In the past, the rules for soaring competitions in the US and many other countries have not permitted gliders (sailplanes) to have working gyroscopic instruments installed, to prevent pilots from being able to "cheat" by continuing their thermal climbs into clouds in violation of the relevant air regulations and/or the rules in place for the contest.
(The hazard of putting dozens of gliders into the same cloud is obvious, hence cloud-flying was sometimes banned by competition rules even in nations where it was permitted by the air regulations.)
As a result of these rules, in the past it was not uncommon to see a glider at a contest with blank hole in the instrument panel where the turn rate indicator had been temporarily removed.
But an ASE answer has stated
These days, AHRS is dirt cheap, and it is available on many common flight computers and varios.
Here are images of a variometer1 with an AHRS-driven artificial horizon display2--
Butterfly variometer in variometer mode
Butterfly variometer in attitude indicator mode
This advance in technology naturally raises the following questions--
Do the rules used in modern soaring competitions still ban dedicated gyroscopic flight instruments such as the old-style mechanical turn rate indicator and attitude indicator?
Do the rules used in modern soaring competitions forbid the use of instruments with the capability of displaying a simulated "attitude indicator" driven by means of AHRS (artificial horizon reference system)?
If an instrument with such a capability is allowed, is there a requirement that the attitude indicator display not actually be used, i.e. that that particular display screen not be selected in flight?
If so, would the selection of that screen be "flagged" in some way such that it will be known after landing-- similar to if a motorglider uses its motor during a contest task?
A close look at the website that is the source of the images included in this question reveals that in the particular case of the "Butterfly" variometer, the articial horizon display "can be deactivated in a tamper-proof manner". Is such deactivation actually required by the rules in place for soaring contests?
Basically I'm asking if, in soaring contests where the rules prohibit cloud flying, there's anything other than "the honor system" in place to prevent pilots from using a modern variometer featuring an AHRS-driven attitude indicator display to "cheat".
Are the flight tracks evaluated afterwards and compared to the forecast or reported cloud bases? That would seem to allow for at least a thousand feet or so of "cheating" due to variations in cloud base over time and space--
My question is not meant to be specific to the USA, but answers should note which nation they are describing.
Any rules that apply to record attempts, badge flights, etc rather than to actual contests would also be of interest.
I'm asking specifically about sailplane competition, not hang gliding or paragliding.
The primary reason that AHRS systems began to be integrated into sailplane variometers was to facilitate the use of accelerometers to provide faster detection of changes in vertical speed than would be practical with an instrument purely based on changes in atmospheric pressure.
Source of images-- "Craggy Aero" website
Some other related ASE questions and answers of interest--
Other resources of related interest--
"Teaching Instrument Flying"-- Instructor Training Notes-- Dartmoor Gliding Society -- note the comment on page 1, "It is recommended that an ‘Attitude Indicator’ is not used for initial training because this leads to over reliance on a single instrument." As hard as it may seem for today's pilots to believe, there is a long history of cloud-flying in sailplanes, especially in European countries and Great Britain, relying on a turn rate indicator as the sole gyroscopic instrument. Older books such as "New Soaring Pilot" by Welch, Welch, and Irving (3rd ed 1977) discuss this practice in detail.
"Instrument Flying Training Notes"-- Dartmoor Gliding Society -- Note the comment on page 3, "The use of the AI is not included within this course."
Cloud Flying endorsement webpage from Motorglide.co.ok