A metric tonne?
Half a billion dollars to move three tonnes?
How could this possibly be worth bothering with?
The huge LEMV* surveillance airships now being built by British designers for the US Army may be able to carry substantial cargoes as an alternative to sky-spy equipment, according to reports. The LEMV airship to be built for the US Army. Credit: Northrop/HAV Might not just be a spy-eye but a sky truck, too. Aviation Week …
If the machine is appropriately shaped and compartmented then could additional lift be provided.
I'm thinking hear of making it a bit 'wing shaped' with retractable stubs into which helium could be expanded as height increases.
It may not have enough power in its own engines to drive it forward to get aerodynamic lift, initially, but a winch or tow plane (or 2 or 3 or many drones) may do the trick. Once Airborne then it has 3D to move in.
Will the upper surfaces be equipped with PV solar cells to recharge the batteries/fuel cells for the electric motors or H2 fueled engines?
Shows you how little I know, I guess.
It always amazes me that simplistic solutions always seem to be adopted, even when they compromise the outcome.
Rather than trying to manage the quantity of the gas by setting it at launch, why not have a small compressor and pressure vessel on board? As the craft gains height, helium could be extracted from the envelope and stored in the cylinder.
As the craft descends, the stored helium can simply be added back to the envelope to re-establish buoyancy,
This is just the same sort of control that a diver uses in water - except that divers vent gas from the buoyancy cell(s) on ascent, rather than trying to scavenge it. But that's because carrying a compressor would not be feasible. We're not airships...
Vic.
Why can't you outfit a helium-filled blimp with one of those miraculous devices that take gas and compress it, storing it into pressurised gas containers? That'd save venting the spendy gas, and enabling its use for another day, or another descent maybe.
Me, I wouldn't mind trying to run the thing on hydrogen. It's not a passenger craft, you know.
The reason why compressors are impracticable in helium balloons is simply because compressing a large volume of gas quickly requires a huge amount of power and heavy weight equipment. Then you need high pressure tanks to store the compressed gas. Any compressor light enough to be carried on an airship without hopelessly compromising payload capacity is going to be nothing like powerful enough. The volumes of gas involved are simply enormous measured. You would need to be able to compress hundreds of thousands of litres in a matter of several 10s of seconds.
A compressor with a total swept volume capacity of 10 litres (which would be fairly big) would require 10,000 strokes to suck in a 100,000 litres (which would probably take a few minutes), and you'd need multi-stage to get it down to a decent volume. and the whole thing would need a lot of power plus fuel and weigh rather a lot.
That's why compressors haven't been used in Airships and ballasting/venting are preferred. The position with subs is not the same. Volumes are much smaller, weight isn't a problem and there's usually plenty of power available. Water has the great advantage of being pretty well incompressible. The atmosphere is anything but.
Thanks. It doesn't exactly answer what the weight ballpark would be, but "too heavy" is clear enough. Since we're talking large and slow-ish things, ten minutes to compress enough of the volume to stop the buoyancy-providing bubble from bursting while ascending sounds reasonable, as in not prohibitively slow, at least to my layman's ear. Then again diesels have become light enough for aircraft use not too long ago so maybe this might be fixed some day too. Or, I dunno, systems with lasers forcing the helium molecules into high-pressure store one by one, who knows. Crazytech, eh.
There's plenty of stuff around compressors on airships. It has been a subject of research and pretty well every designer has decide it is impractical. Every now and then somebody floats (pun intended) a maverick idea, but nothing much comes of it. Do some research on the Internet and you'll find this type of stuff.
As for the weight - measured in the region of several tonnes. As far as time goes, an airship can rise an awful long way in a couple of minutes. There are cases in the old, pre-WWII days, of airships rising many thousands of feet in a minute despite venting hydrogen, which is a lot faster than any practical compressor could achieve. Airships are not only vulnerable to the expansion of their lifting gas as they rise, but also to relatively minor changes in air pressure due to variations in local atmospheric and weather conditions.
Generally using thrust to force the airship down is going to be more efficient than trying to balance bouyancy through compressing relatively large volumes of gas. However, once you lose control then there will be no choice but to vent as nothing will deal with the situation fast enough.
If you run a compressor only for saving helium after offloading, maybe you can afford several tens of minutes rather than several tens of seconds.
If you are doing repeat deliveries, the first item to be delivered could be the compressor, which you keep on the ground at the destination. Subsequent runs don't have the weight penalty of carrying a compressor. On the last run you wreturn with the compressor as (partial) ballast.
