ferram4

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

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On 17.11.2017 at 8:02 PM, Psycho_zs said:

Is there a way to exclude a part from FAR calculations?

I've tried these variants, but it didn't work:

@PART[dmFlexoTubeJr|dmFlexoTube|dmFlexoTubeSr]:FINAL
{
	@MODULE[FARAeroPartModule]
	{
		@isEnabled = false
	}

	@MODULE[FARPartModule]
	{
		@isEnabled = false
	}
}
@PART[dmFlexoTubeJr|dmFlexoTube|dmFlexoTubeSr]:FINAL
{
	!MODULE[FARAeroPartModule] {}
	!MODULE[FARPartModule] {}
}

 

Edited by Psycho_zs

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2 ways of excluding something from the FAR aero calcs. First way is via the FARPartModuleTransformExceptions.cfg. This is a more selective method, and allows hiding select segments of a part from the Aero calcs - Parachute canopies/firespitter propeller blades/etc, but requires said segment to have a PartModule referencing it.
Second way is the nuclear option, via !MODULE[GeometryPartModule] {}, which completely removes the entire part from all aero calculations.

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7 hours ago, SuicidalInsanity said:

Second way is the nuclear option, via !MODULE[GeometryPartModule] {}

Thanks! I think I'm going to just nuke these ports, they aren't going to spend any significant time flapping in the wind outside of fairings anyway.

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I'm not sure if I'm missing something and this is correct behaviour or if there is something wrong. Nose intakes seem to make aircraft have much lower drag.

For instance this craft:
WV3IPZ9.png

With just a nose cone looks like this:
1hPpa8J.png

But with nose intakes:aX7LBRo.png

MQUghDJ.png

 

Should a nose intake have such a dramatic effect on the curves compared to a simple nose cone? With a nose cone and side intakes the aircraft has performance close to the mig 15 it's roughly based on (tops out at full throttle at about mach 8.6). With a nose intake it's able to go supersonic at mach 1.1+. It just seems wrong.

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Air intakes do indeed reduce drag: they provide another path for the airflow to bypass the metal of the plane (that path being through the intake and the engine).

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The difference is probably that with FAR, the airflow is going more or less straight through the body and out the jet, where in reality that design has the slight problem of a pilot and such being in the way.

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7 hours ago, taniwha said:

Air intakes do indeed reduce drag: they provide another path for the airflow to bypass the metal of the plane (that path being through the intake and the engine).

Sure, except with an air intake on a real aircraft you've got ducting followed by fan blades that introduce significant drag. It seems that FAR, with a nose intake, treats the whole aircraft as a hollow tube, which means it gets much less drag than it should.

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13 minutes ago, Citizen247 said:

Sure, except with an air intake on a real aircraft you've got ducting followed by fan blades that introduce significant drag. It seems that FAR, with a nose intake, treats the whole aircraft as a hollow tube, which means it gets much less drag than it should.

While the first sentence is quite true, especially if the engine is not spinning, the intake-engine system will still produce less drag than a nose cone. Not zero, of course, and I don't know how much less, but the main thing here is that those graphs are about area ruling, not drag itself (ie, the relation with drag is rather indirect).

I do not know how accurate FAR's drag model is, but considering ferram studied aeronautical engineering, and even ignoring that, his goal is to produce realistic aerodynamics, I'd say that the results are at least in the right ballpark.

For the sake of area-ruling, ferram does have to make some guesses about the internal shape of the ducting since there is no information about it in the parts. However, he does have the intake area and engine exhaust area to work with (latter maybe empirical) and can probably get away with assuming the cross-sectional area of the ducting is fairly linear between the two. 100% accurate? Surely not, but it's a darn sight better than the "close the intakes to reduce drag" bogosity of pre-1.0 stock (not sure what the story is for post-1.0 stock).

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Fair enough. As I said I wasn't sure if I was just missing something. It just seemed strange to me that the replica that's close in dimensions, mass and powerplant would have ballpark performance to the real thing (slightly slower) with a nose cone, but hugely better performance with a nose intake (i.e. something that should struggle to go supersonic in a dive having the ability to supercruise). Although I also get that KSP, even with FAR, by its lego nature isn't going to ever be a rigorous flight sim.

Edited by Citizen247

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4 hours ago, taniwha said:

the main thing here is that those graphs are about area ruling, not drag itself (ie, the relation with drag is rather indirect)

^^ This. Keep in mind that hollow intake have much less overall cross section compared to full closed part of the same size. Voxeliation is based on coliders from each part, so cross section area should be accurate as much as game engine allow to be. On side note, neither game provide data how air is tuneled trough other parts from intake neither FAR calculate it. Don't know if it is even worth to calculate it if you put in consideration how much it influence drag force, compared to other factors on craft.

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There's a way to make FAR stop altering stock water physics? I love FAR for planes but not with boats. So, there's a line in any of the .cfg files can I delete or change to stop FAR mess with water?

