Titanium spars and composites on F-22

On Thu, 04 Dec 2003 00:59:57 -0800, Hobo wrote:



I've read that the vertical tail buffeting problem on the F-22 prototype
was solved by replacing composites with titanium spars. This makes me
wonder why the titanium wasn't used in the first place. Was it
cost/weight/stealth or something else?


The same thing happened with the wing spars. They were all composite
and apparently when they did the live fire tests on a fuel filled wing
the composite spars got obliterated (did not degrade "gracefully" :-)
) So now every thrid spar is made of titanium. They didn't do this
from the start because of weight. I imagine a machined titanium rib
probably costs more than a composite one. Stealth had nothing to do
with it as the spars are inside the wing.

"Hobo" wrote in message
...


I've read that the vertical tail buffeting problem on the F-22 prototype
was solved by replacing composites with titanium spars.

What you read is speculation that the titanium spar has fixed the F-22's
structural integrity problem. There is no way for anyone to know that until
the aircraft has flown at least 500 hours.

This makes me
wonder why the titanium wasn't used in the first place.

The tail boom was stiffened in the first place and then an air damn was
tried, but both failed to fix the "buffeting" problem.

Was it
cost/weight/stealth or something else?

Shotgun, to fix a poorly understood problem.