Early plane building with FAR

[Rizzee]

Hello, I'm fairly new to KSP(just coming up to 100 hours) and have mostly played just stock. However I decided to restart playing with mods that add more flavour to the career mode as well as playing it on harder settings.

Anyway more to the point one of the mods I picked up was FAR and I've been having trouble building an effective "glider" type plane for those early survey Kerbin contracts. Everything I come up with just seems to get a few hundred metres up and then spin and/or flip out of control due to stalling, regardless of thrust. I've spent the past few hours trying to figure it out through trial and error and just can't seem to build anything this early on with FAR enabled with regards to the SPH. Is it a case of just needing more parts or am I doing something wrong?

This is the craft file of what I've been trying to make work. https://drive.google.com/file/d/0BxtRUw90vYxidU1heHdBV3pQams/view?usp=sharing

(The stock, unrealistic aerodynamics allow this to fly really easily but then, that makes fairings and stuff useless which is why I became interested in FAR.)

Edited February 1, 2015 by Rizzee

[Taki117]

What's your advent path look like? With far you have to be gentle, or slow. Too far from prograde and you will flip. Too slow and you stall. Its all about the pilot. Treat her right and she'll do what you need.

[Zuqq]

With FAR, make use of the graphs and stability derivative calculation page. These will help you figure out if your plane will be stable at specific speeds, and altitudes. The graph will help you understand your max AOA. Make sure CoL is slightly behind your CoM (and DCoM - RCSBuildAid mod helps with this).

Here is a link for the FAR Wiki explaining the symbols and what not

[Alshain]

The best thing you can do with the FAR graphs and numbers is ignore them.

• Center of Lift slightly behind Center of Mass
  
• Rear landing gear in about the same place. (It's a lever and the wheels are the fulcrum, it needs to pivot)
  
• For small low speed planes, drop all the wing strength values to 0.5 on the wings and control surfaces or your plane may be too heavy.
  
• Set your control surfaces to be specific for Roll on the wings, Pitch on horizontal stabilizer, Yaw on the vertical stabilizer. For beginners just do 100% and 0%, forget everything in between... for now.
  
• Flaps help you take off without pulling back on the stick as far and help you stay in the air at slower speeds, making it easier to land successfully.
  
• Spoilers help you slow down quickly, mostly after touching down.
  

If you need an example of a good early glider, try this, but don't just take it, learn from it (note: you can modify that to be "more early career" very easy, just get rid of the battery mostly, it doesn't change the mass that much).

Edited February 2, 2015 by Alshain

[luckyhendrix]

The best thing you can do with the FAR graphs and numbers is ignore them.

That's a bit harsh, don't you think ? xD

I do agree that for a beginner they are not the easiest thing to get. But in the end they can save you a lot of tries and attempts to fly a bad designed plane

[Alshain]

That's a bit harsh, don't you think ? xD

I do agree that for a beginner they are not the easiest thing to get. But in the end they can save you a lot of tries and attempts to fly a bad designed plane

No, not harsh at all. They are completely unnecessary. All they will do is lead you down a path of misery trying to get them to be "perfect", when it really just isn't that difficult to build a plane. Just because those numbers are red doesn't mean a thing, even ferram4 told me that some of those numbers are often red and it's not bad.

[Zuqq]

The best thing you can do with the FAR graphs and numbers is ignore them.

-snip-

All good points mentioned but the quoted part I definitely don't agree with and don't understand why you would ignore these awesome tools if you ddecided to go with FAR. If you don't want the graphs and stability derivatives, go with NEAR.

. In reality, you don't need to understand how the numbers are derived or even what the numbers mean. You can click the button, and if the numbers are green you are good to go. If the numbers are red, you will have problems. Input different speeds and altitudes. Quite easy. If numbers are red, fiddle with stuff until they turm green. Without any prior knowledge, you will slowly learn that when a certain number is red - mess with your wings. Or if a different number is red, mess with the tail. (Edit: As well as which numbers you can safely ignore, or worry less about)

The graph is also quite easy to read and gives quick essential info about your design you wouldn't otherwise know unless you test fairly extensively. You want the yellow line below the x-axis. Input an angle of attack range to see up to what angle your plane is stable, or you can input a mach range.

