Heater Engine

[PositronLance001]

I was thinking that an atmospheric engine might work by heating the air and expelling it. I am not sure whether it will work, but it might. 

[Bill Phil]

Like a thermal turbojet?

Sure, that was the idea behind some nuclear jets.

But it has its own problems.

[magnemoe]

1 hour ago, Bill Phil said:

Like a thermal turbojet?

Sure, that was the idea behind some nuclear jets.

But it has its own problems.

Yes, you can make an ramjet version of the LV-N.
https://en.wikipedia.org/wiki/Project_Pluto

Downside is the radioactivity. You can make other designs who don't produce radioactive exhaust but radioactivity is still an major problem for ground handling and accidents will be an mess. 
It works in space as you can put engines on the end of an long grinder and keep away from it, any engine fail would not be worse than other engine fails, space is radioactive anyway. 

Another idea is to heat the engine with laser or microwaves. 
 

[StrandedonEarth]

2 hours ago, PositronLance001 said:

I was thinking that an atmospheric engine might work by heating the air and expelling it. I am not sure whether it will work, but it might. 

Well sure, just need to heat enough air hot enough. Perhaps by compressing it, then burning some fuel in the compressed air? Better have that hot air drive a turbine to run the compressor as well. Presto, we have a turbojet! 

[sevenperforce]

42 minutes ago, StrandedonEarth said:

Well sure, just need to heat enough air hot enough. Perhaps by compressing it, then burning some fuel in the compressed air? Better have that hot air drive a turbine to run the compressor as well. Presto, we have a turbojet! 

And if that doesn't give us enough thrust, we can maybe push some more fuel into the exhaust so that it burns after the main burn. Like an after burn.

[Shpaget]

Finally, once it gets obnoxiously loud, put a big fan in front of it, connected to the spinnamathingy, so a whole bunch of air goes around the engine making a sound barrier. I bet it would even make the whole thing better, sending ISP to 5 digit numbers.

[DDE]

7 minutes ago, Shpaget said:

Finally, once it gets obnoxiously loud, put a big fan in front of it, connected to the spinnamathingy, so a whole bunch of air goes around the engine making a sound barrier.

Instructions unclear, noise level increasing manifold.

 

[farmerben]

Spoiler

Meredith effect

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The North American P-51 Mustang makes significant use of the Meredith effect in its belly radiator design.

The Meredith effect is a phenomenon whereby the aerodynamic drag produced by a cooling radiator may be offset by careful design of the cooling duct such that useful thrust is produced. The effect was discovered in the 1930s and became more important as the speeds of piston-engined aircraft increased over the next decade.

 

 

[magnemoe]

4 hours ago, farmerben said:

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Meredith effect

From Wikipedia, the free encyclopedia

 

 

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The North American P-51 Mustang makes significant use of the Meredith effect in its belly radiator design.

The Meredith effect is a phenomenon whereby the aerodynamic drag produced by a cooling radiator may be offset by careful design of the cooling duct such that useful thrust is produced. The effect was discovered in the 1930s and became more important as the speeds of piston-engined aircraft increased over the next decade.

 

 

That was very cool. Not heard about it, wonder if formula 1 cars uses this or at least uses the exhaust like an kind of base bleed to reduce drag, Design for Skylon burns excess hydrogen from cooling in an ramjet, primary purpose is base bleed 
https://en.wikipedia.org/wiki/Base_bleed

[jimmymcgoochie]

Late 50s/early 60s: Project Pluto- nuclear powered air-breathing ramjet with nearly unlimited range, possibly allowing cruise missiles to fly for months before going to target. Actually produced a working nuclear ramjet engine.

A few months ago: a Russian rocket exploded after testing releasing a large cloud of radiation; there was talk of said rocket powering a 'revenge' missile with 'infinite range'... 

Anyone else see anything in common with those two events?

(Also, Project Pluto explains the name of the 'Project Eeloo' nuclear air-breathing engine from Near Future Aeronautics mod- learn something new every day!)

