1.0.4 Kerbal Engineer's 'Atmospheric Efficiency' - is it still relevant?

[tutike2000]

Hi all,

I usually look at the Atmo Efficiency readout in KER when launching, and I've noticed that since v1.0.4, the readout doesn't make any sense.

I had a rocket with 3x twin boar doing 450m/s at around 5-10km altitude, and even at full thrust (TWR around 2.0) I could not increase my speed. All this time, the Atmo Efficiency readout was 50-55%.

This sounds... wrong, right? My terminal velocity should have been a lot lower than 900m/s at that altitude, regardless of how aerodynamic my ship was.

Edited June 25, 2015 by tutike2000

[Streetwind]

Are you sure? The Mount Everest is less than 10km high, and the air there is already so thin that humans generally need a breathing apparatus to survive (unless you're an exceptional athlete with a lot of time to acclimatize yourself). And because Kerbin's atmosphere is a lot less high than Earth's, but has the same suface pressure, that means the air on Kerbin at 10km is even less dense than the air on Earth at 10km. That'll put your terminal velocity way up there.

A good test for whether or not atmospheric efficiency is calculated correctly is to launch a simple pod and parachute on a small suborbital hop. As you come down, the pod will eventually slow down to terminal velocity; this counts especially if the parachute is out. If atmospheric efficiency then approaches 100%, that means the calculation is performed correctly.

I use the number as a drag indicator nowadays, by the way, for questions like "should I jettison my fairing now?". It even changes if I turn the broad side of my craft into the airstream, it's really quite handy.

[Sharpy]

Relevant yes, accurate no. Since the coefficients changed quite a bit you might need for KER to update to follow them.

[CalculusWarrior]

You generally start losing a lot of energy to drag once you see the atmospheric effects forming around your vehicle. If you're seeing these, try to either back off the throttle a bit (if you're in the first part of your ascent) or try to add more vertical speed (if you've already pitched over).

[rofltehcat]

I have atmospheric efficiency displayed in my spaceplane customt KER category but I never paid much attention to it... it is mostly for fuel efficiency if I want to avoid crashing into/through the sound barrier with a rocket/non-space plane, right? Other than that my KER tells me that it doesn't support the current patch version, so I wouldn't trust it all too much when it comes to aero-related stats.

[tutike2000]

You generally start losing a lot of energy to drag once you see the atmospheric effects forming around your vehicle. If you're seeing these, try to either back off the throttle a bit (if you're in the first part of your ascent) or try to add more vertical speed (if you've already pitched over).

Yes, I know. It's just that usually atmo effects happened when KER atmo efficiency showed 90% or more, not 50%

Relevant yes, accurate no. Since the coefficients changed quite a bit you might need for KER to update to follow them.

Hmm, that might explain it. KER might need an update.

[monstah]

Yes, I know. It's just that usually atmo effects happened when KER atmo efficiency showed 90% or more, not 50%

Seems to me the atmo effects are related to breaking the speed barrier, while atmo efficiency is related to current vs. terminal velocity.

Those things might be related, but are not interchangeable; with changed parameters in 1.0.4 it's possible terminal velocity has gone up, while mach 1 stays the same, so that when you see the effects there's still a lot more to get to terminal velocity, as opposed to before.

[ajburges]

Atmo efficiency is relevant, just no longer a key attribute. For (near) vertical accent, your optimal speed will remain near 100% efficiency.

I find terminal velocity to be a more useful read out. I avoid supersonic speed until terminal velocity is over 500 m/s. At that point, I just let the engines rip.