The compressor idea is not impracticable, the yanks have been looking at it for a few years now. They have been looking at it from using it for freight.
Look at it this way in a commercial freighting arrangement once the airship has landed the compressors don't even need to be on the airship they can be ground based and powered from a ground based source. This would be the equivalent of taking on ballast except the ballast is in the form of compressed He in pressure tanks.
This "cargo lift" capacity is in the same class as the "need" for cross-range capability in the Space Shuttle was: an idiotic and unnecessary waste of development funds.
Use this thing for what it was originally intended, and either use a current cargo lifter or call for a new design for one.
The cross range capability of the Shuttle was by far not the most dangerous or unreliable aspect of the craft.
The biggest problem with the Shuttle was it's launch system and the tendency for things to fall off of it or to explode. I am not the first person to point this out here.
Two words: O ring.
and I may not be the first person to point out that your answer has no relevance whatsoever to the point that was made.
The comment was that it's generally cheaper and easier to make dedicated craft for each required purpose, rather than wasting time & effort making a multi-purpose craft that fulfills none of the roles particularly well.
Hi folks,
The HAV 304 that Hybrid Air Vehicles in Blighty are developing for the LEMV contract is designed primarily for medium altitude surveillance, however the military do like multi role vehicles and it can be changed over to a cargo transport fairly easily. If however the primary purpose of the HAV was cargo then a slightly different design called the Skycat will be used. The Skycat is similar to the 304 but will have larger engines and a slightly different hull and hoverskirt arrangement, for roll on roll off and an even larger static weight range as a result.
Regards JB ( www.hybridairship.net )
Hi folks,
Some rather odd comments that need a few answers so here goes:
Firstly the HAV 304 is a hybrid air vehicle, which means it is a cross between a blimp and a flying wing plus a hoverskirt undercart. It does not need wings and a layer of PV panels would not justify their weight or work too well in Afghanistan. The amount of Helium is fixed and it does not need to be changed unless there was a big configuration change such as changing from medium altitude surveillance to low altitude heavy lift. Then the Helium would be topped up to increase payload, otherwise almost no Helium is required after initial inflation. All military aircraft have to use JP8 fuel which is a cross between jet fuel and diesel. Hydrogen could be used in a civil version but the present engines are Centurion 4.0 diesels which are very efficient anyway.
Secondly the 517 million dollars was for 3 HAV's not one and half the cost is for the special surveillance payloads. Initial prototypes are always expensive but a production HAV will cost less than an equivalent aircraft and far less to operate in fuel terms.
Thirdly forget about storing or compressing Helium and other research programs as they are all too heavy to be useful at present. Due to it's high static weight capability an HAV does not need such systems.
Fourthly the ballast question only applies to normal airships not to HAV's as they can take off heavy enough to avoid a light landing. Even if an extreme condition did arise then sandbags can always be loaded into the cargo bay.
Regards JB ( www.hybridairship.net )
But thanks for the clarification anyway. So no venting (which was speculated about in the main article, btw). The hydrogen comment was about floating it with hydrogen, not necessarily using that as fuel (but if you have it anyway... but I digress). And, well, we've been told on a couple occasions that extremely light-weight and bendable sheet-like PV is coming our way, and if anything an airship doesn't have a shortage of it's area, so the connection is fairly natural to make. Whether it's viable after all is another thing, of course.
But what I'd really like to know is about the carrying capacity of this thing. Can you give us some numbers, like what happens if you reduce the mission time to, say, one week and drop all the excess kit and fuel, maybe drop the ceiling a bit. How much can it carry then? How far will it go in that time with that cargo?
So these airships can only land by using upward thrust from the engines as they are heavier than the bouyancy of the gas bag. I presume that having landed that then the engines are put into either no up thrust or down thrust to maximise the negative bouyancy. You then claim that the weight penalty of a compression system would be excessive, but why not use the drive engines as compressors, seeing as how they are not needed for lift when the airship is on the ground? This is easily done by using one bank of the V8 as an engine to drive the other bank as a compressor. Half of a 4 l engine running at 3000 rpm will compress at least 3000 litres of gas to 150 psi per minute, 4 engines will compress 12000 litres/min.
The next problem is the weight of the storage system. No problem at all as soon as one stops thinking about dedicated and heavy cylinders. The floor of the cargo deck needs to be strong enough to handle the cargo, and the lightest way of getting the strength is to use extruded box section alloy. Connect all of the box sections together and use that as your storage "cylinder". Compression and storage of excess He for practically no weight penalty.
