Show off your B9 Designs!

[Tripod27]

So I tried making an SSTO that can get 6 orange tanks up into orbit at once

Sadly, the runway did not agree

I did lower the difficulty to make the runway indestructible, and it did take off and fly around no problem, but the physics lag was so high on the thing that I just didn't bother. The one that gets two up at a time already runs at half speed until you get out of the atmosphere, so this one was probably running at 1/6 speed, and I didn't even add the mandatory 50 sets of airbrakes on it yet because it lagged much worse in the hangar

Edited November 25, 2014 by Tripod27

[Hodo]

That is AWESOME! I have never had a craft so heavy it destroyed the runway.

How much did that thing weigh? 671 tons?!

You could actually fix the physics lag if you cut down the parts count, Procedural parts and Procedural wings would save you so many parts.

[Bacon_commando]

Is that inspired by The Space Battleship Yamato/Argo (Uchu Senkan Yamato/Star Blazers, respectively)

Can we get a craft file? And what mods did you use? Just B9?

[Othuyeg]

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Sent a refueler / mothership to eve. It is an SSTO and has 20 000 m/s d-v left in orbit.

Casualgamer reporting in with his OP interstellar builds.

[PCanas]

So, I've tried with wings on bottom and engines on top, but then I had the opposite problem when I had the wings on top and engines below. So I decided to try with wings and engines in the middle. It's way more stable then it was before, but still have the problem of constantly pitching up or down, although much more softly than before. I didn't take any pics because it still needs some tweaking, but essencially, it's same design as posted before, but with the wings in the middle of the fuselage, and the engines mounted in the wings.

[Tripod27]

Check if any of your control surfaces are misaligned. What I mean by this is that when looking at the craft from the side, not all of the control surfaces are facing perfectly nose to tail flat from front to back and one or more are angled slightly

If they are, it destroys your top speed, especially at low altitude, and also if it's unbalanced, makes your plane "scoop" through the air. I'll just take some pictures to explain, since I had the problem with one of my planes

You see the green lines? Those are my rudders, and they're not straight. This causes a ton of drag by scooping a ton of air like a badly made parachute pulling on the top of my plane, which makes my nose angle up (opposite of your problem, but the same cause if it has nothing to do with center of lift or thrust)

I "fix" it by adding the little wing marked with the red line. This "scoops" the air in the opposite direction, which makes my plane want to nose down (which is your problem) but since it already wants to angle up from the other scoop, this evens out and it flies straight.

The only issue is that it causes a ton of drag and makes your plane tear itself apart at high speed and low altitude, but hey at least it looks cool

If this doesn't fix your problem,you can link me a version with the mechjeb part taken off so I can open it, and I'll try to figure it out

Edited November 26, 2014 by Tripod27

[Othuyeg]

My absolutely best design so far.

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The idea is that the baby ship is a refueler used to refuel other ships without the need of docking two large ships.

[Hodo]

So, I've tried with wings on bottom and engines on top, but then I had the opposite problem when I had the wings on top and engines below. So I decided to try with wings and engines in the middle. It's way more stable then it was before, but still have the problem of constantly pitching up or down, although much more softly than before. I didn't take any pics because it still needs some tweaking, but essencially, it's same design as posted before, but with the wings in the middle of the fuselage, and the engines mounted in the wings.

Ok sounds like you are having an SAS issue. In FAR the SAS is way overpowered and has a tendancy to overcorrect this causes a "bouncing" issue, where the craft pitches up and down with SAS on.

There are several ways to fix this.

- Reduce the control angle of your control surfaces.

- Download a PID tuner, there is one that is out there and it is quite good.

http://forum.kerbalspaceprogram.com/threads/100073-0-25-Pilot-Assistant-0-8-Nov-24-Atmospheric-piloting-aids

[PCanas]

Ok sounds like you are having an SAS issue. In FAR the SAS is way overpowered and has a tendancy to overcorrect this causes a "bouncing" issue, where the craft pitches up and down with SAS on.

