Wing wag considerations
I just wanted to share my rationale for how to arrange switches for the landing lights based on functional and safety considerations. This is part of a conversation I have had with Paul at Flyleds. I am building an RV-7A that will be IFR capable with two Duckworth style landing lights.
I looked at how to arrange switches and functions from a couple of considerations.
1. Based on phases of flight
2. Safety and failure modes
1. Phases of flight
a. Startup and taxi for takeoff
i. Landing lights in low power (both on) continuous.
b. Line up and take off (VFR & IFR)
i. Landing lights in high power (both on) continuous.
c. Climb out (VFR)
i. Landing lights in high power (both on) in wing wag.
d. Climb Out (IFR)
i. Landing Lights off
e. Cruise (VFR)
i. Landing Lights in wing wag.
f. Cruise (IFR)
i. Landing Lights off
g. Descent and join pattern (VFR)
i. Landing lights in wing wag.
h. Descent and approach capture (IFR)
i. Landing lights off.
i. Established on Final approach (IFR and VFR)
i. Landing lights on Continuous.
j. Ground ops to parking (beyond the hold line)
i. Landing lights in low power (both on) continuous
2. Safety considerations
a. Probability of loss of function or erroneous function during (a),(c),(e), (g), (j)
i. Not critical < (1:10 E-3 per flight hour)
b. Probability of loss of function or switching to wing wag during (b), (d),(f), (h), (i)
i. Critical < (1: 10E-6 per flight hour)
c. Probability of not being able to switch off landing lights (a) through (j)
i. Critical < (1:10E-6 per flight hour)
I considered day time and night time VFR and IFR operations together with past experiences of having landing light failures at night at critical times on poorly lighted airfields. Training here in the US is focused on being able to land at night without the aid of landing lights so if the lights go into wing wag or start flickering the training is to turn them off and concentrate on flying the plane to a landing.
Of course it is possible to overthink this and make it way more complicated than it needs to be.
Cutting to the chase ? I would go with a variation on your option 2 (DIAGRAM B) where the two switches are labeled
1 (on -off) Landing lights (DPST) Basically a ?kill? switch.
2 (On-off-on) (Taxi - both on low power)? (continuous ? both on high power)? (wing-wag) (DPDT/TPDT ?) This configuration of switch positions makes the sequence of operations match the order of needs. I haven?t thought through the wiring for the DPDT/TPDT switch so depending on how you have arranged the circuit that may not work and it may need some further thought on the switch configuration needed.
This configuration adds a switch to the panel but makes the operational procedures very straightforward for the more critical IFR procedures. Getting distracted by technology is a very real problem even for professional pilots so having a simple way out is important.
I could make a guess at the circuit you have for the wing wag module but my thought was to just add resistors in the ?Taxi? switch contacts to drop the landing light LED power. I am using the Duckworth rectangular models with H3 LED lamps from one of the Amazon suppliers. I have tried a couple of different offerings to check out the beam pattern and settled on one as the preferred solution. I haven?t done any nighttime testing yet to figure out what the ballast resistor needs to be for the taxi function.
Paul suggested an alternate method for the "Taxi" mode that needs more thought and more work.
Keith Turner