GoSlash27

OhioBob, I wish I had your ability to clearly and simply state the salient point! The terminal velocity readout would only be correct (for the purpose of flightpath planning) if the aircraft's current Cd matched what it's Cd would have been at terminal velocity.

Exactly; they're not the same thing because the info shown was not collected while it was in free-fall. Since it's showing the instantaneous terminal velocity of the vehicle and *not* what it's free fall terminal velocity would have been had it been dropped, you cannot use that info to determine an optimal launch profile. Get it? -Slashy

Bryce Ring, What is the mod you're using that allows you to see your cumulative drag and gravity losses? That looks pretty darn handy! -Slashy

Ferram, welcome aboard. It is because the equation assumes the Cd of the vehicle and it's current velocity, and both of those numbers are a result of the vehicle having been accelerated to it's current state. If your ship is hovering, climbing at mach 1, or or falling at 50 m/sec, this equation will yield varying results. Those variations are due to the velocity and state of the ship at the moment, not the state of the atmosphere. In order for the Vt readout to actually reflect what the free- fall velocity would have been had it been dropped, allowed to stabilize at it's terminal velocity, and then measured at that altitude, the user would have to have *actually* done that. Arkie had thought that this display was literally showing that, inferring that it conveyed the change in atmospheric density with altitude at the moment, and basing his launch profile off of it. Best, -Slashy

Bryce Ring, Thanks! -Slashy

Aye... So now that we have confirmed that 1) the display you had been using is, in fact, the terminal velocity of your ship under power and *not* the free- fall terminal velocity as you had thought, and 2) by your own statement upstream It should be apparent that the entire strategy is flawed. You're not saving DV by accelerating at a high rate, you're losing DV by doing that. Best, -Slashy

No, I think you're confusing yourself, and it's way past my bedtime, so last try for this evening. In your video, you state (and the video shows) that terminal velocity *decreases* with altitude for the first 5KM or so. Is this true for a free- falling body? No, of course not. that's absurd. So your readout of "terminal velocity" isn't talking about an object in free- fall at your atmosphere, but rather your ship under acceleration. The only reason terminal velocity matters is because it maps the pressure gradient of the atmosphere vs. gravity, which defines your balance between drag losses and pressure losses for an optimal ascent. That display has nothing to do with it unless you're arguing that objects fall slower when higher above the ground. That's it for me. I need sleep. Best, -Slashy

No, you had it right the first time. You're killin' me, Smalls... The correlation between G and Vt was valid in stock *only* because Cd and area don't change in stock. The changes you're seeing in FAR aren't because the air is different or the gravity is different, but because the CD and area are different. It's still the same planet, so the optimal path off of the planet is the same. Your readout of Vt at mach 1 and 5KM is invalid because an object doesn't free-fall at mach 1 at 5KM. You're looking at data about your ship and mistaking it as data about the air. Your Vt readout is worthless in FAR. It was sorta- relevant in stock, but not now.

Au contraire, it is *everything*. You explained it perfectly earlier; the terminal velocity of a rocket under power has absolutely nothing to do with defining an ideal launch profile. What matters is the terminal velocity of a falling body at that altitude because it demonstrates a balance between gravity and pressure gradient. FAR does not alter the gravity or the pressure gradient, so the ideal profile remains the same.

Negatory. You said yourself (and we all watched) that the terminal velocity decreased as you approached Mach 1, then increased dramatically "no way we can catch it" once supersonic. Does any of that affect the terminal velocity of a free- falling body that happens to be at your altitude? You know it doesn't. It's not talking about the air, it's talking about your ship. -Slashy

Sorry, I got the word from NathanKell back around 2:00 local time. He confirmed that FAR doesn't alter atmospheric values, but rather alters Cd and surface area based on local parameters. These are, of course, functions of the part itself, not the air. Best, -Slashy

Whatever that is in the lower right hand corner of your screen. The readout that said "Terminal Velocity" that you kept referring to in your video. If it's from FAR, then so be it. You *know* that the atmospheric gradient and pressure aren't affected by your mach number, yet you referred to it specifically when describing "terminal velocity" and how it increases. But you just said that the optimal flight path isn't dependent on your ship's terminal velocity. That's clearly what it's referring to if it's changing with thrust and drag. You accidentally conflated the two. -Slashy

arkie, You're right on the edge of confirming what I personally confirmed earlier. Please understand that none of this is an attack on you personally. I'm just trying to explain why your analysis was incorrect and where it went wrong. Your description of terminal velocity and how it relates to the optimal flight path was completely spot-on (and well- written, I might add). It's your reliance on the KER readout of terminal velocity that has led you astray. It's talking about your ship's terminal velocity under acceleration, *not* the terminal velocity of a free- falling body at your altitude. That's why it varies with your Mach number and seems infinite after you go supersonic. Your pressure gradient, pressure, and gravity are the same as they've always been and therefore the optimal ascent path is the same as it has always been. The path your ship takes deviates from that due to changes in the ship, not the atmosphere itself. Stock lumberwagons go higher before starting their turns because stock lumberwagons are draggier than FAR missiles. FAR missiles should begin their gravity turns earlier to take advantage of their low drag coefficient. Best, -Slashy

