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Electronic solutions to modifying glow engines of all sizes to gasoline

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Electronic solutions to modifying glow engines of all sizes to gasoline

Old 09-03-2023, 10:46 PM
  #1826  
Rcplanedan
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heres a clip of my 20cc seagull models decathlon.
The asp ft160 is running rather well after some fiddling with the dremel on the throttle barrel slot for a fairly good mechanical throttle curve..runs a little rich on idle but runs fairly smoothly on all throttle positions from transmitter stick..plane sat for 5 mins and started second flip with a small amount of throttle..
running a 16x6 turnigy wide blade prop. Its giving 7900rpm , static timing is 30 btc ,and clearly sounds like its reaching around 8500rpm in the air or close maybe 8300rpm
Old 09-04-2023, 05:51 PM
  #1827  
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Looks like its running Great Dan.... I would suggest that you might be close to the "danger zone" with your prop selection - I'm at 1400' (430m) ASL and on a 16X8 Master Airscrew (heavy one) i'm turning 7800 static but almost 9000 in the air on a fast WOT pass.. I will try and post some video from last week end but my "revs" sound very similar to yours..

Have had a very busy summer so far but Dug the Boxer out last weekend and fired it up and it flew great - Hope things slow down a bit here to up the participation level...
Old 09-05-2023, 10:20 AM
  #1828  
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I just got some stuff for development. I want to merge Chris's tank pressurization stuff with my solenoid controller for a single controller setup that hopefully works with s.bus. should save a bit of wire.


Old 09-05-2023, 01:27 PM
  #1829  
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Originally Posted by Cat 1
Looks like its running Great Dan.... I would suggest that you might be close to the "danger zone" with your prop selection - I'm at 1400' (430m) ASL and on a 16X8 Master Airscrew (heavy one) i'm turning 7800 static but almost 9000 in the air on a fast WOT pass.. I will try and post some video from last week end but my "revs" sound very similar to yours..

Have had a very busy summer so far but Dug the Boxer out last weekend and fired it up and it flew great - Hope things slow down a bit here to up the participation level...
thanks chris,
Yes its definitely running rather well..a bit rich on idle but pretty smooth anything above that ..knew the prop was on the minimum size, i used the prop i had laying around 17x6 but trimmed it to 16" because i was only getting 7800rpm on the ground..i thought it was a tad low, i wouldn't have thought it could wind out another 1000 in the air..my magnum fs91 on gas sits on 9300rpm on the ground and doesn't sound like it unwinds much more in the air, i could be wrong..i do play it by ear really..i see berts running a 18x6 prop and still achieving a way better rpm..it seems my setup is struggling to get near that..i never checked my elevation but im not too far above sea level, be around 50/100 metres asl ..
Be great to compare the sound of yours..thanks
Old 09-06-2023, 06:58 AM
  #1830  
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Originally Posted by Rcplanedan
https://youtu.be/CPyO3rvxpz0?si=bAr15ki-Fni7jHZ4
heres a clip of my 20cc seagull models decathlon.
The asp ft160 is running rather well after some fiddling with the dremel on the throttle barrel slot for a fairly good mechanical throttle curve..runs a little rich on idle but runs fairly smoothly on all throttle positions from transmitter stick..plane sat for 5 mins and started second flip with a small amount of throttle..
running a 16x6 turnigy wide blade prop. Its giving 7900rpm , static timing is 30 btc ,and clearly sounds like its reaching around 8500rpm in the air or close maybe 8300rpm
If you ask me, it is going significantly over than 8500, and as Chris said, you're in the danger zone then. I know that mine does a measured 8100 on an 18 x 6 wideblade APC in level flight.
Don't guess, measure. But I DO know for a fact that 16 x 6 is too light for that engine, 17 x 6 allready is. 17 x 8 is where you want to be, and even then I would recommend to NOT hold the throttle wide open in descending flight.

Take a listen to this at approx 1:03 sec. That is 8100 RPM.
Compare that to your engine in a dive (your vid, approx 1:30 and further)...

Sooner or later, a rod will go tourist on you.

