The Rebel Railroaders

What with the pandemic and all I’ve been in something of a reflective mood this Christmas season. One diversion has been an almost compulsive reading of Robertson Davies’ 1982 book,The Rebel Angels, which is the first instalment in his Cornish Trilogy. One passage that really struck home was this statement by Hollier during his attempt to explain to Madame Laoutaro what he did for a living:

I am an historian, not of wars or governments, not of art or science - at least not science as people think of it now - but of beliefs. I try to recapture not simply the fact that people at one time believed something-or-other, but the reasons and the logic behind their belief. It doesn’t matter if the belief was wrong, or seems wrong to us today: it is the fact of the belief that concerns me. You see, I don’t think people are foolish and believe wholly stupid things; they may believe what is untrue, but they have a need to believe the untruth - it fills a gap in the fabric of what they want to know, or think they ought to know. We often throw such beliefs aside without having truly understood them. If an army is approaching on foot nowadays, the information reaches us by radio, or perhaps by army telephone; but long ago every army had men who could hear the approach of an enemy by putting their heads to the ground. That wouldn’t do now, because armies move faster, and we attack them before we can see them, but it worked very well for several thousand years. That is a simple example; I don’t want to bore you with complexities. But the kind of sensitivity that made it possible for a man to hear an army marching several miles away without any kind of artificial aid has almost disappeared from the earth. The recognition of oneself as part of nature, and reliance on natural things, are disappearing for hundreds of millions of people who do not know that anything is being lost. I am not digging into such things because I think the old ways are necessarily better than the new ways, but I think there may be some of the old ways that we would be wise to look into before all knowledge of them disappears from the earth - the knowledge and the kind of thinking that lay behind it.

I too like to seek out knowledge about the roots of things and ideas, wondering if anything important has been lost or sidetracked. If you’re a longtime reader here, you know I have something of an obsession about rambling around the roots of model railroading’s hidden history. And it’s not just looking for model railroading’s obscured and ignored beginnings, I find myself applying the same mindset to other areas. I think the first serious occurrence was when I was in school studying aerodynamics. The library had what I think was a complete set of NACA (NASA’s predecessor) reports stretching back to the late 1910s (?). I was obsessed with trying to read them all to figure out how aerodynamic thinking came to be what it was, and maybe find out if anything was lost. I can see myself continuing my digs into the dusty corners of model railroading’s roots - as well as lots of other areas - in 2021 with this Davies sentence in mind: I am not digging into such things because I think the old ways are necessarily better than the new ways, but I think there may be some of the old ways that we would be wise to look into before all knowledge of them disappears …

The Foundations of Samurai Aerodynamics

In Samurai Crafts I mentioned that Kuethe and Chow's book, Foundations of Aerodynamics, has a minor role in Helen DeWitt's novel, The Last Samurai. That was surprising to me because besides the rarity of the mathematics of aerodynamics being discussed, however briefly, in any literary novel, K&C's textbook was the one used in the introduction to aerodynamics course I took when I was an undergrad. The only difference being the edition mentioned in TLS was the 1986 one, and my class used the previous one from 1976. The first edition was published in 1950. The book was one of the best in the field, and maybe still is.

Ludo, the child prodigy and TLS's main character, receives a copy of an aerodynamics textbook from Sibylla, his mother, for his birthday; I think from the story's chronology it was his 7th, maybe 8th. I, on the other hand, didn't buy a copy of K&C until I was 20 or so. When I was 7 or 8 I couldn't spell aerodynamics let alone deal with its mathematics. At this point in the story the book's title isn't mentioned, and Sibylla buys it on the strength of the perceived humour in the passage about calculating the manoeuvrability of a grebe in water by approximating its body with an appropriately sized sphere, and on its use of classic 18th and 19th century math, which she thinks shouldn't be that difficult for her son to grasp.

It seems to me though that he does find it hard to grasp. There are several passages where Ludo picks up the text and tries to make headway, but soon puts it down in favour of some other book. It isn't until much later in the novel that Ludo confesses,

I put down Scientific American and picked up my book on aerodynamics. Sometimes I thought I understood it and sometimes it was hard to follow, and when it was hard to follow it wasn't easy to tell what would help; the thing that would really help would be to be able to ask someone who didn't sum up the mathematics required as 18th 19th century stuff. Any idiot can learn a language, all you have to do is keep going and sooner or later it all makes sense, but with mathematics you have to understand one thing to understand another, and you can't always tell what the first thing is that you have to understand. And even then either you see it or you don't. You can waste a lot of time trying to work out what you need to known and a lot more time just trying to see it.

