ferram4

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

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Err... I did say Jool's atmos seems to start at 200km

And he said why it might seem that way.

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@jofwu: Planes built without accounting for the same kind of body lift and with no need to area rule don't work well? That's not surprising at all. The stock craft are being redesigned. Yes, things are changing that much.

Could anybody help me out with some pointers? (Having trouble designing something stable with the dev build.) I wanted to design a simple subsonic airplane to complete easy survey contracts near KSC. I'm relatively early on in a career so I don't have ALL the parts to work with. But I have the basics. My plane's body wasn't much different from Nerd1000's in this post. It was perhaps a bit shorter, and with the mk1 cockpit in front of the mk1 inline cockpit (wanted room for a passenger). So... the two cockpits at the front followed by 2 or three tanks, one of the inline air intakes, and the basic jet engine. A pointy cylinder with an engine on the back.

From there, no matter how I positioned my various wings and such, I just couldn't get the thing to be stable. I've used FAR in the past and never had so much trouble. The biggest problem was that I couldn't get my pitching moment coefficient to be negative. Kept wanting to do back flips when I tested it. But I could go so far as to put the wings at the tail end of the craft and *still* have this problem. Am I missing something?

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@jofwu - check link in my signature, although those tips are from older FAR, doubt that pitching issue has changed so much. It is just fine tuning center of mass, main wing lift and lift from tail surfaces or canards near nose.

I suggest to deatach tail (if possible) to see where center of lift from maing wings only is. It should be behind center of mass. Then add tail again and fine tune pitching moment. Like everyone else I'm waiting for nuFAR stable release, but if I find some more time I will try dev version and update some of my crafts.

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Could anybody help me out with some pointers? (Having trouble designing something stable with the dev build.) I wanted to design a simple subsonic airplane to complete easy survey contracts near KSC. I'm relatively early on in a career so I don't have ALL the parts to work with. But I have the basics. My plane's body wasn't much different from Nerd1000's in this post. It was perhaps a bit shorter, and with the mk1 cockpit in front of the mk1 inline cockpit (wanted room for a passenger). So... the two cockpits at the front followed by 2 or three tanks, one of the inline air intakes, and the basic jet engine. A pointy cylinder with an engine on the back.

From there, no matter how I positioned my various wings and such, I just couldn't get the thing to be stable. I've used FAR in the past and never had so much trouble. The biggest problem was that I couldn't get my pitching moment coefficient to be negative. Kept wanting to do back flips when I tested it. But I could go so far as to put the wings at the tail end of the craft and *still* have this problem. Am I missing something?

Don't worry about the numbers, they are wrong :P

That is what you get for playing on a WIP, have you tried flying that plane?

COL is also broken, but apparently the AoA sweep is "working", you can use it to check if your COL is not too far forward.

Or better, follow the rule of thumb:

-Put main wings aligned with the COL

-Add horizontal stabilizers.

-Add control surfaces.

Steps 2 and 3 brings the COL back, since it was already at the COM it's certainly behind it now ;)

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I should clarify- Lowering the gear reduced wave drag before I added the bulges. Once the bulges were in place lowering the gear increased the wave drag area, which is more in line with what you'd expect. I suspect that my landing gears just happened to be in the right place to reduce the wave drag when they were deployed- a fact that was no doubt partly a result of my forgetting to retract the gear while I was working on the layout.

An example of the 'happy accident' effect is perhaps illustrated by that bulge I added just below and in front of the cockpit. It's placed directly over the nose wheel because it turns out that the nose gear was in just the right place to smooth out the changes in cross section caused by the cockpit when it was extended. The bulge emulates that effect while keeping the gear retracted.

Edit: I fixed my grammar.

May be a bit late to the party, but it depends on the gear you're using. One of the landing gears has, for some reason, more drag when it is put away rather than when deployed. It's a stock bug, I believe it's mentioned more precisely in the Stock Bug Fix sticky. Take a look at that and see if it's the offending gear, it probably is not nuFAR at fault in that case.

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Could anybody help me out with some pointers?

Step 1) Wait for the official release of NuFAR. The dev build is a dev build for a reason. You can't design properly when you're not sure if the problem is the plane or the physics.

Step 2) See the build guides on my Youtube channel and in the first few posts of the Kerbodyne thread (both linked below). However, as with every other KSP/FAR guide you'll find: they were written for oldFAR. How much of that advice still applies in NuFAR, we'll just have to wait and see.