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I'm having a bit of trouble understanding the drag and lift coefficient values for spherical spacecraft. For example, the following vessel, made using a Procedural Parts fillet tank made spherical:

 

eCEL2lZ.png

 

Since the vessel is completely spherical, I would not expect any dependence of the Cl or Cd on angle of attack. However, the chart shows a quite substantial dependence, which seems a bit odd (and, for due diligence, this vessel only consists of the tank so the CoM is centered on the tank's center). To check if this is a problem with Procedural Parts, I've done this again for a few different spherical fuel tanks, including the hydrogen tank from cryogenic tanks:

L0dMu45.jpg

Here's two PP nose cones back to back, which approximate a sphere:

YAUsS5K.png

Cm dependence on AoA is better, but Cd still changes dramatically as a function of AoA

 

For the purposes of building an trajectory guidance system incrementally, I'm looking for a part that allows me to ignore Cl and Cd dependence on AoA, which in turn allows pointing without having to worry too hard about aerodynamic forces (only dependent on speed). A sphere would seem to satisfy this requirement, since it's perfectly symmetric along all axes, but FAR seems to indicate that all of the sphere-like-shapes I can produce still have lift and drag coefficients that are dependent on AoA. Is there a part that would let me conceal all the internal parts away from airflow while giving AoA-independent drag and lift coefficients? 

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On ‎11‎/‎26‎/‎2017 at 3:17 PM, lushr said:

I'm having a bit of trouble understanding the drag and lift coefficient values for spherical spacecraft. For example, the following vessel, made using a Procedural Parts fillet tank made spherical:

 

eCEL2lZ.png

 

Since the vessel is completely spherical, I would not expect any dependence of the Cl or Cd on angle of attack. However, the chart shows a quite substantial dependence, which seems a bit odd (and, for due diligence, this vessel only consists of the tank so the CoM is centered on the tank's center). To check if this is a problem with Procedural Parts, I've done this again for a few different spherical fuel tanks, including the hydrogen tank from cryogenic tanks:

L0dMu45.jpg

Here's two PP nose cones back to back, which approximate a sphere:

YAUsS5K.png

Cm dependence on AoA is better, but Cd still changes dramatically as a function of AoA

 

For the purposes of building an trajectory guidance system incrementally, I'm looking for a part that allows me to ignore Cl and Cd dependence on AoA, which in turn allows pointing without having to worry too hard about aerodynamic forces (only dependent on speed). A sphere would seem to satisfy this requirement, since it's perfectly symmetric along all axes, but FAR seems to indicate that all of the sphere-like-shapes I can produce still have lift and drag coefficients that are dependent on AoA. Is there a part that would let me conceal all the internal parts away from airflow while giving AoA-independent drag and lift coefficients? 

This is just a wild guess - but could it have something to do with FAR's voxel system, causing the aerodynamic mesh to end up not being perfectly spherical?  Sort of like if you tried to approximate the shape of a sphere as close as you could with perfect cubes, there would probably be some variation.  Again, this is just a shot in the dark.

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33 minutes ago, MunGazer said:

This is just a wild guess - but could it have something to do with FAR's voxel system, causing the aerodynamic mesh to end up not being perfectly spherical?  Sort of like if you tried to approximate the shape of a sphere as close as you could with perfect cubes, there would probably be some variation.  Again, this is just a shot in the dark.

That's a thought! Perhaps if @lushr turned on voxels then there might be a clue revealed.

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Question, is there a way to ignore specific parts? It seems to have a problem with part with animation which grows to kilometers in size.

Edited by FreeThinker

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14 hours ago, FreeThinker said:

Question, is there a way to ignore specific parts? It seems to have a problem with part with animation which grows to kilometers in size.

I had a similar problem just recently, the answer is here:

 

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Hallo all.

First - great work! This is potentially single best mod to KSP.

I tested the mod yesterday and I have a question about reentring. I have built some typical space plane and deorbit. I have lost stability about 40 km over the surface of Kerbin (lack of RCS) and started to spin uncontrolaby, but aerodynamic forces did not destroy my plane. I just decelerated spining around and i regained control low in a dense atmosphere. Why aerodynamic forces did not tear my plane to shreds? What should i modify to gain some challenge during reentry? I have reentry heating on 100% and G-forces on parts and everything on. It it because of Kerbin atmosphere instead of Earth? 

cheers

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2 hours ago, Bies said:

Hallo all.

First - great work! This is potentially single best mod to KSP.

I tested the mod yesterday and I have a question about reentring. I have built some typical space plane and deorbit. I have lost stability about 40 km over the surface of Kerbin (lack of RCS) and started to spin uncontrolaby, but aerodynamic forces did not destroy my plane. I just decelerated spining around and i regained control low in a dense atmosphere. Why aerodynamic forces did not tear my plane to shreds? What should i modify to gain some challenge during reentry? I have reentry heating on 100% and G-forces on parts and everything on. It it because of Kerbin atmosphere instead of Earth? 

cheers

There is a mod called Deadly Reentry, maybe that could be interesting for you, but it changes thermodynamics of crafts not aerodynamics.

