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

[mreadshaw]

There's some brief documentation on it on the GitHub repository - it counts as a very strange object for the basic drag model , I guess. I've been looking at it also as I have a piece which should produce supersonic lift, but I have no idea what sort of numbers are sensible to put in. Anyway, you want FARBasicDragModel added explicitly and some curves set up as shown in the docs. Usually FAR just adds that to parts and leaves everything as default. Don't set things which aren't wings up using the wing module, there will be some awful confusion.

Interesting. I got the data from the instructions above your OP and graphed it in excel. Makes some curves that seem reasonable for AOA vs Cl. I'll test out some new numbers and see what I get. Thanks!

Edit: Actually not sure what the key is suppose to represent. If it is AOA is 0 lvl and 1 90 up? Because that wouldn't match up with the FAR graphs.

Edited February 20, 2015 by mreadshaw

[Jovus]

Ferram, your mod is turning me into an aerodynamics nut. Shame on you.

One question brought up by finding out new things: does FAR model lifting surface interaction like close coupling canards to deflect airflow onto the wing?

If so, would I be correct in assuming that the proper way to set this up would be to give the canards some -%AoA? Or am I misunderstanding how that would work?

Thanks again for all your help and this truly wonderful mod.

[KerbMav]

So here are some pictures of my nemesis of the week ...

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[tetryds]

So here are some pictures of my nemesis of the week ...

http://imgur.com/a/dvYNl

Pick that wing.

Place it on the back of the plane pointing up

[kcs123]

Yep, tetryds is right, you need a lot more vertical surfaces on tail to solve that sideslip/yaw issues.

[KerbMav]

OK, will try, but why is it rolling if I lack yaw control?

[tetryds]

OK, will try, but why is it rolling if I lack yaw control?

You sideslip, then the drag and lift on the craft when moving sideways is not even, which creates a torque that makes you roll, usually throwing you into a stall or instantly killing you.

It's a very simple solution, after you add that massive tail you can make it smaller until you are satisfied with it's size while still being stable.

[kcs123]

Slight dehadrial wing surfaces helps to rolling stability if you don't have enough vertical surfaces on tail. You can also add small vertical surfaces on wingtips to improve roll stability and that also adds a lot to wing lifting.

Roll stability, yaw/sideslip are in direct relations with vertical surfaces on your craft. Experiment with your designs to figure out how much of vertical surfaces you need and on what hull part is most effective.

Try to imagine that craft wings are made of simple string. Attach some small weight in middle of that string and imagine that weight can't deform that string - it remains straight all times. Now let's imagine that weight can freely move to either end of string across all length.

Now try to imagine that you hold ends of string and move around. How you expect that weight will move if you are unable to keep whole string perfectly leveled ?

How it will behave if string is perfectly straight and how it will behave if cetner of string is slightly lowered than edges of string ?

When you figure out answer for that, you will figure out why your craft tends to roll out of control.

[Van Disaster]

Ferram, your mod is turning me into an aerodynamics nut. Shame on you.

One question brought up by finding out new things: does FAR model lifting surface interaction like close coupling canards to deflect airflow onto the wing?

http://upload.wikimedia.org/wikipedia/commons/6/64/Rafale_-_RIAT_2009_%283751416421%29.jpg

If so, would I be correct in assuming that the proper way to set this up would be to give the canards some -%AoA? Or am I misunderstanding how that would work?

Thanks again for all your help and this truly wonderful mod.

As far as I know, not unless the surfaces actually overlap - although if you have a surface right in front of another surface and you stall the front one it appears to stall the one behind it also, so if you are going to use canards it might be an idea to have the main wing piece behind them be it's own strip the width of the canards, that way only part of the wing loses lift. If the canard actually overlaps the main wing then both will be a little less effective.

Which leads me to KerbMav's craft; unless those are non-lifting structural panels at the rear you have a biplane section, that's a big no-no.

[silentdeth]

I'm attempting to get more versed in FAR, and have a couple of questions: In stock it is easy to determine how much lifting surface you need, 1 unit of lift per metric ton. I'm wondering is there similar rule of thumb for FAR? Something like square meters of lifting surface per metric ton, or square meters of lifting surface per metric ton per unit of thrust? Since, as I understand it, the lift and drag coefficients in the graphs are dimensionless, it doesn't really tell me how much lift I am getting, just the relative lift to drag, correct?