When I read that a wave of deja vu and sympathy washed over me.

I'm an aerodynamicist by training, but I had a hard time with my first encounter with the subject. My introductory class seemed to me to approach the subject from a purely mathematical standpoint, and it wasn't clear why certain methods and assumptions were applied. The instruction had a strong air of 'that stuff should be quite self-evident' about it. I should note that the class wasn't taught to the K&C book; it turned out the book was only used as a reference. It took me a long time to dig into the experiments and observations of the early pioneers to finally appreciate why certain mathematical approaches were used. So, to be candid, it didn't help me that experts well versed in the mathematics of the subject were teaching it. What I needed was pre-mathematical insight into the physical nature of what was going on.

Back then I did a lot of reading into aerodynamics' early experimenters and writers. I eventually figured out that many of the fundamental physical insights and observations came from Fredrick W. Lanchester, and were discussed in his 1907 book Aerodynamics. I don't have a copy, but I borrowed it many times from the university library back in the day. The mathematical edifice Ludo encountered didn't exist when it was written, and it turns out it was the work that allowed practical mathematical approaches to be developed. I only mention this old thing because this pioneering work is a great combination of words and pictures, and that's what I think should be the first approach into the subject. 

You don't need to seek out Lanchester's book as there are later ones that will give you a physical sense of the field and are light on the math, but don't talk down to you. I haven't practiced in the field for a very long time, so I'm not up-to-date on good recent books, but there are a couple of old ones that I like. One is The Science of Flight by O. G. Sutton. It was first published in 1949 and updated in 1955. It's a charming Pelican Book, and includes reprints of a number of the more crucial pages from Lanchester's book. Another choice is Aerodynamics: Selected Topics in the Light of Their Historical Development by Theodore Von Karman. It was first published in 1954, but Dover published the second 1957 version in 2004. A somewhat more modern choice is The Simple Science of Flight: From Insects to Jumbo Jets by Henk Tennekes. It was published by the MIT Press in 1997.

I guess from our vantage point 113 years after the publication of Lanchester's book, maybe aerodynamic flight does seem like a simple science, but I continue to think of it as The Beautiful Science. Flow visualization, along with physical observation, have been key to its development as has mathematical insight. I've found that triumvirate fascinating, and have often thought of aerodynamics as a form of sculpture, where what is being sculpted is the air around a moving body.

When I was Ludo's age there was a period when my father would sometimes take me to a local hill to fly a windup toy airplane. It was small and very forgiving in a crash, so it was easy to try and launch it over and over, making small adjustments, until we got a few nice flights. Even for an adult, if aerodynamics and flight is something you want to learn, that's where to start.

600 reasons to go with the flow

This is the 600th post here at 30 Squares, and I know that isn't many posts compared to lots of other blogs, but to me it seems like a huge number. 

Before I started 30 Squares, I dipped my toe in the blogging waters with a blog called Separated Flow. It was supposed to be about scale modelling, aerodynamics, blimps, model railroading, science and the intersection of those subjects. The genesis idea was a project a friend and I built back in the early '90s: a small, flow-visualization windtunnel. The project embodied all the ideas the blog might touch on and seemed a good place to start. 

I posted about that project along with some others, but 10 or so posts in, the tone seemed too ironic and cynical. I didn't like where my head was at, so I deleted Separated Flow. After a year or so, I started 30 Squares of Ontario - today's 30 Squares - for model railroad posts, and retroDynamics for non-model railroad modelling, science, aerodynamics and other things that Separated Flow might have discussed.

Early in retroDynamics' life I reposted the windtunnel project from the remains of Separated Flow as it again seemed integral to its heart and soul. A few years later, 30 Squares was becoming my main blog, so I closed down retroDynamics and figured I'd broaden the scope of 30 Squares a little. 

So, now that I'm 400 posts away from a thousand, it seemed like as good a time as any to again re-post the genesis project that got me started in this blogging thing :-)

A Tale of Two 'Vettes: How to Build a Small Flow Visualization Windtunnel
from 18 Dec 2009 in retroDynamics and sometime in 2008 in Separated Flow

I recall watching an episode of Mythbusters where Adam and Jamie were building and flying concrete gliders. In one scene they were attempting to measure the lift of their airplanes with a makeshift windtunnel and scale. Well, it wasn't so much a windtunnel as a large fan with a flow-straightener made of drinking straws placed in front of the breeze. The rig was ingenious, but it got me reminiscing about a small-scale windtunnel that a friend of mine, David A., and I built in 1988. At that time we had some hopes that we might be able to build a business around flow-visualization photography with small windtunnels and digital analysis of the pictures. Nothing came of that wacky business idea, but we did build an interesting little windtunnel.

