unkulunkulu

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Posts posted by unkulunkulu

  4. I use the roller mount (with Go Pro 2)

    Quote


    1. what feedback does anyone have on the Cookie Roller or Go Pro Swivel mount when on a G3 or other camera?
    2. How much clearance is there when the Camera or mount is not fully attached? Can the visor be opened?


    1. Loving it, consistent camera angle and got rid of lines getting under the mount after landing (hopefully will prevent such things on opening).
    A little bit of a hassle with the hexagonal screw, seems non-standard size here in Russia, so I have to always have the screwdriver that came with the mount, cause otherwise I cannot find a matching one.

    2. When the camera is detached, the visor easily comes past the mount base and doesn't contact it. I have a few scratches on the visor from back when I used the standard sticky mount, but now it's safe.
    I drilled the mount as written in the instruction, it doesn't allow the visor to fully open when the camera is attached and I do see it in my field of view, but this doesn't really bother me, quickly got used to that.

  5. Quote

    However, drag is NOT a linear function of velocity, so the horizontal component of velocity does have an effect on the vertical component of drag and the vertical component of velocity does have an effect on the horizontal component of drag.

    Soo, this is actually the dominating reason why trackers stay longer in the air, right? Not "lift"? Also, this must work for larger canopies (most canopies?)

    And in general, what reading do you suggest on canopy aerodynamics?

  6. Another perspective: imagine a no-wind day and say you're trying to land on a moving vehicle. It's obvious that your descent rate will be the same no matter whether you're landing in the direction of this vehicle moving or in the opposite direction (let's assume that the vehicle is huge and you can easily land on it in those conditions).

    Now the only thing left to understand is that the ground is your vehicle moving in the opposite direction to the wind, because you know, all movement is relative and air moving wrt earth is the same as earth moving wrt to the air.

    Does this make sense?

  7. Quote

    We have different winds at different altitudes for example.

    I'm talking steady and uniform winds and steady condition. Means: no changes in wind speed wrt time and space, so equal winds at different altitudes. Also, after the transitional processes died out (i.e. becoming one with the airmass). Shears do affect the canopy, of course, haven't you been there?

    Quote

    So what I mean by "before interacting" is that I'm picturing a layer of wind flowing horizontally without any obstruction, measured at a certain velocity. Then a parachute descends into it from above, as it moves through the vertical column, and then you've both altered the speed and direction of the wind as it flows around the canopy, lines and jumper's body.

    All this happens in the no wind situation as well and this is accounted for when we say that the "canopy airspeed is 20knots".

  9. Quote

    Do you think I'm wrong and this truly is a simple problem with a simple solution? Am I over-thinking it?



    The relativity principle is very strong and buried deeply in the laws of physics, you can rely on it very confidently. It's way more essential than aerodynamics, lift etc (if you can speak like that). So _my_ opinion is yes, this is simpler in a way, because we only need to know one principle, we don't have no know anything about aerodynamics, because it's dynamics, but the question is about kinematics, i.e. known velocities.

    Quote

    A parachute forward speed of 20 knots, combined with a windspeed of 20 knots BEFORE they interact.

    What exactly do you mean that parachute forward speed is 20 knots BEFORE interaction? It is measured when air and the parachute are interacting. So everything is accounted for when we say that parachute's airspeed is 20 knots. Then, we add wind. But wind -- is just another frame of reference. And even the simplest Gallilean invariance tells us that the ground speed will be 0. It's that simple.

    You see, no one has discovered any changes to the laws of physics when moving to another (inertial) frame of reference.

    Disclaimer: I'm talking Newtonian physics here, relativistic effects and near-light speeds issue is omitted. In near-light speed scenarios the change in lift might become possible :)

  10. Quote

    Assuming a canopy that moves forward at 20 knots, will a 20 knot headwind actually give the canopy exactly zero groundspeed?

    Sure, why not. You see, speeds are kinematics, they're the result. If you know that windspeed is 20 knots and airspeed is 20 knots in the opposite direction, then you defined the kinematics, there's no way they don't sum up to zero :)

    Quote


    I don't think this would be the case. There must be some reduction in the power of the wind from the real physical properties, the mass and form, of the aircraft (which blows faster in the same wind, a feather or bowling ball?), so the headwind would result in somewhat increased airspeed for the canopy and a corresponding increase in lift.

    Yes, but even if you fly downwind all the same effects are happening in the airmass. The only thing that changes is the direction of the windspeed vector that will be added to your airspeed to get your groundspeed.

  14. Oh, man. Now I get what you're trying to say :)

    You mean, it will ascend like this
    ...*..........
    ..*...........
    .*............
    *.............

    versus
    ..............*......
    .........*........
    ....*...........
    *.............

    Well, sure :) So height versus horizontal distance travelled will increase.

    But the OP was asking about descent rate. Rate is per unit of time, not per unit of distance. Height/time. Height/distance -- glide, height/time - rate, ok? :)

  15. Quote

    Yes, from an absolute point of view *.

    So you're saying that when taking off into the a headwind, the aircraft climbs faster? (you see, I ask _climbs_, not takes off, we start timing once the wheels are in the air, not when the engine is warming up)
    So let's say we'll get to 300ft in less time? You really believe that?

  17. Quote

    Any chance anyone with a physics background can explain this in physics terms? My friend is not convinced lol

    It's called the relativity principle, for example http://en.wikipedia.org/wiki/Galilean_invariance
    Basically: if the wind is uniform and steady, you can take an inertial frame of reference that moves with the wind. In this frame of reference the canopy flies the same as in no wind conditions.

    Wind (the wind you talk about when you say "downwind landing") is flow of air masses relative to the ground (every motion is relative). If there was no ground, there wouldn't be any wind to talk about. Your canopy is not bothered with ground, it flies in the air!

    That was uniform and steady. The changes in the wind (be that temporal or spatial) can provide some dynamic effects. To reason about those, you must first understand the basic stuff about steady winds and the relativity. All that matters to the canopy is the relative wind (wind relative to the canopy). For example if you fly into the wind and descent from stronger winds to an altitude where the wind drops momentarily, the canopy will surge, because it lost some speed relative to the wind => the lift is lost as well! If you catch a frontal gust, you will sense an increase in lift.

    But all those are dynamic effects. If you fly in a steady wind without giving any inputs to the canopy, the rate of descent will be the same no matter what your heading is. Downwind the same as into the wind.

  22. wolfriverjoe


    We've got one. Not "in some ideal world," but here and now. It's the snap shackle on the RSL. If you have enough time to decide that you want a delay before your reserve opens, you have enough time to reach up and grab it.

    It's something that needs to be practiced, and I'll bet most jumpers don't practice it anywhere near enough (how often do we practice pulling the cutaway and reserve handles?).

    But it's a valid option.

    And we've got a recent fatality where it appeared that thing is what might have happened.