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[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18


ferram4

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1. Flip the whole capsule upside-down in VAB (airflow comes from top of VAB)

2. Ensure CoM is in front of aerodynamic center.

(3. check the flight analysis tab for Cm at high mach--but step 2 should ensure stability)

That doesn't mean it will *orient* to that attitude if it starts far from it, but it should ensure it will be stable *in* that attitude.

Noob questions:

1. What is the aerodynamic center? The CoM is currently centered pretty much right in the center of the heat shield. Actually after reading Ferram's reply it should be stable as is.

2. I haven't the slightest clue how to use the flight analysis tool. Are there any tutorials anywhere? I feel like I would benefit a lot by learning how to use it.

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The aerodynamic center is the same as the center of lift; it just doesn't imply that drag has no effect on stability like center of lift seems to (at least IMO).

The second Scott Manley video in the OP actually includes him going into a bit of detail on the Static Analysis tab. In the VAB, it works assuming the relative wind is from the ceiling, and that is what the static analysis tab will use as "0 AoA" there.

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Haha I love this mod :)

Just built a monster of a rocket today with over 440 parts and puts a 72.5 ton pay load into a 100x100 orbit

With only two stages :D and I still have a 3 with over 2200 d/v left.

It makes me laugh. From now on I shall be the wack job of FAR! XD

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The aerodynamic center is the same as the center of lift; it just doesn't imply that drag has no effect on stability like center of lift seems to (at least IMO).

The second Scott Manley video in the OP actually includes him going into a bit of detail on the Static Analysis tab. In the VAB, it works assuming the relative wind is from the ceiling, and that is what the static analysis tab will use as "0 AoA" there.

I'll have to watch that video. When I went to look at the center of lift it was off to the side a bit. Removing and replacing the procedural fairings seemed to remedy it a bit. Here it is now:

p7tXNyK.png

I think it just might work this time...

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So, a question: this plane seems to pitch and yaw fairly well, but right after takeoff it tends to roll uncontrollably. To provide a bit more information, the flaps are for roll and pitch, the rudders at the end of the wings are for roll and yaw. The two tailwings don't control anything.

FARQuestion.jpg

fadsfadss.jpg

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So, just messing with procedural fairings and FAR, and a flying "object" as a lifting body testbed, and I accidentally made an almost SSTO (periapsis of 78000 meters) Now if only I added some rockets to it...[...]

Cool idea. 'How intakes'? Realistically I think the intakes wouldn't be functioning well if at all if covered by the fairing though, even with some kind of suction assist. But I'm no rocket surgeon. I've got to try it something like it though.

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In this image, you can see intakes hiding there, I was really surprised that it worked. It worked even with a basic jet, at lower speeds that is. I was surprised the intakes worked too

2jJGs0q.png

Edited by broman
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Hi I could do with some advice on how to make this aircraft more stable at high speeds - mach 1.8+

Upon getting to mach 1.4 I begin to get bad Mw, Zu and N_beta values.

I think i also get pitch-roll and roll-yaw coupling. But I'm unsure on how to fix this intelligently. In have tried brute forcing it by adding every combination of surfaces I can think of but I have thus far not had any look.

Anyway any advice will be greatly appreciated.

This is the link to the imgur gallery

Imgur Gallery

Thanks

P.S. How do you embed Imgur gallery's correctly[--Imgur]http://imgur.com/a/hSC69/embed[/imgur--]

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First, it looks like you have way too much dihedral going on there; you can reduce it quite a bit and still get the same effect, and it might be part of your roll-yaw problems. The second is that the small section of biplane-like wings that you have going on near the fuselage are just going to hurt your stability and add more drag; get rid of them. I also get the feeling that the intakes under the cockpit are doing a lot to make the plane behave poorly.

Overall, the Xw and Zu values aren't as important as the other ones, so except for it becoming unstable in roll during sideslip, I think you're probably fine.

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does this mod have some sort of a problem with procedural fairings?

i've had a couple of (different) rockets now, that do a funky turn and the fairing snaps off, destroying the payload. never happened before FAR, and they launch fine without the fairings..... almost as if the fairings produce an obscene amount of drag.