There are several ways to fix this.

- Reduce the control angle of your control surfaces.

- Download a PID tuner, there is one that is out there and it is quite good.

http://forum.kerbalspaceprogram.com/threads/100073-0-25-Pilot-Assistant-0-8-Nov-24-Atmospheric-piloting-aids

When I said the plane is always trying to pitch up or down by itself, I didn't meant the SAS "woble". It happens with SAS turned off. I guess it's a problem with the CoL/CoM placement. I'll take more pics today.

[theend3r]

B9 + Interstellar + RealSchute + USI SSTO shuttle, FAR compatible:

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Extremely cheaty as it can go anywhere and back in about a week or so.

[PCanas]

Yay, pics!

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So, as you can see, the biggest change was the placement of the wings and the engines, thus changing the CoL and CoT.

I made two test flights:

1- take of, circle around KSC, land (or try...). This was to see how easily the plane flies and is controlled. It takes of quite easily and turns well too. Is way more stable than before. It takes of at about 80/90 m/s.

2- Go as high as possible. I managed to climb to about 27Km (on jet alone), but then the plane started to yaw to the right, and lost control completely. Meanwhile (27.8Km +-) the engines switched to rocket mode.

All test were made with no cargo.

Overall, the plane is constantly pitching down. Constant pulling up is needed. Managed to activate SAS with no wobling... once... but it was heaven!

Download craft file

[Tripod27]

As long as you have that mechjeb part on, I can't open your craft, since it says that I don't have that part. So all the stuff below is more guessing

If it's still unstable in flight (you said pitching up AND down?) try removing the winglets up at the front attached to the cockpit. This should move your center of lift far back enough to stabilize the plane, since planes with centers of lift right where the center of mass is usually fly like they have a "dead zone" where the nose just drifts all over the place

The reason you lost control (I think) at 27km is because those three big fuel tanks in the wings (they are fuel tanks right?). Two of them are located in front of the center of mass, which means that when they empty (and they'll be the first to empty, since the ones farthest from the engine empty first) your center of mass will travel backwards, since the tanks at the front are now empty and weigh less. Right click on the part and drag the fuel slider down to see what I mean. Anyway, because your center of mass moves back behind the center of lift, the plane becomes even less controllable that it was before until it gets to the point where it wants to fly backwards so much that you can't correct it with SAS or control surfaces, and it just flips around all over the place

There's no way to tell the game to transfer all fuel into the engine from all attached containers equally, so I try to keep all of my fuel tanks aligned with the center of mass, so my center of mass doesn't move when they drain. I also make sure that my cargo bays are both the same distance apart from the center of mass as well. In your case, since you only have one cargo bay, put the center off mass into the center of that cargo bay (also make sure to check how far back my center of lift is compared to yours)

Obviously you can't always do this (I doubt you want to put a fuel tank in the center of your single cargo bay, while it's easy to put a fuel tank between my two separate bays) so you have to use stupid workarounds like separating all of your stacked inline fuel tanks with big docking ports, then attaching a fuel line from every fuel tank into the wing, then attaching another fuel line from that wing to the engine. THEN when you load your ship onto the runway, right click on every docking port (or set up a hotkey in the hangar) setting them to not allow fuel crossfeed. This stops the tanks transferring to each other and forces them to all transfer into the wing, and they all transfer fuel into the wing at the same time instead of one by one, and then the wing transfers the fuel to the engine, which it is directly attached to with the fuel line (make sure the fuel line is attached to the ENGINE, and not the fuel tank in front of it, and make sure that it's separated from the fuel tank in front if it with that big docking port that's set to not allow fuel crossfeed)

Edited November 26, 2014 by Tripod27

[Van Disaster]

For FAR spaceplanes TAC fuel balancer is near-essential - it will balance tank drains while keeping some full or empty, letting you move fuel around while it's doing that. Nothing unrealistic about that.

