National Free Flight Society

SEN 2406

  1. Use of accelerometer in F1A
  2. Re: SEN 2405 – Accelerometers
  3. San Valeers Corrected
  4. More SEN stuff


Use of accelerometer in F1A
From: Ian Kaynes

The Free Flight definition includes the prohibition of closed loop control
systems: “Closed loop control systems with active sensors and operating

aerodynamic flight controls or moving mass are not allowed, unless allowed
in the class rules.”

In the case in question the accelerometer is an active sensor but taking no
control action until it reaches the required threshold. It then gives the
signal to release the hook and then takes no more action during the flight.
This is a single trigger action with no feedback of the result of that
action and thus it is not a closed loop control system. So in my view it is
just as acceptable as having a mechanical spring release the hook.

Ian Kaynes

Re: SEN 2405 – Accelerometers
From: Allard van Wallene

Dear Mr. Scat:

On the (il)legality of accelerometers for unlatching a hook, the rule can be found in the General Section of the Sporting code under Free Flight:

B.1.2.1 Category F1 – Free Flight
a) This is a flight during which there exists no physical connection between the model aircraft and the competitor or his helper. Radio control functions are allowed only when specifically stated in the rules for the relevant class. Closed loop control systems with active sensors and operating aerodynamic flight controls or moving mass are not allowed, unless allowed in the class rules.

Let’s strip this down to our case:

1 Closed loop control systems:  No, the g-sensor triggers the opening of the latch and changes of surfaces upon release of the model. There is no closed feedback loop. The action is irreversible.

2 with active sensors: Yes, there is an active sensor (but not used in a closed loop)

3 and operating aerodynamic flight controls: Yes, although a latch is not an aerodynamic flight control, the sensor starts another myriad of changes (e.g. flaps, rudder, stab)

4 or moving mass: debatable as a latch has a mass which is moving. However the gist of this particular addition at the time was to prevent CG changes thereby changing the stability margin. A moving latch does no such thing.

Are not allowed, unless allowed in the class rules.

Note the words ‘and’ and ‘with’, meaning, if any of features 1, 2 or 3 are not present, the rule is complied with. As an example, a weight pendulum to control a stabiliser (=closed loop) is allowed as it doesn’t involve an active sensor.

Ergo, since item (1) is not applied, the system does not breach the FAI rule B.1.2.1 a)

For what its worth, a typical value set for opening a latch is 8g. We have discovered that the actual g-loads are somewhat lower than the values calculated. But this is another (in my opinion very interesting) discussion.

Best regards,

San Valeers Corrected
From: Terry T

Attached is the correct flyer for the San Valeers spring. The one in the scat newsletter I just received shows slow gas which we are not having this year. It wasn’t the latest revision.

APRIL 21st & 22th, 2018 – LOST HILLS, CA.

(SCAMPS/SCIFS contest same weekend with SCAMP CD Dan Heinrich 909 593-5789)


SATURDAY 8 TO 5                              SUNDAY 8 TO 3                         BOTH DAYS
1/2A GAS                                          A GAS                                      P-30, HL & Catapult Glider      
B GAS                                                D GAS                                      1/2A Golden Age
C GAS                                                ABC Nostalgia**                      Nostalgia Rubber
1/2A Nostalgia**                                                                    (all flights same day for each entry)

1st Round at 8am, F1A, B, C, P, Q 240 secs. All other rounds 180 secs. Flyoff begins at 4:00pm

F1GF1HF1S SUNDAY 8 AM TO 11:45 Tie breaker flyoff to the ground7:30 to 8:00 am. Standard (5 rounds  45 minutes long starting at 8:00 am, 120 sec maxes) 2 FO flights starting at 1:00 pm. If tied after 5 flights and 2 FO flights than tie breaker flight determines winner.

SATURDAY 8:00 am-1:00pm (5 1hr rounds) All flights 180 secs flyoff at2:00pm

HUNTER MEMORIAL SUNDAY MORNING(weather permitting)Sponsored by Mike Thompson
RULES: Any gas free flight airplane.  15 second VTO, 12 second H.L. Highest single flight time (no max) Starts Sunday at sunrise with 1 hr window (start time announced). Entry fee ($1.00 per flight)

**NOSTALGIA per latest rulebook except motor runs which shall be 10 sec HL, 13 sec VTO for 1st 3 flights, 7 & 9 secs on all flyoff flights. Classes scored separately for National cup but awards given for 1/2A Nostalgia and ABC Nostalgia combined.

1/2A GOLDEN AGE 1/2 A Models from 1957 to 1969 Engines:TD OR HH .049/.051, motor runs same as Nostalgia

MERCHANDISE AWARDS (engines, kits, fuel, wood, $$$, etc)

***ROSSI .15***  RAFFLE reworked by G. Aldrich & donated by Ed Hopkins (1 ticket for each event entered, or $3 ea, or $5 for 2, or $10 for 5)***

AMA/NOST CD: Ted Hidinger (602) 316-4430   FAI CD: Mike Thompson (805) 404-6173

AMA & Nostalgia: 1ST event: $10.00, Additional events: $5.00 per event or $35 unlimited entry, JRS FREE,  FAI events: 1st event $20 and additional events $10.


More SEN Stuff
SEN issues are archived in the SEN Web site – Sometimes this takes a day or so. There is a Table of Contents down the left hand side and they are done by year. Many times the subject of the SEN will show an indication of the content. So if you are missing an issue or want to back and see something you can go to the site.

In addition the contents is indexed and at the bottom of the table of contents list there is a search item that lets you search all the articles in the site.

While recent issues of SEN have focused a lot on the Fab Feb contests in the USA. The object of SEN is to cover all aspects of FAI Free Flight worldwide and the previous issue and this one have good examples of that. There was a question from Frederic Aberlenc in France followed by two replies, on from Ian Kaynes in the UK and another from Allard Van Wallene in the Netherlands.  Note that 2 of these are not native English speakers and they come from 3 different countries. The USA FAI FF community uses SEN to discuss some items about FAI team selection in the USA (e.g recent piece from Aram Schlosberg) and other USA specific items but this should not discourage contributions from people worldwide.  Over half the SEN readership is outside of the USA. To contribute you just have to send your article to

There is no question that FAI Free Flight along with many other classes of Free Flight and model aviation in general is under a lot of pressure these days.  The object of SEN is to take a positive position and encourage FAI Free Flight and Model Aviation in general.  By sharing information about what we do as positively widely and inclusively as we can promotes what we do.