15ft cargo extraction chute - descent details??

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Salvage-1

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Has anyone used one of these chutes? Do you have any idea of what rate for say, 45lb?

The fruitychutes site states that their L3 Eliptical at 120" (10ft) is good for 50lb at 20fps. The extraction chute is 15ft, but isn't actually a full canopy, so I am guessing about the same descent rate, maybe a little slowe like 50lb @ 17ft/sec?

Anybody any ideas?

cargo chute.jpg
 

tab28682

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Frederocket

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What you have there is a ring slot extraction parachute, primarily used in parachute systems that require high speed deployment, such as a deceleration chute/device in military aircraft requiring a relative high touchdown speed. Examples: Some/most fighter jets, bombers, along with the space shuttle,come to mind. In addition for cargo, low altitude parachute extraction systems,(LAPES), also use the same type designed chute, (your picture is an example). The reason ring slot chutes are used is because if designed properly, they withstand the extreme aerodynamic forces of a highspeed deployment much better than a standard paneled parachute, such as a cargo chute normally used to bring down cargo from higher altitudes. As a result, the design of the particular chute you show, would not make for an efficient lowspeed parachute, for several reasons, two theoretical reasons in particular come to mind:

1. Unless your initial decent speed is well above 100 knots, the time to fully inflate a ring slot is considerably longer than a comparable sized standard chute. As an example, the longer a chute takes to inflate, the greater the possibility for entanglement issues, i.e. the possibility of a streamered chute.

2. Once inflated, prevailing winds become a factor in maintaining chute inflation/efficiency. Let's say for example, you have ring slot chuted rocket coming down at 13 feet per second, (FPS), and the wind at lower elevations have kicked up above the actual speed of the rocket falling at 13FPS. Because the chute is an extraction ring slot, there is a theoretic possibility that the prevailing wind could effect the efficiency of the chute to the point of partial or complete deflation as the prevailing wind blows through the ring slots and the slower escaping air from the leeward side of thechute cause deflation anomalies.


All that being said, there are ring slot designs, specificly designed as a primary cargo and/or special purpose recovery chute... However, the extraction chute shown is not one of those designs.



BTW, it's an extremely exhilarating experience to stand in the aft troop door space, as four to five pallets of cargo are extracted from a C-130E over a drop zone or even more exhilarating, as a palletized duce and a half is extracted via LAPES...


View attachment 306545
 
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Salvage-1

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Yup, we had different things going out the back of the Hercules (C-130) back in the RAF. Usually it was pallets or landrovers (jeeps) or light assault vehicles. Watching them on the skids suddenly go from stationary to GONESKI.... very intense.

<bugger... lost a load in edit> Also used to go out the back of them, guys used to run the length of the deck and throw outselves out the back... the camera above the gate got some crazy videos.

so... open it at a higher altitude to allow for any additional opening time and use a drogue to pull it out quickly to give it a chance to inflate and not snag.

Thanks for all the info....
 
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Lowpuller

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Been there, done that, I agree it's a lot of fun.

Check out this tube from a tailgate. I'm the goofy guy sticking his tongue, I designed this dive also!

https://youtu.be/KfOkpvgexh8
 

georgegassaway

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2. Once inflated, prevailing winds become a factor in maintaining chute inflation/efficiency. Let's say for example, you have ring slot chuted rocket coming down at 13 feet per second, (FPS), and the wind at lower elevations have kicked up above the actual speed of the rocket falling at 13FPS. Because the chute is an extraction ring slot, there is a theoretic possibility that the prevailing wind could effect the efficiency of the chute to the point of partial or complete deflation as the prevailing wind blows through the ring slots and the slower escaping air from the leeward side of the chute cause deflation anomalies.


Chutes do not feel wind from the side. They drift with the wind. With the exception of turbulence or sudden gusts, or gliding chutes. Just like people who fly in a hot air balloon in 10 mph wind, to them they are in calm and feel no wind, the ground below them is moving at 10 mph. For a non-gliding parachute, if it is in 10 mph ind, the chute's perspective is it is falling vertically in "calm" air (again ignoring turbulence/gust issues). Thornburg's "River of Air" principle.

Something I wrote in 2011 along similar lines:

https://www.rocketryforum.com/showthread.php?19812-Clustered-Parachute-Question&p=176199#post176199

I agree with Handeman. If the wind is 6 MPH, the rocket is going to drift at 6 MPH with the wind, no matter whether it uses a plain chute, a ring chute, an &#8220;X&#8221;, chute, a streamer, helicopter recovery, or &#8220;lightweight float&#8221; recovery.

This assumes that the chute and rocket would drop straight down if it was dead calm. There can be chutes that by design could &#8220;glide&#8221;.

Also, some chute, shock cord, and rocket combinations sometimes sway back and forth as the chute &#8220;spills&#8221; air from one side or the other, so as the chute is tilted during those swings it has a bit of a horizontal component to the descent (diagonal descent), compared to dead calm. But in those cases, the sway back and forth &#8220;averages out&#8221; to the same as a vertical descent (the sway in motion would be a long zig-zag-zig-zag all the way down that averages vertical to the air).