But I have to say: Dang, yours runs absolutely marvellous on a simple carb groove mod, way better than I ever managed on mine. For that, absolutely hat off to you. That really runs sweet!
Old 09-06-2023, 07:00 AM
  #1831  
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Originally Posted by Rcplanedan
thanks chris,
Yes its definitely running rather well..a bit rich on idle but pretty smooth anything above that ..knew the prop was on the minimum size, i used the prop i had laying around 17x6 but trimmed it to 16" because i was only getting 7800rpm on the ground..i thought it was a tad low, i wouldn't have thought it could wind out another 1000 in the air..
Mine does 7200 on the ground, in flight-suitable settings. Peaked on the ground it does about 7700, but I need to tune mine 500 RPM rich from "ground-peak" in order to have optimal performance in the air.
Yours really is doing WAY more RPM than mine. Take care because rods are difficult to find, and the material specs of new crankcases (if you lose a rod, you lose a crankcase) are upgraded to unobtanium...

Originally Posted by Rcplanedan
my magnum fs91 on gas sits on 9300rpm on the ground and doesn't sound like it unwinds much more in the air, i could be wrong..
If it does not unwind at least some 500 to 800 RPM, most likely it is running a touch lean. My FS91 does something like 9100 on the ground with an APC 14 x 6, unwinds to close to 10K (9800-ish) in level flight.

Originally Posted by Rcplanedan
i do play it by ear really..
Again, I strongly recommend telemetry. for 35 years I have done everything by ear. I am a mechanic/engineer by profession, and when I started messing with gasoline, I quickly found out that the ear is not enough... Now THAT was a new experience for me...

Last edited by 1967brutus; 09-06-2023 at 07:14 AM.
Old 09-06-2023, 11:41 AM
  #1832  
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"Upgrade to unobtainium".........Ha!, I love it.
Old 09-06-2023, 01:37 PM
  #1833  
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Originally Posted by 1967brutus
Mine does 7200 on the ground, in flight-suitable settings. Peaked on the ground it does about 7700, but I need to tune mine 500 RPM rich from "ground-peak" in order to have optimal performance in the air.
Yours really is doing WAY more RPM than mine. Take care because rods are difficult to find, and the material specs of new crankcases (if you lose a rod, you lose a crankcase) are upgraded to unobtanium...


If it does not unwind at least some 500 to 800 RPM, most likely it is running a touch lean. My FS91 does something like 9100 on the ground with an APC 14 x 6, unwinds to close to 10K (9800-ish) in level flight.


Again, I strongly recommend telemetry. for 35 years I have done everything by ear. I am a mechanic/engineer by profession, and when I started messing with gasoline, I quickly found out that the ear is not enough... Now THAT was a new experience for me...
I went back had another listen to my vid..and definitely you ,s are right it is definitely reving too high ..and i went for another test , i had a 15x12 prop ..same 7900rpm on the ground and it doesn't unwind much and sounds closer to yours now bert, stil got good performance too, i richened topend down to 7700rpm before the flight but she cut out on nose down after a hammered, so tuned back to optimum and was running fine again..
i took a close inspection of the groove in the throttle barrel ..and realised that idle point is almost halfway up that groove so i used a magnified glass and digital vernier to create the groove angle the best i could..even put the dremel disc in a cordless drill to make easy adjustments, (my dremel is stuck on full speed&#128530.
i know i should go grab a 17x8 and see how that goes..
i gotta go back through this thread now and look at crap traps, so far i have a small tank ontop of the fuel tank for exhaust pressure..but is difficult to see the fuel tank filling before the pressure tank takes on fuel..and the dirty dirty crankcase vent is dangling below the exhaust outlet for now..not too messy .
Old 09-06-2023, 11:49 PM
  #1834  
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Originally Posted by Rcplanedan
I went back had another listen to my vid..and definitely you ,s are right it is definitely reving too high ..and i went for another test , i had a 15x12 prop ..same 7900rpm on the ground and it doesn't unwind much and sounds closer to yours now bert, stil got good performance too, i richened topend down to 7700rpm before the flight but she cut out on nose down after a hammered, so tuned back to optimum and was running fine again..
i took a close inspection of the groove in the throttle barrel ..and realised that idle point is almost halfway up that groove so i used a magnified glass and digital vernier to create the groove angle the best i could..even put the dremel disc in a cordless drill to make easy adjustments, (my dremel is stuck on full speed&#128530.
i know i should go grab a 17x8 and see how that goes..
i gotta go back through this thread now and look at crap traps, so far i have a small tank ontop of the fuel tank for exhaust pressure..but is difficult to see the fuel tank filling before the pressure tank takes on fuel..and the dirty dirty crankcase vent is dangling below the exhaust outlet for now..not too messy .
I have looped the connection between fuel tank and craptrap to outside the fuselage, such that that loop can be opened:
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It is the aft, vertical loop on the 2nd picture. When fuelling, I simply pull off that 5 cm of tubing, and the fuel tank will overflow to outside instead of filling up the craptrap.

