Should Jet engines be rebalanced?

[quasarrgames]

It seems (to me) that most people think that jet engines are overpowered and unrealistic. They work completely different from real-life jet engines, and are apparently about 15 times more powerful (although based on my experience with AJE i'd say that it's usually closer to 3-5 times).

However, the REAL question is, should they be rebalanced for stock in the future?

(i think) The pros of rebalancing them are that they will be more realistic, which will be more educational and better for all those realism junkies, and that they will be more challenging to use (which i hear some people like), but still usable for spaceplanes.

(i think) The cons are that we won't have any silly engines to play with anymore, and it will be significantly harder for average players to make spaceplanes, especially ones that they can actually do things with.

Anyways, please vote!

Edited March 21, 2015 by quasarrgames

[Francois424]

I think it's hard enough as it is to make Polished, beautiful space planes as it is, if the jet engines get the nerf-bat, we might as well forget it.

Oh there's the rapier, which is worse in Vacuum and worse in the air.

If anything nerf the jets, but buff the rapier to where the jets are right now, at least for atmo.

[longbyte1]

I'm pretty sure the community has already agreed that jet engines are completely unrealistic, but Squad shouldn't go overboard with realism. So if you want realistic jet engines, there's a mod for that.

[Van Disaster]

~15x more economic, I thought? even as they are the stock ones will need rebalancing for new aero. FAR and B9 have a MM config to cut the stock engines in half, more or less, and they're still good for their size.

The parts really need to be bigger, especially the Rapier - currently they're the end of the engine with no design considerations necessary for the rest of the engine. Jet engines are big! Rapiers aren't jet engines but the cooler part which the stock one doesn't even have would make them as big as an axial flow turbine anyway. What would fit KSP quite well is something of a modular tech tree compatible system of intakes/cores/outputs, which I have some thoughts on but haven't finalized yet ( I think I'll post when I have ).

[Bill Phil]

I don't care all that much, but it would be nice.

What can I say? I'm a rocket man. Planes never really worked for me at all...

[mattinoz]

Bigger range with more realistic power would be my vote, no need to go fully realistic it is KSP after all.

To me there should be a couple of options added each end then balance then out between.

1)a tiny (0.625) basic jet.

2)after burner option for just a bit more kick on take-off and you'd only be able to run it for 30sec or less before overheat.

[Slam_Jones]

The single biggest issue to me in the asymmetric flame-out. Assuming that's fixed in 1.0 (I believe they said it will be), then I could care less what they do with it, since it will be soooo much easier to manage multiple engines.

[Francois424]

The single biggest issue to me in the asymmetric flame-out. Assuming that's fixed in 1.0 (I believe they said it will be), then I could care less what they do with it, since it will be soooo much easier to manage multiple engines.

Time to try my B-52 stratofortress again in 1.0 then. Never was able to make a jet that brings a full orange to space, might be the time now =)

[Columbia]

With the extreme power of the jet engines, I think the actual problem is with the spaceplane parts themselves, especially with the Mk3. It requires up to 12 engines (I'm not exaggerating..) to even lift off. I think they're too large and heavy.

[Armchair Rocket Scientist]

I think if jet engines were rebalanced to semi-realistic levels with no other changes the game would be made almost useless. However, with fixes to Kerbin's soupy air, planes should be able to fly with lower TWRs. It would also be extremely helpful to have 0.625m and 2.5m jet engines, probably with up to 250 kN of thrust or so. At the very least, we should have "basic jet engines" at each scale with good low-speed thrust, and "turbojets" up to mach 3 or so. Perhaps a pre-cooler part could be added to extend the thrust curve of jet engines to higher speeds.

Anyway, however it's done, the jet engine rebalance should allow a well-built SSTO to have a larger payload fraction than a well-built multi-stage rocket (asparagus staging presumably won't be as powerful with aerodynamics fixes). Unless rockets and fuel tanks are dramatically rebalanced as well, this probably means allowing jets to keep producing usable thrust up to at least 1500-1800 m/s in some vehicle configurations.

[Azimech]

^^ this. Smaller and larger jets.

[klgraham1013]

Make them realistic, but also give me some crazy future tech to support SSTOs.

- - - Updated - - -

With the extreme power of the jet engines, I think the actual problem is with the spaceplane parts themselves, especially with the Mk3. It requires up to 12 engines (I'm not exaggerating..) to even lift off. I think they're too large and heavy.

