SSTO issues

[justanotherdude]

I have been playing KSP for a while now, but I have never managed to make an SSTO. the most recent SSTO that I made, it was partially successful, but it would not climb beyond 14km. when I start leveling out to gain speed, I need to angle my craft at 20 Degree angle to get the prograde marker to 0. if I straighten out more, I will start falling. when I get my Prograde to 0 Degrees, I am still losing speed! I made a mod to the craft (2 ramjets that I can detach, to help with the accent) and I still have the issue! 

I have looked on youtube and the forums for help, but nothing has helped me so far... I tried downloading SSTOcraft files as well...

Please help me!

Craft file: https://mega.nz/#!igI0gaIa!aUSLBf1D8VNdZ16HzjNJro6oqfI7PQmG_jBhJiVk_Z4

Edited April 23, 2017 by justanotherdude
Added the Craft file

[Dman979]

Hi, @justanotherdude, and welcome aboard!

I've moved your post to the Gameplay Questions and Tutorials subforum. You should be able to get help there.

[FancyMouse]

1. Use the rotation tool (shortcut key 3) with angle snap off (short cut key C) to slightly make your wings angle up. This creates a small AoA while your fuselage can still point prograde, creating maximum lift with minimum fuselage drag.

2. The engine above wing is making your life harder - because they create torque to pitch you down.

I just ditched the two above-wing engines and rotated all the wing parts a little and it flies perfectly fine to me. At 10 degree climb angle it just constantly builds speed. Very stable. At [email protected]/s I fire the nukes, at 25km I switch rapiers. I'm not in a perfect trajectory, though - since when I switched mode I'm not even at 1.2km/s yet, but it's ok - when oxidizer runs out, I'm at 2.2km/s orbital speed and nukes are sufficient to circularize. After circularize to 90x90 orbit, it's still like 3500 LF left. So your design is generally fine - just fix these small problems and it will fly.

but there are some more suggestions

3. Using nuke is a big decision. Depending on the purpose of your spaceplane (low orbit only, or going further, or refuel at space station before going further?), in most cases you don't really need a nuke. Without nuke you can save a lot of mass on your plane - if you just want to reach LKO, you can definitely do it in half the mass you currently have, and ditching nuke is the first step.

[qzgy]

Mind putting up a picture?

I made some minor modifications. I switched out the landing gear for smaller ones, moved a wing panel back to make the CoL/CoM relation better (I suspect you had flipping issues, yes?), removed some of the RCS ports (there are two many, use RCS buildaid to optimize), clipped in slightly the NERVs to prevent tail strikes, and increased control authority on the canards and elevons slightly. As a recommendation, use RCS for translation and reaction wheels for rotation. Hangar pics below.

Spoiler

CoL infront of CoM. Not good. Try to be nose heavy rather than tail heavy.

Moved nervs in, and front wing panel back.

You had gigantic landing gear, I guess to prevent tail strikes

Slight drag issue. Red lines are bad (they are drag).

 

 

During flight it handled really well. (post slight modification) It SSTO'd fine, and had ~4000 m of DeltaV in orbit, so I don't see why it shouldn't work. It may have been a problem with your ascent profile, so I tried it out and put what I did below.

Annotated Pics of ascent below.

Spoiler

~10 degrees till I hit around 400/500 m/s before ditching whiplashes (added weight)

Pitched up (eventually) to 15-20 degrees.

I have no pics, but turned on nukes at 18000m and switched to ClosedCycle on rapiers after the flamed out and I stopped accelerating. Wait till apoapsis is above 75000 m before switiching engines off and coasting following prograde (On my run, I actually pitched up to 45 degrees or so at 40,000 m and relied on nukes, burning with the rapiers if not sufficient to raise apoapsis. Trickier, but theoretically more efficient I think)

Pre-insertion burn coast orbit.

For the insertion burn, create a maneuver node at apoapsis and push prograde (the one that looks kinda like a plane, its green without the x in the middle) until the orbit circularizes. Burn when the time to node is about half the estimated node burn time.

