FF for Jet Engines?

[Glenn Millam]

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….

[zapkitty]

… dirigibles… dirigibles with FF units providing the power to achieve 600 mph airspeeds at altitude and with the waste heat from the FFs applied to the helium to provide extra lift… dirigibles that can then reduce lift without venting helium and land vertically under power in any crosswinds that a jet can handle… come to the dark side… it is your destiny… 8D

[vansig]

Glenn Millam wrote: OK, let me get this straight. There are a lot of unknowns to me here.
[…]
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….

Some of these answers are readily available. Some can be calculated.

Let’s use the Boeing 747-400 series as a baseline. it has a cruising speed of Mach 0.85; and 282 kN thrust per engine, x4 engines…
http://en.wikipedia.org/wiki/Boeing_747-400#Specifications

by the way, i think the onion is aluminum foil, not lead, and it captures 100% of the xrays. the neutron shielding is 1m thick water and a boron jacket; the gamma ray shielding is lead.

[Breakable]

Is it silly me or is the 0.282 kN = 0.282 MW?
Edit:
Boeng output is probably per second
Where FF is per hour, in that case we need ~203 modules with electrical output
or 102 with full output in case efficiency is similar.

[jamesr]

Breakable wrote: Is it silly me or is the 0.282 kN = 0.282 MW?
Edit:
Boeng output is probably per second
Where FF is per hour, in that case we need ~203 modules with electrical output
or 102 with full output in case efficiency is similar.

1W = 1Nm/s so 0.282MN/s is equivalent to 0.282MW

another way of looking at it is: Power = (force *distance) / time = force *speed

So if we take the maximum speed (rather than the cruising speed) then this should be where the maximum force the engines can produce is just maintaining the speed and not accelerating it.

We have max speed (from the same wiki link above) = mach 0.92 @35000ft = 988km/h = 274m/s
Force = 4*262kN = 1048kN

Therefore Power of 747 at full thrust = 1048000*274 = 287152000W ~300MW

or 60 5MW FF generators!

[vansig]

okay, let’s scale this up by tesselating a spherical onion ~3m diameter with up to 60 anodes, and immersing the entire assembly in water, at the tail of the aircraft. i will bet that the capacitor bank scales sub-linearly. even if we must completely surround the reactor with shielding, i’m getting < 100 tonnes for the whole thing. that's 27..50 tonnes of water, alone; and the rest is equipment.

now i know this ignores failsafe mechanisms, which you’d likely want to do, so maybe we can split this into two reactor compartments, and place them in the shoulders of the wings. this would increase the share of the water shielding somewhat; but in the event of failures, you can run your 5 MW anodes at 10..15MW if you like.

the result is quite a massive increase in payload capacity, ~50..150 tonnes

[nemmart]

jamesr wrote:

Is it silly me or is the 0.282 kN = 0.282 MW?
Edit:
Boeng output is probably per second
Where FF is per hour, in that case we need ~203 modules with electrical output
or 102 with full output in case efficiency is similar.

1W = 1Nm/s so 0.282MN/s is equivalent to 0.282MW

another way of looking at it is: Power = (force *distance) / time = force *speed

So if we take the maximum speed (rather than the cruising speed) then this should be where the maximum force the engines can produce is just maintaining the speed and not accelerating it.

We have max speed (from the same wiki link above) = mach 0.92 @35000ft = 988km/h = 274m/s
Force = 4*262kN = 1048kN

Therefore Power of 747 at full thrust = 1048000*274 = 287152000W ~300MW

or 60 5MW FF generators!

Something is fishy though. According to http://www.howstuffworks.com/question192.htm, a 747 burns 36,000 gal over a 10 hr flight, or about a gallon a second.
A gallon of Jet A has ~121 MJ. 121 MJ delivered in 1 second is 121 MW. Therefore, averaged over a 10 hour flight, you need 120 MW, or 24 FF’s. The difference
might be explained as a peak vs. average output.

