Firstly, is there a specific forum for LOHAN ideas?
Secondly, instead of releasing LOHAN at a pre-deteremined altitude, why not rig up a device to launch LOHAN as soon as the baloon bursts? That way you would get maximum altitude...
How about after burst? Can the parachute be made big enough that the loss in altitude will be less than having to chop the lifting stage short? If it drops 500 feet before the rocket fires, you're still in the money compared with just saying "okay, 60,000 feet" or whatever. Plus you still get to launch if there's a balloon failure before any kind of preset altitude.
Some possible ideas re LOHAN project
First off, I apologize (sorry, apologise—I’m American) if this forum is the wrong place to post these ideas—I’ve tried emailing Mr. Haines directly a couple of times but with no response.
1.) Aircraft configuration:
I realize that by now the Southampton people have probably finalised aircraft design, but I might call your attention to the family of low aspect ratio lifting bodies commonly called Facetmobiles. (As it happens, I was the test pilot for the first human-carrying version, which—among other things—was flown from southern California to the famous Oshkosh, Wisconsin, airshow and back under its own power). See www.facetmobile.com. Note that small-scale unpowered Facetmobiles are regularly dropped from LOHANesque altitudes with scientific instrument payloads and return autonomously to their launch sites; those dropped above 100,000 feet probably exceed M1 during the initial descent.
Facetmobiles offer glide ratios on the order of 6:1, very low structural weight, simple construction (flat surfaces only), and relatively immense internal volume for payload.
Due to its design, a Facetmobile will automatically assume a controllable flight attitude (technical term: carefree re-entry) even if the initial encounter with sensible atmosphere is in an unfavorable attitude (technical term: arsy-versy or, in the USA, ack-basswards).
2.) Launch stabilization:
How about a small but relatively massive (say 50 gm) gyro wheel and brushless electric motor (micro model plane motor) rigidly mounted inside the spacecraft (axis of rotation parallel to spacecraft longitudinal axis). This could be spun up immediately prior to launch (from an inclined rail) by a battery that remains on the launch truss; it would continue spinning long enough to stabilise during powered flight. This would provide rigidity in pitch and yaw until adequate q is attained. As for roll, so long as the thrust vector is properly oriented through the C/G of the vehicle, who cares? (see “carefree re-entry” above).
I call your attention to the Ruby autopilot (www.uthere.com). Weighs about 60 gm, includes its own GPS, plugs into regular RC model servos, costs $345. I’m sure there are many others—I suggest checking websites for the burgeoning FPV (first person video) segment of RC modeling. Note that for the present there are stupid security restrictions that prevent the Ruby from working outside the USA (which means putative terrorists could still use one to control some engine of destruction aimed at domestic targets but not foreign ones…go figure).
Given the planned release altitude, I would hope LOHAN could return to her launch site, metaphorically wagging her tail behind her, even if the balloon system drifts quite a long way downwind during ascent. That said, and considering the export restrictions above, I’d like to close by suggesting…
4.) Where to fly:
The central plains of the USA are not only vast and flat, but crisscrossed by roads at regular one-mile intervals. Not the most dramatic scenery, but ideal for tracking and recovering Unofficial Flying Objects.
Better yet, I’d suggest the annual Burning Man Festival in the Nevada desert (www.burningman.com). Not only is it an (at least) once in a lifetime event to visit, but it includes an ephemeral airstrip on which visitors arrive in everything from Ultralights to turboprops—and there are almost sure to be a couple of helicopters whose owners would very likely be willing to aid in LOHAN recovery.
Best of luck to you all!
You know how distended the balloon can get before it is at risk of bursting, so that's what you aim for, not for a specific altitude. A couple of overlapping conductors, such as aluminium foil, can be attached so that at a certain point of distension they are no longer in contact. Cover them with an elastic membrane to keep them flat and in contact in the wind and you're done: before the balloon bursts, a circuit breaks and you're done: simple.
