Friday, April 11, 2008

The Apprentice's Toolbox

They were told to be there at 0730 and, with rare exception, they always were, at least on that first all-important day. There was never less than thirty-two of them, never more than thirty-six. The youngest had just turned fourteen, the oldest was a day shy of eighteen. There were no exceptions to this rule.

It was always a mixed bag that stood nervously outside that hangar door, with an occasional turban or fedora among the cloth caps. Especially nervous were the Africans, knowing they were in a country where lynching members of their race was still considered an acceptable form of behavior. A sprinkling of Orientals rounded out the racial mix but often confusedly so since some were lanky six- footers. The confusion was compounded by native- born Chilean named O'Hara who spoke better German than Spanish and a Chinese boy whose mother tongue was Portugese.

And English, of course. English was another rule for which there was no exception. English was the language of aviation.

At exactly 0730 the door opened and a man bearing a clipboard stepped out. Without greeting or preamble he called the first name, got a startled reply from the surprised boy who was told "One-one," and saw his name ticked off the alphabetized list. The man went on to the next name and the one after that before he noticed the first boy was still there, a picture of worried indecision.

"Table one," the man said slowly. "Table one, place one. Inside," the man gestured abruptly with his pencil and went on to the fourth name who became 'one-four'. Number five became 'two-one' and the mystery was revealed as soon as the boys entered the building.

The tables were right there, impossible to miss since they occupied half the extensive space. Varnished maple tops a solid two inches thick, four feet wide and eight feet long, supported on steel legs painted grey. The ten tables were clearly marked with their numbers and the four places at each table was also marked. But the boys hardly noticed.

The remaining half of the space was occupied by an airplane. The boys immediately recognized it's make and model although few had never seen one in the flesh. Having their eyes fastened to the plane made it difficult for them to find their places at the tables but all eventually did so, even though their heads remained cocked toward the airplane. The airplane was why they were there. It was a dream come true, a thing too exciting to ignore.

But as soon as they were all at their places the man, who said simply "I'll be your instructor," explained sorrowfully that they would all have to go back outside. Someone had created a bit of a mess - - two cigarette butts -- and it would have to be cleaned up.

First one then the other of the guilty boys confessed their crime and moved toward the door but the man would not allow it. It had to be all or none. That's how things were done here. And so long as he was in charge, it would be all.

Brooms and dust-pans were found and the area in front of the building given a brisk but effective sweep-down. But by the time the brooms were put away several boys had forgotten their numbers. And again, it was all or nothing. Rather than look up their numbers individually the man called the entire roll.

Each table held four drawers and the space under each table was marked off into four sections. Inside each drawer was an identical kit of tools and an inventory sheet. Each boy was required to inventory his tools as the instructor called them out, marking them off on their inventory sheet which the boy then signed. Lining up by their numbers, the boys were conducted to a room on the far side of the building where they turned in their inventory sheet and received back three shop coats of a size appropriate to their build. Or nearly so.

The shop coats were glorious things of white cotton twill, embroidered across the back with the winged symbol of their employer. They were told to reserve one of the shop-coats for special occasions and to keep the other two properly washed and mended, for it was now their daily uniform.

Properly frocked and tabled, the boys were then addressed by an older man in a three-piece suit and gold-rimmed glasses, obviously someone important from the Front Office. The man spoke in a friendly, familiar fashion, smiling often and making it clear he thought them a welcome addition to the company, which is why the company was willing to go through the expense of training them for three years, providing them with their shop coats and working space, their basic kit of tools and of course the all-important toolbox to keep them in...

At which point the Instructor leaned near the Important Man and told him they were out of toolboxes at the moment but just as soon as some came in...

The Important Man didn't care for this news. Not one bit of it. He frowned and when he did so all the warmth went out of that wonderful airplane- filled space. He reminded the Instructor that the apprenticeship program was costing the company thousands of dollars and that there was a right way and a wrong of doing things and any attempt to properly train an apprentice who did not have his own toolbox was obviously wrong. They would have to send the boys home and reschedule the start of their training... at least, for any who were still qualified, for some later date. Insert here a dramatic pause, during which apprentices had been known to faint, burst into tears or lose control of their bladder.

"I suppose I could have them make their own toolboxes," the Instructor mused in a tentative way.

The Important Man gave the Instructor a scornful look. "That wouldn't do. They'll have those toolboxes for the rest of their lives. Everywhere they go people would see those toolboxes with our logo on them. We couldn't allow any shoddy goods... "

"Oh, they wouldn't be shoddy," the Instructor assured him. "Built to spec, every one of them."

