Archive for August, 2008

 

Launch Day 5

Launch Day: 5
Date: 30/09/08 Afternoon
Location: Berry Oval
Rockets: SRT III, H1

The conditions were overcast but with low winds so it was a nice afternoon for launching. We had two wrockets to launch for the first time.  SRTIII with the nosecone removed had a nice hemispherical top due to the type of bottle expanding at the bottom and we had the new H1 wrocket.

SFTIII enjoyed 4 flights with the highest pressure flight at 90psi, which is the highest for this rocket. It wasn’t using any nosecone so it did bounce quite a bit on landing. The last flight at 90psi took off at an angle from the launchpad and nearly flew out of the park. It landed a good 60m downrange. We decided that would be the last flight for the day for SFTIII.

SFTIII - no nosecone

SFTIII - no nosecone

H1 had 4 flights as well. The first flight we launched at 80psi and used 4 turns of the timer to have the parachute deploy at approx 3.5s – apogee hopefully. Unfortunately the chute didn’t deploy. This was a bit of a disappointment, but H1 flew very straight and quite high. From what we could make out the elastic band caught up on the timer mechanism and stopped the door from opening.

H1 on the launchpad

H1 on the launchpad

Damage Assessment

As a consequence of the first crash the following broke on the rocket

  • The weight on the timer broke off and without it the timer wouldn’t function.
  • The timer broke off the nosecone structure, it was just floating around inside the nosecone. It wasn’t something we could fix at the oval.
  • The table tennis ball in the PPNC also cracked but this was minor.

We decided to fly the rocket without the parachute for the next 3 launches, the nosecone was already damaged so we just straightened it out and flew it again. We increased the pressure to 90psi, then 100psi. Both flights were very straight and very high. It was flying that straight that at apogee it looked like it was backsliding for a while until it pointed nose down and headed for earth. I don’t have a video to confirm this though.

On one occasion we flew with a foam (bubble bath) mixture to see if we could get a good rocket trail, however against the overcast sky it was hard to see.

Here is a video  of the 100psi launch, we used virtuadub to go through it frame by frame to get the flight time, which was 8.867 seconds from launch to crash down. Running this through Cliffords simulator using the wrockets size, water fill, weight etc, we get about 90m (296ft). How high it actually flew I’m not sure but it went very high, much higher than SFTIII.

It was a bit of a heavy landing but the nosecone took most of the damage. The top bottle will probably need to be replaced but this is very easy to do with our modular approach.

We did have a bit of an audience. Two local kids came and joined us and loved it, they stayed until we had finished and had a launch as well. Also one family watched from the edge of the oval and even videotaped the launch :) I gave them some information to find our site so hopefully they might come and join us on a future launch :)

Things we learned

  • The new launcher worked very well, sturdy and the wrockets were nicely vertical on the launcher
  • There were no leaks at 100psi so the one way valve leak looks to be resolved
  • Being able to pull the launch cable from the same location we pump from was good.
  • The PPNC nosecone needs a redesigned as to the placement of the timer as well as using a single rubber band. The size of the door probably needs to be a little smaller as well as the vertical height of the nosecone support structure based on our parachute size.
  • The new corrugated removable fins worked very well. In one of the launches in slow motion, the rocket starts to tilt over but by the time its out of the frame it has straightened up again.

Posted by on August 30th, 2008 Comments Off

H1

Name:                       H1 – (Happy V1)
Build Date:                28/08/2008
Capacity:                   2.5L – 2 x 1.25L
Nozzle Size:               9mm
Fill Volume:               ~ 700ml
Launch Pressure:       ~ 110psi
Dry Weight:               245 grams
Recovery:                  Nosecone with Tomy timer + 60cm (24″) ripstop nylon parachute
Status:                      ACTIVE (4 flights)

Notes:

This rocket has 2 x 1.25L bottles connected with a robinson coupling, a nosecone with a tomy timer and 60xm (24″) parachute and a removable fin assembly with trapezoid shaped fins.

Rocket deployment system failed on first launch and was destroyed. Rocket has made 4 flights up to approx 290ft

Pics:

Launch configuration

Launch configuration

Posted by on August 30th, 2008 Comments Off

Minor Launcher Modifications

On our last launch day we had a few small issues that I wanted to fix.

