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


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Then what prevents distribution of sound in space?

No medium. Of course, space is not completely devoid of gas molecules, but "The limitations of the concept of speed of sound due to extreme attenuation are also of concern. The attenuation which exists at sea level for high frequencies applies to successively lower frequencies as atmospheric pressure decreases, or as the mean free path increases. For this reason, the concept of speed of sound (except for frequencies approaching zero) progressively loses its range of applicability at high altitudes" as Wikipedia has it.

In plainer language, when you bump into a gas molecule, there's got to be a decent chance it bumps into another one in the near future, and that ain't true in space.

That diagram shows that sound travels on the edge of space almost as well as it does at sea level.

Not so. It shows that sound travels about as fast as it does at sea level. However, as mentioned above, it doesn't travel nearly so well, especially at high frequencies.

While sound waves do not exist in space at all.

Space doesn't have an edge in reality. This isn't mere pedantry; there isn't a sharp transition but instead a gradual one where the effect mentioned above becomes overpowering.

In case ideal gases would exist how would sound travel through them if their molecules do not interfere with each other by definition?

An ideal gas isn't made of individual molecules at all. It's a theoretical idea with simpler hypothetical properties than real gasses. Asking how the physical properties of something non-existent work is not meaningful.

Edited by damerell
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Then what do you mean by saying how well it travels if not how fast and far it travels?

Sound requires molecules to travel around. So the more time it takes for the molecules to travel between the collisions the slower the overall sound wave advances. And that time between the collisions in turn depends on how fast the molecules travel meaning the temperature and how many other molecules are around the meaning density. I do not quite get what is wrong with these statements?

Then why the sound travels so much farther and faster in liquids and solids then in gases if not because of the greater density?

Regarding the edge of space I did not ever claim that there is a specific boundary or anything no problem here. Sorry if I did not make it clear before.

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how fast and far
Those are two different things. In one material sound might not reduce much with distance, but nonetheless travel quite slowly. In another material it could travel fast but also die away in a short distance.

In general

v = √(K/ÃÂ)

Where v is the speed of sound, K is the stiffness of the medium against being compressed, and ÃÂ is the density.

In a gas stiffness is proportional to pressure which in turn is proportional to density, so changing density changes stiffness and the effects cancel out.

You can I hope intuitively see that a more stiff medium will transmit sound faster. If you shove one end of a medium that's stiff, you expect the whole thing to move nearly-rigidly and thus nearly-instantly. If you shove one end of a medium that's floppy you expect it to squash up near where you pushed. The transmission of that shove through the medium is a sound wave.

It's less easy to see intuitively that increased density slows sound, but that is indeed the case.

The reason solids transmit sound much faster than gases is then that the solids are more stiff while the gases are easily compressible. The higher density of solids actually has the opposite effect but in most solids it's not enough to undo the effect of the higher stiffness compared to gases.

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Then what do you mean by saying how well it travels if not how fast and far it travels?

He means that fast and far are completely different. The sound can travel very quickly rapidly attenuate and can travel very slowly but travel great distances.

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An ideal gas isn't made of individual molecules at all. It's a theoretical idea with simpler hypothetical properties than real gasses. Asking how the physical properties of something non-existent work is not meaningful.

An ideal gas is composed of individual molecules that never attract one another and interact on collision with perfect elasticity.

https://en.wikipedia.org/wiki/Ideal_gas

An ideal gas is a theoretical gas composed of many randomly moving point particles that do not interact except when they collide elastically. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is amenable to analysis under statistical mechanics.
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I guess higher density can decrease the speed of sound in liquids and solids because molecules have less opportunity to move and transmit less energy to each other?

So if the speed of sound does not decrease with increasing altitude than what kind of parameter does?

The distance that it can travel from the source?

Also I heard of many aviation incidents with subsonic aircraft being caught in a mach tuck.

That seems completely logical because an aircraft goes into a mach dive and accelerates quickly aggravating the effect and making the dive unrecoverable. But what about the case when the aircraft descends even more rapidly than it accelerates and while the indicated airspeed remains constant or increases at a certain rate the true airspeed reduces and combined with the descent reduces the mach number allowing the aircraft to regain control?

