[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[celem]

Yeah, I did build a lot of smaller stuff first. These are by no means meant to be realistic or even efficient, and are by no means my first FAR craft, though they are my first real supersonics. I do like using them, they repurpose to be interplanetary shuttles quite well from orbit, with 5k dV, more if i arrange to lose the skippers. the crew capacity is something of a key in this design. I need to lift as many crew as feasible per launch, with enough 'living space' for them to go interplanet in the ssto after a refuel. When this does reach orbit its generally still holding 1.5k dV.

It weighs 220tonnes without the jaydo solids and relies on a TWR of >1 to 'fly'. 3 jumbos, pair of 32's and then the 1.25m core is i think an 800 and a 200. Its got 6 aerospikes, a t30 and a pair of skippers. I get it, its a beast. But i still wanna fly it...think of it as a horizontally launched rocket with some aerodynamics to effect the powerclimb

edit: it's also the lightest of the shuttle designs im currently using. I have 2 others that will reach orbit from the runway, both considerably heavier, based on 3.75m and 5m cores. They dont really get more dV into orbit, but are awesomely useful once refueled at the station. My mod-shuttles are able to ditch their lift-surfaces once in orbit and become interplanetarys or hab sections. I just plain like the idea, all of these would launch better vertically, I just dont wanna since these can always re-enter if they want.

Edited February 4, 2014 by celem

[Surefoot]

@celem: your design has a lot of flaws. First try and drop the biplane idea. For a supersonic you want as little frontal area as possible. That means having a longer, slender design. Too many lateral tanks here... That also means increasing the wing sweep in order to mitigate the mach tuck. I suggest you try p-wings to start with, you'll discover a whole new world...

If you want to do a heavy supersonic, look at existing heavy designs: Concorde, B1-b, XB70,... The space shuttle is another example but consider it does take off vertically. See what those designs have in common (check the russian supersonic bomber too), check some documents that explain the engineering tricks that went into these designs, you'll then understand clearly what to do.

[celem]

cheers Surefoot. I'll have a bit of a rethink and try a single winged design. The lateral tank thing started as a way to stop the com moving steadily backwards as the central tank drains in sections, I'll try and work out something else for that.

[Surefoot]

For the tank drainage, i usually put multiple tanks on front of each other, and use that nifty new plugin that automatically pumps fuel from one to another. I used to move fuel around manually but that was a hassle (and forgetting means tumbling around...) -keep in mind that real world supersonics do this all the time (notably the Concorde and SR71, and all the others too, but these 2 are well documented).

On smaller designs such as the delta wing i posted above i am stable relative to empty COM - i use RCS balancer to tune this properly.

[toadicus]

ferram, or anyone else here who knows the aero subsystems better than me, I've quoted below a post from a user in my TweakableEverything thread, and my response. If I could get some confirmation, further clarification, or correction from you, I'd really appreciate it. Thanks!

Certainly. But I must say, I always use FAR, too. Though, I don't think FAR changes anything in the way control surfaces move.

Actually, my need to tweak control surfaces is tied to spaceships, rather than planes. The control surfaces behaviour is mostly similar for both, but while right/left simmetry is enough for planes, then is often not the case for spaceships: up/down simmetry is required as well.

To show what I mean, please look at the winged spaceship on the pad. I have set the spoilers to max deflection (75°) to better show. All control surfaces move in the same direction, both on wings and tail. The only exception, the upside-down winglets below the wings. But, both winglets on the "up" side of the wings have turned left (on both the right and left wing). The winglets on the "down" side have turned opposite, instead (that is more in line with what I would).

The issue is (far more with FAR then in stock KSP) that using spoilers that way will generate asymetric forces. So, I want to be able to choose (as KSP can't do so correctly) the direction each control surface will move as a spoiler, and so doing keep aerodynamic forces balanced

Correct me if I'm wrong, but just to be clear the behavior you're questioning is these two:

Also, correct this if I'm wrong: you are currently only toggling the "spoiler" control; you are not yawing, rolling, pitching, or flapping.

Consider this:

I don't think that's a control issue with FAR or something to be tweaked. The issue here is that those winglets are a single-axis control surface (like all/most of the control surfaces in the game), with a rotational axis pointing mostly along the yaw axis, or "up" and slightly "back" relative to the base of the part, as I've indicated. The spoiler control commands surfaces to rotate in around the "pitch" axis, with is nearly orthogonal to the control axis of the part. In KSP, control surfaces will rotate if they think they are capable of affecting the axis being commanded (and are allowed to rotate based on the current action). But, to determine that, they do some trigonometry based on their local transform vector and the commanded rotation vector and the center of inertia of the part, to decide if they can help and if so, which direction they should move to do so. So, because the rotation vector in question is pitch, and because they are both on the same side of the center of inertia relative to the pitch axis ("forward" of it, probably), they both decide to turn the same way. What's strangest to me is that on the other side of the wing, they've chosen opposite directions. This might be a 2nd/4th quadrant ambiguity or something like that.