[tetryds]

I'm attempting to get more versed in FAR, and have a couple of questions: In stock it is easy to determine how much lifting surface you need, 1 unit of lift per metric ton. I'm wondering is there similar rule of thumb for FAR? Something like square meters of lifting surface per metric ton, or square meters of lifting surface per metric ton per unit of thrust? Since, as I understand it, the lift and drag coefficients in the graphs are dimensionless, it doesn't really tell me how much lift I am getting, just the relative lift to drag, correct?

They are not dimensionless, but only the highest number shows up on the top left.

About "rule of thumb", no, not really, changes a lot with speed and a lot of other stuff.

My tip is, make it so the aspect ratio does not look too weird (ksc123, yeah, you).

If it's too little, add AoA, if too much, add dihedral and earn some roll stability (don't overdo it).

At the end of the day it's just a matter of how fast you can tap the keys and not let yourself go into a stall spin of death:

[Jovus]

I'm attempting to get more versed in FAR, and have a couple of questions: In stock it is easy to determine how much lifting surface you need, 1 unit of lift per metric ton. I'm wondering is there similar rule of thumb for FAR? Something like square meters of lifting surface per metric ton, or square meters of lifting surface per metric ton per unit of thrust? Since, as I understand it, the lift and drag coefficients in the graphs are dimensionless, it doesn't really tell me how much lift I am getting, just the relative lift to drag, correct?

The answer isn't quite as simple, but it does exist. On the static analysis page of the FAR analysis screen, in the section above all the green (or red) numbers, there are a bunch of readouts. One of them is AoA for level flight (or something like that). You want this to be a reasonable angle instead of an extreme one for all planned flight envelopes. (Reasonable is a broad term that requires judgment and testing, because you just ain't gonna make a plane that requires only 3 degrees while going Mach 2 at 30km.) At a bare minimum you must have this angle lower than the stalling angle as shown in the first screen.

[Van Disaster]

I'm attempting to get more versed in FAR, and have a couple of questions: In stock it is easy to determine how much lifting surface you need, 1 unit of lift per metric ton. I'm wondering is there similar rule of thumb for FAR? Something like square meters of lifting surface per metric ton, or square meters of lifting surface per metric ton per unit of thrust? Since, as I understand it, the lift and drag coefficients in the graphs are dimensionless, it doesn't really tell me how much lift I am getting, just the relative lift to drag, correct?

As has been said, enough to keep a sensible AoA in all the parts of the flight envelope you want to explore. Supersonic stalling is a different process to subsonic, so make sure you're checking the right speeds in all the tabs of the SPH tools. If your wing loading ( that's mass per unit area ) is too high you might also technically be able to fly, but be unable to take off in the available runway ( or land at a sane speed either ).

After a little while you'll be able to judge by eye - procedural wing mods help a lot with that. I generally only use the tools when something isn't performing as well as I think it can, other than a brief once-over to see if there's anything grossly wrong.

[palker]

Need help most of my control surfaces do not work only ones that work are procedural control surface and AVR8 winglet everything else is just not moving at all

this errors appear in KSP.log in large quantity. I looked at the config files for the parts and they seem to be nearly identical. Anybody has any idea what could be causing this?

[EXC 19:40:39.258] NullReferenceException: Object reference not set to an instance of an object

ferram4.FARControllableSurface.get_MovableSection ()

ferram4.FARControllableSurface.FixedUpdate ()

[EXC 19:40:39.259] NullReferenceException: Object reference not set to an instance of an object

ferram4.FARControllableSurface.get_MovableSection ()

ferram4.FARControllableSurface.FixedUpdate ()

[silentdeth]

Thanks for the many helpful responses.

[AlonzoTG]

Hey, I'm kinda puzzled as to why the IXS command module does NOT act as a fairing for delicate payload stored inside... Is there anything that can be done to fix it?

[Van Disaster]

You need to tell FAR it's a fairing/cargo bay, in the config in the KSC scene.

[eeveelution]

Anyone else having problems with pWings? I have the newest version of this and pWings, but they don't generate any lift (if I choose the aero viz for lift, they don't go blue at all) and the control surfaces only stall. Is there a config for pwings or something?

[Khazar]

Hi.

Could anyone help me with this design ?

Is there any way I can tune it to take off and fly ? Or is it dead End and I should think design something totally different ? In order to accomplish recon mision I need to fly quite a long distance (entire ocean), climb to 18,5 k meters and fly around some area. It's early stage of carreer mode, i'm restricted to 30 parts, 20t of weight and so on. I came with idea of plane equipped with 2 jet engines and one rocket engine in the middle which i would start to get 19k alt in area of recon. Is there any chance this could fly ??

