Parachutes that Drift Less

Discussion in 'Recovery' started by jadebox, Feb 10, 2019 at 2:26 PM.

Help Support The Rocketry Forum by donating:

Thread Status:
Not open for further replies.
  1. Feb 12, 2019 at 3:05 AM #31

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    If you repeat the test (dropping something under the parachute) many times, sometimes it will go farther and sometimes it will go less distance. But, the distance the parachute travels over all the trials will average out to the time of descent multiplied by the wind speed.
     
  2. Feb 12, 2019 at 3:12 AM #32

    ThirstyBarbarian

    ThirstyBarbarian

    ThirstyBarbarian

    Well-Known Member

    Joined:
    Feb 11, 2013
    Messages:
    7,623
    Likes Received:
    131
    Yes, it BEGINS moving. It does not experience infinite acceleration and instantaneously move at the speed of the wind. It might not take long to get up to speed, but it take some amount of time. And the amount of time it takes depends in part on its design. If it gets up to speed faster or slower than another chute (or balloon) then those two designs will drift different distances.
     
  3. Feb 12, 2019 at 3:17 AM #33

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    It doesn't take long for a parachute to get up to the air speed. And there would be very little difference in the amount of time for two parachutes that deliver the same rate of descent.

    Plus, any number of things happen at ejection. The parachute may be ejected into the wind or against it. That would have more effect on how quickly the parachute matches the speed of the air than the design of the 'chute.

    Of course, you could design the parachute to not open for a while (i.e. dual deployment or using a Chute Release). Then the rocket would drift less. But, it would accomplish that by reducing the amount of time of descent.
     
  4. Feb 12, 2019 at 3:26 AM #34

    Arsenal78

    Arsenal78

    Arsenal78

    Well-Known Member

    Joined:
    May 8, 2018
    Messages:
    143
    Likes Received:
    10
    Roger, since you seem so content on spreading false information without realizing it is false information, do us all a favor and make a video of a rotating chute and a standard chute to compare them. I can't tell if you're hard headed by nature or by choice but when MULTIPLE people are saying the same information, you choose to block them and continue this blatant argument without realizing you're in the wrong. You still have NO SOLID PROOF. Until you can provide visual solid proof of YOU PERSONALLY disproving what has been said, please for the love of god go talk to a real parachute engineer. You're digging your hole deeper with all these lies and I can guarantee it'll hurt business. Considering you're still carrying this on, you have yet to stop and think that perhaps you are in the wrong about all of this....
     
  5. Feb 12, 2019 at 3:30 AM #35

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    Sorry, that's not the way it works. You are making the extraordinary claim so the burden of proof is on you.
     
  6. Feb 12, 2019 at 3:35 AM #36

    Arsenal78

    Arsenal78

    Arsenal78

    Well-Known Member

    Joined:
    May 8, 2018
    Messages:
    143
    Likes Received:
    10
    On the contrary, we civilized folk have science and people who have worked with parachutes longer than you've been alive so I'd say it is you who should provide proof of your claims.
     
  7. Feb 12, 2019 at 3:44 AM #37

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    To answer a question I asked earlier ... here's how a pilot in an airplane determines the velocity (speed and direction) of the wind:

    https://www.quora.com/How-does-a-plane-measure-the-velocity-of-the-wind-while-flying

    So, if a pilot has to have some ground reference to determine the speed and direction of the wind, how can an unguided parachute accomplish this task?
     
  8. Feb 12, 2019 at 3:49 AM #38

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    In science, the one making the extraordinary claim is the one asked to offer proof. You are claiming to have an unguided parachute which which can determine which way the wind is blowing without any reference to the ground (something pilots are not able to do). Please explain how the parachute is able to reference the ground to determine which direction to travel.
     
  9. Feb 12, 2019 at 3:56 AM #39

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    So you agree that it’s not instantaneous? And you also agree that there is difference albeit very little?
     
  10. Feb 12, 2019 at 4:02 AM #40

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    No one has claimed anyhing of the sort.
     
  11. Feb 12, 2019 at 4:05 AM #41

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    Sure. But, as I explained, any difference there is would be lost in the weeds. For one thing, the rocket may be moving in relation to the air flow and the ejection charge could send the parachute off in any direction. Those effects would dwarf the difference in how long it takes the 'chutes to reach the speed of the moving air.

    Anyway, if you are doubting something I said, would you like to address the question of how the parachute might determine the direction that the wind is blowing when pilots are not able to do that without a reference to the ground?
     
  12. Feb 12, 2019 at 4:06 AM #42

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    How else would it drift less than another parachute design? The only other way would be for the descent rate to increase.
     
