AeroGav

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  1. Well, I started designing a new airplane for this job, and predictably enough i'm running into issues "unsticking" from the water. I think i got lucky with the "puffin" pictured in my previous post. I gave the wings sharp dihedral and had them extend below the fuselage at the centreline, so the innermost/lowest parts of the wing dip in the water and act as hydrofoils. Problem is, when you try to pitch up , the front parts of the wing come out of the water, so the centre of hydrodynamic lift goes well to the rear. That is to say, it really does not want to pitch up at all, and the faster it is going, and the higher the airplane rises out of the water, the worse this gets. Also when you do manage to generate some pitch angle, the rear fuselage dips into the water slowing you down. I eventually got it to unstick at 90m/s (twice the speed it lands at, with full tanks) and then it goes into a vertical climb. So, guess i need to start again. attempt 2.0 will have flat wings, and i'll make separate hydrofoils that extend well below the fuselage, i'll have to make the front ones have tall "legs" so they stay in the water when the airplane is pitched up. The problem with this, is that it's surely going to mean no ground clearance , or almost no ground clearance when land based. Perhaps i should just remove the landing gear completely and have it launch from the runway on a dolly, after that it will only ever see air, space , or water.
  2. Developing a seaplane is tricky however. People often struggle making airplanes, because the game doesn't show them the info they need to see (drag values, static stability plots, thrust curves) unless they install mods. For seaplanes , its even worse. Water drag is not reported anywhere, nor hydrodynamic lift. I think a hydrofoil approach is more elegant than using floats, but the results can vary a lot. I recommend making the seaplane first, then look at modding it for SSTO, then use cheat menu to test it will land on Laythe without damage and unstick again, then think about flying your mission. I've heard that Laythe is slightly harder to seaplane from, because the air density at sea level is like 6km up on Kerbin. Gravity is less, but water drag is not. On the other hand, Laythe is much easier to get to orbit from than the surface of Kerbin. I'd make sure it can get off the water in Laythe and then reach orbit, even if that means it needs drop tanks or booster engines to make orbit on Kerbin. You probably want lots of wing area (hydrofoil lift, and to reduce takeoff/landing speed) and most or all your jet engines will be Panthers, since these have the highest TWR on takeoff conditions. Panthers max out at 800 m/s or so, but from that point getting to laythe orbit is super easy. You could probably try adapting this craft of mine if you like, maybe replace that wheesley with a panther, give it slightly stronger gear and an inline clamp o tron? https://kerbalx.com/AeroGav/Puffin
  3. The counterpoint is that the KSP aerodynamic model generates most drag from fuselage parts rather than wings, and this tends to scale with tank volume. You will get extremely high drag penalties operating a spaceplane with LV-Ns inside an atmosphere. The counter-counterpoint is that you shouldn't be operating LV-Ns inside an atmosphere. I'd retort that this is a game and whilst there is zero chance of the public accepting such a risk today, if you assume Kerbals have attitudes of the early 1950s, the technology itself could be made to work. As regards introducing extra fuel types / tank switchers , that does sound good. Nuclear Thermal rockets can run on non cryo fuels, eg. Ammonia/Hydrazine. ISP drops to 600 or so, but that's still quite an improvement on chemical engines that run off room temperature storables. In reality I suspect that even in the case of a hypersonic waverider spaceplane powered by an NTR, you'd still use LH2, but again the stock aero model does not like voluminous lifting bodies like Skylon/Venture Star, so a denser propellant that can live in wing parts may be preferable in game. Note, jet engines can also run off ammonia , but since a litre of ammonia only releases half as much heat as the same quantity of kerosene when burned in air, ISP would have to be reduced further. Then again, a litre of ammonia requires less oxygen to burn than a litre of jet fuel, so the engine's high altitude performance might get some minor gains to offset this. You don't want to be putting cryogens in wing tanks, because a) high surface area means ludicrous boil off rates and b) ice formation. With all this talk about nerfs to jet engines and more restrictions on lv-ns, it might be worth referring people to Project Timberwind, a 1980s tech pebble bed NTR. The TWR was still low compared even with a hydolox engine, but streets ahead of the NTR in game. Game balance is such a complex subject, the ripple effect of every change spreads far and wide. The fact that stage recovery is almost impossible without mods forces people to ssto or disposable, which makes nerfing engines or adding realism problematic.
