Why does the shuttle throttle on ascent?

"Pat Flannery" wrote in message
...


MichaelJP wrote:
I always think flying an Me-163 in combat must have been one of the most
crazy experiences in wartime aviation, firstly you have all the explosive
fuel around you, secondly you are shortly to be boosted at tremendous
climb rates into the middle of a heavily armed B-17 formation, thirdly if
you survive all that and manage to get a shot in before the couple of
minutes before the motor dies, you have to glide back like a brick to a
tiny airfield and land on a skid!


As a glider it was superb, thanks to Lippisch's background as a glider
designer.
Although the pilots tended to dive away at high speed to escape enemy
fighters once their fuel was gone (and to get back to base ASAP for the
same reason), it had a really good gliding performance, and the pilots who
flew it said its handling qualities were superior to any other German
aircraft.
It's only drawback in gliding flight was that it was _too_ good at it -
once it got down in ground effect near landing, it had a tendency to just
float along above the ground till speed bled off and it would settle down.
Even the addition of underwing extensible spoilers didn't completely solve
the problem, and a lot of pilots were injured or killed by the aircraft
remaining stubbornly airborne down the whole length of the landing field
(they landed on grass generally) and not touching down till it arrived on
the rough ground outside the field's boundaries.

Pat

Thanks Pat - the ME-163 is modelled in the superb combat flight sim IL-2,
trying it last night they must have modelled this aircraft quite nicely as I
found it very difficult to bleed off enough speed in the hold-off, exactly
as you said above. Landing on the grass the skid dug in and certainly a real
aircraft would have been destroyed.

Difference is I could reset for another go

Doing some other testing I found it impossible to recover from a spin
entered from a slow-speed stall. Wonder if that's correct?

"Henry Spencer" wrote in message
...
In article ,
Herb Schaltegger wrote:
(also related to thinner air: rocket engines are more efficient
with less back pressure.

My undergraduate propulsion prof would be gagging at your use of the
term "back pressure" Henry...

This is the difference between someone whose idea of an unsophisticated
audience is upper-year engineering students, and someone who's actually
had practice writing for, and talking to, non-captive audiences. :-)

Is "back pressure" strictly correct? Arguably not, although the issue is
more complicated than it looks (for one thing, ambient pressure at the
nozzle exit isn't necessarily the same as ambient pressure elsewhere on
the engine, which in turn isn't necessarily the same as ambient pressure
on the vehicle -- rocket exhausts can be powerful ejector pumps). But it
*is* what you say if you want to give the right general impression to an
audience that doesn't care to hear the rigorous details.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |


In a similar way that the term "centrifugal force" is generally despised by
experts, but for most people it's quite a good way to describe the
sensations they experience.

On Thu, 11 Jan 2007 21:37:33 -0600, Henry Spencer wrote
(in article ):

In article ,
Herb Schaltegger wrote:
(also related to thinner air: rocket engines are more efficient
with less back pressure.

My undergraduate propulsion prof would be gagging at your use of the
term "back pressure" Henry...

This is the difference between someone whose idea of an unsophisticated
audience is upper-year engineering students, and someone who's actually
had practice writing for, and talking to, non-captive audiences. :-)

Is "back pressure" strictly correct? Arguably not, although the issue is
more complicated than it looks (for one thing, ambient pressure at the
nozzle exit isn't necessarily the same as ambient pressure elsewhere on
the engine, which in turn isn't necessarily the same as ambient pressure
on the vehicle -- rocket exhausts can be powerful ejector pumps). But it
*is* what you say if you want to give the right general impression to an
audience that doesn't care to hear the rigorous details.


I know what you're saying Henry. It's just that every time I hear
"back pressure" in terms of rocket or gas turbing engines, I still to
this day have the mental image of Prof. Wilkerson standing at the
blackboard, closing his eyes as if in pain and squeezing his hand so
hard the chalk snaps . . . ;-)

--
Herb Schaltegger
"You can run on for a long time . . . sooner or later, God'll cut you
down." - Johnny Cash
http://www.angryherb.net

"Herb Schaltegger" wrote in
message .com...

I know what you're saying Henry. It's just that every time I hear
"back pressure" in terms of rocket or gas turbing engines, I still to
this day have the mental image of Prof. Wilkerson standing at the
blackboard, closing his eyes as if in pain and squeezing his hand so
hard the chalk snaps . . . ;-)

He only snapped chalk? You're lucky.

I had a Latin teacher that would throw it... very quickly... at the
blackboard behind your head.

THAT got your attention.



