Streamers VS. chutes

[roundog]

Hey all ,

While theres plenty of fields to launch at near my home , living on the shores of lake ontario leads to very few days where there isnt at least a moderate wind, and even when ground wind is low , winds aloft are usually pretty brisk . So the issue i run into is my chutes getting grabbed by the breeze and landing quite a distance away from where i launch. I've found that streamer recovery is obviously a faster more linear descent, and have so far been lucky without breaking my rockets , but im wondering whats going to happen when i start going to larger/heavier flights. Is there some rule of thumb for streamer/rocket size ? Such as 2-3 time rocket length ? Or X number of inches long for rocket weight ? What length/width of streamer could i put on my big bertha to bring it down safely after a flight on a C-6 ? IS folded streamer just a packing option , or is it a high drag design ?

Sorry for my semi newbish questions and thanks for your help

 

[MarkII]

Streamers ARE recovery devices. They can and have been used in larger rockets, such as the SSRS Lasor 114. The Big Bertha could conceivably recover on a streamer, but there are at least a couple of issues that you would need to deal with. The first would be to find enough room in the Bertha to carry a streamer that was large enough to be effective. That probably wouldn't be all that hard to do, but the other issue has to do with the fins. Bertha has long, thin swept-back fins that will be the first part of her that will contact the ground during recovery. Since she will be descending much faster on a streamer, there is a good chance that the impact will break a fin or two. You could reinforce them by laminating them with cardstock, but that would add weight at the wrong end of the rocket. Rockets that recover on streamers are often designed with fins that do not sweep back beyond the aft end of the rocket for this reason. When they come down, the part that contacts the ground first is the nozzle end of the motor, which is usually the strongest part of the rocket and the part that is least likely to be damaged during a fast streamer recovery.

A better solution would be to use either a parachute with a large spill hole in the center of the canopy or else an X-form parachute. Putting a hole in the center of the parachute canopy decreases the drag that the parachute produces and thus increases the descent rate. It also eliminates nearly all of the wild oscillating that normally occurs with parachutes. X-form or cross-form parachutes have canopies that are made of two strips of material sewn together to form a cross or X shape. These also produce less drag and less oscillating, resulting in a more vertical descent. If you have a plastic parachute, you can create a spill hole in it by simply cutting out a circle in the center of the 'chute. Top Flight Recovery makes a series of X-form nylon parachutes in sizes that are appropriate for model rockets. If you use an X-form 'chute, the standard rule of thumb is to go one size larger than the size of the parachute that you would normally use.

MK

 

[cjl]

I have a Big Bertha with a streamer, and I just put in a huge length of orange streamer. It recovers just fine. I'm sure you could use less than I use, I put in the massive length mostly for visibility (I have a 24mm mount, and I love E6s ).

It can definitely be done though.

 

[MarkII]

I have a Big Bertha with a streamer, and I just put in a huge length of orange streamer. It recovers just fine. I'm sure you could use less than I use, I put in the massive length mostly for visibility (I have a 24mm mount, and I love E6s ).

It can definitely be done though.

Very likely true, especially if the recovery area is covered in grass or soft ground.

Another technique, and probably the easiest to implement, is to simply reef the 'chute. You just wrap some masking tape around the shroud lines a bit above where they attach to the rocket, which prevents the parachute canopy from opening to its fullest diameter. It is equivalent to putting a smaller parachute on the rocket, but with reefing, you can fine tune the amount that the canopy opens in order to dial in the descent rate that you want.

MK

 

[roundog]

Great , thanks for the replies folks I think ill try the reefing suggestion first , as it seems the simplest to implement, and provides a little more learning curve. Going for a walk for a rocket is easier then re-cutting and re-glueing fins.

 

[ScrapDaddy]

If you use an X-form 'chute, the standard rule of thumb is to go one size larger than the size of the parachute that you would normally use.

MK

For some reason I read this on rocketerium, site and I think doing this is against the purpose of the idea.The whole concept of using an X-form chute is to reduce drift and increase desent time, If you increase the size of the X-form isn't it contrary to the whole thing?


SD, X-form user


Ps I have gotten away with using an 18inch X-form in my Cfx-six-footer, which comes with an 18inch chute.