Scott Manley has a video glossing over the graph and stability page, as well as building with FAR. I'm sure there are thousands of other videos giving FAR tutorials.

Edit: As you replied while I was writing this I will also adress the certain red number thing:

Zq and Xq aren't really all that important, but they can make minor changes to the way a plane behaves under very large amounts of pitching.

Generally, Zu and Xw can be disregarded if their magnitudes are much less than the other ones. They basically consider how much additional velocity affects lift and how much additional angle of attack affects velocity, respectively; they can be the "wrong" sign at some angles of attack and Mach numbers due to Mach effects or nonlinear body drag."

Source

So yes, some of the numbers don't have a lot of effect, others however do.

Edited February 2, 2015 by Zuqq

[Alshain]

All good points mentioned but the quoted part I definitely don't agree with and don't understand why you would ignore these awesome tools if you ddecided to go with FAR. If you don't want the graphs and stability derivatives, go with NEAR.

NEAR is not FAR without graphs, that's like saying if you don't like eating the apple skin, eat a banana.

. In reality, you don't need to understand how the numbers are derived or even what the numbers mean. You can click the button, and if the numbers are green you are good to go. If the numbers are red, you will have problems. Input different speeds and altitudes. Quite easy. If numbers are red, fiddle with stuff until they turm green. Without any prior knowledge, you will slowly learn that when a certain number is red - mess with your wings. Or if a different number is red, mess with the tail. (Edit: As well as which numbers you can safely ignore, or worry less about)

-snip-

My whole point was they are completely unnecessary. If your center of lift has the correct relationship to the center of mass and your wings are a good proportion to mass of the craft, it will fly without ever looking at the graphs and without problems.

EDIT: And of course if you don't have some other weird thing, like forward drag or asymmetric thrust of course but all of those are intuitive too.

Note to OP: Keep the intakes toward the back and your engines symmetrical. Left that off my list. The intakes are not a hard rule, you can have some forward of the Center of mass, but too far forward and it will hurt.

Edited February 2, 2015 by Alshain

[Zuqq]

I wouldn't say they are that far apart... The NEAR page lists only 4 major differences between FAR and NEAR, one of which being the analysis tools, the others being things which are intended to make FAR more complicated (physics based on mach, more complicated lift/drag ratios), hence the graphs.

But I do understand your point. The graphs and stability page is not essential to building a plane. But I find it does give me a lot more insight in how to go about building my planes.

I wouldn't go as far as to say they are useless and should be ignored.

[Alshain]

I wouldn't say they are that far apart... The NEAR page lists only 4 major differences between FAR and NEAR, one of which being the analysis tools, the others being things which are intended to make FAR more complicated (physics based on mach, more complicated lift/drag ratios), hence the graphs.

They aren't very far apart but mach effects and aerodynamic dis-assembly are big features that have nothing to do with graphs.

But I do understand your point. The graphs and stability page is not essential to building a plane. But I find it does give me a lot more insight in how to go about building my planes.

I wouldn't go as far as to say they are useless and should be ignored.

Well, if you enjoy obsessing over green numbers, it's your game. All I'm saying is they aren't needed.

[KerikBalm]

Actually, I found them very helpful, my latest lifter is "stable" but only within a certain mach regime at each altitude. I couln't get the darn thing to orbit it kept oscilating really ba and becoming unstable.

I went to the stability derivates page, and found that below certain mach numbers at certain altitudes, it was unstable. I adopted a shallower ascent to allow me to reach sufficient mach numbers before getting too high, and I was able to make it to orbit (the other problem was that my wings, for stability purposes, were above the CoT, and they were big enough to affect the thrust, and my rockets were generating a significant pitching moment which made the circularization burn (small as it was) challenging as well.

Once I got to orbit, I was able to tell the thrust imbalance apart from the aeroforces, and slightly angle the rocket engines, and now my SSTO works much better.

Last run was 122 tons to orbit...

[Zuqq]

They aren't very far apart but mach effects and aerodynamic dis-assembly are big features that have nothing to do with graphs.

Well, if you enjoy obsessing over green numbers, it's your game. All I'm saying is they aren't needed.

