VF-1 Exhaust Internals

[Skull-1]

thanks JBO that makes much more sence.

I denfenatly don't see how you could actualy have an afterburner on an engine that uses nuclear power since your not realy burning anything.

If you are using a combustible of some sort (like a rocket does) then you indeed burn something.

And again, if "AFTERBURNER" is not the proper term for it, then "AFTERHEATER" is.

The principle is the same.

[Skull-1]

Can I just ask because I'm totally confused at this point...

How are these "thermonuclear turbines" supposed to work? Are they like real nuclear jet engine which just passes air over a reactor core (or heat transfer medium) to super heat it or is it something completely different. And what is Reaction mass, is it supposed to be like compressed gas stored on board for space use only or is it an actual fuel that gets burned. I really have no Idea what's going on anymore could someone explain this.

It is a thermonuclear turbofan if you ask me.

1) The heat from the reactor heats air at the N2 fan which is geared to the N1 fan spool.

2) This air (because it has been heated) flows across the N2 fan, spinning it.

3) The N2 fan spins the N1 fan (front of engine).

4) Propulsion is provided by air being pulled in by the N1 fan (some of which goes into the core and is heated, the rest of which is ducted AROUND the heated section--bypass air). The heated air is exhausted at high velocity as thrust. The bypass air is exhausted at a slightly lower velocity as thrust.

At low altitudes the N1 Fan does most of the propulsion. At high altitudes the heated air does most of the work.

An AFTERHEATER would work by heating the bypass air and increasing its velocity, as well as adding additional heat to the already heated core air.

AFTERHEATER.

If you use a combustible RM to do this then it is an AFTERBURNER.

[Nied]

You aren't running RM literally "through" the engine though in the sense of it mixing together. The plasma of the turbine is kept apart from the RM itself. Othewise I think you'd radiate the atmosphere and that would be unacceptable.

The transference of heat from the reactor to the RM (air / water whichever) is what produces your thrust.

Indeed that is exactly what I've been saying. Air is moved through the core of the engine where it is superheated by the heat exchanger. The compendium mentions MHD is involved somehow as well, my guess is there's an MHD section after the heat exchanger to accelerate the superheated exhaust further.

You have two options...

1) Heat a smaller volume of air to a higher total temp to increase the velocity of the exhuast gas to a very high level.

2) Heat a larger volume of air to a lower (but hotter) total temp and increase the velocity of the exhasut gas to a (relatively) moderate speed.

If you choose to do the former you are going to accelerate very slowly.

Or you can heat a large volume of Air/reaction mass to a very high level simply by throttling the engine higher. Though the fusion reactor might be producing more heat, that heat is also being transferred to the Air/RM at a higher rate as well.

The Valkyrie flits about the sky like a mosquito. I don't see how it does so without some chemical / combustible / RM Afterburner to heat the bypass air as well as to provide a "rocket" effect.

Nonsense! You've got the equivalent of a miniature star to produce heat, a chemical reaction is almost wasteful in that kind of environment. Just push the throttles further and dump more air into the heat exchanger so that it can be superheated. "Afterheating" as you call it is redundant, you'd get the same effect by heating the core exhaust to a higher temperature and having that mix with bypass air, and that's in the atmosphere. In space there'd be no bypass air in the first place. There's just no need to do anything close to an afterburner in a thermonuclear turbine, and there's quite a few good reasons not to do it.

[Skull-1]

Nonsense! You've got the equivalent of a miniature star to produce heat, a chemical reaction is almost wasteful in that kind of environment. Just push the throttles further and dump more air into the heat exchanger so that it can be superheated.

Nonsense hardly.

You are not going to get an instantaneous reaction the way we see it in the show without propellant of some sort.

It's akin to "slippage" with a boat screw. The compressor simply cannot shove that much air through the engine that quickly and the engine cannot draw it on its own. Something else is at work here and I think it has to be chemical on some level.

"Afterheating" as you call it is redundant, you'd get the same effect by heating the core exhaust to a higher temperature and having that mix with bypass air, and that's in the atmosphere. In space there'd be no bypass air in the first place. There's just no need to do anything close to an afterburner in a thermonuclear turbine, and there's quite a few good reasons not to do it.

Why heat it to a higher temperature and melt the engine in transition when you can just heat the bypass air using the same temperature ratio as in the primary stage? You will avoid thermal shock to the reactor and increase engine life dramatically.

