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Cake day: June 11th, 2023

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  • At 30,000 feet and +50C, which literally never happens, your density altitude is ~38,000 feet and 100 KCAS will get you 194 KTAS. Not quite 400 😜

    This is why I’m a balloon pilot and not a fixed wing pilot. 30,000 is 12,001ft higher than I’ll ever see, and 30kias will probably collapse my envelope and splatter me in a corn field. 😵‍💫

    and winds aloft forecasts from one of the government agencies the Republicans are desperate to destroy,

    Can confirm: the accuracy of forecasts in general (and vertical wind profile data in particular) plummeted for this year’s flying season. The GOP is needlessly endangering aviation safety on multiple fronts.


  • I imagined it would be relative to wind speed at the craft, as measured by some instrument. Which would make the comic at least true in a general sense, as it does state the altitude is constant?

    That is the misconception I am trying to address. Check out this wind report:

    1kt of wind on the surface, 5kts at 100ft. My balloon is 120ft tall. My balloon is experiencing those 5kt winds while I’m floating inches off the ground. If I have an airspeed indicator in the basket, it’s going to be reading 4kts. (Actually closer to 5kts due to the change in direction as well as speed)

    How about if I’m at 150ft in the basket, in 5kt winds. The top of my balloon is 270ft, in 12kt winds. My airspeed indicator is going to be reading 7kts. I’m going to have 7kts of wind in my face.

    I’m trying to point out that the height of a balloon is very often larger than the gradient between two different air masses.

    I have experienced 15kt shears: my basket is hanging in an air current 15kts slower than the air current that my envelope is riding within. I have felt 15kt winds in my face while riding in a balloon that is carried by the wind.


  • Edit: yep, air speed is relative to the air the vessel is moving through

    Just to complicate it a little bit, “Airspeed” usually refers to “Indicated Airspeed”, which is provided by measuring the ram air pressure into the pitot tube relative to the static air pressure. It’s a measure of dynamic pressure rather than actual speed. It’s how fast your wings think they are moving through the air.

    If your wings need 100kts in the thick air at sea level to lift off the runway, they will need to “think” they are moving at 100kts when you get into the thin air at 30,000ft.

    Depending on altitude, you might actually be moving at 400kts past a weather balloon, but your “Indicated Airspeed” might only be 100kts.


  • Rivalarrival@lemmy.todaytoxkcd@lemmy.worldxkcd #3161: Airspeed
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    10 days ago

    Balloons don’t carry such instruments, but they do experience airspeed. Balloons can climb and descend at over 500fpm. We experience vertical “wind” at those speeds.

    Balloons are tall enough that the envelope can be above a wind shear, while the basket can be below. I’ve experienced 15kt shears, enough to deform the bottom of the envelope into a “question mark”.

    On most flights, pilots will experience 5-7kt shears at certain times.


  • Rivalarrival@lemmy.todaytoxkcd@lemmy.worldxkcd #3161: Airspeed
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    10 days ago

    Randall isn’t a hot air balloon pilot.

    Most balloons are about 100’ tall. The difference in wind speed between the surface and 200’ AGL can be 15kts. (it can be much greater, of course, but shears that strong are below flight minimums).

    It is not at all unusual to descend through a shear such that the envelope is in 20kt winds, while the basket is in 5kt winds. It’s rather scary, actually, because our aerostatic aircraft start experiencing aerodynamic effects: “False Lift”. These effects only exist while the balloon is crossing the shear. Once it passes through the shear, all that aerodynamic “false” lift disappears, and the balloon starts sinking like a rock.











  • Rivalarrival@lemmy.todaytolinuxmemes@lemmy.worldAn enigma.
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    3 months ago

    I think it is a testament of how bloated it is. I mean, we could get 20 Linux users together, list every package we have collectively installed, and produce a new distro with all of those packages that would serve all 20 of us without needing to add anything else. But our new distro would easily be the largest available, and none of us would use everything we’ve included.