Space Elevator

Tim Ward wrote:

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?).

I actually want to fly the 747 pretty fast. If its speed at 45000 feet
is
fast enough so that the spacecraft's airspeed at 100000 feet is at the
spacecraft's best rate of climb speed, then the turning maneuver isn't
required.

pacflyer gave a 1g speed range for the 747 at 45,000 ft and 580,000 lb of
208 kt to 251 kt. I'm assuming those numbers are in KCAS. If so, that
works out to 444 KTAS to 524 KTAS under standard day conditions.

At 100,000 ft, those same true airspeed values work out to 56 KCAS to 68
KCAS. The equivalent airspeed, which is what the wing sees, is a bit
lower at 52 KEAS to 61 KEAS. That means the orbiter needs to have a very,
very low wing loading, which doesn't seem compatible with a re-entry. And
it has to support the weight of the tether too. I'm not sure this idea
will work, unless we can get a much faster tow aircraft.

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

Ahh... at last someone who did what I was too lazy to do... the numbers.
I knew the indicated airspeed at 100,000 feet would be low.

If I can ask a favor, what is the equivalent airspeed at Mach 1 at 100,000
feet, standard atmosphere?

And hey, I've already figured on dropping 20 km of tether, what's a wing
between friends?

Tim Ward

I'm not usually intentionally mean to newbies (well, unless they talk
like tort lawyers wanting a cheap helicopter. And that was more for fun
than meanness).

And I'm not being mean now, Tim. Even if it sounds like it...

The only lazy part here is being too lazy to learn the basic subject
matter before pontificating about it.

The _correct_ question would have been, "What the heck does equivalent
airspeed mean, why is it important, and how do I calculate it?"

I had intended to come back to this discussion and ask if you already
knew that your orbiter was a swing wing design.

But Kevin beat me to it. (From the 3 point line - nothin but net!)


Richard Lamb

"Math - It's not just for sissies any more"

On Thu, 01 Jul 2004 08:02:07 -0700, Tim Ward wrote:


If I can ask a favor, what is the equivalent airspeed at Mach 1 at 100,000
feet, standard atmosphere?


Mach 1 at 100,000 ft is 67 KEAS, rounded to the nearest knot. You
probably need to get to at least Mach 3 to have enough EAS to work with
(201 KEAS), and that is probably even on the low side for speed.
The highly swept shapes that favour reentry generally tend to be quite
draggy at low speed. Just as an example, the Mirage III has a 60 deg
delta wing. It has a speed for min drag of around 300 KEAS at typical
operating weights. It was a real pig at 200 kt. It didn't really start
to fly crisply until you got it up over 400 kt.

--
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 Mon, 28 Jun 2004 20:23:11 -0700, Tim Ward wrote:


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?).

I actually want to fly the 747 pretty fast. If its speed at 45000 feet is
fast enough so that the spacecraft's airspeed at 100000 feet is at the
spacecraft's best rate of climb speed, then the turning maneuver isn't
required.

pacflyer gave a 1g speed range for the 747 at 45,000 ft and 580,000 lb of
208 kt to 251 kt. I'm assuming those numbers are in KCAS. If so, that
works out to 444 KTAS to 524 KTAS under standard day conditions.

Goddammit. That's not right. I interpolated backwards on both
numbers. The 1g chart only allows a max weight of 550,000 lbs for low
speed buffet of 218kts and high speed of 242kts. and this being test
pilot land, I was trying to interpolate another 30,000 lbs into the
equation (for total of 580K: which is just outside the envelope.)
Sorry Guys. I should have ADDED the ten knots to the low speed number
and SUBTRACTED nine on the high speed mach buff number. (hence the
term coffin corner; range narrows as you go up.) So 580K at FL450
would be: 228-233 interpolated out of the envelope. Or you can just
go with the stock 550,000 lbs numbers of 218-242.

So could you recalculate the below values Kevin? I promise not to
play test pilot any more!

