AeroGav

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About AeroGav

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  1. I have just started playing the Ferrram Aerospace again, which accurately simulates wave drag. In Ferram, mk2 parts are as fast as they look, and your ship wiould greatly outperform mine :-). It's still in beta though, and not for the fainthearted. Landing speeds are waay higher too.
  2. There, a picture is worth a thousand words. Red ball from RCS build aid is right on top of my yellow ball - CG is same full and empty. Static Stability analysis graph slopes downhill across the AoA range - in other words , the more the nose pitches up, the stronger the plane's stability tries to pitch it down again. It crosses the axis at about 0.5 degrees AoA, meaning if you let go of the stick and have SAS off, it will settle at an AoA of 0.5. The thin vertical blue line (hard to see unless you click on the picture) indicates it needs about 5 degrees to maintain level flight in the conditions i simulated - 22km altitude and 1150 m/s.
  3. Size isn't important I strongly recommend two mods to help you build stable aircraft - RCS build aid, and CorrectCoL RCS build aid shows a red ball in SPH which indicates where your CoM will be when empty. You can do the same thing by manually emptying all the tanks but trust me , the number of times you need to check this when building a complex spaceplane, it saves much work. CorrectCoL makes the blue ball more accurate. At the moment, the Blue ball only takes account of parts with a lift rating in their description. But in reality all parts interact with the airflow and create forces. You have a lot of fuselage in front of the CoM and it has a longer lever arm than the stuff at the back, it may be that your CoL is further forward than you think it is. That layout you have there btw, has the cargo in front of the CoM, which means it's always going to be either a bit too nose heavy when laden or a bit too tail heavy (flip happy) when empty. Best is cargo bay dead centre of CoM, with half your fuel right behind the cargo bay and half right in front, or on sponsons either side. CorrectCoL has a more sophisticated Static Analysis graph you can bring up too, for pitch and yaw. The nuclear option for stability/flipping problems is to check and tweak incidence angles. Usually, surfaces are attached at zero incidence angle and all aero surfaces on the ship will have the same AoA. If they differ however, it is imperative that surfaces ahead of CoM should have greater AoA than ones behind. That way, wings at the front gain lift slower than wings at the back as AoA increases, as they get into diminishing returns (or even a stall) first. However, because this increases lift on the front end at low AoA, it moves the blue ball forward, so you need to slide the wings back a bit. Short version - Using fine rotate tool, rotate your front Canards up ever so slightly. Rotate the elevons , on the trailing edge of the wing , down ever so slightly. This will cause the blue ball to move forwards in SPH, so you'll need to slide the wings back to keep it behind CoM. But it will now fight back if you try to stall it. Its like being held to a railway line by a strong rubber band, You can steer a few degrees either side of prograde but if you go too far it yanks you back in line.
  4. One whiplash and two rapiers will get him through the sound barrier as easily as four rapiers, but the 2R 1W config is a bit lighter. Both will max out at similar speed if he does the speedrun in horizontal filght, because that is limited by either the cockpit melting down , or the engine hitting diminishing returns on the thrust curve hard You can see that past mach 4.5 (1350 m/s thrust starts to decline fast, it really falls off the earth at mach 5.5 (1650m/s). Adding more rapiers at this point costs you more delta v in extra weight than it gains you in airbreathing speed. Unless he's reaching his airbreathing top speed in a climb, and going well under 1300 m/s when the engines run out of air, in which case even more TWR might help. Before anyone says it, i know that levelling off for speed run takes longer, which is valid if the mission is well within the dV of your craft - not the case here though. I wish i could disagree, because they are such awesome and under used chemical engines. They have Vacuum ISP 10% better than the Rapier, and weigh half as much. But... you're right. Two Rapiers give 360kn thrust in closed cycle mode - which is a TWR exceeding 1. My mk2 spaceplanes have less than 60kn drag in the upper atmosphere, with the wings producing enough lift to keep us up. Assuming his is twice as draggy, that's still thrust:drag ratio of 3 to 1 with two Rapiers. Save the two tons then and leave them home. The extra 2 tons of dry mass won't make up for their 10% better ISP.
