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Post by tikic1 on Oct 30, 2019 15:18:49 GMT -5
hi people, i wonder what is this spark control and why it was used?tnx
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Post by Tom/CalClassic on Oct 30, 2019 17:29:35 GMT -5
It's basically a manual spark advance, which has been automatic in cars for a very long time. It controls the timing of the spark in the cylinders, which needs to change as the power/mixture settings change. In most FS aircraft it is simulated using a dummy switch; I don't know if it has a real effect in the Connies.
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Post by Dennis the menace on Nov 2, 2019 0:55:01 GMT -5
A cylinder can fire at "top dead center", that is, when it reaches the highest travel up on its compression stroke. At that point, the distributor sends a spark through the plug wires to the spark plug, which then fires and explodes the compressed gas mixture. If an engine runs continuously at this setting, poor power and overheating will result. No engine is designed to run at this setting. It is only used by mechanics in order to set the initial timing. So, engines are designed the actually run with the plug firing just a few degrees BEFORE the piston reaches the top of its stroke. That allows the mixture to reach is full exploded mass of energy just as the piston finally reaches the top of its stroke. On a car, the timing is set about 7 to 10 degrees "before top dead center". This is called the "retard" position. After that, the timing is adjusted depending on the speed of the engine. On early pre 1930s cars, it was manually adjusted by a hand lever usually on the steering column. Then came the vacuum advance. That used engine vacuum, along with centrifugal weights, to advance and retard the spark, by physically moving a metal plate in the distributor body that the points were attached to. Today, computers do it all with electronic ignition. A car at highway speed with an automatic will typically run 50 degrees before top dead center. That is called the "advance" position. So why does any of this matter? Because if the spark is not advanced, the engine will not develop full power, it will run very hot, it will eventually foul the plugs and then choke, sputter and quit. If the engine is fully advanced when starting, then the engine will backfire, and pre-detonate. On a hand cranked car, it can and will jerk the crank out of your hand and reverse through it right on your wrist. A heavy steel and brass engine crank will easily break a wrist - I've seen it happen. If the backfire is bad enough, it will blow the piston, throw a rod, or (in the case of a radial aircraft engine) blow one of the jugs off of the crankcase. What that switch does, is after the rpm is low enough, it manually rotates the breaker plate with the points on it at the back of the magneto, and cause the spark to then fire at 40 to 50 degrees before top dead center. At that speed, you will need that many degrees of travel for the fuel to fully detonate just as the piston reaches the highest point of its stroke. The faster the engine runs, the more degrees on the crank you will need to fire the plug to get the full power out of the exploded fuel mixture. Spark knock, or that "popcorn sound" in an engine, is pre-detonation. It is caused by the fuel igniting before the piston reaches its highest travel or stroke. That pre-detonation is actually an explosion, and that sound you hear is the piston being knocked against the cylinder walls. Enough of that, and you'll ruin the piston, or burn a hole in the top of it right clean through it. Gasoline has anti-knock additives put in it. The higher the compression, the more anti-knock additives you will need. These additives delay the flammability of the fuel. It is a common myth to think that premium fuel is more "powerful" than regular fuel. In fact, the fuel is the same, its the amount of anti knock compounds added that cause it to not cause high compression engines to knock. Lead was put in as for a cooling effect for the valves. The lead provided a coating for the valve seats. Without lead, the edges of the valves will decay from the extreme heat, and the valves will begin to leak, losing compression and causing a rough idle, and eventually a misfire. Today's engines have hardened valve seats made from Stellite, so lead is no longer necessary.
I used to drive a 1910 Maxwell roadster. One day, I had been driving around 30 miles in it with no problems. Then rather quickly, it suddenly lost power, wanted to stall, emitted copious black smoke and the radiator (it used an unpressurized radiator) boiled over. Upon unscrewing the radiator cap, it shot a column of boiling water 3 feet high in the air. The cause of the problem, upon inspection, a cotter pin had come loose and fallen out that connected the manual spark advance to the breaker plate on the rear of the high tension magneto (early cars used magnetos, before the battery and points system). The car had suddenly started running on full retard instead of on advance. I solved the problem by walking over to an oil field, and clipping a piece of old wire from a chicken wire fence. Once mended, I spun the crank and drove home. Connies work the same way!
Hope this explains a bit about engines!
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Post by JasonK..AKA "Pal Joey." on Nov 2, 2019 11:45:45 GMT -5
I never would have thought you were that old!  Seriously, thanks for that info. I always wondered about just how important the spark Retard/Advance was and that answer leaves no room for doubt. Now I have a question though; once I throw the spark advance into "advance" I notice that the CHT starts to rise (a good 10 to 15 degrees in most cases.) this leads me to believe it may not be a dummy switch. would this be the case IRL? and why would the temp rise if the idea is to help it run cooler and more efficiently? |
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Post by Tom/CalClassic on Nov 2, 2019 13:03:49 GMT -5
It could be that the engine is putting out more power and that causes the CHT to rise a bit.
