Is lifting an orange tank to LKO with a SSTO plane still possible

[TenienteDan]

Hi!

I have been trying for several weeks to build a SSTO plane with 8 to 16 Rapiers in order to lift a Orange tank to LKO, but I never get enough speed while climbing.

I followed some designs like this one and from this post but I´m wondering if this is still posible or they nerfed rapiers so now It can´t be done nowadays.

Thanks!

[Gargamel]

Moved to Gameplay Questions.

[bewing]

It should be. Nothing's been nerfed in the current versions -- except some Making History rocket engines. And welcome to the forums.

 

Edited January 23, 2019 by bewing

[Gordon Fecyk]

The Fat Star 3 can lift 40 tonnes to orbit in Ferram Aerospace as is, and it can do it in stock aerodynamics as well if you change the fuel loadout. I'd say it's still possible.

[Aegolius13]

Yeah, it is.  Just re-tested it in 1.6, and this monstrosity is still capable of listing a 288-ton 5m fuel tank (equivalent to 8 orange tanks) to orbit, using 20 Rapiers.  

If you want to post a screenshot, I'm sure we could provide advice on your particular plane.  Sounds to me like you've most likely got some unwanted drag somewhere.  

 

 

[Val]

It's an older design. I haven't checked if it works in newer KSP versions.

Did you download and test the original version? There's a craft link in the post you linked.

What kind of ascent profile do you use? Accelerate to 450+ m/s at sea level, or slow climb to 10 km before accelerating? All my designs are meant to do acceleration at sea level, because it takes less real time usually.

If I have time, I'll test it tonight and report back my findings.

[Starhawk]

This is my standard 'orange' tank to LKO spaceplane.  Six rapiers is plenty.

This still worked in 1.5.1.   I would be very surprised if its performance had changed in the latest update.
 

Happy landings!

[Val]

This old 4 RAPIER design still checks out.

SSTO Z-2 High-Five Mk4

I've added a larger vertical fin, some RCS, and updated the craft file to KSP 1.6.1.

Edited January 23, 2019 by Val
Forgot about tail fin

[TenienteDan]

So apparently I can´t past 400m/s at sea level and when I try to climb (10º) It goes back to ~350m/s. Also I takes me that long to accelerate that I lose half of my fuel tanks .

I was trying to avoid downloading an already made up ship, so It´s a bit more challenging for me... but I'm about to throw the towel.

Some pics of the craft.

 

Edited January 24, 2019 by TenienteDan

[Gargamel]

At first glance, you're running to pods of 4 engines each, but only serviced by one air intake each.  Those engines might be air starved.  Unless those ram scoops are making up the difference. 

[Gordon Fecyk]

35 minutes ago, TenienteDan said:

So apparently I can´t past 400m/s at sea level and when I try to climb (10º) It goes back to ~350m/s. Also I takes me that long to accelerate that I lose half of my fuel tanks

Assuming a stock game, those Mk2 tanks will add a lot of drag when your angle of attack (difference from prograde) is significant. You could get less drag and more capacity with Mk1 liquid fuel only tanks.

Others who fly Rapiers in Stock aero will hang out a lot near sea level until considerably faster than Mach 1 before pitching up. In the real world, and in FAR aero, that's asking for trouble in air frame stress, but in Stock apparently you can get away with that.

[Aegolius13]

The struts, RCS thrusters and radial intakes are all pretty draggy,  so removing those might help. (I think one shock cone can feed four Rapiers, but you can confirm intake usage with KER). You could also add a shock cone to the very front.   

Your speed issues sound pretty typical.  There's a lot of drag around Mach 1, and Rapiers aren't great at that speed.   It's common to climb to a few km and then level off (or even dive) to get past that barrier.  Climbing soon also helps your LF consumption.

[bewing]

3 hours ago, Gargamel said:

At first glance, you're running to pods of 4 engines each, but only serviced by one air intake each.  Those engines might be air starved.  Unless those ram scoops are making up the difference. 

Nah. One shock cone can serve up to 7 engines in general. The problem is drag. The MK2 parts on the nacelles are very bad for drag, and the wings have no incidence. The transition from the MK2 to the size 1 quadcoupler is very bad for drag. The ram scoops are redundant and add drag. And there seems to be some one thing adding a HUGE amount of drag on the centerline of the main fuselage. Is there something clipped in there?

