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NASA Designs All-Electric Personal Flight Vehicle

MikeChino writes "NASA is currently working on a personal aircraft that will put jet packs to shame. The Puffin is an all-electric one-man airplane that could be the start of some new and amazing air travel technology. With two prop electric engines, lithium phosphate batteries and a top speed of almost 300 mph, the vertical take off and landing vehicle was originally designed for covert military insertions because it has a lower heat signature than combustion engines. The Puffin would also be super quiet – 10 times quieter than current low-noise helicopters, and since the engine is electric it has no flight ceiling and can fly up to 9,150 meters high, uninhibited by thin air."

48 of 276 comments (clear)

  1. "No flight ceiling" by JoshuaZ · · Score: 5, Interesting

    "since the engine is electric it has no flight ceiling and can fly up to 9,150 meters high, uninhibited by thin air." I presume they mean in this context no substantial flight ceiling where the engine gives out from lack of oxygen and you have a very bad day. That's backed up by the original article which says that "It has no flight ceiling--it is not air-breathing like gas engines are, and thus is not limited by thin air--so it could go up to about 9,150 meters before its energy runs low enough to drive it to descend." So in fact you could fly this much higher than 9,150 meters if you started out high up (from say a larger aircraft) or had a parachute. This leads to a question: How high up could it go before the air becomes too thin to generate enough lift to continue ascending?

    1. Re:"No flight ceiling" by gyrogeerloose · · Score: 5, Interesting

      I'm not an engineer so I can't comment on the operating ceiling of the the thing but speaking as a former private pilot, 9,150 meters (FL 28, roughly) is already well above the point where the pilot-in-command would be allowed to operate without supplemental oxygen.In fact, up that high you'd be messing with the three-holer transport jets and would probably need a pretty high-quality heated flight suit.

      --
      This ain't rocket surgery.
    2. Re:"No flight ceiling" by rockNme2349 · · Score: 4, Funny

      That was my personal favorite quote.

      It has no flight ceiling... so it could go up to about 9,150 meters

      --
      Sewage Treatment Facilities - "Our duty is clear."
    3. Re:"No flight ceiling" by Anonymous Coward · · Score: 3, Insightful

      Not only does it become difficult to generate lift, but to keep the electric motors cooled. You're always going to have losses in the form of heat and that's generally carried away by the air moving past the motor. An overheated motor when that's what's keeping you from plummeting isn't cool... literally.

    4. Re:"No flight ceiling" by Anonymous Coward · · Score: 2, Interesting

      Well Everest is just under 9km up, and people have scaled it without oxygen. However these were mountaineers, and not duty free guzzling pilots.

      I also am completely unqualified in aerodynamics, but I would assume (most probably incorrectly) that the ceiling would be limited by the speed the rotors turn and also the length/surface area they have (assuming the pilot is appropriately dressed for the occasion).

      I'm quite interested actually in any responses that could shed some light on this... seems pretty cool.

      On a side note, we had here (in Australia) on "The New Inventors" some dudes that actually made a battery powered helicopter. It was kind of like a gyrocopter - pretty light weight 1 seater kind of thing. It had a pretty shitty filght time, on the order of minutes, but obviously they only used bog standard batteries (ie they didn't develop any special batteries or anything, "just" hooked them up to a motor and modified the gyro).

      For those not familiar, the show basically has random people that have invented something come and show it to a panel, and they decide on a winner each week. It's pretty cool, you get anything from automatic sheep tilters(yes, that) to stuff that automatically re-sheaths pneumatic hoses. Riveting stuff :) .

