far rocketry

[endl]

my seperatrons are getting ripped off by the air flow i cant separate my srb from the main fuselage without them they collide with the main booster and destroy the rocket.

how do you set up rockets for far? what do i do to fix this problem?

Edited October 24, 2014 by endl

[Taki117]

Without a pic of your rocket it's going to be hard to diagnose. However, I can tell you this, FAR takes part orientation into account when applying drag. If the part is oriented sideways it is going to experience more drag than if it is oriented up and down. You may need to redesign your Seprotron placement to get it to work.

[sedativechunk]

You're "supposed" to use seperatrons to gently move rockets away from your main vessel once disposed. This becomes a huge problem, though, with bigger rockets. Too many seperatrons will destroy your rocket from their exhaust blast. Also in reality, with rockets huge enough do you really think they would want them surrounding the main rocket so closely?...

I've got a new strategy for all my rockets. It's kind of hard to tell in this picture but I use the long girder segments to make my additional rockets/fuel/SRBs farther away from the main rocket/ship. I use hydraulic manifolds because they have the most ejection force, and then I use a structural girder segment and then attach the rocket to the segment. THis keeps everything farther away from my main ship and when I seperate them they don't smash into the main rocket so badly. Just make sure you use struts on the rockets you are attaching as well as the girders otherwise they may fall off. Here is my screenshot, look at the smaller fuel tank right in the middle of the photo to see what I mean:

[sal_vager]

Guys, this is about FAR ripping bits off Endl's crafts, I think the only solution is to not go so fast in the lower atmosphere so they don't get torn away.

[KerikBalm]

Disable aerodynamic failure?

[endl]

Without a pic of your rocket it's going to be hard to diagnose. However, I can tell you this, FAR takes part orientation into account when applying drag. If the part is oriented sideways it is going to experience more drag than if it is oriented up and down. You may need to redesign your Seprotron placement to get it to work.

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Disable aerodynamic failure?

that would defeat the purpose of using far, im pretty sure its how im building it not how im using it

[Taki117]

That's odd, I haven't had that issue with the B9 Seprotrons before. From what I can tell there is no reason why they shouldn't work. At this point I'm inclined to agree with Sal_Vager about not moving so fast during the lower atmosphere.

Edited October 21, 2014 by Taki117

[Empiro]

In .24, I had problems using separatrons and SRBs under FAR. It turns out that the structural failure was actually occurring between the radial decoupler and the booster. I placed struts just connecting the decoupler to the booster, and that seems to have fixed the issue.

[Wanderfound]

That's odd, I haven't had that issue with the B9 Seprotrons before. From what I can tell there is no reason why they shouldn't work. At this point I'm inclined to agree with Sal_Vager about not moving so fast during the lower atmosphere.

Likewise. When it happens, what speed are you doing at what altitude?

[Tortoise]

You must not be launching your rockets correctly with FAR, and going too fast. Slow down.

[biohazard15]

Judging by speed indicator or your screenshots, your rocket is too fast, it probably has TWR>2. This is a BAD idea when flying with FAR or NEAR (especially if you add DRE).

[endl]

i had limit terminal velocity enabled in mechjeb is this still too fast? i made a smaller rocket without boosters but this makes me concerned for the day where my payload is so big ill run into this problem again

Edited October 22, 2014 by endl

[DrMonte]

I can repeat and repeat and repeat. If you are in need of a sepratron for staging boosters your design has issues. Correctly placed booster slides down nicely without any additional force.

Correction suggestions:

- Check carefully vertical centering.

- For huge boosters use Girder Segment + Hydraulic Detachment Manifold.

- Stage while not out of fuel? Might work depending on upper stages design.

[11of10]

You might try clipping them inside the booster, perhaps? That's what I like to do, to keep them prettier.

[Axelord FTW]

Two things people haven't mentioned yet (or expanded on).

Radial decouplers also impart an offset torque to the part they are attached to when they are activated. Not a problem in stock much but with FAR, the part will flip a bit, catch some air, flip some more, catch some more air and that until they hit back into your rocket. They will eventually right themselves into the airflow according to normal aerodynamic rules but that usually happen after they tap dat ass (your rocket).

To fix this, drop the ejection force to zero using TweakableEverything (TE is also a MIGHTY fine and useful tool to use) and voila! Now, they will simply drop away from your rocket. If you want clearance, use separatrons as you would normally in stock.

