Posts Tagged ‘parachute’

 

Dual Deploy Nose Cone – Part 1

The last week we have been busy building a PPNC nosecone that will deploy 2 parachutes using tomy timers. The idea is to have a smaller drogue chute deploy at apogee and the main chute when its closer to the ground.

Drogue Chutes
We have used some simulators to try to work out how big to make the drogue chute, but ended up with mixed results. So we decided to make 2 drogue chutes and see how they test. These were 10cm in diameter and 15cm in diameter respectively. We used the same procedure as we did when making the main chute except reduced the number of chute lines to 4 and 6.

Drogue Chutes

Drogue Chutes

On initial testing, the 10cm chute is just too small and doesn’t get enough air into it . The 15cm chute might be ok, but the hole in the middle is too big. We can just sew a patch over it and give it a further test. Worse case a 20cm one may be called for.

Longer PPNC Nosecone
The two chutes and release systems wont quite fit in a standard 1.25L body section we make the PPNC nosecones out of, so we have made a super sized PPNC (SSPPNC) by adding an additional 1.25L body section.

Super Sized PPNC Nosecone

Super Sized PPNC Nosecone

The bottom section was from a different 1.25L bottle manufacturer and is just used for the mockup, we will use a P&N bottle for the final nosecone.

There join is not perfect and the nosecone structure gets stuck a little. We will need to be more careful when fitting the final bottom bottle as we need to be able to get the nosecone structure in and out for servicing.

Nosecone Structure
The nosecone structure needs to have 2 elastic band powered pressure plates to push out the chutes. To accommodate this we have built another smaller structure as well as a section to join the two chute deployment sections. We needed this to have enough space between the two so they was less chance of lines being caught up.

Here is the drogue deployment structure (pressure plate not fitted yet)

Drogue chute deployment structure

Drogue chute deployment structure

You can see we use wire to join the sections together, this makes it very strong which allows for tighter elastic bands which help throw the chute away from the rocket body better, as well as having a better chance of survival during a crash.

Here is the structure how it will fit inside the super sized PPNC.

PPNC Dual Deploy Structure

PPNC Dual Deploy Structure

From the top down the pieces are

  • Pilot capsule – its main use is to ensure the main parachute deployment structure is below the curved section of the top of the nosecone. This helps the door close better if its flush against the side.
  • Main Parachute deployment section and pressure plate
  • Extension section – This is to position the drogue chute deployment structure down below the join of the two bottles in the nosecone. Having the door across the join is not a good idea
  • Drogue Chute deployment section (note the pressure plate is not fitted yet)

The two doors will be on opposite sides of the SSPPNC. The idea for putting the drogue lower than the main chute is so that when the drogue deploys it will be connected to a lower part of the rocket nearer the CP than the CG, the rocket will orient itself with the nosecone down position and drogue trailing behind. This gives a lot of room for the main to deploy and open being furthest away from the deployed drogue. The main chute will be connected close to the CG so that the main and drogue dont tangle .. well thats the theory anyway :)

Tomy Timers
We received our order of 5 tomy timers yesterday which is good. We also managed to destroy the one we had when glueing it to the structure, too much glue and we managed to glue up the gears … Lucky we ordered a couple of extras

The work for the rest of the week will be assembling the nosecone, testing the dual timer and getting some calibration numbers on the timers.

We will report part 2 later in the week

Posted by on October 1st, 2008 Comments Off

60cm (24″) Water Rocket Parachute

Now that the nosecone is built it is time to make a parachute. One of the things I am quickly liking in this hobby is that you build just about everything yourself from scratch. This is something Im not used to in IT where just about everything is off the shelf.

I decided after doing some research that a ripstop nylon parachute was the way to go. Using this material increases longevity and with water rockets I don’t need to be concerned about it being melted by an ejection charge. I also decided on a 60cm diameter chute, this would be big enough for the next few generations of wrockets then for sustainers when I get to two stage designs.

The ripstop nylon I purchased from Spotlight. This is one of the big material supply type stores in Australia, but you will be able to find it in any good/large material shop. I did look for about 15 minutes through all the rolls of material but gave up and went and asked one of the lovely shop assistants who took me straight too it. BTW the shop assistants were very helpful so don’t be afraid to ask. I decided on luminous yellow, (I have read since that darker colours are better .. oh well we will see how visible it is) and it came in a 1.43m wide length, I purchased 1m (1.0 x 1.43) for about $8 and some 25mm red (1″) binding for $2.50.

I got two pens and tied them 30cm apart then used them to draw a pretty good circle. I used some trusty cans of tomatoes to hold the material tight.

31cm radius circle on the ripstop nylon

31cm radius circle on the ripstop nylon

I then used the tip of a soldering iron to cut out the ripstop nylon. I used this method as it melts or seals the nylon, when you cut it with scissors it tends to fray. The cutting / melting went OK, I was too worried about melting the tablecloth.

