Are the landing gears a physicless part?

[_Astra_]

I always prefer buidling a fully symmetrical craft. However, there is a part which can be mounted downwards only. A landing gear.

Checked the aerodynamics many times and don't see any arrows going from the gears. Even in open state. Please tell are the landing gears physicsless?

[katateochi]

IIRC the concept of physicsless parts has been completely taken out.  But I don't think (from my observations) that landing gears have much (if any) impact on aerodynamics and it definitely doesn't make any difference whether they're raised or lowered (which I think is a pity, I'd like gears to add drag when lowered and suffer damage if they're lowered when above certain speeds).  

[Vegetal]

They *do* add drag, and it differs from stowed to deployed, but not by much.

I agree they should be destroyed if open at high speeds, right now you could go to orbital speeds in the atmo with no consequences to the landing gear.

[AbacusWizard]

Yeah; as far as I can tell the raised/lowered status of landing gear while in flight does not seem to make any difference other than aesthetics. Important for making cool screenshots but that's about it.

[I_Killed_Jeb]

I'm quite certain that they add drag when deployed as I just used them as emergency airbrakes.

[suicidejunkie]

On the other hand, you can take your SSTO to orbit, and then realize you left the gear down when you spin the camera to dock with your space station.

[Tourist]

11 hours ago, katateochi said:

IIRC the concept of physicsless parts has been completely taken out.  But I don't think (from my observations) that landing gears have much (if any) impact on aerodynamics and it definitely doesn't make any difference whether they're raised or lowered (which I think is a pity, I'd like gears to add drag when lowered and suffer damage if they're lowered when above certain speeds).  

 

11 hours ago, Vegetal said:

They *do* add drag, and it differs from stowed to deployed, but not by much.

I agree they should be destroyed if open at high speeds, right now you could go to orbital speeds in the atmo with no consequences to the landing gear.

If they do make a difference, then it barely has any effect. Many times I've gotten a space plane to orbit only to discover, yup, I'd forgotten to raise the gear. Any difference to the remaining fuel however was negligible especially compared to any difference caused by bad flying.

[_Astra_]

19 hours ago, Vegetal said:

They *do* add drag, and it differs from stowed to deployed, but not by much.

I agree they should be destroyed if open at high speeds, right now you could go to orbital speeds in the atmo with no consequences to the landing gear.

Thank you. I asked it primarily speaking of high speeds and atmosphere reentries.

However still unclear whether a pair of gears raise the nose at 3000 m / s or not =)

Edited January 22, 2016 by _Astra_
a typo being corrected

[katateochi]

ah ok, they do apply more drag when down.  The wiki says this 

Quote

as of version 1.0.5, retracting the wheel makes a noticeable reduction in drag.

although it also says that the only change since 1.0 was the part was renamed.  So that seems a bit contradictory (or just not updated), so I guess we have to resort to science! 

Spoiler

 

Here's my experimental craft (it's very scientific) 

Subject took off, retracted gears and flew level(ish) just above sea level.  The "aircraft" got up to 235m/s with the gears raised;

Subject then lowered the gears and the speed was reduced to about 217m/s

Then subject raised the gears again and the craft returned to ~235m/s

 

So lowering the gears does slow the craft down, but is that the same as adding drag?  Note there are no red drag-lines drawn from the gears at any point.  So is it adding "drag" in the same way other parts do, or is it simply altering the craft's speed via a different mechanism? The end result is the same, but if it's implemented differently that may change things.

So next (highly scientific) test craft. This has 7 pairs of rear wheels on both top and underside.  It also has 2 air brakes, 1 above & 1 below set at the same position along the craft's length as the rear gears (as a control, see...science...hmmmm).
In this test the craft is being flown with SAS switched off and the craft will fly mostly level although has a slight tendency to pitch a couple degrees up without anything deployed or any input. But it's the change from its natural pitch that I'm interested in here.

Control: When flying level if just the lower air brake is deployed the craft pitches down, or if just the top airbrake is deployed it pitches up, as expected;

Note the drag lines from the airbrakes. 

Then after returning to level flight (1) the underside rear gears were deployed, and while there was a slight reduction in speed it had no impact on the craft's pitch (2) and the same was true when just the upper rear gears were deployed (3).

