Tips are welcome: wings on Mk3 (large, heavy) spaceplanes?

[Magzimum]

I recently started playing around with Mk3 fuselages. I want to build a large SSTO, which can lift large cargos into LKO. After many failures I compared my designs with successful Mk2 ships, and found that I just needed more wings. I compared the mass of the plane on take-off with the amount of wing. Basically, I need to put around 100 "generated lift" on my ship (which is a dimensionless number?). I was looking for tips, as I so far found only 2 options which I both do not like:

1. Put lots of relatively small wings on the plane. It will look like a Stegosaur, or a Porcupine, but it will fly. Even using the Big-S with Big-S elevons, I need about 14 such wings (7 on each side!). That would make it at least a biplane, if not a triplane.
2. Combine several structural wings into a single large wing. I failed to make this work, because my wings were too floppy and bendy. I failed to put a strut between two wing-segments. It just would not connect.

Any tips to put a metric crapton of wings on a plane is welcome. Pictures too.

 

 

 

[Empress Neptune]

How much are you trying to lift? I find that 8 Big S wings are pretty capable for a ~250 ton takeoff weight.

I prefer using Big S wings over the structural wings, even on small planes, since they carry fuel. So I would recommend sticking with them. They are also easier to work with structurally.

[Magzimum]

I am considering a 100 ton payload - mostly fuel itself, so if it is completely unfeasible I can cut it in half and just fly twice... but I consider it the Kerbal way to try to do it in 1 single impressive fireball. Not really sure how much the take-off weight should be for that, but probably a little over 250 tons.

I do like the Big-S wings. Not just because of the fuel, but they also just seem stronger (less bendy).

@Empress Neptune, what is the take-off speed that you need with 8 such wings and that weight? Did you add any other winglets or canards? (Do you have a picture? I am curious how you distributed 8 Big-S wings over a plane). My initial choice if I needed 8 wings would be a tri-plane in the back, and 1 in the front as a giant Canard/Winglet. But again, I am not really big on the looks of a tri-plane...

[Empress Neptune]

I have an album from a flight that lifted 85 tons to orbit. The takeoff speed is around 120 m/s.

 

http://imgur.com/a/8RrV2

 

I've lifted more weight by putting the payload outside of the cargo bay and filling the bay with more fuel. I don't think it was 100 tons (payload was the largest fuel tank in the game and some additional fuel in the bay tanks), but it was probably close.

[Magzimum]

@Empress Neptune, thanks! You have me some inspiration, and good ideas (at least, I haven't been proven wrong on it). Current model looks like this.

Note that my payload is mostly fuel... I am bringing a little more liquid fuel than strictly necessary  (yes, the entire length of that Mk3 is regular fuel tanks for liquid fuel, and a tiny cargo bay for reaction wheels, monoprop and batteries). I have thirsty a mothership and very ambitious overly complicated plans.

It doesn't make it to LKO yet, as the jets consume the liquid fuel from the rocket tanks, and I cannot pump it around quick enough to replace that. Newest model (not this pic) has slightly larger rocket fuel tanks, hoping that will help. Looking for a solution or workaround now to be able to consume all the rocket fuel... but that is a different topic, probably already answered somewhere else.

But at least she flies. And that's a big improvement from earlier today/yesterday.

[foamyesque]

I dunno, I think you're carrying more wing than really needed.

 

That's a 72-ton lifter. Going to 100t means you need more wing, yeah, but you shouldn't need that much more.

[Signo]

KSP does not care (more or less, you lose a fraction of lift) if wings are "thick."

Edited August 23, 2016 by Signo

[Empress Neptune]

5 hours ago, Magzimum said:

@Empress Neptune, thanks! You have me some inspiration, and good ideas (at least, I haven't been proven wrong on it). Current model looks like this.

 

Note that my payload is mostly fuel... I am bringing a little more liquid fuel than strictly necessary  (yes, the entire length of that Mk3 is regular fuel tanks for liquid fuel, and a tiny cargo bay for reaction wheels, monoprop and batteries). I have thirsty a mothership and very ambitious overly complicated plans.