At 100,000 ft, those same true airspeed values work out to 56 KCAS to 68
KCAS. The equivalent airspeed, which is what the wing sees, is a bit
lower at 52 KEAS to 61 KEAS. That means the orbiter needs to have a very,
very low wing loading, which doesn't seem compatible with a re-entry. And
it has to support the weight of the tether too. I'm not sure this idea
will work, unless we can get a much faster tow aircraft.

Detachable 200' U-2 type Glider Wings? ;-) Well U-2's fly at low TAS
speeds up there don't they? Hence my detachable 200 ft glider wing
idea. Let's see if I understand Tim Ward's logic in getting the
vehicle to 100,000 ft. I might be wrong, but isn't the purpose of
this to just get the vehicle out of the "Max Q" area of the
atmosphere? Building up to "Max Q" is were space vehicles burn most
of their propellant from the first stage isn't it? Do we really care
what speed it's at as long as we can initiate Orbiter burn sequence up
high? (I agree, high altitude AND high speed would be better.)

Now if you want high tow plane ground speed so that it takes less
"Orbit One"-fuel for orbital insertion, the old jet adage is: "You
stay down low if you want to go fast." Power, wing performance, and
curvature of the earth is "more better." If we stayed down at FL 350
we'd have to drag another couple of miles of tether cable but: we'd be
able to fly at a 550,000 lb weight AND do a 45 degree bank (1.41g.)
Low speed stall buffet would start below 249kts ind/cas . High speed
mach buffet would not happen until the absolute top certified speed of
the aircraft .92 Mach (I think that's just about 305kts IAS/CAS in
that bank/alt by interpolation; chart only says VMO.) A 90-year-old
woman could hold this range no sweat in the very forgiving 747. So is
that about 518 kts IAS/CAS? (somebody check my math please.) But our
ground speed will be higher down low, right? Isn't that what we are
really after for orbit insertion: high tow-plane ground speed relative
to the earths surface? Having trouble with this cuz computers figure
this out for us all the time now!

So I guess a trade off is going to emerge between tow plane ground
speed/bank advantage at lower altitudes and extra cable length drag.
Now that I've reviewed the charts; it seems like at FL 450 we're at
the extreme limits of the stock 747-200F with P&W Q powered engines.
It appears to me that maybe we need a lot more thrust if we're going
to do this on a routine basis at FL450. Someone mentioned using GE
C-90's, of which one was hung for testing on the 74 already. Four of
those engines would make getting up to .92 mach easy, but I'm sure
they ain't cheap (10 mil ea?). Maybe Burt would do it anyway and just
fly it under experimental rules since no paying passengers are aboard
that vehicle? This would save tens of millions in re-engine
certification costs.

The reason for me obsessing with the 747 is two-fold. The first is
low cost (I want to say about $10,000 an hour is typical op cost in
some fleets. Does that sound right Kevin?) Of course there are a lot
of variables but if Tim's slingshot idea would work, one hour of climb
time has got to be many many millions of dollars cheaper than doing a
bargain launch-pad t/o as Ron W. was suggesting (I think he said it
could be 20 mil.)

The second reason for the using "the whale" is simplicity. There's
almost no development needed of the first stage at all (beyond winch
fab and tst and possible aircraft re-engining. The 747 is a known
commodity and last I kept track, over 2000 have been built. Parts,
engines, crews, mechs, techs are plentiful at LAX and Edwards. This
system could be sold overseas to other governments; so the project is
potentially profitable. At 1g S&L flight at FL350 the 74 can be at
750,000lbs at M.92 (wing limit); so we pay a big capacity price to fly
it at FL450 or in a 45 degree bank at FL350. Down at FL350 level
Straight and Level means big Low Earth Orbit payloads, (since at light
weights: huge power is available to overcome huge drag.) and this
means Mr Allen and his early shareholders may get rich from the
endeavor.

Still waiting for a RAH engineer to take a guess of the drag
coefficient involved.