-1
-2
-3

Unlike the airbrakes the gears do not alter the craft's pitch (and don't display any drag lines), but they do slow the craft down.

So to summarize; Gears do add drag when they are deployed, but they don't add "drag" when they are deployed.  

To summarize the summary; It appears that they add a different kind of drag to the other parts and this drag is applied symmetrically (at least on one plane, pun not intended).  

To summarize the summary of the summary; 
All(?) other parts ie airbrakes add drag centered around the part ("real-drag") but the gears add a drag centered around the whole craft ("fake-drag").

I can see why they've done it like this, if gears added "real-drag" then aircraft would have a tendency to nose down when you deployed the gears and I guess they felt that would be difficult for new players.  I think that's a pity as it wouldn't take a much to add a flap or top mounted airbrake that you could deploy to counter that pitch as you come into land.

 

TLDS (too long didn't science): Lowered gears do have an impact on a craft's speed, but it's not implemented in the same way as drag from other parts. "drag" from gears is applied symmetrically around the craft so lowering gears (typically found on just the underside) doesn't cause the craft to pitch down. Gears also do not display any drag lines as their "fake-drag" must be applied via a different mechanism to the "real-drag" from other parts.

[Warzouz]

21 hours ago, katateochi said:

IIRC the concept of physicsless parts has been completely taken out.

...

Not really.

Before 1.0, physicless parts had no mass nor drag.

In 1.0, physicless parts ADD their mass and drag to their parent part. Regular parts are handled on their own. So when you have a physicless part, you can stick it anywhere on the parent part, even without any symmetry. Usually physicless part is nice to have on light parts (lights, small science equipment, ladders, batteries...).

Landing struts aren't phyicless parts, so you have to balance them with symmetry of equivalent mass part.

I agree the "deploy" status of a landing strut doesn' seems to matter though.

[Vegetal]

Wait guys. I once tested this subject on a very light, very stable aircraft, flying level with constant speed.

What I noticed:

1- They generate more drag when deployed, but by a small amount - not enough to make a huge difference in your flight, going SSTO with gear down without noticing is indeed possible.

2- The drag is not applied to parent part, but on the gear itself. The little plane pitched down noticeably when I deployed gears.

None of those effects made a huge difference though, that's why people still think gears are physics-less, because it sure seems so. Which is really unfortunate.

Edit: Nothing of this shows on the aerodynamic overlay. That thing is NOT reliable by the way, I always say that.

Edited January 22, 2016 by Vegetal

[_Astra_]

katateochi, what a nice experiment ! =)

 

Really impressed.

 

So an enclosed landing gear is not taken into account, right ?

[Vegetal]

My results were different. They did indeed pitch the craft when deployed.

And it's not a different mechanism, it *is* drag. If you switch aero information on the debug menu, you will be able to see the numbers by right clicking on the part. IIRC, the deployed gear generates double the drag than when stowed.

Again: The aero overlay (F12) is not reliable.

Edit: Katateochi - drag is applied to the landing gear base, not the wheels, that's probably the cause you didn't notice any pitch tendency, they are too close to the center of your airplane.

Edited January 23, 2016 by Vegetal

[Rhomphaia]

1 hour ago, Vegetal said:

My results were different. They did indeed pitch the craft when deployed.

And it's not a different mechanism, it *is* drag. If you switch aero information on the debug menu, you will be able to see the numbers by right clicking on the part. IIRC, the deployed gear generates double the drag than when stowed.

Again: The aero overlay (F12) is not reliable.

Edit: Katateochi - drag is applied to the landing gear base, not the wheels, that's probably the cause you didn't notice any pitch tendency, they are too close to the center of your airplane.

It will depend on which Gear you test, the LY-50 and LY-99 are not Physics-less parts ( the PhysicsSignificance = 1 line has been commented out)  the LY-10 is physics-less so the drag is applied to the parent part, (it will still increase when the gear is lowered)

 

Confirmed by experiment.

Edited January 23, 2016 by Rhomphaia

[Vegetal]

Such names confuse me, I always forget them. I tested only with the smallest retractable landing gear. I could test with the bigger ones...