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Classic Wings Magazine Luftwaffe Resource Center WWII Naval Aviation Research Pacific
Final Cut-The Post War B-17 Flying Fortress and Survivors - 5th Edition


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PostPosted: Wed May 16, 2018 5:17 pm 
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Out of curiosity, and for sake of producing an accurate aircraft systems simulation, does anyone here have any experience operating an aircraft of the 1920's/30's era that is setup with a manual spark advance adjusted from within the cockpit? I know there were a good number of aircraft that were configured that way during that era, with spark advance levers as part of the engine controls/throttle quadrant. I'd like to understand just how much this played into the operation of the engine by the pilot, and if it was something that had to be adjusted/fiddled with a lot by the pilot to get the timing right when making throttle adjustments, or if it was more/less something that was just set and left alone. For instance, would there be a reason to delay the spark during typical engine/flight operation?

Any details/insight into the reasoning and the operation with such a setup would be greatly appreciated!


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PostPosted: Wed May 16, 2018 6:30 pm 
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As I recall the Ryan STA with the Menasco had a manual retard switch which was used for starting and warming up of the engine. It was returned to normal for all other operation.

Sully


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PostPosted: Thu May 17, 2018 6:04 pm 
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Thank you for your reply, Sully! Following what you wrote, I found an article on the operation of a Menasco-powered Ryan STA, and in it the author states that having the ignition control/spark advance/retard is a great asset in the manual prop-swinging startups. I'd like to know more about why exactly that is/the exact benefits (preventing pre-ignition and hard starts?). In the article, the author mentions that the lever is set in the fully delayed/"retarded" position, and once the engine fires off, the lever is quickly moved to the middle position and the throttle adjusted for proper idle RPM. Prior to take-off, the lever is set to fully "advanced" and left there.

So-far I've found examples such as the Lockheed Vega, P-26, Ryan STA, Pitcairn Mailwing, and Stearman 4E and C3R having the spark advance control on the throttle quadrant.


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PostPosted: Thu May 17, 2018 8:58 pm 
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There is no impulse coupling on the Menasco thus retarding the spark manually accomplishes the same task.

Sully


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PostPosted: Fri May 18, 2018 8:13 am 
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JohnTerrell wrote:
I'd like to know more about why exactly that is/the exact benefits (preventing pre-ignition and hard starts?).


The combustion event has a, more or less, fixed duration from spark to maximum pressure. Since rotation speed is slower at start up, either hand propping or using a starter, the spark is retarded - happens later in relation to top dead center- so that pressure occurs AFTER TDC. This prevents kick backs, and gets the engine rotating the right direction and moving faster. As the engine picks up speed the spark is advanced - happens earlier in relation to top dead center- so that maximum pressure still occurs at the right time after TDC.

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PostPosted: Fri May 18, 2018 5:38 pm 
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Gentlemen, thank you very much for these great explanations. Your input has really helped clear this up - I appreciate it!


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PostPosted: Wed Jun 06, 2018 8:25 pm 
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My Fairchild has the same manually-controlled system on the Warner

It's more properly thought of as a spark-retard, not a spark advance. You retard it for starting, like a Model T car, so you don't get kick-back. Then push the control back in for the Advance normal running operation.

As was said (very well), the impulse mechanism made the manual-retard redundant.


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