One thing I should note: all the pictures in this post are scans of old Kodachrome and Ektachrome 35mm slides made with a Canon CanoScan 4400F scanner.

[The windtunnel without the blower and the flow viz gear.]

These are politically correct times, so here is my disclaimer before you read on: fire and smoke was involved in this project, so don't try this at home. And especially don't try it in suburban Toronto garages containing firewood and gasoline as we did. No accidents occurred during this project, but we probably just benefited from dumb luck.

A good place to start this story is at the end. In this case, with some pictures taken in the windtunnel of the air flow around a scale model Corvette and Chevette.

[Flow over a mid-1980s Corvette]

There are a couple more flow viz photos at the end of this story, but we’ll get to them soon enough.

[Flow over a late 1970’s to early 1980’s Chevette]

The windtunnel was sized to be able to take pictures of the flow around 1/24 scale model cars. At that time I was interested in the air flow around automobiles and had a stash of around two dozen plastic model kits my cousin had bestowed on me. It turns out there was a Corvette and Chevette in the pile. Dave wanted to own a Corvette, but an ancient Chevette was his actual ride, so the choice of subjects to start with was pretty clear.

[The difference in hatch slope is quite pronounced.]

There was also some aerodynamic reason to the choice. It turns out that just because a car has a sloped rear window or hatchback doesn't mean that the air flow will stay attached all the way along the surface. There's a range of angles and length where separated flow is possible, and it looked like the Chevette's hatchback had such a configuration - which turned out to be more-or-less true if the photos are to be believed. In contrast, a gradual slope that terminates in a sharp 90-degree down turn at the end of the car - like that on the Corvette - can actually result in the flow being attached all the way along the slope. We thought we'd see if we could demonstrate this with the windtunnel and hoped that it would make for some interesting pictures.

[Unpainted windtunnel at a secret backwoods testing facility :-) ]

I like to use the cheapest and most readily available materials I can get away with for any project. It usually takes a few iterations to get things right, so not blowing all my money on the first prototype is very important. In this case, bristol board that you can buy at just about any craft store or art supply was used to build the tunnel.

The dimensions were scoped out using Rae & Pope's standard text: Low-Speed Wind Tunnel Testing. I don't seem to have my design notes from the time, so I can't properly comment on the thinking that went into the tunnel, but numerous compromises were made to keep it small. One requirement was to be transportable in the trunk of my car.

[It fit pretty well with the backseat turned down.]

But, I think all this emphasis on smallness resulted iin making the cross-section of the test-section where the model car sits too small. I suspect the walls of the test section are close enough to the model to have an effect on the overall flow. However, the ratio of the height to width of the test section is built in accordance with guidelines given in Rae & Pope so that standard correction factors could be applied to measurements. All things considered though, if I built this again I'd make it bigger - but, not so big that I'd need a Hummer to transport it.

[Looking into the test-section at the Chevette]

In the above photo you’ll notice that the long edge of the test section is horizontal and the short edge is vertical. When it came time to actually use the tunnel, as you’ll see in the photos that follow, we flipped it 90-degrees.

[Initial build (no, they weren’t our sponsors - we were just fans with high hopes)]

The problem with using the cheapest materials possible is that they often have poor performance, which was the case with the initial build. Relatively thin bristol board allowed for easy layout and shaping of the main components with simple tools, but there were stiffness problems.

[The walls got sucked in as soon as the blower was switched-on]

Originally the tunnel didn't have any external bracing, and thin clear plastic was used for the test section windows. The motor and blower setup had more power than was originally thought, and the resulting flow sucked in the tunnel's sidewalls as soon as the blower was switched on. I can't find my notes on the pressure differential inside and outside the tunnel, but it was obviously appreciable. We did make a simple manometer to measure the inside and outside pressure differential, but that data has been lost.

[New and improved windtunnel with braces and glass test section]

This lead to folded bristol board external frames to be added to the test section and the transition piece. As well, the test section windows were replaced with glass panes liberated from a couple of picture frames. Those enhancements did the trick and kept the walls from buckling.

[Flow straightening grid attached to the tunnel inlet]

The blower could indeed pull a lot of air through the tunnel, but it had some serious angular velocity components. To straighten out the flow in the test section a couple more enhancements were added. First, a grid panel with 1 inch by 1 inch openings was built - again from bristol board stock - and to one side a sheet of metal screen door mesh was attached. This assembly was then attached to the front of the tunnel. As well, inside the tunnel, at the end of the test section just before the transition piece, another grid frame was inserted - this one was a plastic parts divider from a storage box. I don't recall if a metal mesh was attached to this insert, but it could have been.