In the spirit of KISS - and I know it's nowhere near as fun as GPS or pressure related ideas, why don't you just set a timer to trigger the launch after the time you estimate it'll take the the balloon to reach roughly the desired height? It won't be an exact science but it should be close enough for jazz. If you have any data from PARIS on how long it took the payload to reach it's max height, that should help you make an educated guess as to when to set the timer to go bang.
It sounds too easy, am I being thick?
I'm still concerned about the single launch shaft.
During ascent if the wind buffeting is heavy enough it could cause the wings to smash into the teflon-coated girders and cause some significant damage.
Any thought of extending the teflon strips down until they are just standing off the wing surface? That should minimize the chance of wing damage due to buffeting. You wouldn't want them constantly touching the wing due to the chance of freezing, but a small ( 0.5") gap should give the chance for the wings to move still, freeing them up from any potential stickiness, but reducing the overall roll movement so as to prevent damage.
Good point. If it flaps about it might bend the titanium rod as well. Is there anything to stabilise the plane along the roll-axis while on the launcher?
Perhaps you could have the trailing edge of the wings rest inside a couple of forward-facing (teflon-coated?) U-shaped brackets while in the launch position. No need for them to touch, but it might help to stabilise the plane in case of turbulence.
Not as elegant as Tempest8008's idea, only U-brackets would distribute the restraining force over both wings instead of just one.
So what are your plans regarding the on-board GNC? Have you thought about the controller hardware/software you are going to put into Vulture 2? How about sticking a Raspberry Pi in there (assuming you can get your hands on one – I’m sure you can pull some strings). Would be a good way to engage with a wider community and possibly get some nice coverage for all of you. Would also be nice to open source some of the control software and let the community chip in with ideas/suggestions. I seem to recall reading about some guys using ‘FlightGear’ (as an aero model) to train their auto-pilot software? How about something like that?
Doesn't look too stable to me. Where I live every house has an aluminium channel embedded in the concrete ceiling by the windows, in which nylon glides slide to hold the curtains.
If said channel could be supported the length of the truss, and the glides secured to the LOHAN, it might be a readily available, stable launch runway.
...or rod, or whatever you're sliding along, just to avoid arguments.
I've just suggested this in the last SPB article, but now there's a proper forum for dissecting ideas:
What about using chemical heat pack powder inside a hollow launch guide? The powder will get "up to" 45C according to most heat pack instructions, though the instructions also tend to state "do not disassemble". The ingredients are rust, activated charcoal and water anyway though, so hardly a major risk.
How much thermal expansion the rig will go through can be tested on the ground with a frozen sleeve and heated launch guide. The heat packs are good for anything between 8 and 24 hours when used as sold, depending on what pack you buy. I've noticed the 24 hour ones will take maybe an hour to get to full temperature though.
I did also suggest using resistive wire to make heat, but the various modes of failure plus a honking great battery to melt ice over a 5 or 10 minute period would probably make the chemical powder idea better.
Launch should occur on a clear day therefore the dew point will be below ambient at all elevations. Although the rod will cool rapidly, it should be slightly warmer than the ambient temp so there will be no condensation on the rod or tube. No freezing will occur. The balloon must not pass through any clouds. Stay away from grease of any kind. A light sprinkling of powdered graphite wouldn't hurt. Stay with the single rod. I know of no amateur rocket people that use a tandem rail. Anyone who has ridden in a balloon knows there is no buffeting. Phone up Sir. Richard B., I'm sure he'll concur.
Manual telescope tracking is unlikely to work , but automatic telescope tracking could be used if you are using the right tracking scope, usually the camera is set to track a pinpoint light, but in this case I'm sure a white sphere could be tracked against the blue sky if you were to play with the camera software a bit...
I'm kind of with others in wondering why the big solid backplate too. The rocket is probably going to provide a hell of a thump to that plate when it goes off, and I can't see how it'll do anything but push the whole platform back, especially if there's a halfway-reasonable rocket engine providing the punch.
