Friday 28 December 2012

Garbage bags full of hot air - Solar Balloons

Get a few cheap garbage bags, some sticky tape and some string, fill balloon with air, put in the sun and you have a Solar balloon. 

Tetroon Solar balloon
Tetroon shaped Solar Baloon
I was reading up on weather balloons and noticed an article that mentioned Solar Balloons, which I had never heard of before, and decided to see what they were. I read up on them for a few hours spending a fair bit of that time reading about a local Brisbane hot air balloon operator.

I found another site that had a DIY section and it looked pretty straight forward so decided that I would give it a try. My first attempt was with a garbage bag that we had in the cupboard to put rubbish in, this was not a success. This bag was too high quality, so the plastic was not thin, so the bag weighed too much and any lift generated was not able to lift the garbage bag. This garbage bag was now used to for its intended purpose of holding rubbish.

Upon further reading I learnt that the cheaper garbage bags are better for this sort of thing as they are thinner and thus weigh less. This makes them pretty useless as a garbage bag, but great for a Solar Balloon. So I headed to the local Coles and Woolworths and looked for the home brand Garbage bags, we bought 4 different types and they have been summarized in the table below.

LitersGramsLiter per gram
QualityBrandSizeWeight (1 bag)Size per weight

The Coles home brand Wheelie bin garbage bags were the best bags, and cost about AUD $1 for a pack of four of them from Coles.


Basically we are looking for the greatest volume to weight ratio, as that means that there is a lot of air inside the balloon to be warmed up, with the least weight for the balloon to lift.

How a solar balloon works is the black plastic absorbs the energy from sunlight which will heat the air inside which reduces the density of the air, making it lighter than the surrounding air which creates lift so the balloon will rise. This is similar in concept to a hot air balloon, just that a hot air balloon, the energy is provided by a gas burner, rather than from the sun.

These balloons work better with cold or cool air and bright direct sun, so that there is a greater difference between the heated air inside the balloon and the external 'cooler' air. I have tried them both in Summer and Winter and was able to get it working under hot and cold temperatures. The balloons fly best in the morning when there is less wind and when the air has not had much time to warm up, I have tried a few times in the afternoon and never been able to get the balloon aloft. It will take about 15 minutes for the air to warm up inside the balloon. Direct sunlight works much better than cloudy or indirect sunlight.

Cylinder Solar Balloon
with Sun flare :)
This morning, when I tested it in the park, the air temperature was about 27'C when I put the thermometer on black plastic the temperature was about 38'C which is an 11'C difference in temperature.

The black plastic was 11'C higher in temperature than the surrounding air.

There is not a very large amount of lift produced but their is sufficient for the balloon to rise fairly rapidly into the air. If you build a large enough balloon it can create enough lift to lift a human. Due to their low lift capacity and large surface area these solar balloons are very prone to being blown around by the wind, when flying one of these balloons you need to have a fairly windless day and walk with the balloon following the wind so that you can stay underneath the balloon, to achieve maximum height. If you stand still and let the balloon drift on a tether the wind will blow the balloon down to the ground as the maximum length of the tether is reached.

I always fly the balloon with an attached tether as it is illegal to fly something over 400 foot high without prior CASA approval, and where I fly these balloons is under the flight path from a small aircraft and helicopter airport. I use a kite string for the tether, which works well.You can see in the following video that the string is 'flicking' this is as it is unwinding from the kite holder


This is something that is very easy to build, something that you can build with your kids and is very cheap to test, it just needs some string, some sticky tape, and some cheap garbage bags. The garbage bags that I use cost me about 25 cents ($AUD) each, so the balloon I flew this morning cost me 75 cents. Something great to keep the kids amused one morning this holidays and teach them about some basic science and aerospace.

I have noticed that people do get rather curious about what I am doing when I have about. 600 liter 4 meter long black tube 60 foot in the air, and will often, come up to me and talk to me about it.

