Strange lander behavior

[LordFerret]

I'm running KSP v0.90, with SCANsat and Lazor mods. I've built a Mun lander which has some very strange behavior... despite the engines firing, it has little to no thrust. Picture of the lander is below, taken in the VAB...

I've built several other landers, similar, none of which I've had a problem with... like this one below for example...

So I'm at a loss here. I don't understand why the first craft pictured has no thrust. It should, in fact, have far more thrust than needed. Any ideas?

Edited January 7, 2015 by LordFerret

[Slam_Jones]

Try rotating either the boosters or the landing gear by 45 degrees. I think it could be due to the thrust from the boosters striking the girders and getting cancelled out.

I've had instances where I've had one booster out of three doing this, causing the ship to spin in circles rather than boost forward. Re-arranging the position of the thrust trails (not sure what the real term is) fixed it for me.

Hope this helps!

[sal_vager]

Why are you blocking the thrust of those LV-T30's with those girder segments?

Pipped to the post by Slam_Jones, my hat is off to you sir

[worir4]

Also if you don't want to block off your pod with a booster you could just angle them outwards.

[Motokid600]

As the others have said you need to rotate the engine or girder assembly you have there 45 degrees so it's not blocking the thrust. Also.. just out of curiosity what's with the dual Sr. Docking ports at the bottom?

Edit: Also your solar panels are in danger of being blown off too.

Edited January 7, 2015 by Motokid600

[Streetwind]

There needs to be a certain area behind any engine bell that has to be completely unobstructed, or the engine will not produce any thrust.

You can solve your problem by:

- Moving the engines further up, so that there is more distance between them and the girders

- Moving the engines further outwards, so that they miss the girders entirely

- Angling the engines outwards, so that they miss the girders entirely

- Rotating the engine (or landing leg) assembly by 45 degrees so that they fire through the gaps between the girders

[LordFerret]

As the others have said you need to rotate the engine or girder assembly you have there 45 degrees so it's not blocking the thrust. Also.. just out of curiosity what's with the dual Sr. Docking ports at the bottom?

Edit: Also your solar panels are in danger of being blown off too.

It's docked to the launcher, which orbits Mun while landing and science stuff goes on. The solar panels are retracted during landing/takeoff. I've other landers where I've done the same with no problems.

As for the girder issue, I'll try rearranging things. I didn't think it would matter, especially after putting this (below) monstrosity down... but then again, the girders aren't directly beneath.

Thanks. I'll come back later and change this to "Answered" if it resolves.

[Alshain]

As for the girder issue, I'll try rearranging things. I didn't think it would matter, especially after putting this (below) monstrosity down... but then again, the girders aren't directly beneath

Being right below is exactly the problem. If any part of the animation (including exhaust) touches another part, thrust is reduced to 0. Your other lander is taller and the engines are further away resolving that problem.

[LordFerret]

Yes. Thank you, all of you. That was the problem, now solved. My rearrangement (as shown) allowed me to successfully put the lander down on Kerbin no less as a test.

[Foxster]

Just remember that your TWR and dV will fall as you angle your engines further from vertical.

[Wanderfound]

There needs to be a certain area behind any engine bell that has to be completely unobstructed, or the engine will not produce any thrust.

Has anyone tested yet how this interacts with the new offset tool? If you use that to bury an engine in a fuselage, will it work?

[tomf]

I haven't tested it myself but I think I remember reading somewhere here that thrusting out of a component was fine, it is just thrusting into a component that gives problems. Which is a sensible collision optimization for the engine most of the time.

[Kerba Fett]

Yes. Thank you, all of you. That was the problem, now solved. My rearrangement (as shown) allowed me to successfully put the lander down on Kerbin no less as a test.

One thing to keep in mind about angling your engines is that if you later add a mod that automates your vertical rate like MechJeb Translatron, it will have trouble with the angled engines. Apparently the angle screws with the throttle calculation and it spends all its time hunting for the correct setting.

For stock there's no problem and it even adds some pitch/roll stability.

[LordFerret]

One thing to keep in mind about angling your engines is that if you later add a mod that automates your vertical rate like MechJeb Translatron, it will have trouble with the angled engines. Apparently the angle screws with the throttle calculation and it spends all its time hunting for the correct setting.

For stock there's no problem and it even adds some pitch/roll stability.

So I've discovered!

I've managed to stay away from MechJeb thus far, and am planning to keep it that way. Staying close to vanilla. The only mods I'm using are Lazor for the docking camera (which should be stock!!), and SCANsat. That's it.