Now you could possibly re-use exhaust gas pressure, but that would involve swing wing designs or some way of slotting the whole thing inside a launch tube. Engine goes off, provides pressure in the tube which should fire the rocketplane out of the end like a bullet from a gun. Wings can flip out and sabots can fall off as the aircraft leaves the barrel. Methinks the SPB team are going for something with less moving parts though, as lovely as the idea sounds, and as epic as the launch footage would be.
but wouldn't that require the 'fixed' portion of the gun to have sufficient mass to balance the reaction effect. If not it is as likely to propel the tube, girder and balloon assembly backwards as it is to push the plane forwards. And as previously stated that could swing the girder and alter the angle of the launch.
Better not to have the back plate and rely on the reaction motor entirely...
.. or go back to the vertical launch paradigm. (three balloons, vertical launch tube through the middle, swing wing glider at the bottom of the tube, discarding sabot to reuse the gas pressure in the launch tube (nice)).
The design can be widely adjusted for reaction effects and responsiveness. If there is no blast plate at all, there is a small drag force (from friction) in the direction the plane launches. Installing a blast plate across the exhaust would capture some of the thrust energy and redirect it perpendicularly, canceling it out.
Another option is to enclose the exhaust gases in a piston-launcher, which turns almost 100% of its initial thrust to pushing on both the launcher and plane; this makes a much stronger reaction force. That kicks against the launcher and violently jolts it — which gives a launch pad that retains stability in free-fall, and also protects nearby delicate bits extremely well.
I have photos that demonstrate the thrust containment; I have built a black-powder piston launcher made entirely of combustible materials. It's untouched (save the blast containment tube, which is a bit cooked) after three launches. It launches 1:48 scale F-104 plastic models with Estes engines.
A couple of issues occur to me regarding the use of a launch rod and backplate, at least as shown in the Reg diagrams.
Re the launch rod: First, whilst using a Teflon insert that completely encircles the launch rod to reduce friction seems like a good idea there are a couple of potential problems with this. The major problem is that if anything sticks to the launch rail, from ice build-up due to frozen condensation to tiny bits of grit, then by completely wrapping the launch rail with the insert you've maximised the surface area where anything stuck to the launch rail can jam against it.
A better idea would be to use just two long and thin strips (thin to minimise the swept area and long to bring the contact area back up enough to lower the contact pressure), angled about 45 deg either side of vertical, at the top of the hanger loops (and if you were to go this way then you should also cut/trim them so that they come to a point at the front, giving them a chance to divert anything stuck to the rod around them or, alternatively divert them around anything that won't shift)
An even better idea though, would be to ditch the cantilevered launch rail entirely and just use some curtain rail, which could be attached along its entire length, with a couple of roller glides which would roll over anything but a catastrophic build up of crud. Make sure you completely degrease the rail and roller glides though; any lubricant is likely to freeze and jam (this was a trick learned by photographers in the arctic/antarctic, where the lube in their cameras was prone to freeze)
Re the backplate: This is a _really_bad idea. Y'know rockets work by equal and opposite reaction? Well the rocket will go forwards because of all the stuff it's chucking out the back but all this stuff coming out the back will hit the backplate, forcing it and the entire truss backwards. However, because the truss is suspended from above what will happen is that the truss will pivot backwards, swinging the launch rail downwards just as the plane is moving along it.
Do away with the backplate entirely and just use a 'stop' on the launch rail to hold it in place and prevent it dropping off the end.
Oh yeah - re the plane swinging about uncontrollably in the wind: won't this only be an issue at low altitudes? I thought that high altitude winds were relatively 'smooth' and not very turbulent, so just launch when the low-alt weather is fairly calm; once it gets up high it'll be moving _with_ the relatively un-turbulent air.
