Brodak 40

Hello everyone I just purchased a new Brodak 40 and I am impressed ,a very nice and light motor.My question is with the spray bar.It has 2 holes.They appear to drill straight through the spray bar.What is the correct way for a spray bar like this to sit is the venturi.It is sitting in there at about a 45 deg angle to vertical with the bore of the venturi with the 45 deg being angled towards the rear of the motor?It is somthing I have never seen so I just wanted some input.Thanks Dennis

The holes should be side to side so when you are looking straight down the bore of the venturi you either just see both of them, or just can't quite see either. In other words, even them out.

Oh, and I moved this from the Classifieds since it involved a question of general interest.

Thank you very much Leonard.I felt it was not right but it was a new design to me.
Dennis

Dennis,

Gosh, someone who has never seen a Fox .29 or .35. I'm really impressed!

Ahoy James, are yee at sea still, matey?? Or be yee in port?

Ahoy Ty,

We mariners still be buck'n a bit of da nort continental current. But, we will be mak'n port at 0800 on the 18th! I get on the plane at 4:15 same day and be back in C-O-L-D country at 11:50PM!

Jim Pollock, BBBBrrrrrrrrrr

Jim;

If you walked into most of the hobby shops remaining in business, especially some of the chain hobby shops like Hobby Town, you would be hard pressed to find any Fox products other than glow plugs. Even Tower/Top Flite, maker of the ARF Nobler, the ship that earned its reputation with Duke's 35 in the nose, now recommends the LA 40 with the Nobler. And, if you are a new flyer, you will probably hunt out a local hobby shop. You will see OSs, Magnums, ASPs, etc.

I can't blame the Hobby Shop owners, either. Our local Hobby Town ordered a 50th Anniversary Fox for a guy who never came by and picked it up. It sat there in the display case for over a year until my flying partner felt he needed a new Fox and bought it for less than the dealer's cost.

I guess our knowledge of vintage Fox engines dates us a little bit...

Such is life.

v/r

Just out of curiosity: is there any advantage to any of three spray bar configurations (with variations) I've seen?
1)spray bar passing completely through the venturi. 1a) as in "1)" with a single hole for fuel, 1b) as in "1)" with two holes directly across from each other (i.e. 180 deg apart), 1c) as in "1)" with two holes spaced less than 180 deg apart (or is this a manufacturing error?);

2)the so called "sprinkler bar" where the spray bar passes only half way through the venturi;

3)the spray bar is offset to the side of the venturi

???

The closer to "round" a venturi is, the more efficient the airflow for a given area of passage (subtract the spraybar area from the diametrical area in each case for true passage area). Anyway, air tends to "bunch up" in tight corners, which is why full scale aircraft use fillets between wing and fuselage.

Now, there is a counter argument that a full spraybar turbulates the air and causes the fuel to break up and vaporize better. In addition, you are dropping the fuel into the middle of the airflow too, so it doesn't drip down the venturi walls.

Ron Young discovered that on the C*x Conquest, if he bored out the venturi from the bottom so that there was a sharp ridge just above the fuel inlet hole, he got more rpm. He figured that the turbulence was picking up the fuel and vaporizing it better.

Then there is the Cyclon, where the fuel squirts directly into the crankshaft port and never gets to the venturi at all. Go figure!

Now, a question. Has anyone ever studied what the fuel/air mix at the cylinder inlet port really is? Pure gas? Air plus fuel droplets? All of the above? And what SHOULD it be?

The mixture is a mist. As the pressure increases in the chamber, so does the temperature and this causes the fuel to go to vapor state. The swirling in a cylinder and the turbulence of the compressing air causes the fuel and air to mix. This all happens in a nano second, just before ignition. Or it should happen like this. Air temperature (ambient), humidity, volumn of fuel, amount of nitro, oil, shape and size of the lower chamber and piston speed will be some of the variables affecting this mixture. In an automobile engine, the computer uses several inputs to determine the perfect air fuel ratio, which in theory should be 14.7 to 1. Pounds of air to one pound of fuel or stoiciometric as they call it.
Our engines are timed at a constant, no spark to advance or retard. So we do it with mixture control, rich to lean, which will affect engine ignition timing and burn rate. The leaner the mixture the sooner it will ignite and faster it will burn giving higher rpm's. There is always a point of diminishing returns in either direction. Too rich, no fire. Too lean, no fire. The triangle must be maintained. Fuel, oxygen, ignition temperature.

