Design Features: Flight-Safe Pens

(This page revised October 12, 2015)

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PEN WORLD MagazineThis article is a slightly revised version of one that appeared in the April 2012 issue of PEN WORLD magazine.

Pen clip

“Is your pen safe in airplanes?”

In the 1930s and ’40s, that question wasn’t an idle one. With air travel the coming thing, more and more people wanted — or needed — to go flying. But a pen that wasn’t flight safe could leave its owner with an ugly ink stain on hands or clothing, an undesirable situation at best. Fountain pen manufacturers were not slow to recognize that here was a problem that needed solving, and they spent much time and effort devising pens that could resist the tendency to blot in an airplane.

How did they do it? There was no single solution because the internal architecture of a pen determines the actual form that the problem takes. For most pens of the 1930s, which were lever fillers, the problem was that ink could become trapped in the feed when the pen was turned nib upward and capped in the user’s pocket.

When an airplane, especially the non- or partially-pressurized passenger planes of the 1930s, climbs to its cruising altitude, air pressure in the cabin decreases. But the air pressure inside the pen’s ink sac does not decrease; the sac might expand a little, but the close-fitting sacs used in those days couldn’t expand far enough to do much good toward equalizing the pressure between the inside and the outside of the pen. When the user took the pen out and uncapped it, internal air pressure would eject the trapped ink into the cap and thence onto the gripping section and, probably, the user’s hands or clothing — or both.

FeedThe solution to this specific manifestation, patented all the way back in the days of eyedropper fillers, was George S. Parker’s Lucky Curve (U.S. Patents Nos 512,319, issued in 1894, and 606,231), issued in 1898). In essence, the Lucky Curve is an extension of the feed that projects backward into the reservoir, curving to touch its wall so that there is a path by which the trapped ink can drain out of the feed and back down into the reservoir. There, the release of pressure cannot eject it from the pen.

Parker had invented the Lucky Curve because feed designs in the 19th century lacked buffering capacity, the ability to absorb extra flow temporarily, storing the ink and metering it back out as needed to produce an even flow overall. Improved feed designs, beginning with August Eberstein’s comb feed (U.S. Patent No 750,271, issued in 1904), provided the needed buffering capacity, and Parker abandoned the Lucky Curve feed in about 1929.

Then, in the ’30s, advances in aviation brought the problem back with a vengeance. Parker’s engineers were off working on other things (i.e., the Vacumatic and, later, the “51”), leaving the field open for creative minds in other companies to develop new solutions to what was for them a new problem.

The best-known “flight-safe” lever filler is probably Sheaffer’s SKYBOY. Introduced in 1940, the SKYBOY featured special adaptations described in Sheaffer’s advertising:

SKYBOY has been developed for the hardest of pen ordeals — aviation use. It self-adjusts to extremes in atmospheric pressures and temperatures … with the newly patented Flo-Rite feed.”

FeedThat Flo-Rite feed (U.S. Patent No 2,158,615, issued in 1939 to Howard S. Wright) was the key. What was it? It was a “Lucky Curve.” An outgrowth of Sheaffer’s need for a way to knock the end of the plunger aside for proper flow in its plunger-fillers, it featured a U-shaped ink channel extending out the back of the feed and bent over, as shown here, to touch the sac wall.

Fountain pen Magnifying glass

Put it in a pen, and you have SKYBOY. And just in case the buying public isn’t quite sure, you emblazon the SKYBOY name on the clip, as shown in the photo at the top of this page.

The thing was, Sheaffer also used the same Flo-Rite feed in its other lever fillers, so any one of them could have been called a SKYBOY. But without the SKYBOY imprint on the clip, it was “just” a Sheaffer. The implication, however, was that if they could do it on one pen, they could (and probably would) do it on others.

FeedWahl-Eversharp actually climbed onto the aviation bus even earlier than Sheaffer did. In 1935, the company’s top-line Doric models received a makeover that included the word “Airliner” in its name. Along with several other Wahl-Eversharp models, the Doric acquired a clever modification to its feed. Inserted into a hole in the back end of the feed was a sliver of celluloid made in the shape of the letter J. There was also a hole drilled from the ink channels into the center hole so that — guess what — there was a path for ink to drain back out of the feed.

