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Shut-off for F2D-Combat
Rules for shut-off systems

Shut-off rule clarification

(This is the official clarification to the F2D shut-off rule from the C/L Subcommittee, published 9/12 2008)

From the 1st of January 2009 it will be mandatory that an engine shut-off be used in F2D. In the event of a fly-away the shut-off must activate and stop the engine. Failure to do so will result in disqualification.

The shut-off can either be armed by the mechanics prior to launch or by automatic arming of the shut-off on take off. When the model is prepared the shut-off may also be armed.

A damaged shut-off on a landed or crashed model (for instance as a result of a mid-air collision) must be repaired or replaced before the model is launched again.

Both mechanical and electronic shut-offs will be allowed, providing they do activate and shut down the engine in a fly-away. The fly-away activation can be of any type, mechanical or electronic.

The shut-off rules are intentionally of a basic nature to allow the development of good working systems but it should be noted that flagrant breach of the rules or "ungentlemanly conduct" will result in disqualification.

8th of December 2008

Bengt-Olof Samuelsson
C/L Subcommittee Chairman

Same text at the Control Line's blog, CIAM.

The following text is my personal view on the shut-off rules
Henning Forbech

2009 Rules for Shut-Off systems

Organizers and pilots do not have any experiences with the practical implementation of the 2009 rules on mandatory shut-off systems. This leaves us all with a lot of doubt on how the new rules will be used in competitions.

Some organizers might have a quite different understanding of the rules than the pilots. Some pilots might even have interests in exploiting the rules.

In this winter all pilots have to develop and implement shut-off systems for next year. If your interpretation of the rules does not match the interpretations of the organizers, judges and other pilots you will run into big problems.
This is a good reason for taking a closer look on the 2009 rules.

First problem is that the final rules for 2009 have not been published jet. Only by a combining of the agenda for the CIAM plenary meeting, a report from the F2 Technical Meeting and the 2008 Sporting Code can you get an idea about how the 2009 Sporting Code will be. The next problem is that not all the rules for combat can be found in rules for competitions. Some of the more fundamental rules are part of general rules for CIAM (You will find links to all these documents at the bottom of this page).

I went through all these documents and found two issues that will have a huge influence on the design of shut-off systems.

  • The device must remain functional for the entire flight period
  • The general rules only allow us to use the lines to control the model and engine

Functional for the entire flight period

The first issue is the new 4.4.5 Characteristics of a Combat Model Aircraft:

From the document "ANNEX 8a - 08_F2_Tech_Meet_1.pdf"

The key sentence here is that "the device must remain functional for the entire flight period".

The phrase "the entire flight period" leaves no room for a design with activation after launce. With a shut-off system that is blocked on take off and first will become active after i.e. one quarter of a round it is clear that the model has been flying this distance without a functional shut-off.

The problem with activation after take off might seem a very theoretical problem, but some systems will activate automatically and other designs will not activate before the pilot gives the lines a hard pull or makes a rough manoeuvre. For how long should a pilot be allowed to fly his model before the shut-off system is active? The 2009 rules are very clear on this issue. Take off with a blocked shut-off system is prohibited!

The "entire flight period" rule will also not let you fly a model that gets a damage on the shut-off system in a mid air collision. If it can be proven that the shut-off was out of order during a flight the pilot should be disqualified.

Line control and only line control

The second issue comes from classification of control line models.
This is not a new rule but a general rule that applies to all types of control line model flying.

From FAI Sporting Code, Section 4 - Aeromodelling, Volume ABR - 2008 Edition

The key sentence here is:
"No other means of controlling the model or the engine may be employed during the takeoff and flight except that exercised by the pilot through the line or lines."

The consequence of this rule is:

  • No radio control.
  • No helpers or officials with a remote control.
  • No automatic system that controls the engine.
  • All control must be done only by the pilot and only via the lines.
To make it short:
              The engine must be stopped by something the pilot does with the lines.

This is an extreme set of restrictions on the shut-off design, but this is a general rules for all control line model flying.
Do we really have to follow these rules? Let's take a look on some of the other classes.

Speed and Team Race have a rule on a mandatory cut-off.
It is possible for them to let the pilot use the lines to stop the engine. So they are consistant with this rule.
Stunt lets the pilots use automatic systems for retractable landing gear and timers to stop the engine running.
This is only possible because there is an exception in the stunt rules from the general rule.

