Wind tunnel?

[Ser]

Knaapie, ok, ok, I give up "there's only one wind tunnel in the world that can hit Mach 30. The LENS-X wind tunnel can hit the hypersonic speeds necessary to test the latest ultrafast aircraft, space planes, and NASA's Orion space vehicle"

But the question remains: why would you need tunnels when you've got FAR mod?

[Knaapie]

50 minutes ago, Ser said:

Knaapie, ok, ok, I give up "there's only one wind tunnel in the world that can hit Mach 30. The LENS-X wind tunnel can hit the hypersonic speeds necessary to test the latest ultrafast aircraft, space planes, and NASA's Orion space vehicle"

But the question remains: why would you need tunnels when you've got FAR mod?

And there we agree again ^^.. Wind tunnels are used to gather data and visualize them.. I don't see the need for a data finding process in KSP when you can just visualize them in the hangars and in flight with software tweaks or mods (FAR).

I would like some more info in the stock game without over complicating it for new players. As for really being able to make clear statements on how to do it, I'd like to install FAR again and see how they do it.

Edited May 27, 2016 by Knaapie

[The_Rocketeer]

1 hour ago, Ser said:

Needs another 1000 m/s even for Kerbin's reentry That's not the subject of the thread, I think.

This is only part of the puzzle. Mach is just a way to say how many times the speed of sound you're moving. At altitude, Mach decreases - pressure falls so sound is slower. However, wind tunnels tell you what happens when your craft is bombarded by molecules at speed at a given pressure. The aerodynamic flow of different pressures will be different at the same airspeed (note: not the same Mach) for the same reason that vacuum cleaner suction decreases as the bag gets full - an empty bag (low pressure/high altitude) has more space for the air molecules to move around/out of the way than a full bag (high pressure/low altitude). In other words, the aerodynamics you would see at Mach 4.5 ASL would not reflect the aerodynamics of Mach 4.5 at 20,000m in any reliable way.

@Knaapie politely pointed out I was embarrassing myself with wonky science here. The thrust of my point is right (Mach 1 is slower at altitude and wind tunnel Mach 1 isn't aerodynamically the same as 20km Mach 1) but it has nothing to do with pressure!

Edited May 27, 2016 by The_Rocketeer

[Knaapie]

The thing I forgot and don't understand anymore is how aerodynamics are changing at different air densities and speeds. My seemingly "stable craft" do still tend to only be stable below 10km when the margins are small (CoL close to CoM). I've also seen slight differences at Eve / Duna some time ago.. Or was that a design flaw?   Hmm.. I do potentially see how "tests" could give ppl more info of their plane is stable on Eve or on Duna..  This might also be explained by giving more info somewhere.. Or my margins were just too small ^^

Edited May 27, 2016 by Knaapie

[The_Rocketeer]

@Knaapie

do you mean that below 10km they tend to be stable exclusively when CoL is close to CoM

or

do you mean that when CoL and CoM are close, they become unstable above 10km?

If the former, remember that the CoM us effectively the centre of rotation around which the moment of lift turns the aircraft, so a CoL far behind the CoM will cause a pitch down situation.

If the latter, above 10km you can build very high speeds, so the moment of drag is greatly increased and may also cause rotation around the CoM.

[Knaapie]

@The_Rocketeer I mean the latter and have to agree with the drag part.. We don't seem to have information on how drag influences the momentum around the center of mass.

 

tnx men

Edited May 27, 2016 by Knaapie

[Knaapie]

Hmm I somewhat see how a wind tunnel can be used for a future science overhaul, just like engine testing was suggested some time ago. A wind tunnel could potentially unlock aerodynamic surfaces. An added option in the late game would be to see drag forces on entire crafts... 

 

How is drag even calculated in this game?  does anyone know ?

[SpaceplaneAddict]

The SpaceplaneAddict approves.... would make it a lot easier to test how much lift I may need. \

Personal suggestion for the suggestion: 

-Make it so you can switch around what atmo/altitude it's simulating

[The_Rocketeer]

@Knaapie from wide-reading of this forum over a length of time, I have a rudimentary understanding: parts have a defined 'drag cube' (which provides drag coefficient values representing perpendicular attitudes of part to airflow, allowing calculation of net drag from % facing of surfaces based on actual airflow); forward parts producing aerodynamic 'drag shadows' that reduce the drag of nearby trailing parts; drag cubes of radially attached parts are aded to that of their parent part.

However this is just what I've picked up, I haven't studied the files myself. I recall @GoSlash27 made a personal study of drag cubes at one time, and I dare say he knows who would know now if he doesn't himself

Edited May 28, 2016 by The_Rocketeer