Scottie… how much longer for an answer! The frog Cling-ons are going
to show up with their bird of commercial prey A380 any minute now! We
have to get off this planet before they start cutting into our
business!

pac "push em till they come apart" plyer

On 1 Jul 2004 11:39:07 -0700, (pacplyer) wrote:

Kevin Horton wrote in message ...
On Mon, 28 Jun 2004 20:23:11 -0700, Tim Ward wrote:

Before we go to much further, I think it would be appropriate for the
OP to send out a dated notebook with original facts, figures and
drawings to someone who can sign it "read and understood on this
date".

It's known as prior art. Also establishes a date certain should you
wish to patent the idea.


--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.

(pacplyer) wrote
Now if you want high tow plane ground speed so that it takes less
"Orbit One"-fuel for orbital insertion, the old jet adage is: "You
stay down low if you want to go fast." Power, wing performance, and
curvature of the earth is "more better." If we stayed down at FL 350
we'd have to drag another couple of miles of tether cable but: we'd be
able to fly at a 550,000 lb weight AND do a 45 degree bank (1.41g.)
Low speed stall buffet would start below 249kts ind/cas . High speed
mach buffet would not happen until the absolute top certified speed of
the aircraft .92 Mach (I think that's just about 305kts IAS/CAS in
that bank/alt by interpolation; chart only says VMO.) A 90-year-old
woman could hold this range no sweat in the very forgiving 747. So is
that about 518 kts IAS/CAS? (somebody check my math please.)

Curses. I meant to ask: is that "about 518 kts TAS?" (somebody check
my math please.) NOT IAS/CAS! I'm helpless without a secretary! And
I'm helpless anymore without a TAS readout on the INS. To answer
Kevin's question on the charts: IIRC, it was explained to me in school
that CAS and IAS through the magic of 747 CADC's (central air data
computers) are pretty much the same numbers. The buffet boundry
tables don't say CAS or IAS; but I'm sure they are designed to be
flown off directly. These tables I'm quoting are generic; they were
compiled for the -100 and -200 airframes and engine types in our
fleet. OTOH, I remember seeing CAS data placards on some 74's under
the wiskey compass. I remember wondering if they were left over from
some previous airline. But Boeing would have more "specific to a
certain model" envelopes to draw from if Rutan ever pursued this idea.

pac - out

On Thu, 01 Jul 2004 12:39:07 -0700, pacplyer wrote:

Kevin Horton wrote in message
...
On Mon, 28 Jun 2004 20:23:11 -0700, Tim Ward wrote:


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?).

I actually want to fly the 747 pretty fast. If its speed at 45000
feet is fast enough so that the spacecraft's airspeed at 100000 feet
is at the spacecraft's best rate of climb speed, then the turning
maneuver isn't required.

pacflyer gave a 1g speed range for the 747 at 45,000 ft and 580,000 lb
of 208 kt to 251 kt. I'm assuming those numbers are in KCAS. If so,
that works out to 444 KTAS to 524 KTAS under standard day conditions.

Goddammit. That's not right. I interpolated backwards on both numbers.

Good thing airlines use tabular data so you don't have to interpolate
Vref. Sure hate to go 10 kt the wrong way on that one

The 1g chart only allows a max weight of 550,000 lbs for low speed buffet
of 218kts and high speed of 242kts. and this being test pilot land, I was
trying to interpolate another 30,000 lbs into the equation (for total of
580K: which is just outside the envelope.) Sorry Guys. I should have
ADDED the ten knots to the low speed number and SUBTRACTED nine on the
high speed mach buff number. (hence the term coffin corner; range narrows
as you go up.) So 580K at FL450 would be: 228-233 interpolated out of the
envelope. Or you can just go with the stock 550,000 lbs numbers of
218-242.

So could you recalculate the below values Kevin? I promise not to play
test pilot any more!