  5. For comparison, mk1 inline cockpit ship re-entering. Moderate nose up angle for lift, but like Scott i am aiming at the space centre, so the prime consideration was trajectory control Craft file here - https://kerbalx.com/AeroGav/freedom-fighter Video of me building it and launching it, here - https://youtu.be/XXhIb5OlSRY
  6. Thanks for the pictures. First of all, mk2 fuselages are arguably bugged right now, they produce 4 times as much drag as a mk1 without actually holding any more fuel. It would be much easier if you started off with a mk1 fuselage design, just use an inline cockpit and put it a few modules back from the front so it doesn't get affected by the heat of high speed flight. Inline cockpits are vastly less susceptible to heating - an inline mk1 will be less prone to blowing up the mk3 cockpit because it has to go at the front ! Second, engines are heavy. Rapiers are 2 tons each, Whiplashes weigh 1.8 tons, Aerospikes 1 ton. Your vessel probably weighs 30 tons, but is carrying 10 tons of engines. Allowing for the structure and cockpit, cargo, it must have a fuel fraction under 40%? That is why fuel runs out before orbit. If you can reduce drag, you won't need as much engine. Looking at your ship, i'd try to replace as many mk2 parts with mk1 fuel tanks as possible - if you insist on keeping it a mk2, use them only for carrying kerbals and cargo. Try to put nearly all your fuel in mk1 parts instead. Also I'd recommend an inline cockpit even if you stay as a mk2. Those rapiers can get up to 1600 air breathing in level flight at 22km - but if your cockpit is right at the front it will melt. Profile - A good flight profile reduces the need for lots of engines. Jet engines behave a lot like ramjets in this game, they produce more thrust at supersonic speeds. But, the air down low is really thick and draggy, which makes getting supersonic difficult, also the transonic region (mach 0.9 to mach 1.2) as more drag even than supersonic flight. On the other hand, if you climb too high without speeding up, the air gets too thin for your wings. You end up pulling the nose more than 5 degrees above prograde , which makes for high drag. Here's my latest mk2 - https://kerbalx.com/AeroGav/Penta-Shuttle It's a not as nice looking as yours though :-(. 1 Rapier at the back of the fuselage is enough to get it to 1400 or so air breathing. But not enough to get through sound barrier, so it has 2 Panthers for an extra boost low down. Once the Rapier is on song, it doesn't need them. There's also 2 NERVs which can boost it to orbit all by themselves, and use up the considerable liquid fuel capacity of the wings. As you can see, it can reach minmus very easily.
  7. I'm not sure what's going on with Scott, either he's out of practice making and flying aircraft or he's deliberately creating mishaps for drama purposes. He used to be a really good pilot ! The launch profile on his first flight was obviously terrible (trying to go supersonic in a steep climb, when that didn't work, started his rocket engines early, then runs out of fuel) , now this disaster. Inline cockpits FTW. Mk1 inline cockpit is less prone to overheating than a mk3 cockpit, because you can put it a few modules back from the bow shock, away from the heat.
  8. I think if you're setting yourself the handicap of doing interplanetary with a 90% re-usable ship, then allowing yourself to ISRU is acceptable. It's pretty easy to go anywhere if you're asparagus staging 3.75m boosters to send a little mk1 pod to space. It is still possible to go interplanetary without ISRU of course, check out this vid (not mine!) -
  9. NERVs really are for stuff that goes beyond LKO, which is very possible. Re: size. If you have an interplanetary NERV powered spaceplane with mining equipment, it becomes pointless building beyond a certain size even though you can. I mean, you could make one lift an orange tank , but why the hell would you? Just send the nerv spaceplane to wherever that poodle/orange tank ship was going. Or just use its own drill to support remote ops. I suppose you might want it to carry a lander for somewhere like tylo, eve or moho, that's about it. Are you using any kind of stage recovery mod? If not, then whiplashes do make good droppable boosters, being only a third the cost of a rapier.
  10. So did I - It was based on the premise that real jet engines are unlikely to ever exceed 20% of orbital velocity, so i made a TSTO limiting myself to wheesley tech. The launcher has 5 Wheesleys, the upper stage two NERVs and a Terrier. The terrier doesn't have that much ox, but helps us to mach 3. 3000dV in LKO. Someone else borrowed this craft and made a video with it. He was pulling the nose up further off prograde (not needed on this design because of large wing area and the fact wings have built in incidence angle) - the extra drag cost about 15% delta V but it got the mission done. And he makes much better videos than i do !
  11. Sorry I couldn't seem to find the answer on google or the FAQs, but we're encouraged to mod our own engines, but where are the config files of the mod engines actually stored? Stockalike RealFuels comes with a "Trimodal" version of the NERV engine, for example , and i don't know where to look for it in the mess of txt files. I'm trying to build a spaceplane whose engines use a common fuel source, to the greatest extent possible. Hence, I'd like the NERV and Jet engines to run off ammonia or hydrazine , and keep a small amount of LOX to boost through the launch profile.
