Space Elevator

RN = 778 C V
Where C = chord in inches
V = speed in MPH

I used your EAS numbers (the lowest one too) assuming that would include
the corrections for pressure altitude and temperature. That may or
may not be correct, but it was all I could find at the moment.

Cd of .02 for a round cross section may also be ridiculously low.
But that's a moot point.

Recall that in straight and level flight drag equals thrust.

So I'll SWAG that the 747 total drag at cruise is 273,000 pounds.

That takes up ALL of the avaliable engine thrust.

Oh bloody oops!


Richard

On Sun, 04 Jul 2004 13:25:10 -0700, pacplyer wrote:

So if we double your drag per km number, just for ballpark "do-abiltiy"
wag calcs, and call it 3500 lbs of drag per Km of cable exposed
perpendicular to the stream, since it'll be semi-vertical just prior to
towship 45 degree bank maneuver, that yields: 84,000lbs of drag for 24km
of line.

Let's see: four engines producing 67,000lbs of thrust at SL… [note: we
don't know yet what it is at FL 410 but, P&W has those charts and we can
guess it's pretty high since we can pull 1.71 normal climb EPR at FL410
which is only .02 off the max value on the table.] Four engines pulling
67,000lbs plus 5,000 lbs of thrust from the APU chugging out the tail (no
I'm not making this up) gives us 273,000 lbs of potential pounds of
thrust (minus minor alt effects) to overcome the line drag coefficient
with. Now most of this is going to be used just getting the mated
vehicles to 41,000 ft. But once I get that 150,000 lb OrbitOne off my
back (I keep forgetting about the 100,000lbs of winch and cable so the
OrbitOne wt limit is 150,000lbs),
I'll have 190,000 lbs of thrust avaiable for aircraft speed control
above whats required to overcome the line drag. That is, when the line's
pulled out all the way 24km out the roof (84,000lbs of drag.) But at
vehicle split the line will still be short so the drag from it is
negligible, and I can accelerate up to .92 mach, in a shallow descent.
Once I get down to FL350 (where the 747 was designed to make money,) and
pay out all that heavy cable in the process (say 75,000 lbs of Vetran) I'm
lighter than **** at 445,000 lbs [380k empty wt+40Kgas remaining+25k
winch pallet wt] so will 84,000 lbs of line drag have me struggling to
hold MMO .92? Don't know, lets go try it.


But, jet engine thrust falls of quite a bit with altitude. Don't be
fooled by that EPR. EPR is Exhaust Pressure Ratio. An EPR of 1.71 just
means that the total pressure in the engine exhaust is 1.71 times as high
as the total pressure in the inlet. But, the total pressure at altitude
is a lot lower than the total pressure at sea level, so the absolute
values of the inlet total pressure and the exhaust total pressure are much
lower than sea level.

Jet engine thrust varies with Mach too. High bypass engines make less
thrust the faster you go. I don't have the rules of thumb at hand, as my
text books are at work, but a quick look at a couple of web pages suggest
that thrust at FL410 might be on the order of 1/3 to 1/4 of sea level
thrust.

http://adg.stanford.edu/aa241/propulsion/tvshv.html
http://www.aerospaceweb.org/design/u...opulsion.shtml

I think the drag from the orbiter, plus the drag from the tether will be
too high to allow it to be towed at anything over the mid-thirties, and
that might well be optimistic. More thrust Scottie

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

Kevin Horton wrote in message ...
On Sun, 04 Jul 2004 13:25:10 -0700, pacplyer wrote:

So if we double your drag per km number, just for ballpark "do-abiltiy"
wag calcs, and call it 3500 lbs of drag per Km of cable exposed
perpendicular to the stream, since it'll be semi-vertical just prior to
towship 45 degree bank maneuver, that yields: 84,000lbs of drag for 24km
of line.