>The mixture is a mist. As the pressure increases in the
>chamber, so does the temperature and this causes the fuel to
>go to vapor state. The swirling in a cylinder and the
>turbulence of the compressing air causes the fuel and air to
>mix. This all happens in a nano second, just before
>ignition. Or it should happen like this. Air temperature
>(ambient), humidity, volumn of fuel, amount of nitro, oil,
>shape and size of the lower chamber and piston speed will be
>some of the variables affecting this mixture. In an
>automobile engine, the computer uses several inputs to
>determine the perfect air fuel ratio, which in theory should
>be 14.7 to 1. Pounds of air to one pound of fuel or
>stoiciometric as they call it.
>Our engines are timed at a constant, no spark to advance or
>retard. So we do it with mixture control, rich to lean,
>which will affect engine ignition timing and burn rate. The
>leaner the mixture the sooner it will ignite and faster it
>will burn giving higher rpm's. There is always a point of
>diminishing returns in either direction. Too rich, no fire.
>Too lean, no fire. The triangle must be maintained. Fuel,
>oxygen, ignition temperature.

Ron B.
F4Fguy

TY:
Close,but no cigar!You're right about the mixture being a vapor,but,in a decently designed engine it's vaporized in the crankcase,and introduced to the cylinder as such.You're also right that the chemically correct mixture is stoichiometric@~14.7:1.However the best power and the easiest ignition is not at stoichiometric.It will always be at a richer mixture,usually around 12-12.5:1.These numbers ,incidentally,are for gasoline.THe same condition for methanol is much richer,around 6:1 or even richer depending on the nitro content.These F/A ratios apply only to the actual fuel,the oil content not included.Also,within the ignition limits, the leaner the mixture the harder it is to ignite and the slower it burns,and the the richer,the easier and faster.This is due to flame being better able to propagate with the more closely spaced feul droplets in the rich mixture.
All the above is easily demonstrated by the way we usually start our engines.You will never be able to start if the engine is more than the tiniest bit lean,but it will readily start even if it'slobbering rich.
In terms of timing,and within fairly wide limits,F/A ratio is pretty far down the list in importance.The primary control is compression ratio,the next the glow plug i.e.hot/cold,third is the fuel itself in terms of volitility and ignition point(usually determined by the amount of nitro and ignition propagators such as propylene oxide),then mixture strength.

There is a difference in gasoline and methanol, but they both burn only in the vapor state. Liquid gasoline and liquid methanol will not burn. A rich mixture is introduced when the engine is cold so more vapors are present in order to cause ignition. Thus the choke on automotive engines or the cold start injector on modern engines.
Same for the extra prime on a cold model engine. The stuffer also helps in causing the fuel and air to mix into a vapor, as it keeps up the pressure and thus the heat neeeded, but when cold this does not happen as quickly as we would like. Thus it always helps to let the engine warm up a few seconds before launch and recheck the rpms just before launch to make sure it is where we want it. The colder, the less likely the fuel will vaporize properly and this is what floods out the plug. At KOI last year, many had to resort to lighter fluid to get their engines to even start. Oncxe it was warmed up, then the engine performed as advertised. I do nbot believe that the fuel is truly vaporized in the crankscase on our little engines, but is more so in the cylinder as the piston ascends causing a rise in temps which will truly vaporize the mixture. All things being equal, glow plug, engine size, bore and stroke, the fuel mixture will determine when it actually ignites and it's burn rate. Too rich or too lean and any additives all act upon that ignition point and burn rate. Remember Nitro
Benzene?? Banned. It causes cancer among other things, but it sure made an engine sing.

The stoichiometric mixture is strictly for emissions and economy, not power. That I know. More fuel= more power. More cubic inches + more fuel= even more power, ad infinitum. Kinda.

Ron I stated lower chamber meaning crankcase, but I never think of it as such on model engines. On Diesels I do. To me the "crankcase" on a two stroke model plane engine is a mixing bowl. but I still believe based on other factors, that the final vaporization of the fuel takes place above the piston on its way up to TDC.