It doesn't make it to LKO yet, as the jets consume the liquid fuel from the rocket tanks, and I cannot pump it around quick enough to replace that. Newest model (not this pic) has slightly larger rocket fuel tanks, hoping that will help. Looking for a solution or workaround now to be able to consume all the rocket fuel... but that is a different topic, probably already answered somewhere else.

But at least she flies. And that's a big improvement from earlier today/yesterday.

Nice, once you have something works, fine tuning should get you the rest of the way. One idea that might help with the fuel drain issue is playing with the pylon decouplers, you
 can enable/disable fuel flow across it and play with staging to force draining from certain tanks while leaving others full.

4 hours ago, foamyesque said:

I dunno, I think you're carrying more wing than really needed.

 

That's a 72-ton lifter. Going to 100t means you need more wing, yeah, but you shouldn't need that much more.

It depends on what you want to do besides optimizing payload carriage. My aircraft is overbuilt if you only care about payload fraction. I sacrificed some weight and drag to allow it to rotate before the end of the runway, maneuver easily in case of runway overshoot, and give it essentially unlimited g tolerance. Magzimum may have goals outside of raw payload fraction that would make more wing beneficial.

[Magzimum]

Thanks for the feedback. I think I'd rather just disable the tanks manually, then quickly enable two tanks (one on each side) before activating the rockets... and then click quickly through all other tanks to enable them all. A decoupler on the ship means that I will eventually decouple whatever it is holding on to. Also, putting in a decoupler now would mean I have to redesign the whole thing, as that should be put in between the main tank and the two side tanks.

Regarding "too much wing", that may be true, but this one still does not take off before the end of the runway. One main reason is that I need really heavy landing gear at the back (I use a total of 6 extra large gear in the back), but I want to be able to steer the plane on a runway, or for example on Minmus' flats to face the way I want it to. That means steering on the front gear is needed... and that limits it to the medium gear (3 of them). And that in turn means that its nose is pointing slightly down on the runway, because the medium gear is so short. I could obviously tweak that too... but as you saw this is a work in progress. 

For now, I am happy to report that v1.1 also flies (pic below, only small changes to v1.0). She's a little unstable on the controls... if I pull up, she also turns to the right a bit, but it is workable. She made it to fly at around 700 m/s, and 9 km altitude before crashing my game. Will try more later. Gotta run now  

Also, Burson, Bill and Bob were enjoying themselves tremendously. Pity that Jeb is already in LKO. He would have liked this.

[Signo]

If you do not give AoA to your wings you will waste fuel and available payload space. Moreover you will lift less "per engine".

[Magzimum]

1 hour ago, Signo said:

If you do not give AoA to your wings you will waste fuel and available payload space. Moreover you will lift less "per engine".

I realize that I created a few problems. But I have not been able to solve them... All I did so far was learn to live with it.

@Signo, how would you solve my problem of needing the XL landing gear at the back, and medium gear in the front, leading to a nose-down-on-the-runway-design?

I'd rather not turn the wings, because then the wings and main fuselage do not line up anymore. I considered to put the gear on a structural pylon, but it looks a little funny, and I am one keystroke away from decoupling my gear. [edit] and other girders are out of the question to me because of drag.

I'm risking that we derail this thread from wings to landing gear, but in a way it is all part of the same issue: if you build big you find new problems. Ideas for wings and wing-attachment tricks are still welcome! 

Edited August 24, 2016 by Magzimum

[Signo]

Stick the bigger ones on side nacelles and then offset them to the correct (wanted) height. 

Struts are "the devil" for planes but you need a few to avoid bending, that might be why your craft turns slightly when you pull up. 

(this craft can lift to LKO 40t)

 

KSP loves "leverage", you do not need so many control surfaces if you give them enough distance from the CoM to act - a "crowbar" works too, like in the pic above.

Careful with engines at the back - they may end offsetting your dry CoM.

KSP hates open nodes in terms of generated drag - try to close'em all if possible (notice the nosecones at the back of my rapiers)

You can deactivate the staging for structural pylons, I had a few crafts with that solution but I then scrapped it due to part and drag reduction. 

