Why No Plane Parachutes? And Other Questions.

This week I was approached with a question. Why don’t passenger aircraft have emergency parachutes? Whole plane emergency parachutes are available for light aircraft, and have been used to great effect in many light aircraft engine failures and accidents.

But the truth is that while parachutes may be effective for light aircraft, they don’t scale. There are a series of great answers on Quora which run the numbers of the size a parachute would need to be for a full size passenger jet. I recommend reading the full thread, but suffice it to say a ballpark estimate would require a million square feet (92903 square meters) of material. This clearly isn’t very feasible, and the added weight and complexity would no doubt bring its own risks.

flightsD
Accidents/No. of flights by year. Data compiled from 1 and 2.

There’s a deeper issue hiding in the questions though. A question of flight safety, and perhaps our inherent fear of flight. It’s easy to worry about the safety of passenger aircraft, particularly in light of the spate of high profile accidents in the last couple of years. However, the truth is that air travel is not only very safe, it’s getting safer every year.

The figure to the right is compiled from a couple of publicly available sources. It shows the number of airplane accidents per year divided by the number of flights. Since the 1970s accident rates have consistently dropped. There’s an excellent write-up covering this by an ex-Boeing employee which I also urge you to read.

One aspect of air flight that breeds fear is the lack of information that often accompanies accidents. The unknown fate of missing aircraft allows the media to feed on speculation, and with it our natural fear of the unknown. Our inability to locate aircraft often seems confusing, in a world we feel like significant effort is required to avoid having our locations tracked by the NSA every second of every day, why can we not locate something as large as a passenger jet?

The fact is that aircraft are constantly monitored when possible, and that the information is widely available! Aircraft transmit their GPS coordinates over ADSB. The popular flight traffic monitoring site FlightAware 24 uses this as one of its data sources. It’s also pretty easy to acquire and decode ADSB signals yourself using an RTL SDR dongle.

However ADSB is used by aircraft to communicate with ground stations. It therefore doesn’t work over oceans. A solution to this would be to use satellite uplinks but that’s expensive, and some say of limited utility. Other suggestions are to create a kind of mesh network between aircraft as they travel over oceans. No doubt such tracking solutions will become more common as user-demand for in-flight WiFi continues to grow, and Twitter becomes cluttered with users tweeting pictures of their in-flight meals.

Whatever the root cause of our fears. Air travel is very very safe. But another recent “What-if”, prompted me to consider what air travel might be like if safety was not our paramount concern. The recent and controversial amazon TV series “The Man in the High Castle” shows a world where the allied power lost World War Two and the Americas are ruled by a coalition of the Japanese and Nazis. There’s one point when a supersonic flight (the featured image above) lands in San Francisco, having taken only two hours to arrive from Europe. In a world, perhaps more willing to take risks with human life, and more willing to compromise on the wishes of its citizens. Would supersonic flight still be commonplace?

Commonplace Supersonic Travel

We of course, used to have supersonic passenger aircraft. Until the year 2000, Concorde was considered one of the safest aircraft in the world. It’s one, and only crash in that year, the slump in air traffic following 9/11 and the fact that supersonic commercial aircraft were banned over land all conspired to make Concorde un-economical. Commercial flights ceased in 2003.

sonicrocket
A hobbyist rocket, capable of supersonic speeds.

While supersonic flight may currently be impractical for commercial flight, hobbyists have been trying to get in on the supersonic action. The fastest RC aircraft have not yet quite reach supersonic speeds, but supersonic rockets have been built. This instructable describes the process of modifying a $70 rocket (with $360 of components) to achieve supersonic speeds. On a test flight [gizmologist] achieved a speed of 801mph (Mach 1.07).

There was no audible sonic boom from [gizmologists] rocket, by the time the rocket reaches supersonic speeds it’s already 450 meters up, and the sound waves generated radiate out sideways.

Supersonic aircraft however, do produce a sonic boom. And it was this invasive sound, that caused commercial supersonic flight to be banned over land, helping to seal Concorde’s fate.

Sonic booms are caused by the same mechanism as the Doppler effect. In the Doppler effect an object moving toward you appears to produce a higher frequency sound. Because the source of the sound waves is moving toward you it “catches up” with the wave front effectively compressing the waves and generating a higher frequency in the direction of motion.