Let's see: four engines producing 67,000lbs of thrust at SL? [note: we
don't know yet what it is at FL 410 but, P&W has those charts and we can
guess it's pretty high since we can pull 1.71 normal climb EPR at FL410
which is only .02 off the max value on the table.] Four engines pulling
67,000lbs plus 5,000 lbs of thrust from the APU chugging out the tail (no
I'm not making this up) gives us 273,000 lbs of potential pounds of
thrust (minus minor alt effects) to overcome the line drag coefficient
with. Now most of this is going to be used just getting the mated
vehicles to 41,000 ft. But once I get that 150,000 lb OrbitOne off my
back (I keep forgetting about the 100,000lbs of winch and cable so the
OrbitOne wt limit is 150,000lbs),
I'll have 190,000 lbs of thrust avaiable for aircraft speed control
above whats required to overcome the line drag. That is, when the line's
pulled out all the way 24km out the roof (84,000lbs of drag.) But at
vehicle split the line will still be short so the drag from it is
negligible, and I can accelerate up to .92 mach, in a shallow descent.
Once I get down to FL350 (where the 747 was designed to make money,) and
pay out all that heavy cable in the process (say 75,000 lbs of Vetran) I'm
lighter than **** at 445,000 lbs [380k empty wt+40Kgas remaining+25k
winch pallet wt] so will 84,000 lbs of line drag have me struggling to
hold MMO .92? Don't know, lets go try it.


But, jet engine thrust falls of quite a bit with altitude. Don't be
fooled by that EPR. EPR is Exhaust Pressure Ratio. An EPR of 1.71 just
means that the total pressure in the engine exhaust is 1.71 times as high
as the total pressure in the inlet. But, the total pressure at altitude
is a lot lower than the total pressure at sea level, so the absolute
values of the inlet total pressure and the exhaust total pressure are much
lower than sea level.

Yeah, I was grinning even as I typed "minor alt effects" in the above
post. Line pilots don't deal in lbs of thrust much. I vaguely
remembered back in 88' calculating lbs of thrust in ground school, and
that it dropped off badly with altitude but you have to remember what
my job is: To sell this idea first; worry about the details later!

Just like the Jim Bede battle cry: "First sell them the airframe.
Worry about supplying engine thrust later!" ;-) Just kidding.
Thanks for keeping me honest Kevin. As you said airlines ops use
weight capability tables and EPR charts. But I didn't remember
that the drop-off in pounds of thrust is so severe! So you guys may
be right; we may be in deep do-do drag wise with stock engines. One
third of 273K lbs thrust at Sea Level is 91,000 lbs of thrust
available! Subtract our line drag guess of 84,000lbs for a two inch
dia line and that gives us 7,000 lbs to overcome 747 vehicle drag
with. Not going to work.

However, before we abandon ship like the rest of the world, I think
maybe we're being too conservative on the drag figures. Tim
calculated a 24mm line which is 0.944882 Inches wide. So Richard
you need to recalculate your formula using numbers for a *one inch*
line instead.


Jet engine thrust varies with Mach too. High bypass engines make less
thrust the faster you go. I don't have the rules of thumb at hand, as my
text books are at work, but a quick look at a couple of web pages suggest
that thrust at FL410 might be on the order of 1/3 to 1/4 of sea level
thrust.

http://adg.stanford.edu/aa241/propulsion/tvshv.html
http://www.aerospaceweb.org/design/u...opulsion.shtml

I think the drag from the orbiter, plus the drag from the tether will be
too high to allow it to be towed at anything over the mid-thirties, and
that might well be optimistic. More thrust Scottie

