How to thread drift in 720 posts!!!
The same timing marks are used for static and dynamic.
Static timing is a very sensitive thing, heavily reliant on technique. It is affected by the surface condition of the points. Unless they are new with perfect surfaces, the actual point of make and break varies depending on where the points meet. This moves around on the surface of the points with each make/break by maybe 0.5mm. If there is any surface pitting from spark erosion it quickly becomes unworkable. Also the shaft clearance has a significant effect. Any shaft "slop" will result in variation / lack of precision of timing because it moves the cam position. Any wear in the wear block of the points will similarly cause slight differences as the path it traces on the cam varies slightly. During the timing process the engine can never be rotated backwards - even a little - because it changes the backlash in all the gears and things. There is significant hysteresis in the system. I'd be doing something like 5 readings to look for the spread.
Dynamic timing generally gets a different reading. I've never thought deeply about it, but I guess centripital force plays a role in changing the point behaviour. And rotating gears (even straight cut) will provide some end load to the shaft which will change the cam / rubbing block position a bit. TDC itself probably varies a little as the crank moves around as hydrodynamic lubrication takes effect and lifts the crank off the bearing surface. And the conrod / piston assembly stretches a little. On a car, the only time I would ever use static timing is after a rebuild for its first start.
If you were really serious, you'd check the TDC mark. These can be out a couple of degrees. Especially if there has been a replacement or ground crank.
And its worth thinking about the accuracy of the measurement devices. I would have thought that +/- 1 deg would be the very best you could hope for with the various mechanical measuring devices that are commonly used. For race engines its common to use engineers protractors (as in drawing board type ones). As soon as you see a printed / stamped scale on anything you can assume an accuracy of marking of +/- 1mm. I wouldn't have huge confidence in the aviation ones I've seen. And as for the "flower pot" arrangement!
I think the same issues apply between distributors on cars and magnetos in aircraft.
Most bog standard piston aero engines don’t have mechanisms that automatically advance/retard the timing in proportion to RPM. The static timing is fixed so that the actual timing is best at higher RPM, and is artificially retarded for start by an impulse coupling. (There are also fancy ‘shower of sparks’ starting systems for some aero engines, but those have an extra set of points – called, you guessed it: the retard points/breaker - in the magneto and different starter/mag switch configuration.)
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We'll I can say I'm fully aware of forces on an airframe and the internals of an engine.
I've done and been involed with some serious design work in the area of stress.
Now I don't need to be unlearned if we had serious problem with aircraft maintenance aircraft would be falling out of the sky. Ethier which I don't see what happening.
Cheers
I've done and been involed with some serious design work in the area of stress.
Now I don't need to be unlearned if we had serious problem with aircraft maintenance aircraft would be falling out of the sky. Ethier which I don't see what happening.
Cheers
This is not about aircraft falling from the skies rather reducing the cost of maintenance.
A lot of the decline of GA in the last 15 years has been due to cost of operation. I was directly involved in a company that collapsed due to the weight of cost increase on it's fleet of ageing aircraft. If the company had been smart with it's operations earlier and introduced more trend based maintenance and operational procedures it may have maintained a cost advantage over it's competitors, maintained it's customer base and maybe still be going today. This was seen as an additional cost rather than smart investment. Instead we just flew things to time limits or when they broke and didn't look into why. The manufacturers time limits, operating techniques etc... are all based on a conservative average of what they think the machine will be exposed to. We had the chance to set up a maintenance program and operating procedures for our fleet that was specific to our needs, but it was deemed too hard.
A lot of the decline of GA in the last 15 years has been due to cost of operation. I was directly involved in a company that collapsed due to the weight of cost increase on it's fleet of ageing aircraft. If the company had been smart with it's operations earlier and introduced more trend based maintenance and operational procedures it may have maintained a cost advantage over it's competitors, maintained it's customer base and maybe still be going today. This was seen as an additional cost rather than smart investment. Instead we just flew things to time limits or when they broke and didn't look into why. The manufacturers time limits, operating techniques etc... are all based on a conservative average of what they think the machine will be exposed to. We had the chance to set up a maintenance program and operating procedures for our fleet that was specific to our needs, but it was deemed too hard.
Last edited by 43Inches; 14th Apr 2014 at 02:44.
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Re: Timing set and ACTUAL timing of the spark event.
In the TIO-540 J2BD:
When the timing is set properly to 20 degrees btdc, the ACTUAL spark event occurs at about 16d BTDC NOT at the set 20 degrees. This is by measurement.
I am certain that Lyoming is not aware of this and did not "design" for it.
This has nothing to do with all of the reasons discussed in this thread.
BTW, it saves the engine to not fire at the timing mark. If the sparks occurred at 20d btdc, the engine would suffer heavy detonation.