[jamesr]

nemmart wrote:
Something is fishy though. According to http://www.howstuffworks.com/question192.htm, a 747 burns 36,000 gal over a 10 hr flight, or about a gallon a second.
A gallon of Jet A has ~121 MJ. 121 MJ delivered in 1 second is 121 MW. Therefore, averaged over a 10 hour flight, you need 120 MW, or 24 FF’s. The difference
might be explained as a peak vs. average output.

Sounds about right… I doubt they would operate at anything near full power while cruising. I’m surprised these back-of-the-envelope type calculations are in that close agreement.

[Breakable]

Just to clarify FF module output is MW and not MWH?

[vansig]

Breakable wrote: Just to clarify FF module output is MW and not MWH?

yes.

[Breakable]

It seems the output is ~6.4 mj per shot.
https://focusfusion.org/index.php/site/article/how_will_we_get_there_from_here/
So its not MW or MWH but joules(not power but work), because it is per shot not per second.
If we have 1000 shots per second the the power would be ~6.4 gw
if 1 shot per hour then only 1.7 kilowatts.
It probably boils down into thermal and radiation flux management. EE part probably is hard only at mult-hertz.
I think the first prototypes as well as first generation units will be low frequency to reduce complexity of radiation and thermal management.
As the escaping radiation flux is probably a function of frequency, at this low frequency the shielding requirements probably can be considerably reduced
to fit a FF unit into a backyard, a truck, maybe with improved shielding materials even into a car.
Probably after a few generations of reactors are developed we will see it climb into MW or GW range and made smaller to fit onto a plane.

[zapkitty]

Breakable wrote:
I think the first prototypes as well as first generation units will be low frequency to reduce complexity of radiation and thermal management.

… apparently there is a caveat brought up by vansig of capacitor leakage rates.

Such leakage rates tend to climb quickly when the capacitors are running at full charge.

I don’t have any details on the FFX caps and so I don’t know at what frequency this becomes a problem for those particular caps…

… but it’s certainly theoretically possible to run at such a low frequency that the caps leak just a little too much between shots to fire the next pinch.

But is this a problem for these particular caps at 100 hz? 10 hz? 1 hz? Once per fortnight?

I guess the solution to this “throttling” limit would be to use bigger caps so you aren’t running them at full charge.

Are the FFX caps going to be running near max to achieve the desired goals? Could be. If so then in that case running at a lower frequency could be more of a problem than a solution.

But to have an FF unit able to run efficiently at less than a megawatt would be very useful in space applications. To have one that could run at less than 100 kilowatts would enable plug-and-play adaptation to current large spacecraft designs 🙂

[Tulse]

Commercial aircraft operate between extremely well-equipped points, so there is really no reason that they have to carry their power generation actually on board — they could more easily be run on batteries that are swapped out between flights, or (as has been pointed out before), powered with conventional jet engines using synthetically-produced fuel. Successful and cheap FF will be a game changer, but it doesn’t have to be directly used to have that effect — no one is going to drive a FF-powered car, and there’s no real reason to use FF in jets. (It makes far more sense for vehicles like ships and submarines, where travel times are very long, and space, where refueling isn’t really much of an option.)

[Aeronaut]

Can several FF cores share the same shielding envelope? I believe this is the 5th time I’ve asked.

[nemmart]

Breakable wrote: It seems the output is ~6.4 mj per shot.
https://focusfusion.org/index.php/site/article/how_will_we_get_there_from_here/
So its not MW or MWH but joules(not power but work), because it is per shot not per second.
If we have 1000 shots per second the the power would be ~6.4 gw
if 1 shot per hour then only 1.7 kilowatts.
It probably boils down into thermal and radiation flux management. EE part probably is hard only at mult-hertz.
I think the first prototypes as well as first generation units will be low frequency to reduce complexity of radiation and thermal management.
As the escaping radiation flux is probably a function of frequency, at this low frequency the shielding requirements probably can be considerably reduced
to fit a FF unit into a backyard, a truck, maybe with improved shielding materials even into a car.
Probably after a few generations of reactors are developed we will see it climb into MW or GW range and made smaller to fit onto a plane.

The units are wrong – it’s 6.4 kj not mj. See the “how_will_we_get_there_from_here” doc. Also, I think in Eric’s google tech talk, he mentioned 330 hz.

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