  4. Screechcraft Kalbatross https://www.dropbox.com/s/nq8684a3khc0bgb/Screechcraft Kalbatross.craft?dl=0 The first new airframe from Screechcraft in quite some time, the development of this Very Large Transport was largely funded with government money in order to ensure retention of "skilled personnel vital for the national interest" , at a time of contraction within the aerospace industry. Jeb poses with the remains of the prototype after completing the high speed RTO test. Category - SST, Jumbo Jet Range - Kerbonavigation possible (stock scale) Pax - 336 Cruise Speed - Up to 1400 m/s at 23km altitude Cost - 776 million (!) .. it's a government program The aircraft achieved its design goal of mach 4.5 cruise at altitude The aircraft is propelled by afterburning turbofans and ramjets, but is capable of subsonic flight on the turbofans alone, with the afterburners off, in noise abatement areas. Action Group 4 - Toggle Afterburner Action Group 8 - Toggle Ramjets The pilot's seat features a bubble canopy, and there is a basic autopilot (SAS Prograde hold mode) included. Three trim flap positions are included : Action Group 1 - Nose Up Trim Action Group 2 - Neutral Trim Action Group 3 - Nose Down Trim Nose up trim is recommended setting for takeoff and landing, neutral trim is recommended for cruise. However, the settings can be changed freely while autopilot is active in order to suppress porpoising while establishing cruise flight. Cruising speed is a significant fraction of orbital velocity, resulting in half normal gravity for most of the flight. This enables the cabin crew to handle food and beverage carts twice as large as normal, which is likely to prove popular with passengers. The prototype is also fitted with experimental booster engines, whose precise details are classified. They can provide additional acceleration at the expense of a large increase in fuel consumption. For environmental reasons, use below 10km (over water) or 20km (over land) is forbidden. Note, overuse of these engines may make landing impossible. Action Group 6- Toggle Boosters Note, whilst the aircraft experiences low G in cruise, parabolic trajectories with zero or negative G must be avoided at all costs, as the restroom plumbing is not equipped with check valves in the wastewater system. The consequences are too dire to imagine.
  5. Yeah fair enough, i just hate seeing planes with diddy little vertical stabilizers and then have people struggle with preventing roll excursions / sideslip on the flight to orbit. Not only does yaw instability make an airplane horrible to fly, the drag from the fuselage while it is sideslipping more than offsets what you saved by fitting a smaller surface. If you're min maxing , i like big S strakes turned vertical like this - gives you a bit of fuel too
  6. I tend to go for efficiency over sheer size, so there others who can advise better on very large aircraft. This is my heaviest , 250t on takeoff I use autostrut, but also you need to try and limit the amount of force passing through each joint. Therefore, don't attach all the wing parts to a root wing part and have that one wing section bond to the fuselage and carry the lift forces generated by all the other wing parts. In this design , the outboard sections connect to different inboard wing sections, each with their own connection to the fuselage, so each wing/fuselage join is only carrying the lift from 2/3 wing parts , tops. Also, bending relief, something used on real airplanes. The heavy engines (especially NERVS) are mounted direct to the wing. If they were mounted to the fuselage, the lift to support their weight would have to go though the wing/fuselage joint. It may also help that the wings are all wet, and this craft has all its fuel in the wings, which again reduces the forces transmitted vs the fuel being in the fuselage. The fact that it's a liquid fuel only design probably helps with all this. download here if you want to dissect https://kerbalx.com/AeroGav/Monstrosity-225L