In a sonic boom the wave fronts are being pushed so close together that they catch up with each other. Multiple wave fronts therefore lie on top of each other. All that sound is compressed together, and reaches your ear in one big bang.

NASA however have been working on plans to “fix” the sonic boom issue in super-sonic aircraft. They’ve invested $2.3 million in research projects to predict, and reduce the sonic boom effect.

Who Killed the Electric Plane?

Supersonic aircraft were an impressive technological leap, but existing designs are still powered by fossil fuels. In a world where consumer vehicles are beginning to transition to all electrical systems this feels a little old fashioned. Building small electric planes is possible, but has been held back in the US by FAA rulings, though a few are available.

Existing electric aircraft are all pretty conventional using electric motors (generally of the brushless DC variety) to generate motion. But spend much time on YouTube though and you’re likely to come across a very different type of “craft” with many videos claiming to have created anti-gravity UFO. These stem from Thomas Townsend Brown. In the 1960s he created devices which he believed were using electric fields to modify gravity. Unfortunately this was not the case.

What he had actually built was an Ionocraft.

The basic propulsion mechanism is quite simple. Put a pointed electrode near a smooth one then throw a few thousand volts across them, this simple setup will then generate thrust. It accomplishes this by creating an electric field focused on the tip and spreading out to the smooth surface. Where the field is strong electrons are pulled off atoms in the air, ionizing it. These positively charged atoms fly toward the negative electrode. This in itself does not generation thrust, but as the ions move they hit other uncharged atoms in the air, creating what is known as “ionic wind”.

A related technique has successfully used by NASA and JAXA in their space probes. Because there’s no air in space to ionize however, they need to take their own gases to ionize with them. While the ion thrusters produce very little force, they are extremely efficient, which is of paramount importance in space travel.

However aside from the odd YouTube video they’ve found limited utility here on earth. It’s possible that this could change. While Ion thrusters generally produces very little force, recent studies have shown that they may be an order of magnitude more efficient than jet engines. There are some pretty significant challenges to solve, like the huge voltages (10s of kilovolts are used even in a small lifter) required to generate the required lift, or the large physical size of the thrusters. But it wouldn’t be entertaining if, the future of both space and terrestrial flight rested in what was once considered the work of an anti-gravity crank?

Whatever happens in the future, lets hope that as planes become faster and more efficient as their unremitting march of every increasing safety continues.

53 thoughts on “Why No Plane Parachutes? And Other Questions.

    1. The Gimli Glider was a case of everyone having horseshoes up their butts. Not only did it happen near the old airstrip, but the F/O had flown out of it while in the forces. What many also do not know is that Air Canada renamed the bird “The Gimli Glider” and put a large plaque to that effect on the forward bulkhead of first class. I know this to be so because I myself flew on it twice.

      1. Technically, they are. Flying an aircraft unpowered is pilot school 101. I can tell you from experience that it’s a real nervous moment when the instructor chops the throttle and the plane noses over. It doesn’t matter that the engine is still running and can be throttled back up at any moment, it’s a scary ride. I was less than 100 feet above a lake when my instructor finally brought the engine back up. In 30 years, I’ve never forgotten those few minutes, nor how I felt. Had I gone on to get my pilot’s license, I would have gone through similar training again many times over.

    2. A large plane also usually has triple redundant systems and multiple engines which adds a greater margin of safety then a parachute would give it.
      Another issue small planes usually travel at much lower speeds often not much higher then the stall speed of an airliner.
      Pulling a chute at 500mph probably would destroy the aircraft.

      1. Parachutes are designed with a “slider”, which holds all the lines bunched up together, so on deployment, the parachute is all bunched up. As you slow down, the “slider” moved down the lines allowing the parachute to open up more.

  1. Efficiency? it is a ratio. So 1 (or 100%) is the best efficiency possible, and void thermodynamic law, and 0 (or 0%) is the worst possible.

    The original paper says “the MIT researchers (…) found that ionic wind produces 110 newtons of thrust per kilowatt, compared with a jet engine’s 2 newtons per kilowatt or 55 times more efficient.” Which is already a non-sense.

    The HaD “writer” deforms that into “they may be 100s of times more efficient that jet engines.” … Oh wow.

