Jump to content


  • Posts

  • Joined

  • Last visited


1,055 Excellent

1 Follower

Profile Information

  • About me
    Rocketry Enthusiast
  • Location

Recent Profile Visitors

7,445 profile views
  1. I'm really not used to the interface of the B9 Procedural Wings mod.. I've spent ages perfecting a design, only to mangle it beyond repair with a single misclick. I'm also at bit confused about what the "leading edge" and "trailing edge" sweep numbers meant. Though they did make me realise i'd put the wings on upside down, forcing another start over. Anyway, before i lose all sanity, i made a quick comparo of 3 different wing planforms. Yeah unfortunately I wasn't able to change only one parameter, because i don't know what i'm doing with PRocedural parts. Previously, I would use multiple wing parts so get an increasing sweep angle as you move outboard... since that looks like the waverider shape that keeps as much of the wing as possible inside the bow shock http://www.aerospaceweb.org/design/waverider/figures/fig14.jpg If the above link doesn't work, suffice to say that planform looks a lot like a "starfleet logo". Not sure it's worth the hassle though as bow shock is not modelled. Arrgh.. for science i should really build such a wing and attach it to this body and see how the numbers look. Anyway, first iteration. Apparently the "mid chord sweep angle" is 73 degrees. It has a taper of 0.3 and a mass of 3.18 (tons?). This design is best for wave drag and cross sectional area. Unfortunately, while i'm optimising my area ruling to four decimal places, i've failed to notice this wing doesn't hold much liquid hydrogen. We've got such a good TWR (1.27) that the wing isn't really needed, but the burn time is only 3 min 41 seconds with a Vac dV of 3276 Next i tried playing with the sliders to try get a 60 degree sweep. I ended up with 65 degrees and a slightly larger wing overall. It's mass is 3.92 instead of 3.18, and the taper is less, at 0.2. It has about the same mach 1 wave drag area though the cross sectional area is twice as much. This version of the craft holds a lot more LH2. Our TWR drops to 0.98 but the burn time is now 6 min 26 seconds, with 4757dV. Still seems under-fuelled. Finally I tried to make a data point at 50 -ish degrees of sweep. This results in a "taper" of only .024 - which i find odd as the wings have almost zero chord at the tip, and are almost the whole length of the fuselage at the root - and a truly enormous wing of 7.84 tons. The max cross sectional area hasn't improved much, but our mach 1 wave drag area has about doubled. Then again i haven't spent a lot of time optimising this version but i'd be surprised if you can improve much with such a vast wing. The good news is, that wing holds a lot of fuel and we have 6662dV and a TWR about 0.49. Now comes the (not) fun bit - making screenshots of the L/D plot then counting pixels with MS paint to see if one peaks higher than another. All are plotted as an AoA sweep from 5 to 10 degrees at mach 6. The gigantic 50 degree swept wing does ok here, with a peak L/D 44 pixels above the zero line. For some reason, the intermediate 60 degree wing is rubbish, with an L/d only 38 pixels tall. The smallest wing does best though, with 58 pix. However it doesn't hold enough fuel and in the process of writing this, noticed that i also married that wing to an earlier, smaller version of the fuselage too which may account for some of the differences. edit - further experimentation with the 50 degree wing... reveals that a finely tapered leading and trailing edge profile actually worsens performance. The best airfoil profile appears to be a rectangular slab. Increasing or decreasing thickness over quite a large range does not seem to matter at all. Leading edge sweep appears to have a wide sweet spot, and the trailing edge sweep is best when it is about a third of the leading edge sweep angle. A wing chord that drops to zero at the tips is desired..
  2. The design point is the transition to NERV power after the airbreathers quit.. so I'd say mach 6 plus. This is where our TWR will be at its worst and so our L/D needs to be as good as it can be for us to gain energy. Over time, we'll get lighter as propellant is used and our TWR will improve. As we start getting up past 50% of orbital velocity gravity will start to reduce from orbital freefall which again will help us. The challenge is I am targeting a higher mach number than you are, but on the other hand i can fly as high as i want , whereas you have to stay low enough to get air into your RAPIERs.
