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Everything posted by AeroGav

  1. The problem with drag is that you need lots of engines to get past mach 1, each engine weighs 2 tons, which then needs lots of oxidizer to lift into orbit. It's the weight of all that oxidizer and all those jet engines that really make the craft so heavy. The other problem your craft has is that when the fuel tanks are empty it is tail heavy and unstable. I need to find a way to get more dry mass up front without spoiling the looks, and more fuel mass in the back. Using wet wing parts for the tail surfaces might help with the latter. Some ISRU equipment placed behind cockpit would help with the former. The huge fuel tank in front of cargo bay would have to go or get swapped for a much shorter one. That's a major job because everythign else attaches to it .
  2. Edit - finding 1 The engine mount method for your main engine cluster is incredibly draggy. You have a 3.75m engine mount, which has one attach point for a 3.75m engine. You are putting one 1.25m engine on it. The game calculates the surface area of the 3.75m, subtracts the surface area of your 1.25m engine and then assumes the rest (90%) plus has just been left as a flat plate, and applies drag accordingly. It doesn't see the extra engines neatly mounted around the outside of the central one, it treats them as separate 1.25m stacks, which you have 6 of, and because they don't have pointy cones on the front, it gives them flat plate drag too. Remember - a craft file is a root and branch structure. Every branch needs to end in a pointy object. No weeping stumps. All transitions from one diameter stack to another need to be handled by a size adapter. You've solved the high drag by adding more jet engines, then more oxidizer to lift those heavy jet engines to space. Not enough wings or nukes to support the resulting heavy craft on Duna. Radial mount vs using adapters.
  3. I don't have time to fully rebuild your ship but i might have a look for easy mods. The mk3 cockpit is right at the front so gets the worst of the heat. At mk2 or even mk1 inline cockpit , if placed some way back from the front , does much better heat wise. I agree with @Foxster though, moar boosters doens't work on airplanes. I have a couple of Duna mk3s, all the same -
  4. Many of my SSTOs are Duna-capable (have a look on my KerbalX link, a lot of these Duna vehicles have landing videos too), they have a generous amount of wing area though, strong landing gear and some Vernor thrusters to lower landing speeds. I take off and fly to orbit with LV-N only. Until I can get home and DL your craft file I won't know how it's built, but three mk3 fuselages sounds like an extremely heavy beast. I'd be very surprised if it has enough wing area to actually fly like an airplane on Duna. Remember - wings support you while building up to orbital velocity in horizontal acceleration. Sounds like you're taking off vertically, running out of oxidizer, and falling back to the ground before your nukes are able to circularise?
  5. It was a TSTO spaceplane I'd made in career mode. Two jets and two hydrolox coxswains either side of the main fuselage. These boost to mach 4.7 / 37km and the rear of the main fuselage, containing a fuel tank, lander can and another coxswain, decouples. This upper stage fires its RCS to stabilize the fuel then ignites the motor. The burn is over in 25 seconds by which point the AP is well out of the atmo. Then switch back to the airplane and fly it back. Obviously being on the rear fuselage, it cannot already be firing at separation , or it won't ever separate. Thinking about it, this became a problem after I switched the root part to be the launcher's cockpit, not the lander can. I have a video of the shenanigans I could always upload.
  6. Two docking ports add a fair bit of drag, though probably not as much as all that mk2 fuselage you have atm. You can get a fairing to cover this area if you want the ultimate in efficiency. The main problem is time added to the mission , why i don't do this more often. Redocking with the airplane again at the end when you just want to go home and cash in. I suppose you could put a radial chute on this section and land it separately - if the airplane handles ok with its tail off.
  7. I use CorrectCoL, which helps improve the accuracy of the blue marker , but it also has a stability analysis function. You give it the height and speed you want it to simulate and it plots a graph of how strong your nose up/down tendency is across the range. Crucially, it also plots a blue vertical line which shows how much AoA you need to sustain level flight at that speed and altitude. So, I give it the altitude of 22km, and the speed of 1125. I'm looking for an AoA of less than 5 degrees, because more than that is draggy. This is a typical speed for the start of a speed run, and 22km is about the max height you'd want to do your speedrun at (after that, loose a lot of power). I also simulate 1350m/s , which is mach 4.3, when the rapier starts to loose power rapidly with increasing speed. I don't want my level flight aoa to be less than 2 degrees, that means i probably have too much wing. The thing is though, if you've got nuke engines and are using wings that contain fuel, it's hard to have "too much wing" in a monoplane design, that doesn't wobble apart on the runway. If you're doing a 20 ton challenge, or 30 ton challenge /whatever, too much wing could eat into payload to orbit. If you're doing a "4 engine challenge" , to lift as much as you can with just 4 engines, then more wing helps you lift more weight with less engine. So don't sweat it too much, but your design should be able to keep AoA below 5 degrees and still get enough lift, if keeping the AoA to less than 5 degrees causes overheating on ascent, you don't have enough lift. I recommend CorrectCoL is just an awesome mod for all sorts of reasons.
