Pulled back to Earth in the DGIV??

[ijuin]

When using the Mark IV/V engines and turbopump, you have a thrust-to-weight ratio greater than 1.0 even with full fuel and payload, so you should not need the hover engines at all once you have lifted off and are flying at the correct heading for your desired orbit.

Second, get out of the troposphere as soon as you can! When the air is too dense, you have to waste energy fighting your way through it. I recommend keeping your nose at least 30 degrees above the horizon until dynamic pressure drops below 10 kPa.

 

[destinos]

During the ascent, keep an eye on the AoA displayed by SurfaceMFD. It you need an AoA over 7 degrees to maintain altitude, you are too high.

Is this true at all alts? even the 50-70k range?

Oh and also I haven't been using any hover engines. I've been doing runway takeoffs from Canaveral, are hovers still part of the equation? I AM however using RCS thrusters above 45 or 50k. is that what you mean?

 

[ijuin]

No, RCS usage once the atmosphere becomes thin enough is normal. Anyway, if dynamic pressure is below 100 Pascals, then you should not be expecting any significant aerodynamic lift.

 

[Tommy]

Is this true at all alts? even the 50-70k range?

Especially in the 50 - 70k range. At that point it indicates that you aren't going fast enough to generate enough centrifugal force to balance out the loss of lift. It best not to go much over 5 degrees AoA above 60k, even if it means temporarily sinking down a bit. As your velocity increases you'll start to rise again. If you're under 7km/s velocity at 60k, you may want to level out. The air gets to be a bit to thin above 65k, so you need to have sufficient speed here. The target is a bit over 7.55k (when your ApA is high enough) by 70k alt. If you don't have it by 70k you'll have to pitch up and use some dV to maintain VS, so the 60k to 65k range is crucial to this ascent profile.

It's possible to have the required velocity at a lower altitude (not much lower in a DGIV or XR, due to heating) but that's also inefficient - you'll lose more to drag and probably need to "boost" your ApA again later.

Also, the Vertical Speeds I listed in previous posts are Maximums, and it's best to try to average 30 - 40% less.

As for the runway Takeoff, it should use less fuel. I just fired up the stock scenario, figuring the Hover Takeoff was a "worst case". For a runway takeoff, remember to keep the speed down under 250m/s until you are on heading, and get on heading as quick as possible. Generally speaking, above 10k, fly lower than you think you should!

 

[destinos]

Thanks again Tommy. I'll give it another shot today and let you know how it goes.

 

[Jer95]

I recommend keeping your nose at least 30 degrees above the horizon until dynamic pressure drops below 10 kPa.

About 1.4 Psi, which is about 40-55 mile alt

 

[Tommy]

About 1.4 Psi, which is about 40-55 mile alt

At what velocity? At 7.54km/s at 70k alt dynamic pressure will be 2.817kPa.

This profile will have a peak Dynamic pressure of about 15kPa at around 25k alt (870 m/s) falling below 1kPa by 35k alt (1.5km/s).

Also, keep in mind that decelleration from aerodynamic drag will never exceed about 2 m/s/s, while gravity is around 9 m/s/s. The Oberth effect also comes into play, it's more efficient to gain velocity when closer to the gravity source.