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

[praise the suuun]

@rhoark:

And a known issue that I've found: don't use a cargo bay as the root part of a ship. The entire ship will be unaffected by aerodynamics. This will be fixed in the next version.

Is this the reason why my center of lift stubbornly points up no matter where my wings are? the COM is inside some wayland cargo bays.

[ferram4]

@Dragon01: tan(x) doesn't explicitly appear anywhere; it's probably more likely that I'm taking the square root of 1 - cos²(x) somewhere and floating point errors are causing that to be negative.

@Samuel Jenks: No, that issue was fixed. The problem appears to be that you're trying to analyze your ship in the VAB where the air vector points downwards rather than out the front.

[praise the suuun]

@Dragon01: tan(x) doesn't explicitly appear anywhere; it's probably more likely that I'm taking the square root of 1 - cos²(x) somewhere and floating point errors are causing that to be negative.

@Samuel Jenks: No, that issue was fixed. The problem appears to be that you're trying to analyze your ship in the VAB where the air vector points downwards rather than out the front.

OH! So the design hangar used has a specific wind vector for either vertical rockets (VAB) or horizontal planes (SPH) but not both? That's amazing thank you so much ferram. I hope I can transport construction to the SPH without hiccup. I've seen those kind of bugs before.

[SchroedingersHat]

Does anyone know how to get around the strange bug with the COL going way off to one side on a symmetric craft?

It's happened on and off since 0.18 (whenever I have FAR installed), but lately it's gotten really bad.

Picking up most of the craft just past the root node and placing it again has often fixed it in the past (or at least the editor showed it as fixed and the craft behaved reasonably well). Lately the editor shows it as fixed when I do this (until I change anything else) and I've been getting (symmetrical, well strutted) craft that flip before they're off the runway or veer heavily to the left (it's always left) after takeoff.

It's been especially bad with the B9 cargo bays (attaching a wing anywhere near the bay seems to do it, although it happened on other craft too.

Edit: Fixed it for some craft by reinstalling everything and updating mods, didn't fix it for everything.

@Ferram: How does one reduce the amount of trim needed to sustain level flight above mach 2? Some of my craft are fairly good, some aren't great. The only active strategy I know of is to move the COL/COD up and the centre of thrust down, the rest is just lucking out.

Here's an example of one craft that could do with improvement (and I can't use my usual strategy of offsetting thrust/mass/drag because it needs to carry cargo).

Edited July 13, 2013 by SchroedingersHat

[praise the suuun]

@Ferram: How does one reduce the amount of trim needed to sustain level flight above mach 2? Some of my craft are fairly good, some aren't great. The only active strategy I know of is to move the COL/COD up and the centre of thrust down, the rest is just lucking out.

I've read others have had this issue but I cant recall how they fixed it. I've only had an unexplainable occurrence of non-symmetrical COL when I was placing symmetrical wings. Your picture shows that your issue is nothing like mine because my COL was all the way underneath one wing; off to a side. Sometimes it's a perspective illusion and the COM is off center not the COL which is what I found with my recent craft.

[taniwha]

SchroedingersHat: strategies for reducing needed trim:

• move CoL forward relative to CoM (remember: the CoL shifts backwards in supersonic flight), but still keep it behind for sub-sonic flight as we don't have active stabilization.
  
• move pitch control surfaces back from the CoM (this increases their torque).
  
• increase the surface area of the pitch control surfaces.
  
• increase the maximum deflection of the pitch control surfaces (avoid stall, though).
  

The craft is supported by the CoL, so the further back the CoL is from the CoM, the harder the pitch control surfaces need to work (ie, they need to apply more torque) to keep the nose up. The first point above reduces the needed torque, the others increase the available torque. This is why most planes have the elevators and rudder at the back of the plane and the ailerons near the center but near the wing tips: to maximize the torque where it's wanted and minimize it where it's not.

t = r x F (torque = radius cross force, or just t = r * F if everything is at right angles)

[ferram4]

A good thing to try for fixing trim issues is to change the angle of incidence of the tail / wing / canard to reduce the necessary trim for your vehicle. If you need downward trim when you first take off then you're probably fine.

[White Owl]

I ran into a problem with the latest version, where some procedural wing parts had almost no drag. It was a lot like flying one of the infinigliders in stock aerodynamics. Switching back to .9.5.1 fixed that problem.

I'm hesitant to share a craft file since I use so many mod parts, and I can't rule out a conflict with some other plugin(s). Maybe I'll try to duplicate the bug with a simpler vehicle.

[ferram4]

@White Owl: There were no changes to the WingAerodynamicModel class in the update, so either it is a problem with Procedural Wings or there is some other interaction there that you're not mentioning (such as cargo bay parts, which might cause a problem).

[SchroedingersHat]

I've read others have had this issue but I cant recall how they fixed it. I've only had an unexplainable occurrence of non-symmetrical COL when I was placing symmetrical wings. Your picture shows that your issue is nothing like mine because my COL was all the way underneath one wing; off to a side. Sometimes it's a perspective illusion and the COM is off center not the COL which is what I found with my recent craft.

