if flying head down has a lift upwards relative to the earth (i.e. craft wants to "fly" away from earth) and head up has lift downwards ( craft wants to "fly" into the earth ) then rather than roll between full head up and head down during re-entry would I be bonkers to assume that an attitude of side on to the earth (90 degree roll ) should hold the lift in balance resulting in neither increase or decrease in lift and hence G forces ?
#Gemini: Flying the re-entry wing
cursive horizon
shadow gazelle
Well you aren't wrong. But it'll "lift" you sideways. Establishing around 15°/s roll rate is a true "null lift". Basically you make the lift vector wobble all around your predicted path.
cursive horizon
ha ha..đŸ¤£ I hadn't considered that. It wouldn't be the best look to slam into the earth sideways. Makes sense to establish a continuous roll. A bit like Mercury. I assume this is why the reentry phase was often described as a bit of a rollercoaster ride.
shadow gazelle
Yeah. Same for Apollo, but as the range is greater you tend to keep your lift vector pointed up or down longer. Key is to always roll in the same direction, so when you change your lift up/down you essentially null your cross range error.
If you roll left the right then left and so on, you'll constantly add cross range error to the same side. Whereas having it always right make you go both sides cross the path, thus minimizing the accumulated error
cursive horizon
Good advice - I don't think I was doing that.
cursive horizon
I don't think the idea that the Gemini pilots "flew" re-entry is often appreciated as most of the literature sort of implies they sat there and watched it go all firey.
shadow gazelle
Earth orbit entry is pretty forgiving. The capsule stabilises itself and the worst that can happen is missing the landing point.
Unless you really have a bad attitude (that aerodynamics try to don't allow you to do)
Of course you could go full heads up and risk heavy G's, but it would probably not break up.
Lunar transfer speed entry on the other way is way less forgiving, and you have to carrefully manage the G-load.
cursive horizon
So waht you are saying is that having a really bad attitude causes break ups ....
shadow gazelle
Yeah, like entering SEF and trying to maintain it. Or keeping it heads up and diving too fast.
But as I said, the capsule is self-stabilizing aerodynamicaly BEF. And I'm not sure keeping the lift vector down would be enough to destroy it.
After some research, Gemini structural limit is 15g. But 13g already shows damage, which is the peak g of a pure lift down entry. 9g was the operationnal limit. Typical entry was 5g. So yeah, toying with lift is really pushing it to the limit.