camacju
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I actually forgot that I posted this thread! I recently did exactly that, and took an Aeris to Laythe and back. But I haven't found the motivation to edit the video yet.
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You may be using too much wing area then. 5 degrees is close to the optimal value for SSTO craft (I think 4 degrees is slightly better but it's pretty close). Maybe you're used to low wing incidence requiring more actual wing area so when you rotate your wings upward you get a lot of drag. I like to aim for at least 6 tons per wing area, which leads to quite small wings for the plane's size but the increased lift from the wings makes up for that.
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One Juno Circumnavigation!
camacju replied to Watermel00n's topic in KSP1 Challenges & Mission ideas
I probably put way too much thought into this flight. In KSP, engines have a specific impulse - they consume fuel for a given thrust. Since work=force*distance, power=thrust*speed, so for a given thrust we want to be flying as quickly as possible. This means minimizing drag. And since the Juno has low thrust, this also means not including as much fuel as I can physically take off with. If I do that, I get stuck around the sound barrier and have to eat a very big lift to drag penalty. Interestingly enough, the Juno tops out at around Mach 2.05, which also is near a peak in lift to drag ratio. So this is my desired flight regime. Craft in SPH. One Juno, one control surface, and as much fuel as I can pack while still being able to go through the sound barrier. At this point, I point near the horizon and don't try to manage altitude or thrust at all. Full throttle is better because I can fly faster and at a point farther to the right on the Juno's thrust curve, which increases specific power output of the engine. I just keep a -1 degree angle of attack for maximum L/D and let the aerodynamics balance themselves out - it'll naturally balance at the correct point where the Juno's thrust is just enough to overcome drag, which is also the maximum speed it can attain for a given mass. Final result - 7 laps around Kerbin, single kerbal craft -
One Juno Circumnavigation!
camacju replied to Watermel00n's topic in KSP1 Challenges & Mission ideas
I got eight laps around Kerbin but I misread the rule that required only one Juno engine. A few hours wasted - back to the drawing board... -
I was more talking about mass per effective wing area - a heat shield's wing area isn't very large. Also if I remember correctly a 0.625m heat shield doesn't have an internal attachment node, which means it can't really be used as a magic wing. 0.625m heat shield with all ablator drained is 125 funds and 25 kg. The small hardpoint is 60 funds and the structural pylon is 125 funds, both of which have the advantage of being radial attachable. The 0.625m decoupler and separator are 10 kg, the small docking port is 20 kg, and the TT-38K radial decoupler is 25 kg. Lift to drag ratio is also very important for range. If you have a higher L/D, you can achieve the same lift for less drag. This means if you are flying at the same speed and altitude, you need less thrust to maintain level flight. This would mean less prop torque = less electricity usage. KSP wings are symmetric - zero AoA means zero lift. If you go into AeroGUI it should tell you your actual AoA. If 2 degrees wing incidence is making you struggle and fly slower, that means your wing area is too high - it'll produce more lift but also more drag - so you should reduce your wing. It'll help reduce mass also. Not at all - the idea is that they provide a superior lift to drag ratio in all flight regimes. It's just that they take less of a penalty from Mach effects, so their relative advantage over standard wings is magnified when at supersonic speeds.
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There's still plenty of funky aerodynamics stuff to work with. For example there's a few different types of parts that can be used as "Magic wings," basically parts that can produce a higher lift to drag ratio than any of KSP's normal wings: -Heat shields. These are the "standard" magic wing parts, but they're quite heavy and our ultra-low-power props will probably have a hard time getting them up to speed. -Landing gear. These are slightly lighter than heat shields but have a lower lift to drag ratio. Also you can land on them. -The small aerodynamic nose cone. Doubles as node occlusion for a fairing, but the required angle means it has less occlusion power. Very light but relatively low lift to drag compared to the above options, probably still a pretty good choice for this challenge. -Fairings. This one's a free optimization because our existing crafts can easily be adapted to take advantage of this effect. It actually ends up hurting the partial run I did yesterday because the small magic wing effect is canceling out some of my wing lift. -Flags. In 1.12 this is fixed, but in 1.11 (which I play for mostly unrelated reasons), flags are the most overpowered part in the game. They have incredibly high lift and also zero drag, meaning that your only source of drag will be the body drag from your hull. Additionally propellers with flags are extremely broken - I've created flag prop crafts with TWR of over 100 before, as well as pulling one all the way to Kerbin escape velocity while still in the atmosphere. Flags also make for great single-use landing gear and they're very light. Actually I believe that my original entry also had offset blades by exactly the same amount. I just reduced mass and optimized the characteristics of the motors.
