Page 3 of 3

Posted: Thu Jun 12, 2008 4:57 am
by djolds1
Mike Holmes wrote:Time to get out the old plans for the Spruce Goose...

Think something 10x larger than an An-124. 4000 metric tonnes loaded, 1500 metric tonnes payload. Using BFR/QED you could probably get the loaded weight down to 2000-2500 tonnes with 1500 tonnes payload. The cargo capacity of an early 20th century medium freighter.

The maximum (and IIRC unrealized) theoretical potential of the early 20th C. airships (~1000 tonnes) at hypersonic speeds.


Posted: Thu Jun 12, 2008 5:00 am
by djolds1
esotERIC D wrote:For kicks and giggles, see the aries ... noplan.htm
Cruising speed - 450-500 km/h (250 Knots)
Range - 4000 km
Cruising flight height - 1 to 4 m
Take off weight - up to 400 t
Length overall - 73.8 m
Breadth overall - 44.0 m
Height overall - 19.2 m
Fuel stock - 80-120 t
Cargo capacity - 40 t

General characteristics

* Crew: 6
* Capacity: 88 passengers
* Payload: 150,000 kg (330,000 lb)
* Length: 68.96 m (226 ft 3 in)
* Wingspan: 73.3 m (240 ft 5 in)
* Height: 20.78 m (68 ft 2 in)
* Wing area: 628 m² (6,760 sq ft)
* Empty weight: 175,000 kg (385,000 lb)
* Loaded weight: 405,000 kg (892,875 lb)
* Useful load: 230,000 kg (508,000 lb)
* Max takeoff weight: 405,000 kg (893,000 lb)
* Powerplant: 4× Lotarev D-18T turbofans, 229.5 kN (51,600 lbf) each


* Maximum speed: 865 km/h (467 kn (537 mph))
* Cruise speed: 800-850 km/h (430 kn (490 mph))
* Range: 5,400 km (2,900 nm, 3,360 mi (5,410 km))
* Service ceiling 12,000 m (35,000 ft)
* Wing loading: 365 kg/m² (74.7 lb/sq ft)
* Thrust/weight: 0.41

For hypersonic flight I'd consider swing wings - either the traditional design or the switchblade design.


Posted: Thu Jun 12, 2008 5:02 am
by djolds1
MSimon wrote:
JohnP wrote:
Cruising flight height - 1 to 4 m
Err.. miles? Meters? ???
Could be a ground effect machine.
It is. Wing in Ground Effect.


Posted: Thu Jun 12, 2008 5:12 am
by djolds1
rj40 wrote:How would a BFR produce thrust? I can imagine one on a C-130 using electric power to turn props, but other than that, what are the other options?
REB (Relativistic Electron Beam) to heat airflow/fuel in a ramjet (M6 max). Perhaps a pseudo-scramjet good for up to say Mach 15.

My brain still insists that heating flow-through air mass alone would be sufficient reaction mass for thrust. I.e. no need for "fuel" to burn beyond the reactor's pB11. Perhaps said brain is being stubborn.
rj40 wrote:Any good links for the layperson on Polywell rocket power? Something, perhaps, with lots of pretty pictures? Something that might be used in the USA today newspaper?


Posted: Thu Jun 12, 2008 5:32 am
by 93143
The only problem is cooling. If you can get rid of the waste heat from the reactor without dumping hydrogen (pipe it into the engines via a SABRE-style preheater after the compressor? Or just dump it to the air somehow), you're good. The only thing fuel does besides heat the airstream is add a little mass, and the propulsive effect doesn't depend on that.

Both the Americans and the Russians actually flew planes with nuclear reactors capable of the necessary power level onboard, including shielding for the crew. The idea in both cases was that the air from the compressors would pass through the core as coolant, then go to the turbine section. No fuel required. I don't think either of them actually did this; most of the testing for the Russian one was supposedly with the reactor off.

But if a fission-powered airplane is technically feasible, surely we can pull off a BFR-powered one...

