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Adjusting the AeroVee Secondary Ignition Timing
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Lessons-learned submissions follow a standardized format designed to identify the issue, draw out the relevant factors and present useful guidance to others facing a similar situation. The submitter answers the following 5 questions:
1) What went wrong (or right), and why?
2) What were the shortcomings, and why did they exist?
3) What actions were taken to fix the problem?
4) What preventive actions should be taken into account for future efforts?
5) What overall recommendations should be made for future projects?
The length of the write-up and amount of detail presented are left up to each individual. Some lessons learned can be perfectly conveyed in a few simple sentences, while others will require much more. The goal is to be as clear and succinct as possible, not to generate literary masterpieces!
All posts submitted to this forum are held in a review queue for approval by a moderator. Information in the posts will be reviewed, vetted, and modified as needed before going public. Additionally, any replies that are submitted would also be reviewed to ensure they add value and remain on topic. This will avoid normal threat drift of general discussions.
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Adjusting the AeroVee Secondary Ignition Timing
by sonex1374 » Sun May 10, 2020 2:55 pm
Ignition System Overview:
The AeroVee engine is equipped with two separate ignition systems that utilize different principles and components. The primary ignition system is a pair of "magnatron" units that are energized by the large flywheel magnet as it rotates with the flywheel. The magnatron units and the large magnet are fixed into non-adjustable positions, resulting in a fixed ignition timing of 28 degrees before top dead center (BTDC). This setting has proven reliable over the years, and results in a good compromise between power and reliability.
The secondary ignition system uses a pair of coils and a triggering module. The coils are energized by the aircraft battery and then triggered by a small magnet embedded into the alternator cap. The secondary ignition is fully adjustable and must be set by the builder. Normal practice is to adjust the secondary ignition timing so that it exactly matches the (fixed) magnatron timing. The AeroVee Turbo installation places increased stress on the engine, and therefor turbo installations modify the secondary timing to 18 degrees BTDC for improved reliability (consult the AeroVee Turbo manual for more details).
Adjusting the Secondary Ignition Timing:
Because the magnatrons are fixed, timing the AeroVee only requires adjusting the secondary ignition system. This is accomplished by adjusting the position if the trigger cap located on the back of the flywheel (see AeroVee manual for more details). The trigger cap is secured in position by a socket head screw, and loosening the screw allows the trigger cap to be rotated clockwise to retard the timing, or counter-clockwise to advance the timing. Care must be used when making adjustments to the trigger cap, as very small rotations will have pronounced effect on timing. Users should attempt to rotate the trigger cap no more than 1-2 degrees at a time, and then re-check the results before adjusting again. It is very easy to over-do the changes, so move slowly.
How to Determine if Timing Changes are Required:
Timing Synchronized:
When the secondary ignition is timed properly, it will match the magnatron timing very closely. This can be verified by observing the engine's performance at various times. When the engine is running at a medium rpm or higher (2000+ rpm), switching between the magnatrons and secondary ignition will produce very little drop in rpm, and the engine will continue to run smoothly on either ignition.
Too Far Advanced:
If the secondary ignition is too far advanced, it is firing sooner than the magnatrons. This can sometimes be observed as an excessive change in rpm when switching between magnatrons-only operation and secondary-ignition-only operation. Relying on rpm change (e.g. "mag drop") is not definitive, however. Other indications of advanced timing are excessive engine vibration and higher cylinder head temperature (CHTs).
Too Far Retarded:
Secondary ignition timing that is too far retarded is hard to detect because the primary ignition system has already fired the cylinder before the secondary system attempts to fire. Under normal operation with both ignition systems engaged the combustion event has already been started by the time the secondary fires, and this produces very little change to the overall engine operation. However, when running on only the secondary ignition, the effect of a retarded ignition system can bee seen as reduced power output, and in extreme cases rough running. Because retarded ignition results in reduced power output, CHTs will typically fall when running secondary-only.
In-flight and Ground Tests:
Advanced or retarded secondary ignition timing can be determine by using an in-flight test or a ground test. The AeroVee manual outlines the in-flight test procedure. Essentially, the plane is flown in level flight at normal cruise power and CHTs are observed. Initially, only the primary ignition system is engaged and operating, and the CHTs are allowed to stabilize for several minutes. This is the baseline CHT. Next, the secondary ignition is engaged and the primary ignition turned off, and the engine is once again allowed to run for several more minutes to stabilize. CHTs are again noted. By comparing the secondary-only CHTs to the baseline CHTs the pilot can determine whether the temps increased or decreased when running on only the secondary ignition. If CHTs increased, the timing is too far advanced, and the trigger cap should be rotated counter-clockwise a few degrees to correct.
