The sole effect of wing lift on ascent is to make it harder to get to orbit.
The trajectory optimization problem is, rather simply put, to maximize the
fraction of propellant energy that winds up in the sum of vehicle kinetic and
potential energy for the desired orbit. Wings only subtract energy. Lift is
defined as being at right angles to the velocity vector, while drag is defined
as parallel to the velocity vector. Since work (i.e. energy change) is the dot
product of force and distance, the rate of work going into the vehicle is the
dot product of each applied force with the velocity vector. The dot product of
lift with velocity is zero, so no matter how much lift one applies, LIFT does
not change vehicle energy at all. However, the drag due to lift does change
vehicle energy. It reduces it. Using brute force trajectory optimization will
get one a “least bad” use of lift compared to an optimal gravity turn, but it
will never give an improvement. That doesn’t stop some people from looking for
one, but it’s equivalent to searching for a perpetual motion machine.
Sent from Mail for Windows 10
From: Henry Spencer
Sent: Tuesday, May 28, 2019 7:11 PM
To: Arocket List
Subject: [AR] Re: SpaceX Single Stage to Orbit
On Tue, 28 May 2019, Nels Anderson wrote:
... It seems perfectly reasonable that air breathers would have lower
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), and 2)
would not eaten up by larger drag losses.