DINGDINGDING!! We have a winner!! This about a million. So now given that *Kerbin's* atmospheric pressure and gradient haven't actually changed between stock and FAR, what does this imply about your previous analysis of the terminal velocity and how it relates to an optimal path? Hint: The readout you've been using was of your rocket's terminal velocity under acceleration Expectantly, -Slashy

Hmm... Bi-elliptic transfer is actually preferable after all... I hadn't run the numbers (although this post has inspired me to start doing that). It was just a hunch. Best, -Slashy

#1, we don't have any "clear and present evidence" of anything at all, other than you don't know what your numbers are, but are attempting to draw conclusions from them anyway. Specifically, the conclusions you prefer. That's just plain bad science. #2, I have already given you a clear and detailed explanation of why your reasoning is flawed, but it's in one of the several other threads you've posted on this topic.

Actually, this was a point I confirmed today with the folks at FAR: Kerbin "acts" as it has always acted. FAR doesn't change any of it's properties. Same gravity, rotation, radius, surface pressure, and scale altitude. Kerbin doesn't act any different at all. It's your rocket that acts different. This is a critical point. Best, -Slashy

This wouldn't answer anything, since I'm not running FAR. You really need somebody who uses FAR to test it. Best, -Slashy

Going into an experiment with a bias towards a specific outcome and coloring the results isn't "science", it's "lobbying". I don't personally have a dog in this fight one way or the other. If somebody tells me that launching rockets down the toilet will get my payload to orbit more efficiently and I can confirm it, then I'll happily launch rockets down toilets. But you're not testing this theory, you're *selling* it. And from everything I can tell (including my own testing), it's wrong. Best, -Slashy

I am, actually. I no longer have any confidence in any numbers you're posting here. How do you know if your spreadsheet is right, or if FAR is right, or if KER is right? *My* numbers from my test are 100% solid. No questions, no variations. If you really want to *know* you should open this up for peer review. Post your craft file and have somebody else who uses FAR confirm whether your rocket is *truly* more efficient than the norm or less. I'm thinkin' it's a lot less and your numbers are gacked. Best, -Slashy

Going by the numbers on that spreadsheet, 4,087 m/sec is reasonably accurate. Not enough variance to make a fuss over, since I only use 3 digits of resolution. I couldn't tell how many m/sec you removed due to the overshoot, so I can't confirm what the final DV would've been. For the vertical shot, it would be the 4,087 m/sec plus a little of the second stage, but since the KER numbers are suspect, I don't know how much. It said stage 0 weighed 3.54 tonnes, which is also incorrect according to your spreadsheet. Best, -Slashy

3 different answers. I got the figures from the video in the lower right hand corner where it said "total mass". And you certainly wouldn't use sea level Isp figures for that. They don't apply on Kerbin above 5Km or so. vacuum is more accurate. You seemed more than happy to use the numbers that add- on generated before, now all of a sudden they're "fishy"?? Dubious, -Slashy

Look, this is really simple... You *claim* to be "seeking answers", but all the while you're "highlighting advantages", which isn't asking questions, but rather making statements. This is what they refer to as a "rhetorical question", where you ask a question not wanting an answer, but rather as a pretext for making an argument. I got sucked into this because I was genuinely trying to answer your question, but you don't seem to be willing to listen to the answer because you're too busy trying to promote your argument. This is highly exasperating. If you want an answer to a question, then listen when people tell you. If you don't want an answer, then don't ask. Best, -Slashy

I calculated your DV expenditure from the mass. 42.6 tonnes on the pad and 10.7 tonnes at burnout. Looks like a mainsail to me. Please correct me if any of this is incorrect. Your prograde launch was 4,880 m/sec DV. Minus the correction for overshoot. 9.82Isp* ln(Mw/Md). The math don't lie. For vertical, it was the same plus your stage 2 burn. I couldn't get the type of engine. Looked like an LV-T30, but not sure. You were 4,900 m/sec on a mission that should've only been 4,270 for FAR. So yeah, that's what I mean by "drag- monster". If you've added over 600 m/sec due to inefficiency, *of course* it'll bury some of the 300+ m/ sec you waste by going vertical. Inefficient rocket is inefficient no matter which way you point it. Also the point that KER misled you about how much DV you had actually used, just as it did about your terminal velocity. -Slashy

If any of this were true, you would spend less time arguing and more time listening. And yeah, you're trying to "highlight it's advantages". That's why you're continually posting these threads. The reason you're working so hard to "highlight it's advantages" is because it's hard for you to fly a proper gravity turn and you want someone else to validate your reasons for not doing that. You don't *need* anyone else to validate your choice. Fly like you want to fly. But what you're posting here is highly confusing and misleading to the newbies who are going to read this later on. That's a disservice to them, and I don't personally care for it. Rockets that glow on the way up are bad. Launching straight up is bad. It's inefficient and wasteful. Disabling atmospheric stress because you can't make rockets work properly is bad. Maybe that's *your* thing, but it's not good advice to pass onto others and I'm tired of arguing with you about it when you're not listening. Now... when you grow tired of wasting all that energy and want me to explain to you where you're going wrong (and actually *listen*), I will be more than happy to lend you a hand. Until then, play your game however you see fit. Regards, -Slashy