Analysis of the previous launch shows that the balloon horizontal speed increased up to a specific altitude after which the rise was almost vertical. Indicating that the wind speed at launch should be negligible.
As far as the backplate is concerned I still maintain that the vertical launch tube is the bets option. The veritcal arragment prevents issues of launch swing and the tube can be used to reduce freezing problems. It would be possible to seal the tube completely by blocking the 'muzzle' end with wax paper, cling film or a light cap so preventing ingress of moisture. This blockage (or could we say hymen) would be broken on launch either by the launch vehicle or it's exhaust gasses. The tube could be loaded in a dry as atmosphere as possible and something like silica gel could be included to further prevent moisture build up. The tube can be insulated by expanded polystyrene to reduce the freezing effects further. maybe chemical hand warmers could be included too.
A vertical launch tube is a nice idea except that you'd have to rig it between at least three balloons for any degree of stability and it would need to be (at a rough guess) at least twenty metres long, to reach from the bottom of the tethers up past the mid-point of the balloons, to ensure that the end of the tube clears the hugely expanded balloons. This tethering rig would have keep the tube centered throughout the considerable expansion range of the balloons. It could be done but it would add a _lot_ of weight, not to mention a folding wing system for the aircraft (which would mean both extra weight and complexity).
There's a simple problem with putting any sort of air-tight cap on the launch tube too. Any cap that's flimsy enough for the aircraft to simply fly through would have burst at a relatively low altitude i.e. < 30,000 ft due to the outside air-pressure drop.
A couple of other people have worried about achieving lift from the wings during the rocket burn phase. This is actually a bit of a reverse issue because if the wings generate any real lift during rocket burn then there's a risk of the plane looping. This is because sub-sonic lift is proportional to airspeed whilst the attitude of the plane, whilst under thrust, is pretty much irrelevant; the lift will always act nearly perpendicularly to the wings so, for example, if the plane were to reach the vertical then any wing-generated lift would tend to pull it back past the vertical to inverted - not good. The wings really don't want to generate too much lift and are really only there for getting back down in a controlled manner after the rocket has burned out. For similar reasons, the launch rail need only be long enough to stabilise the plane whilst the rocket thrust stabilises. Once the rocket is burning steadily that's really the only force that's significant - all other forces will be tiny in comparison.
I agree about the length of the launch tube. probably a show stopper but given the difficulties of the PARIS separation (attributed to freezing) wouldn't the complexity be worth while? As for the pressure differential, we are only concerned with ingress of air to launch tube and as the pressure would generally be dropping throughout the accent a one way valve would fix the problem.
What about a mixed solution with a launch tube suspended at an acute angle a long way below a single balloon? The angle should be high enough to ensure that the rock expends most of it's thrust gaining altitude and the distance below the balloon would be enough to ensure that the upward trajectory did not intersect with the balloon.
"As for the pressure differential, we are only concerned with ingress of air to launch tube..." umm... I think you may have got that the wrong way around. It'll be the _outside_ air pressure that's dropping, meaning that the pressure inside the tube will be increasing relative to the outside; the issue won't be _ingress_ of air in to the tube but air trying/wanting to leave the tube, to equalise with the outside pressure.
This presents another possible problem: when you get a a sudden pressure drop in a system containing any water vapour you're likely to get the formation of clouds i.e. water droplets, which could then freeze.
Another potential issue with using a long tube is that the plane will need to displace the air in the tube ahead of it as it traverses the tube, effectively acting like a piston, which will cost it launch energy. In an open air launch though, i.e. not in a tube, the air can also be displaced around the plane/rocket. To be sure, the expanding gas from the rocket will ameliorate against this factor and aid in pushing the air out of the tube but someone (a rocket scientist?) would have to work the numbers to find the trade-off balance.