Is such a scenario plausible in any way? Does that count as acceleration or deceleration of the aircraft? And what does the ability to recover depend upon? Not talking about the aircraft control authority but how to determine whether the mach number will increase or decrease in the dive?

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Also I think these kinds of discussions are even more interesting in the context of the game and how the things discussed are modeled. In here there are many people who like airplanes and things related to them and know a lot about aerodynamics.

I think if any mod or game specific issues arise there will be no problem with these two existing alongside peacefully.

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Actually, sound doesn't get quieter faster in space by significant amounts. In space, the problem is that there's not enough air to create a sound in to begin with. However, if you have say, some unreasonably large cymbals, and crash them together in very low orbit (definitely under 200km), they may still be able to make an audible sound, and that sound will still propagate at a similar speed to sound at the surface. Only similar, however, as it may actually travel faster, since the uppermost reaches of atmosphere can be hotter.

EDIT: reconsidering, there's probably no orbital altitude where even unreasonably large cymbals could create audible noise, and the velocity of orbit would interfere. But say you were on a floating platform at 50 km or more - pressure is getting remarkably close to vacuum levels. Here, such cymbals may be able to make some audible noise - but it would only barely be audible. However, as suggested before, that sound would travel just as fast - by the graphs provided before, around 330 m/s at 50 km, versus 343 m/s at sea level.

As for your other question, I'm not sure what you're trying to ask, honestly. A plane in a dive will experience a "forward" force component from gravity as its flight path is tilted, and at any significant tilt, this will always cause acceleration. It's only possible to keep speed under control in a descent by taking it very gently - for modern airliners in a clean configuration, this can easily mean descending at less than a two degree angle, to keep the aircraft at a constant speed, because the airframe is so efficient that it requires that little forward pull from gravity to go forwards.

Edited by Iskierka
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I am talking about a situation where the indicated airspeed increases but not quickly enough and the true airspeed decreases because of the descent.

I heard that such a situation can help pull subsonic planes out of a mach tuck dive.

The second question here is that does such a dive situation count as aircraft acceleration or deceleration.

If we look at the indicated airspeed we see it increase rapidly and think that the aircraft has not reached its current terminal velocity because the air drag increases but the aircraft still accelerates.

But if we look at the true airspeed we see it decrease with altitude and think that terminal velocity is reached and the aircraft decelerates as the terminal velocity itself decreases with altitude.

Does the aircraft actually reach terminal velocity and if yes then why the opposite statement is false and vice versa?

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For IAS to increase as TAS decreases takes a very specific, very shallow (and notably, not dangerous) dive. Additionally, the dangerous mach tuck dives are caused when mach tuck reduces control authority on elevators to the extent that the aircraft cannot remain level - not only do you lose control and thus would be unable to pull into a safe dive, but you would likely over-stress and destroy the airframe in the process, so such a dive is something you'd just avoid altogether by providing sufficient control authority. If your aircraft did survive, it most likely stalled, then being at very high alpha it'll have very high drag, so it'll slow down by itself, regain authority, and you'll just perform regular stall recovery manoeuvres, totally unrelated to attaining a specific dive rate that causes IAS and TAS to trade.

And such a shallow dive would most definitely be deceleration - by all external measures, the aircraft is losing speed. IAS is not a measure of actual speed, only an equivalence for getting reference aerodynamic performance, as things like the maximum L/D point remain almost unchanged IAS across all altitudes. Thus increasing IAS is not an indicator of acceleration or deceleration, so we only take TAS, the one that actually represents something external to the aircraft's dynamics.

Edited by Iskierka
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When opening cargo bays the game became laggy, especially with big crafts. Is that a known issue or maybe I just have bad luck? I also use Kerbal Joint Reinforcement and it actually give me some headaches sometimes.

But in the big picture I think FAR is trying to calculate voxels for each frame and than it lags.

thanks for your attention

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For the trans-sonic cross sectional displays, would it be possible to add the option to show the first derivative of the area too? I know the general idea I'm trying to achieve, but I'm finding that often times, it's difficult to tell exactly why the yellow curve is behaving the way it is, and I end up just dragging parts back and forth to try an minimize the area.