  8. Landing on the Mun is a very tall order. The delta V requirement is much more than for Minmus, in fact it's probably more than a round trip to Duna, given that an airplane can aerobrake and glide in to land. Improvements - The mk2 fuselage is a bit draggy and the pointy cockpit is a bit vulnerable to heating effects, but that just forces you to use more jet engines and you aren't carrying those past flameout anyway, so it's only a cost issue. As regards the heating , Whiplash probably don't get fast enough to be an issue. How much velocity are you managing on air breathing? 900 m/s is max power on those engines, but you've got four so you should be hitting 1100-1200. Assuming we're still set on the Mun, I'd go with the "detach rear fuselage in orbit" trick. At the back of the fuselage, put a terrier engine, then an inline mk1 cockpit, then a fuel tank, then some docking ports to attach it to the rest of the airplane. Make some tailbooms off the wing for vertical stabilizers (or strakes rotated vertical hanging off the trailing edge). In orbit, transfer the remaining fuel to this rear tank and undock that section , go to the moon, on the way back, dock with the airplane again and make your re-entry.
  9. Distance from KSC would have been a better X axis , but how do i get the game to display that for me? Also, it would have to be distance "as the crow flies" not "as the worm burrows" if you know what i mean...
  10. It got increased in the last update i think - from a low drag to a rather high drag part - damit, i can't find that Russian guy's videos now where he did rocket races in 1.2.2 with different configs. He should have been stickied !
  11. With the cheat enabled, the engine had a full temp bar, even though it was only 220K/3600K I tried waiting for the temperature to go down further before starting the engine, but i hit the ground first. So I started the engine, and it the overheat bar shrank as the temperature climbed past 600k. Is there "too cold" for the Coxswain, or SolverEngines is getting negative and positive integers confused?
  12. Another question - I just had a mission fail because the "Coxswain" melted its internals from heat after separating the stage containing that engine. It wasn't even active yet? The separation occurred at mach 4.7, 36km. Didn't know that liquid fuel rocket engines were at risk from this? I am also using Advanced Jet Engine and have Interstellar installed. Is is a conflict, or is there a flight envelope i need to be aware of when using the hydrolox Coxswain?
  13. Probably doesn't climb as fast as Wanderfound's, but it has pretty good "go anywhere" ability.
  14. The mk3 engine mount has 3 mounting points for 1.25m engines, which you are using . However, it also has a 2.5m mount in the middle, which does not appear to have anything on it. If you don't want to put an engine there, you should at least use a 2.5m rocket nose cone to cover this or you end up with monster drag. The 2.5m node is treated by the game as a 2.5m stack ending abruptly in a flat plate. Also, for best drag you should attach 1.25m nose cones to the back of your rapiers, then offset them forwards inside the engine so they don't block thrust. It's ridiculous but it's something you need to do given the simplistic way the game models drag. Airframe - I suspect your CG is very close to the back of your ship. You are controlling pitch with elevons and tailplanes that are also very close to the back. Elevons and Tail planes raise the nose by pushing the tail down. Because they are so close to CG, they will have to push down very hard to have any effect. They must be producing nearly as much downforce as the wings are producing in lift - and creating drag to do so. You could address this by adding canards, but it's more important to do something about that rear CG. All your fuel and cargo must be in front of CG. When it's gone, your plane will surely be uncontrollable, and if it isn't, that means when laden, it is so nose heavy that it cannot be an efficient flier - the trim drag to keep the nose up must be enormous..
  15. Yeah I need to fix this. It is time/vs altitude from one of my recent flights. I was only climbing at about 5 degrees pitch angle, but because we were going so fast horizontally, the vertical speed was huge. Anyone who has better skills with Excel and MS Paint, feel free to jump in.
