Space Elevator

In article ,
(pacplyer) wrote:

The airplane is op specs limited to +2.5 g's and -1.0g. Not worried
about stalling a 747. There's so much mass the tow rope would break
before any instant degradation would show up on the airspeed
indicator. Airspeed trends take A LONG LONG time to develop on this
bird. It's not like anything you've every flown before. I use the
analogy of surfing on a mountain of metal to describe a visual
approach on the 74 because the previous vector it was on before you
made the change [control input] is what it will be on for a number of
seconds. By the
time you've pulled off the thrusters because you're too fast, the huge
inertia will keep it accelerating.


Alan Baker wrote

Read a physics text and then say that again...



Inertia: a property of matter whereby it remains at rest or continues
in uniform motion unless acted upon by some outside force.

The uniform motion in my example was acceleration. In this bird it

Acceleration is not uniform motion.

takes longer for the opposing force: drag to arrest the motion. Due
to it's large Kinetic Energy. Can you be more specific? What part do
you disagree with?

That an object will keep accelerating in the absence of an external
force on the object. Inertia will keep it moving at a constant velocity,
but it won't keep it accelerating.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

Richard Lamb wrote in message ...
I think I understand what you were saying, but...?

I was addressing the 'crack the whip' idea that someone thought
might could be used to toss the tow-ee into orbit.

First, the tow line 'can't' break for this maneuver, or the whole
idea 'breaks down' with it. But we'll come back to that after the
commercial.

Sure, you hope for a smooth intentional release. "Can't break?"
Anything can happen in flight test. :-) I believe designing for the
line to break before high momentary loads are transferred through the
aft pressure bulkhead area is an important engineering goal: You don't
want the keel-beam of the aircraft to be pulled apart or
stringers/longerons to stretch and allow the pressure bell to blow
like it did at JAL. They lost all four hydro systems and crashed.
There is no manual reversion system (cables) in the whale. All four
hydro systems run to the elevators in that area.


Next, remember that we want to be as high as practically possible.
VERY high density altitude?

Same kind of idea: High *Pressure Altitude*. Out of 17,000 (in the
cont.U.S.) everyone switches over to Standard 29.92 so the term
Density altitude is not used (since the pressure part of the equation
is constant.) ISA+/- (non-standard) temperature becomes important for
climb/cruise performance and mach number. Our actual, true altitude
above MSL varies from day to day at the same flight level.


Stall speed at extreme altitude would not the benign 180 knots,
but something appreciably higher (can you help me out with the
high altitude 747 data - actual stall speed at FL 450?).

Just cause you asked, I spent an hour digging through boxes and
finally found my "buffet boundry" charts. Initial Low and High Speed
Buffet (standard temp) is dependant on aircraft weight and G
load/bank. But you're right, at FL450 you are up in "coffin corner"
and on the straight and level chart (1G) at 400,000lbs the LSB (low
speed buffet) is like I remembered at 178kts. HSB (high speed buffet)
is VMO/MMO (.92 mach)

Now let's take our theoretical weights (subject to tweaking.)
Empty Weight: ~380,000lbs
Skinny Fuel: ~70,000lbs (30k up, 10 dwn, 10 aprch, 20k res)
Winches and 20km tether: ~100,000lbs
Drag ‘weight' ~30,000lbs (a complete WAG till somebody gives me a
#)
Total 747 T/O WT ~580,000lbs

Orbit One plus fuel and three plastic pax: 200,000 lbs


[note: the space vehicle with swept glider wings really weighs nothing
since Tim Ward promised us that it will lift itself after t/o. ;-)
So we're at the modest t/o weight of 580,000 (lot's of margin here
since the 747 gross is 820,000.)

So we take off with Orbit one in tow and arrive an hour later, fat
dumb and happy at FL450 again. (which must be done in smooth air at
GA thrust since we have no upset margin) The 1G chart yields a Low
Speed Buffet onset of 208kts and a high speed mach buffet of 251. In
other words: we stall outside that range. No sweat.

But you hotdog rocket jocks aren't going to be happy in straight and
level at 1G! You're going to want old "Hand Solo" Cargo Dog here to
do some hair brained "deathwhip" maneuver at a 45 degree bank and risk
my pink little ass in a flat spin if the ****ing cable breaks or if it
pulls the Jesus rivets out of the goddam tail (in which case the cabin
blows taking out all elevator control on the way out! What a ****
poor deal! You rocket jocks get all the glory and I crash and burn.
*******s!

So just for you *******s here's the 45 degree bank chart at FL450 and
1.41G's: XXX to XXX…… **** what does that mean? I'm going to have
little X's in my eyes? I'm going to fall out of the sky and do a
supersonic recovery like China Airlines did at SFO? So we can't do a
45 degree bank over 400,000lbs (that's empty) or else we do the
****ing Hoot Gibson High Dive…Gulp!

