Question about wing position on real space planes.

[The Pink Ranger]

I just started using FAR and I've been making an effort to make my space planes as realistic as possible. For inspiration I've been looking at real life concepts. If you Google "space planes" almost every concept you see has the wings far below the center of mass at the bottom of the fuselage. Does anyone know the reason for this?

Edited August 10, 2014 by The Pink Ranger

[Pecan]

1. There aren't any real space planes (so feel free to design what you like)

2. They would need to go really fast (obviously) so are generally designed to absolutely minimise drag.

3. Which means they don't want to have lots of wing-area and big control surfaces.

4. That could make them handle very sluggishly.

5. But low wings (or anhedral) makes a plane more manoeuvreable.

6. In contrast google "heavy cargo planes" and notice they nearly all have high wings.

[The Pink Ranger]

The space shuttle is a space plane.

Edit: Here's some more space planes:

X-15, Buran, SpaceShipOne, and X-37

Also why would a space plane need to be maneuverable? Does the low wing position somehow compensate for the small area of the control surfaces in terms of maneuverability?

Edit 2: Also of note is that SpaceShipOne is the only one of the spaceplanes listed with wings above its COM. It's also the only one designed to ascend under its own power. Correlation?

Edited August 10, 2014 by The Pink Ranger

[problemecium]

Scott Manley has a nice video explaining it, although I lost the link. Should be easy to find though.

Long story short, having the wings up high makes the center of mass hang down like a necklace, which is stable, whereas having them low makes it balance on top like uh... something that balances on something else. Less stable. Less stable means perturbations such as turbulence will affect the flight more, but equally so will perturbations in the form of wiggling the control surfaces to make it go the way you want. It's hard to make a plane pitch or roll when the center of mass is much lower than the center of lift.

[Pecan]

Oh, I thought you meant ones that flew from runway to orbit and back.

Designing shuttle-like craft in KSP is very tricky, which is why nearly everyone that has one relies on one or more specific mods.

[RexKramer]

Also, a mid-mounted wing would need a carry-through spar, right through the center of the fuselage. A wing mounted low or high allows the spar to not travel through the center of the vessel.

A low wing also allows the horizontal stabilizer to be mounted above the wing, keeping the air over the horizontal stab undisturbed. You could do it backwards, with a high wing and low stabilizer, but then the stab is closer to the ground and may contact during takeoff or landing.

[The Pink Ranger]

Also, a mid-mounted wing would need a carry-through spar, right through the center of the fuselage. A wing mounted low or high allows the spar to not travel through the center of the vessel.

A low wing also allows the horizontal stabilizer to be mounted above the wing, keeping the air over the horizontal stab undisturbed. You could do it backwards, with a high wing and low stabilizer, but then the stab is closer to the ground and may contact during takeoff or landing.

Oh I see. All of the space planes I've seen with low wings are also designed to carry cargo to orbit. Guess that spar wouldn't be a concern in KSP. Don't suppose FAR simulates that last part either.

[Laie]

If you Google "space planes" almost every concept you see has the wings far below the center of mass at the bottom of the fuselage. Does anyone know the reason for this?

IIRC, you want one large flat surface to point towards prograde during re-entry. Protruding bits, edges and corners are problematic. A low wing that seamlessly joins the fuselage may create problems of its own, but computerized stability control is comparatively lightweight.

[Jett_Quasar]

A couple of things you need to keep in mind, first of all the wings mounted on the bottom can be used as a heat shield to block the damaging heat of re-entry. It's not really necessary in KSP unless you're using the deadly re-entry mod. Second, it doesn't matter where you put your wings, higher stability can be achieved by angling them upwards toward the tip so that the body of the craft is lower than the centre of lift.

JR

[Taki117]

IIRC, you want one large flat surface to point towards prograde during re-entry. Protruding bits, edges and corners are problematic. A low wing that seamlessly joins the fuselage may create problems of its own, but computerized stability control is comparatively lightweight.

Not to mention having that low-slung wing provides lots of protection to the squishy sides of the shuttle. If you notice on the shuttle the entire bottom is coated in heat resistant tiles, while the top part (The white parts) were made out of what amounted to quilted blankets.

See here for more info.

[RexKramer]

Oh I see. All of the space planes I've seen with low wings are also designed to carry cargo to orbit. Guess that spar wouldn't be a concern in KSP. Don't suppose FAR simulates that last part either.

No, it doesn't. You asked why real spaceplanes or hyper-sonic planes generally have low wings. You're getting explanations of why you see that in real life. In KSP, many of the design considerations real aerospace engineers face are less relevant, or not relevant at all.

I don't use mods, and find it most convenient in KSP to make planes with mid-mounted wings. The issues that would present in real life do not occur in stock KSP, and having bits mounted around the center of the ship generally makes them handle better (not always).

[Wanderfound]

The space shuttle is a space plane.

I'd call it a reentry glider, personally. Which reportedly flew like a brick.

[Alshain]

I'd call it a reentry glider, personally. Which reportedly flew like a brick.

More accurately Spaceplane is a broad classification and "rocket glider" is a more specific type of Spaceplane which all existing real world spaceplanes happen to be. It's kind of like saying "Motor Vehicle" vs. "Truck"... a truck IS a motor vehicle.

[The Pink Ranger]

No, it doesn't. You asked why real spaceplanes or hyper-sonic planes generally have low wings. You're getting explanations of why you see that in real life. In KSP, many of the design considerations real aerospace engineers face are less relevant, or not relevant at all.

I don't use mods, and find it most convenient in KSP to make planes with mid-mounted wings. The issues that would present in real life do not occur in stock KSP, and having bits mounted around the center of the ship generally makes them handle better (not always).

Yes well I'd rather build something that looks like it can actually fly in real life and learn something in the process. Thanks for explaining my own thread title to me btw. Should've posted this in the science labs. Thanks to everyone who actually took the effort to answer my question.