  7. The problem is he wants the CoM in the middle of the cargo bay - which is why the heavy rapiers are clustered around the CoM. Up front, there is only the cockpit to serve as counterweight for all the engine mass - about enough for the relatively light panthers he's got at the back. Putting rapiers on the back of the mk2 tanks would cause dry CoM issues as that's further back, also the drag of the mk1 nacelles they are currently on is negligible compared to the mk3 and mk2 parts on his design. The lift from mk2 parts is negligible. About 100th of what a big s wing makes. Meanwhile they have over 3x the drag of a mk1 of same capacity. If he's min maxing he should swap for 2.5m tanks on the sides. But he's already said he cares more about looks. Also, at this point he is not drag limited. The incorrect flight profile means he needs twice as much rocket delta V 2200 orbital velocity minus 900 m/s airbreathing = 1200 m/s required from close cycle mode if he got to 1500 on air breathing engines, = he'd only need 700 m/s I have concerns that Boeing 707 tail fins will melt when he starts flying corect profile. But it would be a straight swap to shuttle one if this happens, no big deal. No, no , no! You are conflating vertical stabilizer surface area, which always improves lateral stability , with excessive rudder use/overcontrolling. Most players never touch the rudder controls and indeed there is little need to if you've got enough vertical stab area to give the necessary passive stability. If you think SAS might overcontrol the rudder, you can always right click and limit authority on the rudder. As for drag, turn on the F12 display and see how little it generates compared with the cargo bay and various rocket fuel tanks being lugged around. Also this airplane has over 15 tons of engines and a 4 ton cockpit... not sure the weight is notable either.
  8. The pictures aren't telling us very much that we need to diagnose, but i'll do my best 1. appears you are running out of oxidizer just short of orbital velocity. That's with no cargo aboard, correct? 2. You are pitched up more than 5 degrees above prograde. Optimum lift drag ratio (as produced by wings) above mach 1 is at 5 degrees, so i'd normally say hold the nose at exactly 5 degrees once you go to close cycle mode and keep it there no matter what. You are pitching up more than that, creating extra drag, but aren't climbing very steep and are only reaching 40km. This suggests your design is a bit low on lift. I reckon on about 6 pairs of big S wings for a 150 ton takeoff weight... what's your ssto grossing ? That said, the small amount of extra drag should not affect a design with 6 rapiers. Each of those suckers is doing 180kn in close cycle mode - three times as much as the nerv engines i use on my sstos. An extra 40 or 100kn of drag isn't going to matter much. Sounds like you've either just got to add a little bit more fuel, or have an incorrect ascent profile. What speed are you reaching before switching to close cycle burn ? You should be able to get at least 1500 on something with 6 rapiers like that. Are you levelling off at 17-21km for a "speedrun" before going close cycle mode?
  9. The V1 prototype (no oxidizer) took 13 minutes to get from launch to starting the rocket engines. The V2 with 50% greater takeoff weight, needed 18 minutes to reach that same point. Main engine cutoff (MECO) is about 20 minutes after launch on V1, about 25 minutes on V2. You've then got another 5 minutes coasting to get out of the atmosphere, after which you can do non-physics time warp. The orbit ends up getting circularised on the dark side of the planet, i had to warp to the PE (another half orbit) to get enough light to show payload deployment. If this is a criticism, I have to say , "what do you expect?". Payload fraction , Delta V, and TWR are the three basic parameters of a vehicle - one can only be improved by reducing the others. I am raising delta V and payload fraction, so TWR decreases. Using lots of wing parts to improve lift/drag ratio is a way of making the lower TWR not cause excess gravity losses. Swapping some RAPIERs for Panthers is about sacrificing some performance above mach 2.5 to get better performance below mach 1 - enabling you to break the sound barrier with less tons invested in jet engines. If you don't want to lower TWR from your original design, then this whole exercise has been a waste of time. Getting higher lift drag ratio implies raising the part count doesn't it ? Your original design is efficient in terms of parts per tons of payload, but negatively affects l/d. I still must disagree here. All rapier means you have the problem, which a lot of newbies fail at, getting past mach 1. A mix of rapier and panther gives a flatter overall power curve and means you don't have to worry about the engine curve so much. Adding nervs does make things complicated, because that triples the number of engines you have to find a place for. I suppose some newbies will break mach 1 when expect to climb at 20 degrees and still pass 20km at mach 4. With a rapier / panther design you need to