|Jan 12, 2013, 11:54 AM|
Joined Feb 2007
I think, however, that it might be worth a closer inspection to see if the manifold modification and/or igntion timing tweak could gain some more hp. (as per your you comment)
Btw SrTele, I'v been following your CDI related comments and posts with great interest. It's so nice to get educated. Thank you!
I Happen to have a Saito FA-125a that I 'm planning to convert to CDI (probably by using the CH ignition) and then run on gas or glow fuel. I haven't made any final decision yet although I'm tempted to try the gas as I'm a bit tired of wipeing the oil residue off the model, etc. The reason for converting the engine to CDI (as I see the things) are that I'm trying to achieve:
if run on glow fuel:
1. lower dependable idle (the stock FA-125a idles reliably at 2100rpm, I would prefer 1800-1900 rpm if possible)
2. easier to handle, less kick-back on starting etc.
3. less oil residue on the plane duel to lesser fuel consumption (maybe?)
(4. maybe more power, I actually do not need any more but power gain never hurts)
if run on gas:
1. lower dependable idle (the stock FA-125a idles reliably at 2100rpm, I would prefer 1800-1900 rpm if possible. With gas fuel I might have even lower idle rpm, say 1700?)
2. easier to handle, less kick-back on starting etc.
3. practically very little of oil residue (if any) on the plane due to lesser fuel consumption and oil content in the gas fuel
(4. lower operating costs. A nice thing but not a major thing)
drawbacks if run on gas:
1. higher risk of engine failure -> a proper cooling arrangement (baffling, etc) is probaly a must. the FA-125a does not feature bronze valve seats such as is the case with the FG-21.
2. less power -> if run on gas the engine might make, say, 500-1000rpm less as max RPM compared to CDI/ 15% nitro glow fuel ( makes me wonder if the power is enough for an aerobatic plane weighing 8,7 lbs dry)
Am I on the right track with my synthesis on glow / gas comparison? Did I miss something?
|Jan 12, 2013, 03:23 PM|
Personally I am in favor of running glow fuel W/CDI. The differnce in power output when converting to CDI while retaining glow fuel is a 5-6% increase in HP. The differnece when converting the same engine to gas is about a 15% loss in HP. That comptes tp a 20-22% HP advantage for glow fuel over gas when running CDI.
As far as engine life? Not only is there a question of increased heat from gasoline use, I can not see how 5% delivered @ such lower fuel volume than glow fuel can properly lubricate the non-roller bearing crank throws of the Saito engines.
That brings us to another interesting point. I have been told that when CDI is used in lieu of glow ignition, oil content can be reduced to10%. I assume that is true because the CDI initiates a stable ignition timing event not affected by ambient temperture, engine temperature, nitro content, or compression ratio. Lowering the oil content results in more power. Less oil % delivered @ 20% less fuel volume would lessen the oily mess.
I have pesonally run O'Donnell 30% nitro 8% lube in my High Compession (12.77:1) Saito FA180HC CDI engine W/dramatic results. 8850 RPM W/an 18X8 Dynathrust prop. That's about 850 RPM & 1 HP better than the larger displacement FG36 (2.20 ci) Saito gas burner. There still seemed to be plenty of oil coming from the outlet tube of my positive case venting system.
Therein lies another way to lessen the oily mess. By installing an inlet check valve in the back plate
then installing an outlet only check in the cam housing
crankcase oil can be pulled through the main crank bearing into the cam housing better lubricating the cam lobes/lifters. It can then be routed to a tube attached to the end of the muffler to divert oil that would normally be sprayed into the cowl to the exhaust slipstream.
|Jan 12, 2013, 04:21 PM|
It is a fact that oil mixed with gas, easily provides lubrication; even if it is at much smaller percentages.
Most 'normal' gas engines will do 'very well thank you', on just 20:1-50:1.
That not only applies to specialized, high-tech 2-stroke lubes. Klotz specifies that its own BēNOL castor oil, should also be mixed with gasoline at these ratios!