I think I was able to get a basic Mk3 cargo plane off the ground with 6, but I was using wet wings for my fuel.

- - - Updated - - -

The biggest issue is there's still very little to do with a non-SSTO plane. We need reasons to actually traverse planets. I personally have set up polar bases that require life support resupplies.

[Wahgineer]

Anyway, however it's done, the jet engine rebalance should allow a well-built SSTO to have a larger payload fraction than a well-built multi-stage rocket (asparagus staging presumably won't be as powerful with aerodynamics fixes).

Technically impossible. Multistage rockets are initially superior to SSTOs because they can deliver more cargo at a smaller size/mass (Hence why our (and NASAs') SHLLVs are multistage).

[Mr. Speed]

the stock jets are good for stock aerodynamics. with the new aerodynamics coming they will probably need to be rebalanced (and they probably will be).

[pincushionman]

…The parts really need to be bigger, especially the Rapier - currently they're the end of the engine with no design considerations necessary for the rest of the engine. Jet engines are big!…

I agree with this, as an engineer who works with engine nacelles. Jets, especially ones with the power necessary for the kinds of things we meed for KSP, are gigantic mofos. In particular they're long. The biggest problem I have making planes, particularly early in career, is trying to balance the plane. Engines are (somewhat) accurately portrayed as the most massive individual components on a plane, but all that mass is concentrated in what should be seen as the nozzle. In reality, the turbine is ahead of that, preceded by the combustion chamber, preceded by the compressor, preceded by the ducted fan (if they have it). And THAT'S where the weight of an engine lies. The component CoM should be roughly midway up the fuel tank we normally have attached in front of it in KSP.

[Frozen_Heart]

nerf the jets but keep the rapier how it is.

[rcp27]

The problem with jet engines is less due to the engines themselves and more due to how intake air is implemented. In the most basic sense, the gross thrust of a rocket engine or a jet engine is the mass flow leaving the engine * the velocity that mass leaves at (let's call them m_ex and V_jet). In a rocket motor, all of the m_ex comes from the fuel and oxidiser carried on board, so V_jet is the ISP. In a jet engine, a small amount of fuel is burned in a very large amount of air, and the resulting mass flow all leaves at V_jet. In terms of ISP, of a jet engine, V_jet = ISP * m_fuel/m_air. Because m_air is very much larger than m_fuel, V_jet is very much smaller than ISP. The important issue, though, is where the m_air comes from. In essence, an air intake is a reverse-rocket. Air enters the intake at a high velocity, and is slowed down to the speed of the aircraft. If the gross thrust of a jet engine is m_ex * V_jet, then the intake drag (ram air drag) is m_in * V_air (V_air is the aircraft speed). For a high bypass ratio airliner engine, a typical V_jet might be in the region of 300 m/s, and for a military engine for a fast jet might be 1500 m/s. For a rocket, V_jet might be something like 4000 m/s. What this means is, if you have a jet engine with a V_jet of 1500 m/s (a reasonable value for the turbojet), the combination of jet + intake will generate full thrust while stationary, 2/3 of thrust at 500 m/s, 1/3 thrust at 1000 m/s and no thrust at all at 1500 m/s. Because the rocket engine doesn't use atmospheric air, it suffers no ram drag. While I'm not entirely sure how the game models air intakes, the fact that jet powered aircraft can be flown up to well over 1500 m/s on jet engines alone, I strongly suspect that the impact of ram drag is not at all properly represented.

[Renegrade]

I don't know what this hullabaloo about "we won't be able to make worthwhile spaceplanes" nonsense is all about. I've made post-nerf BasicJet powered spaceplanes in FAR. They might not be able to bring sixty times their own mass into orbit for 8 funds, but it is a doable thing, and still fully reusable. Well...assuming FAR doesn't eat 'em on the way back in.

While I'm not entirely sure how the game models air intakes, the fact that jet powered aircraft can be flown up to well over 1500 m/s on jet engines alone, I strongly suspect that the impact of ram drag is not at all properly represented.

