Thinking about making the switch to FAR.

[Van Disaster]

We're talking about static wing loading, which is total mass/wing area. I can speculate on L/W but without checking the source I don't know what it is exactly. I do know the plane I just took off was at 1.0 at takeoff & still at 0.8 at 20km, for comparison.

Edit:

 L_W = geeForce * mass;
 L_W = LiftArea * q / (L_W * 1000);

So that's wing area * dynamic pressure / dynamic weight, which would be (effective) area per unit of mass instead .

Edited March 23, 2015 by Van Disaster

[cantab]

wings in FAR are assumed to be optimized for the supersonic, so they produce less lift, relatively, than those high-lift airliner wings.

Interesting, that certainly makes life harder for my tanker aircraft.

Have there been any thoughts to making airfoil shape a tweakable option, with FAR then using appropriate parameters? That would add even more to the design possibilities, and also really help set FAR above newstock.

On the flipside I'd be all for coarser options for wing strength. A choice between .1, .2, and .3 is useful, but a choice between 0.24, 0.25, and 0.26 seems a bit over-fine and I find it makes it fiddly to actually set a chosen number.

[capi3101]

Well, y'all were right - I really just needed a bigger tail:

Can't call this an unqualified successful flight, though - the plane broke right at 45k going 1900 m/s (wasn't looking at the Mach meter at the time). I was able to correct the spin and get the plane into the ugly ass orbit it's in in that screenie - but it took nearly every last drop of fuel I had to do it (including what was in the payload - TAC saves the day again). Time to check what the fuel load is doing in flight. Might fly with a little bit of ballast up towards the nose; the tank was empty in this flight. I also need to move the plane's solar panels - I didn't do that when I moved the side nacelles up so at this point they clip into the air intakes. I imagine y'all are going to tell me that tail needs to be swept back a little more too...

I suspect that I would have issues landing that plane (if it had any fuel left, that is), given the lack of flaps or airbrakes. I'll play around with it some more to work the rest of the kinks out. I consider last night's flight "progress" in any event.

Edited March 25, 2015 by capi3101

[Wanderfound]

What I would do:

* Halve the span of the canards.

* Cut the wingspan by a third, reduce the sweep a smidge, increase the chord a smidge.

* Move the tailplane as far back as it can go, raise it to the top of the core fuselage so it's out of the way of the lateral engines. Give the tailplane a few degrees of dihedral, increase its chord a bit.

* Add small pitch control surfaces to the bit between the lateral and central fuselages.

* Shift the lateral fuselages forwards a touch to give the tail more leverage.

* Change the mass tweakable on all horizontal surfaces to .75, on the vertical stabiliser to .6.

You're also a bit light on for engines given the size of it. Consider adding an extra jet or two.

Edited March 25, 2015 by Wanderfound

[capi3101]

What kind of aspect ratio should I really be aiming at for my wings and stabilators? I was shooting for a 6:1 ratio; I got just about there with the wings but definitely overshot on the tailplane (8:1). Canards while I'm at it - those were just copied from the tail, so they're also at 8:1. And what kind of sweep angle should I aim for?

Definitely will try moving the tailplane as you've stated - my first attempt yesterday I had the lateral engines shooting into them, which was working right up until I switched to rocket mode, the entire tailplane overheated and poofed out of existence...

All the wing surfaces are currently at 0.7 strength

[Wanderfound]

A wide variety of aspect ratios can work:

As a general rule, though, heavier ships need more chord. Razor-thin wings are fast, but they don't give you a lot of grip at low altitude.

[cantab]

All the wing surfaces are currently at 0.7 strength

I'd say that's on the heavy side. The weight penalty can be noticeable. My Curtis Special uses minimum strength wings. It does need babying, violent control inputs will break it, but flown with care it's OK. Admittedly the Curtis Special benefits from huge wings that give a super gentle re-entry (and it's a Basic Jet spaceplane so the requirements are very different to a turbojet or RAPIER design).

[UnusualAttitude]

Can't call this an unqualified successful flight, though - the plane broke right at 45k going 1900 m/s (wasn't looking at the Mach meter at the time). I was able to correct the spin and get the plane into the ugly ass orbit it's in in that screenie - but it took nearly every last drop of fuel I had to do it (including what was in the payload - TAC saves the day again).