It just requires a little thinking outside of the norm.
Hi there,
There is reasearch into Helium compression for ballast control of normal blimps, but although they have got the weight of the compressor and power source within reasonable limits, the bottle is a different story as any kind of metal cylinder is too heavy and the composite cylinders explode in a fire or if they get hit with a high velocity round. No way at present as it would be like flying with a potential bomb.
For a hybrid air vehicle there is no requirement for ballast due to the lifting body allowing very heavy take offs using aerodynamic lift with a short take off run. Vectored thrust is also used to help but most of the gain is pure arodynamic lift and as only 30 kts is the sort of speed required the take off run is very short and any flat surface will do.
Regards JB ( www.hybridairship.net )
'Massive new US spy airship 'could be used to carry big cargoes'.
Uh? Massive? El Reg, stop exaggerating! In English, 'massive' means 'massive' -- as big as or bigger than the biggest.
This airship is a toy when compared to the Hindenburg, for starters it's a puny 300ft in length, the Hindenburg was over 800ft--and, to boot, it was built over 74 years ago out of crappy materials. A few stats here:
http://www.airships.net/hindenburg/size-speed
http://www.airships.net/hindenburg/interiors
(Always knew IT types either failed history or never studied it.)
>-)
Hi there,
No real worries about getting shot down as the HAV 304 normally operates at 20,000 ft and Bin Laden and his boys don't have anything better than a Russian heavy machine gun, which is good for about 5000 ft. It would be good if they did try shooting though, because it gives away their position to the targeting folks. Even if they manage to buy and import larger IR homing missiles, they will find they just wasted a bunch of money as the 304 has diesels that won't give a good enough signiture for a lock, even on the ground runs. In reality they will be much harder to shoot down than a helicopter.
Regards JB ( www.hybridairship.net )
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I agree with 'heliumblimp', airships are much harder to shoot down than you'd think.
In WW-I there were many accounts of where German airships over London were shot at and the bullets passed right through them without significant damage. Even filled with highly flammable hydrogen, the airships did not catch fire. The only damage to the ship was to the gas cells (bags) that were specifically hit, these simply lost their gas (hydrogen). As there were many gas cells, the buoyancy lost by bullets passing though a few bags was small; even then--with a cell taking a finite time to deflate--any noticeable loss of buoyancy only occurred after the ship had left the combat zone.
It was not until the British developed incendiary 'bullets' that would specifically catch the hydrogen on fire that airships were very vulnerable.
However, today, any such airship would use helium and not hydrogen, thus both bullets and incendiary shells would have little effect. In fact, the cellular nature of the airship combined with helium and the use of modern materials not available back then, would make the airship quite a formidable device (especially so given that its size and large lifting capacity would also allow it to be extremely well armed both with attack and defensive weaponry).
Unlike a plane, even if hit with a missile and badly damaged, its large size and that it's mostly cellular 'packets' of helium, large parts of it would likely remain buoyant (at least until it could escape the danger zone--as did the German Zeppelins of WW-I).
Combine the airship's intrinsically buoyant properties with an operationally redundant design (i.e.: where multiple copies of operational systems are widely distributed across the airship) and it's likely to still function, even with significant damage.
In order to bring down a helium filled airship you need helium tipped bullets.
The helium tipped bullet hitting the helium gas causes the helium to fuse and create a chain reaction causing the helium at 0.1786 g/L to convert to carbon at ~2.3 g/cc, causing an almost instant implosion of the gasbag and the generation of an additional very strong negative lift.... as the 1000 cubic meters of helium converts to 120Kg of carbon....
One bullet downs one airship.
It's elementary.
Hi there,
It does help to have full function up and down vector for the main engines of a normal blimp like a Skyship has, but for a hybrid air vehicle it does not matter, as they are shaped like a flying wing, albeit a fat one and produce so much lift with a short take off run that they can start so heavy that the finishing up light and having to valve off Helium problem, no longer exists. That is why the US military chose a hybrid design.
Regards JB ( www.blimpingaround.com )
It's especially silly as the asterisk on the first page refers to a note on the bottom of a second page.
Encumbering readers with this sort of unnecessary bother is a travesty, I tell you! A travesty! I've half a mind to delete The Register from my bookmarks.
When offloading in Afghanistan, could one of these ships fitted with some oversized shopvacs simply slurp up some sand and rock? You'd only be able to unload where the ground is sandy, but that might be plenty of places over there...
Paris, because she'd suffer no such restrictions...
