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Originally Posted by aeppel_cpm
I'm guessing that they can use the grid fins to hold a slight angle of attack, and 'fly' the booster to some extent. (Adding some lift into the mix.) Don't Soyuz capsule do something a bit similar?
What caught my eye on this flight was the speed and alt gauges on the booster. It really bleeds off speed in the last 10k or so. Without a burn. Just lots of air.
When I first became a BAR, I spent a number of flights trying to deliberately back-slide a purpose-built rocket. I watched the sustainer of my Little Beth X-2 downscale (my first scratch build) backslide on its own, and dug into the articles on the subject.
I never succeeded. I think I (or my rocket, rather) fell victim to the modern 'shotgun' ejection charges. I was using a vent port under the nosecone as a thruster to turn the model horizontal. It always turned nearly 180 degrees and lawn darted.
My attempt at the 'Flying Stovepipe' design suffered from strong ejections, too. It's a Scout inside an annular wing. The ejection charge is supposed to kick the motor back against an extra long retainer clip and the momentum dislodge the Scout from the glider. Mine always blew the motor clean away.
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*Nods* Yes (as they also mentioned in other postings on the NASASpaceFlight.com Forum), they're using the grid fins to literally fly the first stage, using its inclined body as a crude "flat plate" airfoil (the cylindrical first stage isn't a flat plate, of course, but it produces lift the same way an un-airfoiled flat plate does--simply due to the airflow meeting it at an appropriate angle to produce a lift force; it isn't as efficient as an airfoil, but it works). As you noted from the on-screen velocity read-out, this type of "airfoil" can easily be angled to generate a huge amount of drag, which--happily, as it doesn't require any expenditure of energy (beyond that needed to move the grid fins)--is just what is needed during that phase of the flight. Also:
The Soyuz (like the Gemini and Apollo capsules--Dragon, Orion, and Boeing's CST-100 Starliner capsule may also have this feature) does indeed also fly during re-entry, by means of a deliberately offset Center of Gravity, using its thrusters as an airplane uses its control surfaces. (Such capsules also can--and have been--spun to re-enter in purely ballistic trajectories if the guidance system fails, which has happened on a few occasions.) This capsule lifting flight capability was dramatically demonstrated by the translunar (Earth-Moon-Earth trajectory) Zond spacecraft, which were "stripped-down" (to save weight) Soyuz capsules--they performed dual-re-entry, aerodynamic "skip" maneuvers that brought them down in the Soviet Union. The U.S. Viking Mars landers, while still encased in their saucer-shaped aeroshell heat shields, also performed high-speed glides--under thruster control--during entry into Mars' atmosphere (the more recent Mars landers and rovers may also have done this). In addition:
I discovered tail-slider boost-gliders entirely by accident in the early 1990s. One day, while flying an MRC Wildfire (which is a long, narrow rocket, see:
http://plans.rocketshoppe.com/mrc/m...RC+Wildfire.pdf ), its parachute failed to open fully. I was amazed to see it assume an inclined attitude and begin gliding--in a stable, steady manner--in wide circles, while sliding backwards through the air! It stayed airborne for the better part of a minute. Thinking it was a fluke, I launched it again (with its parachute deliberately reefed, in order to duplicate its more streamer-like drag characteristics when it had incompletely opened in the previous flight), and it glided the same way it had before. For the rest of its "career," I flew it that way. As well:
While a vent/thruster will work to "flip" a rocket into the correct attitude to glide backwards, it isn't necessary if the rocket's fineness ratio is sufficiently high--in fact, a thruster might shorten the glide duration (if it caused the model to "over-correct"; it would lose altitude in a fall while 'rocking' into its correct-for-gliding attitude). This is true of any boost-glider or rocket glider, but it's particularly significant and noticeable with low L/D gliders such as tail-sliders and lifting bodies, because they have high sink rates even under the best of circumstances. They do not soar (gain altitude) under normal conditions (thermal lift or slope lift would have to have a high upward velocity to make *these* gliders ascend, or even glide at a constant altitude! :-) ).