SpacePlane Question

[funkcanna]

Hi, I'm trying to design a spaceplane as a shuttle for my Mission to Duna.  I have a decent design but i need to get another 200-500/ms DV for the rocket part (approximately) and I don't know how to do it.  Ive tried adding more fuel, but that increases mass resulting in kind of the same net DV at the end.  See the screenshot of the SPH view, happy to upload the .craft if anyone is interested.  Im playing on 1.1 PreRelease.

Mods used to build it are:

• MK2 Stockalike Expansion 
• Tweak scale for the wings

Parts Used from Cockpit back:

• Mk2 Clampatron
• Mk2 Crew Cabin
• Mk2 Monopropellant Tank
• Mk2 Liquid Fuel Fuselage
• Mk2 Rocket Fuel Fuselage
• X44 MATTOCK Engine (from Mk2 Stockalike)

Wings:

• Structural Wing Type A (Made bigger with Tweakscale)
• Mk2 Twin Circular Intake (Mk2 Stockalike)
• Mk2 Pre Cooler (Mk2 Stockalike)
• Mk2 Rocket Fuel Fuselage
• X44 MATTOCK Engine
• BigS Elevon 2

Take off and control are perfect, but getting into space leaves me with about 200dv, which is not enough to circularise let alone rendezvous and dock.  This is my very first attempt in 1000hours of KSP to build a spaceplane and not just download a craft so really want to get it right!

Any help AT ALL will be appreciated!

 

[Empiro]

The biggest thing to do is pare down on any mass you don't need. My first suggestion would be to remove the mono-prop section, saving you a bit in mass. The docking port has mono-prop built-in, and it should be enough to do docking. Try to use slightly smaller elevons for pitch control. You shouldn't need something that big for a mk2 craft.

I don't know the particulars of the engine (which I will assume to be similar to the RAPIER), but it looks like you have more TWR than necessary. You could try removing one of the engines. Do the pre-coolers actually do anything? If not, you can probably take it out. You can also reduce drag a bit by removing some of the intakes. Generally, you only need 1 per-engine.

Finally, make sure that you're flying the craft well. Ideally, you'd get up to at least 1200 m/s at 20+km before switching over to rocket mode, and you'll want to have just burned all of your liquid fuel. In stock aerodynamics, you'll want your velocity to be pointed at about 10+ degrees switch over, because increasing your AoA creates tons of drag.

I can't see the delta-V statistics for how much you have in rocket mode, but your rocket-only mode needs about 2600 m/s delta-V at the minimum. About 1400 will be needed to get into orbit around Kerbin. Then another 1100 to transfer to Duna, and another 100 for corrections around Duna. I'd want to have a bit more just to be sure. Your craft shouldn't be close to the point of really diminishing returns, so make sure that the fuel is properly fed into the engines.

[funkcanna]

Hi Empiro, thanks for your reply.  Just wanna start by saying this is just the shuttle to get the crew to the Hab Module which will take them to Duna so I only need dV to get to Orbit and then Rendevouz (and of course de-orbit).

Is it possible to see how much DV you have when switching to Rocket mode?  These engines are almost the same as Rapiers but have slightly more thrust.  Ive noticed when I switch (usually around 30km altitude and at about 1300m/s the total DV drops to about 1000m/s (there is only one DV value I can see as the MATTOCKs are both my atmospheric and non-atmospheric engines).  

Edited April 14, 2016 by funkcanna

[Empiro]

Ah, okay I misunderstood you. If you only need to get into orbit around Kerbin, then 1800 m/s should be more than enough to let you make orbit, make any corrections for rendezvous, and de-orbit. That should make the design much easier.

In the hanger, you can right click on each engine to switch them to rocket mode. If you switch everything, it'll show the rocket-only stats. The extra wrinkle is that by the time you switch when piloting the craft, you'll have burned away some of your liquid fuel, so you'll need to drain one of the tanks a bit.

[seaces]

This is way to big for a craft that will go to LKO with only crew. You can get up there with less fuel and smaller plane if you are carying only crew.