There's certainly no other reason to have a "third stage reactor mixer" in the feet.

You try flitting about the sky with those instantaneous bursts of power we see and watch what happens to your reactor temps. Might as well use what's left to make pots and pans 'cause it isn't going to last more than a couple of seconds.

[Nied]

Nonsense hardly.

You are not going to get an instantaneous reaction the way we see it in the show without propellant of some sort.

It's akin to "slippage" with a boat screw. The compressor simply cannot shove that much air through the engine that quickly and the engine cannot draw it on its own. Something else is at work here and I think it has to be chemical on some level.

I'm not sure what you mean by instantaneous reaction, Valkyrie engines behave the same as traditional jet engines in an atmosphere. They do seem to have the ability to switch on and off in space pretty quickly, but the compressor wouldn't have anything to do with it there since there's no air to move.

Why heat it to a higher temperature and melt the engine in transition when you can just heat the bypass air using the same temperature ratio as in the primary stage? You will avoid thermal shock to the reactor and increase engine life dramatically.

There's certainly no other reason to have a "third stage reactor mixer" in the feet.

You try flitting about the sky with those instantaneous bursts of power we see and watch what happens to your reactor temps. Might as well use what's left to make pots and pans 'cause it isn't going to last more than a couple of seconds.

Third stage reactor mixer? Again you wouldn't have to worry about melting the engines because you're also moving more air through them as well which helps them maintain their temperature. Air isn't only acting as a reaction mass it's also cooling the fusion reactor, in later designs like the FF-2500Es in the YF-19 or the FF-2450Bs in the YF-21 the FADEC has to limit their power in atmosphere because they simply aren't capable of sucking in enough air to cool the engines. I won't deny that using an overboost setting might screw with the TBO of the engines, but that's why there are rules to limit it's use today and almost assuredly in Macross.

[David Hingtgen]

Back to how a fusion turbine etc works:

Is Skull-1's explanation for atmospheric ops only? And are we going for "pure rocket effect" in space, basically ignoring all blades/fans/stages?

[Nied]

For the most efficiency liquid or even powdered solids would be best as areacton mass. I alwasy assumed that reaction mass would just be sprayed right into the core of the engine in space.

[JB0]

If you are using a combustible of some sort (like a rocket does) then you indeed burn something.

There's no strict requirement for combustibles in a rocket. And the Valkyrie design strongly implies that the only "combustible" on board is the fuel for the fusion reactor. Which isn't exhausted.

You are not going to get an instantaneous reaction the way we see it in the show without propellant of some sort.

It's akin to "slippage" with a boat screw. The compressor simply cannot shove that much air through the engine that quickly and the engine cannot draw it on its own. Something else is at work here and I think it has to be chemical on some level.

There's no need for any chemical reaction.

If you can't get enough air, you just inject some of the mass you use for space travel into the engine core.

Why heat it to a higher temperature and melt the engine in transition when you can just heat the bypass air using the same temperature ratio as in the primary stage? You will avoid thermal shock to the reactor and increase engine life dramatically.

The reactor will be running at a constant temperature. Always. It's a fundamental aspect of the fusion process.

If by reactor you mean the core of the "jet", that temperature may very well be variable, but there's no reason at all to assume there's a serious thermal stress involved given the vehicle was designed for space operation and unassisted atmospheric re-entry. Both situations will be VERY thermally stressful on every component.

It's very difficult to cool anything in space because there's no matter around you to conduct the heat away. Your exhaust will provide your most significant cooling for your engine, since every particle that leaves the back of the vehicle has pulled heat out of the engine.

And since you can't use the effects of air flowing over your control surfaces for anything, changing your velocity in ANY direction requires thrust from the engines, including slowing down along your current vector. Which obviously puts the engine under more stress than the equivalent job in an atmosphere.

Re-entry should be self-explanatory.

So I'd argue thermal issues are a non-issue just from the design goals.

Even without factoring in the overtech hyperalloys, structural reinforcement fields, and whatnot that allow you to crash a jet in freefall and mid-transformation through a building without utterly destroying the vehicle, then use your exhaust nozzles as feet for a 50-foot robot without damaging them significantly.