For methanol they state ratios of only up to 5:1.
Oil suspended in methanol, apparently does not provide ample lubrication at low percentages.
This just is, despite the 60% lower fuel volume for gasoline.
The oil obviously does not care, whether you trust it to lubricate at these small amounts. It just works that way with gas engines.
That high C/R (12.77:1) works with methanol, but I would be very weary of using gasoline with it, unless you can add some Octane booster to it.
|Jan 12, 2013, 05:39 PM|
Most 'normal' gas engines will do 'very well thank you', on just 20:1-50:1.
Almost all "normal" gas engines have roller/needle bearing on the crank throw & most, on the wrist pin too
The Saito FG engines have neither..
It was concieved from the beginning as a CDI/methanol engine.
It exceeds the output of the larger FG36 gas engine by .about .5 HP, even on 15% glow fuel & on 30% nitro 8% lube fuel it produces 4HP besting the FG36 HP output by 33% in a much smaller, lighter package.
Even a standard FA180 running CDI W/glow fuel will equal the power output of an FG36.
In order to compare the weights of the engines sans ignition systems we can compare the glow FA220 to the glow FA180.
The FA220 is 216g heavier (7.7 oz), 6mm wider, 11 mm longer & 17mm taller than the FA180
That is the reasoning behind the CDI/methanol equasion. More power in a smaller, lighter package. Since the extra weight/volume of the fuel does not have to be placed in the nose, the weight deficite of that factor is easier to overcome.
When practcal, I locate the fuel load over the CG to mitigate any detrimental affects on fligt characteristics as it is consumed. Fuel starvation due to tank location can be eliminated by using regulated crankcase pressure for fuel delivery.
BTW: Methanol is about 1/2 the price of gasoline, it is the packaging that drives up the cost.
|Jan 13, 2013, 12:54 AM|
Of course most gas engines have needle bearings in the con-rod (most at both ends).
But even those that do not (Saito FG, Evolution GX 10 cc and NGH 9 cc, to name a few), do very well with 20:1-25:1 oil.
Not so for methanol...
Regarding power, see Brian Hampton's fuel chart.
Methanol does have roughly half the specific energy of gasoline; 9,970 btu/lb to about 19,000 btu/lb.
But methanol's much lower stoichiometric ratio range, dictates the same amount of air can oxidize more than twice and a half as much methanol, bringing an engine's power up considerably; at a cost of much more fuel being consumed.
Regarding cost; packaging may detrimentally affect the price of FAI glow fuel, but the major contributor to glow fuel prices in general is nitromethane, which most American R/C hobbyists consume like drug addicts...
As to spark-ignition; yes, it can increase power measurably with methanol...
With glow ignition, timing relies on the mixture setting and the glow-plug's heat-range.
So, getting the mixture ignited at exactly the right advance for power, along with the ideal air-fuel ratio for power - is a shot in the dark. A hit-or-miss affair.
|Jan 13, 2013, 02:30 AM|
Joined Feb 2007
Regarding your comment on the non-roller bearing connecting rod is valuable! (although Zor has interesting remarks on this, too) Makes me wonder why the design remains pretty much the same with the FG-21, too?
Thank you again I'm leaning towards the route to run the engine on glow fuel but let's still gather as much information as possible on both alternatives.
As my primary objective to convert the engine to CDI is to achieve a lower reliable idle:
If I run the engine on glow fuel I still need to find way how to install a carb barrrel spring into the FA-125a carburettor. For some odd reason the carb design does not feature it and the carb barrel moves in and out as the engine vibrates making the engine hunt at idle as the mixture keeps variying randomly. (Some people say this lack of the carb spring does has no effect; this may be the case if you let the engine idle at higher rpm range, say 2200-2400rpm which I dislike)
Your cam housing (oil circulation modification) is very interesting as I personallly have experienced poor lubrication of the cam occasionally); Did you have it explained in more detail in some other thread? (maybe RCU or Flying Giants?)
|Jan 13, 2013, 06:54 AM|
I think your spot on with the deverter for extra lubrication! I can see this as a benifit in the fact that by deverting the oil you can reduce the oil to gas ratio and increase the efficency of the engine and not fowling a plug prematurly. This is a great thread for 4 stroke gas engines.
