Space Plane Issues

[jbdenney]

I am running 1.9.1 KSP.

I am having no luck with Space Planes. I followed a tutorial done by the Great Manly Kerbal God and followed him Step by Step and part by part to build a neat looking Space Plane that looked like a SR-7 and could carry small payloads into orbit. I followed every step in the take off and flight and it just would not work. Where he would get better than 900 m/s at a 30 degree climb and I was lucky to get an maintain a 200 m/s speed at a 15 degree climb. I could never get above 19,000 to 25,000 meters before running out of fuel. I never even got close to anything orbital.

I get the distinct feeling the engines have been heavily nerfed.

I need a tutorial/hints on how I can build a SSTO plane with the current version (or near enough so it still works) that can carry payloads. Every thing I have found either will not carry a payload or is old and will no longer work.

 

Thanks.

[OHara]

Engines nerfed (made weaker) relative to when ?   and which engines?

Version 1.8.0  had a bug in atmospheric drag, making space-planes much much easier, until version 1.8.1 fixed it.  

Some engines from the Making History mod had unusually high Isp and thrust, until version 1.6.1 brought them closer to the rest of KSP (thread link)

I just tried an early-career space-plane that barely makes it to Minmus, in each of 1.3.1 and 1.91, and both versions left me with the same fuel in orbit.   Space-planes from kerbalx should work in the latest version of KSP, but technique is important because space-planes in general are challenging to get to orbit without running out of fuel.

[purpleivan]

@jbdenney this spaceplane, built for Laythe but tested at home first, will make Kerbin orbit in playing in 1.8.1 and has stock engines, so spaceplanes are still workable.

I'd suggest that either yours has too much drag or you're climbing too fast. You need to build up some speed where the atmosphere is dense to allow the engines to have a high enough intake of air at higher altitudes. However you say that you run out of fuel but 19-25,000m which is really low and sound like you just need more fuel.

It would help if you could post a pic of your spaceplane. In the hanger would be best so we can see the amount fuel it carries at launch.

My ascent angle started at about 15 degrees until my speed started to really pick up, then I pull up the nose gradually to around 25-30 degrees.

I.m by no means a spaceplane expert having only made 5 or 6, but this is advice I've read from others when hitting the same problem.

However it doesn't carry cargo (and has detachable landing gear), but it is quite small.

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions. 

[jbdenney]

Here is the Hanger View

Here is on the runway with Parts listed.

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Flight Screen shot. I am at a 15 degree climb at 211 m/s and my speed acceleration is had dropped to almost nothing and my thrust is starting to drop. In Scott Manley's tutorial, at this point with the same engines, he is pulling a 30 degree climb at over 300 m/s and gaining speed and thrust fast.

[Sky Vagrant]

Stay in level flight at about 300m or less until your speed is over 400m/s. Then pitch up. When the atmosphere bar goes to medium blue, pitch down to 15 degrees until your speed is over 1400m/s and your intakes start to whine (about 9m/s in your intake on that craft). Then hit the closed cycle (and close your intakes) and pitch up carefully to raise apoapsis out of the atmosphere.

[jbdenney]

in speed are you referring to Surface Speed or Orbit Speed. Surface speed - in level flight at 300m the best I can get is 350 m/s. If I climb to middle atmosphere and pitch down to -15 degrees the fastest I can get is about 500 M/s - if I pitch back up and light my rockets I can hit 1200 m/s but i reach an AP of about 75km with 8 seconds of fuel left at an actual altitude of 65Km. This is not enough to pull into a stable orbit.

 

I have no clue what I am doing wrong. It is acting like my two outboard whiplash ramjet engines are just not putting out the thrust. I have to kick in my inboard swivels too soon which does not leave me fuel for orbit.

[AHHans]

I just tried to re-create your plane. It's not exactly the same: my craft has only 42 parts, but weights 34.157 t fully fueled.

