The LLC vehicles have had almost no aerodynamic constraints. The Rocket Racers of Armadillo and Xcor used off the shelf airframes with established functional aerodynamics. Not even spacex has yet dealt with aerodynamics in any complciated way. The Spacex falcon 1 did have aerodyanmic Max Q issues, and probably aerothermal issues, but there were no aerodynamic controls and aerodyamics does not get much simpler than a long round tube with a pointy end.
(The recovery parachutes of the F1 first stage either were not included or failed)
Spacex is about to fly the dragon capsule with hypersonic aerodynamics, aero thermal, and stable parachute deployment and recovery issues. Armadillo is starting to fly to higher altitudes, Masten hopes to soon follow and or surpass what Armadillo has been doing.
Xcor is planing their next rocket vehicle where the aerodynamics include transonic and some aero thermal issues.
From a rocketry stand point the smaller New Space organizations (Masten ,Armadillo and Xcor) are nearing the level of rocketry sophistication reached by the Germans at the end of WWII. Please note that the Germans never flew a supersonic aircraft. (Yes the V2 was supersonic) Get in your time machine fly back to 1946 and ask Chuck Yeager if supersonic is a big deal?
If an LLC L2 vehicle was flown on an airless earth with zero drag and maintained a steady state 4G acceleration (3 g net) it would run out of propellant near 30Km and coast to 119Km before falling back to earth. Using my really simple aerodynamic model... assuming a Masten Glow of 900 lbs, and 25" diameter with very good aerodyamics removing the 25Kg payload and flying the same 4G flight Mastens L2 vehicle would reach about 116Kf or 35Km. Now in practice you would probably have to throttle back to reduce max Q if you picked 300Knots as max Q equivalent then you would have your velocity limited by maxQ until at least 40Kft and one would trade more gravity loss for reduced aerodynamic losses and get to about the same place just over 115K ft.
This not an up and soft land simulation, this is a up up and away simulation with a crash landing at the end. So given the stated goals of both armadillo and Masten to fly payloads to space they will need vehicles that are both higher performing and more aerodynamic than what they presently have.
(A max Q of 300 knots equivalent may not seem like very fast in a world with 500knot airliners, but a skydiver released into a 300 knot airstream would experience more than 8 g of deceleration.)
I vaguely remember Henry Spencer making a comment that the Apollo command module heat shield had an eqiuivalent ISP of 7000. If your going to build reusable vehicles that fly to space and come back its never going to make sense to kill your velocity via propulsion as long as we are using chemical fuels. So when reusable suborbital vehicles start flying to 100km they will need to use aerodynamics to scrub off the energy from the gravitational potential.
Will this look like the space ship 2 shuttle cock? will it look like NASA's hypersonic ring slot parachutes developed for viking and used on every mars landing since? Will it be airplane like?
I think this is going to be a harder problem than many think. Mr Musk of spacex has been quoted as saying that a fly back first stage booster would be a really useful thing to reduce space access costs, but it would cost > $1B to develop. Some solutions look simple like the rocket becomes winged vehicle as shown in Charles Pooley's Microlauncher presentation. I don't think that an easily fabricated simple wing will function well with supersonic shocks, flutter stiffness etc... One wants a shape that can give you decelerating lift at high altitude, does not provide much drag on the way up and is structurally stable at all points in between. This is a you pick any two sort of problem. The U2 had very long thin wings to get get lift at high altitude. Yet it it was a subsonic aircraft and as a result operated in a very narrow box where a few knots faster and it hit Mach buffet and a few knots slower and it stalled.
One can work around these issues by using a combination, like a hypersonic parachute to decelerate you to subsonic followed by rotate open wings to glide back to base.
Whatever features will be used they will require testing. With the exception of xcor all of these vehicles are unmanned. The regulatory environment for testing rockets under the amateur or experimental permit rules are now well defined and reasonable friendly. If one is developing a glide back system one would like to test the basic aero controls, flight, landing etc in an incremental manner. Just try getting the FAA to give you permission to fly such an unmanned vehicle in their airspace? The Aircraft side of the FAA is significantly less understanding than the AST. (Just ask John Carmack) So from a regulatory standpoint one is going to have to fly it as a rocket under AST's jurisdiction. This is not testing that can easily be done under tether, or even at the locations that Armadillo and Masten are currently flying from.
None of this is impossible, its just another layer of problems to be tackled. Anyone have any good recommendations for a good book on supersonic aerodynamics ?