Timing Suicide Burns with Maneuver Nodes

[KerbalSpaceJockey]

Many people point to this post from Red Iron Crown as a good way to time suicide burns -

I'm not understanding something though. If I'm in orbit and set a maneuver node over the point of impact, when I drag retrograde the Ap doesn't hit the surface. Wherever the Ap started in the orbit, it winds up directly over the point of impact, but will never touch the surface. My "orbit" would drop straight down onto the surface when my retrograde burn exactly matches my orbital velocity. But that doesn't seem like a safe landing since it's not leaving anything to cancel the speed gained by falling. What am I missing?

[bewing]

He's talking about one step further than you are already -- after you have burned some to get out of orbit: when you are already suborbital, with your impact point at your selected landing site.

Then when you are creating the maneuver node, you have two Aps. One is on your blue line, and one is on the orange "post maneuver" line. The Ap he means is the orange one -- the "node" Ap.

 

[KerbalSpaceJockey]

Oh! That makes sense. Thanks!

[DrLicor]

Indeed, that's a method I used to have before I used mechjeb. Not that I'm autolanding my crafts, but I let mechjeb do the calculations. In a custom made screen I can readout the time of impact and how many seconds before or after the suicide burn is completed. When the suicide burn gives me 30 seconds, it means I'll hover over the certain planet about 30 seconds before impact, when it says -5 seconds, it means my suicide burn is completed after touchdown. So it will be a rough landing or a crash. 

This method is very useful when you have a very limited delta-v or limited ignitions.
If you're against mechjeb 'because you think it's to cheaty', you can make it as cheaty as you want. Personally I never use the autolander or other autopilots. I only use the calculations mechjeb makes for me