    5. Re:"No flight ceiling" by spidkit · · Score: 2, Informative

      The reference to max altitude being un-inhibited by thin air due to the powerplant not being combustion based is misleading. The term "service ceiling" is used to define the altitude at which (generally), aircraft will not climb at a rate faster than 100 feet per minute in a sustained climb attitude. This is a factor of air density (and max available power) - which affects both power output of the "engine" if this were a combustion engine, as well as the airfoil, and the lift (and drag) it produces (in a fixed wing craft). If the powerplant is electric, one still contends with air density which as a factor in the lift formula: L = (1/2) d v2 s CL, where * L = Lift, which must equal the airplane's weight (and pilot) in pounds * d = density of the air. This will change due to altitude. These values can be found in a I.C.A.O. Standard Atmosphere Table. * v = velocity of an aircraft expressed in feet per second * s = the wing area of an aircraft in square feet * CL = Coefficient of lift , which is determined by the type of airfoil and angle of attack. reference: http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/lift_formula.html If the air gets too thin - you're lift value will drop, and if it drops out (pilot plus craft weight) before the battery runs down, the craft will cease to climb because of the drop in air density.

    6. Re:"No flight ceiling" by garyebickford · · Score: 4, Informative

      The other factor is that the typical propeller does become less efficient as the air gets thinner, so there is still a ceiling. Jets (turbofans) have less of an issue with this. From a quick Google, It appears that above Flight Level 240 (24000) the majority of the thrust of a turbofan comes from the jet exhaust, while at sea level most of it comes from the fan.

      For me, the sheer fear factor of looking down from 9000 meters (30,000 feet) in not much more than my flight suit would be more than I'd be ready for.

      But I think this could be the inspiration for the long-awaited personal aerial commuter vehicle - especially if operation can be automated, and if the redundancy mentioned in TFA can achieve no-single-point-of-failure. If routing were handled by a central traffic control system, and local traffic position were handled by an agent swarm, it could work pretty well. The VTOL capabiliy means you could land in a parking space, or on the roof. And the 80 mile cruising range would be sufficient for commuting.

      --
      It's easier to be a result of the past, but more fun to be a cause of the future! http://www.spacefinancegroup.com/
    7. Re:"No flight ceiling" by nicc777 · · Score: 2, Informative

      "For me, the sheer fear factor of looking down from 9000 meters (30,000 feet) in not much more than my flight suit would be more than I'd be ready for."

      As a skydiver with HALO experience I can tell you that there is nothing to fear. You do not really have depth (or is that height) perception at that altitude. Yes, everything does look tiny and as a skydiver I sometimes wonder if I will make the target (a football field looks like a tiny dot or button below). However, since this is powered flight, that's not really an issue.

      --
      Need an ISP in South Africa?
    8. Re:"No flight ceiling" by FlyingGuy · · Score: 3, Informative

      Your about 10,000 feet off.

      Class "A" Airspace begins at FL180 (18,000 ft AMSL) and continues up to FL600 (60,000ft AMSL). AMSL = "Above Mean Sea Level"

      To fly in class "A" airspace you must be following a filed IFR Flight Plan and have two way radio communication. These are the only requirements.

      There is one instance where one is required to fly VFR in class "A" airspace. Look it up! I will give you a hint: FAR part 91 and AIM 6-x-x

      yes I am a pilot.

      --
      Hey KID! Yeah you, get the fuck off my lawn!
    9. Re:"No flight ceiling" by gyrogeerloose · · Score: 2, Informative

      Well Everest is just under 9km up, and people have scaled it without oxygen.

      That may very well be true but, at least in the US, the pilot-in-command of an unpressurized aircraft is required by FAA regulations to use supplemental oxygen when flying at 10,000 or feet for more than a certain amount of time.

      --
      This ain't rocket surgery.
    10. Re:"No flight ceiling" by khallow · · Score: 3, Informative

      At those altitudes, wouldn't the fact that the air be EXTREMELY cold? (I think -52c or so at 30k feet?)

      The problem is that air is far less dense at those altitudes. There's roughly a third the air at sea level. For example, suppose you're trying to keep the engine below 80C. An air flow at sea level and 20C that barely does it, would be equivalent to a third the airflow at -100C.

    11. Re:"No flight ceiling" by StarsAreAlsoFire · · Score: 2, Interesting

      Speed of sound is related to temperature ONLY. It is for this reason (ultimately) that turbo-props are most efficient for short flights, and turbofan for long flights.

