Why does the shuttle throttle on ascent?

Henry Spencer wrote:
Yep, lots of compromises in some of those wartime designs... Some of the
photo-recon versions of the Spitfire had a tail tank that compromised
stability even more drastically

_Tail tank_?! Oh, I've got to see a cutaway of this! :-)
Apparently, some Soviet jets used fuel tanks in the vertical fin.
The Monogram (now it's Revell after the two companies merged)
transparent model of the P-51D has the fuselage fuel tank in it:
http://www.hobbylinc.com/htm/rvl/rvl04726.htm
The really amazing model was the transparent Monogram 1/24th scale Bell
UH-1 "Huey" helicopter.
It took forever to spin up to full speed, but God help you if that main
rotor ever hit you at full RPM. :-D

Pat

"muff528" wrote in message
news:z4Coh.2414$%Q4.1156@trnddc06...

"Morgans" wrote in message
...

"Brian Gaff" wrote

Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Sorry, but you got that one wrong.

The foam does the damage because of the high speed that it has when it
hits the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary
atmosphere slowing the foam so effectively and rapidly, that causes the
relative closing speeds of the now nearly stationary foam hitting the
speeding shuttle.
--
Jim in NC


OK, now I'm trying to figure out how to insert a magical, imaginary
conveyor
belt into this scenario. :-)

Please tell me you're not referring to that silly Straight Dope thing on a
plane on a conveyor belt.



TP in FL (Go Gators!)

"Greg D. Moore (Strider)" wrote in message
ink.net...

"Blueskies" wrote in message
et...

"Tim Rogers" wrote in message
...
:
: "Blueskies" wrote in message
: . net...
:
: "Danny Deger" wrote in message
: ...
: :
: : "Danny Deger" wrote in message
: : ...
: :
: : Why does the shuttle throttle to 3 Gs on ascent?
: :
: :
: : The 3 G throttling is done late in the flight (about 7:30)and has
: nothing to
: : do with dynamic pressure. It was designed in to allow "regular"
people
: fly
: : the shuttle.
: :
: :
:
: Yes, the aerodynamic loads are highest early in the flight so the
engines
: are throttled then back up. The shuttle rolls
: over on its back to fake the occupants into feeling 3 gs when in fact
the
: vehicle is pushing 4 gs....
:
: No.
: The 3 Gs is at the backs of the occupants (and along that same axis for
the
: vehicle.) This is the same if they are heads up or heads down.
: If you lie with your back on the floor, you feel the same 1 G if your
head
: is facing north or south.
:
: Tim
:
:

Not talking about facing north or south, they're talking about hanging
from your feet or standing upright...

Considering the velocity vector is forward, it still doesn't really matter
which way they are.

That was my point exactly.
Thanks for the clarification, Greg.

Tim

"Greg D. Moore (Strider)" wrote in message
ink.net...

"muff528" wrote in message
news:z4Coh.2414$%Q4.1156@trnddc06...

"Morgans" wrote in message
...

"Brian Gaff" wrote

Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Sorry, but you got that one wrong.

The foam does the damage because of the high speed that it has when it
hits the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary
atmosphere slowing the foam so effectively and rapidly, that causes the
relative closing speeds of the now nearly stationary foam hitting the
speeding shuttle.
--
Jim in NC


OK, now I'm trying to figure out how to insert a magical, imaginary
conveyor
belt into this scenario. :-)

Please tell me you're not referring to that silly Straight Dope thing on a
plane on a conveyor belt.


I don't know what you're talking about

In article ,
Pat Flannery wrote:
Yep, lots of compromises in some of those wartime designs... Some of the
photo-recon versions of the Spitfire had a tail tank that compromised
stability even more drastically

_Tail tank_?! Oh, I've got to see a cutaway of this! :-)

Not literally in the tail, if (dim) memory serves, but it was called that
because it was in the aft fuselage.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article ,
Blueskies wrote:
: The 3 Gs is at the backs of the occupants (and along that same axis for the
: vehicle.) This is the same if they are heads up or heads down.
: If you lie with your back on the floor, you feel the same 1 G if your head
: is facing north or south.

Not talking about facing north or south, they're talking about hanging
from your feet or standing upright...