For muffler pressure, I tap BOTH exhausts, and connect then through a T-connector (preferrably NOT an Y-connector). Due to the alternating pressure pulses, the crap shoots straight through to the other muffler, and that keeps the craptrap mostly dry. Out of all my planes, this particular barely ever needs cleaning the trap, and all there is, usually is a bit of water.

If your twin does not spin up on a smaller prop, it probably means you are running above RPM of peak power, any more RPM is not going to result in more power, but basically, in a WOT dive you're doing what is called a "shaft run". Not advisable. This engine likes heavy props and in a dive, throttle back a bit.

My crankcase vent is rerouted via a T-connector to both rocker covers. No more valve lash adjustments

Bit puzzled by the cutting out on a richer setting. For mine, invariably tuning to peak on the ground results in cutting out at times even in level flight, or at the very least very inconsistent running behaviour.

Genuinely impressed by your approach to groove modification, you seriously took that to levels I never achieved! Hats off!

Last edited by 1967brutus; 09-06-2023 at 11:53 PM.
Old 09-07-2023, 01:21 AM
  #1835  
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Dan, very nice job on the barrel mod, that thing runs like a sewing machine.

I haven't flown in a long time so my ear is a bit out of tune for rpm, but it sounded like that FT160 was winding up pretty tight to me too. The rods! The rods!! is what came to mind while watching your vid.
Old 09-07-2023, 01:00 PM
  #1836  
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Originally Posted by 1967brutus
I have looped the connection between fuel tank and craptrap to outside the fuselage, such that that loop can be opened:
Attachment 2273291
Attachment 2273292

It is the aft, vertical loop on the 2nd picture. When fuelling, I simply pull off that 5 cm of tubing, and the fuel tank will overflow to outside instead of filling up the craptrap.

For muffler pressure, I tap BOTH exhausts, and connect then through a T-connector (preferrably NOT an Y-connector). Due to the alternating pressure pulses, the crap shoots straight through to the other muffler, and that keeps the craptrap mostly dry. Out of all my planes, this particular barely ever needs cleaning the trap, and all there is, usually is a bit of water.

If your twin does not spin up on a smaller prop, it probably means you are running above RPM of peak power, any more RPM is not going to result in more power, but basically, in a WOT dive you're doing what is called a "shaft run". Not advisable. This engine likes heavy props and in a dive, throttle back a bit.

My crankcase vent is rerouted via a T-connector to both rocker covers. No more valve lash adjustments

Bit puzzled by the cutting out on a richer setting. For mine, invariably tuning to peak on the ground results in cutting out at times even in level flight, or at the very least very inconsistent running behaviour.

Genuinely impressed by your approach to groove modification, you seriously took that to levels I never achieved! Hats off!
Thats a great route of all the plumbing, i will be doing mine just the same..great idea 👍
il be trying the 17x8 tomorrow, i am learning that for this plane and engine that i wont have a high powered machine ,but instead it is a brilliant air cruiser, and i have a habbit of being a engine rever🤣.
but i will take a seat with this one and enjoy the steady side of this engine..the awesome sound!!

Old 09-07-2023, 01:05 PM
  #1837  
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Originally Posted by Glowgeek
Dan, very nice job on the barrel mod, that thing runs like a sewing machine.