Damn we can only do a 30 degree bank at this weight and live; let's go
back to that chart and not embarrass ourselves in front of CNN:
FL450, 500,000lbs max (damn,) 1.15G, 30 degrees bank equals 229kts
low speed stall, and 238kts high speed mach stall. That's only a
nine knot range! I can't do that! I can only hold a tolerance of
about plus or minus one inch on the gauge! You crazy "Jet-eyes" are
trying to get me killed! I quit!

pacplyer – over and out!

"pacplyer" wrote in message
om...

Inertia: a property of matter whereby it remains at rest or
continues
in uniform motion unless acted upon by some outside force.

The uniform motion in my example was acceleration.

Disclaimer: It's 5:30AM. I'm an engineer, not a physicist. BUT...

Acceleration **by definition** is **not** uniform motion! ;-)

pacplyer wrote:


Damn we can only do a 30 degree bank at this weight and live; let's go
back to that chart and not embarrass ourselves in front of CNN:
FL450, 500,000lbs max (damn,) 1.15G, 30 degrees bank equals 229kts
low speed stall, and 238kts high speed mach stall. That's only a
nine knot range! I can't do that! I can only hold a tolerance of
about plus or minus one inch on the gauge! You crazy "Jet-eyes" are
trying to get me killed! I quit!

pacplyer – over and out!

Thanks for the info, Pacman.

And for the correction - Pressure altitude - not density.

Aw heck, the U-2 guys did it tighter than that for hours on end.
Stall at 90 knots (indicated?) and mach buffet sets in at 95 knots???

(Reality really sucks, don't it.)

Richard

Sorry dude, I wasn't refering to the release itself.
Just the problems associated with _getting_ there.

I'll refer you to Pacman's post (and conclusions) with the
gentle reminder that he _does_ know what he's talking about
as opposed to my questionable speculation).

Also, Keith gave us some first hand info on what is actually
involved in tow ops - something I've never even tried to do.

PAWKI is a mean and evil term that stands for "Physics as we know it".

Please don't be too upset with the 'ain't gonna work' mentality
you find here. The guys on this group are a different kind of
dreamer. Fantasy, with a hard dose of reality blended in.

You have to expect that attitude from people who actually BUILD
and FLY their own dreams.

I once heard it said that we don't really build airplanes.
We build bridges - between dreams and reality.

Well, I gotta go clean up my messy shop now.

Later.

Richard

"Richard Lamb" wrote in message
...
Sorry dude, I wasn't refering to the release itself.
Just the problems associated with _getting_ there.

I'll refer you to Pacman's post (and conclusions) with the
gentle reminder that he _does_ know what he's talking about
as opposed to my questionable speculation).

Sure. I never really thought a stock 747 would work for an idea as extreme
as this one. I was actually thinking of a 747-sized canard design -- gets
all the control surfaces out of the way, makes hooking to the CG easier --
and so on. From Pac's information, it will probably have to have a lower
wing loading and higher aspect ratio if we want it to tow at FL450.


Also, Keith gave us some first hand info on what is actually
involved in tow ops - something I've never even tried to do.

Oddly enough, I have. I aerotow my sailplane on weekends. I used to
aerotow and ground launch hang gliders with both straight auto tow (long
line with a tensionmeter), and the payout winch. Out at El Mirage dry lake,
in the 80's, we got six thousand feet of line out one evening.
That was just to see if we could do it. The sag in the line made the
release altitude not as high as you might think. There were diminishing
returns.


PAWKI is a mean and evil term that stands for "Physics as we know it".

Please don't be too upset with the 'ain't gonna work' mentality
you find here. The guys on this group are a different kind of
dreamer. Fantasy, with a hard dose of reality blended in.

I'm not upset. But I do find it interesting that some posters have argued
against concepts I never proposed: e.g. 8:1 speed ratios between the towed
and towing aircraft. The use of a stock 747.
Of course PAWKI limits the possible. Right now, we _know_ that it's
possible to tow a smaller aircraft with a 747-sized aircraft. It's been
done six times with a thousand foot tow line.
That gives us one data point. What _are_ the limits imposed by PAWKI? I
doubt that it's a tow line of 1001 feet. How high could you reasonably
expect to get the towed vehicle on a CG to CG aerotow? How much advantage
is that for a rocket launch? I don't know, but it's kind of interesting to
speculate.

Tim Ward

You have to expect that attitude from people who actually BUILD
and FLY their own dreams.

I once heard it said that we don't really build airplanes.
We build bridges - between dreams and reality.

Well, I gotta go clean up my messy shop now.

Later.

Richard

"Tim Ward" wrote in message
...

