15th Apr 2012, 21:16
FAR 23.221 requires stall demonstrations with one ball width displacement on the slip-skid indicator. However, I have yet to find a matching specification for the sensitivity of the slip indicator. Presumably such a specification exists, otherwise a designer could satisfy the requirement more easily by fitting an extra sensitive instrument.
Can anyone point me at the requirement?
16th Apr 2012, 10:22
Although my answer is not authoritative, and TSO C3e does not seem to describe a specific requirement for this, I would think that referring to the slip indicator specified for that aircraft, as a part of it's design, would be a good start.
If someone is trying to "trick" certification by subbing in an indicator with different properties, I would think that the test pilot would catch this pretty quickly. Similarly, the test pilot for a new design will probably not pass a slip indicator which is not affective.
Keep looking though, there may be a prescribed design for this somewhere....
Genghis the Engineer
16th Apr 2012, 12:06
I've not seen any requirements.
I have however before now come across companies who leaned heavily upon their TPs, particularly in part 23 singles and smaller, to bend the way they did their testing to ensure the aeroplane complied - rather than produce a better, safer aeroplane. Unedifying when it happens, although thankfully reasonably rare.
17th Apr 2012, 03:42
Looking through TSO-C3e, paragraph 3 states:
3. REQUIREMENTS. New models of turn and slip instruments identified and manufactured on or after the effective date of this TSO must meet the MPS qualification and documentation requirements in SAE Internationalís Aerospace Standard (AS)8004, Minimum Performance Standard for Turn and Slip Instrument, dated September 1, 1975.
I don't have access to this standard but it should give you a specific lateral acceleration (g) for the slip indication.
17th Apr 2012, 21:50
FAR 23.221 deals with spins. The ball-width requirement is to be applied only for airplanes certified as "spin resistant." I don't have a copy of SAE Aeronautical Standard 8004 which should list the sensitivity of the ball to lateral acceleration.
17th Apr 2012, 22:42
Yes, my query was prompted by Icon's claim that they had demonstrated that the A5 complies with the requirements to be certified as spin resistant.
20th Apr 2012, 12:39
I have now consulted SAE AS8004. It does not specify the sensitivity of the slip instrument. Any other suggestions?
21st Apr 2012, 07:33
If you have a spare 36 quid, try this: BS G 125:1950 - Specification for turn and slip indicators for aircraft purposes (http://shop.bsigroup.com/ProductDetail/?pid=000000000000113538)