How to use KER to build SSTO?

[Jestersage]

Hey guys,

I am trying to build a Mk 3 SSTO capable of reachign Mun or even Minmus. However, I have issue with building up speed (the one extra Mk3 bay and ISRU/Drill may have something to do with it...(

What figure do I need to read on KER to ensure I can build up enough speed in atmosphere?

[FancyMouse]

Since you mention "build speed in atmo" I assume you're talking about spaceplane.

In SPH probably only TWR.

In flight probably drag related stuff like terminal velocity.

TBH, the most useful info for spaceplane atmospheric flight doesn't come from KER - it's more about piloting skills (trajectory matters more when TWR is low), and low-drag design (you could enable stock aero debug data to figure out what's the drag for each part, so that you can find the part with the most drag and optimize from there)

[Jestersage]

40 minutes ago, FancyMouse said:

 

Since you mention "build speed in atmo" I assume you're talking about spaceplane.

In SPH probably only TWR.

In flight probably drag related stuff like terminal velocity.

TBH, the most useful info for spaceplane atmospheric flight doesn't come from KER - it's more about piloting skills (trajectory matters more when TWR is low), and low-drag design (you could enable stock aero debug data to figure out what's the drag for each part, so that you can find the part with the most drag and optimize from there)

 

My TWR is at 0.53, with delta V of 13100k

Not sure how to enable stock aero debug.

[bewing]

14 minutes ago, Jestersage said:

Not sure how to enable stock aero debug.

Debug menu (Mod F12), Physics/Aero tab, and then click the checkboxes that you like.

[Jestersage]

Okay, enabled it. What is the action menu, and how do I use AeroGUI?

[AeroGav]

41 minutes ago, Jestersage said:

Okay, enabled it. What is the action menu, and how do I use AeroGUI?

The action menu is the right click menu,  with this box enabled you get to see how much drag (and lift) each individual part is making.

By the way, when i started using these options my game started crashing lots.   To stop this, go into the graphics options off the main menu screen and turn off "highlight fx". 

AeroGUI

The wall of data looks intimidating at first, here's how i pick what i want from it -

 

Mach - this is useful because the engine thrust / speed curves are quoted in mach not m/s.  From the wiki

We can see that the RAPIER peaks at 3.75, still gives a good amount out to mach 4.3,  then starts to gimp out really quickly.  This chart shows why you should try to get mach 4.3 air breathing, but adding more engines to go even faster would be diminishing returns,

 

Pitch  /  Total Lift / Grav Force (Weight)

This data can help make your flying more accurate.  I mainly control pitch with trim controls on my designs (ALT S , ALT W) with SAS off.    Seeing that lift is less than weight, and that the pitch number is decreasing, gives you early warning to add more nose up trim, well before you'd notice it from just looking at the plane.  Note that in really steep climbs,  lift does not have to = weight, because engine thrust is directly pushing against gravity.  Also at very high speeds,  orbital effect is taking over and supporting more and more of your weight.

 

Aoa   and  Lift / Drag ratio

Taken together, they can help improve your flying.   They help me find the best nose angle during ascent.   Raise the nose slightly, your AoA goes up.  Has your lift/drag ratio gotten better or worse? What if i lower it instead.     On its own, the Lift/Drag ratio helps you see how efficient your design is.  At supersonic speeds,  2.5 is good in a mk2 or mk3 ship.  Mk1 can get over 3.  Last night i did build a mk3 that came in with a freakish number of 3.417.   Really underpowered ship so it's the only thing that gets her to orbit.

 

Total Drag vs Total Thrust

 

This is the big kahuna.  So long as thrust is the bigger of the two numbers, you can go to space today.  If it is not, then although you may be climbing (by bleeding off airspeed)  or getting faster (by shallow dive) you are in fact loosing energy with every second.