As for the separatrons blowing up/getting ripped off due to aerodynamic stress, slow down. Mechjeb's 'limit to terminal velocity' is not terribly useful with FAR. Use the limit acceleration instead (15m/s to 20m/s max) until you reach 25km. Also, anything working within low atmosphere should NOT have a TWR of more than 1.7. Generally, my best and most economic launch stages run with 1.4 TWR. The Vessel Info or Delta-v Stats page (with All Stats clicked) will give you the information you need.

[MisterFister]

http://imgur.com/a/ysaWx

This picture is absolutely insufficient to help you diagnose your problem. We need to see closeup shots, preferably from several angles, of the offending sepratrons in question, preferably in flight, and preferably during stage events. This last part is exceedingly difficult, though is doable with repetitive quickloading to get the right shot. Alternatively, you can post your craft file with an exact list of mods used and a description of your flight / launch parameters, so as to allow someone else to recreate the problem.

i had limit terminal velocity enabled in mechjeb is this still too fast?

Wow. Ok. Yes, that is your exact problem. With FAR enabled, with or without DREC, you must key your TWR to no more than 1.42 at liftoff. For optimal fuel efficiency, try to key all subsequent stage TWRs to match across stage events. In other words, if MECO is at TWR 2.0, do what you can to tweak the next stage's TWR to the same number, since I've found that mid-launch aerodynamic failures can be made more likely by herky-jerk G-force changes across stage events, moreso than actual high G-load. (High G-load itself is a problem for DREC, but that's a separate issue.)

Keep in mind that MechJeb is explicitly and exclusively familiar with stock aerodynamic values, not FAR or NEAR aerodynamics. Indeed, the whole reason that stock aerodynamics is so awful is that it essentially simulated flying through mayonnaise. FAR-atmosphere is much thinner, much more "wispy," which much less drag on most designs (FAR calculates drag by aspect ratio and collision mesh values with respect to the airstream, and takes some other calculations with respect to the size of the attachment nodes [the green spheres where parts interlock in the editor] whereas stock just does a flat calculation based on mass and only mass and nothing but mass -- an aerodynamic nosecone, having mass, will only INCREASE drag, for example.)

This means that MechJeb is calculating terminal velocity based on how fast you'd have to be going for stock aerodynamics (digital mayonnaise) to cancel out your acceleration and give you a constant speed, which requires ENORMOUS comparative thrust. Since you're flying through FAR aerodynamics, which tends to be much less atmospheric drag than stock would present even at high altitudes, your MechJeb-governed throttle is WAY in excess of what would otherwise be called for to limit your acceleration to below terminal.

It's important to know what terminal velocity even is. Even if you know what it is, some readers of this thread won't, so I'll explain it anyway: thrust accelerates you forward / away from exhaust, drag accelerates you backwards / away from aero-dynamic prograde. When thrust EQUALS drag, then speed doesn't change, and you continue flying at that speed until the balance between thrust and drag is upset. When drag is greater than thrust (or thrust drops below drag) speed in direction of travel decreases, resulting in a net acceleration backwards. When thrust is greater than drag (or drag drops below thrust) then forward speed increases, resulting in a net acceleration forwards. The math can get frustrating, especially during vertical launch, because downward gravity is ALSO acting parallel to drag, thereby effectively increasing it -- which is exactly why in a FAR-model ascent you want to begin your gravity turn asap, typically before 1000m altitude, to begin the process of splitting the gravity value from the drag value. In stock, since the aerodynamics are GREATLY worse than the gravity losses, it's important to get out of the lower atmosphere (highest drag envelope) asap before turning horizontal, which is why you see people going from 0-45 pitch at 10,000m altitude.

MechJeb has some devbuilds that can more or less fake their way through FAR-based calculations, but since FAR itself is a mod and is constantly being updated to keep up with changes in the game, it's difficult to accurately peg MechJeb's inner workings to compensate. Generally, in FAR-regime launches, you have to learn to control your ascent manually. Using MJ to circularize at apoapsis is fine, however, and these problems would obviously not present in vacuum (relaunching from Mun / Minmus, for example.) Alternately, you can manually program in a series of vector changes in SASS, or manually modify the launch curve int he default MJ launch ascent module, though that's not for the faint of heart.

As a further alternative that most assuredly will not solve your problem but will minimize the inconvenience of the symptoms, is to use tweakable settings on your launch and mid stages to limit your thrust values to a TWR of ~1.3 at liftoff as I describe. Below 1.2, and you lose way too much dV to gravity. Above 1.4, you run a very heavy risk of aerofailure toward the end of the stage, where TWR spikes (because thrust remains constant but mass decreases due to empty fuel tanks, yielding higher TWR.)