Edited August 24, 2016 by Signo
Leverage

[Empress Neptune]

You can disable staging on decouplers, making them purely structural. That will keep your nose gear fixed to the craft but it will still look funny.

The lack of large steerable gear is a problem with the current parts list, but there are a few work-arounds. You can offset the main gear into whatever it's attached to which will effectively make it shorter. Doing this also hides the gear fairing which is arguably a more realistic look. You can also use smaller gear instead of the Extra-Large gear for your mains, you will just need more of them. The XL gear has very high stress tolerance though, so using smaller gears will probably be heavier overall. The other downside with these two suggestions is that it lowers the height of the plane, which can make tailstrikes more likely. If you want to be able to steer yet still have nose level or nose up attitude, but don't necessarily need to do both at the same time, you can have two sets of nose gear. A tall set for runway takeoff and a Medium gear set for ground maneuvers. I've never tried this arrangement, but it should work on paper.

When it comes to wing AoA relative to fuselage, I have not seen big benefits from that arrangement. I've actually seen it make things worse. That doesn't mean it's not a good design choice, but I'm not sure if it should be universal. I like to go prograde at times during ascent and keeping the wings level results in minimum drag when doing so.

Edited August 24, 2016 by Empress Neptune

[Signo]

Empress, that depends on your flying path (and AoA of intakes too). It is not a matter of drag but a matter of pure lift - 8 rapiers can lift 280t (90t payload), if you waste that on engines you lose payload and you use a lot more fuel. Horizontal speed rules and you can attain orbit with a 0° pitch. The craft in the pic can lift stuff to orbit for a mere 150V$ per t of cargo.

Edited August 24, 2016 by Signo

[Empress Neptune]

Horizontal speed is certainly the most important factor, but I find vertical speed to be beneficial as well. A pure horizontal launch will suffer from drag losses, which are noticeably below 30,000m. I like to get above that altitude as quickly as possible. Vertical speeds of 200-300 m/s make it pass by quickly without requiring an overly steep ascent. I don't know how well angled wings work in that situation because most of my focus with them was on low speed flight. I have a bit more testing to do before I figure out the real advantages and disadvantages, so feel free to correct me when I make a mistake.

 

On cost, if I use the images from my album, I get a cost per ton around 120 funds/ton. I'm probably carrying more oxidizer, but it's cheaper than liquid fuel.

[Signo]

I am sorry but I could not find anywhere in the album either how much does the craft weight or how much does it cost.

 

You can obtain 150/200 m/s of vertical speed on wing lift just "going straight" with 5° wings AoA.

Edited August 24, 2016 by Signo

[Empress Neptune]

29 minutes ago, Signo said:

I am sorry but I could not find anywhere in the album either how much does the craft weight or how much does it cost.

 

You can obtain 150/200 m/s of vertical speed on wing lift just "going straight" with 5° wings AoA.

I subtracted initial and final fuel, found the cost and divided by payload. As a sanity check, I did the same with the image you posted showing fuel and I got 156 funds per ton for 40 ton payload. I'm assuming this (fuel cost only) is how you calculated cost, as SSTO costs should be recoverable otherwise.

[Signo]

Sure, that's it - but I was missing datas regarding your craft. Could not find'em in the pics.

I was not implying your "pay per t" price was a fake.

Edited August 24, 2016 by Signo

[Mikki]

There is no need for excessive wings on Mk3 fuselages, this SSTO is my ultima ratio 72ton lifter with some additional lift from Mk2 engine nacelles, it does surprisingly look like the skylon, with a single small elevon at the rudder far back (makes a powerfull pitch lever!).
It depends on many other things, if the plane goes up with little drag for example, and that CoL stays very near behind CoM all the time...



And it does fly excellent when emptyed (no need for pumping around fuel or shutting/ opening tanks during flight):

Edited August 24, 2016 by Mikki
Typooooooooooooooooooo:D

[foamyesque]

@Mikki: Yeah, Skylon-style balancing really is the way to go for heavier spaceplanes. The engine clusters just start weighing so much you have to get them as close to the midbody as you can to reduce your CoM shifts. You're carrying way more intakes than you need, though; one shock intake can feed six RAPIERS, maybe with a radial ram for some margin.

