RocketRage Quantum chutes?

[eengelgau]

Hi Cjl,

since I don't forsee putting hundreds of uses on almost any rocketry chute. Besides, if I did make it to a hundred uses on a parachute without shredding it, losing it, toasting it, or tearing it, I don't think I'd mind replacing it

I have to admit that is funny:lol: I can certainly agree - If I could count on even 20 uses from a Chute or Rocket that would be amazing!

Thanks for the order - I have it!

 

[troj]

(Oh, and when I say that it isn't as durable, I mean that it degrades significantly in performance after a few hundred uses. It's a significant difference for skydiving, but I wouldn't worry about it for rockets, since I don't forsee putting hundreds of uses on almost any rocketry chute. Besides, if I did make it to a hundred uses on a parachute without shredding it, losing it, toasting it, or tearing it, I don't think I'd mind replacing it).

Hey, Chris?

If you put a couple hundred uses on your reserve, you have issues....

-Kevin

 

[cjl]

Hey, Chris?

If you put a couple hundred uses on your reserve, you have issues....

-Kevin

I agree

(That's why my reserve is the easier-packing F-111, while my main is ZP)

For the record, my reserve has never been opened, except for inspection and repacking every 6 months. The same cannot be said about my main.

 

[troj]

For the record, my reserve has never been opened, except for inspection and repacking every 6 months. The same cannot be said about my main.

Hopefully it continues that way! A friend has about 1800 jumps, and has only put his reserve to use twice.

-Kevin

 

[rfjustin]

I have a 15, 30, and 50, but as you suspected, I definitely do not want to part with any of them - I like them too much.

cjl,

Did you use the RRQS30 in your AMRAAM?



Justin

 

[cjl]

cjl,

Did you use the RRQS30 in your AMRAAM?



Justin

Yep. It survived the cato too, luckily.

 

[AlphaHybrids]

I've made many Rocket Rage clones. They all perform excellent. Here in Colorado where the air is thin I've used them at a starting elevation of 8800' and I've never had a problem. Very stable descent and they pack tiny. I used a 60" one of my L3 to over 27k. I have patterns from 48-120" and they work great.

A descent rate chart can be seen at:

Descent Rate Chart

This is based off of actual data on many flights to come to a conservative value.

About twice a year I get group orders together and make about 20 parachutes each time. Generally I make them in April and September (before our two big launches).

If people would be interested I would consider doing a third run of sizes.

Edward

 

[AlphaHybrids]

Cost performance is key. For any given size it will take a bit more fabric (maybe 6% more area),

Interesting you have more fabric. Every derivation and comparison I've ever done (I've done a lot to develop these chutes) has less area. Though I have found they utilize fabric much more efficiently than other shapes.

Edward

 

[eengelgau]

Hi Edward, It's to extend and flair the very end of the gore so the apex can be pulled down. It's minor but needed to keep the overall shape close to ideal.

I'm pushing for a prototype this weekend, and to fly it next...

 

[AlphaHybrids]

Okay, so you are using an elliptical gore an pulling the apex down. I did find a difference from just pulling the apex down versus a true toroidal derived shape in performance.

Edward

 

[eengelgau]

Hello, yes, I'm going for a more optimized shape. We'll see once I have the prototype done if I need to tweak the pattern some.

 

[eengelgau]

Hi all,

This is based off of actual data on many flights to come to a conservative value.

So I have a question about the performance information provided here or at the very least I don't understand how these chutes are sized.

Let's take for example a 60" chute, one of our most popular chutes - we've sold a bunch of these. We've established that the semi-ellipsoid design has a Cd of about 1.5(+- a bit). My own flight data and many others have born this out. For our 60" chute @ 20fps that means 13.3 lbs weight. To be a bit conservative we sell it as a 12lb chute @ 20fps. I provide a Descent Rate Calculator spread sheet To help my customers calculate the proper chute size. If you enter in 13.3 lbs (213oz) and use 1.5Cd you get 19.93fps.

So looking at the Alpha data and at least how I read it they say their 60" toroidal design can support 26lbs at sea level. If I use our descent rate calculator and plug in 26 lbs we need a Cd of 2.8 to support 26lbs. So what am I missing here. Is this possible?

So there are two possibilities as I see it:

1 - The 60" Alpha chute rating is not representative of the overall opening of the chute under flight - maybe it's really 72" opening in flight?

