Jet engines Flame out

[Santi]

Hello everyone!

How high I can climb a shuttle with jet engines that need oxygen to ignite? I read that the atmosphere of kerbin reaches 69000 m tall, but if I turn the engines 63000 m not work and appear with the state "flame out" I have put the air intakes, is the shuttle that is preset with the game "Learstar A1"

Someone could help me with this? Thank you

[Raincloud Man]

Um... The atmosphere goes all the way up to right under 70km but it's way too thin to support airbreathing engines for much higher than 22km.

A shuttle uses rocket engines all the way for this reason, with detachable tanks. What you are probably thinking of is an SSTO plane, and to get those into orbit you need to do some very plane specific things. Basically you want to climb to 10 km and then put all your engine power into increasing your horizontal velocity with a very small amount of vertical velocity, then when you climb over 20k or therearound you switch your airbreathing engines off and engage cloced cycle engines, such as the RAPIER or regular rocket engines.

[jcekstro]

Depends on how many air intakes you have. The amount of oxygen dissipates quickly once you get into the second level of atmosphere. Also it really depends on how many engines you have. If you only have one you can push it to the limits. If you have an engine on either side of the plane one will flame out quicker than the other and you will start spinning with the assymetrical thrust. I haven't tried it with the new aerodynamics, but you used to be able to abuse the physics and build what were called air hoggers where you had a crap load of air intakes for the amount of engines you have making it possible to run the engines much higher. Not sure if you can still do this or not, but I usually try to stay around 15-20k meters and build up as much speed as I can so I can do a quick pop up and switch over to a rocket engine to circulize my orbit. Anything over 20k and you are going to start pushing the limits of your intakes.

[Raincloud Man]

Originally posted by jcekstro:

Depends on how many air intakes you have. The amount of oxygen dissipates quickly once you get into the second level of atmosphere. Also it really depends on how many engines you have. If you only have one you can push it to the limits. If you have an engine on either side of the plane one will flame out quicker than the other and you will start spinning with the assymetrical thrust. I haven't tried it with the new aerodynamics, but you used to be able to abuse the physics and build what were called air hoggers where you had a crap load of air intakes for the amount of engines you have making it possible to run the engines much higher. Not sure if you can still do this or not, but I usually try to stay around 15-20k meters and build up as much speed as I can so I can do a quick pop up and switch over to a rocket engine to circulize my orbit. Anything over 20k and you are going to start pushing the limits of your intakes.

Well, with RAPIERs you still kind of need to go air hog still, they use a lot more oxygen than any other engine in airbreathing mode.

[jcekstro]

I'm not a big fan of the raipers. As you said they suck down so much oxygen they really aren't that useful in vacuum. I prefer the normal air breathing engines with a separate fuel/rocket engine for space. Although usually this results in me needing two air breathing engines and running into the assymetrical thrust issue stated above. I still find it easier and more useful to build this way rather than just taking a crap load of oxidizer for the rapier.

[=)]

Each rapier needs only 1 ram type intake. Time was in older versions that you could just add more intakes and fly higher but now there is a pretty solid celing where it turns off even if you have enough intake air to theoretically keep them running. Rapiers fly up to around 27-28km (almost 40km up on laythe oddly, though the air is thinner and space is 50km there... maybe representing higher oxygen content?) but their power output starts to drop around 20km up so as previously said, you need most of your accelerating done around 10km up. My usual is to climb to 5-10km, get up to 500m/s+ (once past 400ms your engine power jumps) then pitch up at 15-20 degrees and let it climb whilst accelerating (otherwise you'll overheat trying mach 4 that low before climbing!) till it starves.... best case you come out around 1450m/s surface speed when the engines die. Flip over to rocket/closed cycle and burn towards your direction of travel (should be still climbing) to minimise drag in the air (pitched up even a few degrees causes a huge spike in drag still which is wasted fuel) and come out at 70km apoapsis with maybe a 300m/s burn to circularise

Oh ps for re-entry remember airbrakes... deploy the landing gear it all counts towards higher drag... and come down pitched up so the body of the plane is causing drag too.. even with airbrake spam, I get better braking by simply pulling up hard, but it all counts towards not burning up which you will do otherwise. Right click on control surfaces and hit the state button. Deploys them as flaps... caution though: can make the plane unstable depending on where the flaps are and which way they deploy