These are the Stunt rules:

From FAI Sporting Code, Section 4 - Aeromodelling, Volume F2 - 2008 Edition

The exception is "f)" and the "1.3.2 of Section 4 of Volume ABR" is the general rule above.
Please note that no types of wireless remote control are permitted in the Stunt rules.

If Stunt needs an exception from the general rule just to allow a retractable landing gear or timers to stop the engine we will also need an exception to allow an automatic shut-off system.

As far as I know there is not any exception from the general rule in the new 2009 Combat rules.
We have to design shut-off systems where all control must be done only by the pilot and only via the lines.

Hot or Not Systems

Let's see which technical solutions can be used and which not under these very restrictive rules.

All systems based on radio control or similar wireless techniques are out.
Systems based on electric detection of acceleration (g-force), GPS, etc. are out.
Mechanical systems based on acceleration (swing arm or similar) are out.
Systems based on line tension should be OK. The pilot pulls the lines to keep the engine running. If he stops pulling (line brake) the engine will stop.
Some typical line tension systems are: "String-over-the-Wing" or "Moving bellcrank".
Maybe it is also OK to send electrical signals through the lines and let a system on the model detection these signals. The pilot sends the signals to keep his engine running. If the signals stop the system will shut-off the engine.

Designing a system that remains functional for the entire flight period will be a tough challenge for all shut-off designers. Especially the take off will be difficult. At take off you have no line tension and the shut-off will try to kill the engine.
A small reservoir with extra fuel under pressure connected to the fuel line between the engine and the shut-off can give some extra run time before the engine stop. This should be just enough to get the model in the air and to generate speed and line tension enough to open the shut-off. Remember that the run time at the demonstration should be less than 3 seconds. I takes the engine about 2 seconds to stop so there shut be room for an extra half a second runtime.
I actually used
such a system in one of my first test flights in the early spring 2006.
I think it is time to go back and give that idea an extra chance.

Rules or Gentlemen Agreements

Do we really have to follow the rule book by the letter?
Can't we just make a gentlemen agreement on how to read the shut-off rules.

Imagine that all pilots, judges and organizers on this forum made a "gentlemen agreement" to allow radio controlled shut-off systems for the next season.
Now if a pilot at a World Cup competition next year finds that other pilots are using equipment that are unconsistent with the rules he can complain to the judges and officials on the flying field. The judges will probably stick to the gentlemen agreement and allow the radio controlled shut-off.
If the pilot is not satisfied with this decision he can make an official protest. This protest will be processed by the official Jury at the competition (not by the judges on the flying field). The Jury will check with the official rules and make their decision.
For a protest on a radio controlled shut-off system the Jury just has to check if the rules allow remote controlled equipment in combat models or not. Since the gentlemen agreement is not in the official rules the result can only be that the radio controlled shut-off is not allowed.

A competition organizer that insists on following the rule can also force all pilots to adopt their equipment to these rules. Even if all pilots want to use the gentlemen agreement they will be forced to follow the organizer's interpretation of the rules.

A gentlemen agreement can not be a stable solution to this problem.

Links to documents

Volume ABR:
FAI Sporting Code, Section 4 - Aeromodelling, Volume ABR - 2008 Edition (sc4_abr_08.pdf)
Volume ABR gives general rules for CIAM activites, competitions and records.

Volume F2:
FAI Sporting Code, Section 4 - Aeromodelling, Volume F2 - 2008 Edition (SC4_Vol_F2_ControlLine_08.pdf)
Volume F2 contains the rules and regulations for model aircraft competitions
Combat rules from page 34 to page 40
Stunt rules on page 11

General Section:
FAI Sporting Code, General Section - 2008 Edition (GS-2008.pdf)
General Section contains the rules and regulations common to all FAI activites
Complaints and protests in Chapter 5

CIAM plenary meetings:
The agenda for the CIAM plenary meeting, Lausanne (Switzerland); 27-29 March (ciam_200803_agenda.pdf) page 19
Minuts: (ANNEX 8a-08_F2_Tech_Meet_1.pdf).At page 35-36 you will find the new rules for combat.

Documents from CIAM:
You will find these documents at the CIAM homepage.
Under "Meetings" and "2008: Bureau/Plenary; Lausanne (Switzerland); 27-29 March".
To get the agenda with all proposals you must download the Agenda (476 KB). Proposals for F2D start at page 19.
To see which proposals that have accepted you must download the zip-file: Annexes 2,3,4,5,7,8 to the Minutes.
F2D is on the page 35 and 36 in: "ANNEX 8a - 08_F2_Tech_Meet_1.pdf".

Documents can also be found at CIAM Documents Page


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