DoctorEvo
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Posts posted by DoctorEvo
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I approve of this reference. I do, however, demand ONE MILLION DOLLARS in royalties for it.
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I think it might be doable with tweaked .cfg files. Setting all the drag values to some miniscule number may make it just slippery enough to pull it off.
But yeah, the 34.5km transition is much too sharp to pull this off in a realistic fashion.
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The score from the entries so far (thanks for trying!
)Nova (320 x 39515.2) = 12644864 - 18663 = -6484685032
JZavala - (376 x 44280.6) = 16649505.6 - 13973 = -2709748267.4
DoctorEvo (490 x 38872) = 19047280 - 1063 = 17856264
So DoctorEvo's flight has created the only positive score so far. Good going! I haven't even got close to that yet!
Heh. Here's a few helpful hints:
-Your priorities should be: 1) Don't crash, 2) Stay low, 3) Everything else. Excessive height has a big impact on your score.
-Make the first turn towards the ocean as low as possible. Once you've done that, drop down and don't go any higher than that height.
-Playing with the throttle helps a lot for controlling altitude.
-Don't rush it. Trying to 'hover' the whole way is too slow and hard to do, but flying headlong at full throttle can be hard too.
-Crashing at the end is better for your score than ballooning up for a landing.
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Winglets do add deflection lift force. It's a force perpendicular to the velocity direction, that is affected by the angle of attack of the winglet.
This lift force is applied to the center of mass of the winglet. The liftCoeff parameter determines how much force will actually be applied. The model itself has almost no influence over the winglet dynamics, except for the position of the center of mass.
The winglet's angle of attack will also influence how much drag is produced. The lifting force will also start to decline as the winglet enters a stall AoA.
Now, what winglets don't do yet is simulate airfoil lift. They are about as effective as a 2x4 as a source of lift. They are meant mostly for stabilization. Later the idea is to add a Wing module, that will actually simulate airfoil lift, and will have control surfaces as well.
Cheers
Besides an absence of pitching moment modeling, I fail to see what is missing from your description here that a true 'airfoil-lift' model would have. Airfoil lift coefficients vary with AoA (which you seem to have already done)... and they drop off suddenly at a critical AoA (which, according to your description, you have already done)... and drag also varies with AoA/lift (which you ALSO claim to have done)... Seems to me that - as far as your description goes - you've got your bases covered.
Now, what I've found on my own is that there are several (unmentioned) issues with the winglet's behavior:
-Pitching moments are not modeled properly, often doing the precise opposite of what they are supposed to
-Stall (or post-stall) model seems flawed; maximum lift can be achieved at 90 degrees AoA (where lift should be falling back to zero in a sinusodial fashion)
-Induced drag seems off. Sometimes it seems nonexistent, other times it seems to be much too severe. I suspect the configurable 'dragCoef' parameter has influence over this.
In any case, I understand that this is still in development and am very much looking forward to seeing the 'wing module' when it comes out. Hopefully the behavior will be properly nailed-down by then.
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I think you know what I mean. Alter the direction or strength of the force by config file.
The values in the .cfg are LABELED as coefficients (well, in the winglets anyways), which makes sense, because there's naturally no way to dictate the velocity or dynamic pressure of a part through configuration. However, I'm not certain that they actually are coefficients, as that would mean that the program would have to dictate the characteristic area being used to determine the drag FROM this coefficient (and velocity and density and whatnot). This COULD be done via a simple calculation of frontal cross-sectional area, or an on-the-fly calculation of head-on area with respect to the direction of travel (doubtful), or more likely, this 'coefficient' is actually the 'drag area,' that is, the true drag coefficient TIMES the characteristic area. I still need to test for this; if this is indeed the case, the part developer would need to manually input higher drag values for larger parts of the same shape.
A little insight from the game devs would be wonderful right now...
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I was JUST THINKING that that'd make a pretty cool challenge.
Let me see what I can cook up...
