New Rocket Jockey SSTO Problems

[TheDarkMechanic]

With change. You people are so freakin beautiful. And Slashy, you are a steely-eyed rocket whisperer. I will probably steal that design soon.

I present the x1.3 final, re-designated "Toothless." Yes...

Lost the struts, turned the rams down 5 deg, went with the locked swivel. I rely heavily on RCS to maneuver (to my station at 110,000m because I'm stupid) but I had way too much. This will suit me more than fine. Can we/I mark this thread answered? Thanks again all. You will be annoyed with questions again soon. I still miss B9 and Interstellar which made this so much easier.

Sled, not a fighter. So noted.

[GoSlash27]

Congrats on your first practical SSTO! Lookin' good.

It was actually a sound design the whole time. The only thing that was holding you back was the struts.

Best,

-Slashy

Edited August 25, 2015 by GoSlash27

[ajburges]

Since Slashy actually played with the craft, I'd follow his specific pointers. I'll just offer some observations.

Anaerobic power plant. Unless you plan on missions beyond LKO, Isp is a luxury. Getting good TWR is much more important. Due to the ascent profile, you need to double your speed without the time you would get from a more ballistic trajectory. This means you need around unity TWR to avoid passing Ap while you accelerate. That kind of power also allows you to transition to ballistic flight and get out of the higher pressure regions and escape drag losses .

I don't recommend taking single stage craft much past LKO without a refuel. You can't push chemical engines much past 4 km/s while keeping unity TWR and the dead weight of a plane.

Winglets (the vertical surface at the wing tips) are for drag efficiency IRL. They are a poor stabilizer because of the small cross product between the lift and CoM displacement vectors (IE they can't make much torque). KSP does not model the vortexes they reduce so they just add drag . Ditch them and increase the size of the rear stabilizer (which is much more efficient). I find the early tail wing piece works fine for most Mk2 planes.

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Saw you got it up. Very good.

[Nothalogh]

I still miss B9

So say we all

[GoSlash27]

Since Slashy actually played with the craft, I'd follow his specific pointers. I'll just offer some observations.

Anaerobic power plant. Unless you plan on missions beyond LKO, Isp is a luxury. Getting good TWR is much more important. Due to the ascent profile, you need to double your speed without the time you would get from a more ballistic trajectory. This means you need around unity TWR to avoid passing Ap while you accelerate. That kind of power also allows you to transition to ballistic flight and get out of the higher pressure regions and escape drag losses .

FWIW, I disagree with this part. Space planes are all about mass- efficiency, and IME you can get by with low t/w ratios once the jets starve out and still come out ahead due to the Isp bump. I generally design for .5 t/w and have gone as low as .35. It really depends on how aggressive the initial climb is.

I don't recommend taking single stage craft much past LKO without a refuel. You can't push chemical engines much past 4 km/s while keeping unity TWR and the dead weight of a plane.

Agreed. In fact, I *never* design spaceplanes to do any more than LKO with rendezvous and docking. Any more than that and you're best- served by not using something with wings/ landing gear/ etc.

Winglets (the vertical surface at the wing tips) are for drag efficiency IRL. They are a poor stabilizer because of the small cross product between the lift and CoM displacement vectors (IE they can't make much torque). KSP does not model the vortexes they reduce so they just add drag . Ditch them and increase the size of the rear stabilizer (which is much more efficient). I find the early tail wing piece works fine for most Mk2 planes.

Also agreed here. Aero fins are really just drag and mass that you have to shove into orbit, so "less is more" so long as you have enough to keep it pointed where you want to go. This design would fare better without them IMO.

Best,

-Slashy

[Nothalogh]

Also agreed here. Aero fins are really just drag and mass that you have to shove into orbit, so "less is more" so long as you have enough to keep it pointed where you want to go. This design would fare better without them IMO.

I like to use a pair of ventral fins for yaw stability when pitching up, of course that's with FAR, where your vertical stabilizer can get occluded from the airflow

[GoSlash27]

I like to use a pair of ventral fins for yaw stability when pitching up, of course that's with FAR, where your vertical stabilizer can get occluded from the airflow

Nothalogh,

Ain't nuthin' wrong with that. FAR is more realistic than stock, so it demands consideration of details that normally wouldn't apply to a stock install, like ventral fins, area ruling, etc.