I have heard of people releasing these balloons and achieving heights of 20,000 feet, one day when I get time, I will look into releasing one with telemetry and an altimeter to see how high and how far it goes, but I will need to be nowhere near controlled airspace to be allowed to do this.

There are two shapes that most solar balloons tend to be either a long cylinder, or a tetroon, I recommend starting with the long cylinder shape first as they are the easiest to make and will only take about 30 minutes to put together, the tetroons takes about two hours to make is a fair bit harder to make, but is a more efficient shape (larger volume for the same amount of garbage bags). Try not to use too much sticky tape as that is just added unnecessary weight.

Give it a try with your kids these holidays, an easy fun experiment that will teach them something.

Thursday 27 December 2012

Why Aerospace

Many people have asked me recently 'Why Aerospace' while there is no simple answer the easiest one is probably why not.

I recently realized that I did not really have a hobby, other than training for a marathon, which is not really a hobby and decided that I would look around for one.

So one day I was watching a documentary that mentioned rocket engines, so being the curious person that I am I decided to research how rocket engines work and spent a few days reading on the current rocket technology and upcoming rocket technology, and from this I found model rockets online and decided that I would be interested in pursuing this further.


Callisto rocket ready to be fired on F40 motor
My rocket ready to fire
on launchpad 3.
I then looked around for local rocket clubs and found there was one located close by the QLD Rocketry Society, and decided that I would drop out with +Sunnie Snell for a look and see what this local club was like.

I had read up a lot on model rockets and understood the basic concepts, but wanted to speak to some people who fired rockets regularly. From the moment we arrived we found everyone there to be extremely helpful and ready to help with anything to do with rockets. We watched a few rockets getting launched, which is a real adrenaline rush and I decided that I would join the club.

Callisto rocket fired on F40 motor
Wind blowing my rocket off course.
Callisto rocket fired on F40 motor.
A few days later I dropped in to see Australian Rocketry, and joined the Queensland Rocketry Society club, and bought some rocket equipment ready for my certification flight. And had some more questions about constructing the rocket and how to fire it, all of which was answered happily. I had researched much of this already on the Internet, but wanted it confirmed and clarified.

I also read a lot about rocket technology and the theory of rocket flight, what was very surprising was that many of the articles and papers where. From the 1960's and 1970's, especially about rocket flight. There was one more modern papers on rocket engines, specifically Hybrid engines, which are a relatively new invention.

When the curiosity rover from NASA landed on Mars, I was able to understand a lot better what technology was being used, and how hard it was to get it there, I was also able to answer a lot of questions my friends had about how and why they did different things with the landing of the rover.


My background is in GIS (Geographic Information Systems - computerized maps), so I have always been interested in drones, in my searching around for rocket information I came across the DIY DRONES site, which promised make a drone as easily as attaching this hardware to a remote control plane, it was a bit more complicated than that, as I didn't have any experience of remote control planes, or even cars for that matter. But in essence once you have the basic remote control knowledge it is plug and play to make a drone.

Due to safety concerns and my lack of remote control flying skills I decided to start with a rover as my first autonomous vehicle. I bought a remote control car from Woolworths as well as two remote controlled helicopters, with the idea that I would automate the car and use the helicopters to begin my flying skills. I came home and pulled the car apart and quickly realized that it looked nothing like any of the pictures I had seen on the Internet of the how remote controlled cars worked, and realized that this would not help me, so this car was relegated to become spare parts. The simple remote control helicopters were used for practice and as a simple step towards flying a fixed wing model.

The irony with remote controls is that the simple 3 channel helicopters are easy to fly and pretty well designed for kids and indoor flying. But once you get to full control remote control helicopters they are much harder to fly than an airplane.

EasyStar 2 A proper remote car was noticed on special in the local toy world store and was purchased and this was modified to create our first rover. Once we got this rover working we took it to the large park behind us and one of my friends pointed out as we were excitedly congratulating each other in the park, after our first successful mission that to the other people in the park it just looked like we had just driven a remote control car around the park ;).