But it seems to make more sense to use hydrogen. Then you can effectively convert between lift and ballast using fuel cells in conjunction with atmospheric oxygen.
It also means that if you need to get rid of lift in a hurry you can dump the hydrogen and make more from water later.
Reckon it is silly. As I said in another post, the German WW-I Zeppelins over London weren't vulnerable to bullets but they were so when the British eventually developed incendiary fire.
History has shown that significant damage can occur to an airship without its hydrogen catching fire but when it actually does then it's absolutely catastrophic. Despite it's few disadvantages*, helium has one incredibly important feature which is that it's chemically totally inert--nothing short of nuclear fission will make it 'burn'.
Formula learned for history:
Airships + H2 = Madness.
_____
* If I recall correctly from my physics days, in practice, helium has about 6-8% less lift than hydrogen. Experts, correct me if I'm wrong.
_____
BTW Purple People Eater, with that alias you must be a refugee from 1958, Sheb Wooley et al. Oh, perhaps too, you're very one-eyed on many issues. ;-)
Formula learned from hysterical radio reporters live-on-air. The H2 didn't mix with air to supersonically go boom. It just burned, and the ship came down placidly. Most deaths, in fact, were from panicked people jumping from 30 metres up. Looking at the death toll and comparing it to a "much safer" kerosene-filled sardine can^W^Wairliner crash, and keeping in mind they've had some century or so to improve upon fire safety.... I'd like to see that hydrogen-floated blimp with the benefit of a hundred years of airline fire safety applied.
Wikipedia claims 8% and calls the difference neglible. Time in a 1924(!) piece claims:
``The total lift of a helium-filled dirigible is accordingly some 10% less than that of the hydrogen-filled airship. The difference does not appear important at first sight, but the total lift of the gas carries the structure, the motors and the crew. It is only the last 20% or so that is available for carrying fuel, and hence a difference of 10% in the gross lift may spell a difference of 50% in the fuel-carrying capacity. On long-distance flights this difference is vital.''
http://www.time.com/time/magazine/article/0,9171,786149-2,00.html
Only Bin Laden himself thinks the LEMV should use hydrogen!! The last thing we need is a Hindenburg mk 2. It would make the HAV very vunerable to sabotage on the ground, silly accidents by engineers or lightning strikes. Helium is the only approved lifting gas for airships and no one is talking about any changes at present.
Regards JB ( www.blimpingaround.com )
I can easily see these replacing the current unmanned drones that the US government already has spying on its own people. All those scifi movies that showed city skylines filled with airships will soon be commonplace. It's just that all those airships will be filled with spy equipment.
There's an awful load of waste being generated around those bases, some of it toxic.
Flying it back to base as ballast wouldn't be such a bad thing.
WRT helium recompression kit being too heavy..... it depends how you do it and how much you need to tweak the the bouyancy but anything's better than venting the stuff.
Let's just hope the skin isn't painted with rocket fuel like the Hindenburg was.
Hi there,
There is no need for a lifting body hybrid air vehicle to vent Helium. That is the very thing that HAV"s are designed to avoid by doing a very heavy rolling take off when required. Valving off Helium after a long flight is a blimp and Zeppelin problem only.
I like the trash idea as it would keep the Greenies happy, but it would also be good to pay the locals to clean up.
Regards JB ( www.blimpingaround.com )
A submarine carries bottles of compressed air. When the sub dives, it vents its tanks to the atmosphere and once submerged will change depth dynamically with the forward and aft dive planes. To surface the sub closes its vents and uses the air stored in the bottles to force the water out. The compressors are only used on the surface to replenish the air in the bottles. Compressors are never used submerged, too much noise, ballast pumps too.
Now add a few mini-guns, hellfire missiles and perhaps the rest of the gunship kit to that airship and have it hover over the battlefield at high altitude to keep johnny Taliban in his hole!
Wasn't there a story recently about the US selling off its supplies of helium? If these things are going to become useful, it might be worth buying up a few gigalitres of their He and flogging it back to them at grossly inflated prices?
1. Buy helium.
2.
3. Profit.
Evil Bill - because he is.
Hi there,
If you look at the Helium page of my Gasbags comedy site www.hybridblimp.net there is a lot of info on the global supply situation. There is no need in the long term to have a strategic Helium reserve as large as the current one in Amarill Texas. The biggest Helium refinery in the world will shorly be working at full capacity in Qatar and the US will then be in second place in supply and reserves.There will also be new Helium rich gas fields developed in Australia soon and there are still new souces being found due to the increase in natural gas exploration.