If you want to balance fuel drains around a long single cargo bay, just put one at each end of it. You don't need the ramp in space

[Rune]

For FAR spaceplanes TAC fuel balancer is near-essential - it will balance tank drains while keeping some full or empty, letting you move fuel around while it's doing that. Nothing unrealistic about that.

If you want to balance fuel drains around a long single cargo bay, just put one at each end of it. You don't need the ramp in space

[Van Disaster]

Yep, although shifting fuel around manually to move CoM in stock is very annoying. B9 is not stock yet anyway

[Bacon_commando]

B9 is not stock yet anyway

Don't think B9 would ever become stock, way too many parts.

[Hodo]

Don't think B9 would ever become stock, way too many parts.

[Van Disaster]

Don't think B9 would ever become stock, way too many parts.

Compare the new Mk3 parts with the HL series sometime...

But no, not all of it.

[PCanas]

As long as you have that mechjeb part on, I can't open your craft, since it says that I don't have that part. So all the stuff below is more guessing

If it's still unstable in flight (you said pitching up AND down?) try removing the winglets up at the front attached to the cockpit. This should move your center of lift far back enough to stabilize the plane, since planes with centers of lift right where the center of mass is usually fly like they have a "dead zone" where the nose just drifts all over the place.

Just down. If I don't touch the controls, the plane will pitch down by himself.

If I put the CoL behind the CoM, even if just slightly, won't I have the same problem?

The reason you lost control (I think) at 27km is because those three big fuel tanks in the wings (they are fuel tanks right?). (...)

No, they are pre-coolers, with no fuel at all. They are there mainly for aesthetic reasons.

The only fuel tanks are 2 fuselage sections before and after the cargo bay, and the tail. I can try different fuel configurations, for example, instead of having all the oxidizer in the tail, spread it over those two fuselage sections I mentioned, and keep the tail empty, or with less fuel.

But even if they were fuel tanks, when they get empty and the CoM changes, wasn't it supposed to change the pitch? I mean, the CoM will change forward/backward, not sideways, right? The problem I had was with yaw, not pitch. I guess it was some aerodynamic failure, although FAR just warned about stall/side slip when I was already out of control, not when it started yawing.

About the MechJeb part, can't you remove it from the .craft file? If not, I'm only able to upload again tonight.

Edited November 27, 2014 by PCanas

[Hodo]

Just down. If I don't touch the controls, the plane will pitch down by himself.

If I put the CoL behind the CoM, even if just slightly, won't I have the same problem?

No, they are pre-coolers, with no fuel at all. They are there mainly for aesthetic reasons.

The only fuel tanks are 2 fuselage sections before and after the cargo bay, and the tail. I can try different fuel configurations, for example, instead of having all the oxidizer in the tail, spread it over those two fuselage sections I mentioned, and keep the tail empty, or with less fuel.

But even if they were fuel tanks, when they get empty and the CoM changes, wasn't it supposed to change the pitch? I mean, the CoM will change forward/backward, not sideways, right? The problem I had was with yaw, not pitch. I guess it was some aerodynamic failure, although FAR just warned about stall/side slip when I was already out of control, not when it started yawing.

About the MechJeb part, can't you remove it from the .craft file? If not, I'm only able to upload again tonight.

I will take a look at it and give you an assessment on what I think is wrong and see if I can fix it and send you a updated version in a few.

So I flew it, and I seen NO problems with that craft. At least no major problems.

It is actually a dream to fly, really nice design.

Without using my TAC Fuel Balancer to maintain fuel balance it actually flew pretty well, even though I expected the nose to get heavy at hypersonic speeds, but it didn't. The craft had pretty serious yaw issue at subsonic speeds but it wasn't uncontrollable. The craft is a bit twitchy at low speeds, but that is because the CoL is SO close to the CoM. The only problems I had with it was it had a great deal of drag, more than most of my design, by about a multiple of 5, most of my SSTOs only have a .02-.03 drag rating in FAR. But that comes with experience and time.

The flight profile I used was my standard flight profile.

