Orion PDR slides to mid 2009

On Wed, 03 Sep 2008 11:29:22 -0500, Pat Flannery
wrote:

Derek Lyons wrote:
Von Braun's actions have no bearing whatsoever of the question of
whether or not such problems are unusual.

Since building manned spacecraft shares a lot in common with building
high performance aircraft, when's the last time you heard of a aircraft
coming in significantly _under_ the planned weight? :-)

Actually, I don't think a new airplane has ever even made its first
take-off _at_ the planned weight.

Then there's the difference between predicted and actual drag. I
remember the discussions about how some new fighter, I think the F-16,
was a hundred drag counts over prediction. That's huge, a delta of
0.1 in the drag coefficient. They were moving antennas, replacing the
radome, and doing all sorts of drag-reducing tweaks. It's still a
short-legged airplane, but they did improve it over the original
version.

Mary "Then there's trim drag, which is always wrong"
--
Mary Shafer Retired aerospace research engineer
We didn't just do weird stuff at Dryden, we wrote reports about it.
or
Visit my blog at http://thedigitalknitter.blogspot.com/

On Thu, 11 Sep 2008 20:58:23 -0700, "Reunite Gondwanaland (Mary
Shafer)" wrote:

Then there's the difference between predicted and actual drag. I
remember the discussions about how some new fighter, I think the F-16,
was a hundred drag counts over prediction.

....The F-14 reportedly had similar issues, but not quite *that* much.
Something like 30 or 40, but it's been a while since I read that one.
A LONG while, in fact :-(

(Dammit, Henry! Come back!)

OM
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Reunite Gondwanaland (Mary Shafer) wrote:
Actually, I don't think a new airplane has ever even made its first
take-off _at_ the planned weight.

Then there's the difference between predicted and actual drag. I
remember the discussions about how some new fighter, I think the F-16,
was a hundred drag counts over prediction. That's huge, a delta of
0.1 in the drag coefficient. They were moving antennas, replacing the
radome, and doing all sorts of drag-reducing tweaks. It's still a
short-legged airplane, but they did improve it over the original
version.

Mary "Then there's trim drag, which is always wrong"


My favorite is still the original prototype of the Su-27 "Flanker".
Sukhoi was supposed to design a aircraft that could beat the performance
of the F-15.
The first prototype proved to be inferior to the F-15 in all major aspects.
Sukhoi went back to the drawing board and made a few "minor
modifications" to the design...
Or, as the chief designer of the Flanker later admitted: "Well, we made
no changes on the wheels of the nose landing gear..."
Anyway, what designer of any combat plane wouldn't think of around a
hundred things they could improve if they had the opportunity to start
right back from the beginning again?
Sukhoi, from necessity, actually got the opportunity to do it. :-D

Pat

OM wrote:
...The F-14 reportedly had similar issues, but not quite *that* much.
Something like 30 or 40, but it's been a while since I read that one.
A LONG while, in fact :-(

(Dammit, Henry! Come back!)


You want to see drag predictions gone wrong, check out the history of
the YF-102:
http://en.wikipedia.org/wiki/F-102_Delta_Dagger
That was learning the "area rule" of transonic drag reduction design of
airframes the hard way.

Pat