  3. I appreciate the effort you put into the post. I am however fully aware that spaceplanes are hard, and have gotten into some bitter spats with people on this forum who seem to delight in gloating about this fact. Obviously, the folks I was arguing with could always just point to the indisputable fact that in real life, the only way to put a man in space is with a fully expendable rocket. The stock game is balanced so that both ways of getting to space are viable, at least in sandbox mode - but I am frustrated by the fact Ferram effectively blocks off the non-rocket path by clamping L/D below 2 above mach 4. This would be justifiable if it were based on a law of aerodynamics, but it appears to originate from Kucheman's equation he devised by extrapolating the trend of supersonic aircraft development in the 1950s : http://www.aerospaceweb.org/design/waverider/equations/eq08.gif Even then, Ferram appears to apply the cut more aggressively than the above formula implies, creating balance issues when combined with RSS. http://www.aerospaceweb.org/design/waverider/figures/fig12.jpg I've looked through a few dev posts from the folks who maintain this mod : It appears that "all" it does is area rule your craft in real time and use that to apply an amount of drag at mach 1. Which is quite an achievement given the need to not kill a person's PC in the process. It is a significant improvement in realism on stock aerodynamics though which admittedly is a low bar. It neatly solves the problem of a player combining two delta wings to make a square one - without their Voxel based method to test the end result, the game will not know whether a low speed or high speed airframe was the outcome. However it doesn't appear to simulate other aerodynamic effects, so you can cheese the game and make unrealistic aircraft with Ferram too : for example, it doesn't seem to mind tandem wing designs , and it appears you can make a supersonic biplane if you want, so long as both wings are swept ! From a few test shapes created in SPH, it appears that aspect ratio and taper don't affect lift drag ratio at all, and drooping the wingtips like an XB-70 Valkyrie makes your L/D worse, which confirms a dev post who said that Ferram doesn't model compression lift. The only things that appear to influence high mach L/D are the proportion of your craft that is wing - like in stock game, the more wing area, the higher max L/D you can get, because the fuselage makes only drag, no lift - and transonic drag. So I'm guessing I need to make the skinniest possible fuselage that holds only Kerbals and Engines, and then attach the largest swept wings I can, and fine tune the sweep angles to minimise transonic drag. And put all my liquid hydrogen in those wings because surface area to volume ratios don't matter for boiloff apparently ! Well, if I had a nuclear thermal engine that could switch between operation on Ammonia and hydrogen available, i wouldn't cheese that so hard. As you can guess I've been reading on http://www.aerospaceweb.org/design/waverider/design.shtml whilst dreaming up these designs. Whilst sites like this lure the prospect of better performing waverider designs, they also indicate that these numbers are only achieved at the design mach number. What I'm hoping to do is get to mach 5 or 6 on ramjets, then switch to NTR and hopefully have a L/D > 2 for a couple more machs. After that, supplement with some conventional rocket thrust and for the final leg of the journey our TWR will be good enough to brute force things with most of the propellant gone...
  4. So I've spent all these years doing easymode stock space planes, but I want to get a feel for what it might take to create something like that in real life. So I installed Realistic Progression 1 modpack which scales the planet up to earth size (orbital velocity now something like mach 21 instead of mach 7) as well as Ferram Aerospace. I am not too hung up on 100% reusability and am ok with dumping off empty tanks and any engines that are cheap enough to miss, so long as the majority, preferably 70% or more, of my craft goes to space and comes back again. What is really the essential thing for me is that the wings actually play a part in getting us to space... rather than just for coming back down. In the stock game, I create craft with Lift/Drag ratio of 3 to 1 or better so I can get to orbit on fuel efficent jet and nuclear engines, not being tied to a thrust weight ratio > 1. The problem is when you combine Ferram and RSS ... you can get a lift to drag of 7 to 1 or so at mach 1.4, once you're though the high drag transonic (mach 0.9 to 1.3) region. This is about twice what i get in stock. But, with Ferram the L/D inexorably declines as we get faster. By mach 5 it's heading below 2:1, and that's not even a quarter of the way to space. With the stock aero model, L/D ratio us unchanged from about mach 1.4 onwards. I've built SSTO spaceplanes for RSS with stock aero that were still doing L/D 3 to one at mach 20, albeit at a very high altitude. And yeah things were kinda toasty by this point. Is there any way to improve my L/D at super high mach, super high altitude flight ? Would drooping outer wing sections like an XB-70 Valkyrie, create compression lift, or trying to make a waverider planform ? Or do i just need to do more of what makes a good mach 2 airplane, sweep the wings back at an even sharper angle, reduce span, lengthen the fuselage, try to improve area ruling even further ? Of course, do too much of those things and it won't be able to lift off the runway before the tyres explode, which is a separate issue..
