Engine exhaust occlusion

[Guest]

So I'm trying to land this crazy tiki-house thing on the Mun via skycrane and everything works great up until I reach 20K altitude or so, at which point the crane's engines cease to do anything. Mind you, I've already used them for the last part of the braking burn after my transfer vehicle is spent, so I know they do thrust.

I've heard KSP respects parts in the way of exhaust, but why would it only do that below a certain altitude? Also, it doesn't look like the exhaust itself has any problems passing the part below it, but the engine itself might be slight over it, so may be calculation gets beefed up close in to a body?

It's maddening. I'm going to try again later with the engines rotated 45deg and not at all occluded.

[SuperWeegee4000]

Are you using an unmanned crane? It needs power. Add some solar panels if this is the case.

[Sof]

Picture please

Do they stop working all together, or do you see flames still but aren't slowing down anymore?

Perhaps your engines aren't powerful enough to counter the gravity of the Mun.

[Whackjob]

I'm guessing a power outage issue.

[Guest]

TWR is 0.78 so landing on the Mun shouldn't be a problem. I've got a reactor on the thing to ensure I don't run out of power; control isn't the issue here, the fact that the engines going full-bore doesn't do anything (yes, they do exhaust and consume fuel as normal, but they don't affect the craft at all).

I'll post a picture when I'm back from breakfast.

[Whackjob]

If you right-click an engine going, does it say, "Blocked by (part)"?

[Guest]

Didn't know I could do that, I'll have to check.

[Guest]

Here's a side-view of the crane + house, you can see the engine might have some problems clearing the landing leg but, at least on the launch pad, KSP doesn't say the engine is blocked.

Either way, I'm rotating the crane 45deg and trying again. Fifth time, I think?

[Whackjob]

I could be wrong, and I can't get into the game to double check, but it appears you've got liquid fuel for jet engines and solid rocket motors that require oxidizer.

[Sof]

That shouldn't be blocked by anything. And the fuel is the right sort too.

You must just not have enough thrust to counter gravity

[Whackjob]

You must just not have enough thrust to counter gravity

Could be. My munar lander had twelve atomic engines, but that was only because I build larger than reasonable.

[FITorion]

I could be wrong, and I can't get into the game to double check, but it appears you've got liquid fuel for jet engines and solid rocket motors that require oxidizer.

what? He's got liquid fuel and liquid fuel engines. There is no such thing as solid fuel motors that don't come with solid fuel already attached to them.

As far as engine blocking goes... To my knowledge that only happens when you have something physically attached to the engine blocking it. Engine exhaust can cause damage to things down stream of it though. If things aren't exploding when you activate your engines then you're alright in that regard.

.78 TWR... I think is your problem. If that isn't greater than 1 then you're going to fail at reducing your speed to 0.

[Brofessional]

Are you sure you have your fuel lines set up correctly? The image is too low-quality to tell.

If the engines are turning on and creating exhaust then it's probably them being blocked or just not enough thrust. If they're not turning on at all then it's an issue of fuel/power/staging/etc.

[Guest]

.78 TWR... I think is your problem. If that isn't greater than 1 then you're going to fail at reducing your speed to 0.

Nope, that is plenty for the Mun, I've landed tons of things there with +/- 0.1 TWR.

I think I found out what the problem is, though. The engines work great in the position they are at until I lower the landing legs, at which point their hitbox probably occludes the engines. That explains why the engines didn't work below a certain "random" altitude, but were working perfectly fine to finish off the braking maneuver. I might verify this later today on a purpose-built craft.

For now, I've got a rover to park and a Kerbal who needs a rest in his new home what I just landed. Rotating the engines did the trick.

E: Also, pro-tip:

Are you sure you have your fuel lines set up correctly? The image is too low-quality to tell.

Open the image in a new tab and you'll see it in its actual resolution.

[earth]

what? He's got liquid fuel and liquid fuel engines. There is no such thing as solid fuel motors that don't come with solid fuel already attached to them.

As far as engine blocking goes... To my knowledge that only happens when you have something physically attached to the engine blocking it. Engine exhaust can cause damage to things down stream of it though. If things aren't exploding when you activate your engines then you're alright in that regard.

.78 TWR... I think is your problem. If that isn't greater than 1 then you're going to fail at reducing your speed to 0.

On kerbin yes, not on the moon.

[Lucius Sejanus]

Yup, it's the extendable landing legs blocking exhaust. I've had this exact thing happen to me landing Kethane mining gear on Minmus.

[sgt_flyer]

upon seeing your design, i agree with lucius it's not that the engines exhaust are blocked under a certain altitude, it's just that you block your exhausts when you extend your landing legs prior to landing

[Lazro]

Above two are completely right, try grabbing the skycrane (and only that!) and rotating it through 45 degrees or so.

[Scotius]

Yup. Install Kerbal Engineer Redux and check TWR on Mun.