AeroGav

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About AeroGav

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  1. I generally go with one jet engine per 30 tons of gross takeoff weight, a mix of Whiplash and Rapier . The Whiplash fatten out the bottom end of the power curve making it easier to get supersonic. The max top end speed you can get is soft capped by the engine velocity curve , meaning that adding more engines to get faster than 1400 m/s air breathing runs into diminishing returns hard If your craft does not have any part attachment issues causing excess drag you should be able to get through the sound barrier easily. Generally I use up to 20% of my fuel getting to air breathing top speed. From 1400m/s, you need another 900m/s velocity to make low orbit. My designs have a low thrust-weight ratio so gravity/drag losses mean my delta V (as reported by Kerbal Engineer System) has fallen by up to 1200 or so by the time we reach orbit, but you shouldn't see losses worse than that. Nukes, I generally bring one per 15 tons if I'm making an oxidizer free ship. A minimal amount of oxidizer allows you to halve that number of nuke engines. Wings - I prefer adding more wing to my designs, but a lot of it is down to individual preference. After takeoff, I prefer to climb to a higher altitude where drag is less, before levelling off and attempting to penetrate the sound barrier. However, as the air gets thinner you need more wing to support the craft at the comparatively low speed, without having to yank the nose more than 5 degrees above the prograde vector, which generates drag. At a minimum, you want enough wing area that you can fly around at 7km altitude , subsonic (under 250m/s) without having to yank the nose more than 5 degrees above prograde. I did try the other method of getting supersonic, by just doing it at sea level , flying level after takeoff till over 440 m/s with tiny sub wings. But I found this used a lot of fuel, drag is huge at zero altitude, it's partly disguised by the massive amount of power your engines have down there but the fuel flow rates are scary. Liquid fuel only SSTO need even more wing area in my opinion, motor-glider levels of lift:drag ratio help a lot when getting a craft to orbit with relatively low thrust (this is a low tech panther/nerv ssto that can go to the surface fo the mun and back)
  2. I'd say the OP simply has centre of mass a bit too close to the centre of lift, he needs to allow a greater margin of safety given that the centre of lift indicator of the stock game is not 100% accurate (doesn't calculate aero forces from parts that don't have a lift rating in their description). Deleting the canard removes some lift from the front of the ship but you'd get the same overall effect just moving the wings back a little. The jet fuel tanks are slightly in front of CoM so it's possible the plane's becoming unstable from the slight shift that occurs towards the end of the jet powered phase as most of the jet fuel is used. If you're having issues making the craft sufficiently stable in some phases of flight, while not sufficiently controllable in others, you're better off putting the cargo bay right over the CoM, instead of ahead of it as he has here. Might run into issues with not taking off with a full cargo bay and flipping out on an empty one. Also, the main fuselage is a mk2 but it's transitioning straight into a mk1 sized reaction wheel at the back, without an adapter. Need a mk2 to mk1 adapter or you end up with a ton of drag.
  3. OK, I had a go at recreating the craft from the picture. I didn't realise you had a cargo bay, instead of a fuel tank immediately behind the cockpit. This means you have a similar amount of fuel ahead and behind CoM, it doesn't move all that much and actually goes forward as it burns off (red dot) But, my CoM ends up much further aft than yours, which is halfway between the two short rocket fuel tanks. You must have a heavy payload in the cargo bay, and once you unload it, the ship becomes tail heavy. My "copy" had no cargo.
  4. Problem 1 - CG moves aft as fuel burns away Let's briefly add up the major dry mass items of your plane - Ahead of CG (by approx 2 long mk2 fuselage sections distance) = cockpit , 2 tons Behind CG (by approx 2 long mk2 fuselage sections' worth of distance) = NERV, 3 tons Behind CG (by approx 0.5 long mk2 fuselage sections' worth of distance) = 2 x 1.8 ton whiplashes Behind CG (by approx 075 long mk2 fuselage section's worth of distance) = 2 x 2ton rapiers You can see that you have far more dry mass behind CG than ahead of it. On takeoff, this is countered by having most of your fuel stowage in front of CG. But once that burns off, your CG will move aft. The easiest way to avoid falling into this trap again is to get RCS build aid, it shows a red dot which is where your CoM will move to when the tanks are empty. Problem 2 - Blue indicator not allowing for aero forces on non-wing parts Even with your CG/CoM at its furthest forward position, before the fuel burns off, you have 66% more fuselage length in front of CG than behind it. The stock blue indicator only takes account of wing and control surface parts. I strongly recommend you get CorrectCoL mod installed so it takes account of aero forces acting on every part, including the fuselage. Makes airplane design much less prone to trial and error. I suspect your CG is way further forward than you think. RCS build aid and CorrectCoL are very small mods with a tiny memory footprint that won't affect loading speed, because they don't add any new parts and therefore have no extra textures to load on startup. .