[Skull-1]

I'm not sure what you mean by instantaneous reaction, Valkyrie engines behave the same as traditional jet engines in an atmosphere. They do seem to have the ability to switch on and off in space pretty quickly, but the compressor wouldn't have anything to do with it there since there's no air to move.

Well no offense intended as you are obviously very sharp...BUT... Jet engines, regardless their type--turbofan or turbojet, Kerosene or Themonuclear--have a definite lag between the time when power is applied and when it is felt. The larger the bypass ratio the smaller the lag time is at low altitudes as a large N1 fan is in effect a propellor of sorts. The lag is still quite large. The Valkyrie appears not to have such a lag. The only way this can be overcome is with a rocket-type effect IMHO.

You can't just add extra heat. The N2 fan will melt.

Third stage reactor mixer? Again you wouldn't have to worry about melting the engines because you're also moving more air through them as well which helps them maintain their temperature. Air isn't only acting as a reaction mass it's also cooling the fusion reactor, in later designs like the FF-2500Es in the YF-19 or the FF-2450Bs in the YF-21 the FADEC has to limit their power in atmosphere because they simply aren't capable of sucking in enough air to cool the engines. I won't deny that using an overboost setting might screw with the TBO of the engines, but that's why there are rules to limit it's use today and almost assuredly in Macross.

I totally understand the cooling effect that air has on an engine. HOWEVER, you cannot go from nominal to maximum rated power in a matter of moments without overtemping the engine. There's simply not enough airflow fast enough to get you there.

Try it with your car on a hot day sitting still. Rev the engine rapidly and momentarily. The temperature *WILL* spike. The airflow over the radiator is not going to instantaneously cool enough to prevent it. That's a combustion engine. Imagine a "star heat reactor".

OUCH.

Your only hope is to "AFTERHEAT" or "HEAT" the bypass air in conjunction with some sort of explosive, expansive, rocket-effect RM in the tail feathers to boost you forward. That is probably what "OVERBOOST" actually means.

Also, the more area you have exposed to the air flowing over the reactor the more efficient the heat transfer. Thus an additional heater downstream is more efficient than a single *HOTTER* reactor would be.

[Skull-1]

It's very difficult to cool anything in space because there's no matter around you to conduct the heat away. Your exhaust will provide your most significant cooling for your engine, since every particle that leaves the back of the vehicle has pulled heat out of the engine.

Yet the ambient temperature in space is magnitudes lower than it is in the atmosphere, thus negating some of that problem.

[Skull-1]

Back to how a fusion turbine etc works:

Is Skull-1's explanation for atmospheric ops only? And are we going for "pure rocket effect" in space, basically ignoring all blades/fans/stages?

I am confining my PRIMARY argument to atmospheric operation, yes.

In space you have no other choice but a rocket effect, i.e. a reactor heats RM (water, heavy water, plasma, whatever you choose).

[JB0]

Yet the ambient temperature in space is magnitudes lower than it is in the atmosphere, thus negating some of that problem.

Not really.

Just keeping an old 386 cool is a major undertaking while you're in the sun.

Surface temperature on the Moon in the sun is something like 240 degrees F. Mainly because there's no atmosphere absorbing or deflecting the sunlight like on Earth.

Admittedly, it's easy to radiate heat in the dark, and a fusion powerplant should have no problem keeping things warm enough. But you can't assume you'll only operate in shadow.

In sunlight, things get toasty fast, and getting rid of that heat is a batty.

[Skull-1]

Not really.

Just keeping an old 386 cool is a major undertaking while you're in the sun.

Surface temperature on the Moon in the sun is something like 240 degrees F. Mainly because there's no atmosphere absorbing or deflecting the sunlight like on Earth.

Admittedly, it's easy to radiate heat in the dark, and a fusion powerplant should have no problem keeping things warm enough. But you can't assume you'll only operate in shadow.

In sunlight, things get toasty fast, and getting rid of that heat is a batty.

Good point.

[eugimon]

Yet the ambient temperature in space is magnitudes lower than it is in the atmosphere, thus negating some of that problem.

doesn't matter if the ambient temperature is low or not as the denisty of space is so low that conduction wouldn't happen. Heat is only going to be transmitted through radiation.

actually, without convection, heat in space is a big problem. you'll have huge temperature shifts depending on the orientation of the space craft to the sun (or whatever star).

