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How to tell when your aeroplane is out of IntakeAir?


Zuni
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* Click the resources tab in top right of screen; along with fuel and oxidiser, there's an entry for intake air. A bit of experimenting will let you work out how close you can run it to the edge.

* Install a flight info mod like Kerbal Flight Data or Mechjeb. These can give you "air available" and "air required" figures.

* Build with an odd number of engines, and when you're getting into flameout territory shut down everything except for the central engine. No more asymmetric flameouts.

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Rapiers, I find, tend to be more forgiving when they run short of air. Instead of flaming out completely, the Rapier reduces thrust.

You can try watching the directional gauges in the lower left - when SAS starts skewing, one of your Rapiers is running short of air (forcing SAS to turn against the lost thrust) and you should throttle down.

Or you can Alt-right-click your Rapiers, and watch the displayed thrust for variance.

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You can run engines on insufficient air. There's some warning signs when you start to overdraw the account, like the sound of the engine changing slightly, but you can continue past this point for a good long while. By the time an engine flames out, it has merely 10% of the air it actually wants to have. There's no sign to warn you shortly before things become serious.

You'll need mechjeb or kerbal engineer if you want a clear indication of where you are in your air supply. Some experience will go a long way, though.

You may also want to read the following threads:

http://forum.kerbalspaceprogram.com/threads/84217-Explaining-burnout-asymetry

http://forum.kerbalspaceprogram.com/threads/64362-Fuel-Flow-Rules

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In general, I find that you can run your engines full blast until you've got roughly 0.05-0.07 units of intake air per engine safely. You can go past that mark, but you do risk a flame out/flat spin, and in general the higher your throttle setting is at that point, the less time you'll have to respond before a flame out occurs. Here's what you can do - pull down to about 2/3 throttle and keep going. If your plane starts yawing to one side without you giving any input, kick it down another notch or two and put yourself back on your original heading. Rinse and repeat. I've been able to use Turbojets with as little as 0.01 units of air per engine before keeping this method going. Key thing is to keep on accelerating; if you throttle back and you start losing speed, it's time to light your rockets.

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Other tricks: if you want a better chance of getting away with high-speed asymmetric thrust, a pair of Vernors on either side of the nose do wonders. Bind them to an action group and keep them toggled off until you need them, though, or you'll waste a fair bit of fuel.

Also good for lower speed aerobatic hijinks.

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Assuming you already understand and use the trick with interleaving intakes and engines to let them reduce thrust gradually before they start flaming out, there are a few more tricks regarding number of engines:

1 engine - no asymmetric flameout is possible (naturally)

2 engines - with interleaving it still generates asymmetric flameout when running out of intake air, although the effect is way weaker

3 engines - avoid. Or you have to switch them off manually and run on single engine when you start running out of air

4 engines - placed either in circle (placed clockwise or counterclockwise) or in line (outer left - inner left - outer right - inner right) are great as when flameout occurs, two outer engines will flameout at once. Then you can reduce thrust and continue flying. Final flameout when the air does not suffice even for every second engine is way weaker.

6 engines - placed in circle (clockwise or counterclockwise) are just perfect. First flameout reduces number of running engines to 3 placed symmetrically, second flameout will switch off two of them and start up the one in between them, still producing symmetrical thrust. Note that there is no reasonable in-line setup for six engines.

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You can run just fine on a 3 engine design. But only if you place the outer (left and right) engines first and the center last.

The last engine placed will be the first to flame-out. When your center engine is flaming out you'll either have to throttle down or switch modes.

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When you have a ship with multiple engines you can typically fly it fine until around 0.07 IntakeAir. At that stage, slowly start throttling down so at 0.04 you're at half throttle. At this stage make sure your vertical speed is as close to 0 as possible so you get the maximum jet performance at minimum air resistance. Pay attention to your gauges at the lower left; whenever you see the gauges go off center, one of your engines is starting to flame out so throttle back.

As an alternative, you could design your craft with a center of mass close to the front and have your thrust going through the CoM by slight rotation of your jet engines. Using this design, your craft won't spin out when one of the engines flame out and you can throttle down and recover as showcased in the StaboJet thread.

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Do not rely on any value in the IntakeAir resource gauge - it is only relevant to this particular plane. What you see in the Resources gauge is the remainder after ship scan, i.e. all intakes were processed and their production added to the pile, and all engines were processed and their consumption was removed from the pile. How exactly is this production, consumption, and remainder handled depends on how you built your ship.

Most of my planes produce thrust safely long after the resource gauge shows I have no IntakeAir at all.

Just yesterday someone asked about it so I re-ran one of my experiments today with the resources box open. There was 0.64 intake air reported, yet over half of engines were flamed out. While the other experiment, using exactly the same parts, just placed in different order has the same number of engines running and the gauge shows no intake air.

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Edited by Kasuha
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The gauge must be reporting how much is in the pool when it reaches the end of the .craft description before looping around to the start again. So in the first example above, over half the IntakeAir generated by the intakes is in the pool before starting at the top left again, while in the second example all the IntakeAir has been used before it gets to the end.

I'm assuming that Kasuha placed the engines left-to-right, top-to-bottom, with the intakes before the last five engines in the first example, and before all the engines in the second example. I think if the second example changed to have the intakes placed after all the engines, the flameout pattern would be the same but the gauge would show the full production of the intakes. The gauge is next to useless IMO.

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In other words if you want actual usable data in the resource tab you'll need to place all intakes first then all jet engines in the reverse order you want them to flame out in.

That would give more useful info in the gauge but the ship itself would perform less well than if the intakes are interleaved with the engines. Basically to get best performance you have to sacrifice the usefulness of the gauge.

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That would give more useful info in the gauge but the ship itself would perform less well than if the intakes are interleaved with the engines. Basically to get best performance you have to sacrifice the usefulness of the gauge.

I'm pretty sure you can interleave and let the engine that you want to flame out first at the border of the looparound

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