Drag nerfed too much?

[Fwiffo]

Quick question – in recent versions, did atmospheric drag basically become negligible for small, aerodynamic rockets?

I’m new to the game and have been exploring optimal launch profiles. All the material on the web says you shouldn’t exceed ~200m/s in the lower atmosphere (e.g. until ~10km). I spent a couple days trying to test this, using very basic rockets and “straight up†trajectories to compare. Surprisingly, I’m getting consistently better results when I burn more fuel earlier, even if it results in high speeds and strongly visible atmospheric effects. It's leading me to the conclusion that as long as your rocket is aerodynamic, burning off mass faster trumps any negative drag effects (and the importance of controlling ascent velocities is overrated).

e.g. For this rocket:

Mk16 Parachute

Mk1 Command Module

SC-9001 Science Jr.

RT-10 “Hammer†Solid Fuel Booster

3x Delta-Delux Winglet

Tweaked to 100% thrust: Reaches 200m/s at ~600m, runs out of fuel at 10km (going 1000m/s), reaches altitude 70.3km

Tweaked to 49% thrust: Reaches 200m/s at ~1.6km, runs out of fuel at 17.1km (going 897m/s), reaches altitude 61.7km

This seemed to be the case for my liquid fueled rockets as well. I found myself actually sabotaging my rocket's sleekness to TRY and replicate some drag effects, and they didn’t really seem to kick in until I had fairly unaerodynamic constructions (e.g. 3 science juniors radially mounted with flat surfaces up).

Is it just me? Am I doing something wrong? Or is this something that will become a bigger issue later in the game when I have more complex rockets with more leading surface area?

I think this guy is seeing similar results:

https://www.reddit.com/r/KerbalSpaceProgram/comments/34ap9m/optimal_ascent_profile_for_v10/

I know Squad reduced drag effects in v1.0.3. I’m wondering if they may have nerfed it a little too much...

Edited July 18, 2015 by Fwiffo
Answered

[Streetwind]

All the material on the web that tells you not to exceed 200 m/s while low in the atmosphere is for 0.90 and older, and no longer applies.

Much like in real life, rockets now do not generally hit terminal velocity going up, even when they accelerate really hard. The Atlas V that launched New Horizons, for instance, held between 4 and 5 g for the entire first stage burn despite its giant payload fairing encapsulating the whole two upper stages, and I suspect the only reason it even throttled to keep it in that range was because the payload (or the upper stages, or both) wasn't rated for more. The Saturn V, similarly, only switched off its center engine midway through the first stage burn to make the acceleration less crushing for the astronauts on board, not because of aerodynamics. For something shaped like a needle, atmospheric drag is pretty much irrelevant in most scenarios. Case in point: there are military anti-missile rockets that accelerate at 100g off the 'pad' (launch tube). They glow white-hot within a few seconds of launch but still keep going, 'cause they need to get to that enemy ICBM before that reaches its target, at all costs!

In KSP, even half the acceleration of an Atlas V class rocket feels insane because you get reentry effects going up, but that's only because KSP generates reentry effects at artificially low speeds. A real life capsule reentering at 2 km/ wouldn't even produce a visible glow, much less a giant plasma trail. So now you have a halfway realistic atmosphere in KSP and can accelerate really hard, but you also have utterly unrealistic reentry effect behavior, because the planets are all so tiny and orbital speeds are all so low. It's not optimal, but it's better than no reentry effects at all, right?

Edited July 18, 2015 by Streetwind

[Scarecrow88]

A lot of the info on the web for KSP is out of date as the aerodynamics model changed significantly a couple of patches ago. In 0.90 and previously, the atmosphere was affectionately known as the souposphere as it was so thick, and it was beneficial to go straight up for a large portion of the initial launch to escape the worst affects. This is no longer the case in the latest release.

[NathanKell]

It's definitely true that there's a bit too little drag high up...but if high up got draggier, Kerbin reentries would be even easier, so it's a tradeoff.

[Sharpy]

...also, with the new thermal system, you really don't want to exceed some 1500m/s in the lower atmosphere... while before 1.03 you'd be unable because of the drag, past 1.03 you'll just burn up.

[Fwiffo]

The more I experiment, the more I feel Squad backed off too much on drag. Here's an arbitrary example of a ship I'm designing as a fuel tanker (i.e. get a full orange fuel tank up to orbit). It's not particularly aerodynamic (although it's not a total flying brick, either). The best straight-up altitude I can get is ~1.8 million km, by thrusting 100% until I run out of fuel. If anyone can pilot this thing in a more efficient manner, and gain higher altitude by working the throttle more proactively, please let me know!

https://dl.dropboxusercontent.com/u/1056718/Kerbal/Tanker1.craft

I'd be really keen on hearing others' opinions on this:

Since 1.0.4, have you created any rocket designs where a slower ascent yields better fuel efficiency?

This has not been the case for any of the rockets I've designed so far over the natural course of career-mode gameplay. The only reason I've ever had to go slower than Mach, was to maintain stability benefits from my control surfaces (i.e. prevent tipping over). And that's been a dubious one in any case, since careful piloting (i.e. slower gravity turn) usually does the trick, allowing me to maintain full throttle and making better use of my fuel. So far, the only time drag has had any impact on my rocket piloting is with contrived designs that are purposely un-aerodynamic.

I did find some drag sliders in the Debug window. May play with those a bit.

[mhoram]

Since 1.0.4, have you created any rocket designs where a slower ascent yields better fuel efficiency?

Yes: http://forum.kerbalspaceprogram.com/threads/128509-Goddard-Problem-Maximal-launch-altitude-Challenge

It was not about reaching orbit, but about the highest altitude that can be reached, which is regarding drag equally important.

Especially have a look at the desctiption in Nao's post.

[Nich]

The problem with straight up tests is drag has very little effect as you get into supper thin atm very very quickly. If you want a real test of drag you have to do 70x70 orbits with gravity turns. My new rules of thumb are <1000 m/s below 10km <2000 m/s below 20k which is pretty easy to do with a TWR < 3.

YAAAA!!! oberth effect