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.
@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 will consider the result satisfactory when the formula I proposed will give a result with an error of 0.1%, now it is 0.5%, for this you need to enter the parameters responsible for the efficiency of the screw into the formula
@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?
@Ku this game does not simulate real aerodynamic phenomena, it is a simulation, this must be understood in order to obtain a satisfactory result
@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)
need a simple formula for calculating
DragPointsand not empty reasoning! I suggest thisDP=(EP/IAS)*((EP*10^8)/IAS^3)power in horsepower, speed in kilometers per hour
as an example I posted a couple of aeroplans
@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?
@Graingy I am in the process of making a tutorial for making a realistic model. May I tag you when out, if you're interested ?
About drag, I can say that the drag points can be used to get a realistic drag performance. Like if you need to go 2 Times faster, you will need 4 times less drag points.
@Graingy
Smooth surfaces without unnecessary bumps and/or depressions, no flat surfaces pointing into the wind, generally teardrop/cigar-shaped outlines, and cover any non-smooth part with smooth fairings wherever possible.
@Graingy
Just remember the target drag value should be somewhere around
0.02 * [wing area] / 0.0010145and you should be all set.This.
A transonic aircraft should have a near-constant cross-sectional area excluding the nose and the tail. Or, basically, make sure your wingtips are located where your fuselage is the thinnest, or conversely "tuck in" your fuselage near the wingtips.
For super/hypersonic aircraft, it's "make sure all your parts are tucked behind the shockwave cone created by your nose".
As in...? If you meant the LERX then it's for maneuverability at high AOA.
I'd say.... not necessarily, but likely to be yes. Granted, I'm a mechie undergrad so my understanding about aerodynamics is still rather limited, but IIRC it's more about the part where flat surfaces don't tend to transition smoothly into and out of other shapes so more chance for influence drag.
@ThomasRoderick area rule?
And the funny thing is, I don’t know what counts are streamlining.
Look at, say, the F-15. Are the curves over the engines important? Are flat surfaces on the sides of an aircraft bad? It’s weird.
@Graingy
Kek.
Also.... SP doesn't really double as wind tunnel simulators so.... Still, follow IRL design principles whenever possible, remember things like streamlining and area rule etc, I guess?
.... and go wild.
@ThomasRoderick I like your funny words magic man
@Ku huh, neat.
But no way to determine if, say, your jet fighter is actually aerodynamic in design.
@Ku
@Graingy
Bonus point: a streamlined aircraft usually have drag coefficient of around 0.02 at subsonic speeds, which, when multiplied by the wing area of around 20m^2, gives a drag area of about 0.4m^2 for general aviation.... or about 400 in-game drag units.