Help-a-Whack: SSTO edition

[Whackjob]

After this last break, I think I've decided on my next build. I think I'm going to go with freakshow SSTO. Something big. Something really big.

SSTOs are territory largely unknown to me. This thing I will be building will be necessarily huge and heavy. Is there any kind of rough formula I can use to kind of Kentucky-windage guess what thrust I need for weight? I will be using lift... wing surfaces I will use as a core component of construction, but this will look nothing like a plane. It will definitely be on the this-should-not-fly watchlist.

Anyone more familiar with this turf have any advice for me? This KSP newbie's going into brand new territory.

I figure I will use the high-altitude jet engines, as well as a moderate array of rapier engines which will double as sort of a ghetto transplanetary drive. I will have landing engines at a 90 degree angle (facing down, not back) that I figure I could use to elevate when at almost-out-of-air turf.

I know to hotkey the air intakes to close them to cut down on drag when going for orbit. Any other suggestions?

[Spartwo]

Replace the Rapiers with more turbojets and a skipper.(More of a personal preference as the ISP is a bit worse)

Edit:put a third row of wheels at the back of your ship off the ground.This will prevent tailstrikes if done right.

EditEdit:the rocket stage does not need a TWR above 1 as long as you have enough of a head start(you could use nukes)

Edited January 13, 2014 by Spartwo

[ferram4]

Go for a TWR somewhere around 0.5 - 0.7 or so at launch if you want to load it as heavy as you can. Make sure to sit on the brakes on the runway until the jets spool up to help get some extra acceleration. Consider using your "landing" engines to help get it up more than actually land it, since an empty SSTO (I'm assuming it'll be empty anyway) is a lot lighter than you think. If you're going with stock aero rather than FAR feel free to stick wings on top of each other and try "doubling up" on them where you have two wings in the same place to double the lift.

Make sure to mount the main gear on fuel tanks radially attached to the bottom of the craft right below the CoM so that it rotates very easily at the end of the runway and avoids tailstrikes. Consider designing the engine block at the back so that it has a slope at the back of it (sort of like modern planes have on their tails) to give it a little more room to pitch up. Put intakes at the back of the spaceplane to help make it more stable if you need that.

Piloting is an exercise in patience. Watch for a pair of engines making less thrust than the others; this means that you're running low on intake air and those engines are being slightly starved of air and that you should throttle back to prevent an asymmetric flameout.

Finally, consider replacing the RAPIER bank with a Mainsail or two set to an action group. Turn them on to get more acceleration on the runway, cut them off for acceleration to just shy of orbital velocity, use that for orbital maneuvering.

[FlamedSteak]

Prepare for frustration at the extreme end of the scale.

Tips:

1. Always keeping your centre of lift slightly in front of your centre of gravity is the most important.

2. Put your real wheels just very slightly behind your centre of gravity. Helps you to pivot off the runway.

3. Turn off snap to angle to mount your wheels, any deviation from dead centre will cause you to veer.

4. Keep it symmetrical or prepare to be a smoking hole in the side of the runway.

5. Keep your resources tab open to maximise your airscoops and engage rockets at the exact flameout point.

6. Strut it up: Rigid ships are less likely to smack a wing tip into the runway.

7. Climb up to 10,000m quickly, then level off and keep your prograde marker just above the horizon to get the most out of your jets.

8. Keep your rockets on the same central plane as your centre of gravity, as soon as your out of atmospheric influence you're going to flip wildly.

9. If you can get it off the ground you're halfway there.

Edited January 13, 2014 by FlamedSteak

[Whackjob]

Replace the Rapiers with more turbojets and a skipper.(More of a personal preference as the ISP is a bit worse)

Hrm. I'll consider this. Sounds reasonable.

Go for a TWR somewhere around 0.5 - 0.7 or so at launch if you want to load it as heavy as you can.

SSTO wise, I'm probably going to redefine heavy.

Make sure to sit on the brakes on the runway until the jets spool up to help get some extra acceleration. Consider using your "landing" engines to help get it up more than actually land it, since an empty SSTO (I'm assuming it'll be empty anyway) is a lot lighter than you think.

That was my plan... the image of this thing in my mind pretty much makes using the lander engines to detach from the runway mandatory.

If you're going with stock aero rather than FAR feel free to stick wings on top of each other and try "doubling up" on them where you have two wings in the same place to double the lift.