Dang. Bet you're right. Not only that, but getting our hands on a
-200F is going to be impossible. Everybody loves that thing. What's
a C-90 engine worth? Ten mil each? Re-engine program (experimental
category only: no pax's) would be what another ten –twenty million?
So say it costs 60 million to re-engine one of those old -200
Continental birds that my brother used to fly that are sitting out at
Mojave. He says they are in good shape with all the section 41, 43
etc mods done, and new pylons and fuse pin work done, but that they
parked them because of the fuel consumption. He remembers them at
about 780,000 lbs gross (smaller landing gear than my old -200F
freighter.) We could pick one up for about 50 million. What kind of
TBO do you think we could get out of one of those C90's running it
hard all the time? If we could only get say 240 one hour cycles out
of a new engine, we could afford to burn up about one million in total
tailpipe & total operations cost per slingshot and still break even at
60 slingshots (sell the engines and airframe after retiring in
Tahiti.) That's still cheaper than twenty million on the launch pad
every time at Vandenburg. 20X60 is... hmmmmm One point Two Billion
dollars over at Vandenberg with conventional rockets cost after 60
launches. ...minus our 110 mill cost for aircraft and re-engine-ing
equals one billion ninety million in tow-ship company savings (like my
math?) Let's say we price it for half what Nasa can, and put the
rest in our pocket as shear old profit... 60 shots a year... Yeah, I'm
willing to fly five slingshots a month... Half a billion dollars
tow-ship company profits per year... One percent rah "space-slingshot"
thread-member's fee, Jesus, there's gold in them there slingshots! :^D

Christ! I think I see our ship coming in! Dammit Richard! Give me
some new drag numbers based on a one inch line! Kevin find out how
much thrust in pounds a C-90 can put out at FL410! :-O

pacplyer

up periscope!, damn the torpedoes, full speed ahead! (you guys are
going to need big hangars to put all you're new toys in!) ;-)

pacplyer wrote:


However, before we abandon ship like the rest of the world, I think
maybe we're being too conservative on the drag figures. Tim
calculated a 24mm line which is 0.944882 Inches wide. So Richard
you need to recalculate your formula using numbers for a *one inch*
line instead.

pacplyer

up periscope!, damn the torpedoes, full speed ahead! (you guys are
going to need big hangars to put all you're new toys in!) ;-)


It won't help, Pac.
The cable is not the problem.

The only thing that counts is _excess_ thrust.
That's what ever is left over after the airframe is straight and level.

Then, there is the _second_ airframe! Strangely enough, at the same
speed and altitude, the second ship will have perty near the same
drag as the tow plane.

A simple way to tell (real rough estimate) how high this rig can go
might be to pull all four go levers back to half power.
Whatever altitude you finally stabalize at is gonna be right near the
service ceiling of the combined lash up.

Just for grinn and giggles, check with NASA and see how high the
747/Shuttle piggyback arrangement cruises. 22K maybe?

And that would be balls to the wall, barely hanging in the air!

When the glider _starts_ to manouver, we goin' _down_. Fast.

Other than that, Mr. Lincoln, how was the play?

Richard

Richard Lamb wrote

Oh great! There goes my chance at getting hired!


One thing I already know about is that the Cd increases (a lot)
in the transonic range, and again (even more) for supersonic.

Problem is, the drag bill gets paid before anything else does.

So it's entirely likely that the 'zing' is gonna 'fizzle'...

Good One Richard. Sorta of a "dirty string," that's going to break in
half and wrap me up like a mummy? But wait, cranking into a turn's
going to put Mr Newton and his centrifugal force to work against that
drag, right?

Still, it will be interesting to see what the cool guys say.
(a little kissing up might keep them from laughing so hard?)

Richard

Well I chickened out in sending it to him until we massage the numbers
a little more! But I'll email the thread link to him for comic relief
later tonight after I've had a couple beers! They're going to laugh
no matter what, but hey, If you can't be good: Be Colorful! (That was
Pete Conrad's battle cry, as I understand it, and he became the third
man on the moon.)

Anyway, My pal at scaled suggested what Bill D. did he hang four GE
C90's on it. "But the wing is the thing," here as far as I am
concerned and it can do it at FL350. It's just a matter of Kevin
coming up with enough power. He's the steely-eyed jet engine man
here. If Big Fans can't cut it; then dammit, well mount some SRB's
between the inboards and the fuselage...

pac "don't wantta hear no more excuses" plyer

"pacplyer" wrote in message
om...
"Tim Ward" wrote in message snips throughout
...

No, viewed from the front, the "joined wing" looks like a big diamond.
It
attaches under the nose and at the top of the rudder. In the dismount,
the
front wing pivots down, away from the orbiter, around the rear attach
point -- which can just slide out backwards.