--
Herb Schaltegger
"You can run on for a long time . . . sooner or later, God'll cut you
down." - Johnny Cash
http://www.angryherb.net

"Greg D. Moore (Strider)" wrote in message
news:TeMph.13533
"Herb Schaltegger" wrote in

I know what you're saying Henry. It's just that every time I hear
"back pressure" in terms of rocket or gas turbing engines, I still to
this day have the mental image of Prof. Wilkerson standing at the
blackboard, closing his eyes as if in pain and squeezing his hand so
hard the chalk snaps . . . ;-)

He only snapped chalk? You're lucky.

I had a Latin teacher that would throw it... very quickly... at the
blackboard behind your head.

Why would your Latin get upset when you mentioned "back pressure"? g

"Steve Foley" wrote in message
news:8mMph.7617$GL.3332@trndny06...
"Greg D. Moore (Strider)" wrote in
message news:TeMph.13533
"Herb Schaltegger" wrote in

I know what you're saying Henry. It's just that every time I hear
"back pressure" in terms of rocket or gas turbing engines, I still to
this day have the mental image of Prof. Wilkerson standing at the
blackboard, closing his eyes as if in pain and squeezing his hand so
hard the chalk snaps . . . ;-)

He only snapped chalk? You're lucky.

I had a Latin teacher that would throw it... very quickly... at the
blackboard behind your head.

Why would your Latin get upset when you mentioned "back pressure"? g

Because we were conjugating it properly. Geesh :-)

(Henry Spencer) wrote:

In article . com,
John wrote:
During the few test shots of Trident missles that I have seen, I always
thought that the angle at which the vehicle flew was remarkable; like
nothing I had ever seen, save for the occassional errant Estes rocket.
The angle seemed close to 45 degrees, although I had no way of really
knowing, almost immediately after emerging from the water and ignition.

I wonder, though, if it actually ascends in that direction, or if that's
just a transient error -- perhaps something to do with the dynamics of
breaking the surface -- that the guidance system sorts out a second or
two later.

There can be attitude transients caused by hydrodynamic effects of the
passage through the water as well as the effects of breaking the
surface. ('Tail slap' as the missile exits is of particular concern.)
Polaris was acutely sensitive to this because of their need to perform
a roll maneuver immediately upon ignition.

In the early days they even tested a set of flow velocity sensors
mounted on the SSBN to attempt to predict wave action and the
calculate the best moment for launch!

They do tend to fly a steeper trajectory than is usual as well.
Partly to encourage seperation between birds (which are being salvoed
at short intervals) and partly as a safety measure to the get the bird
away from the boat as soon as possible.

Also, SLBM launches are typically filmed at much shorter ranges than
is usual for NASA launches - which messes with your ability to
estimate flight angle.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Henry Spencer wrote:

The big reason why you might need tank insulation is if the tank holds
LH2, in which case you need to insulate to prevent liquid air from
condensing... and that'll happen even at subzero temperatures, so you
can't get away with leaving it off.


In the case of a carrier aircraft, the airstream should carry away any
liquid air on the tank.


Although a completely rreusable LV will have a TPS to take reentry
heating, and therefore will already have exterior insulation, the drop
tank solution makes for far easier design as far as vehicle weight goes.


The gain is actually rather questionable, after you consider reentry --
the drop tank leaves behind a heavy, dense vehicle that makes a severe
reentry. At reentry time, it's *good* if lots of the volume inside the
TPS is empty tanks. The drop tank does make for far easier design if you
can "throw the TPS problem over the fence" to the materials team...

I'm really surprised that the small air-launched orbiter with giant drop
tank concept didn't get anywhere- both we and the Russians thought the
idea had enough merit to do designs of the concept:
http://www.buran.ru/htm/busfact.htm#maks-op
http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld053.htm

Pat

Henry Spencer wrote:
I wonder, though, if it actually ascends in that direction, or if that's
just a transient error -- perhaps something to do with the dynamics of
breaking the surface -- that the guidance system sorts out a second or
two later.


No, I've seen films of the launch; it comes out of the water straight,
then immediately pitches over and climbs at a steep angle;
There's a video of a launch he
https://wrc.navair-rdte.navy.mil/war...bs/trident.mpg

Pat

Pat Flannery wrote:



Henry Spencer wrote:
I wonder, though, if it actually ascends in that direction, or if that's
just a transient error -- perhaps something to do with the dynamics of
breaking the surface -- that the guidance system sorts out a second or
two later.


No, I've seen films of the launch; it comes out of the water straight,
then immediately pitches over and climbs at a steep angle;
There's a video of a launch he
https://wrc.navair-rdte.navy.mil/war...bs/trident.mpg

That's one launch out of many Pat. I've seen pictures of a Polaris
coming out at about 30 degrees from vertical.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL