PAW .60 mix
10-07-2015, 11:24 PM
#26
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I dunno Lou, every time that I see that the claim that a model diesel makes more torque than a glow engine I see that the design has not been optimised.
Witness four stroke glow engines, they pride themselves on torque and when converted to diesel do they make even more?
Or lets take an engine that comes in both glow and diesel formats, the MVVS 49. Optimise the glow design and use a factory resonator on the exhaust and perhaps a touch of nitro and which one pulls the hardest?
And there really is not that much difference between some thoroughly modern and optimsed engines like the Parra 2.5cc glow or diesels. The glow has a tad more power and the high revving diesels do not like large props.
When I read about engines that respond well to dieseling I am really left wondering if the donor engine was the best design as a glow in the first place.
I get the ability to lug a bigger prop thing (even then RC pattern glow engines on a pipe can turn 'square' 12x12 props going vertical) but are they really the 'big tractors' in comparison that some think they are?
Cheers.
Witness four stroke glow engines, they pride themselves on torque and when converted to diesel do they make even more?
Or lets take an engine that comes in both glow and diesel formats, the MVVS 49. Optimise the glow design and use a factory resonator on the exhaust and perhaps a touch of nitro and which one pulls the hardest?
And there really is not that much difference between some thoroughly modern and optimsed engines like the Parra 2.5cc glow or diesels. The glow has a tad more power and the high revving diesels do not like large props.
When I read about engines that respond well to dieseling I am really left wondering if the donor engine was the best design as a glow in the first place.
I get the ability to lug a bigger prop thing (even then RC pattern glow engines on a pipe can turn 'square' 12x12 props going vertical) but are they really the 'big tractors' in comparison that some think they are?
Cheers.
Last edited by Chris W; 10-08-2015 at 12:17 AM.
10-08-2015, 03:37 AM
#27
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Hi
You understand my point.
Only a correct measurement and comparison will do.
I have read accounts by people who have studied small engines deeply who kept "Standard" props to mount on different engines. They then measure RPM with tachometer and record.
They then could mount a series of props on an engine and record max RPM for that engine.
There was one manufacturer who made a dynamo. An electric generator that could be loaded to record torque and rpm to calculate HP.
Just because a given engine turns a big prop, does not matter.
THe old long stroke engines could turn very big props.
Until we actually measure a running engine, we are rendering an opinion.
Enjoy the oily engines.
You understand my point.
Only a correct measurement and comparison will do.
I have read accounts by people who have studied small engines deeply who kept "Standard" props to mount on different engines. They then measure RPM with tachometer and record.
They then could mount a series of props on an engine and record max RPM for that engine.
There was one manufacturer who made a dynamo. An electric generator that could be loaded to record torque and rpm to calculate HP.
Just because a given engine turns a big prop, does not matter.
THe old long stroke engines could turn very big props.
Until we actually measure a running engine, we are rendering an opinion.
Enjoy the oily engines.
10-08-2015, 01:51 PM
#28
Chris,
Thanks for your thoughtful comments! I did briefly mention that there were highly developed, high RPM specialty diesels. They are - generally - exceptions for a specific application, yet many are "normally aspirated" types, as required by the specific competition events.
The idea that our engines are basically air pumps remains true for "normally aspirated," two-cycle engines. The limitation on pumping capacity is inherent. 2-cycle engine cylinders forfeit many degrees of shaft rotation to provide for "transfer", power, and exhaust functions.
4-cycle engines fudge the 100% of stroke potential in each phase to account for charge- and exhaust-flow inertia, just as spark advance "fudges" on the 100% combustion stroke. The spark fires before TDC so that combustion pressure best 'matches' piston motion. Too soon before TDC it kicks back hard, wasting combustion pressure. Too late and the pressure rise suffers from chasing the piston down more than pushing it down.On the same fuel, a 4-stroker should provide more torque at the same RPM, but the valve operating machinery generally limits its upper RPM range.
