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12/04/09
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Mach is the speed of sound, but the speed of sound is progressively slower as you get higher in the atmosphere since it gets less and less dense, so Mach 21 in the upper atmosphere may not be all that impressive.
Is there a standard altitude or air density which determines Mach or is it variable? Is this Mach 21 as if it was at 30,000 feet?
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So basically, the capsule hits the atmosphere and the compression heating of air forms a plasma. The field acts on the particles, which does a few things:
1. The plasma is directed away from and around the craft, cutting down on heat transfer and preventing the surface of the craft from superheating.
2. The magnetic field reacting with the plasma creates a drag force on the electromagnet, which slows down the capsule.
3. The plasma presses against the air, forming new plasma to replace that which has been pushed away.
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Either that, or they're using a buttload of Crisco.
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I mean... do mag lev trains generate friction along the field that supports them? or magnetic bearings along their track? I wouldn't think they do. There's nothing coming in contact with anything, so there are no molecules available to interact and cause friction.
In any case, even if this does not entirely eliminate friction, it must reduce it to close to zero. If nothing else because it's an active force pushing molecules away from the ship, instead of letting them hit the skin and slide along it.
12/03/09
I think the majority of re-entry heat is from compression anyway, but I'm not 100% sure. Either way, the vehicle isn't going any faster, or marginally so.
12/03/09
All the re-entry heat is from compression. Friction is a red herring.
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No matter how hot air might get from compression, if it does not touch the skin of the ship there is no possibility of heat transfer from convection. Haven't you ever had a vacuum thermos? it's the same principle! They've been around for like... a hundred years.
12/03/09
Guy, I don't even know what to say to you. This system most certainly does not work like a vacuum thermos, and it does not work by reducing friction.
At the velocities they are talking about, radiative heating may be a bigger problem than convection anyway.
Would you like me to explain why vacuum thermoses are silvered?
12/04/09
Why don't you just explain it to me Kyle "XY" Huff? Why don't you explain why a vacuum does not insulate, and how delfecting air does not reduce friction.
Why don't I just make myself a tea, settle in to an armchair, and Kyle XY here is going to give me a goddamn lesson in how to read an article. So, Kylie. Let's go. Here's your chance. Dazzle us. Do it.
05:44 PM
Vacuum insulates, but heat can still be transferred through radiation. Thus why things will eventually freeze in space and heat-sinks do work (though they need to be larger).
Deflecting the air certainly changes the friction since air molecules aren't getting caught on the molecular ridges of the vehicle's surface, however air molecules are still slamming into each other creating plenty of heat and the magnetic field may not be perfectly smooth either.
A perfectly frictionless vehicle will still be slowed down and heated up when travelling through a medium unless it was perfectly aerodynamic (both "perfects" are impossible).
02/02/09
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If you're going to comment on a technical blog, the least you could do is not show your ignorance by using ridiculous terminology. The correct phrase is rudder thingies.
Sheesh.
11/24/08
I just cant wait until they put a credit card swiper at the lavatories...
11/24/08
Oh, now that's just crazy. That's like saying, "wait until they start charging you exorbitant fees for your normal luggage and carry-ons." As if that kind of thing could ever really...
Oh. Wait.
11/24/08
Also, if it's only 15mph faster than the 747-8 like Lite says, and it flys much higher. Isn't it actually slower? Because the high altitude means a larger circumference to traverse?
I do see one huge advantage though. Skydiving with oxygen and thermal gear for a solid 3 minutes. Good times.
11/24/08
We're mostly limited to ~.85 mach for efficiency reasons at the moment. Boeing was going to build a plane prior to the 787 that would have cruised at like .97 mach, but w/ the rapid run-up in fuel costs the last few years, that plan was scrapped outright in favor of the 787's increased fuel efficiency.
What amazes me is that a plane designed in the 60's is still being revised and improved 40 years later. (747 Series)
11/24/08
Let's see, it flies... 15 mph faster on paper than a 747-8 at cruising speed. It is also only a twin-engine design which limits some routing as well.
11/24/08
My curiosity, though, is where's the vertical and horizontal stabilizers? Or are the winglets sufficient for yaw control? The horizontal stabilizer on conventional planes also allow for large variations in CG of the plane that you don't find so much in a "flying wing" design. Don't know how well this'll work for commercial service...
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