The Changeling

[drewscriver]

Ladies, Gentlekerbs and Jebediah , from the designer of Dragonshy, presenting Pegasus Carriageworks and Discount Haberdashery's latest craft: the Changeling

Clocking in at up to 125 tons and 856 parts on takeoff (including sample cargo), the Changeling can haul a Rockomax Jumbo-64 tank into 100x100 orbit without breaking a sweat. Upon reaching your desired orbit, simply undock and pivot the wing nacelles open to reveal the generous internal cargo bay.

If this is a straightforward orbital cargo run, just drop off your cargo, close the bay and fly back down. Otherwise, you can undock the still-fully-fueled fuselage from the aero section, and set out on a longer journey.

At this stage, the fuselage functions as a transfer vessel, capable of landing on low-gravity, non-atmospheric bodies. When you've run out of SCIENCE! and/or snacks, simply return, pick up your wings, and proceed to land on Kerbin.

For a fuller demonstration of the Changeling's capabilities, please refer to the following:

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Interested?

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On the proper care and feeding of your new Changeling (the long version).

- Action groups -

1 - Outermost Turbojet engine pair

2 - Middle Turbojet engine pair

3 - Inner Turbojet engine pair

4 - Tail Turbojet engine

5 - Main Atomic engines

6 - Vertical descent engines

7 - Landing gear (excluding legs)

8 - Nacelle opening Ant thrusters

9 - Toggle lower atmosphere intakes (8 fuselage mounted intakes)

0 - Toggle high altitude intakes (all the others)

the Abort group is configured as well

If you need to use the deorbit engines on the aero section, I'm afraid you'll have to turn them on manually via right-click - I simply didn't have enough action groups left.

Flight guidelines:

- Pre-launch -

Stage once - this should be the only time you have to stage, unless you will be landing via parachute.

Hit 0 to close unnecessary intakes to reduce drag

Hit 5 & 6 to shut down rockets.

- Ascent to orbit -

For an overall profile, check out pa1983's great post on cargo spaceplanes. I learned a lot from him, and have basically adopted the ascent profile he outlines for all my flights. The Changeling has more intakes-per-engine, so it's ceiling is a little higher, but the basic principles are the same. Additionally, his Laythe base delivery video was one of my big inspirations when starting work on SSTOs (way back when I first made the Chalice).

Anyway, as far as the Changeling goes, once you've completed pre-launch, throttle up, and take off! With a full load of 36+ tons, the Changeling should be able to lift off at about 75 m/s - just a bit past the SPH. Pitch to 45 degrees and sit back and watch the altimeter rise.

At around 15,000 feet, you will start to run low on intake air - hit 0 to open up the high altitude intakes.

In the 18,000 - 27,000 range, begin to gradually drop the nose, so you moderate your vertical velocity, and begin to build speed.

At around 28,000 be prepared to level out. Your goal is to kill your vertical velocity so you can linger in the 32,000 - 34,000 meter range, and build speed.

I find the most effective way to do this is to toggle back and forth to the map view and monitor the apoapsis. The vertical speed indicator, and especially the altitude, are lagging indicators. The apoapsis reflects your change in vertical velocity more directly - to use it, you want to adjust your attitude so that the apoapsis continually stays just a few seconds ahead of the aircraft.

Once your velocity reaches 2,000 m/s or above, you can relax your vigilance on your altitude, and let the craft begin to ascend. As the air thins, it should continue to pick up speed, as well.

At 35,000 feet or above, you will begin to run out of intake air again. When the craft first begins to yaw, immediately hit '1' to shutdown the outermost turbojets (you can delay this slightly by throttling down, but it's ultimately easier to kill engines). Continue to ascend, and you should again begin to gain both altitude and speed.

After you've shut down the two most outermost engines, the Changeling becomes more flameout-friendly, as from now on, the engine that seems to cut out first is the central, rearmost one. Monitor it, and kill additional pairs of engines as necessary. When you're down to the last three engines or so, the Changeling keeps gaining altitude, but the jets begin to loose the battle on acceleration. It may be more efficient to continue to ascend on jets, but I usually just kick on the rockets at this point and nose up past 20 degrees.

On reaching 44,000 feet, your final engine will probably flame out - shut it down, and don't forget to hit '9' and '0' to close intakes. From here on, you should be able to coast into orbit, though you may need the occasional boost from the atomics to counteract atmospheric drag.

- In orbit -

Now you should be in orbit, hopefully with a good chunk of fuel left (low-to-medium orbits, should be fully supplied by the aero stage, leaving the fuselage resources at 100% ). Anyhow, onto the good stuff!