Sometimes there are bad assumptions in this hobby. Someone who half-knows about things comes up with a theory that &#8220;sounds good&#8221; to others, and their bad theory gets passed on and accepted as fact. This is one of those, and the likely source for this assumption is one or both of these:

1 - I have heard many times that &#8220;X&#8221; Chutes do not drift in the wind like regular chutes do. Wrong, wrong, wrong. Whoever first came up with that may have been thinking of is that &#8220;X&#8221; type chutes do not tend to SWAY as much as other chutes do, since the open corners of the &#8220;X&#8221; type chutes lets air vent out that otherwise might spill out and cause a sway if it was a normal chute.

But swaying, or lack of sway, has nothing to do with drifting with the wind.

2 - Of course one true thing of &#8220;X&#8221; chutes versus others is that for the same DIAMETER of chute, the &#8220;X&#8221; chute is less efficient, so any rocket will descend faster with an &#8220;X&#8221; chute than with a normal chute of identical size. And on average, landing faster means drifting less. So that is the possible kernel of truth to where that &#8220;old flier&#8217;s tale&#8221; came from. But then using a smaller diameter round chute would do the same thing.


The models that tend to bust the &#8220;drift with the wind&#8221; things wide open are gliders. If a glider ends up flying in a perfect straight line, without turning, then it might fly into the wind and could land upwind. Or, it could transition flying away from the wind, and land far more downwind than any model with a chute would, for the same time in the air. Totally depending on the way the glider was pointed when it transitioned into a glide (some might suggest a glider will &#8220;face into the wind&#8221;, but that is another one of those bad assumptions some take as fact which is wrong. See the River of Air analogy later). However, most gliders turn in circles. So, as the glider turns in its circles, it is drifting with the wind, and &#8220;by average&#8221;, the center point of the circle is drifting with the wind the same as a rocket with a chute would. In the attached drawing, how a glider circle would look like plotted against the ground, drifting with the wind, even though from the glider perspective it is in a constant circle.

An R/C Model Sailplane flier, Dave Thornburg, wrote a superb article series about the &#8220;River of Air&#8221;, over 30 years ago. Part of the way he explained things was to think of the wind as being like a river. The main current may speed up or slow down in spots, and might even have some eddys. If you were in a boat, or swimming in it, you&#8217;d have to contend with the fact that the river is moving. If you are sitting in your boat with no power (no sail, no engine, not using paddles), and no anchor, in the middle of the river, then to you it would seem like the river is still, but the land is moving past you. Also the boat would randomly point in any given direction, not necessarily upstream or downstream. And there is no magic shape of boat, life vests, or human body shape, that prevent the river&#8217;s current from making everything move with it (assuming no anchor is used. And ignoring any wind than can make floating objects move along the surface despite the water current).

Likewise, there are no magic chute designs that prevent rockets from drifting with the wind, or &#8220;drift less&#8221;. SWAY less, yes. DRIFT less, no. Any model with a chute that seems to &#8220;drift less&#8221;, it&#8217;s not the chute, either it is for some reasons gliding a bit and the glide&#8217;s horizontal vector is randomly pointing into the wind, it is in &#8220;down air&#8221;, or the wind itself has happened to temporarily decrease (the wind is never constant, except on those rare times when it is dead calm. And it varies the most on days with a lot of thermal activity)

The only way to &#8220;drift less&#8221; in the wind is to LAND SOONER. Unless you can make it glide and cause it to steer into the wind.

Now having said all the above, I&#8217;ll get to Wingnut&#8217;s original question. Going from one big chute to three chutes won&#8217;t change how it drifts in the wind, IF the three chutes cause the descent rate to be the same. If it descends slower, it will drift more, if it descends faster it will drift less.

But, multi chutes do tend to make a rocket SWAY less during descent.

Below, the type of ground trace that a glider makes when it circles and drifts with the wind. Let's say for this one, the wind is blowing to the SouthEast. That is where the center of the glide circle would drift - downwind to the SouthEast. While the actual path the glider takes as it drifts would be a linear spiro-graph type of spiral.

- George Gassaway
&#65532;
 
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Frederocket

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Chutes do not feel wind from the side. They drift with the wind. With the exception of turbulence or sudden gusts, or gliding chutes. Just like people who fly in a hot air balloon in 10 mph wind, to them they are in calm and feel no wind, the ground below them is moving at 10 mph. For a non-gliding parachute, if it is in 10 mph ind, the chute's perspective is it is falling vertically in "calm" air (again ignoring turbulence/gust issues). Thornburg's "River of Air" principle.

Say what George??? "Chutes do not feel wind from the side". How in the heck do they drift, if they don't feel wind??? How does sail on a sail boat propel the sail boat faster than the prevailing wind effecting the sail??? I know you know the answers... However, try to keep your post in context, when you quote me.. Go back and re read my response... My response had nothing to do with drift. Only the fact that a ring slot extraction chute is not an efficient load chute and, with design issues if used as a main load chute... The two issues I mentioned are theoretical fact of this particular ring slot extraction chute... I also said: " All that being said, there are ring slot designs, specificly designed as a primary cargo and/or special purpose recovery chute... However, the extraction chute shown is not one of those designs".
 

Salvage-1

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I think that George was using the analogy of the wind currents acting like currents in a river. The river may be 50ft wide, but have many different current tracks through it. The parachute is flowing along those currents, the only time that it should "feel" any movement itself is when it transitions between different currents. Once it is in a current, it moves at the same speed as that current.
There is a raisin for how things happen in currents (bad pun)
 
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