  12. True, an ascent that's as shallow/close to a straight line as possible is best. But, you statement there makes it sound like lift is a bad thing and that ideally you'd decouple the wings at the moment you switch modes. If you have a lot of lift potential, I say use it, by pitching to a 5 degree AoA. If you watch this video from the 4 minute mark, I am flying level at 22km, which is the altitude for getting max speed at level flight on the RAPIER. My AoA is only 1.5 degrees, to keep us from climbing. By 1400 m/s. drag has risen to 75% of my thrust. This means that even though my RAPIERs have 4x the ISP of the nukes, I am better off starting them when three quarters of that thrust is being cancelled out by drag. When I start the nukes, I add nose up pitch trim (hold down the ALT key and tap S) until the craft settles into a 5 degree positive AoA. This is the AoA that gives best l/d ratio in supersonic flight. Drag rises from about 60kn to about 105kn, but lift rises by a lot more, our l/d ratio goes from 2.5 to one to nearly 4 to 1. The increase in drag is temporary - in less than 30 seconds we gain 3km in altitude, which sends our drag below 60kn again. Conclusion - lift is a good thing, you just want to make sure you're getting the best possible trade when you use them to exchange drag for lift. Once you hit closed cycle mode and are no longer holding the plane artifically low to so the jets can breathe, maintainng the best l/d is the only consideration.
  13. Please post a copy of the craft file. A design can look aerodynamic but due to the way the game calculates drag, some methods of attaching parts cause huge drag. Are space planes insanely hard ? Space is hard. The SPH / VAB is hard to use, and poorly explained. If you're building anything complex, it can be very frustrating until you know its quirks. However, I actually made my first orbit in a space plane, because i could not fly any of the stock rockets and the ones i designed were even worse. Gravity turns are very hard, and are completely unfamiliar to anyone that's never played a space game. Someone who is interested in aircraft / has flown a few flight sims will have learned a few of the principles of aerodynamics during their life, but what about the aerodynamics of rockets? What keeps the correct end pointing at space? How do you stop it becoming flip happy when fuel burns off ? How do you calculate TWR and delta V? I remember my first Kerbal aircraft. It was a canard, and i thought, why not put the vertical stabilizer up front too? Exit stage left. Lesson learned. The next one became pitch unstable at high speed because of body lift and fuel burning off. I put the fuel tanks in the middle and two of my engines either side of the fuselage instead of all at the back... and off it went. 2 rapiers and 1 nerv. That first ssto even gave me a Munar flyby, once i figured out how to use the map screen..
  14. Well now, I tried to make a wave rider to exploit compression lift. That involved a large number of modular wing panels and a considerable amount of time. Stuck an aerospike on the back, set infinite fuel cheat, and off we went. It was rubbish. At subsonic speeds it is desperately unstable in the roll axis, and has the L/D ratio of a brick. At mach 4, in the upper atmosphere, it was more stable, and at one point I saw L/D of 1.9 to 1 . Ahah, this must be where the hypersonic compression lift takes over, i thought. Mind you, my scimitar-winged ssto was seeing similar numbers at that point, and was a heck of a lot better at slower speeds. Unfortunately, as speeds increased, L/D fell just as it did with the swept wing aircraft, so I can't say it was better at any point in the flight envelope, no sign of compression lift actually working. Whether FAR models this or whether I'm just not as good as NASA at building Hypersonic waveriders (hmm, how many of those have actually flown again?) is the question. After having a lie down, I spent the afternoon building an unswept version of my airplane. Literally just rearranged the pieces to make a straight wing of low aspect ratio (a shade over 2 to 1) of the same area. Wave drag area doubled to 0.55m3 , which still isn't terrible - i think the fuselage layout, with the long nose and engine nozzle appearing just before the wing starts, with the canard layout keeping the wing mounted far aft, has inherently good area ruling. But, stall speed was about 5-7 m/s lower only. So , is the reason that supersonic fighter planes land so much faster than say, a Cessna 172, not because of their swept wing planform, but more because The Cessna is an empty tin can, with a pair of deck chairs to sit on and a ribbon on a stick for instrumentation The fighter jet is loaded with boxes of top secret, obsolete and staggeringly expensive electronics except for the bits that are filled entirely with Kerosene. Every cubic centimetre of space inside that is not a grey box with wires hanging out the side, is filled entirely with fuel In contrast, the Cessna's fuselage is mostly empty space, except for cobwebs, dry leaves, and food wrappers The Cessna's fuel tank is the size of a lawn mower's, as is it's engine So, to make this into a Cessna 172 trainer, I'd need to swap the cockpit for a service bay and command chair, replace the Panther with a Juno, reduce the strength of the parts to 5g, and carry only 50 units of LF.
  15. I dabbled with FAR in the early days of my KSP learning curve and got put off. Yesterday I installed the thing again and tried to make a supersonic aircraft with non-widow making landing speeds. I need to set up Infernal Robotics next and try a swing-wing config, but this is my fixie - I wasn't sure what the landing speed would be, and ended up overshooting the runway by a considerable margin. That's about 120 knots in real money, which i suppose is reasonable for a supersonic jet. There's two hardpoints under the wings. I decided to hang a couple of NERVas under there, and we ended up playing space invaders. The nuke engines have their own parachutes and can be decoupled before landing, which makes life easier for Val.