How do you increase thrust on jet engines?

[Columbia]

Hello, forums! I was recently testing new aircraft, and I oddly noticed that the "Wheesley" jet engine was pretty much static at 100kn thrust. This was vital (and way off compared to actual turbofans,) and it was apparently possible to push the thrust up all the way to 167.994, but I had no idea how.

I had engine precoolers, and the intake air supply was adequate as far as I could tell.

Here are some images of the aircraft (and if you're wondering, yes it is indeed a Boeing 737 replica)

Javascript is disabled. View full album

Are there any ways I could still increase thrust on the engines? Suggestions would be appreciated.

Thanks in advance!

Edited April 30, 2015 by Columbia

[Blu_C]

Nope. Other than using the engines in the conditions they were made for. I'm not actually sure precoolers actually do anything other than provide intake air.

Standard Jet Engines are mostly for use at low altitude and low speeds. At higher altitudes/speeds their power drops off significantly.

The turbojets are weak at low speeds/altitudes, but once you get above around mach 1 begin to pick up thrust impressively and can function at much higher altitudes (beginning to get rapidly weaker somewhere after about 18k above sea level). It actually isn't difficult to create an aircraft that will blow up from aerodynamic forces using turbojets.

[Columbia]

Nope. Other than using the engines in the conditions they were made for. I'm not actually sure precoolers actually do anything other than provide intake air.

Standard Jet Engines are mostly for use at low altitude and low speeds. At higher altitudes/speeds their power drops off significantly.

The turbojets are weak at low speeds/altitudes, but once you get above around mach 1 begin to pick up thrust impressively and can function at much higher altitudes (beginning to get rapidly weaker somewhere after about 18k above sea level). It actually isn't difficult to create an aircraft that will blow up from aerodynamic forces using turbojets.

Thanks for the reply!

Welp, I guess I'll be using turbojets more from now on.. It's a bit of a letdown.

But anyways, thanks again! Repped!

[Mister Spock]

I was wondering the same thing about the Wheesley. What's its effective ceiling? I can't seem to push a small craft higher than about 11,000m with it. Then again, that's a pretty decent service ceiling for an early jet.

[Old Foxboy]

The Wheesley can go up to about 13.000m if you construct a craft that has a low stall speed (add more wings, make it look like a glider). And no, that's not impressive. It's more like what you would expect from a normal turbofan.

As for the Mk3 crafts: The Wheesley is too small for them. You'll simply need more of them. Try modeling a 707 instead of a 737. The older 707 had 4 engine nacelles.

A nice addition for MK3 parts would be a bigger Wheesley engine, like a modern turbofan which is used on the 767 or 777

As for the so-called "Turbojet": I don't know what the KSP developers had in mind. If it simply was a low bypass turbofan (like in most military aircraft today), it would get you to mach 2 at best. Or a RAMjet? (Which will practically produce 0 thrust at 0 speed). I guess it's something like the Pratt&Whitney J58 (like the ones in the SR-71 Blackbird), which have a normal turbojet stage combined with a RAMjet that leads compressed air at higher speeds directly into the afterburner stage http://de.wikipedia.org/wiki/Pratt_%26_Whitney_J58#/media/File:SR71_J58_Engine_Airflow_Patterns.svg

However: such an engine would require a suitable intake, so using a KSP "turbojet" should force you to build a shock cone intake or equivalent.

Given the variety of rocket motors in KSP, i'd love to see at least 2 more aircraft engines: One on the lower end (maybe a prop on lvl 1?), and one SCRAMjet engine that would not b able to provide thrust below mach 1, but would boost the plane beyond mach 3 up to orbital speeds (as long as you are still flying through any atmosphere). The Rapier's are science fiction anyway, so why don't combine them with a stronger SCRAMjet stage?

[Mister Spock]

If I had my druthers, we'd get a piston-drive prop and a turbo-prop, so that we can make things that look vaguely like a Cessna 172 or Cessna Caravan or a Bonanza or whatnot. Then again, more parts do mean more RAM, but one can always delete extra parts.

[eddiew]

Speed. All engines have an optimal speed at which they deliver a thrust above and beyond their static (stationary) output. In the case of turbos and rapiers, 2-3x static thrust is viable with a good run up, with a theoretical maximum of 1000kN. But you'd burn up if you actually managed it, since it requires low altitude at hypersonic speeds

Best speeds:

- Basic jet, mach 1.7

- Turbo jet, mach 3 (3.5?)

- Rapier, mach 3.7

The flight ceilings are pretty much artificial and don't relate to your intake air at all anymore.

