Starting with strobe on

Today I was starting the airplane with the strobe lights on. The starter turned over and over and the engine wouldn't start. When I turned off the strobe lights, it sarted fine. A couple of things I noticed:

1) When I released the starter switch, the prop would stop but briefly jerk in the opposite direction to normal rotation, before coming to rest. What is the cause of this? Backfire?

2) After the flight someone on the ground noticed that my left strobe flashtube is burned out (the right wing and tail both work). Would it be expected for currents caused by the starter to burn out a flash tube?

3) Does it make sense that having the strobe lights going would make the engine difficult to start?

I would guess that it is unrelated, or something is amiss in your plane. I start with the strobes on, and never noticed any problems. I was taught to fire up the storbes/beacon prior to starting by my instructor years ago to let anyone on the ramp know the airplane was about to start.

When assembling my plane at the airport a few months ago, my right strobe wouldn't fire. Tracing it back from the wingtip revealed a backwards connection at the power supply. After I was flying for a few hours, the strobes stopped working. It turned out to be another connection issue.( I think I hit the wires with my feet while under the panel)

Do you have an electronic ignition that needs battery power to fire?

I do have one electronic ignition and one mag. Perhaps it was a coincidence. Two questions then:

1) Is it uncommon for these flashtubes to fail? They're quite expensive.

2) When I had trouble starting, after periods of cranking the prop would very briefly turn in the opposite direction before coming to rest. What could be the cause of this?

My thoughts

prkaye said:

Today I was starting the airplane with the strobe lights on. The starter turned over and over and the engine wouldn't start. When I turned off the strobe lights, it sarted fine. A couple of things I noticed:

1) When I released the starter switch, the prop would stop but briefly jerk in the opposite direction to normal rotation, before coming to rest. What is the cause of this? Backfire?

2) After the flight someone on the ground noticed that my left strobe flashtube is burned out (the right wing and tail both work). Would it be expected for currents caused by the starter to burn out a flash tube?

3) Does it make sense that having the strobe lights going would make the engine difficult to start?

Click to expand...

1) Probably just coming up on the comression stroke for a cylinder with not enough power to get the the gaseous mixture in the cylinder fully compressed past top dead center to where the path of least resistance is continued rotation to the downward travel of the piston in the normal power stroke and instead the compressed mixture pushes the piston back down the way it came up. You should be very careful if you ever make a compression check on your cylinders without understanding this.

2) No. Your strobe may be OK but the circuit in the left strobe part of your system is shorted. I have burned out strobes but they were over thousands of hours. Your airplane is new so that seems unreasonable to me.

3) Evidently on your airplane it does. If my battery is low with my LASAR electronic ignition the engine will turn over for a time but it will not start. Starting is of course the most demanding task your battery has to accomplish and I never have anything on at that time except that required to start the engine. I never start with the strobes on.

Bob Axsom

prkaye said:

I do have one electronic ignition and one mag. Perhaps it was a coincidence. Two questions then:

1) Is it uncommon for these flashtubes to fail? They're quite expensive.

2) When I had trouble starting, after periods of cranking the prop would very briefly turn in the opposite direction before coming to rest. What could be the cause of this?

Click to expand...

Phil,

The engine should start with the strobes on, but it did not so there may have been a voltage drop that caused the EI to not work. They do have a bottom voltage limit.

If the mag is non-impulse coupled, it could be firing when the switch is out of start and it would kick backward since timing is 25 BTDC. If the mag is impulse coupled the engine should have started no matter the voltage drop (or whatever is going on).

Another factor - the starter - if it is wire wound there should be no problem with voltage drop. IF it is magnet induced, it could be a voltage drop that is occurring with the strobes on.

I broke a starter ring once with an EI that lost its brain due to a voltage drop with an older starter. Switching to a B&C starter cured that problem.

I don't have a clew as to what's going on with the a strobe not working that was working. Starting with the system on is OK, but a very loud "PROP CLEAR" announcement gets as much or more attention. Once an engine is running, its noise is evidence it is running. I turn the strobes on just before take off.

Your strobe may be OK but the circuit in the left strobe part of your system is shorted.

Click to expand...

But wouldn't a short like this cause the fuse for the entire strobe system to blow?

Not necessarily. When a strobe fires, it is discharging a capacitor. The current draw comes from the timing circuit charging the capacitor back up.

The Skytec NL starter seems to work well. What is your battery, starter type, prop?

How do you start the engine?

Did a competent person time your mags?