[Spacescifi]

1 hour ago, jimmymcgoochie said:

Late 50s/early 60s: Project Pluto- nuclear powered air-breathing ramjet with nearly unlimited range, possibly allowing cruise missiles to fly for months before going to target. Actually produced a working nuclear ramjet engine.

A few months ago: a Russian rocket exploded after testing releasing a large cloud of radiation; there was talk of said rocket powering a 'revenge' missile with 'infinite range'... 

Anyone else see anything in common with those two events?

(Also, Project Pluto explains the name of the 'Project Eeloo' nuclear air-breathing engine from Near Future Aeronautics mod- learn something new every day!)

 

It does not have unlimited range. It's range is limited by how long it's engine can last before overheating or malfunctioning, something quite possible given the changes in weather tempertature as it travels for miles on end.

Even nuclear reactors expire at some point.

I will grant you that if the engine is made of sufficiently heat resistant materials that it will outlast all other rockets in the air.

[DDE]

3 hours ago, jimmymcgoochie said:

Late 50s/early 60s: Project Pluto- nuclear powered air-breathing ramjet with nearly unlimited range, possibly allowing cruise missiles to fly for months before going to target. Actually produced a working nuclear ramjet engine.

A few months ago: a Russian rocket exploded after testing releasing a large cloud of radiation; there was talk of said rocket powering a 'revenge' missile with 'infinite range'... 

Anyone else see anything in common with those two events?

 

[Guest]

4 hours ago, Spacescifi said:

It does not have unlimited range. It's range is limited by how long it's engine can last before overheating or malfunctioning, something quite possible given the changes in weather tempertature as it travels for miles on end.

Even nuclear reactors expire at some point.

I will grant you that if the engine is made of sufficiently heat resistant materials that it will outlast all other rockets in the air.

Note that nuclear airbreathers do not run nearly as close to thermal limits as nuclear rockets do. They have a lot of air to work with, so they can run quite cool. So "unlimited range" is an accurate description, in practical terms. Nuclear reactors have a lifetime of years. Such a missile would be able to circle the globe several times, able to reach any point on Earth, from any given direction. Even Pluto was supposed to be able to do that, as were nuclear-powered bomber designs.

[jimmymcgoochie]

15 hours ago, Spacescifi said:

 

It does not have unlimited range. It's range is limited by how long it's engine can last before overheating or malfunctioning, something quite possible given the changes in weather tempertature as it travels for miles on end.

Even nuclear reactors expire at some point.

I will grant you that if the engine is made of sufficiently heat resistant materials that it will outlast all other rockets in the air.

Anything that can fly continuously for several months or even years at several hundred miles per hour has enough flight range to cover the whole world many times over. The 'maximum range' is a moot point when it can go literally anywhere on the planet whenever it wants to.

Sounds like exactly the sort of thing that would drastically cut aviation emissions especially on long-haul flights: get the plane flying, switch on the nuclear engine(s) and cruise with zero emissions (except a little bit of radiation, but then high altitude flight gives you quite a bit of radiation exposure anyway) to the destination, then switch back to regular engines to land the thing. If and when electric/hybrid aircraft engines reach the point where they can get a heavy airliner off the ground, those two things could be combined to create a plane that runs entirely on electricity (nuclear reactor on board will top up the batteries/capacitors while flying).

Not the easiest sell from a PR point of view especially to the airport ground crews, but the green credentials will make it a reality sooner or later if the alternative is nobody flying at all.

[Guest]

Actually, the problem with nuclear airliners isn't radioactive pollution (it's a trivial problem to fix, Pluto had a deliberately unshielded reactor, which also reduced its lifetime), but rather shielding the reactor itself. It's easy to shield a small crew, as in a bomber, but with passengers, you'd probably need to put the reactor at the very back of the plane, messing with your COM. Not only that, a shadow shield only protects people inside the plane. Both ground crews and other aircraft would be at risk, just look at the monster they made to service such planes.

That said, a compact reactor with an effective all-around shield would be a viable option. It'd have to be at least somewhat crash-proof, though.

[Nothalogh]

On 11/25/2019 at 11:37 AM, PositronLance001 said:

I was thinking that an atmospheric engine might work by heating the air and expelling it. I am not sure whether it will work, but it might. 