Post insertion burn

And it should be nicely in orbit

 

What seems to work best (in general) is to get to past 400 m/s on rapiers at sea level, then go up slowly (10-20 degree climb) before switching when the air breathing mode on the rapiers cut out.

Overall, its not too bad (apart from the CoM/CoL thing) for an SSTO, and should work fine. Just try practicing more.

Hope this helps. Modified craft file on KerbalX (link in signature).

EDIT:Also, the mods I'm playing with shouldn't affect stock performance. For the control authorities, it was 150 pitch on the canards and rear pitch elevons, and turning off roll on the vertical stabilizers

Edited April 23, 2017 by qzgy

[AeroGav]

12 hours ago, justanotherdude said:

when I start leveling out to gain speed, I need to angle my craft at 20 Degree angle to get the prograde marker to 0. 

Hi Justan -  the correct name for this is your angle of attack.   It is the difference between where the nose is pointing and where the plane is going.   Optimum lift : drag ratio occurs at 5 degrees or less.   You are describing a 20 degree AoA, which is huge, very close to the stall, and very draggy.   You either need to gather more speed before trying to get up into such thin air, or you need more wing area for your weight.

11 hours ago, FancyMouse said:

Use the rotation tool (shortcut key 3) with angle snap off (short cut key C) to slightly make your wings angle up. This creates a small AoA while your fuselage can still point prograde, creating maximum lift with minimum fuselage drag.

FancyMouse gives this advice because fuselages generate far more drag than wing parts.   Wing parts get best l/d ratio at about 7 degrees AoA,  but for fuselages 0 AoA, pointing straight into prograde, is best.    I call this an advanced construction technique.  

Alternatively, avoid mk2 fuselages.    They have about 3 times the drag of mk1 parts of an equivalent fuel capacity, unless you resort to tricks like this it is very hard to build a useful SSTO, or even one that SSTOs at all.

12 hours ago, justanotherdude said:

I have been playing KSP for a while now, but I have never managed to make an SSTO. the most recent SSTO that I made, it was partially successful, but it would not climb beyond 14km.

The key to a good flight profile -

1. Don't let AoA rise much above 5 degrees 
2.  Avoid flying around in the transonic region, which has unusually high drag. (240 m/s to 420 m/s)

So, after takeoff, climb steeply enough to keep your speed below transonic (240 m/s) but not so steep that AoA exceeds 5 degrees.  Eventually, you reach a point where the air is too thin to get enough lift whilst keeping AoA reasonable, and if you let the nose fall then speed will exceed 240.    At this point,  reduce your nose up input so AoA is halved, and let it shallow dive through the sound barrier.   Once over 440 m/s, resume climbing.

 

Level off for the final speedrun at 21km or so, when you've more or less gotten as fast as you can in level flight, pitch to 5 degree AoA and switch to rocket mode.

 

[justanotherdude]

18 hours ago, FancyMouse said:

using nuke is a big decision. Depending on the purpose of your spaceplane (low orbit only, or going further, or refuel at space station before going further?), in most cases you don't really need a nuke. Without nuke you can save a lot of mass on your plane - if you just want to reach LKO, you can definitely do it in half the mass you currently have, and ditching nuke is the first step.

3

The SSTO was meant to be a refueling ship for a mun space station that I was building. that is why I put the over-wing engines there, just to get the ship out of the atmosphere, just that once.

 

17 hours ago, qzgy said:

As a recommendation, use RCS for translation and reaction wheels for rotation.

Thanks for the tip!

 

6 hours ago, AeroGav said:

Alternatively, avoid mk2 fuselages.    They have about 3 times the drag of mk1 parts of an equivalent fuel capacity, unless you resort to tricks like this it is very hard to build a useful SSTO, or even one that SSTOs at all.

I just used the MK2 because they looked cool, and i thought that they were more aerodynamic. Matt Lowne also uses them, and i use him as my example...

