Vans R L Both Start Switch Question

[mfshook62]

My schematic shows that the R post on the R L Both start switch is connected to the right mag p-lead, and the L post is connected to the left mag p-lead. The jumper to the right p-lead is removed. I have previously tested to be sure that during a mag check when the key switch is in the R position, the right mag is enabled and the left mag is grounded to the p-lead, and vice-versa. So, Im just curious why is the R is on the left side of the key switch and the L is on the right side.

While we are on this topic, I think that the arrangement that makes most sense to me would be a key switch for: OFF L Both R with a separate start button powered from the key switch. This way its one click to the right for a right mag check, and one click to the left for a left mag check. Is the reason for the double click to R so you can compare the R to L mags with one click and to have the BOTH next to the START?

[scsmith]

The switch comes with a jumper that grounds the right mag when the switch is turned to start. If you want, you can move that jumper so that the left mag is grounded when you turn to start.

But that is different from the left and right positions of the switch. When you select left, the right mag is grounded and you are running only on the left mag.

When you select right, you ground the left mag, and you are running on only the right mag.

When the switch is off, both mags are grounded.

When you select both, neither mag is grounded.

When you select start, the mag to which the jumper is wired is grounded (usually the right).

Make sense?

[ExtraKatana]

But why is the order of the switch (when reading from the left) R L and not L R?

Always seemed to me better labeling would be TOP BOTTOM

[AirbusPilot]

Originally Posted by mfshook62

My schematic shows that the R post on the R L Both start switch is connected to the right mag p-lead, and the L post is connected to the left mag p-lead. I also see a jumper to the right p-lead. I have previously checked to be sure that during a mag check when the key switch is in the R position, the right mag is enabled and the left mag is grounded to the p-lead, and vice-versa. So, Im just curious why is the R is on the left side of the key switch and the L is on the right side. I know that its been like this for a long time, but it seems to me that one click back from Both should be a right mag check and two clicks back should be a left mag check.

Mike Shook

You are right, position of left and right magnetos are reversed on the switch and I would like to know the reason too

[John R. Graham]

Because of traditional mag check order, perhaps? "Left," which is traditionally checked first during run up, is closer to "Both".

- John

[Bob Kuykendall]

Originally Posted by ExtraKatana

...Always seemed to me better labeling would be TOP BOTTOM

That's not necessarily appropriate in a typical mag installation. In most of the installations I've seen, the left mag fires the upper plugs on one side of the engine, and the lower plugs on the other side. So there is typically not an "upper mag" and a "lower mag."

In fact, until I saw a Lightspeed ignition, I had never seen an airplane ignition where one system fired all the upper plugs, and another fired the lower plugs.

Thanks, Bob K.

[cfiidon]

Perhaps in the "olden days" the switches were labeled on the bottom. Then you would see

START BOTH LEFT RIGHT OFF

With the key rotated clockwise. Notice that in this case Left is on the left and right is on the right.

Don

[Av8torTom]

The way it was explained to me, Off - Right - Left - Both, came from the days when some airplanes (e.g., early Piper Cherokees) had a separate button start switch, and those engines were started off the left mag. Once the engine started it was one click clockwise to get to Both without having to go through Right - *shrugs*