It bears mentioning that overreliance on sepratrons can itself be an inefficient way of coping with other design flaws, as elsewise suggest above. That said, using sepratrons is not necessarily a bad thing. One possibility is to aim them differently, perhaps at 80 degrees to vertical instead of inward at hard 90 -- 10 degrees up would result in slight retrograde thrust, pushing the booster aftward much quicklier, 10 degrees down would blow the booster slightly forward to compensate for airstream drag during sep.) Similarly, altering your control inputs to allow for stage sep in the final moments BEFORE booster cutoff (allowing the boosters to still be under thrust at time of sep, allowing them to not be so violently smacked by the retrograde airstream) or, the opposite, cutting throttle at booster cutoff so as to coast through booster stage sep, so that can drift outward on decoupler force alone, before re-maxxing throttle to fly off (total coasting time typically ~3 seconds, +/-, if well timed).

[Starman4308]

This means that MechJeb is calculating terminal velocity based on how fast you'd have to be going for stock aerodynamics (digital mayonnaise) to cancel out your acceleration and give you a constant speed, which requires ENORMOUS comparative thrust. Since you're flying through FAR aerodynamics, which tends to be much less atmospheric drag than stock would present even at high altitudes, your MechJeb-governed throttle is WAY in excess of what would otherwise be called for to limit your acceleration to below terminal.

Small quibble: I'm pretty sure that, for your typical FAR ascent, you are never even close to terminal velocity. If you're going up, you pretty much by definition need a TWR >= 2 to hit terminal velocity.

The issue is that flying at terminal velocity is a very bad idea in FAR, because in FAR, the primary limitation is aerodynamic stress: go too fast, and the atmosphere will be very unforgiving of even the slightest deviation from prograde, and if you have DRE, your rocket is also likely to burn up. You build for max-Q, not for terminal velocity.

Ferram wrote a couple good articles, originally for RSS, but the theory is the same for any FAR installation. The big deal is that, with FAR, flying anywhere except directly prograde will cause aerodynamic wobbles, and if you go too far, your rocket will flip over with usually-catastrophic results. As such, your gravity turn is designed to gradually go down to a reasonable angle once you hit upper atmosphere, where you can start to have your own ideas about where your rocket should be going without worrying about aerodynamics.

[MisterFister]

Small quibble: I'm pretty sure that, for your typical FAR ascent, you are never even close to terminal velocity. If you're going up, you pretty much by definition need a TWR >= 2 to hit terminal velocity.

A fair point. In my quoted snippet, I was speaking explicitly toward the OP's indication that MechJeb was set to track terminal velocity, and what kind of flight behavior that would result in with a FAR-environment. Beyond that, you are exactly correct.

[endl]

i angled the seperatrons and dropped my TWR it seems to have made it stable, i tried changing the struts around and doing it without seperatrons but the SRB always wanted to make contact i cant avoid not using seperatrons so given that i tried all the other things how exactly do you build where you dont need them? short of hacking the ejection properties which is basically like using seperatrons to being with.

Edited October 23, 2014 by endl

[MisterFister]

i angled the seperatrons and dropped my TWR it seems to have made it stable, i tried changing the struts around and doing it without seperatrons but the SRB always wanted to make contact i can avoid not using seperatrons so given that i tried all the other things how exactly do you build where you dont need them? short of hacking the ejection properties which is basically like using seperatrons to being with.

Um?

Legibility notwithstanding, here's the real no-crap answer to your question: you provide zero useful information on your scenario. To give you ANY answer that is ANY more useful than the generalities already displayed in this thread, you absolutely must do one or more of the following (the more you do, the more helpful your answer):

1, post the craft file.

2, provide an extremely detailed and exhaustive list of your mods. Listing "FAR, MJ, and some other mods that are not in use with this craft file" will most definitely not cut it. "But some of these other mods won't have anything to do with the parts available." Perhaps narrowly accurate, but the mods modify the game, and as a result, modify your available options for a solution. Without this mod list, downloading the craft file will not accomplish anything.

3, describe this vessel's intended mission profile, preferably with the role it'll play in your overall save. (Specifying sandbox / classic / career could help, too.) "But what does that have to do with my boosters whacking into my fuselage?" It has everything to do with why you need such payload capacity as to necessitate boosters to begin with. -- If this is a career save, perhaps consider posting the savefile as well, so as to replicate your available tech tree and partlist.