[Nied]

Well no offense intended as you are obviously very sharp...BUT... Jet engines, regardless their type--turbofan or turbojet, Kerosene or Themonuclear--have a definite lag between the time when power is applied and when it is felt. The larger the bypass ratio the smaller the lag time is at low altitudes as a large N1 fan is in effect a propellor of sorts. The lag is still quite large. The Valkyrie appears not to have such a lag. The only way this can be overcome is with a rocket-type effect IMHO.

I'm aware of the lag time between throttle commands and the engine spooling up, I just don't see anything that a Valkyrie can do that can't be explained by a good FADEC verniers and FBW.

You can't just add extra heat. The N2 fan will melt.

I totally understand the cooling effect that air has on an engine. HOWEVER, you cannot go from nominal to maximum rated power in a matter of moments without overtemping the engine. There's simply not enough airflow fast enough to get you there.

Try it with your car on a hot day sitting still. Rev the engine rapidly and momentarily. The temperature *WILL* spike. The airflow over the radiator is not going to instantaneously cool enough to prevent it. That's a combustion engine. Imagine a "star heat reactor".

OUCH.

Your only hope is to "AFTERHEAT" or "HEAT" the bypass air in conjunction with some sort of explosive, expansive, rocket-effect RM in the tail feathers to boost you forward. That is probably what "OVERBOOST" actually means.

Also, the more area you have exposed to the air flowing over the reactor the more efficient the heat transfer. Thus an additional heater downstream is more efficient than a single *HOTTER* reactor would be.

As JB0 pointed out the amount of heat generated by a fusion reactor is going to stay pretty much constant, the only diffence is how much air you transfer it to. If anything you'd risk overheating at lower throttle settings, not higher.

[Skull-1]

I'm aware of the lag time between throttle commands and the engine spooling up, I just don't see anything that a Valkyrie can do that can't be explained by a good FADEC verniers and FBW.

My airplane has FADECs and one of the fastest spoolup times in the industry. It is NOT instantaneous as we see in Macross. It can't be. Physics.

Even if you had an instantaneous spoolup you will still not see the acceleration rates we see in the animation. There is something else at play.

Edited January 6, 2007 by Skull-1

[Nied]

My airplane has FADECs and one of the fastest spoolup times in the industry. It is NOT instantaneous as we see in Macross. It can't be. Physics.

Even if you had an instantaneous spoolup you will still not see the acceleration rates we see in the animation. There is something else at play.

And as I originally stated the only place I've seen instantaneous thrust is in space. In atmosphere it acts like a normal jet engine. The best example off the top of my head would be Hikaru's infamous first kill, you can hear and see the engine spool up over the course of about a second before frying that poor man. If you've got some specific counter examples I'm all ears but until then I stand by my claim.

[Skull-1]

And as I originally stated the only place I've seen instantaneous thrust is in space. In atmosphere it acts like a normal jet engine. The best example off the top of my head would be Hikaru's infamous first kill, you can hear and see the engine spool up over the course of about a second before frying that poor man. If you've got some specific counter examples I'm all ears but until then I stand by my claim.

Max's dogfight wit Milia is a prime example of instantaneous thrust responses.

The Battroid flits about the sky like it is being held with guide strings.

*NO* conventional engine can react that way. Are we going to base this on the engine running at full power almost the entire time with thrust being vented in all different directions to control output? I don't buy that explanation.

Also, blue flamed exhaust implies a very efficient *COMBUSTION*, not just some gee whiz thermonuclear reactor heating air.

Edited January 6, 2007 by Skull-1

[Skull-1]

Here is a summation that a buddy of mine provided. I think it is pretty succinct regarding why we see "AFTERBURNER" at any rate.

"Afterburners work by adding energy to a supersonic flow. The equations are ugly, but basically in de Leval nozzle supersonic flow, it's possible to dump more energy in and have it go very efficiently into flow velocity (rather than mostly into heat). That's what an afterburner is. Dump fuel into the superheated exhaust, it combusts with the remaining oxygen, but most of the energy goes straight into flow velocity and not heat.

"In a reactor engine, they're probably dumping more fusion plasma into the exhaust flow. Same principle, except no combustion, so the term "afterburner" is simply a legacy term no longer strictly accurate, but close enough to be retained.

