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Shut-off for F2D-Combat
Risk analysis

What is risk:
Risk is proportional to the losses which can be caused by an event and to the probability of this event. The harsher the loss and the more likely the event, the greater the overall risk.

Risk = (probability of an accident) x (losses per accident)

"Probability of an accident" is the chance that a model flies away and hits somebody.
"Losses per accident" is how bad the victim is injured. (More information on Wikipedia)

Rare events and dramatical consequences:
When dealing with rare events and dramatically consequences there is a common pitfall we must be aware off. The human psyche wants to focus on the catastrophic loss and ignore more subtle risks.
Statisticians call this response "Risk Telescoping". The danger of Risk Telescoping is that we overestimate statistically small events and remove focus from more meaningful and avoidable large risk areas.

Are the risks of fly aways really a problem so big that it can justify the gigantic work of introducing mandatory shut-off systems? If the same amount of resources and effort was used on safety fences, better equipment, disciplining pilots or similar, would our sport not be much safer?

Risk free flying is an illusion:
Better quality of lines and change in flying styles have reduced the number of fly aways in the last couple of years, but it does still happen that a combat model flies away. With models flying far away there is a probability that somebody outside the flying field can be hit by a model. This risk is quite small but there will always be a risk. Decideing if the actual risk is too high or acceptable is a political choice. A mandatory shut-off will reduce the number of fly aways but there will still be a very small risk. Whether the risk with shut-off systems is low enough is also a matter of politics.

Risk in other control line classes?
Fly aways are not frequent in Speed, Team Race or Stunt, but they do happen and there is the possibility that somebody outside the flying field is hit and injured.
The speed and/or weight of these models make them even more dangerous than combat models. Just take a look at the impact energy of some typical control line models:

  Speed:   400 g - 80 m/s (~290 km/h) 1.28 kJ    
  Stunt:   1,800 g - 25 m/s (~90 km/h) 0.56 kJ    
  Team Race:   400 g - 55 m/s (~200 km/h) 0.61 kJ    
  Combat:   450 g - 42 m/s (~150 km/h) 0.40 kJ    

Impact energy = x (Model weight) x (Flying speed)2           Weight in kg and speed in m/s

New! Calculate the Impact energy, choose "Crash force"

For more information on impact energy see this Critical Review of Safety from the CIAM Electric Flight Subcommittee

Mandatory shut-off in all F2-classes:
After a mandatory shut-off in Combat the next logical step would probably be mandatory "anti-fly-away device" in Speed, Team Race and Stunt.
Cut-Off systems are already mandatory in Team Race and Speed. But these systems are only able to stop the engine if the lines are intact and the pilot is actually holding the handle. If the lines brake or the handle slips out of the pilot's hand, these cut-off systems will have no effect and they can not be categorized as "anti-fly-away devices".

Dangerous Stunt:
Normally Stunt is considered to be a quite safe event, but imagine a 1.8 kg stunt model with a 15 cm3 engine leaving the flying field at 90 km/h. The impact energy of this model is 40% higher than a combat model! Stunt models are also bigger than combat models and have a greater chance of hitting somebody. There is no minimum line thickness and stunt models are often flown on very thin lines and even single strand lines. The pull test is only 10 times the model weight and a safety strap on the handle is not mandatory. Maybe stunt pilots should also start developing an "anti-fly-away-device" to reduce the threat to people outside the flying field!

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