Nuclear Powered Helicopters

[Lindley]

^It's not the motors that weigh a lot, it's the batteries. How long can those planes fly compared to petrol powered aircraft?

The average plane, not long. However, as I mentioned up-thread, there is now at least one electric UAV which can remain aloft indefinitely on solar power.

 

[sojourner]

Ah, but try and build a plane that can carry people and cargo.

 

[Nomad V]

I think the biggest problem with an airborne nuclear plant would be the fact that it has to heft its own weight plus the rest of the structure. Nuclear plants are big and heavy.

If I am thinking about this correctly, you'd need to generate 9.8 watts per kilogram per second just to counteract the force of gravity. I checked around and it looks like the largest capacity of any nuclear plant is 1.6GW. This means the largest mass you could even cause to hover would be about 163 million kilograms.

I'm having a hard time finding numbers to put that in perspective. Anyone have any idea how much a full nuclear plant weighs?

This is really rough, and I don't have the weight of a long ton. A Trident sub weighs approximately 20,000 (18,750 long tonnes). Assuming that 1/2 of that deals with the power plant we are looking at 9,071,847 Kg for the power plant. The output is 60,000 horsepower or 4,471,992 watts.

 

[JustAFriend]

^It's not the motors that weigh a lot, it's the batteries. How long can those planes fly compared to petrol powered aircraft?

With the batteries that have come out in the last couple of years, I can fly as long or longer than a standard-glo-fueled plane.

I have one aerobatic plane (3ft wingspan) that would normally be powered by a Cox .049 glo engine and stay up 5-10 minutes. I have personally flown that plane for nearly 40minutes using thermal lift and normally set my flight timer for 10-12minutes.

.....things have changed a lot this last year on the battery front...

 

[STR]

I think the biggest problem with an airborne nuclear plant would be the fact that it has to heft its own weight plus the rest of the structure. Nuclear plants are big and heavy.

If I am thinking about this correctly, you'd need to generate 9.8 watts per kilogram per second just to counteract the force of gravity. I checked around and it looks like the largest capacity of any nuclear plant is 1.6GW. This means the largest mass you could even cause to hover would be about 163 million kilograms.

I'm having a hard time finding numbers to put that in perspective. Anyone have any idea how much a full nuclear plant weighs?

This is really rough, and I don't have the weight of a long ton. A Trident sub weighs approximately 20,000 (18,750 long tonnes). Assuming that 1/2 of that deals with the power plant we are looking at 9,071,847 Kg for the power plant. The output is 60,000 horsepower or 4,471,992 watts.

Well, you're certainly being generous there. I'll try to narrow your range down. First, the submerged displacement of an Ohio boomer is indeed in the 20,000 ton range, but that's not what the ship weighs. That's the ship+ballast. Surface displacement, which is the ships actual weight is ~16,500 tons. However, for balance reasons, some water will be left in the trim tanks. So the actual weight is going to be in the area of 16,000 tons.

Of that 16,000 tons, some of that is fixed equipment and structure, the rest is stores, weapons, and other things that frankly, aren't bolted down. These add about 10-20% to surface ships, regardless of whether the ship is nuclear or not. So this takes it down to roughly 12,800 tons, roughly half that savings is from removing the Trident II missiles.

Of the 12,800 tons remaining, roughly half is probably going to be the actual hull of the ship. That leaves 6,000 tons of fixed machinery. That's sonar, weapons launchers, and of course the powerplant. We'll take half of the 6,000 for the power plant. This 3,400 tons is the reactor, reactor shielding, steam turbines, reduction gearing, silencing measures, coolant. Everything involving propulsion of the ship. So 3,400 tons for a reactor plant and associated machinery.

Given that the 8,600 ton Seawolf class uses a modernized and downrated version of the Ohio plant, we can use that as a checksum for the figures above. Using the same percentages as above, we arrive at a figure of 3,440 tons. So a sub reactor is indeed probably in the area of 3,400 tons.

A long, or naval, ton is 2,240 pounds, or 1,016kg, which means that lifting 3,000 tons means generating 33,853,120 watts, a number a bit higher than the 4MW that the reactor generates. Keep in mind that this is a compact, high power to weight/size reactor.

 

[Maurice]

Not nuclear, but a wonderfully nuts idea for a super-giant Saturn V-catching helicopter!

 

[trekkiedane]

^

Thunderbird 7!

 

[Nomad V]

I think the biggest problem with an airborne nuclear plant would be the fact that it has to heft its own weight plus the rest of the structure. Nuclear plants are big and heavy.

If I am thinking about this correctly, you'd need to generate 9.8 watts per kilogram per second just to counteract the force of gravity. I checked around and it looks like the largest capacity of any nuclear plant is 1.6GW. This means the largest mass you could even cause to hover would be about 163 million kilograms.

I'm having a hard time finding numbers to put that in perspective. Anyone have any idea how much a full nuclear plant weighs?

This is really rough, and I don't have the weight of a long ton. A Trident sub weighs approximately 20,000 (18,750 long tonnes). Assuming that 1/2 of that deals with the power plant we are looking at 9,071,847 Kg for the power plant. The output is 60,000 horsepower or 4,471,992 watts.

Well, you're certainly being generous there. I'll try to narrow your range down. First, the submerged displacement of an Ohio boomer is indeed in the 20,000 ton range, but that's not what the ship weighs. That's the ship+ballast. Surface displacement, which is the ships actual weight is ~16,500 tons. However, for balance reasons, some water will be left in the trim tanks. So the actual weight is going to be in the area of 16,000 tons.

Of that 16,000 tons, some of that is fixed equipment and structure, the rest is stores, weapons, and other things that frankly, aren't bolted down. These add about 10-20% to surface ships, regardless of whether the ship is nuclear or not. So this takes it down to roughly 12,800 tons, roughly half that savings is from removing the Trident II missiles.

Of the 12,800 tons remaining, roughly half is probably going to be the actual hull of the ship. That leaves 6,000 tons of fixed machinery. That's sonar, weapons launchers, and of course the powerplant. We'll take half of the 6,000 for the power plant. This 3,400 tons is the reactor, reactor shielding, steam turbines, reduction gearing, silencing measures, coolant. Everything involving propulsion of the ship. So 3,400 tons for a reactor plant and associated machinery.

Given that the 8,600 ton Seawolf class uses a modernized and downrated version of the Ohio plant, we can use that as a checksum for the figures above. Using the same percentages as above, we arrive at a figure of 3,440 tons. So a sub reactor is indeed probably in the area of 3,400 tons.

A long, or naval, ton is 2,240 pounds, or 1,016kg, which means that lifting 3,000 tons means generating 33,853,120 watts, a number a bit higher than the 4MW that the reactor generates. Keep in mind that this is a compact, high power to weight/size reactor.

Thanks, I just thought an existing mobile plant might be a good place to start, also I knew some of us would have the experience to sharpen the calculations. Good job /answer. Also, thanks for not commenting on the significant digits used in the assumptions.