[Blind0ne]

A lot of really bad answers here. It has to do with your velocity. You can use a jet engine even with low intake upto about 33km but the higher you go the faster you will need to go to take in air as the atmosphere thins out. Try getting up to 15km and then slowly going up to 30km. Make sure you are using space plane parts and have nothing hanging off the side of your craft. Once at 30km a rapier or second stage rocket jet can be fired to accelerate you out of the atmosphere but just keep in mind the rise to 30km needs to be very slow, it should take you a little while to get there because you need to accelerate moreso than you need to assend.

[=)]

Originally posted by Blind0ne:

A lot of really bad answers here. It has to do with your velocity. You can use a jet engine even with low intake upto about 33km but the higher you go the faster you will need to go to take in air as the atmosphere thins out. Try getting up to 15km and then slowly going up to 30km. Make sure you are using space plane parts and have nothing hanging off the side of your craft. Once at 30km a rapier or second stage rocket jet can be fired to accelerate you out of the atmosphere but just keep in mind the rise to 30km needs to be very slow, it should take you a little while to get there because you need to accelerate moreso than you need to assend.

Nope not true anymore. Challenge you to try that since v 1.0. Used to be able to fly my SSTOs over 30km with air intake spam but not anymore (plus excess intakes are now wasteful drag)

[Blind0ne]

Originally posted by =):

Originally posted by Blind0ne:

A lot of really bad answers here. It has to do with your velocity. You can use a jet engine even with low intake upto about 33km but the higher you go the faster you will need to go to take in air as the atmosphere thins out. Try getting up to 15km and then slowly going up to 30km. Make sure you are using space plane parts and have nothing hanging off the side of your craft. Once at 30km a rapier or second stage rocket jet can be fired to accelerate you out of the atmosphere but just keep in mind the rise to 30km needs to be very slow, it should take you a little while to get there because you need to accelerate moreso than you need to assend.

Nope not true anymore. Challenge you to try that since v 1.0. Used to be able to fly my SSTOs over 30km with air intake spam but not anymore (plus excess intakes are now wasteful drag)

You didn't read my post I said nothing about intake spam I explained the actual physics of how spaceplanes work in reality and KSP.

[=)]

Originally posted by Blind0ne:

Originally posted by =):

Nope not true anymore. Challenge you to try that since v 1.0. Used to be able to fly my SSTOs over 30km with air intake spam but not anymore (plus excess intakes are now wasteful drag)

You didn't read my post I said nothing about intake spam I explained the actual physics of how spaceplanes work in reality and KSP.

Reality yes, KSP not anymore.
They coded the power levels to drop off as you climb higher and that drop eventually reaches zero no matter how fast you go and how much air you have coming in and I have see this in action via mechjebs info windows telling my my air intake amount vs needed... tons of air but they still shut down. You cant get much faster than 1450m/s with rapiers and at that speed its ceiling is about 28km regardless of how many intakes you are running.

https://www.dropbox.com/s/80nz5rvhki2of0t/Screenshot%202015-08-14%2017.33.17.png

Intake air: 11.47Kg/s
Needed: 4.220Kg/s
Yet the engines have already shut off See max thrust:0 though the engines are clearly on (because their fuel gauges are visible)

[jcekstro]

Originally posted by Blind0ne:

A lot of really bad answers here. It has to do with your velocity. You can use a jet engine even with low intake upto about 33km but the higher you go the faster you will need to go to take in air as the atmosphere thins out. Try getting up to 15km and then slowly going up to 30km. Make sure you are using space plane parts and have nothing hanging off the side of your craft. Once at 30km a rapier or second stage rocket jet can be fired to accelerate you out of the atmosphere but just keep in mind the rise to 30km needs to be very slow, it should take you a little while to get there because you need to accelerate moreso than you need to assend.

