Fuselage Stations & Water Lines

By The Metric Maven

My first employment as an engineer was with a large aircraft manufacturer in southern California. I had the good fortune to have a number of engineers, who were north of 50, and willing to instruct an engineer who was younger than most of the neckties they owned. Among other duties, I performed scale model antenna tests on aircraft. At that time, computer power was still anemic, and this type of testing was of great utility in determining the performance of glide slope antennas. A glide slope antenna assures an aircraft approaching a runaway is at the proper angle with respect to the ground for a safe landing.

In those days, aircraft designs were still drawn by hand, on drafting boards. The engineering drawings were stored in the same manner that scrolls in the ancient library of Alexandria might have been, and this could pose a challenge when looking for a desired drawing. The first time I saw an aircraft drawing, the nomenclature was mysterious. The older engineers explained that FS stood for Fuselage Station, and WL was for Water Lines

An online reference defines Fuselage Stations thus:

A station line is a vertical plane that is perpendicular to the center line of the airplane. station line numbers increase from the nose to the back of the aircraft. station lines are spaced one inch apart. These stations are planes cutting through the fuselage at the right angles which are numbered.

Water Lines: A water line is a horizontal plane that is parallel to the passenger floor. Water lines are spaced one inch apart.

Aircraft Numbering System: the number of a station tells how many inches it is from station 0. The reference point is called the datum.

I was told that generally Fuselage Station 0 was at the tip of an aircraft, and then with a chuckle I was informed that often the nose would be extended and then reside at a negative fuselage station value. The system seemed rather kludgey, but clearly high performance aircraft had been created with this system, it must work. I only learned enough about the drawings to understand my design constraints. When CAD (computer aided design) arrived, I don’t recall seeing this type of designation. Modern CAD programs appear to use a standard x, y, and z Cartesian axes. My design software does, as do most mechanical engineering CAD programs. I also found myself dealing with missile drawings, but I don’t recall how they were drawn as it has been a very long time.

Recently, I began to wonder how these designations might be readily changed to metric for future metric-only designs. Certainly, in my view, millimeters is the logical choice. I found a drawing of a McDonnell F2H Banshee, to illustrate fuselage stations and waterlines, which is reproduced below

The Fuselage Stations and Waterlines use decimal inches. The one-inch separation of FS’s and WL’s does not appear at all to be sacrosanct, or of much utility. I don’t recall seeing a single decimal inch tape measure in the lab where I worked at the aircraft company.

I do recall my first drawing and fabrication request. I did it in metric, sent it over to the fabrication shop, and had it rejected with extreme prejudice. The head of the shop was viscerally upset that I had the temerity to perpetrate such a dastardly deed. There was whispering that I “was going to be a problem.” I had been using metric throughout my University engineering education. Suddenly, I was told that it was completely unacceptable. It was clear I could not win, and capitulated, as do engineers in aerospace to this day. Metric could only be used for computation, all fabrication output had to be in Ye Olde English, or eagles would fall from the sky, and the US Constitution spontaneously combust .

We did have many calipers, which are graduated in decimal inches. They had some very long ones, to accommodate large objects, but no decimal tape measures, or rules.

What strikes me as I look at the old F2H drawing, is that the inch, like the centimeter, is too large to use without a decimal point. The final Fuselage Station is 478.42 inches. One could express this in millimeters as 12 152 without a decimal point. One can quickly see the length of the aircraft is a little over 12 meters. How long is it in feet? I’ll wait. After the mandatory computation, it’s 39.868 feet. With millimeters, one could use the same number of symbols. The current designation for the final Fuselage Station uses six symbols, five numerals and a decimal point. The other uses six symbols and a space. They are equivalent to metric construction, which is quite efficient.

One day a drawing of a V2 rocket caught my attention. The drawing had large integer numbers, and is reproduced below:

I also found a post World War II, V2 drawing with dual-dimensioning in millimeters, and decimal inches:

Of course no drawing in the US will survive long with metric dimensions, and I soon found this:

Only in the US does using two separate units of length to describe a single distance make sense. The conversion of German metric drawings into Ye Olde English has been done for the ME262, and these “original blueprints” are offered for sale online. I imagine few Americans are the wiser.

