Spaceplane trouble: New Areo? Or my new designs?

[Brainlord Mesomorph]

Since I started 1.0, I’ve been working on some new heavy spaceplanes and they handle strangely, and I’m trying to figure out if it’s my new designs are simply the new aero system.

My new designs are all variations on a MK2 delta wing biplane, 350 plus tons. They all take off nicely, climb and accelerate nicely up to about 300 m/s and/or 6 km. At which time I have to totally level off (0 degrees) to get any further acceleration. Assuming I do, I can accelerate horizontally to about 400 m/s, at which time I can begin climbing and accelerating again. (it’s almost like there’s some sort of “barrier†at the speed of sound!)

The other problem is throughout that time the ship is very difficult to steer, ridiculously easy to overcorrect , I can only call it “slippery.†(esp. roll) and if you lose control, you just tumble out of the sky. Once we’re above 750 m/s she’s easier to handle, and by 30 km or so, we’re maneuvering primarily on the gyros and retros so that’s okay.

So my question is, is this a problem with my design (hypersonic deltawing biplane?) Or simply a more accurate simulation of what is like to break the sound barrier?

[Guest Space Cowboy]

Simple answer to the roll instability or lack of roll authority in any regime is more ailerons. Also, it's possible your CG is just a smidge too far fwd. Try a flight with that adjusted. Also, your center of lift might be below your center of mass, making your vehicle handle like when you're trying to balance a broom, vs just holding it from the handle, hanging down, and letting gravity stabilize it.

[Brainlord Mesomorph]

CoM CoL and CoT are all perfectly aligned.

CoL is a hemisphere stuck to the back of the CoM ball. (that IS perfect right?)

[Red Iron Crown]

My new designs are all variations on a MK2 delta wing biplane, 350 plus tons. They all take off nicely, climb and accelerate nicely up to about 300 m/s and/or 6 km. At which time I have to totally level off (0 degrees) to get any further acceleration. Assuming I do, I can accelerate horizontally to about 400 m/s, at which time I can begin climbing and accelerating again. (it’s almost like there’s some sort of “barrier†at the speed of sound!)

There is a bump in drag around the speed of sound, as in real life. It is not uncommon to have to level off or even pitch down to punch through it, especially if you're using Rapiers as your atmospheric propulsion (they don't come into their own thrust-wise until supersonic).

For stability issues, a picture of one of your affected craft would be very helpful.

[GoSlash27]

Brainlord Mesomorph,

I'm having a hard time picturing a 350t Mk2 design. Could you post some pics?

Best,

-Slashy

[Brainlord Mesomorph]

There is a bump in drag around the speed of sound, as in real life. It is not uncommon to have to level off or even pitch down to punch through it, especially if you're using Rapiers as your atmospheric propulsion (they don't come into their own thrust-wise until supersonic).

For stability issues, a picture of one of your affected craft would be very helpful.

Still working on my "Spaceplane Sandwich" concept. That's an 85 ton ISRU mining/refinery platform in the fairing.

This is Baker2 Foxtrot. ( I think you have Baker2 Charlie)

It gets to orbit .. if you're verrrrry careful at 300m/s

Edited September 25, 2015 by Brainlord Mesomorph

[Red Iron Crown]

That blunt fairing step out is causing a ton of drag. I would also consider struts between the wingtips so the planes can't roll relative to each other, see if that helps with stability.

[Brainlord Mesomorph]

That blunt fairing step out is causing a ton of drag.

Sorta required given the shape of the payload,( guess I could add a spacer to push t he nose father out)

I would also consider struts between the wingtips so the planes can't roll relative to each other, see if that helps with stability.

They're there. (can't see them well) Specifically, directly above and below the landing gear.

I'm thinking maybe too much control surfaces? That;s 8 BigS Ailerons Plus the 8 vertical "delta deluxe winglets" (OH plus 2 sets of canards, although they seem to really help)

Or that may just be how an 85 ton coke bottle strapped between 2 Concordes would fly.

Edited September 25, 2015 by Brainlord Mesomorph

[GoSlash27]

I concur with RIC.

A draggy nose is a recipe for all the control issues you're having. See if you can extend the procedural fairing and give it a more gradual ogive.

As for the control surfaces, I really can't tell by that picture.

Cool concept, BTW

Best,

-Slashy

[cantab]

I believe the "speed barrier" in KSP is down not so much to drag as to thrust. The turbojets and RAPIERs have a strong ramjet effect that kicks in somewhat above the speed of sound and makes the thrust go way up and the plane accelerate hard, but getting to the needed speed in the first place can be a bit tricky.

[Brainlord Mesomorph]

OK, OK, OK, (most educational game ever!) Drag can cause airplane stability problems?!

I figured drag could cause speed problems, fuel consumption would be higher, but I don’t understand how (even, symmetrical) drag could cause handling problems? Or the overcorrection that I’m seeing.

(EDIT: light-bulb goes on: Once I start turning, my even symmetrical drag isn't even or symmetrical anymore! now its causing more drag on one side - is that it?)

I need to understand more of this “drag†of which you speak.

suggestions for further reading?

Edited September 25, 2015 by Brainlord Mesomorph

[Red Iron Crown]

If the center of drag is ahead of the CoM the plane will try to flip around, just like a rocket does. Unfortunately there is no CoD indicator in the editor.

[Brainlord Mesomorph]

If the center of drag is ahead of the CoM the plane will try to flip around, just like a rocket does. Unfortunately there is no CoD indicator in the editor.

boy do we need that!

So it’s obviously my payload modules that have too much to drag, and are moving the CoD forward. So: pointier payload modules (obviously) and adding fins to the back of the payload module?

Any other ideas?

EDIT: Wait more than fins; an *extension* off the back of the payload module (long girder segment or 2) and fins on the end of THAT. like the tail on a dart! I can certainly visualize how that would help keep my nose(s) forward!

EDIT II: another question: what about the "suction" drag (i'm sure that's not the right term)of a flat bac k end vs. a pointy back end. Does KSP model THAT? would that move my CoD aft?

Edited September 25, 2015 by Brainlord Mesomorph

[GoSlash27]

EDIT II: another question: what about the "suction" drag (i'm sure that's not the right term)of a flat bac k end vs. a pointy back end. Does KSP model THAT? would that move my CoD aft?

It does model that... sorta. But it's a very small amount of drag and it disappears rapidly as you approach Mach 1.

For best results you always want to have the nose as clean as possible. You can compensate for the stability issues with fins, but you really want to avoid adding drag wherever you can when building spaceplanes. That's the whole key to their performance.

Best,

-Slashy