Ron B.
F4Fguy

Ty:
Re posts #16, #17, and#18,again close ,but no cigar.
The mixture whether in the crancase,orin the combustion chamber consists of air and fuel droplets.The fuel is burned by vaporizing the surface of the droplets allowing it to chemically combine with the air.The size of the droplets is governed primarily by pressure drop at the point of introduction to the airstream, the configuration of the orifice or jet,by turbulence in the crancase and ports and in the combustion chamber.The smaller the droplets the faster they burn in any given combustible mixture.While it's true the temperature is rising as the piston rises,the pressure is rising at approximately the same rate,so that the vaporization of the fuel is at about the same rate as at atmospheric.If anything,the low pressure during induction has more effect on vaporization than pressure/temperature rise during the compression stroke.The cold start injector,choke,and cold start prime all do the same thing(the former more efficiently than the latter),they richen the mixture for easier starting.A mxture will still be combustible with gasoline at 6:1AF almost 8 points rich,but is unable to support combustion above 16:1AF,1.3 points lean.the rich/lean limits on methanol are considerably wider but with the same bias.The reason richer makes more power is that since (with very rare exceptions)combustion is very inefficient,more fuel than the chemically correctamount is needed to ensure consuming all the air,which is the true measure of power.The excess ,unburnt fuel IS vaporized during the power and exhaust stroke and is the source of most of the cooling in a model engine,(I refuse to be drawn into a discussion of castor oil as a cooling source),the balance being taken care of by airflow around the outside,
Crankcase,lower chamber,it doesn't matter,it's still the lowest pressure in the system and the most turbulent area,and that's where the smallest droplets and the most homogeneous mixture is formed.Actually if you can get the fuel finely enough devided,mixed evenly enough with the air,and turbulate the mixture enough,you can improve power with less fuel than would be possible under poorer conditions.This is the primary reason for fuel injected auto engines.We found in our tests that we could improve both power and economy with a leaner mixture by using a highly turbulent chamber and individual cylinder fuel injection at the port.Emissions have much to do with combustion efficiency and complete reaction of all the mixture than they do with mixture strength as such.If a portion of the fuel is not fully reacted you get CO and a host of other unburned HCs,if there's partially reacted air you get NOXs up the wazoo(scientific term).
The FORD and TEXACO lean burn and multi-fuel engines used thes principles to get low emmissions,good economy,and excellent power using very low grade fuels.
As I said above,the real measure of an engines power is it's ability to move air through the system,and to react as much as possible of that air to heat with a fuel.Another advantage of high turbulence is that the much faster burn allows much less advance as the mixture is forced into intimate contact with the ignition source.

Larry,
The smaller the fuel droplets are the more efficient the combustion.
the fuel burns only on the surface of the droplets. With a fuel injecton project I have some history on. The HP got a huge jump when the fuel pressure was increased an a nozel that made a finer mist was used. A side result was less fuel burn in the exhaust as the mixture burnt more compleatly in the chamber.
My own use. On a VA 049 going to a *ox TD venturi and needle made a big difference than jsut dumping fuel in from the side of the hole out of the spraybar.
The Conquest info is very interesting.

Tom:)

Since this came up on the forum, I wish to share my thoughts about the latest batch of B-40s. The two problems which were most frequently mentioned in the earlier rounds seem to have been solved. The needle valve will shut off the fuel with no "tweaking" of the assembly. The Prop nut will run all the way down the shaft without having to chase it with a 1/4 -28 die. The four that I bought all had the sleave in the proper position.

I think John is to be commended for addressing these problems and I still think it is a great engine for the money.

Shark 35 with B-40 Power

>Hello everyone I just purchased a new Brodak 40 and I am
>impressed ,a very nice and light motor.My question is with
>the spray bar.It has 2 holes.They appear to drill straight
>through the spray bar.What is the correct way for a spray
>bar like this to sit is the venturi.It is sitting in there
>at about a 45 deg angle to vertical with the bore of the
>venturi with the 45 deg being angled towards the rear of the
>motor?It is somthing I have never seen so I just wanted some
>input.Thanks Dennis

DENNIS. Make sure that the CYCLENDER Sleeve is in the right position; mine was off by a 1/16”. Just look down the exhaust stack and see if you can see the edge of the exhaust port; It the (sleeve) might have to be turned left or right a little.

Scott

Thanks guys and I fly by myself out here so I do not see all brands ect and do not have any interest in buying a Fox.I have been flying since the late 70s but most of it up until the last 3-4 years has been R/C.People have always said there was no stupid question but?Oh well! Thanks Dennis

>People have always said
>there was no stupid question but? Oh well! Thanks Dennis

There are no stupid questions, Dennis, only stupid answers. Stick around long enough and most any of us can supply you with the latter.