  • We had a leak near the one-way valve at around 100psi
  • The way the old launcher was molded the launch cable was at 45 degrees to the fill cable. Would be nice for them to be together
  • The launch tube was slipping down the launch pole support so I wanted to make it sturdier
  • Wanted to fix the launch cable to the launcher to make it easier to carry out to the launch site

These are all only small things and I had time tonight to do them before the planned launch this weekend.

One Way Valve Leak

I have used some Teflon tape on the threads of the one way valve and tightened them all. I was able to test at 30psi and no leaks, held that pressure for 5 minutes, couldn’t really go any higher as it is late, don’t want to wake the neighbors. We will do a hydrostatic test before the launch to see if we have any leaks at 100psi.

One Way Valve and Gardena Quick Release

One Way Valve and Gardena Quick Release

Release Cable Position

I just cut off the molded section we were using on the old launcher, put a metal L bracket on it and screwed it with a 75mm (3″) screw into the launcher base. Its very sturdy and not going anywhere. Tested fine. The launch cable and the air line can now run really parallel.

New String Release Point

New String Release Point

Launch Pole Modification

I purchased a 90 degree elbow to fit the 13mm launch tube pipe. I put this at the base so that it supported the vertical part of the launch tube. I also cable tied the launch tube to the metal support and the gardena female adapter is sitting on the lip of the metal support. Its very sturdy now.

Launch Tube Elbow

Launch Tube Elbow

I also cut down the height of the launch pole by about 25cm (10″), it didn’t need to be that high.

Fix the Release Cable to the Launcher

This was just a convenience matter and one less thing to juggle when carrying the equipment out to the launch site. I just screwed 2 long screws into the launcher base and wrapped the 10m (30ft) of launcher cable around it .

New Modified Launcher

New Modified Launcher

Posted by on August 30th, 2008 Comments Off

Air Flap Launch Detect & Deployment Timer Calibration

Air Flap Launch Detect

The Air Flap detects launch and releases the timer that in turn releases the parachute. I modified the Air Flap to make it longer and narrower. I expected that the original one which was shorter and wider would probably have been pushed down by the air resistance at launch, but I couldn’t make it release by blowing hard on it.

Its possible the original one would have worked but I cant be sure it would be at or just after (less than 0.5s) launch . The new one is able to be released by blowing hard on the end of it. The longer flap uses mechanical advantage by making the lever of the flap longer so it takes less force to push it back against the body of the rocket and in turn start the timer off.

Here is the flap in the ready to launch position . It is made from a section of corrugated plastic

Air Flap in launch position

Air Flap in launch position

The Air Flap is glued against the side of the nosecone and also has 3M strapping tape to help keep it against the side of the nosecone. I found when the timer is wound up a lot that the edge of the flap attached to the nosecone was starting to lift. This solution keeps it in position.

Close up of Air Flap attachment

Close up of Air Flap attachment

When the rocket launches the air flap is held back against the side of the rocket causing minimal aerodynamic disturbance, I think :) Here it is ready for launch.

Launch configuration

Launch configuration

Deployment Timer Calibration

In order to have the parachute deploy at the right time I needed to know how many turns of the timer would equate to how many seconds. This way as I increase the pressure in the rocket and the apogee height increases, I can tune in the right amount of delay in the timer so the parachute doesn’t open too soon or too late.

To do this I setup the rocket in launch configuration and timed how long it took from launch detect until the chute door opened and the chute was ejected from the nosecone. I can use this time and add another second or so to give me the time when the chute should open.  The results were

Timer Turns Seconds to Parachute Eject

4

3.5

5

4.2

6

4.6

7

5.4

The results were not linear possibly due to the non-linear spring mechanism or the varing tightness of the elastic band, however these are in the ballpark that I need.

I will use the water rocket simulators like Cliffords to approximate the apogee of the rocket prior to launch at a certain pressure and water fill, then dial in the number of turns on the timer to hopefully get the parachute ejection time correct. I will take this table with me on Launch day to use as I increase the pressure.

Posted by on August 28th, 2008 Comments Off