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Shut-off for F2D-Combat
Links to more information and
the debate on the Internet

Links to more information:
      Last update: 1/3 2009
  Online debat forums:
CL Combat, Combat-1 and CL_Combat_Shutoffs (Yahoo Groups)
Russian Aviamodelny Sports Forum - Translat to English by Google
Barton Model Flying Club
f2d.free.fr - Translatet to English by Google

Homepages with shut-off info:
Preston Briggs has a collection of Shutoffs for Fast Combat
An atempt to develop a electronic shut-off system here: Towards a new shutoff
Mark Rudner's F2D News: October 2007, February 2008 and January 2009
Experience with shutoff in Fast Combat
Bod Busters start World War III
Czech shut-off system
Mike Willcox - Blog
Alex Prokofiev
F2D.dk (this site)


The debate on the Internet:
Shut-off in all classes - 24/2 2008
CIAM and the shut-off debate - 24/2 2008
Shut-off and DQ problem - 28/11 2007
3 and 5 second rules - 19/11 2007
Bill Lee - 27/11 2007
Tactical reflights - 22/2 2006
  There has been a big debate on shut-offs and rule changes in a couple of Yahoo Groups.
This page contains some of my contributions to this debate. To avoid any conflicts with copyrights I have chosen only to bring my own comments.
Some of the contributions are comments to the contributions of others and some of my comments have been commented by others.
Please follow the links to the Yahoo Groups to see my comments in the right context.
/Henning Forbech
Shut-off in all classes:
From Yahoo Group: Combat-l - 24/2 2008 - Message 15735
  Most people probably think that the new shut-off rules only concern combat.
It is not so. The side effects of this rule are much deeper and wider than most model flyers realize.

Let's take a look into the future and see how the situation will be after shut-offs have been made mandatory in combat.

Now, imagine a situation where somebody has been injured or even killed in an accident with a Speed, TeamRace or Stunt model. How will our positions be and which arguments will be used against us in a lawsuit?

Two facts:

1) We have introduced the mandatory shut-off system in combat because we have considered that a combat model is dangerous in the event of a fly-away.

2) Stunt, Team Race and Speed models do have higher impact energy than combat models. This meaning that these types of models are more dangerous than a combat model.

In court the pilot, contest director and the control line model flying organizations now have to explain why this Speed/TeamRace/Stunt model did not have an anti fly-away device when it is mandatory for the less dangerous combat models! It is hard to find any arguments that justify this and there will be basis for a really huge lawsuit.

The fact that dangerous events are very rare in these classes do not change the situation. There will still be a probability of an accident and a huge lawsuit against all involved. The key point here is to understand the difference between the chance of an event and the consequences of the event. One example: The problem with "Russian Roulette" is not the chance of "winning" but the consequence if you "win". You can not turn Russian Roulette in to good clean family entertainment by changing the odds of winning to, lets say, one in a million. The problem is the fatal consequence if you win, not the odds for winning.

By letting the less dangerous class be the first to introduce the mandatory shut-off we put the other classes in a real bad position.

Competition organizers will be under threat of a huge lawsuit. If nobody dares to run this new risk, the only solution will be also to introduce mandatory shut-offs in these classes.

As you can see the shut-offs rule is not an issue that only concerns combat. Speed, Team Race and Stunt pilots will be highly affected by this new rule. It would therefore be reasonable also to hear their opinion in the discussion.

A reasonable debate on this new subject can not be done before the CIAM meeting.
I recommend that the shut-off rules be postponed for a year.

Regards, Henning Forbech

You will find more on the impact energy calculations here:

See the difference between chance and risk here:

CIAM and the shut-off debate:
From Yahoo Group: Combat-l - 24/2 2008 - Message 15734
  In a month the CIAM meeting in Lausanne will decide which rules will be effective from January 2009. For combat the most radical change of the rules is the mandatory shut-offs.
Last November there were a lot of discussions about shut-offs in this forum. When I look back I can see that there are two arguments from that discussion that I would like to comment on:

"One accident can kill combat"
This is simply not true. A fatal accident would be a catastrophe but is not going to close down combat permanently. Other sports and hobbies have been hit by accidents but that did not close down these sports. I find that this argument has been highly overestimated in the debate. To me it almost looks like a fear campaign. A campaign that tries to state that something has to be done right now. Calm down - we are not under any direct threat and there is no need to panic.
If there really was a threat against combat right now the shut-off rules could be implemented from 2008 as safety rules. Nobody has suggested that so we can't be in any immediate danger.
If one accident could kill combat the same must be true for the other control line classes. Are we going to see proposals for mandatory anti-fly-away devices in these classes too? As far as I know there is not even a debate on fly-aways in Speed, TeamRace or Stunt. The fact that fly-aways happen less often in these classes than in combat does not make any difference. Fly-aways do happen in these classes and if it only takes one accident to kill a class they must be under the same threat as combat.
How come that these shut-off rules must be implemented in such a hurry for combat if other classes, with a similar threat, can go on completely unaffected?
To me this indicates that there must be time enough to develop systems and think out new rules before the shut-off is made mandatory. It can not be a problem to postpone the introduction for a year or two.

