Sticky Launchpad?

[thereaverofdarkness]

(I am aware of a sticky launch pad bug with the old launch pad, I am reporting on the new launch pad.)

I have long felt that the launch pad was a bit sticky, as rockets I felt certain should have enough TWR to launch were unable to get off the pad. Recently I discovered a simple way to estimate the TWR, which is ~1 tonne per 10 thrust. Using this formula I have verified that the launchpad is indeed sticky, as rockets that can hover over the launch pad with 95%+ fuel remaining at 40% thrust require sometimes 70% thrust or more to take off initially. If I land these elsewhere, on any other terrain, I do not have this issue.

Has anyone else noticed this? Is there a workaround other than always designing rockets that have almost double the thrust they need?

Edited September 11, 2013 by thereaverofdarkness

[Spyritdragon]

I almost always launch from Launch Stability Enhancers, so when those are decoupled my rocket is already a few metres off the launchpad.

Also, isn't TWR just your thrust divided by your weight, i.e. tonnes/kilonewtons?

[Tiron]

I almost always launch from Launch Stability Enhancers, so when those are decoupled my rocket is already a few metres off the launchpad.

Also, isn't TWR just your thrust divided by your weight, i.e. tonnes/kilonewtons?

Yes, sort of, except it's more complicated because of the units involved(specifically, the thrust being in KiloNewtons). There's some math on the subject on the wiki but I'm not sure they did it right. They're reporting a TWR for the Kerbal-X with the math that's quite a bit higher than what Mechjeb reports.

[Hannu]

I have noticed it too. It happens sometimes if engine is on the floor of the launchpad. My solution is to use TT-18A Launch Stability Enhancers. With them I have never detected that problem.

[Spyritdragon]

Yes, sort of, except it's more complicated because of the units involved(specifically, the thrust being in KiloNewtons). There's some math on the subject on the wiki but I'm not sure they did it right. They're reporting a TWR for the Kerbal-X with the math that's quite a bit higher than what Mechjeb reports.

I looked the definition up - which made me realise i was working in kilograms, which are units of mass rather than weight. TWR is calculated as newtons of thrust divided by newtons of weight. In space, the TWR of your ship as a whole would indicate how many G's it will accelerate at. So TWR would be calculated, i think, as: (1000 x thrust in kilonewtons ) / (1000 x mass in tonnes x 9.81 N/kg). Which simplifies to thrust in kilonewtons / 9.81 N/kg x mass in tonnes.

I think thats how it works, but i'm not entirely sure.

[Alfondoo]

I ran into this the other day. Testing with various sizes I actually found that if the engine exhaust is touching the launchpad the thrust is effectively "blocked". If you make a craft small enough, you can actually start with it on the floor and thrust up, you won't move until you rock the vessel sufficiently to topple it and as soon as the exhaust finds air you'll lift off.

Launch clamps are a winner.