      Most of a ~200 mile commercial flight is spent ascending and descending. Not so much time spent at cruising altitude. Props are significantly more efficient at low altitudes, compared to turbofans. Recall that we are talking about turbine engines in both cases! The 'burn fuel in air' part of the engine is *exactly* the same. The efficiency comes down to the type of blades you're spinning - a few very long unenclosed blades work great -- right up until you have to spin the blades so fast that the Mach-effects of one blade start interfering with the air around the next blade. The fan in the turbofan uses a bunch of smaller blades designed to avoid Mach-effects of this nature. So when those effects start to come into play you see the efficiency of turbofans stay the same (basically) while the efficiency (and eventually capability, if you keep climbing) of the turboprop plummets.

      Of course there's all sorts of craziness regarding gear ratios and a bazillion other things that I completely ignored here. But as a high level overview, it's not worthless.

      If you can do VTOL, you design for sea level -- a huge portion of your fuel/energy tends to go into getting you up and down. So how high can you CRUISE on a prop designed for optimal performance at sea level? At a guess, closer to 5km/12k feet than to 10km/33K feet, driven by the weight-cost of pressurizing the beast. But there are a bunch of variables:

      - What speed do you want to cruise at?
      - What is your range? Is it WORTH getting to 30k (40k, 50k, 12k) feet, only to start descending as soon as you do?
      - How much can you feather your prop blades? (Change their pitch, letting you spin the blade faster at high altitudes while decreasing blade turbulence)
      - What is your L/D? (Lift to drag ratio) At sea-level, your optimal speed may be 200mph. At 30K feet you have to go 300mph for the same amount of lift. Lift to drag ratio tells you that the amount of energy required to overcome that induced drag is the same for 200 mph and sea level as it is for 300mph and 30K feet.
      (But that doesn't take prop drag into account. If your prop flies apart because you have to turn it at 20K rpm to stay in the air at 30K feet, all bets are off.)
      - more and more, and weather, and a lot about temperature, and how much does it cost to pressurize the cabin, etc).

      As for ultimate limits, the difference between stalling and breaking the sound barrier was about 50 knots for the U2 flights. That may have been plus or minus 50', but I think it was actually +/-25. Memory fails. Anyway, 68K feet is a *seriously* nerve-wracking place to fly if your airplane can't do Mach.

      The F-15 managed a zoom-climb 'somewhere in the region of' 70K (I've seen 80k cited) feet. That is 'go as fast as you can at the highest altitude that your engines stay lit, and then dive, to go even faster. Then, at a very exact point determined by guys with slide rules, kick on the after-burners and start climbing at a particular angle. Then your engines burn out, then you coast. If you are in the united states and flying an F15, you launch a missile that destroys a satellite. Then plummet back to earth completely out of control, because there is no air going across your control surfaces. And hope you don't enter at the wrong angle, because there are ways you can come back to earth which would preclude you re-lighting your engines in time to save the plane. Nobody WANTS to eject.'

    12. Re:"No flight ceiling" by Anachragnome · · Score: 5, Interesting

      Ask the fucking craziest of them all, http://en.wikipedia.org/wiki/Joseph_Kittinger .

      Personal experience is as good as it gets...

      "Capt. Joe W. Kittinger achieved the highest and longest (14 min) parachute jump in history on August 16, 1960 as part of a United States Air Force program testing high-altitude escape systems. Wearing a pressure suit, Capt. Kittinger ascended for an hour and a half in an open gondola attached to a balloon to an altitude of 102,800 feet (31,330 m), where he then jumped. The fall lasted 4 minutes and 36 seconds, during which Capt. Kittinger reached speeds of 1142 km/h (714 mph) [9]. The air in the upper atmosphere is less dense and thus leads to lower air-resistance and a much higher terminal velocity."

      Gives the phrase "No Fear" a whole new meaning.

    13. Re:"No flight ceiling" by wagnerrp · · Score: 3, Informative

      From a quick Google, It appears that above Flight Level 240 (24000) the majority of the thrust of a turbofan comes from the jet exhaust, while at sea level most of it comes from the fan.

