Has anyone done the math on how much lift you need per ton?

[Crowbot]

After crashing into a planet I started to wonder if anyone's done the math on how much lift we need per ton.

My "Lander" weighed a bit over 3 tons btw.

[Thalyn]

It's fairly basic physics, provided it's been implemented properly. F = M x A, or Force (in N) = Mass (in kg) x Acceleration (in m/s/s).

If we assume G (force due to gravity) to be 10m/s/s (it's actually a hair over 9.8, but 10 is easier for the math) than you basically need 10N per kilogram of weight simply to overcome gravity. If your ship weighs exactly 3 tonnes, that means 30,000N, or 30kN, just to hover.

Any additional force you apply will create lift. That means either accelerating upwards or slowing downwards, depending upon which direction you're moving (assuming you're referring to specifically up or down, with bottom thrusters only). If you give it 60kN, for example, than it will accelerate or slow down at a rate of 10m/s/s - or going from 0-100m/s or 100-0m/s in 10 seconds. 90kN will double the rate of ac-/de-celeration, 120kN will triple, and so forth.

Of course, that all assumes a constant 1G being applied externally. If you're at lower than 1G than you can proportionally lower that initial 30kN, until 0N is required to work against gravity at 0G (because there isn't any). Different directions will also have different effects from gravity.

When working with those numbers, remember that Atmospheric thrusters aren't 100% efficient, even at ground level, and Ion thrusters don't reach 100% efficiency until you're in thin atmosphere.

NB Either their sim isn't entirely accurate or the thrust values for the thrusters are wrong, as you sometimes need as little as half that much thrust to get the same effect.

[SickTag]

It's called Delta V, no?

[SpetS]

ship mass * 10
a little bit more if you have cargo

Edit, you can check here to see trhusters max N force
http://www.spaceengineerswiki.com/Thruster

[Astasia]

The wiki is out of date and the game doesn't use "real physics." The thrust numbers in game don't even appear to be accurate in relation to each other, IE atmo thrusters aren't that much better than ion thrusters in atmosphere than the numbers would lead you to believe, and small atmo thrusters on a large ships don't seem to be even remotely close to the power of large atmo thusters on small ships even though the game says they are only a few points apart. You also have to consider whatever crazy mutilation of physics is involved with making thrusters perform similarly accross the different storage size settings, I don't think it's a simple x10 thrust on x10 storage size.

[ronidude]

evry 40 or 30 tons you need a lardge thruster

[Jota]

I once created a formula to determine the combination of small and large thrusters you need to lift a ship out of a gravity field based on mass and cargo, but as some have stated, the game currently does not follow newtonian physics as it should, if it did, the formula the following:

n[(f/b) + t] + N[(F/b) - T] = M + C

Where,
n : number of small thursters
N : number of large thursters
f : thurst of a small thurster (N)
F : thurst of a large thurster (N)
t : mass of a small thurster (Kg)
T : mass of a large thurster (Kg)
M : mass of the ship without bottom thursters (Kg)
C : mass of the amount of cargo you want to lift (Kg)

b is a constant representing the acceleration you want to archive, it can be calculated as

b = a + 9,8g

g : the gravity of the planet you are in, as displayed in the HUD (e.g. Earth gravity = 1G) (G)
a : the acceleration you want your ship to escape the planet (a = 0 means the ship has only the minimum number of thursters to counter the gravity) (m/s²)

[Ancient]

To find the max thrust of a thruster, place one and use the override to max it out, if you then control + click on the override slider, it will let you copy the max thrust in N, which you can then paste here to calculate number of that thruster needed by your ship's mass and intended operational gravity (do not go by the wiki):

http://www.ratuska.fi/se/thruster.php

It is out of date, i.e. it still primarily worries about platinum even though non-moons have none, but the calculations really do not change and it does account for cargo mass accurately enough to use as a rough guideline. It's tricky to use to calculate more than one type of thruster, but it will give you a pretty good idea what each type/grid/size is capable of.