 

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I know Deadly Reentry but as you sad, i was thinking about aero forces, not temperature.

cheers

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6 hours ago, Bies said:

Hallo all.

First - great work! This is potentially single best mod to KSP.

I tested the mod yesterday and I have a question about reentring. I have built some typical space plane and deorbit. I have lost stability about 40 km over the surface of Kerbin (lack of RCS) and started to spin uncontrolaby, but aerodynamic forces did not destroy my plane. I just decelerated spining around and i regained control low in a dense atmosphere. Why aerodynamic forces did not tear my plane to shreds? What should i modify to gain some challenge during reentry? I have reentry heating on 100% and G-forces on parts and everything on. It it because of Kerbin atmosphere instead of Earth? 

cheers

Let me make sure I understand - you want there to be an appreciable risk of structural failure during re-entry? In that case, you might try tweaking your wings and control surfaces - put you control surfaces to maximum deflection and turn down the... the name escapes me right now; it's the multiplier for your wing mass. Try a value of 0.3-0.4 for all surfaces. If that still doesn't do the trick, tweak it down lower.

My own self, I try to fly safe; I'd be interested in seeing your design, to see why you're losing control around 40km. About what speed are you going at that point?

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18 hours ago, Bies said:

Hallo all.

First - great work! This is potentially single best mod to KSP.

I tested the mod yesterday and I have a question about reentring. I have built some typical space plane and deorbit. I have lost stability about 40 km over the surface of Kerbin (lack of RCS) and started to spin uncontrolaby, but aerodynamic forces did not destroy my plane. I just decelerated spining around and i regained control low in a dense atmosphere. Why aerodynamic forces did not tear my plane to shreds? What should i modify to gain some challenge during reentry? I have reentry heating on 100% and G-forces on parts and everything on. It it because of Kerbin atmosphere instead of Earth? 

cheers

As others mentioned, I usually turn the mass of my wings down to save delta-v; this also results in your plane being much more fragile.  I think you can also tune the failure limit in settings.

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On 11/24/2017 at 8:32 PM, Citizen247 said:

Fair enough. As I said I wasn't sure if I was just missing something. It just seemed strange to me that the replica that's close in dimensions, mass and powerplant would have ballpark performance to the real thing (slightly slower) with a nose cone, but hugely better performance with a nose intake (i.e. something that should struggle to go supersonic in a dive having the ability to supercruise). Although I also get that KSP, even with FAR, by its lego nature isn't going to ever be a rigorous flight sim.

Well, the characteristics of the nose cone vs other nose cones would have a massive impact on performance. Comparing a nose cone to a nose intake? apples and oranges here. Specifics between each apple will have broad differences on performance. Apples to oranges? Massive.

 

FWIW, the curves look good for the cone and intake in question. And with that curve, I am not surprised about it having much better acceleration performance.

As far as having KSP match aircraft performance, its going to depend on a bunch of factors that are simply not that detailed in KSP. Things like CG evolution due to fuel tanks being partly drained, effectiveness of baffles in reducing slosh, different materials having different parasitic drag, general inability to control CG... you can make an aircraft in KSP and FAR that has the same shape as an F-16, but by moving the CG forward you will end up with drastically different performance than the real jet (and also by virtue of not having a flight computer to fly it for you).

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22 hours ago, capi3101 said:

Let me make sure I understand - you want there to be an appreciable risk of structural failure during re-entry? In that case, you might try tweaking your wings and control surfaces - put you control surfaces to maximum deflection and turn down the... the name escapes me right now; it's the multiplier for your wing mass. Try a value of 0.3-0.4 for all surfaces. If that still doesn't do the trick, tweak it down lower.

My own self, I try to fly safe; I'd be interested in seeing your design, to see why you're losing control around 40km. About what speed are you going at that point?

capi3101lordcirth thanks fo yur answers.

I'm afraid i didn't balance my plane before reentry and i had the center of gravity too close to my tail after burning more than 90% of my fuel. I lost control after i exceed the critical angle of attack having about 2000 m/s at 40 km or lower.

I built two similar aircrafts. With one i was close but finally i burnt during reentry. It was nice. :) 

With second i exceeded AoA of ~15 -20deg in similar conditions and my plane desintegrated due to G-forces and aero pressure as i think it shoud. I was pleased :) Really. 

I'll test some other aircrafts. I stand by what I said, this mod, just an idea of this mod is just fantastic. It's easy to modify some aspects of flights in a vacuum, additional parts, life support etc. but this mod is something. Fluid mechanics in the atmosphere is the weakest part of stock KSP :) .

cheers

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