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archonspeaks Since: Jun, 2013
#626: Jun 14th 2018 at 5:10:55 AM

Energy density is just the amount of energy contained in a given volume. It doesn’t require combustion, it applies to energy released by any reaction. It’s measured in Joules per meter cubed.

They should have sent a poet.
matti23 Matti23 from Australia Since: Apr, 2013
Matti23
#627: Jun 15th 2018 at 2:38:58 AM

Archonspeaks, that's precisely it. in my setting I've got a point where the energy density of capacitors reaches the energy density of jet fuel then continues to rise. After this point "plasma engines" become commonplace in jet fighters. These run electrical energy from capacitors across some propellant substance, causing it to heat up and violently expand as plasma. This is directed out of the engine to provide thrust. Some magnetic fields push the plasma out of the engine with great force to get additional thrust. No oxidizer needed. The more energy you pump into the substance the faster it expands. The capacitors, not the propellant provides the energy. Only small amounts of propellant are needed.

So I've looked up the energy density of some types of fuel but was wondering whether the oxidizer was included in that number. This was because if it wasn't then the point at which capacitor energy density meets jet fuel energy density would still see the plasma engines be vastly inferior in atmospheric combat since the oxygen presumably provides quite a bit extra energy on top of that number. As somebody just pointed out, rocket engines don't breathe oxygen and this is essentially an exotic tech rocket.

So a jet with a certain amount of energy loaded into it via jet fuel with an oxygen breathing engine could be smaller and lighter than a plasma engine with an equivalent amount of energy loaded into it via capacitors. This is assuming that the main weight and size comes from the energy storage part and not the engine part due to timeline shenanigans.

So I guess my question was if the energy density of that timeline's military capacitors and jet fuel was equal, which engine and storage system would be more space efficient to install on your weapon system?

P.S. thanks for your help and sorry for the long post. I may have over thought the futuristic tech of this timeline.

edited 15th Jun '18 2:41:28 AM by matti23

ManInGray from Israel Since: Jul, 2011
#628: Jun 15th 2018 at 2:43:21 AM

Do you think it would be terribly inconvenient for a pistol to eject its cases downward, behind the grip? Not immediately behind, at least 4cm from the magazine, and possibly as much farther than that as needed. The cases shouldn't be dangerously hot.

I've been thinking about the guns developed in the CTSAS program, which seem to have a chambering method similar to the Steyr ACR's; The chamber is a small section of barrel that's open at both ends, blocked in the back while in line with the rest of the barrel. It moves downward, and the next cartridge is inserted to it, pushing the empty case out as it does. Either direction would work for entry since there's no tapering in the cartridge or the inside of the chamber. By putting the chamber behind the magazine that's in a pistol's grip, you make it into a kind of bullpup, moving much of it backwards where it may be better-balanced, or allow it to be longer overall and still easy to use as a pistol because it's not made so front-heavy by that.

edited 15th Jun '18 2:51:24 AM by ManInGray

archonspeaks Since: Jun, 2013
#629: Jun 15th 2018 at 7:23:12 AM

[up][up] Real-world plasma engines would need a frankly exorbitant amount of energy to propel a tactical fighter through the air. Capacitors or batteries with an energy density equal to or greater than jet fuel would be a hell of a breakthrough, but even then you might actually need more energy to make plasma engines work compared to a jet engine.

Assuming everything is equal between the two, you'd then have to consider the other characteristics of each engine. Size, logistical support required, environmental byproducts, that kind of thing. If the jet engine and plasma engine are equally efficient but the plasma engine requires 10 hours of maintenance per 100 hours and the jet engine only requires 5, the jet engine would be a better choice.

I don't think plasma engines will be able to beat jet engines in the atmosphere. The energy requirements for a plasma engine are just too high for too little thrust.

[up] Downward behind the grip would be ejecting casings directly into your arm. Anyone who's ever done the hot brass dance can tell you that would not be ideal at all.

Ideally you want to get the brass away from the body of the shooter. That's the reason top-ejecting pistols went out of style. There are a few bullpup pistols, but they all eject out to the side like what you'd typically expect. Forward ejection would work, but the other thing you have to consider with a handgun is that it should be easily operable with one hand. If it's massive and heavy to allow for a complex mechanism it might not be very effective.

