EPTKerbal Space Program - Page 26
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Veldril
Thailand1817 Posts
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Jetaap
France4814 Posts
It goes to the moon and back without any issue, 17 parts ( the aim was just to have a rocket that is as simple as possible, it's of course possible to do much better as far as efficiency goes) It has 9.5k delta V | ||
Teoita
Italy12248 Posts
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felisconcolori
United States6169 Posts
On April 07 2015 07:18 Teoita wrote: Cyro's stuff is the definition of "slightly overkill" For the definition of "oh my goodness what have we done" overkill, I think there's a guy named Whackjob on the KSP forums. Not sure of his recent activity, though - last I saw he killed his computer from insanely high part-count constructions. The tyranny of the Rocket Equation means that sometimes less is more - but then it can be a lot of fun to just throw efficiency out the window and see just how big of a monster you can get into orbit. | ||
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Cyro
United Kingdom20345 Posts
On April 06 2015 23:23 Epoxide wrote: You should look for engines with high ISP when outside of the atmosphere, typically the nuclear engine is the most efficient for transfers between planets/moons. What's ISP and what does it mean/do? On April 06 2015 23:16 nimbim wrote: xD well there is nothing efficient about that design. Just look at all the reaction wheels you needed to compensate for its insane mass (don't use nose cones unless you've installed FAR btw). There's nothing wrong about what you're doing ofc, but it's not efficient^^ It's like Simberto said, you only need a certain TWR for the critical burns, i.e. while fighting gravity and atmosphere. Once you're in LKO you definitely don't need a specific TWR anymore and the Mün has very low gravity obviously (1.63 m/s²). It's perfectly normal IRL that rockets have a TWR barely above 1 after decoupling boosters, they pick up speed while the fuel depletes. Also, using just 1 engine while you don't need the extra thrust is always best in terms of efficiency. Don't attach 8 LV-N to get more thrust, that's actually less efficient than another single engine with lower Isp. I can't find the table right now, but iirc anything above 4 LV-N is less efficient than using 1 LV-T30 (Isp=370s). There are some cases when a smaller engine will be more efficient than a LV-N, but in general just use them for space. http://imgur.com/a/iNqmQ#0 This is kinda over my head :D nice 17 part rocket | ||
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Mordanis
United States893 Posts
A few areas ISP is used : Thrust = g0 (surface gravity at Earth/Kerbin) * ISP * dm/dt (rate you're getting rid of fuel) delat V = g0 * ISP * ln(m/m0) (the last term in the last equation is the natural log of final mass divided by initial mass) Wikipedia article for Specific Impulse Wikipedia article for rocket equation | ||
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Cyro
United Kingdom20345 Posts
Can anyone explain to me or link good resources for how air breathing engines work in this game? I'm clearly missing some stuff with the physics simulation, because i don't understand why my crafts are flying (or more importantly, not flying) in particular, thrust to weight ratio not being at all representative as ability to pitch up. I can put my nose straight up with a TWR of 3.6 at full throttle and i drop like a rock - but more importantly i have no indicator in my UI for why this is happening, my air intake is completely fine and i'm not sure what mechanism with the game physics simulation is causing the drop off in thrust, or how to game it. i first noticed that trying to ascend at an angle (like 30-40 degrees up from the horizon) and my effective thrust just wasn't where it should have been Some of my craft with air breathing engines can fly up at steep angles or even straight up, others can't I was in a skype call with friend who is more experienced with the game when i was trying to figure it out, he said maybe the rapier engine TWR was displayed wrong as it switches modes but it wasn't that at all. I can post the craft in question (that has reached orbit and landed again safely without a chute) if it helps. --- I had some theories like drag, but that doesn't make sense - pitching down the nose towards the horizon would make me gain altitude way faster than flying up at a steeper angle, while also gaining speed on that axis too. It's like the engines just don't work properly at certain angles on certain craft because of some mechanism that i should be taking into account but i'm not even aware exists I know that aircraft rely on relatively flat angles to get lift from wings - but also that with a good TWR, planes IRL (and in-game, i tested it) should be able to go straight into a vertical climb | ||
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stenole
Norway869 Posts
With a max TWR at 3.6 you should still be able to ascend even at 50% so there is probably something else going on too. If you are pointing straight up and falling down without backwards pointing air intakes, your engines are likely to get air deprived. But that usually makes your craft spin uncontrollably because it tends to happen asymmetrically. Maybe not all engines are activated or aren't getting fuel. Maybe the TWR calculation was wrong... | ||