As we were getting the rover ready for use, I was also trying to teach myself how to fly remote control fixed wing airplanes, I bought an Easy Star II and pretty quickly learnt that it is not that easy to fly one without any experience - as I crashed the plane from about 100 foot into the air and bent the propeller shaft. I then learnt how to repair a propeller shaft :).

Much of what i have learnt, I learnt from doing wrong the first time. 

I then decided that the 'experts' where right and I needed to start on a simulator, which is when I downloaded the excellent free R/C desk pilot remote control flight simulator, which allowed me to add my planes into it and learn to fly them on a simulator. I also purchased a much smaller lighter plane that traveled a lot slower and used that to improve my 'real world' flying skills, before I moved back to the larger Easy Star II.

Once we were confident with the APM 2 hardware and software and our setup of remote control, we set an easy star II plane up with all the components and put it up for a test and it all worked pretty well in the first few goes, it is very interesting, and nerve racking - watching a plane fly around the park following a program that you entered for it. You still need to watch the plane closely and be ready with the R/C handset in your hand to revert the plane to manual mode - so that if something goes wrong a human (me) - can take over control of the plane and make sure it is safe.


Since my aerospace interest involves high explosives and high speed propellers I have been very cautious and have been taking things slowly. Any friends that have been helping me get a safety lecture and are trained in correct handling procedure, and any vehicle, engine or device is considered dangerous and appropriate handling procedures have been implemented, my friends thought I was over the top at first, so I found them some images of what can happen when things go wrong, they soon realized that I was being responsible and realistic rather than over reacting and are now more than happy to follow the safe handling procedures.

Wednesday 26 December 2012

I had an 8 hour 48 minute phone call because of this blog.

Blogs are meant to start conversation, and my first post started one, and this was one long conversation nearly 9 hours. 

Last night an old mate of mine John Pritchard (of Techroom) contacted me at about 10:45 PM on Christmas Eve to say that he had heard some common friends talking about my Boeing 737 blog post, and asked me what the URL was, we then typed a few season greetings messages in Skype to each other and then we started a voice chat at 11:00 PM. This Skype call finished at 7:48 AM Boxing day - a total duration of 8 hours 48 minutes and 17 seconds.

I have been on Skype for over 8 years and use it very heavily, and am part of their beta / testing program and have actually had a client for 5 1/2 years that I dealt with mainly through Skype, but my conversation last night was the longest Skype call or phone call that I have ever had in my life. I realize that the length of the call was more to do with the fact that we were both on Christmas break so had the time to chat all night, watch the sun come up and then chat for a few more hours.

I have not been very active blogging in the past but know that I should be doing more and many people have noticed that i have been more active on Social Media for the last two months, and I have spent the previous few months preparing and organizing for starting this blog.

I have had several great friendships that have been formed with people, who I have met by reading their blog. A very good example of that is +David Novakovic who had a blog for his company that was discussing the semantic web. I was doing a project that was very closely related to what he was doing and reached out to him, and arranged for a meeting, when we met we had very similar interests and used his company's service as one of the back end processes for our project. If David had not been blogging, we still may have met up but it may have taken longer or may have never happened.This was about 5 years ago and David and I Are still in pretty regular contact.

I have come to realize that +Duncan Riley is correct Blogging is not a spectator sport, and now understand what he means by that and I have now jumped in with two feet and within days I am already seeing the benefits.

Sunday 23 December 2012

I was run over by a Boeing 737 at Flight Experience

I was fortunate today to be invited by a mate of mine to watch him as he flew a 737 simulator at Flight Experience yesterday afternoon, which happened to be a very cool way to end the work year off.

They start with a discussion with the trainer asking what you want to gain from the experience, and what your flight experience is. My friend was interested in doing a proper flight (taxi - takeoff - circuits - landing), and stated that he has held a commercial light airplane license for about a decade.

