Chutes: X-Form versus Others

[ApolloMaker]

Hello All -----

I have ordered a couple of X-Form chutes for a new model coming down the pike. On comparison, I am wondering how the X-Form chutes perform (drag coefficient) compared to similar sized hex or octagonal "flat" chutes? It appears the X-Form chute may have a larger canopy effectively for the same diameter as others but not sure.

I have never used X-Forms so have not done any drop tests or have any other data. Any veterans out there who have experience with X-Forms, any comments certainly appreciated. Comments on deployment ease also of interest.

For reference, I am targeting a 24" X-Form for a Aerotech Strong Arm desiring gentle landings. Enough chute???

Many Thanks --- Bob ---

 

[rocketsmith]

X-form chutes will bring your rocket down faster with less lateral drift than a round chute of similar size. I might go up to a 30" x -form for the strong arm. Generally, x-form chutes are heavier than a hemispherical because they usually have heavier shroud lines. I only use x-forms for my drogues on dual deploy.

 

[dixontj93060]

For reference, I am targeting a 24" X-Form for a Aerotech Strong Arm desiring gentle landings.

Simulating a stock AT Strong Arm with a G64 and utilizing the standard kit chute which is a 30" round nylon the descent rate is 21.2 ft/s. This is already on the upper end of typical desired descent velocity. I look for 15 to 20 ft/s, others are comfortable with a bit higher range of 17 to 22 ft/s. But a 30" round will have a higher drag coefficient than an X-form. Within Rocksim for a round chute I usually use 0.75 drag coefficient versus 0.6 for an X-form. I don't know the exact size of what you ordered, but approximating a 24" X-form in Rocksim under the same conditions above gives a descent rate well over 30 ft/s--too fast for my liking.

 

[ApolloMaker]

Thanks for the replies. As I expected. Well, there are other things I can do with the X-Forms. That points me in the right direction and calibrates the size arena for me. Yes, the over 30 FPS range is too hot -- smells of broken fins to me :eyepop:
Will work on a round chute solution and plug the numbers into RockSim.

Thanks --- Bob ---

 

[tonypv]

Here's the decent rate page on the Top Flight web site.
Should give you a good idea of the difference between the two.

 

[bobkrech]

And here's a calculator of sizes not listed.

https://www.rocketreviews.com/tool_descent_rate.shtml

Bob

 

[ApolloMaker]

Yes, thanks for the added info. There is a general correlation between the two basic styles of chutes (loose correlation) but nevertheless, it clearly requires more X-Form chute to obtain the same effect as a "regular" style chute. Depending on the final weight of my Strong Arm, I will probably end up with something in the order of 30-36" of traditional nylon for a chute. I will probably have several to select from on the launch field to be able to compensate for wind and weight changes.

Thanks Again --- Bob ---

 

[MarkII]

If you use an X-form parachute in place of a conventional hex- or octagonal 'chute in order to get less drift, but use one with a larger diameter in order to get the same descent rate, doesn't that basically defeat the effect that you are trying to get by using the X-form? IOW, if a certain size of an X-form parachute has the same descent rate as a certain size of a hexagonal or octagonal parachute, won't it also have the same drift rate as the conventional 'chute? So you can't match the descent rate without also matching the drift distance?

MarkII

 

[Stymye]

An x-form with the same decent rate as a typical hemispherical chute is claimed to reduce drift by as much as 70 %.

 

[ApolloMaker]

Hi Mark and Andy ----- in general, you are both correct. The limiting factor for me is going to be space and weight. Especially if I eventually go to a DD (dual-deploy) chute arrangement. So there are a bunch of trade-offs. I will start with a single chute and experiment a bit, but I think what RockSim is showing me is going to be pretty close to reality.

But you never know about gusty winds, thermals, etc. I guess there is only so much you can do to protect your rocket, and then the rest is up to mother nature. Actually I don't mind chasing my rockets a bit, but its the impact damage that I don't want.

All great comments --- Thanks -- Bob --

 

[Handeman]

The smallest chute, material wise, with the highest Cd is a hemispherical. It has the highest CD with the least amount of material. The Elliptical is close and then the sheet type chute. The x-form is going to have the lowest Cd per diameter.

If you are looking for least amount of weight and packing area, the hemispherical is almost certainly the way to go.

You can do some searching but I believe the reason the x-form claims less drift for the same decent rate as the hemi type chutes is that the hemi type can act as an airfoil and actually create lift in high cross winds.

I don't have specifics on this, but I've had several rockets come down to low level and catch the ground level winds and never drop further. They were last seen 1/4 to 1/2 mile away at the same height they started the sideways drift at, and one was even going back up. I'm not sure they ever came down, they're probably in OZ by now.

 

[ApolloMaker]

Hello Handeman and All ---

Hey, thanks for the info. I have been deep into a couple of the more famous rocketry handbooks and what you noted was stated there too. I think I am going to equip my field rocket box with a number of chutes so I can pick to suit the wind and field size situation. Seems like cheap insurance --- it will be a while yet since I am just starting out in the "build mode" but won't be too long before I am ready to start launching and testing. Am really enjoying reading all the good posts here on the board --- great meeting and chatting place to get good expert input.

Thanks again -- Bob --

 

[Micromeister]

Another consideration is to look at the actual area of these different size Chutes.
24" hemi has a surface area of 904.78 Sq. In., 24" Round/Hex has 452.39 Sq. In., and an standard X-Form 320.0 Sq. In.
By Volumn it can be easily seen they will have radically different decent rates.

It's been my experience that X-Forms with about the same volumn still come down a bit faster then standard Hex or round chutes but I don't recall this being anywhere near 70% faster.

It has also been observed that most X-form chutes Spin rapidly during decent. I'm not sure if this has anything to do with decent rate but it sure makes a difference on model damage at touchdown. Model with decending fins really are not good candidates for X-form chutes.