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Electronic solutions to modifying glow engines of all sizes to gasoline

Old 09-21-2022, 03:27 AM
  #851  
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Originally Posted by Cat 1 View Post
Has anyone set Eyes on a turbo header? - just wondering as their Patent Language is very odd - I searched the patent and the claim is an "ornamental design for an exhaust manifold" and makes no claim or does not document any internal structure design. Seems like the patent only covers "how it looks" not what's inside... Is it just a Header?

I think I might take a stab at building some custom Chambers for the twin... Autumn is upon us here and I probably won't get into the air with the twin before the cold sets in... some R&D time this winter...

Chris
I had my hands on one last year, on a customer's Saito FA100. I borrowed it to do testing on a few other Saito engines and the gains over the stock cast mufflers ranged from 180 to 220 rpm.

I had a close look at it, nothing special, no pipe protruding into the slightly larger expansion chamber, so no anti-reversion. I attributed the top end gains to the very short header, just a threaded stud really, and the unbaffled design. There is really nothing special going on, just a low back pressure system. It didn't make as much tank pressure as the Saito cast mufflers either, I had to richen the hsn on the engines tested.
Old 09-21-2022, 07:13 AM
  #852  
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Originally Posted by 1967brutus View Post
I don't have an oven that reaches that kind of temperatures...
But I think I can simply use a piece of steel pipe, put the Alu inside and heat the pipe to dull red for a few minutes. That should be about 500 deg C andspread the heat fairly evenly, especially if I pre-cut the aluminium tube to pieces of approx 10 cm
How long to maintain the temperature? Slow cool or rapid cool to anneal Aluminium?
I anneal copper a lot (where you cool the item in water in order to maintain annealed state, but never did that with aluminium.

Edit: I assume at least that this stuff is annealable, since I think this type of tubing is made by extruding.
Can it be re-hardened, and if so, how? Heating again then rapid cooling?
++

That will work with the heated pipe... just leave it in there for 5-10 minutes... the surface of the aluminum will change in appearance as it reaches the anneal temp.. its a subtle change.. compare it to one that hasn't been annealed... Aluminum work hardens through the extrusion process, and heating will anneal it... quenching in water or oil has no effect on re-tempering the aluminum... only through work hardening, or chemical harden processes.

Originally Posted by 1967brutus View Post
Can it be re-hardened, and if so, how? Heating again then rapid cooling?
Not in that same sense.... liquid nitrogen is used to rapidly work harden at the molecular level by rapid deep contraction and expansion of the part... water tempering does something similar, but the mass of the part is key to getting it to work harden by contraction and expansion... try it, it will take a few cycles to get it to where it will start to temper.


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Old 09-21-2022, 07:24 AM
  #853  
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Originally Posted by Glowgeek View Post
I had my hands on one last year, on a customer's Saito FA100. I borrowed it to do testing on a few other Saito engines and the gains over the stock cast mufflers ranged from 180 to 220 rpm.

I had a close look at it, nothing special, no pipe protruding into the slightly larger expansion chamber, so no anti-reversion. I attributed the top end gains to the very short header, just a threaded stud really, and the unbaffled design. There is really nothing special going on, just a low back pressure system. It didn't make as much tank pressure as the Saito cast mufflers either, I had to richen the hsn on the engines tested.
Well there you go, so their patent only covers their design and construction... adding the reversion chamber will improve on the design, the trap chamber will capture the pressure waves coming off the end of the inlet tube that protrudes into the chamber, still retaining the low restriction... it may improve on the amount of pressure provided to the fuel tank, but you can also increase the ID of the pressure tap as well.
Old 09-21-2022, 09:31 AM
  #854  
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Originally Posted by John_M_ View Post
++

That will work with the heated pipe... just leave it in there for 5-10 minutes... the surface of the aluminum will change in appearance as it reaches the anneal temp.. its a subtle change.. compare it to one that hasn't been annealed... Aluminum work hardens through the extrusion process, and heating will anneal it... quenching in water or oil has no effect on re-tempering the aluminum... only through work hardening, or chemical harden processes.



Not in that same sense.... liquid nitrogen is used to rapidly work harden at the molecular level by rapid deep contraction and expansion of the part... water tempering does something similar, but the mass of the part is key to getting it to work harden by contraction and expansion... try it, it will take a few cycles to get it to where it will start to temper.
Great, thanks!
Old 09-21-2022, 09:32 AM
  #855  
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Enlarging the ID of the expansion chamber in relation to the inlet pipe seems to create the largest gains in pressure, without creating more restriction/back pressure. I tried enlarging the pressure nipple and pressure lines using a straight header years ago and saw no measureable gains in tank pressure, probably due to the low flow rate. At that low of a flow rate the pressure measures virtually the same at both ends of the pressure line.