Yep, stock. This thing will look gossamer-like, but instead of trusses, I plan to experiment with using wing sections.

Make sure to mount the main gear on fuel tanks radially attached to the bottom of the craft right below the CoM so that it rotates very easily at the end of the runway and avoids tailstrikes.

I expect this to land more like a VTOL. Um... it might be something like half a kilometer long.

Consider designing the engine block at the back so that it has a slope at the back of it (sort of like modern planes have on their tails) to give it a little more room to pitch up. Put intakes at the back of the spaceplane to help make it more stable if you need that.

I'll probably be having engine clusters more than an engine block. This will be large enough to require "boosting" all along it. Stability I'm not overly concerned with... I've got that whipped for the most part, with my large builds. I don't doubt I can shoehorn anything into controllable status.

Piloting is an exercise in patience. Watch for a pair of engines making less thrust than the others; this means that you're running low on intake air and those engines are being slightly starved of air and that you should throttle back to prevent an asymmetric flameout.

I usually do that during a shakedown run and let it asphyxiate on purpose, then note the flameout level. Then launch for real.

Finally, consider replacing the RAPIER bank with a Mainsail or two set to an action group. Turn them on to get more acceleration on the runway, cut them off for acceleration to just shy of orbital velocity, use that for orbital maneuvering.

Mainsail might be a bit too much and heavy (I think I'll need 7 large engines in the back, not counting the jet engines... that might be more like fifty to two hundred)

Thanks for advice guys!

[Whackjob]

Prepare for frustration at the extreme end of the scale.

Me and frustration are old drinking buddies.

1. Always keeping your centre of lift slightly in front of your centre of gravity is the most important.

Gotcha.

2. Put your real wheels just very slightly behind your centre of gravity. Helps you to pivot off the runway.

This thing isn't going to have wheels so much as wheel clusters. The largest tires.

3. Turn off snap to angle to mount your wheels, any deviation from dead centre will cause you to veer.

Odd note... I'll actually be building this in the VAB, then moving it over to the SPH.

4. Keep it symmetrical or prepare to be a smoking hole in the side of the runway.

I've left quite of few of those already. On small things.

5. Keep your resources tab open to maximise your airscoops and engage rockets at the exact flameout point.

Right. I'll do a shakedown run and note the flameout level. I don't plan on airhogging, really. Maybe just a little.

6. Strut it up: Rigid ships are less likely to smack a wing tip into the runway.

As big as this thing is, there's no hope of it ever being rigid. I'm not talking big plane big. I'm thinking Arkingthaad tower lander plus boosters big.

7. If you can get it off the ground you're halfway there.

I think the lander engines will help greatly there.

[FlamedSteak]

Ahh sorry whack, I thought you were doing a runway take off with this.

[Whackjob]

Ahh sorry whack, I thought you were doing a runway take off with this.

I am. Join gonna build it in the VAB because of size concerns, then copy it over to the SPH. I'll launch from runway.

[FlamedSteak]

This is going to be interesting, make sure you put some update shots in here. I can't wait to see it.

[Captain Sierra]

I'm not talking big plane big. I'm thinking Arkingthaad tower lander plus boosters big.

Oh dear God! May KSP Aerodynamics have mercy on your soul!

[Sirine]

Note:I always admire your 'big' whack building.

You might want to consider this.

Build it at VAB will cause some 'balance' issues, due to the part placement are not...serial enough. Especially the wheels.

With this mod, KSC is your SPH.

http://kerbalspaceprogram.com/hangarextender/

Edited January 13, 2014 by Sirine

[vexx32]

Keep us posted, eh?

I'd like to see you try to fly a plane in Seconds Per Frame mode, hehehehe

[tmanrules97]

1. Always keeping your centre of lift slightly in front of your centre of gravity is the most important.

I'm not convinced that always making the center of lift in front of the center of gravity is the best idea. Placing the center of lift in front of the center of gravity makes the SSTO more maneuverable, which is good for slower speed SSTOs (which I think this SSTO will be), while placing the center of lift behind the center of gravity gives more control and aerodynamic stability (the center of lift [drag] tends to point retrograde from the center of mass) to the SSTO but possibly harder to maneuver and therefore control but not completely flip out. But then again, none of these "standards" could apply to this nonstandard SSTO. Just something to think about.

