how hard can a fox 46 run
06-22-2008, 11:32 PM
#26
RE: how hard can a fox 46 run
Some time ago I got curious about how oil flows through an engine and what affect it could have as far as carrying away heat out the exhaust so I did a very rough off-the-top-of-my-head calculation. First, oil can only come out the exhaust as fast as it's coming in through the carb so it's dependent on both fuel flow and oil content. To make calculations easy I used metrics.
So I considered a 10cc engine running at 10,000 revs with a 300cc (10 ounce) tank filled with a fuel that had 20% oil. That means there's 60cc of oil in that tank. Then I guessed it'd run for 10 minutes on that tank. In 10 minutes the engine would turn over 100,000 times and 30cc of oil would pass through it. In one rev then there'd be 30/100,000cc of oil or .0006cc/rev. With oil having almost exactly the same SG as water then this is .6 milligrams/rev.
I don't know the latent heat of vaporisation of oil but I'll say it's the same as water which is 2260kJ/kg so that mass of oil would absorb .001356kJ or .0013BTU/rev. But only if all of it completely vaporised which obviously isn't the case or we wouldn't have to wipe down the model every flight
. Now there's something interesting that I'd never realised before but the metric and Imperial systems for heat energy give almost exactly the same numbers.
So I considered a 10cc engine running at 10,000 revs with a 300cc (10 ounce) tank filled with a fuel that had 20% oil. That means there's 60cc of oil in that tank. Then I guessed it'd run for 10 minutes on that tank. In 10 minutes the engine would turn over 100,000 times and 30cc of oil would pass through it. In one rev then there'd be 30/100,000cc of oil or .0006cc/rev. With oil having almost exactly the same SG as water then this is .6 milligrams/rev.
I don't know the latent heat of vaporisation of oil but I'll say it's the same as water which is 2260kJ/kg so that mass of oil would absorb .001356kJ or .0013BTU/rev. But only if all of it completely vaporised which obviously isn't the case or we wouldn't have to wipe down the model every flight
. Now there's something interesting that I'd never realised before but the metric and Imperial systems for heat energy give almost exactly the same numbers.
06-23-2008, 01:55 AM
#27
Senior Member
RE: how hard can a fox 46 run
Brian,
It did seem strange to me that the fuel components table you had published years ago, did not include any of the oils that we use in our glow engines...
Are you sure that oil (synthetic/castor) and water have the same latent heat of evaporation?
Compared to some petroleum distillates, water is roughly 7 times as great...
It did seem strange to me that the fuel components table you had published years ago, did not include any of the oils that we use in our glow engines...
Are you sure that oil (synthetic/castor) and water have the same latent heat of evaporation?
Compared to some petroleum distillates, water is roughly 7 times as great...
06-23-2008, 11:01 AM
#28
RE: how hard can a fox 46 run
ORIGINAL: DarZeelon
Brian,
It did seem strange to me that the fuel components table you had published years ago, did not include any of the oils that we use in our glow engines...
Brian,
It did seem strange to me that the fuel components table you had published years ago, did not include any of the oils that we use in our glow engines...
Are you sure that oil (synthetic/castor) and water have the same latent heat of evaporation?
06-24-2008, 05:41 AM
#29
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RE: how hard can a fox 46 run
The Fox .46 is an ABC engine, it is bassically a .50 with a slightly smaler bore and ABC piston and cylinder set up. I have converted .46s to .50s by simply installing a .50 ringed piston and cylinder. Fox does recommend 20% all castor for the .46. It is a virtually indestructable engine as I have run them as both glow and Diesel. The .46 and the .50 make identical power on 5% nitro. The .46 weighs more than the .50. Of all the .50 sized engines I have, the Fox .50 is the lightest. The .46 is one of the best kept secrets in this hobby.
06-24-2008, 07:17 AM
#30
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RE: how hard can a fox 46 run
ORIGINAL: downunder
Some time ago I got curious about how oil flows through an engine and what affect it could have as far as carrying away heat out the exhaust so I did a very rough off-the-top-of-my-head calculation.
I don't know the latent heat of vaporisation of oil but I'll say it's the same as water which is 2260kJ/kg so that mass of oil would absorb .001356kJ or .0013BTU/rev. But only if all of it completely vaporised which obviously isn't the case or we wouldn't have to wipe down the model every flight.
Some time ago I got curious about how oil flows through an engine and what affect it could have as far as carrying away heat out the exhaust so I did a very rough off-the-top-of-my-head calculation.
