Flight sim-like afterburners

[Guest]

Since we can now easily have afterburners using switchable engines, I have a suggestion on how to make it work better with the UI. Right now, it's a bit of clumsy to switch to afterburners with an UI button. However, there's already an element on the throttle slider that would be perfect for this. I propose we use that as afterburner indicator. This is an important part of most supersonic engines in use today, very few ones can actually supercruise (fly supersonic without afterburner) and even then, if you want to get anywhere near space with a normal jet, you've got to have an afterburner.

So, here's what I'd like to see: Throttle axis would be divided into two parts. For example, 90%/10% (ideally, this would be user-configurable). The first would throttle the first engine mode from 0 to 100%. The second would throttle the second mode, also from 0 to 100%. The second mode would usually have a non-zero minimum thrust, but it could be anything, config set-up would be just like RAPIERs. To avoid accidental activation when flying with keyboard, it shouldn't be possible it go to the second mode in a single key press, you'd have to release, then press "shift" again for it to engage afterburner.

Of course, this would be mostly useful for afterburning jets and LANTR nuclear engines, so a config toggle would be needed to disable that behavior for RAPIERs and other engines on which throttle-based toggling doesn't make sense. I believe this would really improve experience with afterburners (jet or nuclear) for all players.

[technicalfool]

I wouldn't mind an afterburner as an extra bit that could be attached to the exhaust of jet engines. Ultimately all an afterburner is, is a big tube that you squirt a ton of fuel into and reburn (or, ahem, afterburn) any unburned oxygen in the exhaust stream. Almost like an exhaust-powered scramjet really.

So long as it does really, really gulp fuel. That's the main thing about an afterburner. While using it, your jet I_sp would drop to something around rocket-engine levels of efficiency.

[horndgmium]

I like your idea, and you can probably find a mod for it currently (there're a few that seem to do what you've mentioned, at least in part) like Davon TC systems mod.

What you're talking about isn't really an afterburner though. Supersonic engines can be just turbofans, and are more common than you think also. An afterburner takes an engine (like the F/A 18 turbofan, for example), that is already running at max thrust, and adds essentially another fuel line to it. This is incredibly inefficient (for ratio, if you double the fuel delivery to the engine, you get like an 18% increase in thrust), but adds more thrust by making the exhaust essentially more explosive. It is only using for short bursts, like carrier take offs, or buzzing the tower. An engine at max thrust is essentially then completely different propulsion system than the same engine when afterburn is activated.

Long story short, you only really want afterburner in passing, so if you want to maintain supersonic speeds, add another turbojet to your plane, and grab a mod, some of which let you control an engines thrust individually.

Edit: I oversimplified. Technically, an afterburner puts an engine at what you would call maximum power, and an engine without afterburner is what you would call military power.

Edited January 2, 2014 by horndgmium

[technicalfool]

Long story short, you only really want afterburner in passing...

Pretty much this. It could be a more elegant solution to getting a tricky design off the runway than "moar booster". Also perhaps a nice way of kicking a spaceplane into top gear to use up the last of the jet fuel before transition to rocket mode.

[Guest]

Well, while non-afterburning turbofans can be supersonic (F/A-18 and F-22 do that, so could Tu-144), it's a recent technology. SR-71 could cruise on afterburner, for example, though in it's engine it acted more like a ramjet at velocities at which it cruised. Still, it was a kind of afterburner, perfectly doable with the system I propose.

Also, afterburner needs to be integrated into engine. You can't just slap one on and expect it to work, it's not as simple as "pour fuel into engine with a hose". A dedicated afterburning engine would be the best solution, IMO. It could be of SR-71 type, since we're doing spaceplanes with it, afterall. Though they could also just add an afterburner to existing engines.

It will also definitely be good for increasing TWR for runway takeoffs and for the last leg of ascent, where you're trying to gain as much speed as possible before leaving atmosphere. It should make taking off with large spaceplanes much easier, letting them liftoff before striking the runway lights.