Sure. I never really thought a stock 747 would work for an idea as
extreme
as this one. I was actually thinking of a 747-sized canard design -- gets
all the control surfaces out of the way, makes hooking to the CG easier --
and so on. From Pac's information, it will probably have to have a lower
wing loading and higher aspect ratio if we want it to tow at FL450.


Heck, if you want to build a million pound homebuilt with, say, eight GE
C-90's with 110,000 pounds thrust each, why not resurrect the Northrop B-49
idea. That way the towrope could be attached exactly on the CG with nothing
behind it.

Fly the tow formation to FL400 and then zoom climb the spacecraft ala a
winch launch as the tug pilot firewalls all eight.

BTW, a million pound breaking strength carbon nanotube tow rope might be
only .250" in diameter so not too much drag there.

Bill Daniels

Depending on how you look at it, your could fly/drive your RV on solar
energy.

Plants store solar energy in 2 forms:
1) Sugars
2) Oils

Put one of new fangled turbo diesels in your RV and go take it out on
plant oils. Or... ferment the sugars, make alcohol, burn it in your
engine and call yourself a kamikazi. Carbon captured, carbon
released.

But we're not out of mineral oils yet, they're still harvesting in
order of cost. Its still cheaper for oil companies to use your tax
money/kids to fight wars to provide cheaper access to more easily
recovered/refined reserves.



(BlakeleyTB) wrote in message ...
Why don't we just pile the cash up and burn it...wouldn't that be much
cheaper???

What kind of idiots would give them 2.5 million dollars to research this and
NASA gave 1/2 a million.

I wish NASA and congress would take about 10% ofNASA's budget and invest in
researching affordable alternative energy uses that EVERYONE can afford!!!
Solar, etc type of "stuff"......wouldn't you love to be able to fly your RV-6
on the energy of, heck, from the stars??? Solars cells that can pik up energy
from the stars, not to mention our sun. Or affordable batteries for vehicle
that will run your car, aircraft, boat for 800 miles or more at speeds we know
today. I know, I know...this is some BIG pipe dream...but heck, we've gone to
the moon and we perform body transplants EVERYDAY..in fact, I have both
transplanted corneas......if we can do stuff like this..why can't we take some
of what I believe is wasted money and research something that ALL OF US can
utilize and especially afford??? I want to say "SCREW YOU" to OPEC, etc and
just get out in my car and go anywhere I want in something that's not
polluting our skies.

Oh well, just an idea...I can dream, can't I.

Alan Baker wrote in message ...
In article ,
(pacplyer) wrote:

The airplane is op specs limited to +2.5 g's and -1.0g. Not worried
about stalling a 747. There's so much mass the tow rope would break
before any instant degradation would show up on the airspeed
indicator. Airspeed trends take A LONG LONG time to develop on this
bird. It's not like anything you've every flown before. I use the
analogy of surfing on a mountain of metal to describe a visual
approach on the 74 because the previous vector it was on before you
made the change [control input] is what it will be on for a number of
seconds. By the
time you've pulled off the thrusters because you're too fast, the huge
inertia will [make it seem like] it's accelerating.


Alan Baker wrote

Read a physics text and then say that again...



Inertia: a property of matter whereby it remains at rest or continues
in uniform motion unless acted upon by some outside force.

The uniform motion in my example was acceleration. In this bird it

Acceleration is not uniform motion.

takes longer for the opposing force: drag to arrest the motion. Due
to it's large Kinetic Energy. Can you be more specific? What part do
you disagree with?

That an object will keep accelerating in the absence of an external
force on the object. Inertia will keep it moving at a constant velocity,
but it won't keep it accelerating.

You're right. It would be *decellerating* abeit at a very slow rate of
decay. My error. Thanks Allen. I've modified above in [brackets] for
clarity. But I swear, when I was brand new in the box it really
seemed like it was accelerating away from my intended Vref speed even
after slamming back to idle! The snickers from the back of the
simulator made it seem to accelerate even more!

pac

I missed this post of yours Tim, since I was in the middle of a "High
Anxiety" spiral/flat spin flashback. O.K. I'll come back to work for
you guys if you promise me: no banks over 30 degrees up there in the
tow/tug plane and no ‘walking the dog' type stunts with the cable.
(now I see why Rutan built his own high-G' White Knight "toss"
airplane. He was able to release at up to 90 degrees bank if he
wanted to.) But we're going for Low Earth Orbit here, so getting to
the ‘barber pole' (VMO/MMO; airspeed limit pointer) is probably
important. I figured on a tow plane release weight of 550,000 lbs in
a 30 degree bank, which is 50,000 too heavy to prevent upset (damn.)
Also we only get five minutes of GA thrust to get up to MMO (Mach Max
Operating) after leveling off at FL450 or we may start cooking some
engines. "If I give you any more Captain, she going to blow!"


