Re: Launch rail (rod) and backplate issues (reprise)
This sounds like an increasingly sane proposal.
THEREFORE, I am going to take a number of previously-mentioned points and amalgamate them into one coherent counterproposal to El Reg’s approach.
Centrally, the core flaw in the Register’s Official Design (the ROD) is the rod itself. It’s too prone to jamming due to icing or to the tube freezing in place; it’s going to be too flexible to provide significant guidance since (a) the launcher will be dangling in mid-air, not anchored, and (b) it will only be attached at a single point at the tail end; it’s going to be rather heavy no matter what, if it’s long enough to hold the plane in a straight line as the craft launches; finally, it will impart a wild and unpredictable rotational moment on the launcher platform due to inevitable friction when the plane launches. The last point will render the direction of launch entirely unpredictable and will make the launcher useless for capturing takeoff video.
Therefore I suggest a totally different approach to the launcher, a π-shaped configuration with a transversely-mounted equipment bay; four short longitudinal trusses bracketing the wings; a piston-launcher which both contains initial exhaust to protect the instruments while providing dynamical stability that utilizes the launcher mass as a launch anchor; and gyro-stabilization for both the launcher and the plane, powered by batteries in the launcher.
As the plane approaches launch altitude, the gyros will spin up. These will lock in the direction of the launch, and the ones in the launcher could in principle be used to provide launch directional control (if they are spun up first). The gyro on the plane will be powered by a tether line; on launch this will separate and the drop in input voltage can trigger a timer that will, after a few seconds, engage a braking circuit in the fashion of an H-bridge which will slowly stop the gyro and allow the autopilot to perform aerodynamic control as the craft gains speed.
Once the gyros are are spun up, their momentum should be maintainable without too much power input, so this can confer directional stability even if the balloon unexpectedly blows. An accelerometer should easily detect this event, and can trigger immediate launch if the gyros are at speed and the device suddenly finds itself in low gravity.
Initial launch energy will be substantially amplified using a piston-launcher, which will (a) contain launch exhaust to protect the launcher payload, (b) magnify the initial thrust by at least an order of magnitude, and (c) lock the position of the tail w.r.t the launcher at the time of ignition, providing a positive lock on launch direction.
The legs of the π consist of a pair of short trusses around the wing bases with PTFE-coated rails that enforce the initial direction of separation, two-axis constraint can be achieved with rails along the fuselage as well. While these will be much, much bulkier than a launch rod, they will not be heavier because they can be built in a stiff space-frame style rather than relying on the rigidity of a slender rod or tube: they can be MUCH stiffer for the same weight.
It’s also worth considering that a compact payload will be easier to transport to the launch site than a long slender one; it also provides camera mounting points on either side of the aircraft, permitting better launch video and still images. Finally, by having a launcher that symmetrically encloses the tail of the aircraft rather than dangling the plane below it, the problem of torque moments causing wild gyrations is greatly reduced.
If any interest is shown in this proposal I would be happy to draw up schematic proposal plans.