Issues with the back plate being asymmetrically attached to the launch rail...the effect of the thrust, (I agree with many of the posters here), will be to apply a rotational moment on the rail. The solution may be to have the back plate not being flat. A V shaped back plate, perhaps with a small central perforation will collect the exhaust from the rocket and be more effectively propelled directly backwards, acting more like the recoil of a gun.
In the electronics enclosure on the truss
could you (for sheer interest sake) put a thermometer, and a pressure gauge and transmit/store the data so it can be recorded for the purpose of a beautiful looking graph (or 2) post mission?
happy to help with this one, would probably be easier to store the data rather than transmit it and the whack it into excel/other spreadsheet post mission to build the graphs
Is the launch rail long enough to build sufficient airspeed for the wings to generate lift in the thin atmospher?? or just relaying on rocket power to keep the nose pointing upwards?
if the aircraft stalls as it leaves the end of the rod and pitches downwards, will the flight systems apply elevator to correct the attitude, or will the arcraft rocket propell its self nose down??
With negligible air for the wings to work with, could swinging them back out of the way be beneficial? If so, here's an idea.
How about pivoting the wings so that just momentum swings them back when the rocket is burning. A small amount of spring loadedness could bring them back to position for the glide phase.
Another possibility would be to mount the rocket in such a way that it's forward thrust against a mechanism (rack and pinion kind of thing) swings the wings back.
Problems: complicated and heavy for little benefit. If the plane was being launched on a big rocket and was going supersonic during upward cruise, then folding the wings away would be useful. But since the aerodynamic effects prior to engine ignition are negligible, the weight and complexity are not worthwhile.
On a model scale I'm not sure if a swing wing would really be that complex. You need a thick enough peg-like spring to bear the wing (or one length of metal coiled in the right places to mount both wings to), and some fishing line attached to a servo somewhere via a couple of pullys off a model yacht or whatever. Shape the body with the first couple of inches of wing built-in so that the sprung parts are supported and won't wobble about on the single spring holding them on. Obviously the mounting points for the springs will need reinforcement, but the wing struts should be pretty reinforced for a rocket plane anyway shouldn't they? This also means that you can tuck the wings right back against the body for the launch, and then use airspeed and altitude to decide when to start slowly loosening the wire.
Now if only I had money, a laser sintering thingummybobsit and some time I'd test it myself!
The moment resistance of a fixed wing can come from the mechanical properties of the skin, which will be far lighter than a hinge (because the opposite edges will be further apart and therefore subjected to much smaller tensile/compressive forces). Additionally this would obviate the requirement for energy storage for unfolding the wing — and using the engine thrust to open the wing is the worst possible approach, since that would mean unfolding the wing near the maximum airspeed. If you were to unfold the wing you would want it to happen near apogee, where the airspeed stresses are minimal.
The two advantages of swing-wings would be a more compact body at launch (which, given the essentially unlimited space around the craft, is an insignificant benefit) and the nullification of lift forces during the high-speed portion of the flight. But those could be zero anyway, if an airfoil section which is nearly symmetrical is chosen and flaperons are positioned at a slightly negative angle for the launch. Come to think of it, they needn’t even be flaperons; they could be standard ailerons with a lightweight, simple device to give slight negative displacement for the launch.
I'm strongly inclined to agree.
The benefits of folding wings are relatively small when set against the increased complexity and the resulting increased potential for things to go wrong.
Not only is there the wing swing/folding mechanism to consider but also the aileron control linkages running inside the wings (so far, the images seem to suggest that LOHAN will have ailerons).
RL swing/wing aircraft use hydraulics to actuate the wing-mounted flight control surfaces but this isn't an option on LOHAN - it'll have to use electro-mechanical servos located in the fuselage with push/pull linkages and cams. Note to the SPB team: you'll probably want to degrease any servos and cams to prevent freezing - after all, you're not going for longevity.