  5. I don't play KSP that often anymore and only saw the thread yesterday. So here is a belated entry. Ladies and Gentlemen, I present the Sloth Ray. https://www.dropbox.com/s/brtkt4ejf8t10ft/Sloth Ray.craft?dl=0 It has 9 Seats and weighs just under 60 Tons. It has three Nervs, One Rapier (only operates in airbreathing mode), and a Panther. Action Group 1 deploys some elevons that push the nose down a few degrees to stop it climbing above altitudes where the jet engines can work, before we're good and ready. Action Group 3 retracts said same flaps. Action group 5 toggles the nukes. It needs those to get though mach 1. Action group 9 toggles the afterburner on the Panther. The TWR that appears on the stock game staging indicators show the following : Airbreathing Stage TWR 0.20 At 20km altitude, the NERV stage reports a TWR of 0.24, getting into the dangerously sporty territory. Of course with the jet engines, the static thrust rating here is highly misleading. Their output falls with altitude, increases with velocity (up to a point) then fall off again as you get faster still. This is what Kerbal wind tunnel says about the air breathing stage. https://imgur.com/ttXElmK https://imgur.com/IaM1wcQ https://imgur.com/pLj7nqo Flight details hidden in spoiler .. Incidentally, I found out this thing can land on Duna. https://imgur.com/h6PLj2E https://www.dropbox.com/s/7n9fibg2a9cb1ep/FINAL.sfs?dl=0 Here's a save file if you want to land it yourself. Remember to put RCS on. "K" key fires the ventral thrusters which help us touch down slower. Space bar opens the drag chutes which can help it stay straight on the rollout. The biggest danger is getting sideways and flipping over. https://imgur.com/5YuZTmc
  6. So, after spending a weekend on the totally awesome Atomic Rockets site http://www.projectrho.com/public_html/rocket/ I was thinking about an inner solar system passenger liner, working the routes between Earth, Mars and the Asteroid Belt. Near the front would be a rotating habitat cylinder. Length greater than diameter because we don't want to jut out beyond the protection of the shadow shield from the engine section nor the whipple shield/forward fuel tanks from micrometeroids coming at us from the front. The outermost decks of the rotating hab are going to have the most gravity and imagine you want the most gravity for 1. Cardio Suite (gymnasium) - a treadmill in low gravity is going to frustrate most users Next - the Bathroom - terrible things happen here in zero G. As well as failure to achieve separation from things you very much want to be separated from, there is also the issue of drowning while having a bath or shower which requires at least some gravity to mitigate. In the "some gravity is highly desirable" category you have the mess hall/restaurant as well as the kitchen. Your peas should stay on the plate, not float off, turn rotten, then land in someone else's soup a week later. However, a lot of people might prefer sleeping in very low/zero G and by no means all of the pressurized volume need be in the rotating hab. Which got me thinking - how would power, water, and air be transferred from the rotating parts of the ship to the non-rotating parts ? Is this an engineering problem that is already solved ? Slip rings or wireless power transfer ? What about fluids ? I'm guessing there are automobile engineers with some experience handling similar problems..
  7. Grats on your first foray to the SPH. I Like to zoom in a bit on that Stability analysis graph by setting a smaller scale. A quick check to make sure the line keeps sloping down at up to 30 degrees is good to make sure there's no nasty deep stall tendency, but outside of aerobatics you're going to be using no more than 10degree AoA. Lift to drag ratio goes to the toilet after that. So I usually fine tune with an AoA range of 10 and marks every 1. As for the continual rolling problem, I think there is a bug in the game engine that can cause a continual roll in one direction or other for no apparent reason. Its normally about 3 degrees per second or similar. It may have something to do with attachment order or joint flexure. Some of my craft do it , some dont. It makes long range atmospheric flight a real PITA without some kind of mod FBW/Autopilot. As for the lawn dart tendency... Yeah when fully fuelled your Center of lift is too far behind your centre of mass. Blue arrow touching the back of the yellow ball is how