Next was a pre-flight briefing video that shows you the basic cockpit controls and talks a bit about the Boeing 737, which is the most popular commercial airliner in the world.

We then walked into the simulator, which is basically a large room, with a projector screen set up in as you can see on the right here. The Simulator has all the switches and dials that a real 737 has and they function as it would in a real 737, so when you adjust the electric trim - the trim wheels spin, the throttle levers moved relative to the power that the autopilot was giving the engines as we adjusted height or bank.

There are 4 seats, the pilot sit on the left, the co-pilot (trainer) sits on the right and there are two seats behind these ones where the passengers sit, which is where I was sitting - behind the pilot - with another friend sitting behind the copilot.

There is a large curved screen outside which has the scenery projected on to, which was pretty realistic, I was able to recognize it as Brisbane airport.

Once inside the cockpit the pilot and copilot were strapped in - using a 5 point harness as the real planes used, the whole process was done as realistic as possible, a 5 minute run through of all the controls was gone through, this was the most interesting part for me of the whole process, as when you first look at the cockpit it looks like controls and buttons everywhere, but once the logic and grouping of the controls was explained, it made things lot easier. This also helped the back seat passengers be aware of what was happening with the plane. We knew where to see air speed, vertical speed, Angle of attack and so forth.

We began taxing and I was impressed at how realistic the experience was - I have spent a lot of time using flight simulators on computers before - but having this large a screen that totally encompassed your view and having the cockpit layout increased the realism effect.

Watching my mate taxing this plane, really made me think about and realize how large and heavy these planes really are, there was a noticeable lag between applying engine power and the plane beginning to move, and the same when power was reduced on the engines  it made  me aware of how hard it is to get 70 tonnes moving.

We were using runway 19 (which means it runs at 190'), we taxied the correct way to the beginning of the runway and then once lined up properly the trainer began explaining in detail the take off procedure, it was while we were sitting here, that i noticed that another Jumbo was lining up for takeoff and was driving right through our plane, the three of us were all IT guys each with over 25 years experience so understood what was happening and commented on it. The trainer was slightly embarrassed and told us to 'ignore that', this did not detract from the realism of the event and to me added a coolness factor, as its not often you get to sit in a realistic 737 cockpit and have a 737 run you over.

We were uninjured from the other 737 running over us and we let that plane clear the runway and my mate applied power and we started to roll down the runway - he did a very good job of keeping it in the center of the runway and once "rotate" was reached we gently climbed into the air. We were soon at 3000 feet and the trainer instructed my friend to start doing gentle turns and talked him through the turns, this is where it became obvious that his experience as a real pilot was advantageous. He was very quickly able to turn a 737 to the exact required heading and too level it out in one smooth operation - where as I tend to do a series of smaller jerkier movements when i am adjusting a plane - whether a real plane, remote control plane or one within a simulator - but i am getting better.

We continued to do some circuits around Brisbane, and occasionally the trainer would pause the simulation which surprisingly did not detract from the realism of the experience for me or the other people with me. When the simulation was paused the trainer would explain things in more detail about the operation that was going to be done next and then we would do that operation.

Once several circuits were done, we were going to do a Touch and Go, which is you land as normal, then instead of applying reverse thrust and brakes, you apply full power and take off once again. From what I understand Touch and Go is a pretty common procedure in pilot training as you get to practice a landing and takeoff.

Once the touch and go was completed we came in for a full landing. and then taxied the plane off the run way and then our time was up.

All up I think this was an amazing experience and was glad that my mate invited me along for the ride, but I think with my limited piloting experience I wouldn't get my moneys worth out of the experience. I am sure that for beginner pilots like me they would have a simpler procedure that they took me through, but then I could do that on my home flight simulator.

Once we walked out - we were all slightly buzzing from the experience as it is a very realistic experience, but soon reality came back and we had to return to work for a few more hours.

See for more details.