"The exhaust would be blue because that would be its blackbody temperature: in the 8000-10000 Kelvins (or degrees Celcius, if you prefer - the difference is small) range."

Edited January 6, 2007 by Skull-1

[JB0]

I'm aware of the lag time between throttle commands and the engine spooling up, I just don't see anything that a Valkyrie can do that can't be explained by a good FADEC verniers and FBW.

As JB0 pointed out the amount of heat generated by a fusion reactor is going to stay pretty much constant, the only diffence is how much air you transfer it to. If anything you'd risk overheating at lower throttle settings, not higher.

On the other hand, I seem to recall Misa battying at him before his first launch about full throttle being bad for the engines(at least at a standstill in atmosphere).

Makes a strong argument for a variable amount of heat transferred into the engine.

Max's dogfight wit Milia is a prime example of instantaneous thrust responses.

The Battroid flits about the sky like it is being held with guide strings.

*NO* conventional engine can react that way. Are we going to base this on the engine running at full power almost the entire time with thrust being vented in all different directions to control output? I don't buy that explanation.

A flying battroid in and of itself is a serious power expenditure. I would assume high throttle is the norm for GERWALK and flying battroid just on principle.

If I recall, the verniers use a separate propulsion mechanism than the main engines(it certainly makes more sense than routing heat transfer devices all over the places, especially through the wings), so the foot thrusters are dedicated to hovering and primary acceleration.

The verniers probably(but by no means are guaranteed to) use a standard propellant/oxidizer mixture similar to the modern space shuttle.

Or something fun like hydrogen peroxide and a catalyst. That's how the current "rocket belt" works. Pump hydrogen peroxide over silver plates, and it rapidly decomposes into oxygen and steam. It expands violently when this happens, resulting in a burn-free rocket. Of course, hydrogen peroxide isn't exactly the most efficient of propellants, but I'm sure you can find chemicals that will work on the same principle and yield better performance.

Also, blue flamed exhaust implies a very efficient *COMBUSTION*, not just some gee whiz thermonuclear reactor heating air.

Actually, blue exhaust just implies really hot exhaust. The glow is generated by simple heat, not an exotic EM radiation effect unique to fire.

[Nied]

Max's dogfight wit Milia is a prime example of instantaneous thrust responses.

The Battroid flits about the sky like it is being held with guide strings.

*NO* conventional engine can react that way. Are we going to base this on the engine running at full power almost the entire time with thrust being vented in all different directions to control output? I don't buy that explanation.

Also, blue flamed exhaust implies a very efficient *COMBUSTION*, not just some gee whiz thermonuclear reactor heating air.

In batroid mode his main engine thrust would be augmented with backpack thrusters, "armpit" thrusters and an ungodly amount of verniers (21 going by a quick count on my Yamato) all of which would provide instantaneous thrust while the main turbines catch up. Actually since the intake shutters are closed in Batroid it could be that the engines revert to "rocket" mode and are just dumping RM in instead of using air like they would in space.

[T.V.]

Hi there, I'm new to the forum and I just thought I could chime in the debate.

Haven't read it all, so I might be retreading some points made by others already.

Nice discussion btw, though I suggest using the more diplomatic brittish term of "reheat" instead of afterburner.

That's more ambiguous and can be explained as designating both an "afterburner" or "afterheater" and sounds better IMO.

On the original question about the slits, they maybe gass flow regulators, much like a diffusor on the back end of the underside of a race car.

It keeps the gas flowing straight down, preventing it from bleeding too much out the sides through the V-shaped openings between the toes/main thrust vector vanes.

It could be a sign of a lack of of an exhaust driven compressor stage as well, but more on that later.

I don't know why the change between slits and more traditional turbine engine exhaust rings took place, but it could've been mere artistic license rather than well thought out fantasy engine design.

Disregarding that the engines in the variable fighters are entirely impractical from an aerodynamic standpoint alone, the engines shouldn't give an instantanious response if they have a centrifugal engine core.

By virtue of the inertia and centrifugal forces of fast spooling fan discs in the compressor stage, there always will be some lag in throttle response, as opposed to rocket engines, internal combustion engines and other engines not using a rotating expansion chamber elements.

A FADEC system regulates throttle response, so that you can't "choke" a jet engine, dumping in too much fuel for it's own good.

It needs to be gradual in order for the compressor stage to catch up, because the compressor is driven by the exhaust gasses - causing yet more lag - just like a turbo on an internal combustion engine in a car.

