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Flipping spaceplanes

finky45

By finky45
in KSP1 The Spacecraft Exchange

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finky45

finky45

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I've been trying to build a small LV-N shuttle to get my kerbals up and down from KO, and possibly from further out with orbital refueling. I really like the combination of Turbojets and LV-N, it seems like they are meant for each other by using one type of fuel. Anyway, I've had some issues building the smallest spaceplanes. I tried at first using a single LV-N and two Turbojets but the LV-N didn't have enough power to get a 17T craft to orbit. The LVN TWR was just too low at ~.55. Maybe I wasn't flying it right, but I tried many times. I read around and saw that most people use 2 LV-N and a single Turbo. I tried that and indeed the craft was able to reach orbit, but I didn't like how I had to use 2 LV-N which were expensive and also very heavy. Once in orbit the extra LV-N would be dead weight.

The solution was to have a single LV-N and a single Turbojet to have the smallest plane possible. But there is one major problem: You can't have them both face the same way without them being offset from the CoG which causes the plane to flip. The solution: stick the other engine on the other side and have them face opposite ways! I made an airframe that doesn't change CoG with fuel consumption and the CoL in the same spot. I didn't use any control surfaces and opted to use 2x medium stabs. The result: A light spaceplane with a single LV-N, and a single Turbojet. It flies very well and has about 1000 DV left over once in orbit. It's not done yet, but the proof of concept works.

How to fly it: Very simple. Not the most optimal but fly at a 30 degrees until the jet cuts out by itself then flip the plane over (sideways, not over the top!) and ignite the LV-N. Also the pod is facing the way of the LV-N, so control from there once you switch. Very stable plane. Haven't tried re-entry but that's usually easy to solve.

Lb4KJzd.jpg

Anyone have other ideas for small 1 LVN and 1 Turbojet plane designs? This has a downside that I don't have a place to attach a claw, or docking port that is not sideways. I found that sideways facing modules create too much drag and I try to avoid them...

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finky45

finky45

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It's a really interesting design. Have you thought about rotating the engines instead so their direction of thrust goes through the centre of mass?
The engines need a bit of clearance to work and that would mean I would have to have a large gap behind the engine.
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Val

Val

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...

Anyone have other ideas for small 1 LVN and 1 Turbojet plane designs? This has a downside that I don't have a place to attach a claw, or docking port that is not sideways. I found that sideways facing modules create too much drag and I try to avoid them...

Your concept looks very cool! A new take on the X-wing :D

My idea looks like this.

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Craft file

The RAPIER can be replaced with a Turbo-Ramjet, as the RAPIER is only used air-breathing. With the Jet being slightly weaker at high speed. The ascent above 10 km should probably be 10 degrees, not 15 as the instructions in the Imgur Album explains. And possibly engage nuke already at 18-20 km. You'll want pass 20 km with atleast 1200 m/s, preferably closer to 1350 m/s.

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selfish_meme

selfish_meme

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The engines need a bit of clearance to work and that would mean I would have to have a large gap behind the engine.

I meant instead of having an engine facing forwards, have them in a normal configuration but rotated so they fire through the centre of mass.

- - - Updated - - -

Like Val's second one...ninja'd

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finky45

finky45

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I meant instead of having an engine facing forwards, have them in a normal configuration but rotated so they fire through the centre of mass.

- - - Updated - - -

Like Val's second one...ninja'd

Ah yeah that was my first attempt and I think it would work.

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Val

Val

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I meant instead of having an engine facing forwards, have them in a normal configuration but rotated so they fire through the centre of mass.
Ah yeah that was my first attempt and I think it would work.

Two important lessons I learned while developing these is:

  1. Have your command pod and vacuum engine aligned in same direction.
    - Otherwise it gets real annoying when doing burns in space. The U-1 taught me that.
  2. It's no problem at all to have the air-breathing engine not thrusting directly towards CoM.
    - As long as control authority and gimbaling can compensate, it works beautifully that the jet engine loses power at the same rate as control authority, while you ascend.
    - It can even be used for advantage to help the nose up on a nose heavy craft.

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Doke

Doke

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I like these designs. Very... Kerbal. OP, have you tried putting a fairing (nosecone+decoupler) over the nuke? You might be able to squeeze a bit more delta v out that way. I usually do that on my SSTO nukes, even when they're facing backwards.

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Val

Val

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Funny thing about nosecones - I don't think they work. I did some tests and if I remember correctly they actually added drag.
Before 1.0 that was certainly true. But I don't think it is now.

Evidence seems to suggest that tail cones reduce drag.

And regular nose cones, certainly do: On the particulars of drag in 1.0.4.

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