Regards JB ( www.hybridairship.net )
"No real worries about getting shot down as the HAV 304 normally operates at 20,000 ft and Bin Laden and his boys don't have anything better than a Russian heavy machine gun, which is good for about 5000 ft."
Hmm, can't claim any sort of expertise in the field, but few points come to mind:
1. This thing, when on the ground, will be a pretty large, unmissable object. It would be much easier to hit from a distance with whatever you want then almost anything around it.
2. The 20,000 ft operating altitude is all good and well - but I'm assuming it doesn't teleport to that height in a split of a second. How long does it take to gain the first 5000 ft? Will it be 10 minutes, 20, 30? We could be talking about 10, 20 or 30 minutes of high level of vulnerability after take off and before landing - specially as it is so large and easy to spot/lock onto - and it doesn't move as fast as some other types of aircraft.
Hi there,
Any aircraft on the ground is vunerable to damage, but the HAV 304 uses Helium and would be very difficult to set fire to, even if it was hit in the gondola as it uses JP 8 fuel which has a flashpoint of 50C.
It will only operate from secure bases away from the front line and do what many aircraft do and spiral climb if the area is hot. You also have to remember that when on station after the delivery flight it is an un manned vehicle and the control and command folks on the ground would like nothing more than to have some cave dwellers to shoot at it, as it gives their exact position away for a swift response, normally from long range artillery or ground to ground missile batteries.
Regards JB ( www.hybridairship.net )
Surely we could save loadsacash by just giving a bunch of our twattish MP's a free holiday cruising around in this hot air balloon thingagummyjig? The self-sustaining hot air supply could keep it (and them) upstairs for yonks, and if you ever needed to get rid of some ballast then just chuck 'em overboard.
Stupid not to make best use of the abundant resources which we've got.
I will tell you this, if you lads run out of tw@ts over on your side of the `pond`; then there are plenty more here, on my side.
As far as chucking them overboard; why??? That would only contribute to the pollution of the planet's oceans. But, then again, if you were to arrange for those 'ballast drops' to occur over shark infested waters, then it MAY BE A GOOD THING. After all, the sharks have to eat too!!!!
The uplink will suck this way or that way, or both. Think the latency of satellite with the reliability of a just-out-of-reach wireless. Yes, I have some experience with that sort of link. And playing games all day, meh. But a bookreader, a desk for studying and a couch for relaxing and sleeping would be spiffy. So yes, I'd still take it, given reasonable pay.
Looks like the US and its allies have a monopoly on developing military equipment. If anyone else tries to develop anything that could be in some remote way be used as a weapon, then there are sanctions against them. You cannot launch satellites without American permission, look at Iran. You must allow others to have live war practise next to you, look at North Korea.
It's all well that we talk about Israel and the US having all these new technologies for war, but it would be better if the money spent on war was spent in helping those who are poorer by improving their transport links and farming. Many are into terrorism because they are brainwashed by fanatics because they see no other future. If they had freedom and happy lives, then maybe peace will be welcomed.
Your article and many of the comments focus on carrying cargo to or inside Afghanistan. Why? Cargo needs to be carried to and from many places and not all of them contain armed insurgents trying to shoot down airships. If they were used to carry cargo between continents they could conveniently use ports, which already have access to an infrastructure of roads and rail. They also have access to large quantities of water which makes an excellent ballast.
Very true, as the military are looking at both the use of the HAV 304 conversion for cargo in a sudden needs situation and at the similar Skycat which is a dedicated civil cargo version for long range point to point cargo, which is greatly needed in Northern Canada and areas of Africa etc.
Regards JB ( www.hybridairship.net )
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You get a scope (give me something that can stay a long, long time, and carry a sensor package)
Next thing somebody is saying, "hey cant we add....... and make it do ......"
Slow moving area sensor drone, good idea
Slow moving, naff lift weight cargo carrier, Uh, why?
Cargo transport capacity is how much you can lift, multiplied by how many trips you can make in a set timeframe, airships fail on all counts as cargo carriers.
Hi folks,
The comment from Anonymous coward is partly true if you are talking about general air frieght operations, assuming you don't care about fuel burn costs or upper air pollution. A hybrid air vehicle uses about 20% of the fuel of a similar sized fixed wing transport like the C130 or An12 that could be compared to the lift and range capacity of the Skycat 20. So in the long term there is a case for using HAV's for air frieght of any type BUT in the short term there is a very serious need for an all surface point to point cargo HAV that can fly thousands of miles from an air base or just a clear area of flat land or water (The Skycat uses a hoverskirt not undercart, so any surface good enough to operate a hovercraft on is OK) to another isolated landing site with no infra structure, no fuel just a clear area of a few hundred meters to do a vertical landing if required.