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Well, my computer didn't crash, but sometime during the night my frames dropped through the floor and I barely made any progress. Currently KSP is closed but I might try flying it some more today. Not at all - I'm not offsetting the props enough for the torque flip to take effect. Instead, I'm simply reducing the radius of the propeller, reducing the torque needed to accelerate it up to speed. The same effect would occur in a real life propeller. There is no free energy. The lift and drag points of the prop are still on the same side of the axis of rotation. Also the prop blades aren't clipped inwards into each other - they just appear to be attached end to end. You've touched on the main reason why it's so hard to determine what counts as cheaty in KSP. Everyone has a different threshold for what mechanics they'll be willing to abuse, whether it be part clipping, root fairing body craft, magic wings, or even Kraken drives. I think that offsetting the props one tick inward isn't too cheaty, as you aren't getting any torque reversal (No free energy) and thus the motor still requires some energy to operate. Again, the energy cost is reduced, but that matches the real world. Meanwhile, offsetting them further to create infini-props would be too cheaty for me as you're getting free energy. And it seems that you think any amount of prop offsetting is cheaty since you're reducing the required torque to drive the prop. I don't think there's any way to reconcile this without someone changing his (or her) opinion. Huh, I never realized that basic fins actually have a better mass ratio. Interesting, but this probably won't be useful for the SSTO craft I like because of the fin's terrible heat tolerance.
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One final update before I go to sleep: 20 electric charge used. Around 81 degrees of longitude have been covered. That's about 848 km. Total estimated range is now 4241 km. The craft seems to be perfectly stable at this height and speed, so I think I'll go to sleep and see where it's at when I wake up. Hopefully my computer doesn't crash.
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Actually I'm almost certain that KSP was simply rounding the current down to zero. Right now I'm at 4% thrust limit and drawing about 0.01 units of charge every 5 seconds. Meanwhile, in my earlier picture, I was at 3% thrust limit, which meant I should have expected to draw 0.01 units of charge every 7-8 seconds. But I went a full minute and didn't see any current draw. Small update: I'm over the continent where my last mission landed. I'm actually still increasing speed slightly, so this next estimate is again an underestimate of the maximum range of this craft. 91.89 / 0.00206 * 89.8 = 4006 km remaining. Maybe we could have an alternate leaderboard for using only ten units of electric charge?
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And... we've finally done it! I found that flying higher is actually beneficial, as I can fly faster for the same drag and thus the same motor output power. This only really breaks down when I start reaching Mach effects around the propeller, where I'll want to fly lower to take advantage of the higher speed of sound. However, Mach effects are insignificant here. 0.00204 electricity used per second. 95.48 / 0.00204 * 84.6 = 3960 km. I wouldn't describe anything I'm currently doing as a cheat. I'm not taking advantage of any magic wing effects - in fact, I'm doing the opposite, as I'm flying at a -1 degree AoA right now and so I actually get a penalty from fairing body lift. The props aren't spinning infinitely and in fact take a positive torque to maintain. They're slightly offset inward, but I'm not generating any phantom torque. I don't know what happened with the zero power draw, but it felt a bit too cheaty for me, so I purposely increased torque limit in order to draw a measurable current.
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Okay, this is getting ridiculous. My power usage is so low that KSP flatly refuses to tell me the motor is drawing any power at all. In fact, after a full minute, KSP tells me that less than 0.01 units of electric charge have been used. Doing some quick back of the napkin math: Assume 0.01 electric charge used per minute (Upper bound of what's actually possible given my readouts) 9974 minutes * 60 seconds * 55.6 m/s = 33273 km The problem is that this will take a full week to actually finish! My computer probably can't go that long without blue screening. So this is firmly in the realm of a theoretical mission. Increasing the throttle a little bit, finally I start to see some power draw! Each motor is drawing 1.03 milli-units per second, or 2.06 milli-units per second (0.00206 u/s) in total. This translates to a flight time of 48252 seconds, or about 13 hours. This is actually pretty reasonable, but still far too long for me. This also implies a max range of 3339 km. A full circumnavigation of Kerbin is 3768 km. It's tantalizingly close!
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Interestingly enough, single blade propellers do exist in the real world: But I suspect they'd be impractical in KSP due to the difficulty of balancing them. Have you tried further reducing motor size? A smaller motor would have less weight and draw less power. You'd need to have a higher torque limit, but that is likely a good thing - it gives you finer control over your overall torque. Another thing you could do is angle your fairing upwards so you get some body lift. It'll be minimal but it will help reduce drag.
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A slightly more Kerbal way to do this (at least on a vacuum body) is to have the mothership orbiting extremely low above the surface and plant the flag when it's within physics range. This probably isn't practical but would be really funny. This wouldn't work on Duna but would be fine on Ike.
