True for the Cirrus but parachutes would not be capable of safely handling a commercial size passenger plane, which is the type of plane Musk is envisioning as powered by batteries.
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Elon Musk
- Thread starter graham
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True for the Cirrus but parachutes would not be capable of safely handling a commercial size passenger plane, which is the type of plane Musk is envisioning as powered by batteries.
Elon has mentioned supersonic VTOL electric aircraft before. It sounded fantastic at the time (unbelievable really). Now he mentions no wings, rudder or elevator, and gimbaled engines like a rocket.
That sounds a lot like the SpaceX grasshopper, but with electric fans instead of rocket engines. I think he said 70% of mass would be batteries. interesting.
How to land safely if (when) the electric fans fail? Perhaps redundant fan systems? Perhaps rocket engine backup? Perhaps jettison the crew/passenger module and do a parachute landing? Maybe some combination of the above.
GSP
That sounds a lot like the SpaceX grasshopper, but with electric fans instead of rocket engines. I think he said 70% of mass would be batteries. interesting.
How to land safely if (when) the electric fans fail? Perhaps redundant fan systems? Perhaps rocket engine backup? Perhaps jettison the crew/passenger module and do a parachute landing? Maybe some combination of the above.
GSP
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I got the feeling he was thinking of small business aircraft, not say an A320 commercial size. Could be totally wrong on that, but during his MIT talk that's the distinct feeling I got. Don't remember what he said that made me think that.
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About the aircraft.
Well, for it to be supersonic it needs to have a jet engine with supersonic output fumes which is kind of similar to a rocket engine, you basically need a nozzle. Its not gonna be an open rotor as far as I understand. In supersonic mode you have no use for regular wings or the streamlined aerodynamics of a conventional boeing 7x7. Just think about what fighter jets look like, stubby wings, sharp edges. Supersonic aerodynamics are very different.
Though, when he is talking about supersonic, I'm not sure he actually means locally supersonic. The plane is supposed to fly really high to take advantage of the low density atmosphere. Though, the speed of sound up there is much higher, so maybe the plane exceeds what we call the speed of sound on ground level, but actually travels in the subsonic regime continuously but at higher speeds as the atmosphere gets thinner. In that case a regular fan could be employed and regular streamlining is necessary.
Instead of having lots of flaps and stuff he just wants precision control of the motors.
Regarding the vertical take off and landing. Assuming the aircraft is truly supersonic, starting and landing in the inevitable subsonic regime is really inefficient anyway as the airplane will have terrible subsonic aerodynamic properties (that is being unstable and having a comparably high drag coefficient). And as this truly supersonic craft anyway needs a precision controlled jet-engines, maybe the most energy economical way is to go "straight up" to the lower density layers of the atmosphere and rapidly get into the supersonic speed where it is most efficient. And if the plane is not truly locally supersonic (but "regular" instead), maybe going "straight up" still isn't too much of an energy penalty as compared to a runway take-off.
Landing vertically seem like a smaller problem from an energy perspective. Gravity is on your side for the major part of the descent. In the end you need to make a halt but this could be a really short period of time given you have a high enough power density. For a short burst it doesn't have to require too much energy.
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Actually also the vertical take-off can be for only a few seconds until the aircraft is a few meters of the ground and then it can ascend like a regular craft. When he says that an electric jet is suitable for VTOL he might be referring to the fact that precision control of the engines both regarding power and tilt is done more easily with an electric system. Having electric motors on the other hand also makes it suitable for high altitude flight at high speeds. Meanwhile, high altitude high speed is not necessarily directly correlated with the VTOL properties per se.
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*off the ground...
Well, for it to be supersonic it needs to have a jet engine with supersonic output fumes which is kind of similar to a rocket engine, you basically need a nozzle. Its not gonna be an open rotor as far as I understand. In supersonic mode you have no use for regular wings or the streamlined aerodynamics of a conventional boeing 7x7. Just think about what fighter jets look like, stubby wings, sharp edges. Supersonic aerodynamics are very different.
Though, when he is talking about supersonic, I'm not sure he actually means locally supersonic. The plane is supposed to fly really high to take advantage of the low density atmosphere. Though, the speed of sound up there is much higher, so maybe the plane exceeds what we call the speed of sound on ground level, but actually travels in the subsonic regime continuously but at higher speeds as the atmosphere gets thinner. In that case a regular fan could be employed and regular streamlining is necessary.
Instead of having lots of flaps and stuff he just wants precision control of the motors.
Regarding the vertical take off and landing. Assuming the aircraft is truly supersonic, starting and landing in the inevitable subsonic regime is really inefficient anyway as the airplane will have terrible subsonic aerodynamic properties (that is being unstable and having a comparably high drag coefficient). And as this truly supersonic craft anyway needs a precision controlled jet-engines, maybe the most energy economical way is to go "straight up" to the lower density layers of the atmosphere and rapidly get into the supersonic speed where it is most efficient. And if the plane is not truly locally supersonic (but "regular" instead), maybe going "straight up" still isn't too much of an energy penalty as compared to a runway take-off.
Landing vertically seem like a smaller problem from an energy perspective. Gravity is on your side for the major part of the descent. In the end you need to make a halt but this could be a really short period of time given you have a high enough power density. For a short burst it doesn't have to require too much energy.
