Visualize Drag In Editor

[JumpsterG]

EDIT: (Originally, a suggestion for a "Center of Drag" indicator, this has been updated as a more general suggestion for visualizing drag)

I've been building SSTO spaceplanes lately, and something I learned was that uneven drag is a significant element in the stability of my designs, but that I have no visual indicator of where the drag is.

My understanding is that high drag parts (intakes, mainly) want to pull themselves behind the center of mass with respect to the forward (prograde) motion of the plane and inversely, low drag parts (nosecones, cockpits) tend to pull themselves toward the prograde vector.

This can be used to improve stability like an arrow: Putting intakes far back and nosecones up front helps the plane maintain it's nose facing the prograde direction (it will naturally tend to pull it's nose to the prograde vector).

or misused hilariously: Putting intakes in front and using aesthetic nosecones on the rear, resulting in the plane wanting to fly backwards once you pull far enough off the prograde direction.

Currently, we have to remember to check the drag statistic on parts and eyeball where drag concentrations are. New players (myself very much) quickly ignored the drag value on parts when they realize most parts have the same drag, and those that don't, seem to have only a small effect.

The suggestion is that we could have a way of seeing where the average drag of our parts is in the editor. This would highlight drag as a design consideration.

My first suggestion (which is not so good, as pointed out by ferram4 below) was to use a "Center of Drag" indicator. Seeing where the indicator sits could tell us some useful information about our craft:

-Sits on the center mass
The vehicle can face in any direction during atmospheric flight with no (or minimal) drag turning.

-Sits ahead of center mass
The vehicle will tend to turn backwards during atmospheric flight.

-Sits behind center mass
The vehicle will tend to return to prograde direction during atmospheric flight

-Is off the center thrust / center mass line
The vehicle will tend to pitch or yaw away from prograde towards the indicator

-Is very far away from center mass
The effect of drag turning is stronger

A better suggestion (noted by ferram4 as well) is to combine the drag effect with the existing "center of lift" vector we currently have, creating an "aerodynamic center" for our vehicle that takes into account both the lift and drag effects. This ties directly in with possible overall improvements to the aerodynamic model in which drag and lift are more realistically calculated based on surface area, but could also be applied using the game mechanics we have now.

Edited January 20, 2014 by JumpsterG
Updated based on ferram4's feedback

[minerman30]

Yes, this is a great idea.

Another idea could be toggleable lines that go through the indicators at 90 degree angles so that you can see thrust-mass indicators evenly.

[Kodiak42]

Have you made sure that it wasn't your center of lift that was in front of your center of mass? In ksp's current state, your center of drag and mass are the same, aside from slight deviations due to a few low mass parts. From what your accounts say... um... pics please... I can't think of a single craft that would do this outside of a mod.

[ferram4]

No, this is a terrible idea, entirely caused by the name of the Center of Lift. In theory the Center of Lift (also called the Aerodynamic Center, which is a better name, IMO) would also include the effect of differences in drag across the vehicle. By implementing this you'll just confuse people.

Honestly, this sounds like a good argument for combining drag effects into the current CoL and changing the in-game name of the CoL to AC, since that's where this confusion is stemming from. It would help reduce player's confusion while also not feeding them bad information (the implication that lift is the only thing that matters for stability, not drag, as the CoL name seems to imply).

[JumpsterG]

Have you made sure that it wasn't your center of lift that was in front of your center of mass? In ksp's current state, your center of drag and mass are the same, aside from slight deviations due to a few low mass parts. From what your accounts say... um... pics please... I can't think of a single craft that would do this outside of a mod.

You're right, I should demonstrate the current effects of the stock drag model with some pics; hopefully I'll have some time tonight to do this. Truthfully, the effect of uneven drag is not huge and isn't an issue in most circumstances, but with specific configurations, I have noted that planes are more likely to spin backwards, and reentry capsules will free fall in such a way that the "drag-heavy" end faces upward (important for heat-shield orientation, if that's your thing).

No, this is a terrible idea, entirely caused by the name of the Center of Lift. In theory the Center of Lift (also called the Aerodynamic Center, which is a better name, IMO) would also include the effect of differences in drag across the vehicle. By implementing this you'll just confuse people.

Honestly, this sounds like a good argument for combining drag effects into the current CoL and changing the in-game name of the CoL to AC, since that's where this confusion is stemming from. It would help reduce player's confusion while also not feeding them bad information (the implication that lift is the only thing that matters for stability, not drag, as the CoL name seems to imply).

I feel you are right and I will need to retract my suggestion (or at least clarify the specific circumstance it was trying to address).

Thanks very much for enlightening!

After thinking about it this way, the "Center of Drag" only makes sense if we expect the stock aerodynamic system to remain as it currently is, which creates a drag force (separate from lift force) based on adding up the drag values of parts (Furthermore, each part adds it's full drag value regardless of it's location or exposed/amount of surface area, but that's another suggestion).

What I think I understand now is that if the aerodynamics were closer to reality, all protrusions (wings or otherwise) on a craft would affect overall drag and lift, both of which could be included in a single, calculated vector, as Ferram4 states.

I will update the original post to downplay the "center of drag" concept and perhaps change the suggestion to combine drag with the "center of lift" to make the "Aerodynamic Center" ferram4 mentions. This is coming close to an "Improve Aerodynamics" thread, but I really just wanted to suggest a way to visualize drag effects in the editor, so regardless of changes in the physics engine, I think the suggestion stands.

[coolitic]

Excellent idea. It would definitely help make building space planes easier.