Both the CI-122 and the CI-292 cover the same frequency, 118 to 137 MHZ per the spec sheet attached below.
http://www.cobham.com/media/9104/ci 122 data sheet.pdf
http://www.cobham.com/media/9312/ci 292-2 data sheet.pdf
I believe the difference between the two is the CI-292 has a larger diameter element which would be an advantage when mounting on the top of a helicopter. The constant
beat of the rotor blades may cause the thinner CI-122 element to fatigue where the larger diameter would be more resistant to mechanical resonance and flutter. Having the antenna element break loose and contact the rotor would be $$$.
Aircraft antennas have been known to flutter, the effects are are not as dangerous as a control surface flutter but the departing component could strike the aircraft.
Based on a conversation with an engineer that develops military antenna hardware, the top RV speeds are below the 225 - 250 KTS where he has seen this occur.
If you are looking for the best TSO'd VHF Com antenna on the market purchase the D&M (Dorne & Margolin) C63-2
http://www.aircraftspruce.com/catalog/avpages/c63_2.php
The D&M has a tapered element which resist flutter and vibration much better than a straight element, the element is also at DC ground which reduces the effects of "P" static or the annoying buzz when flying through dusty or rainy conditions. The internal impedance matching network provides a low VSWR over the entire com frequency where some of the competitors do not.
Based on testing I have completed with lab grade equipment, If I was required to install a TSO'd antenna on my aircraft, it would be a D&M C63-2.