Now tell me what other aircraft can do that kind of point to point operation and I will let the good folks at HAV in Blighty and the US Army and Air Force that they have got the wrong idea. A helicopter has only about a 500 mile range with a limited payload, needs fuel after landing and worst of all burns 10 times the fuel!! The tilt rotors are better but will still need fuel on landing and although faster don't have much more range than a helicopter and worst of all they have fairly limited payload at full fuel. The answer is the hybrid air vehicle and the best design team in the game from Northrop Grumman and Hybrid Air Vehicles from Cranfield in Blighty.
Regards JB ( www.hybridairship.net )
Litterally and figuratively.
The article missed an obvious question, given the cross section on this thing, how is it effected by weather, and winds?
As somebody who has managed to hover a glider in 35 knot headwind (who needs Harriers!), I can testify there is a reason they teach you the difference between Air Speed and Ground Speed, and yes it is possible in the right/wrong situation to have an aircraft at full power going backwards. That number is higher for somethings, like a 747, and likely to be very low for something with the cross section and power of an airship.
Anon coward is a glider pilot and he will get a surprise to find the HAV 304 or Skycat are both faster than a glider. Obviously cruising at high speed burns more fuel than station keeping or surveillance or long range flying for a fuel conserving cargo operation, but because you can operate point to point the fixed wing alternative will be spending days trans shipping to rail, ice road or expensive helicopters at either end of the flight. Wind is a factor with any aircraft but I think you will find an HAV does not suffer the same problems at 80 kts cruise a small blimp or zeppelin has at 30kts.
Regards JB ( Gasbags comedy site www.hybridblimp.net )
Couple of bits, the glider was just used as a personal example,
I have also more than a few hours on prop fixed wing, and used to teach basic aerodynamics.
Whilst Lighter than Air Vehicles have a place in low impact transportation, the military need to focus on how effective it is. (not being able to resupply a position because the wind is too high and from the wrong direction will not go down well with the squadie that wants some ammuntion)
My suspicision is this will be an improved version of other LTAVs, too susiptible to weather, by comparrison to a medium or heavy lift helo, and of limited usefullness in transport capacity due to limited cargo weight and speed. Given the size of target, speed and manuvurability, it would also be restricted to "rear areas", and those dont exist any more, except on MoD press releases.
PS
you can make a glider hits 180kt Air Speed, if you dont mind skirting the structural air speed.
The main benefit comes from the fact it's heavier than air so there is no need to vent.
This also makes the craft easier to land.
This was designed as a surveillance aircraft, so the lift helps reduce fuel consumption, so a large sensor payload can be kept aloft, autonomously, for long periods of time.
All article is saying is that it could potentially be used for cargo.
These things don't need to be fast, I have no understanding of it's max speed etc or relative to a glider.
The aim of this thing isn't speed but fuel efficiency.
2500lb would be enough for a group of soldiers? They could parachute down from the airship. It all depends how fast it is I suppose, if it crawls then it isn't practical but if it can move fast enough it should easily be able to hold 5 or 6 men for a fast reaction force.
Or as someone else mentioned, load it up with hellfires and you've got firepower on station for 21 days at a time.
Is somewhat tricky as you suddenly have all this lift available - in my ballooning days, releasing a hang-glider (we did a few high level 'launches') required a fast decent before the release after which the balloon levelled out and often rose if you vented no hot air. It was tricky in a hot air balloon where vertical control can be surprisingly precise - not so easy in a gas filled one....
Lots of them and it would leak like a sieve.
It does not have to go "POP" to bring it down.... just lots and lots of almost impossible to find little holes - will cripple it's altitude, range and endurance....
The three week mission scrubbed cause they lost enough gas to fuck it all up after 2 or 3 days....
Shit even a decent bow and arrow with a razor sharp broad head will make it piss helium...
It's pretty simple,
Helium/hydrogen gas bags, inside an air bag, when you want to go down, pump air into the external gas bag, which which will compress the helium gas bags, at the same time as adding weight, reducing lift...
No need for a hefty preasure vessel..
I am sure i've seen this design before in an old book somewhere...
and since you can do this on the ground before you release the cargo, it doesn't matter if it takes you half an hour to do it unless you need to detach the cargo in an instant, in which case suddenly your VERY boyant!