Climb at best speed to 12km. In this case, it was 30deg nose up.

Bring nose down to 10deg and accelerate to Mach 5, at 25km.

Once at 25km, switch over when air flow is below 120% required.

After the switch over to closed cycle nose up to 24deg slowly, and climb till AP is desired altitude, in this case 75km for your craft.

Once desired AP is achieved cut engines and coast to AP, then perform circulization burn.

Your craft did all this with about 800m/s Delta/V left in the tanks. For some odd reason I was unable to look at the craft in the SPH, it just doesn't appear in there to me but I can fly it just fine. So I am unable to make any tweaks to it.

My only suggestions would be cut some of the dead weight, like the landing gear on the wing tips. You don't need them.

Otherwise it is a great craft. Good job, now you just need to learn how to fly it.

Edited November 27, 2014 by Hodo

[PCanas]

Thanks!

The wheels on the wing tips are like those little wheeles kids have in their bikes lol in the few tests I made I never managed to land leveled, and even a few degrees of roll would be catastrophic, so I add the wheels.

Since you can't access the craft in the SPH, I presume you didn't try it with cargo...

How can I solve the yaw problem at "low speeds", and drag?

Edited November 27, 2014 by PCanas

[mythbusters844]

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A space shuttle w/ carrier plane I made a rreeaalllyy long time ago. I don't have the .craft file as it's on my old computer. .

[Hodo]

Thanks!

The wheels on the wing tips are like those little wheeles kids have in their bikes lol in the few tests I made I never managed to land leveled, and even a few degrees of roll would be catastrophic, so I add the wheels.

Since you can't access the craft in the SPH, I presume you didn't try it with cargo...

How can I solve the yaw problem at "low speeds", and drag?

No I didn't get a chance to load it with cargo, so that sucked.

But as for the drag issue, you could remove a lot of redundant things that would help cut drag. The wings are something that is going to generate a fair amount of drag and there isn't much you can do about that. But the added wingtip gear are drag you don't need. Just go through and see about cutting useless parts, like some of those intercoolers, they are added drag and mass. They don't add any fuel and do nothing other than add drag. It will change the way your CoM sits, but they wont move it that far as they are pretty light when empty.

Like look at these three pictures of three completely different SSTOs I have built and all three of them are at the same point in their flights. Look at the C/D line on the FAR display. That is the drag display.

F/A-106A Thundergod, 0.024 C/D at .45Mach

SP-225, .023 C/D at .34 Mach

SP-501, .023 C/D at .57 Mach.

See a trend?

[PCanas]

No I didn't get a chance to load it with cargo, so that sucked.

But as for the drag issue, you could remove a lot of redundant things that would help cut drag. The wings are something that is going to generate a fair amount of drag and there isn't much you can do about that. But the added wingtip gear are drag you don't need. Just go through and see about cutting useless parts, like some of those intercoolers, they are added drag and mass. They don't add any fuel and do nothing other than add drag. It will change the way your CoM sits, but they wont move it that far as they are pretty light when empty.

Like look at these three pictures of three completely different SSTOs I have built and all three of them are at the same point in their flights. Look at the C/D line on the FAR display. That is the drag display.

See a trend?

Yeah, I see the trend: you have at least one kerbal with awful hair styling

Jokes aside, a C/D value between 0.020 and 0.025 at about 0.5 mach is desirable, right?

[Hodo]

Yeah, I see the trend: you have at least one kerbal with awful hair styling

Jokes aside, a C/D value between 0.020 and 0.025 at about 0.5 mach is desirable, right?

Ideally you would like a low C/D value the lower the better. I think my worst C/D craft in service right now has a value of .034 and it is MASSIVE, 630tons at take off without its 150 ton cargo.

It flies like a small moon and handles like an oil tanker. But it flies and reaches space... granted the frame rate lag is so bad, that it takes 30min to get to a 100km orbit in what it says is 15min.

The sad thing is I am not even sure if I will ever use it.

Edited November 28, 2014 by Hodo