Shields used to create aerodynamic bubble for ships in atmosphere.

"A triumph of thrust over aerodynamics" was an early dig against the Phantom, especially from the single-seat, single-engine fighter community. But the aerodynamics weren't really bad, they were actually quite sophisticated and dealt very effectively with the demanding and sometimes competing requirements on the design. The Phantom wing was very strong but overall only around a 5% thickness ratio, about the same as the much lighter F-100B.

 

^^ the F-104 is a better example I guess. what wings? and half of it is engine.. or as I mentioned before Mig 25, nickel steel brick and REAHEAHEAHEAAAAAAAAAALY big engines.

As for the shuttles, again, they have incredibly powerful engines, to our standars indestructible hulls so aerodynamics are rather blah blah..

 

MiG-25 lives on... Russia is currently adopting/adapting its surviving MiG-31s as launchers for ballistic and hypersonic missiles, as there's very little other use for these all-engine monsters in the current fighting environment.

But how the shuttles move close to planetary surfaces has always been a bit of a mystery - ever since "The Galileo Seven" and its frustrating double- and tripletalk on what makes the thing go. There's fluid fuel, there's a mass limit, there's the ability to recharge from phaser clips, there's the fact that a launch to orbit is not particularly hobbled by a bunch of cavemen clinging on to the craft for an extra minute after liftoff...

In light of the latter bit especially, I'm inclined to think the shuttle lifts off and maneuvers mostly on gravitics. At takeoff, it's an elevator (or perhaps a blimp, capable of floating up not just on very low mass but on negative mass for extra buoyancy) rather than a rocket, and it just happens to be an elevator capable of being powered by its space engine (which in the episode becomes unavailable as the fuel leaks out) or by any number of auxiliary power sources (which in turn do no good in spaceflight).

Aerodynamics would matter little to a craft that lifts off at walking pace. Of course, the heroes would typically opt for more speed, in which case they might apply the shield trick, or then raw power from alternate propulsion systems, or then a combination. But "The Siege" suggests that impulse engines do little or no good within an atmosphere, which is another factor in our speculation on shuttle propulsion; perhaps raw power is difficult to channel into atmospheric propulsion after all?

Timo Saloniemi

 

Shuttles are kinda strange, yeah... but impulse engines have really hot exhausts, draw air into that and it will expand like it does in a jet engine so they actually might work that way in an atmosphere, add antigraphs and you've got about what we see.

 

The obvious "intakes" and "exhausts" in modern shuttles fit that model very well, especially with the "hot air shimmering" effect coming from them in DSC visuals.

It's just that impulse engines seem to be at a disadvantage in atmospheres, as per "The Siege". Two types of winged craft fight down in the soup. The bigger ones obviously have more power, and have impulse engines; the smaller one has sub-impulse propulsion, whatever that is, and still wins out in the atmosphere even when doomed to lose a sublight fight in vacuum. This because, as Kira outright states, "They won't be able to use their impulse engines down there".

Might be a limitation on these specific craft, of course - Kira supposedly knows the specific hardware in and out.

Then again, did we ever actually learn that shuttles would have impulse engines? That is, I'm pretty sure there's at least an instance or two in VOY about a shuttle "dropping to impulse", but I can't come up with any specific references.

Timo Saloniemi

 

Watching the episode points to this explanation that jives with Kira's statement, "They won't be able to use their impulse engines down there". When they are in the atmosphere Kira notes, "All right. They've gone to thrusters. That evens things up a little." Their thrusters look just like the "sub-impulse" thruster on Kira's raider.

We know from other examples that impulse engine works fine in the atmosphere. A good reference is the Klingon BOP from "The Voyage Home". She uses thrusters for initial lift-off but while hovering switches to impulse engines for flying around in the atmosphere. As far as I can tell, there are no particular disadvantage of impulse engines in general in the atmosphere and it's just these Bajoran ship's impulse engines that have a problem with atmospheric flight.

Thrusters seem to be preferred for initial takeoff and landings though. Why that is I don't think it has ever been stated, AFAIK. I'm guessing it allows for more fine control.