2 - Since I at least am skeptical of any chute having a Cd of 2.6 the information may be in error?

Comments? I thought this was worth more discussion.

 

[AlphaHybrids]

They are actually 60" when inflated. They are not 72". Are you using the correct canopy area. My parachutes are not elliptical patterns with the gores extended. They are true toroids. When I flew my L3 I estimated 16 fps at 5500' using my data I had gathered. I came in at 16.4 fps as an actual descent rate. I built a larger chute for a customer that was flown in California at LDRS. We predicted a descent rate with the parachute of 13 fps, and the actual descent rate was around 12 fps. I'm very confident in my data. I've trusted it for my own recovery needs since I started making them.

Edward

 

[UPscaler]

I agree

(That's why my reserve is the easier-packing F-111, while my main is ZP)

For the record, my reserve has never been opened, except for inspection and repacking every 6 months. The same cannot be said about my main.

Ever considered BASE? :smile:



Braden

 

[cjl]

Ever considered BASE? :smile:



Braden

Considered? Yes, but I don't think that I will anytime soon. I like being high enough that a reserve is still useful if the main were to fail.

 

[jaz]

Wow that sounds like a very effective chute to pull such high cd. I am going to have my pennies out to side when these become available.

 

[eengelgau]

Hi Edward, I'd be interested in a pic of your chute inflated? Is your chute 60" across the opening when inflated? In other words if your chute while inflated were projected against a 2d surface it would be 60" diameter. Maybe a drawing might help as well.

Thanks and just trying to understand and thanks...

 

[cjl]

Hi all,



So I have a question about the performance information provided here or at the very least I don't understand how these chutes are sized.

Let's take for example a 60" chute, one of our most popular chutes - we've sold a bunch of these. We've established that the semi-ellipsoid design has a Cd of about 1.5(+- a bit). My own flight data and many others have born this out. For our 60" chute @ 20fps that means 13.3 lbs weight. To be a bit conservative we sell it as a 12lb chute @ 20fps. I provide a Descent Rate Calculator spread sheet To help my customers calculate the proper chute size. If you enter in 13.3 lbs (213oz) and use 1.5Cd you get 19.93fps.

So looking at the Alpha data and at least how I read it they say their 60" toroidal design can support 26lbs at sea level. If I use our descent rate calculator and plug in 26 lbs we need a Cd of 2.8 to support 26lbs. So what am I missing here. Is this possible?

So there are two possibilities as I see it:

1 - The 60" Alpha chute rating is not representative of the overall opening of the chute under flight - maybe it's really 72" opening in flight?

2 - Since I at least am skeptical of any chute having a Cd of 2.6 the information may be in error?

Comments? I thought this was worth more discussion.

That is a surprisingly high CD. I have seen data on my own Rocket Rage chutes showing a CD of >2.2 though, so it might not be in error. I'll definitely be interested in seeing your numbers when you get around to testing your toroidal design.

 

[eengelgau]

Hi Cjl, I agree that it seems very high. I think there are some theoretical limitations on how high this can be but I can't say what that is. But 2.8 seems way out there. For now I am skeptical until I have more information...

 

[AlphaHybrids]

eengelgau,

I have never claimed a Cd as high as you are claiming, those are your figures based on your assumptions made on my design. Don't put words in my mouth. The figures in the table are based on an approximate Cd of 1.8. This is a conservative value based on the data and what I feel suits most flying conditions.

When inflated and projected against a 2d surface or slicing a plane through them, they are the diameter I've posted. A 60" would be 60". A 60" design I can fit into 6" of 64mm tube (including all the shroud lines). When I really try I can get down to 4.5". Now, this shouldn't really matter as what matters more is area of the canopy and relative density of the air that the canopy is operating in.

Edward

 

[cjl]

eengelgau,

I have never claimed a Cd as high as you are claiming, those are your figures based on your assumptions made on my design. Don't put words in my mouth. The figures in the table are based on an approximate Cd of 1.8. This is a conservative value based on the data and what I feel suits most flying conditions.