But I did manage to get it into orbit. My flight profile was about so:

1. Start climbing at ca. 20 deg nose-up.
2. Make sure that I keep accelerating. If it looks like I'll stop accelerating, then I lower the nose. (I tap the <F>-key, which temorarily disables SAS, which in turn causes the nose to lower.)
3. I made sure to get through the sound barrier well below 10km (ca. 7-9km), I needed to lower the nose to about 5 - 10 deg nose-up. You know that you got through the sound barrier when both the speed and the engine thrust increase while you are still climbing (at around 340 - 380 m/s).
4. Don't input pitch-commands anymore, the increasing speed and the curvature of Kerbin will raise the nose (well, relative to the surface) on its own.
5. When I stop accelerating with the whiplashs alone, then I activate the swivel engines. (At > 15km and > 900 m/s.)
6. When the thrust of the whiplashs drops below 50 kN (I keep a PAW of a whiplash open) I shut them off and close the air intakes. (I have both on the same action group.)
7. When the time-to-apoapsis gets above 1 min I switch to prograde-hold.
8. When the apoapsis reaches 80 km, I throttle down, coast to apoapsis and circularize.

One issue with your design is that you don't have any Lf-only tanks, but you do have a significant portion of the flight where you use the whiplashs in air-breathing mode. On the first try I had ca. 700 units of excess oxidizer after getting to orbit. So change some of the rocket-fuel tanks for Lf-only tanks.

P.S. In case you didn't know: both the whiplash and the RAPIER in air-breathing mode have a significant increase in their thrust at supersonic speeds. So once you get through the sound barrier the craft will accelerate a lot quicker.

Edited March 25, 2020 by AHHans

[fourfa]

If the video the OP is working from is the one I think it is, this would have been in v1.0.2.  So post-release and not the ancient souposphere.  But I wouldn't expect the speed/thrust curves on those old engines to be the same.  Drag and heating curves have changed as well.  The game has changed a lot between v1.0 and v1.9, so it's reasonable that there are large differences in performance in craft over that time.  It might even be accurate to say the engines have been 'nerfed' - there were lots of features of the early game that were wildly overpowered, and those jets at that time may have been one of them.

But yeah I see no reason the craft won't reach orbit; it looks broadly similar to planes I fly all the time.  You just need to try your own flight profile rather than copying from the five year old video

FWIW it's kind of unfortunate that people are still recommending Scott's videos all over the internet in 2020.  They're high quality and entertaining and engaging to be  sure, but so badly out of date.  There needs to be some modern equivalent, and I haven't really seen it.

edit - the last couple of posts have good ideas on flight profiles.  What @jbdenney describes in his last post sounds like some kind of crazy drag error, like parts are not node-attached correctly, or objects in the cargo bay are not shielded from drag properly.  Try turning on the aero debug overlay (F12) and see what parts have very long red backward-pointing arrows attached to them.

 

Edited March 25, 2020 by fourfa

[Sky Vagrant]

42 minutes ago, jbdenney said:

I have no clue what I am doing wrong. It is acting like my two outboard whiplash ramjet engines are just not putting out the thrust. I have to kick in my inboard swivels too soon which does not leave me fuel for orbit.

Sorry, thought you were using Rapiers - that’s what my advice was based on.

[jbdenney]

I hit the Debug mentioned above. I get quite a bit of drag from the central Fuselage Tanks and storage. The problem is that I don't know if the level I get is unusual.

The only "Node" I am aware of is the node in port in the cargo bay holding an independently maneuverable Grabber Unit in place. It does not extend outside of the cargo hold. I use the ALT (I dont know if that makes a difference - I saw that done in a tutorial) key when I attached the unit docking port port on the grabber to the port on the end of the cargo hold. I just placed/connected the fuselage tanks together in the SPH. Is there some other type of attachment that I am not aware of?

 

Also is there a difference between just placing the docking pots together as if I was docking and connecting them as a node?

[OHara]

I attached my build of that ship so you can compare drag.  5--10kN at the speed in our original screenshot, but that triples if you pitch outside the  prograde circle.

The  'nodes' are those green spheres you see when assembling, and yes the usual way of snapping parts together connects the nodes.   

It is possible to 'surface attach' tanks on the side of the fuselage (like you do with the two round tanks) and then move them in-line to the fuselage so that it looks connected, but KSP's simplified calculation of drag treats that moved tanks as if it were stuck to the side in the airflow.  It sounds crazy but it is possible to do accidentally.  Another similar thing is to connect to the part inside the cargo bay, rather than the cargo bay.