 

@Magzimum: Why are you insisting you need the biggest gears? I'd downgrade to the large landing gear. I've found them perfectly adequate, especially if you use more than two, for very heavy spaceplanes. If you mount them on the side of a fuselage, and the mediums on the underside, you can then use the offset tool to get them dead level with each other.

Edited August 24, 2016 by foamyesque

[Mikki]

10 minutes ago, foamyesque said:

@Mikki: Yeah, Skylon-style balancing really is the way to go for heavier spaceplanes. .... You're carrying way more intakes than you need, though; one shock intake can feed six RAPIERS, maybe with a radial ram ....

Good to know, i putted them somehow for the looks...  But i have stiil the grief for making a larger Mk3 plane that effectifely flies well and doesn`look like a warthog or such . Thank you anyway for advice!

Edited August 24, 2016 by Mikki

[Magzimum]

53 minutes ago, foamyesque said:

@Magzimum: Why are you insisting you need the biggest gears? I'd downgrade to the large landing gear. I've found them perfectly adequate, especially if you use more than two, for very heavy spaceplanes. If you mount them on the side of a fuselage, and the mediums on the underside, you can then use the offset tool to get them dead level with each other.

Because one of the test flights is always to take off (fully loaded), make a 180 degree turn, and land on the grass next to the runway. Using large landing gear (or just 2 XL gear) it collapsed through its gears, and then went up in an impressive fireball. 

Sure you do not need this feature - I also don't need the Mk3 cockpit, a little OKTO2 would be sufficient - but I like to have it as a feature: It needs to be able to land fully loaded. And a 2nd part of that answer is that I am not such a brilliant designer or pilot, and it sometimes comes down rather hard... So, with that test from my side, and my pilot skills, a little extra robustness is definitely a feature for me.

@Mikki, I did take notice of the 3 Mk2 hulls wrapped together to make a larger round engine nacelle (kinda) in your design. Those provide lift, as well as a place to mount your engines. It's a neat trick. 

Unfortunately, I don't have RAPIERs unlocked, so that has to wait for at least one interplanetary mission, for which I am now going overboard with the mothership and this tanker (yes, yes, I could just send a drone and get some science cheap and easy... but that's not the point of this game :)). 

[Edit] Guys, a little thanks is in order: you've provided me with a bunch of good ideas and answers, and in the meantime given me some good advice on other aspects of heavy lifters. Much appreciated! 

Edited August 24, 2016 by Magzimum
Thanking everyone for their help so far :)

[Magzimum]

Hmm... little update on my design. I made it to space the 1st time, and almost made LKO (I missed about 300 dV, I consider that quite close to LKO)... but on re-entry, all ordinary round fuel tanks overheated and eventually blew up.  That was not something I had encountered with the smaller space planes. I guess the big ones don't slow down so easily and heat up more as a result. So... back to the drawing board, replace all Mk1 fuel tanks and 2.5m rocket tanks with something more heat resistant. That is not a small fix.

[edit] Gonna try to incorporate a few other lessons learned here too.

Edited August 24, 2016 by Magzimum

[Stoney3K]

I have never been able to make an SSTO with the FAT wings, only with the Big-S ones. Are the airliner wings too draggy to be any good at supersonic speeds?

[foamyesque]

34 minutes ago, Magzimum said:

Hmm... little update on my design. I made it to space the 1st time, and almost made LKO (I missed about 300 dV, I consider that quite close to LKO)... but on re-entry, all ordinary round fuel tanks overheated and eventually blew up.  That was not something I had encountered with the smaller space planes. I guess the big ones don't slow down so easily and heat up more as a result. So... back to the drawing board, replace all Mk1 fuel tanks and 2.5m rocket tanks with something more heat resistant. That is not a small fix.

[edit] Gonna try to incorporate a few other lessons learned here too.

This is an angle of attack issue, I think. You're carrying lots of wing, so coming in dry you should be able to come to a stop quite quickly. Put your wings up to at least a 45 degree AoA and hold 'em there until you drop below 1200m/s or so. Also, if you're 300m/s short, you probably had a very steep re-entry profile; my descent from LKO normally has a periapsis of around 45km.