Why does my spaceplane run out of fuel attempting a West-bound/CW Orbit?

[Laie]

3 minutes ago, sebjf said:

I tried the just fly faster approach, but I get into orbit with much less dV. I am not sure why.

In fact, I find using the jets to throw up the AP while they still can at high speed/low altitude the best ascent for all my planes.

It's because the "just keep flying" approach keeps you in the thicker atmosphere for longer. -> more drag.

Pulling up first, then catching up on speed later, is more efficient... if you can pull it off. It comes at the risk of pulling up too hard at first, then failing to catch up, and ultimately dropping back.

[AeroGav]

I'd say its all about lift drag ratio.   You want to get the best exchange rate possible,  that means maintain the nose 5 degrees above wherever the prograde marker is pointing.    When you deviate a couple of degrees off this 5 degree angle of attack your lift to drag ratio goes to hell.

 

Looks like you're able to make this work by getting into a 30 degree zoom climb after reaching 1200m/s at 10km when the Whiplash is still making a lot of power - by the time your upward momentum has run out,  you've gained enough horizontal orbital velocity.

 

My designs are intended for a level flight speedrun at 17km,   then start the nukes, and once the jet power is dying away about 1350 or so,  ease the nose up so it's 5 degrees above prograde and keep it there.   If your lift drag ratio is good enough it should work.    To do that in the above craft i'd want 3 times the wing area and switch to an inline mk1 cockpit.    Pointy cockpits get much hotter,   and with smaller wings relative to your weight,  your craft goes lower in the atmosphere for any given speed when means more friction heating.