Parachute upgrades in the UK...

One of the only online suppliers for model rocketry in the UK sells these chutes in their upgrade kits.


I'm a complete noob still, can we discuss the benefits of these compared to the usual stock chutes. It's obviously worth the investment right? Anything I can do do improve the quality of this chute even more?
What material do you guys use over the pond?

Ben

for use below 5C (40F) ripstop nylon is my choice(plastic chutes tend to not open in cold weather).
rex

Hi Ben,

What you need for a chute(s) depends on the application. The heavier a rocket, the more critical it is that it come down in a controlled fashion. The faster it can go, the more critical it is that the recovery system can take very high loads.

On the largest projects, people use man rated chutes or their equivalents or near equivalents without the rating. On the fastest projects, the drogue chutes may be designed for successful deployment at speeds exceeding mach 1.

At the smallest and lightest end, hobby rockets have used tumble recovery, streamers, plastic chutes, helicopter recovery...

The recovery system needs to be sized to the intended rocket. One is typically aiming for a descent rate of between 15 and 25 fps. The rate should be slow enough to essentially ensure that there is no damage to the rocket upon landing (or minimal, in certain special cases) and minimal risk of damage to whatever the rocket might land on!

One can see that if one targets 20fps descent rate, and the flight is to 500', then the rocket has 25 seconds to drift under main parachute. It won't drift all that far. But, if the flight were to 10000', the rocket would have 500 seconds to drift... That would be a problem! Wind speeds are higher at greater altitude above ground. The recovery crew would be in for a bit of a drive.

So, for flights which go at least a moderate altitude, one doesn't really want to open the main at apogee. But one also doesn't want to delay opening any recovery as the rocket will be gaining speed quite efficiently on the way back down! The shock of opening a main at high speeds would quite possibly rip the rocket apart and at least would do some damage. We absolutely do not want to rain parts down on spectators!

At apogee, the minimum we do is break the rocket apart. We want to render it a non-aerodynamic structure, without stability. This way no matter what else happens, the rocket cannot attain high speed on the way down. Some heavy fiberglass rockets have a terminal velocity in the hundreds of miles per hour. They can go completely subterranian on impact. This situation is to be absolutely avoided!

Usually, but not always, breaking the rocket apart at apogee also deploys a chute.

A small chute intended to provide a controlled but fast descent is called a drogue chute. These are typically very small chutes compared to the size of the rocket. They are also often relatively solidly constructed. If a rocket launch goes haywire for some reason, apogee may be accompanied with rather high horizontal speed... This stresses the recovery system and the drogue needs to be able to take it. Ditto the attachment points, lines...

If a drogue is being used, then the main does not have to be able to take high speed deployment. Such a main does not need to be as beefy. Drogue chutes are typically sized to control the rocket descent at somewhere between 50 and 100 fps.

As for the chutes themselves, at the smallest end, a simple plastic chute may suffice. At the biggest end, a commercial cargo chute may be in order for the main, and the drogue would be suitable for hanging off the back end of a dragster or a jet, or to slow the descent of a bomb released at high speeds.

Better chutes are typically made of rip-stop nylon. As the name implies, the intent of the fabric is to prevent a tear from spreading. Being nylon, these chutes should not be left for long exposure to sunlight. Sunlight (UV) degrades nylon.

Better chutes have stitched shroud lines. The picture you posted appears to have shroud lines that are stitched near the edges of the canopy. This is good. There are multiple ways to stitch the lines onto the canopy and some are definitely better than others.

https://spherachutes.com/construction.asp - Read this over; it will likely answer some of your questions.

I apologize if my post was aimed at too low a level. I just figured to start with some of the basics.

Gerald

Thanks, some really good information there.
Not that I'll be needing it, but out of interest how would you go about implementing a drogue chute system?
Electronics would have to be introduced surely?

Well, possibly someone can come up with a non-electronic method, but electronics are easy nowdays.

One can use motor ejection to split the rocket in the middle, and deploy a drogue. Then one can deploy a main at a later time from the upper section using an altimeter hooked up to some sort of pyro charge or other pressurization system. Typically the nosecone would be pinned in such an arrangement, to prevent deploying the main early.

One can use tether retention of the main in its own bag. The drogue tries to pull the main out, but it is restrained by a tether. The tether is released when one wants to deploy the main chute.

One can eject the main wrapped snugly in nomex, held closed by nylon wire ties. These wire ties are inserted through linecutters. The main in the blanket acts as the drogue. When one wants the chute to open, fire the linecutters to let the main unfurl.

For launches which are not all that high, one could use a linecutter (carefully) to prevent the main from fully opening. Fire it lower down to release the shrouds so the main can open the rest of the way. This method is probably a bit hard on the main so I wouldn't really recommend it but it could be made to work.

Etc.

Reliable deployment of chutes is established by using a proper packing method. In low power rocketry people are often taught to roll up the chute and wrap the lines around it. This is NOT a reliable method of packing any chute and I highly recommend avoiding the practice. Chute packing is a complete subject by itself, but looking at how riggers pack man rated chutes would be a good idea. There are established practices which have proven to work reliably, for when a chute absolutely positively must work correctly.

On my Sprite rocket, which weighs 60-80 pounds depending on motor, I use a rather small drogue to drop it down pretty quickly - on the order of 100fps or even a little faster. Ejection is via CO2 pressurization of the upper compartment, and can be triggered by either of two altimeters. I use CO2 instead of the more usual pyro methods because this rocket could potentially go 20Kft with the right motor, and black powder is more difficult to make reliable at that sort of altitude. The entire lower compartment can be filled with motor so there is no room there. I deploy everything out the top. So the nosecone is attached to the drogue by a short line, and the rocket is attached by a longer line. This long line runs down to a tether which anchors the line to the upper bulkhead of the electronics bay. That tether can be released by either of the two altimeters. There is a deployment bag for the mains which is also held down by a short line from the top of the bag to the tether. So when the tether is released, the drogue is only pulling on the deployment bag and not attached to the rocket. Inside the deployment bag there are two chutes - a large one for the rocket, attached to the electronics bay upper bulkhead, and a smaller one for the nosecone. These are side-by-side in the bag, and deploy together. The nosecone chute is needed because the drogue isn't big enough to drop the nosecone slowly enough to be safe. Once the mains are deployed, the nosecone under its main and the drogue, and the rest of the rocket under its main, come down as two separate components. This is what is called a freebag system, as the bag is 'free' from the rocket. Deployment bags are often used in larger projects because they increase the odds of successful orderly deployment of a chute. Using more than one chute within the bag is not common though.

Dual deployment in its various forms makes for a very pretty rocket flight. The main is typically released at relatively low altitude - say 400 - 900 ft. So the action is easily seen by everyone. The rocket puts on a show!

Gerald

In moderate-sized to small rockets, the new Archetype Rocketry cable cutter turns any rocket that has room for electronics into dual deploy: you wrap the parachute in a fireproof fabric like a burrito and bind it closed with an electrical tie running through the device. When you fire the ematch in the cable cutter, it cuts the electrical tie allowing the parachute to open easily.