Finally, I would question whether or not you actually want "spoiler" behavior on those winglets. If looks like you're building a VTO spaceplane and those are your vertical stabilizers: you probably do not want them to actuate when you are trying to spoil your aerodynamics. Those are primarily for yaw stability, and I don't think you will get the behavior you want by commanding them on the spoiler controls.

So, all of this to say: I could make a tweakable that, in theory, would reverse the direction of a part when commanded as a flap or a spoiler. But, that would not work well with your configuration above because the winglet that is "correctly" turning opposite its mate on the "bottom" of the craft would also reverse (thanks to symmetry).

[Surefoot]

Thanks to Ferram's suggestion, this beauty:

is now fully functional (as in, able to take off by herself). Moving the rear landing gears forward did it. Makes take off a delicate affair in order to avoid tail hit, but that's still quite easy.

Flies to mach 8.5 on Laythe (!!), mach 6 (maybe more ? didnt try) on Kerbin.

Is able to refuel in orbit thanks to a concealed, articulated dock port (in a cargo bay section). Also has leading edge flaps for these shorter take off and landings, airbrakes for re-entry management, ladders, generators and lights. And over 2500dV in space .craft file available on demand (if people want it i'll put it on dropbox)

I like the delta wing flying properties, it's behaving nicely at any speed including the usually horrendous transonic...

[Agathorn]

That IS a beauty!

Care to share?

[wasmic]

What is the recommended TWR for rockets with FAR? I heard that more TWR is better when working with FAR, but the result is that I can't make a gravity turn (even if i start right after liftoff), I'll only get to pitch over to 45 degrees before my apoapsis is above my targeted LKO.

[ferram4]

@toadicus: What's really happening there is that spoilers are intended to reduce lift, wherever they're placed. Apparently the vertical ones create a very tiny downwards force by deflecting to that side, so they'll deflect to that side. The spoiler assignment algorithm isn't designed for purely-vertical parts.

@wasmic: Whoever told you that more TWR with FAR is better is wrong. Best initial TWR range is between 1.2 and 1.6.

[Surefoot]

That IS a beauty!

Care to share?

Here you go

https://www.dropbox.com/s/oxc7homerzv008k/Delta%20Rapier.craft

Action groups:

1 - lower flaps (for take off / slow landing)

2 - raise flaps (once airborne)

3 - switch engines mode

You need the following mods: B9, Procedural wings, Magic Smoke Infernal Robotics (for the rotating dock in the cargo, i can remove it if you want). And of course FAR.

Enjoy !

[Boamere]

Here you go

https://www.dropbox.com/s/oxc7homerzv008k/Delta%20Rapier.craft

Action groups:

1 - lower flaps (for take off / slow landing)

2 - raise flaps (once airborne)

3 - switch engines mode

You need the following mods: B9, Procedural wings, Magic Smoke Infernal Robotics (for the rotating dock in the cargo, I can remove it if you want). And of course FAR.

Enjoy !

Hey nice job, i was wondering what the "set as flaps" option was in the SPH, i'm guessing it causes the centre of lift to change foward/backward?

[Raptor831]

Hey nice job, i was wondering what the "set as flaps" option was in the SPH, i'm guessing it causes the centre of lift to change foward/backward?

That option just tells the control surface to deflect to add lift to the wing. Results in more total lift at the expense of more drag. It varies on how much deflection you give it, as there's a point where if you give it too much deflection you've just made an airbrake more than flaps! Your CoL does adjust accordingly, but that depends on where you place them. It's nice for lowering your stall speed (like real life) and getting airborne on takeoff.

[Surefoot]

Raptor said it all On this plane, as you notice the wing sweep is quite extreme, and as such it's not suited for low speed flying at all, making take off / landing difficult. The flaps (here you can see them on leading edges) mitigate this problem here also allowing low speed manoeuvers without stalling. Quite needed as it is a space going plane made for Laythe, and landing there is quite tricky (mostly mountains on small islands..).

Oh also pressing the 'B' or whatever key activates the brakes for you will also toggle the airbrakes.

(edit) more eye candy, over Laythe with 8K textures:

Edited February 5, 2014 by Surefoot

[jpinard]

I'm having a bit of an issue I can't figure out. I had the gimble rocket motor on this rocket and was getting wobble when I got up to speed. Then I added fins and I still had it. Then I removed the gimbled rocket motor so I just had fins, and I still have the same wobble when using SAS. Do I need reaction wheel thingie to fix this? You can see at low speed it's fine, then higher speed it's bad, and when I cut the video off as I nearly entered space it stops wobbling again. Thanks for the help!

I turn SAS on and off so you can see it better.

Edited February 6, 2014 by jpinard

[ferram4]

The problem is that you have too much roll control, which causes SAS to way over-react to minor deviations in roll. Use tweakables to shut off roll on the fins and you should be fine.

SAS is terrible if it has too much control authority. Always bring less control then you think you need.