  13. Feb 12, 2019 at 4:13 AM #43

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    We are not talking about rockets and ejection we’re talking about free falling parachutes.
     
  14. Feb 12, 2019 at 4:16 AM #44

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    It does not have to determine the direction of the wind. It only has to react to it. And different parachutes can react to changes in the wind differently. And none of them, not one, will react by instantly matching the wind speed and direction as they constantly change. Any difference no matter how small will make a difference.
     
  15. Feb 12, 2019 at 4:42 AM #45

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    In order to reduce drift it has to react to the wind by turning into it or traveling against it. To do either of those things, it would have to be able to determine the wind direction.

    A wind is blowing east at ejection and the parachute drifts west for a while. When the wind turns 90 degrees, a parachute that reacts slower (as someone suggested that the rotating parachute does) would continue further west before turning, and, therefore, drift farther. But, I doubt parachutes react much differently to changes when they are already both moving at the same speed through the air.

    When the wind changes, the parachute is already moving with the air. So, it can only react to the change in the wind, not the absolute speed or direction of the wind. So when the airflow passing it changes it isn't like the parachute is being hit by wind from the side. The parachute travels downward at an angle and the air flowing past it comes from the direction it is traveling. A change in the airflow would result in a change to that angle (based on the difference of the previous and new wind speed), not the new wind speed hitting the side of the 'chute.

    And, again, we are comparing two parachutes with the same descent rate so they would have the same drag coefficient and how they react to a change of airflow would be negligible. Certainly not enough to claim less drift.

    If the change in airflow causes the parachute's descent rate to change, then it may cause less drift if the descent rate increases when the airflow changes.
     
    Last edited: Feb 12, 2019 at 4:57 AM
  16. Feb 12, 2019 at 5:32 AM #46

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    ... falling from rockets.

    If you are suggesting starting with the parachute released from a specific point above the ground, then the claim that the parachute drifts less, even if true, would need a big asterisk beside it. :)

    Basically you would be providing the parachute with a reference to the ground which it wouldn't have when used in a rocket. As soon as the rocket lifts off, the parachute no longer has a reference to the ground.

    Maybe anyone attempting George's test should allow the quadcopter or whatever it is to drift with the wind when the 'chutes are released.
     
  17. Feb 12, 2019 at 6:09 AM #47

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    I looked at some stuff on the web about rotating parachutes. It appears they are intended to reduce glide and provide more stability for the payload (less swinging from side to side).

    And here is a neat twist ... Some rotating parachutes twist the shroud lines when they inflate, thus reefing the canopy then untwist them to allow the payload to fall faster at first to reduce drift then land slower (dual deployment without electronics!).
     
  18. Feb 12, 2019 at 6:14 AM #48

    ThirstyBarbarian

    ThirstyBarbarian

    ThirstyBarbarian

    Well-Known Member

    Joined:
    Feb 11, 2013
    Messages:
    7,623
    Likes Received:
    131
    If there’s no way for the parachute to know which way the wind is blowing, then how could mine be gliding into the wind?

    Don’t worry about answering that. It’s a rhetorical question to point out you are contradicting yourself.

    I don’t think the chute was gliding, and I did not say that I felt wind on the ground but the chute came straight down. The wind was gusty that day, not a steady, consistent breeze. The chute did not come down perfectly straight, but it also did not drift as far as other chutes in the competition. I think this chute is resistant to wind gusts. Other designs might catch the gusts and drift further with them. But this one stays very steady, it doesn’t swing or oscillate, it doesn’t tilt into or away from the wind, and the rotation absorbs some of the energy of the wind.
     
  19. Feb 12, 2019 at 6:29 AM #49

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    No contradiction. If a parachute is not moving with the air, then it is gliding. If there was no wind, and it wasn't moving, then it probably wasn't gliding.

    Parachutes sometimes glide into the wind. Sometimes they glide other directions. You can only count on them to reduce drift about half the time.

    But, in your case, I think your chute (which is really nice looking) reduced gliding (one of the benefits of rotating chutes according to info I read). Other chutes may have glided more than usual if the gusts made the chutes rock which can cause lift (and decrease the rate of descent) allowing the rocket to drift farther. Or, since the gusts were variable, they may have just worked out a little better for you.

    Even if gliding due to the gusts wasn't an issue, others may have simply used parachutes that provided a slower descent rate which would have caused them to drift more.

    So, based on your experience and what I read, I would be comfortable saying that the rotating parachute reduces gliding which can reduce drift (at the expense of increasing the descent rate).