  5. Well, the RTGs are coming back to Kerbin so money is not an issue. With the fuel cell, you're going to want to more efficient big converter or you won't come out ahead, correct?
  6. Yeah, if the nose angle is locked by SAS, you will see that as speed decreases, so does lift, and rate of descent increases. With a constant nose angle this leads to rising AoA. If you throttle up so as to keep the velocity vector constant with respect to the nose angle, rate of descent will be under controlled and aerodynamic forces should stay within limits.
  7. Sorry for initially misunderstanding how you wanted the thing landing, when I heard "propulsive" I immediately thought SpaceX. It basically flies like a normal rocket on the way up and like a normal airplane on re-entry, but at some point it makes like a VTOL airplane and comes to a stop in mid air, then settles down to the ground on propulsive thrust, is that correct? In which case it is just a normal airplane except for the fact that there's almost no wing and you're mostly relying on body lift - at landing weights, it should still be possible to pull out of the dive and flare to almost level flight at 150 m/s or so. Then fire up the vertical engines and gradually throttle them up as lift dies down. As a stable airplane it wants to go prograde so if a really high vertical descent rate appears with no horizontal movement, ithe aerodynamics will try to push the nose down and at some point that'll overwhelm your RCS/reaction wheels/vector thrust. However, you aren't intentionally going to get into that situation anyway on landing. I recommend you get RCS build aid and correct CoL. That second design has two four ton vectors at the back and one four ton cockpit up front, so i suspect when empty the CG is aft of halfway back. The cargo bay is forward of the halfway point. I suspect that when you open it, you have more stuff catching the wind ahead of CG than behind it. The design might be unstable in yaw, seeing it spin with the nose pointing due west? Again, the blue indicator in the VAB only shows the effects of the strakes and control surfaces you are putting on, not the body lift or the drag from open cargo bays - that's where CorectCoL really helps.
  8. Here's a WIP, unfortunately I'm getting less time to play these days so haven't finished it. Someone on the "Gameplay Questions" forum was after a Laythe seaplane in career mode, he had IRSU techs, NERVs and rocketry was well advanced, but he hadn't unlocked much in the way of jet engines. It got me thinking, what's the lowest tech self refuelling IRSU spaceplane I can come up with. As a kicker, it has to be able to take off and land on water, though not necessarily fully loaded. What I came up with was this thing, I'm kind of fond of the way it looks Climbing with 2 panthers - Nukes help us through mach 1. Takes about 45 seconds to go from 250 m/s to 400 m/s Nukes off again once past the sound barrier - This is about as fast as the panthers will take us, feeling daring, i use the space bar to start the nukes and surprisingly, the shrouds don't cause my craft to disassemble as they pop off - At this point we bring in the incredible power of our Terrier boosters Booster separation. The non-reusable component is actually pretty cheap, mk1 lf tanks aren't worth much empty (unlike rocket fuel tanks) and the Terriers are low rent too. Also, structural pylons are cheaper than rocket decouplers, for some reason. The underside is covered in wing panels to make it hydrofoil across the water The cargo bay has a science junior, a load of solar panels and enough batteries to mine all night long https://www.dropbox.com/s/93e76xjbxmaqci0/laythe mk2c.craft?dl=0 The idea was, this craft would land on Minmus, refuel itself and then go to Laythe. But, it just falls short of making a landing on minmus. After correcting inclination (70m/s) I had about 240 dv left after getting an encounter with Minmus, which isn't quite enough. So I need to add more fuel. Yeah I know, people always say that and it seldom ends well, though i really feel this craft could lift more fuel easily enough - it takes about 45 seconds to cross the transonic region, and makes it to space easily. The problem is it would mean a major redesign of the craft to shoehorn more tanks in. I already have 6 mk 0 tanks in the cargo bay, can't get more in without abusing clipping. They have me another 350 dv in kerbin orbit. I suppose the obvious answer is to lengthen the booster pods. Make them 3 mk1 tanks each instead of 2? I'll need to add more LFO, because I'd timed it nicely so the oxidizer for the terriers (stored in the bicouplers and mk2 adapters) runs out just as the drop tanks run dry on liquid fuel.
