Question about Fairings.

[bandi94]

I watched numerous videos about KSP and i saw that many players use the fairings ( parts from modes ) so i was wondering if they really help during launch ( reducing air friction , etc so with the same amount of fuel i will be able to go higher) or they are used for aspect / reproducing real rocket models ?

Edited December 13, 2014 by bandi94

[mckamx]

I haven't done an engineering study on it, but the strong impression I get when using farings is that the drag is reduced. The main effect of this that I use is there is less of a tendency for rockets to want to tumble end-over-end as their speed increases in the mid-atmosphere.

EDIT:

Doing a bit more research, it appears that the drag effect of fairings in stock atmospheric model is minimal. According to MechJeb, the drag coefficient goes up slightly after jettisoning the fairings, but the effect is only about 1%.

Edited December 13, 2014 by mckamx
further information

[Trentendegreth]

most who use fairings are also using FAR/Near, though there are some who are just reproducing, depends on the person, but a fairing in stock Aerodynamics is more a hindrance because of the added weight.

[The_Rocketeer]

Stock physics doesn't account for slipstreaming parts - basically, all your drag coefficients are added up at the total decides drag force.

I haven't used fairings mods so I don't know if they count as massed parts or not. If they do, they'll add to overall drag. If not, they won't help drag in stock.

[Tex_NL]

Exactly. In the stock game drag is largely based on weight instead of shape and surface area. An empty fuel tank experiences less drag than the same tank full. Weird, yes, but that's the way the stock aerodynamics works. Adding fairings adds weight and therefore drag.

FAR/NEAR use a more realistic model. Now it's all about shape and surface. Adding fairings smooths the airflow. The reduced drag more than enough makes up for the slight increase in weight. And of course it looks a lot better.

[bandi94]

Thx for the informations, i will take a look at FAR. At the end i am looking for a realistic gameplay

[Tex_NL]

FAR can be a bit intimidating at first. If you find it too complex you could go for NEAR. A bit less realistic but much more forgiving and still a tremendous improvement over stock.

[Starman4308]

FAR can be a bit intimidating at first. If you find it too complex you could go for NEAR. A bit less realistic but much more forgiving and still a tremendous improvement over stock.

Maybe it's because I haven't built many planes yet, but I've never really had a problem with FAR vs. NEAR, and FAR does make some things easier (for example, more gentle reentries).

The single biggest piece of advice I can give is to forget everything you learned about how to get to LKO. Using FAR/NEAR, what you do instead is design for 1.2-1.6 TWR (I strongly recommend 1.2-1.4 unless you are using short-duration SRBs), and make sure you have fins at the bottom (to pull center of lift/pressure/drag behind center of mass). You then begin a true gravity turn: at 60-100 m/s, make a 2-5 degree turn (earlier and steeper for high TWR rockets), wait for your prograde vector to catch up, and then ride that prograde vector all the way through to upper atmosphere. Once you're at 20-30 km altitude, you can begin to have your own ideas about where to point your rocket, but until then, aerodynamics will screw you if you try to deviate from prograde by more than ~5 degrees*.

*Under 5 degrees, though, aerodynamics (if your rocket has fins) will tend to pull your rocket back to prograde. Thus, if you nailed the 2-5 degree turn at exactly the right moment, you can literally go "Look Ma, no hands!" all the way up.

The primary factors behind this all.

#1: FAR removes the souposphere, and you as such have much less atmospheric drag.

#2: With proper fin placement, aerodynamic stability will return you to prograde if you stay close to prograde.

#3: Regardless of fin placement, moving far from prograde in low atmosphere is a quick way to flip out.

#4: A consequence of #1-3: you've got to start your turn early, because otherwise you will waste a lot of dV going straight up, because you'll be unable to turn horizontal until very high atmosphere.

#5: Another consequence: you can generally get away with a lot less TWR than in stock, because you're not losing nearly as much to atmo drag.

#6: Build for 1.2-1.6 TWR (probably best in the 1.2-1.4 range), have fins at the bottom, and turn 2-5 degrees at 60-100 m/s.

#7: You will probably want to use KIDS (KSP Isp Difficulty Scaler) or some RSS config, because your dV to orbit will shrink drastically and make your LKO boosters seem laughably small. I personally use 6.4x RSS and RealFuels with the stockalike config.

*From personal experience of building many 1.6 TWR rockets: not worth it. You will struggle and curse to get your velocity vector closer to horizontal.

EDIT: Also, fairings. You'll need them for anything except already-aerodynamic payloads: I tend to remove fairings around 45km altitude, but I'm really not sure where the crossover point is. There will be some point at which the reduced atmo drag is no longer worth carrying the mass of the fairings.

Edited December 13, 2014 by Claw

[bandi94]

Yes i just downloaded FAR and houahhh a pin straight rocket starts wobbling short time after launch , huh. I think this is not made for me , at least for the heavy lifts as MKS modules , it will take to much time just to put them on LKO.

Well until now my LKO was : - straight up to 9-10k km , slow turn to 45 degree ( in 4-5 stepts) , got a 75-80 km periapsis , circularization node , and it was done.

[Claw]

Yes i just downloaded FAR and houahhh a pin straight rocket starts wobbling short time after launch , huh. I think this is not made for me , at least for the heavy lifts as MKS modules , it will take to much time just to put them on LKO.

Well until now my LKO was : - straight up to 9-10k km , slow turn to 45 degree ( in 4-5 stepts) , got a 75-80 km periapsis , circularization node , and it was done.

It would be helpful for us if you can post a picture of your wobbly rocket. Then people can offer you specific advice on how to adjust your rocket to work better in FAR or stock, whichever you prefer.