    Cclickbait efficiency of HaD articles may be growing, but the average quality is geting lower every day …

    1. Kind of like the Specific Impulse discussion here the other day. Innumeracy and scientific ignorance is rampant, and the bar gets lower and lower for people to prove that.

      Now, when I jack up my car to change a tire, I’m producing a force of around 2500 Newtons, with a power input of maybe 10 watts. That’s 250,000 Newtons per kilowatt! Almost 2300 times more efficient than an “ion thruster”, and 125,000 times more efficient than a jet engine! Whoot! I must be Superman! Or an ignorant idiot.

    2. The original paper states the following: “The ratio F/P for EHD propulsion was experimentally shown to reach 110 N kW−1. Modern jet engines produce approximately 2 N kW−1 by comparison, although helicopters are higher. Conceptually, the reason for this high efficiency (in the F/P sense) of EHD is because the same thrust can be produced with a narrow high-speed jet (as with jet engines), which leaves kinetic (and thermal) energy in the exhaust stream, or a low-speed wind over a large area.” (http://rspa.royalsocietypublishing.org/content/469/2154/20120623).

      “100s of times more efficient” was retained from an early draft, I have amended the article.

      Many thanks for your “comment”.

      1. A “narrow high-speed jet” is precisely the reason they can fly fast, and modern high-bypass ratio engines are exceptionally efficient while doing so, in the (correct) sense of work done per unit energy in. The poorly understood and shoddily characterized EHD propulsion scheme might exhibit comparatively high force for a given power input, but that is in no rational sense a measure of “efficiency”, because the velocity and thus actual work done is not stated. There’s no magical breakthrough here. There is no way an EHD widget is going to produce jet-like speeds with the force/power ratio stated, and it is a (very) safe bet it’s actually much less efficient than a jet engine, when efficiency is measured or stated correctly.

        Presenting sloppy units and shoddy science like this does readers a disservice. It is counterproductive to really understanding the topic.

        1. Hopefully any disservice can be somewhat corrected by having a reasoned discussion.

          You wrote “a “narrow high-speed jet” is precisely the reason they can fly fast”.

          What the paper was suggesting is that the EHD also produces a narrow high-speed jet I believe? Or was this your point? A second paper discusses thrust density in more detail (http://rspa.royalsocietypublishing.org/content/471/2175/20140912.abstract)

          You wrote: “because the velocity and thus actual work done is not stated”

          In their paper, as I understand it, there is no velocity. They are using a stationary EHD, and measure the thrust using a scale. They only seek to compare the static thrust of EHD and other engines, and the ability to convert power to static thrust. They note here:

          “Here, we reopen this issue, noting that the appropriate metric for the ‘efficiency’ of stationary propulsors is thrust per unit power, F/P, and not propulsive efficiency (which is zero) or kinetic energy in the exhaust stream (which represents wasted energy).”.

          You wrote: “Presenting sloppy units and shoddy science like this does readers a disservice”

          Most EHD research appears to be poor. However this paper was published in a Royal Society Journal with a non-zero impact factor (2.372) by researchers from MIT. While I don’t like arguments from authority, this suggests that it might be worth paying some attention to.

        2. Well, they concludes:
          “We conclude that EHD propulsion has the potential to be viable from both an energy efficiency perspective (our previous study) and a thrust density perspective (this paper), with the greatest likelihood of viability for smaller aircraft such as unmanned aerial vehicles.”
          Since, it was already demonstrated that it works for a drone propulsion (http://jnaudin.free.fr/lifters/orville/index.htm) that included a mouse, I’m tempted to accept their conclusion as valid. As for the scale up, everything is already said, it’s (currently) not possible to scale this technology up to reach jet-like abilities.

          1. Naudin is a pseudoscientists/fraud.

            That demonstration is bunk because it didn’t lift its own power supply. That’s the problem with those “lifters”. Once you include the power supply and batteries, they drop down like a stone.

          2. You’re completely right. Yet, it’s not what I was trying to prove. The most important point is that the design scales up. He started with 300g lifter, that barely lift itself up (without the powersource), but the 1Kg version lifts itself plus a mouse. That seems to match the paper’s conclusion above that it *could* be possible to build a autonomous drone with a lifter (it’ll be very very large indeed).

