R.A.P.I.E.R. engines... do they suck or am I using them wrong?

[Wanderfound]

http://www.skyrender.net/lp2/ksp/spp_ssto3.jpg

Turns out FAR and RAPIERs get along better than I'd realized. Yes, that is 10 crew cabins.

Any reason for the ram intakes rather than shock cones BTW?

Incidentally, you could tidy it up a bit if desired by running the fuel lines under the wings and between the lateral tanks before using a single pair of connections to the core. SP+ passenger cabins are crossfeed enabled.

Edited September 1, 2014 by Wanderfound

[SkyRender]

...which is good. Finally we can build serious passenger liners that don't look like Whackjob monstrosities [1]. I'm hoping to do better than a 100 Kerbal audience for the Minmus ice races.

Given the interplanetary fuel range of the Migration​, you could easily add another four passenger cabins on the nacelles and still make it to orbit, BTW.

100+ Kerbals? You mean something like this?

(That thing was a nightmare to fly! It made it to orbit with 10% of its fuel left. Still, fully fueled in orbit it can easily do interplanetary.)

[Wanderfound]

Planning on taking half a dozen Migrations instead. I want a crowded parking lot as well as full grandstands.

At least four Porklifters for use as start/finish line marker posts, too.

Edited September 1, 2014 by Wanderfound

[Wanderfound]

http://www.skyrender.net/lp2/ksp/spp_ssto4.jpg

100+ Kerbals? You mean something like this?

(That thing was a nightmare to fly! It made it to orbit with 10% of its fuel left. Still, fully fueled in orbit it can easily do interplanetary.)

I want screenshots of you landing that thing on the Minmus ice flats, BTW.

[Random Tank]

Huh... No wonder why I've found RAPIERs quite effective! I play with NEAR, and I imagine it makes the same changes to Turbos and RAPIERs that FAR does; I made a simple SSTO the other day with 3 FL-T800's, 2 RAPIERs and some batteries and stuff, and that landed on the Mun with fuel to spare!

[SkyRender]

I want screenshots of you landing that thing on the Minmus ice flats, BTW.

You mean like this?

[Wanderfound]

http://www.skyrender.net/lp2/ksp/spp_ssto5.jpg

You mean like this?

Cool.

Got an entry for the ice racing championships?

[Cirocco]

I swear I must be doing something wrong in my flight profiles for SSTO's because I just can't believe it when people go "oh you can go up to 35 000m easy with pure turbojet", and I like to think I've become pretty good at spaceplanes. My latest and most efficient heavy-duty SSTO (interplanetary spaceplane with 4 turbojets, 4 rapiers and 4 nuclear engines) starts liquid fuel engines around 1400-ish m/s and 27 000 m up. And yes, I throttle down, cut excess turbojets, use the ramjet effect, all that stuff. Mind you, I use stock aero and I flat out refuse to intake spam to the point that I almost never mount any radial intakes on planes ever. A lot of people will call me crazy for going stock aero, but tried FAR and I kinda like the fact that it's harder to get in orbit in stock.

Back on topic: I find rapiers to be good for two things:

1) very light SSTO spaceplanes with a single stack. Looks nice, lots of power, easy design, fairly efficient.

2) very heavy SSTO spaceplanes where you simply do not have enough attachment points to mount the required combination of aerospikes and turbojets. Replacing a few turbojets with RAPIERs on those craft can help give them the thrust they need to make the orbital insertion.

So yeah, in my experience turbojet + aerospike combo is superior in terms of efficiency, but RAPIERs make for far simpler and sleek designs. And in FAR and NEAR, that matters.

[Wanderfound]

I swear I must be doing something wrong in my flight profiles for SSTO's because I just can't believe it when people go "oh you can go up to 35 000m easy with pure turbojet", and I like to think I've become pretty good at spaceplanes. My latest and most efficient heavy-duty SSTO (interplanetary spaceplane with 4 turbojets, 4 rapiers and 4 nuclear engines) starts liquid fuel engines around 1400-ish m/s and 27 000 m up. And yes, I throttle down, cut excess turbojets, use the ramjet effect, all that stuff. Mind you, I use stock aero and I flat out refuse to intake spam to the point that I almost never mount any radial intakes on planes ever. A lot of people will call me crazy for going stock aero, but tried FAR and I kinda like the fact that it's harder to get in orbit in stock.

First up: stock aero does make it a lot harder; soupmosphere drag is a killer. It can be done in stock, but it takes forever. FAR-induced aerodynamic failures are only a problem if you fly like a suicidal twit.