      While possibly true in practice, it has nothing to do with altitude. Thrust comes from the mass flow rate, times the change in velocity. Aside from fighter jets on afterburner, the exhaust coming out of a jet engine will be subsonic. The speed of sound is proportional to the square root of temperature, so the hot core flow will be much faster than the relatively cool bypass flow.

      So what relevance is this to anything? By 'sea level' the quote you saw probably meant 'take off', or zero forward velocity. FL240 would be cruise at 500-550 knots. You have high mass flow but low velocity through the bypass fan, and high velocity but low mass flow through the core. At cruise speed, the velocity differential of the bypass flow may only be 1/4 what it was static, while the much hotter and faster core flow still has more than half its differential. Modern high bypass turbofans have ratios of 9:1 or better, so the bypass will still be producing more thrust than the core even at the reduced efficiency.

    14. Re:"No flight ceiling" by wagnerrp · · Score: 2, Funny

      As for ultimate limits, the difference between stalling and breaking the sound barrier was about 50 knots for the U2 flights. That may have been plus or minus 50', but I think it was actually +/-25. Memory fails. Anyway, 68K feet is a *seriously* nerve-wracking place to fly if your airplane can't do Mach.

      It was +/- 5 knots. Luckily at that altitude, there are no gusts.

    15. Re:"No flight ceiling" by ravenspear · · Score: 4, Informative

      Well Everest is just under 9km up, and people have scaled it without oxygen. However these were mountaineers, and not duty free guzzling pilots.

      Also that's a totally different scenario. High altitudes like that without oxygen while mountain climbing are achievable only by letting the body acclimatize for several weeks at progressively higher altitudes during the climb.

      You take anyone at sea level and put them immediately at 9km up without oxygen, they will pass out within minutes.

    16. Re:"No flight ceiling" by aug24 · · Score: 3, Funny

      For me, the sheer fear factor of looking down from 9000 meters (30,000 feet) in not much more than my flight suit would be more than I'd be ready for.

      Yeah. To correct the GP:

      In fact, up that high you'd be messing with the three-holer transport jets and would probably need a pretty high-quality heated flight suit with a built in diaper.

      Justin.

      --
      You're only jealous cos the little penguins are talking to me.
    17. Re:"No flight ceiling" by Uzik2 · · Score: 2, Insightful

      I don't get fear of heights at 30000ft... At 30ft it's another story.

      --
      -- Programming with boost is like building a house with lego. It's a cool but I wouldn't want to live in it
    18. Re:"No flight ceiling" by garyebickford · · Score: 2, Interesting

      Hmm. Interesting point. Also, to some extent I think it is a matter of choice. I never had issues with height when I was a kid - climbed 200 ft. fir trees like a monkey, used to hang out in the top and read books. More recently I've had issues. But then I bought a sailboat. It took me a while to get myself to start climbing the mast but once I got up there (65+feet above ground at the time) and started appreciating the view, the fear went away. I still respect the height but I don't seem to have the fear like I used to. So in part maybe it's a mental habit.

      --
      It's easier to be a result of the past, but more fun to be a cause of the future! http://www.spacefinancegroup.com/
  2. CG concept only by QuantumG · · Score: 5, Insightful

    By March, the researchers plan on finishing a one third-size, hover-capable Puffin demonstrator, and in the three months following that they will begin investigating how well it transitions from cruise to hover flight. They are already looking past the Puffin, however.

    And that's why we'll never see a full sized vehicle.

    The next-generation of this design might incorporate more than just two pairs of prop rotors, so that if one was struck by, say, a bird or gunfire, the aircraft could survive on redundant systems. "We could make it so there's no single point of failure--that's the cool next step," Moore says.

    Ya know what a cool next step would be? Actually making the vehicle.

    --
    How we know is more important than what we know.
    1. Re:CG concept only by scdeimos · · Score: 2, Informative

      Your V-22 video was an unfortunate example. The V-22/XV-15/BA-609 tilt rotor platform is generally stable and easily controlled, ala this video.

    2. Re:CG concept only by ZosX · · Score: 2, Insightful

      4 crashes since its inception? That really isn't so bad. You should compare with other military planes. Also at least half of those crashes were due to maintenance, parts failure issues and really have nothing to do with the actual design of the craft. I would say the press did a pretty good job of convincing everyone that the V-22 was a flying deathtrap.....