I think you could get without those big fuel tanks at the wing or at least have them be smaller and with less engines since this kind of craft should be lighter. Unfortunately I do not own that mod so I do not know how those engines behave. However I think that this could get to orbit despite inperfect design. I think you should maybe improve the flying. The one thing that it bothers me about this craft is, do you need that huge control surfaces at the back?

If you want I can try later today to put some SSTO design for crew only using stock parts and show it to you?

[funkcanna]

Hey, your advice worked!  I removed the Monopropellant and the radial intake and gave it a test.  Got to Orbit with ~530dv remaining - which is enough to dock and deorbit.  Thanks!  

3 minutes ago, seaces said:

 

If you want I can try later today to put some SSTO design for crew only using stock parts and show it to you?

Thanks that would be awesome.  Ive now got it working - but yeah im sure its not as efficient as it could be!

[seaces]

29 minutes ago, funkcanna said:

Hey, your advice worked!  I removed the Monopropellant and the radial intake and gave it a test.  Got to Orbit with ~530dv remaining - which is enough to dock and deorbit.  Thanks!  

Thanks that would be awesome.  Ive now got it working - but yeah im sure its not as efficient as it could be!

OK once I get home I will try to make something tinny yet high performance

[AeroGav]

Your Spaceplane has a lot less wing than the stuff I generally build, leading to inefficient flight above 20km - requiring the nose to be far above the prograde to get sufficient lift , creating drag, and also resulting in cosine losses to the rocket thrust - basically a lot of the thrust is going straight down, fighting gravity rather than accelerating you in the direction of travel.  To get success with this approach requires a high thrust-weight ratio which means carrying a lot of engine mass all the way up to orbit.   Finally, a MK2 monopropellant tank is a metric f-ton of RCS.  That and engine mass is probably eating most of your payload fraction.     I honestly never bring RCS because the ISP is so bad.    Most of my spaceplanes don't even bring oxidizer or leave the tanks mostly empty, just a little bit to power any Vernier lift motors that are fitted.  Reaction wheels FTW.

 

My mark 2 has 4 pairs of big S delta wings.

One Rapier (ISP 3800) that is only used in Air Breathing mode.

Two NERVs that are switched on above 24km (ISP 800)

Two Panther "boosters"  attached to the rear of the NERVs.    They operate in Dry mode (ISP 9000) except when passing through sound barrier and above 15km altitude (ISP 4500 in reheat).  They get dropped above mach 2.7.

Two long cargo bays.  Most of the fuel tankage is in the wings, but there is a little bit in the mk2 to mk1 adapters and a smidge in the pre-coolers also.

>>cruising to orbit.  The large wings make sufficient lift at small nose angle, even at this altitude.  So, we have low drag and can get away with the low TWR of two NERVs as our only propulsion, and take advantage of their high ISP.

 

Spoiler

The panthers are needed because the big wings of the aircraft mean it does not want to go supersonic below 10km.  The Rapier has poor thrust below mach 1 and because we only have one of them it only has slightly more thrust needed than to maintain level flight when subsonic.   This means the climb to 10km is very slow and wastes a lot of fuel, whilst it can still make orbit without them, the  Panthers make this part of the flight vastly more efficient.  Panthers are much cheaper than Rapiers and NERVs so i don't feel too bad about throwing them away. 

 

I filled the cargo bay with IRSU stuff and found this plane can still get to Minmus direct from Kerbin.  From there it can refuel and easily make Duna, Laythe, Pol, then Eeloo.   Because of the large wings it can land pretty comfortably off-world -

That said, I have to give credit to your design in that it looks a lot more like real rocket planes.   Certainly wins a "looks like it's doing 1000mph standing still" award.   Use of monopropellant for orbital maneuvering etc. is good RP.  

Just some ideas for you perhaps.   Since you're using tweakscale, you could make a much more elegant version of my plane by upscaling the wing and canard parts.   I'd tried to keep things stock, but that means the design is pretty much going to need kerbal joint reinforcement if it's not to flop around like crazy.

