My burns take a lot longer than what the maneuver node calculates.

[Chik Sneadlov]

I pull the maneuver node things and set up an orbit. At the bottom of the screen it tells me how long the burn will last but I always end up burning for a lot longer. When I do the burn I roll the navball to the blue pip that looks like three T's with the bottom of each T pointing at the center of the pip. Is that right way to do it?

Edited March 31, 2014 by Chik Sneadlov

[Taki117]

It is, but the calculation uses your last thrust, so if you had a really powerful engine when you set up the node, and then dropped it for a more efficient engine, the times are going to be different. The best way to do things is get lined up and then about a minute before the burn perform a very short "Test Burn" to reset the timer.

Also if your more efficient engine is significantly less powerful you might not have a very high TWR, in which case your burns will be very long. Another thing to consider is to make sure that there is not a decoupler blocking the thrust of your engine. This ensures that your engine is actually providing thrust (And the effects are not just showing up) and that you are actually performing the burn.

Edited March 27, 2014 by Taki117

[HoustonDave]

When doing your burn, make sure you time it so half is before and half after the node.

So if the calculated burn is 50 seconds, start it 25 seconds before the node and finish 25 seconds after the node.

[Drew Kerman]

use this. Works like a charm - there is a reply a few posts down with a link to a Google or Wolfram equation you can just plug new numbers into. Just don't forget to re-calculate each burn with the new weight You can use VOID to get vessel weight, right-clicking on an engine will give you the ISP but you should note the max thrust in the VAB/SPH prior to the flight

[SRV Ron]

Generally, the burn time is based upon 100% thrust of the last burn measured. If you end up staging during the burn, the time will change. Practice will determine how best to set up when to start a burn when you know you will have to stage. Watch the orbit as it changes and cut power with the X key when you have achieved the desired result. You can also reduce thrust when nearing the capture or desired path for more precise cutoff.

The mod tools do help but in the long run, it will be your experience that will help in planning when to start the burn with the ship you are flying after setting up the maneuver.

[SofusRud]

Also remember that the maneuver node assumes that you make your delta-v change instantaneously, and since you can't do that, the longer your burn needs to be the more inefficient it will be and that adds an inaccuracy