One engine flames out even with intake?

[Rutabaga22]

I have a dual engine plane, but when I launch it both engines start up, but one flames out immediately. But with two mk1 intakes both light! So with 2 mk zero intakes they don't light, but with 2 mk1 intakes they do! How does one engine only need the air of one mk0 intake, but the other needs a mk1 intake?
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Edited August 14, 2022 by Rutabaga22

[Caerfinon]

It's not a one to one thing. Air intakes provide a resource to the craft and each engine requires a minimum amount of that resource to function. A single Wheesley might run on one small cone but two will have more demand for air than 2 small intakes can provide.    

If you use Kerbal Engineer Redux mod you can see the values required during design time. If you don't the stock value of intakes and engine requirements can be found here: Air intake and Jet engine

[swjr-swis]

On 8/14/2022 at 2:25 AM, Rutabaga22 said:

How does one engine only need the air of one mk0 intake, but the other needs a mk1 intake?

A Wheesley needs more air than a single mk0 intake can provide. If you check the PAW on the engine that does fire. you'll notice it says 'Prop. Requirements Met: xx.x%', with xx.x being less than 100%. It is still firing because it gets *some* air, just not enough to function at 100% thrust.

Now, the reason why the other engine flames out (almost *) immediately is because the KSP resource code doesn't do equal distribution of resources. It fills the needs of the first engine in its internal list, if there's more than one engine needs it then fills the needs of the next one, and so on. Which means that instead of all engines burning at say 45% because there's not enough air for all, it burns one at 90% and the other gets absolutely nothing.

(* almost, because all intakes in KSP have a tiny internal 'tank' of air. This small internal buffer isn't subject to the limitation of 'air/sec' an intake can suck, so for a brief instant, even a single mk0 can provide full air to all engines. The hungrier the engines, the more brief that instant is.)