As for CASA approval for the APS class, we have made no attempt to ask them for "approval." The APS class was approved by the FAA for 16 hours of A&P (LAME) annual certification the first year it was presented. The FAA thinks it's OK!
As for Yr Right, I wish he and others like him (there are a few others, ya know?) would become better informed. They and their clients would be the better for it. OTOH, there are none so blind as those who will not see.
In the TIO-540 J2BD:
When the timing is set properly to 20 degrees btdc, the ACTUAL spark event occurs at about 16d BTDC NOT at the set 20 degrees. This is by measurement.
I am certain that Lyoming is not aware of this and did not "design" for it.
This has nothing to do with all of the reasons discussed in this thread.
BTW, it saves the engine to not fire at the timing mark. If the sparks occurred at 20d btdc, the engine would suffer heavy detonation.
As for CASA approval for the APS class, we have made no attempt to ask them for "approval." The APS class was approved by the FAA for 16 hours of A&P (LAME) annual certification the first year it was presented. The FAA thinks it's OK!
As for Yr Right, I wish he and others like him (there are a few others, ya know?) would become better informed. They and their clients would be the better for it. OTOH, there are none so blind as those who will not see.
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Walter, as you may have seen earlier mention was made of the legality of LOP.
For example, the Cessna 207 POH has the statement in normal procedures section "Operation on the lean side of peak is not approved".
We all know how litigious the USA system is, so how does LOP sit in the legal framework, and with the FAA?
In Australia we have a regulation CAR 138 which states,
On the face of it I'm assuming that LOP can not be supported legally in Australia, unless specific mention is made approving its use, as is the case with the Chieftain.
Thoughts?
BTW I do support the LOP theory of operation - not a piston driver though.
For example, the Cessna 207 POH has the statement in normal procedures section "Operation on the lean side of peak is not approved".
We all know how litigious the USA system is, so how does LOP sit in the legal framework, and with the FAA?
In Australia we have a regulation CAR 138 which states,
Pilot to comply with requirements, etc of aircraft’s flight manual, etc
(1) If a flight manual has been issued for an Australian aircraft, the pilot in command of the aircraft must comply with a requirement, instruction, procedure or limitation concerning the operation of the aircraft that is set out in the manual.
Penalty: 50 penalty units.
(2) If a flight manual has not been issued for an Australian aircraft and, under the relevant airworthiness standards for the aircraft, the information and instructions that would otherwise be contained in an aircraft’s flight manual are to be displayed either wholly on a placard, or partly on a placard and partly in another document, the pilot in command of the aircraft must comply with a requirement, instruction, procedure or limitation concerning the operation of the aircraft that is set out:
(a) on the placard; or
(b) on the placard or in the other document.
Penalty: 50 penalty units.
(3) An offence against subregulation (1) or (2) is an offence of strict liability.
(1) If a flight manual has been issued for an Australian aircraft, the pilot in command of the aircraft must comply with a requirement, instruction, procedure or limitation concerning the operation of the aircraft that is set out in the manual.
Penalty: 50 penalty units.
(2) If a flight manual has not been issued for an Australian aircraft and, under the relevant airworthiness standards for the aircraft, the information and instructions that would otherwise be contained in an aircraft’s flight manual are to be displayed either wholly on a placard, or partly on a placard and partly in another document, the pilot in command of the aircraft must comply with a requirement, instruction, procedure or limitation concerning the operation of the aircraft that is set out:
(a) on the placard; or
(b) on the placard or in the other document.
Penalty: 50 penalty units.
(3) An offence against subregulation (1) or (2) is an offence of strict liability.
Thoughts?
BTW I do support the LOP theory of operation - not a piston driver though.
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We'll I can say I'm fully aware of forces on an airframe and the internals of an engine.
I've done and been involed with some serious design work in the area of stress.
Now I don't need to be unlearned if we had serious problem with aircraft maintenance aircraft would be falling out of the sky.
I've done and been involed with some serious design work in the area of stress.
Now I don't need to be unlearned if we had serious problem with aircraft maintenance aircraft would be falling out of the sky.
Seeing you are so better prepared for this than I will ever be, I want to offer you the spare microphone kit and you can take the 2.5 days (about 19 hours full on) training course for me and Andrew Denyer and I will sit at the back of the class.
What is more if you do this I bet all the folk on this thread will chip in for George Braly to fly out from Ada OK and sit down the back with us. We will then ask all the heckling questions you can handle. If you think I am easy to blow off, try George.
I reckon Walter would not miss the show either!
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Creampuff, DDI to find top dead centre of piston, degree wheel on crankshaft, to confirm timing mark in relation to top dead centre of compression stroke.
Now working with electronic distributed, set up on No1 firing and fit using degree wheel to locate 12 degrees before TDC.
