Wanderfound

Okay, to start with: * Too many intakes. It has massive drag. One ramscoop per engine is plenty for an atmospheric ship. * No rockets that I can see. Not a spaceplane yet. * Not enough lift. There's barely any wing on that thing. * No lateral stability at all. Planes have tailfins for a reason. * Barely adequate thrust. Two turbojets are enough to propel a plane with normal sized wings; they're massively inadequate for an ultra-low drag/lift design like this. Have a look at post #2 and #3 of the Kerbodyne ​thread linked below.

Dihedral = aero surfaces angled up. Anhedral = aero surfaces angled down. Dihedral increases roll stability, anhedral increases roll agility. Both also add a bit of longitudinal stability, increasing with distance from CoM. The offset weight distribution induced by vertical stabilisers often gives spaceplanes a bit of engine torque. You can fix this by angling your engines, or by shifting mass. Shifting wings moves a bit of mass, shifting engines (most easily done with lateral engine/fuel/intake pods) moves a lot (as well as moving torque). Balancing anhedral vs dihedral on wings and tailplanes (horizontal) can provide a bit of longitudinal stability at the cost of a bit of lift. Angling vertical stabilisers (tailfins) outwards gets a reduced version of the dihedral tailplane effect, but trades longitudinal stability for lift. Everything in airframe design is a matter of competing tradeoffs.

BTW, y'all get that the Alkahest variants and the Archer are basically the same airframe? It's another case of "get something that works, tweak it into everything you need". The new SPH tools make dihedral and thrust balancing very easy. Set RCS Build Aid to Engine/Thrust mode, and put just the space engines in the first stage. Offset or rotate (depending on if you want anhedral/dihedral wings) the lateral engine pods to minimise torque. An/dihedral wings can be offset with an angled tailplane.

Behemoth: pitch up problems mean a lack of longitudinal stability. Either shift CoM forwards (to give the tailplane more leverage), reduce lift forward of CoM (reduce pitch-up force), or increase lift rear of CoM (increase pitch-down force). As you gain altitude, the air thins. This reduces the force available to your aero surfaces. Thus, increased speed is required for stability at increased altitudes. An aerodynamically messy craft can be forced through the upper atmosphere by gaining sufficient speed at lower altitudes. From the pic, you've taken the Wedgetail airframe, shifted the wings forwards a bit and added a small tailplane. The tailplane partially compensates for the wing shift, but not enough. Try removing the canards and cranking up the control authority on the elevators. Shifting the wings forwards would have also slightly reduced lateral stability (the dihedral wingtips have a small rudder effect). Some dihedral on the tailplane may help, as would cloning the forward extension of the central fin to the lateral ones.

I'm finding that the new upper-atmosphere drag has my spaceplanes reentering from LKO slowing down to below hypersonic (< Mach 5) before they even reach 30,000m. This is making default-difficulty DRE irrelevant unless I'm coming in for a direct reentry from interplanetary. Is this working as intended? It's the latest version of each.

BTW, the other probe launching trick: if the probe is in an orbit that the spaceplane can't reach, don't launch to a circular orbit: burn straight into an extreme elliptical orbit direct from launch. Don't raise your periapsis out of the atmosphere at all; burn until your fuel is 99% gone and your apoapsis is as close to the desired orbit as possible, then drop the probe. Use the probe's own ÃŽâ€V to circularise at apoapsis (a couple of monoprop tanks can easily give several thousand ÃŽâ€V to a small probe, and circularising a high elliptical orbit takes very little fuel) , and rely on aerobraking to slow the spaceplane down.

Red FAR numbers don't necessarily mean "unflyable"; they mean "not neutrally stable at this speed/altitude". With enough control surfaces (or vectored thrust: the high gimbal range of all those RAPIERs is probably helping a lot), you can control almost anything. It's usually nicer not to have to, though. BTW, see the "need some cash?" story above for how to launch a probe into a high orbit virtually for free. Just drop 'em off on the way to elsewhere. Where the low TWR ships come into their own is interplanetary; strip it back to the minimum possible jet thrust, and use the weight saved for fuel and LV-Ns. My Duna and Laythe planes had barely enough kick to get off the runway.

This: http://s1378.photobucket.com/user/craigmotbey/Kerbal/Spaceplane%20economics/story Alternate format http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Spaceplane%20economics

Need some cash in your career game? Like this: http://s1378.photobucket.com/user/craigmotbey/Kerbal/Spaceplane%20economics/story Alternate format http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Spaceplane%20economics

There have been big changes in FAR. 1) Wing weight/strength is now a tweakable. Default wings are very strong but very heavy. 2) SAS is destructively hypersensitive. You need a PID tuner; Kerbal Pilot Assistant ​has a good one.

The supersonic CoL shift is why you'll get planes that are a bit unstable at subsonic speeds that suddenly become much more stable once supersonic. Run an AoA sweep on your ships at 0.8 Mach vs 1.1; you'll often get stalls at the subsonic speed but not for the supersonic. The drag at the back of the plane tries to push the nose towards the airstream; the more distance between CoM and CoL, the more leverage available to this force. This is normally a good thing; nose to airstream is what you want to keep your plane stable. However, since planes always require a bit of AoA to maintain level flight, too much of a tendency to point the nose to the wind will make sustained flight impossible: you won't be able to keep the nose up, and the plane will go into an uncontrollable dive. CoL right on top of CoM is ideal for maximum manoeuvrability, but it isn't essential. Not everything is built as a dogfighter. I tend to like a good amount of stability, but with the option to disrupt it when necessary; a bit of CoM/CoL distance, combined with a lot of pitch authority (thus the prevalence of canards on my designs).