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Thanks Ferram. I'll reduce the dihedral, remove the über cool bi-plane bit and sort out intakes under the cockpit and see if that sorts the problem.

One none related question does negative Xw translate to "aircaft decelerates when there is vertical velocity component"?

Thank you

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@Commissar: Using v0.12.5.2? If so, then it sounds like you're just overspeeding and allowing the forces on the fairings to become too strong. In that case, you need more aerodynamically shaped fairings, a lower angle of attack during flight, or a lower dynamic pressure (velocity^2 * density).

@Swifty: It means that it will be pushed backwards (in craft-relative space, not movement-relative space) as downwards velocity (in craf-relative space) increases. It basically means that pitching up creates less lift at high angles of attack and more drag at low angles of attack. Looking at it closer, I don't think the sign of that one matters too much.

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@Commissar: Using v0.12.5.2? If so, then it sounds like you're just overspeeding and allowing the forces on the fairings to become too strong. In that case, you need more aerodynamically shaped fairings, a lower angle of attack during flight, or a lower dynamic pressure (velocity^2 * density).

@Swifty: It means that it will be pushed backwards (in craft-relative space, not movement-relative space) as downwards velocity (in craf-relative space) increases. It basically means that pitching up creates less lift at high angles of attack and more drag at low angles of attack. Looking at it closer, I don't think the sign of that one matters too much.

wat? it is a 3.5m diameter fairing, the same as the rocket beneath. i'm below what ferram says is terminal velocity as well. I should mention that this is a VAB, as opposed to SPH rocket.

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It would help to have a picture of your rocket!

Generally speaking; without FAR, KSPs sticky atmosphere means you can get away with a lot that wouldn't work in real life. The atmosphere slows you down so much that it is hard to get enough airspeed (during vertical launch) to break up any reasonable rocket design. When you add FAR you are liable to find your liftoff velocity climbs far faster than you are used to, so any instability results in a very high airspeed breakup - just like happens in real life if rocket stacks have any instability.

As for where the instability comes from, designs that are stable in stock will be unstable under FAR, and vice-versa.

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@Commissar: I'm asking if you're using the most recent version of FAR to rule out old bugs. You'd be surprised how many people come in complaining about issues that would be solved if they updated.

Also, I am going to need to see pictures, because I can't just keep guessing what you're doing. Hell, it could be the payload is failing and then crashing into the fairings for all I know.

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@Commissar: I'm asking if you're using the most recent version of FAR to rule out old bugs. You'd be surprised how many people come in complaining about issues that would be solved if they updated.

Also, I am going to need to see pictures, because I can't just keep guessing what you're doing. Hell, it could be the payload is failing and then crashing into the fairings for all I know.

well, it's happened on multiple different payloads, the first was my orbital tug, which launched fine w/o a fairing. anyhow, this is a version, where I stuck a smaller fairing on. I just installed FAR maybe a week ago, but I see no way of telling what version it is. not in the xml, not in the .cfg....

bxdq0M0.png

edit: i see, it's in the UI. yes, it's 0.12.5.2

Edited by Commissar
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The version number is on the top of the GUI that you minimized, like pretty much every other mod with a GUI out there.

Oh, I see the issue. You have a stupid high TWR and you're letting MechJeb try to fly it into orbit. Let me guess, it's fine up until the "gravity turn" when it all falls apart? Or it falls apart after MJ gets a good oscillation going? Get rid of the boosters, get the TWR down to about 1.5, keep it aimed prograde, and start your gravity turn at about 100 m/s (wherever that ends up being). You don't want to try and reach terminal velocity, because your rocket will tend to fly apart if you get near it. If you insist on using the autopilot, change the ascent path settings so that it actually follows a gravity turn (you'll need trial and error I'm afraid) rather than the goofy ascent profile that most people fly in stock.

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The version number is on the top of the GUI that you minimized, like pretty much every other mod with a GUI out there.