 

6 hours ago, AeroGav said:

The key to a good flight profile -

1. Don't let AoA rise much above 5 degrees 
2.  Avoid flying around in the transonic region, which has unusually high drag. (240 m/s to 420 m/s)

So, after takeoff, climb steeply enough to keep your speed below transonic (240 m/s) but not so steep that AoA exceeds 5 degrees.  Eventually, you reach a point where the air is too thin to get enough lift whilst keeping AoA reasonable, and if you let the nose fall then speed will exceed 240.    At this point,  reduce your nose up input so AoA is halved, and let it shallow dive through the sound barrier.   Once over 440 m/s, resume climbing.

 

Level off for the final speedrun at 21km or so, when you've more or less gotten as fast as you can in level flight, pitch to 5 degree AoA and switch to rocket mode.

1

Thanks for the help. i will try that and see if it will help.

 

6 hours ago, AeroGav said:

Hi Justan -  the correct name for this is your angle of attack.   It is the difference between where the nose is pointing and where the plane is going.   Optimum lift : drag ratio occurs at 5 degrees or less.   You are describing a 20 degree AoA, which is huge, very close to the stall, and very draggy.   You either need to gather more speed before trying to get up into such thin air, or you need more wing area for your weight

 

Yeah... i know that i am playing for a while... but i am not professional, and i am still a teen. i only have about 30 hours under my belt...

Anyways. Thanks to all of you for the help. I love the game, but when i hit such a big problem (and after so many failed attempts) i just stop playing. I am surprised at the response speed of the community. You rock!

[AeroGav]

I had a bit of a play with this ship.    Low hanging fruit -

1. More mk2 fuselage than strictly necessary, due to the poor drag/capacity ratio only use for cargo and crew if at all possible.

2. loads and loads of radially attached clutter  - countless batteries, rcs thruster quad blocks, solar panels, parachutes, airbrakes.  Admittedly, on a draggy mk2 it's never going to be slick, but i think you may have been reading outdated info about "physicsless parts".  Unfortunately they do have physics (drag) these days, and plenty of it

3.  not using the reversed nosecone trick on the back of engines, to reduce drag

4. pointy cockpit - too susceptible to heating effects due to being right at the front, it will prevent you flying the shallowest, most efficient ascent profile safely.

5. engines all at the back, cargo and fuel at the front.  Not a performance problem, but will cause problems on re-entry when the fuel and cargo have gone. They are the only things keeping it balanced with all the heavy engines to the rear, with that stuff gone it will be tail heavy and unstable.    I moved the heaviest engines (nukes) forward and put the whiplash amidships out on the wing tips.

6. wing parts that don't contain fuel.   Big S wings give you free capacity..

I went to town a bit, and added angled wings (wing incidence angle) to get the best possible drag, which may not have been necessary since i kept your original concept of two jettisonable Whiplash boosters.  However, i moved them so they are inline with your CoM and won't cause pitching issues.

I managed to get to orbit with 12 tons of mk1 ore tanks in the cargo bay, and 1000dv of liquid fuel left in the tanks, which is not bad for a takeoff weight (including cargo) of about 42 tons.  Note that although it dumps the Whiplashes,  if you took this thing to Laythe it would be able to orbit again without them, because Laythe is much easier to SSTO from than Kerbin, especially as you probably would be coming back to orbit with no cargo (or only a very light "science" one) and would not have refilled oxidizer.

On a light load you can most certainly SSTO from KErbin without oxidizer.

https://www.dropbox.com/s/y0jwqt4gra1c1n9/SSTO attempt gav2.craft?dl=0

...craft file is with 12 ton ore test cargo already loaded

Action group 1 - deploy nose down trim flaps (lowers nose a couple degrees) 

Action group 2 - retract trim flaps

Action group 3 - nukes toggle

AG 4 - Rapier switch mode

AG 6 - Cargo bay doors open/shut

AG 8 - Solar panel deploy/retract