"The big lawsuit"
The fear of an accident followed by a lawsuit against all pilots, mechanics, officials, contest directors and organisations was used as an argument in that debate.
This risk of a big lawsuit is an US issue. The rest of the world does not have these outrageous legal issues. "The big lawsuit" is a "local" problem in the United Stats and should not be used as an argument for how the combat rules should be organized for the world as a whole. Some times I get the impression that the risk of the "big lawsuit" is more important than the safety of persons. We could have a lot more security for the same effort in time and money if we spend it on a safety net around the flying circle. But only the safety for persons outside the event (a man walking the dog in the park) seems to have any interest. And the concern is not about his health. No, it is about the risk of a big lawsuit!
I see the pressure on CIAM to introduce shut-off as an attempt to solve this local problem through an international organisation. I think the CIAM meeting should withstand this pressure and take the time that is needed to find some good solutions for the fly-away problem.

The risk of a lawsuit is a real problem for the American model flyers and they need to find a solution. From my point of view the new shut-off rule is not a solution to this problem. I fact it is going to make things much worse!
I will explain how and why in my next comment: "Shut-off in all classes"

Regards, Henning Forbech

See an example of the use of these arguments here:
Message 15301

Shut-off and DQ problem:
From Yahoo Group: Combat-l - 28/11 2007 - Message 15443
  Proposals for new rules that have been send forward to the CIAM Control Line Subcommittee meeting this weekend. One rule is concerning disqualification if the shut-off is not working:

4.4.15. Cancellation of the Flight:
y): In the event of a flyaway where the engine shut-off device does not stop the engine within 5 seconds.

This simple rule can lead to some unexpected problems:

Imagine a situation with a DQ rule for a not functioning shut-off and pilots fly with shut-off systems with a success rate of 90 %. (Some pilots will probably even block the shut-off systems because the risk of a DQ is lower than the benefits of avoiding the trouble with unreliable shut-off systems).

If a pilot is about to lose his fight some might be desperate enough to go for there opponent`s lines. If his model flies away and the shut-off doesn't work he will be disqualified and the "desperate pilot" will be declared the winner.
Just the chance of the shut-off not working will be enough for some pilots to try out this tactic in some situations.
If you don't think some pilots will go for a fly-away to win a match then just take a look around. Today we see pilots do the same just to get a reflight! If the reward for cutting your opponents lines was a good chance for an instant win I think we will see an increased number of dangerous fly-aways (remember some of these models will have non working or blocked shut-off systems and can fly really far away).

A solution to this problem could be to let both pilots be disqualified in the event of a fly-away.
The first problem here is that pilots sometimes act as parts of teams. If a pilot from one team is about to lose to a top pilot from another team he could go for a fly-away (his opponents or his own, doesn't matter here). By causing a fly-away he gets a DQ (no problem, he has lost anyhow) but he also takes out the top pilot from the other team. This could be a big help for his teammates and at the end of the day this could rank his team higher than if he just accepted that he lost that bout.
A second problem is that fly-aways do also happen just as results of simple accidents. If both pilots get a DQ after a fly-away there would be a higher element of randomness end luck in the competition. This is not the way to make combat more interesting and it is in direct opposition to the wish to let the fight be settled in the air.
A third problem could rise when a pilot with two lives left meets a pilot with only one life in the final. If the 2-life pilot could arrange a fly-away both pilots would lose a life and he would be declared the winner since he will be the only pilot with a life left.
A really odd problem could come up after a fly-away in a final with two one-life pilots. No winner but a group of pilots that all have the same score. This would be a real nightmare to all organizers.

I see no simple solution to this problem but good and reliable shut-offs would minimize the problem. If the shut-off rule is implemented too early we might end up in a scenario with even more dangerous situations than we see today.

Once again: I recommend that the shut-off rules are postponed for a year !

Regards, Henning Forbech

See also:
Message 15249
Message 15242
Message 15225

Re: 3 second shut down problem...........
From Yahoo Group: Combat-l - 19/11 2007 - Message 15355
This commet was a respond too Message 15340

  If you read the proposals for new combat rules you will find both a 3 second AND a 5 second rule.

The 3 second rule:
"Demonstration of the engine shut-off device may be required by the judges before each heat. The engine shut-off device must stop the engine within 3 seconds of activation. Additional demonstrations may be requested by the judges after the heat"

The 5 second rule:
"In the event of a flyaway where the engine shut-off device does not stop the engine within 5 seconds"

This discussion on the activation time is not new.
One year back Doc Jackson made the first proposal for mandatory shut-off in combat and he used a 2 second rule. Back then I made an alternative proposal with the 3 and 5 second rules.