If your're interested in funky pistol designs, this ([1]) might be one of the funkiest of all time. It's an early prototype for the P90 designed to be fired with one hand, it puts the entire mechanism in front of and level with the grip to minimize recoil and ejects downward. As far as I know it was only tested a couple times and didn't get great reviews.

They should have sent a poet.
ManInGray from Israel Since: Jul, 2011
#630: Jun 15th 2018 at 8:07:42 AM

The cases are polymer and shouldn't be very hot, but having them fall on you is still a distraction. So yeah, they should probably eject sideways. I think I'll have a compartment where the case is held right after being pushed out of the chamber, and then ejected at the same time the chamber rises back to the barrel. Forward ejection shouldn't be complicated for the shorter pistols, if this moving chamber system isn't too complicated already; The port is under the barrel, but with a tube that extends it forward(like the F2000) so that you won't block it with your other hand.

That is an interesting design, though maybe redundant when the P90's ammunition has so little recoil to begin with. But I'd prefer something more back-oriented like the Bullpup 9, for easier use of longer barrels and suppressors.

archonspeaks Since: Jun, 2013
#631: Jun 15th 2018 at 8:21:27 AM

[up]Even polymer cased ammo is still pretty hot after ejection, maybe not to the same degree as brass but enough that it would sting.

The thing to keep in mind here is the size of the weapon, and the layout of the mechanism. The magazine has to go somewhere as well, and on a handgun you're more restricted as to the layout. Don't forget that you also need room for the ejectors and their linkages, the ejection tube itself, and all of the other parts for the action. It's also worth considering the complexity of the weapon, more complex designs tend to fail more often.

The reason the P90 is considered to have low recoil is because of the inline layout of the gun, the higher above the grip the action and barrel are the more the gun tends to tip back when fired. That's why very flat-shooting handguns like C Zs tend to have a low barrel and slide.

edited 15th Jun '18 8:21:55 AM by archonspeaks

They should have sent a poet.
ManInGray from Israel Since: Jul, 2011
#632: Jun 15th 2018 at 8:34:22 AM

Yeah, it's probably going to be more bulky than usual. But not necessarily heavier if smartly designed out of somewhat advanced materials. I'm trying to keep a plausible layout in mind, but it'll probably remain pretty vague.

And I meant the ammo itself; I compared the average of a few loads to a military 9mm load, and estimated that the latter's recoil is 91.9% greater.

edited 15th Jun '18 8:36:06 AM by ManInGray

matti23 Matti23 from Australia Since: Apr, 2013
Matti23
#633: Jun 16th 2018 at 3:16:50 AM

About the capacitor thing earlier, thanks for the feedback. I suppose the rocket jet thing isn't going to work. Let's try a different route. If electric engine tech was up to the task, would having an electric rather than a jet fuel run engine be viable for atmospheric combat?

The exhaust might be cooler and the jet would run quieter. Also had a concept for refueling to work with a light absorbent panel (like a solar panel but built to take higher light intensities) and a recharging laser. No more trying to line up fuel pipes with jets mid air, just fly into range with your light panel pointed in the re fuel craft's general direction and it'll beam power to you. If there's several recharging lasers then it might refuel several craft at once.

Is it going to waste energy into the atmosphere? Yep, but would it be worth the waste to have less hassle, multiple simultaneous refueling ability and the ability for your refuel craft to perhaps double as a point defense craft?

edited 16th Jun '18 4:50:47 AM by matti23

Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#634: Jun 16th 2018 at 4:49:50 AM

My understanding, which is not complete, is that exothermic chemical reactions are the fuel of choice for high-performance aircraft because of the energy density and the thrust-to-weight ratio. We've experimented with electrically powered aircraft, and while it works well enough for ultra-lights and such, it's just not viable for larger craft because batteries weigh too much.