The engines themselves have a simple thrust/speed curve that's based off of the airspeed in stock. The TurboJets have a curve like so:

	velocityCurve
	{
		key = 0 0.5 0 0
		key = 1000 1 0 0
		key = 2000 0.5 0 0
		key = 2400 0 0 0
	}

The columns are speed(surface, m/s), power (1.0 being full thrust number), and two tangents that help describe the curve (not used here). So the TJ still has 50% power at 2km/s, and eventually peters out at just past orbital speed. Lack of IntakeAir will also scale back an engine's power, but you can just spam intakes, and each of 'em will provide a given amount of intake air at a given speed and pressure (The TJ will require about 15x it's fuel intake in air intake, which is usually around 2 units/s or thereabouts, based on the right-click flow rates shown on the intakes).

Based on what you said, a more proper value for the second key (assuming V_jet is 2400 here) would be about 0.58333..., and the third value 0.16666...

Here's the BasicJet if anybody is interested:

	velocityCurve
	{
		key = 1000 0 0 0
		key = 850 0.2 0 0
		key = 0 1 0 0
	}

[rkman]

KSP's jet engines already are about 10 times more powerful compared to real life rocket engines vs jet engines (assuming the Mainsail is equivalent to the F1).

Making jet engines yet more powerful would be more unbalanced. Making them less powerful and at the same time introducing a 'futuristic' (cheaty) jet engine would also not help game balance. For people who want scifi in KSP, there are mods.

Bigger range with more realistic power would be my vote, no need to go fully realistic it is KSP after all.

Bigger range? It already is possible to fly around the planet several times on a single tank, in part due to a bug that makes jet engines ISP much to high.

So if anything, range should be reduced.

Also, i think jet engine parts (and the Rapier) should not consist of only a nozzle as they currently do.

[Red Iron Crown]

IMO jets are way, way too fuel efficient for game balance (realism aside, that's been discussed to death). Whether you use rocket-style or plane-style lifters the turbojet is almost always the most economical choice, assuming you are recovering at KSC.

Some sort of nerf is definitely in order, by increasing their fuel consumption and possibly having their thrust die off at lower speed.

[klgraham1013]

Making jet engines yet more powerful would be more unbalanced. Making them less powerful and at the same time introducing a 'futuristic' (cheaty) jet engine would also not help game balance.

How, exactly, would adding a near future jet engine higher up the tech tree screw up game balance?

[Jouni]

How, exactly, would adding a near future jet engine higher up the tech tree screw up game balance?

For many of us, sandbox balance is more important than career mode balance.

Near future engines are fine, as long as they are plausible near future engines and not magic sci-fi engines. The SABRE is a good example of a plausible engine. In airbreathing mode, it's essentially an intermediate engine between turbojets/ramjets and rocket engines. The SABRE is less efficient than turbojets below Mach 2, and less efficient than ramjets above Mach 1. On the other hand, its TWR is much higher than that of turbojets and ramjets, while still being much lower than rocket engines.

[regex]

KSP boasts relatively realistic rocket engines that are balanced for use on Kerbin (with a few notable exceptions that should be fixed) by extra mass. These engines also have varying isps that really make no sense, mainly because no one has any idea what the liquid fuel/oxidizer superfuel combo is, but are at least internally consistent and within the realm of possibility (aside from some ASL isp values). I see no reason why jet engines shouldn't receive the same treatment, especially with a new aero model.

This does mean that spaceplanes would end up being far more than 1/3 rocket and the payload to orbit would be far more realistic, and these planes would also be much harder to build. I recall some spaceplane enthusiasts lamenting the RAPIER because it made the planes easier to build. They should be rejoicing over a jet engine nerf/rebalance because spaceplanes will once again become artisinal craft with their own brand of black magic.

[klgraham1013]

For many of us, sandbox balance is more important than career mode balance.

Near future engines are fine, as long as they are plausible near future engines and not magic sci-fi engines. The SABRE is a good example of a plausible engine. In airbreathing mode, it's essentially an intermediate engine between turbojets/ramjets and rocket engines. The SABRE is less efficient than turbojets below Mach 2, and less efficient than ramjets above Mach 1. On the other hand, its TWR is much higher than that of turbojets and ramjets, while still being much lower than rocket engines.

I am a sandbox player. I understand that I will have access to high tier parts. In reality some things are simply better than others.

[Jouni]

I am a sandbox player. I understand that I will have access to high tier parts. In reality some things are simply better than others.

Better parts would not be a problem, if Squad had infinite developer resources and the 32-bit memory limit was a less serious issue. Until them, I prefer having a minimal set of non-redundant parts with potential for as diverse gameplay as possible.