SSTO not getting fast enough

[chris-kerbal]

Hi there,

I am trying to get a SSTO build working, however I can't figure out how it will accelerate enough to get to orbit. I followed @Matt Lowne build on the beautiful SSTO, however my build will never get fast enough. It stops around 300m/s. So I tried his craft file from the video and it is even worse. ;-)

So now I am stuck on how to go on? Adding engines only gives small increments on the max speed and probably would need 10 more rapiers to hit ~400m/s.

Is it something with the aerodynamics? Is there a way to analyse that?

I put my craft on pastebin: https://pastebin.com/WDympGyR

Playing on 1.10.1 with Tantares, Habtech2, KIS, Kerbal Engineer, Docking Port alignment indicator.

[Wobbly Av8r]

With R.A.P.I.E.R.s accelerating in the low, thick atmosphere is key - once you get up to speed, they produce a great deal more thrust.

Immediately after takeoff, stay very low and level (any climb will reduce your ability to get fast enough) while accelerating - once you get past Mach 1 (~330 m/s down low) you will start generating more thrust - they put out the max output between Mach 3-4 (3.75?) Somewhere around 19,000 m you'll want to switch them over to Closed Cycle and complete the climb into LKO.

YMMV, good luck!

[ I downloaded and flew your SSTO - had no problem accelerating to 700+ m/s before pitching up to ~15 deg and continuing to accelerate. If you activate one of the RAPIERs PAW, switch over to Closed Cyble when you thrust = 179.5 kN... ]

Edited September 9, 2020 by Wobbly Av8r
[After test flight of X-AC-6]

[chris-kerbal]

16 minutes ago, Wobbly Av8r said:

With R.A.P.I.E.R.s accelerating in the low, thick atmosphere is key - once you get up to speed, they produce a great deal more thrust.

Immediately after takeoff, stay very low and level (any climb will reduce your ability to get fast enough) while accelerating - once you get past Mach 1 (~330 m/s down low) you will start generating more thrust - they put out the max output between Mach 3-4 (3.75?) Somewhere around 19,000 m you'll want to switch them over to Closed Cycle and complete the climb into LKO.

YMMV, good luck!

That is exactly what I try to do.... i basically do not climb at all and just fly straight a few hundred meters above sea level, however speed maxes out before reaching the magical Mach 1.
I tried adding more air ducts, however that did not change anything.

[Wobbly Av8r]

Not sure what to tell you, @chris-kerbal. I just literally took off, stayed about 200-300m above the water at full thrust, accelerated straight-away to over 700 m/s and climbed until about 16,000 m, used your "0" Action group to switch to Closed Cycle, but ran out of fuel before being able to achieve LKO, FWIW. The .craft I flew had an error but what loaded flew the low profile no problem...

Do you have like a MechJeb set to "limit Q" to some lower value? Even when the autopilot is not engaged, it can mess with your throttle setting...

Are you familiar with monitoring the performance of the RAPIERs using the PAW menu?

Edited September 9, 2020 by Wobbly Av8r

[chris-kerbal]

Huh, so you used my plane I put on pastebin? Weird, but would explain, why Matt's craft wouldn't fly in my setting as well.

I don't have MechJeb. What is limit Q (can I see that somewhere) and the PAW Menu?

[Wobbly Av8r]

Right-click on one of the RAPIERs and watch the thrust in kN, about 4 or 5 lines down from the top of the Parts Action Window. When you takeoff, you press Z for full thrust and then the space bar (activating the stage). You should see the thrust continually increase to ~400 kN before pulling it up to 15-20 deg to get out of Kerbin's atmosphere. When the PAW indicates a gradual decrease to 180 kN, switch modes (the 180 kN is what you get from closed cycle mode, otherwise it will continue to decrease below 180)

39 minutes ago, chris-kerbal said:

Huh, so you used my plane I put on pastebin? Weird, but would explain, why Matt's craft wouldn't fly in my setting as well.