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@ferram4: I havent seen any mention of this subject. Everybody seems to be going CRAAAZY about the changes to supersonic and transsonic aerodynamics (that I love to bits, btw.)

Yesterday I've tried gliding an airplane built for supersonic testing of the new FAR aero and the nuStock heating mechanics back to base. I managed to maintain Mach 0.8 with a dive angle of 2° (!). Craft weighs about 20t and has 8.1 m^2 max crossection area and 2.5 m^2 Mach 1 wave drag area. Is nuFAR supposed to have such low subsonic drag if the aircraft is built correctly? (Flight data tells me I have a terminal velocity of 700 m/s at 2000m altitude).

Another thing I noticed is that the indicator for the center of aerodynamic forces isn't where it's supposed to be. The plane shown in the pictures (imgur album: http://imgur.com/a/FspgS) has it in front of the CoM indicator and it flies stable subsonic and supersonic.

I can further confirm that the voxelbased aero works together with TweakScale. The elevators are the resized small tail fins.

On the stock turbo jet I can get it up to mach 3.6 (where it combusts because of the new heat mechanics). It has a range of 13000 km according to the FAR flight data.

Greeting

4plains

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Yeah, actually placing the aerodynamic center in the right place is actually a difficult challenge to get right, unfortunately. The indicator is currently wherever the forces are applied, but with a moment attached that can also vary with angle of attack, and that kind of defeats the purpose of using it for stability. Frankly, I prefer the graphs myself, they're clearer, but people want indicators, so I'll see what I can do.

The subsonic zero-lift drag is probably a little low simply because I'm not accounting for all the interference drag and what not, I may be able to add a factor to increase that based on variations from a nice, simple body of revolution, but I don't know how bad that might be.

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You could average the CoL for some reasonable AoA's, or just display the one for 0 AoA. I see it as a quick way of assessing stability, not really meant to be the end all be all for it. The graphs are there for a reason after all.

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Yeah, but remember not everybody can read a graph straight away, that would make the learning curve steeper.

And often what you need is just tweak a few things, not needing to go read the graphs every time is way faster, esp when you are making subsonic designs anyway.

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You could average the CoL for some reasonable AoA's, or just display the one for 0 AoA. I see it as a quick way of assessing stability, not really meant to be the end all be all for it. The graphs are there for a reason after all.

There is no lift at zero AoA unless you angle the wings. Ideally it would be for small AoA, but it's not immediately apparent to me that this would even work - if CoP changes with AoA^2 (to leading order) then you can make a good approximation but if it changes with AoA (to leading order) then there's not much you can do.

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Yeah, actually placing the aerodynamic center in the right place is actually a difficult challenge to get right, unfortunately. The indicator is currently wherever the forces are applied, but with a moment attached that can also vary with angle of attack, and that kind of defeats the purpose of using it for stability. Frankly, I prefer the graphs myself, they're clearer, but people want indicators, so I'll see what I can do.
How was it done in old FAR? Because it seemed to mostly work.

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ferram, I'm all for as much realism as possible. A realistic atmospheric model is great.

But that's only useful when we can also design and build realistic planes and rockets. Which we cannot.

So, I would really like it when I could make mostly-realistic based stuff (according to what components I have available), that would behave as realistic as possible. Which almost certainly requires a drag model, especially supersonic, that is more lenient than what would be realistic.

Make it configurable, if you like.

I would prefer that the whole Kerbal solar system would be an exact copy of ours, and that all parts would be procedurally generated and realistic, with the required cross-sections. But until that's possible (and without the stupid joints between parts, give me a structural skeleton or make things rigid), we won't be able to build the realistic vehicles needed to enjoy you greatly appreciated mod as it requires. Because if it would be realistic, it would mostly severely limit the craft you could make that don't explosively disintegrate.

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If you don't want realistic aerodynamics, then why are you even looking at FAR? That's what NEAR is for.

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Hi, great mod first at all!

