SSTO Help

[Val]

30 minutes ago, Aethon said:

My rapiers seem to asymmetrically flame out at around 18-19km on air breathing.

Probably what @GoSlash27 said.

You can limit asymmetric flame-out by making sure to always mount Intakes in sequence. What I mean by that is always mount Intakes before Engines. And if you have multiple sets of intakes and engines, mount each set of intake and engine.

Example: You have a created a craft with 2 intakes and 3 engines. 2 engine pylons with intakes and a center engine with no intake.

Now that it's done pull off all the engines and intakes. Then mount them like this.

1. Reattach the first intake in symmetry.
2. Reattach the first engine in symmetry.
3. Reattach the center engine.

Mounting it in that sequence ensure that the center engine flames-out first, and the 2 engines on pylons will flame-out together.

If you have just 2 engines in symmetry and 1 or 2 intakes, then just pull the engines off and reattach them.

That should ensure they flame-out together.

[GoSlash27]

5 minutes ago, Aethon said:

It has a pre-cooler inline and everything aft of the docking port slid over it with the offset widget (at this point I don't care about clipping, I just want it to work). 

Aethon,

1 precooler isn't enough for 2 RAPIERs. You'll want to add a couple radial mount variable ramp intakes to that or another precooler. 

Or better yet, get rid of the extra unnecessary RAPIER. Spaceplane design is backwards from standard KSP engineering practice; you want to look at what you can ditch instead of what you can add.

Best,

-Slashy

Edited December 5, 2015 by GoSlash27

[AeroGav]

Assymetric flameout = not enough intakes.   The rapiers should keep going then stop together at 29.5km.

How I'd arrange things personally - 

2 into 1 splitter -> pre-cooler -> RAPIER

that way you have 2 pre-coolers and 2 RAPIERs

or 

2 into 1 splitter -> pre-cooler -> pre-cooler -> RAPIER

which would give you 4 pre-coolers for 2 RAPIERS ,  overkill !

 

Re: ascent profile

yeah that picture of 360 m/sec at 16km is way too slow, at least for your craft.   My "vark" can just about stay subsonic up to 16km but it has a lot of wing area for its size, so under the same conditions has a much lower angle of attack.     Then again your subsequent attempts sound like they're going off the other extreme - too fast.

Remember -  330 m/sec  = Mach 1 ,  significantly increased drag

240 m/sec ->  460m/sec = transonic region, increased drag

you want to spend little time operating in this region , either be below it, at lower altitudes when the air is still thick enough to support your craft at such a low speed,  or above it.

If I recall correctly, drag goes down after crossing the sound barrier and is lowest at 460-660 m/sec before it starts going back up again.

I'd definitely change your wings for big-s delta ones, they have a little more area and they store liquid fuel, this will stop your rapiers pulling on your rocket fuel tank reserves while in airbreathing mode.

It's hard to stay on an exact number while handflying but try to stay on a particular AoA if possible , to minimise drag.   If i'm only planning on going a few degrees above or below my prograde , i often fly with prograde set on the SAS and just make inputs through that.

[Aethon]

4 hours ago, GoSlash27 said:

Aethon,

1 precooler isn't enough for 2 RAPIERs. You'll want to add a couple radial mount variable ramp intakes to that or another precooler.est,

-Slashy

Facepalm.  I was thinking precooler provides 5 intake air and a RAPIER needs 4.016, but of course I'm using 2 rapiers.  I'll also look into the delta wing tomorrow.  

Thanks again guys.

[Dispatcher]

Looking at the OP image, while the COL is actually slightly behind the COM, I wonder if it might be better to rearrange so that the COL is a little further back from where it is now?  Perhaps you'll experience more agile control, but that's just a guess.  At any rate, I didn't notice other comments addressing this, so it must not be a serious issue.

Good luck!

[Val]

@Dispatcher It depends on what you want to do with your craft.

A craft with CoL right on top of CoM, makes a SSTO spaceplane very easy to take to orbit, because it will not drop its nose every time you make small adjustments to attitude. You can inch the nose carefully in any direction without having to compensate for unwanted movements. But it also makes the craft very allergic to large control throws and you can easily get the craft to spin out if you deviate from prograde.