    3. Re:CG concept only by jcr · · Score: 3, Insightful

      4 crashes since its inception? That really isn't so bad. You should compare with other military planes.

      Hell, just compare it to the early helicopters. The tilt-rotor concept is a major advancement. The accidents are regrettable, but not at all surprising.

      -jcr

      --
      The only title of honor that a tyrant can grant is "Enemy of the State."
    4. Re:CG concept only by timeOday · · Score: 2, Informative

      The people that tend to get all vitriolic about the Osprey are generally the people who don't like any spending on military hardware ever.

      To be fair, it has a body count of 30 people in 3 separate incidents, even before it reached operational status. Very few defense programs must own up to that kind of numbers.

      That said, I now see them flying around most days of the week and they are sure cool!

  3. psst, NASA, just one little thing. by 140Mandak262Jamuna · · Score: 5, Funny

    Those little bars on the display that shows the charge remaining? Don't trust it. It does not work.

    --
    sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
  4. Cool toy, but we can't have it. by zeugma-amp · · Score: 2, Insightful

    The U.S. government will never allow widespread use of such a craft. The FAA is trying to essentially eliminate community airfields with their regulations and "anti-terrorist" programs. While I'd love to be able to fly to work, it's just not.going.to.happen.

    --
    This is an ex-parrot!
  5. Re:My question is.. by R3d+M3rcury · · Score: 4, Informative

    Well, let's see...

    FTFA:

    [...] the Puffin can cruise at 240 kilometers per hour [...] With current state-of-the-art batteries, it has a range of just 80 kilometers if cruising [...]

    So it can stay up about 20 minutes.

    It would work for me. I could get to work in about 15 minutes and plug it in. At the end of the day, it's all charged up and I take it home.

    So, yes. I want one.

  6. Been there, done that by arcsimm · · Score: 2, Insightful

    Somewhere in Switzerland, Yves Rossy is wondering what took NASA so long.

  7. Is Elmer Gantry Available? by b4upoo · · Score: 2, Insightful

    I will believe it when I see it. Batteries that good are a dream. And as far as the nearly 30,000 foot ceiling of this device cold and thin air might be a serious issue. Pilots generally like to breath and being turned into a frozen, air starved corpse is not a goal for most of us. Or are we supposed to think this thing with have a closed cabin with oxygen and heat available? Jesus, we can't even get good batteries for electric bicycles yet.

    1. Re: Is Elmer Gantry Available? by Tablizer · · Score: 2, Funny

      being turned into a frozen, air starved corpse is not a goal for most of us.

      Exceptions for lawyers, politicians, and SCO employees.
         

  8. And part of the project is named Icarus? by JoshuaZ · · Score: 5, Insightful

    I don't understand why so many flight related programs are named Icarus. Let's remember what happened in the myth of Icarus: He flew too close to the sun and so he died. I can't tell if such program names are deliberately humorous (hah! Let's see if we can get pilots to fly in something named Icarus! Yeah, I already did that. Let's try to see if we can get them to test out a project named after a flightless bird. Maybe something like a kakapo http://en.wikipedia.org/wiki/Kakapo that sometimes gets hurt from thinking it can fly when it can't), or if they just don't know any other myths related to flight, or if this is a deliberate comment about how many classical claims about "hubris" simply hold humans back from genuine progress. But would it hurt if occasionally a program was named after Horus or after Odin's raven?

    1. Re:And part of the project is named Icarus? by jcr · · Score: 2, Informative

      I don't understand why so many flight related programs are named Icarus.

      It's because most people don't know who you're talking about if you say Daedalus.

      -jcr

      --
      The only title of honor that a tyrant can grant is "Enemy of the State."
  9. Re:Go the "Green Spin" by jcr · · Score: 3, Interesting

    how quickly will it hit the ground if it runs out of power.

    You should be able to auto-rotate like you can with a helicopter. Also, there's always the parachute option.