I abandoned the Saito straight pipe on a Saito FA-65 which provided approx 0.3 at full throttle and swapped it for Saito pipe with a small expansion chamber and the tank pressure improved to approx 0.6. Swapped that for a Saito cast muffler with the large expansion chamber and saw just over 1.0 psi. The Saito cast mufflers, sometimes called trash can mufflers, are not the sexiest looking things out there but they do perform well for a baffled design. Enlarging the baffle holes in the muffler tail piece wakes the engine up a bit but there are limitations in how far you can go before the tail piece becomes structurally unsound.
Old 09-21-2022, 10:34 AM
  #856  
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Lonnie and all,

Im really trying to wrap my head around this tap pressure vs back presssure issue - I fully underrstand difuser theroy (from turbines) and that slowing gas flow down will increase the pressure - The trouble with applying this to and exhaust system is that its a pulsed flow of high pressure and low presure waves, and it is an intermittent flow (flowing about 25% of the time in my estimation). Is it actually possible to have a muffler pressure tap produce a relitively high constant pressure while having a low back pressure exposure for the engine. The more I think about this, the more I think that the tap pressure is simply a function of the back pressure the system provides and thus as we strive to make a system produce more tap pressure we will affect performance. Johns idea of a revision area is interesting but i cant wrap my head around it. I have read the "tech" on some applications of "resonance chambers" on 4 stroke bikes but it has more to do with a bit of "scavanging " during the valve overlap.

Here is my issue - If we used a "megaphone" type pipe - based on diffuser theroy,one would think that it would be possible to find a high pressure tap point based on difusion - but we know this is not the case as the pipe is open ended and at atmospheric pressure at its outlet and there is a constant pressure drop. The only way to make this pipe produce tap pressure would be to restrict its outlet and negate the effect of the megaphone.

Its an interesting issue as this is one of the few cases with our engines where we don't really require a muffler (at least where I fly) I would love to have a big straight pipes on it but it seems to negate the ability to get a usable amount of tank pressure.

Lonnie - How did the Saito straight/small expansion/ large expansion exhaust compare for power output....

Old 09-21-2022, 11:18 AM
  #857  
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Originally Posted by Cat 1 View Post
Here is my issue - If we used a "megaphone" type pipe - based on diffuser theroy,one would think that it would be possible to find a high pressure tap point based on difusion - but we know this is not the case as the pipe is open ended and at atmospheric pressure at its outlet and there is a constant pressure drop. The only way to make this pipe produce tap pressure would be to restrict its outlet and negate the effect of the megaphone.
That megaphone thing is not valid, because that is basically an open system. what a megaphone exhaust does, is NOT creating a high pressure at the wide exit. The atmosphere is the bigger system, so the atmosphere is dictating its pressure at the outlet of the megaphone.
What the megaphone exhaust does, is that BECAUSE the pressure at the wide end is atmospheric, and the pressure at the narrow end HAS to be lower, it generates a kinda-sorta "pull", the pressure at the exhaust valve (once open and a "stable flow" is established) is actually lower than atmospheric. Or at least, that is the intention and reasoning behind the megaphone exhaust system, and why it was used in racing.

But if you have a muffler with an inlet, a body and a tailpipe, the body will have a higher pressure than the restrictions of headerpipe and the tailpipe on their own would create.

FWIW: I did check the backpressure of my Boxers twin mufflers (they are parallel connected to tankpressure via a T-connection). It made a difference of 5~6 clics of the main needle.
Old 09-21-2022, 11:22 AM
  #858  
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Here's a good read:

https://www.motortrend.com/how-to/ct...ine-reversion/
Old 09-21-2022, 02:03 PM
  #859  
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Originally Posted by Cat 1 View Post
Lonnie and all,

Im really trying to wrap my head around this tap pressure vs back presssure issue - I fully underrstand difuser theroy (from turbines) and that slowing gas flow down will increase the pressure - The trouble with applying this to and exhaust system is that its a pulsed flow of high pressure and low presure waves, and it is an intermittent flow (flowing about 25% of the time in my estimation). Is it actually possible to have a muffler pressure tap produce a relitively high constant pressure while having a low back pressure exposure for the engine. The more I think about this, the more I think that the tap pressure is simply a function of the back pressure the system provides and thus as we strive to make a system produce more tap pressure we will affect performance. Johns idea of a revision area is interesting but i cant wrap my head around it. I have read the "tech" on some applications of "resonance chambers" on 4 stroke bikes but it has more to do with a bit of "scavanging " during the valve overlap.