Ed,

If your chute has an inflated diameter of 60 inches, and carries 26 pounds at sea level at 20 fps, that's a coefficient of drag of 2.8 (using the projected chute area as the reference area, which is fairly standard). In other words, that is the Cd that you are claiming (I'm not saying it's necessarily wrong though, just that it is in fact what the Cd would have to be to support your numbers). With a Cd of 1.8, your values would have to be significantly lower in your table (oh, and Cd is usually calculated using the frontal area of the chute when inflated, not on the area of the fabric used).

 

[AlphaHybrids]

So, does that area of the canopy have anything to do with it? I thought that was a key part in the Cd calculation.

In the Recovery Systems Design manual, by T.W. Knacke, they state this "It is convenient to relate parachute drag coefficients to the canopy nominal area, So, derived from the design dimensions because accurate measurement of the inflated canopy for the determination of the projected area and Cdp is seldom feasible." I use the canopy area because it is accurate when calculating the Cd.

Edward

 

[cjl]

So, does that area of the canopy have anything to do with it? I thought that was a key part in the Cd calculation.

Edward

Area is a key part, but the area that's usually used is the area perpendicular to the flow. You can actually pick whatever area you want, but the Cd is kind of meaningless unless a common standard is used. For most objects (cars, balls, parachutes, etc), the standard area is the area projected into a plane perpendicular to the flow. For aircraft, the area typically used is the wing area (which is much larger than the area normal to the flow, which is also why airplane coefficient of drag values are so small typically). If you want a more universal value, Cd*A is sometimes used. It's no longer size-independent, but it is independent of the selected reference area. Cd*A is also useful because it tells you how much aerodynamic force is created for a given dynamic pressure. Two parachutes with identical Cd*A values should create the same force at the same descent rate, regardless of other parameters (which is why it is convenient).

 

[AlphaHybrids]

Chris, I agree that it would be useful if given a Cd*A value. It would be a much better comparison apples to apples. If they were given independently you could easily compare sizes.

Edward

 

[eengelgau]

Very well said Chris...

For most objects (cars, balls, parachutes, etc), the standard area is the area projected into a plane perpendicular to the flow. For aircraft, the area typically used is the wing area (which is much larger than the area normal to the flow, which is also why airplane coefficient of drag values are so small typically).

Chris, you must be in aeronautics since a good buddy of mine her in the SF bay area who works at NASA Ames said the exact same thing!

Edward - were looking at about a 19.6 sq' projected area, that is our 60" chute projected frontal area... So let's talk in those terms.

From the markets perspective another way to look at this is that a 60" chute has a certain size and performance expectation when presents to those evaluating a chute's performance - it's a 5' diameter chute. At FC we rate our chutes very simply as the projected frontal diameter (and area) of the chute has perpendicular to the flow - the opening is 5' round. So calculate the area is about 19.6 ft ^2 and and the math as related to air density is what is that is it (unless your on Venus or Triton). I'm, going to go way out on a limb here are say it - if your 60" chute as projected onto a 2D plane (the effective frontal area) is 19.6 sq' and can support a load of 26 lbs @ 20fps I'll say at this point of time that you are in error - you need a higher atmospheric density than we have here on this planet. You better look closer at how you come up with this number. Folks on this thread make purchasing decisions based on this information and it is simply not correct.

By the way if were going to compare apples to apples, our 60" chute can fit into < 4" L in a 6" airframe. Base strictly on our actual measurements our 60" chute will fit into 66 cu" if jammed in. Obviously your mileage may vary.

 

[AlphaHybrids]

When I calculate the area of a 60" diameter true hemispherical parachute I get a total canopy area of 39.27 ft^2. I know an elliptical parachute has less canopy area , but it depends on your height to width ratio. A 60" toroid that I make has just over 30.53 ft^2 of canopy area. Either way a 60" circle has an area of 19.63 ft^2.

Edward

 

[eengelgau]

Hi Ed, ok... Maybe a pic would help us understand. But keep in mind it is _not_ the canopy area that is determining the total drag, but the projected flattened area as perpendicular to the air flow. If they are a 60" circle (as you verify) then you have 19.63 sq' (pi * d^2 / 4). And given your rate this at 26lbs @ 20fps that means a drag coefficient for the chute of 2.8. I maintain that this is not possible - much too high.

So I think what you may be doing to considering the canopy area of 30.5 sq' to make this determination? That area is equivalent to a 74" round circle. In fact 26 lbs @20fps in that case works out to a very reasonable Cd of 1.8 or so. That Cd I can believe. But you can't look at the chute size in terms of canopy area to do your rating.