I don't have MechJeb. What is limit Q (can I see that somewhere) and the PAW Menu?

Yes - the X-AC-6, correct?

Look around the PAW to see what is limiting your thrust, because the intakes and design in general did not have enough drag to slow it down. I did NOT light the LV-N engine at all.

The "limit Q" is one of the settings of MechJeb autopilot and automatically throttles down engines to prevent high dynamic pressure (whatever you've chosen, but defaults to just below Mach 1), but don't worry if you don't have it installed...)

Edited September 9, 2020 by Wobbly Av8r

[chris-kerbal]

Yes, the X-AC-6. I reduced the fuel, to check if it is a weight issue, however it only makes a marginal difference.

Ah, OK, the right click menu. Know that ;-) I am actually not completely new to KSP, but apparently missing some lingo...

So I stayed below 5° climb angle, so didn't climb above 500m before maxing out on speed. The engine maxes out at 210kN thrust using 1.33U of fuel on full throttle.

This is really weird....

[Wobbly Av8r]

Yeah - you've got something restricting your thrust output - I'll post "nominal values" for the PAW menu here in a few minutes...

I got 210 kN right at Mach 1. Something, either a mod or your settings is preventing you from exceeding Mach 1. If you stay level, you should have no problem continuing to accelerate right past 330 m/s. Stay as low as possible - you did retract your landing gear, right? [I was still able to exceed Mach 1 with the gear down, so scratch that...  The flow should get up to over 2.4 or so if I recall correctly ]

Edited September 9, 2020 by Wobbly Av8r

[chris-kerbal]

But that must be something different than the craft, as you don't have the limitation?

Yeah, the gear was up (but also it does not limit too much).

But what could limit this?

In my Physics Menu, I have the following:
Aero:
- First 3 unchecked
- Force Display Scale 0.5
- Global Lift Multiplyer 0.036
- Lift/Drag Multiplier 0.015
- Body Lift Multiplier 18.000

Drag:
- Apply drag checked
- Replace drag cubes... unchecked
- Apply Drag as acc... unchecked
- Apply Drag To Non.... checked
- Apply Non-Physical Part... checked
- Global Drag Multiplier 8.000
- Drag Cube Multiplier 0.100
- Angular Drag Multiplier 2.000

Edited September 9, 2020 by chris-kerbal

[Wobbly Av8r]

Here's your SSTO at 800 m/s and numbers (intake, RAPIER)

[chris-kerbal]

Lovely... that is how it should be. (I edited my post before and added my physics details) Below a screenshot of the vessel at max speed

https://imgur.com/a/uWg2Qxb

(Forum just won't let me post it as an image?)

[Wobbly Av8r]

Re: Pasting image... use the BBC Code, but remove the "img" "/img" coding (including brackets] is what I've found works. Should be a .jpg file, not a link to address at imgur.

I can only offer a couple of comments: First, what are the two mods I see above KER on the right? If one of them is FAR, that could be part of the issue. Second, you're at 1000 m even though you don't have a lot of pitch, it really, really makes a difference to keep it low (you see 300 m in my image), the lower the better until you get up around 700+ m/s. Also note that I am at 300 m at 1:08 Mission Elapsed Time, i.e. keep low, low, low until you get that speed - and therefore thrust - higher.

Edited September 9, 2020 by Wobbly Av8r

[Wobbly Av8r]

Again, FWIW, your physics settings match my settings (aka Default) perfectly.

Edited September 9, 2020 by Wobbly Av8r

[chris-kerbal]

The flight below 300m is just the same. Tried it just now in a new sandbox game.
So it is not the craft, not the game session, will now try the mods one by one... (The two you see there, are the Docking Port alignment indicator and the Transfer window planner)

Thanks so far for your help! Really appreciate you taking the time to check this.

[JadeOfMaar]

@chris-kerbal I've tested this craft and found that its drag problem is in the convert-O-Tron. The center of that part is beyond the shielding radius of the forward cargo bay, or behind the collider of the part attached to an outer node of the bay so it's not being aero shielded. (It's clipping entirely through the forward docking port even.)