Sorry, the picture was unrelated to the first issue; I wanted to ask ferram a question and didn't want to double post. That craft is fine at the moment, although it did exhibit the issue several times with the tail (requiring me to move it). The wide-body fuselage from the other series in the B9 pack is the one that consistently causes me issues (as well as sometimes just having it happen on stock parts until I change the craft).

The craft is supported by the CoL, so the further back the CoL is from the CoM, the harder the pitch control surfaces need to work (ie, they need to apply more torque) to keep the nose up. The first point above reduces the needed torque, the others increase the available torque. This is why most planes have the elevators and rudder at the back of the plane and the ailerons near the center but near the wing tips: to maximize the torque where it's wanted and minimize it where it's not.

t = r x F (torque = radius cross force, or just t = r * F if everything is at right angles)

Thanks, I was applying most of that already (most of my supersonic designs are a touch unstable just before they break the sound barrier) without considering it as 'strategies to try'. I guess I could move wings forward and increase the tail size to add more surfaces and more pitch authority.

A good thing to try for fixing trim issues is to change the angle of incidence of the tail / wing / canard to reduce the necessary trim for your vehicle. If you need downward trim when you first take off then you're probably fine.

That could help a lot. Any ideas on how to pitch parts less than 5 degrees for greater control? The other thing I was hoping for was that there was something I was missing about wing geometry and wing geometry vs tail geometry with regards to how far the CoL moves.

In trying to fix another issue I wound up modifying the tail of that design slightly for other reasons and it greatly improved the supersonic behavior (above mach 2) without impacting subsonic behavior. Any ideas why this would work so much better (CoL is right above and a tiny bit behind CoM on takeoff just like the other variant)?

Edited July 14, 2013 by SchroedingersHat

[ferram4]

I'd guess that one reason is that you now have significant thrust vectoring, which probably accounts for most of the changes.

The next possibility is that the elevators being closer together helps give them more control; the original design would have allowed pressure to "spill" from one surface to the other through the space in between them while the redesign makes that less of an issue.

Finally, the reduction in the tail chord would make the control surface a larger percentage of the tail, increasing their effectiveness. A thing to keep in mind is that at low angles of attack at supersonic speeds the lift coefficient of a wing is proportional to the angle between the airflow and a line connecting the leading edge and the trailing edge of that wing, while the cambering effect doesn't do anything to change lift at supersonic speeds. That means that a tail that is mostly control surface is a better choice for supersonic speeds while a tail that is mostly non-moving can be better at subsonic speeds.

Also, I don't think there's a way to get finer control of the default angle than 5 degrees without going into the craft file and messing with things there.

[praise the suuun]

Ferram, ive been chasing this issue about why the stock engines are frozen at 140 at ive found it finally when i trial and errored all my modulemanager.dll mods.... finally!

you have assigned the thrust value 140 to both the stock engines in FerramAerospaceResearch.cfg. may i ask your reasoning behind this value? are the engines overpowered? surely it balances out due to the heavy nature of all the stock parts compared to IRL aeroplane parts.

[ferram4]

The engines are way overpowered compared to real-life engines; they're comparable to the thrust produced by rocket engines. I actually think they should drop a bit further, but it just seems wrong anytime I do that.

Also, while the stock parts are "heavy" compared to real life airplane parts, that's because the stock parts are mostly chock full of fuel, while the cabin of a jet transport is notably not chock full of fuel. The stock wings seem to be lighter than they should be as well.

[asmi]

Hi ferram! I'm trying to "FARize" BobCat's Buran shuttle, but there seems to be the problem - lift vector is in odd position, and debug values in game (btw you should leave them on - very useful!) show that it is not just a visual glitch. Please take a look at screenshots: http://imgur.com/a/Nj48f

Configs for left and right wings are here: http://www.asmitech.com/Stuff/KSP/Buran_Configs.zip Thank you!

[praise the suuun]

The engines are way overpowered compared to real-life engines; they're comparable to the thrust produced by rocket engines. I actually think they should drop a bit further, but it just seems wrong anytime I do that.

Also, while the stock parts are "heavy" compared to real life airplane parts, that's because the stock parts are mostly chock full of fuel, while the cabin of a jet transport is notably not chock full of fuel. The stock wings seem to be lighter than they should be as well.

Yeah sure man I understand. I just need to be able to change the value for some cheaty mc cheap skate designs I think it would make a little more sense if you put the jet engine at a lower thrust value than the turbo engine as they're both at 140.

I cant wait till we get some fuel in our wings; it would probably act like a passive SAS wheel.

[ferram4]

@asmi: There are a few problems I can suspect:

Is the part origin at the center of the wing root? If not, this is a problem.

Is the wing attached through a stack attach node or a surface attach node? It should be using the latter, which FAR uses to get some information about how the wing is oriented. If this is all set up properly and there are still problems, try changing the sign on the "Up X" value; FAR could be placing the Aerodynamic Center of the wing in the wrong place.

If the right conditions aren't met, then FAR will cause some very weird things to happen.