I don't know the latent heat of vaporisation of oil but I'll say it's the same as water which is 2260kJ/kg so that mass of oil would absorb .001356kJ or .0013BTU/rev. But only if all of it completely vaporised which obviously isn't the case or we wouldn't have to wipe down the model every flight
.
Now...you've calculated what latent heat of evaporation takes away. So that's the energy required to change a liquid at its boiling point to a gas at the same temperature.
What about specific heat required to heat up the oil from, let's say 20 deg C to several hundred deg C. That may account for a bit more cooling effect.
06-24-2008, 09:38 AM
#31
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RE: how hard can a fox 46 run
ok, this friday im going to hook it up to a gallon jug and let it rip. one thing i thought of, i had once got the wrong engine from tower hobbies, a fox 46bb ABC Control line motor, that had no throttle. just a wide open bore. and one neddle. this tells me that fox is ok with that engine running WFO for some times.
this engine is still a very low time engine, and dosent quite run as good as it should. im thinking it needs to get some good hard time on it before i trust it to the sky. i have its twin that has about 3 years worth of running on it and it runs so good.
so, the next question, is how do i get it to feed off a gallon jug with out going lean or to rich, i herd of some kinda vent, where the pressure tap off the pipe in under the level of fuel in the jug. the jug will be layed on its side, right behind the motor, unless it leeks, then i will have to do something else. keep filling the 10 oz'er i guess.
this engine is still a very low time engine, and dosent quite run as good as it should. im thinking it needs to get some good hard time on it before i trust it to the sky. i have its twin that has about 3 years worth of running on it and it runs so good.
so, the next question, is how do i get it to feed off a gallon jug with out going lean or to rich, i herd of some kinda vent, where the pressure tap off the pipe in under the level of fuel in the jug. the jug will be layed on its side, right behind the motor, unless it leeks, then i will have to do something else. keep filling the 10 oz'er i guess.
06-24-2008, 11:26 AM
#32
RE: how hard can a fox 46 run
ORIGINAL: Harry Lagman
What about specific heat required to heat up the oil from, let's say 20 deg C to several hundred deg C. That may account for a bit more cooling effect.
What about specific heat required to heat up the oil from, let's say 20 deg C to several hundred deg C. That may account for a bit more cooling effect.
06-28-2008, 07:16 PM
#34
RE: how hard can a fox 46 run
To all:
Parting shot on Fox's steady-run legend (Sounds true in general, I'd check if surviving details remain accurate.
) - As with an endurance record attempt in Control Line, many years ago, possibly before Duke F wasted that barrel of SuperFuel, the fatal weak point has not yet been mentioned in this thread...
The glow plugs fouled out after several hours, even though the RPM and load conditions remained reasonably constant...
The CL Endurance attempt was made before sensible rules had been worked out. It was more publicity effort than serious record shot. The model had the usual two flying lines (elevation only) carrying a thin fuel line. At certain times, the idea was to pump more fuel to the on-board tank. It turned out that centrifugal loads on the fuel in the line provided ample pumping. A spare can of fuel was carried in a harness by the flier. Fliers alternated, doing the handle and gear switch during flight. The spare can was easily replaced or refilled as necessary. (All old memory, no certainty of the details. Someone here may have records or the ads I remember seeing about the event.)
I'm not sure whether the engine used in the "record" attempt was a Fox or a K&B. Again, not sure, but seem to recall that the engine was modified by adding a second glow plug. They did get many hours, possibly over 15, before the (second?) plug finally fouled out. ENYA did a similar run, testified to in ads about 25 years ago. They stopped the engine at regular intervals - 1 hour? - and checked or replaced the glow plug. Photos of the wearing parts after something like 100 hours of soft, steady-condition running, were publicized side-by-side with brand-new specimens of the same parts, and showed very little wear.
FYI: The AMA (USA National Aeromodelling Club) recently changed CL Endurance Rules. Until this change, 4 fluid ounces (about 115 cc) of fuel could be carried, but not replenished in flight. Engines .09 cu in (1.5cc) to .36 cu in (about 5.8 cc?) No restriction on type of engine. Specs for min and max line length, and line diameter. A few other technicalities... The new fuel limit is 1.0 fl oz (~ 29 - 30cc?). Way back when, I was interested enough in giving this a try under the 4 fl oz rules to "develop" a DDD converted OS Max 10.
Best consumption rate was about 60 minutes/ fl oz, on the bench. 3,000 - 3,300 RPM on a much modified 12-8 wooden prop; stuffed boost port; 1/32" ID sprinkler intake choke, 1/16" ID exhaust hole in a baffle plate over the exhaust. Nearly silent! Expected mechanical problems: ANY mote of dust could stop the intake hole; accumulated tarry exhaust in the stack could plug the small exhaust hole; the leisurely speed possible at that RPM on a very fragile prop made weather a very significant variable.
