Why don't militaries use ram-air parachutes?

Question

Military parachutes for use by humans (both paratroopers and distressed aircrew) tend to be of simple round or (more recently) cruciform design:

(Image by the United States Army, via Wikimedia Commons.)

(Image by the United States Army, via Flickr, via Wikimedia Commons.)

These are simple drag parachutes, generating no lift. In contrast, sport parachutists nowadays almost invariably use much-more-advanced rectangular or elliptical ram-air parachutes, which generate much lift and relatively little drag:

(Image by John [shebalso] at Flickr, via Wikimedia Commons.)

Military use of ram-air parachutes is essentially limited to display teams.

This seems rather odd, given that lifting ram-air parachutes:

• allow for much lower descent rates (and, thus, softer touchdowns - something which would be especially important for paratroopers, who jump with lots more heavy gear than sport skydivers, and ejectees, who are likely already injured, and, thus, tend to have less ability to tolerate hard touchdowns) than drag parachutes, due to their greater aerodynamic efficiency;
• allow their users to glide considerable horizontal distances once deployed and can be manoeuvred nimbly, which would:
  • allow paratroops to be dropped some distance from a target and glide silently in;
  • allow wind-induced dispersal of a large paratroop unit to be negated;
  • allow paratroops to manoeuvre to land in a suitable area or to evade antiaircraft fire;
  • allow ejectees to glide towards territory controlled by friendly forces and/or terrain with the least potential for further exacerbating any injuries to the ejectee.

So why do military users stick with drag parachutes rather than moving to lifting ram-air parachutes?

Answer 1

You’ve made some faulty assumptions there as the military does use square chutes for specialist parachuting, but rounds are popular for several reason:

• Static-line round chutes are deployable en-masse from a much lower altitude / height than square chutes. The lowest that we can drop the round chute is 400’ (which is very low) versus circa 1500’ for a square.

• They require the least amount of training to get the user competent to jump out of the two. Since the chute isn’t steerable, the soldier is reliant on the aircraft crew to make sure they are despatched in the correct position in space to arrive at the DZ. So their only job is to run forward when the light goes green and follow the guy in front out of the door then action their drills and brace. Remember this is only their method of egressing the aircraft to get to the ground and fight and it’s not a particularly covert method of entry. This provides a large degree of force concentration, the largest number of people out of the aircraft and onto the ground in one go.

• Square chutes are steerable and can be deployed in several ways and at much higher altitudes/ heights to allow the user to either free fall from height down to a low altitude before actuating they chute, or to use static line or pull immediately after jumping to fly in to the DZ from as far away as possible. This is a much more covert method of entry and requires a lot more training to achieve with inherently greater risks. Hence it’s not for everyone and isn’t usually given the media attention that round chutes get. This boils down to some assumptions that people have that the government / military operations have almost infinite resource to train and keep people competent in high-end skills whereas almost the opposite is true and keeping it simple is usually the preferred option.

Answer 2

As Arkem stated, they use both, but the primary reason for the use of a simplified parachute is just that it's simplified. In general Airborne troopers are supposed to fall where they are told to, as intended by the pilot, as instructed by the wing commander, as ordered by the REMFs.
When you give that same trooper the ability to adjust their flight path then you add in all manner of variables that are not only unnecessary, but dangerously unpredictable.

Answer 3

There are serious military advantages to using a round "non steerable" parachute for mass tactical assaults. (And there are sometimes military reasons to use ram air or steerable rounds, generally for special operations forces operating in small teams...)

First, keep in mind the purpose of "regular" airborne operations. We aren't talking about inserting a highly trained and experienced 12 man Green Beret A Team behind enemy lines and land them all in a volleyball court sized clearing.

We are talking about dumping at least 500 fully equipped infantrymen on a drop zone that is probably at least two miles long and a half mile wide... we want them on the ground safely, with 100+ pounds of combat equipment, as quickly as possible, and we don't really care where on that DZ they land. For larger operations, well have to use larger DZs or multiple DZs, and may well be dumping 20,000+ troops. We also want the troops to be able to walk out of a relatively short course with a very low number of practice jumps, and be ready to make a combat jump for real the week they report to their unit. (There were two brand new E-1 privates who literally hadn't even reported to their units after Basic, AIT, and jumpnschool, whose first jump after jump school was a combat jump into Grenada with another unit - these privates were engineers and qualified to drive bulldozers, were so new they could be soared from their unit without costing serious combat capability, and thus available to jump in with the Rangers to drive away the heavy construction equipment the Cubans left parked all over runways the Rangers needed to sieze and put into service. They jumped at 500 feet into combat as their "cherry blast", before they even met their own platoon leader.)