What precipitated this essay, was an email I received from a resident of Germany. He wrote to find out where I obtained my millimeter-only metric tape measures. After reading some of the essays on this website, he realized that metric is much more streamlined for everyday applications, and for technical use, using millimeters. To his surprise, he could not find a mm only measuring tape in Germany, only cm. After telling him that looking for mm only tape measures in the US is a fool’s errand, I directed him to a large variety of mm only measuring tapes in Australia. I pointed out that England uses millimeters for their construction, and that, although I’ve never found any, he might locate a mm only tape measure there. The fellow told me he had looked, and was as unsuccessful as I had been in locating one in the UK. His university roommate is becoming an architect and uses millimeters, but I’m very curious if German’s use millimeter construction like many English speaking metric nations.

I’ve often suggested that countries that adopted the metric system early on have never re-evaluated its best use, and then reformed their measures further. It is interesting, that for many years, Germany has been reported as generating the second largest number of hits on the Metric Maven website each month. I had often hoped that some Germans might take notice and perhaps there might be an upgrade of everyday metric use in Germany—-long before the US contemplates yet another faux attempt. I’m always for better metric, even if I can’t have it here.

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Metric Cookbook 2.0 Reloaded

The Covid-19 pandemic has brought to light aspects of “metric cooking” I’d not previously thought about. It involves all purpose flour and cake flour. The last time I went to a grocery store, the shelves were empty of all purpose flour, but thankfully some cake flour was still present. How does one convert recipes from using all purpose flour to cake flour? One redditor, in reaction to my cookbook, pointed out that:

While volume over weight is common in the US, that really has nothing to do with the system of measure. I assure you that many restaurants, especially chain restaurants with set recipes, use weight, perfectly happily using avoirdupois.

Indeed, I would rather call it using mass (not weight), but the system of measure does make a difference in ease-of-use. US mass may be in decimal on a scale, but the recipes are generally expressed in fractions. Per Naughtin’s Laws, prefer measures that use integers without decimals. In my view, grams compared with fractional pounds are like comparing Hindu-Arabic numbers with Roman Numerals. Grams are the simplest, and most straightforward unit.

The conversion of cake flour to all purpose flour using volume for a recipe is not straightforward. Converting to metric volume for ease of expression, 590 mL of all purpose flour is equal to about 660 mL of cake flour. Now what is the conversion factor for mass? Well, 300 grams of all purpose flour, is equal to 300 grams of cake flour. They are identical, the conversion is 1:1. In other words, with a scale there is no conversion.

I tried cake flour in my ginger cookies recipe, and the result appeared identical. I used cake flour in my from scratch pancake recipe, and the only apparent difference was each pancake was fluffier, and increased the total number of cakes.

I was also challenged on reddit, after stating in my cookbook that everyone should invest in an infrared (IR) thermometer:

I think the IR thermometer for pan heat is over-the-top and engineerish, an expensive piece of equipment that is akin to a pothead’s six-foot bong err two meter I guess I should say. It’s expensive and is little return on investment.

I ended up with an IR thermometer after my father’s passing. He had been using it in his kitchen, and their is no question he was a “thrifty person,” and not inclined to purchasing anything he thought had “little return on investment.” I took it home with me (I have an IR thermometer in my engineering lab) and put it in my kitchen next to my probe thermometers. The first time I thought to use it was when I was preparing some hamburgers. My Significant Other (SO) is big on hamburgers with just the right amount of mallard reaction. With gas, I would try to guess about how long it took for the pan to get “hot.” One day I used the IR thermometer to measure the temperature of the pan surface, and went for about 300 F. They looked great afterward. I continue to do this, and it produces very consistent results. I used a probe thermometer to make sure they were done.

Recently, I decided to make pancakes from scratch for the first time. The electric skillet had been purged long ago, and we had a single flat griddle to go on the stove. My SO kept saying I needed to put drops of water on it to “check the temperature.” In the face of much confidence on her part, I let the griddle heat up to 350 F, then applied pancake batter. She was astonished when they came out an almost perfect brown—first time. You can see a photo of the first time I made them in the Pancakes from Scratch recipe in my cookbook. Clearly, one can check the pan temperature for grilled cheese, french toast and other stove top recipes. I plead guilty to being an engineer, but I really think an IR thermometer, once used for a while, will become an important tool in a kitchen for everyone.