[Yakuzi]

The center of mass will change during flight depending on where you put your fuel tanks. You might want to keep this in mind when placing them, based on your track record there might be more than a couple...

You could try to overcome this problem by placing all fuel tanks at the center of mass or by putting your center of lift forward if your center of mass would move forward during flight, or backward if it moves back. Alternatively you could manually adjust the fuel flow to keep your plane balanced (good luck ) or use the TAC Fuel Balance mod by TaranisElsu for sanity purposes (I know it's you, but I feel obliged to give you the option).

Good luck WJ, can't wait to see what monstrosity you come up with!

[Vanamonde]

Since this is a how-to kind of question, thread moved to gameplay questions. Proceed.

[Yakuzi]

This thing isn't going to have wheels so much as wheel clusters. The largest tires.

Just noticed this. IIRC, any wheel units other than the landing gear will burst over a certain speed (tested this last in .22 so don't quote me plz).

[Whackjob]

The tireburst shouldn't be too much of an issue. I won't rely entirely on forward speed for lift. I'll use the lander engines until the aerodynamic forces are sufficient. Given what I have in mind, I should have oodles of fuel to spare.

I suppose I could make it just a VTOL, but since it'll be a giant rover also, I don't see why I shouldn't take off from the runway.

I'll put together a small proof-of-concept model right now.

[Whackjob]

Holy CARP. You guys weren't kidding about how feeble the big tires are under acceleration. Even with landing engines engaged to offset the weight, they crumple at high speed like they're made of tissue paper. And this is with the small scale model! I may have to instead do a crazy landing-gear-mass-assembly instead just to make it viable.

... that'll be an interesting engineering challenge.

Javascript is disabled. View full album

#EDIT: A reminder, this is a proof of concept model. I start with these because I expect failure like this. The actual should be considerably bigger.

The failure was just as expected. Them tires can't handle what I'm throwing at them, even with considerable reinforcement. I will have to rely on massive arrays of landing gear. Which will look absolutely silly on a really large ship. But... function over fashion. I'll have to deal with it.

#EDIT2: Huh. There's a "lift direction" I have to factor in. This will be... annoying.

Edited January 13, 2014 by Whackjob

[tavert]

None of the rover wheels are going to stay intact up to takeoff speeds on anything heavy. Aircraft landing gear are it for high speeds, as far as stock parts go.

[KvickFlygarn87]

Whackjob: Hilariously, the Imgur album gave an ad "Order now and get flight trip worth 300SEK"

[Soda Popinski]

Whackjob and Ferram on the same thread?! Worlds collide!

[Whackjob]

One thing I ran into: Wings of course have a direction of lift. I didn't think about that. Accounting for it will be... difficult. Not to mention the lander / wheel assemblies. That'll be annoying.

[John FX]

You could always just go pure VTOL if you have wheel issues.

One more thing, if you want thrust over about 20km you`ll need to spam intakes. 8 intakes per turbojet is a good start depending on how much thrust you want over 35km.

I don`t know if you would want to take advantage of any bugs but if you place your intakes facing the wrong way they still intake air but cause no drag...

[Pecan]

It will definitely be on the this-should-not-fly watchlist.

People just don't read the OP, do they? Everyone trying to help but ignoring the 'unlikely' requirement. If it becomes too difficult to avoid success feel free to call on my spaceplane piloting skills - I have a 100% failure rate so far.

[numerobis]

One thing I ran into: Wings of course have a direction of lift. I didn't think about that. Accounting for it will be... difficult. Not to mention the lander / wheel assemblies. That'll be annoying.

No; wings are symmetric.

I build SSTOs as big as 45t. Hopefully things scale linearly for you:

I use 1 turbojet every 15-20t.

I use 1 intake per tonne.

That gets you to within 50 m/s of orbit, so I use very little rocket fuel and wimpy engines to make orbit.

With that many jets flying full throttle, a small control surface nets you 5 kN or more of lift (depending on angle of attack) until 10 km. After that, you have to start to rely on jets. A wing connector gets a bit less lift than a small control surface, particularly at high angles of attack.

I use mechjeb to regulate the intakes (i.e. close excess intakes) and to throttle back automatically when you run low on air.

Edited January 13, 2014 by numerobis