Cheers,

~Claw

Edited December 13, 2014 by Claw

[NathanKell]

bandi94, not sure what you mean by wobbling, but you will have to fly quite differently in FAR. You should pitch over to about 85 degrees once you reach 100m/s in speed, and then keep slowly pitching over until you're horizontal at about 40km, keeping inside the circle of the prograde marker the whole time. If your liftoff TWR is > 1.8, reduce it; 1.5 is the sweet spot, with 1.2 totally possible.

[Claw]

Off topic posts have been moved here: http://forum.kerbalspaceprogram.com/threads/102850-FAR-and-Stock-Drag-Calculations

Please take the discussion of FAR/Stock drag to that place, and leave this thread for directly helping bandi94.

Cheers,

~Claw

[Starman4308]

Off topic posts have been moved here: http://forum.kerbalspaceprogram.com/threads/102850-FAR-and-Stock-Drag-Calculations

Please take the discussion of FAR/Stock drag to that place, and leave this thread for directly helping bandi94.

Cheers,

~Claw

Err... the first post I had (vis-a-vis FAR ascents) seemed to be fairly relevant, as a poor ascent profile could explain wobbly rockets. Should I repost that section here?

One possible explanation I have is that his rocket lacks fins, which would cause a lot of wobbling in FAR, something I'd addressed in that post.

[OhioBob]

With all due respect, my posts were not about FAR vs. Stock. They were about whether it better to launch with a nose cone or not launch with a nose cone. Since the OP asked if fairing parts help during a launch, the discussion seemed to me to be exactly on topic.

For the record, I've never used FAR and I know almost nothing about it, so I don't see how I could possibly be having a FAR vs. Stock debate.

[Tex_NL]

Some posts became a bit technical but most others where completely ON TOPIC. Like when I tried to summarize to answer the OP question:

Long story short: With stock aerodynamics you're better of NOT using nose cones and/or fairings. In some very select cases you might get a tiny benefit but in general the pros don't outweigh the cons.

And the wobbling? I do have some idea's but to be sure I would need to see what you're doing.

Could be a high angle of attack, could be unstable payload, could be something completely different.

Edited December 13, 2014 by Tex_NL

[Claw]

Err... the first post I had (vis-a-vis FAR ascents) seemed to be fairly relevant, as a poor ascent profile could explain wobbly rockets.

Fair enough, it's been copied back. I also thought your post made a sensible starting point for a new thread, so it's also still there.

With all due respect, my posts were not about FAR vs. Stock. They were about whether it better to launch with a nose cone or not launch with a nose cone. Since the OP asked if fairing parts help during a launch, the discussion seemed to me to be exactly on topic.

Some posts became a bit technical but most others where completely ON TOPIC.

I agree with you guys that they are on-topic with the discussion of aerodynamics (which is why I didn't just delete them right off). I also tried to split the thread such that the other one made sense.

However, I can honestly say that I don't think this line of posts is really answering the guy's question. Is it relevant? Tangentially yes. But try to help the guy solve his problem, and solve the stock drag equation in another thread please. Discussions about nosecone drag doesn't really address his question about wobbly rockets.

Also, I ask that we get back to the topic of this thread again. If you guys have real heartburn, take it up with me via PM. Nobody is in trouble here, I'm just trying to help trim down the thread so the guy can find an answer outside of a sea of technical posts.

[OhioBob]

Fair enough. I'm not out to cause trouble.

[WuphonsReach]

FAR + Zero Point's fairings work very well.

The big no-no's with FAR:

- Not putting enough / big enough fins at the bottom of the rocket

- Unbalanced drag forces

- Not having enough RCS or not putting reaction wheels at the CoG

- Leaving the center of lift in front of the center of mass, then trying to turn below 25km

- Trying to turn right off the bat to 10 degrees

Ascents with FAR tend to be straight up affairs below 10km with no more then a 3-5 degree turn. Past 25-30km and you can start to make the turn for real and you are home free to go 45-60 degrees at around 45km+.

Once you get used to the ascent profile, FAR launches are fairly routine.

Planes are also not bad if you design properly and FAR comes with all sorts of nifty tools to help you design something stable, and then helps to fly it.

[bandi94]

Yes that 3-5 degree turn around 50-100m/s works very well , a smaller probe delivery rocket to Mun did almost all the job on it's own after i started at 50 m/s a 5 degree turn it was "no hands" up to 25 km from there i did a maneuver node.

That wobbling was from the SAS it looks that if i activate SAS on launch it will induce a nasty wobbling.

Thx.

[John FX]

Some tips for launching in FAR.

Always have fins on the bottom of your craft.

Start to tip over when you are at 40-50m/s. Just a bit then as your speed increases a bit more. If you turn too quickly then this can have bad effects. Just outside the orange circle is about right.

depending on how much thrust you have there will be a point between 75 degrees and 45 degrees that you will need to aim for (the more thrust you have the more you tip over)

On a TWR=2 craft at launch I am at 45 degrees by 6-7km...

Activate SAS to keep your heading. If your rocket starts to tip toward kerbin you may have tipped over too far.

When you are at about 330m/s mach forces kick in and your SAS will start to shake your craft more and more so turn it off (no really it is OK). By this point you should be more toward 45 degrees than anywhere else

as long as you still have fins on then they will keep you pointing prograde from this point on.

Keep prograde and adjust throttle to keep your time until Ap at about 50=60 seconds. When you are over 30km then you can move further than the orange circle with less bad effects. At 45km you can pretty much ognore it and burn in the direction you like.

when your Ap is roughly where you want it make a maneuver node to circularise and turn off your engines. You`ll have about 30 seconds until you need to burn if everything has gone right.

If the circularisation burn is for 300Dv or more then you needed to tip over more at the start. With practice you can get it down to 50m/s or less.