Well as I was suggesting, there isn't all that much extra complexity on a model scale. The transmission can basically be two fishing lines attached to a relatively strong servo toward the tail that's powerful enough to counteract a spring that'll keep the wings straight at 50, 60mph or whatever speed you're going to go to "fully extended". Having wings of a reasonable size would mean a much better glide ratio, even if you don't think drag during the rocket burn on smaller fixed wings will be a problem. I'm not sure how much wind resistance there is at 80,000 feet, but once the rocket has been burning for a couple of seconds I'm pretty sure LOHAN's velocity will be enough for even that rarified atmosphere to start tugging on any sticky-out bits with quite a force.
As for the aileron linkages, any decent model has a seperate servo for each control surface, usually with one for each aileron mounted inside the wing, forward of the aileron. These can be mixed either with a physical onboard mixer or in the transmitter (and presumably in the open source autopilot the SPB team are apparently using). It also allows ailerons to be flaperons (and elevators to be elevons) with a bit of clever mixing. At 9g or less for a decent micro-servo it's not going to be a bother on a craft of LOHAN's, erm, proportions.
Having ailerons would also mean you don't need a V tail, plus I've seen models land safely after losing one of their elevators completely. Little harder, especially for an autopilot, to do that after getting a whole wing torn off.
Also, try and make the autopilot aim straight up half a second second after leaving the platform. Use some kind of umbilical jack lead, or maybe a powerful magnet stuck to two contacts on the aircraft as an easy way to detect a launch. You also get to keep the aircraft's lightweight batteries topped up with something more heavy duty in the launch system that way. Yes, it probably won't give us much additional altitude and yes, there isn't much air up there but it's going to have some effect and it'd still look cool on a camera. Plus it might limit the damage of an odd launch angle.
Last thing, uhm, have you considered apogee detection? I'm sure you'd like to go from burn mode to glide mode in the most efficient way you can.
As to “how much atmosphere”: we can expect only a few percent of sea-level air pressure. 80,000 feet is about 24km, which is the lower stratosphere. The pressure at 20km is about 5500 Pa or about 5.5% of sea level pressure.
Now, using the formula $F_D = 1/2 /rho v^2 C_d A$  for incompressible flow aerodynamics (LOHAN is not supersonic), we can see the drag is proportional linearly to the air density $/rho$ and quadratically proportional to the airspeed $v$. It’s also linearly proportional to the frontal cross-section area (which would be improved by folding wings) and the drag coefficient (which would probably be impaired by folding wings causing a lumpier shape).
A servo motor would not be particularly heavy, but if it was located in the tail as you suggest it would wreak havoc on the balance even for a light motor — but there is really no need for that motor to be anywhere but near the hinge point. However it would take a long time, probably 30 seconds or so, to extend the wings. By that point the most optimistic benefits of folding wings are certainly gone.
You do have a good idea, though, having a relatively heavy battery in the launcher; it could be used as a heater for the touchy bits of the plane. It would also add mass to the launcher, which would add to dynamical stability on launch.
I agree that having folding/swing wings would allow longer wings and a better glide ratio but I still don't think that the added complexity and risk would be worth it because it's not going to be doing much gliding anyway. At the proposed altitude you'd not only need unfeasibly long, high-aspect ratio wings, but a pretty high airspeed as well, to gain sufficient lift for a meaningful glide.
I'm afraid I don't understand a couple of your other comments: "Having ailerons would also mean you don't need a V tail...". A V-tail doesn't replace ailerons but just reduces the number of flight/control surfaces in the tail empennage by combining the horizontal stabilisors with the fin i.e. two surfaces instead of three. Yes, you then need to mix the pitch control with the rudder control, but that's not rocket science.
Then: "plus I've seen models land safely after losing one of their elevators completely. Little harder, especially for an autopilot, to do that after getting a whole wing torn off". Do you mean the entire hstab on one side was lost, or just the elevator on one side? In either case, as long as the remaining hstab/elevator retains enough control authority then it'll still be controllable, albeit not as controllable as as you'd like (the A-10 was designed to be flyable after losing one entire hstab & rudder). But why would one of LOHAN's wings get torn off? And if one wing is torn off then you're going to be stuffed anyway (although I've heard one story of a Japanese F-15 that managed to land after getting _most_ of one wing torn off in a collision).