Sr is refering to 4 stoke gas engines that have way more moving parts than a 2 stroke gas engine that you refere too. All of my 2 strokes I run 40:1 but when I had a Satio gasser I had to have another can with the 24:1 in it. If I would of knew about this conversion that Sr. has showed us I could eliminate the extra gas can.
|Jan 13, 2013, 08:28 AM|
I know Sr. was referring to four-strokes. After all it is the the title of this thread...
Klotz do not address this issue for gas engines, but regarding glow engines, they wrote this in the link I included:
"R/C Model: 2-Stroke glow engines mix at 15-18% 4-Stroke glow engines at 5-10%"...
This would suggest; in contrary to your statement regarding the number of parts; that less oil is needed for a four-stroke than for a two-stroke...
|Jan 13, 2013, 09:37 AM|
The added oiling of the main bearing & cam are a much needed, IMO, added benefit. I am also contemplating machining some grooves in the lifter bores & installing nipples in the rocker boxes, Those lines could then be run to a "T", then an inline out only check valve to force the oil flow up the pushrod tubes & through the rocker boxes. That added bit of mostly internal plumbing will then insure positive oiling to the top end of the valve train as well as the cam/lifters.
I will do some searching for the thread that addresses the check valve addition.
|Jan 13, 2013, 09:50 AM|
Maybe a 15% total oil content is a good "minimum" for four-stroke mills...
Dear DarZeelon & SrTelemaster:
The PIPE Here again - the Clarence Lee-authored RC Modeler Magazine four-stroke engine book had an interesting observation concerning oil content for four-stroke mills' fuel mixture needs. The particular question was shown on page 29 of the book, in "Chapter 6 - Operating Four-Stroke Engines" on running an older Enya 35-4C open-valvetrain mill.
Mr. Lee's observation on what PERCENTAGE of oil in the answer to that question is what I'm getting at, as Mr. Lee seems to have stuck to specifying a 15% total lube percentage for glow ignition four-stroke mills. I quote from that second paragraph, with clarifying comments from me in [bracketed text]...
"Most 4-stroke engines seem to work better with less oil than the 2-strokes. The crankcase [on 4-stroke engines, when run on 2-stroke fuel] seems to load and cause erratic operation. I first experienced this with the Damo twin [Swedish opposed twin cylinder four-stroke]. Anything over 5% oil [that's a 20:1 mix, and the Damo Swedish twin is the specified engine] would cause rough operation. However, most single cylinder 4-strokes seem to work best with about 15% oil."
Now, I KNOW that book was written and first published in the late 1980s, a bit of time before more powerful and sophisticated four-stroke mills like the YS series, most of the 21st century-designed Saitos and current OS engine lineup had even been thought of. Today's glow ignition four-stroke mills USUALLY specify a total oil content of around 20%. but perhaps...IF a small amount of castor oil is used, not beyond 2% of the entire fuel volume - and one makes certain not to over-lean a four-stroke glow mill, and habitually set the high speed needle valve about 90ļ on the rich side of its peak RPM setting, found with an electronic engine tachometer - it COULD be quite possible to operate a 21st-century design, well-run four-stroke glow mill ON 15% oil, especially if that oil content contains the aforementioned 2% of castor oil in the lube mix.
