Solved Why do SFS measure both thrust and mass in tons?

#1
I recall that 1 metric ton is equal to 100kg. That is a unit of mass(without gravity). But then I see that thrust generated by a Hawk engine is also 115tons(a measure of force). So I'm confused about when to divide by and multiply by 9.8. They should've just used kilonewtons for thrust and tons for mass. This really makes calculations a pain.
 
#2
I recall that 1 metric ton is equal to 100kg. That is a unit of mass(without gravity). But then I see that thrust generated by a Hawk engine is also 115tons(a measure of force). So I'm confused about when to divide by and multiply by 9.8. They should've just used kilonewtons for thrust and tons for mass. This really makes calculations a pain.
Ya, my bathroom scale should measure kilonewtons too, I don’t see any altimeter on it
 

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#3
It's cos the thrust isn't worked out properly ingame. The hawk actually generates 1150kN of thrust, rather than 1150kg / 1145kN as the tooltip states. It means the Isp is also slightly off as well
 
#4
Since specific impulse is given in seconds I assume that all the fuel data is calculated using the weight of the fuel.

Is it safe to do the following:
  • Whenever I need to know the thrust, I'll convert tons to kN for calculations.
  • Whenever I need weight, I'll use the number the game provided in tons
  • Whenever I need the mass, I'll divide the number given by 9.8(or whatever the gravity is).
 

Horus Lupercal

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#5
Since specific impulse is given in seconds I assume that all the fuel data is calculated using the weight of the fuel.

Is it safe to do the following:
  • Whenever I need to know the thrust, I'll convert tons to kN for calculations.

For thrust, all you need to do is change the t for 0kN, and that's it. Essentially the game uses 10 rather than 9.8 in the conversion, so a Titan generates 3000kN of thrust rather than 300t of lift. A Titan on Earth will push just over 306t off the ground.
Weird, I know, but it's something Altair figured out a little while ago when doing his in-game experiments on aerodynamics as the calculated ΔV was off from what was actually being delivered in-game. He narrowed it down to the thrust being off (3000kN), which knocked the Isp off slightly (244.89 seconds), which affected the ΔV.

It just means everything is slightly more powerful and slightly more efficient that it's supposed to be.


Whenever I need the mass, I'll divide the number given by 9.8(or whatever the gravity is).
Yeah, if you want its mass in Newtons for when you're working out TWR 'elsewhere'
 

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#6
Ah, those thrusts are really confusing indeed.
Actually there are 2 problems with those values:
- It's supposed to be thrust in kN divided by 9.8, but the game uses a factor 10 in this case
- Values are rounded down, so for some of them, just multiplying by 10 doesn't even give the correct result.

To make it short, the correct values are:
- Hawk: 1150 kN
- Broadsword: 400 kN
- Grasshoper: 96 kN
- Titan: 3000 kN
- Frontier: 1120 kN
- Ion engines: 24 kN
 
#7
Ah, those thrusts are really confusing indeed.
Actually there are 2 problems with those values:
- It's supposed to be thrust in kN divided by 9.8, but the game uses a factor 10 in this case
- Values are rounded down, so for some of them, just multiplying by 10 doesn't even give the correct result.

To make it short, the correct values are:
- Hawk: 1150 kN
- Broadsword: 400 kN
- Grasshoper: 96 kN
- Titan: 3000 kN
- Frontier: 1120 kN
- Ion engines: 24 kN
Thank you, everyone, for your support. Spaceflight Simulator forum is really a considerate and helpful community for all players of SFS. The forum is like a compass in a desert, guiding players to their goals in the game. Three months ago, this forum taught me how to dock. Today, this forum allowed me to gather more data on the engines. I just took a screenshot of the list. Now I can continue my "experiment" to bring a 88t payload to the moon in base game and create a great leap for mankind. Thank you.
 
#9
There are many configurations of the supporting stages of the rocket(eg how many engines I'll need to use; what thrust to weight ratio is the best; how much fuel to put in booster rockets...). Despite the best calculations, one would still need to test out the configurations and determine the best one. Testing differnt prototypes would be a better pharse to describe the procedure but experiment also works.
 
T

TtTOtW

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#10
Thank you, everyone, for your support. Spaceflight Simulator forum is really a considerate and helpful community for all players of SFS. The forum is like a compass in a desert, guiding players to their goals in the game. Three months ago, this forum taught me how to dock. Today, this forum allowed me to gather more data on the engines. I just took a screenshot of the list. Now I can continue my "experiment" to bring a 88t payload to the moon in base game and create a great leap for mankind. Thank you.
This makes me happy.
 
#11
I have a follow-up question. I know this is marked as solved but my follow-up question is related to this thread:
The Torque of the capsule is 5kN. Last time I checked torque = force*distance with units of Newton*Meters. So what's up with SFS? Thanks.
 

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#12
I have a follow-up question. I know this is marked as solved but my follow-up question is related to this thread:
The Torque of the capsule is 5kN. Last time I checked torque = force*distance with units of Newton*Meters. So what's up with SFS? Thanks.
To be accurate, the FORCE that the capsule can exert is 5kN.
You don't know the torque until you put it on a rocket and let the game measure X, the distance between the capsule and the centre of mass of the rocket behind the scenes.

If my answer is wrong, now you'll get a right one quick. :D
 
#13
To be accurate, the FORCE that the capsule can exert is 5kN.
You don't know the torque until you put it on a rocket and let the game measure X, the distance between the capsule and the centre of mass of the rocket behind the scenes.

If my answer is wrong, now you'll get a right one quick. :D
Oh ok. Fair enough. Me big dumb.
 

Mooncrasher

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#14
Oh ok. Fair enough. Me big dumb.
Well, it's quite reasonable to get confused, in this case.
Stef dumbed it down just right (by not using words properly) for slightly smart people like you and me to get confused. o_O