Here the Important Man turned toward the boys. He didn't look pleased. "Are they up to that? Some of them don't have any training at all... "

"I'm sure they can do it if we give them the chance," the Instructor coaxed. Thirty-six rigid faced boys silently screamed 'Yes! Give us a chance!'

And so it was. The boys were trooped to another building where four sheets of sixty-thou 17ST was sheared into strips sixteen by forty-eight inches. In another shop each boy was given a piece of one- by-one by eighth-inch aluminum angle along with a paper cup half filled with rivets. In the Steel Shop each boy received a section of piano hinge, two luggage latches, a small hasp and a piece of 3/8" cold-rolled steel bar ten inches long. Juggling this crazy assortment of stuff, cutting themselves on the sheet metal, dribbling rivets, they scurried back to their classroom. It wasn't yet nine a.m. of the first day of their apprenticeship and things seemed to be going to hell in a hand basket. Or in a toolbox.


It was all a bit of a show of course.

Over the next two weeks each of the apprentices, save those who slipped quietly away and never returned, used the materials to build his toolbox. The sheet of aluminum -- when properly cut -- provided enough material to fabricate a toolbox approximately sixteen inches long, eight inches wide and ten inches deep. The corners of the box were reenforced with angle while the steel rod was bent to form the handle. The box was assembled with eighth-inch rivets having a one-inch pitch.

For many of the boys it was their first exposure to metal-work. For others, it was their first use of feet and inches and all those confusing fractions, so unlike the innate simplicity of their native metric system. And for most, it was their first experience with dust pans and brooms and working alongside a total stranger from exotic lands such as Nigeria or Oklahoma.

If the truth be told, a few of the toolboxes were less than spectacular when it came to workmanship. But each was built to spec. And each passed a rigorous inspection, not only from the Instructor but from the student's peers for here again, it was All or Nothing.

The resulting box was acid-etched with name of the apprentice and with the logo of the particular school. The details of the toolbox -- and of this story -- vary from school to school, with a Northrop toolbox being distinctive from a Spartan, as a Loughead differed from a Fleet. But the principle remained the same for all: With the manual arts, you learn through experience. Building your own toolbox was simply the first step on that path. But there was a far more subtle lesson being taught, one having to do with the nature of airplanes and teamwork.

Many a mechanic... and not a few executives... still have their 'apprentice box', often prominently displayed on their Trophy Wall among their photos, diplomas and other tokens of accomplishment.


How about you?

Ever used a cleco? (or know how they got their name?) Ever made a buck-head? Have you been properly introduced to Mr. Smiley?

Building the basic box is akin to building the basic airplane in that you first fabricate the parts then assemble them into subassemblies and the subassemblies into the whole. Along the way you must do some accurate cutting and filing and drilling as well as figuring out half a dozen problems built-in to such a project, such as 'How do I get all twenty pieces of sheet metal out of this 16x48 panel?'

Frankly, it's a lot of work. And nowadays work is considered a bit old-fashioned, especially if it involves something you've never done before.

But the concept behind the Basic Box applies equally well to composites, welded steel or even wooden construction practices -- the Basic Box is meant to provide the means to an end rather than an end unto itself.

Want to build the Basic Box from fiberglas? No problem. There are at least four acceptable methods of arriving at the desired finished product. Howabout wood? The same applies to wooden construction. Or to steel. And in each case the object is not to provide you with a toolbox, it is to teach you welding or wood-working or many possible variations when working with composites.

So you do the work and in doing so, learn the required techniques. But it isn't some Quick & Easy, smear a little epoxy on the table sorta thing. Nor do you weld half a joint and skip off to the next booth to get a three minute 'education' in scarfing plywood. Under the Old Rules you not only acquired an in-depth knowledge of the required techniques and procedures, you made a useful thing, something that would last your lifetime, something better than anything you could buy... and something that could only be made by human hands.

Want to buy a 'prentice box'? I'll be happy to sell you mine. For ten thousand dollars :-)


Thursday, April 3, 2008

AV - Vapor Lock

Re: Vapour Lock (Question for Mr. Hoover)

--- In, Stefan Vorkoetter wrote: > Can you tell me (and the group I guess) what vapour lock is?