For break-in, though, I DO usually prefer to spike the oil content upwards to 19% for at least the first three 10-oz tanks (just UNDER a litre) worth of glow fuel used to break-in a glow ignition four-stroke mill. With the 17% synthetic oil content, 10% nitro FHS Red Max four-stroke glow fuel I've always used, that meant spiking a 10-oz tank of such a fuel with about 0.2 ounces (5.9 millilitres) of the FHS synthetic lube in such a tank of glow fuel to get to the desired 19% figure for fueling a brand-new mill's break-in run. After the break-in run gets past the first U.S. quart's or litre's worth of 19% oiled fuel, then it should be all right to use the 15% lubed fuel, but run the engine as rich as possible to get it to complete the break-in runs until a good U.S. gallon (or almost four litres) of fuel has been run through it on the ground, before mounting the freshly broken-in mill on an aircraft.
When I can finally get back to the RC hobby after finding employment once again, I'll be sticking to those parameters to run in some of my "new-to-me" four-stroke engines I've acquired...some might be well broken-in already, but I want to take my time with each and every one of them in my test stand, to be sure I can operate them properly on the fuel mixes I'd prefer to run...
...and for some of the larger glow-ignition single-jug four-strokers running on methanol based fuel, spark ignition conversions with glow fuel at 15% oil content are quite likely to be tried when the time comes in the future.
Hope this helps a small bit...
|Jan 13, 2013, 09:53 AM|
Actually the oil ratio needed to lubricate a glow engine properly varies with that engine's displacement. A small engine such as a .020 engine may need as much as 33% oil in the fuel whereas a big 30cc engine may only need 8% to 12% oil in the fuel.
ref Model Airplane News January 2010. http://www.modelairplanenews-digital...001?pg=51#pg51
In reference to Model Airplane News article in May 1974, they had really good success running 14% oil in a .40 engine for high performance too.
Duke Fox in the MAN 1989 August issue staed that larger motors need less oil than a smaller motor did. The reason was as the engine size increases its displacement goes up as the cube while the area to be lubricated goes up as the square. This is known as the lubricating area to displacement ratio. A engine with a 1.5 inch bore would be lubricated well with a 10% ratio of oil as well as a engine with a .75 inch bore would be at a 20% ratio.
They had a chart in the article that shows a 2.2 cubic inch engine requiring 10% oil whereas a .60 engine needed 16% oil.
Actually the glow fuel manufacturers have taken note of those articles and over time reduces the oil in the glow fuel to those levels too.
How much oil is needed with bushed rod gasoline engines is still a issue though. I would think everyone needs to err on the side of having more oil than is needed, due to the special needs of four stroke engines.
A engine with all needle bearings, roller bearings or ball bearings on all of the rotating surfaces along with advanced cylinder to piston plating methods may be able to get away with very little oil lubrication in it too.
If I remember right a Swedish engine company made the Daimo 1.20 twin glow four stroke engine and when it first came out, they suggested no oil at all for lubrication. Later they changed it to suggest something like 5% oil.
The larger gasoline engines are still holding up to this engine displacement versus oil needed rule although the base oil levels needed is different. The big gas engines are typically running 40:1 to 50:1 ratios in them. The mid size engines running around 32:1 ratios and the smaller engines running 20:1 to 25:1 ratios.
|Jan 13, 2013, 10:21 AM|
My posts are NOT pertaining to 4-stroke glow engine rather 4-stroke CDI engines running glow fuel.
CDI takes a lot of volitility out of the equasion by introducing a fixed ignition timing event that is not affected by mixture temeprature, etc. The rules of oil content & to a lesser extent, needle settings are therefore changed.
If I were to go 90* rich on the HSN setting when peaked out on CDI, the engine would be slobbering. Anyting more than 2-3 clicks really loads up. There is however a quite liberal range @ peak RPM where needle settings have little affect & I err on ther rich side of that setting W/O going so far as to have RPM fall off.
That's yet another advantage of CDI over GI, less critical fuel mixture parameters.
I no longer use GI on any of my Saito engines. That being said, my smallest is an FA91S. If I were to go much smaller than that, say an FA72 or smaller, I would stick W/glow ignition.
If the airframe is large enough to carry the added bulk of the CDI (or an on board glow system), the engine displacement will be large enough so that the required fuel load weight savings (of CDI) for a 10 minute flight will out-weigh the weight of the CDI system.