More exotic drives like ion thrusters are very power-efficient but their thrust is way too low to use in an atmosphere, or at suborbital velocities. Nuclear power (fission) isn't viable, mainly because the power plant is so heavy and requires so much shielding. You get a very high energy density from the fuel but there's an incredible amount of overhead. Fusion power ... well, it's still not something we can use on a practical level, and even if we could, we have no expectation that it could be miniaturized to fit in a combat aircraft.

edited 16th Jun '18 4:50:17 AM by Fighteer

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
archonspeaks Since: Jun, 2013
#635: Jun 16th 2018 at 4:55:38 AM

Electric turbofans are definitely possible, small-scale ones are used in hobby aircraft. There’s a ton of research going into making them work for military aircraft. The problem is that like with the plasma engine you need a insanely dense source of energy. We’re really just waiting on battery technology to make electric jets feasible. The batteries you’d need for an electric military aircraft would be nothing short of revolutionary.

Laser recharging is pretty common in fiction, and it’s totally workable. The one issue is that any laser powerful enough to recharge an aircraft in a reasonable amount of time is also powerful enough to shoot that aircraft out of the sky. Error or misalignment could be catastrophic.

For exotic aerial refueling systems, I’d look towards autonomous systems. Swarms of mini-tankers could cover a huge area, and if they were staged properly could stay airborne almost indefinitely.

edited 16th Jun '18 4:56:30 AM by archonspeaks

They should have sent a poet.
matti23 Matti23 from Australia Since: Apr, 2013
Matti23
#636: Jun 16th 2018 at 7:32:45 PM

Archonspeaks, Good idea for the refueling system.

Archonspeaks and Fighteer, So electric turbofans seem to not be viable for now. How about if we jump further into the future? Let capacitor energy density continue to climb steadily over the decades and it might eventually get to the needed energy density. How long might that take? When that happens how much better would electric fighters be?

For now though let's try something more mundane. Normal jet engines this time. How effective would a ground effect vehicle be as a passenger vehicle? Its got a good speed and higher capacity than an aircraft of comparable weight.

edited 16th Jun '18 7:35:32 PM by matti23

archonspeaks Since: Jun, 2013
#637: Jun 16th 2018 at 8:34:43 PM

I guess theoretically the performance can scale up as much as you can scale up battery and electric motor technology, but very high speed aircraft tend to have a lot of performance and handling issues. Once you get up above the sound barrier maneuvering becomes extremely difficult and the engines have trouble breathing due to the intense boundary layer around the body of the aircraft.

Even though we can build much faster aircraft in general, our combat aircraft aircraft usually top out around Mach 2 for practical reasons.

They should have sent a poet.
matti23 Matti23 from Australia Since: Apr, 2013
Matti23
#638: Jun 16th 2018 at 11:43:42 PM

Archonspeaks, so perhaps we'd see a division of aircraft? Mach 2 and below conventional jet fighters might be the way to go. Rocket plasma engines, more expensive, less efficient but perhaps a niche application as a long distance interceptor?

Got a target close to an airbase? Send a jet fighter. Got a situation needing an aircraft a significant distance across the world? Send a plasma fighter, possibly climbing into the upper atmosphere (or space) to reduce air resistance and drag. Like Australia trying to commit aircraft to a battle in South America or the South Atlantic at short notice. Perhaps they could attack by lobbing munitions down from orbit or swooping down if needed.

Jet fighters have a bit of trouble engaging satellites currently although a few rare and expensive weapons exist for that purpose. The orbital fighter could just stay in space and look for targets. Depending on weapon load out it could launch very long range attacks from orbit or pick out a target and swoop down for an attack run without warning before climbing back up to orbit.

P.S. yep, this is looking like it may be getting pretty far into the future.

edited 16th Jun '18 11:45:02 PM by matti23

Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#639: Jun 17th 2018 at 5:28:28 AM

There's a sharp division between engines that perform well at low speeds (up to Mach 2 or so) and engines that perform well at higher speeds. Scramjets, ramjets, and the like all have high minimum speeds that they require to function, but go absolutely nuts at faster speeds. Putting both sorts of engines on the same craft is impractical for weight reasons.

There's also the problem that controlling a combat aircraft at speeds above Mach 2-3 becomes almost impossible for a human.

