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uhoh
uhoh
12:30 AM
@ymb1 great point, just what I was hoping for, thanks! The speed of sound in a gas is proportional to the average speed of the molecules. Temperature is proportional to the average kinetic energy per molecule so we can write T ~ mv^2 and therefore v^2~ T/m or v ~ sqrt(T/m). Jupiter's atmosphere is primarily molecular hydrogen (H2) which is 14 times lighter than N2 on Earth, and the temperature in the 1 bar to 0.1 bar pressure region is about 160 K or 0.6 times 273 K (0 C).
@ymb1 so the speed of sound will be sqrt(0.6 * 14) almost 3x faster than on Earth, or about 1000 m/sec. I will look at your linked Aviation SE post, but naively this sounds like a good thing.
Atmosphere of Jupiter
The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is mostly made of molecular hydrogen and helium in roughly solar proportions; other chemical compounds are present only in small amounts and include methane, ammonia, hydrogen sulfide, and water. Although water is thought to reside deep in the atmosphere, its directly measured concentration is very low. The nitrogen, sulfur, and noble gas abundances in Jupiter's atmosphere exceed solar values by a factor of about three.The atmosphere of Jupiter lacks a clear lower boundary and gradually transitions into the liquid...
 
uhoh
uhoh
12:48 AM
@ymb1 I see airplane words like Mach and Reynolds here: agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/98JE01766 (open access) from the Wikipedia article, and there's also lpl.arizona.edu/~showman/publications/ingersolletal-2004.pdf and lpl.arizona.edu/~yelle/eprints/Yelle04c.pdf
 
ymb1
ymb1
1:27 AM
@uhoh near, at, and just beyond Mach 1 drag is much higher (compressibility)
two or three other pointers:
1. lift equation is based on rho; hydrogen density at 1 bar is still very low, so little lift for same speed ignoring compressibility
2. have no idea about hydrogen's viscosity, but it would affect the stall angle
 
uhoh
uhoh
@ymb1 I think that that question is in need of an additional answer that addresses these issues.
 
ymb1
ymb1
it needs Peter Kampf, I'd be way out of my depth
:D
 
uhoh
uhoh
ya they've answered a few of my questions (and a zillion others) and those answers are uniformly authoritative and simultaneously thorough/authoritative, and clear and easy to read.
I can invite them to answer here in Space SE, or alternately I can write a new and very specific question there in Aviation.
The latter seems better to me because of course there's nothing I like better (when procrastinating) than to write Stack Exchange questions
 
ymb1
ymb1
:D I was about to suggest that, a question on Aviation
I'd only recommend you word it in terms of wanting to understand the variables, instead of the hypothetical scenario (may not go down well over there)
consensus is would be OT and best suited for the Physics site
 
uhoh
uhoh
@ymb1 ya I know exactly what you mean and will scope the question carefully such that answers will be textbook aircraft aerodynamics discussions. I was (a little) lucky here but won't count on repeat luck.
4
Q: Why this inertial regulator of dragonfly wing pitch reduces self-excited coupled flapping and feathering vibrations and improves gliding flight speed

uhohThe pterostigma of insect wings an inertial regulator of wing pitch is linked in this answer to Why do dragonflies have these special little spots on their wings? (open access copy here) The Summary of the paper includes the following points. I've highlighted some in bold. Question: Is it possibl...

aerodynamics wing flutter vibration
 
ymb1
ymb1
1:42 AM
WIP since September :D
 
uhoh
uhoh
WIP? (I'm acronymisic-efficient)
 
ymb1
ymb1
the answer has a section labeled WIP (work in progress) :D
should have read: WIP UFN (until further notice)
aviation acronyms :D
 
uhoh
uhoh
oh yes :-) I know that I have 2 or 3 WIPs out there myself, which will be resolved once I am able to get an "around tuit".
In a former life WIP was "Wafers in Process" and we reviewed the WIP sheet every morning.
After my first readthrough of PK's answer to the question you've linked to, I see that the Jupiter question should cite it and can draw heavily from it. It would be more of a "How would this kind of analysis apply under the following different conditions?" (e.g. hydrogen, density/temperature profile, higher gravity, perhaps severely limited power availability)
Perhaps just "Where might the least-worst altitude be? If not a sweet-spot, at least a least-sour spot?" That seems like it can have a clear and definitive answer, not be a duplicate, and rely solely on standard aerospace canon.
 