Secondly: see the piloting guide I posted upthread. Get to the thin air, flatten out, toggle and tweak to get the most out of your jets before you fire up the rockets.

And ditch the LV-Ns. Those things are boat anchors. You can get to Minmus and back just fine with RAPIERs alone. Add some Aerospikes or LV-909's and you can go anywhere.

If you want to, grab some of the designs linked in my .sig, take them into the SPH and tear them apart to see how they're built. Piloting is the primary factor, but minimising drag isn't far behind. It's not about relying on SP+, either; the Benchmark can casually hit a 70x70 orbit with tanks half full, and that thing is pure stock. It goes to orbit just as easy in stock aero as it does in FAR.

Or, if you lack patience, have a play with the Goblin. It can hit orbit in well under four minutes. The major difficulty with that one is in avoiding detonating the airframe through shock heating or excessive dynamic pressure on the way up.

Edited September 1, 2014 by Wanderfound

[MarvinKitFox]

FAR-induced aerodynamic failures are only a problem if you fly like a suicidal twit.

aHa! Found the flaw in my spaceplane!

[Wanderfound]

aHa! Found the flaw in my spaceplane!

It's a fine line between "suicidal twit" and "the true Kerbal spirit".

[Cirocco]

see the piloting guide I posted upthread. Get to the thin air, flatten out, toggle and tweak to get the most out of your jets before you fire up the rockets.

I already read it. It's a good guide, but I already use all of said techniques.

And ditch the LV-Ns. Those things are boat anchors. You can get to Minmus and back just fine with RAPIERs alone. Add some Aerospikes or LV-909's and you can go anywhere.

I can try, but my aim isn't Minmus, it's Duna surface and back in a single stage without ever refueling. And I don't think the Isp of aerospikes or LV-909's will cut it when going interplanetary.

If you want to, grab some of the designs linked in my .sig, take them into the SPH and tear them apart to see how they're built. Piloting is the primary factor, but minimising drag isn't far behind. It's not about relying on SP+, either; the Benchmark can casually hit a 70x70 orbit with tanks half full, and that thing is pure stock. It goes to orbit just as easy in stock aero as it does in FAR.

Or, if you lack patience, have a play with the Goblin. It can hit orbit in well under four minutes. The major difficulty with that one is in avoiding detonating the airframe through shock heating or excessive dynamic pressure on the way up.

I'll have a look at those, see what I can learn I set myself some pretty stringent conditions when building spaceplanes though

EDIT: had a look at the pictures of the goblin and the benchmark. I'll load a few designs up into the SPH when I get home (at work now) to take it apart and look at design, but from what I can tell most seem to be a lot smaller and lighter than the interplanetary ones I use. (The Dauntless comes in at an 83 ton spaceplane when fully fueled...)

Edited September 1, 2014 by Cirocco

[Wanderfound]

I already read it. It's a good guide, but I already use all of said techniques.

I can try, but my aim isn't Minmus, it's Duna surface and back. And I don't think the Isp of aerospikes or LV-909's will cut it when going interplanetary

I'll have a look at those, see what I can learn I set myself some pretty stringent conditions when building spaceplanes though

Apart from my specialist long-haul jobbies (e.g. Longreach), they'll all need an orbital refuel before going interplanetary. I'm okay with that.

OTOH, for the extremely easy way of getting to Duna: stick your Duna lander in the cargo bay of the Longreach. Fly out into Kerbol orbit, release lander, fly home. You can get away with a seriously tiny lander if you can give it a several thousand ÃŽâ€V headstart.

Keep in mind that stock vs Ferram aero is radically different, and all of my planes are tuned for FAR. Have a peek at the Cratermaker challenge thread (linked in .sig) for a visual demonstration of the difference it makes to the CoL markers.

I'm with you on the self-imposed limitations, BTW; the Goblin was partly done as a demonstration of the pointlessness of airhogging. Runway to orbit in 3 minutes 32 seconds, and exactly one intake per engine.

[Laie]

I swear I must be doing something wrong in my flight profiles for SSTO's because I just can't believe it when people go "oh you can go up to 35 000m easy with pure turbojet", and I like to think I've become pretty good at spaceplanes. [...] I flat out refuse to intake spam to the point that I almost never mount any radial intakes on planes ever.

Well, the latter is your reason. As things work out in the stock atmosphere, one intake/engine will start snapping for air at 18km. Two intakes, 24km. Three intakes, 26km. (Give and take a little for variations in airspeed. Emphasis on "a little".)