An alternate method of determining secondary ignition timing is to use an automotive timing light. An example timing light procedure is reproduced below for illustration.
-----------
Hi all, Mark 179ES here
Scott asked me to outline the procedure to set the secondary timing to the primary. As Scott stated it takes two to do this and a good inductive timing light also. You need the tools to do the adjustment. A small allen wrench to loosen the secondary pick up coils and an allen wrench to adjust the timing magnet.
First make the marks on your prop hub the same way you would for static timing. The prop bolt works best because then you can find exactly 180 degrees very easily and mark that point also. Then hook the timing light to #1 primary spark plug wire. This should be the top wire on the left side as you're sitting in the seat. You may want to make a pointer to aim exactly to the painted mark you put on the prop bolts. Start the engine and adjust the pointer to the painted mark on the bolt. Line the pointer up to the mark. Then hook the light to the lower plug on #1 secondary spark plug wire. Start the engine and with the light, the marks should line up exactly to be in time. I wouldn't make an adjustment yet. Just make a note of how far it is off and which direction from the pointer.
Now hook the timing light to the Primary #3 spark plug wire. Make sure you have marked the 180 degrees from the other mark you have been reading then start and check the pointer to that mark. Do not move the pointer after your first setting. It should look the same as #1 primary with the light. Then check the lower plug with the light. If they line up as they should, they are timed correctly. If not then make note of how far and if both secondaries are of the same distance. If so adjust the center magnet the opposite direction that you need to move the mark on the prop hub to bring it into line with the pointer. If the timing marks are off a different distance on the secondary then you need to loosen the pickup and slightly move them around the center pickup until they read with the light the same timing on front and rear.
When you are done all four light readings will be in the center of the pointer. This isn't hard but if you can find someone that has done timing with a timing light they will help a lot. Also there is no need to check timing on #2 and #4 they will be the same.
Mark 179ES
----------------
Common Errors:
The following errors are common, and should be avoided. Ensure the CHTs are allowed to stabilize when conducting in-flight test, otherwise changes or trends in CHT movement while switching between ignition systems can't be determined. Ensure that ignition switches and/or mag kill switches work correctly to disable the associated ignition system. Ensure that only small rotations of the trigger cap are made (1-2 degrees) to prevent overshooting the desired timing correction. Ensure the trigger cap screw is tightened sufficiently after making adjustments to prevent the cap from rotating unexpectedly.
References:
AeroConversions AeroVee Assembly Manual
http://www.aeroconversions.com/support/ ... Manual.pdf
The AeroVee engine is equipped with two separate ignition systems that utilize different principles and components. The primary ignition system is a pair of "magnatron" units that are energized by the large flywheel magnet as it rotates with the flywheel. The magnatron units and the large magnet are fixed into non-adjustable positions, resulting in a fixed ignition timing of 28 degrees before top dead center (BTDC). This setting has proven reliable over the years, and results in a good compromise between power and reliability.
The secondary ignition system uses a pair of coils and a triggering module. The coils are energized by the aircraft battery and then triggered by a small magnet embedded into the alternator cap. The secondary ignition is fully adjustable and must be set by the builder. Normal practice is to adjust the secondary ignition timing so that it exactly matches the (fixed) magnatron timing. The AeroVee Turbo installation places increased stress on the engine, and therefor turbo installations modify the secondary timing to 18 degrees BTDC for improved reliability (consult the AeroVee Turbo manual for more details).
Adjusting the Secondary Ignition Timing:
Because the magnatrons are fixed, timing the AeroVee only requires adjusting the secondary ignition system. This is accomplished by adjusting the position if the trigger cap located on the back of the flywheel (see AeroVee manual for more details). The trigger cap is secured in position by a socket head screw, and loosening the screw allows the trigger cap to be rotated clockwise to retard the timing, or counter-clockwise to advance the timing. Care must be used when making adjustments to the trigger cap, as very small rotations will have pronounced effect on timing. Users should attempt to rotate the trigger cap no more than 1-2 degrees at a time, and then re-check the results before adjusting again. It is very easy to over-do the changes, so move slowly.
