RJ85 Nose
 

A friend asked me if I knew what this was on the side of an RJ85. I haven't got a clue. The grooved part rotates round.

Any ideas chaps?

place to upload pictures

Serrated rotor ice detector.

Hi,

I believe it's a rotary ice detector: when powered, it rotates and as ice accumulates and contacts the fixed triangle shaped part, it causes a higher torque demand thus indicating possible ice build up on the structure of the aircraft. The Let L-410 has something similiar.

Many thanks :-)

History Lesson.
 

My experience of this "ice detector" was that it was a waste of weight and complexity. It usually illuminated the warning long after the 'frame had accreted ice or alternatively gave frequent false warnings. Why BAE abandoned the "hot rod" ice detector as used on the 111 and the 125 is a mystery. It was a delightfully simple and foolproof device, the only quirk was the tendency to "hum" at certain AOAs!

More information on this and other ice detectors of the same period is available here.


That report is dated 1993. Has the technology moved on since then?

I thought it was where you put the hand crank to turn the engines over. No? :p

Yes, it is indeed an ice detector. Dunno if it's a quaint DH/HSA/BAe design specifically but it is certainly identical to that used on this aircraft's direct predecessor; the DH/HS Trident.
(Either that or it's a spud peeler).

BAC One-Eleven had it as well.
The ground test was to operate the switch in the ground headset socket panel and slow the rotor with a finger or thumb, then check the Ice warning light was on in the cockpit.