Your jets can of course go on while short on air, and depending on how much raw thrust you've brought along, you may keep going on jets for a good long while. Tough three engines times three intakes or four engines times two intakes isn't that much of a difference, intake-wise. So it boils down to intakes in the end.

32km is a magic altitude because drag has dropped enough that moving at 2km/s becomes possible, AND 2km/s at 32km is pretty much escape velocity. Just maintain that airspeed and you'll fly off into space. AND the higher you get, the less thrust you need to maintain that airspeed. Your starving jets can still provide most if not all of the thrust you need. It's called the 32km barrier because if a plane can get that far, it can also get much farther.

My 300-ton tanker goes to space on 32 jets and two(!) nuclear engines.

[Cirocco]

Apart from my specialist long-haul jobbies (e.g. Longreach), they'll all need an orbital refuel before going interplanetary. I'm okay with that.

Oh I'm perfectly fine with my craft refueling as well (though I really need to build a refueling station, up to now I just parked it into orbit, sent up a tanker and did a rendez-vous) doing runway-duna surface-runway without refuel in a spaceplane is just a challenge I set myself to prove to myself that it can be done. I basically wanted to land a spaceplane without refuel on another celestial body. Laythe and Duna are the obvious candidates, and I figured that a) Duna is closer, has a thinner atmosphere and less gravity and as such needs less delta-V and the no-oxygen thin atmosphere would provide its own unique challenges (and boy does it ever. Landing a plane in a conventional manner in a low-gravity, low-atmo environment with irregular terrain is a pain in the arse.)

I plan to re-design the Dauntless at some point to do runway-Laythe surface- runway. Not sure if I'll be able to do it, what with laythe being a LOT farther out than Duna, thicker atmosphere and higher gravity, but then of course I can use the turbojets while I'm there. Also I've never been to the Jool system yet so I imagine I'll have several issues pop up that I don't know about yet

[Cirocco]

32km is a magic altitude because drag has dropped enough that moving at 2km/s becomes possible, AND 2km/s at 32km is pretty much escape velocity. Just maintain that airspeed and you'll fly off into space. AND the higher you get, the less thrust you need to maintain that airspeed. Your starving jets can still provide most if not all of the thrust you need. It's called the 32km barrier because if a plane can get that far, it can also get much farther.

Now THAT is something I did not know. Very interesting indeed. It did always bug me that I needed those 4 RAPIERs just to do a single burn about 20-30 seconds long and then never use their rocket mode ever again (everything else is done on the nuclear stage).

I wonder if I can adjust the design on the Dauntless to get to 32 km on airbreathers. If I could rely completely on the nuclear stage for all liquid fuel burns, I could drastically cut on the liquid fuel amount, making the craft far lighter. I could try full-on turbojet with additional nacelles for added air and fuel...

To the design mobile! (also known as my ledger and ballpoint pen)

[cantab]

I can try, but my aim isn't Minmus, it's Duna surface and back in a single stage without ever refueling. And I don't think the Isp of aerospikes or LV-909's will cut it when going interplanetary.

For a Duna mission chemical engines can be competitive, less mass of engine offsetting more mass of fuel. Four nuclear engines weigh 9 tons, or the same as a Rockomax-16 tank. Since you've got chemical engines anyway, you might well get more delta-V without the LV-Ns. If not, consider switching to one or two nuclear engines not four.

[Laie]

Duna & LV-Ns:

If your ship is big enough, you can go hybrid. LV-Ns work well on Duna, their ISP should still be better than any other even in the deepest valley. So there's no reason to not run them. They may not be enough, of course -- in that case you'll need a few aerospikes or even plain old LV-T30s to get you off Duna. Over the entire mission, the high-powered engines may run for a full 40 seconds, everything else can be done on nukes.

[Cirocco]

For a Duna mission chemical engines can be competitive, less mass of engine offsetting more mass of fuel. Four nuclear engines weigh 9 tons, or the same as a Rockomax-16 tank. Since you've got chemical engines anyway, you might well get more delta-V without the LV-Ns. If not, consider switching to one or two nuclear engines not four.

One engine i'd prefer to avoid since I'd like to use the nuclear stage to take off from Duna again and I don't think a single LVN would have the thrust. And I'd prefer to avoid having to burn any engine other than the LVN's because of Isp.