Posted: Thu Jun 12, 2008 1:51 pm
by Mike Holmes
Well, except that the pB-11 reaction doesn't produce heat directly, but accellerated ions. So you have to figure out how to convert that to heat. Of course, if you can make it into electricity, you can make that into heat (as somebody suggested). But it might require more gear to get that done. Than finding a way to do it purely electrically.

Or is there a way to as easily convert the mechanical energy of the accellerated ions to heat? Something that would be as compact as the electricity generating process (which somebody elsewhere on the site has proposed might actually be rather large)? Somehow that sounds like carrying a lot of water.

Again, with props on electric engines, this is no problem at all. The reason for proposing the "spruce goose" and C-130 is simply because these are viable extant flight platforms that could easily be powered by a BFR as envisioned. (There's something very romantic to me about the idea of a slow-moving prop-driven gun platform firing a laser casually down at ground targets).


Posted: Thu Jun 12, 2008 6:21 pm
by 93143
Yes, there is. All you have to do is not use trap grids, and they'll smash straight into the outer wall and generate heat. Of course, this exacerbates the first-wall problem, but only by a factor of maybe 5.

Considering the usual efficiency of converting electricity to heat (pretty much 100%), plus the potential for using significant amounts of power for non-thermal applications (turning things), plus the fact that if you use REB heating you don't need to convert the bulk of the power at all, minus the potential for losses and extra weight trying to efficiently heat the air by piping stuff around - it might turn out to be better to use direct conversion, despite the fact that the reactor weighs more.

There's no good historical comparison for this trade, because fission piles do produce heat directly, and the efficiency and weight penalties for turning heat into electricity are large.

Posted: Thu Jun 12, 2008 6:27 pm
by ravingdave
For what it's worth, how about plasma powered aircraft ?


Posted: Thu Jun 12, 2008 6:49 pm
by ravingdave
I suppose I should have added a bit more in the way of comments.

I once thought that MHD could be made to work in air, so I took a 12kv neon sign transfomer and hooked it to a couple of electrodes spaced an inch or so apart. I then covered the electrodes with a piece of plate glass, and then placed a powerful magnet on top of the glass close to the electrodes where the 12Kv was arching between them.

Just as I expected, the path of the arc was bent into a sort of oval. Alternating cycles of the voltage were being bent by the magnetic field in oposite directions, thereby indicating that the plasma could be moved by the magnetic field.

I had speculated that if the field was large enough and the electrodes were elongated into parallel rails, then a DC arc between the rails could produce air flow in the manner that Magneto Hydrodynamic Drive works in water or other conductive liquids. (think of a Jacob's ladder turned on it's side)

I was actually thinking it would be cool to produce a "Plasma Gun" and wasn't so interested in the idea that it might be propulsive

I don't know what the efficiency of this would be for propulsion, but it would seem to me that it wouldn't be very high.

Probably a better approach would be an ion powered "lifter" design.


Posted: Thu Jun 12, 2008 7:43 pm
by 93143
I've done BOE calculations on atmospheric ion propulsion. Using ECR or something to provide ~0.004% ionization (~0.06% single ionization per molecule) fairly evenly throughout a 300 kg/s airstream (reasonable-sized turbofan @ M=0.9 and 40,000 feet), and applying ~10 kV of accelerating potential, you get ~400,000 lbs thrust for the oft-baselined 6 GW, assuming you can maintain those conditions (600 kA ion current!) without massive ECR heating (you need 10 MW or so just for the ionization energy) and electron counterflow losses.

I have no actual experience in atmospheric plasmadynamics, so I can't tell whether this is a reasonable idea or not. My initial plan was to come up with an engine that could be ground started and would make bird ingestion survivable for both parties, but I suspect heating will still be substantial - perhaps so substantial that a compressor/nozzle arrangement would be necessary to make some use of it. Perhaps so substantial that there's no point even trying to get the additional ion acceleration thrust in the first place...

Posted: Fri Jun 13, 2008 3:15 pm
by Mike Holmes
Might make a great high-speed chicken fryer and delivery system, however...