[Smoke jet in the test section]

The combined effect of both of those grids was to straighten the flow out fairly well as can be seen from the photos of the smoke jet.

A simple wooden stand was built to support the tunnel while in use. This structure is pretty simple: some adjustable shelf brackets were mounted to a freestanding wooden frame in order to allow for height adjustment. I don’t know why I painted it blue. I think I had some old blue paint around that needed to be used up. And the pin striping? Who knows why, but I it does look faster :-)

[The motor and blower assemblies]

The blower and motor assembly was Dave's handiwork and this part functioned very well right from the get-go.I don't have any specs on the set up, but I believe the motor was a 1/4 hp unit. No special power supplies were required, it was configured so it could be plugged into a standard wall outlet. As you can see in the photo, the blower exhaust went straight down so we had to put in an angled board to defect the stream. When we operated the tunnel in the garages we made sure that both the main door and the side-doors were opened so that you'd get flow through the whole space and didn't recirculate the air. Typically we'd set things up so that the exhaust from the blower was near the side-door.This made sure that smoky air exiting from the tunnel got vented directly to the outside. No doubt that today this would earn us a visit from the local police or fire department.

[An early test of the smoke generator with a bunsen burner as a heat source]

The smoke generator was admittedly a Rube Goldberg affair. And it took a bit of trial-and-error to get a rig that generated enough smoke. That picture above is one of the earliest attempts. We filled a simple Badger airbrush with mineral oil and shot it into a heated brass tube. In the earlier prototypes we just used a high school bunsen burner to heat the input end of the tube and you can see that it generated only a little puff of smoke.

[Heating the entire length of the tube generates the most smoke]

From those early attempts we moved on to some more heavy duty smoke production as you can see in the above photo. To be honest I can’t quite remember what we used as a heat source on this prototype - no doubt I inhaled when I shouldn’t have! - but I think it was some sort of electrical set up, but I also seem to recall that it got too hot. As you can see it generated lots of smoke which is what we needed. The key idea was that the entire tube needed to be heated so that all the mineral oil was burned and converted to smoke. In the end we settled on a rig where the tube was heated by a couple of propane torches with flame spreaders attached. You can sort of see the end result in the photo below. As I mentioned previously, at one end of the rig, mineral oil was blown into the heated tube with an airbrush and emerged from the other end as smoke. The cooler output end of the heated tube was connected to a plastic tube, which in turn was connected to a long, small diameter aluminum tube - which was supported by a tripod - whose output end was snaked through the flow straightening grid into the test section. This was quite a rig when it was all up and running. Once again, these day's I'd think of some other, safer way to do this.

[Full setup in action.]

The photo above shows all the components set up and ready to do a test run. To the far left - and unfortunately in heavy darkness - is the workmate with the smoke generator clamped to its top. To the right is a set of four photo lamps aimed more-or-less straight down the tunnel inlet, below and to the right of the lamps is the smoke wand inserted into the flow straightening grid and into the test section and finally to the right of that is the windtunnel itself. A photo lamp is also clamped to the windtunnel support stand and aimed down into the upper viewing port on the test section. A black blanket was taped on the garage wall opposite the windtunnel window in order to minimize extraneous reflections from appearing in flow visualization photos.

To finish-up, here are a couple more photos of the Corvette and Chevette. In these pictures the smoke wand is placed a little higher relative to the roof on each car. The result is a somewhat better defined smoke stream along the entire length of the body.

In the end the project was more fun than scientific. There are still numerous unresolved technical issues surrounding the use of crudely detailed models, the small size of the tunnel, and so on and so on. But, maybe the world would be a better place if every suburban house had its own windtunnel room - with appropriate smoke filtering of course :-)

----

It won't be an anniversary post without ending with a list of the top 5 most popular of the 600 posts. From 1st to 5th, they are,

E. L. Moore's Legacy in the 21st Century: The Elizabeth Valley Railroad

A review of Model Railroader's 75-year collection, part 1

E. L. Moore's Legacy in the 21st Century: Balsa, cost, a handcar shed and organic veggies

Amtronic Ranch

HO-scale logging airships?

Eagle Spacecraft Models, meet the Balsa Disk Fliers

[Cover image of Eagle Book of Spacecraft Models sourced from John Guy Collick]

Vince sent me a link to a review of a most excellent old book published in 1960 called Eagle Book of Spacecraft Models by Ray Maimstrom. I’m a sucker for these sorts of old-school model building books. I searched and found it for sale at an online reseller, and although it’s a little pricey for me, the seller had a photo of this interior page describing  how to build a free-flying model airplane in the shape of a ‘Martian Flying Saucer’.