i go. It looks like your Centre of mass shifts rearward as fuel burns off, and you had to set the wings real far back to stop the plane flipping out when the tanks are low. You can see that from the yellow (low fuel state) line on that graph being a much shallower slope than the full fuelled one. To fix that CoM shift, you've either got to : leave forward fuel tanks empty (but pay the drag penalty for these empty fuselage sections regardless), find a way to shift engines futher forward, or find a way to add more fuel in the rear. ( Perhaps some big S strakes orientated vertically instead of the tail fin you chose, since that will add fuel tankage to the back end of your plane. Likewise Big S strakes with elevons attached to the back instead of tailplanes. Not enough to fix the problem on its own though) Yeah this is a perennial problem with KSP.. Just wait till you try balancing a plane with NERVAs... RE: rolling for some reason this plane doesn't do it and is quite steady. Which proves that size and part count are nothing to do with it then.. Notice again, how i'm trying to get my dry CoM forward without making it look too wierd. 3 ton NERVs are mounted as far fwd as possible. Next go 2 ton rapiers. The 1.2 ton Panther engines are hung off the back....
  8. This is difficult because i think it is night time where i live when it is daytime where you live. Now, Major Issue I can't believe I didn't see this earlier. Where are your vertical stabilizers ? What is keeping you stable in yaw ? When you mentioned losing control, I always assumed you mention in pitch, because that is the harder problem to solve. I like to use big S wing strakes rotated vertical, and slide them to the back of the airplane. maybe one on top of each outer engine pod. But any tail fin is better than none ! Moderate Issue In your latest pic, I see two extra Whiplash engines on the back of the NERVs. I think this is a bad idea. That is another four tons the NERVs will have to push to orbit, after the jets have stopped working. I normally find you need twice as many nervs as jet engines. Minor Issue. In the last pic you added a pair of shuttle vertical stabilizers as tailplanes. They are very large for a craft this size, but ok. The main thing is they are not mounted as far back as they could be, they are quite close to your centre of mass. IF this is your only pitch control surface, this means they have to generate a lot of downforce to get the tail down and the nose up, and that downforce subtracts from the lift you are making. If they are further from Centre of Mass, they have more leverage and can get the same effect with less down force. Minor Issue 2 The solar panels are still not in service bay. I don't think you need such a big solar panel. A smaller one might take longer on Laythe, but it doesn't matter really because you will be in high time warp while making fuel. RE: BTW i still don't see any Big S wing parts on your plane or am i looking at an old pic ? RE: Using KAL intake exploit on NERVs so they work better in atmosphere I think you asked this earlier. I sometimes use NERVs on Kerbin above 7km to help me get through sound barrier, if levelling off from my climb is not enough. Otherwise it's a waste of fuel , I don't put them on until i am at 17km, in level flight and the jet engines are not able to accelerate me any faster. NERvs are a lot more fuel efficient than normal rockets but still terrible compared to jets. On Laythe, same principle. On Duna, the atmosphere is so thin, the NERVAs work great even at surface. Which is lucky because Jets don't work on Duna (no oxygen)
  9. Just, remember kids, "Angle of Attack" and "Pitch" are not the same thing. Angle of attack is the difference between where the nose is pointing, and where the plane is actually going (prograde marker in surface mode). With a powerful engine like the Whiplash, at times you will have a pitch of 10 - 20 degrees because of the steep climb rate. But you never want your Angle of Attack to get much more than 5 degrees. Above 5 degrees, the lift to drag ratio gets worse, and you want to be trading at the best rate possible. To fly well (not melt) in the upper atmosphere, whilst keeping angle of attack at no more than 5 degrees, it is nice to have quite a lot of wing. But the Whiplash engine thrust falls away very quick above 17km. So you might be using much less than 5 degrees when flying on jet engine. This is OK, because the most important thing is to get as much speed out of the jet engine as possible. Once you are using NERVAs, their thrust doesn't decrease with altitude, but the ISP is much less than the jet's. So the only thing that matters is to have the most efficient lift : drag ratio you can get.