[a__gun]

Here you go

https://www.dropbox.com/s/oxc7homerzv008k/Delta%20Rapier.craft

Action groups:

1 - lower flaps (for take off / slow landing)

2 - raise flaps (once airborne)

3 - switch engines mode

You need the following mods: B9, Procedural wings, Magic Smoke Infernal Robotics (for the rotating dock in the cargo, i can remove it if you want). And of course FAR.

Enjoy !

Awesome, but also seems to need one part from the spherical tank pack. Some structural part I think.

[jpinard]

The problem is that you have too much roll control, which causes SAS to way over-react to minor deviations in roll. Use tweakables to shut off roll on the fins and you should be fine.

SAS is terrible if it has too much control authority. Always bring less control then you think you need.

Wow, learning something new everyday. So now I need to figure out this tweakables thing

[jpinard]

The problem is that you have too much roll control, which causes SAS to way over-react to minor deviations in roll. Use tweakables to shut off roll on the fins and you should be fine.

SAS is terrible if it has too much control authority. Always bring less control then you think you need.

This worked beautifully. Ferram I can't thank you enough as not only do my rockets work right now, but I learned something new that will make the game so much more fun (tweaking engines and fins and stuff).

[Boamere]

That option just tells the control surface to deflect to add lift to the wing. Results in more total lift at the expense of more drag. It varies on how much deflection you give it, as there's a point where if you give it too much deflection you've just made an airbrake more than flaps! Your CoL does adjust accordingly, but that depends on where you place them. It's nice for lowering your stall speed (like real life) and getting airborne on takeoff.

Thanks

I guess trial and error finds the right deflection levels

[Surefoot]

Awesome, but also seems to need one part from the spherical tank pack. Some structural part I think.

Ahh i'm terribly sorry, i totally forgot i used that small square strut in the cargo bay to support the articulated dock port. Replaced it with stock octogonal struts (as the stock girder is too big to fit) so you dont need the toroidal pack, just in case:

https://www.dropbox.com/s/oxc7homerzv008k/Delta%20Rapier.craft

If you have the toroidal tanks pack i advise you either download that one (and replace the octogonal struts if you want, just open the cargo bay and do whatever you want in there) or fix the "brakes" action group as it includes control surfaces (my mistake too, forgot to remove them), should be only controlling the airbrakes and wheel brakes.

[SkyHook]

So originally I just thought I was a terrible pilot, but I may have some interesting behavior to report.

This is my shuttle. Recently I have noticed that on reentry, my craft flips over and will not deviate from a "tail first" orientation. I have been trying to readjust my orientation, as I thought it might have to do with my reentry angle, etc. I noticed that the S2 cockpit (as well as the part behind it) from b9 produces 150 units of drag during reentry, and the fuel tank at the rear of the shuttle in the same conditions produces 15 units of drag. Could anyone help me in determining the reasoning behind this? The fuel tank (with about 400 units of LFO) has 4 times the surface area, but less than 10% of the drag of the front section of the orbiter.

[ferram4]

Well, that's simple. If you're flying straight into the airstream the cockpit has to deflect all of the air in front of the vehicle, creating a very high-pressure shockwave. That adds a lot of drag. On the other hand, at very high Mach numbers the fuel tank at the back is only dealing with skin friction drag. When it flips around and flies backwards the situation should reverse (mostly) with the cockpit making very little drag (which it will in 0.13, I finally got a handle on that issue) and the engine making most of the pressure drag.

Probably the reason it's flipping are the canards at the front and all the fuel at the back. You'll want to get rid of the canards and get pitch control using elevons instead.

[SkyHook]

Well, that's simple. If you're flying straight into the airstream the cockpit has to deflect all of the air in front of the vehicle, creating a very high-pressure shockwave. That adds a lot of drag. On the other hand, at very high Mach numbers the fuel tank at the back is only dealing with skin friction drag. When it flips around and flies backwards the situation should reverse (mostly) with the cockpit making very little drag (which it will in 0.13, I finally got a handle on that issue) and the engine making most of the pressure drag.

Probably the reason it's flipping are the canards at the front and all the fuel at the back. You'll want to get rid of the canards and get pitch control using elevons instead.

OK I will do that. I have a couple of questions though. I normally fly a heading of 90 degrees and a pitch of 20 degrees. Might that help with the issue as well?

[ferram4]

That angle of attack should be about okay, I think. I don't see why it wouldn't be for a stable spaceplane during reentry.

[SkyHook]

That angle of attack should be about okay, I think. I don't see why it wouldn't be for a stable spaceplane during reentry.

So after hours of testing so far, I have discovered that my fuel load does in fact play a factor in this problem. 650 units of LFO or more makes the spaceplane freak out and enter backwards, but 500 units of LF (no oxidizer) gives the craft a slight pitch forward tendency. This is a lesson that I had learned earlier in my shuttle building, but neglected to take it into account. Weight and balance is very important when reentering apparently . Testing will continue tomorrow, but thanks for your help!