  16. That is because by default, most control surfaces have a max deflection of 30 degrees, and because most people fly with keyboard (and ksp joystick support is poor) when people nose up they are getting all 30 degrees deflection, which acts like airbrakes. Also, these "all or nothing" pitch adjustments send the whole aircraft into a large AoA change and you'll see 5 or 6 G being pulled when you;re making the adjustment. I do make pitch changes in my flight profile, because during the speedrun i'm keeping AoA very low to stop us climbing to an altitude where the engines loose power, but once we go closed cycle mode you want to run the aoa at the one that gives best lift / drag ratio. You can reduce the drag that comes from pitch changes reduce the authority of the control surface in tweakables or use one with a lower max deflection angle. Eg. use an elevon with a 30deg max deflection at 30% authority limit, or an advanced canard at 100% (max deflection 10 degrees) Change flight path by using pitch trim instead of WASD keys. Increase nose up trim with ALT and S, decrease it with ALT W. Note this doesn't work with SAS on example here - or, you can use fine rotate tool on elevons/canards to make your aircraft fly naturally at 4 degrees AoA or whatever is optimum for lift drag ratio. During the speedrun i'm using nose down trim , when the speedrun ends i use alt + x to reset trim to neutral, which causes the aircraft to return to it's built in trim angle Or you can have some trim flaps bound to an action group to make the change , with the "authority limiter" of the trim flaps adjusted to give the right angle (i use RCS action group for trim flap here)
  17. A long range SSTO needs to have a fairly high fuel fraction and carry a minimum of oxidizer. That means keeping engine mass down to a minimum, which means boxing clever with your flight profile, as well as designing for low drag and high lift (in stock aero, wings generate very little drag, but large wing area reduces fuselage drag by raising your altitude and lowering your AoA). As a rule of thumb, I'd say you want one jet engine per 25-30 tons. The limit is getting supersonic. Once you are supersonic, ramjet effect makes engines much stronger, and you only need one RAPIER per 50 tons to hit 1500 m/s in level flight at 22km. So, half the jet engines should be Whiplashes (lighter, much bit better performance below mach 1) , half should be RAPIERs. BTW, you can even use nukes to help go through sound barrier if you're struggling with that. They produce 75% of max thrust from 6km upwards. For rocket mode, you want 60kn of thrust per 15-20tons of launch weight. One RAPIER produces 180kn in closed cycle mode, so if you took my previous advice, you already got way more closed cycle thrust than you need. However RAPIERs in closed cycle have terrible ISP. Generally I switch over only some of the RAPIERs to close cycle when air breathing acceleration peters out, and leave the rest running on air breathing until they quit completely at 30km. I only bring enough oxidizer to boost my speed 300 m/s. By that point orbital freefall effect is supporting 85% of your weight, so combined with residual lift from the wings you'll soon be cruising at over 35km, at which altitude drag is negligible. One nuke per 30 tons is easily enough to carry you the rest of the way to orbit. Some of mine - 150tons, 3 rapier, 2 whiplash, 5 nukes (this was someone else's design i fixed up, has a drill if i remember correctly, but isn't finished) Interplanetary cargo ramp , all my own work this time ! Interplanetary CR100 bay ship, 5 R 6 Nuke - As regards your design - 1. I prefer not to use large fuselage tanks for my liquid fuel. Big S wings and strakes can do the same job while contributing useful lift. Fuselage pieces are always draggy. 2. Quad couplers should have only 33% more drag than tri couplers as they only mount 33% more engines, but from what i remember they have something like 50 or 77% more drag. 2.5m Tri couplers are the sweet spot 3. The X wing config isn't optimal. Flat wings generate 100% lift, dihedral wings sacrifice a bit of lift for extra roll stability. Anhedral sacrifices lift ot make negative stability. Just stick to a combo of flat and diheddral wings. 4. Cones on the back of nuke and rapier engines to reduce the drag from their rear attach nodes. like in this video. Finally, what you are trying to do is very hard. Ramps add a lot of drag and weight. Rovers tend to flip over at lower speeds than an aircraft capable of carrying one. Why cargo when you have interplanetary spaceplane ? Unless you're trying to build a base i suppose. you can help yourself a bit by compromising on 100 % re-usability. mount some Whiplashes radially on decouplers as well as drop tanks, to help you get off kerbin fully loaded.
  18. Flat tailplanes - more stable, flat canards less stable . If you have both, they cancel each other out. This debate ran on and on on another thread and got quite heated. In KSP , with CorrectCoL installed, I built a simple aircraft and converted it from tail to canard, moving the main wing to make yellow and blue ball only just touch on both versions. Identical handling, max pitch angle you could pull was the same. Using F12 cheat menu, I sent them both in on a re-entry trajectory with radial out set on SAS, the reaction wheel fighting to hold the nose up as aerodynamic stability of the two aircraft was trying to pull it back on prograde. Guess what? The altitude where the reaction wheel lost that battle and the nose fell below 30 degrees of pitch was the same. The real reason most aircraft are tailed is because of laminair flow. You get less drag when air flowing over a surface is non-turbulent, designers go to strenuous efforts to keep airflow over an airframe non-turbulent as long as possible. This is especially important on the main wing because it's got a large surface area. If the air hitting the main wing has already been disturbed by the canards, expect worse fuel consumption in cruising flight, which is the most important consideration for civil aircraft. Non FBW canards - Saab Viggen STOL fighter of the 1970s , can operate off roads instead of airbases - Burt Rutan VariViggen homebuilt Mine under Ferram Aerospace - 0.27m3 mach 1 wave drag area and landing speed under 62 m/s The advantage of canards is that you pitch up by lifting with the canard rather than pushing down with the nose, so total lift can be higher. Also, in a supersonic aircraft, having the main wing further back means you can make it bigger without getting wave drag penalties. However, there is a second drawback in that it's harder making a high lift system (flaps). Flaps already pitch the nose down, but on a canard they'll be even further aft of CG so the pitch down moment is stronger. You need to install flaps on the canard as well, which is too much complexity and expense for a civil a/c, or just don't bother with flaps (like the Rutan Variviggen) , or use relaxed stability, which requires FBW.