I haven't flown in a long time so my ear is a bit out of tune for rpm, but it sounded like that FT160 was winding up pretty tight to me too. The rods! The rods!! is what came to mind while watching your vid.
hey thanks..after alot of complications of playing with carbs , getting out the magnified glass and vernier helped me achieve a grove worth using..i was quite amazed how well the engine ran i haven't even bothered to test the other throttle barrell i grooved ,since it runs so well, i know i know,that is reving too high! Il save them rpms for my mag fs91
Old 09-07-2023, 01:08 PM
  #1838  
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Originally Posted by Glowgeek
"Upgrade to unobtainium".........Ha!, I love it.
thats a new one, i was puzzled for a second when i seen that word, never heard that one before(bert)
Well i was told yesterday that a guy has made him self a new conrod for his os ft160..well handy to know, but there is the odd engine still kicking about,,
Old 09-07-2023, 01:18 PM
  #1839  
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Originally Posted by Rcplanedan
thats a new one, i was puzzled for a second when i seen that word, never heard that one before(bert)
I borrowed it from the movie "The Core"...The Core - Wikipedia

Originally Posted by Rcplanedan
Well i was told yesterday that a guy has made him self a new conrod for his os ft160..well handy to know, but there is the odd engine still kicking about,,
It would be great if rods would become availlable again. A GOOD machinist should be able to make one without too much trouble, but I may be a lot of things, a good machinist not being one of them...
Old 09-07-2023, 01:34 PM
  #1840  
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Originally Posted by Rcplanedan
il be trying the 17x8 tomorrow,
That prop should, by my estimate, result in about 60N static pull, and about 100 kph theoretical airspeed, most likely resulting in an actual 100 kph-ish as well, since a not too draggy plane (and your Deccy definitely is slicker than my old BigLift) usually slightly exceeds the pitch-speed.

Mine has, with the 18 x 6W a theoretical airspeed of around 75 kph, but the pitot-tube indicates around 80kph in level flight, no tow. I believe the pitot to be reasonably accurate.
I have a measured static pull of 60N, and the 6,3 kg plane pulls a 70 degree climb indefinitely without stalling, at a climbrate of well over 400 m/min (according to the telemetry I can reach 200 metres within 20 secs from opening the throttle at take-off).
So I would expect your plane, which I estimate to be around 5,5 kilo due to the ASP being relatively heavy, to perform pretty well with near unlimited vertical on a good 17 x 8.
Old 09-07-2023, 05:47 PM
  #1841  
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Originally Posted by 1967brutus
That prop should, by my estimate, result in about 60N static pull, and about 100 kph theoretical airspeed, most likely resulting in an actual 100 kph-ish as well, since a not too draggy plane (and your Deccy definitely is slicker than my old BigLift) usually slightly exceeds the pitch-speed.

Mine has, with the 18 x 6W a theoretical airspeed of around 75 kph, but the pitot-tube indicates around 80kph in level flight, no tow. I believe the pitot to be reasonably accurate.
I have a measured static pull of 60N, and the 6,3 kg plane pulls a 70 degree climb indefinitely without stalling, at a climbrate of well over 400 m/min (according to the telemetry I can reach 200 metres within 20 secs from opening the throttle at take-off).
So I would expect your plane, which I estimate to be around 5,5 kilo due to the ASP being relatively heavy, to perform pretty well with near unlimited vertical on a good 17 x 8.
As always bert, that is great information 👍
on my house scale its 5.8kg ..
in my video the plane would climb rather well almost vertical but run out of steem ..
the 15x12 wasnt any good for much vertical ..
But will see how the apc 17x8 goes.. should do it pretty well
Old 09-07-2023, 10:38 PM
  #1842  
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Originally Posted by Rcplanedan
As always bert, that is great information 👍
on my house scale its 5.8kg ..
in my video the plane would climb rather well almost vertical but run out of steem ..
the 15x12 wasnt any good for much vertical ..
But will see how the apc 17x8 goes.. should do it pretty well
Yeah... At the RPM range this engine is capable of, 15" diameter reduces the tip-velocity quite a bit, and 12" pitch causes the blade profile to stall when airspeed drops off, like in verticals.
17"will return some of that tip velocity and a pitch of 8" reduces the tendency to stall.