The total lag can be reduced, but never eliminated.

You can think of FADEC much like fly-by-wire.

It regulates your commands so you don't damage the equipment yet can maintain easy control of it.

Engine thrust depends on mass flow: The amount of mass the engine spews out of the back over a period of time.

You can either push a lot of mass at a slow speed or a tiny amount of mass at a high speed, and the amount of thrust will be the same.

Top speed won't be the same though, since the speed of the aircraft can never exceed the exhaust speed.

Therefore, pure jet engined aircraft can go faster than turbofan or propellor driven craft, even though their

thrust-to-weight ratio, or more importantly thrust-drag curve might be similar, because the exhaust speed of pure turbine jet engines is faster.

In regard of the thermonuclear reaction engines supposedly fitting the Macross VF series, they simply take in air from the front, add heat (read: energy) with a heat exchanger element, causing it to expand rapidly out of the back, producing a thrusting force.

But with an thermonuclear fuel source, there's no need for combustion inside the compressor stage, so the reaction mass is only the enviromental air.

The compressor could either be driven by exhaust fans or by the thermonuclear reactor, but I don't know the specifics of that.

I reckon that if the compressor is driven directly by the reactor, the lag would be severely lower than if driven by the exhaust gasses and be less dependable on the mass flow in the exhaust stage. For example, the chance for compressor stall to occur due to disruption of the exhaust flow, will be non existent.

However, using exhaust fans leads to an overall better energy effiencency, since you recycle some of the expelled energy.It would also be less complex engine, that's possibly lighter and more compact to build.

The direct-drive system would be more akin to a supercharger compressor, and the other more to a classic turbine compressor.

Since the engine has to operate both in gasious and vacuüm enviroments such as space, it cannot depend on enviromental gas alone as the reaction mass. Therefore it has to have internally stored reaction mass it can expell.

The engine would probably some hybrid of the previously mentioned enviromental gas compressor and plasma ejecting (rocket) engine, ejecting plasma at very hign velocities.

Of course, this leads to severe radiation issues, but I'm not sure of there would be a safer and still practical enough engine hybrid type.

Maybe the ejected mass is being fed additional radiation absorbant material, but that would it give a rather short operating time.

However, the up side of space is that you don't have to use prolonged bursts, apart for momentum changing manoeuvres.

The FAST packs, obviously store extra fuel and possible RA material.

The hybrid rocket mode could be engaged to provide a temporary extra "overboost" in atmospheric conditions as well.

Practically, when the rocket element isn't used, such engines wouldn't lead to the gratious and nice looking afterburner plumes as seen in the anime, but artistic license is good to have at times.

To only 'lightshow' would possibly be the lighting up of released plasma particles and heat distortion.

The sound of a continuous combustion jet engine would certainly not be heard, though a compressor whine would probably still be very noticable.

A so called "afterheater" wouldn't make much sense, since the thrust is already derived from heating air and not combusting a fuel.

It makes as much sense as using multiple ovens to bake a single bread.

What an afterburner does, is using the excess oxygen in the exhaust flow - that always passes through an engine and otherwise it would stall - and use that for a secondary combustion stage by dumping a lot of extra fuel in the already heated exhaust flow.

An afterheater could not do the same, nor reach the same effeciency levels, because it can't practically add release more usable energy to the airflow than a single stage heater would.

It's more efficient to use a large single stage heater, than using to or more seperate heaters down the airstream which have the same total thermal energy out put.

The single stage heater would also be lighter and more compact, resulting in a far better thrust-to-weight and size-to-weight ratio, while also being less complex, more durable and cheaper to make.

Using an afterheater to exclusively heat the bypass airflow would also be less practical and efficient than simply using a bigger single stage heater, for both structural and aerodynamic reasons.

On a side note, in space, even moreso than in an atmosphere, thermal management is a real problem, due to only being able to dispense heat through radiation rather than releasing it to the (flowing) air, since there pretty much is none.

Therefore it's actually more difficult to get rid of excess heat rather then becoming too cold.

I hope that provides some useful insight in the workings of a fictional engine.

Cheers,

Thom Vermazeren.

Edit:

Oi.. That turned out to be more longwinded than I expected.

Edited January 6, 2007 by T.V.

