What speed should I stay under at each atmosphere "layer"?

[SlabGizor117]

I wanna know what speed will start getting reentry effects and thus high drag at 10, 20, 30, and 40 km so I can stay under there and save some fuel from drag.  Anyone know?

[Ultimate Steve]

As long as you have a pointy rocket and aren't going twenty kilometers per second, you should be fine no matter what.

Above 10-15k the atmosphere isn't really thick enough to matter. Try and stay relatively low-velocity before then.

[SlabGizor117]

4 minutes ago, Ultimate Steve said:

As long as you have a pointy rocket and aren't going twenty kilometers per second, you should be fine no matter what.

Above 10-15k the atmosphere isn't really thick enough to matter. Try and stay relatively low-velocity before then.

Well that much I know..  What speeds specifically should I stay under to keep from making reentry effects, that's pretty much my guide for keeping drag down according to the thickness of the atmosphere.

[Chaos_Klaus]

1 hour ago, SlabGizor117 said:

Well that much I know..  What speeds specifically should I stay under to keep from making reentry effects, that's pretty much my guide for keeping drag down according to the thickness of the atmosphere.

You are going about this the wrong way. Reentry effects don't matter. They are purely cosmetic. 

All in all, losses to atmospheric drag are small. You are more likely to overheat you nose cone then to loose too much delta v to drag. 

Don't worry about speed. The important thing is to point prograde while you go between 250m/s and 350m/s because that's where you'll encounter lots of transonic drag. As long as you go pointy end prograde, you're fine.

With the pre-1.0 aero model, you wanted to stay below terminal velocity. Now, terminal velocity is super high during ascent, because drag is waaaaay lower.

Edited March 12, 2017 by Chaos_Klaus

[fourfa]

Most kerbal pilots will find that planes simultaneously get their best fuel economy and highest speeds at the very highest altitude possible, with re-entry effects going as hard as possible.  Basically the visual effect is a poor indicator of actual drag (or heat for that matter).  Maybe a better question is what exactly are you looking to do, with what plane, and what's the problem you're encountering?

To answer the question directly, I don't care about drag at various altitudes, I only care about heat.  I can make any plane explode at any altitude below say 20km, given enough power and time holding course.  20+ km, it's much harder to burn up despite the fire effects.  I can safely go 1200m/s at 8km altitude, if I'm doing it very quickly on the way to orbit or a 22km cruising altitude.  

EDIT: I was misreading this as being about spaceplanes.  

Edited March 12, 2017 by fourfa

[AeroGav]

I don't do very many rocket launches as i'm mostly into space planes, but generally go supersonic at 7-10km up.  Below 5km you'd probably be getting significant drag.

When plasma starts to appear, so long as i'm above 15km i don't care about the drag.    My main concern after that point is not falling back down into the atmosphere, as it can mean i gravity turned too early.

[Grounder]

Under 10 I limit my speed to about 300 m/s.  20 to 30 I go up to 600 m/s.  After 40 I open it up to my desired apo, cut engines, lay flat, then circulize at about 15 to 20 seconds from apopsis.  Any faster and you have drag and heating effects.  If you haven't checked them already, tutorials on gravity turns are super helpful for efficient ascent velocities.

I read somewhere that heat has an exponential rate of 3 with velocity.  I.E.: 1m/s would generate 3Kelvins of heat.  Doing 1100m/s in the thin upper layers (15 to 35km)  will cause the reentry effects you refer to.

Edited April 10, 2017 by Grounder
Just to be clear

[Razorforce7]

@SlabGizor117

The re-entry flame effect is not a good indicator to decide if you run into atmospheric Delta-V drag losses.
If your rocket is really pointy with a small base radius and lots of aerodynamic cones it will lose little due to drag well within the boundaries of the re-entry flame effect.
The less aerodynamic your rocket, the steeper your ascent curve must be. Many of the least Delta-V to orbit rocket launches are those with the most shallow ascent profiles. Some of them burned with the overheating gauges nearing their maximum on ascent. So that should say something.
Then all what depends is the heat tolerance of all exposed parts. You should use the most heat tolerant parts on the outside and the parts that aren't should be concealed in cargo bays.
Ofcourse a least Delta-V rocket design is usually not to best for mission specific purposes. But it does prove my point.
This also means that ascent profiles differ based on design. So theres no specific answer to your question. It depends on your rocket.

Edited April 10, 2017 by Razorforce7

[WanderingKid]

On ‎3‎/‎11‎/‎2017 at 7:13 PM, SlabGizor117 said:

Well that much I know..  What speeds specifically should I stay under to keep from making reentry effects, that's pretty much my guide for keeping drag down according to the thickness of the atmosphere.

The old guides for this are no longer valid.  They were for the old aero model, which is why you're seeing references to it as you poke around.  Plasma effects are just pretty.  Overheat bars, however, are a concern if you're nearing the edge.

Some of my rockets Trans-sonic before 5k, if I've overwhelmed the TWR on the pad for one reason or another (I typically aim for a launch TWR of 1.6-1.8 these days).  Just do a clean gravity turn and enjoy the pretty effects.  LANDING is another story if you don't have heat shields, but seriously, you shouldn't worry about takeoff unless you're trying to skim the ocean before climbing out.  If you're actually overheating radial parts (they're exploding, not just heating up), just adjust your gravity turn a little higher.