When you fix it:

Interestingly, I had no problem getting past Mach 1 with the drag problem. I know to fly low with spaceplanes that have certain engines like RAPIER.

Edited September 9, 2020 by JadeOfMaar

[chris-kerbal]

30 minutes ago, JadeOfMaar said:

@chris-kerbal I've tested this craft and found that its drag problem is in the convert-O-Tron. The center of that part is beyond the shielding radius of the forward cargo bay, or behind the collider of the part attached to an outer node of the bay so it's not being aero shielded. (It's clipping entirely through the forward docking port even.)

@JadeOfMaar Thanks for looking into this! i removed the convert-o-tron from my build. It does not change anything.
As you can already get to Mach 1, it seems that you are as well not affected. Having the convert-o-tron not clipping might improve it in higher speeds, however I am not even on the Mach 1 level. :-(

Edited September 9, 2020 by chris-kerbal
mixed docking port with convert-o-tron

[Wobbly Av8r]

Yeah, I get the high drag on the Covert-O-Tron as well, but it doesn't seem to hinder the general performance... things that make you go "Huh?"

Well, there's always the ol' verify the integrity of the files (Steam has a convenient way to do that, not sure what to do with other platforms) but nothing else seems out of place. Wish I could be more help, but I'll just have to keep poking around...

[Wobbly Av8r]

Don't know if it helps, but the pastebin file was a .txt file that I simply saved as a .craft file to use; it did so with the following two errors - I wonder if either one might weigh in on the issue:

Vessel X-AC-6 is missing part module ModuleB9PropagateCopyEvents

Vessel X-AC-6 is missing part module ModuleDockingNodeNamed

Neither error seemed to have any negative effect on the trial runs.

[chris-kerbal]

So I just finished testing all Mods and of course it was the last one to add. Habtech2 or one of the bundled mods is the culprit. Will check tomorrow these parts in detail. As soon as I added it, the same behaviour comes up. Removing it and it is gone.

Sorry for wasting your time with a broken mod. Again thanks a lot for your help and time!

BTW: How did you get readings per part on the drag? To see that the convert-o-tron is placed badly?

[Wobbly Av8r]

In the Debug Menu (where you accessed the physics values) under Physics>Aero is an option similar to Display Aero Data in Action Menus - then when you select the part with Right-Click (PAW) it will be under the Debug text at the bottom. Glad you found out what it was - more than happy to help flatten the KSP curve when I can...

Edited September 10, 2020 by Wobbly Av8r

[hemeac]

7 hours ago, chris-kerbal said:

Hi there,

I am trying to get a SSTO build working, however I can't figure out how it will accelerate enough to get to orbit. I followed @Matt Lowne build on the beautiful SSTO, however my build will never get fast enough. It stops around 300m/s. So I tried his craft file from the video and it is even worse. ;-)

So now I am stuck on how to go on? Adding engines only gives small increments on the max speed and probably would need 10 more rapiers to hit ~400m/s.

Is it something with the aerodynamics? Is there a way to analyse that?

I put my craft on pastebin: https://pastebin.com/WDympGyR

Playing on 1.10.1 with Tantares, Habtech2, KIS, Kerbal Engineer, Docking Port alignment indicator.

Have you tried the same craft with the same combination of mods in 1.9.1?  Am also curious if you had removed the solar truss from Habtech2 in your 1.10.1 install. A lot of people in the Habtech2 thread found that the game would not load with it installed.  I don't know how that would impact your craft file, but I can't see anything in the Habtech 2 mod or the bundled mods that should impact your craft to that degree.

[JadeOfMaar]

@hemeac Evidently HabTech2 has a broken plugin which is somehow causing his plane (even with the drag cube problem I spotted, fixed) to be unable to pass Mach 1. As for the solar truss this happens to any part that has ModuleDeployableSolarPanel{} + mesh animation + procedural drag cubes. Define a DRAG_CUBE{} with a single/fixed state (and delete any such node that defines procedural or multiple states) in the part config and KSP will stop choking on it.