[Sourced from an ad at Abe books; won't say which one as I might still buy it :-) ]

I immediately flashed back to some posts at my now defunct blog, retroDynamics, about some simple disk-wing hand-launched gliders I made some years ago from balsa wood and styrofoam. They won’t go to Mars :-) but they’re good for some pleasant backyard fun. For a change of pace, here are the old posts:

13 April 2009

Circular Wing Glider

I’ve been reading about airplanes with circular planform wings, and building some simple flying models, for a year or so. Hopefully I can write more about them in the future, but, thusly inspired, I built this very simple balsa glider back in January.

The wing has a diameter of 6 inches. The mass of the glider, less the nose weight, is 10 grams; the clay nose weight adds 3 grams and puts the balance point ahead of the wing’s quarter-chord.

It flew fairly well. For awhile. I launched it from the back deck of the house by pitching it high over the snow drifts piled up in the backyard. During construction I had inadvertently glued a small twist into the tail fin - which I couldn’t quite twist back out - which caused the glider to turn to the right, sail over the 8 foot side-yard fence, and crash against a wall of my neighbour’s house precipitously close to her kitchen window. Luckily no damage was done and I was able to inconspicuously retrieve the plane without having to explain to her, or my wife, why a man of my age was assaulting her house with a toy glider.

That was the last flight. The raw balsa had absorbed a lot of snow and the whole thing warped too much to be flyable after that. That and the impact on the nose-weight snapped the canard from the fuselage. Now that summer is almost here I’d like to try and build a few more of these; some from foam as well as balsa.

21 July 2010
First flight of a disk-wing glider with a K-F step

I tried flying this disk wing glider with a Kline-Fogleman step in the backyard last evening after the wind had died down.

The disk has a diameter of 6 inches and the total mass of the glider is 5.5 grams. A paper-clip attached to the nose was used to place the centre-of-mass a bit ahead of the quarter-chord.

Synopsis: It felt too light when it left my hand, veered in a large arc to the left, crashed into a tree, and broke off the canard.

I clumsily tried to glue the canard back on with super-glue - it was originally attached just with white glue which was no doubt why it broke off ! - but, I got the alignment all wrong. I decided to call it quits for the evening, and spend a little quality time some other day on fixing the plane.

I did try to fly it immediately after the crash without the canard. It didn’t flip end-over-end, just made a short and graceful arc to the ground.

17 August 2010

Trimmed flight of the K-F disc glider

I fixed-up the broken KF disk-wing glider and gave it another try. The wing and canard were re-glued with a thick super-glue, and the balancing clay mass was moved all the way forward to the nose. Total mass is now 8 grams. The centre-of-mass is about halfway between the leading edge of the disk and the trailing-edge of the canard.

I flew it a little in the backyard to get the trim worked out before trying to fly it in a larger field. This way I can run down to the workshop to easily fix things if needed. I shot a short video of some of the backyard test flights, but for some reason I couldn't get them uploaded, so some imagination is required at this point :-) The glider was launched from roughly 5 feet above the ground, and it flew for about 22 paces before crashing. It seemed surprisingly resilient and didn’t break or distort after a few fly-and-crash sessions.

I think the model has a lot of drag, the canard is getting a bit beat-up from a few crashes and re-glues, and the disk is probably too thick for such a small wing and low-speeds. Anyway, I’ll try flying it in a larger field before starting to build another variation.

19 August 2010

Disk wing glider without K-F step

This glider is the same basic size as the one with the K-F step. I took it out to the backyard to get it trimmed for flights in a bigger field.

The centre-of-mass is just a little bit ahead of the disk's leading edge, and the total mass is around 6 grams.

Once trimmed, it seems to fly ok - well, I know that isn't too quantitative :-) I think it flies a little worse than the one with the K-F step, but this too isn't based on any quantitative. I need to devise some sort of test that would demonstrate what sort of effect the K-F step does have.

19 March 2012

Unfinished: Disk wing glider with curved K-F step

Back in 2010 I was playing around with disk wing gliders and one that had a Kline-Fogleman step. I made up some parts for a variant that had a curved step, but never got around to gluing the pieces together. I thought the model with the K-F step flew better than one without, but that was just a feeling and never proven. I need to get out the glue and give this one a try.

I checked around my workbench and those pieces are still there - maybe a summer project.