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Cargo Airdrops with the MK3


IllicitMedic
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I've been focusing very heavily lately on exploring Kerbin itself and am doing so with atmospheric flight. Anyway, I've had great success so far driving rovers into the cargo bay of the MK3 then letting them roll out down the ramp over my drop sites. However, I'd like to setup a science lab on the poles.

I have been testing and practicing dropping things off the coast of KSC for the last 2 days and cannot get anything other than pods to not explode upon exiting the cargo bay down the ramp. I'm not sure whats going on, I've dropped the science lab going as slow as 120 m/s and the second it makes contact with the air it blows up but the landing legs and parachute survive. I've tried all different kinds of chutes hell even no chutes to see if they were the culprit and even if its just the lab it explodes as soon as it leaves the bay. Any ideas on how to get this to work? I'll be using the same method to resupply the base with life support items should I ever get this thing working.

On a side note I've already flown and dropped the rover that will be used up there and it was a success.

...and yes, I know I could launch it on a rocket but that's not the point.

P.S. Also, its not a collision with the hull causing the explosion, I've also tried setting the decoupler to 0 and let it fall onto the floor and slide out and it was fine until it left the plane.

P.S.S. I've also tried encasing it in a faring and even still....as soon as it leaves the aircraft it explodes, even inside the fairing yet the faring and everything attached to the lab survives.

So as you can see I've tried almost everything I can think of and it won't work. ANY IDEAS?!?!?!

Thanks!

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Just to be sure you know, pressing Function-3 after a collision shows you what KSP considers to have collided into what.  I think you will see "M-P-Lab collided into Mk3 Cargo Ramp" but often pressing F3 clears up mysteries.

The science lab has a lot of drag relative to its mass.  With KSPs simplified aerodynamics, when that lab is decoupled laying loose in the cargo bay, as soon as the bay doors are open even a crack, it feels the full force of the wind as if it was outside the aircraft, and that gets it moving pretty quickly.   Once it starts sliding down the ramp, its velocity relative to the aircraft reaches 6-10m/s pretty quickly, and apparently skidding along the ramp above the 'impact tolerance' velocity causes destruction just as badly as hitting it squarely.

I had a moderate success rate https://imgur.com/a/KnW2Hf0 (craft file).  Slowing the aircraft below 80m/s and opening the bay wide worked; so did decoupling the lab then slowly opening the cargo bay.  

(KSP versions 1.4 -- 1.5.1 do have a bug where crossing the joint from an Mk3 bay to an Mk3 ramp faster than the 'impact tolerance' velocity can destroy parts, even though there is no wall on the connecting ends of these bays.  But, when I tried the cargo plane in 1.5.1 that didn't cause any trouble; avoiding damage from sliding along the bay walls forced me to go slow enough.)

It is easier to drop fragile things out the belly of an aircraft, with Mk3 bay with doors opening downward, because the parts are clear of the aircraft before they have had time to build up much relative speed.

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It may be a bug--possibly with the sudden impact with the air not registering correctly--but it may also be that something attached to the lab flexes and causes impact damage once exposed to air.  I can't guarantee that it's the problem, so in lieu of a proper solution, I suggest three things to test:  one, try reducing speed to under 6 m/s (the impact tolerance of the lab) before you release the payload.  That means stalling the plane, so be careful that you don't crash into the lab when you let it out.  Two, try increasing the crashTolerance value in LargeCrewedLab.cfg in the Gamedata\Squad\Parts directory.  See whether 50 works.  Three, put a probe core on the lab if you don't have one already and set it as the root part so that when you decouple, the focus stays with the lab and not with the plane.  That way, the destruction--if the lab is destroyed--will appear on the F3 report.

Another possibility to consider is that your lab is bathing in engine exhaust from the plane when it decouples, which overheats it to failure.  Given the thermal tolerance, it's worth investigating.  I don't know whether you would see temperature bars on decoupled parts--my guess is no--so that would be one for the probe core test.  You may consider trading the ramp-style cargo bay for an inverted standard bay such that the doors open on the belly.  I don't know what that will do to the lift characteristics when you open it but dropping the lab straight out the bottom of your plane will help avoid problems with the engine exhaust, if there are any.

Edited by Zhetaan
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2 hours ago, Zhetaan said:

it may also be that something attached to the lab flexes and causes impact damage once exposed to air

As stated I've tried dropping nothing but the lab with the same result.
 

2 hours ago, Zhetaan said:

try reducing speed to under 6 m/s (the impact tolerance of the lab) before you release the payload

As stated also, I've also tried this with the same result yet pod's and some other parts with the same tolerance or less exit the aircraft just fine.

2 hours ago, Zhetaan said:

Another possibility to consider is that your lab is bathing in engine exhaust from the plane

Not possible with my engine configuration.
 

2 hours ago, Zhetaan said:

try increasing the crashTolerance value in LargeCrewedLab.cfg in the Gamedata\Squad\Parts directory.

Prefer not to quote "cheat" other parts of similar stats work.

2 hours ago, Zhetaan said:

put a probe core on the lab if you don't have one already and set it as the root part so that when you decouple, the focus stays with the lab and not with the plane.  That way, the destruction--if the lab is destroyed--will appear on the F3 report.

Will try this later today when I play again, never thought about it thanks.

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4 hours ago, IllicitMedic said:

As stated also, I've also tried this with the same result

You said 120 m/s. He said six m/s.

And how do you get a bare lab out of the bay without wheels attached?

Also isn't a 2.5m part way too big to get down the ramp? The ramp is only a couple meters wide at most. If it's too wide for the ramp, then of course it's gonna blow. Or do you not mean the MPL when you say "lab"?

If it were me, I'd be using an interstage fairing on the cargo plane, and forget about the ramp.

 

 

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9 hours ago, OHara said:

so did decoupling the lab then slowly opening the cargo bay.

Why did I not think of that? Lol, I have tried to decouple then open but never a slow open! Success! 5/5 so far during tests between 120-180m/s at 1200m altitude. I start at 1 and slowly open to 52% where she exits the aircraft intact!

Thanks everyone!

21 hours ago, bewing said:

And how do you get a bare lab out of the bay without wheels attached?

Also isn't a 2.5m part way too big to get down the ramp? The ramp is only a couple meters wide at most. If it's too wide for the ramp, then of course it's gonna blow. Or do you not mean the MPL when you say "lab"?

It slides out if you are pitched up a few degrees. 2.5m round its almost a perfect fit.

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Edited by IllicitMedic
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On ‎12‎/‎5‎/‎2018 at 5:49 AM, IllicitMedic said:

So as you can see I've tried almost everything I can think of and it won't work. ANY IDEAS?!?!?!

It worked fine in 1.3. 

With the 1.4 upgrade a new Unity engine came into play and the Mk3 ramp became too destructive to use for airdrops (among other things).  I recorded this mission in 1.3 a little over a year ago, and have not been able to reproduce it without catastrophic explosions since...  Some will claim it's by design.  For me, the Kerbal Airborne Corps is permanently grounded.  I don't expect it will be fixed.  I don't expect to do these missions anymore.  I gave up.

 

Edited by XLjedi
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