[asmi]

@asmi: There are a few problems I can suspect:

Thank you for the quick response!

Is the part origin at the center of the wing root? If not, this is a problem.

I don't have source model files, but from what I see in config file (attach node coordinates) it most certainly isn't

Is the wing attached through a stack attach node or a surface attach node? It should be using the latter, which FAR uses to get some information about how the wing is oriented. If this is all set up properly and there are still problems, try changing the sign on the "Up X" value; FAR could be placing the Aerodynamic Center of the wing in the wrong place.

Again, looking at config files, I can tell that it's stack node.

Is there any way to make this work at all? Again, as I've said I have no control over the way it is built, I'm merely a user... This model is the only Shuttle that actually works and doesn't require a lot of skill to fly (I can fly it manually with no problems whatsoever), but with FAR installed it's completely unplayable - I can get it to orbit, but on reentry it turns tail-first and there is absolutely nothing I can do about that as far as controls go...

[ferram4]

You should try talking to the Bobcat guys about tweaking things to make it FAR-compatible. The origin would have to be moved for it to work, and that's something only the guys making the assets will be able to do. They'll have to change it to meet the aforementioned requirements for FAR to work properly, but I think they'd like to have more inter-mod compatibility and it is probably a small change compared with what they've already done. Try giving them the changes you made and requesting FAR compatibility; I'd be happy to help them out if they need clarifications on anything.

[rpayne88]

I don't have time to flip through 95 pages of this thread, so sorry if this has already been asked. Is it possible to build an SSTO with FAR. All my attempts seem to spin out at 12km despite the fact the only engines I'm running up there are rockets. I burn very little jet fuel, and this happens right after I ignite the rockets. The jets are off and rocket thrust is not hitting any other part of a perfectly symmetrical space craft. Another problem I've noticed is that the max speed I can get on jets is at most 400m/s, and this is usually while they are careening all over the place. This is a far cry from the 1500m/s at 25km suggested for SSTOs.

[ferram4]

First, you should try looking at some of the craft included with FAR; some of them are SSTOs. It's quite possible that your designs are becoming unstable as they drain rocket fuel and the CoM moves backwards.

As for getting a good top speed with jets, first, make sure you're using the turbojet engine, not the basic jet engine; the latter doesn't make much thrust beyond Mach 1. Second, make sure that you climb steadily up to the proper altitude and speed; you will not reach top speed on jets as quick as you are accustomed to. Third, make sure your vehicle is properly streamlined with highly swept wings; unswept wings and short, fat fuselages generate far more drag than swept wings with thin, long fuselages. Fourth, make sure that the rocket thrust vector passes through the CoM; make sure that the fuel drains in the way you expect it to. Fifth, make sure that the CoL isn't too far behind the CoM; this can make trimming the vehicle at supersonic speeds difficult.

There are also the suggestions in the readme file, but I assume that those didn't help if you're coming here.

Pictures will help a lot in diagnosing whatever problem you have, so please post those if you want more specific help.

[Van Disaster]

And it's quite possible to make SSTOs without highly swept wings too I'm going to be in trouble when you fix that. Maybe the p-wings will be able to make delta shapes without being thicker than the fuselage at the root by then...

For some reason recently I've been getting an extra 1-200m/s out of my planes, so they tend to transition at 1700m/s - lowest would be 21km, but I've been trying to use the jets at reduced throttle at higher altitudes, fairly successfully. The air is so thin up there the thrust/drag ratio doesn't seem to suffer much. The problem area will probably be around 10-12km and transonic, that's usually when keeping the nose up becomes a big problem. Pumping fuel around helps.

Here's a near-stock demo I did for something recently. Not much use other than flying around, but it's got no hidden mysteries.

Two FAR turboramjets, one nuclear rocket, three small stock rocket tanks, one Mk1 fuel tank, and the missing circular components would be TT inline wheels.

[asmi]

You should try talking to the Bobcat guys about tweaking things to make it FAR-compatible. The origin would have to be moved for it to work, and that's something only the guys making the assets will be able to do. They'll have to change it to meet the aforementioned requirements for FAR to work properly, but I think they'd like to have more inter-mod compatibility and it is probably a small change compared with what they've already done. Try giving them the changes you made and requesting FAR compatibility; I'd be happy to help them out if they need clarifications on anything.

I remember some time ago I've asked Bobcat about that and his position was that it only ensures it works in stock. I'll ask again, but if his position is still the same, I guess I'll have to fix FAR - since I'm developer myself it would be easier

[asmi]

Speaking of which, Ferram, some time ago I've got sick of Editor GUI resetting its' position every time I go to VAB, so I've made small change in source code to save this position in config file. Would you be interested in integrating this change into your source code? I'm sure I'm not the only one who is bothered with this That's just around 10 lines on code in one file, and four more in another

Edited July 16, 2013 by asmi

[Senshi]

Big Plus for the "make FAR GUI button fixed pos". I move it manually every single time because it's simply in the way where it is by default, so if FAR would remember GUI pos changes, that would be awesome .

[EvilNando]

I would like to know how to set up flaps on my airplane , step by step if possible

thanks