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I still don't believe the viability of the sidemount, or that the people who suggested it aren't RisingFury's "McExperts". RisingFury is pretty knowledgable about aerodynamics (more so than myself), I doubt he is just talking nonsense.
Furthermore, in lieu of complaining about Energia-Buran's engineless sidemount;
There are various spaceplane designs that sit atop launch vehicles; while none of them might be quite as large, in relative terms, as Eridanus, I don't see why they wouldn't create "dangerous shockwaves on the boosters in transonic and supersonic flight", if that was a problem.
The major problem I can see with the in-line configuration is as RisingFury mentioned:
I don't see why that couldn't be corrected with elevator trim/thrust vectoring.
A mounting point for an inline vehicle should not be a problem; interstages and payload mounts, are not really problems. In fact, you could even reduce mass by minimising asymmetric forces.
And remove the TPS shield, and whatever fairing you seem to have on top of the propellant tanks.
It should be noted that both Energia and STS have the vehicle center of mass quite close to the bottom of the tank/stage. Side-mount Eridanus is quite far away from the engines. I can't help but thinking, that this mass is trying to buckle over the tank structure, on the pad and during launch. Think almost, of a tall tower; attach a mass to the base of the tower, and things will be fine (more or less). Attach the same amount of mass to the top of the tower, and the tower will have far more of a tendency to bend over.
It should be noted that Eridanus has quite large wings (as opposed to vehicles such as Avatar or Hermes), larger in proportion than those on STS, but STS also has pretty large wings, because of its large crossrange requirements (for AOA from polar orbit).
The one area where a sidemount might be better than an in-line configuration, is payload handling, because the payload bay is lower down. You might, in some cases, be able to load the payload into the vehicle at an earlier stage in processing.
Furthermore, in lieu of complaining about Energia-Buran's engineless sidemount;
There are various spaceplane designs that sit atop launch vehicles; while none of them might be quite as large, in relative terms, as Eridanus, I don't see why they wouldn't create "dangerous shockwaves on the boosters in transonic and supersonic flight", if that was a problem.
The major problem I can see with the in-line configuration is as RisingFury mentioned:
The problem then becomes instability... wings will start acting like canards. Even a small deflection that cannot get corrected by elevons will topple the space craft over.
I don't see why that couldn't be corrected with elevator trim/thrust vectoring.
A mounting point for an inline vehicle should not be a problem; interstages and payload mounts, are not really problems. In fact, you could even reduce mass by minimising asymmetric forces.
And remove the TPS shield, and whatever fairing you seem to have on top of the propellant tanks.
It should be noted that both Energia and STS have the vehicle center of mass quite close to the bottom of the tank/stage. Side-mount Eridanus is quite far away from the engines. I can't help but thinking, that this mass is trying to buckle over the tank structure, on the pad and during launch. Think almost, of a tall tower; attach a mass to the base of the tower, and things will be fine (more or less). Attach the same amount of mass to the top of the tower, and the tower will have far more of a tendency to bend over.
It should be noted that Eridanus has quite large wings (as opposed to vehicles such as Avatar or Hermes), larger in proportion than those on STS, but STS also has pretty large wings, because of its large crossrange requirements (for AOA from polar orbit).
The one area where a sidemount might be better than an in-line configuration, is payload handling, because the payload bay is lower down. You might, in some cases, be able to load the payload into the vehicle at an earlier stage in processing.
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