Start engine and confirm dynamic is same. Using electronic timing llIghr at No1 lead. I have vacuum advance locked out, adjust timing to best vacuum at idle. Timing all in by about 3200 RPM of 24.- 26 degrees
That's my 302 Windsor
Now working with electronic distributed, set up on No1 firing and fit using degree wheel to locate 12 degrees before TDC.
Start engine and confirm dynamic is same. Using electronic timing llIghr at No1 lead. I have vacuum advance locked out, adjust timing to best vacuum at idle. Timing all in by about 3200 RPM of 24.- 26 degrees
That's my 302 Windsor
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Now I don't need to be unlearned if we had serious problem with aircraft maintenance aircraft would be falling out of the sky. Ethier which I don't see what happening.
In the TIO-540 J2BD:
When the timing is set properly to 20 degrees btdc, the ACTUAL spark event occurs at about 16d BTDC NOT at the set 20 degrees. This is by measurement.
I am certain that Lyoming is not aware of this and did not "design" for it.
This has nothing to do with all of the reasons discussed in this thread.
BTW, it saves the engine to not fire at the timing mark. If the sparks occurred at 20d btdc, the engine would suffer heavy detonation.
When the timing is set properly to 20 degrees btdc, the ACTUAL spark event occurs at about 16d BTDC NOT at the set 20 degrees. This is by measurement.
I am certain that Lyoming is not aware of this and did not "design" for it.
This has nothing to do with all of the reasons discussed in this thread.
BTW, it saves the engine to not fire at the timing mark. If the sparks occurred at 20d btdc, the engine would suffer heavy detonation.
Does the measured delta between the static and actual vary with RPM?
When you say “this” has nothing do with all of the reasons discussed in this thread, are you referring to the delta between static and actual, or Lycoming’s lack of awareness?
If you are referring to the delta, to what do you attribute the delta if not the rotation of the crankshaft during the short period between points opening and the voltage in the secondary building sufficiently to cause the spark? (4 degrees at 2700 RPM takes only 0.25 milliseconds….)
(NH: Sorry, you’ve lost me. “Set up on No1 firing and fit using degree wheel to locate 12 degrees before TDC. … Timing all in by about 3200 RPM of 24. – 26 degrees.” Where does the 12 come in? If static’s the same as actual and the vacuum advance is locked out, the RPM shouldn’t make any difference…
)
For example, the Cessna 207 POH has the statement in normal procedures section "Operation on the lean side of peak is not approved
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SIDS program has nothing to do with the engineer. It's a development of what they have learnt over the years to cya themself. Further more as lame we like to look at stuff people like your self scream blue murder I'm not paying for that. At least this gives us reasons to follow up now with being told we cu$&s. Plus you see there is reporting also back to manufactures when we find stuff and they even buy back old aircraft and then proceed to inspect them and test to destruction May be you could offer your aircraft to them.
Cheers
Cheers
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Jaba
Nah I don't need to stand up on a soap box and talk jibberish sorry. If you and your course were Casa approved then I may be interested. But as they are not dosent really do it for me sorry. I'll just learn my science the old way like I is been doing.
But hey thanx for the offer but.
Cheers
Whoops but has anyone still know how to test your fuel system quickly.
Nah I don't need to stand up on a soap box and talk jibberish sorry. If you and your course were Casa approved then I may be interested. But as they are not dosent really do it for me sorry. I'll just learn my science the old way like I is been doing.
But hey thanx for the offer but.
Cheers
Whoops but has anyone still know how to test your fuel system quickly.
yr right, you seem to lump all aircraft owners into the same bag. Sorry, I know quite a few, myself included that want the extra yards spent inspecting and looking. I also replace the "will last another 100 hours" components on the spot. In short, any recommendation my LAME makes to me I follow through on.
I also educate myself by spending big on courses like Jabber offers because i like to understand what goes on.
I also tend to think you look at names on this forum like "Creampuff" and judge the character by his "name". Long term readers of this forum know creampuffs and their like write articulate accurate facts and will admit when wrong. Although a self confessed resident of The States, Creampuff even seems to spare us American English.
Creampuff (and others including you Mr. Right), I thank you for your inputs.
I also educate myself by spending big on courses like Jabber offers because i like to understand what goes on.
I also tend to think you look at names on this forum like "Creampuff" and judge the character by his "name". Long term readers of this forum know creampuffs and their like write articulate accurate facts and will admit when wrong. Although a self confessed resident of The States, Creampuff even seems to spare us American English.
Creampuff (and others including you Mr. Right), I thank you for your inputs.
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I guess you missed this piece further up the page. Or deemed a CASA approval that would not exist or be worth having is far superior.
Still not one answer to a question posed or a link to any "public record" for the benefit of educating me.
I am impressed to say the least.
The APS class was approved by the FAA for 16 hours of A&P (LAME) annual certification the first year it was presented. The FAA thinks it's OK!
I am impressed to say the least.