[I.C.E.]

To determine how much thrust you will need - there is already good answers. 1N is the force needed to accelerate 1kg with 1m/s.

To determine how much thrust you got from 1 engine:
Get yourself into enviroment, where your thrust is intendent to apply.
Put 1 desired thruster on your ship.
Disable it.
Override it to max.
Look at the readings.

You will see that Ion thrusters in the atmosphere will give you around 0N force, 0 divided by 10 is 0, so... you can be sure that it will lift 0kg in the chosen enviroment :)

Same is applied to Atmos thrusters on a chosen height. Try to check overrided readings at the ground and then at 3km above. You will have different numbers.


AFAIK Hydrogen thrusters will always provide you their maximum, disregard the enviroment.

[Puppet #7]

Originally posted by SickTag:

It's called Delta V, no?

No, he's asking about TWR, thrust to weight ratio, not total mileage per tank :)

[Astasia]

Originally posted by I.C.E.:

You will see that Ion thrusters in the atmosphere will give you around 0N force, 0 divided by 10 is 0, so... you can be sure that it will lift 0kg in the chosen enviroment :)

Ion thrusters in atmosphere will at minimum provide 30% of their normal thrust value, they don't 0 out. Supposedly that's a small fraction of the thrust of atmospheric thrusters at the same level, but in practice the difference isn't that great. This is what I was talking about in my post. Small ship small ion thrusters are supposed to be 4kn minimum, compared to the ~80kn of the SAT at the same altitude, yet you need far fewer than 20 ions to match the lift of one SAT.

[Twelve]

yes there is math for this.

no its doesnt work in se becuase for somereason the thrusters dont follow math, they are set values which currently dont make sense.

see here: https://www.youtube.com/watch?v=wHNByN7iklM

i beleive this was before the 20% increase.

[Thalyn]

Just thought I'd touch back on this one.

Seems there is no definite constant for gravity. It varies qutie a bit between each thruster, as outlined in the video Twelve posted. I found amounts ranging from 540.3kg/kN on LS Large Ion Thrusters up to 892.5kg/kN for LS Large Atmospheric Thrusters (inefficiencies taken into account). Upon finding a difference between Large Hydrogen Thrusters depending on if they were SS or LS, I decided to stop - as much as it would be nice to know, it's pointless given it will definitely be getting changed at some point.

At a guess, there's some kind of multiplier being applied which isn't immediately visible, which is also different for each and every thruster. Alternatively they're using some off-the-wall maths no-one outside of Keen fully understands, since we lack the decoder ring.

FWIW, I managed 4.3M kg with a LS Large Atmospheric, 4.4M kg with a LS Large Hydrogen, 584K kg with a LS Large Ion, and 350K kg with a SS Large Hydrogen. All done within 50m of ground level on a planet (1G with atmosphere).

[Crowbot]

All I know is even with 6 LS Large thrusters (+2 Large hydrogen) my ship can't stay in the air which seems crazy. Especially for an empty ship.

[Thalyn]

It does actually get more curious. Due to my earlier findings (1x LS-LHT being capable of 4.4M kg) I attempted to build another large vessel. At just over 1.2M kg, 2x LS-LHTs (theoretically able to negate 8.8M kg) proved inadequate to lift it. Not by much, but enough to keep it grounded. This would be the expected behaviour for 12MN of thrust, which is what 2x LS-LHTs provide.

*ed: Adding a 3rd LS-LHT, for 18MN of thrust, allowed it to lift again.

It seems there's other factors involved. Either the size of the ship (number of blocks/parts in use?) is taken into consideration, or cargo has a reduced effect. All I know for certain is my previous testing used very small vessels (LS-LHT would have been 40 cubes in total, made from 13 different parts) and oodles of cargo (Cobalt Ore), where-as this one was genuinely heavy by virtue of its size alone.