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
TuefelHundenIV Night Clerk of the Apocalypse from Doomsday Facility Corner Store. Since: Aug, 2009 Relationship Status: I'd need a PowerPoint presentation
Night Clerk of the Apocalypse
#640: Jun 17th 2018 at 8:05:42 AM

Fighteer: While two engines are problematic dual mode engines have been successfully tested and are part of active development for future combat aircraft with the goal of high mach speed. As for speed limitations and control. That is not simply true. You can control combat aircraft at speeds of mach 3-4. With verified occurrences in both Russian made interceptor aircraft designs and the SR-71.

For the interceptors it was really hard on the engines without being designed for the abuse and reportedly they had to be replaced after a run like that. However the SR-71's engines were designed to handle the abuse and made regular flights at those velocities without needing to replace the engines and over 11,000 hours of flight at those velocities. The SR-71 regularly exceeded Mach 3 and was still quite controllable with pilots claiming that evasive maneuvers hitting higher velocities evading Soviet missiles fired at them. It was also a rather large aircraft hitting that velocity. The space shuttle was also controllable at post re-entry hyper sonic speeds in the glide portion of its descent and has been the basis of research for powered hypersonic aircraft flight across multiple projects. It isn't that high supersonic or low hypersonic is almost impossible to control for people it is is that it requires aircraft a number of difficult to design features.

It is part of the reason there was so much interest in variable geometry wings and in current interest with shape changing control surfaces and wings. US fighter craft aren't designed for Mach 3 velocities partly because such aircraft are really damn expensive to design and build. Given the fact missiles kept improving in their intercept velocities we needed something other than just blinding speed and is partly why the US went so heavily into stealth. The craft that can hit those velocities are a huge pain in the ass to apply stealth coatings. Shaping works decently for them but they are already using specially designed surfaces and coatings to help them hit the higher velocities.

Who watches the watchmen?
archonspeaks Since: Jun, 2013
#641: Jun 17th 2018 at 8:49:31 AM

Above around Mach 2 or 3 the definition of controllable changes a lot. When people say an aircraft is controllable at supersonic and hypersonic speeds they generally mean that the aircraft can be kept in flight and navigate safely, it’s not exactly performing combat maneuvers. The effectiveness of any control surface is reduced in supersonic flight and the effect scales with speed. All-moving control surfaces are the best way to combat this, since a larger control surface gives greater authority, but even then there are limits.

If you’re going for a future setting, there are a lot of theoretical technologies that could fill a fighter’s role in part. Hypersonic missiles, like what we’re developing with Prompt Global Strike could very well replace long range strike fighters. ASAT weapons will also begin to proliferate sooner rather than later, so more platforms will start to have anti-missile capabilities. Dedicated anti-missile aircraft are something that’s been proposed, and that role would be a good fit for autonomous aircraft.

Swarming autonomous aircraft are also gonna be everywhere. Swarming gives you a lot of advantages, and if you can afford to base and maintain the aircraft the downsides are minimal.

They should have sent a poet.
Belisaurius Since: Feb, 2010
#642: Jun 17th 2018 at 10:45:52 AM

Hell, flight characteristics change between landing speeds and regular cruising speeds. It's why we have flaps on darn near everything.

Macross Plus had an interesting idea of a morph wing aircraft. The VF-21's wings deformed to take on new geometries. I have no idea how you'd make that structurally sound but future tech

TuefelHundenIV Night Clerk of the Apocalypse from Doomsday Facility Corner Store. Since: Aug, 2009 Relationship Status: I'd need a PowerPoint presentation
Night Clerk of the Apocalypse
#643: Jun 17th 2018 at 12:35:57 PM

Archon: From the accounts of SR-71 it was a lot more control than that. Again the whole evasive maneuvering at Mach 3. The Shuttle, SR-71, Wave Rider, Pershing II warhead, and other high supersonic and hypersonic craft are not using the same kind of control surfaces we use on our more generic fighter craft. It still boils down to a matter of designing different control surfaces and changes to the engines to make it work. The Shape of the wings, engine intakes, and control surfaces of the SR-71 definitely look different than what you see on say an F-22, F-18 Super, or F-16 and were purpose designed to allow the SR-71 to something other than fly in a straight line. They won't be doing any dog fighting but they definitely can do the missile evasion. I would doubt it from the interceptors that managed it they weren't exactly designed for such rough handling and needed some serious maintenance after the fact. Hypersonic capable fighters are increasingly looking like we will be turning them into drones given you can get more aggressive with your G-Force tolerances without a squishy meat sack in it and build the fighter to handle the abuse. The Hyper Sonic Glide Vehicle used on the Pershing 2 could pull turns or breaking maneuvers with forces as high as 25 G's and remain perfectly functional. No way you could do do the same with a meat sack in the seat. We may get to see how that pans out with SR-72 if they ever build it.