But I have absolutely no experience with FAR, as I never use any mods whatsoever. This is so whatever info I manage to figure out (or more likely need) will always be applicable to as broad a range of users as possible.

But yeah... ventral fins make perfect sense where real life physics like airflow occlusion apply.

Best,

-Slashy

[Nothalogh]

Nothalogh,

Ain't nuthin' wrong with that. FAR is more realistic than stock, so it demands consideration of details that normally wouldn't apply to a stock install, like ventral fins, area ruling, etc.

But I have absolutely no experience with FAR, as I never use any mods whatsoever. This is so whatever info I manage to figure out (or more likely need) will always be applicable to as broad a range of users as possible.

But yeah... ventral fins make perfect sense where real life physics like airflow occlusion apply.

Best,

-Slashy

It's hard to say whether FAR makes things harder or easier, but it does make you have to pay attention to a few more little things in design.

The beauty of FAR though, lies in the fact that even a cinderblock can have lift, given enough velocity

[GoSlash27]

even a cinderblock can have lift, given enough velocity

Proof of concept

The old running joke for the F-4 Phantom was very similar; "You can make a barn door fly if you put a big enough engine on it".

Best,

-Slashy

[TheDarkMechanic]

I should have joined ages ago. I love you guys.

[Jett_Quasar]

So let me get this straight... Putting struts on your space plane increased the drag to the point that it couldn't get into space? That's so un-Kerbal!

JR

[Nothalogh]

So let me get this straight... Putting struts on your space plane increased the drag to the point that it couldn't get into space? That's so un-Kerbal!

JR

I rarely use struts anyway

[Jett_Quasar]

I rarely use struts anyway

Well you should they make your craft 20% cooler (and less explody)!

JR

Edited August 25, 2015 by Jolly_Roger

[TheDarkMechanic]

So, does that mean we're just biting the bullet and adding a lot of drag to our rockets every time we use boosters? Or am I the only one still strutting boosters down?

[Streetwind]

Well, a side booster tends to give more than you lose from strutting it down, so using side boosters is a sound decision. Especially with crossfeed to the core, which leaves a fully fueled single stack to fly on after jettisoning the boosters.

But yes, if you can achieve the same thing with a single stack, then using side boosters is often worse. This counts double for the step from 1.25m with boosters to 2.5m single stack, because the 2.5m engines outperform the 1.25m ones to an absurd degree nowadays (especially the Twin Boar and its 32+ TWR plus gimbal).

[GoSlash27]

So, does that mean we're just biting the bullet and adding a lot of drag to our rockets every time we use boosters? Or am I the only one still strutting boosters down?

Well... I use struts when I have to, but I minimize their numbers. Good struts are really more about geometry than numbers.

If you do use struts, be sure to root them on the part that's getting discarded. It's the root node that makes all the drag.

And of course... I don't use struts if I can avoid it.

Best,

-Slashy

[Nich]

Not to mention SSTO planes are doing 1400 m/s at 17 km to maximize air breathing engines where as rockets are doing 600-800 m/s Drag is 4 times less important.

[A_name]

http://hdwallpapersfit.com/wp-content/uploads/2015/03/f4-phantom-wallpapers.jpg

Proof of concept

The old running joke for the F-4 Phantom was very similar; "You can make a barn door fly if you put a big enough engine on it".

Best,

-Slashy

Same was said of the F-15 after an Israeli pilot managed to land one with only one wing. There's a video out there where they interview the pilot, basically he says that anything will fly given enough thrust, "like a rocket" (actual quote).

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OP, I don't know if you've had better success since you last posted but I wanted to pitch in some additional advice: understand the performance range of your jet engines. They produce their max thrust at a certain altitude and speed (don't remember the numbers right now). Make sure you design your ascent profile to take the most advantage of that "sweet spot".

[Jett_Quasar]

Well if struts are good enough for Space-X they're good enough for me.

"Several hundred struts fly on every Falcon 9 vehicle, with a cumulative flight history of several thousand."

JR

[GoSlash27]

Well if struts are good enough for Space-X they're good enough for me.

"Several hundred struts fly on every Falcon 9 vehicle, with a cumulative flight history of several thousand."

JR

JR,

Ahh, but that is "real life" and we're talkin' KSP.

