I LOVE Handpropping

[taylorcraftbc65]

Re: I LOVE Handpropping

You did not Bore me at all Bill.

[wmfife]

Re: I LOVE Handpropping

Hope not.

And now I have an engine that doesn't need an impulse mag. The O-145 Lycoming can be pulled through two compression strokes with one pull! LOL

[3Dreaming]

Re: I LOVE Handpropping

Hope not.

And now I have an engine that doesn't need an impulse mag. The O-145 Lycoming can be pulled through two compression strokes with one pull! LOL

The need for an impulse coupling has nothing to do with the fact that you can pull it through two compressions when propping. The impulse is about retarding the spark and spinning the mag real fast at just the right time for starting the engine.
When I had my Lycoming powered T Craft it started OK cold, but when it was hot it could be a handful. I could get it through 3 compressions and maybe 4 if I tried, but it didn't matter because the spark was coming at the wrong time. Also I couldn't spin the mag fast enough to get a good spark when it was hot.

[birdlegs]

Re: I LOVE Handpropping

Geeze Hank, when she's sittin out on the ice in front of the house I'd never get to fly if I followed all of those rules

The best thing I learned to do is prop from behind instead of in front.
I have had the bird slowly start to wander away on glare ice on start up, but since I was standing on a ski & am very diligent about throttle setting it was nothing to get concerned about.

I had to prop my J-3 that way when I was a kid,left foot in front of the starboard tire and right hand flipping the prop downward.

[wmfife]

Re: I LOVE Handpropping

The impulse is about retarding the spark and spinning the mag real fast at just the right time for starting the engine.
When I had my Lycoming powered T Craft it started OK cold, but when it was hot it could be a handful. I could get it through 3 compressions and maybe 4 if I tried, but it didn't matter because the spark was coming at the wrong time. Also I couldn't spin the mag fast enough to get a good spark when it was hot.

This one is the same when hot. General rule is to give it about half an hour to cool before trying.

Cold though it's about the fact that the lower compression means I can spin the crankshaft fast enough without the need for impulse coupling to accelerate. And I haven't worked out in years!

Did not know about advancing /retarding the spark. Thought that was just a feature on large radials! Maybe then will look into getting an impulse for one of these Bendix mags.

I do need to get both mags advanced though for 100LL. An engine designed to operate on 80 octane can't deliver full power with 100 unless the adjustment is made. Fortunately, it is legal.

[robbie]

Re: I LOVE Handpropping

How much more can you advance it?

[high time cub]

Re: I LOVE Handpropping

Keep in mind that most trained monkeys never forget,lol.....

I think you're headed down a slippery slope, Kevin.

http://www.youtube.com/watch?v=Xm4jWwWfqaY

HT

[3Dreaming]

Re: I LOVE Handpropping

How much more can you advance it?

The engine was designed for 73 octane fuel and a timing advance of 20°. With 80 octane or higher you could advance the timing to 25°.

Bill, here is a little about impulse couplings. Your mags without the couplings rotate with the engine and will fire when the points open at 25° before TDC. With the coupling between the mag and the engine it stops the rotation of the mag at a point somewhere before the mag would normally fire, and starts to wind a spring. At a point somewhere near TDC the coupling releases allowing the mag to catch back up and fire. With the ignition near TDC it makes it easier for the engine to start. Once the engine starts running the centrifugal force keeps the coupling from being able to stop the mag and the timing goes back to 25°. The 2 benefits of the coupling are the reduced timing making the engine easier to start, and the spring spins the mag faster than you are turning the engine giving a nice hot spark.

[Guest]

Re: I LOVE Handpropping

Good explanation of impulse couplings. Thanks.

For what its worth the a couple downsides of the couplings are maintenance/inspection and possible surprise start of the engine.

What I mean by surprise start is that you can move a prop just a milli-micron and the wound spring snaps and generates a spark if the p-lead is open and a possible engine start. That's why we never want to touch or rotate a prop.

Dave

[VanDy]

Re: I LOVE Handpropping

Is there a service bulletin for this or is it just one of those things?

[Guest]

Re: I LOVE Handpropping

Some Bendix have a bulletin and AD for a 500 hour inspection.

There may be others. I am aware of only the Bendix one.

Dave

[3Dreaming]

Re: I LOVE Handpropping

The Bendix AD was changed to a Lycoming AD, and now only applies to the 540 series engines. The service bulletin may still apply to your mags, so you might want to check.

[Hank Jarrett]

Re: I LOVE Handpropping

That's why I made the little "Y" grounding strap that I can hook to the "P" lead terminals and a ground under the cowl with alligator clips. You don't want to RELY on it as a safety device, but it is a nice redundant way to keep the mags from firing if you are at an airshow or fly-in and some knucklehead opens your door and messes with the Mag switch. I have seen Mags turned on when someone came back to their plane and they were SURE they had them OFF when they left. Someone moving a prop for a picture (also a STUPID thing to do to when it is not your plane, but I have seen it done) and the impulse coupling could fire, starting the engine.
It also makes you look REALLY dumb if you forget to remove the clips before trying to start up to leave. If any of you ever see me under the cowl passed out from exhaustion, remind me about the clips. ;-)

Hank

Good explanation of impulse couplings. Thanks.

For what its worth the a couple downsides of the couplings are maintenance/inspection and possible surprise start of the engine.

What I mean by surprise start is that you can move a prop just a milli-micron and the wound spring snaps and generates a spark if the p-lead is open and a possible engine start. That's why we never want to touch or rotate a prop.

Dave

[lynnlpitts]

Re: I LOVE Handpropping

My old BC12-D N43213 had Eiseman mags, AM-4, if I remember forty years back , with a Continental A-65 with timing set at 30 degrees. No impulse...always started easily. Don't think I would set the timing to 20 degrees.

[3Dreaming]

Re: I LOVE Handpropping

My old BC12-D N43213 had Eiseman mags, AM-4, if I remember forty years back , with a Continental A-65 with timing set at 30 degrees. No impulse...always started easily. Don't think I would set the timing to 20 degrees.

He has a Lycoming 0-145.