Thinking about making the switch to FAR.

[Wanderfound]

When you're measuring the drag, you need to do it with the landing gear up...

[eddiew]

When you're measuring the drag, you need to do it with the landing gear up...

Ohw, good spot... Yeah, I had a design recently that was better with the gear down because I'd designed it for lower wave drag like that xD

[capi3101]

You do love dem drones I also note your style is evolving in positive ways!

I've taken one one of NASA's later philosophies - you don't need to risk the lives of seven astronauts just to deliver a communications satellite when a disposable drone rocket can do the same job (usually for cheaper, too...).

Don't worry, I've got passenger craft on my radar. I've been paying attention to y'all's advice; I definitely appreciate all the help y'all have given me to date.

Are you filling the wings with fuel? If not, that might get you your extra delta-v to come home

Whoa - you can do that now? Didn't realize that - I'll have to give it a shot.

When you're measuring the drag, you need to do it with the landing gear up...

Ah - okay, I'll try that and see what that does. I'd been wondering about that, actually...

[Crzyrndm]

Whoa - you can do that now? Didn't realize that - I'll have to give it a shot.

B9 PWings have always had the capability. It's right down the bottom of the editor UI, but you can switch between LF, LFO, and RCS tankage (or use RF/MFT if you have those). LF can be drained by jets without CrossFeed Enabler installed, but you'll need the 1.0 version for rocket engines.

[Hodo]

Alright - another day, another new design:

http://imgur.com/a/Y4kZ5

I did intend to try out a cranked arrow design with a traditional wing and tail configuration. The V-tail, however, was a spur of the moment decision.

This design was almost successful - it made it into orbit under its own power and launched a fully-loaded payload without issue. But, it didn't have enough Oxidizer afterwards to de-orbit. I'm guessing my flight profile had something to do with that, though (maybe I lit the rockets too low), so I'm going to try again tonight.

The main thing I'm worried about at the moment is whether or not the plane will still be dynamically stable after fulfilling its mission (i.e. during descent and landing). It strikes me that the main wing may be a bit too far forward, and RCS Build Aid is telling me the CoM is going to shift back quite a little ways (the RCS you're seeing in the SPH screenies is for the probe; the plane itself has no RCS capability). Makes me wish I could rely on the CoL marker to be accurate. FAR green lit me up to 30k/M4, but that was with tanks full. I might see what it says with tanks empty before I try the next launch. Maybe put the wing a little further back (it's not like I don't have plenty of room to do that) and move the Mk1 Fuselage tanks forward.

I am pretty sure something was borked with my instance of KSP last night - I had some weird behaviors going on later on when I switched over to my career game. The NaN readings I was getting from KER were not a good sign either. Couldn't tell if the voxels I was seeing with the Ballista's wings were good or not; I know there have been issues between B9 Procedural Wings and FAR.

A bit of advice on the design that may help a bit.

If you sunk the radial fuel tanks into the hull a bit more to give it a more streamlined shape it would smooth out the overall airflow issue. Also if you were to extend the point of the nose a fair bit more, try adding an antenna on the tip of it to give you a point in the airstream. DONT extend the antenna it will just blow off. Lastly move the solar panels behind the wings or into your cargo bay so that they are not blocks metal in the airflow.

[capi3101]

This past weekend I was able to unlock enough technology in my career game to start seriously utilizing spaceplanes in it. Just a quick status update there.

So I figured the first thing I'd try to do in career was build a manned rescue plane, the Night Hawk 7 - just a simple little two-seater design. Here's its drag profile:

What the crap is going on there around the cargo bay? Is that a known bug? It's like it's treating the bay as being non-existent - I've got a Reaction Stabilizer, a couple of batteries, some solar panels, two roundified RCS tanks (it's a rescue craft so it does have RCS capabilities) and a quad of linear RCS ports in there (two forward, two back, don't know why it took me this long to come up with that particular idea - and it works, BTW).

Anyway, I had some serious problems with this design. First, FAR borked; gave me NaNs on lift and drag and try as I might it went into the drink. I would've reported that one to ferram but it hasn't happened since and I don't know how to get the error log he needs to fix these sorts of things anyway. After restarting KSP, it was pretty obvious the CoL was too far forward; it see-sawed up and down until parts started flying off. No problem - I moved the wings back a bit. Then I started experiencing parts breaking off at low altitudes, by which I mean the elevators. I repurposed the flaps to serve as an auxiliary pair, which worked on a relatively successful flight; it tells me I need to tone down the pitch control of the main elevators. Got it up around Mach 3.8 at 20k. Lit the rockets...and failed to make orbit. I made orbital altitude but didn't have enough juice to circularize.