That brings up yet another subject.
IMO on board glow is a waste of money when for a little more $$$$ CDI will have many more advantages, & is simpler in the long run as it does not require a different voltage/Ma rated battery/charger than the RX.
|Jan 13, 2013, 10:49 AM|
Unless the carburetor on the FA125 is different than the Saito carbs on their big block engines, the retaining screw should control the in-out position of the barrel. It rides in a spiral groove in the barrel. The barrel can't move in-out W/O rotating.
In the picture below, you can see the groove in the top middle of the carb barrel to the right of the venturi bore. That would be the WOT end of the groove.
I think you idle problem lies in a sloppy throttle linkage.
I ALWAYS use a ball link on the throttle arm, that.coupled W/a snug "Z" bend @ the plastic servo arm eliminates ANY slop in the linkage.
Furthermore, just as insurance, I ALWAYS use nylon pushrods like the Sullivan "Goldenrod" to eliminate ANY possibility of RF interferance from the pushrod being in close proximity to radio components.
Non conductive throttle pushrods are always a good idea W/any type of spark ignition.
With an engine W/a long stroke such as the FA125, you sould be able tyo get a stable idle of 1600 RPM, probably less W/CDI.
As far as whether to go W/glow fuel or gas after switching to CDI?
My suggestion is to do the ignition conversion 1st> Fly your plane that way for a while, then see if you want to spend the additional $$$ for a carburetor/manifold.
I think that once you do the conversion to CDI, you'll be so satisfied W/the improved characteristics that you will forget all about gasoline.
|Jan 13, 2013, 12:37 PM|
|Jan 13, 2013, 02:40 PM|
Joined Feb 2007
To put things in a nutshell:
The barrel of the FA-125a carb DOES move in and out without rotating..I first thought my carb was worn out so I went to a LHS to inspect a brand new one...it was all the same making the fuel mixture be less precise as desired at idle..Actually there is a thread on the subject in RCU that describes the problem but does not address any solutuin to fix it. (can't find the thread right now..)
To my best knowledge most of the other Saito carbs have the spring that pushes the barrel to the lever end (see below)
extract from Bill Robinson's Saito notes:
Carb barrel spring
Why does my FA-125 have no barrel spring in the carb?
It's not a stupid question. But it is a testimony to the excellent machine work in the Saito carb.
When you work the throttle lever you'll notice the throttle barrel also moves in and out of the carb body. This is what makes the metering (low speed) needle vary the mixture as the throttle setting changes. By moving nearer and farther off the LS needle the fuel port gets larger and smaller, changing the amount of fuel delivered.
Now, since we are depending on the consistency of the variation we have to be sure it changes only with turning the barrel, and not by the barrel moving straight in or out. The spring prevents this, keeping the barrel pushed toward the lever end.
All twin needle carbs except the cheapest possible ones, have this spring.
Carb barrel spring revisited.
Since writing the last note Iíve given the spring and the excellent machine work more thought.
No matter how well machined the throttle stop screw and the groove in the barrel are, they are subject to wear. When the groove gets the first few thousandths free play, then thereís going to be the hammering from vibration causing the barrel to vibrate sideways, this will make the wear even faster.
When the wear is sufficient to allow movement in and out without turning the barrel, the mixture control will also be less precise.
The spring on the barrel not only holds it firmly to one side of the groove for precise mixture control, by its very side tension it keeps the barrel from hammering on the edge of the groove.
When I get one of these engines without a barrel spring Iíll have to get a spring to fit the throttle barrel.
(w8ye note: People are having trouble getting a spring to work in their new 125s. There is not enough room for the spring.) (end of extract)
-> I guess I have to have a closer look to the carb design to see if some machine work might do the trick and help install a carb barrel spring of some kind.
I think your remark of checking the throttle linkage is another thing I have to do as I do not have ball link on the throttle arm so this may worsen the phenomenon in question.
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