Cutting the ripstop nylon with the soldering iron

Cutting the ripstop nylon with the soldering iron

I then measured using a can of beans and cut out the centre hold. I wanted the centre hole to ensure that the parachute worked to slow the descent, but not too well that it carries the wrocket into the trees.

Measuring the centre hole

Measuring the centre hole

Here is the nylon cut out, the centre hole has a radius of about 4cm (1 3/4″). The centre is pretty much in the middle, just the angle I took the shot at makes it look off centre

cut out nylon showing dimensions

cut out nylon showing dimensions

Next step was to mark the positions for the 8 tie lines. To do this, fold it in half, then half again, then half again. Each time press down to make a crease in the nylon and when you unfold it you will have the exact locations, I marked these spots around the circumference.

Tie line locations marked

Tie line locations marked

Next I sewed the hem of the parachute over about 0.75cm, this was just to strengthen the nylon at the tie locations. I hand sewed it first, this took about 2 hours, (ok so my sewing is not the best but the backstitch from my high school home economics days did come in useful … )

Hemmed edges with red

Hemmed edges with red

The shot above also shows the yellow better (it is very bright).  After my 2 hours of hand sewing I decided that the sewing machine would be faster to master than hand sewing on the tie location binding pieces, so my wife set it up for me and off I went. I decided to do another stitch around the edge. I used (for those interested) a double stitch on the machine, it basically sews the stitch twice. I then went about sewing a 4cm piece of binding (4.0cm x 2.5cm) over the locations where the tie lines would be located.

Its not easy to sew and take pictures :)

Its not easy to sew and take pictures :)

Do this for the 8 locations over the top of the places you marked above and you get the photo below. I did also sew around the inner circle, whether this was needed or not I dont know, but I had the machine out and was feeling confident :)

Parachute with bindings and eyelet holes

Parachute with bindings and eyelet holes

The sewing machine has some cool (I don’t believe I just said that) stitches to do eyelets, so I used a 5mm hole  with a 7mm hole around it. Straight through the middle of the binding. This gives the hole the tie line goes through extra reinforcement. You could also use small metal eyelets for this.

close up of binding and eyelet for tie line attachment

close up of binding and eyelet for tie line attachment

To get a nice even hole and to seal the nylon I got out my trusty soldering iron again and used it to poke approx a 4mm hole straight through the middle of the eyelet. This method worked very well and left me with neat holes in the binding and nylon underneath. Be careful don’t touch the rest of the parachute it melts very easily.

binding with neat hole for tie line

binding with neat hole for tie line

Next I measured the tie lines and cut them. I cut 4 lines; each was 2.2 x diameter of the parachute, in my case 1.32m (52″). I tied them through the eyelet then to the opposite eyelet so that each line made up 2 tie lines. When all four where done I gathered the lines in the middle and tied them off so that they made a nice loop.

Parachute with tie lines

Parachute with tie lines

Next I needed a shock cord for the parachute. This absorbs some of the force on the line (and hopefully stopping it form breaking) while the parachute is opening. I used some elastic that I found (pinched) from the sewing kit. This piece was probably 25cm (10″) long but stretched out to 55cm (21″) at full stretch so it should be ok. I folded the ends over and sewed across them to make a nice loop in the ends. Again my sewing is not the prettiest but it is strong at both ends.

Elastic with ends turned over and sewed

Elastic with ends turned over and sewed

Again I used the double stitch. Next I added a loop of tie line through the eye of the elastic and a keyring ring through the other (I didnt have 2 keyring rings .. I will replace the tieline loop with a keyring ring) to attach it to the rest of the parachute. Here is a pic of it assembled. Its 105cm (41″) from the top of the parachute to the rocket attachment ring.

Finished Parachute

Finished Parachute

Here is a pic of the rocket attachment ring on the end of the parachute, attached to the line from the rocket. The line uses a barrel swivel with a snap lock (from any good fishing tackle store). This hopefully will let the rocket spin without tangling the tie lines and it also makes it easy to attach and detach the parachute (I saw this idea on another website …. very clever).

Attachment point to the rocket

Attachment point to the rocket

I will probably need a second attachment line to the rocket in case one breaks. I did a few indoor tests and it was opening and filling out fine. I also attached my 1 bottle rocket and threw it off the back balcony (its about 5m to the ground .. good test facility) and it was opening from being fully packed just before hitting the ground. When I tested it with the tielines already out it opened in about 2m and flew to the ground nicely.

Testing

Testing

Here is a pic of it folded up in the rocket nosecone

Parachute inside nosecone

Parachute inside nosecone

and lastly a video of it being thrown out of the nosecone using the timer and the door. I previously had some sponge behind the deployment plate however the nosecone was deforming when the door was shut which stopped the timer, so I took out the extra sponge, it fitted better and the timer worked again. Here is a video of the parachute being pushed out of the nosecone.

Only thing left to do now is build the new wrocket based on the 1.25L bottles, attach the nosecone and give it a proper test.

Posted by on August 18th, 2008 3 Comments