"On our little tiltrotor, it may turn out that we do not have the space / weight to provide 4 seperate channels - the conceptual designer has imposed a weight limit of 64kg on the entire avionics system. Yes, we laughed too... "
My guess is that if you look at,say, one of the integrated VLJ Avionics fits, you should be getting down around that range EXCEPT for the Power Drive Units needed to actuate surfaces and, of course, the rotor or nacelle tilt. A lot of current Autopilots already have the equivalent of four Flight Director channels. MEM sensors give the equivalent performance of much larger gyros - look at what's contained in an Integrated Standby Instrument - Air Data Computer, PFD & Attitude sensors all in about 2kg. Also, if your aircraft is small, you won't have the burden of long wiring runs & the production breaks necessary in larger types.
A comment on Flight Control Panel indications - most current panels do have light indicators for engaged FD mode with some also having two so the pilot can verify that both left & right channels are selected correctly. Sadly the "schematic" type of system control panel has died with the introduction of cheaper & easily configurable synoptics on EICAS. The latest screens also allow the pilot to call up the information decks he wants and position them within the larger display unit - effectively giving many more than six EFIS.
Last edited by ICT_SLB; 24th Nov 2010 at 00:51.