I find the "Hold Prograde" SAS feature usually counters any upper atmosphere instability perfectly well. Once your time-to-apoapsis is high enough (KER should tell you this, I suggest just under two minutes) switch on Hold Prograde and burn until you have your desired apoapsis.

Unless you find that cheaty and want to fly it all by hand...

[capi3101]

So, last night I decided to build another FAR plane. My original intent with this one was a general purpose parts tester - something that could fit an object the size of a Mainsail engine in the cargo bay - but I decided I should go ahead and try to design it to where it could be used as a large cargo orbital transporter in a pinch. FAR gave me red lights for beta and r on the runway at Mach 0.35 and at 10k/Mach 1, but in both cases the simulations showed decreasing oscillations; it greenlit the plane at 15k/Mach2, 20k/Mach3 and - for the first time - 30k/Mach4. Sounded like I had a winner on my hands - so I launched the thing. Discovered after it rolled over and crashed that the SPH had kicked me over to radial symmetry on the main wing (I think it had to do with how I'd set up the outboard engines) and it wouldn't let me reattach the stupid wings in mirror symmetry. To say I was annoyed at this turn of events is an understatement, one I'm only using due to the rules of the KSP forums regarding the use of profanity.

Anyways - can I walk y'all through the design process I used for this craft? I'm still looking for help on this score - what I'm doing is largely based on the advice I've received on this thread up to this point. This will be math heavy.

Okay - so as always, I start with my payload. I want to haul a Mainsail engine to orbit - so I've got six tonnes of payload. 25% design payload fraction means I want to build a plane that has a mass of around 24 tonnes. I'll need a Mk3 Cargo Bay to contain the Mainsail due to its size, but I should be able to use the shorter bay. I want a 0.75 TWR on the Runway (per eddiew), and I know RAPIER engines output 80 kN of thrust each on the Runway (from observation), so I know that each RAPIER will conservatively support about 10.75 tonnes of airplane: TWR = T /(mg), (mTWR) = T / g, m = T / (gTWR) = 80 / (9.8 *0.75) = 10.88 (which is not a nice figure to work with, hence I round it down). Since I want a 24 tonne aircraft, I'll need three RAPIER engines. And since I've got three RAPIERs, I know my plane oughta be able to support up to 32.25 tonnes (10.75*3 = 32.25), so I'll actually design it for that mass instead. Knowing that, I can calculate my fuel needs: 40 units per tonne of both oxidizer and liquid fuel, assuming a kickover to rocket mode above 30k going about 1400 m/s. That comes out to 1,290 units of both LF and LOX. If I want to use the plane for its original intended purpose, I'll just drain the LOX before loading up the payload.

So I begin building my fuselage, starting with a large RGU followed aft with a Z-4k battery. To the nose I add a Protective Nose Cone. I then add a 2.5m-Mk3 adapter, put in the Mk3 Cargo Bay, put another 2.5-Mk3 adapter (going back down to 2.5), then a short 2.5-1 meter adapter. I decide to put a single RAPIER in the centerline tail and put the other two outboard, each with a Radial Engine Body. To the front of the outboard units I attach a short 1m-Mark 2 adapter, and on each of those I added a Mk2 Bicoupler, with a pair of Shock Cone Intakes on the ends of those. I've got more fuel in the craft at that point than I need, so I decide to drain the 2.5-1 meter adapter as well as the outboard components, and balance the remaining fuel between the two 2.5-Mk3 adapters, running fuel lines inside the cargo bay between the two tanks. I also run fuel lines from the aft tank to the outboard units. Checking the mass distribution, I see that I'm a little heavy aft, so I add a large RCS tank for ballast immediately aft of the battery. RCS Build aid tells me that my CoM will remain reasonably stable, so I run with this setup. I set up tricycle gears - one gear up by the nose, two on the outboard units. I'm using my customized Large Gear Bays for this since I've got a big plane.