If you've got 1 g buffet numbers of 228-233 at FL450 at 580,000 lb, you
don't have a practical envelope to do this mission. You'd be in buffet
the first time someone sneezed. So, I'll use 550,000 lb.

218 KCAS at FL450 equals 463 KTAS, which equals 54 KEAS at 100,000 ft.
242 KCAS at FL450 equals 508 KTAS, which equals 60 KEAS at 100,000 ft.

This still isn't anywhere close to a practical envelope for the orbiter.


At 100,000 ft, those same true airspeed values work out to 56 KCAS to 68
KCAS. The equivalent airspeed, which is what the wing sees, is a bit
lower at 52 KEAS to 61 KEAS. That means the orbiter needs to have a
very, very low wing loading, which doesn't seem compatible with a
re-entry. And it has to support the weight of the tether too. I'm not
sure this idea will work, unless we can get a much faster tow aircraft.

Detachable 200' U-2 type Glider Wings? ;-) Well U-2's fly at low TAS
speeds up there don't they? Hence my detachable 200 ft glider wing idea.
Let's see if I understand Tim Ward's logic in getting the vehicle to
100,000 ft. I might be wrong, but isn't the purpose of this to just get
the vehicle out of the "Max Q" area of the atmosphere? Building up to
"Max Q" is were space vehicles burn most of their propellant from the
first stage isn't it? Do we really care what speed it's at as long as we
can initiate Orbiter burn sequence up high? (I agree, high altitude AND
high speed would be better.)

Well, the orbiter needs to have enough speed to be above stall speed. The
drag will be very high if it is too close to stall. So 100,000 ft is way
too high to tow the orbiter, if we have a subsonic tow aircraft.


Now if you want high tow plane ground speed so that it takes less "Orbit
One"-fuel for orbital insertion, the old jet adage is: "You stay down low
if you want to go fast." Power, wing performance, and curvature of the
earth is "more better." If we stayed down at FL 350 we'd have to drag
another couple of miles of tether cable but: we'd be able to fly at a
550,000 lb weight AND do a 45 degree bank (1.41g.) Low speed stall buffet
would start below 249kts ind/cas . High speed mach buffet would not
happen until the absolute top certified speed of the aircraft .92 Mach (I
think that's just about 305kts IAS/CAS in that bank/alt by interpolation;
chart only says VMO.)

I don't know how position error is handled in the 747 Classic. M0.92 true
works out to 530 KTAS and 318 KCAS at FL350. But there may be a bit of
position error in the machmeter, so your 305 KCAS could be right too.
If you held a 45 deg bank turn, I think your turn radius would be just
under 25,000 ft (if I didn't screw this up - I've just had a couple of
beer). So, if you had a 20 km tether, and the orbiter was at 75,000 ft, I
figure his radius of turn would be about 77,000 ft, and he would be going
about 3.1 times as fast as you, or a TAS of about 1640 KTAS or about 350
KEAS. This might be achievable.

A 90-year-old woman could hold this range no sweat
in the very forgiving 747. So is that about 518 kts IAS/CAS? (somebody
check my math please.) But our ground speed will be higher down low,
right? Isn't that what we are really after for orbit insertion: high
tow-plane ground speed relative to the earths surface? Having trouble
with this cuz computers figure this out for us all the time now!

So I guess a trade off is going to emerge between tow plane ground
speed/bank advantage at lower altitudes and extra cable length drag. Now
that I've reviewed the charts; it seems like at FL 450 we're at the
extreme limits of the stock 747-200F with P&W Q powered engines. It
appears to me that maybe we need a lot more thrust if we're going to do
this on a routine basis at FL450. Someone mentioned using GE C-90's, of
which one was hung for testing on the 74 already. Four of those engines
would make getting up to .92 mach easy, but I'm sure they ain't cheap (10
mil ea?). Maybe Burt would do it anyway and just fly it under
experimental rules since no paying passengers are aboard that vehicle?
This would save tens of millions in re-engine certification costs.