And, as with Sheaffer’s design, the Wahl-Eversharp “Lucky Curve” appeared on pens across the line, even including the bottom-line Wahl-Oxford. Here it is in a Doric Airliner:

Fountain pen Magnifying glass

This vest-pocket pen is one of the rare blue pens of the period, and it features silver-colored trim, which was usually applied only to gray pens.

FeedBut there’s more. As Wahl-Eversharp moved into the 1940s and became Eversharp, the celluloid went away, to be replaced by a tubular piece of hard rubber that was cut away and — you guessed it — curved to touch the sac wall.

Waterman alone among the Big Four seems to have ignored the aviation trend, clinging to its archaic combless Spoon feed, which it did go so far as to rename, calling it the “Inquaduct” feed, but it was still annoyingly blot-prone if shaken. Like Waterman, second- and third-tier manufacturers failed to cash in on the marketing possibilities in aviation, but most of them at least had comb feeds and were therefore better off than Waterman.

But what about pens that weren’t lever fillers? In the U.S.A., this group would include primarily the Parker Vacumatic and, in the ’40s, the “51”; and it presented a special challenge. There was no problem with ink trapped in the feed; it could drain right down the pen’s breather tube. But the breather tube introduced its own problem: in order to make the pumping action of the Vacumatic filler work, the tube had to provide the freest path into and out of the pen. And, as the user uncapped the pen, ink could go right up the breather tube and out of the pen.

For its Vacumatic-filling models, like the 1945 Vacumatic pictured here, Parker solved the problem by reducing the length of the breather tube (U.S. Patent No 2,400,768), issued in 1946 to David F. Mohns). This change obviously reduced the ink capacity of the pen, and Parker carefully said nothing about that aspect of the new design. What it also did was to ensure that when the pen was turned nib upward, the level of the ink in the reservoir would not rise far enough to cover the breather tube. When the user uncapped the pen at altitude, only air rose through the breather tube, and there was no blot: mission accomplished!

Fountain pen Magnifying glass

But the shortened breather tube was only a stopgap measure. Kenneth Parker, who was fascinated by flight, had decided in 1943 that Parker would not produce any future pen models that were not flight safe. Engineers went to work on the problem, and the result, the Aero-metric filling system (U.S. Patent No 2,612,867), issued in 1952 to Marlin S. Baker and Harlan H. Zodtner) appeared in 1948.

At first called Foto-Fill because of its transparent sac, the Aero-metric system featured a squeezable sac with a breather tube that extended almost its full length. The magic that made it flight safe was a combination of the breather tube’s smaller-than-usual diameter and a tiny hole drilled laterally into the tube just behind the feed. With the nib positioned upward, a squeeze on the sac — or expansion of the air in the sac when the pen is uncapped — pushes a very small amount of ink into the pen’s collector, which has tremendous buffering capacity. Then, air bleeds through the small hole, and there is no blot. Parker capitalized on this feature in 1949 with the introduction of the stainless steel-bodied “51” Flighter, which is today among the most desirable “51” variants.

Fountain pen Magnifying glass

With the advent of pressurized aircraft such as the Lockheed Constellation (introduced into civilian service in 1945, shown below in Capital Airlines livery), the need for special engineering to make pens flight safe was thought in some quarters to have ended. Eversharp appears to have given up on it by introducing a full-length breather tube in its all-time most popular pen, the Skyline, to provide for increased ink capacity. The Skyline and its successors, the Symphony and the Ventura, are definitely not flight safe.

Lockheed Constellation

Are modern fountain pens flight safe, then? Not necessarily. Do they need to be? Today, with jets flying at altitudes up to 40,000 feet but pressurized only to an effective cabin altitude of 6,000 to 8,000 feet, there’s still plenty of opportunity for pens to eject ink into their caps in airplanes unless they’re fitted with feeds having ample buffering capacity. It especially behooves users of cheap pens, which are more likely to have inadequate feeds, to be aware of this possibility. The wisest course is to leave suspect pens tightly capped while in flight.


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