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.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page.

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.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page.