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Actually also the vertical take-off can be for only a few seconds until the aircraft is a few meters of the ground and then it can ascend like a regular craft. When he says that an electric jet is suitable for VTOL he might be referring to the fact that precision control of the engines both regarding power and tilt is done more easily with an electric system. Having electric motors on the other hand also makes it suitable for high altitude flight at high speeds. Meanwhile, high altitude high speed is not necessarily directly correlated with the VTOL properties per se.
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*off the ground...
Skotty
2014 S P85 | 2023 F-150L
I like the idea of a way to land safely in the event of engine failure, but it's not like you have that with current aircraft. When a critical failure happens on a modern jet forcing it to leave the sky prematurely it is usually referred to as a crash landing. Emphasis on "crash". It would be nice if future aircraft had improved safety systems in the event of an emergency. I think they already have a lot of redundancy and such built in, but improved flight abort systems would be appreciated.
jeff_adams
Member
Sinking ships have lifeboats, would be nice if planes figured out a way to do it as well.
Actually you have this back to front. The speed of sound at sea level is about 750mph, while at 40,000' it's about 650mph. It increases again when you go MUCH higher, but I doubt we're talking about those kinds of altitudes.
Skotty
2014 S P85 | 2023 F-150L
While I didn't cross check it's accuracy, this site has some pretty nice information on temperature and speed of sound at different elevations: http://www.aerospaceweb.org/question/atmosphere/q0112.shtml
Re the need to have jet engines in order to fly at the speed of sound.
Whilst this is true of current technology, it is not necessarily true. What is required is enough thrust to accelerate the vehicle to the required velocity. In general this means moving a lot of air with enough energy.
Propellers are excellent at moving lots of air, but lose out on efficiency at high altitude (due to air density) and at high speed, propeller tips travelling at or exceeding the speed of sound just don't work very well.
Jet engines on the other hand work quite well at altitude, they too have problems at supersonic speeds. The problem is the airflow through a jet engine at supersonic speeds can cause flame out and loss of power. I did learn about this millions of years ago during my apprenticeship, so I am a little rusty. As far as I am aware, must supersonic capable jet aircraft employ ramps in the air intakes to slow the airflow into the engine to sub-sonic speeds. Concorde did this and it was all controlled using analogue computers!
So all you need (sic) is a means of moving subsonic air in very large volumes backwards - One device capable of this that needs scaling up is the ducted fan. A large proportion of Radio control model aircraft employ this method of propulsion.
Could it work for a VTOL aircraft - Its all about thrust to weight. Just move enough air and voila.
I suspect the main issue will be energy density vs mass. The ideal would probably be high energy for a low mass. Hmmmm...
Whilst this is true of current technology, it is not necessarily true. What is required is enough thrust to accelerate the vehicle to the required velocity. In general this means moving a lot of air with enough energy.
Propellers are excellent at moving lots of air, but lose out on efficiency at high altitude (due to air density) and at high speed, propeller tips travelling at or exceeding the speed of sound just don't work very well.
Jet engines on the other hand work quite well at altitude, they too have problems at supersonic speeds. The problem is the airflow through a jet engine at supersonic speeds can cause flame out and loss of power. I did learn about this millions of years ago during my apprenticeship, so I am a little rusty. As far as I am aware, must supersonic capable jet aircraft employ ramps in the air intakes to slow the airflow into the engine to sub-sonic speeds. Concorde did this and it was all controlled using analogue computers!
So all you need (sic) is a means of moving subsonic air in very large volumes backwards - One device capable of this that needs scaling up is the ducted fan. A large proportion of Radio control model aircraft employ this method of propulsion.
Could it work for a VTOL aircraft - Its all about thrust to weight. Just move enough air and voila.
I suspect the main issue will be energy density vs mass. The ideal would probably be high energy for a low mass. Hmmmm...
Johan
Ex got M3 in the divorce, waiting for EU Model Y!
Biggest issue for traditional planes at high altitude is not enough O2 to combust the jet fuel. Battery + fan has no such issue.
To moderator: move this discussion to Electric Planes thread?
Ibdvideo. Well i think you have to think like this: a propeller/turbine/jet in subsonic motion creates thrust both from the pressure distribution it creates and from conservatioin of momentum when throwing stuff backwards. In supersonic flight the pressure wont help you so its alla bout throwing, like a rocket enginge. The wind you take in travels a supersonic speed, and thats all the air you have, so in order to overcome the resistance of takin in that air, you have to send i out at even higher speed. and to compensate for the rest of the air resistance, you probably need to expell it multiple times faster than that. So the exhaus really has to be supersonic. Anyway, supersonic engines already exist to somehow it works.
Though the air low air density is actually a good thing for it alows for higher speeds, but as Johan says, thats only of you dont need the oxygen intake.
Though the air low air density is actually a good thing for it alows for higher speeds, but as Johan says, thats only of you dont need the oxygen intake.
Tesla CEO Elon Musk (2014) - YouTube
Must watch for every Elon fanboy, Interviewer asks very personal questions "how much coffee do you drink"
quite interesting view into his daily life.
Must watch for every Elon fanboy, Interviewer asks very personal questions "how much coffee do you drink"
quite interesting view into his daily life.
So are we saying 70-80K feet in altitude so the sonic boom also doesn't reach the ground?
There are a number of factors which determine at what height a sonic boom will be heard on the ground.. This article indicates that 30,000 feet may sometimes be enough for T38 military jets.
medved
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