/Henning Forbech

PS: Here is some of the old background information to 3 and 5 second rules:

Section 4.4.6: Controls - Technical Verification:
"In the demonstration the shutoff must stop the engine within 3 seconds of activation."
Last year I did some experiments with a simple spring system that shuts off the fuel supply by squishing the fuel line. The engine stopped after approximately 1.9 seconds which is very close to the 2 seconds proposed by Laird Jackson.
A 2 second limit might lead to discussions on how to measure the response time in the demonstration. When has the engine actual stopped? When the engine is not making any combustion any more, when it is not turning over anymore or when the propeller comes to a complete stand still?
With a shutoff system that stops the fuel supply a combat engine will normally stop working after 1.5 seconds and will typically come to a complete stand still after 2.5 seconds. Therefore a 3 seconds limit seems more suitable for practical use.
You will find a video clip with the test here:

Section 4.4.15: Cancellation of the Flight:
"In the event of a flyaway the pilot shall be disqualified if the shutoff device does not stop the engine within 5 seconds." In this situation the time limit is set a little higher than during the demonstration.
The idea is to let the technical verification ensure that the shutoff system is capable of bringing the engine to a fast stop. In the event of a flyaway it should then only be necessary to observe if the shutoff system is working or not.
During a flyaway it will be very difficult to measure the exact reaction time for the shutoff system. The time keepers will typically be seeing the midair collision but hearing the engines stopping. The distances involved are far too big for a visible observation of the propeller movement, so the time keepers must rely on the sound of the engines.
In a situation where a model is flying away from the timekeepers the delay of the sound can be as much as 0.35 seconds! (distance across the circle: 35 m, model flying 2 seconds at 42 m/s, speed of sound: 344 m/s)
By setting the time limit for the flyaway situation higher than the test situation, we can eliminate a lot of discussion on how the time measurement was done during the flyaway, but we will still be able to disqualify a pilot with a non-working shutoff.

For more information visit:
https://www.modelflyvning.dk/f2d.htm - look for: "Early proposals for shut-off rules:"

or find it here:
https://www.f2d.dk/shutoff/docs/Forbech comments.pdf

Re: CL_Combat_Shutoffs
From Yahoo Group: Combat-l - 27/11 2007 - Message 15427
This commet was a respond too Message 61

  Re: CL_Combat_Shutoffs

I have transferred some of the comment in the "Combat-Shut-Off" group to this group since my response to it is more a general comment than a technical issue.

In a response to Göran Olson's comment on my shut-off project Bill Lee wrote:
> "Third. What did he base his decision of failure on? His website
> seems to document success. He developed a shutoff, it worked, he
> flew competitions with it. And when he didn't he had two fly-aways.
> Maybe I missed something, but in reading his website, I really saw
> nothing that gave his reasons for the conclusion he made. That's
> why I thought that perhaps he made the combat-l post in jest."

Maybe I didn't make my point clear enough on my website so please let me try to explain the idea behind my shut-off project:

First, I didn't give up on my mechanical shut-off because it didn't work. I shut it down because it could not be used as a general shut-off system in F2D-combat !

I was (and still am) looking for a shut-off design that can generally be used in combat. Not just by me and other DIY nerds but a system that will suit all pilots. This ideal system should solve the fly-away problem with minor side effect on rest of the F2D combat as possible and it should be made available to all pilots.

Any shut-off design will have an effect on the whole F2D combat buisness. A very expensive shut-off system would ground those pilots that can't affort them. Self-made shut-offs would ground those who can't produce their own system. Complicated systems will set pilots without a well trained pit crew out of the game. Etc.

If the shut-off rules are introduced before we have a well designed, well tested, available ready-to-use systems and a set of consistent rules there is a high chance of a serious reduction in the combat activity in the next years. I have not yet seen any of these matters been fulfilled but more people are now starting to work with these problems. This is why I recommend that the shut-off rules are postponed for a year. More time is needed to develop the shut-offs and to get the rules ready for this new situation.
I think it would be a big mistake to make the shut-off systems mandatory from 2009.

Henning Forbech

Tactical reflights:
From Yahoo Group: cl_combat - 22/2 2006 - Message 433
  Flyaways do happen as simple accidents. That's bad enough.
But some flyaways seem to be part of a tactical game where a pilot in a "hopeless" situation sees a flyaway as his chance for a second attempt.

A small change to the rules might prevent pilots from attempting to cut lines as a part of a tactical game:

If a pilot has a flyaway, he can ask for a reflight. But he should only be given the reflight if his score is higher than his opponent!
This would block desperate pilots from trying to get reflights by dangerous flying.

Well, we might see fewer pilots asking for refligths after "simple" accidents. If the unlucky pilot isn't sure of his position, he will probably let the fight go on instead of risking not getting a reflight.

Henning Forbech

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