4, provide detailed and annotated screenshots of your launch in progress, including, if possible, several angles during the booster sep. Yes, this will likely mean a few launch attempts, along with a likely several quickloads mid-launch (I suggest alt-quicksaving to a point when you have less than 150m/s remaining in your boosters -- you said you run MJ).

You're asking an extremely situational question. We can likely examine it and provide a detailed working answer that covers what you're asking, but it would involve us understanding your situation. For that, we need the above info.

Edited October 23, 2014 by MisterFister
suggested including savefile for tech tree purposes

[MarvinKitFox]

FAR, rockets, and seperatrons... My observations, based purely on trail-n-error

1) it works fine, except for staging off big SRB's while still climbing in lower soup-o-sphere.

2) side-mounted seperatron is *much* more vulnerable, can fail even at Q=14000. Top-mounted horizontal sep is good up to Q of about 28000.

thus: I typically only use seperatron on the S1 booster, when booster is radially mounted.

I mount one sep right on top, angled to thrust out and down, about 30degree off horizontal(orientation as at VAB, of course)

I make sure that at sep I have something else thrusting the main rocket, as that Seperatron *will* fail and explode about 1/2-3/4 second after firing. By then my rocket needs to be out of detonation range.

For virtually all other booster staging separations, i rather use a spot of rapid rotation's centrifugal force to "propel" the spend boosters away from the main rocket.

[endl]

You're asking an extremely situational question. We can likely examine it and provide a detailed working answer that covers what you're asking, but it would involve us understanding your situation. For that, we need the above info.

i posted the general rocket information and situation already, i notice this problem extends to all my rocket designs so i wanted to know the GENERAL issues i should be aware of so that i can apply this knowledge to all my rocket designs. basically from what i gather SRB separation is a tricky area no matter what and i should avoid it and use an inline delivery system if possible

[The_Rocketeer]

Um?

Legibility notwithstanding, here's the real no-crap answer to your question: you provide zero useful information on your scenario. To give you ANY answer that is ANY more useful than the generalities already displayed in this thread, you absolutely must do one or more of the following (the more you do, the more helpful your answer):

1, post the craft file.

2, provide an extremely detailed and exhaustive list of your mods. Listing "FAR, MJ, and some other mods that are not in use with this craft file" will most definitely not cut it. "But some of these other mods won't have anything to do with the parts available." Perhaps narrowly accurate, but the mods modify the game, and as a result, modify your available options for a solution. Without this mod list, downloading the craft file will not accomplish anything.

3, describe this vessel's intended mission profile, preferably with the role it'll play in your overall save. (Specifying sandbox / classic / career could help, too.) "But what does that have to do with my boosters whacking into my fuselage?" It has everything to do with why you need such payload capacity as to necessitate boosters to begin with. -- If this is a career save, perhaps consider posting the savefile as well, so as to replicate your available tech tree and partlist.

4, provide detailed and annotated screenshots of your launch in progress, including, if possible, several angles during the booster sep. Yes, this will likely mean a few launch attempts, along with a likely several quickloads mid-launch (I suggest alt-quicksaving to a point when you have less than 150m/s remaining in your boosters -- you said you run MJ).

You're asking an extremely situational question. We can likely examine it and provide a detailed working answer that covers what you're asking, but it would involve us understanding your situation. For that, we need the above info.

Totally unnecessary, unfriendly and uncalled for. The issue described isn't hard to understand, and the OP isn't asking for specific solutions to a problem with a particular craft.

SRB separation isn't necessarily problematic, but if parts are being destroyed by drag during launch I would immediately go to a lower powered ascent. The more you increase realism, the more realistic you should try to be - real launches don't take off at maximum possible thrust, they maximise fuel efficiency to gain as much altitude as possible at a steady climb-rate and then make a power-burn to accelerate to orbit speed. If your burning off parts, you're committing to too much acceleration in the thick atmosphere.

[NathanKell]

See HERE for Claw's plugin to fix the decoupler bug.

[sdj64]

You're using KW Rocketry, doesn't that still have the SRB nosecone with a built in separatron? A part designed EXACTLY for this problem...

Here's some general info:

From my somewhat limited knowledge of FAR, you need much less thrust than in stock to maintain a good climb rate.

MJ Terminal Velocity doesn't work with FAR.

If you're getting white mach effects or flames on the way up you're probably going too fast. Tweak down the thrust on your SRBs or just don't use them at all and add more fuel to the main stage.

Side mounted boosters are iffy at best in FAR since they can erratically swing around and hit each other or your rocket. The air doesn't slow them down very much so you have to angle separatrons both down and away.