    The stability of the parachute and reduced gliding would definitely be a benefit as it would make things more consistent and it would be less likely that your rocket would be slammed into the ground by a rocking parachute. So, you could let it fall a little quicker (which is a sure way to reduce drift).
     
    Last edited: Feb 12, 2019 at 6:49 AM
  20. Feb 12, 2019 at 6:34 AM #50

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    how does it glide into the wind if it doesn't know which way the wind is blowing?
     
  21. Feb 12, 2019 at 6:49 AM #51

    ThirstyBarbarian

    ThirstyBarbarian

    ThirstyBarbarian

    Well-Known Member

    Joined:
    Feb 11, 2013
    Messages:
    7,623
    Likes Received:
    131
    No.

    The chute does not need to determine the direction of the wind to resist drifting with the wind. All it needs is momentum, which all things in the universe with mass possess. If a parachute and its payload are drifting along in the wind (or falling straight down in a dead calm), and the chute is hit by a new horizontal gust, the chute and its payload will have momentum in the direction of travel, and will resist moving in the direction of the new wind gust until overcome by the force of the wind pushing on the chute. ALL chutes will do that. Some chutes will catch more of that side breeze than other designs and will drift further with the new gust than others.

    Also there is a mechanism by which a chute can actually react to a new gust of wind by turning into or away from it without “knowing” which direction the gust is coming from. This is different from turning into or gliding into a steady breeze, which is what I think you were suggesting. When a new gust of wind blows from a new direction on a parachute and the payload dangling below it, the wind exerts a force on everything it is blowing on. The chute catches much more of the wind than the payload does, and the chute has much less momentum than the payload does. So the chute is going to react to the wind gust more rapidly than the payload dangling below it. The chute will not remain directly over the payload, and the chute may tilt to the side and catch more of the breeze. It didn’t “know” the direction and speed of the gust, but it did react to it. And the strentgth of that reaction could depend on the chute design and other factors like the length of the shroud lines and shock cord.
     
  22. Feb 12, 2019 at 7:07 AM #52

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    Momentum is the product of mass and velocity. We have to assume that we are talking about two comparable masses, so there would be no difference in momentum. And, even if there was, the momentum would have to be in a favorable direction ... and you would want a gust that increases that momentum? The only way for a parachute to have momentum in the desired direction is for it to be drifting into the wind.

    And, yes parachutes react to changes in the wind. But, those reactions won't necessarily add up to less drift. They are just as likely to increase it.
     
  23. Feb 12, 2019 at 7:12 AM #53

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    There is no "side breeze," just a change in the angle of the airflow coming at the parachute. Yes, it could affect different chutes differently, but not as dramatically as suggested by the phrase "side breeze."
     
  24. Feb 12, 2019 at 7:14 AM #54

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    That’s kind of the entire point of this thread and the discussion. One parachute may have less or more drift than another.
     
  25. Feb 12, 2019 at 7:15 AM #55

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,362
    Likes Received:
    102
    Location:
    SEPA
    So you again agree that it could affect different chutes differently?
     
  26. Feb 12, 2019 at 7:20 AM #56

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    Oh .. I just realized that you probably meant inertia rather than momentum. But, the same probem occurs. There's no guarantee that resistance to wind changes would decrease drift. Some changes may increase drift.
     
  27. Feb 12, 2019 at 7:22 AM #57

    jadebox

    jadebox

    jadebox

    Roger Smith/JonRocket.com

    Joined:
    Jan 18, 2009
    Messages:
    5,358
    Likes Received:
    23
    Yes, but not in any specific direction. Any difference in effect is just as likely to increase drift as to decrease it.

    Again, the parachute has no reference to the ground. So it is impossible for it to consistently be steered in the right direction to reduce drift.

    Please tell me how the parachute can have some reference to the ground.
     
  28. Feb 12, 2019 at 8:29 AM #58

    mdnehez

    mdnehez

    mdnehez

    Member

    Joined:
    Mar 15, 2017
    Messages:
    18
    Likes Received:
    5
    Gender:
    Male
    Wow, stepped into the deep end of the pool here. I like parachutes with spill holes, like Public Missiles uses, because they seem to drift less.
     
  29. Feb 12, 2019 at 10:06 AM #59

    cwbullet

    cwbullet

    cwbullet

    Obsessed with Rocketry Staff Member Administrator TRF Lifetime Supporter Global Mod

    Joined:
    Jan 24, 2009
    Messages:
    20,288
    Likes Received:
    688
    Gender:
    Male
    Location:
    Glennville, GA
    Ok, this thread is done. That is 4-5 complaints now. Move along.
     
Thread Status:
Not open for further replies.

Share This Page