What percent throttle do you use on take off?

[skendzie]

I saw an old video on youtube where a player says to use 66% until about 10,000m and then to let it out to 100% on a 90 degree angle because of atmospheric resistance. Is this true? Does engine efficiency work like this in KSP?

Thanks!

[ThatBum]

Varies widely depending on the rocket and ascent profile. If you use SRBs, those can't be throttled, so you might want to throttle down while those are burning, to save some liquid fuel. Also avoid overheating, of course. You generally want to limit yourself to terminal velocity, however much throttle that takes. If you go faster than that you're just wasting energy. This is a concept called max Q, where the force of the rockets pushing you up is equal to the force of drag pushing you down. Any more and the drag force wins out.

There's probably terminal velocity numbers for Kerbin somewhere.

[musicpenguin]

I do 75-100 depending on weight.

[sal_vager]

It's not engine efficiency, it's atmospheric drag, basically you don't want to push so hard that you end up just wasting fuel.

Depending on your design you may find you get more out of your rocket if you throttle back after hitting 100m/s (rockets are inefficient at low speeds)

Best way to see this is to fly straight up at full throttle in a small rocket, then try again and throttle back, you will get higher before running out of fuel if you keep your acceleration under control

[RoboRay]

All of it, until you approach terminal velocity. Then, adjust to stay just below terminal velocity to minimize both drag and gravity losses. Once you're above 10km, terminal velocity increases so quickly that throttling back is no longer required.

[allmappedout]

Sal, proving that science works; theorise, test, analyse, improve!

[Deadpangod3]

My way (Jeb GREATLY approves of this method) is put it to full throttle, hit that staging button, and let em fly.

But I do find that when their about to explode if you cut the thrust (via x button) the heat will go away in just a few seconds, then you can continue at full thrust once more

[ThatBum]

Yeah, if your thrust-to-weight ratio is good, you can full throttle and speed up quickly, then slow down when you're hitting the atmospheric limit.

[Swifty]

I've always just gone for 100%

[Noticeably FAT]

When I let MJ fly it seems to be around 75% unless I'm lifting something heavy. When I fly it's at 95% most generally, otherwise my mainsails like to get all 'splody. 'Balls out' seems to be the Kerbal way of doing it.

[SmallChange]

One of the biggest gains in performance I've had came from learning to lay off the throttle in the lower atmosphere. You'd be amazed how much fuel gets wasted from atmospheric drag, which I think increases exponentially from your speed. I'm sure my numbers are far from optimal, but the rule of thumb I go with is 100 m/s plus 10 for every km of altitude, so below 1 km keep it around 100 m/s, 150 at 5km, and 200 at 10km. After 10-12 KM I usually run pretty close to full throttle.

I highly suggest following Sal's experiment. You'll be shocked at how much fuel you are wasting, especially on your higher TWR craft.

[Boris_T_Roach]

Since I take off on a 5 mainsail lifter that has 8 SRBs strapped to it, the throttle setting always goes to 100% on liftoff , but the srbs/launch clamps fire only when I've confirmed all 5 engines are running (I've spun outa of control too many times )

Then its 100% until the ship hits about 90-100 m/sec and start throttling back to hold that speed until the srbs burn out, then throttle up to hold 120 m/sec until 10km when the gravity turn starts and its full throttle from there upto a 2G limit on the acceleration and throttle back to maintain that, until the outer 4 mainsails are dumped, then go for orbit at 85% on the last mainsail

The SRB burn out heights/ throttle settings/ heights always depend on what payload is going into orbit,plus the fact I fly the thing like I'm drunk

[spikeyhat09]

i go full throttle (or as much as possible without overheating or causing structural damage) until 150 m/s, then i follow the terminal velocity curve up to 9 kilometers, then i do my gravity turn from 9 kilometers through 11 kilometers (45 degrees at first, and then slowly tilt further, going completely horizontal by 65 kilometers), then full throttle again

Edited April 22, 2013 by spikeyhat09

[Syre]

My average rocket has 4 orange tanks with a half gray tank and a mainsail with the same thing in the middle, then a 1m tall tank with a lv35 (or w/e) and the half 1m tank with a 909 and a 1 man pod for the lander, and I use ~25%

[SkyRender]

Throttle is entirely dependent on TWR. A rocket with 2 TWR is going to need a heck of a lot more throttle than one with 4 TWR to get up to speed. That said, yeah, not the sort who thrusts at a constant rate the entire ascent. That's almost always horribly inefficient.

[rflrob]

I tend to find that when I go above about 80% on my standard heavy-lift rocket (6+1 mainsails, plus 8 more large SRBs), my parts tend to squish into each other, causing a very expensive fireworks show.

[WhiteWeasel]

SRB's so I don't waste any of the good fuel.

[RFK128]

100%, MAXIMUM BURN. What's the point of a pile of explosive material if you don't light it up?

[SuperFastJellyfish]

Kerbin's terminal velocity for specific altitudes are approximately:

100 m/s - sea level

110 m/s - 1000m

120 m/s - 2000m

130 m/s - 3000m

160 m/s - 5000m

215 m/s - 8000m

260 m/s - 10000m

Beyond that and it shoots up pretty quickly.

[tommygunyeah]

I go full throttle and ease off as I rocket 100-150m/s

[EndlessWaves]

I saw an old video on youtube where a player says to use 66% until about 10,000m and then to let it out to 100% on a 90 degree angle because of atmospheric resistance. Is this true? Does engine efficiency work like this in KSP?

No, it works the opposite way.

Two engines at 50% throttle use the same fuel and produce the same thrust as one engine at 100% but they're twice the weight. More weight means you go less distance and less speed on the same amount of fuel.

There is a small bonus by having more thrust once you clear ~30km but in practice if you're throttling down then chances are you'll use less fuel overall by removing an engine or three.

[maro]

The fuel you save between 1000m and 10000m you can use much better later in flight. You get much more speed out if you limit your acceleration early in flight. From 0 to 1000m you can give full thrust, and then you take out as much as you can so that you not decrase speed (m(s).

up to 100m/s at ~1000m is good and 200m/s at ~10000m - when you pass 10000m you can increase thrust again.

Look at your engines - they should not go hot.

Look at your G-meter - should be within green scale - robust constructions can take more stress.

Construct a small test rocket.

Activate ASAS set full power and launch straight up until burnout - you will get a result for maximum speed and height.

And then you launch teh same again and try to optimize fuel efficency - you will see a much better result

[Pixel of Life]

Full power until 100 m/s, then throttle down to maintain 200 m/s until booster separation which usually happens at 10-15km, during the gravity turn. After that it's pedal to the metal again.

[brooksy125]

Full throttle all the way to orbit, screw efficiency!

[SargeRho]

Depends on the rocket. Mainsail on it? 85%. No mainsail? 100%.