Resonant exhaust (or even intake) plumbing is not "normal aspiration." It stuffs more charge into the engine than it, as an air pump, can. Of course, that effect can, and has been, used to "tailor" output whether for torque at a desired limited RPM range (e. g., CL Stunt), or for ultimate high-RPM power (e.g., CL Speed, possibly also FF Power), or for a boost as needed for RC vertical pull.
Of course, few of our mass produced engines have been 'perfectly optimized.' Any optimum sought defines how to achieve it. A general purpose engine should be adaptable, to a degree, towards differing specific goals.
For a "Normally Aspirated" general purpose engine, the developed flow path volumes and shapes become a fact of production - the inherent optimal flow should coincide with the max Volumetric Efficiency RPM for that configuration. The differences among engines, true or converted diesels, glows run as glows, and perhaps glows run as gasoline engines, too, reflect the mfr's intent to allow different uses.
We can modify some stock specifications slightly, - in regards to shaft position regarding BDC (or TDC) for: -
----Shaft (or case) inlet duration;
---- cylinder transfer (bypass) opening, closing - hence duration,
---- and exhaust opening, closing, duration,
We can "improve" internal flow channels' smoothness and volume. Sometimes this does more harm than good.
Diesels may need more internal flow velocity and turbulence than glows, to keep a fresh charge mixed well. Kerosene doesn't evaporate to gaseous state as easily as methanol. What reaches the combustion chamber is likely to be more a finely atomized spray of droplets than a blend of air with an evaporated gaseous flammable. Gaseous mixtures ignite more easily than droplets sprayed into air.
Another quick example: glow engines, too. The Fox 35 Stunt (glow) engine had small bypass volume for over 50 years while it earned its reputation for 'correct' running manners in the CL Precision Aerobatics event. Apparently, bypass volume was increased a while back (for more power?) To restore the original manners, now, many fliers using this engine block part of the bypass channel. Their method causes no significant loss of power for the RPM and load conditions of the event!
(note: copied and somewhat reworded from an email, today, in reply to Chris.)
Thanks for your thoughtful comments! I did briefly mention that there were highly developed, high RPM specialty diesels. They are - generally - exceptions for a specific application, yet many are "normally aspirated" types, as required by the specific competition events.
The idea that our engines are basically air pumps remains true for "normally aspirated," two-cycle engines. The limitation on pumping capacity is inherent. 2-cycle engine cylinders forfeit many degrees of shaft rotation to provide for "transfer", power, and exhaust functions.
4-cycle engines fudge the 100% of stroke potential in each phase to account for charge- and exhaust-flow inertia, just as spark advance "fudges" on the 100% combustion stroke. The spark fires before TDC so that combustion pressure best 'matches' piston motion. Too soon before TDC it kicks back hard, wasting combustion pressure. Too late and the pressure rise suffers from chasing the piston down more than pushing it down.On the same fuel, a 4-stroker should provide more torque at the same RPM, but the valve operating machinery generally limits its upper RPM range.
Resonant exhaust (or even intake) plumbing is not "normal aspiration." It stuffs more charge into the engine than it, as an air pump, can. Of course, that effect can, and has been, used to "tailor" output whether for torque at a desired limited RPM range (e. g., CL Stunt), or for ultimate high-RPM power (e.g., CL Speed, possibly also FF Power), or for a boost as needed for RC vertical pull.
Of course, few of our mass produced engines have been 'perfectly optimized.' Any optimum sought defines how to achieve it. A general purpose engine should be adaptable, to a degree, towards differing specific goals.
For a "Normally Aspirated" general purpose engine, the developed flow path volumes and shapes become a fact of production - the inherent optimal flow should coincide with the max Volumetric Efficiency RPM for that configuration. The differences among engines, true or converted diesels, glows run as glows, and perhaps glows run as gasoline engines, too, reflect the mfr's intent to allow different uses.
We can modify some stock specifications slightly, - in regards to shaft position regarding BDC (or TDC) for: -
----Shaft (or case) inlet duration;
---- cylinder transfer (bypass) opening, closing - hence duration,
---- and exhaust opening, closing, duration,
We can "improve" internal flow channels' smoothness and volume. Sometimes this does more harm than good.