Post-mordem then - What's wrong with the design? FAR gives my Max Cross Section as 3.59 square meters and the wave drag area as 3.25 square meters, critical mach is 0.768, if that's at all helpful. Only other thing I did to the design after making those screenies was to put a small antenna on the nose (which incidentally overheated and exploded during the flight - so I guess I might need to work a bit more on my flight profile).

I suppose I could fill in the little gap there between the fuselage and the wing towards the tail. The fin probably needs to be redesigned to a more traditional fin-and-rudder; I don't really have a reason to have an all-moving fin (I was being lazy again there).

Edited June 1, 2015 by capi3101

[Wanderfound]

The main thing wrong with your design is a bug in FAR: the voxelisation isn't picking up the bottom half of the cargo bay. This is why your green line takes that massive dip behind the cockpit. It's causing huge drag, and doing it in the worst possible place.

The bug is fixed in the dev build; either switch to that, or avoid Mk2 cargo bays until the next official FAR release.

[capi3101]

I was hoping it was something as simple as that. Okay then - the dev build is on GitHub, right? What should I be looking for, file-wise?

[eddiew]

Pretty sure you want...

https://github.com/ferram4/Ferram-Aerospace-Research

And the Download Zip button in the lower right is all you need. There's a gamedata folder in there, and I'm seeing it as having been published 20 hours ago

On another note, I did not know about this bug... I shall have to see how my designs perform without it!

- - - Updated - - -

Also if you were to extend the point of the nose a fair bit more, try adding an antenna on the tip of it to give you a point in the airstream.

Wait, FAR is actually sensitive to such tiny parts?

THIS CHANGES EVERYTHING!

[Wanderfound]

Wait, FAR is actually sensitive to such tiny parts?

THIS CHANGES EVERYTHING!

Put it in place, open the drag curves, watch them change as you extend the antenna.

[capi3101]

Pretty sure you want...

https://github.com/ferram4/Ferram-Aerospace-Research

And the Download Zip button in the lower right is all you need. There's a gamedata folder in there, and I'm seeing it as having been published 20 hours ago

Much obliged, thanks. I'll get this installed and then see what all that does; won't happen until later tonight, though (Monday, so probably not until well into the evening, around 0230Z probably).

Put it in place, open the drag curves, watch them change as you extend the antenna.

...just don't leave it extended in actual flight, right?

Kinda like "check your drag curves with your wheels up, but don't forget to put them back down before you try to fly". No way I did that over the weekend with this very plane. Nope. Never. Never ever. No.

[Wanderfound]

Actually, do leave it out:

...but don't rely on it as your only antenna if comms matter.

[eddiew]

Put it in place, open the drag curves, watch them change as you extend the antenna.

It's at this point where antennae become my most used part xD Wonder if I could put them behind shock cones, then displace them forward to give a point there too... there's definitely scope for a nosecone parts mod to go with nuFAR...

Kinda like "check your drag curves with your wheels up, but don't forget to put them back down before you try to fly". No way I did that over the weekend with this very plane. Nope. Never. Never ever. No.

I consider it a test of joint strength to prove that a plane can stand up under its own weight Although you do definitely want to do that before you hit the throttle, yes xD

[capi3101]

So, success with the Night Hawk to report to you guys this morning. Makes me wonder how many more of the problems I've been having of late have been due to that bug with the Mk2 Cargo Bays...

I got to say - I've only used Kerbal Flight Data just this once, but I likes it...

Any suggestions for what I could do with the tail? I've still got a pretty big dip in the yellow curve going on there. Also, I'm finding it hard to pitch up during the speed-up part of the flight - you know, the part where I'm trying to get to Mach 4 (which is finally happening!) before 20k and stuff starts to overheat. Last night I blew a Pegasus ladder off the side of that same plane because I started getting temperature warnings and couldn't steepen my rate of climb sufficiently. At least it wasn't anything critical, but it did make getting Diissa into the ship harder.

Ship made orbit but it still took almost all the juice it had available to do it; I had something like a 4% oxidizer reserve after orbital insertion. Made the rendezvous on RCS thrust alone, which was further complicated since I switched out the mid-line rocket fuel tank with a full-size Mk2 rocket fuselage and forgot that I'd mounted the forward firing RCS ports to the thing (so I couldn't do any RCS reverse thrusting; good thing I wasn't actually doing any docking with this plane). Something I'll fix before the next flight of the craft...

Next up is re-entry to landing. I'm hoping I'm not too out of practice with that bit. Meantime I need to get a couple of other designs ported into my career game from the litterbox...

[Wanderfound]

That sort of tailless no-canard delta often has pitch trouble; your only pitch controls are the elevons up back, they're close to CoM and there's a lot of nose to lift. But you can usually make them work by cranking up the maximum deflection on the elevators.