Now I begin calculating what I need as far as wing surfaces are concerned - for these, I'm using those formulas I came across the other day. First, my final fuselage dimensions are 21.8 meters in length, 6.3 meters in width and 3.8 meters in draught. Fuselage should be 70-75% of the total wingspan; I go with 70%, so I know I want the wingspan to be 31.14 m (21.8/0.7 = 31.14). Chop that in half for a single wing - 15.57 meters - and then subtract half the fuselage length from that: 12.42 meters is the desired span of the wing. As far as the wing chords goes, I want it to be 1/6 the total wingspan, so 31.14/6 = 5.19 meters. I should have a total wing area of 5.19 * 12.42 * 2 = 128.92 square meters. I'll generally shoot for a 45 degree sweep of the wings if I can manage it. Horizontal stabilizers are 25% of the total wing area - 32.23 square meters, and the vertical stabilizer should be 10% of the total wing area - 12.89 square meters.

I'm assuming I want the fin to have a 4:1 aspect ratio - so 4x * x = 12.89, 4x^2 = 12.89, x^2 = 12.89/4, x = sqrt(12.89/4) = 1.795 meters, the chord of the tail. The span will therefore be 7.18 meters. Again I'll shoot for 45 degrees sweep. For the horizontal surfaces, I'll have two canards at 2:1 and two stabilators at 4:1, so that's 2x^2 + 2x^2 + 4x^2 + 4x^2 = 32.23, 12x^2 = 32.23, x^2 = 32.23/12, x = sqrt(32.23/12) = 1.64 meters. So my canards will have a span of 3.28 meters each and the stabilators will have spans of 6.56 meters.

With the dimensions calculated, I whip out Procedural Wings (going to install B9 Procedural Wings today to see if I get better results) and build the various surfaces to the tolerances I've calculated, and then start attaching them. Fin first, then canards, then stabilators, wings last. After that I adjust their positions so that the CoL is not too far aft. Each wing surface is set to .7 strength and 100% of the axis to which it's designed to control. When I think I've got a plane that might fly, I head to FAR and check its stability with the usual benchmarks: 0k/Mach0.35, 5k/Mach0.85, 10k/Mach 1, 15k/Mach 2, 20k/Mach 3, 30k /Mach 4. If I get a red number, I check the simulation for the subscript indicated with an initial value of 5 and see what the graphs do - I know I'll have problems if the graphs diverge or it shows an increasing oscillation, and that the problem is tolerable if it shows a steady or decreasing oscillation. After all that, I hit the Intake Build Aid magic button, make sure the front gear is set up properly, and go test it out.

Alright - flaws in this process: I want to hear about it if there's something I'm doing wrong (besides, perhaps, any accusations of over-analyzing things).

[Wanderfound]

We need pictures to get a proper idea of what you're doing.

It's not as simple as a handful of formulas; the best wing dimensions vary based upon TWR, planform, wing strength, flight profile and mission. Faster ships can get away with higher AoAs, different wing configurations distribute the wing area differently, stronger wings can tolerate higher wing loading and different design priorities arise for an aerobatics show vs a careful ascent to begin a long-range space mission.

A nose cone up front is a wasted opportunity; stick a shielded docking port or atmo sensor pack there if you've got 'em.

Larger ships are tricky to build. Something like this would handle that cargo, though:

http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1804064&viewfull=1#post1804064

Edited March 27, 2015 by Wanderfound

[Van Disaster]

A few points:

* 25% payload fraction is pretty low - I've managed half the takeoff mass as actual payload, but I'm not sure that'd work in current FAR.

* My usual runway TWR for larger cargo craft is somewhere in the 0.3s. 0.75 is excessive.

* As was mentioned those formulae are for RC aircraft which have a very narrow range of operating speeds & heights, and probably relatively insane mass/str ratios. Also probably minimal wing loading, I'd imagine. Look at existing supersonic craft and you'll find the fuselage is probably quite a bit longer than the wingspan ( the F-104 is an extreme case, that thing's takeoff & landing speed were higher than the Shuttle's landing speed ). Of full size things that have actually flown the XB-70 is probably the nearest we've got, if you allow for it using compression lift. The ideal is a long thin shape, so if you're using a fat bay then you're not going to want a short fuselage.