The reason for me obsessing with the 747 is two-fold. The first is low
cost (I want to say about $10,000 an hour is typical op cost in some
fleets. Does that sound right Kevin?)

No idea. I work in the flight test world, so I don't have to bother
myself with the bean counters (no FAs or pax complaining if I go over 30
deg of bank either). Fuel cost is fairly easy to calculate, but I don't
know what maintenance and other costs are.


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

"Dillon Pyron" wrote in message
...
On 1 Jul 2004 11:39:07 -0700, (pacplyer) wrote:

Kevin Horton wrote in message
...
On Mon, 28 Jun 2004 20:23:11 -0700, Tim Ward wrote:

Before we go to much further, I think it would be appropriate for the
OP to send out a dated notebook with original facts, figures and
drawings to someone who can sign it "read and understood on this
date".

It's known as prior art. Also establishes a date certain should you
wish to patent the idea.

Well, as the OP, it's just a goofy idea I had. I'll put my rights to it in
the public domain. Google should archive it well enough.
OTOH, I wouldn't mind attending the launch :-)

Tim Ward



--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.

"pacplyer" wrote


Detachable 200' U-2 type Glider Wings? ;-) Well U-2's fly at low TAS
speeds up there don't they? Hence my detachable 200 ft glider wing
idea. Let's see if I understand Tim Ward's logic in getting the
vehicle to 100,000 ft. I might be wrong, but isn't the purpose of
this to just get the vehicle out of the "Max Q" area of the
atmosphere? Building up to "Max Q" is were space vehicles burn most
of their propellant from the first stage isn't it? Do we really care
what speed it's at as long as we can initiate Orbiter burn sequence up
high? (I agree, high altitude AND high speed would be better.)


pac "push em till they come apart" plyer

A while back in this thread, it was kicked around, about where the tether
should be attached to the tow plane. I think what I am about to say has not
been kicked about, but who knows; so much has been kicked about! g

How about taking off with the orbiter on the 747's back, a-la shuttle
transporting? When the duo is at altitude, the tether could start to reel
out, with the orbiter pulling it out. This would do two things; less drag
(no tether) while getting to altitude, and secondly, the wings on the
orbiter could be designed to work best _at altitude_.
--
Jim in NC


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"Morgans" wrote

A while back in this thread, it was kicked around, about where the tether
should be attached to the tow plane. I think what I am about to say has not
been kicked about, but who knows; so much has been kicked about! g

How about taking off with the orbiter on the 747's back, a-la shuttle
transporting? When the duo is at altitude, the tether could start to reel
out, with the orbiter pulling it out. This would do two things; less drag
(no tether) while getting to altitude, and secondly, the wings on the
orbiter could be designed to work best _at altitude_.


Geez Morgan,

You are good for something after all! ;-) I think you just earned
your pay for the week. One of the things I didn't want to bring up
was wake turbulence on take off; since I knew it would probably kill
the project. Even heavy jets wait at least two minutes before
following the jumbo on t/o; to give the house-sized wake vortices time
to roll off the runway. Otherwise you wind up on your head if you're
light, and temporarily out of control even if you're a 727. They are
very likely to bounce a glider wing into pieces on the t/o attempt;
but I don't have any experience in glider ops, so I was just living in
fear on that one. Your idea solves that and the initial cable drag
problem, and it solves the cable tether attachment position problem as
well. Now we can pay out Cable near 747 CG through the roof with
élan! With up to three 747 pacs to pressurize with, we could leave a
large hole in the roof, no sweat. O.K Jim, you can ride along in the
jumpseat as a technical advisor.

We're going to have to get the waitress to bring us some more cocktail
napkins to write on…

pac

That's why enjoy discussing experimental space solutions on an
un-moderated homebuilt aircraft NG like RAH. I don't think a
moderator could be well versed enough on all the disparate backgrounds
necessary to plan something like this out. He just couldn't make good
decisions on who to post and who to block. Take Tim for example.
This guy has actually taken a TRUCK and surfed behind it, in tow, with
his hang gliders! You just can't buy better real world experience
than that.