      2. still incorrect, I believe, but imprecision in language is the most likely culprit. without a re-definition of efficiency one should conclude you mean thermal, possibly mechanical or propulsive efficiency. In which case since turbofan propulsive efficiency exceeds 10%, an order of magnitude improvement is impossible.

    1. Back when I was at University, and had much more time and money spare, I joined the skydiving club. I did about 50 jumps in total, but when we were learning, we would use the pool of club gear. among the learners, there would be a scrabble over who would get the smaller parachutes, because of how much you’d get battered about by the wind with the larger canopies.

      Granted, the design of a parachute for skydiving, is fundamentally different to the round parachutes used in emergency landing gear, but the principal has to be the same.
      On paper, I can see that a massive parachute would be able to gently lower a plane to the floor, but then you’d have to engineer a plane in such a way that you could have the plane suspended from a single point.

      The extra weight you’d have to add to every single plane in fabric and wire would make the safety system impractical.
      The extra maintenance that would have to go into checking the integrity of your safety parachute would be massively impractical.
      Even if you could take care of those factors, how would you deal with a fully loaded 747 landing vertically downwards over a city?
      Just has “nope” written all over it

  2. if one could coordinate the lift characteristics of a parafoil with the general airframe then one could perhaps decrease the effective stall speed of said airframe, giving it a greater chance of landing safely.
    if such a system is worth it or even feasible is quite another matter and one i am not qualified to answer.

  3. +1 for EHD craft or ionic wind. You are awesome Nava. Check this out as well http://arc.uta.edu/publications/td_files/roseberry.pdf Air Arc propulsion for hypersonics.

    There is a reason as well space x doesnt land the falcon 9 with a parachute, number one you cant control where it is going and number 2 using the engine is actually more effecient than a parachute. You have to take it with you anyway might as well use it to land.

    1. Using the engine is massively less efficient, because you have to leave fuel for the return instead of using it all to accelerate your payload.

      It takes just as much fuel to get the rocket up to speed as it takes to stop it. If you apply the Tsoikolsky rocket equation and calculate what the fuel fraction has to be to 1. get up to speed (horizontally) 2. brake to zero 3. accelerate back to speed in the opposite direction 4. kill that speed 5. drop down and brake…

      The fuel fraction approaches very close to 1 which means you’ll have no room left for any payload, and the only thing that goes up there is the rocket.

      That’s why SpaceX is trying to land on a barge. They can save some fuel mass by skipping steps 2,3,4 and letting the stage fall where it’s going anyways. The lighter the load they have, the more fuel they have left over so they may attempt to land closer to home.

      A parachute and an inflatable float would be a much smaller penalty than the fuel mass that is needed to lift the fuel mass that is needed to lift the fuel mass that is needed to land the rocket. In fact, they could just dump the fuel tanks and save just the engines, which is what Boeing is planning to do.

      1. Sorry I disagree. In order to land safely in the direction of the launch (obvious) fuel weighs much less than a equivalent parachute/airbags. The equation is the same for mass of fuel compared to mass of airbags/chutes. I think you forget that once the payload is gone the engine has much higher thrust to weight, thus massively reducing the fuel it needs to slow down to land in a suicide burn scenario. Meaning it has to carry very little extra fuel.

        You need a rentry burn or a massive balute/drogue. Then to land about 500m/s dV compared to 350 m/s dV with a 1 ton landing parachute. 1 ton of fuel has much more than 150m/s dV. Then you have added complexity of a parachute system, if the engine worked on launch and the re-igniters work it is much simpler. I think ultimately large rare earth magnets on the legs and a large repulsive coils on the pad would be better than the last 50m/s dV. Could also correct any last second tilt much easier than gimbaling the engine that way.

        Sea water isn’t great on rocket engines either I don’t see how Boeing has a solution there. Airbags won’t keep the thing from capsizing in rough seas unless you are willing to add even more mass for a keel. Yes that might be a solution on land.

        Thanks for the thoughtful response anyway.

        1. >” I think you forget that once the payload is gone the engine has much higher thrust to weight”

          I think you forget that SpaceX is already using more than a third of the fuel in the stage to “land” on the barge. A parachute and an inflateble rubber bladder just to drop the engines down safely will weigh far less than that.

