Re: Ariane5 FAQ, Professional version, first draft

["Robert I. Eachus" <rieachus@attbi.com>]

rc211v wrote:

> imagine a car maker designing a new car with an old engine but with a
> different gearbox without testing? And nobody in the engineering staff
> says uh oh ... 
> 
> This "bug" is so extraordinary that it deserves a FAQ...

Replace that with putting a new engine in a new car model, but using the 
brakes, tires, and suspension from the previous version, and you have a 
mistake so frequent it deserves a FAQ.  (Or a whole generation of 
"muscle cars" depending on your point of view.)

In fact for a similar generation of mistakes look at Allied military 
aircraft during WWII.  There was a period in 1942 when the 'solution' to 
all combat aircraft problems was to modify the engines to provide more 
horsepower.  Most of 1943 was spent fixing the problems caused by the 
bigger engines.  The net result was better aircraft, but it was very 
expensive in lives of pilots, many of them in training.

My favorite example of the result of all this was a chapter in a book 
"Fork-tailed devil: the P-38" by Martin Caidin 
(http://tinyurl.com/j4yn).  But the chapter is about another airplane 
the P-47 Thunderbolt, and about the differences made by replacing the 
propeller.  They had improved the engine to provide more horsepower, 
without changing the propeller to match.  (Technically since the Jug had 
a variable pitch propeller, all that was actaully changed were the four 
blades.)  With the new propeller, the Jug was a completely different 
aircraft in terms of handling.

The P-38 went through a similar set of problems, but the major fix was 
the addition of dive brakes.  Dive brakes were first introduced on the 
P-38 and later needed on most jet aircraft.  At a certain speed, the 
airflow over top of the wings is transonic.  When this happens, it 
doesn't matter what the pilot does, the aircraft doesn't respond to 
control inputs, in fact all the control surfaces seem frozen.  (First 
order approximation, it takes infinite force to move a control surfacte 
into a transonic airflow once established.  The dive brakes are small 
flaps to create turbulance before the airflow becomes transsonic.)

-- 
"As far as I'm concerned, war always means failure." -- Jacques Chirac, 
President of France
"As far as France is concerned, you're right." -- Rush Limbaugh