Space Oddity
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- Mar 3, 2014
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I have question regarding a recent launch failure.
Last weekend I decided to launch a rocket. It is the largest one I've built, 6'6" high. It was windy last weekend, measured wind speed around 12mph with gusts up to 20mph.
I always have problems with recovery in wind and usually launch a small pilot rocket to test the conditions. In this case it was a small 15" rocket. This was the second rocket I built, designed using OpenRocket and accurate to the design in terms of dimension and C.o.G.
I've flown the rocket five times before using both C and B motors. On all previous launches the flights were straight, stable, and visually consistent with the design.
On this occasion however things were different. I launched the rocket with an Estes C motor. The launch site was about 20' in front of an 8' hedge. The wind direction was exactly normal to the back of the hedge.
The rocket ignited well, the igniter remained on the ground attached to the clips.
The rocket rose cleanly from the rod and flew approximately 50' vertically into the air before turning 90 degrees then spiralling downward to land in the top of a ditch (in front of the hedge) about 70' from the launch position. The trail of smoke marked it's path visibly.
After a couple of seconds following it's landing in the ditch, the ejection charge audibly and visibly fired.
On inspection the rocket was undamaged, the nose cone and parachute had separated, the shock cord was intact. There was no apparent reason for why the rocket had become unstable.
For the first time I'd decided to video the launch. In stop frame the video confirmed a clean launch off the rod. I do not believe that any instability occurred at that level.
I was able to capture the rocket at a few points in the spiralling phase. Initially the rocket appeared normal in shape (though it should be said, very blurred on the image). On later images however, there appeared to be two distinct but indeterminate shapes. One conclusion I've drawn is that the nose cone separated during the latter part of the flight. This was following the initial unstable and spiralling flight.
The condition of the spent motor was normal in all respects.
I know that the separation was not initiated by the ejection charge as it had not ignited in the air. I can only conclude that the separation resulted from the unstable conditions rather than it causing the unstable condition.
In short and following the previously successful launches, I haven't got a clue why this one failed.
Can anyone help with a reason? I'm really keen to know why this one went wrong so that I'm aware of whatever risks there may be in larger rocket behaviour.
Needless to say I still haven't launched my 6'6" rocket.
Knowing why this happened is obviously important in making sure it doesn't happen again. There is however a far more important lesson to be learnt.
Because of the wind direction my grandson and I had moved to the far side of the field that we usually launch in. As such the usual mob of hecklers and forced spectators (my family) were watching from the far side of the field. The landing position of the unstable rocket may well have been where my family might normally have been standing!
Having had 100% success in all of our launches to date! it's clearly easy to become over confident and complacent.
Even low powered rocketry is very dangerous and carries risk.
There is much to learn by failure and much to gain from experience. For the time being I'll stall may ambitions to "fire higher" until I fully understand what can go wrong at a low level. Your help to explain will be appreciated.
As a footnote, I read an old thread last week from a guy that wanted to launch a car battery as a rocket payload. At the time I smiled at the comments and reminders of the Top Gear episode when they launched a Reliant Robin car.
In hindsight the launch suggestions in that thread were clearly horrific!
SO.
Last weekend I decided to launch a rocket. It is the largest one I've built, 6'6" high. It was windy last weekend, measured wind speed around 12mph with gusts up to 20mph.
I always have problems with recovery in wind and usually launch a small pilot rocket to test the conditions. In this case it was a small 15" rocket. This was the second rocket I built, designed using OpenRocket and accurate to the design in terms of dimension and C.o.G.
I've flown the rocket five times before using both C and B motors. On all previous launches the flights were straight, stable, and visually consistent with the design.
On this occasion however things were different. I launched the rocket with an Estes C motor. The launch site was about 20' in front of an 8' hedge. The wind direction was exactly normal to the back of the hedge.
The rocket ignited well, the igniter remained on the ground attached to the clips.
The rocket rose cleanly from the rod and flew approximately 50' vertically into the air before turning 90 degrees then spiralling downward to land in the top of a ditch (in front of the hedge) about 70' from the launch position. The trail of smoke marked it's path visibly.
After a couple of seconds following it's landing in the ditch, the ejection charge audibly and visibly fired.
On inspection the rocket was undamaged, the nose cone and parachute had separated, the shock cord was intact. There was no apparent reason for why the rocket had become unstable.
For the first time I'd decided to video the launch. In stop frame the video confirmed a clean launch off the rod. I do not believe that any instability occurred at that level.
I was able to capture the rocket at a few points in the spiralling phase. Initially the rocket appeared normal in shape (though it should be said, very blurred on the image). On later images however, there appeared to be two distinct but indeterminate shapes. One conclusion I've drawn is that the nose cone separated during the latter part of the flight. This was following the initial unstable and spiralling flight.
The condition of the spent motor was normal in all respects.
I know that the separation was not initiated by the ejection charge as it had not ignited in the air. I can only conclude that the separation resulted from the unstable conditions rather than it causing the unstable condition.
In short and following the previously successful launches, I haven't got a clue why this one failed.
Can anyone help with a reason? I'm really keen to know why this one went wrong so that I'm aware of whatever risks there may be in larger rocket behaviour.
Needless to say I still haven't launched my 6'6" rocket.
Knowing why this happened is obviously important in making sure it doesn't happen again. There is however a far more important lesson to be learnt.
Because of the wind direction my grandson and I had moved to the far side of the field that we usually launch in. As such the usual mob of hecklers and forced spectators (my family) were watching from the far side of the field. The landing position of the unstable rocket may well have been where my family might normally have been standing!
Having had 100% success in all of our launches to date! it's clearly easy to become over confident and complacent.
Even low powered rocketry is very dangerous and carries risk.
There is much to learn by failure and much to gain from experience. For the time being I'll stall may ambitions to "fire higher" until I fully understand what can go wrong at a low level. Your help to explain will be appreciated.
As a footnote, I read an old thread last week from a guy that wanted to launch a car battery as a rocket payload. At the time I smiled at the comments and reminders of the Top Gear episode when they launched a Reliant Robin car.
In hindsight the launch suggestions in that thread were clearly horrific!
SO.