Really, Bill?
No design and program risk from a lifting-body to orbit, which has never
been done?
On 2019-05-28 17:09, William Claybaugh wrote:
Rand:
Ok, I’ll bite: what additional design and program risk?
Bill
On Tue, 28 May 2019 at 18:08, Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
In other words, an insignificant advantage, not worth the design or
program risk.
On 2019-05-28 15:52, William Claybaugh wrote:
Henry:designs
A careful like-to-like analysis of the DC-Y and the WB001 SSTO
found a very slight (circa 1%) payload advantage for the wing bodyif
the wings were used to loft the trajectory to get out of the<hspencer@xxxxxxxxxxxxx>
atmosphere faster.
Bill
On Tue, 28 May 2019 at 16:21, Henry Spencer
wrote:and
On Tue, 28 May 2019, Nels Anderson wrote:
... It seems perfectly reasonable that air breathers would havelower
gravity losses. What's not clear to me is that they 1) would be*much*
lower (in the context of a total delta-V budget of 9000+ m/s),
doesn't2)
would not eaten up by larger drag losses.
Note, there are actually two separate issues here: airbreathing
engines,
and wing lift. Winged rockets are a reasonable possibility, as
witness
Pegasus and various unflown designs like RASV (the Shuttle
incount
because it made no attempt to exploit wing lift during ascent).
Wingless
airbreathers are also possible in theory, although pretty useless
that
practice because the T/W of airbreathing engines is so dismal.
One might think that, other things being equal, wing lift should
show a
net gain even with typically-poor hypersonic L/D values, given
onlythey
are still well in excess of 1. Unfortunately, wings incur not
morea drag
penalty, but also a mass penalty, especially when they have to be
protected against high-speed heating. That makes the gain much
of
arguable, and also rather harder to estimate. You might get some
enginethat
mass back if it lets you reduce your engine thrust and hence
thatmass;
you might get more back if you believe you want wings for
reentry/landing
anyway. Maybe.
A more subtle issue with both wings and airbreathing engines is
atmospherethey
tempt you to modify your ascent trajectory to stay in the
death
longer, to exploit them more. That often seems to produce a
spiral
of escalating drag and heat and mass, in which the design never
closes.
Henry