Diesels may need more internal flow velocity and turbulence than glows, to keep a fresh charge mixed well. Kerosene doesn't evaporate to gaseous state as easily as methanol. What reaches the combustion chamber is likely to be more a finely atomized spray of droplets than a blend of air with an evaporated gaseous flammable. Gaseous mixtures ignite more easily than droplets sprayed into air.
Another quick example: glow engines, too. The Fox 35 Stunt (glow) engine had small bypass volume for over 50 years while it earned its reputation for 'correct' running manners in the CL Precision Aerobatics event. Apparently, bypass volume was increased a while back (for more power?) To restore the original manners, now, many fliers using this engine block part of the bypass channel. Their method causes no significant loss of power for the RPM and load conditions of the event!
(note: copied and somewhat reworded from an email, today, in reply to Chris.)
10-08-2015, 02:56 PM
#29
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Of course, few of our mass produced engines have been 'perfectly optimized.' Any optimum sought defines how to achieve it. A general purpose engine should be adaptable, to a degree, towards differing specific goals."
Reducing the distance between the inner head surface and the piston towards the optimum increases power considerably by increasing the compression. Even reducing the shim thickness can give good results. I can and will supply an excellent article on this.
Outside the US, there is a vibrant diesel culture in the FreeFlight and Control Line domains. There are many excellent new diesel engines designed for use in club level competition available. Their performance contradict the "conventional wisdom" and dogma's often cited on this forum.
Perhaps Lou you are not aware of recent developments?
10-08-2015, 03:07 PM
#30
My Feedback: (1)
Hi
You understand my point.
Only a correct measurement and comparison will do.
I have read accounts by people who have studied small engines deeply who kept "Standard" props to mount on different engines. They then measure RPM with tachometer and record.
They then could mount a series of props on an engine and record max RPM for that engine.
There was one manufacturer who made a dynamo. An electric generator that could be loaded to record torque and rpm to calculate HP.
Just because a given engine turns a big prop, does not matter.
THe old long stroke engines could turn very big props.
Until we actually measure a running engine, we are rendering an opinion.
Enjoy the oily engines.
You understand my point.
Only a correct measurement and comparison will do.
I have read accounts by people who have studied small engines deeply who kept "Standard" props to mount on different engines. They then measure RPM with tachometer and record.
They then could mount a series of props on an engine and record max RPM for that engine.
There was one manufacturer who made a dynamo. An electric generator that could be loaded to record torque and rpm to calculate HP.
Just because a given engine turns a big prop, does not matter.
THe old long stroke engines could turn very big props.
Until we actually measure a running engine, we are rendering an opinion.
Enjoy the oily engines.
Yes indeed!
There is a table of standard prop sizes and their respective power absorption curves. They are still used for published engines tests. Regrettably they tend to favour the smaller props more suitable for smaller engines. However extrapolation to the larger sizes may be possible.
It seems to me that with the development of larger powerful electric motors for model aircraft and very accurate devices for measuring their power, that it should be possible to produce a set of fresh calibrations for much larger props.
Last edited by qazimoto; 10-08-2015 at 03:10 PM.
10-08-2015, 07:36 PM
#31
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what are you, a mind reader?
I don't want to start a kurfuffle here but its just that when I see something like performance built Parra engines there is little difference between the styles, and the biggest difference really comes from non purpose built engines.
And if a generic off the shelf two stroke engine is OK for use as a glow but shines as a diesel it is not proof that the fuel choice is an overall panacea but simply that it suits that engine all the batter.
Thanks.
10-09-2015, 05:21 AM
#33
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Lou, just for kicks, here is a picture of my Saito .80 with 15.5 to 1 compression ratio turn a Bolly 13.5x8 at 8,792 rpm. It starts un aided and idles beautifully at about 1,550. I hope I got the correct pictures. Note that it makes very little smoke. It's Davis ABC blend fuel.
