Breakable - 24 June 2010 04:55 PM

Would be interesting if some reaction-less drive would come online
http://en.wikipedia.org/wiki/Reactionless_drive

According to that article,
“The underlying problem [with reactionless drives] is that breaking the law of conservation of momentum shatters the entire mathematical framework [of physics].” These devices by their very nature violate the law of conservation of momentum

Let’s propose a reactionless drive that does not break conservation of momentum. All we need to do is to find a way to make weakly-interacting particles interact a little more strongly, and then find, among them, a favoured direction.

dennisp - 24 June 2010 05:40 PM

are you proposing heating via electric resistance? I think we just invented the flying toaster!

No. A 5MW Focus fusion generator, operating at 50% efficiency, will generate 5MW heat. Use that in your “jet” engine.

vansig - 25 June 2010 08:06 AM

dennisp - 24 June 2010 05:40 PM

are you proposing heating via electric resistance? I think we just invented the flying toaster!

No. A 5MW Focus fusion generator, operating at 50% efficiency, will generate 5MW heat. Use that in your “jet” engine.

If FF gets too efficient I think we can add microwave heating with oxygen or nitrogen resonant frequency.

Breakable - 25 June 2010 09:28 AM

If FF gets too efficient I think we can add microwave heating with oxygen or nitrogen resonant frequency.

Arrgh!

Please let FF get more efficient… do you know what trying to jettison 5MW of low-temp waste heat in return for 5MW of electrical power gained does to spacecraft margins? It should be a crime… :(

Microwaving air is a really bad idea - you end up with lots of nasty NOx compounds

jamesr - 25 June 2010 11:43 AM

Microwaving air is a really bad idea - you end up with lots of nasty NOx compounds

Does it generate more NOx than a kerosene powered turbojet?

These devices by their very nature violate the law of conservation of momentum

They only do that locally, while in the universe as a whole momentum is conserved.

The physics kinda intrigues me. He’s got an elegant explanation for inertia, based on relativity alone. The only other inertia theory brings quantum physics into it. And his theory is pretty similar to Cramer’s transactional interpretation of quantum mechanics. Maybe, contrary to the cartoon, the universe really is like that.

I admit I’m not exactly holding my breath for this one, but it seems worth the experiment. Given that it’s only evident under very contrived conditions, if it’s true it’s not something we would have noticed so far.

Will - 25 June 2010 11:56 AM

jamesr - 25 June 2010 11:43 AM

Microwaving air is a really bad idea - you end up with lots of nasty NOx compounds

Does it generate more NOx than a kerosene powered turbojet?

While an interesting question in itself it seems pretty much moot.  5 MWt at 426 degrees C isn’t going to move much air by heating. Even times 20… assuming you could somehow duct the air past the FF cluster…

... but an FF-powered fanjet could have a sideline in de-icing runways while waiting for takeoff clearance…

... MWe = MWt…
We’re going to have to face it…
... no way around it…
... the primary application of FF to air travel will be…
...
... high-subsonic dirigibles carrying passengers and cargo…

(dives into previously prepared foxhole)

vansig - 23 June 2010 06:40 PM

or place the reactors in the tail section, then have just a single shield for the bunch

Misses the point. About half of the energy from FF derives from capture of the X-rays using the onion-skin. So the space issue is real, as each FF must have its own onion-skin. Twenty of those would easily fill a 747, leaving no room for payload.

Much easier to use FF as an energy source from which to create hydrocarbon fuel.

But multiple cores can share the same shielding envelope, no? Say 4 cores in a container slightly larger than a single core’s shield. Remember, this is going to preferably be placed near the wing root’s center to help with trim while decreasing length of cable runs.

Aeronaut - 25 June 2010 04:04 PM

But multiple cores can share the same shielding envelope, no? Say 4 cores in a container slightly larger than a single core’s shield.

The fabled 20MW DPF box!

KeithPickering - 25 June 2010 02:33 PM

About half of the energy from FF derives from capture of the X-rays using the onion-skin. So the space issue is real, as each FF must have its own onion-skin. Twenty of those would easily fill a 747, leaving no room for payload.

and i thought the onion was about the size of a large pumpkin, say ~1 m diameter

The first prototypes FF will be probably heavy and large, but with time miniaturization will probably run its course…

OK, let me get this straight. There are a lot of unknowns to me here.

To get a 747, fully loaded, into the air you would need to know:

- The amount of thrust necessary to get the thing flying at cruising speed

- The amount of electric fans necessary to produce the thrust

- The difference in weight between the electric and liquid-fuel engines they are replacing (hopefully a nice savings)

- The landing weight the plane must have to land safely

- The number of DPFs to provide energy and some level of redundancy

- The weight of those DPFs

- The weight if the capacitors and other plumbing to make the DPFs work

- The weight of the transformers and other equipment used to capture the energy and direct it for use by the airplane

- The weight of the lead-foil “onions” to capture X-ray energy bleed-off

- The weight of extra X-ray shielding to keep ANY hint of X-ray radiation outside the reactor chamber

- The weight of neutron shielding

- The weight of the superstructure to house the entire reaction chamber and keep it stable on a moving vehicle

- Considerations such as extra equipment or personnel necessary to run the reactor (assuming that the pilots or other crew cannot be trained to handle this task

- Safety considerations for such events as lightning strike and turbulence. Would a DPF be affected by a lightening storm? Would its magnetic nature be disrupted by passing directly through one, or near one? Would you need more shielding, or would the X-ray shielding work for this problem?

- How much of the cabin must be sacrificed to deal with the energy plant being housed in the fuselage

Then compare all this to what current technology is providing in terms of weight, volume, and aerodynamic performance.

Does anyone have these answers? I know that the current plan for FF is to be housed in garage-sized power plants. Thats very small for a power plant but kind of big on a jetliner. But where there is a will there is a way….