Who watches the watchmen?
archonspeaks Since: Jun, 2013
#644: Jun 17th 2018 at 1:37:40 PM

[up]I think the point of confusion here is that "maneuverable" means something very different in supersonic and hypersonic flight regimes.

The Blackbird didn't pull evasive maneuvers like fighter craft. The basic evasive maneuver taught to pilots was to just speed up, but they also did long turns as well. As far as I know there was never an instance where a Blackbird pulled a hard evasive maneuver, it just wasn't built for that kind of thing. Low speed maneuvers had an alarming tendency to damage the aircraft, maneuvering at speed wasn't even tried during testing. The control surfaces on the Blackbird aren't really fundamentally different from the ones on smaller aircraft. The big difference on the Blackbird is the lift from its chines, though that doesn't really impact maneuverability.

Information on the Pershing 2's maneuvering capabilities is pretty scarce, but from what we know the 25G turn was made during the initial atmospheric entry for its boost-glide trajectory. It was a fairly shallow turn, it was just made at an extremely high speed. The hairpin turns were made at much lower speeds while in the atmosphere.

As far as we know now, the design sensibilities of conventional aircraft don't translate well to hypersonic flight. For example, it's impossible to make a hypersonic vehicle with a high L/D ratio, which is a main goal for conventional aircraft design. The way we design the control surfaces for hypersonic flight is going to need to change too. A combination of large canards, all-moving tails and thrust vectoring seems like the best option right now, though I assume there's better stuff in the works.

They should have sent a poet.
TuefelHundenIV Night Clerk of the Apocalypse from Doomsday Facility Corner Store. Since: Aug, 2009 Relationship Status: I'd need a PowerPoint presentation
Night Clerk of the Apocalypse
#645: Jun 17th 2018 at 2:50:00 PM

The Pershing's attack run post breaking maneuver was still hypersonic velocities in the neighborhood of mach 7 which is down from re-entry velocity which was appreciably higher and why it pulled the high G breaking maneuver. It was rather very accurate for one of our ballistic missiles to boot at 30m CEP. The whole point of the Hypersonic Glide Body made for Pershing II was to provide both a accurate and fast warhead to counter various Soviet missile sites but also strike known TEL launch unit staging areas. It wasn't hitting higher velocities of weapons like The Minute Man or Peace Keeper warheads at terminal phase at mach 20+ but it was still a hypersonic projectile and a pretty accurate one for a ballistic missile.

You also have to do more than a mere long curving turn to evade the SAM's or their fastest interceptor missiles mounted on their interceptor aircraft. Pilots have described doing some aggressive turning dives to outrun missiles with a few claiming that by the time they pulled out they had hit around Mach 4. By all accounts from the pilots they had little trouble controlling the craft at speed. Rather believable given it was built to be controllable at speed. Its control surfaces are not the same at all especially given the fact the various surfaces weren't the same on other aircraft and had to account for the fact the skin on the craft expanded and shifted once it was speed. You can't slap normal flaps and ailerons on a craft like that and call it day.

Who watches the watchmen?
archonspeaks Since: Jun, 2013
#646: Jun 17th 2018 at 4:16:53 PM

[up]Blackbirds didn't do hard maneuvers at speed. And again, controllable for a Blackbird and controllable for a tactical fighter are two very different definitions of the word controllable.

Like I said, they relied on speed and altitude to evade missiles. You can read accounts of the North Korea missile incident, the pilots made what they described as a calm turn out over the ocean and then watched as the missile dropped behind them. SAM systems of that era were somewhat limited, which helped as well, but hard maneuvering wasn't even on the table.