Just as an example: I have an older (end '80's, early '90's, the era where they held the middle between ballistic rocketships and hig speed motorgliders) F3A plane, running a 12 x 11 prop at around 9,5K. At take off and during the climb-out the prop is partly stalling, and sounds funny, a bit like a grinding noise. About 10 seconds into the flight, when the plane picks up speed, there is a sudden "jump" in acceleration, the noise stops as if hitting a switch, and the plane really picks up speed.
As long as you keep speed up, vertical is unlimited, but enter a vertical line with insufficient speed and the plane will sag and drop out from it's line.

Your 15 x 12 most likely will face a similar issue.

Last edited by 1967brutus; 09-08-2023 at 11:11 AM.
Old 09-08-2023, 01:02 AM
  #1843  
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Originally Posted by 1967brutus
Yeah... At the RPM range this engine is capable of, 15" diameter reduces the tip-velocity quite a bit, and 12" pitch causes the blade profile to stall when airspeed drops off, like in verticals.
17"will return some of that tip velocity and reduces the tendency to stall.

Just as an example: I have an older (end '80's, early '90's, the era where they held the middle between ballistic rocketships and hig speed motorgliders) F3A plane, running a 12 x 11 prop at around 9,5K. At take off and during the climb-out the prop is partly stalling, and sounds funny, a bit like a grinding noise. About 10 seconds into the flight, when the plane picks up speed, there is a sudden "jump" in acceleration, the noise stops as if hitting a switch, and the plane really picks up speed.
As long as you keep speed up, vertical is unlimited, but enter a vertical line with insufficient speed and the plane will sag and drop out from it's line.

Your 15 x 12 most likely will face a similar issue.
i see,
Yes the 15x12 does make a grinding sort of noisefor sure,ansuthe enginedont quite got the grunt to get that prop moving sufficiently for sure, well atleast the 17x8 prop will do the job just well..but i will take care incase over rev,, got one guy at the field doesn't think that a 4 stroke glow engine has enough fin surface to keep cool, he tells me my saito fa120r3 would overheat, cause he had drama with a fg21 and was upset with his purchase, well il definitely be able to show him how durable the little radial is through this summer..and bit of luck the boxer wont have issues,
Old 09-08-2023, 01:39 AM
  #1844  
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Originally Posted by Rcplanedan
i see,
Yes the 15x12 does make a grinding sort of noisefor sure,ansuthe enginedont quite got the grunt to get that prop moving sufficiently for sure, well atleast the 17x8 prop will do the job just well..but i will take care incase over rev,, got one guy at the field doesn't think that a 4 stroke glow engine has enough fin surface to keep cool, he tells me my saito fa120r3 would overheat, cause he had drama with a fg21 and was upset with his purchase, well il definitely be able to show him how durable the little radial is through this summer..and bit of luck the boxer wont have issues,
The ASP can perform fairly well on gasoline: Mine easily exceeds 2 hp on the APC 18 x 6W according to the propcalculator. Somewhere in the range of 2,2 hp IIRC. EDIT: looking back in my notes, I have seen 2,5 HP after about 20 runhours (fully broken in).
Overheating is a big word, I have never held WOT until it broke down, I limit myself to an indicated 135 deg C at the cylinderhead, but that exact number is meaningless, because if you move the temp-probe 5 mm you will allready get significantly different numbers, so that 135 deg C is for MY engine, with MY probe locations.

Then again, I can, coming from the starting line with a warmed up engine (70 deg C CHT) I can hold WOT for 75~90 seconds with a tow behind the plane before temperature approaches that 135 deg C, and reducing by about 500~1000 RPM from WOT will hold forever, towing or not towing.
90 seconds WOT will bring my plane well over 600 metres of altitude, so in my opinion, there IS no overheating problem: I need to reduce throttle anyway to keep RPM in check during descent.

I can assure you: Starting in early 2016, I have now converted at least 12 engines for own use and about 25~30 for customers, ranging from simple 2-strokes to the ASP radial (which is even at its budget level, still a pricey engine). Some are more heat-sensitive than others, but in all these 7 years I have had exactly ZERO heat related damages.
Some engines I modded for better cooling, some engines I had to baffle, two engines had no cooling issues at all to begin with, and mind you, there is NO substitute for the use of common sense.