But right now, as someone else pointed out, either the KSP install is corrupted or this is the effect of an incompatible plugin (whether in HabTech2 or its associated mods).

[hemeac]

1 hour ago, JadeOfMaar said:

@hemeac Evidently HabTech2 has a broken plugin which is somehow causing his plane (even with the drag cube problem I spotted, fixed) to be unable to pass Mach 1. As for the solar truss this happens to any part that has ModuleDeployableSolarPanel{} + mesh animation + procedural drag cubes. Define a DRAG_CUBE{} with a single/fixed state (and delete any such node that defines procedural or multiple states) in the part config and KSP will stop choking on it.

But right now, as someone else pointed out, either the KSP install is corrupted or this is the effect of an incompatible plugin (whether in HabTech2 or its associated mods).

I did a quick check and was able to reproduce the issue in 1.10.1 by using only the latest versions mods listed as well as the most updated versions of any required dependencies.  It definitely occurs only after the inclusion of something within Benjee10_sharedAssets and/or HabTech2 folder (had to remove the pieces that would not load within 1.10.1).  It seems interesting in that there are no dll's within those folders, they are only models, textures and config files.  I don't see anything in the logs that suggest that the Habtech configs are patching any parts that are used in the craft.

The associated dependencies for Habtech are B9PS and the Community Resource Pack,

Edited September 10, 2020 by hemeac

[chris-kerbal]

7 hours ago, hemeac said:

Have you tried the same craft with the same combination of mods in 1.9.1?  Am also curious if you had removed the solar truss from Habtech2 in your 1.10.1 install. A lot of people in the Habtech2 thread found that the game would not load with it installed.  I don't know how that would impact your craft file, but I can't see anything in the Habtech 2 mod or the bundled mods that should impact your craft to that degree.

Just for completeness: Yes, I removed the duo solar truss, otherwise it won't start. I haven't tried that combination in 1.9.1. My tests yesterday were focussed on 1.10.1

7 hours ago, JadeOfMaar said:

@hemeac Evidently HabTech2 has a broken plugin which is somehow causing his plane (even with the drag cube problem I spotted, fixed) to be unable to pass Mach 1. As for the solar truss this happens to any part that has ModuleDeployableSolarPanel{} + mesh animation + procedural drag cubes. Define a DRAG_CUBE{} with a single/fixed state (and delete any such node that defines procedural or multiple states) in the part config and KSP will stop choking on it.

But right now, as someone else pointed out, either the KSP install is corrupted or this is the effect of an incompatible plugin (whether in HabTech2 or its associated mods).

Again for completeness: The install was not corrupted, I did the tests on a completely new install.

5 hours ago, hemeac said:

I did a quick check and was able to reproduce the issue in 1.10.1 by using only the latest versions mods listed as well as the most updated versions of any required dependencies.  It definitely occurs only after the inclusion of something within Benjee10_sharedAssets and/or HabTech2 folder (had to remove the pieces that would not load within 1.10.1).  It seems interesting in that there are no dll's within those folders, they are only models, textures and config files.  I don't see anything in the logs that suggest that the Habtech configs are patching any parts that are used in the craft.

The associated dependencies for Habtech are B9PS and the Community Resource Pack,

Thanks for confirming and detailing. Yesterday I was only able to test with updated B9PS and Community Resource Pack. So yes it seems to be something within the HabTech2 stuff itself. The sheer availability of parts configured by the mod seems to cause the issue, as I tested everything in a clean game without any builds other than the craft itself.

Funny enough that the game seems to run well otherwise, just SSTOs are a nightmare. Despite the craft being titled X-AC-6. This was not my 6th attempt, more desperation to copy something that apparently was working for others.... :-D

Will mark this thread close and continue in the habtech2 thread. Thanks again to everyone for your kind help!