  10. This is strange. Stability should not change with speed or altitude - if the amount of air hitting the plane gets more (because of speed) or less (because of altitude) the strength of the aerodynamic forces will change, but not their position on the craft. If the center of lift is behind the center of mass, the craft will still want to point its nose prograde. Is it anything to do with fuel burning off ? "RCS Build Aid" shows a red ball in SPH / VAB so you can see what happen to centre of mass when fuel is used. Or maybe its just drag from the fairing. It is a very big one.. like i say the converter and ore tanks don't need to be inside, only the drill. One other thing.. it's not to do with Angle of Attack is it ? I would have thought if this was your problem you would notice on takeoff already. A plane that looks stable at low angle of attack but suddenly becomes unstable at high pitch is either bending in flight from G forces, or you've got some aero surfaces angled up a bit at the rear of the air plane. This gives the back end more lift and makes the blue arrow look like it is in right place in hangar, but when you pitch up, the rear end stalls first. I am also confused by your statement "too much wing to take off". It should be easier to take off with more wing. Strakes - yes Big S wing strakes weigh the same as other wing parts that make the same lift, and have the same drag. But they also store fuel, which makes them over powered.
  11. That doesn't sound like a viable propulsion system for SSTO. One NERV is only 60kn, same as a Terrier. Close cycle Rapier is 3 times as much power. If you are not going to use oxidizer engine, then you will need 2 nervs at least. And lots of wing, and low drag. Wheesely engines have hardly any power above mach 1. If you really want to cruise around at low altitude and low speed on LAthe without using much fuel, use a Panther. Or just mount a Whiplash for SSTO and put a pair of little Junos on the wing tips for cruising around. If you are using NERVs to get to orbit try to store as much of your LF as you can inside mk1 strakes, rather than fuselage tanks. They will help it fly in the upper atmosphere when the jet engines have stopped.
  12. That design looks fairly promising. Is that a 2.5m fairing though, attached to a 1.25m fuselage piece with no size adapter ? Will make drag there. Also , it looks like you are using two wheesley and one nerv engine ? I would maybe use 2 rapier and 1 nerv or 2 nerv and 1 whiplash
  13. Two things worry me : 1. Those engine pods at the top seem to have 1.25m engines attaching to 2.5m parts then a 1.25m part at the back. All axial attach nodes should have something on them - if only a nose cone - and both attach faces that meet should be the same size. If you are joining a 1.25m to a 2.5m you should use adapter or get big drag. But ideally try to minimise size tranistions 2. Heavy nervas right at the back. Nothing to balance the weight up front. Just some fuel tanks, which will empty out and leave your plane tail heavy. Get RCS build Aid mod, it makes this stuff clearer. 3. That shuttle type adapter at the back can be draggy if you don't put a 2.5m nose cone on its central 2.5m engine attach node. FRom what i can see, you are only using the three 1.25m
  14. The blue arrow in the Spaceplane Hangar only takes into account aerodynamic forces from wing parts... so putting very draggy non-wing parts at the front can mean your Centre of Lift is further forward than indicated, leading to aerodynamic instability. From my testing , the resource converter (both the small one and the big one) are surprisingly low drag, as are the ore tanks. But the drill,solar panels, and radiators make a lot of drag, even when folded away. Put them inside a 1.25m service bay. The drill might be too big for a 1.25m bay. The 2.5m bay is quite draggy. Procedural fairings are very low drag. Maybe use a fairing as the nose cone and hide your drill inside it ? I disagree ! Mk1 are probably the easiest to make. They have such little drag, the NERVA can push it to orbit by itself very easily. I made two extreme mk1 planes as an experiment, one with virtually no wing, one with loads of wing. They both went to orbit very easily. But fitting a drill in one is hard. Fairing maybe ?
  15. Give us some clues please... Does your craft blast off vertically from the pad, or takeoff horizontally from the runway ? Is it rocket only or jet ? What is KAL ? A mod ? The S3 Vector engine is part of the base game. If you are not allowed to use it for whatever reason, Vernor thrusters are much more powerful than normal RCS , and can work at Sea level unlike normal RCS systems that are designed for space. My best guess is that you're trying to build a vertical launch space shuttle type thing. You've probably got non-symmetrical engine placement, which is causing the thing to flip, before it gets going fast enough for aerodynamic forces to keep it straight. Space shuttle replicas are the hardest type of launch vehicle to make.
  • Create New...