 

Maybe it's so that you don't set the people congregating around the LZ on fire.

 

Yet impulse exhaust isn't a flame of fire as such. Ships and craft just happen to have a (quite possibly really hot) radiator or "tailpipe" for their impulse engines, one that glows regardless of whether the ship is under thrust or not; people keeping their distance from that radiator ought to be fine.

Still, it might make good sense (in terms of consistency) that impulse engines work better high up in the atmosphere, which is closer to their "natural" environment, and underperform in thick air. If they also pose risks close to the ground, all the more reason to switch to thrusters or gravitics or those "gravitic beams" NCC-1031 used in the Qo'noS cave.

This is a bit odd, really. These things have wings and streamlining. And wings. If they work exceptionally poorly in an atmosphere... What is driving their design?

Timo Saloniemi

 

Right. We mostly see the impulse radiator but only rarely do we see impulse exhaust. In "Blaze of Glory" we do see a runabout modify it's "flow regulators" to release it's impulse exhaust to detonate the gases in the Badlands. Interestingly we see the exhaust come out of the blue grills of the warp nacelles - so at least on some Federation ships impulse and warp appear to be very connected together. Anyway, if impulse engines were normally a heat danger then we'd see these explosions all the time in the Badlands but since we don't I would suggest that impulse engines don't usually exhaust hot gas.

I dunno. We've seen impulse engines consistently perform well in thick atmosphere/gas environment (see "Starship Down" and "The Immunity Syndrome"). Is there some specific (from TOS, TNG/DS9/VOY/ENT) episodes that have federation impulse engines struggling in the atmosphere? Discovery has so many differences in operation that they are more likely to be connected to the Kelvin timeline than TOS or TNG so for examples with them it might be specific to just how Discovery tech works.

Maybe that's why they still have wings and streamlining? Since it's established in that episode that those Bajoran ships can't operate their impulse engines in the atmosphere then they would have to rely on aerodynamics to fly around with their thrusters. That would connect back up with this thread - if you had impulse that worked in the atmosphere you would not need to have an aerodynamic design. As to why their impulse isn't as useful as the Feds and Klingons, etc, does it matter? Maybe the Cardassians kept the Bajorans back or the Ferengi cheated them with defective impulse engines?

 

From TUC [http://www.chakoteya.net/movies/movie6.html]:

SPOCK: Gas. ...Gas, Captain. Under impulse power she expends fuel like any other vessel. We call it 'plasma' but whatever the Klingon designation is, it is merely ionised gas.​

Ionized gas aka plasma is pretty hot, yo.

 

Of course Spock doesn't say anything about the temperature or the density. In "The Voyage Home" we see a BOP hover at close range on impulse over a whaling boat without incinerating the people below and at full impulse in the atmosphere leave no heat trail or any other indication that it is blasting out a ton of heat. The "expended fuel" of ionized gas aka plasma doesn't appear to be hotter than a plasma TV (unless you realign the flow regulator!)

 

So is Jet Engine Exhaust!

 

On most Fighter Jets you'll see a heat mirage at best, if you see fire (then they're using After-Burners at that point)

 

No, the BoP was diving down at altitude towards the whaler at full impulse. But for all we know, while it was hovering over the whaling vessel (that was always an impressive VFX, by the way), it was just using thrusters.

For the record, my post was partially facetious, intended to be jocular, and I assumed so obviously so that I didn't think a winky was necessary. But alas, never assume; it was apparently necessary. (I see your smily, so I realize you're being partially facetious too.)

But as for the non-facetious part, real plasma is very hot. By definition, it's hot enough to ionize gas. For example, the plasma in a plasma TV display is 1200 °C (2200 °F) or more, but that's not being used to propel the TV, and only enough of it is present to trigger the display's phosphors. For the name "plasma" to apply, the mean energy per particle has to remain high enough to keep enough of the particles ionized. And, if the density is too low, its momentum will not be high enough to work as a practical rocket propellant.