So flat sheet chutes do work on simple area since it's unpredictable how the chute would project into a flat surface, hence the Cd of about .7 or so. If I looked at our chutes and the total canopy area I get a number close to this as well.

Anyway let's leave it as that, we can go round and round on this... My 72" prototype was finished sewing yesterday and I'll soon have actual performance info, not calculated expected performance. The chute looks great with eye popping colors.

 

[AlphaHybrids]

Parachute Comparison


I drew a simple CAD drawing to help explain things. All three parachutes drawn have the same projected area, but differ vastly in canopy area. The blue line is a true hemispherical parachute. The green line is an elliptical parachute, with a 70.7% aspect ratio. The red line is a toroidal parachute. Canopy area does have an affect on descent rate. If it didn't, then we wouldn't need to make larger parachutes for heavier objects. Projected area is a way of comparing parachutes, but as T.W. Knacke stated, it doesn't work for every case nor is it appropriate for every case. Just like a simple flat board will not produce lift, once molded into an airfoil it can, shape matters in a parachute, not just projected area.

What method are you using to determine descent rate? I used a Featherweight Parrot altimeter coupled with a handheld weather station that gave me the density altitude, relative humidity and barometric pressure. I found using the Featherweight gave me many data points to average over the descent, rather than taking when the parachute came out and when it hit the ground. You can also look the data and determine easily if the parachute is caught in wind and be able to disregard that data.

Edward

 

[cjl]

Parachute Comparison


I drew a simple CAD drawing to help explain things. All three parachutes drawn have the same projected area, but differ vastly in canopy area. The blue line is a true hemispherical parachute. The green line is an elliptical parachute, with a 70.7% aspect ratio. The red line is a toroidal parachute. Canopy area does have an affect on descent rate. If it didn't, then we wouldn't need to make larger parachutes for heavier objects. Projected area is a way of comparing parachutes, but as T.W. Knacke stated, it doesn't work for every case nor is it appropriate for every case. Just like a simple flat board will not produce lift, once molded into an airfoil it can, shape matters in a parachute, not just projected area.

Ed,

While I see the point you're trying to make, the standard area used for parachute computations is in fact the projected area, not the canopy area. Canopy area does matter, as it determines many things, such as how tightly a given parachute will pack, and how much the materials cost is, but the projected area is the area which will directly affect the flow.

Also, I don't understand what you're trying to say with this comment:

Canopy area does have an affect on descent rate. If it didn't, then we wouldn't need to make larger parachutes for heavier objects.

We use parachutes which have a larger projected area (and a larger canopy area, typically) for heavier objects, so this comment in no way supports the use of canopy area over the use of projected area as the correct reference. Also, as I said before, the value of Cd*A is what really determines the weight characteristics of the parachute (two different parachutes, with different canopy areas and different projected areas but with the same value of Cd*A will descend at the same speed under the same load).

Also, keep in mind that the area being discussed here is only a reference area. The math actually works out just fine no matter what area you choose as a reference. So, you can absolutely define a Cd that is based on the total fabric area if you would like. In some ways, this Cd would be an excellent indication of how tightly a given chute will pack, as it would effectively describe the drag per quantity of fabric used. However, the standard reference area used for parachutes (and, to be honest, pretty much everything except aircraft) is the projected frontal area normal to the flow, and if you use any other area, your Cd values will not be easily comparable with those of most parachutes (since to properly compare parachutes, a standard should be followed).

 

[mikec]

While I see the point you're trying to make, the standard area used for parachute computations is in fact the projected area, not the canopy area.

I don't know if this is standard across the literature, but "Parachute Recovery Systems Design Manual" by T W Knacke does use the canopy area, not the projected area, as the reference area -- see page 4-11. "... parachutes use the canopy surface area. The selection of the wing planform and the parachute surface area as references was made for practical reasons... the surface area of the parachute canopy is fixed; however, the frontal projected area of the inflated parachute canopy changes with airspeed, porosity. line length, and type of parachute."

That said, I totally agree that using the frontal area would be much better for making apples-to-apples comparisons between chute types, since that's what most rocketry simulation software could most easily make use of. But the effective Cd seems to vary with descent rate/load to a pretty significant degree for many designs.