I was finally convinced that an IR thermometer should be in every US kitchen when I watched Alton (Al-ton, not All-ton I understand) Brown’s Good Eats Reloaded on eggs. The official title is: The Egg Files: Reloaded. Alton has seen the light, and given up non-stick pans. He did not embrace a cast-iron skillet, as Pierre might, but instead was pushing carbon steel pans. He then dramatically removes all of the knobs from his gas range cook top, and announces he has a better way to cook eggs!

Alton puts his ten inch carbon steel pan into an oven set for 450 degrees F, and when the oven reaches this temperature, he leaves it in for another 30 minutes. According to Alton, you also need a lid to use this “superior method.” We are now ready to properly fry two large eggs. He obtains 1 Tbsp (tablespoon) of unsalted butter at room temperature on a square of parchment paper. Said butter is introduced into the pan after retrieval from the oven, and its placement onto the room temperature cook top. Two eggs are added from a bowl, with a pinch of salt on top, just as the butter is almost melted. The lid is put on the carbon steel pan, and a timer set for 4 minutes.

If one wants to make a single egg, then choose an eight inch carbon steel pan heated the same way, with only 7 grams of butter—what?—he went from tablespoons to grams! Everything you need to know about Alton’s understanding of use of the metric system is succinctly expressed at this point. He suggests 3 1/2 minutes for the single egg. If he needs to feed many people–just heat up a bunch of pans at the same time, according to Alton, they’re inexpensive!

For scrambled eggs, heat the ten inch pan in a 350 degree F oven. Then Alton states:

Yes, of course you could do this on the cook top alone if you happen to have one of these (he produces an IR thermometer), or a really great eye for spotting a pan at 350, which I don’t. Besides, odds are it’s breakfast, and odds are I’ll have some bacon going here, and yes I roast my bacon, and yes that’s another show.

It seems to me that the investment in an IR thermometer would save you a number of pans, and perhaps needing an extra oven? In Alton’s universe, he trusts the temperature of an oven? Most oven’s are notoriously inaccurate. I had to buy a calibration thermometer for mine after I purchased it, and it was a couple tens of degrees off, and not really very linear.

Alton wants you to teach yourself metric during the pandemic, but clearly has no ability to offer metric instruction himself. Invest in a mass scale, a probe thermometer, and
an IR thermometer, and use them, your taste buds will thank you.

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Inches in a Mile

By The Metric Maven

Isaac Asimov Edition

Those who have read my essays realize that I see Isaac Asimov as the greatest science writer that ever lived. I still purchase hardcover copies of his books to augment the paperbacks I own, and then re-read the essays. Isaac was an unwavering promoter of implementing the metric system in the United States throughout his life. Asimov claimed what allowed for his prolific writing was that he was a “speed learner.” I thought about this when I read his essay: “How Many Inches in a Mile?” 1

The good doctor points out that in most ordinary situations this question would never come up, but then shifts to an every day question:

Suppose you have a rectangular living room that is 12 feet 6 inches in one direction and 18 feet 4 inches in the other. You are going to carpet that from side to side and fore to aft, and would like to get some sort of an idea what it will cost. The carpeting is sold at a price which is so much per square yard. Therefore, you have to know the area of the of the room in square yards.

You are welcome to work this out for yourself right now. The necessary information you may need is that there are 12 inches to the foot and 3 feet to the yard. It may also be useful to know that there are 144 square inches to the square foot and 9 square feet to the square yard. Or perhaps you prefer to make use of the fact that there are 36 inches to the yard and 1,296 square inches to the square yard.

This essay was written in 1971, in an age where electronic calculators were an expensive novelty, and most computations were done by hand. Many times in my father’s print shop I would see boxes of paper with numbers and calculations scrawled on them. It is something which has completely vanished in modern times. Isaac points out that it took him about four times, using different conversion methods to determine the value consistently. He then interjects “(Actually, the area of the room is almost 25 1/2 square yards: 25.46 to be a little more exact.)”

He then goes on to observe:

But why is it so hard to do such a problem? After all, to work out the area of a rectangle we need only multiply the lengths of adjacent sides. A rectangle that is 12 feet by 18 feet is 12 x 18 or 216 square feet in area.

The trouble seems to be that what is easy where only feet are involved becomes difficult when inches and yards are dragged in as well, because one unit goes into another an inconvenient number of times. Why are there 3 feet to the yard? Why not 2, or 4? Why 12 inches to the foot? Why 5280 feet to the mile.