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The center of gravity doesn't matter if the drag is at the bottom and the thrust is at the top. The only reason having the CG further forward would help is if you were traveling on velocity alone, without power (like a dart), because then all the momentum is in the front, and the drag behind pulls the rocket into alignment. However, the same principle works if it's thrust instead of momentum. As long as the drag is behind far enough, it doesn't matter where the weight is.
That is wrong. You are STILL wrong. Do I have to draw a frickin' picture?
If your rocket begins to spin, the engine will spin with it. The engine will NOT keep thrusting in the direction you were going - it will thrust in whatever direction you point it. Drag, on the other hand, always pulls opposite the direction you are moving (not necessarily opposite of where you're pointed), and inertia will of course ALWAYS tend to keep you moving in the direction you are already moving. Since inertia acts at the center of mass, it DOES help to push this point forward, and to push drag aft. The location of thrust along the thrustline is completely irrelevant, just as long as the total thrustline is inline with the rocket's axis. (Note that, for a rocket which is not aligned perfectly, having the thrust CLOSE to the center of mass, rather than forward or aft, will reduce the torque moment caused by this imprecision - but that's a whole different ballgame).
Seriously, bro. You're denying the findings of Robert-frikin'-Goddard, here. It's just rocket science, not brain surgery.
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Hmm... using the engine module (either solid OR liquid) for this wouldn't do, as the engine only provides thrust in the direction it is pointed (which is not necessarily up). Using a modded parachute or other drag model wouldn't do either, as drag is velocity-dependent (for direction as well as magnitude).
Also, apparently setting a negative mass value doesn't create antigravity, so we can forget about that. :
Haha, I tried making a ramjet with negative drag. It kind of worked but was incredibly unstable, the slightest deviation from vertical would produce a gigantic sideways reverse-drag sufficient to rip it right off. You could get several hundred mps below a thousand feet -- usually downwards, as it would accelerate you down as fast as you were going up even butt-first. If drag were a vector instead of a scalar, maybe...
What an AWESOME idea!!
I see the problem with it producing thrust in the yaw direction though... that kinda sucks. I'm trying to think of a workaround...
I know that most parts have separate minimum and maximum drag parameters, which I presume are for forward flight and for sideways flight. Obviously, for a ramjet, we'd only want the FORWARD-FLIGHT value (i.e. minimum drag) to be negative. However, this alone is still not fully sufficient, as it would still cause a divergent situation at low AOA until the (presumably interpolated) drag value crossed the zero mark. To make up for this, I'd probably look into using the winglet module instead and adding some degree of lift to pull the net-force vector back to (or at least close to) the centerline of the rocket.
[Also, drag IS a vector. By definition, it is always in the direction opposite your direction of flight (which is NOT necessarily the direction you're pointed, mind you). The other component of total aerodynamic force is lift, which is - by definition - PERPENDICULAR to the direction of flight.]
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Yeah, I eventually got to that design, but I couldn't find the thread again. I usually put a pair of winglets on; they make the landing much, much easier.
Winglets? BAH! What a waste of money.
(No, but really, I like your style. A winged SSTO with 3x LFT and 1x LFE is an elegant minimalist design.)
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Allow me to rephrase what I think I meant to say. Having the thrust at the bottom means that the air resistance in-atmo is always trying to push the rocket over.
Not if the center of mass is forward to the center of pressure. Putting heavy components such as engines in the back of the rocket will of course shift the center-of-mass back, but it isn't the lengthwise-positioning of the thrust that is directly causing this issue.
if there is any flexibility in the stack, the top of the rocket will bend to one side or the other, and that will lead to a spin-out.
If your rocket is bending under compression such that your thrustline is thrown out of alignment, that's a structural issue (one which, mind you, will not go away if you fire the rocket in a vacuum instead). Yes, I suppose a rocket built to be under tension when firing will tolerate elasticity better, but it sure is a hokey way to build a rocket vs. simply stiffening the thing as needed.