As far as control surfaces, there's nothing that exotic going on. You can see the control surfaces here ([1]), there's four elevons and the all-moving rudders. The inlet spikes are technically control surfaces too but we're not counting those here. That's not exactly complex, it's actually fewer control surfaces than most fighters since it doesn't have leading edge flaps or a split tail. The most notable thing about them is the number of actuators, 20 per elevon. This was to fight the tendency of surfaces to not want to move when the aircraft is at high speed.

The Pershing 2 I'll concede, though it's somewhat limited compared to you'd want from a fighter. Hypersonic aircraft design does seem to be trending towards the more missile-like though, which goes against the conventional wisdom of large wings and high L/D.

edited 17th Jun '18 4:32:12 PM by archonspeaks

They should have sent a poet.
TuefelHundenIV Night Clerk of the Apocalypse from Doomsday Facility Corner Store. Since: Aug, 2009 Relationship Status: I'd need a PowerPoint presentation
Night Clerk of the Apocalypse
#647: Jun 17th 2018 at 5:58:38 PM

Fair enough in turn i will concede on the SR-71.

Some of the hypersonic vehicles look barely removed from missiles. The crazy project to launch marines was basically revisit of older projects comes to mind.

Who watches the watchmen?
archonspeaks Since: Jun, 2013
#648: Jun 17th 2018 at 6:06:27 PM

Of course they’d load Marines into their crazy transport rocket grin

Hypersonic aircraft more or less work on the “flying brick” principle, they have low L/D ratios but they’re moving so fast it doesn’t matter. The problem is that control surfaces stick, protruding areas like LERX generate weird eddies, and big wings just don’t even work. That leads to the other point I’m wondering about for a hypersonic combat aircraft, which is weapons carriage. Obviously everything is going to have to be carried internally, which limits capacity, but I don’t think conventional-style bays will work. Having doors swing open and down is going to be a challenge, and doors that catch the air too much will be torn clean off. Any weapon being launched is also going to have to be able to get clear of the intense airflow surrounding the aircraft, which is an added challenge.

Any ideas?

edited 17th Jun '18 6:07:07 PM by archonspeaks

They should have sent a poet.
TuefelHundenIV Night Clerk of the Apocalypse from Doomsday Facility Corner Store. Since: Aug, 2009 Relationship Status: I'd need a PowerPoint presentation
Night Clerk of the Apocalypse
#649: Jun 17th 2018 at 7:15:06 PM

Well one of the reasons they never armed the SR-71 was it was a very challenging thing to do. I know it was considered though but nothing really came of it as far as we know.

However something from an older project comes to mind. The XB-70 Valkyrie project which could hit Mach 3 and managed to damage itself on a few flights because we were still learning, had a companion project that spun off from Pye Wacket. The Lenticular Defense Missile which was planned to use a fairly powerful rocket at some point. The overall project had some tentative ties to US studies in nuclear propulsion via shaped charge nuclear warheads. They created a dispenser that was a spindle like device that would rotate the LDM to the correct heading and eject it through a hatch into the air stream below the craft. It had a rather unusual shape and unique control surface design.

The Valkyrie was killed by a combination of politics, high procurement cost (this thing makes the whole F-35 Program look cheap), and the revelation that altitude and speed were not enough to spare the craft thanks to the U2 shoot down. The LDM was considered to offer little protection for the overall added cost and was ultimately dropped.

Astronautix has a good article on Pye Wacket and a segment on the LDM

Basically I think some sort of internal storage that ejects the missile into the air stream with some force to allow it to clear the craft before igniting any propulsion would be called for. The bay would have to open and close very quickly and prevent the airstream from tearing into the storage bay.

Who watches the watchmen?
zepv Since: Oct, 2014
#650: Jun 19th 2018 at 3:21:53 AM

Would a pistol with a .22 LR cartridge be useful for intelligence agencies? It would have a FN P90 style magazine on the top for extra capacity. An infantryman might miss the lack of range or penetrating power in an environment where many of his opponents might be wearing body armor. Would the intelligence agent perhaps be more likely to be in an environment where he is closer to his target and be more likely to fight unarmored targets?


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