Asimov then examines the obscure origins of the farrago of units that some call US Customary, and I call Ye Olde English, or medieval units as they pre-date the British Imperial System of units, and originated in medieval times. When thinking of the confused list of US units, my mind goes back to a conversation in the movie Apocalypse Now! where Willard is sent up river to terminate Coronel Kurtz’s command, and states that part of the reason for this, was that his methods were deemed unsound. Kurtz asks if now that he was there, if his methods appeared unsound, Willard replies “I don’t see any method—at all.”

After an interlude with Roman miles, furrows, fluid ounces, gills, pints quarts, gallons, firkins, hogseheads, gallons, pecks, bushels, Imperial gallons (gas sold in Canada at the time), ounces, pounds (Troy and Avoirdupois)….and you get the idea, he finally settles down to discussing the metric system, and his original problem:

Suppose, for instance, you have a rectangular room which is 32 decimeters, 4 centimeters long and 49 decimeters 6 centimeters wide, and you want to carpet it completely at a price of so much a square meter. That sounds like the earlier problem in yards, feet, and inches, but—-

Anyone using the metric system sees at once that 32 decimeters 4 centimeters is equal to 32.4 decimeters or 3.24 meters; and that 49 decimeters 6 centimeters is equal to 49.6 decimeters or 4.96 meters. The area is 3.24 x 4.96, or just about 16.07 square meters. You have that one nasty multiplication to make and no divisions.
All the rest is taking care of the decimal point.

Oh, my, this is an example of forcing pre-metric thinking on the metric system. Decimeters are treated like tiny feet, and centimeters are virtual inches. There is no reason to use two units to describe a single distance! As I’ve pointed out ad nausum here, metric construction uses millimeters only! It is still true that to this day you will find feet and inches with fractions on a US tape measure; on a proper metric tape measure, you have only a single unit, millimeters. In the case of Isaac’s example, we would have measured 3240 mm and 4960 mm in each direction. Clearly the unit we want is square meters, so, using the idea that metric is better by 1000, we see this is 3.240 meters by 4.960 meters, and we multiply those together without involving any mixed units at all!

But remember, this essay was published in 1971. English speaking nations viewed metric conversion as something in their future, and still used Olde English Units or Imperial everyday. New Zealand and Australia had only begun metrication in 1969 and 1970. Canada began two years later in 1973, and is still not complete. There was very little experience with using metric at the time, or any examination of its best usage.

By the 1980s, enough experience had been achieved by nations such as Australia, New Zealand, South Africa, and others to see the rational for using only millimeters in housing construction, milliliters for volume, and grams for mass. Isaac, the speed learner, wrote the book The Measure of The Universe in 1983, and by then had come around to realizing that centimeters were a hindrance, and millimeters produced smooth metric usage. He dropped the idea of multiple units, and entered more modern metric usage. The United States on the other hand is a no learner, and not even a slow learner when it comes to metric, despite the passing of more than three decades since Asimov’s updated work was published.

Dr Asimov saw a number of problems associated with lack of the metric system in the US:

For one thing, only American children will waste incredible numbers of hours trying to ram into their heads an unlearnable system, when they might be learning something useful instead. Only American children will have this additional reason for learning to hate school. All other school children, including Russians and Chinese, dismiss the measurement system in a day of explanation and a week of practice.

What else? All scientists everywhere, even in the United States, use the metric system exclusively in their scientific labors. Everywhere else, scientists use the metric system in daily life and learn it as children. In the United States, scientists learn the metric system only late in life and have to keep on using the common system also. It means that American scientists are never quite as much at home with their basic language of measurement as are all other scientists.

The lack of the metric system in everyday use, also isolates the US public from science, at a time when most serious problems we face require scientific understanding to address them.

What else? Only American industry makes use of the inches and pounds. The rest of the world is on the metric system. A double standard must therefore be used in international trade, with ourselves on the losing side.

The United States must accept the metric system sooner or later, then. It is not too late now. Would that it had been done long ago in the infancy of the republic, but better now than later.

The political powers that be in the US have chosen an indefinite later, to our disadvantage as a nation.

1 Asimov, Isaac, Today Tomorrow and …… Doubleday & Company, Inc. Garden City, New York 1973 pg 147.

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Postscript:

Fisherman Jeremy Wade was in Sydney Australia looking for an extinct fish which might still exist. He began his research by visiting a fish market there. I could not help but note the clearance sign at the market, and the units it used:

Now if they would only use lower case mm, as others in Australia do.