Major-Major

Does anyone know how exactly the simulation calculates drag? Calculating the optimal trajectory is a balance between the gravity turn--which should be initiated as early as possible--and the need to minimize atmospheric drag. So to do it mathematically (which I have still made 0 progress on) I need to get some idea of the drag forces in play. The paper I mentioned earlier was a dead end, but I found something a little more promising on MIT Open Courseware. He covers the idealized case of a constant T:W ratio, which still turns out to be tremendously complicated. I guess they don't call it rocket science for nothing...

Using a 3-engine, 9-tank rocket, which can make it 300k straight up but doesn't have enough energy to come close to an actual orbit...I was able to escape Kerbin by keeping the throttle as low as possible. That's when I realized there must be a bug. I still have that little guy orbiting the sun, as a cautionary tale.

In the current release, the fuel flow is bugged. Cut your power to 50%, and your thrust will decrease by half...but your burn time will increase by a factor of four. So you've effectively doubled your engine impulse, which is not how it's supposed to work. Try it--build a rocket with a very high T:W ratio, then launch at the minimum allowable throttle setting. If you can launch at, say, 25%, the delta-V you'll achieve will be 10-16 times higher than what it 'should' be. So yeah, it's necessary to do everything at full throttle for now, at least as far as launching.

This is a real can of worms. It's a system of 2 coupled differential equations, which are only numerically solvable. There's no way to find a reusable algorithm to solve for the ideal angle, each solution is going to be specific to a particular rocket. Wikipedia has the two basic equations of motions listed on its Gravity Turn page. (I'm new here, what's the best way to write/post equations?) There's also a useful paper, "Universal Gravity Turn Trajectories," from 1957, that describes in detail how to do this, but...it's confusing. I think I'd be able to crack through the math, but that would be a project for next week. One other thing: T:W ratio is actually lowest at launch. Both the mass of the rocket (due to losing fuel) and the gravitational acceleration drop off as altitude increases, losing to a drastic reduction in weight--thrust remains constant. It would probably be most efficient to pull back on the throttle as altitude increases, but since the fuel flow is currently bugged, this is 'cheating.' Anyway, the non-constant T:W ratio is the primary difficulty in solving the equations above.

Yeah, I kind of realized after the fact that I hadn't really answered your question. Anyway, that's the correct formula--the algebra works, and it's dimensionally correct, since you have (weight/weight), yielding a unit-less quantity. If you take that number and round up to the next fuel tank, it should work well. Also, I think I'm going to undertake a Delta-V surface-to-orbit study, since empirical testing seems to be the only way to sort it out, what with all the complicating variables. Hopefully I can graph some meaningful results within a couple days. I'm particularly interested in how T:W ratio affects the achievable altitude...that might take some testing as well. Oh yeah, and I love Catch-22. Sometimes I'll catch a Yossarian online somewhere, but I've only seen one other Major Major out there.

You're good, as long as you recognize that 'ln-1 is actually the exponential function, e. So you have e^dV/(9.*81*Isp), which is just some number. Multiply the denominator, then solve for x. The equation stays linear in x, so it's not a big deal. HOWEVER, I don't think it's going to give you integer values for x. I usually go the other way--pick a number of tanks, find the delta V for that number, and so on. All part of the fun.

Hi everyone, I'm an Astro Engineering student at Wisconsin right now, so I'm obviously in love with this game. I had a couple quick questions right away: 1) I've seen reference to the 'Fuel Flow Bug,' but haven't seen a straightforward description yet. I would presume it's related to the non-linear growth of burn time that comes with throttle reduction? (Excel says it's an inverse square). This quirk doesn't seem to make physical sense, and really screws up my attempts at finding Delta-V for a rocket, so I'm hoping it's a bug. 2) Any tips for attaching control surfaces to wings? I haven't been able to get my ailerons parallel to the wing yet, they always snap perpendicular, which obviously looks like nonsense. Thanks!