[Skull-1]

Consider the term REACTION *MASS*. The heavier the mass expelled the more thrust per unit of volume. Just like flash retardent JP-5 (?) (Navy / Marine Corps) had more thrust per gallon than standard JP-4 (Air Force) so too will a combustible or water-based RM have more thrust than the air itself as the latter is not as heavy.

Not all of a jet's thrust is expanded air. The weight of the fuel burned does affect thrust output.

At least it did when I last actually paid attention to this stuff 15 years ago...

Using an afterheater to exclusively heat the bypass airflow would also be less practical and efficient than simply using a bigger single stage heater, for both structural and aerodynamic reasons.

How are you going to duct this heat?

Are you implying these Valkyrie engines do not have any bypass air at all? That is a dubious prospect at best, IMHO.

The "Afterheater" concept is more efficient because it is only used when needed. The additional "heater core" is simply that much more area to allow for thermal transfer to the RM. By definition it will be more efficient.

Also, heating a larger volume by a lesser amount is much easier than heating a smaller volume by a higher amount. Heaging 100 cubic feet by 20 degrees C is certainly easier than heating 50 cubic feet by 50 degrees C... (Insert your own numbers).

Edited January 6, 2007 by Skull-1

[T.V.]

It appears we have a missunderstanding.

Not all of a jet's thrust is expanded air. The weight of the fuel burned does affect thrust output.

That's only true for traditional jet turbine engines, but not for a thermonuclear reaction engine.

There's no chemical reaction taking place in the airstream, and thus no addition of chemical energy, nor reaction mass from adding fuel to the air.

It doesn't combust a mix of fuel and air, but simply heats the air with the energy from a nuclear reactor using a heating element in the airstream.

It's more like a ducted fan engine, with a heating rod expanding the air to provide a lot of additional pressure.

It's nothing more than a fancy blowdryer, really.

Are you implying these Valkyrie engines do not have any bypass air at all? That is a dubious prospect at best, IMHO.

No I'm not.

I'm simply saying that a single heating chamber is more effective than 2 seperate heating chambers for heating the same amount of gas.

It's better to have a slightly bigger heater stage and less bypass air, then using two seperate stages with one of them heating the bypass air, because there isn't any combustion involved but merely heating through heating elements in both stages.

Heaging 100 cubic feet by 20 degrees C is certainly easier than heating 50 cubic feet by 50 degrees C... (Insert your own numbers).

See. Even you agree. Edited January 6, 2007 by T.V.

[eugimon]

Hi T.V.

Welcome to macrossworld and thanks for your insight and knowledge into this discussion!

[Skull-1]

It appears we have a missunderstanding.

...

It doesn't combust a mix of fuel and air, but simply heats the air with the energy from a nuclear reactor using a heating element in the airstream.

It's more like a ducted fan engine, with a heating rod expanding the air to provide a lot of additional pressure.

No misunderstanding at all.

I am fully aware of the CW that implies a Valk's engine uses nothing but air for RM in the atmosphere.

I cut my teeth on this discussion ten years ago with nuclear physicists and the like. Trust me I am fully aware of what is being discussed--they had my head spinning with equations.

I'm simply saying that a single heating chamber is more effective than 2 seperate heating chambers for heating the same amount of gas.

And I respectfully disagree.

It's better to have a slightly bigger heater stage and less bypass air, then using two seperate stages with one of them heating the bypass air, because there isn't any combustion involved but merely heating through heating elements in both stages.

There are numerous reasons to use a bypass fan, one of which is heat signature. There is no need to light yourself up to the entire world through your thermal signature.

See. Even you agree.

No I don't agree.

Heating everything in one spot to a higher temperature is harder than having two "heat transfer manifolds" of a greater surface area to do the job as needed (IMHO). Perhaps we should define "efficient".

Edited January 6, 2007 by Skull-1

[BEAST]

The reactor engine talk is fascinating and all, but other threads already exist for that. I was kinda wanting to limit this one to just the funky junk stuck up the Valks' tailpipes.

No offense.

Heat diffusers, eh?

[David Hingtgen]

I vote for vectoring in battroid and GERWALK mode, as the nozzles are spread open then and unable to vector (or at least, not as well) as in fighter mode. Thus, the slots are "supplemental" vectoring vanes.