 

[bobkrech]

Hey all,

While theres plenty of fields to launch at near my home, living on the shores of lake Ontario leads to very few days where there isn't at least a moderate wind, and even when ground wind is low, winds aloft are usually pretty brisk. So the issue i run into is my chutes getting grabbed by the breeze and landing quite a distance away from where i launch. I've found that streamer recovery is obviously a faster more linear descent, and have so far been lucky without breaking my rockets, but I'm wondering whats going to happen when i start going to larger/heavier flights. Is there some rule of thumb for streamer/rocket size? Such as 2-3 time rocket length? Or X number of inches long for rocket weight? What length/width of streamer could i put on my big Bertha to bring it down safely after a flight on a C-6? IS folded streamer just a packing option, or is it a high drag design?

Sorry for my semi newbie questions and thanks for your help

The Team America Rocketry Challenge for 2010 involved recovering a rocket containing an egg on a streamer. https://rocketcontest.org/index.cfm

Streamers are sized by the weight of your rocket, and the most efficient streamer has a length to width ratio of 10:1. The Cd of a streamer ranges from 0.15 for a plain streamer to as high as 0.4 for a folded streamer. It is harder to find the design rules for streamer recovery than it is for parachutes, but the TARC Yahoo group contains several papers on the topic including the attached file.

A simple design rule of thumb for an unsophisticated streamer that will descend at a 23 fps rate is:

Streamer Area in square inches = 100 x Rocket Weight in ounces.

This assumes a simple flat streamer of mylar or other thin plastic film that is 1-2 mils thick. This type of streamer has a Cd=0.15.

A more sophisticated folded streamer can have drag coefficients ranging from 0.15 < Cd < 0.4, and area could be reduced by the ratio of the Cd, or the descent velocity would be the square Root of the ratios slower if the area was not reduced.

Streamers are most efficient when the streamer is rectangular with a 10:1 ratio. If you know the required streamer area, then width is simply:

Width in inches = sqrt (Area in square inches/10) or if you know the rocket weight the

Width in inches = sqrt (10 x Rocket weight in ounces)

and the length is 10 times the width.

Bob

View attachment Streamer Recovery Tutorial (Jul 09).pdf

 

[roundog]

Thats exactly what i was looking for Bob , thanks alot

 

[jadebox]

The whole concept of using an X-form chute is to reduce drift and increase desent time ...

That's a common myth. Actually, the drift distance is directly proportional to the descent time. The form of the parachute doesn't make any significant difference.

-- Roger

 

[RoyAtl]

Streamers ARE recovery devices. They can and have been used in larger rockets, such as the SSRS Lasor 114. The Big Bertha could conceivably recover on a streamer, but there are at least a couple of issues that you would need to deal with. The first would be to find enough room in the Bertha to carry a streamer that was large enough to be effective. That probably wouldn't be all that hard to do, but the other issue has to do with the fins. Bertha has long, thin swept-back fins that will be the first part of her that will contact the ground during recovery. Since she will be descending much faster on a streamer, there is a good chance that the impact will break a fin or two. You could reinforce them by laminating them with cardstock, but that would add weight at the wrong end of the rocket. Rockets that recover on streamers are often designed with fins that do not sweep back beyond the aft end of the rocket for this reason. When they come down, the part that contacts the ground first is the nozzle end of the motor, which is usually the strongest part of the rocket and the part that is least likely to be damaged during a fast streamer recovery.

A better solution would be to use either a parachute with a large spill hole in the center of the canopy or else an X-form parachute. Putting a hole in the center of the parachute canopy decreases the drag that the parachute produces and thus increases the descent rate. It also eliminates nearly all of the wild oscillating that normally occurs with parachutes. X-form or cross-form parachutes have canopies that are made of two strips of material sewn together to form a cross or X shape. These also produce less drag and less oscillating, resulting in a more vertical descent. If you have a plastic parachute, you can create a spill hole in it by simply cutting out a circle in the center of the 'chute. Top Flight Recovery makes a series of X-form nylon parachutes in sizes that are appropriate for model rockets. If you use an X-form 'chute, the standard rule of thumb is to go one size larger than the size of the parachute that you would normally use.

MK

You can also use thin kevlar (or really any tough thin thread) and attach the shock cord to the OUTSIDE of the rocket, a little behind the normal center of gravity. This will allow the rocket to hang horizontally, adding somewhat to the drag of the streamer, and the impact will be less stressful to the fins. Of course, the disadvantage is the thread hanging out of the rocket on ascent. But it just depends on what's important to you.

