Jet engines are way overpowered

[Red Iron Crown]

Most of the aerodynamic parts are ridiculously light. The big swept wing? 50kg.

Not sure if that's a reaction to the drag model being mass-based.

[Kasuha]

Not sure if that's a reaction to the drag model being mass-based.

I doubt it since they also have ridiculously low drag - 0.01, compare with 0.2 standard for other parts.

I think it evolved this way: they added normally massy wings with and found they have too much drag. So they reduced the drag. Then they found the plane won't lift because together with fuel and engines it was too heavy. So they reduced the mass as well.

[Red Iron Crown]

That sounds plausible to me. Tough balance to get right, as mass, drag and lift all interact with each other.

[Twreed87]

Apparently, according to these forums, every single part in the game is overpowered.

[rtxoff]

Apparently, according to these forums, every single part in the game is overpowered.

Well, i am perfectly fine with struts

[chaos_forge]

I think one thing to keep in mind here is that the space plane parts are some of the oldest parts in the game currently. I expect that once we get the long-awaited atmospheric model update, we'll also get rebalanced jet engines (although I for one hope they're not nerfed *too* much). Also, fixing the ISP to scale thrust instead of fuel flow would help with this.

[bartekkru99]

Jets over powered? Try to build realistic and nice looking ssto with with FAR.

[Jouni]

Jets over powered? Try to build realistic and nice looking ssto with with FAR.

The Skylon is probably the best example of a realistic SSTO spaceplane. If it's ever built (and if the design actually works), it's expected to have a similar payload fraction as the Saturn V, the Energia, and the (still hypothetical) SLS. Given that KSP rockets can reach 15% payload fraction without using the magic fuel lines, the payload fraction of an SSTO spaceplane should be at most 15-20%. If it's more than that, the airbreathing engines are too efficient and/or powerful, and they'll most likely break career mode balance, when budgets are introduced.

[Clockwork_werewolf]

The intakes are the key not the engines.

The intakes need to be much heavier AND have more intake. With heavy intakes, Rocket SSTO's start to have very low payloads if they want to get air above 12k. Planes can still stay light if they don't need to go above that. SSTO's with wings can have a low TWR but still have reasonable payloads.

Nerf the engines and they have no purpose. The normal jet is already only useful at low to medium altitude. All the engines need to stay useful in low Atmo. I would love to see the atmosphere mechanics changed but that is a lot of work and not happening any time soon. So my earlier post stands. Make the normal intakes heavier and make the RAMs a LOT heavier and take in more air. No more rocket jets, no more 15 intakes to an engine, SSTO's still viable.

[bartekkru99]

Some people were saying, that jet engines consume too less fuel, than they should. I don't know, but, my PAK-FA (T-50, Su-50) replica, was built without any mods and it's consuming 1/5 of my fuel in 2.5 minutes = all fuel in about 12min. If we multiply it by 10 (kerbal world is 10x smaller, so planes have 10x smaller range) it'll gives us 2h of non stop flying at full throttle in real life, which isn't that much.

[Red Iron Crown]

Some people were saying, that jet engines consume too less fuel, than they should. I don't know, but, my PAK-FA (T-50, Su-50) replica, was built without any mods and it's consuming 1/5 of my fuel in 2.5 minutes = all fuel in about 12min. If we multiply it by 10 (kerbal world is 10x smaller, so planes have 10x smaller range) it'll gives us 2h of non stop flying at full throttle in real life, which isn't that much.

No fighter plane can do full throttle for two hours. Nowhere near it.

[Jouni]

Some people were saying, that jet engines consume too less fuel, than they should. I don't know, but, my PAK-FA (T-50, Su-50) replica, was built without any mods and it's consuming 1/5 of my fuel in 2.5 minutes = all fuel in about 12min. If we multiply it by 10 (kerbal world is 10x smaller, so planes have 10x smaller range) it'll gives us 2h of non stop flying at full throttle in real life, which isn't that much.