Yes, this would be a thermal ramjet, you can do the same with a turbine engine as well, just replace the combustors with heat exchangers.

[PositronLance001]

1 hour ago, Nothalogh said:

Yes, this would be a thermal ramjet, you can do the same with a turbine engine as well, just replace the combustors with heat exchangers.

I meant using heating coils instead because why not

 

[Nothalogh]

6 minutes ago, PositronLance001 said:

I meant using heating coils instead because why not

It's gonna be less efficient, but yeah, it would sorta work.

You could definitely build a ramjet with electric heat, it just won't have a very good TWR

[magnemoe]

On 11/30/2019 at 3:00 PM, Dragon01 said:

Actually, the problem with nuclear airliners isn't radioactive pollution (it's a trivial problem to fix, Pluto had a deliberately unshielded reactor, which also reduced its lifetime), but rather shielding the reactor itself. It's easy to shield a small crew, as in a bomber, but with passengers, you'd probably need to put the reactor at the very back of the plane, messing with your COM. Not only that, a shadow shield only protects people inside the plane. Both ground crews and other aircraft would be at risk, just look at the monster they made to service such planes.

That said, a compact reactor with an effective all-around shield would be a viable option. It'd have to be at least somewhat crash-proof, though.

It would have to be an pretty unobtainium shielding however, very nice, I would still not made an nuclear jetliner however. 
First is the weight of the reactor itself, second is the somewhat crash proof would make it an super material in it self because of the strength and some planes crash at cruising speeds. 
Simply stopping replace coal and gas with nuclear would have an much larger impact and be way safer. 
Then start looking at large ships. 

[Guest]

Not really unobtainium, just something dense. Once nice thing about it: if you use the right shield material, making it crash-proof is pretty much a given. If the reactor is small and dense enough, it'd be essentially a solid capsule made of a few different metals, with a very though (and heavy) shield. Tungsten might work, and such encapsulated reactor would probably be able to be removed entirely for servicing. 

Making a small reactor with enough thermal power to run a jet plane (one that can carry a fully shielded nuclear reactor, at that), as well as servicing it would be a problem, however. TBH, price would probably kill it, just like it killed nuclear merchant ships. The problems are not unsolvable, just very expensive to solve. It would also be a very large plane, to lift a tungsten-encapsulated reactor and any cargo you might want, you'd need a lot of wing, and to make it economical, you'd need to make it carry a lot of cargo. This conspires to make it a large, heavy machine. Likely too big for most use cases (and airports). You'd need the best small nuclear reactor tech has to offer in order to make a nuclear airliner, and you can forget about making it small (and small airliners is where the money seems to be these days).

One interesting idea is a nuclear-powered airship. A lot easier to do, more space for everything, and it doesn't really care about weight all that much. It'll be big, but they all are. Very safe if using helium, doesn't go too fast, and it doesn't disintegrate if you don't do something stupid like fly it into a hurricane. Of course, it still has the same basic problem nuclear-powered freighters do. The price tag. Nuclear is hard to make competitive with coal and gas even in a power plant.

[PositronLance001]

1 hour ago, Nothalogh said:

It's gonna be less efficient, but yeah, it would sorta work.

You could definitely build a ramjet with electric heat, it just won't have a very good TWR

yeah i think it could be a secondary "cruising" engine using normal jets for takeoff

[Nothalogh]

37 minutes ago, PositronLance001 said:

yeah i think it could be a secondary "cruising" engine using normal jets for takeoff

More like barely able to overcome the drag of its own intake.

[PositronLance001]

good point.

[magnemoe]

45 minutes ago, PositronLance001 said:

yeah i think it could be a secondary "cruising" engine using normal jets for takeoff

An hybrid plane could make sense, but then I would use propellers driven by electrical engines, retract propellers after use.  
This has some benefits, short takeoff and landing perhaps even VTOL, or low noise level. 
Require less powerful jet engines as they don't need do do more than cruise as long as you don't try to fly over oceans with them, but this would be an shorter range design. 

Next step would be an hybrid turboprop, only propellers driven by an single jet engine running an generator and batteries.