When all the forces (engine thrust and air drag) are from your back to
your chest or vice versa, being head-up or head-down is precisely the same
as being head-northward or head-southward while lying on your back on
Earth, i.e. it makes not the slightest difference in what you feel.

The shuttle in ascent is in free fall except for thrust and drag. The
ascent path, and the shuttle's orientation during ascent, are carefully
chosen to *avoid* having the wings generate lift. The wings are not
strong enough to provide any useful amount of lift during ascent, and
the dominant concern is to avoid tearing them off by overloading them.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Henry Spencer wrote:
Three specific snags also aggravated this problem on the SSME:

[...]

In his book "Advanced Engine Development at Pratt & Whitney," Dick
Mulready devoted a chapter to the competition to develop the space
shuttle engine. By the time of selection, P&W's XLR129 had over 251
seconds of operation, versus 0.461 for Rocketdyne's engine.

During a visit, Dick Bissell, a consultant for United Aircraft and
formerly of the CIA and progenitor of the U-2 and Blackbird, said,
"I am sorry, but you cannot win. It was already decided in advance.
The only reason for the competition was to transfer your technolody
to them."

Does anyone have any opinion on the relative merits of the P&W and
Rocketdyne designs? On the politics?

Thanks,

Paul

Absolutely correct!

Bud



On Jan 8, 6:00 pm, "Greg D. Moore \(Strider\)"
wrote:
"Blueskies" wrote in odigy.net...







"Tim Rogers" wrote in message
...
:
: "Blueskies" wrote in message
.net...
:
: "Danny Deger" wrote in message
: ...
: :
: : "Danny Deger" wrote in message
: ...
: :
: : Why does the shuttle throttle to 3 Gs on ascent?
: :
: :
: : The 3 G throttling is done late in the flight (about 7:30)and has
: nothing to
: : do with dynamic pressure. It was designed in to allow "regular"
people
: fly
: : the shuttle.
: :
: :
:
: Yes, the aerodynamic loads are highest early in the flight so the
engines
: are throttled then back up. The shuttle rolls
: over on its back to fake the occupants into feeling 3 gs when in fact
the
: vehicle is pushing 4 gs....
:
: No.
: The 3 Gs is at the backs of the occupants (and along that same axis for
the
: vehicle.) This is the same if they are heads up or heads down.
: If you lie with your back on the floor, you feel the same 1 G if your
head
: is facing north or south.
:
: Tim
:
:

Not talking about facing north or south, they're talking about hanging
from your feet or standing upright...Considering the velocity vector is forward, it still doesn't really matter
which way they are.



- Hide quoted text -- Show quoted text -- Hide quoted text -- Show quoted text -

"Pat Flannery" wrote in message
...

The really amazing model was the transparent Monogram 1/24th scale Bell
UH-1 "Huey" helicopter.
It took forever to spin up to full speed, but God help you if that main
rotor ever hit you at full RPM. :-D

I didn't have a transparent UH-1, but the one I did their regular UH-1 model
(at least I think it was a Monogram). I modified so that it would spin the
top rotor via an electric motor and a couple of LEGO gears. Luckily on this
model the fuselage cover easily slid on and off, so everything was hidden.
Boy that thing would spin that main rotor *fast*. ;-)

Unfortunately, my painting skills weren't that great at the time, so the
overall appearance was rather shabby and like almost all of my (poorly
built) models from that era, it was likely destroyed by fire crackers.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

Mxsmanic wrote:
Anno v. Heimburg writes:

Well, a lot of people have never flown in combat, but one could have
deduced from the fact that we were talking about the P-51 Mustang (a
WWII fighter plane) and the "war" part in "war emergency power" that
the most likely application of war emergency power was indeed, um,
during wartime? War, as in, combat?

A lot of aircraft have flown in a lot of wartime, but they didn't do
it at emergency war power. Obviously, more than just wartime is
required to justify it.

Look Anthony, the engine is designed to fly at X power setting without doing
undue harm to itself so the plane can land and fight another day. In combat,
X might not be enough at some moment to get the pilot out of harms way. So
the aircraft is capable of providing X+ which while it will give the pilot
some added power and maybe the chance of saving both himself and the
airframe it will cause the engine to be replaced.

It is very much like the parachute that Cirrus is using today. If they are
used something is going to break but the a pilot has a chance to survive
that they might not have otherwise had.