This thinking also applies to military emergency parachutes, like bail out and ejection seat rigs. And those military pilots, by and large, are not parachutes, so it needs to work well the first time theybuse it, even if they are unconcsious or injured when the canopy deploys, it's too dark to see anything, and they don't know what's on the ground other than "bad guys".

1. Static line rounds are able to drop from FAR lower altitudes (even if you use a static line to open the ram-air automatically 20 feet after leaving the airplane, you still need it to open at least 3 times as high as you would a round.)

2. Non-steerable "round" parachutes can be deployed twice as fast as steerable rounds (to say nothing about ram air, which have to have even greater deployment separation than even steerable rounds), because you can use both doors in the aircraft simultaneously. You cannot with steerable chutes, because to be steerable (whether round steerable or ram air), the parachute has to have forward drive. Since an off-heading opening is common with combat equipment jumps (and hardly uncommon even with "Hollywood" jumps), the odds that two jumpers will open simultaneously on a closing course, separate by less that the width of the fuselage, is very high. Even more so when you consider that line twists (which mean you cannot steer the parachute until they are cleared) are normal in static line jumps... my one collision and entanglement out of more than 150 military round canopy steerable jumps was caused by tight exit spacing and no time to react - we collided almost instantly on exit because we were flying at each other. This is really not an issue with nonsteerable round parachutes - the jumpers tend to drift along the same rough angle of decent and always with the wind (and collisions and entanglements are much less of a safety hazard with nonsteerables - there is no chance of what is called a "death spiral" where the parachute are thrusting in opposite directions).

3. PVT Snuffy tends to steer toward what he is looking at. This is common for all methods of moving. And PVT Snuffy tends to focus on the jumpers closest to him, as he has been trained to try and pay attention the the jumpers around him for safety reasons. So, PVT Snuffy tends to unconsciously steer towards the other jumpers, in addition to doing things like turning before looking, turning at low altitude (which is a leading cause of injury and death among skydivers), etc. If you can't steer, you cannot steer into a collision.

4. Steerable canopies MUST be landed into the wind, and the jumper MUST get pointed into the wind at a reasonable altitude - 200-250 feet for a round steerable, and the landing pattern for a ram air starts at 1000 feet above the ground. Most new jumpers have a hard time "reading" the wind and have to rely on being told what the surface wind direction will be (not always possible for a combat jump, and almost impossible for a night jump under operational conditions). And you have to get the wind speed right with a steerable (round or ram air)- depending on the parachute, you're looking at adding 8-25 knots of ground speed to the wind speed if you land downwind. If the nonsteerable guy screws up wind direction? Eh, not too big a deal - while you're supposed to "slip" into the wind direction, that's only a few knots of movement at best. You are going to be landing downwind regardless, unless the winds are nearly non-existant.

5. Non-steerables are simpler and have less to go wrong (try being a jumper with an inverted canopy that has you flying backwards at 10 knots, or with a single jammed control line that means you are spiraling, or having both steering lines broken, entangled, or otherwise inoperable - now you are AUTOMATICALLY flying downwind, or you're a pilot who has ejected and is unconscious BECAUSE of the ejection), are easier (amd faster) to pack, and are cheaper to buy and maintain (which adds up when you're buying and maintaining equipment for an entire airborne division, 90% of whom will never need the capabilities of a steerable parachute.

6. If you're going to go into the trees, having a parachute that isn't producing any ground speed of its own is a GOOD thing - better to fall down through the trees and maybe get the canopy hung up, than to slam into a tree trunk at 10 or 20 knots like George of the Jungle. And going into the trees is likelier for a combat paratrooper or pilot than it is for a civilian skydiver.

7. Lastly, for military bail out and ejection parachutes, it is entirely lilely you will be leaving the aircraft at several hundred miles an hour- a C-9 canopy will function properly at up to 300 knots, even if you are in a weird opening attitude and unstable. That makes the C-9 canopy a damned good choice if you are planning on exiting an airplane because someone just shot you down and you don't have time to try and bleed speed. Ram air? Eh, not so much, generally.