To get at your cargo, open the wing nacelles via undocking the connecting ports (I recommend saving first, just in case). I tried to undock via action groups, but it isn't working for some reason, so you'll have to do it manually. There are 5 connections - two clamp-o-tron jr ports in the rear, two standard clamp-o-trons at the front, and one clamp-o-tron jr. underneath. To get at them, I recommend using the Chase camera - all of the others typically have wonky orientations, and don't like to go inside of the craft. Once the nacelles are undocked, make sure all other engines are shut off, then enable the nacelle thrusters by hitting 8. It may take a little practice to know how much to throttle, and for how long. The Changeling uses the structural pylons as hinges. Unfortunately, they can potentially bend at either end, so their motion is unpredictable. To accommodate this, the Changeling has attachment points for both possible situations, though this means that the wings will not open symmetrically when the two pylons bend differently.

At this point, the rear clamp-o-tron jr. ports should have engaged, and the craft is probably spinning / wobbling a bit. I'm afraid you'll have to wait for it to damp down on its own. I recommend leaving SAS OFF for the most part. Judicious SAS use will arrest the spin, but leaving them on often makes the wobble worse, as the reaction wheels are at the far end of the wobbling, flexible booms, and KSP isn't expecting the changed craft geometry. I usually only turn SAS on for brief periods, until the wobble has died down, at which point you can leave it on for station-keeping.

Be very careful with the wings open. Remember, the whole bendy pylon thing is basically a glitch, and in this state, the Changeling is extremely vulnerable to the KSP physics engine. Do not time warp, unless you want your craft converted into a debris field as soon as the warp ends. Moving out of physics range before closing them isn't a very good idea either, so be very careful when switching between craft. Likewise with saving/loading. Save before hand, do your stuff, and only save again once the dust has settled.

While the wing nacelles are open, you can detach any payload you may have in the cargo bay. If this was just a cargo run, things are simple - just undock your cargo, and boost away a bit. Then go to the rear of the craft, undock whichever clamp-o-tron jr. ports engaged, and the wing nacelles will swing closed and re-dock automatically. They may swing back and forth a bit, but they'll eventually settle down.

If this is an orbital cargo run, congratulations, you're almost done. Skip down to the Deorbiting section.

If this isn't a cargo run, now is when you decouple the main clamp-o-tron sr. port, and start voyaging. Once you've moved away a little bit, be sure to switch back to the wings briefly and close them - leaving physics range when the wings are not in their neutral state is a recipe for trouble.

- Planetoid landing -

If you're going to land, you'll want to use the atomics as much as possible. I'm not an expert at landing, but what worked for me was killing the orbital velocity and then bringing it in nearly vertical at the end. When you're down to 1000 meters or so off the deck, use one last burst of the atomics to kill your vertical velocity and then rotate around so the belly faces what will be your takeoff prograde. After that, drop the nose down until you're horizontal and engage the vertical engines for the very last portion of landing. There is a clamp-o-tron jr. docking port on the top that you can use to 'control from here' if you prefer that viewpoint.

Taking off again is pretty simple - use a quick burst of the vertical engines to get some clearance from the surface, and then nose up and kick on the atomics. If you didn't land pointed in the right direction, you'll have to do some more maneuvering, but it should be doable. Now head back to wherever you stashed the wings (or the wings of another changeling - they interchange just fine).

I suspect it's Duna capable, but I haven't tested it yet, so no guarantees.

- Redocking -

Redocking is probably the trickiest part of working with the changeling. As discussed earlier, opening the wings usually results in a lot of wobble, SAS doesn't help much, and time warping is a no-no. So again, patience, and after the wobble works itself out, and you can move in to dock (it is a little wobbly rotating, but not nearly as much as opening the booms). A couple of things to note; this is docking together two reasonably large craft, so even with all the RCS thrusters, it's not all that easy. Also, orientation matters - the side docking ports will not engage the fuselage if it is off by more than a few degrees. On the plus side, the craft weight and thrusters are arranged so that it is well-balanced, and translation maneuvers do not induce undesired rotation.

Warning - the moment you succeed in docking, KSP physics will flip out on the aero section. I'm not sure about the exact cause, but I think the nacelle positions are reset to neutral, but they are still docked to the tail, which immediately wrenches them away and the causes them to swing back and forth violently. Don't panic, turn SAS off, and let it calm down. Now is a good time for a cup of coffee or a bathroom break. You can speed the process up slightly by waiting until both wing nacelles are swinging inwards and briefly activating the nacelle opening thrusters to kill a little bit of momentum. Once it calms down, undock the rear clamp-o-tron jr. ports, watch the wings close, and pat yourself on the back. Congratulations! You've just accomplished a rather tricky task (and probably a cool mission in the middle).

- Deorbiting -

In the event you are unable to re-dock with the aero section, it has its own guidance and deorbit thrusters plus a small reserve of fuel, so it is capable of self-deorbiting. Actually landing In this configuration is challenging, but possible - you may spin out during re-entry, but after regaining control it is flyable (barely). In this state, it flexes quite a lot, and at low speeds the wing nacelles may start to oscillate - turn SAS off if it starts to shake itself apart.