  19. If all else fails, alt f12 , cheats, hack gravity and use your jetpack to fly to the cockpit
  20. yeah landing gears are more robust than rover wheels. I made a very kerbal career spaceplane (jettisonable jet engines) with mk1 inline cockpit , and a terrier, and it was a tandem wing design because stock aero right? One pair of wings right at the front of the fuselage, one pair right at the back, and landing gears on each wing tip. So now we have an airplane that is also a 4 wheeled car, with a long wheelbase, wide track and low to the ground. you can either land on top of a mountain, and dab the brakes as you roll down to the flats - you'll collect 4 or 5 biomes for no fuel, then can do a v efficient horizontal takoff from the flats - or land on the flats, and dab the throttle as you climb a mountain. @bewing Minmus wheel friction improved in last update, but rovers are still terrible, always have been and probably always will be
  21. The most efficient solution is to use aircraft landing gears and drive over the surface, that uses practically no fuel because there is no air drag and minimal friction. Other than on the flats however, you got to keep your speed way down so this isn't the option if "real time" is an issue. Rocket biome hopping takes a lot of delta V, so the lander needs to be absolutely minimalist. Command chair and experiment storage module and leave the pod, heatshield in orbit? I'd even be tempted to leave off the science jr for that reason, it's a relatively heavy science instrument. If you bring it, take only one and a scientist who can reset. You'll want some way to get the benefits of a pilot though - second chair for jeb, probe core or comms for remote assist. The trouble is, if you visit 5 or more biomes it practically wins the game for you - you'll complete most the tech tree in this one mission. So yeah, these days i make one or two landings only and don't futz with time consuming rovers or in orbit rendezvous for minmus. Gvies me a reason to actually go to Duna
  22. There's two fixes. The first one, invented by @bewing , is to use friction control override and turn the traction of the front wheel right down and the back wheels up. It's like putting fatter tyres on the rear of a car so the handling tends towards understeer. Yes, this works on rovers too ! Second, your gears might not have attached perfectly straight. This is less common than it used to be, but the fix for that is to go into SPH, select the rotation tool, make sure you're in angle snap mode, then click on your gear. Before rotating, press F to toggle between local and absolute rotation modes. Make sure you're in absolute, then rotate the gear one notch left or right then snap it back again, this ensures it points true north.
  23. But remember kids, if you're going to add incidence to your wings, add it to the strakes, elevons and canards as well. Or Mr Flip gets happy. Surfaces behind the CoM having less incidence than those in front moves your CoM forward, so you'll have to shift the wing further back to compensate. But it increases stability the further the nose pitches up, because the wings at the front stall first. In fact it can be difficult to pull more than 8 degrees of pitch with this in place. Surfaces at the front not having any incidence, but the main wing having it, is bad. It is effectively a nose down trim that makes the CoL marker in VAB look further forward than it really is. When your AoA gets large , the main wing will stall while your canards are still unstalled and making lift. Your craft will swap ends or get into an unrecoverable deep stall. Yeah,I've started playing with Ferram Aerospace again and it makes the game reflect the laws of aerodynamics much more closely. Silly tricks like this are irrelevant, it actually rewards you for building sleek, graceful stuff. I think when an engine is running the exhaust stream greatly reduces drag off the back of the aircraft, but yeah engine bells on non-running engines are draggy as heck. I think when the shuttle was being transported on a plane they put covers on for that reason. You could mimic that with decouplers + cones, but when you start the engine you'll get hit with drag that isn't there on a real running engine.
  24. Then I'll also shout out to CorrectCoL. The blue indicator only takes account of parts with a lift rating, this one makes it more accurate by computing the effects of aero forces from non wing parts. If you only install two mods in KSP, get these two.
  25. Space shuttles are probably the hardest to build because of off-axis thrust, asymmetric layout, and the cg shifting as your fuel burns off. Try putting four boosters around the aircraft like this, that way everything is symmetrical, thrust , fuel etc. so it should go straight and stay straight even towards the end of the burn. Sounds like the airplane itself is flyable, and only narrowly falls short of getting to orbit on its own. With assisted launches like like you can replace engines with good sea level isp for ones with a good vacuum rating on the orbiter itself - poodles, terriers, nervs, ions. Just make sure whatever combo you choose has about the same weight as the old engines or the change may upset the handling.