* Engines don't support a set mass of aircraft; you can have the same mass which looks like a needle vs the same mass that looks like a wall, which one is the same engine going to drive better?

[eddiew]

* My usual runway TWR for larger cargo craft is somewhere in the 0.3s. 0.75 is excessive.

I have never had any success with a TWR this low... 0.6 is usually a pain in my experience, and those I've made that had less simply failed to go fast enough and high enough. I can certainly imagine that it's possible to build a viable spaceplane with low starting TWR, but when someone's having problems with a design the last thing I'd recommend is reducing thrust ^^; Most SSTO builders seem to start with TWR > 1, since it'll basically forgive any piloting mistakes and just take you to orbit with the magnificent ISP of air breathers.

[NathanKell]

That's the thing, though: TWR has no relation to top speed. Maximum speed at an altitude is that speed at which drag and thrust are equal. Do you see weight in this equation?

[Van Disaster]

Thrust to drag ratio is what matters

There's two issues you'll have with low TWR; getting off the runway before it ends, and somewhere about 20km there's a bit of a wall where you need to get higher to get faster, but you can't get higher without getting faster because you're pitched up to hold altitude & can't generate any more lift without accelerating. Working backwards, one solution to the wall is to add some more wing, but then you'll get drag issues or structural issues and it's probably easier just to add more thrust instead; if I've filled up so my wing loading is that high that I'm pitched up too much I tend to add some large droptanks with jets ( fairly feasable given they're the size of a mk1 aircraft ), but of course the other answer is to just offload some payload. Note I've only ever run into the wall that badly with < 0.3 TWR, I think occasionally I launch with 0.28.

The runway issue has a few solutions; you can add droptanks & take off with rockets lit too, you can use SRBs, you can use powered wheels, you can just run off the end of the runway of course, or you can install that bigger desert runway from Kerbinside. We've got a bunch of issues with KSP that make life a bit more awkward than real life - high empty mass, no complete customizeable shapes, no ground effect, short runway.

Finally of course there's the matter of it taking half an hour to get to orbit ( in my worst case, it took two times round the planet to get to orbit ) which is maybe not something you want to do all the time. In my case I usually set a climb rate or a pitch hold and just keep half an eye on it while I do something else, but that's not for everyone. I'd say if you're making >1.0 TWR aircraft then you might as well just drop the wings, they're useless weight at that point.

Edited March 28, 2015 by Van Disaster

[capi3101]

* 25% payload fraction is pretty low - I've managed half the takeoff mass as actual payload, but I'm not sure that'd work in current FAR.

I know; I've used 25% as a very conservative figure since my stock days (because even a lousy spaceplane in stock should be able to do at least 25%). Of course, I've yet to hit that figure in FAR - it's the fuel doing me in. I haven't had a design make it past 1400 in airbreathing mode - it's the wing drag doing it to me, of that I'm sure.

We need pictures to get a proper idea of what you're doing.

Alright - give me some time and I'll get a pic or two of this plane up there.

A nose cone up front is a wasted opportunity; stick a shielded docking port or atmo sensor pack there if you've got 'em.

Neither the ability to dock nor the gathering of sci data was in that particular craft's intended mission profile - but I'll keep that in mind for future designs.

It's not as simple as a handful of formulas...

I understand that, but are there any general guidelines? I consider myself lucky to have come across those RC guidelines; surely there are similar ones for supersonic planes somewhere...

I can guess a few. The SR-71 and X-15 had wingspans that were 45-50% the length of the fuselage, with an aspect ratio somewhere between 1.75-2; if I'm doing the math right, cutting "the span of the wing by one-third" on my Horned Owl Design would've put the aspect ratio at 1.97, within that range. I might give that a try tomorrow.

You also mentioned the Horned Owl (that last one for which I put up pictures) was light on engines - its takeoff TWR was 0.75 - would you recommend a higher TWR, and if so, what?

Finally do you have any unmanned plane designs I can look at?

Sorry if any of this sounds smart-assed or if I sound ungrateful in any way; I really am trying to figure out how I can make my designs better than they currently are.