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By the way, increased drag from denser air probably isn't a factor here, as all else equal, higher drag will mean higher lift so your plane will simply reach equilibrium higher in the atmosphere. I suspect it's due to two things: -Colder air means lower speed of sound, so you're shifting the Mach curve. If you're using a supersonic jet engine at max speed, this means your max speed is reduced. -Centripetal force is reduced because you're farther north, so you need more lift to cancel out gravity - which means more drag, but not because the air is denser
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Well, I've got this: Airspeed = 52.30 m/s Electricity usage = 0.0032 u/s Electricity remaining = 86.47 This translates to 27022 seconds of powered flight remaining, or 1413 km. And that's not including the initial bit of flight to get here, or the glide down to the ocean. I am completely unwilling to fly for 7.5 hours even with an autopilot. But this shows that a twin engine design is still quite capable! (I went back to two engines because a motor casing is only 18 kg and this way Smart A.S.S. can actually fly the craft without completely dying).
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Oh no If you continue pushing the bar I'll have to either graciously bow out of this challenge, or begin to abuse aero exploits
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It seems like you've fallen for the map projection - "straight lines" on this projection don't necessarily correspond to great circles. Here's an example of a geodesic that follows a path very close to sea level: Taken from one of Stratzenblitz's videos. On a rectangular map projection this looks like a curved path, but on Kerbin's surface this will just be a straight line.
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I would never have even considered this optimization! Wow, you've smashed this challenge out of the park. I might have to start getting crazier with my aero optimizations. Or maybe start using an autopilot mod, or both
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I talked to Lt_Duckweed about this and he confirmed that this is actually a real effect and he's used it before. I'm considering carefully balancing the prop so the phantom torque cancels out lift-induced drag and prop drag as much as possible, so I can massively reduce the torque limits on my motor and still fly at high speed. However that might be a bit too cheaty for me I suspected something like this would be better, as you get a superior lift to drag ratio at lower speeds. I think that in our recent submissions, my craft was more drag optimized, but range was similar, and I'm pretty sure it was because I was flying faster and getting a lift/drag penalty. So you'd want the RPM limit to be as high as possible but set torque limit incredibly low and play with prop angle until you can just barely take off. The slower the better probably? I tried to maximize speed because I'm impatient and wanted the mission to be over with quickly Note that for jet endurance missions this flips on its head because reaction engines have a specific impulse so their specific energy increases with increasing speed, but props drop off sharply as speed approaches Mach 1. Another possible approach that I investigated (but couldn't get to work reliably) was a propeller made from ailerons or wing panels. I've found that in some cases these can perform better than the DLC prop blades, but they also seem to be pretty power hungry. KSP's drag cube model means that any part can have zero WDrg values corresponding to a fully occluded node - I think the fan shroud just increases mass and drag with no real benefit. Ideally you'd put the prop motor entirely inside a fairing and keep the propeller blades outside the fairing.
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The propeller is completely off, but a phantom torque force is causing my propeller to spin up. Basically autorotation on steroids. It works because KSP calculates propeller blade lift at a point offset way out from the axis of rotation to compensate for Unity's rotation limit. But lift also comes with a lift-induced drag acting opposite to the motion, which is applied at the base of the propeller. Normally this is just fine, because the lift induced drag acts on the same side of the propeller as the lift point, causing a negative torque. But when the props are offset inward far enough, the drag acts on the opposite side of the propeller, which actually produces a positive torque. This means that when the propeller produces thrust, the thrust induces a torque that further accelerates the propeller. So all I need to do is get the prop moving initially and then glide infinitely. If I remember correctly, the original infiniglide glitch centered on producing a phantom force by spamming control surfaces. It's no longer present in the latest version of KSP. On 1.11, which is the version I play on, there's a version of the infiniglide glitch that involves spamming the flag panels at a precise angle. I'm not using it in my runs, but I did consider it.
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I was playing around with offset props to try to reduce the torque required to spin them. Instead, I think I found a new glitch
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Not going to submit right now, but I suspect that a Rapier+Nerv plane will actually be very viable in this challenge. Here's a design I had lying around: This plane can actually deliver over twice its own mass to orbit. Here it is with a payload... And here it is without the payload. 70K funds to deliver just over 75 tons to orbit. This is the same craft but downscaled for the payload to be 50 tons. And here it is without the payload, for 65k funds. Note that this value can probably be improved by converting this into a three cores design. Have the Rapier engines on the outer cores and have the Nerv engines on the center core, and drop the Rapiers when they run out. This should be able to reduce cost further. The reason this is so low cost is because of the insane payload fraction possible with Rapier and Nerv. And with recovery cost included as well, this is even better.
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Yeah I checked and I made a mistake, for some reason I forgot to put ".7" after 35. Your number is correct
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Wow, that's far too close for comfort. I've noticed that I'm flying a lot faster than you are - I wonder if I'm running into some inefficiencies from Mach effects around the propeller. Maybe it's time to downsize my engine once more? I tried Mechjeb Smart A.S.S. but it couldn't handle the constant torque (probably a poorly tuned PID). Maybe its dedicated aircraft autopilot module could handle it?