    --
    The only title of honor that a tyrant can grant is "Enemy of the State."
  10. Re:thin air? by Thagg · · Score: 4, Interesting

    Note well that the highest flying prop plane ever, the Aerovironment Helios, flew to 96,000 ft -- far higher than almost any other plane (probably the only one that could sustain that altitude was the SR-71). The Helios was powered completely by solar cells and electric motors.

    --
    I love Mondays. On a Monday, anything is possible.
  11. Innumeracy? by gyrogeerloose · · Score: 2, Interesting

    From TFA:

    electric aircraft are much quieter than regular planes—at some 150 meters, it is as loud as 50 decibels, or roughly the volume of a conversation, making it roughly 10 times quieter than current low-noise helicopters.

    I admit that I never have gotten a handle on math beyond algebra but am I wrong by being bothered by statements like 10 times quieter? Wouldn't be better to say "makes only one-tenth the noise?" Or am I being pedantic?

    --
    This ain't rocket surgery.
    1. Re:Innumeracy? by evilWurst · · Score: 2, Informative

      You're not being bad. The "x times less" construct is really clumsy. IMO, it's mainly journalists and marketers using it; they're just punching (small new number) / (big old number) into a calculator, rounding it, and then the brain shuts off and they just say the new one is (result) times less.

      The slashdot summary blurb is even worse, since sound is measured in decibels, which aren't linear. (IIRC, 3 db is a factor of two... so 33 db would be twice as loud as 30 db, and half as loud as 36 db). So if a normal helicopter was 120 db and the electric was 12 db and someone said "ten times quieter" they'd be very, very, very wrong. The actual article at least gives the electric volume as 50 db and compares it to the volume of spoken conversation, so you can at least ignore the potentially misleading math part in this case. Then again, it says that's the volume from 150 meters away... obviously it'd be much louder for the one flying it.

  12. Battery powered aircraft:Completely unrealistic by viking80 · · Score: 3, Interesting

    Li-ion-anything has an energy density equaling 1% of gasoline. Lithium phosphate batteries are worse than others in energy density, but safer.

    So for the same fuel weight, instead of a 2 hour flight reserve, you would have 72 seconds.

    Until there is a radically different battery, this is unrealistic.

    --
    don't cut it off www.mgmbill.org
  13. Re:Earth to Orbit vehicle? by Brett+Buck · · Score: 3, Informative

    This is odd that someone hasn't already cashed in on this. Is this a possible precursor to a simple earth to orbit vehicle?

        Not in any way, shape, or form. Getting to 20-30000 feet, if it was capable of that, with a very small payload, it essentially worthless in terms of orbital. To get into orbit the chief challenge is velocity. To get that (without other far more interesting technical breakthroughs) you need a HUGE rocket with very large amounts of fuel. So there is really no role at all for this teeny little helicoper/VTOL airplane.

              Brett

  14. Re:Earth to Orbit vehicle? by bertok · · Score: 4, Informative

    I'm not implying they could get into orbit with this vehicle as it obviously will require atmosphere for the rotor blades to be effective, but in a general sense. Specifically getting a launch vehicle as far into the atmosphere as possible before switching to a different means of propulsion like a typical rocket.

    Achieving orbit is about speed ('delta v'), NOT altitude. It takes much more energy to get the horizontal speed to the required level than to reach the required altitude. Getting above the atmosphere helps, but not all that much.

  15. Thank you, Google! by _merlin · · Score: 5, Funny

    PSA: don't blindly search Google if you want to find out what a "three-holer" is - I don't think any of the top hits are what he's referring to.

  16. Re:My question is.. by jamesh · · Score: 2, Funny

    "Puffin Man" doesn't have quite the same ring to it though, compared to the names of other super hero's...

  17. I see... by DieByWire · · Score: 4, Funny

    I see dead people.

    --
    Never shake hands with a man you meet in a fertility clinic.
  18. Battery powered aircraft by Make · · Score: 2, Informative

    The Antares 20E made its maiden flight in 2003. It is a self-launching glider with battery powered engine:

    http://www.lange-aviation.com/htm/english/products/antares_20e/antares_20E.html

    A wonderful glider. Sad it's so expensive (several 100k euros).