[Wanderfound]

The Owl had enough engine to work, but excess TWR can cover a host of aerodynamic sins. Given enough power, a brick will fly. And there's no reason to go to orbit in a truck when you can do it in a sportscar.

The general guidelines are "build something that looks like a real plane, check the FAR numbers, adjust as appropriate". Yaw problems call for more tailfin, roll wants dihedral or wingspan, down/forward means you need more lift or less weight. Get your CoM as far forwards as you can manage, and design to balance weightshift as the fuel drains.

Have a look at my thread (linked in the sig). There are design tips and a few hundred example craft there. Most an of them can be flown as a drone by slipping a probe core into the cargo bay or similar.

You might also get some use from my design vids (also in sig).

[Van Disaster]

Guidelines? assuming pWings

* Pick a cockpit. Pick a cargo bay. Pick some engine mounts. Now pick what you think will be enough tankage to get to orbit, and distribute it either side of the cargo bay. That's your fuselage, now add the mass up and note it down.

* Now stick a pair of wings on, for your main wings. Pick some sort of target wing loading given the fuselage mass ( say 0.3kg/m^2 at this point, the wings themselves will have significant mass and you haven't added a payload yet presumably ) and work out how much wing area you want ( I don't actually do this, but I'm pretty good at estimating by looking ) . You'll probably want the semispan to be at least the root width unless you're making a single delta, other than that drag the wing around until you find a shape you like, which is not excessively weighted in either span or width. Long thin wings can give structural issues and excessive supersonic drag, while stubby wings with wide roots are going to give excessive mach tuck for no benefit. To be honest I have had some pretty excessively long spans with entire engines stuck on the end without issue, but I try not to do that.

* You'll need some sort of horizontal stabilization; you can do this all as a single delta wing but unless it's a small craft that doesn't end up working out too well. The fuselage layout will make a canard vs rear tail choice for you, probably.

* You'll also need one or more vertical stabilizers somewhere, I don't have a rule of thumb for those at all because they'll depend on the fuselage length and where the fulcrums are. You'll probably want one that's in the same order of size as one horizontal stabilizer. Don't make it too tall or you'll get roll coupling issues, the tailfin is one place you can have a short span & long root without any problems unless you're building an acrobatic aircraft.

* Use the wings as tanks when you're test flying to add any extra fuel you might need.

Wanderfound has tons of examples, I don't have many small craft but this one is probably around the size you're building:

No calculations involved there, mostly "if it looks right it'll fly right".

Edit: I just realised the top pic is a slightly later version of the craft than the bottom, which would explain why they don't quite match.

Edited March 29, 2015 by Van Disaster

[NathanKell]

Van Disaster had some excellent advice. Here's a bit more:

1. No wing/tail should overlap another from any of the three views (side/top/front). If the tailplanes are "in line" with the main wing they'll have reduced effectiveness; raise or lower one or the other.

2. Parts in KSP are denser than they appear. You need more wing per chunk of fuselage than you would in real life.

3. Give the root parts of your main wings a slight angle of incidence (no more than 1 degree) with the rotation tool. Verify that at desired speed and altitude your AoA is 0 degrees (via the static analysis tool).

4. You need half the intakes you used to.

Here's some examples, 100% stock parts (they'd be much better with pWings, and I install proc mods by default, but I was limiting myself to stock only). .25.

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[Pixel of Life]

Another little tip: FAR does not like SAS at all. The default 15 degree control surface deflection is way too much - the SAS will overcorrect its own movements and you'll have a very hard time getting the plane to fly where you want it to. I've found that decreasing the maximum deflection to somewhere between 5 and 7.5 degrees works great. I usually use 7.5 for ailerons and elevators and 5 for rudders and canards.

[Van Disaster]

To be honest you probably want to replace SAS with Pilot Assistant - which has it's own SAS replacement - it's tuned specifically for aircraft ( and is most definitely not an autopilot ). If not then find a SAS tuner mod.

* There's no aeroelastic divergence in FAR ( or stock ) so you can use forward sweep without worrying about that. You can get long span wings flapping as if there was some if you exceed their happy dynamic pressure range, but they won't diverge because of any built-in instability.