The 3+ to 4 hour potential caused me some sober thought... I had also "developed" a Fox BB Schneurle .15/DDD and stood out there in the center for 45 minutes while the poor beast staggered around. Only able to use half the tank's 4 fl oz capacity, as I hadn't considered the nose-up attitude required to maintain level flight, and the nose-out yaw attitude to provide some benefit in line-pull at the slow speed. The tank had a traditional CL mid-height fuel pick-up, and the flight attitude puddled all the fuel forward of the pickup tube end, and below the height of the tube.
My knees didn't much enjoy turning with the model for extended time either. The standing record under the 4 fl oz rules was around 2.5 hours. I figured I could pass that time, but the questions became 1) did I really want to do 3+ hours pivoting within a 5' cirlcle, and, perhaps more critical, 2) WHO could I con into timing and counting laps for 3+ hours? As flier, at least I'd have had something to do... Then there's the horrifying thought - what if some 'minor mechanical' terminated an attempt short of the standing record? You gonna do THAT again?
Parting shot on Fox's steady-run legend (Sounds true in general, I'd check if surviving details remain accurate.
) - As with an endurance record attempt in Control Line, many years ago, possibly before Duke F wasted that barrel of SuperFuel, the fatal weak point has not yet been mentioned in this thread...The glow plugs fouled out after several hours, even though the RPM and load conditions remained reasonably constant...
The CL Endurance attempt was made before sensible rules had been worked out. It was more publicity effort than serious record shot. The model had the usual two flying lines (elevation only) carrying a thin fuel line. At certain times, the idea was to pump more fuel to the on-board tank. It turned out that centrifugal loads on the fuel in the line provided ample pumping. A spare can of fuel was carried in a harness by the flier. Fliers alternated, doing the handle and gear switch during flight. The spare can was easily replaced or refilled as necessary. (All old memory, no certainty of the details. Someone here may have records or the ads I remember seeing about the event.)
I'm not sure whether the engine used in the "record" attempt was a Fox or a K&B. Again, not sure, but seem to recall that the engine was modified by adding a second glow plug. They did get many hours, possibly over 15, before the (second?) plug finally fouled out. ENYA did a similar run, testified to in ads about 25 years ago. They stopped the engine at regular intervals - 1 hour? - and checked or replaced the glow plug. Photos of the wearing parts after something like 100 hours of soft, steady-condition running, were publicized side-by-side with brand-new specimens of the same parts, and showed very little wear.
FYI: The AMA (USA National Aeromodelling Club) recently changed CL Endurance Rules. Until this change, 4 fluid ounces (about 115 cc) of fuel could be carried, but not replenished in flight. Engines .09 cu in (1.5cc) to .36 cu in (about 5.8 cc?) No restriction on type of engine. Specs for min and max line length, and line diameter. A few other technicalities... The new fuel limit is 1.0 fl oz (~ 29 - 30cc?). Way back when, I was interested enough in giving this a try under the 4 fl oz rules to "develop" a DDD converted OS Max 10.
Best consumption rate was about 60 minutes/ fl oz, on the bench. 3,000 - 3,300 RPM on a much modified 12-8 wooden prop; stuffed boost port; 1/32" ID sprinkler intake choke, 1/16" ID exhaust hole in a baffle plate over the exhaust. Nearly silent! Expected mechanical problems: ANY mote of dust could stop the intake hole; accumulated tarry exhaust in the stack could plug the small exhaust hole; the leisurely speed possible at that RPM on a very fragile prop made weather a very significant variable.
The 3+ to 4 hour potential caused me some sober thought... I had also "developed" a Fox BB Schneurle .15/DDD and stood out there in the center for 45 minutes while the poor beast staggered around. Only able to use half the tank's 4 fl oz capacity, as I hadn't considered the nose-up attitude required to maintain level flight, and the nose-out yaw attitude to provide some benefit in line-pull at the slow speed. The tank had a traditional CL mid-height fuel pick-up, and the flight attitude puddled all the fuel forward of the pickup tube end, and below the height of the tube.
My knees didn't much enjoy turning with the model for extended time either. The standing record under the 4 fl oz rules was around 2.5 hours. I figured I could pass that time, but the questions became 1) did I really want to do 3+ hours pivoting within a 5' cirlcle, and, perhaps more critical, 2) WHO could I con into timing and counting laps for 3+ hours? As flier, at least I'd have had something to do... Then there's the horrifying thought - what if some 'minor mechanical' terminated an attempt short of the standing record? You gonna do THAT again?