Interestingly, the power curves also differ. While rapiers deliver far more power by mach 3 than a turbojet, the turbo will be 50% better at mach 1; which is making mixed-engine spaceplanes exceedingly powerful right now.

I doubt any of it relates to reality however

[Old Foxboy]

I doubt any of it relates to reality however

Take the Rapier out, and the basic Jet resembles a high bypass turbofan and the turbo RAMjet resembles a P&W J58 pretty well. However, the atmosphere of Kerbin is weird. It is similar to Earth up to 15.000 or so, and then it falls off much quicker. However, the gravity is the same, but the diameter is WAAAY less. There are many comparisons to be found in the internet.

If Kerbin's atmosphere was up to scale, you would run out of air with the basic Jet engine at 1500 metres. However, the Kerbin atmosphere is about 1/2 that of earth, which means your Jet engine should run out of power at about 7000 metres (which it doesn't). This means: The atmosphere scaling compared to earth is not linear, but it resembles earth's atmosphere up to about 20.000 metres, and then it starts to fall off dramatically. A real Blackbird SR 71 (with the Kerbal turbo RAMjet equivalent) or the Mig-25 would fly Mach 3.2 at 20.000 to 25.000 metres on earth and would be able to make a ballistic zoom flight to about 35 km. That's pretty much what we get in KSP. But everything beyond 25.000km on Kerbin is scaled down to make things easier.

What's different: The thrust at sea level is dramatically higher from what i feel. I have no numbers to prove it, though. But being able to zoom up from liftoff, reaching Mach 1.0 in a 70° steep climb and reaching almost Mach 3 before the engine runs out of air feels not right to me. But hey, that's a game.

[NathanKell]

Nope, Kerbin's atmosphere is a pretty exact 80% Earth atmosphere: the atmosphere (pressure, temperature, density) at 8km on Kerbin equals that at 10km on Earth.

[juanml82]

The Wheesley can go up to about 13.000m if you construct a craft that has a low stall speed (add more wings, make it look like a glider). And no, that's not impressive. It's more like what you would expect from a normal turbofan.

As for the Mk3 crafts: The Wheesley is too small for them. You'll simply need more of them. Try modeling a 707 instead of a 737. The older 707 had 4 engine nacelles.

A nice addition for MK3 parts would be a bigger Wheesley engine, like a modern turbofan which is used on the 767 or 777

As for the so-called "Turbojet": I don't know what the KSP developers had in mind. If it simply was a low bypass turbofan (like in most military aircraft today), it would get you to mach 2 at best. Or a RAMjet? (Which will practically produce 0 thrust at 0 speed). I guess it's something like the Pratt&Whitney J58 (like the ones in the SR-71 Blackbird), which have a normal turbojet stage combined with a RAMjet that leads compressed air at higher speeds directly into the afterburner stage http://de.wikipedia.org/wiki/Pratt_%26_Whitney_J58#/media/File:SR71_J58_Engine_Airflow_Patterns.svg

However: such an engine would require a suitable intake, so using a KSP "turbojet" should force you to build a shock cone intake or equivalent.

Given the variety of rocket motors in KSP, i'd love to see at least 2 more aircraft engines: One on the lower end (maybe a prop on lvl 1?), and one SCRAMjet engine that would not b able to provide thrust below mach 1, but would boost the plane beyond mach 3 up to orbital speeds (as long as you are still flying through any atmosphere). The Rapier's are science fiction anyway, so why don't combine them with a stronger SCRAMjet stage?

Actually, the Rapiers are based on the Sabre engine ESA is working on for the Skylon project

[Old Foxboy]

Nope, Kerbin's atmosphere is a pretty exact 80% Earth atmosphere: the atmosphere (pressure, temperature, density) at 8km on Kerbin equals that at 10km on Earth.

If this is true, the Jet engines are hopelessly overpowered.

[eddiew]

If this is true, the Jet engines are hopelessly overpowered.

That would imply an earthly jet engine could send you up to 56km altitude by virtue of it's thrust at 18

[Old Foxboy]

Actually, the Rapiers are based on the Sabre engine ESA is working on for the Skylon project

Quote: "Reaction Engines is still years away from a completed engine and the construction of SKYLON is years after that, though the company remains optimistic and is currently seeking additional funds to continue development."

[NathanKell]

Yes, KSP jets are quite OP in lots of ways. That said, KSP players also have a penchant for putting tons of jets on their vessel--imagine an SR-71 with about 8-10 engines rather than 2. I dare say that could zoom-climb quite well.