Also, it looks like you're hauling a lot more oxidizer than you need.

Edited January 24, 2019 by bewing

[1straycat]

1 hour ago, TenienteDan said:

So apparently I can´t past 400m/s at sea level and when I try to climb (10º) It goes back to ~350m/s. Also I takes me that long to accelerate that I lose half of my fuel tanks .

 

Building and refining SSTOs is largely about minimizing drag. Opening the AerogUI (alt F12, go to aero, check show UI) will show you some crucial info in understanding how your flight profile affects your drag. Most notably, the Angle of Attack (AoA) and Total Drag will show you how much your drag increases when you angle up. If you get to 400m/s, you should be able to maintain and gain speed from there as long as you don't pitch up too much. A slow, steady climb is ideal with only a fews degrees AoA, ideally 0 until your thrust is well above your drag. Adding wing incidence as should help a lot, so you can still have lift while flying perfectly straight. All of Bewing's other suggestions, too.

Sometimes you get extra drag for unexpected reasons, due to oddities in KSP's modelling. It could be something not shielded properly or not connected properly. When you see thos massive drag lines, if you show aero data (alt F12, go to aero, check show aero data), you can see how much drag each part is contributing in its context menu when you right click it. Make sure parts inside the cargo bay are properly shielded and you're not getting massively disproportionate drag from similar parts.

Edit: this guide is the best one I've seen for spaceplanes. It says MK2, but concepts within apply to any plane.

 

Edited January 24, 2019 by 1straycat

[Val]

I recommend starting with a simpler craft and consider what the other posters suggest.

• Avoiding drag is the very important.
• Drag can be unintuitive in KSP in some situations
• Fuselage drag can be reduced drastically by adding Angle of Incidence to the wings.
• Cargo bays only reduce drag for items that are inside the bay AND connected to the attachment nodes inside the cargo bay or attached to something that is attached to the nodes.
• Multiport RCS pods are very draggy. Use the single port instead, if it needs RCS.

Also downloading and flying someone else's craft to see what a working one feels like is a good way to learn.

[AeroGav]

17 hours ago, TenienteDan said:

 

 

 

The overwhelming majority of drag comes from fuselage tanks in this game.   2.5metre tanks have good capacity to drag ratio,  mk2 tanks have the worst.

I made a comparison of different size tanks here -

However,   Big S wing tanks are the best for drag vs fuel.   I recommend you swap all your aero surfaces to big S ones if possible,  and keep your fuel for the air breathing phases of flight in these  -  do not add mk1/mk2 liquid fuel tanks for jet fuel,  and definitely do not haul LFO tanks around with the oxidizer emptied !

Spoiler

note , the first big S strake you see if the horizontal orientated one, that's contributing lift to the back end of the airplane.   The second is the vertical one acting as a tailfin.  It does not produce lift except when correcting sideslip (it lifts the tail sideways to kick it back into line).

 

Quote

So apparently I can´t past 400m/s at sea level and when I try to climb (10º) It goes back to ~350m/s. Also I takes me that long to accelerate that I lose half of my fuel tanks .

I was trying to avoid downloading an already made up ship, so It´s a bit more challenging for me... but I'm about to throw the towel.

Some pics of the craft.

I recommend you get the mod Kerbal Wind Tunnel,  it will show the best height to attempt to bust the sound barrier.

For example, with one of my more marginal designs,  the performance envelope looks like this -

This airplane most easily passes mach 1 at 7km,  it cannot do it right down at sea level.   At 16km it reaches almost 1600m/s.

Drag doubles with every two degrees you pitch the nose above prograde.  For high speed flight,  you want to be able to limit the angle of attack to 5 degrees.       Your design might benefit from more wing area - this will allow it to fly higher, where the fuselage produces less drag,   without having to pitch the nose more than 5 degrees above prograde (which also causes drag) in order to get sufficient lift.

Finally,  I would consider swapping half of the RAPIERs for Panthers.   The Panthers are much lighter, but give more thrust at low speed.  The Panthers will quit at 800 m/s, but by that stage your rapiers are so strong with ram air boost,  you can get by with 1 rapier per 60 tons of ship.