  19. And we'll never be allowed to have one by Leo+Sasquatch · · Score: 2, Insightful

    Go read Bob Shaw's 'Vertigo'.

    The changes this would make to society are too great. The politicians would never allow common people to have that much freedom. No borders, no passports, no way of stopping people from going where they wanted, when they wanted. And that's without assuming any purpose more nefarious than a cheap weekend in Amsterdam.

    One asshole with one of these and a pocketful of golf balls could cause carnage in a city centre at rush hour - no way to track or find the culprit afterwards. As long as there's idiots who think throwing rocks off motorway bridges is a fun thing to do, there'll be idiots who'll be delighted to abuse this even worse. Drug dealers, criminals of any kind who want to make a clean getaway (get 10 feet off the ground and nobody's catching you, no matter how fast the police car).

    It's not the physics of flight, or fuel capacity, or engine efficiency that will stop us ever getting personal flight vehicles - it's the politicians who will legislate it out of existence for all but the very rich, because whatever rich people want is always all right. And they'll do it in the name of safety, and it'll be for our own good. There'll be a huge furore in the media when the first one crashes and kills someone, and that'll be it done with.

    1. Re:And we'll never be allowed to have one by alobar72 · · Score: 2, Interesting

      The politicians would never allow common people to have that much freedom. No borders, no passports, no way of stopping people from going where they wanted, when they wanted. And that's without assuming any purpose more nefarious than a cheap weekend in Amsterdam.

      I wonder if there was someone a hundret years ago, who said something like this about cars.... I think, if you put some technology into those thing - most of the problems you adress could be solved. Could be some kind of electronically "check-in" when entering special areas or such... come on... I realy _want_ this :-)

  20. Capt. 'Cannonballs' Kittinger by rts008 · · Score: 3, Interesting

    Wow! And I thought I was nuts for loving HALO[High Altitude, Low Opening] jumps!
    [With full equipment/kit load+body wt. @ around 275 lb./125 Kg] I was told that the max. velocity was around 130 mph/209 kph...compared to 714 mph, I guess I was a piker!

    Offtopic side note:The highest we ever jumped from was around 17,000 feet altitude; I found my minimum altitude for releasing my chute was approximately 385 feet, but it hurt!
    (we were advised that the minimum altitude was 500 feet...I had to test this)
    [using the US Army version of the Ram Air-square type 'chute]
    That was also where I got over my fear of heights, once I was thrown out of a perfectly good airplane!

    --
    Down With Slashdot BETA!!! I've been around the corner and seen the oliphant; you can only abuse me from your perspecti
    1. Re:Capt. 'Cannonballs' Kittinger by Zordak · · Score: 3, Funny

      I found my minimum altitude for releasing my chute was approximately 385 feet, but it hurt! (we were advised that the minimum altitude was 500 feet...I had to test this)

      So are you still chasing that Darwin Award, or have you given up ;-)

      --

      Today's Sesame Street was brought to you by the number e.
  21. Re:Earth to Orbit vehicle? by camperdave · · Score: 2, Insightful

    No. Rocket staging has nothing to do with requiring different propulsion systems in different parts of the atmosphere. Rocket staging is about shedding weight and attaining velocity. The more mass you are trying to lift, the more propellant you require. The more propellant you require, the more tankage you need. The more tankage you need, the greater the mass you are trying to lift. Since, after a while, the tanks are mostly empty, why bother continuing to lift them? They aren't needed anymore. Divide the propellant into separate tanks, and when one tank is empty, ditch it.

    Now, it's a lot easier to drop the tail end off of a rocket than the forward end, so you drop the engines and the tanks, then switch to a different set of engines. Coincidentally, once the first stage is done you've left the thickest part of the atmosphere, so it makes sense to switch from engines that are efficient on the ground, to those that are efficient in a vacuum.

    So, the process isn't "Hey, I'm in a vacuum now, so I need to switch engines.", but "Hey, I'm carrying a lot of dead weight. Let me cut some loose.".

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