Similarly, the fuselage can land independently as well via parachute, if it is not heavily laden. Make sure it is level when the parachutes catch the air just above the ground, and briefly use the landing rockets to kill velocity on touchdown (given the current strength of the landing struts, it should touch down at 5 m/s or less).

If you have reconnected the two pieces, it should fly in pretty normally. COG should remain ahead of COL, and if it does spin out, it's not too hard to get back under control. Just be careful that the wings don't fall off in high-G maneuvers. It also does not play nicely with time acceleration. In straight and level flight, I've gone up to x3 and very briefly x4, but it looked like the wings were going to come off at any instant. Under normal acceleration, it still flexes a fair amount, and at low speeds the nacelles can start to oscillate up and down - if this happens, the best approach I've found is to just turn off SAS for a bit. On landing, be sure to use the landing gear group '7' to deploy the landing gear, instead of using 'g', or you will deploy the landing struts as well.

Note - the nacelle opening thrusters and the de-orbit thrusters on the aero section share a private fuel supply. This is intended so you can't accidentally drain your ability to open the nacelles, as well as providing an emergency deorbit buffer. If you're running on fumes, however, you can transfer this fuel back into the main tanks for a small emergency reserve.

- Are we done yet? -

... right. So that was a ton of writing, but it pales in comparison to all the time I spent building and flying this thing. Anyhow, I'm pretty happy with the results, and I hope you enjoy it as well.

Download Link

Happy Flying!

Sincerely,

Drewscriver

Edited November 5, 2013 by drewscriver

[Save Ferris]

This is incredible! Really great design

[NASI Director]

Let me get this straight: You built a space plane capable of splitting in half and delivering a payload, so you decided to make a Munar spacebus in conjunction with it?

Awesome.

[drewscriver]

This is incredible! Really great design

Thanks! I'm glad you like it.

Let me get this straight: You built a space plane capable of splitting in half and delivering a payload, so you decided to make a Munar spacebus in conjunction with it?

Awesome.

Umm, yes?

Heh, getting the fuselage right was actually the hardest section; the wings were relatively simple, except getting the rear docking ports positioned so they would connect under both possible pylon-bending cases was... an exercise in patience.

[Rune]

Bravo! A very original take on hinges. I can only imagine the work it was to get everything working right . One minor point, but did you know that the last engine placed in the SPH is the first that flames out? So just take the central one out and in again, and you will get that nice flameout warning you talk about at all times. Weird rule not everyone knows about.

Rune. Now you do!

[Cranium]

Wat.....

WHAT IS THIS SORCERY? MOVING PARTS???

Props to you, man... Although, you might be able to accomplish this in .22 with the new landing legs. They make just about the same angle as what you have there, and it might be more stable as well.

[drewscriver]

Thanks, Rune, I'm glad you like it, and I did not know that particular trick! I'll have to go back and tweak the design accordingly. As-is, flameout warning is vital; with the forward engine positioning to help with the COM, the Changeling is basically using an anti-stabojet design.

Interesting thought on the legs, Cranium, when I get some time, I might have a look at using legs instead of the radial Ant thusters to open the wing nacelles. It wouldn't get rid of the need for bendy pylons and the rear docking ports, I think, but you wouldn't have to worry about fuel for the rockets. One tricky bit, though, is that the nacelles bend at slightly different angles, depending on which end of the pylon ends up pivoting...

[Tw1]

That hinge system is very impressive. I might have a go of this, when I start refuelling stuff.

[briansun1]

Nice, like the name and refrence

[Comrade Jenkens]

nice looking design with moving parts and a cargo bay, wow!

[drewscriver]

Thanks, guys, I'm really happy to see folks getting a kick out of it. Originally, I was just trying to figure out a decent way to implement a stock docking bay, and I ended up going a bit overboard...

[Goldham]

Really cool, would download if the part count wasn't so high.

[drewscriver]

Really cool, would download if the part count wasn't so high.

Yeah, part counts are one of my weak points - sorry. I'll see if I can make a pass to cut out a few, but there's only so much I can do before it comes to eliminating features.

[128MB]

Can you post a video of it unfolding?

[barrenwaste]

Dang this thing is sexy with the unfolding wings on a stock craft. That part count is killer. Heh, I had been congratulating myself on building smooth, streamlined, craft that push boundries. Now I can see I need to work a lil harder for that. Beautifully done, sir.

[tom1499]

Nasa get your damn priorities straight, a detachable fuselage SSTO is the way to go! Gonna download this now!

[Kerbies_are_my_Minions]

JasonLii says "You are welcome for the hinge design. " Your docking ports do not work with keybindings because the craft stays one craft and it creates a hierarchy issue. We are working on a work-around on making the ports still work on keybinding.

[chinchulin]

Don't know if I'm doing something wrong but I can barely get this craft of the ground and highest horizontal speed I've been able to get is 85ms tried following exact instructions but can't do it

[jmiki8]

Wow! Amazing design!

...And i can't even build a single stock cargo door...

[ExplorerKlatt]

Does anyone know if this still works in .23.5