Another design featuring the hot new anhedral look that's all the rage this summer: the Kerbodyne Archer. Annotated test flight at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Archer/story Alternate format at http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Beta/Kerbodyne%20Showroom/Archer Craft file at https://www.dropbox.com/s/c2gg8rd6rxjrkpu/Kerbodyne%20Archer.craft?dl=0

Plug the values shown above into the Stock SAS mode of KPA, and if you're flying a Kerbodyne whatsit it'll perform roughly as intended; that's what I use when I'm test flying 'em. BTW, Crzyrndm: as suggested above, I use KPA mostly just to tune the stock SAS. I usually don't bother adjusting the PID on the surface SAS because I don't use it. With an untuned SAS, I get pitch oscillations; tuning fixes that. Sometimes, when I come out of pilot assist mode (which I mostly just use as a long-distance cruise control), pitch oscillations reoccur. It looks like the stock SAS PID tuner isn't taking effect when toggling the pilot assist features off. In the most recent flight, it kept oscillating until I reselected "control from here" on the cockpit. I have no idea why that worked, but it did; pitch wobbles instantly disappeared.

If you're comfy with math, see http://en.m.wikipedia.org/wiki/PID_controller. If not, just use this: They're labelled a tiny bit differently in KPA, but you should be able to work it out. Don't change the ones with zero values for now.

Hold down alt to disable radial attachment, don't let payload parts clip into the walls, strut inline-mounted payloads for stability, use docking ports or decouplers on cubic octagonal struts to mount payload radially. See the illustrated tutorial in the third post of the Kerbodyne​ thread linked below.

Have a poke at the tutorial linked at the bottom of this post: http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1353891&viewfull=1#post1353891 Once you've got your head around how to use the tools provided, things become a lot easier.

Chutes ain't designed for supersonic use. What sort of reentry trajectory are you using? Is there anything else bolted onto the pod? Setting periapsis to 20km or so should see you safely subsonic long before you hit the ground.

Advance warning: I build to my own tastes, and I like fast, responsive planes. Most of 'em aren't designed to tolerate heavy-handed piloting. They'll fly just fine if handled appropriately, but if you tell them to kill you, they will happily oblige. Gain some altitude (i.e. 5,000m+) before going supersonic and keep an eye on the G-meter while manoeuvring. The more recent designs are better than the earliest ones, and anything built before 0.25 will have serious weight balance issues due to the changes in wing mass.

Gotcha RAPIERs? Time to upgrade! Kerbodyne Alkahest RP4. Annotated flight test at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Alkahest%20RP4/story Alternate format at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Alkahest%20RP4/story Craft file at https://www.dropbox.com/s/wc763czscxqwzpq/Kerbodyne%20Alkahest%20RP4.craft?dl=0

Another low-tech high-practicality offering: the Kerbodyne Alkahest. Haven't unlocked RAPIERs yet? Got a probe you need deployed? Got some Kerbals that need training? We have the universal solution. Craft file at https://www.dropbox.com/s/0xqrszlbnmlm1gj/Kerbodyne%20Alkahest.craft?dl=0 Annotated flight test at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Alkahest/story Alternate format at http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Beta/Kerbodyne%20Showroom/Alkahest

Just in time for Christmas.

I've been getting good training value from a six-seater spaceplane. Send it up with five on board, rescue a Kerbal, return to KSC. Six insta-trained Kerbals plus a little bonus cash.

Behemoth: If you have a neutrally set elevator to start with, and then pull the nose up to a 10° AoA: * If it is set it to 100% AoA, it will deflect to 10° down (relative to the plane, not the airstream; it's now effectively 20° down relative to airstream), helping to stop the nose from climbing too high. * If it is set to -100% AoA, it will deflect to 10° up (again, relative to the plane) making it effectively 0° deflection relative to the airstream. But if the maximum deflection of that control surface is set to 10° and you then pull the AoA up further to 20°, the surface will not be able to continue compensating for the AoA and will stay at 10° up (relative to the aircraft, now effectively 10° down relative to airstream). Again, this can get you out of an excessive pitch-up situation.

First, you have insufficient power for the weight. Second, you have massively excessive amounts of roll authority and insufficient amounts of pitch and yaw authority. More rudder, more tailplane. Lose the wingtip vertical fins; they won't do anything in that position. Control surfaces need to be distant from CoM in the axis they control.

Go to the next page, look at the numbers. Hover your mouse over the red ones. That'll bring up a tooltip telling you what's wrong. If you're having pitch instability problems, you've probably got too much lift at the front of the aircraft or not enough horizontal stabilisers. Let your CoL move backwards; most of the time, it does not need to be as close to CoM as it would be in stock aero. You'd likely get some use from this tutorial: http://s1378.photobucket.com/user/craigmotbey/Kerbal/Tutorials/Hangar%20to%20Landing/story