In real life, even one second of immersion in plasma rocket exhaust powerful enough to lift a real rocket would be fatal, but that would be because of the thrust alone. However, flames or not, there would be a great deal of heat that would have to dissipate into the environment. Even without direct contact with the exhaust, it could be harmful or fatal if nearby. Cotton self-ignites at about 400 °C (760 °F), so plasma heat is more than enough to set clothes made of cotton on fire.

 

Exactly. I'd expect to see some heat effect if impulse flight was blasting out tons of heat with its plasma exhaust. But we see none of that in "The Voyage Home".

It doesn't look like thrusters though. In "The Voyage Home" they showed what it looks like with the BOP using thrusters to takeoff or land (even while cloaked) and there was a very obvious amount of wind blowing around below the ship. The saving the whale scene exhibited none of the thrust blast disturbing the water or the boat below. Here's the whale scene on youtube.

Instead, the hover looks just like what the BOP looked like when she was on 1/4 impulse as they were leaving Vulcan.

No worries.

Oh don't get me wrong, I'm not debating that plasma rocket exhaust is not hot. If I were to go the hard science route I'd also point out that there's no way that the BOP or any Star Trek ship could carry enough fuel to hit 0.8c (but we see the Enterprise do that in TMP).

What I am pointing out is that the dialogue in "The Undiscovered Country" with the "ionised gas" or "plasma" lacks enough specifics that it still falls in line with the benign aspects of impulse use in the atmosphere and safely hovering over the whalers in "The Voyage Home".

The TUC dialogue doesn't say the temperature or density of the gas. From just observation, the impulse engine could be generating a magic energy field that reduces the amount of energy needed to move a ship so that is only needs minute use of thrusters and the plasma exhaust is so small that it requires special gaseous anomaly sensors to detect it.

 

Yep.

 

I usually think that the impulse engines are specialized sub warp coil engines and the exhaust comes from the fusion reactors powering them, fusion reactors would exhaust helium plasma.

 

http://memory-alpha.wikia.com/wiki/One_Little_Ship_(episode)
In this ep of DS9, the Rubicon in shrunked mode; enters the Defiant from it's Impulse Drive Conduits.
They have to leave, or else the Super Heated Plasma would kill them should they fire up the Impulse Drive.
And they barely make it.

The Heated Plasma is what makes the Defiant Accelerate at STL speeds.

 

I had thought about this episode (one of my favorites). However, this only confirms that super heated plasma flows inside a conduit that is part of the impulse pre-start sequence. Also the Rubicon entered via the "aft plasma vent" to gain access to the internal conduits to reach an access hatch to engineering. They didn't enter in through an impulse thruster so this episode doesn't connect the dots that heated plasma is the magic used for impulse acceleration. Instead, we're just seeing them flying through an EPS conduit that is part of the engines.

However, this episode does jive with "Blaze of Glory" where heated internal plasma exists that can be vented if necessary.

 

Venting of impulse plasma is confirmed. Use of said plasma as a Newtonian propulsive jet is not, and indeed is heavily contradicted by

1) impulse engine "nozzles"/vents pointing whichever way, including at the structures of the ship itself
2) impulse vents glowing all the time, regardless of the ship's state of motion
3) nobody actually getting burned or blasted away by a jet coming from the impulse engine.

But while warp engines expel plasma only in emergencies (it supposedly forming a closed loop in normal operations, either flowing around or then just sitting there so that warp energies can flow through it), impulse plasma seems to be vented basically all the time. Which I guess is the interesting bit here. Is the venting necessary for providing motion? Or for keeping the engine from overheating or blowing up? Do all engines turn the venting into a propulsive asset, or do just some, or none?

Perhaps worth mentioning is that the glow from the (impulse?) engine of the BoP in "Search for Spock" does not significantly die down when the ship lands on Vulcan, yet our heroes readily exit through a ramp right below this glowing doodad. Perhaps even at its worst, an impulse engine vent puffs out truly minuscule amounts of hot helium, not enough to make the air shimmer or the heroes' hair get messed up? Or perhaps idle and full thrust modes just happen to be visually identical for reason X.

Timo Saloniemi