Electronic Design

Letters

Easy Luggage Transport
The unmanned space-flight theme is a jewel \["Man-In-Space Is An Ambition Whose Time Has Passed," April 2, p. 152\]. I also scanned your Web site. The luggage-handling system you propose is in existence at the Kloten Airport in Zurich, Switzerland. The carts can be used on steep escalators. They can be "stacked" horizontally so that only the wheels of the first and last carts touch the ground for easy transport.
Janusz Dzieduszko

Omit Humans From Dangerous Rides
In "Electronic Missile Guidance Changes Tactics And Strategy" \[Dec. 4, 2000, p. 179\], I take it that you were proposing turning our cutting-edge re-search on developing a newer stratagem without scrapping our current use of weapons that fought "the last war."

My only caveat is that air support is traditionally used to control the air space over a battlefield. In close-in fighting, such as the fiasco in the Balkans, fighters are a hindrance, and attack helicopters are a good idea gone wrong. But in any conflict, some form of air cover is needed. So we require a new form of support. I agree we don't need a fighter that can pull 7 Gs to strafe guerrilla partisans.

Aircraft carriers may be tempting targets, but they're usually in the middle of nowhere, and they should stay there, as opposed to refueling in a foreign port of dubious security. They serve as forward air bases, which can deploy sorties sooner for a rapid response. We probably have enough.

I hear the Army is in the midst of a quandary over the next generation of armor: tread versus wheels, or a combination. Also, would this vehicle serve more as firepower, or personnel carrier? Where do you come down on this push to build x-by-wire vehicles?

Keep on questioning conventional wisdom. It will undoubtedly be the genesis of something better—eventually.
Pat Di Giacomo
Analog Research

Lawrence J. Kamm's reply:
I argue that the guided missile makes fighter planes, aircraft carriers, and tanks obsolete. Bombers carrying air-to-air missiles as well as air-to-ground guided bombs don't need protective fighters (who now fight with guided missiles anyway).

Why do we want "air superiority?" It is to provide, or prevent, bomber access; the air space itself has no value (nor does surveillance plane access). If the bombers can provide their own with their missiles, we need no fighters. An aircraft carrier carries only about 100 small bombers and is the world's most tempting target.

A fleet of heavy bombers costs less, carries fewer exposed personnel, carries many times the bomb load, and gets there sooner. Bombers at 600 mph give pretty rapid response. Infantry with man-carried missiles kill tanks.

Next-generation army armor will support the indispensable infantry as personnel carriers. Again, my position is only to omit humans from dangerous rides, and to make the vehicles smaller by omitting life supports.

A Call For Better Documentation
"It's High Time We Bring Back The Profession Of Engineering Writing" \[Jan. 8, p. 46\] really struck home with me. I'm not a "tech writer" but an engineer who has written many manuals and instructions for proper use of equipment and software. I agree that too many writers haven't the foggiest notion of what they're writing about. Yes, in a writing class, they would probably get excellent grades for the "style" and the "form," and probably several other accolades.

But the point is really to convey the correct important information to the reader without any interest in the style or form in which it's presented. I'm not attacking all written publications, but there are too many that really leave me hanging and wondering who the person was that generated the chaff contained therein.

The problem seems to be the bottom line that management has hanging over it, and so the engineers are moved to work on the next big program. "Let the tech writer do the manual for that equipment or software!" Then the poor customer has to struggle and call tech support for the clarification that should have been made in the manual. Let's hope things improve and we start getting better documentation!
Dale Blackwell
Consultant
Design Group Limited

Twice The Bits Halves Reliability
I read the 40 Years Ago column "Redundancy Promises High Reliability" \[Feb. 19, p. 58\] with great interest, as I have worked with redundant control systems for civil aircraft. There's a comment in the second paragraph which I suspect is down to lax terminology, however, as it claims that having a second channel doubles reliability. As there are twice as many bits to fail, this halves reliability (approximately, to be strictly accurate).

Depending on the switch-over architecture, though, it may double availability. This would be the case if the second channel is a "hot standby" manually selected. But if the switch-over is automatic, it will also halve availability. This is because at failure, two systems can only disagree, and hence disengage, or switch off. Thanks for an interesting column.
Alan Dedden
Flight Refuelling Ltd.

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