actually level off at 18km to hit mach 4, and some people aren't capable of doing that, or will lose control or break their wings off trying. to quote a clever person I As you probably know, the exhaust of a nerv does not contain any radioactive materials, but the reactor makes X rays, gamma rays and neutrons when operating. For weight reasons, only the side of the reactor facing the crew is shielded (via a shadow shield) so you don't want to overfly a city at low altitude with nervs running. A reactor that has never operated does not emit radiation, but once you start the nervs , nuclear reactions don't neatly stop on engine shutdown. So, for RP reasons i think you have two assume one of two political realities for your game 1. "No nukes (present day political attitudes)". Never fired RTGs and LVNs can be launched from kerbin, but may not be operated within its SOI. Once an RTG or LVN has been activated for the first time, it may never enter Kerbin's SOI again, so there is no possibility of it re-entering the atmosphere. 2. "1950s style nuke power is great" . These are the rules i am operating under. My use of LVN's is over the ocean, or so high in the atmosphere that people on the surface would be protected. After landing, the SSTO would have residual radiation emission so you'd leave the vessel and walk back to the hangar via an approved route that keeps the shadow shield between you and the hot stuff, rather than hang around taking selfies under the nozzles. A practical chem only SSTO is hard however. Furthermore, if you're not going to use LVN's, there is no use for high L/D ratio and no use for my skillset. I might as well quit the game. For chem only, I think TSTO is more practical. With high thrust chem engines however, there is no need for the orbiter stage to have wings at all. Why not develop a pegasus style system, where the giant launcher craft is RAPIER powered (air breathing mode only), that drops a Rhino rocket stage to do the rest ? Yeah it was my attempt at a joke. 18 tons of fuel was in orbit, just no longer contained within a tank. Grab a net or some plastic bags and go EVA, maybe you can catch some of it. Ah good tip. Actually, i do find marginal takeoffs exciting and imagine having the space centre surrounded by high terrain and trying not to hit any of it on the way out.. something to play with
  10. OK, version 2.0 of this craft has now been test flown. https://www.dropbox.com/s/tb0x9qdylyp59il/Bright Hawk2.craft?dl=0 I got rid of that fustercuck of strakes at the front end and put a short mk3 tank at the front of the cargo bay. For front end lift (and control) , a pair of shuttle tail fins acting as canards. Much more efficient in terms of part count. I've saved three parts by simplifying the landing gear too. The dry centre of mass is now too far forward, what a nice problem to have. The panthers now get moved alongside the rapiers (which looks better and reduces tail strike risk). We need more LF aft of CoM - so, i add a bunch of mk1 tanks in front of the panthers all the way to the CoM, with a shock cone fronting the stacks. Finally, the oxidizer tanks are filled. I was leery of doing this, but i decided to imitate SpaceX and iterate, iterate. I can see the logic in swapping wings for mk3 in the name of part count efficiency, but was it right to replace with mk1s ? So, v1 of this craft is 82 parts, 102t wet . V2 is 145 tons, but only 77 parts. Oxidizer is much of this extra mass. If you're trying to win payload mass fraction, i can see why going liquid fuel only can help you win, because your takeoff weight will be significantly less. To make the 15% payload fraction , this v2 craft is going to have to lift much more because it is heavier itself. Not feeling terribly optimistic, I loaded a rockomax 32 tank and crossed my fingers... It now needs about three quarters of the runway to get airborne, and climbs out at 5-10 degrees. But, i think it flies better with extra wing loading. I'm not fighting the tendency to climb too high for the airbreathers to work. And that huge ballooning effect you got when going prograde at the end of the speedrun, is gone. The climb is steadier. Right about the point where the v1 airplane starts to fall down again, v2 has just burned off all its LFO courtesy of the rapiers, and thus lightened, it just stagnates for a bit then starts to go up some more. As you can see this is very much a prototype. Payload deployment doesn't exactly go to plan, but the contract only said deliver 18 tons of rocket fuel to orbit, at least the airplane survived.