So what do we have now? The OrbitOne vehicle on top of the tow
aircraft courtesy Jim Morgan's good idea. It just has to clear the
74 vertical stab at release; but the Space Shuttle "Enterprise" test
vehicle proved that can be done. I like Tim Ward's two wing
component idea: an SS1 type "re-entry" inner wing with a 100ft
swingable detatchable glider wing on each tip to be deployed after
detach from the mother ship?….. Both these RAH built wings would be
shed upon reaching 75,000-100,000 ft. And Kevin Horton calculated
that we can get over 3 times the steady state speed with Richard
Lamb's snap-whip maneuver (a 45 degree bank initiated by the 747
towship at .92mach; ~310TAS at FL350….) This gives Orbit One at
75,000ft a leg up on escape velocity as it blows the cable and lights
the Orbital Insertion rocket engine….

There just may be enough brain power on this NG to put together a
computer model!

Here's the 680k t/o weight 747 tow-ship vertical profile as I see it
so far: V2 + 10 to 1000ft agl, clean up accel to 3000ft agl, call for
climb power, accel to 250, IAS hold to 10,000msl, alt hold, accel to
best rate of climb about 320kts is a good guess unless that exceeds
glider/OrbitOne "piggyback stability" speeds, then continue climb up
to 24,500 ft, switch over to Mach .82 climb and hold that with Mach
Hold, and call for MCT (max continuous thrust) power when rate of
climb drops off, then call for G/A (go around) thrust (five minute
limit) when rate of climb drops off, and level off at FL410 (since an
[up to] 250,000 lb space vehicle is now riding on our back we can't
make FL450.) Note we will be at about a 650,000 joined vehicle weight
upon reaching FL410 in this senerio. Detach OrbitOne with
coordinated push over maneuver and descend 747 tow aircraft back down
to FL350 accelerating to MMO .92 mach in the descent (pull back to MCT
power.) Pay out cable and let OrbitOne/glider ascend as high as
possible (75,000-100,000 ft.) Level towship at FL350, call for G/A
thrust and enter 45 degree bank, bracing for possible cable break and
resultant pitch down and overspeed. When Colonauts release the cable
(coordinated,) slam to idle 747 power, deploy full speedbrakes, level
wings, pull up with authority, and recover from resultant mach buffet.

Ya know, I hate to say it guys: but this Rube Goldberg type solution
may just be nothing short of brilliant. It IS, as described above,
from a preliminary perspective, all just barely within the
capabilities of a stock B747-200F with JT9D-Q or -70A engines and more
importantly: does not require superior ****ing airmanship skills on
the part of the tow ship PIC.

We need to further explore several tow tether candidates like Tim's
"Vetron" rope. 1: We need to calc the tension involved using Kevin
Horton's 3 to 1 speed slingshot target (77,000ft radius.) 2. We need
to calculate a drag number for this 24km tether at a selected average
thickness.

Well, what you are waiting for? An engraved invitation? Get to work
and make some engineering decisions! I'm just a towship driver. I
don't know how to calculate the tether load we're going to experience
in the 45 degree bank…

pacplyer

Not a bad idea, even for a much shorter towline, and not too far different
from truck towing with a payout winch and a hang glider. There, the
basebar is sitting in a bracket and the nose is tied down to about the right
angle. You lay proned out in your harness, and when the truck has 25 or 30
mph airspeed, you pull the nose release, and start pulling out line.
When I first tried it, I thought the turbulence off the truck cab would
make those first few feet exciting, but it's a non-issue.

But the disadvantage is you need the infrastructure to mate the two. One
advantage the Kelly Air and Space idea (of just a straight tow to altitude)
is that you could launch from any airport with a long enough runway. No
special equipment. Just roll 'em out, hook 'em up and wag the rudder.

Tim Ward