Last edited by Hobbsy; 10-09-2015 at 05:23 AM.
10-09-2015, 06:55 AM
#34
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Hi
Interesting saito
Did you replace the glow plug? I assume you used an electric starter.
Have you run the same prop with the Saito on glow fuel , at what RPM?
Interesting saito
Did you replace the glow plug? I assume you used an electric starter.
Have you run the same prop with the Saito on glow fuel , at what RPM?
10-09-2015, 03:47 PM
#35
So far in my recent diesel conversion experiments, I've found that my converted glow engines make less power (turn fewer rpm) on diesel than they do on glow fuel. The difference is how they behave to the prop loads. My Fox .40 would run hot and sag on an 11x6 & 11x7 on 5% nitro fuel, but just ran and ran on a 12x6 on diesel without sagging or running away. Fuel consumption is on-par on diesel when comparing to glow. My diesel conversions are all larger displacement engines - .40, .45, .50, & .51 though. I raised the same concern awhile back - it makes more power on glow, so why convert? The engines don't heat up and sag on diesel where they would on glow.
10-10-2015, 03:38 AM
#38
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Not too bad the 4500 turns a 22x12 at 6,600 and the 3000 a 20x8 at about 7,900. I need to get busy and run the 4500 with the new Bisson Pitts muffler I've had for about 2 years and haven't tried.. The J-Tech pictured is loud and leaks all over more than anyplace else.
10-10-2015, 11:53 AM
#41
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I purchased nearly all of my heads from Mr. Davis, the SuperTigre 4500 head I bought from Dennis. I bought the 3000 and the 3000 head from Mr. Davis, the 3000 was well used but a Frank Bowman ring made it like new, it still has it's original bearings in it.
Eric, the only fuel I use is Mr. Davis' fuel, ABC blend for ball bearing engines or his Plane Fuel for bushing engines.
Eric, the only fuel I use is Mr. Davis' fuel, ABC blend for ball bearing engines or his Plane Fuel for bushing engines.
10-10-2015, 02:39 PM
#42
I have a few items I picked up and found useful over recent (2 to 5) years which some of us here might enjoy playing with.
One is a scan I made of Dave Gierke's 1970's engine lab project. He was a high school science teacher at the time, and incidentally, a recent US NATS CLPA champion, at the time. He and his students worked through problems defining the basics of engine performance. Among the equipment they built and used were a balance beam torque measuring unit, which - with measured RPM - allowed direct calculation of brake HP. (Engine torque reaction at the motor mounts, balanced by a sliding weight on the opposing arm: a frictionless 'brake.') and flow measuring into the engine via calibrated nozzles, and many other relevant aspects. I have this series (3 articles in Flying Models magazine over about 6 months) in either MS Word or .pdf. Medium large files. Could attach to an email for the interested. I'll first confirm the scan includes all the relevant pages.
Personally, this was familiar stuff I'd had the privilege of learning almost 25 years earlier. The presentation in FM magazine is an excellent refresher!
The other item of direct interest is an MS Excel spreadsheet that uses measured RPM on props whose 'power coefficients' were developed separately. Many are, perhaps, a few years to soon to include the most recent "high efficiency" props. but a lot of still current props are in it. The 'parameters' needed are temperature, barometric pressure, and altitude above sea level, RPM, etc. Data in both metric and traditional Imperial units. Results include thrust and HP at the parameter conditions. Prop and RPM entries are easily changed to compare the results of changed RPM, prop(*1), altitude, barometric pressure and temperature, etc.
____(*1) Props are listed by manufacturer and type within the manufacturer's range of 'styles' or applications - such as MA Scimitar, CF, normal - or APC designated as for pylon, racing, combat or general use, etc. Apparently, the characteristic formulae were used when confirmed to be consistent for the range of prop sizes for supposedly similar props .