[technicalfool]

Also, afterburner needs to be integrated into engine. You can't just slap one on and expect it to work, it's not as simple as "pour fuel into engine with a hose". A dedicated afterburning engine would be the best solution, IMO. It could be of SR-71 type, since we're doing spaceplanes with it, afterall. Though they could also just add an afterburner to existing engines.

Well of course. However, this is Kerbal physics. Building a real rocket is a little more complex than "drag the engine onto the fuel tank", too. I guess now tweakables are here, it could be an option for jets. "This engine has an afterburner". Adds a bit of weight, and a boatload of thrust in return for very little efficiency when activated.

It will also definitely be good for increasing TWR for runway takeoffs and for the last leg of ascent, where you're trying to gain as much speed as possible before leaving atmosphere. It should make taking off with large spaceplanes much easier, letting them liftoff before striking the runway lights.

Also mach diamonds.

Mmmmm, mach diamonds.

[vexx32]

I think they used to have an afterburner-ish type setting -- before initial release, even, but it was removed. It used to occupy the slot in the UI where the SAS is now, I believe, and basically just functioned as a switch. You'd run max thrust, punch the button, and if you ran it for too long, it'd overheat your engines (back then, engines wouldn't overheat until you pushed this 'turbo' button).

[horndgmium]

Now I want a turbo...

[Guest]

I think they used to have an afterburner-ish type setting -- before initial release, even, but it was removed. It used to occupy the slot in the UI where the SAS is now, I believe, and basically just functioned as a switch. You'd run max thrust, punch the button, and if you ran it for too long, it'd overheat your engines (back then, engines wouldn't overheat until you pushed this 'turbo' button).

Overthrottling, yeah. It was removed because it was stupid. Rocket engines can't do that. Max thrust is max thrust. Here, we're talking actual jet afterburners.

Also, adding a rocket engine to a tank is about as simple as just mounting it on the tank and adding the plumbing. Not so with afterburners, the nozzle needs to be designed to support it, and it's an integral part of the engine. It should be like that in KSP, too.

[Spica]

Rocket engines can actually do that, look at the space shuttle main engines, at launch they throttle up to 104%, and can co up to 120%.

[vexx32]

That might not be an afterburner. I'm not familiar with NASA's tech by any means, but it sounds more like the engines are deliberately set so that 100% is the max you can without overheating or something, and they can temporarily go beyond that if need be. If that's the case, leaving it at 120% throttle for too long would simply blow the engine up, I'd think...

[datubaman]

If my understanding is correct, the reason that NASA does that is that the 100% mark was the estimated maximum amount of power that the SSME's could safely produce in flight when they were being designed. Once they were actually built and put in service, it was discovered that they could actually produce considerably more power than was anticipated, and that amount of power increased through upgrades and improvements. So, to reduce confusion, they locked the 100% mark where it was (1670 kN @ Sea Level/ 2,090 kN in Vacuum) and referred to any output above it as its appropriate percentage. And after a bit of looking and a trip to Duna, I find that the highest that any of the SSME's could go was 111%, which would only have been used in an emergency.

[vexx32]

Not quite how I thought, then, but I wasn't far off... thanks for that!

[JiWint]

we have afterburners? you mean,nitro or stuff?

[technicalfool]

we have afterburners? you mean,nitro or stuff?

Not yet, hence the suggestion thread.

And an afterburner isn't like nitro, no. The really basic principle is that there's an extra section in the exhaust of the jet engine. Jet engines are not completely efficient, and there is still plenty of oxygen in the exhaust stream that comes out of the back. An afterburner is where a boatload of fuel gets pumped in and ignites, consuming some of that leftover oxygen and giving the pilot a big kick in the pants. So, it causes another burn, after the main burn. See?

When you see fighter jets taking off, and they have that brilliant blast of flame coming out of the engines? That's the afterburner activated. Go back a page and find the picture I embedded in this thread to see.