On the ground, because of the propwash reducing to zero the closer you get to the prop hub, cooling is WAY less effective than intuition might suggest: The cylinder head usually is closer to the hub than to the tip, and the entire crankcase area does not take part in the heat dissipation on the ground, where it DOES take part in flight. Therefore: Do NOT, NEVER run your engine continuous full throttle on the ground. Short bursts (up to 20~30 seconds, enough to dial in the HS needle, but do not overdo it).
Airborne, cooling increases by a large bit. PROPERLY cowled and baffled engines cool BETTER than fully exposed engines. Air guidance around the engine however, is pretty critical and small changes in airflow can have dramatic large effect.
Without telemetry, you have no info that can make you worry, but you also won't know what caused the issue in case something goes wrong.

Go for the largest prop that the engine can pull: reduced RPM will reduce heat generation.

But in general, in a plane like yours, just reducing throttle in a dive should allready be enough to allow WOT for the rest of the time.

Last edited by 1967brutus; 09-08-2023 at 11:13 AM.
Old 09-08-2023, 02:32 AM
  #1845  
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Overheating is a big word, I have never held WOT until it broke down, I limit myself to an indicated 135 deg C at the cylinderhead, but that exact number is meaningless, because if you move the temp-probe 5 mm you will allready get significantly different numbers, so that 135 deg C is for MY engine, with MY probe locations.

Then again, I can, coming from the starting line with a warmed up engine (70 deg C CHT) I can hold WOT for 75~90 seconds with a tow behind the plane before temperature approaches that 135 deg C, and reducing by about 500~1000 RPM from WOT will hold forever, towing

I can assure you: Starting in early 2016, I have now converted at least 12 engines for own use and about 25~30 for customers, ranging from simple 2-strokes to the ASP not overdo it).
Airborne, cooling increases by a large bit. PROPERLY cowled and baffled engines cool BETTER than fully exposed engines. Air guidance around the engine however, is pretty critical and small changes in airflow can have dramatic large effect.
Without telemetry, you have no info that can make you worry, but you also won't know what caused the issue in case something goes wrong.

Go for the largest prop that the engine can pull: reduced RPM will reduce heat generation.

But in general, in a plane like yours, just reducing throttle in a dive should allready be enough to allow WOT for the rest of the time.[/QUOTE]
Definitely my saito fa120r3 is a test engine..it cops full throttle for most of my 10/15min flyts will go a solid 2/3mins before easing the throttle for a moment..i would say its reving about 9k or so and definitely peaks well on a steep decent..it seems rather happy and no noticeable change ..usually 100ml per 10min flight and its definitely seen 10lt at a field plus some litres of fuel doing ground time when i first got the engine and would have also drank 2lt of glow at the start of ownership, and the previous owner broke in the engine, great little engine, punished i know..
I will go easy on the boxer
Old 09-08-2023, 07:29 AM
  #1846  
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Originally Posted by Rcplanedan
Definitely my saito fa120r3 is a test engine..it cops full throttle for most of my 10/15min flyts will go a solid 2/3mins before easing the throttle for a moment..i would say its reving about 9k or so and definitely peaks well on a steep decent..it seems rather happy and no noticeable change ..usually 100ml per 10min flight and its definitely seen 10lt at a field plus some litres of fuel doing ground time when i first got the engine and would have also drank 2lt of glow at the start of ownership, and the previous owner broke in the engine, great little engine, punished i know..
I will go easy on the boxer
The issue with "OS-derived" engine designs, is that the engine has a steel liner with a topflange, on which the head rests.
Aluminium is an excellent heat conductor, steel is not, not so much.
Virtually all Saito's have a cylinder and liner cast in one piece out of aluminium, with the bore directly chrome plated. This results in excellent heat dissipation, and Saito's seem to have zero issues with the heat generated by gasoline. They run high, but acceptable temperatures.
The OS-derivates, due to that "heat-dam" (the steel liner) are having trouble getting the heat removed from the head. If I measure the temperature at the top fin of the cylinder casting of any of my ASP's, I see no higher than 80 deg C even at WOT.
If I measure at the lowest fin of the head,, just 3 mm higher up on the engine, I see 145 degrees within a minute.