Edited April 14, 2016 by AeroGav

[funkcanna]

Thanks @AeroGav - appreciate the pics and the details.  Ill definitely try something with larger wings soon, I have to say I'm  bit liquided that I didn't try space planes sooner, its been amazing fun even though frustrating! I ditched the Mono and successfully docked on a test run just using the mono in the Mk2 Clamp o Tron as suggested by @Empiro, but it was admittedly VERY close to running out.

 

EDIT: LOL @ it changing my word to "Liquided" haha

Edited April 14, 2016 by funkcanna

[EivlEvo]

Funk. Let me chime in here as I've just accomplished what you're attempting (maybe).

My quick version is... I ended up launching 2 components of a landed base for Duna somewhere around .9 (don't remember) and then I moved across the country, and came back to a version where the atmosphere on Duna changed a bit. So I didn't have enough chutes to land safely and my science bay ended up with blown tires at the south pole, and my mining bay ended up at the north pole. Also with blown tires.

I sent a ship up that could hop about the surface, and refuel as necessary, but it couldn't achieve orbit on Duna once it landed. I sent it with a pilot (obv) and a level 2 engineer. Wellll... level 2 engineers can't actually fix wheels like it says, so I de-orbited my solar base hoping that one of those engineers had gotten enough experience to get to level 3, and went BACK to my original idea of designing a Duna plane. Which I did (pics below).

Anyway. First... I don't believe that plane will fly that well on Duna. For my craft, after struggling with trying to go as light as possible (I really wanted to use ION), I ended up using the mk2 cockpit (I think) with mk1 parts behind it, and the huge 737 wings. I mounted the main gear along the centerline (like a U2) to prevent any pitching or yawing about on the surface. I ran 2 nukes (wing mounted (inline)), and I put an aerospike on the tail so that I could be sure I could get off the ground as quickly as possible. The plane lands completely via parachute. Fly to site. Deploy drogues, deploy mains. Use reaction wheels to control everything (though it's well balanced) and it floats on down.

(I thought I had better pics) but... it uses 2 of the hypersonic jet engines to fly itself off the runway to altitude (mounted to the back of the nukes). This... as you're experiencing uses lots of fuel. I carry 3 drop tanks (which you can see in the photo), and I stage them first to ditch the frontal area. Once we're at altitude, and pushing hypersonic speeds (900-1000m/s), I fire the aerospike, ditch the jets, and light the nukes. This leaves me JUST enough to achieve orbit.

Once in orbit, I send up a tanker, dock to the jr. port just under the nose, and it has again... just enough delta v to get to Duna (at the phase I sent it at anyway... I think it carries about 3k dV iirc) Once at Duna, I aerocapture (carefully, as heating is an issue) and use whatever fuel I have left to finish the maneuver. Then the craft glides forever (even at high altitude). Get where I'm going... pull the chutes, and sink the drills.

It flies on Duna beautifully at about 20% throttle on the nukes. Aerospike to get off the ground and climb like whoa.

The ONLY thing I forgot... was the bloody storage container for the ore. But I posted about that, and a few people put a mod out that enables the ISRU to "store" 1 unit of ore, so it can function as designed. My logic here was that if this were the case IRL, they would just shovel the ore directly into the bloody thing, and make it work.

Anyway... a few pics (thought I had better screens tbh, but whatever)

Ready for takeoff. Fully loaded.

Just landed and refueled on Duna. Going to deliver the level 3 engineer to the first outpost!

And last but not least... after delivering components and people to each pole. Launching the main hab (which has a jetbridge type docker on it) as well as a tug type general rover, AND relocating everything to an ore heavy area (based on my satellite, and the surface scans)... docked up and refueling at the base with all of my equipment. (Please consider that this base was designed close to 30 game years ago... and my aesthetics and whatnot weren't all the same back then. Ha...

If anyone wants the craft file... and I can figure out how to do that... I'll make it available.