ymb1
ymb1
that would certainly work! I recommend the Q to list the values of the conditions
 
uhoh
uhoh
yes, exactly. I'll do my homework first. I've had my morning coffee and now ready to dig in. Like I said, "because of course there's nothing I like better (when procrastinating) than to write Stack Exchange questions"
 
ymb1
ymb1
1:55 AM
and tag it airplane; don't use the word aircraft, or someone is bound to comment fly a balloon over there
 
uhoh
uhoh
The winds on Jupiter are formidable and a lot of them go in big circles; the only way to get from one scientifically interesting place to a different one is to fly and not just get blown around.
therefore good point!
 
ymb1
ymb1
interesting point! if the Jovian jetstreams are fast enough, I bet they are, you are found to fly in one direction only to get anywhere
As ground speed = true airspeed - head wind
looks more and more like you need a waverider
fell into a Wikipedia rabbit hole? :D
 
uhoh
uhoh
15
Q: Would it be possible to "ride the wave" on Venus?

uhohUpdate: Newly published paper in Nature Geoscience Atmospheric mountain wave generation on Venus and its influence on the solid planet’s rotation rate has open-access links in Science News, Motherboard, and Science. There is a stationary gravity wave in Venus's very dense atmosphere. It is int...

planetary-science venus jaxa akatsuki
4
Q: In which situations can a Dual-Aircraft Platform (atmospheric satellite) remain nearly geostationary?

uhohThe Dual-Aircraft platform described by William Engblom of Embry-Riddle Aeronautical University on this NASA feature page and in the first half of the video of the 2016 NIAC Symposium uses the wind sheer (difference in horizontal wind velocities) between two altitudes to allow a well-programmed p...

glider solar-power
 
ymb1
ymb1
@uhoh that's a different kind of waveriding :D
> A waverider is a hypersonic aircraft design that improves its supersonic lift-to-drag ratio by using the shock waves being generated by its own flight as a lifting surface, a phenomenon known as compression lift.
 
uhoh
uhoh
2:10 AM
I wonder if a pair of tethered gliders in Jupiter could solve the power problem?
 
ymb1
ymb1
@uhoh how so?
 
uhoh
uhoh
Oh, I remember that now, there were tests, they dropped it from a plane and it took off and achieved some absurdly high speed?
(how so?) 2nd question
 
ymb1
ymb1
2 mins ago, by uhoh
I wonder if a pair of tethered gliders in Jupiter could solve the power problem?
this ^
 
uhoh
uhoh
If the Dual Aircraft Platform can achieve zero ground speed in one configuration, probably there are different configurations that result in non-zero ground speeds. What I like about it is that they can be gliders
 
ymb1
ymb1
all this talk reminded me of my first ever SE question: astronomy.stackexchange.com/q/18367
 
uhoh
uhoh
2:13 AM
 
ymb1
ymb1
interesting concept
 
uhoh
uhoh
 
ymb1
ymb1
Scientists Finally Know What Time It Is on Saturn 2019
nice!!
> "The researchers used waves in the rings to peer into Saturn's interior, and out popped this long-sought, fundamental characteristic of the planet. And it's a really solid result," said Cassini Project Scientist Linda Spilker. "The rings held the answer."
this is super awesome
 
uhoh
uhoh
Your question was highly relevant and a real challenge to science and recently there are some answers that get close to addressing it, but they all need to be prefaced with "It's a little complicated, but..."
Yes, the things that happen in Saturn's rings and what has been learned from them are really jaw-dropping.
 
ymb1
ymb1
2:32 AM
correction, that wasn't my 1st SE question, rather 2nd Astronomy question
 
uhoh
uhoh
2:43 AM
got it! okay gotta scoot, cheers!
 
ymb1
ymb1
ta-ta! :)
 
 
14 hours later…
Everyone
Everyone
4:55 PM
'o @RoryAlsop
 
 
5 hours later…
Rory Alsop
Rory Alsop
10:23 PM
@Everyone Good evening!
 
DrSheldon
DrSheldon
10:39 PM
The company blog is currently running a series on software in space, and there are zero mentions of space.stackexchange. The company does not even know we exist.
 

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