          1. Your “more than a third of the fuel” figure is completely false. The amount of fuel necessary for landing is only about 3% of the takeoff mass, or about 5% of the takeoff weight in fuel. If the fuel needed to land was 30% of the takeoff fuel they wouldn’t be able to get anything to orbit _at_all_. The main struggle in making rockets reusable is that the payload mass is usually that 2-3% of the launch mass, so you need to make the [fuel reserves + landing gear + other landing hardware] weigh far less than that.

            Please do not bluster with false information. ULA’s ideas are about as advanced as Jules Verne’s were back in the 19th centuries, and the cost savings from reusing the engine block are a joke. Reintegrating them on a new stage introduces possibility of FOD, and it’s why the SSMEs still cost a huge amount to maintain even though they were “reusable.”

            It doesn’t make me happy to pick on you, but you keep making these silly claims in the comments. If a parachute and inflatable rubber bladder (that magically can autonomously seal a 5 meter/side cube while in freefall, and not burn up due to reentry forces) happened to cost less than the lost payload to orbit, with the “discount” of the recovered engines, then companies like ULA would already be doing it. Their me-too presentations are a bit silly. SpaceX may be a painful place to work, but they get stuff done. It’s becoming increasingly obvious that there’s a huge advantage to their creation of the Falcon architecture mostly from scratch.

            shoutout to axmpaperspacescalemodels.com – that guy is super awesome, and his models are ridiculously accurate.

      2. In real physical world you fly full throttle to separation. You use fuel against drag and gravity. Payload is detached dropping several tons. At this point first stage consumed 70-85% of its fuel. Drag is a waste, gravity combined with altitude at this point results in tremendous amount of potential energy that can be used to go back.

        There is obviously rotation and little bit of braking required, but essentially most of the trip down is a free fall. To land on the barge they use supersonic fins that deploy and they brake using atmospheric drag. They most likely have to do short engine burn to aim onto that tiny platform, but it is fraction of the fuel used to go up.

        The only significant amount of fuel is required to perform final braking and landing. But you are fraction of your launch mass and your speed is very low. Somewhere Elon stated that landing on a barge requires extra 15% of propellant. Full round trip requires 30%.

        Simple analogy. Its like going uphill on your bike. Do you put the same energy to go down? Even if you’re going to stop and turn around you still have ton of energy to recover.

  4. On the Big Island of Hawaii they have a rule: you may not divert a lava flow from its path. You save your house, you destroy someone else’s. When that parachute brings an airliner down on top of my house instead of yours, you can bet that I (or my survivors) are going to raise holy hell.

    1. You must have a really bad town plan for it to be a zero-sum game. At the very least, the guy with the lowest house can divert the flow with no risk, as there’s no one down stream.
      The chances of an airplane hitting a house if dropped randomly from the sky are very low – even ignoring the fact that they spend most their time over the ocean. And even dropping one on a residential area, the population density of a plane is much higher than a house.

      1. Not MY town. Hilo (the town most often punished by Pele these days) is a nice place to visit, but I wouldn’t want to live there (and not just because of the lava…). Hilo and the surrounding settlements were in place long before that slope of Kilauea started feeling the burn in modern times, so the residents can perhaps be forgiven for unfortunate planning. And when the lava does come it tends to be rather relentless (kinda hot & heavy, y’know), so a zero-sum result is somewhat inevitable. You could steer it (if permitted), but it would take something pretty drastic to actually stop it. Maybe one of those civil engineering nukes they used to talk about could blast out a big enough hole, but that would be a tad counterproductive.

        Anyway, the chances of a plane dropping onto a populated area aren’t so low because, as others have noted, most crashes happen on takeoff or landing and most airports are in cities. It’s relatively rare for a plane to crash in the middle of an ocean. Of course, at very low altitudes a parachute would be useless even if there were a way to deploy it effectively, so the whole discussion is rather moot. In any case, NIMBY please.

        1. I dunno, airports use a lot of land, city land is expensive. Old airports are often in cities, newer ones they like to build out of town, where it’s cheaper, and rely on road and rail links to get passengers there.

          In the case of Japan and Hong Kong, you build your own land in the sea, and that works out economically.

  5. Parachutes for large planes are quite possible and doable. There was a proposal years ago to separate passenger compartment, in the case of need, and use parachutes for that part only. But … $$$ is more important than human lives. Thousands could have been saved already.