I don't have the provenance or source of these sheets(*2) but I've used it (them) for at least three years with no computer problems. Medium sized XL spreadsheet. Again, willing to attach it to email to those interested. Received this into XP, and just confirmed it is fully functional in at least Win7.
____ (*2) Other 'included sheets' analyze noise problems, list prop nut specs for many popular engines.
If any (many?) are interested, I'd prefer to combine as many into one 'mailing' as possible - one by one over several days would be a nuisance.
One is a scan I made of Dave Gierke's 1970's engine lab project. He was a high school science teacher at the time, and incidentally, a recent US NATS CLPA champion, at the time. He and his students worked through problems defining the basics of engine performance. Among the equipment they built and used were a balance beam torque measuring unit, which - with measured RPM - allowed direct calculation of brake HP. (Engine torque reaction at the motor mounts, balanced by a sliding weight on the opposing arm: a frictionless 'brake.') and flow measuring into the engine via calibrated nozzles, and many other relevant aspects. I have this series (3 articles in Flying Models magazine over about 6 months) in either MS Word or .pdf. Medium large files. Could attach to an email for the interested. I'll first confirm the scan includes all the relevant pages.
Personally, this was familiar stuff I'd had the privilege of learning almost 25 years earlier. The presentation in FM magazine is an excellent refresher!
The other item of direct interest is an MS Excel spreadsheet that uses measured RPM on props whose 'power coefficients' were developed separately. Many are, perhaps, a few years to soon to include the most recent "high efficiency" props. but a lot of still current props are in it. The 'parameters' needed are temperature, barometric pressure, and altitude above sea level, RPM, etc. Data in both metric and traditional Imperial units. Results include thrust and HP at the parameter conditions. Prop and RPM entries are easily changed to compare the results of changed RPM, prop(*1), altitude, barometric pressure and temperature, etc.
____(*1) Props are listed by manufacturer and type within the manufacturer's range of 'styles' or applications - such as MA Scimitar, CF, normal - or APC designated as for pylon, racing, combat or general use, etc. Apparently, the characteristic formulae were used when confirmed to be consistent for the range of prop sizes for supposedly similar props .
I don't have the provenance or source of these sheets(*2) but I've used it (them) for at least three years with no computer problems. Medium sized XL spreadsheet. Again, willing to attach it to email to those interested. Received this into XP, and just confirmed it is fully functional in at least Win7.
____ (*2) Other 'included sheets' analyze noise problems, list prop nut specs for many popular engines.
If any (many?) are interested, I'd prefer to combine as many into one 'mailing' as possible - one by one over several days would be a nuisance.
10-10-2015, 02:44 PM
#43
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Hi lou
I am not sure how to send a PM so
I would like the info you have
[email protected]
Thanks
Dennis
I am not sure how to send a PM so
I would like the info you have
[email protected]
Thanks
Dennis
10-10-2015, 04:58 PM
#46
https://www.youtube.com/watch?v=QkCVRpx_qyQ
This is my simi-long and simi-boring video of fuel mixing and PAW running. Seems on point.
Running a PAW it really pretty straight forward. Factory recommend fuel mixes work well for me.
Bill
This is my simi-long and simi-boring video of fuel mixing and PAW running. Seems on point.
Running a PAW it really pretty straight forward. Factory recommend fuel mixes work well for me.
Bill
10-11-2015, 12:05 AM
#47
I know the horse is dead, but I may be a sadist - I enjoy continuing to beat it... Bear with me a bit longer?
Of course it's true many of the newer small engines do well as both glow and converted-diesel. I've benched NorVel 1cc (RJL) converts at around 10% lower RPM than as nitro enhanced glows. 20-ish rather than 22-ish RPM. The matter of internal flow 'effectiveness' is a bit different from its 'efficiency.' The RPM (rate of producing combustion 'events') of such advanced engines provides one term for the power calculation.