If you've already maxed out the elevator deflection and still can't lift the nose, then you either need to add canards or shift the wings forwards a bit.

If you spend some time fine-tuning the tail drag, you can probably cut a fair bit off it. Shift the vertical stabiliser back and forward by the smallest possible amounts; find its lowest drag position. Then do the same with the Thuds, the wings, the intakes and any other widgets you have in the region. Then do it all again because any changes you made late in the process will disturb the positions set early in the process...

You can see where the big wiggle in the yellow line is, and how it relates to the peak of the cross-section curve. Smooth out the curves in the green line and the yellow line will flatten out. Pulling your wings forwards a bit might help with both your drag and your pitch problems.

[eddiew]

Re pitch, the usuals really;

- canards

- tail

- increase control surface size

- supercharge the elevons (right click, increase control deflection)

The last is the least likely to disturb your aerodynamics

For the big drop in area at the aft end, that's coinciding with where all the white bits of of the fuselage run out, so maybe worth looking at...

- moving the rockets forward a bit

- tuck the rockets tighter into the fuselage (offset tool) so they don't create the initial bump before the dip. Imho you'd be clipping the empty space of the engine's support beam and it's therefore legit

- dragging the tail back so it sticks out behind the turbojet

- consider a pyradmidal tailfin, so that the back end of it slopes the other way and meets the rear fringe of the turbojet

*edit* Wanderfound stole my thunder. Again :<

[Wanderfound]

A demonstration of a nosespike at work:

[capi3101]

I had to tweak the design of the Ballista 7 after porting it from my litterbox over to my career game, owing to not having all the parts I needed unlocked yet. That effort was successful, though, and last night I made my first operational launch of a Ballista probe for a contract mission.

(The probe actually was fully fueled in that screenie; I had turned the thrust limiter on the Spark down to zero and had forgot to re-set it prior to launch, hence the 0 m/s delta-V reading).

The suggestion to use put fuel in the Procedural Wings helped, I think; if anything I think the plane now has too much fuel (not that I'm complaining, mind you). I was able to get it up without running out of gas, without anything 'sploding, and with more than enough in the tanks to de-orbit.

Got the Engine Nacelles too hot and they 'sploded...and all of my engines were attached to the Nacelles. I was dead-stick over the sea to the east of KSC - not a speck of land anywhere in sight, and then the plane's battery died and at that point she went into the drink.

So obviously I need to work on re-entry procedure. I did have the airbrakes going in the uppper atmosphere (for all the more good they were doing me that far up), both sets of flaps fully extended and my nose was up to about 10 degrees above the horizon. I wasn't trying to perform S-turns, which is one of the things that I suspect did me in here. How do you keep the temperature down when you're heading for re-entry?

Did notice Q was pretty low throughout the re-entry procedure; I think it was something like 27 kPa maximum. The plane got up to 50 kPa or so during the ramp-up portion of the flight.

I'm kinda concerned about this...I have a similar engine setup (Whiplash and Twitch engines attached to a Nacelle) on the Night Hawk, which is the manned plane I sent up with Jeb in it to snatch Diissa out of orbit; I haven't tried to land them yet. I don't want a repeat to happen when the time comes, though I know from experience that in a pinch a Mk2 Cockpit makes for a reasonable boat if you land it going slowly enough...

[Wanderfound]

Most heat transfer is by conduction; the nacelles have a lot of engines attached to them, and the only conductive escape for that heat is forward to the LF tank. Adding some small fins to the nacelle as radiators may help. It also helps to lose the ascent heat before reentry: do a few orbits to enjoy the view before you come back down.

Did you keep your airbrakes open once the air thickened up? If not, why?

Usually I just rely on the Kerbal Flight Data temperature warnings. If it's yellow I try to climb gently, if its red I try to climb sharply. And then I don't come back down until the reported temperature is decreasing, and try to come down at a rate such that it stays out of the red.

Once you have vertical control, you have temperature control. If it gets too hot, just fly higher. Most of my "overshot KSC" incidents are due to unexpectedly needing to stay at altitude for cooling purposes.

Edited June 5, 2015 by Wanderfound

[capi3101]

Bit late to add fins to the designs there, but I'll keep it mind for the next flight.

I did keep my airbrakes open; popped them on as soon as I hit atmo. Though that does bring up another question: at what point should I retract the things? I ask because there have been incidents where they've ripped themselves off of the plane...

I might have the airbrakes too sensitive - that could be part of my issue. They are set for full deflection at the moment...

I'm also finding climbing to be a tricky proposition once the atmosphere gets thicker. Generally I'm lucky if I can hold the nose to 10 degrees once I'm back down to 30k or so. I'm usually going Mach 4 and trying to pull up at that point even a little usually rips my plane apart. I'm obviously doing something wrong - I just don't know what it is yet. I need to figure it out though; I tried to get Jeb and Diissa home three times last night and each attempt ended badly. First time, the Mk2 Cockpit overheated and blew up. Second and third times I had structural failures and smacked the water going too fast. I've reverted the flight again so I can make more attempts later.