Oh, I see the issue. You have a stupid high TWR and you're letting MechJeb try to fly it into orbit. Let me guess, it's fine up until the "gravity turn" when it all falls apart? Or it falls apart after MJ gets a good oscillation going? Get rid of the boosters, get the TWR down to about 1.5, keep it aimed prograde, and start your gravity turn at about 100 m/s (wherever that ends up being). You don't want to try and reach terminal velocity, because your rocket will tend to fly apart if you get near it. If you insist on using the autopilot, change the ascent path settings so that it actually follows a gravity turn (you'll need trial and error I'm afraid) rather than the goofy ascent profile that most people fly in stock.

yeah. the TWR was only 2.42. it's a standardized design I use for most launches over 50t. i fixed it by changing the ascent to a 75deg turn. makes sense. thanks.

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Hey, sorry it's taking longer than I expected to update the tutorial vid. I'm going to do some research so I know a bit more about what I'm saying, and I'm going to plan it out and polish it a little more thoroughly (Rather than doing the whole thing in one take, going off a rough outline I'd written out a couple days before).

In the meantime, I'll add some annotations to the original vid to correct a few things!

Edit: Actually, I had a question: I think I understand the difference between CoL and CoP, but which does the blue marker in KSP indicate? I'm guessing CoP, because as I rotate a rocket in small increments in the VAB it shows up pretty far outside the rocket at times.

Also, my "unstable rocket" wasn't quite unstable enough for my liking-- does anyone have a rocket that would work fine in the stock game, but reliably flips out with FAR? I may just take my original design, use the half-height grey tanks, and go up to 6 or 8 way asparagus staging. A higher TWR, lower CG, and more drag up high should do the trick...

Edited by Traches
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<a  href=%7Boption%7Dhttp://i.imgur.com/AwcFA5p.jpg' alt='AwcFA5p.jpg'>

Universe background does not appear in game but at start screen and i get these weird aero dynamic problems when launching a Mk3 ravenspear i think it was.

-List of all the stuff in gamedata

Toolbar

AIES_Aerospace

blizzy´s achievements

DeadlyReentry

Engineer redux

ExtraplanetaryLaunchpads

FASA

FerramAerospaceResearch

KerbalJointReinforcement

Kethane

KWRocketry

LifeSupport ECLSS

MechJeb2 ( i know it affect the numbers werid but my vehicle got ripped apart )

ModularFuelTanks

MultipleSavesDA

NavyFish docking helper

NovaPunch2

PersistentTrails

-RealismOverhaul (mini pack from medievalnerd Real progressions LITE Milestone18b i belive )

Realsolarsystem

RPL Tweak pack by nathankell and medinerd

SceneJumper

Stretchytanks

thunderaerospace

treeloader

Triggertech

ModuleManager_1_5_6.dll

toolbar-settings.dat

000_toolbar

Edited by tryder
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Been having a lot of fun with this, DRE, Procedural Wing & Taverio's ramjet, trying to design a stable ~hypersonic drone. :)

I managed to get all numbers but one into the green for a M4+ prototype with the aerodynamic center (what is even the proper term for the blue ball in KSP?) almost inside the CoM.

Do you have any PW supersonic designs you're particularly proud of, ferram?

Edited by MAKC
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@Traches: It's supposed to be CoL, but the CoL only stays in one place for linear aerodynamics; it can actually shift quite a bit for nonlinear aerodynamics, and body lift + drag happens to be highly nonlinear.

It's actually quite hard to build an unstable rocket on purpose; it's a little bit easier than it should be given the mass distribution of rockets (engines are way too heavy) to try and make it easier for people. Given how tall and narrow your payload is it might actually not be possible to make an unstable launcher for it. I'd try building the launcher around the payload rather than under it, since that's something that's encouraged by stock aerodynamics.

@tryder: I need an output_log.txt and I need to know the version numbers of all the mods you're using. Honestly, this doesn't look like a problem with FAR, this looks like you're using some other mod that hasn't been updated for KSP 0.23. Odds are if you're still using the old ModularFuelTanks that's part of the problem. Update your mods.

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