[sketchley]

Agreed. Though it may be only the original visual interpretation by the creators of Macross, as vectored thrust is retroactively added to the VF-1 with the release of the DYRL? game for PS1 and SS in the mid-90's.

Also, if I remember correctly, the VF-0 in Macross Zero is seen with the vector plates together in gerwalk and battroid while flying/hovering (eps. 2 & 3).

EDIT: though, if they act as heat diffusers, it does make sense. It kindof supports the 'afterburner' setting in the throttle - heat is pumped into those things (when it normally isn't) to add just a little more heat expansion/thrust at the back end of the engine, in addition to providing a little more finely tuned vectoring to the thrust. Or something like that. Anime isn't reality afterall.

Edited January 8, 2007 by sketchley

[Wicked Ace]

The reactor engine talk is fascinating and all, but other threads already exist for that. I was kinda wanting to limit this one to just the funky junk stuck up the Valks' tailpipes.

No offense.

Heat diffusers, eh?

I've actually enjoyed the (hyper)technical back-and-forth in this thread. Macrossworld.com -- come for the sci-fi, stay for the education.

[Nied]

EDIT: though, if they act as heat diffusers, it does make sense. It kindof supports the 'afterburner' setting in the throttle - heat is pumped into those things (when it normally isn't) to add just a little more heat expansion/thrust at the back end of the engine, in addition to providing a little more finely tuned vectoring to the thrust. Or something like that. Anime isn't reality afterall.

Like I said at the beginning of the thread they're more likely to be thrust diffusers than heat diffusers. Even with the two halves of the feet splayed out, without the diffusers thrust is going to come out in a pretty much cylindrical column half a meter wide. Add 23000 Kg of superheated supersonic thrust and you could easily punch a hole right through quite a few things (like a runway or a nice expensive carrier deck). It's called ground erosion and it's one of the biggest concerns when designing VTOL aircraft.

[Skull-1]

This assumes you are running at high power settings at all times, neh?

If so, this is countered by the animation when the VF-1D crashes into the Zentraedi. The exhaust goes from low to high and the heat signature increases dramatically along with thrust output.

The reactor has to be "throttleable" (for lack of a better term) or it is unworkable. Besides, it is a FUSION reactor and my understanding is that FUSION reactions are much harder to sustain than FISSION ones, relatively speaking (and from a faded memory).

There is definitely a diffusive effect for reasons mentioned, but you're not going to be putting out 23K kg of thrust (how heavy is this Valk any way???) all the time during VTOL ops.

Edited January 9, 2007 by Skull-1

[anime52k8]

There is definitely a diffusive effect for reasons mentioned, but you're not going to be putting out 23K kg of thrust (how heavy is this Valk any way???) all the time during VTOL ops.

from the Compendium:

MASSES AND LOADINGS:

Mass empty: 13250 kg

VF-1X Plus 13850 kg

with FAST Pack system 19200 kg

Mass: VT-1C (estimated), with rear and leg booster packs 13750 kg

Max propellant capacity: FAST Pack system 11000 kg

Standard T-O mass: 18500 kg

Standard operational mass: with 16200-kg GBP-1S system 37100 kg

Standard T-O mass: with FAST Pack system 45000 kg

Standard liftoff mass: with atmospheric-escape booster system 120500 kg

Max T-O mass: 37000 kg

with FAST Pack system

somehow this sounds light though. I would think it would be more with all the moveing parts needed to make a transforming fighter work.

[David Hingtgen]

Valks (all of them) are unbelievably light, we usually just write it off as using OT and that hypercarbon is far lighter than any alloy or composite.

[JB0]

This assumes you are running at high power settings at all times, neh?

GERWALK seems to require it.

The reactor has to be "throttleable" (for lack of a better term) or it is unworkable.

The engine does. The reactor is almost guaranteed to run at a fixed rate.

Remember, the fusion reaction doesn't happen IN the engine. It happens outside it, and the heat is transferred into the engine.

Besides, it is a FUSION reactor and my understanding is that FUSION reactions are much harder to sustain than FISSION ones, relatively speaking (and from a faded memory).

Indeed they are. Fission happens automatically, fusion has to be forced.

On the other hand, fission is far easier to regulate(just stick some neutron-absorbing rods in to slow it down, pull 'em out to speed it up). Fusion is pretty much a fixed-rate reaction, as I understand things.