Super large cargo plane question. COM position.

[Arugela]

I have a large cargo plane I'm finishing. It's designed to take 1000 tons to orbit and hopefully far beyond.(Especially when/if I fit ground and asteroid mining gear in it.) I have it set up as best I can to minimize forward movement of the COM at full. I'm have it basically finished and I use a tri wing setup allowing me to easily move the wing tips up or down to make it slightly above or below the COM. It's normally centered/inline, but will it help to have it higher or lower and not inline? It's very laggy to test as it is 1k parts atm. So, I'm not sure. I'm trying to achieve earlier runway takeoff(if even possible given the weight to wing surface), and anything that makes the wings fundamentally stronger for rentry and higher speed adjustment of the nose. Do either higher or lower COM achieve any of that logically? I'm not sure which is better for empty/near empty landings either. That and my lack of break power are about my only concern at this point. IF I decided to add drones and increase the parts count I will also potentially add a lot more wheels to try to save DV by adding more litho-breaking headroom via higher speed landing.

So, far high COL seems to help with keeping the plane straight on takeoff at max weight. Or I think it does. I can't tell if I'm imagining it or not. It's very hard to tell in super slow motion. 8)

Craft:

https://www.dropbox.com/s/36bn94l5rbe5jzd/KB-52 1_5_1_2335 x100.craft?dl=0 (updated)

New Panther version with full fuel and cargo. (632 Parts, 2868 tons, 581.6 Wing surface)

https://www.dropbox.com/s/bgghfjyi0thfeub/KB-52 1_5_1_2335 x100 PE.craft?dl=0

Parts: 1000

Weight: 1200tons empty; 3500tons max full fuel/cargo(3600 absolute max when/if drones added)

Fuel: 88,000oxidizer; 172,000LiquidFuel(100,000Dedicated); 500tons LF; 800tons LF+OX

Known Relative Wing Area: 500+30+18.56+14+12.32+6.72+8.22+1.8+1.5=593.12

Wings surfaces: 100xBigSDelta; 100xMK2 bicoupler; 20xMK2RocketFuelFuselage; 16xBigSElevon2; 16xBigSElevon1; 16xElevon3; 6xSweptWings; 6xElevon2; 6xElevon1

Other lift bearing surfaces: 32xMK3toMK2Adapter; 18xMK3CargoRamp; 14xMK3CargoCRG-100; 7xMK3LiquidFuelFuselageLong; 4xMK3CargoCRG-50; 4xMK3RocketFuelFuselageLong

Potential Drag producing parts: 100xShockConeIntake; 18xLY-99ExtraLargeLandingGear

Internals: 1xRC-L01RemoteGuidanceUnit; 1xZ-4KRechargeableBatteryBank; 8xPB-NUKRadioisotopeThermoelectricGenerator; 17xAdvancedReactionWheelModuel,Large; 18xClamp-O-TronDockingPortSr.

Cargo: 44xLargeHoldingTank; 14xRockomaxX200-32FuelTank; 14xEAS-4StrutConnector

Engines: 100xLV-N"Nerv"AtomicRocketMotor; 100xT-1TeroidalAerospike"Dart"LiquidfuelEngine; 100xCR-7R.A.P.I.E.REngine; 100xJ-X4"Whiplash"TurboRamjetEngine

These pictures are in the high COL positions. The wing tips of the main and back winglets can be adjusted to make it High COL(current), Center(inline), or low COL. The maximum position easily achieved is only one square(the square on the side of the ball) above or below the COM approximately.

Pics: (At full cargo and fuel position)

More Pics:

Hint. If anyone actually flies this. Unless you really want to, don't fly over like 1900m/s before 19k or you loose rapiers and whiplashes and have to use more expensive engines. Sadly air intakes stop working around there. Unless you can get up to where nukes fly on their own. So, either slower or faster. I'm not sure what altitude nukes can maintain velocity in this newer design. Or I could be wrong and this is optimal to maintain speed into orbit. No idea.

Edited November 22, 2018 by Arugela

[swjr-swis]

It's very hard, near impossible really, to give any meaningful suggestions about a craft based on just a single picture from a single orthogonal angle. You add a lot of text, but it adds more questions than clarification.

One thing I notice immediately though: you're using a diverse spread of angles of incidence on your wing sections, which will basically cancel out any beneficial lift and leave just the detrimental drag. That's not going to help you get this craft to orbit - it's like flying the whole time with giant airbrakes/spoilers deployed.

As best as I can tell from your text, you're wondering which is better: to have the CoL higher, lower, or at the same height as the CoM. It won't make a difference for how fast you can take off - that's purely about lift/weight ratio. It won't affect wing strength either - that will depend on attachment method and (auto)strutting. I can't figure out what "higher speed adjustment of the nose" means, so I can't say if it would make any difference for that either. If you mean a more reactive plane to control inputs - that depends on your control surfaces and how far away from the CoM they are (your CoL and CoM are already relatively close, that won't need much change).

The height of the CoL relative to CoM mostly affects flight stability and behaviour at high angles of attack or when banking. In my own experience, having it slightly above CoM, combined with a bit of camber, tends to help with stability during reentry. Theoretically the aero forces would then keep the craft heading belly-first, or trying to get back into that attitude if disturbed. But it's a delicate combination of factors that can't really be taken individually only - sometimes it adds more instability instead. It highly depends on the specific craft.