  9. He'll be landing back on Kerbin almost empty, right? So it should be possible to do so with far less in the way of engine.
  10. So, the OP wants an SSTO rocket that's stable going forwards on the way up, stable going forwards during re-entry, but then at the last minute can flip around and be passively stable going backwards for propulsive landing. Passive stability in first one direction, then another, without staging any parts away and with a similar fuel/payload state - that's hard ! Perhaps near-neutral stability with strong control authority to pitch the craft around on landing is more realistic. Only way I can think of doing this would be to put some control surfaces with a 30 deg max deflection angle (tail fin connector, big S elevon) right on the nose, set authority to 150%, but disable pitch/roll/yaw. "deploy " them on an action group, to add a large amount of drag to the front end, hopefully make it flip on command. If a service bay is at the front and can be opened at the same time, so much the better. Also, the OP is trying to do aerodynamics on a rocket, with very little wing and mostly body parts. The problem is the stock centre of lift indicator doesn't take account of aerodynamic forces acting on parts that aren't wings or control surfaces, which, being a rocket , are most of his ship. Therefore it is completely untrustworthy. I strongly recommend the mod CorrectCoL for this reason. Also RCS Build Aid so he can see where his dry CoM is, though as a rocketeer i suspect there's a high chance he's already using it.
  11. You can get a big drill inside the 2.5m service bay if you're careful with the offset tool. However, i'm not sure a Laythe miner will benefit from big drill and converter. From what i remember, these things give you much more ore per unit of fuel, and the big drill has a much better mining rate. The problem is you're limited by electric charge out on Laythe due to its distance from the sun. So, out there you might be better off with just one small drill and one small converter, and a small thermal control system to stop it overheating. Once into a high rate of time warp electric consumption decreases, and 4 x RTGs can keep up, but you'll need a few batteries to handle the transition.
  12. I like the sound of this, but to get any degree of realism we're at risk of drowning in battery parts unless we make them configurable somehow? Eg. just have batteries for each size class then provide dialogs to set the type in VAB. After all, if you add NiCad and NiMH as well as the various non-rechargable types used by nasa and the military (lithium thionyl chloride for very high energy density and long shelf life, thermal batteries for high power/short duration) we'll end up with a lot of batteries ! BTW I think the way it currently handles charge/discharge rate ( Lead = slow, Lithium = fast ) isn't quite realistic since that has more to do with how the battery is constructed than cell chemistry. Car batteries are capable of very high discharge rates when cranking an engine, whilst a laptop or phone battery is designed for steady power release. High rate batteries use a large number of much thinner anode / cathode plates for a high surface area for reactions, with a thinner layer of active materials on the anode/cathode. The drawback is that a higher percentage of the battery's mass is made up of the base metal of these anodes and cathodes as well as the associated separator sheets, leaving less for the active materials that store energy. Temperature/degradation Lead acid loose capacity when stored at low states of charge. The longer they are left there, and the deeper the discharge, the more permanent capacity loss results. Lithium Ion loose capacity when stored at high states of charge (over 66%). The higher the temperature and the closer to full, the worse this gets. Also, they are damaged by charging them below freezing . If you avoid these pitfalls however, current lithium ion cells accept an almost unlimited number of charge/discharge cycles. Near future batteries Lithium Sulfur - more power to weight than lithium ion, but have not yet made a commercial impact because degradation with cycling occurs much faster than with current lithium ion. A space agency might not care so much about that however.. Silicon Anode Lithium ion - Using silicon instead of carbon anodes gives an immediate boost of 33% to any lithium chemistry, but they also degrade rapidly with cycling.