"Tim Ward" wrote the following are excerpts
from his longer post earlier in the thread

spacecraft's best rate of climb speed, then the turning maneuver isn't
required.
This is a booster. It just happens to get its oxidizer at 45000 feet. The
assumption is that there is enough excess thrust on the 747 to overcome the
drag on the towline and whatever is attached to it. If that means extra
engines, that's okay with me.

You may be right about the need for bigger engines (or more of them;
hanging engines will mean re-certifing the airplane; and that's going
to run the cost up by tens of millions.) I don't think a -400's going
to work because; the tailplane is probably smaller; this was a trick
used by later designs to increase range. They pump gas back to the
smaller horz stab to get a more aft CG (equals better range.) It's
closer to upset than a -200 airframe AFAIK.

That drag reduces the 747's speed by some amount, causing the 747 to
have to fly at a higher angle of attack (AoA) already.

I would expect it to require quite a lot of additional power. That's why I
originally suggested extra engines on the 747. I wasn't envisioning it as a
dynamic maneuver. More like impedance matching. The 747 is buzzing around
at a relatively low altitude. The spacecraft is up really high (we hope),
and so it's minimum sink speed is probably very high, because there's durn
few air molecules bumping into it. There's a constant force between the two
aircraft, but the spacecraft probably needs to be flying faster. By
turning, the 747 can fly at some reasonable speed, and the spacecraft can
fly at a higher speed.


This methodology sounds very promising. I'm a little worried about
the centrifugal recoil of the cable after release, but maybe the
payout winch will absorb some of it? That lanyard's gotta sling
across down somewhe "Break left! Cable at Two O'clock!" Don't
need a string tangled up in the Slats or gear on approach either. ;-)

No, there's a constant tension. This is not difficult with a payout winch,
since the mechanism pays out cable above a certain tension, which lowers the
tension, so it slows down the payout, raising the tension... it stays
pretty constant. The line length changes.


Pretty clever. I like it.

So we get to the disconnect point.

ALL the energy transferred to the kite comes from the 747.
All of it.
All of that energy is removed (just as quickly?) from the 747.

No. You have a 747 being slowed by cable tension. (Dammit! the cable has
to carry the aerodynamic drag as tension-- so that _is_ something I
overlooked. I figured on cable weight and the tow force, but the drag on the
cable adds another load.)
The kite's energy is energy of position, which it's already got. When the
cable is released, or breaks, the 747 is going to accelerate, not slow. An
instant additional 100,000 lbs of thrust. (or reduction in drag) It'll
still be a kick in the butt, but it will be speeding the 747 up, not slowing
it down.

And at some critical point, big momma finds herself below critical
flight speed and above critical AoA, and things could get a little
- critical?
Now in reality, all of that could probably be dealt with. Some of
those perimeters would define the limits of this kind of operation.

From a PAWKI standpoint, it's probably cable tensile strength.

Probably. This basically puts a limit on how long the towline can be.


But if that held, I'd suspect this event is going to feel a lot like
catching a Three Wire - at FL 450.

I think it would be more like a cat shot -- though I haven't experienced
either one.

Not sure it's the same, but a 74 jock in training changes thrust by
nearly 100,000 lbs on empty go-arounds from idle and I'm here to tell
you: it's a frickin earthquake in the air. You commonly bust your
level off altitude as a student, even after you've slammed the thrust
levers to idle. There's just too much power to weight. Those Big
Fans wagg on the pylons like a dog's tail. It scared the **** out of
me riding in the supernumerary area (the hump) while letting the other
student do his bounces in SMF on "MLO" one of our two PAX birds.
Without the weight of 531 other bodies, belly freight and large fuel
load, a go-around is a violent maneuver. Looking down out the window
from the upper deck at the inboard engine: one second you're looking
into the intake, the next you can only see the outer engine cowling,
the next your looking into the engine inlet….. I was just waiting for
a loud SNAP! of the pylon, since I thought: "NO Way would they design
it to do THAT!

So I think the airplane can handle a 100,000lb change in
acceleration/deceleration if you can time release to coincide with
idle pwr, speed brakes and pull up. Actually the aircraft pitch up
from the down moment at the tail attatch point would help in
preventing overspeed stall. Remember at 30 degree bank, I've only got
nine knots to play with.

Think I'll call in sick on that day. Better call Bob Hoover to take
that flight for me! If he's too old than call one of those U2 guys.

On a commanded release, you could gradually decrease the tension on the
payout winch over a number of seconds prior to cutting loose, and you might
be able to throttle down at a similar rate, but if the line breaks, you're
gonna speed up.

Tim Ward


Any way you slice it, it's going to be an interesting ride for both
vehicles. But as Chuck Yeager once said after drinking whiskey the
night before and falling off a horse while drinking and driving and
busting his ribbs and showing up for the mission the next morning and
lighting the candle: "I don't advise it mind you, but it *can* be
done."

pac "no wonder these guys are all on the bottle" plyer