A few more screenshots from other angles would be useful. Ideally, a craft file. Help people understand the craft, so they can help you.

[Arugela]

I added a craft file. I'll add more pics after I get done flying it. It's almost to orbit. By adjusting the nose I meant readjusting it during flight to lower angle of attack or to pull up to gain altitude. It's fairly strong as is but I wasn't sure if making a lower or higher COL helped with the strength of wings. I'm assuming from what you said I need a higher COL as it needs the most help atm with re-entries.

Added some pics from flight. Not sure which angles help explain the craft.

Edited November 20, 2018 by Arugela

[swjr-swis]

23 minutes ago, Arugela said:

I added a craft file.

That's not a moon...

I'm at a loss for words. It's a thing alright. Going for some records?

I notice that the screenshot angle is deceiving: there is actually no angle of incidence on those wings, as far as I can tell at all. The lower wings are just cambered progressively up to bring the tips together. So you can ignore my previous remark about that.

Angle of incidence would help, a lot, with getting this craft to take off faster, and to get to orbit with more dV left (or less fuel/engines required). It's the main suggestion I can make, the thing that would make most difference in the performance of this craft.

Second suggestion: the engine nacelles on the main body are too clipped into the fuselage. Those engines are either not providing any thrust at all, or too little to justify them. KSP penalizes blocking the exhaust path of engines with a severe loss of thrust. Pull them out so their exhaust path is clear, it will make a ton of difference. Or... just delete them entirely. Like this, they're almost just dead weight.

Curious to see how this develops.

[Arugela]

I've been confused if partial blocking was effecting engines or not. I was assuming it was not and so ignoreing that. I think several people have told me it no longer partially blocks but only all or nothing. There seems to be some confusion on this. I still can't tell from flight.

I couldn't think how to test this as partial and full would be hard to differentiate.

The point of the craft is to get 1k tons to orbit the to minimus to mine and go as many places as possible. I have a smaller version with only 64 engine pods that might get to orbit. But not to minimus.

The craft is a personal milestone thing. Seeing how far I can take the 1k tons of cargo. Without using the cargo fuel that is. Although with a mining cargo plane that is a bit stupid. But it probably helps if the cargo doesn't posses large amounts of fuel.

I'm actually a little confused if the dart and nerv aren't interfering with each other or the burn time indicator isn't messed up. I'm going to have to use the cheats and take it to orbit to test. The dart is technically in one half space. It might be being effected somehow. Could be something else entirely though.

Edit: NVM, I forgot you could see the total thrust in the aerogui. Assuming it's always accurate...

According to the aerogui it's not loosing thrust in it's current configuration. So, hopefully that is true.

Here is an empty version with updated aerodynamics. Hopefully it has less distance between the full weight and empty position. It flies very nicely regardless. Bit hard to stop though still.

Craft: https://www.dropbox.com/s/pk4xuwr4aeqgqnl/KB-52 1_5_1_2335 x100 empty.craft?dl=0

Edit: Yep, much better com on full. I will update the original craft file when I test fly it.(updated, but not test flown.)

I think the one issue this has is that I put too much LF+OX and not the normal larger or equal ammount of LF I do on my planes with this engine setup.

Edited November 20, 2018 by Arugela

[bewing]

11 hours ago, Arugela said:

I couldn't think how to test this as partial and full would be hard to differentiate.

On the runway, just activate the engines in question (by clicking the button in their context menu) and then go to full thrust. If nothing happens, then they are occluded.

 

[Arugela]

I was more confused if there is partial thrust blockage and how to test it.

Either way. I removed all the engines and added 64 panthers, 8 nukes, 28 rapiers. It's now 700 parts and 2880 tones with a minimum weight of 580 tons(1580 tons with cargo) instead of 1200(2200 tons with cargo). I'm hoping to slowly get it into orbit and get it to laythe. If not I'll add mining drones to let it skip to destinations. I was able to fly my 100 rapiers up to 400kn of thrust. I'm hoping to push them to some lower altitude high thrust and get out of orbit. The Jpanthers are to get it off the runway and aimed up in time. I'll have to see. If it works it will have some very nice high isp cruising engines for laythe.

I think afterwords I'll make a smaller 500 ton cargo version(if I can get this to orbit) that halves everything and reduces the parts count to around 350 so it's manageable. It will be a nearly identical half stated version with half weight, half engines, etc. Should be easier to fly and probably lack the bad lag.

Edited November 20, 2018 by Arugela

[Guest]

You, sir, are entirely insane.

I like it. 

Now make it a flatbed or underslung design, so you can loft bigger cargoes than what fit into those Mk3 bays.  

[bewing]

15 hours ago, Arugela said:

I was more confused if there is partial thrust blockage and how to test it.

There is no such thing as partial thrust blockage. Each engine is checked individually and if there is anything directly behind the engine, then that engine's thrust gets exactly counterbalanced by an opposing force placed on the part behind the engine.

You will not see the thrust blockage in the context menu. All the aero readouts show full thrust, but the thrust does not produce any motion. I have not loaded your plane, but I guarantee that many of your engines are just wasting your fuel and producing no net force on your plane.