WRT v-tail, I was on about losing the entire stabiliser. Given independant servos, you've a chance of bringing an aircraft in with half the stabiliser gone if it's a nice airframe. Lose half of a v-tail and you're pretty buggered.
Anyway, the glide ratio doesn't need to be massively brilliant at 100,000 feet. With the wings swept back you could go for a high-speed descent, tearing toward the landing site like some NASA black ops test vehicle until the atmosphere becomes thick enough to support a more gentle glide that won't tear the bottom of the aircraft off when it hits the floor.
Plus, you know, added awesome, and all.
I agree that’s a possibility — so I refer people once more to my sketch here:
What’s not really visible in plan view is the tail structure, which is in fact TWO opposed T-tails: one pointing up, the other pointing down. This will (a)provide the largest possible aerostabilization surface, (b) leave the sides of the fuselage clear for boosters/gyros, (c)provide redundancy if one of the tails snaps off, and (d) provides a nice automatic-landing feature: when it reaches the ground, even if it’s flying nearly horizontally, the tail will strike first and drop the nose to the ground, inducing a large negative AOA and firmly landing the craft with no guidance needed.
When will you guys be ordering your radiation hardened electronics for the mission? (http://en.wikipedia.org/wiki/RAD750). I suppose you could save a few bucks by buying the stuff from Radio Shack but you'll cry when you reach the Van Halen belt. The rays you'll encounter are unlikely to be the Ray of Hope. Better to shell out some $$$'s and get the proper stuff.
When the rocket motor is activated it will reduce the weight of the balloon payload, causing the balloon to rise. As rockets tend to accelerate very slowly to start with, will the Vulture 2 craft acelerate quickly enough to escape the launch rail at all?
I suggest that instead of a launch rail, Vulture 2 is attached to the payload spar with slow-burning fuse, ignited by the rocket motor (with appropriately fire-proof connections to the craft). This will achieve separation of the components irrespective of relative acceleration.
Otherwise my guess is that the balloon will accelerate as quickly upwards ar Vulture 2 does, so you might as well attach the rocket motor to the payload spar and release Vulture 2 when it has ceased firing. Vulture 2 could then be a glider with better aerodynamics and less weight.
Just a thought but what about if the glider/rocket/launch mechanism was mounted parlty inside the balloon?
The motor ignition could be could held back by the pressure inside the balloon. When the balloon bursts the pressure in lost and the rocket fires, right at the point of maximum altitude. Yes, it would be tricky to arrange but the advantages might be worth while.
The balloon would protect the rocket and launch system from the damp and the wind. The heavy and tricky air pressure launch trigger would no longer be required. Launch could be vertical (or very nearly) and rotation and swing effects would be minimised. Also it could be guaranteed that the balloon would not interfere with the launch and maximum launch altitude would be attained.
I'm thinking of a sealed box or canister containing the rocket/glider. the lid of the canister is hinged upwards and is held open with a spring. The lid is also rigged as the trigger for the rocket firing mechanism. The lid is held closed while air is pumped out of the canister. The lid is then prevented from opening by the outside air pressure. The canister is then fitted into the neck of the balloon so that the top and lid of the canister are inside the balloon (and subject to the balloon pressure) and the bottom is outside the balloon with the instrument package tethered to the base. The canister is then held on a nominally vertical position between the lift of the balloon and the weight of the instrument package. A timer may be required to prevent the accidental launch in the early stages of the accent. but at some point the lid of the canister prevented from opening only by the difference in the pressure between the balloon and the canister. At some point the balloon bursts (explosively) and the pressure difference is lost, the lid 'pops' and the rocket is ignited.
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