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Cyro
United Kingdom20345 Posts
On April 07 2015 23:53 stenole wrote: I think the disparity you are experiencing is related to air breathing engines have a "velocity curve". You can find the values of this in the cfg-files for the engines. It causes the engine to give a fraction of its maximum thrust depending on the velocity (relative to the atmosphere). For example at 0 m/s turbojets will at most give you 50% of maximum thrust. But it will be able to reach maximum thrust at 1000 m/s, 50% again at 2000 m/s and 0% at 2400 m/s. With a max TWR at 3.6 you should still be able to ascend even at 50% so there is probably something else going on too. If you are pointing straight up and falling down without backwards pointing air intakes, your engines are likely to get air deprived. But that usually makes your craft spin uncontrollably because it tends to happen asymmetrically. Maybe not all engines are activated or aren't getting fuel. Maybe the TWR calculation was wrong... I snapped my wings off by jerking the plane to the sides on the ground and then took off, and the same craft then flies with a similar TWR but magically manages to go straight up. They're not air starved AFAIK, my air intake was completely overpowered to allow for only ~2-3% intake usage at a few KM altitude, and to allow for air powered engines to around 35km. The intake looks waaaaaay into the green from any stats i can see, and the actual thrust displayed on the engine is unchanged. The plane in question has a rapier and two basic jet engines, but i'm talking about a variety of altitudes from right off the runway to about 20km in the air I've noticed that behavior (change in thrust and maybe efficiency with altitude) but i don't think it explains it. The craft that has those troubles has a long wingspan, maybe that's related - or maybe it's a combination of things, like only 60% of the thrust working at 200-1000 meters (yet not being displayed properly on TWR) coupled with air drag from the wings themselves being much, much higher than i anticipated overall i think i'd like better stats if i can be falling while pointed straight up with a "TWR" of 3.6. Staring at horizontal and vertical velocity numbers isn't as fun or effective as having better stats to go on | ||
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Jetaap
France4814 Posts
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Cyro
United Kingdom20345 Posts
![[image loading]](http://puu.sh/h52Zf.png) ship with some modifications (added fuel links, changed the wings in a way that might actually be bad, IDK) http://puu.sh/h53iX.craft | ||
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Ljas
Finland725 Posts
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Cyro
United Kingdom20345 Posts
edit: You're actually right and it was just the engine vs wing position completely fucking up the craft/s. It flies fine now. wow >_____> thanks | ||
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SKC
Brazil18828 Posts
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Cyro
United Kingdom20345 Posts
On April 08 2015 03:21 SKC wrote: Is that a plane or a rocket? Yes. :D Two air breathing engines and a rapier | ||
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Ljas
Finland725 Posts
Edit: On April 08 2015 03:17 Cyro wrote: I changed the wings to dodge the engines because of a message that wings were being damaged edit: You're actually right and it was just the engine vs wing position completely fucking up the craft/s. It flies fine now. wow >_____> thanks Well there you go. You're welcome. | ||
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stenole
Norway869 Posts
That is my theory, even though logically you would think that thrust could get around the wing... | ||
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Cyro
United Kingdom20345 Posts
The funny thing is that i got to orbit and back for a clean landing with it broken in that way. I'd like to see what's doable with a fixed up and improved craft! :D Full throttle, pointed it up and it reached 26 kilometers when the jet engines were finally air deprived, and a final apoapsis of over 40km. Gotta turn off the basic jet engines at a certain altitude. When i first flew it, they had their 40 fuel and no more so it fixed that for you automatically, but it wasn't optimal | ||
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Ljas
Finland725 Posts
On April 08 2015 03:34 Cyro wrote: Gotta turn off the basic jet engines at a certain altitude. When i first flew it, they had their 40 fuel and no more so it fixed that for you automatically, but it wasn't optimal Well, yeah. I just went full vertical to test if it has the thrust to do so. | ||
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Cyro
United Kingdom20345 Posts
so i've been thinking, gotta check wing mass etc. With any significant mass on wings, it's probably better to ascend at like 15-20 degrees ish with a spaceplane? how do people usually do that, or generally make craft capable of maneuvering in orbit for a while and returning? I can get to orbit but the fuel costs with rocket engine are so huge compared to air breathing engines | ||
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