The issue is not so much the cylinder head temperature, the 145 degrees in itself is no problem. The issue is the temperature of the exhaust valve disc. This temperature is unmeasurable, but the gasoline autoignition temperature is around 375 deg C.
At that temperature, ignition of the fuel by sheer contact with the valve is guaranteed, BUT.... it takes time (the fuel needs to heat up before it ignites, and normally, the spark arrives WAY earlier than that the critical point is reached).
At or around 600 deg C, ithis time delay approaches the regular ignition timing (arrival of the spark), and once you pass this point, ignition will occur BEFORE the spark. This too early ignition will not only rob power, it will also cause a sudden increase in thermal and mechanical stress. All you need to do is to reduce a bit of throttle (half is enough) and the danger is gone, but of course you then also need to allow for the engine temperature to drop.

In my experience, this critical temperature is reached at (for my preferred probe location) an indicated 145 degrees.

I have so far never seen a Saito exceed 140 deg CHT, and never noticed the drop-off in power due to pre-ignition, but I have seen it in OS and OS derivates. So don't feel too bad about punishing the Saitos...

Twostrokes, due to lack of an exhaustvalve, seem less affected, but around 150~170 degrees CHT, I have seen signs of the ground electrode of the sparkplug spoiling the fun with similar behaviour.
Old 09-08-2023, 08:40 AM
  #1847  
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I do enjoy the tech talk, Bert. Even though your numbers are anecdotal based on your temp probe placement the science of controlled combustion is always an interesting read.

My Saitos have handled the heat quite well on the bench, whether FG gassers or conversions with heat insulators on the intake tract. Still haven't flown a conversion yet, life is still getting in the way. I fear it's going to continue on this way for a time longer.
Old 09-08-2023, 09:02 AM
  #1848  
1967brutus
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Originally Posted by Glowgeek
I do enjoy the tech talk, Bert. Even though your numbers are anecdotal based on your temp probe placement the science of controlled combustion is always an interesting read.

My Saitos have handled the heat quite well on the bench, whether FG gassers or conversions with heat insulators on the intake tract. Still haven't flown a conversion yet, life is still getting in the way. I fear it's going to continue on this way for a time longer.
Yeah, I want to be VERY clear about that, that temperatures mentioned by me, are valid for MY engines, because of temp sensor placement. It is extremely easy for someone not aware of this to assume everything is AOK because he sees, say, 85 deg tops at WOT because of sensor placement.
Glad to see a shared interest in combustion control. That subject fascinates me to no end. Especially "methods to figure out what is going on in places where the human eye has no direct view".

As a funny anecdote (since we're talking "anecdotal" anyway): When I initially ran my Boxer, I saw very different temperatures between the two units, and the difference was not consistent, no matter what I did. From pre-solenoid to well after.
Spent ages trying to get those cylinders to run more close to each other, never a positive result. Not even a better consistency in the relation "throttle position => deviation". It was all over the place. More so pre-solenoid, it improved with the solenoid but remained elusive.
Until I took the time to locate the probes to as exactly as I could get them in the same location on both heads. I think I got it to within 1 or 2 mm, and BAM!!!! from 3000 RPM to 7000 RPM within one, maybe 2 degrees equal. Below 3000 one cylinder really cools down to about 20 deg C lower, above 7000 the other cylinder rises about 10, maybe 15 degrees over, but that's it, and both deviations only happen after prolonged constant RPM in those ranges. Normal use (variable throttle as needed) the cylinders run equal.

One could argue, what is the point? Those temperatures are going to be what they are going to be, no?

Well, here's the point: The Taranis can work with averages of multiple values. So instead of my engine temperature(s) being called out as two numbers (which I have to remember, then mentally compare, in order to figure out if everything is OK), I have a single "average" value which is easier to mentally process, and for each individual cylinder an alarm if the actual temperature deviates too much from average. So anything that will cause one cylinder to misfire or overheat will trigger an alarm.
Two cylinders, it is really distracting from flying to have the TX call out two temperatures and taking time to judge those numbers, but on the radial, 5 numbers were simply impossible to remember and judge. So I needed a simple average, and a deviation alarm.

