I'm sure people have definitely done it before but I've never been able to find a post about it anywhere. So, I took it upon myself and solved for the Drag Coefficient and how it correlates to the in game drag value. I will also discuss how drag seems to work in this game.
Long story short:
- Every drag point corresponds to around
0.0010145in drag coefficient - If the game tells you that your plane produces 1000 drag points, your drag coefficient is effectively
1.0145 - This drag value is purely the drag produced by your fuselage at 0 degrees angle of attack!!! This will from now on be referenced as parasite drag.
- This drag value does not include the drag your wings produce when they generate lift. This value will from now on be referenced as induced drag.
- The parasite drag can and will change depending on your angle of attack, aka the orientation at which you are moving through the air.
- You can calculate the parasite drag force that your aircraft is experiencing at 0 degree angle of attack any given speed using the formula
F=D*0.0010145*0.5*rho*v^2, where F is the total drag force, D is the drag the game displays to you, rho is the air density, and v is your True Air Speed. - Thus, for realism, The drag value of your plane should really never exceed 100-200 (for small-medium sized aircraft), corresponding to a parasite drag coefficient of around 0.1 to 0.2. Where you should be getting the majority of your drag is from your wings, which you can ramp up the drag forces of to compensate and obtain realistic performances.
Bonus!
Since I used springs/shocks to calculate these values, I was also able to get the spring constant, if anyone is curious
- At 100%, the spring constant of Shocks is approximately 49603
- This is proportional to the percentage strength of your Shocks. Aka if your Shocks spring strength is set to 200% the spring constant would be 99862
- Damper has no effect on the spring constant.
This information may or may not be mildly useful to some people.
Looking back I also realized that the game seems to already take into account the wetted area of objects when it spits you the drag value, since in all my testing, even with different geometries, the value of 0.0010145 was consistent.
Thus the in game drag value is not the drag coefficient, rather the Drag coefficient times wetted area. The proper drag force experienced by your aircraft can still be calculated with the original equation in post.
@Subsere
Yurp! Actually b/c I can't find the legacy pic on the SP site I had to get a low-res pic from google then use every tool under the sun to enhance it back into what it should look like...
@ThomasRoderick I see.
Using the legacy profile picture now, eh?
@CACHA That highly depends on how the rest of your plane is built. You could potentially turn whatever you want to measure onto it's butt and measure the drag force when the entire belly of the plane is headed into the wing (aoa of 90 degrees) and the correlation of aoa and drag force should be roughly linear.
The parasite drag can and will change depending on your angle of attack,but how will it change?
We may also take into account that engines are massively overpowered to compensate that difference, especially on prop engines. The slider that gives says 1000hp is more like 2000hp in game
Well.
After having searched for a drag coeficient to reach 650kph tol speed, i found that i had to get 0.055 Cd. Tests in game with various drag point values, i got to reach 650kph at sea level with 2180 drag points, while, as i said earlier, i got to 950kph with 780 drag points, nearer to what i should have with 0.055/0.001045=52.63 ≈ 53 drag points.
Is there an error in this?
If you want to see for yourself, here the datas:
25.5 m² wing suface, 2092.38hp, 3468kg, 2210kg empty, 0,212 HP/Weight ratio.
@ThomasRoderick yes
Alr. I saw this, i readed as much as i could (everything) but i still find issues making it same ratio with my turboprop.
I had, at ~2300 drag points, a top speed of 615km/h. Which means with a drag coeficient of 2,4035.
I wanted to see, but with drag coeficient at ~0.78, the plane reaches over 900kph... i don't quite understand how to counter it.
If you need specifications, i got a LOT. Just tell me if it is needed.
@Ku
... N/m, right?
@Subsere The area of the aircraft exposed to the airstream. Or, basically, the total external area of the aircraft.
Wetted area means what?
@ThomasRoderick I’m not too sure if I can add too much to the convo, but I’ve seen multiple definitions of the reference surface area (the area used in the lift/drag equations) in both academia and industry. In times when you only care about the wings, then the wing area (planform) is a great choice. If you are doing some sort of analysis where you really need the drag coefficient of the entire aircraft, then a wetted surface area or a cross-sectional area may be the best choice. I think the last code I used auto-calculated SREF for lift/drag calculations as a cross-sectional area depending on the geometry that I put into it. I guess the moral of the story is that the area should be whatever is most convenient, or makes the most sense to the engineer. If we have a vehicle such as a re-entry vehicle, then cross sectional area may be best, though for vehicles that depend most upon a traditional wing configuration, I can see the wing planform area being the most important. Also take what I say with a grain of salt lol. I am not an aerodynamicist — most of my work is conceptual design related. Anyway I was lurking on the forums when waiting for my delayed flight while sending this. It’s nice to see some ppl that I recognize on the forums still lol. Good to see you man!
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Edit: looks like you said more or less what I said already. Oops. My reading comprehension isn’t too good today haha
@Ku
Yes, parasitic drag is proportional to the wetted area (IIRC skin friction drag is proportional to the total skin area, while form drag is proportional to the frontal cross-section); however, last time I checked the aerospace industry defines the drag coefficient of an aircraft as the parasitic drag force divided by the wing area, not the wetted area, nor the frontal cross-section.
@ThomasRoderick no this finding is indeed based on wetted area of an object, because i tested this with only fuselage blocks. In addition, wings do not change the drag value the game displays to you. This is pure parasite drag. The total parasite drag must be found and added up with the wing profile drag and induced drag, then be non-dimensionalised by dividing it with dynamic pressure and wing area, giving you the overall drag coefficient of the aircraft.
@Ku
Dimensional Homogeneity FTW!
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Also, pretty sure the reason why you forgot the wetted/reference area was because you were an order of magnitude off with aircraft drag coefficients (which, once again, is not based on the cross-section unlike it is for cars and everyday objects, but rather the wing area.... probably because they're trying to compare it to the amount of lift the plane got). For example, a plane with a drag coef of 0.02 and a wing area of 10m^2 will get you a drag area of exactly 0.2m^2.... which translates to about 200 points of in-game drag.
@XEPOH It in fact, to some degree, does; it’s how physics work.
What kind of satisfactory result r u looking for?
@ThomasRoderick mk i thought abt it a little more
You are right in that the Drag is proportional to wetted area. Then the parasite drag force felt by the whole aircraft equation should be
‘D=ACd0.5rhov^2’
You are also right in the Cd is indeed dimensionless, so units on both side of the question must cancel out. The only way that would happen is if the equation is arranged as above (Force cancels Force, remember that the right side of the equation is basically dynamic pressure times area = force)
@SilverStar eh shoot, why not?
@ThomasRoderick I see…
@ThomasRoderick I understand.
@SilverStar
Not as if I can even test those either way.... my phone's a potato among potatoes, and my laptop's even worse; incidentally, both came from the bottom of the bargain bin.
Plus, those things look good and realistic and that's all it takes for me to mass-upvote. Personal codes and morals should never be used to judge others with, afterall.
@ThomasRoderick Hey thanks a lot for the upvotes ! And you tested none of them...!
@ThomasRoderick Yup
@SilverStar Because drag force is proportional to the square of the airspeed?