 

[ScrapDaddy]

That's a common myth. Actually, the drift distance is directly proportional to the descent time. The form of the parachute doesn't make any significant difference.

-- Roger

So do X-type parachutes work? Or are they just a fancy way to turn a 18" chute into a 12" chute?

 

[cjl]

That's a common myth. Actually, the drift distance is directly proportional to the descent time. The form of the parachute doesn't make any significant difference.

-- Roger

Agreed. You will have the same drift for a given rocket at a given descent rate*. If you flew a rocket and had half a mile of drift on a hemispherical chute, you would have had the same half mile of drift on a streamer, as long as the streamer was sized for the same descent rate.

The reason that an X form or streamer gives less drift typically is that if you swap out a normal chute for an x-form or streamer, you will often size the x-form or streamer to give a higher descent rate. With the higher descent rate comes less drift.

*Unless you use something like a parafoil chute...

 

[gpoehlein]

You can also use thin kevlar (or really any tough thin thread) and attach the shock cord to the OUTSIDE of the rocket, a little behind the normal center of gravity. This will allow the rocket to hang horizontally, adding somewhat to the drag of the streamer, and the impact will be less stressful to the fins. Of course, the disadvantage is the thread hanging out of the rocket on ascent. But it just depends on what's important to you.

This is fairly common in parachute and streamer duration events - the drag of the external shock cord is more than offset by the clean inside for a larger streamer or parachute. And larger laundry usually means better thermal action. I usually cut a small notch about halfway along the fin root and thread the kevlar thread through the hole - build it into the fin fillet and it isn't going anywhere. I then use a wrap of silver mylar tape at the CG to hang it horizontally.

 

[BobH48]

There is also the streamer calculator over on EMRR.

https://www.rocketreviews.com/cgi-bin/resources/recoverybox.cgi?streamer

 

[BEC]

Interesting reading.

One error in the "tutorial" posted by Bob: Coverite Micafilm does NOT have an adhesive layer - this is one of the reasons it is lighter than other iron-on coverings. So in this context creases in a Micafilm streamer could be set by ironing.

 

[MarkII]

You can also use thin kevlar (or really any tough thin thread) and attach the shock cord to the OUTSIDE of the rocket, a little behind the normal center of gravity. This will allow the rocket to hang horizontally, adding somewhat to the drag of the streamer, and the impact will be less stressful to the fins. Of course, the disadvantage is the thread hanging out of the rocket on ascent. But it just depends on what's important to you.

I was going to mention that, but it would have made a long post longer.

MK

 

[MarkII]

Agreed. You will have the same drift for a given rocket at a given descent rate*. If you flew a rocket and had half a mile of drift on a hemispherical chute, you would have had the same half mile of drift on a streamer, as long as the streamer was sized for the same descent rate.

The reason that an X form or streamer gives less drift typically is that if you swap out a normal chute for an x-form or streamer, you will often size the x-form or streamer to give a higher descent rate. With the higher descent rate comes less drift....

Exactly. I didn't mean to imply that choosing the larger 'chute was meant to produce the same descent rate. It would still be faster from what I understand. I've never used one, though.

MK

 

[roundog]

Just happened to find this on the apogee site in their "Free for today" section . They must have known i needed help too ! https://www.apogeerockets.com/education/downloads/Newsletter128.pdf

Seems all my questions and preparation was for naught anyways ....My poor bertha burnt up on the launch pad when the engine failed and spit the nozzle out the tail end . Torn motor mount tube relegated her to the heap before she ever left the ground . Guess i can still gut her and recover 90% of the materials ...but man ...what a let down

I think the nice Estes folks are gunna send me a new one though

 

[luke strawwalker]

So do X-type parachutes work? Or are they just a fancy way to turn a 18" chute into a 12" chute?

Yes they work and work quite well...

The point being made was that, if you increase the descent time, (by lowering the rate of descent obviously) you will by definition ALSO increase the drift, regardless of parachute type.

That said, if you have an 18 inch parachute, one round or hex without a spill hole and one X-form, the X-form usually drifts less due to the design, which has less surface area than the round/hex and therefore less drag, so a higher rate of descent. BUT if you put a LARGER X-form in the rocket to slow it down more on the descent (increasing the descent time from the same altitude) then the X-form would probably drift about the same distance as the smaller round or hex chute without a spill hole.