But as @fourfa pointed out, your original suspicion is correct.  That video was from very early in version 1.0.x, and I can see where he reveals the thrust that it is 1.5× what I can get today in the same conditions.   In version 1.0.3 the Wheesley was significantly 'nerfed' (bottom of this linked page) --- maybe because they saw that video and realized they had made spaceplanes too easy for KSP to be a fun game.

That design is very very difficult to get into orbit, but you might enjoy improving it, but first you might rather try a recent spaceplane design from KerbalX since version 1.2.

[AHHans]

16 hours ago, jbdenney said:

Flight Screen shot. I am at a 15 degree climb at 211 m/s and my speed acceleration is had dropped to almost nothing and my thrust is starting to drop. In Scott Manley's tutorial, at this point with the same engines, he is pulling a 30 degree climb at over 300 m/s and gaining speed and thrust fast.

After having made the same mistake a number of times I had a closer look at your screenshot. And indeed: the button for the landing gear is still lit, indicating that the gear is still deployed. That increases the drag quite a bit.

[jbdenney]

I also noticed the landing gear - unfortunately pulling them up makes almost no difference.

[AHHans]

4 hours ago, jbdenney said:

I also noticed the landing gear - unfortunately pulling them up makes almost no difference.

Hmmm...

Well, anyhow. As I wrote: I didn't have serious problems getting my attempt at re-creating your plane into orbit. If you put the craft file somewhere where I can download it, then I can have a look and see if that gives me trouble.

[FlyingGeeze]

Pressing "F11" opens drag vectors (red lines) to showcase drag. The part drag multiplier activated from the debug menu as suggested only shows the amount of drag per part, which, can be any.

Try to accelerate to top speed of 350m/s and see if red vector lines appear. If a center red line amounts to a increased length that seems to be quite long there is a serious drag effect from the center stack.
F5 "quick save" put "pitch authority" on control surfaces to max and do a pull up. One of the great red vector lines would be visible coming of a clipped part inside a fuel tank, or as I might expect coming from the cargo bay. If you pull up at speed one of the lines would cross sect the area it's coming from.

If it comes from the center cargo bay something is badly attached. The drag shielded unto a part inside a cargo bay has certain attachment rules.

• Center or cross center of shielded part should not be situated outside the exterior walls.
• Everything placed directly surface attached on or in the cargo bay is protected while not sticking out.
• A stacked attached part should be node attached to the cargo bay itself. You could have it attached to the fwt or aft fuel tank or capsule by mistake, just disconnect the cargo and reattach unto the cargo bay node.
• Everything surface attached to a center stack inside a cargo bay (correctly attached) is protected from drag also if not sticking out.

What i.e. doesn't work is attaching cargo to any other part besides the cargo bay and then dragging it inside. If only one part is badly attached as such like a non fair-ed fuel tank inside the cargo bay it's similar to riding a spaceplane to orbit without a nosecone.

[IronMaiden]

The Whiplashes are turboramjets. They need to get going supersonic before their thrust really starts ramping up. So stay at sea level until you reach ~mach 1.3 then slowly pull up to about 15°, no more, and climb to at least 15km. There you'll want to level off and start accelerating in the thin atmosphere. Aim to get to at least 1400m/s with just your Whiplashes before allowing your altitude to reach 20km. Then keep your pitch nice and low (<5°) and light up your rocket engines. Remember, orbit is about going fast, not up, the only reason you need to go up is to keep from blowing up. Drag is basically negligible if you keep your angle of attack close to 0° so let your engines focus on building up that orbital velocity and let your wings handle keeping you in the air. Aim to roughly circularize around 35km, maybe a little higher since this cockpit is prone to overheating as it takes the brunt of the heat as the front part, the inline cockpit allows for much more efficient ascents.

Your plane has way more thrust and fuel than it needs, both open and closed cycle, so you can definitely take this plane to orbit if you pilot it right. If you want you can check out my SSTO tutorial video. I use RAPIERs in that design but the ascent profile will still look the same, you'll just get a few hundred m/s less out of open cycle and therefore your payload fraction will be significantly smaller.

[jbdenney]

Thank you IronMaiden - I will check out your series.