Atmo Delta V

[Steampunked]

 

Hello again all.

So a question about KER / MJ and Delta V readouts.

When building ships with KER and MJ to see projected dV but I have a hard time taking drag and gravity in to account when estimating my lifter's dV.

Any advice or rules of thumb?

 

Many thanks!

[Temstar]

A decent gravity turn and first stage with decent combined Atm Isp should be able to put the payload into orbit with 3500m/s of vac delta-V.

[OhioBob]

In most cases, a launch from the surface of Kerbin will add about 1000-1500 m/s in gravity and drag losses.  Since orbital velocity is about 2300 m/s, this equates to about 3300-3800 m/s.  How much exactly depends on many factors.  For instance, early in a career game I usually budget more Δv because I haven't research fairings yet and I'm launching draggy payloads.  Later on, as I advance along the technology tree, my launchers become more aerodynamic and the required Δv goes down.  Also, the ascent profile that you fly makes a big difference.  Flying an efficient ascent just takes practice.

One piece of advice, don't get obsessed with trying to minimize the amount of Δv it takes to get to orbit.  If you are playing in career mode, then cost is a more important consideration.  Experience has shown that cost efficiency does not correlate to Δv efficiency.  If it's costing you 3500 m/s to get to orbit and somebody else tells you that they are using only 3300 m/s, don't worry about it.  It's entirely possible that your 3500 m/s launch system is more cost efficient than the other guy's 3300 m/s launch system. 

Also note that the Δv given above are the "vacuum" values.  That's what most people use when discussing Δv.  The "atmosphere" values become important when discussing liftoff thrust-to-weight ratio.

Edited December 10, 2015 by OhioBob

[Venusgate]

I aim for 4000m/s in KER and build fugly rockets. 

I also keep my launcher stage(s) high(er) on the asl isp. so, obviously, im not taking off with terriers.