      1. Remember Air France few years ago? It stalled at high altitude during storm, pilots lost orientation and it plunged into Atlantic. Then oxygen loss in cabin over Greece few years back. Even Russian jet downed by Daesh could have been possibly saved. This is just off the top of my head.

        1. Parachute in the middle of a storm? The high winds would destroy it. Oxygen loss? If it is too fast for the pilots to deploy emergency oxygen how are they going to deploy a parachute? Planes downed by bombs? If the fuselage is split open how is it going to cope with being hung from paracord? Not much chance there either.
          Light aircraft are much more likely to be at an altitude and speed where a parachute can help, as well as needing a much less substantial system.

          1. 1. Properly designed parachutes can be deployed even at supersonic speeds (some Mars landings used that).
            2. System would automatically deploy is oxygen falls bellow certain level. Greek plane was flying for hours while people slowly died.
            3. On three you might be right. Still, if even remains were lowered slowly, some people would probably survive. Bomb did not kill everyone outright.

          2. Mars has a very thin atmosphere. On Earth the nearest you get are spacecraft reentering the atmosphere here, and they start by aerobreaking, then deploy drogue ‘chutes to stabilise and help slow them to terminal velocity before deploying their main chute. Storms can rip the wings of aircraft, you are convinced that a parachute can survive that? And at a size and weight that is practical?
            Automatic deployment of the ‘chute at speed, while the pilots are potentially trying to deal with other problems and against the power of the engines? Much safer and cheaper to have the autopilot automatically descend unless overridden.

        2. The Greece one could have been saved just by a software upgrade…
          If there is a life-threatening condition and the pilots do not react by pushing a “dead man switch” in time (like in some trains, where if they don’t press it when asked, the train just stops), the autopilot takes over and descends into a safe altitude.
          Planes being destroyed by AA fire are very unlikely to be saved by parachutes…even if the parachutes systems are not damaged and the remaining parts of the plane won’t get ripped apart by them, the bad guys could just wait and mow them down with machineguns on Toyota pickups once they land…

    1. @Miroslav
      When safety costs dollars, safety features are a zero sum game. Which do you think ends up giving better safety per dollar: taking up weight and space with a gigantic parachute system, or giving pilots additional training? Remember that most accidents happen on landing or takeoff, and most of the remainder is still the result of somebody screwing up. Also remember that you would then have to train crews in using the parachute system and determining *when* to use it.

      Point is, flying is already the safest form of travel by faaaaar. This is not accident or coincidence. The airlines care very, very much about the safety of their passengers. Regardless of whether the reasons are cynical or altruistic they’re in the unenviable position of having to maintain that level of safety while remaining solvent, and (this part frequently seems to be forgotten in these sorts of discussion) keeping the cost low enough that *people can afford to fly.*

      Though I suppose never flying would guarantee no one dies in an aircraft accident.

  6. Rather than parachutes, it would be more useful to increase the possibility of survival in the event of a crash, as an aircraft relies on electrical and mechanical systems which WILL break down, yes we have triple redundancy, but they still crash, although less than they used too. A fundamental change in design to massively increase the longitudinal rigidity of the fuselage would have this effect. Many of barnes-wallaces WW2 designs were famous for being flown home with huge holes blown in them, and likewise some USA designs. The present monocoque and bulkhead construction loses most of its strength when slightly distorted. Like some have said above, if it costs dollars, it won’t happen!

  7. 3-5 illogical fallacies and high mathz. associated with our lines of thinking.
    1.) Piliots get stuck in thinking they can “fix it”.
    2.) What is more important? The Luggage, Freight or persons life.

    I’ve always been of the opinion the way they count loss of life is scorched stand alone metal buckled belts to know how many pay outs they have to do. Five point buckle means they care.

    Back in the day amateur rocket hobbyists created $200-2k rockets. With a long plastic ribbon that cost less then 2 dollars.

    Osprey is one of the worst failures in aviation design no free counter rotation like a standard helicopter.

    3.) If it breaks, let it break up… like Legos. Dump everything and 2 seconds later rail out the passenger rows at time and one chute per row.

    4.) It was easy to think when were children as things being modular. Lego’s, Lincoln logs, tinker tools, etc. Yet as adults we can’t?

    If you are gonna pack in like sardines and have to a pull a 16 flight, Fuq ALL. Gimme a pod like 5th Element to sleep in.

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