Question about designing cargo transport space planes

[RainDreamer]

When designing cargo transport space planes, which of these two approaches, in your opinion, is better:

1. Designing around the cargo - each type of payload have a different design fine tuned to it and different ones will not fit/unbalanced. This would give an easier time flying, but you will have to have different design for each payload.
   
2. Designing around the space plane - focus as much as possible to get the space plane fly most efficiently, with generalized cargo space that fits most payloads. This may cause some problems from flight to flight due to different payloads with different mass and this require pilot skill to compensate, but you can use one design for a lot of things.
   

Edited November 25, 2014 by RainDreamer

[Wanderfound]

Depends on situation and preference.

The key to a multipurpose cargo spaceplane is to place the cargo bay directly on CoM; that way you can alter the cargo mass as much as you like while having minimal impact on the aerodynamic balance.

[RainDreamer]

The key to a multipurpose cargo spaceplane is to place the cargo bay directly on CoM; that way you can alter the cargo mass as much as you like while having minimal impact on the aerodynamic balance.

That is a very good tip. I have been looking for a way to transport most of my space station parts to orbit for cheap, and I think of space planes, but since the parts varied in mass significantly, I am having second thoughts. If I have to design a different space plane for every single part, it might be better to just launch a few at once with a bigger rocket. Though I will give it another go and see if I can make a multi-purpose cargo plane.

I will mark this as answered since there doesn't seem to be much response and I will be asking something else, but if anyone got more tips for building general purpose cargo transport planes I would gladly take note.

[Wanderfound]

You'd probably get some use from http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1353891&viewfull=1#post1353891 and http://s1378.photobucket.com/user/craigmotbey/Kerbal/Tutorials/Hangar%20to%20Landing/story

[Heagar]

In my opinion it is the best, to set a goal for a plane and then develop it. Building a plane around a cargo isn't the right way for me. Because i want a plane witch i can use whenever i want and don't have one risticted only for one mission.

I had the some problems, when i first tried to build a sort of space shuttle with the new parts. The first plane sucked really.

Then i had an idea for getting the payload bays in the vincinety of the CoW/CoM. Pairing them beside the fueselage of the craft. The result is the Excalibur:

However, the payload bays are smaller (shorter) then i wanted them (they consist one big and one small one). The plane is designed as an shuttle to an 150 km orbiting spacestation, witch it have to refuel and realeasing small sattelites/spacecrafts.

Issues of sutch a design:

• Due the weight out of the center it isn't as agile then other crafts. Witch causes a slow docking process for example.
  
• If you want to launch an single sattelite e.g., you have to have a counterweight. For me a fueltank in the opposite cargo bay. After releasing the sattelite the fuel from the conterweight is pumped into the center of the craft. The remaining difference can be handeled.
  

Depending on the fuel and payload - witch alters the CoW - the tank in the nose is used for trimming out the plane. The outter tanks are usually empty, but can be used in to have the max fuel ammount availible - the craft weights then 60t (normal weight 50t, dry 29t). With sutch an configuration i flew to Duna, using up all that fuel (i barely made it). But if i would refuel it at the spacestation, it would be easy.

The screenshots where made during the WIP process, i can take new pictures if you like.

Javascript is disabled. View full album

[capi3101]

DocMoriarty specializes in transporter spaceplanes. He had a pretty comprehensive guide on the subject going for v0.24.2, located here. The guide focuses on the use of the RAPIER engine (largely to keep part count and mass/drag down) in stock aero. So far the only thing I've seen that's undergone major changes between 0.24.2 and 0.25 is that the new Wing Connectors are functionally equivalent to Delta Wings, Shock Cone Intakes are equivalent to 1.2 Ram Intakes and 4 of the new Structural Intakes are roughly equivalent to a single Shock Cone Intake. I have heard that the RAPIER was nerfed as well but I do not know how.

The Doc utilizes approach number 2 - designing around the spaceplane. His guide includes numbers you can utilize based on the number of engines in the design; from there you have a "maximum take off weight" for which you can set the rest of the plane's general attributes. In his guide he builds a three engine craft - he knows his maximum takeoff weight will be 39 tonnes simply based on that general design premise (13 tonnes per RAPIER is the guideline he gives) and he designs the rest of the plane based on the assumption that it'll be 39 tonnes when it's done. His final plane winds up with an unloaded weight of 27.39 tonnes, leaving 11.61 tonnes for payload.

He does have a design capable of lifting a 27 tonne space station core, if you're curious. Biiiig plane.

Of course, the big issue is making sure the CoM of the payload aligns with the CoM of the plane - shifting CoM in flight can (and occasionally has) rendered aircraft unflyable in mid-air in RL, with the expected outcome. RCS Build Aid is a powerful mod tool when it comes to spaceplane design for this very reason (I would consider it an essential mod for anybody who spaceplanes frequently, much like I'd recommend Docking Alignment Indicator, KER or KAC).

[RainDreamer]

-post

It is a good guide. I am using B9 and NEAR, however, so I can't use those design. But it does serves as a good guideline in space plane design.

-post-

Interesting design, I didn't think about two cargo bays on the sides to allow more cargo to be sent at once.

[Alshain]

I design around a general cargo weight and size. If you don't, after delivering your cargo your plane could not longer be able to land. You have to make sure it's capable of lift off with cargo and landing without it. If your not careful, removing the cargo could shift your center of mass well behind the center of lift. You could do as Wanderfound suggests and put the cargo directly on the CoM, but don't forget fuel weight. Your spending fuel to go up which will alter the CoM too. If you have identical tanks equidistant from the CoM, it's real easy, but that can be difficult to design.

Edited November 25, 2014 by Alshain