  13. Getting to orbit involves accelerating to 2200 m/s. Engines, thrusting horizontally, provide the power to do this. As you get closer to orbital velocity, orbital free fall effect supports more and more of your vessel's weight against gravity, but until you get there the shortfall must be made up for with lift. Drag is the enemy, it's the main thing you want to minimise. A low drag design can get through the sound barrier with one jet engine per 30 tons of takeoff weight, and 60kn of closed cycle thrust per 15 tons (ie one nuke or terrier per 15 tons). For oxidizer, you only really need 200 units or so per 40/50 tons if you've got one nuke per 40 tons. If you've got one nuke per 15 tons or so, you can actually forget oxidizer altogether and go liquid fuel only. Jet engines are very heavy and a draggy airplane will need a lot of them to get hypersonic. this adds loads of dry mass and cuts delta V. I suspect your main problem is drag because I can see potential problems from that one picture. For us to fully diagnose it, show more angles or better yet share the craft file The main fuselage is a 2.5m stack, but it appears to end abruptly in a flat plate. This creates huge drag. There should be a 2.5m tail cone on the back or series of adapters tapering the back end down gradually to a smaller cone. Looks like you got some side stacks of FT-800 tanks (the black and white stripey things). Do they all end with cones or are there more flat faces poking the air stream? Lots of stuff hanging off the outside. I see drills (!) and radiators for a start. I bet you got four way thruster blocks too? These things should be inside a service bay or cargo compartment, and only be exposed after landing or while in space. Pointy headed mk1 cockpit - because it is at the front it will tend to suffer overheating, you are better off with inline cockpit since the most efficient flight profiles involve flying at 1400m/s + on jet power. Far too much oxidizer As regards the mining setup, you've gone for the big drill and converter. They are more than 10x as efficient but also much heavier, which pushes the size of the craft up by a lot. One thing to remember is that the rate at which it mines doesn't really affect you very much, since you can go into a high rate of time warp once you've started and be done in a minute or two either way. What does matter is the craft having enough power to keep mining overnight. If it runs out of juice the drills shut down and have to be manually restarted each morning, which gets seriously annoying. Either bring a large amount of batteries or use RTG as your power source. Also, those large radiators are useless. They only pull heat from the part they are attached to , and won't stop the drills overheating. Use the deployable thermal control system radiators instead. Much easier to stow in a cargo bay too. Building for low drag Even if you build a craft that looks like a skinny glider, you'll find that in KSP > 80% of the drag is coming from the fuselage, not the wings. Every stack must begin and end with something pointy. Pointy = nose cone, air intake, or jet engine. When joining parts via attachment nodes , both nodes must be of same diameter. Eg. Joining a 2.5m tank to a 1.25m tank = bad, high drag. Joining a 2.5m tank to the 2.5m node at the fat end of a 2.5m to 1.25m adapter = good ! Keep stuff as close to prograde as possible. You should have enough wing that your spaceplane can get lift by flying with a nose angle only 5 degrees above prograde, at an altitude of 7km and a speed of 240m/s. If it can't do that, you can either add more wing, or try angling the wings up a few degrees where they attach to the fuselage The latter technique can be tricky to get right however. Also, you need to be aware that some parts are better than others for drag. Mk2 fuselage parts are terrible, despite their sleek appearance, they have 2 or 3 times more drag than mk1. Mk3 are similar to mk1 in terms of drag to fuel volume ratio. 2.5m are the best, having hardly any more drag than mk1 but much larger capacity. However, they are fragile and there are no 2.5m liquid fuel tanks. Perhaps make a craft with a 2.5m main fuselage? Hitchhiker module, mk2 lander can (for control pod), 2.5m converter, and some service bays? Keep your liquid fuel in the engine pods, big S wings and strakes? Final drag saving tip - this is a minor one compared to the others, but remember what i said about every stack ending in something pointy? The problem is that rocket engines, and RAPIERS, with rear attach nodes create much more drag than jet engines like panthers and whiplashes that do not. The issue is that the game sees the unused rear attach node of the engine, and assumes your stack is ending with a flat face. To get around this, you can put a cone on the back of the engine. However, the collider that checks for blocked nozzles will see this and stop the engine working. Solution? Use the offset tool to move the cone so it's hidden inside the engine, that way the nozzle is not blocked. https://kerbalx.com/AeroGav/SSTL-gavd The above ship is 60 tons, has 2 rapiers and 2 nukes. Note that nearly all fuel is in the wings and mk1 tanks. The main fuselage is all crew and cargo bay (the rear cargo bay is upside down so the drills don't have to poke through the floor). The only fuel in the mk2 sections are the LF/O in the bicoupler at the rear of the fuselage and the mk2 to mk1 adapter in the front. This is also the only oxidizer tankage on the whole ship. Reaches kerbin orbit with 4000dV , so a straight shot to Laythe is possible.