Just to be clear - at this point it's not necessarily the design, it's my flying that's giving me problems, right? The plane is the Night Hawk, which I launched to orbit on Monday (damn, it's been a long week...). Tail-less delta; aileron, spoiler, elevator on the back of the wing.

Edited June 5, 2015 by capi3101

[Wanderfound]

Are you using Dynamic Deflection?

[capi3101]

No, I'm not.

[Wanderfound]

Highly recommended. Makes high-speed manoeuvring much safer.

[Wanderfound]

With airbrakes, basically just keep them open until you start to feel them negatively affecting the stability of the ship, then close them. Keeping them balanced and set well behind CoM will help (although the further from CoM, the more they restrict your ability to manoeuvre).

Are you using proper airbrakes, or just flaps/spoilers, or both?

You want your control authority set so that the plane will always do as you tell it, but won't flip out of control when you apply full stick. Ideally, full stick should take the plane close to its g and stability limits, then stably hold it there.

Finding the exact settings for that is a matter of fiddly trial and error. Dynamic Deflection helps (it allows you to have effective deflections in thin air without them being overpowered in thick air), but so do the assorted stability-inducing build tricks. Position of lifting surfaces, control surface settings, etc.

Stalling is only an issue at low speed; once you're comfortably supersonic, you can get away with huge AoA so long as you remain stable. Forward surfaces (canards etc) stall more easily than rear surfaces. There are two responses to this: set the max deflection on forward surfaces lower than the rear ones, and/or use negative AoA settings on the forward surfaces. This will also improve stability at high AoA, but if overdone and not balanced against powerful rear surfaces, may make it harder to keep the nose up when you want to.

You need to mess around with the settings to get a feel for them. Build a basic mid-wing plane with canards and a tailplane. Set it up with various patterns: deflections high rear / low forward and vice versa, positive AoA vs negative etc. Take them for short test flights and see what happens.

Run a static analysis at a speed that requires a decent AoA for level flight; maybe Mach 3 at 20,000m. Watch the control surfaces as you do so; the AoA settings will kick in and move the surfaces to match the level flight AoA. This should help you get an understanding of what they're doing. You can also test spoilers and flaps like this.

[capi3101]

Highly recommended. Makes high-speed manoeuvring much safer.

Will give that a shot, thanks.

Are you using proper airbrakes, or just flaps/spoilers, or both?

Just spoilers on the recent designs; I've only recently unlocked the dedicated A.I.R.B.R.A.K.E. part and I've only got the Level 2 SPH at the moment, and I've found manually tweaking flaps in flight to be tedious.

<snip />

I'll keep the rest of what you wrote in mind when I go to design my next craft.

Meantime, progress report. It was ugly - but I'll take it:

You may notice that's not Jeb and Diissa's ship. There's a story there - last night I did the fourth attempt to bring the two of them home in the Night Hawk. The fourth re-entry went pretty much the same as the previous entries, where I tore the airbrakes off as the Q got too high. But, I managed to get the temperature under control and brought them into subsonic flight about a hundred klicks downrange from KSC. As I closed to fifty klicks, I did a quicksave and then tried to make an adjustment to my course to align with the Runway and the plane came apart, with the expected end results (it wasn't that violent of a maneuver either, just a quick little tap on the elevator to bring the nose up - at a Q of about 28 kPa). When I did a quickload, the Cockpit promptly exploded with the plane dangling in mid-air. Reload and this happened again - I did this three times before I finally said "screw it" and went to the space center. Naturally, I'd lost the money for Diissa's rescue contract, but I noted the Astronaut Facility listed her and Jeb as MIA - so I knew I had been hit by a Kraken, and I still had access to both of them. The game gave me a new rescue contract shortly thereafter - Pepe's contract - which gave me an chance to make some key fixes to the Night Hawk design (among them, adding struts to the inside of the cargo bay and adding a few cooling fins to the Nacelle).

Pepe's contract only took two tries to get right; I promptly whacked the damn fins I'd added when I took off and still cooked the ladder off the side of the cockpit, but otherwise there were no mishaps in the ascent. Ripped off the spoilers on both re-entry attempts (the second time while trying to retract them at Q=9 kPa), and both times I got the plane subsonic and to the KSC Runway; the first time I botched the touchdown and destroyed the craft, the second time I was able to produce the screenie above.

So I've got some testing and a few more tweaks to make to the design at this point; I'll take all your advice to heart and we'll see what happens.

Edited June 7, 2015 by capi3101