably towards the end of their useful life, replacement Dacron would be around $2,200 (link), but would probably go one or two more seasons.  This would need to be tested.  The machine has an almost complete set of vortex generators, but is missing a few and would probably need to be replaced or eliminated on sail replacement. The machine appears to be well built, but was involved in a minor mishap (2004), which is well documented.  The current owner was unable to start the motor, probably the result of old pre-mix gas.  Yes, this requires premix (oil/fuel) gas. But there may be other concerns, as the Rotax (and other 2-stroke engines) do want special care and feeding (there are courses). Links to non-ethanol gas stations in NC. 

There are others Hawks for sale, even listed on one site, and there are a number of similar machines available at various prices, such as the Challenger, Rans S-12/S14 series, Quicksilver, Kolb (M3X), Flightstar, and others.  Check out UFlyit for sales and courses.

CGS Hawk Service Bulletins.

Saturday, June 12, 2010

Airplanes in a box

For many years, I have thought about building an airplane. This goes back many years, when my father and I had the notion of building a Volksplane. In fact, I build a 1/4 scale model when I was doing a lot of models (and a bit a glider flying), powered by a SuperTigre (0.35) engine, which were pretty hard to get hold of in rural Quebec. Still have 'em. Since we're moving, I've started looking into these again. And it is amazing to see how the technology has developed, particularly with the appearance of ultra-light aircraft. I'm currently thinking about something from Fisher Flying Products. The Avenger in the ultra-light configuration is particularly interesting for the rank beginner. The 28 hp Hirth F33 (and here) engine -- single cylinder, two stroke, air-cooled -- is amazing since it weighs in a 35 pounds. Good for 1000 hours between overhauls. Amazing. I think I will go with electric start, recalling just how battered my fingers got starting the SuperTigres, which would either backfire or catch, in both instances chopping your digit with a sharp prop blade. But there are many other options out there. Check out the Challenger. The dream machine would be the BD-5. But that is all metal, a pretty serious machine, and there were problems. The current machine is available from BD-Micro, and powered by a 65 hp two cylinder, two stroke Hirth engine. There are turboprop and jet options.

It is amazing to me that you can fly an ultralight without a license. Thankfully, you can get training from the good folks at USUA and USPPA. Probably a good idea. Helmets are required for motorcycles in North Carolina, unlike Illinois, but I wonder if this includes ultralights. Another good idea in any event.

MotoCzysz E1PC

Finally, an electric bike that packs some serious performance. The E1PC produces 100 hp and can top at least 140 mph. Not close to the stock Hayabusa, but still very impressive. True it broke down at the recent Isle of Man TTs, but this may well be a peek at "the motorcycle of the future". Not indications of weight and cost is astronomical at this time. Well, they are using batteries built by the same folks that build 'em for NASA. Check out related article here. My next bike?

Friday, May 21, 2010

More Google Goodies

Russ pointed out two new Google APIs which are of particular interest. The Prediction API "enables access to Google's machine learning algorithms to analyze your historic data and predict likely future outcomes". It will take your labeled data, run supervised learning algorithms, and allow you to predict. I've not looked too hard, but I don't see just which ML algorithms they are offering (Naive Bayes, SVM, KNN, etc). But how cool is this? Well, pretty cool. But, Russ also points out BigQuery by Google: "a web service that enables you to do interactive analysis of massively large datasets. Scalable and easy to use, BigQuery lets developers and businesses tap into powerful data analytics on demand". Terrabytes, billions of rows per seconds. Wow.

Also check out Lessons learned developing a practical large scale machine learning system. And the first lesson? "Keep it simple (even at the expense of a little accuracy)".

Now these, all by themselves, are a really good reason to learn Python. :-)

Tuesday, December 1, 2009

Berkeley DB/GDBM Links

PhiloLogic uses GDBM (GNU Database Manager) for word searches. As we are starting to think about a new PhiloLogic series (the infamous "4"), we have been looking at a number of design and implementation issues, including advanced indexing schemes. For example, Clovis did a preliminary examination of various fuzzy matching systems. Richard and I have been starting to look at newer GDBM tools as well as Berkeley DB. Here are a few links and alternatives Richard proposed which I think we should experiment with and/or read:
Older perl-5 style: the tie function:
this lets you tie any complex data structure into a perl scalar, array, or hash, as you wish.
This is great for "hiding" object-oriented interfaces in a simple, "perl-ish" way. It can wrap GDBM or Berkeley, or MySQL, or SQLite, or Hadoop...and so on.

The low-level perl GDBM_File module:
tie and dbmopen both use this core perl module. On some mac's, I have had to Recompile perl to get GDBM_file working. You can't get it from CPAN.

The low-level perl Berkeley DB module:
Pretty nice, but doesn't support all of the awesome Berkeley DB features, like joins. the python binding will do joins for you, at C speed. the $db->associate($secondary, \&key_callback) function lets you automatically maintain a secondary index. the DBM Filter functionality will do customized byte packing and unpacking for you transparently.

One other DBM product you might want to look at it is Tokyo Cabinet:
It runs Mixi, the Japanese equivalent of Facebook, as I understand it, and some googling suggest that it's quite hot in the noSQL world. It's certainly faster than BerkeleyDB, and lightweight, and has nice Ruby bindings--Perl, not so hot.
Some people claim it's more stable than Berkeley. There's an impressive set of benchmarks here:
This should be compared with Oracle's benchmarks:
which shows bulk read of 5,000,000 records/sec. "un de ces" indeed.

Berkeley has more features, Tokyo might be faster, we'd probably want to test both of them out at scale to see how they hold up. Tokyo is designed to do cloud-style partitioning and stuff.

We also might want to look at Project Voldemort, which runs LinkedIn:
This one keeps its database in-memory, and has really sophisticated protocols for distributed hash tables, load balancing, consistency, etc.
Lots to think about indeed. And he sent along a little script as an example to tinker with, which I won't post here....

Thanks, Richard.