Make sense?? OL JR

Sorry, posted before I read the whole thread-- explained very well above by cjl-- even a streamer sized for the same descent rate as the parachute it replaces will drift just as far from the same altitude in the same ambient conditions...

 

[bobkrech]

However, drag is not the only factor.

A parachute also has lift, and under the right circumstances, if your parachute develops additional lift due to a thermal or cross-wind, it's descent rate can slow or ever reverse, which will cause serious horizontal displacement.

I don't believe this will occur with a streamer, so it is likely that a streamer with the same drag as a parachute will not drift as far as the parachute.

Bob

 

[cjl]

However, drag is not the only factor.

A parachute also has lift, and under the right circumstances, if your parachute develops additional lift due to a thermal or cross-wind, it's descent rate can slow or ever reverse, which will cause serious horizontal displacement.

I don't believe this will occur with a streamer, so it is likely that a streamer with the same drag as a parachute will not drift as far as the parachute.

Bob

Drag and lift only differ by direction. They both scale the same with airspeed, density, etc. If a thermal or cross wind occurs, a streamer and a parachute should respond almost exactly the same, aside from a short transient period of equalization. It's true that they will behave differently in the short transient right after they enter the new wind, but other than that, it should be about the same.

 

[slogfilet]

So do X-type parachutes work? Or are they just a fancy way to turn a 18" chute into a 12" chute?

To rephrase Scrap's question... is there anything an 18" X-form can do that a 12" parasheet won't? (Pardon my arbitrary sizes)

Are there any other considerations, such as drag vs. packed volume? Do they just look cooler?

 

[cjl]

Basically, no. Anything an 18" X-form will do, a 12" round will also do (assuming that's the roughly equivalent size - I haven't actually calculated it). The X-forms do look cool though...

 

[ScrapDaddy]

Ok thanks guys, I have been wondering about that for a while

 

[Peartree]

Maybe someone has answered this already (if so, I apologize), but is there a significant (or any) difference in the ease of packing an x-form vs. a parasheet vs. a hemispherical 'chute?

 

[ScrapDaddy]

Maybe someone has answered this already (if so, I apologize), but is there a significant (or any) difference in the ease of packing an x-form vs. a parasheet vs. a hemispherical 'chute?

(i have all 3 of these) Well there is no signifiant difference except for the actual folding, an X-form is folded across the center diagonally and they folded diagonally again to form a shape that looks like rectangle with a small right triangle on top of it, then the lines are wrapped around.In hemispherical parachutes, the folding closely resembles that of a parasheet, par estes instructions. getting them in the tube is a different story, assuming you had a X-form, Standard, and hemispherical parachutes of the same weight nylon and all 18", due to the way the measure these parachutes, the Hemispherical would take up the most room, followed by X-type (due to the nature they must be folded) , then standard. I know this because i have gotten a 24" standard in a BT55 with ease, and yet a 18" X-form would bearly fit, and my 18" fruity chute would not even get close to getting in there.

 

[cjl]

Scrap: It also depends on the material the chute is made of. For a given size (and all of the same material and construction quality), generally you're right (though I would say that an X form takes up less room than a parasheet if they're the same size). For a given carrying capacity though, I would exactly reverse it. If all are sized to give the same descent rate, a hemi will pack the tightest, followed by a parasheet, followed by an X-form.

 

[ScrapDaddy]

Scrap: It also depends on the material the chute is made of. For a given size, generally you're right (though I would say that an X form takes up less room than a parasheet if they're the same size). For a given carrying capacity though, I would exactly reverse it. If all are sized to give the same descent rate, a hemi will pack the tightest, followed by a parasheet, followed by an X-form.

The word I think you are looking for is efficent, i agree that a Hemisphereacal parachute does Its job much more efficently than a parasheet.

X-form parasheet take up more room due to the nature of the folding required. Just remember that less meterial doesn't always equate to smalled volume.

 

[cjl]

I know, and I'll be the first to admit that I haven't flown many x-forms. I still think I could pack one smaller than a parasheet of the same diameter though.

(I don't have any right now to try it though)

 

[ScrapDaddy]

Nor have I, I have only flown one X-type, but I fly that very often (flight 49!) and I was making a comparison using my TFR 24" standard and a 18" X-form, and I want to clear this up, a 24" standard will have greater volume, bur an X-form will have a larger diamiter for packing.