Landing Gear Weight limits.

[Leszek]

I know that landing gear have a set limit for which is the max they can hold and land.  I think that it also matters if you land on the runway or out in the field somewhere.

I understand that for the basic fixed land gear the max tonnage was something like 5 tons.  (At least it was a few game version ago.) Hence I never use them because all of my basic science planes are heavier. 

But recently I overloaded the LY-10 gear and so now I was looking for a chart.  Imagine my surprise when I see that the Kerbal Wiki says the max limit is 7 tons.  I just landed my 17 ton plane just fine with them!  So the question is, does anyone know what the max weight is for these gear and for a bonus the practical effect of spring and damper strength?

[bewing]

7 tonnes per wheel. How many wheels does your plane have? And the number varies whenever a new Unity engine gets built into the game, which happened in 1.4.0. The numbers in the wiki are also rounded estimates, of course -- for the max workable landing weight without suffering damage in 90% of landings. So feel free to do a bunch of landing tests at higher and higher weights, and then update the wiki for the current version.

 

[Leszek]

Thanks for that update.  Just two for the main touchdown.  And I am still on 1.3 pending some mods and the completion of my current career.

 

Thanks though for the tip though.  If I double the landing gear so the pair both touch down at the same time I should be able to land heavier then.  Thanks.

[Gargamel]

12 hours ago, bewing said:

7 tonnes per wheel.

Is that per wheel, or per landing gear?   Ie, IIRC the small landing gear has two wheels, the medium has 4, etc.  So the small would hold 7 tons or 14 tons?  The medium 7 tons or 28 tons? Obviously, if it's per gear, that doesn't make sense.... so.....

[Leszek]

4 hours ago, Gargamel said:

Is that per wheel, or per landing gear?   Ie, IIRC the small landing gear has two wheels, the medium has 4, etc.  So the small would hold 7 tons or 14 tons?  The medium 7 tons or 28 tons? Obviously, if it's per gear, that doesn't make sense.... so.....

I don't know.  The wheels and the options for them are really quite poorly explained in the game.  If I increase the spring strength does that increase the load it can carry or how much it squats?  I don't seem to have a problem with squatting so what does it matter what I set them to?  AFAIK there is no in game way to see what the part can do without stress testing it.

[GoSlash27]

As of the last Unity update, it worked like this:

Spring rate is what it sounds like. A higher number for spring rate will compress less for a given load, and will oscillate at a higher frequency. Perversely, this means you can have too much landing gear and will have to reduce the spring rate under light loads.
The damper rate, OTOH, is the percentage of criticality. 0% is undamped; oscillations will carry on forever. 100% is critically damped; oscillations will be eliminated by the end of the first cycle. A typical rough terrain suspension is damped around 30%, whereas a 60% damping is used for a smooth surface. Going beyond 100% damping tends to make it difficult for the wheels to maintain contact with the ground, jacking down the suspension over rough surfaces.

 Since there was a new Unity update, I don't know if the same rules still apply.

Best,
-Slashy

 

[AeroGav]

I seldom economise weight on my space planes,  with the NERVs I like to carry, a few kg for the landing gear seems moot, though i focus hard on drag.

The limiting factor for me is elimination of tail strikes.   

Even the big S wing part has quite a short span - in order to get enough area,  I find myself mounting two back to back in a double diamond or attaching strakes.   The wing root therefore runs most of the length of the fuselage.      When you add 5 degrees of incidence,   this means the trailing edge is often the lowest point of the aircraft and it's right at the back of the plane too, raising the tailstrike risk.     You can't shift the whole wing upward because fuel is stored there and that results in centre of thrust issues/CoM shifting as the fuel burns off.

So,  even my smaller designs tend to use medium main landing gear legs.

40 tons gross weight on that thing - probably doesn't NEED mediums

https://kerbalx.com/AeroGav/MK1-Griffon-Deep-Space-Crew-Shuttle

[Perttijarla]

It took me some time to realize this: my plane weighs a bit over 5 tons, and there are three wheels each capable of taking about 5 tons, so theoretically the landing gear takes 15 tons. But that is only if all the wheels hit the ground simultaneously. If the plane weight is reduced to under 5 tons, you don't have to make a perfect landing. Any wheel can hit the ground first and not break.

By reducing the plane weight to just under 5 tons (by limiting fuel) I managed to make my first successful landing.

[AeroGav]

My latest ssto was one where i went for the lowest tech option for every part except the NERVS - so i used 5 small landing gears instead of 2 medium and 1 small.

I must say. it is very stable on the ground as  a result.    One wheel up front,  one pair just behind CoM a little way out from fuselage, and  the rearmost anti tail strike pair on the tips of the delta wing at the back.     Coming back from space empty, touchdown speed is 25 m/s  and it is immune from cartwheeling.   You can land just about anywhere.

[Laie]

On 4/7/2018 at 11:32 AM, Leszek said:

does anyone know what the max weight is for these gear

I'm afraid it's not that simple... landing gears are stressed more on bumps on the ground, or on touchdown. More/Stronger gear means you can survive a harder landing.

Something I noticed a sort while back (KSP1.4.3): When you roll out your plane, engage brakes, and the plane starts slipping/sliding/turning on the spot, this is the first sign of overstress. Not much of a problem, as usually as plane weighs much less by the time it lands. And some miner slippage also doesn't make takeoff from the runway impossible.

However, in my particular case the plane was expected to take off from Laythe under a full load, and the slippery variant couldn't go faster than 40-50m/s over even the most gentle fold in the ground. Increasing the number of wheels so it wouldn't slip raised the safe ground speed to 80m/s, adding any more wheels beyond that didn't improve matters anymore.