If the thrust is at the top of the rocket, the drag from the rest of the rocket trailing behind will try to keep it on target. That's what I was talking about when I said this:If there is drag from below the boosters, it will help, somewhat, to stabilize the rocket.Your reasoning is still fallacious. It is the center of gravity, NOT the location of thrust, that will help stabilize the rocket by being placed at the front.
If things aren't balanced, though, it does matter a great deal. Take a look at Sunday Punch's medium SRBs and how moving them along a radial coupler affects their flight characteristics-- or how you can make an L, and use that to build a spin-stabilised doom machine.
Even with regular SRBs you can find a pronounced effect on atmospheric flight characteristics on shorter rockets, by simply moving them up and down. This is because of the issue I mentioned before - if the center-of-gravity is lower than the center-of-pressure, your rocket will be aerodynamically unstable. Adjusting the height of side-mounted SRBs affects BOTH of these, and the direction in which they should be moved to improve stability may vary from rocket to rocket (heavy rockets lacking in aerodynamic surface will prefer to have the SRB's drag to be added down low, whereas light rockets with lots of surface will benefit from the mass of the SRBs being moved forward).
Another thing worth mentioning is that a rocket that is TOO aerodynamically stable will resist diverging from a nose-forward, ballistic orientation. If you are off-course, or if your intended course is not fully ballistic, you MAY not be able to steer back onto course once the stabilizing aerodynamic forces overcome your control forces. It is important to recognize this situation, and understand that it does not mean your rocket is unstable, but rather uncontrollable. After fiddling with Entroper's rocket a bit, it seems like this may be a large part of the problem - it diverges during the initial acceleration (possibly due to flex) and then STRONGLY resists turning in any direction but the one it is going. This is aggravated by the fact that, after the SRBs are ejected, the design becomes tail-heavy and UNstable due to the significant weight of the three LFE at the very bottom, and the light and draggy tricoupler, capsule, and the (now-emptying) upper LFTs at the top.
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You people with your decouplers... and parachutes...
One Mk. 1 Command Module: 1600 credits.
Three FL-T500 liquid fuel tanks: 1650 credits.
One LV-T30 liquid rocket engine: 850 credits.
Achieving SSTO for just 4100 with enough propellant left over for a (marginal) powered landing: priceless.
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Jeez, guys... you do know your scores are supposed to be POSITIVE numbers, right? ;P
17,856,264 points. Of course, my Kerbals didn't survive... :'(
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EDIT: This is really difficult. I can't get a ship above 300 m/s in the lower atmosphere without it flipping end over end, even though it should be a tail-heavy design.
It's because the thrust is at the bottom, so if the weight's off-center, it wants to fall over. The drag at the bottom helps some, but in order for it to actually make a difference, it would have to be below the engines.
Both of you (semininja especially) need to read this: http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy
It doesn't matter WHERE along the thrustline the thrust is being applied, just so long as everything else balances around the thrustline. Furthermore, having a bottom-heavy rocket does NOT aid stability - in fact, it aggravates it when aerodynamic forces are taken into consideration. (ever wonder why darts are weighted in front?)
Alternatively, your rocket may be (and probably is, judging by the behavior of some of my high-thrust rocket designs) suffering structural issues; i.e. twisting or bending in a fashion that causes the CG to no-longer be lined-up with the thrustline. If you're running 0.9, I recommend trying out those struts; if not, look at rearranging your SRBs so that all loads and stresses are balanced-out (I was forced to run a star-shaped pattern on my 13-SRB cluster).
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I do believe it's a Rocketdyne RL-10.
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Breaking Gravity
in KSP1 The Spacecraft Exchange
Posted
Well... aren't WE negative?
Despite the somewhat childishly excited tone, rwb1971 here DOES have a legitimate bug complaint. His addons are not to blame (though they DID help him to make it out far enough to discover it expediently).
Lighten up a little.
. . .