* You can use the AoA setting as a trim for your horizontal flight control surfaces - I think, at least, I've experimented a little & I think it's working but it can be a bit hard to tell. The main idea is to stop them stalling by deflecting excessively because unstalling a FAR surface is a bit awkward.

[capi3101]

Good morning, y'all. Quick update on my weekend's shenanigans. Actually, I had a pretty good weekend all told - had three designs that made space (but not orbit).

Let's start with the plane I designed in my last post:

If y'all will recall, this was the one that I couldn't get going even though FAR green-lighted it because it got hit with a symmetry bug - it attached the wings in radial symmetry instead of mirror and refused to switch back. After this debacle I decided to bit the bullet and download B9 Procedural Wings. I must say I like it a lot better than the other Procedural Wings mod; I still have both installed at the moment due to the fact that the earlier designs incorporate the other mod, but I may be doing some redesign work in the future.

Good airliner design, perhaps. Not so great a design for a spaceplane...

Anyways, I decided to give this adjustment to the design a try:

I didn't think for one second I was going to get anywhere with those chicken wings, and yes the design had roll issues. But believe it or not, this one made space (inverted...) - and it would've had the delta-V to circularize and make orbit, except that I found myself lacking the ability to control the plane once it was in space. Its behavior in space with the rockets lit was consistent with a misalignment of the CoM and CoT, and yet I know the two were aligned. Ordinarily I'd have fixed that issue by adding a SAS module - so I did that with the final design of the weekend, the Screech Owl 7:

I literally designed and test flew the Screech right before I went to bed last night, so I haven't had time to make adjustments yet; I've already given strong thought to replacing the tail cone with a drag chute and am thinking about what I might want to tweak up at the nose. With this one, I went back to the RC glider ratios and I added a Large ASAS Module. FAR also green-lit this one at the crucial 30k/Mach 4 mark - in fact, it only gave a single red-light for the standard benchmarks for the entire flight profile, and that was to the M_δe parameter at 0k/Mach 0.35 (one I don't know how to test in the simulators). This one ran out of oxidizer before making orbit - the only fuel tanks in use ~as~ fuel tanks on this plane are in the outboard nacelle assemblies, and I'd drained the oxidizer from the forward bicouplers...

Fuel again - for FAR the general advice I've received is "1 liquid tank and 1 rocket tank per engine". My reply: what size of rocket tank?

I wasn't necessary happy with the mass balance of this plane either - the CoM was forward of the center of the cargo bay and shifted aft in flight by about half a meter according to RCS Build Aid. That's not enough to destabilize the plane, but I imagine I might've had some issues had there actually been payload in the bay. I imagine I just need to adjust the positioning of the nacelles on that one. Maybe add a little bit of fuel to the forward fuselage for additional ballast or something.

Anyways, the flight of the Screech Owl ended in a fiery crash, and that's something I'd like to talk about: the process of de-orbit. I obviously screwed something up there - the plane's dynamic pressure exceeded 40 kPa; FAR gave me the Q warning and seconds later I was treated to the sight of the wings and canards ripping themselves off like something out of a 1920s Bugs Bunny cartoon. How do I avoid that? I'm assuming what happened was that I was going too fast as the atmosphere thickened up; I've heard that the shuttle performed "S-turns" to bleed off speed during the approach and I'm assuming that I should've been doing the same (rather than just letting the increase in density slow me down; rather a stock aero approach come to think of it) - how do you execute that maneuver properly?

[Van Disaster]

If you have enough control authority, deorbiting is just a case of gliding down to land without drama; the problems come when you don't have enough horizontal control surface area and your CoM is shifted way off CoL, then you'll just lawndart. I deorbit about 1/3d an orbit before the runway, using the Trajectories mod modified for FAR I'll put the target on the runway which gives an orbit track for the default orbit view over the runway of about 15km I think. Sink rate will get up to about 150m/s or so but if I hold the craft pitched up a couple of degrees, or just 0 pitch then usually it'll reduce to something useful of say 30m/s well before dangerous levels of dynamic pressure build up, provided my CoM is roughly around CoL. If I'm starting to nosedive & Q is building I'll pop spoilers out, they're mostly there on craft that need them to pitch up again, I've found spoilers don't do an awfully good job of actually slowing down no matter what I do . I'll also pump fuel around if necessary - TAC fuel balancer is a really great mod for FAR spaceplanes, although I've found using Goodspeed fuel pump & setting the tank priorities carefully in the SPH is enough.

