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