Staged Aircraft?

[nwillard]

Here's something I don't hear about too often. Take the the general coolness of taking off and landing on a runway., and combine it with the delta-v benefits of staging. It's naturally going to be more part-intensive and expensive than a regular launch, but I've been messing around with a three-stage plane and am wondering if anyone has any experience or general tips to share.

The first stage of mine is a real monster, to accommodate getting into orbit the second interplanetary (but still flight capable) electric engine stage, with the final stage being a relatively normal jet. I don't have any solid plans on what to actually DO with it but I should be able to make one that could orbit anywhere, then of course the next step would be to make a juggernaut four-stager that can fly to Laythe, land, and return to the Kerbin runway. Oh, I should probably add a driller if it's already going to be pretty heavy...

[EveMaster]

Your idea of a staged plane is a good one. I have built a 3 staged plane that can bring 100 Kerbals to the surface and back: 

I assume you have some basic knowledge on how to desing a plane, so my tips are:

Having the engines at the rear of plane is convenient, but it shifts the center of mass backwards which tends to make it unstable when empty on fuel. To balance out the weight of the engines at the back it is a good idea to have mining equipment, crew cabins and payload near the front of the craft. If you go for a design with engines at the rear, as I did you also want to design the craft as short as possible. Stick to a larger radius for the components just until the front of the craft. Having a longer craft shifts the center of drag to the front which is a bad thing if your center of mass is at the back.

You can only see the center of lift, not the center of drag in the vehicle editor. But you can look how the center of lift moves if you rotate the craft in the editor (pitch up or pitch down). If the center of lift jumps in front of the center of mass when you rotate the craft slightly, it is not stable.

Vertical tail fins near the end of the craft keep it stable in the yaw direction.

With a heavy plane, I found it the most efficient ascent profile is steeply at the beginning, and then gradually reducing the angle. I also found it most efficient to fly with full throttle and to reach high speeds, while still in the atmosphere. I only throttled down, if the heat resistance of the part required it. To be efficient on the ascent, you should also stay close to prograde.

If you have problems with pulling up the fully fueled plane after takeoff I found it useful to drain the front fuel tanks first. If the plane is to instable during reentry it helps to keep some fuel in the front tanks as a counterweight.

[Arugela]

I was going to build a multi part ship back before nukes were fuel only. It was going to have solar/ion for sun oriented and nuke and other things for the outer system. But then the changes. And now the close to sun stuff isn't mineable and renewable. It made it less desireable. At least let you scoop ion fuel from the sun and convert it or something..

I wanted to use such a design to get stuff off eve... This could now be doable with helicopter designs.

Edited October 10, 2019 by Arugela

[EveMaster]

I don't think a nuke/ion design would have worked to get off Eve. They both don't have enough thrust to weight ratio. Back then the nukes were not as heavy as they are now, but I still think it would not have been enough.

[Arugela]

The design was to multi stage it so you cold take only one part down and up then reconnect. A mothership to do everything basically.

[EveMaster]

Even from surface to low Eve orbit is just barely possible with a single stage.

[Arugela]

Even using electric helicopters?!

[EveMaster]

Starting from higher up in the atmosphere helps.

How high can you go on Eve with electric helicopters?

[Arugela]

That is what I'm going to test out. I know you can easily lift off a couple hundred tons with only a few rotors on kerbin. It's probably more on Eve. Plus you can use LF+OX and Fuel cell arrays for insane fuel efficiency. 14 fuel cell arrays only use 0.25 LF and 0.35 RF. Taht is enough for around 8 large rotors. that is enough to lift around 800-1k tons on kerbin I think. I could be wrong though. I haven't quite figured helicopters yet. Counter rotating would work nicely.

Edited October 10, 2019 by Arugela

[EveMaster]

I'm interested to see if you can make it to Eve orbit with your helicopter design. You'll have to find out which engines work best for the circularization. The engines with a higher ISP have a lower thrust and you don't want to spend too much time on Eve fighting gravity or the gravity losses are too high. It will be a tradeoff.

[AHHans]

11 hours ago, EveMaster said:

How high can you go on Eve with electric helicopters?

@ShadowZone manages 18.9km here: https://www.youtube.com/watch?v=lFgd1ZOnq1k (ca. 58 min into it). I think I managed to get somewhat higher with my design (mostly because I had blade pitch on an axis group and could fine-tune it) but I don't think I managed to exceed 20km.

Also IIRC the new helicopter blades don't really perform better than the elevon based blades.

[Guest]

15 minutes ago, AHHans said:

@ShadowZone manages 18.9km here: https://www.youtube.com/watch?v=lFgd1ZOnq1k (ca. 58 min into it). I think I managed to get somewhat higher with my design (mostly because I had blade pitch on an axis group and could fine-tune it) but I don't think I managed to exceed 20km.