The specific fuel consumption of the J-58 turbojet used in the SR-71 is 53.8 g/(kN*s) at Mach 3.2. This is probably the closest real-world example to the KSP turbojet. If the KSP turbojets had similar efficiency, they would burn about 12.1 kg of fuel per second at the full 225 kN thrust. This is 2.42 units of liquid fuel, meaning that the fuel in a single Mk1 fuselage would last for 62 seconds.

[bartekkru99]

I've tested my pak-fa again and it can last for about 7.5 minutes.

[bartekkru99]

225kN is a max thrust, but at sea level it has about 120kN.

Edited June 4, 2014 by bartekkru99

[Red Iron Crown]

I've tested my pak-fa again and it can last for about 7.5 minutes.

That's a somewhat realistic level of endurance. Have you got a pic of it? I love that plane.

[bartekkru99]

Wait a minute I'm uploading it on Imgur.

[bartekkru99]

Ok there it is, maybe it isn't looking like an original craft, but it's really manouverable, stable and easy to fly.

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[NERVAfan]

If they are really 16x more efficient than the listed Isp, yeah, that definitely needs to be fixed.

The Skylon is probably the best example of a realistic SSTO spaceplane. If it's ever built (and if the design actually works), it's expected to have a similar payload fraction as the Saturn V, the Energia, and the (still hypothetical) SLS. Given that KSP rockets can reach 15% payload fraction without using the magic fuel lines, the payload fraction of an SSTO spaceplane should be at most 15-20%. If it's more than that, the airbreathing engines are too efficient and/or powerful, and they'll most likely break career mode balance, when budgets are introduced.

(I thought someone already pointed this out, but I can't find the post now...)

The big thing there is that the Skylon is supposed to be only airbreathing up to Mach 5 (or 5.something, can't remember) which is only about 1/5 of the way to orbit (~Mach 25).

But KSP orbital speeds are so much lower, and the jet engine-attainable speeds don't scale down...

So KSP jet engines should probably stop working around 500 m/s or something...

[bartekkru99]

Speeds are not, but the fuel is.

[KerikBalm]

If they are really 16x more efficient than the listed Isp, yeah, that definitely needs to be fixed.

(I thought someone already pointed this out, but I can't find the post now...)

The big thing there is that the Skylon is supposed to be only airbreathing up to Mach 5 (or 5.something, can't remember) which is only about 1/5 of the way to orbit (~Mach 25).

But KSP orbital speeds are so much lower, and the jet engine-attainable speeds don't scale down...

So KSP jet engines should probably stop working around 500 m/s or something...

Post #31, mine, in a list of many things.... towards the bottom of my post.

I tried making a SSTO with basic jet engines, and I was able to without much trouble.... I got into LKO 80x76km orbit, and still had 1020 m/s of dV remaning, only using an Aerospike, 2x basic jets, 2 ram intakes, and 2 radials (so 1 ram, 2 radials per engine). A larger design could carry a nuke or ions, and get much more dV.

If turbojets were nerfed down to basic jet performance, we could still make plenty of SSTOs.

I got to over 400 m/s and over 20km before firing the aerospike (chosen for its ISP being tied for the best non-nuke, and a TWR better than a lv-909, maybe a LV-T30 would be better due ot lower mass).

I'm sure I could still make some ridiculous SSTOs... simply by virtue of only needing another 2,000 m/s of dV to get to orbit, as opposed to 4,000 m/s in RL.

The better mass ratio of tanks in RL only would make up for about 30% of that... the better ISP (421) also wouldn't get you to double that... and that is assuming starting from a scramjet going 4,000 m/s, which we aren't able to do (yet?).

The engine mass IRL also helps a lot... but still... what makes SSTOs so easy in KSP, and so hard IRL, is the orbital velocity.

Basic jets can get you to 1/5 of orbital velocity in KSP, and thus would be quite realistic standins for ramjets (minus their extreme fuel efficiency, and low altitude, low speed performance)

I think we need a SSTO challenge where rapiers and turbojets aren't allowed