Retractable Landing Gears; Pretending

[SpacedCowboy]

You take off from the runway with your perfectly designed plane/spaceplane or whatever. You tuck in the landing gears just as it lifts off, and it looks so cool. Sometimes you forget. Hit F-12 to check out the aero-drag situation. Low and behold, it makes no difference if the landing gear are extended or retracted. One would think that it would be one of the first things to consider with the new (not so new) drag and aerodynamics. But I'll go on pretending, because at least it "looks cool."

Edited September 8, 2015 by SpacedCowboy

[carneyvich]

i know right!

[smjjames]

Huh, I thought it did matter. At least they do have an effect when extended while aerobraking or doing reentry.

[Brainlord Mesomorph]

I think it depends on the gear.

Seems to me the heavy gear have drag. I deployed them accidentally, and wondered why my plane stopped climbing.

[GoSlash27]

From the drag cube files:

Squad/Parts/Wheel/SmallGearBay/smallGearBay/SmallGearBay

DRAG_CUBE

{

cube = RETRACTED, 0.4521211,0.7627845,0.3066207, 0.4520826,0.8104974,0.3040655, 0.5826902,0.772536,0.3548338, 0.5822667,0.839036,0.4308696, 0.1399506,0.4975044,1.325763, 0.1399506,0.4120106,1.374865, 0.0002161413,-0.007407606,0.03587955, 0.451569,0.4463044,1.588728

cube = DEPLOYED, 0.6103878,0.7908927,0.4164931, 0.610309,0.8359724,0.3245069, 0.6089301,0.7589338,0.9493425, 0.6082603,0.7966789,1.153156, 0.3554553,0.7040969,1.700721, 0.3554553,0.6543361,1.388922, 0.0002161413,-0.3682571,0.02673525, 0.451569,1.167697,1.607016

}

It *does* make a difference. There are also differences for the larger retractable gear.

Squad/Parts/Wheel/LandingGear/GearMedium/GearMedium

DRAG_CUBE

{

RETRACTED = RETRACTED, 1.34515,0.8165293,0.4764051, 1.34515,0.8154734,0.4764051, 1.255602,0.8251827,0.5392171, 1.255602,0.8000292,0.6835146, 0.4617555,0.5293906,1.089661, 0.4617555,0.2736183,1.809438, 2.980232E-07,-0.06152177,-0.03202891, 0.7565614,0.7683123,2.349208

DEPLOYED = DEPLOYED, 2.185883,0.8828952,0.6261107, 2.185883,0.8829924,0.6261107, 1.459697,0.7678789,2.439235, 1.459697,0.7622477,2.551643, 1.032085,0.6081987,1.930527, 1.032085,0.505362,2.060562, 3.576279E-07,-1.010557,-0.03277326, 1.057151,2.666383,2.350696

}

Squad/Parts/Wheel/LandingGear/GearLarge/GearLarge

DRAG_CUBE

{

RETRACTED = RETRACTED, 2.668421,0.7828922,0.7107495, 2.668421,0.78283,0.7107495, 2.770018,0.8184504,0.7037734, 2.770018,0.7823612,0.7437038, 0.9675053,0.5827737,1.15612, 0.9675053,0.2873546,2.339442, 3.039837E-06,0.08524656,0.1619515, 1.227095,1.072782,3.268359

DEPLOYED = DEPLOYED, 4.769676,0.8709047,1.2333, 4.770842,0.870423,1.2333, 3.373985,0.7576349,3.416735, 3.373985,0.7137473,3.610135, 2.119894,0.6172727,3.291952, 2.119894,0.5126448,3.05974, 2.980232E-06,-1.40114,0.1545382, 1.815971,3.909752,3.283185

}

Best,

-Slashy

Edited September 8, 2015 by GoSlash27

[SpacedCowboy]

From the drag cube files:

It *does* make a difference. There are also differences for the larger retractable gear.

Best,

-Slashy

Slash I know you always mean the best, but, sorry, I failed algebra in the 9th grade, so all those numbers mean nothing to me. I'm only questioning why, when you hit F-12, and landing gears are extended there are no red lines exhibiting drag. Wouldn't that be a major "drag"?

[regex]

Low and behold

"Lo" and behold.

The gear probably still have drag cubes because you can never be sure where it'll be placed. On one plane they'll be clipped, on another they'll be hanging.

[SpacedCowboy]

Huh, I thought it did matter. At least they do have an effect when extended while aerobraking or doing reentry.

Don't know about the way down, but on the way up it doesn't seem to matter if landing gear are up, or down. You'd think having the landing gears down (extended, deployed) would be a big factor.

[Mipe]

A dead simple experiment.

Flying at 100 m/s, hit G, gears retract, speed increases. Hit G again, gears extend and speed drops.

I'm confused. Where is the "no difference"? The OP can't be wrong, so my game must be bugged.

[March Unto Torment]

The F12 aero model is a very basic analysis and doesn't account for all drag cubes. You need FAR if you want a full aerodynamic overlay, I believe (although I don't use it myself).

[Alshain]

Slash I know you always mean the best, but, sorry, I failed algebra in the 9th grade, so all those numbers mean nothing to me. I'm only questioning why, when you hit F-12, and landing gears are extended there are no red lines exhibiting drag. Wouldn't that be a major "drag"?