Mach and dis-assembly have lots to do with the graphs. The graphs show how your plane behaves at different mach values... It's right there in the name so to speak. Planes that are stable below mach 1 may suddenly spin out when reaching mach 1. Too much G causes dis-assembly, which you can get an idea from when the drag on your graph triples at a certain AoA.

[Rizzee]

I figured out the problem. A mix of being a bad pilot and not viewing the graphs while the craft was in the horizontal position(my launch position is vertical due to not being able to actually use the runway without aircraft gear) I was planning to say that I'd actually already done what people had advise which was read guides and watch videos, but the problem I appeared to experiencing(last night) was that I couldn't build a stable flyable aircraft with very early parts. I was able to build stuff in sandbox where I have access to all the parts in the game.

Anyways the issue seems to mostly be coming from the actual launch and not the stability of the craft itself as I've actually managed to get to successfully glide, pretty well actually ableit only for a short distance. But it's progress. God FAR is much harder than the stock system for planes.

For those intrigued, this is a image of the glider. http://i.imgur.com/47XZKD1.jpg Pretty simple build, but like I said, it's very early career.

[KerbMav]

My luck/aptitude at building planes goes up and down ... there was a time I could build planes that at least just flew, but reaching space I only managed with two designs and these days I am lucky if my planes make to the ocean!

Regarding FAR/NEAR: NEAR - according to what I read - comes without the graphs window in the editor and has mach effects as well as aerodynamic disintegration disabled. But FAR has optional settings for the latter two and you can just keep the window closed too. Someone has a signature quoting Ferram saying basically that NEAR is FAR without looking like FAR/the graphs and people just think it is the easier one. So ... huh ... ?

Putting the COL a bit/right/just/... behind the COM is one of the first things in airplane building it seems - but what is a bit/right/just/...?

And how far may the COM move as fuel gets used up?

[Zuqq]

-snip-

Putting the COL a bit/right/just/... behind the COM is one of the first things in airplane building it seems - but what is a bit/right/just/...?

And how far may the COM move as fuel gets used up?

For your first question, right/just/a bit behind the CoM is really up to you.I usually have half of my lift marker or so behind the DCoM.. Which may or may not be halfway or 3/4 of the way behind the CoM. (I try to build planes as balanced as possible). In reality, as long as its behind its not that big of a deal. Your CoL shifts about with speed and what not

As for your second question, a mod called RCSBuildAid will show you how your CoM moves when tanks are dry. Or you can manually right click on all the tanks and drain them of fuel to see where you CoM ends up.

I figured out the problem. A mix of being a bad pilot and not viewing the graphs while the craft was in the horizontal position(my launch position is vertical due to not being able to actually use the runway without aircraft gear) I was planning to say that I'd actually already done what people had advise which was read guides and watch videos, but the problem I appeared to experiencing(last night) was that I couldn't build a stable flyable aircraft with very early parts. I was able to build stuff in sandbox where I have access to all the parts in the game.

Anyways the issue seems to mostly be coming from the actual launch and not the stability of the craft itself as I've actually managed to get to successfully glide, pretty well actually ableit only for a short distance. But it's progress. God FAR is much harder than the stock system for planes.

For those intrigued, this is a image of the glider. http://i.imgur.com/47XZKD1.jpg Pretty simple build, but like I said, it's very early career.

Glad you got things working somewhat. It can be hard to vertically launch a plane sometimes as you generally have to travel through some unstable attitudes before you are in stable flight again.

It may help if your glider had a bit more wingspan on it by the looks of it. But, it can definitely be a challange making planes with low tier tech.

Edited February 3, 2015 by Zuqq

[Hodo]

I can say from experience with FAR, the two biggest helpers in aircraft building is RCS build aide and TAC Fuel Balancer.

With those two mods you can check your dry CoM and Loaded CoM, you can also adjust your fuel load in flight to keep your CoM where you want it in relation to your CoL. Real aircraft do these things in flight automatically now but it is something that isn't possible in KSP without mods. I like to leave one fuel tank empty or half empty depending on the craft to shift my CoM forward or back depending on the craft and the design.

This is an old picture from two versions ago but the principle is still the same.