How to Determine if Timing Changes are Required:
Timing Synchronized:
When the secondary ignition is timed properly, it will match the magnatron timing very closely. This can be verified by observing the engine's performance at various times. When the engine is running at a medium rpm or higher (2000+ rpm), switching between the magnatrons and secondary ignition will produce very little drop in rpm, and the engine will continue to run smoothly on either ignition.
Too Far Advanced:
If the secondary ignition is too far advanced, it is firing sooner than the magnatrons. This can sometimes be observed as an excessive change in rpm when switching between magnatrons-only operation and secondary-ignition-only operation. Relying on rpm change (e.g. "mag drop") is not definitive, however. Other indications of advanced timing are excessive engine vibration and higher cylinder head temperature (CHTs).
Too Far Retarded:
Secondary ignition timing that is too far retarded is hard to detect because the primary ignition system has already fired the cylinder before the secondary system attempts to fire. Under normal operation with both ignition systems engaged the combustion event has already been started by the time the secondary fires, and this produces very little change to the overall engine operation. However, when running on only the secondary ignition, the effect of a retarded ignition system can bee seen as reduced power output, and in extreme cases rough running. Because retarded ignition results in reduced power output, CHTs will typically fall when running secondary-only.
In-flight and Ground Tests:
Advanced or retarded secondary ignition timing can be determine by using an in-flight test or a ground test. The AeroVee manual outlines the in-flight test procedure. Essentially, the plane is flown in level flight at normal cruise power and CHTs are observed. Initially, only the primary ignition system is engaged and operating, and the CHTs are allowed to stabilize for several minutes. This is the baseline CHT. Next, the secondary ignition is engaged and the primary ignition turned off, and the engine is once again allowed to run for several more minutes to stabilize. CHTs are again noted. By comparing the secondary-only CHTs to the baseline CHTs the pilot can determine whether the temps increased or decreased when running on only the secondary ignition. If CHTs increased, the timing is too far advanced, and the trigger cap should be rotated counter-clockwise a few degrees to correct.
An alternate method of determining secondary ignition timing is to use an automotive timing light. An example timing light procedure is reproduced below for illustration.
-----------
Hi all, Mark 179ES here
Scott asked me to outline the procedure to set the secondary timing to the primary. As Scott stated it takes two to do this and a good inductive timing light also. You need the tools to do the adjustment. A small allen wrench to loosen the secondary pick up coils and an allen wrench to adjust the timing magnet.
First make the marks on your prop hub the same way you would for static timing. The prop bolt works best because then you can find exactly 180 degrees very easily and mark that point also. Then hook the timing light to #1 primary spark plug wire. This should be the top wire on the left side as you're sitting in the seat. You may want to make a pointer to aim exactly to the painted mark you put on the prop bolts. Start the engine and adjust the pointer to the painted mark on the bolt. Line the pointer up to the mark. Then hook the light to the lower plug on #1 secondary spark plug wire. Start the engine and with the light, the marks should line up exactly to be in time. I wouldn't make an adjustment yet. Just make a note of how far it is off and which direction from the pointer.
Now hook the timing light to the Primary #3 spark plug wire. Make sure you have marked the 180 degrees from the other mark you have been reading then start and check the pointer to that mark. Do not move the pointer after your first setting. It should look the same as #1 primary with the light. Then check the lower plug with the light. If they line up as they should, they are timed correctly. If not then make note of how far and if both secondaries are of the same distance. If so adjust the center magnet the opposite direction that you need to move the mark on the prop hub to bring it into line with the pointer. If the timing marks are off a different distance on the secondary then you need to loosen the pickup and slightly move them around the center pickup until they read with the light the same timing on front and rear.
When you are done all four light readings will be in the center of the pointer. This isn't hard but if you can find someone that has done timing with a timing light they will help a lot. Also there is no need to check timing on #2 and #4 they will be the same.
Mark 179ES
----------------
Common Errors:
The following errors are common, and should be avoided. Ensure the CHTs are allowed to stabilize when conducting in-flight test, otherwise changes or trends in CHT movement while switching between ignition systems can't be determined. Ensure that ignition switches and/or mag kill switches work correctly to disable the associated ignition system. Ensure that only small rotations of the trigger cap are made (1-2 degrees) to prevent overshooting the desired timing correction. Ensure the trigger cap screw is tightened sufficiently after making adjustments to prevent the cap from rotating unexpectedly.
References:
AeroConversions AeroVee Assembly Manual
http://www.aeroconversions.com/support/ ... Manual.pdf
- sonex1374
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