On the radial, it was sheer HELL to get all 5 probes in the same location, but it was well worth the trouble, because I would never have managed to figure out fuel distribution without that. As it is, I have the average on a switch (voice call out) and a deviation alarm calls out that single cylinders temperature every 5 seconds, easy enough to judge whether one unit is running hot or is misfiring. The call-out stops when I extend the landing gear in order to minimize distraction in case immediate landing is warranted. Works like a charm.

Last edited by 1967brutus; 09-08-2023 at 11:53 AM.
Old 09-08-2023, 09:47 AM
  #1849  
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Originally Posted by 1967brutus
The issue with "OS-derived" engine designs, is that the engine has a steel liner with a topflange, on which the head rests.
Aluminium is an excellent heat conductor, steel is not, not so much.
Virtually all Saito's have a cylinder and liner cast in one piece out of aluminium, with the bore directly chrome plated. This results in excellent heat dissipation, and Saito's seem to have zero issues with the heat generated by gasoline. They run high, but acceptable temperatures.
The OS-derivates, due to that "heat-dam" (the steel liner) are having trouble getting the heat removed from the head. If I measure the temperature at the top fin of the cylinder casting of any of my ASP's, I see no higher than 80 deg C even at WOT.
If I measure at the lowest fin of the head,, just 3 mm higher up on the engine, I see 145 degrees within a minute.

The issue is not so much the cylinder head temperature, the 145 degrees in itself is no problem. The issue is the temperature of the exhaust valve disc. This temperature is unmeasurable, but the gasoline autoignition temperature is around 375 deg C.
At that temperature, ignition of the fuel by sheer contact with the valve is guaranteed, BUT.... it takes time (the fuel needs to heat up before it ignites, and normally, the spark arrives WAY earlier than that the critical point is reached).
At or around 600 deg C, ithis time delay approaches the regular ignition timing (arrival of the spark), and once you pass this point, ignition will occur BEFORE the spark. This too early ignition will not only rob power, it will also cause a sudden increase in thermal and mechanical stress. All you need to do is to reduce a bit of throttle (half is enough) and the danger is gone, but of course you then also need to allow for the engine temperature to drop.

In my experience, this critical temperature is reached at (for my preferred probe location) an indicated 145 degrees.

I have so far never seen a Saito exceed 140 deg CHT, and never noticed the drop-off in power due to pre-ignition, but I have seen it in OS and OS derivates. So don't feel too bad about punishing the Saitos...

Twostrokes, due to lack of an exhaustvalve, seem less affected, but around 150~170 degrees CHT, I have seen signs of the ground electrode of the sparkplug spoiling the fun with similar behaviour.
As an additional to this post: Favoured probe locations (MY favoured positions): on single cylinder foursstrokes, I "jam" the probe between the lowest set of fins on the head, dead center between intake and exhaust port. That location is shielded from the airflow and seems to give a repeatable reading with predictable engine behaviour. 145 deg C, approximately, is where I see the power loss occurring. I limit myself to 135 deg C by means of an alarm via telemetry, and when possible, 140 degrees causes the throttle to reduce to approximately half as an additional safety measure. This position also is used for the radial, which basically is 5 singles in a circle WRT cylinder orientation to the airflow.
On the boxer, placement between the ports will expose the probe to the airflow, so here I use the position most shielded at the rear of the head, on the intake side. This affects read out a bit, power loss seems to occur at a slightly lower indicated temperature (and I have the limit at 130 degrees, but because of the towing use of the plane, no automatic throttle reduction.
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In 2-strokes, I grind a channel in the head, where the probe is clamped between head and cylinder.
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Old 09-09-2023, 03:08 AM
  #1850  
Rcplanedan
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Nice couple of flights with the boxer today with a 17x8 apc propeller, flys rather well paced at half throttle, and the top rpm in a dive is not reving too high , im learning to use max throttle for aerobatic manoeuvres and reduce throttle otherwise,

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