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Post by johnhinson on Nov 2, 2019 14:12:49 GMT -5
In a motor vehicle, you only use "Advance" if you want a little extra power to help you up a hill. Otherwise you run in around mid-position.
John
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Post by Dennis the menace on Nov 2, 2019 22:18:25 GMT -5
Distributors have a "mid position" for spark ignition, not fixed positions - what you are referring to is a mid range of degrees. The number of degrees will depend upon engine load, ambient heat, and fuel used. All vehicles, since the very first, have run on a full spectrum from about 4 degrees before top dead center for the retard position, to about 50 degrees in the full advance position. The points and the retard and advance do not add power per say, but they provide for power by determining when the explosion occurs. When per-detonation occurs, power is lost and engine damage is the result. It is the RPM of the engine that determines the retard/advance position of the breaker plate to which the points are attached. Let's use my 1962 Ford Galaxie as an example, it is fairly typical with a 6.5 liter V-8 and automatic drive. At idle, the breaker plate with the points are at their setting of 8 degrees before top dead center. I assume that would be the position (or something like it) of the connie ignition switch in the off position. When you step on the gas, the engine speeds up. In the distributor are a set of counter weights 180 degrees apart from each other. They are teardrop shaped, and fixed to pins at one end, from which the swivel from. The other end of the weight is fat, and as the base plate (which is driven off the cam) rotates, the weights begin to fly outwards due to centrifugal force. As they move outwards, they will move the breaker plate and that will move the points in relation to each lobe on the distributor shaft. The lobe determines when the points open, and when they close. Moving the breaker plate in one direction will advance the spark, and moving in the other direction will retard the spark. The weights do this automatically according to RMP. There is also a vacuum advance, but that is used to smooth the action of the weights, and more importantly, to counter act the weights in cases when a spark advance is not desired, such as climbing a hill. If either the weights, or the vacuum advance is absent, or malfunctions, the distributor will not work correctly. Here is a diagram showing what I am talking about.  The rear of a magneto looks the same, but instead of weights and a vacuum advance, it is mechanically rotated. That can be accomplished through means of a hand operated rod, or a rod connected to an electric solenoid. Nonetheless, it works exactly the same as a car distributor.
Since RPM determines the position of the points, what happens when we get a hill is that the car slows down, so the engine is sped up. That decreases manifold vacuum. Manifold vacuum is always highest at idle. Nonetheless, there is still enough vacuum to operate the vacuum advance. With the engine, now under load climbing the hill, the breaker plate weights would naturally want to advance the spark. This would cause per-detonation, spark knock. Under such a heavy load, the spark must be retarded to the point that the engine will not knock. The vacuum advance takes over from the weights, and manually through a small rod connected from it, to the breaker plate, pulls the plate a few degrees in the retard position. Thus, the engine does have more power, but only because it can now take full advantage of the explosion of the gas charge into cylinders. I assume this is what happens in the Constellation.
In a nutshell, whether its aircraft, boats or cars, the mechanic sets the engine at "top dead center". Then it is tuned to its "initial advance timing". From that the distributor and its mechanisms take over control and it is automatically adjust to full end advance and then back to initial advance timing. Under the load of hill climbing, pulling a trailer, or takeoff and climb, you want to retard the spark to the point that no spark knock occurs. Once you have removed the load off the engine, that is the time to run the spark at as full advance as it can. Let it go as far as it wants!
The Connie notes do not say what to do about the switch (that I ever saw) in descend mode, but I assume you have the switch in the off position. Running an engine at low RPMs and advance means a backfire.
I assumed the Douglas planes had this switch also.
Thought I would share a few photos of my in my younger, skinnier days when I had a 29 inch waist and a full head of bushy brown hair.
Here's my 1910 Maxwell model AA two cylinder, 12 horsepower runabout. Hand cranked, high tension magneto ignition, acetylene headlights and kerosene side lights and tail light. The windshield and the top were extra cost items. My car had the windshield, but no top. It was originally owned by a doctor in the Catskill mountains who drove it from 1910 to the early 1940s when he died. It was made in Tarrytown New York and cost $650 new ($17,553.93 in today's dollars). I know it was delivered by the New York Central. Once I had a date and said how about I pick you up in my car. I have a red sports car, real snappy, with bucket seats and a stick shift. The look on my date's face when I squeezed the bulb horn and pulled up in this was indescribable. I didn't lie - it is a sports car, it does have bucket seats, and a stick shift, I just neglected to mention the year lol. Here I am with Santa at an LA Raiders game during the halftime show at the LA coliseum.
I also had a 1909 Jackson model H sports touring car. Four cylinder, 40 horsepower and 3 speed sliding gear transmission. Hand crank, magneto ignition, acetylene and kerosene lights. This was made by the Jackson Motor Car Company in Jackson, Michigan. It was an expensive car, costing $3500 new ($94,319.63 in today's dollars) My '55 Ford Fairlane is in the background.