Having CoL right on top of CoM is also the only way to make a craft that flies straight with SAS turned off, without use of trim.

On the other hand, a craft with CoL further back and more control authority, makes a good fighter or aerobatics craft. You can throw it around violently, but it'll always stabilize as soon as you stop trying to break it. But it's tedious to use such a craft as a SSTO spaceplane, because it'll drop the nose a little anytime you try to adjust its attitude.

Well, that my opinion and experience on the matter, anyway.

[Aethon]

 

...  And there was much rejoicing.  

Ok so the precoolers are shoved up into the MK2 bicoupler, but hey it works and is a good basis for some mission specific modifications.  Perfect is the enemy of good enough.  I would have given up long ago without all your excellent advice.  Thanks again all.  What a great community.

 

 

Cobra reentry makes heating a non issue.  I overshot a bit, but reverse Immelmanned and put her down right on the runway.

 

Edited December 6, 2015 by Aethon

[GoSlash27]

Congrats!

 I love seeing people make orbit!

-Slashy

[AeroGav]

Nice, that's a definite improvement.    Fair old bit of liquid fuel left over there.    Maybe put a nuke powered orbital tug up there to dock with, so you can offload some of that.     Or,   make a trimotor variant of that plane with a mixture of nuke and RAPIER engines :-) You could use the nukes from 20km upwards...   would be pretty easy to increase the LF tankage further...  attach big - s wing strakes to the leading and trailing edges of delta wing - looks pretty good in an F-15 sort of way,  as well as on the fuselage head of the wing, like on an F-18

[cyprio]

if your really that concerned about overheating, try slapping a couple of small radial single radiator panels to the parts that overheat first but install them in a way that they wont cause much drag also offset them more into the body of the craft to minimise drag again, youll get a bit more speed out of your airbreathers hopefully that way before your climb with rocket ignition, who knows ,might work, i can build space planes but nothing that reaches much further than the mun but these days i focus more on humongous, single shot and return rockets,  capable of mass kerbal transit, i find the best way to get anything out far is to send it to duna first and use ike for slingshots

Edited December 6, 2015 by cyprio

[Vegetal]

I've seen a lot of good advice from some really good spaceplane guys here. But...you're still clipping things inside the fuselage right? These parts WILL add drag to your craft, no matter if you clip them inside or not. I think your original plane would fare a LOT better if you just ditched the clipped parts.

Like those precoolers on your last craft. They have *nothing* in their front node, so they will act like a wall to your aerodynamics.

Your original ascent profile seems reasonable. If you get 1400m/s or more in air-breathing mode, you are fine. You HAVE to let those clipped parts go man!

 

EDIT: Ninja'ed by the OP himself. This new forum got me confused....
Now I see the precoolers are actually attached to the end node of the double adaptor. Nice job there! Empty nodes are one of the things that cause the most drag. Your plane is now *very* streamlined.

Now I want to see orange tank to orbit by spaceplane SSTO. GOOO

Edited December 6, 2015 by Vegetal
Ninja'ed

[Wanderfound]

5 hours ago, Vegetal said:

.Now I want to see orange tank to orbit by spaceplane SSTO. GOOO

 

Craft file at https://www.dropbox.com/s/xpxdx1egyatwz8y/Kerbodyne%20Herakles.craft?dl=0

 

[Vegetal]

Not from you, from the OP

[Vance One]

On 12/5/2015, 2:59:54, Aethon said:

 

Cobra reentry makes heating a non issue.  I overshot a bit, but reverse Immelmanned and put her down right on the runway.

 

A Reverse Immelmann = split S

 

You guys are blowing my mind with the stuff you all have created... so much inspiration

[Stoney3K]

On 5-12-2015 03:38:58, Aethon said:

It has a pre-cooler inline and everything aft of the docking port slid over it with the offset widget (at this point I don't care about clipping, I just want it to work). 

That will occlude the intake so it stops working. Try attaching two precoolers to the aft bicoupler and attach the RAPIERs to that.