Good. A single piece so that you can't get asymmetrical detachment.
How would it be recovered I wonder? Remote fly down? probably it
would flutter end over end until a chute deployed? Sorry but unlike
gov ops this mission has to be profitable!

Spoilsport. If you want it to be profitable, you probably don't do manned
missions.
snippage

With the payout winch, until you run out of line, the tension in the
line is
whatever the payout winch is set for.

So you'd raise the payout winch tension up against max line tether
strength just prior to the bank maneuver?


Drag on the line: not only at the selected thickness, but there's a big
altitude difference as well. Fortunately, the thick end of the line is
up
where the air is thinner.
When you're doing the turning maneuver, the speed continuously varies
from
one end to the
It's non-linear with line length because of the caternary in the tow
line.

Looks like this post got cut off. Could you elaborate some more on
this for me? Talk more about "caternary" for me and the dynamics of
this line.

Caternary is just the six dollar word for the sag in the line. It seems to
me calculating the drag on the line has a number of variables -- variation
of density with altitude, taper of the line, and probably other stuff I
don't know about. Then the vary the curve depending on the tension, and my
head spins.



Tim Ward

snip

"Richard Lamb" wrote in message
...

Other than that, Mr. Lincoln, how was the play?

If I wasn't dead, Richard, - I was assassinated just a few minutes
ago - I'd be happy to provide a short review. Why not ask my wife?
;-)

Tim Ward wrote:


Caternary is just the six dollar word for the sag in the line. It seems to
me calculating the drag on the line has a number of variables -- variation
of density with altitude, taper of the line, and probably other stuff I
don't know about. Then the vary the curve depending on the tension, and my
head spins.

Tim Ward


Which is exactly why all I tried to address was the portion
of the cable perpendicular to the slip stream.



Stick sharply forward, opposite rudder.
When the spin stops, recover from the dive...


Richard

pacplyer wrote:

Richard Lamb wrote

Oh great! There goes my chance at getting hired!


One thing I already know about is that the Cd increases (a lot)
in the transonic range, and again (even more) for supersonic.

Problem is, the drag bill gets paid before anything else does.

So it's entirely likely that the 'zing' is gonna 'fizzle'...

Good One Richard. Sorta of a "dirty string," that's going to break in
half and wrap me up like a mummy? But wait, cranking into a turn's
going to put Mr Newton and his centrifugal force to work against that
drag, right?

If the cable breaks, it could easily go _thru_ the airframe.
That's going to be one massive piece of 'string'.

As the toe-ee swings out and up, I think IT will feel an increaded
portion of of the cable drag. At least initially.

The cable will feel the added forces, but look where it's anchored.
Newton will definately have his way with the tow plane...



Still, it will be interesting to see what the cool guys say.
(a little kissing up might keep them from laughing so hard?)

Richard

Well I chickened out in sending it to him until we massage the numbers
a little more! But I'll email the thread link to him for comic relief
later tonight after I've had a couple beers! They're going to laugh
no matter what, but hey, If you can't be good: Be Colorful! (That was
Pete Conrad's battle cry, as I understand it, and he became the third
man on the moon.)


Tell them, 'color me green' - with envy!


Anyway, My pal at scaled suggested what Bill D. did he hang four GE
C90's on it. "But the wing is the thing," here as far as I am
concerned and it can do it at FL350. It's just a matter of Kevin
coming up with enough power. He's the steely-eyed jet engine man
here. If Big Fans can't cut it; then dammit, well mount some SRB's
between the inboards and the fuselage...

pac "don't wantta hear no more excuses" plyer

Ok, I'll come around and try to help some (for a change).

Put the nose down (WAY down!) before the sling manouver starts.
Then wait for the 'colorful' language to commence!
Shouldn't take long.


Richard
(colorful enough?)

Felger Carbon wrote:

"Richard Lamb" wrote in message
...

Other than that, Mr. Lincoln, how was the play?

If I wasn't dead, Richard, - I was assassinated just a few minutes
ago - I'd be happy to provide a short review. Why not ask my wife?
;-)

I think she had the good sense to stay on the ground for this one...

But I take your point.


Richard