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For the trans-sonic cross sectional displays, would it be possible to add the option to show the first derivative of the area too? I know the general idea I'm trying to achieve, but I'm finding that often times, it's difficult to tell exactly why the yellow curve is behaving the way it is, and I end up just dragging parts back and forth to try an minimize the area.

That is the reason why the green one is shown.

I don't have anything against plotting S' as long as I can hide it.

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Is the latest update being uploaded to Ckan anytime soon?

It appears to be on CKAN. In any case, anything CKAN related is out of ferram4's hands. CKAN pulls updates automatically from KerbalStuff. If you're having trouble then post in the relevant CKAN thread.

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Another few questions regarding the discussion on the previous page.

If you are descending with a constant indicated airspeed the true airspeed will decrease with altitude and the aircraft will decelerate. But if you descend steeper and let the indicated airspeed increase what is the threshold or how to call it after which the true airspeed will stop decreasing and start increasing also?

If you descend from a very high altitude in a long dive the calculations show that even if you increase the indicated airspeed over two or more times you could still be going slowing down.

I do not know exactly how precise those calculations really are but for me they look quite plausible.

How is that actually possible?

If the two airspeeds are exchanging does it mean that the aircraft is going at its current terminal velocity? If yes why does the indicated airspeed and drag increase further? If not why does it decelerate while loosing altitude? I guess if it really was terminal velocity the indicated airspeed would be constant with altitude and it would be impossible to increase it further by diving harder without applying more power?

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Question regarding FAR and 1.0.4:

One of the big reasons I wanted to use FAR was to have nose cones and fairings actually do something other than ADD mass and drag to my crafts. I saw in a video from Scott Manley (though it was several versions ago) where a simple rocket without a nose cone would outperform a rocket with one. I decided to do my own testing now that 1.0.4 is out and have confirmed that nose cones and fairings do have aerodynamic benefits. While the rocket without a nose cone (or faring) will initially outperform the one without, the one with the nose cone will eventually overtake the one without since it has better aerodynamics. I don't know if that was the case in other 1.x releases. It seems like this test pretty much nullifies the first statement about FAR:

  • Shape-Based, Vessel-Centered, Aerodynamics - Long, thin shapes drag less than wide, flat shapes, and smooth changes in body width reduce drag. The shape of the vessel as a whole, not individual parts, controls drag, so shape the vessel as you see fit.

I haven't done any testing with wide vs. thin designs, but wondered if anyone else had any input on what benefit I'm getting from FAR in that regard.

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I haven't done any testing with wide vs. thin designs, but wondered if anyone else had any input on what benefit I'm getting from FAR in that regard.

FAR is still a higher-fidelity, more realistic simulation than stock aero, even though stock aero has greatly improved in that regard. Current stock aero basically calculates the drag for each part based on attitude and stack occlusion and sums them; it ignores part clipping and has no stall effects or area ruling. FAR is much more sophisticated in that regard, creating a voxelised model of the entire vessel and performing its calculations on the vessel as a whole rather than merely summing the parts.

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Guys, these are the parameters for the Delta Winglet-Deluxe (winglet3). Can anyone recalculate parameters for the same part with rescaleFactor = 0.6 and rescaleFactor = 0.8? Or is it not necessary and FAR will do it automatically? Thanks.

MODULE
{
name = FARControllableSurface
MAC = 1.695
MidChordSweep = 22.1
maxdeflect = 15
b_2 = 1.587
TaperRatio = 0.449
ctrlSurfFrac = 0.2
}
}

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Red: Actually, stock does account for stalling, it's just pretty minor. What stock doesn't account for is wing sweep and aspect ratio.

That said, prior to nuFAR, even FAR didn't account for clipping; regex (and I do too, actually) find 1.0.4's aero to be rather like FAR-on-.90 in terms of "feel"*, minus wing aspect/sweep accounting.

*when used within expected parameters, i.e. flying a craft the way it looks like it should fly.

Also, I should point out I'm a proud user of FAR since .20 and will always be so. :)

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