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We see double fuselages in both the huge Stratolaunch vehicle and in Virgin Galactics high altitude launch vehicle. What about this design makes it desirable?

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  • $\begingroup$ I edited the title as you seem to be asking about air-launch planes. If this is incorrect feel free to edit it back. There are lots of high altitude mono fuselage aircraft. $\endgroup$ – Dave Apr 27 '18 at 18:35
  • $\begingroup$ @Dave - Yes, you are correct. Thanks for the clarification. $\endgroup$ – David Apr 28 '18 at 1:22
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It is simple to maintain symmetry if the launch vehicle is in the middle, with two fuselages on either side.

With only one fuselage, the departure of the launch vehicle would change the symmetry, and therefore the lateral stability.

One possible exception is if the launch vehicle is directly above or below a single fuselage. This was done with the M-21 carrying a D-21 launch vehicle, where the D-21 was directly above the centerline of the M-21.

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  • $\begingroup$ I think there is a also a height advantage having it slung below a wing vs being slung under a standard cabin. With an engine/tail assembly then on both sides of the payload, that would help with takeoff stability, giving the benefit of 2 engines without the need of a 4-engine plane and being slung under 1 wing only. $\endgroup$ – CrossRoads Apr 28 '18 at 1:11
  • $\begingroup$ @CrossRoads: Think about the Space Shuttle and its modified 747 carrier, which was used to "launch" the Shuttle for drop tests. Now think about how you'd put a Shuttle and its fuel tank on that single fuselage. $\endgroup$ – jamesqf Apr 28 '18 at 18:15
  • $\begingroup$ I think that was more a matter of what was available to carry something that big & heavy, vs customizing for the state of the art now. What's less expensive to get up in the air - 4 engines on one of worlds largest aircraft (maybe the largest at the time) or two engines on a custom body designed from the ground up as a launcher? $\endgroup$ – CrossRoads Apr 29 '18 at 22:15
  • $\begingroup$ I envision the Stratolaunch being able to carry payloads that end up looking like the cabin section on this high wing twin, see 1:22 into the video youtube.com/watch?v=u_YTWgCuORc $\endgroup$ – CrossRoads May 1 '18 at 17:17

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