@ChiChiWerx
But you right that mass isn't the major factor, drag is. I'm just trying to work out what that means in game.

@ChiChiWerx

I have, there is a difference. I took one plane and cut the fuel in the wings from full to 50% and did see a boost in speed. If I recall correctly it was around 15% for that particular airplane. I only noticed it because I was looking for it, and testing a plane that was flying at over 2000 mph, making the difference (300 mph) more noticeable.

In real life mass does factor into aircraft speed, I've used the real world equations. Basically the plane has to generate enough lift to counteract it's weight. If the wings aren't moving fast enough to do this on their own, then the aircraft has to use a steeper Angle o Attack (more drag) and the engines make up the difference (Less available power/thrust for speed) which results in a slower plane.

Yeah, I've see the deflection control effect, although if a plane has good trim it's not as much of a problem.

You, know, come to think of it, if more control deflection is required to keep the nose level or up, that does cause more drag in game, so when testing, throw that into the mix. If varying weight and the CG move forward and more elevator (or possibly trim) is required to keep the nose up, your build will probably fly slower. Mass itself doesn’t effect top speed, it’s the other effects as a result of increasing mass. So, if you want to isolate mass’s effect in game, you’ll have to make sure the CG stays in the same place on your build.

I have no idea why mass is getting thrown around in this discussion on top speed. Mass effects acceleration, but has little effect on top speed. In RL, it may affect top speed because more weight requires more lift = higher AoA = more induced drag, but not significantly so. And I’ve never seen this effect in SP (again not RL physics, simply an emulator). You can investigate to see if I’m correct but taking the same build and varying the dead weight or the fuel and seeing if there’s a difference I top speed, but I think you’ll find little or no difference.

Honestly, the physics in this game are screwy compared to real life and you just need to sort it out by trial and error.

Interesting question. I’ve wondered what the value of a drag point is myself.

Thanks, that's very interesting. I'm building a couple of test craft with the same weight and give one two engines and try for twice the drag and see what results I get.

I think my booster sled was a surprise because my initial drag was so low that the increase affected it much harder than it would a more typical build. Going from 0 drag to 400 drag isn't the same as going from 400 to 800.

@randomusername
"M=1 T=2 D=1
The top speed should double."

What makes you believe that? it's not how it works in real life, and isn't how it works in SP either. Take a jet at full throttle and top speed. If you throttle back to 50%, your speed won't cut in half, but will probably be closer to 70%. The exceptions are either speed limited by altitude (where speed tops at at below 100% throttle) or very underpowered (and need most of their thrust to keep aloft).

@randomusername

In your examples you varied the mass . You varied the mass and drag, but not the thrust. What I need is an example with the same mass, but one that varies in drag and thrust.

For example:
M=1, T=1, D=1
M=1,T=2, D=1
M=1, T=1, D=2

I can do the first two in game. Take a jet that isn't speed limited by altitude, bring it up to full throttle and get it flying level at 5000 feet. Note the speed. Now cut the throttle back to 50%. It's speed won't drop in half, but to around 70%, probably a little less. And that's how it works in the real world too.

But what I can't test in game is to run a plane at 100% throttle but someone double the drag.

In the real world thrust and drag force are rated with the same terms, so I know that doubling the thrust or doubling the coefficient of drag cancel out as far as speed goes.

@randomusername The only way to make good planes on here is to test them, fix them and test them again.

@randomusername That would not tell him anything useful. It would give him information about the performance envelope of that specific vehicle and nothing more. As soon as he changed anything, all that information would become irrelevant.

@randomusername

But do you know what the math is in game? From a builder's standpoint, is it worth adding a second J15 engine to a plane if it raises the drag from 100 to 200? 100 to 150? 200 to 500?
Without know the relationship between thrust and drag in the game we're stuck with trial and error?

@randomusername

SP is diffrent when it comes to drag SP only well dose a calculation that's consistent instead of IRL when the faster u go the less time the air has to move hence the sonic booms and why supersonic aircraft are normally made from heat resistant metals

Short version

Irl the faster u go the more drag
Example if ur not moving ur drag is effectively 0 becuse there is no force acting apon it
SP stays consitant

@atgxtg Always test to be sure. So many crap planes on here that coulda been good if someone bothered to test before they uploaded.

@F104Deathtrap Thanks. I was just wondering if anybody knew how it works, so I can tell when adding more engines are worth it, and when they aren't.

@atgxtg You're correct, it's not a precise model of drag coefficients. Think of it more like a rough indicator.

Sorry but that isn't how it works. Drag points are not the same as coefficient of drag. I have a airplane with 0 Drag Points, and while fast it doesn't have an unlimited top speed-even when fitted with an "unlimited" fuel tank. In fact, it is partly responsible for my posting this question.

In the real world reducing the Cd (coefficient of drag) of a jet will increase speed by approximately 41% because drag force is proportional to the square of the speed. I said approximately because the second engine (and fuel for it) will increase the drag, as well as the weight of the aircraft (requiring more lift), which will reduce speed.

The upshot of this is that there are times when adding a second engine will actually slow a plane down and just make it use up more fuel. There are lots of builds out there will lots and lots of engines piled on top of each other that would be faster if you took off some of the engines and fuel.

In my own case, I have a 0 drag airplane that got slower when I added two detachable booster engines. The added thrust was more than offset by the added weight and drag.

I was just wondering if anybody knew what the in game relationship was.