Also IIRC the new helicopter blades don't really perform better than the elevon based blades.

My Evecopters have service ceilings between 26.5 and 38 km. Takes between 20 minutes and an hour or so. I use custom blades made from control surfaces rather than the stock ones though, they perform much better in thin air.

Edited October 11, 2019 by Guest

[KerikBalm]

Wouldn't this include air launch to orbit?

Examples of my staged spaceplanes for a more efficient reusable system sans nukes on a scaled up kerbin:

Spoiler

I have to switch back fast enough to get to the falling carrier aircraft that was on a suborbital trajectory, then pull it around 180 degrees, light the engines again, and cruise back to KSC:

Then of course the orbiter should be recovered too:

Depending on the payload, I use a mammoth powered orbiter instead of a Rhino powered one. I Didn't want to redesign the carrier aircraft, so I use the same carrier for both orbiter variants.

 

Edited October 11, 2019 by KerikBalm

[AeroGav]

I have built quite a few staged spaceplanes.    The vehicle editor makes piggy back airplanes harder than they need to be.    

If you are new to this,  I recommend just trying a variant of the normal spaceplane ssto with engines on detachable pods hanging under a high mount wing.  That way when you blow them off, they are close to centre of mass and won't cause the plane to become nose or tail heavy,  and by hanging them underneath  a high mounted wing,  the thrust should be in line with centre of mass too.

A similar approach can be taken with regard to drop tanks.

Take a look at this simple, low tech one -

Download it here if you want -

https://kerbalx.com/AeroGav/Kranker

Or this more whistles and bells one - 

(download from) https://kerbalx.com/AeroGav/Learstar-A2

 

Think about the components of spaceplane that don't need to go all the way to orbit -

 

1.   Panther and Whiplash engines - punch em off !

They cost under 2000 kredits each , less than a third of what a rapier does, but are still quite heavy.   The second example I posted would normally need two or three Rapiers to get through mach 1,  but with 2 panthers to get us to mach 2,  a single rapier is able to take us to mach 5 because of the ramjet effect at high speed.   An all rapier design would only get slightly faster airbreathing, because the Rapier thrust curve rapidly falls between mach 5 and 6. 

2.  Rapiers - keep to orbit 

See above.  Too expensive to chuck away.

3.  Empty fuel tanks - punch em off !

The issue is not so much the weight of the empty tanks,  but the drag they make in an atmosphere.  Most of an airplane's drag comes from fuselage parts in ksp aerodynamics.

4. Wings - keep 

If the part of the airplane that continues to orbit is nerv powered and liquid fuel only,  you'll definitely need those wings.  NERVs get great ISP but they are heavy and low thrust,  so any vehicle with a decent fuel and payload fraction will have  TWR less than 1.   This is actually fine,  provided your lift to drag ratio makes up for the weakness of your TWR.   With sleek mk1 size fuselage parts, a generous wing area and moderate angle of attack (5 degrees) you should be able to manage lift to drag > 3:1, meaning the orbiter stage will fly fine on a TWR of 0.3 or better.    Tip - ideally, don't use any fuselage tanks at all on the orbiter stage.   Big S wing and strake parts contain all the LF NERVs  are able to haul out of the atmosphere on their own,   and the drag/fuel capacity ratio is much better with wing parts than fuselage lf tanks.

 

Idea for a three stage design -

 

 If the orbiter, NERV stage is really underpowered, it may be unable to accelerate after the jet engines quit.   However,  if you can get up to 1700-1800 or so,  even a single NERV design can make it the rest of the way,  because you are approaching orbital velocity which reduces the craft's apparent weight.  This in turn allows the wings to get it up into the really thin air at 35km or so, where there's not much drag.    So,  some cheap LFO engines and tanks on drop pods under the wings can bridge this gap for you.

I've built some for earlier versions of KSP,  can't guarantee they still work.   

This is another retired stock craft I did some upgrades to, the Stearwing.  Originally a Whiplash/Terrier 2 stage,  I made it into a 3 stage Whiplash / Spark / NERV.   Here it is undergoing kerbal-rating qualification,  you can see the staging sequences..

https://kerbalx.com/AeroGav/Stearwing-D45N-Lite

 

[Guest]

TSTO is my go-to mode of spaceplane design. Like why would you not add droptanks for the jet portion of takeoff? They're so cheap, planes disposed of them by the thousands during WWII. Enceos made some wonderful tanks perfect for this purpose.

https://forum.kerbalspaceprogram.com/index.php?/topic/154044-1xx-kerbal-hacks-droptank-wrapper/

[Athen]

On 10/10/2019 at 11:10 AM, nwillard said:

...Take the the general coolness of taking off and landing on a runway., and combine it with the delta-v benefits of staging. It's naturally going to be more part-intensive and expensive than a regular launch, but...

I feel like this is a description of the space shuttle. lol