Edited February 23, 2015 by Khazar

[futrtrubl]

Hi.

Could anyone help me with this design ?

http://s15.postimg.org/3o1glpffb/001.jpghttp://s15.postimg.org/uxcu07gif/002.jpghttp://s15.postimg.org/uzwpn1k5z/003.jpghttp://s15.postimg.org/pd0cpkhnb/004.jpg

Is there any way I can tune it to take off and fly ? Or is it dead End and I should think design something totally different ? In order to accomplish recon mision I need to fly quite a long distance (entire ocean), climb to 18,5 k meters and fly around some area. It's early stage of carreer mode, i'm restricted to 30 parts, 20t of weight and so on. I came with idea of plane equipped with 2 jet engines and one rocket engine in the middle which i would start to get 19k alt in area of recon. Is there any chance this could fly ??

What specifically is the problem with it?

[gmpd2000]

Hi.

Could anyone help me with this design ?

http://s15.postimg.org/3o1glpffb/001.jpghttp://s15.postimg.org/uxcu07gif/002.jpghttp://s15.postimg.org/uzwpn1k5z/003.jpghttp://s15.postimg.org/pd0cpkhnb/004.jpg

Is there any way I can tune it to take off and fly ? Or is it dead End and I should think design something totally different ? In order to accomplish recon mision I need to fly quite a long distance (entire ocean), climb to 18,5 k meters and fly around some area. It's early stage of carreer mode, i'm restricted to 30 parts, 20t of weight and so on. I came with idea of plane equipped with 2 jet engines and one rocket engine in the middle which i would start to get 19k alt in area of recon. Is there any chance this could fly ??

Just test it and see if it flies, if not, you should then request help.

[Khazar]

Well i doesn't fly. I just thought there must be some critical error i make and it would be obvious for you.

Despite many changes i made it just can't get off the ground. I sometimes could reach speeds of about 200 m/s and it still runs flat, or more recently it starts to roll left and right until it hits the ground.

Edited February 23, 2015 by Khazar

[Crzyrndm]

• Rear landing gear look like it may not be aligned with the direction of travel. If they aren't straight, they will flex and can cause all sorts of mischief
  
• Rear landing gear also looks to be a long way back. How close are they to the CoM? It will take a lot to rotate if there is significant seperation.
  
• Rear landing gear looks to be lower than the front. This will pitch the craft down on the runway and force it into the ground. You want to reverse that.
  
• That's an awful lot of jet fuel (3 tanks per basic jet). You can almost certainly drop that down to a single tank (each for structural purposes) and probably remove about half the fuel and still get to most places.
  

If problems persist:

• A side on screenshot with CoM and CoL indicators showing would be helpful
  
• A screenshot of the stability analysis (the one with all the numbers) run with 0km altitude and 0.35mach would also be helpful
  

[tetryds]

Well i doesn't fly. I just thought there must be some critical error i make and it would be obvious for you.

Despite many changes i made it just can't get off the ground. I sometimes could reach speeds of about 200 m/s and it still runs flat, or more recently it starts to roll left and right until it hits the ground.

I see a rocket engine there.

Your Center Of Mass is behind your Center Of Lift, almost certainly, that will cause your craft to flip over.

Also, you have roll instability, angle the tip of your wings upwards a bit.

Your craft is very heavy (assuming all tanks are full), thus you also need more tail, by that I mean bigger tail.

If you did not have the rocket fuel tanks on the middle you wouldn't need more tail, though.

A screenshot of the stability derivatives for 0m altitude Mach 0.35 and Mach 0.8, as well as a Steady-state "Sweep AoA" plot from 0 to 45 degrees, at Mach 0.35 and 200 pts would help a lot.

The "roll left and right" thing is because your landing gears are angled outwards.

Place them on the fuel tanks and you will fix that issue.

Edited February 23, 2015 by tetryds

[Sentmassen]

So I'm having a small issue and I think its that I'm just unfamiliar with FAR's proclivities (had it two days). I'm able to make planes that fly just fine, but I'm noticing a tendency for them to oscillate. Now they are not flexing structurally, its more that I feel like it constantly overcorrects when cruising, making the thing wobble. I feel like it stops when I'm in a solid climb so I think it has something to do when I'm trying to remain stable and floating around my minimum AoA. I'm not noticing any difference if I have the flight assist stuff on or not.