  11. Well, at least you won't be needing to compose any music for them
  12. Here's a video of the climb under nerv power. At no point does drag exceed 200kn (most of the time it is much less) and we have 480kn from 8 engines, so it's fairly comfortable. Max thermal percentage is 78% , reached on the faring that covers the probe core, batteries and stuff at the front.
  13. Takeoff is not as exciting as yours. Hmm, i need to fix the lack of pitch authority. Not being able to command more than 2 deg above prograde is ok on ascent to orbit, but might make for some rather firm landings..
  14. RE: My airplane has a lot of LV-N's + wings Indeed - i don't know if changing the engine ratio on your SSTO will work though, since it was designed that way from the outset. It might be a case of you have to go all in on something like that , or not at all. Alternatively, it's about aerodynamics. For an spaceplane to be able to gain energy during the start of the non airbreathing part of the ascent , TWR x (L/D Ratio) must be greater than 1. If your engines are RAPIERs that weigh 2T and kick out 160kn, it's easier to just add more thrust and concentrate on reducing mass of things that are not engines, fuel or payload. If your engines are NERVs that weigh 3T and only have 60kn, it's easier to add more wings to improve L/D, and reducing mass of other stuff won't have much impact. When you're going NERV heavy, lift/drag ratio and drag / fuel capacity ratio trumps all. That's the main reason i had so many wings, the Big S wing part has about the same drag as a mk1 liquid fuel fuselage, I was worried about adding mk3 tanks as that adds a lot of extra drag without any lift. The design could use more fuel. I normally reckon on one NERV per 15 - 20 tons on stock scale for a comfortable and easy flight. On 3x, i still think 1 per 15 T would be ok because i've designed low tech Panther SSTOs on that ratio whose air breathers only get a small fraction of orbital velocity. However, this design has 8 LV-N at 100T. As soon as you stop forcing the nose down during the air breathing speed run and go to prograde hold, starting the nukes, it balloons up to 40km (still accelerating) then dips back to 30km before going up again for good, by that point, it has a TWR of 0.78 to 1, with thrust nearly 10x my drag value. I should probably try putting on some mk3 fuselage, right now it's hard to find room for more wings without giving an unrealistic and ugly appearance. Also, I found it really problematic finding room for engines on this design. Panthers, NERVS, Rapiers... i'm effectively using 3 engines to do the job of 1, but saving on fuel burn as a result. However, this makes it hard to find a place where your exhaust wont be blocked by a wing , and i have lot of wings. Just to re-iterate, this airplane has a lift to drag ratio in the hypersonic climb of > 3.5 to 1 when you go on prograde hold mode. That is what i think enables it to do well with nerv-heavy design.
  15. I'm trying to limit myself to one cup of coffee a day ATM, so basically there's a one hour window after drinking coffee where stuff makes sense and i can build an object in KSP, after that i turn back into a moron, that's why i like mods like this because you can use that hour more productively. Without RCS build aid i've only managed to solve fuel CG issues by keeping vessels really simple, with a minimum number of tanks - this one is basically 4 rocket fuel tanks arranged in a "+" sign shape around a central liquid fuel tank. As for the mod, no it doesn't add any new parts, it just gives extra info in the assembly building. So you've now got that red ball showing the dry CoM of this lander, as well as torque. Means you'll be able to iterate through designs much faster , without having to stop to empty and fill tanks - the floor of SPH looks like a real mess when i've been working in there from all the discarded stuff. Unfortunately it's not just a single download these days, there are two dependencies - just like his other mod, CorrectCoL. Neither CorrectCoL nor RCS Build Aid appear to be on CKAN, but the dependencies are at least (i had issues due to googling and installing out of date versions)