Optimized for glow conditions, an engine may have excess flow capacity for running as a diesel. Our diesels (strictly:- compression ignited things with combustibles and lubricants blended into the fuel) are still limited by the air/fuel ratio consideration, but the needle valve - metering the liquid fuel entering the innards - helps. The compression adjustment helps, as when turning a larger prop, a lower compression setting works best. Corollary:- it requires higher compression settings to advance the ignition timing to match operation on a smaller prop at higher RPM. (NB: This can - and has - destroyed engines when overdone..).
Today, with the RPM that moderately expensive, specific-event-'aimed' engines work at, inefficiencies either way are less problem. They are masked by the rate of producing power (e. g., RPM) and the tolerance that that brings to less than ideal "use" of the air and fuel.
Ideally, all combustibles are burned, leaving no unburnt fuel and no unused oxygen in the exhaust products. With glow engines particularly, fuel with a characteristic scent leaves that scent in the unburnt portion of the exhaust stream. "Diesels" may operate closer to consuming all the combustibles - good fuel exhaust at good settings can be nearly odorless.
Just a few observations... maybe the horsemeat is by now sufficiently tenderized?
( 'at's a joke, son...)
Of course it's true many of the newer small engines do well as both glow and converted-diesel. I've benched NorVel 1cc (RJL) converts at around 10% lower RPM than as nitro enhanced glows. 20-ish rather than 22-ish RPM. The matter of internal flow 'effectiveness' is a bit different from its 'efficiency.' The RPM (rate of producing combustion 'events') of such advanced engines provides one term for the power calculation.
Optimized for glow conditions, an engine may have excess flow capacity for running as a diesel. Our diesels (strictly:- compression ignited things with combustibles and lubricants blended into the fuel) are still limited by the air/fuel ratio consideration, but the needle valve - metering the liquid fuel entering the innards - helps. The compression adjustment helps, as when turning a larger prop, a lower compression setting works best. Corollary:- it requires higher compression settings to advance the ignition timing to match operation on a smaller prop at higher RPM. (NB: This can - and has - destroyed engines when overdone..).
Today, with the RPM that moderately expensive, specific-event-'aimed' engines work at, inefficiencies either way are less problem. They are masked by the rate of producing power (e. g., RPM) and the tolerance that that brings to less than ideal "use" of the air and fuel.
Ideally, all combustibles are burned, leaving no unburnt fuel and no unused oxygen in the exhaust products. With glow engines particularly, fuel with a characteristic scent leaves that scent in the unburnt portion of the exhaust stream. "Diesels" may operate closer to consuming all the combustibles - good fuel exhaust at good settings can be nearly odorless.
Just a few observations... maybe the horsemeat is by now sufficiently tenderized?
( 'at's a joke, son...)
10-11-2015, 12:37 AM
#48
I don't know the what the residues consist of, chemically, but there is no combustion engine that can run totally clean if it uses ambient air and hydrocarbons in the combustion.
10-11-2015, 01:24 AM
#49
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Considering that a model diesel runs at about a 15:1air fuel ratio and a methanol engine about 8:1 totally counteracts the fact that kerosene has twice the calorfic value of alcohol fuels.
In other words it is the amount of fuel that you can get through a combustion cycle that determines the amount of power produced.
So since the calories burned in one cycle is about the same then the amount of power produced should be very similar, the issue may be that since diesels run a much leaner mix ( about half) you will suffer half the oil content per cycle.
Now kerosene has a lubrication value of about 2% of castor oil and if you accept that that its not hard to see diesels will always need a higher % oil content to detriment of the base fuel %.
(The 2% rating comes from a doctorate done in relation to fuel pump wear comparing kerosene vs methanol).
In other words it is the amount of fuel that you can get through a combustion cycle that determines the amount of power produced.
So since the calories burned in one cycle is about the same then the amount of power produced should be very similar, the issue may be that since diesels run a much leaner mix ( about half) you will suffer half the oil content per cycle.
Now kerosene has a lubrication value of about 2% of castor oil and if you accept that that its not hard to see diesels will always need a higher % oil content to detriment of the base fuel %.
(The 2% rating comes from a doctorate done in relation to fuel pump wear comparing kerosene vs methanol).