My dad and I had about a dozen or so old cars over the years, but this was my trusty steed, my 1965 Mustang convertible. I had the original window sticker, the car listed for $3460 ($27,157.20 in today's dollars). Here ready to haul me to the beach again for a little more sun, sand and surfing.
I usually don't share photos, but now you can see who occasionally turns out some classic scenery, and occasionally a few repaints now and then!
cheers, Mike
P.S. I would like to know more about this switch and its operation. Perhaps Tom has something in one of his manuals that he can tell us more about it.
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Post by Dennis the menace on Nov 2, 2019 22:33:48 GMT -5
As I suspected - it is a manually operated spark advance, apparently operated by an electric relay. I did learn that each bank of cylinders fires in the opposite direction! Clever design of the low-tension ignition system features fully redundant electrical paths from a single 9-cylinder dual magneto. Spark advance was eventually removed from all models. 
Clever design of the low-tension ignition system features fully redundant electrical paths from a single 9-cylinder dual magneto. Spark advance was eventually removed from all models.
"The engines that we use: DA4s, -42s, -93s and a couple of others, were all initially rated at 3,250 hp with 115/145. The EAs were rated at 3,450 hp. All of these engines were de-rated to 2,880 hp using 100/130 simply by reducing the allowable power settings. I’d have to look it up, but I think that the original take-off setting for the DA was 56” or 246 BMEP and 2,900 RPM. Using 100/130, we are allowed 53” or 234 BMEP and 2900 rpm (standard day at sea level). With only 100LL available, we use 50” and 2,900 rpm not to exceed 234 BMEP. We are also restricted to low blower and the spark advance has been disabled."
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Post by Tom/CalClassic on Nov 3, 2019 0:49:30 GMT -5
Love the jaunty cap!
The spark advance system on the R-2800 actually controlled the magneto and distributor to change the spark advance from 20 deg. BTC to 25 deg. BTC. The R-3350 instead used two separate sets of points, one for retard and one for advance, changing from 25 deg. BTC to 30 deg. BTC.
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Post by johnhinson on Nov 3, 2019 6:26:13 GMT -5
Distributors have a "mid position" for spark ignition, not fixed positions - what you are referring to is a mid range of degrees. That is exactly why I said " around mid-position". I might not have a 1910 Maxwell Roadster but I do have a 1935 Dennis Lancet bus with 5.7 litre petrol engine so I am not an idiot. And you can do more than break a wrist with that if you start that on the handle wrongly. John |
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Post by stansdds on Nov 3, 2019 7:43:17 GMT -5
I love vintage aircraft and vintage cars. Thanks for posting the pics!
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Post by johnhinson on Nov 3, 2019 10:57:36 GMT -5
I didn't want to steal the thread but if you are interested, this is the bus I was talking of: purenostalgia.org.uk/vehicles/dennis-lancet/restoration/Interestingly, my wife's 1954 car had the timing adjustment fixed prior to it coming her way. Apparently this is often done on this model (at least) because modern petrol (for all its disadvantages with old vehicles) is far better quality and this makes starting and running much easier. Picture: purenostalgia.org.uk/vehicles/other-vehicles/riley-car/However, modern fuel will be of no benefit to us old codgers pretending we are flying aeroplanes in the good o;' days. John |
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Post by mrcapitalism on Nov 3, 2019 23:34:57 GMT -5
Hi guys! While you provide some interesting discussion on ignition timing in relation to automobiles, I personally believe that Spark Advance has a different function for high power piston aircraft engines. A good (IMVHO) description is from the Aircraft Engine Historical Society, and is excerpted from an FE's recounting of C97/R-4360 handling. From: www.enginehistory.org/Operations/R-4360Ops/r-4360ops1.shtmlWhile you guys mention spark advance in association with higher power/RPM, In the 1649A handling instructions Spark Advance is associated with aggressively lean mixture settings, with stated maximum RPM limitaion ("only permissible in the blue arc (cruise power) range"). Spark Advance does actually increase BMEP in the Team Connie aircraft in FSX. The appropriate handling notes for each aircraft instruct the user on when they should advance the ignition, and when it should be retarded. |
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Post by emmemm on Nov 4, 2019 17:00:31 GMT -5
Hi, nice that we have got the curve from automobiles back to the aircrafts. Since the DC-7's also had the R-3350 Turbo Compounts, there was also the spark control here. The switches, one per engine, were in the overhead panel between the starter switches and the magneto switches. You can see them i the attached picture.  MM |
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Post by Erik on Nov 4, 2019 18:38:58 GMT -5
Great link, interesting read! And the importance of 'running square' in certain conditions resurfaces, if I'm not mistaken. 
Many thanks to all,
Erik
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