Gasoline, or whatever passes for gasoline nowadays, has a low boiling, typically between 80* and 90* on the Fahrenheit scale, the range depending on the formulation of the fuel, in that 'gasoline' containing a higher percentage of alcohol boils at a LOWER temperature. And to make matters worse, the boiling point decreases as the air pressure is reduced.

Heat your gasoline to its boiling point, it starts to do just that. Not like your tea kettle, but the liquid gasoline is still rapidly turning into gasoline vapor.

Did you get that bit about pressure? Reduce the pressure on your hot gasoline and it will start to boil at temperatures well below 80 to 90F (I forget the Celcius). Higher you fly, the lower the boiling point.

The pressure factor is really important if you have a fuel pump anywhere in your system and is of CRITICAL important is you're using the typical two-chamber automotive type pump, such as a stock VW mechanical fuel pump. That's because when the pump's diaphram is pulled down it effectively REDUCES THE PRESSURE on the fuel that appears in the inlet-pipe of the pump. And if the liquid fuel is close enough to the boiling point, the drop in pressure fills the lower chamer with gasoline VAPOR instead of liquid fuel. (This is the classic definition of Vapor Lock, by the way. Which never happened on the early Fords because they used a gravity-fed system.)

Wanna know the main difference between gases and liquids? (They're both 'fluids,' by the way.) You can COMPRESS a gas whereas liquids are virtually incompressible. And that's exactly what your fuel pump does -- it compresses the bubble of vapor in the lower chamber. The bad news is that compressing the bubble of vapor does NOT allow any gasoline to be pumped.

The really bad news here is that an automotive fuel pump (and most others) are not positive displacement devices. The outlet pressure of the typical fuel pump is generally less than 1 psi. If the lower chamber were filled with LIQUID, 1 psi would be more than enough to push the check-valve off its seat and force liquid gasoline into the upper chamber, where it would bet fed to the carb according to the position of the carb's float-valve. But when the lower chamber is filled with vapor, the pressure of the return spring under the diaphram simply compresses the bubble. Some of the vapor may get into the upper chamber but the bottom line is that within three or four cycles the fuel pump stops delivering fuel to the carb, the engine burns off the fuel in the bowl (if its a real carb) then dies.

That's the typical 'vapor lock' scenario. But there are others.

If the hot gas is in a pipe at atmospheric pressure, you're going to get SOME amount of vapor formation. In a properly designed fuel delivery system, your fuel pipe should ALWAYS have some degree of slope toward the carb, even when the airplane is climbing at its steepest angle. The reason for that is to allow any vapor to travel UP the pipe and be vented from the tank and for any debris that got past your finger-strainer to travel DOWN the pipe and end up in the gascolator. (Your fuel line is always sized to PERMIT the down-hill passage of any debris large enough to get through the strainer in the tank.) Sounds like plain old fashioned Common Sense but you'd be surprised what a rare commidity that has become :-)

One of the other vapor-lock scenarios is when the body of the carburetor becomes so hot that the flow of gasoline through the carb is not enough to cool it off. The gasoline boils and since the bowl is vented to the atmosphere, escapes. But in some cases, especially with automotive carburetors, the bowl is vented into the throat of the carb resulting in a mixture so rich that it can kill the engine. The Tillotson and, I think, most of the Zeniths, are vented directly from the bowl to the atmosphere so this type of 'vapor lock' but the Solex (all models) and most other automotive carbs dump the boiled-off vapor into the manifold.

As you can see, the root-cause of vapor lock is pretty simple, which makes its prevention a no-brainer. Unfortuantely, in the case of the VP, in an effort to keep the costs down the fuel system violates a lot of rules, such as mounting a Solex carb on top of the engine, forcing you to use a fuel pump. Which is fine for a car, where you can pull over and park, but it's not real smart on an airplane. (Yeah I know, Rotax does it too. Of course, when you pay twelve grand for a 1300cc engine you expect it to come with fully insulated fuel lines.)


PS -- a lot of modern vehicles use positive-displacement pumps with pressures as high as 135psi. (Under that kind of pressure you don't have to worry about vapor lock.) A pressure-regulator controls the feed to the injectors and any excess is returned to the fuel tank, which is usually fitted with a vapor recovery device and electronically controlled venting system, hilariously complex, ridiculously expensive and not repairable at all; replacement only. Which is one reason my daily driver is forty years old :-) (Runs fine, thanks. And its emissions are barely a tenth of the legal minimum.)

(the above was posted to the Volksplane Group in 2005)