"Basic physics are the same as real life such as gravity, but the rules are like those in any computer program. Some can be bent, others broken..."

In KSP, every strut is a little parachute, even if it doesn't *seem* to be exposed to airflow. As has been shown here, even struts that *seem* to be aerodynamic really aren't and they can render an otherwise acceptable spaceplane incapable of achieving orbit. The moral of the story is to avoid struts if you're going to be spending time inside the atmosphere. If you must use them, triangulate to keep them at a minimum and ditch them whenever possible.

"Do you think that my engines or my wings have anything to do with me being faster or more powerful in this place? Do you think that's air that your engines are breathing now?"

Best,

-Slashy

Edited August 26, 2015 by GoSlash27

[Jett_Quasar]

JR,

Ahh, but that is "real life" and we're talkin' KSP.

"Basic physics are the same as real life such as gravity, but the rules are like those in any computer program. Some can be bent, others broken..."

In KSP, every strut is a little parachute, even if it doesn't *seem* to be exposed to airflow. As has been shown here, even struts that *seem* to be aerodynamic really aren't and they can render an otherwise acceptable spaceplane incapable of achieving orbit. The moral of the story is to avoid struts if you're going to be spending time inside the atmosphere. If you must use them, triangulate to keep them at a minimum and ditch them whenever possible.

"Do you think that my engines or my wings have anything to do with me being faster or more powerful in this place? Do you think that's air that your engines are breathing now?"

Best,

-Slashy

Thanks for the heads-up on struts - I generally try to avoid them anyway because I like to keep part counts low, but when you're trying to get an SSTO to go to Minmus with and on-board ISRU it can be pretty tight. Also the random explosions due to excessive aerodynamic stress makes them a necessity sometimes.

So basically what you're saying is that the aerodynamics in V1.0 is not more realistic, it's just more complicated. Makes me wonder why Squad made the change. To me, having strut nubs keep a space plane from getting to orbit is just plain wrong and like many things about the aerodynamic model in V1.0.4 it needs to be fixed.

JR

Edited August 26, 2015 by Jolly_Roger

[GoSlash27]

Thanks for the heads-up on struts - I generally try to avoid them anyway because I like to keep part counts low, but when you're trying to get an SSTO to go to Minmus with and on-board ISRU it can be pretty tight. Also the random explosions due to excessive aerodynamic stress makes them a necessity sometimes.

So basically what you're saying is that the aerodynamics in V1.0 is not more realistic, it's just more complicated. Makes me wonder why Squad made the change.

JR

Well... the physics are what they are, for better or for worse. There's quite a few people who understand them better than I do. The important thing is to accept them as they are and just roll with it. There are some things that are easier in KSP than real life and some things that are harder. You have to account for the reality you're dealing with.

The standard KSP mantra of "moar boosters" works well enough for rockets, but spaceplanes are all about efficiency so the reverse applies here. You always want less boosters, less struts, less dead weight... less stuff that's getting in the way and not adding anything to achieving the objective.

Instead of thinking "what do I need to add to make this work", you want to think "what can I get rid of that's getting in my way".

If you get into that mindset, spaceplanes are pretty easy. It's not really a matter of being smart so much as just having a proper state of mind.

Best,

-Slashy

[Jett_Quasar]

That's a great attitude and I'm sure it has served you well but unfortunately the new young players that I've introduced this game to don't feel the same. They look at the space plane mechanic as overly complicated and difficult and quickly get frustrated and lose interest. Don't get me wrong, I love space planes I just think the aerodynamic model needs to be adjusted to take into consideration the more junior players - and basically it just needs to be fun again. For all those hard-core space plane aficionados, there's the FAR mod (which is still used by many), for the rest of us the aerodynamics should should be enjoyable.

JR

[Nothalogh]

Calling FAR hardcore is a bit of an overstatement, and as for spaceplanes being a little tough, NASA feels your pain

[Jett_Quasar]

I don't want to hijack this thread with back-and-forth about how game mechanics should work but the simple fact is SSTO space planes don't exist in the real world, so who's to say how they should actually work in the game.

...but I refuse to accept that strut-nubs will cause an otherwise perfectly fine space plane to be unable to reach orbit.

JR

Edit: There's no spoon, but there is a difference between knowing the path and walking it.

Edited August 26, 2015 by Jolly_Roger