The previous incarnation used 3 of them, but for design puposes I chose to go with an even amount this time. I'll have to check if 2 engines can provide enough thrust to lift off from Duna because 9 tons is an awful lot like you said. I might go back to the original 3 engine design, but that really makes them stick out the back, making tailstrikes a real danger, especially on uneven terrain like Duna.

[Jouni]

Well, the latter is your reason. As things work out in the stock atmosphere, one intake/engine will start snapping for air at 18km. Two intakes, 24km. Three intakes, 26km. (Give and take a little for variations in airspeed. Emphasis on "a little".)

Your jets can of course go on while short on air, and depending on how much raw thrust you've brought along, you may keep going on jets for a good long while. Tough three engines times three intakes or four engines times two intakes isn't that much of a difference, intake-wise. So it boils down to intakes in the end.

One intake/turbojet gets you to 32-33 km without throttling down, or above 43 km if you do throttle down. If you can't reach those altitudes before running out of air, you're either climbing too fast or don't have enough engines in the plane.

I used to build non-airhogging spaceplanes with stock aerodynamics. In my standard ascent path, I climbed quickly to 12-15 km, then tried to get the climb rate down to 100 m/s at 20 km, and then down to 50 m/s at 25 km. Moderate reentry effects at 20-30 km were a sign that everything was going as planned.

[Wanderfound]

Oh I'm perfectly fine with my craft refueling as well (though I really need to build a refueling station, up to now I just parked it into orbit, sent up a tanker and did a rendez-vous) doing runway-duna surface-runway without refuel in a spaceplane is just a challenge I set myself to prove to myself that it can be done.

Interested in having a go at that myself, now. FAR would certainly make it easier, though; stock air eats fuel.

The Longreach can do KSC runway -> Minmus surface -> KSC runway, but only just; it needs a direct-from-Minmus aerocapture to manage it. A Duna version would be a fair bit tougher, but there's plenty of slack in the Longreach; it's a high speed cargo hauler.

Are you willing to drop a lander from Duna orbit, or do you want to get the whole thing down into the red dust?

[Wanderfound]

BTW: planning on a VTOL, HTOL or parachute landing when you get to Duna?

[Cirocco]

Are you willing to drop a lander from Duna orbit, or do you want to get the whole thing down into the red dust?

The whole shebang. No landers, no rovers. One plane goes up, one plane does the entire mission, one plane comes back. That's the hard part: lugging all that dead weight around all the time. Oh and did I mention it's a 3-seater that uses the Mk III parts? I really think those don't get enough love.

BTW: planning on a VTOL, HTOL or parachute landing when you get to Duna?

HTOL. Using parachutes is hard unless you want to land her on the nozzles (which is what I did last time, and it just feels wrong for a spaceplane to do that) and vertical landing is also very hard because it is really hard to determine where exactly the CoM will be when I land: the CoM shifts during flight due to fuel drainage and I have no way of telling exactly how much fuel I'll have left upon arrival.

Plus, I figure it's a plane, so we land her and take off like a damn plane. It's quite challenging in an atmosphere as thin as Duna's, but fun!

Edited September 1, 2014 by Cirocco

[Wanderfound]

HTOL. Using parachutes is hard unless you want to land her on the nozzles (which is what I did last time, and it just feels wrong for a spaceplane to do that) and vertical landing is also very hard because it is really hard to determine where exactly the CoM will be when I land: the CoM shifts during flight due to fuel drainage and I have no way of telling exactly how much fuel I'll have left upon arrival.

Plus, I figure it's a plane, so we land her and take off like a damn plane. It's quite challenging in an atmosphere as thin as Duna's, but fun!

The whole shebang. No landers, no rovers. One plane goes up, one plane does the entire mission, one plane comes back. That's the hard part: lugging all that dead weight around all the time.

Found a good flat landing spot? With an atmosphere that thin, you're going to come down hard and fast. A few strategically placed Vernors and/or Sepratrons might not be a bad idea.

[Cirocco]

Found a good flat landing spot? With an atmosphere that thin, you're going to come down hard and fast. A few strategically placed Vernors and/or Sepratrons might not be a bad idea.

No pre-determined landing spot. Fuel will probably be pretty tight so I'll have to improvise a little once I'm in orbit, I don't think I'll have the luxury of spending fuel to manouver to a pre-determined landing spot Anything below 4000m and not *too* hilly should be fine.

I hadn't thought of vernors yet to slow vertical speed, but I am (or perhaps more accurately, Bill, Bob and Jeb are) painfully aware of the problem of coming in fast

I have a way of dealing with it, but I'll keep that a surprise for when I post pictures