It's more likely a problem with the overlay than the drag.

[Streetwind]

Landing gear is physicsless, isn't it? In fact, the small gear bay has always been hardcoded physicsless, so you couldn't even force it to be an active physics part via its config. I once read that this was done in the early days of KSP because things would go Kraken if landing gear wasn't physicsless.

Now keep in mind: "physicsless" does not mean that the part has no mass or drag. This used to be the case in some earlier versions, but only due to a bug. It has since been fixed, and nowadays it works correctly: physicsless parts add their mass and drag to the parent part instead of managing it themselves.

You do not see individual drag arrows for landing gear because there are none to display. The part itself does not have drag. It has offloaded its drag to the fuselage it is mounted to. The arrow you are not getting to see is in fact present as a small part of the much larger drag arrow of the plane body (and quite likely invisible because body arrows tend to be clipped out of view inside the body).

[Alshain]

Landing gear is physicsless, isn't it? In fact, the small gear bay has always been hardcoded physicsless, so you couldn't even force it to be an active physics part via its config. I once read that this was done in the early days of KSP because things would go Kraken if landing gear wasn't physicsless.

Now keep in mind: "physicsless" does not mean that the part has no mass or drag. This used to be the case in some earlier versions, but only due to a bug. It has since been fixed, and nowadays it works correctly: physicsless parts add their mass and drag to the parent part instead of managing it themselves.

You do not see individual drag arrows for landing gear because there are none to display. The part itself does not have drag. It has offloaded its drag to the fuselage it is mounted to. The arrow you are not getting to see is in fact present as a small part of the much larger drag arrow of the plane body (and quite likely invisible because body arrows tend to be clipped out of view inside the body).

Yes, it does look like in the configs they are indeed physics-less.

[GoSlash27]

To settle this once and for all...

Also, this rig hits over 1000 m/sec with the gear retracted and 870 with them deployed.

So yes, retracting the gear does reduce drag.

Best,

-Slashy

Edited September 8, 2015 by GoSlash27

[PCanas]

I guess FAR solves the problem...

[Warzouz]

Difference is marginal though. Once I totally forgot to close it and went in space with the same dV left

Same thing on Air intakes. Does it matter to close them ? I didn't noticed any difference too.

I still do it for RP, though

[Starhawk]

Difference is marginal though. Once I totally forgot to close it and went in space with the same dV left

Same thing on Air intakes. Does it matter to close them ? I didn't noticed any difference too.

I still do it for RP, though

It has been established that there is no benefit from closing air intakes.

Happy landings!

[magnemoe]

It has been established that there is no benefit from closing air intakes.

Happy landings!

The equipment bays generates more drag then open, has used this to slow down pods faster. Not sure about the cargo bays or if content in the bays matter here.

[SpacedCowboy]

Okay guys, thanks for clearing that up for me. Now I only have to pretend that those red lines are there. Also, right now I'm pretending to eat crow.

[GoSlash27]

Slash I know you always mean the best, but, sorry, I failed algebra in the 9th grade, so all those numbers mean nothing to me. I'm only questioning why, when you hit F-12, and landing gears are extended there are no red lines exhibiting drag. Wouldn't that be a major "drag"?

SpacedCowboy,

I just learned today how to decode all of the numbers.

Here's the important part:

State Area/ Drag coefficient

Retracted Forward 0.140/0.498

Retracted Backward 0.140/0.412

Deployed Forward 0.355/0.704

Deployed Backward 0.355/0.654

Best,

-Slashy

[Temeter]

SpacedCowboy,

I just learned today how to decode all of the numbers.

Here's the important part:

State Area/ Drag coefficient

Retracted Forward 0.140/0.498

Retracted Backward 0.140/0.412

Deployed Forward 0.355/0.704

Deployed Backward 0.355/0.654

Best,

-Slashy

So they create less drag when you place them the wrong way round? Or is that negated by the low pressure area that's created behind them (however that's called)?

[NathanKell]

Correct, there's lower drag from turning them around.

It's also worth mentioning that even if a part does have a drag arrow, that arrow may be short enough that it's inside the part graphics and thus you can't see it.

[panzer1b]

If you retract em into a bomb bay you get drag-free gear (i use this for one of my recent SSTL fighters).

Really as great as new aero is, there are many shortcuts they took to cut down processing, so there is no dynamic drag simulation (say you partially or evn fully clip something inside your vessel), so moving stuff inside doesnt do squat (although i do believe it

does shield from heating effects somewhat)..

perhaps this will change in the future, but for now anything radially attached will add drag, sometimes even ALOT of drag to the craft, and unless its inside or partially inside a bomb bay (those disable drag on anything inside) it will be subject to drag forces.

[cantab]

I've been told that the lines do not show aerodynamic forces, but rather the results of a completely separate calculation that's run *only* to work out what the lines should show. Which means the aerodynamic overlay can be wrong. I cannot see this as anything other than *completely idiotic", but that's KSP for you.

[RocketBlam]

Okay guys, thanks for clearing that up for me. Now I only have to pretend that those red lines are there. Also, right now I'm pretending to eat crow.

If I were going to pretend to eat something, it would be, like, a hamburger.