I would love to understand how you think any of the answers given are "really bad". You didn't explain anything that hasn't been said in a different way. Yes speed does affect how much intake air you get, but it is not the only factor. It has been said multiple times you start dropping power off exponentially once you start getting above 20k to the point where you will actually lose speed due to the amount of drag vs the amount of power supplied. Again, as stated multiple times, the ceiling is usually between 25-30k m depending on the design and engines used and around 1500 m/s.

[Naiba]

SSTO spaceplanes are still in the 'not really worth the time and effort' category of things in this game. :)

[=)]

Not so. I have a Mk3 spaceplane that lifts 26T in its cargobay. It built a space station.
Have a MK2 lifts about 15T
Have a MK1 using rapiers and a nuke that once refilled in orbit (without oxidizer) has 5000m/s deltaV or 4000 if filled with oxidizer too plus a full science suite and a flybywire nose cone so is piloted by a scientist.. Just completed a series of rally/challenges with one visiting jool, duna and eve +moons (refuels at gilly, ike, laythe and bop mines) plus done a full science farm of laythe while there. SSTOs are very usefull they just arent as easy.
Will share the files if anyone is interested.

[Ottomic]

Before 1.0 intakes took in air independently of speed, just accounting for atmospheric density, and engines didn't account for how much air there was to push against. That made it possible to accelerate to speeds in excess of 1500 m/s on a single turbojet. After 1.0, speed does matter and drag is more relevant, and jets depend on density not only for intake but also for output. So no, you won't be able to do what you could pre-1.0 in terms of ludicrous atmospheric performance.

It is still possible to get very high engine performance, but it's of course way harder. Shallower angles of attack at the right altitudes do help. At least in FAR.

[Blind0ne]

Originally posted by jcekstro:

Originally posted by Blind0ne:

A lot of really bad answers here. It has to do with your velocity. You can use a jet engine even with low intake upto about 33km but the higher you go the faster you will need to go to take in air as the atmosphere thins out. Try getting up to 15km and then slowly going up to 30km. Make sure you are using space plane parts and have nothing hanging off the side of your craft. Once at 30km a rapier or second stage rocket jet can be fired to accelerate you out of the atmosphere but just keep in mind the rise to 30km needs to be very slow, it should take you a little while to get there because you need to accelerate moreso than you need to assend.

I would love to understand how you think any of the answers given are "really bad". You didn't explain anything that hasn't been said in a different way. Yes speed does affect how much intake air you get, but it is not the only factor. It has been said multiple times you start dropping power off exponentially once you start getting above 20k to the point where you will actually lose speed due to the amount of drag vs the amount of power supplied. Again, as stated multiple times, the ceiling is usually between 25-30k m depending on the design and engines used and around 1500 m/s.

Just because things are said a lot doesn't make them true. I just tried it and I can easily get a lightweight spaceplane upto 27km. All 1.0 did was remove the ability to gain orbit with rcs and jet fuel. So yeah you can't get to 33km I was wrong but you can get to 27 km if you know what you're doing and then you can eject from the atmo with a second stage. Still the same thing. Teling people that the max height is 22km is just wrong.

[Black_Rat]

Originally posted by Blind0ne:

Originally posted by jcekstro:

I would love to understand how you think any of the answers given are "really bad". You didn't explain anything that hasn't been said in a different way. Yes speed does affect how much intake air you get, but it is not the only factor. It has been said multiple times you start dropping power off exponentially once you start getting above 20k to the point where you will actually lose speed due to the amount of drag vs the amount of power supplied. Again, as stated multiple times, the ceiling is usually between 25-30k m depending on the design and engines used and around 1500 m/s.

Just because things are said a lot doesn't make them true. I just tried it and I can easily get a lightweight spaceplane upto 27km. All 1.0 did was remove the ability to gain orbit with rcs and jet fuel. So yeah you can't get to 33km I was wrong but you can get to 27 km if you know what you're doing and then you can eject from the atmo with a second stage. Still the same thing. Teling people that the max height is 22km is just wrong.

Blind... are you actually blind? your own quote proves you wrong...

"It has been said multiple times you start dropping power off exponentially once you start getting above 20k to the point where you will actually lose speed due to the amount of drag vs the amount of power supplied. Again, as stated multiple times, the ceiling is usually between 25-30k m depending on the design and engines used and around 1500 m/s."