If I'm landing at KSC I'll always do a circuit entry a little south of it, pass over generally around 8-10km alt & turn onto final approach somewhere around the island with the airfield on it, to land on 27. Given I'm descending at 20-30m/s still that'll give me a nice glide to the runway to land at a reasonable speed without having to use engines at all. If it's a heavy craft I'll just delay the final turn until a bit further out so I can approach flatter.

I'll do a little hop up to orbit & back in that craft I linked at some point and take a bunch of pics.

I'd at least double the main wing area of that craft if not more, if that was me.

Edited March 30, 2015 by Van Disaster

[capi3101]

I'd at least double the main wing area of that craft if not more, if that was me.

Span or chord, and why?

[Van Disaster]

Span or chord, and why?

For that craft, chord - and why, because eyeballing it would suggest to me from experience that it would work better with more wing area. I randomly eyeballed something resembling the craft - only with two engines and more wing - and it worked ok. I'd probably make my version a delta if I was going to do it properly.

Here's an annotated trip up & back.

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Mods used, ignoring the payload:

* KER

* FAR

* B9 core

* B9 pWings

* Aviation Lights

* Bahamut0's adjustable landing gear

* RealChute

* TAC fuel balancer ( Goodspeed pump is installed, but that craft has no priorities set ).

* NavUtilities

* Pilot Assistant

* Mechjeb, briefly

* Kerbal Flight Data

* Popup RCS thrusters from somewhere ( I think that's another Bahamut0 mod )

* KerbalKonstructs gave the icons on Kerbin's surface telling us where KSC is, but that's just sauce.

Edited March 30, 2015 by Van Disaster

[capi3101]

I can report a successful flight to orbit last night in the Screech Owl:

Turns out having enough fuel makes a difference. So does making sure the action group that closes your air intakes includes the ones on the Radial Engine Bodies, and then making sure you actually hit that group once your RAPIERs switch to closed-cycle.

Did forget about doing my adjustments before taking off, and this flight had no payload. Good question there - how much payload do you think this plane would be able to handle given its end conditions? 34 tonnes / 0.96 TWR at takeoff. The numbers would say 11 tonnes for a 25% payload fraction; my TWR at takeoff in that scenario would be 0.73, which would be low but acceptable - my principal concern then would be whether or not I'd have sufficient fuel to make orbit.

This one exhibited the same behavior as the other plane I was flying over the weekend - once it was in space, I couldn't get it to fly straight. I verified the CoT and CoM were aligned in the SPH...so I'm wondering why it's doing that. I imagine the only reason why I got it into orbit was the fact that I had set the Ap a bit higher than 75k this time and had time to make corrections. An ugly orbit but an orbit nonetheless.

So...landing. Yesterday I began with my usual starting point halfway across the planet and Trajectories helped me put the red cross right over my KSC ground markers. The deorbit went relatively okay up to about 20,000. That was when I was watching my Q, my rate of descent and the data from NavUtilities - I was attempting to keep my rate of descent around 150 m/s and had to pull up my nose. At 10k, still going Mach 2, I pulled up a little hard and went into a spin. Recovered from the spin at Mach 0.5 and 4000 meters, so that part worked out - but that's definitely not the way I want to lose speed and reduce Q, I imagine. I should mentioned I was crabbed out (if that's the proper term) at the time - spoilers deployed, flaps fully extended. Probably should've retracted the spoilers when I entered the spin...

Anyways, I got into the pattern, relatively lined up on the Runway, slowed my rate of descent to 5 m/s, then fouled the approach and crashed. I think it was because I wasn't level at touchdown; that sort of thing used to screw me up with stock aero on occasion. It's been a few weeks since I've done a landing of any kind - and my first attempt at one in FAR. I did quick-save the game so I can try again; any pointers on things I should do differently this time (like, not put myself in a spin to lose speed)?

Edited March 31, 2015 by capi3101