  14. Normally by the time you've got to Jool my entire tech tree is unlocked, yet the OP seems to have very few airplane techs. Normally I do laythe with a spaceplane with mining capability, which actually gives it the ability to planet hop to most of the Kerbol system. The question is, what's the lowest tech level you can do that at, and also the OP wants to explore the oceans, which I haven't normally bothered with. My starting point was a mk2 fuselage with seating for 6, and cargo bay large enough for a resource converter and science junior. With ISRU ships, the key factor is not mining rate, but whether the ship can be trusted to mine by itself at high time warp or whether the drills shut down every night for lack of power and need to be restarted each morning (over the months it takes to refuel, that is seriously annoying). As such it packs a serious amount of batteries to keep the operation going overnight. RTGs are not an option at the OPs tech level, and fuel cells probably require the more efficient larger converter to be viable. Then I put wings and panthers on , and verified it can take off from the water. It can, thanks to the wing panels acting as hydrofoils on the bottom of the fuselage. Of course, the water takeoff test was done before i added NERV engines and extra fuel tanks, but it won't be taking off fully loaded for a flight back to Kerbin, for the simple reason you can't mine the sea. With a modest fuel load and no oxidizer, takeoff from the water should be no problem. The airplane would make a final call at one of Laythe's islands before brimming the tanks for flight to orbit. You can make interesting shapes with these modular wings but i miss not being able to keep fuel there. It was indeed tough finding places for more fuel that did not involve lengthening the mk2 fuselage (drag), and major redesign. more fuel tanks at front of the nerv nacelles (makes us nose heavy when full with a significant rearward shift as fuel burns off) moving the nervs further back to make room for more fuel tanks on the centreline (makes dry CoM too far aft) In the end, i hit on the idea of putting liquid fuel tanks on the Terrier nacelles , which are droppable boosters to enable us to get off Kerbin (Laythe is much more forgiving spaceplane territory and it can manage a flight to orbit there liquid fuel only). The Terriers use the oxidizer stored in the mk2 adapters of the main fuselage. By lucky coincidence, the 1600 units of LF in the Terrier nacelles runs out at about the same time we run dry on oxidizer The plane makes orbit rather easily, on its first full test flight. But again, we don't quite have enough fuel. It could easily lift more , because the flight to orbit was easy and it accelerated convincingly the whole time, but again the question of how to modify such a tightly integrated design. I suppose the easiest answer is put some sponsons on the wings around the CG. but at this point i've gotten fond of how it looks and don't want to ugly it too much. Maiden flight, just about enough fuel for an encounter with Mun. Another 300-400 m/s and we could reach Minmus and refuel. I have managed to cram 6 mk0 liquid fuel tanks in the cargo bay, but have yet to fly this config. Hope that's enough. Here's the WIP craft - https://www.dropbox.com/s/93e76xjbxmaqci0/laythe mk2c.craft?dl=0 ag 1 - toggle solar panels and radiator ag 3 - afterburner ag 4 - toggle trim flap (nose up by a couple degrees) ag 5- toggle nukes
  15. OK Aerograde, I made two "crew shuttles" with Hitchhiker passenger module and a Poodle engine. I was going to control via lander can but a misunderstanding with Kerbal engineer had me strip it back to a Stayputnik (grossly overestimated delta V requirement of upper stage). The horizontal takeoff version has two Wheesleys. They only get us to about 3km at 240 m/s, but after starting the Poodle we go supersonic. At mach 2 and 15km or so i finally drop them. Went to space with plenty delta V, but it's a barebones, no solar panels , docking or attitude control. https://www.dropbox.com/s/grlfa52tecbuahk/unTeiteled.craft?dl=0 This is the vertical version, with 4 Thumpers to get it off the deck. https://www.dropbox.com/s/13wv55dkhbmsbku/Standing Teitel.craft?dl=0