Just a simple question and excuse me if i'm not the first, is this mod the closest to the real aerodynamics mechanics or the new stock aerodynamics fine? And you will continue this mod? basically i'm waiting to play for FAR and deadly reentry news :D

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I would prefer that the whole Kerbal solar system would be an exact copy of ours, and that all parts would be procedurally generated and realistic, with the required cross-sections. But until that's possible (and without the stupid joints between parts, give me a structural skeleton or make things rigid), we won't be able to build the realistic vehicles needed to enjoy you greatly appreciated mod as it requires. Because if it would be realistic, it would mostly severely limit the craft you could make that don't explosively disintegrate.

False.

There are some techniques to area rule your airplane using the available parts.

Keep an eye on stock crafts for some of them ;)

Also, you don't need a perfect flawless area ruled airplane to fly well or go supersonic, just a decent one.

Remember this is not the only thing to care about, there is this plus all the other things you had to care about on the previous FAR version.

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@SymbolicFrank: Already planned. However, you'd be surprised, area ruling something sufficiently isn't that difficult. For example:

hINQyvI.png

That is the redesigned Firehound M. It's supermaneuverable, is capable of Mach 1.1 at SL, and Mach 1.9 at 10km on the basic jets, and only stock parts. I'm only playing with the slightest amount of smoothing available necessary to handle the discreteness of the voxel (and even now that's less of an issue that I've added a measure of "partial filling" for each voxel to improve lower-res voxelization), and the drag at full realism, and with a pair of engines that perform fairly close to the F-15's engines, it behaves pretty close to an F-15 in terms of speed.

I don't think that lego parts are going to be an actual issue.

@Vitasalato: Even oldFAR was better than the current stock aero, if perhaps a little less robust. The soon-to-be-released-whenever-I-stop-finding-issues-that-I-really-should-squash version of FAR will be a whole lot more accurate than oldFAR was.

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Vita - the current stock aerodynamics are much better than old, but FAR will still be way more realistic. It will model the transonic and supersonic regimes far better (better even than old FAR), and in the current stock model you basically can't stall. Essentially, stock gives a very cartoonified version of stability, lift and drag, where FAR gives you as close to the real deal as Ferram can give us.

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Just a simple question and excuse me if i'm not the first, is this mod the closest to the real aerodynamics mechanics or the new stock aerodynamics fine? And you will continue this mod? basically i'm waiting to play for FAR and deadly reentry news :D

No offense, but it would have taken less time to just look at the posts directly above yours to find the answer than asking it.

But to answer your question: NuFar seeks to be as realistic as realistically possible, it's significantly more realistic than nuStock and even oldFar. The mod is very obviously continuing and you can even download the dev version now (look through the last few pages for the download). Although I hear deadly reentry is having some problems with nuFar, the stock heat system may be good enough for your desires.

Edited by FG_Regulus

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May be a bit late to the party, but it depends on the gear you're using. One of the landing gears has, for some reason, more drag when it is put away rather than when deployed. It's a stock bug, I believe it's mentioned more precisely in the Stock Bug Fix sticky. Take a look at that and see if it's the offending gear, it probably is not nuFAR at fault in that case.

I'm pretty sure it was just my weird design rather than anything nuFAR was doing. We're only discussing one part of the drag equation here after all- I have no doubt that the extended gears added lots of parasitic drag.

On that topic, shouldn't nuFAR's voxel based drag system ignore any weirdness that is causing stock bugs in favor of its own calculations?

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I have been using the voxelAeroPort branch. I have a couple issues to report, although I haven't pulled since this morning so they may be fixed.

1. The stability derivatives sometimes are +/- infinity. This doesn't seem to affect the in-flight behavior, but I've been having to design with the AoA sweep, intuition, and many reverts.

2. The FAR analysis window in the SPH doesn't seem to remember its position. Every time I return to the SPH, I have to drag it from the middle of the screen to the top right corner.

Other mods are:

Kerbal Engineer Redux

Kerbal Joint Reinforcement

kOS

Precise Node

Kerbal Alarm Clock

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It's a lot less hassle to deal with area rule when you can clip parts and have that actually matter ( and use variable thickness wings too ). Not so easy for large craft like the HL/Mk3 shape unfortunately, but that is no failing of FAR, of course.

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It's a lot less hassle to deal with area rule when you can clip parts and have that actually matter ( and use variable thickness wings too ). Not so easy for large craft like the HL/Mk3 shape unfortunately, but that is no failing of FAR, of course.

B9 procedural parts has variable thickness wings. I don't know about pwings.

I can't wait. This is going to be awesome.

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