Here is my issue - If we used a "megaphone" type pipe - based on diffuser theroy,one would think that it would be possible to find a high pressure tap point based on difusion - but we know this is not the case as the pipe is open ended and at atmospheric pressure at its outlet and there is a constant pressure drop. The only way to make this pipe produce tap pressure would be to restrict its outlet and negate the effect of the megaphone.

Its an interesting issue as this is one of the few cases with our engines where we don't really require a muffler (at least where I fly) I would love to have a big straight pipes on it but it seems to negate the ability to get a usable amount of tank pressure.

Lonnie - How did the Saito straight/small expansion/ large expansion exhaust compare for power output....
Indeed, the engine is creating exhaust gas pulses about 25% of the time, but before the tank can bleed off pressure back through the nipple it gets hit again with another pressure pulse. When I tee in a 0-5 psi gauge to the pressure line the gauge needle does oscillate because it happening too quick.

According to the Bernoulli principle as velocity drops pressure rises, if mass remains constant. That why the pressure nipples are located near the point where the inlet pipe enters the expansion chamber. The bigger the expansion chamber in relation to the inlet, the higher the developed pressure is. In the case of a straight header velocity slows more over the length of the pipe, so a pressure nipple will see the highest pressure near the end of the pipe.

On the FA65 tests, the straight pipe and the pipe with the brass expansion chamber made the same power and had the same size outlet. The cast muffler had a larger expansion chamber and a larger outlet and made the same power. I'm assuming the larger outlet was needed due to the back pressure created by the baffle.

Last edited by Glowgeek; 09-21-2022 at 02:20 PM.
Old 09-21-2022, 03:39 PM
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Where did you get the idea you could pressure tap off a megaphone style exhaust from my example regarding the conical exhaust outlet... I just stated it is anti reversion by design, it stops the reversion wave from returning up down the exhaust system, it can only propagate forward along the cone... an anti-reversion chamber is an expansion chamber with a reversion trap built into the chamber which traps the pressure wave off the end of the inlet tube... you should be able to tap the reversion chamber for tank pressure.

So on the boxer, the longer the exhaust header length is, the larger the ID of the tube should be... The anti reversion chamber should be in the straight section of the 8mm ID exhaust tube, close to the exhaust port... then come off the chamber with 12mm ID, or even 10mm ID, as long as the outlet tube is larger than the inlet ID... 12mm ID may be too large for the length of your particular exhaust run... you're creating a series of tube dia that reduce the overall restriction, but traps any exhaust reversion at the reversion chamber.
Old 09-21-2022, 07:51 PM
  #861  
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I've typed long winded explanations out twice and lost them as I clicked the wrong button - long day!!! John - I didn't mean to suggest that you implied a megaphone would work - that's something that lived in my head and it was because I often confuse theory from different processes - Usually incorrectly I think I get it now but will read up on the anti-rev theory a bit more... Bert and Lonnies comments show that Increased tap pressure is possible without serious power losses...

SOOOO.... Since we have an electronic needle valve how about electronic tank pressure control - I can here the groans now BUT... I did a little mock up of the "method" and I think it would work in a relatively simple form. The test pressurizes a 4oz tank using a tiny air pump that runs on 5-6v with a low amp draw . Im using a needle valve to create a Bleed (for testing) but that would be covered by a fixed orifice. As the test shows its easy to achieve a very linear and repeatable tank pressure based on voltage and good response. My thought would be to use an simple MPU (Arduino) to measure engine RPM from the ignition and set a tank pressure (as pump voltage) on a simple curve - the tank pressure would follow RPM and should mimic muffler pressure - except its tuneable and could be adjusted to help out as the engine unloads in the air.

positives would be no crap trap and tune-ability - you know the negatives

video just finished processing - here it is.. gauge is in mmHG - 50=1PSI

Old 09-22-2022, 03:22 AM
  #862  
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Very cool Chris.

How is the pressure bleeding off so quickly? Carb fully open?

As it is, when the tank is at full pressure (wot) the tank pressure bleeds off fairly quickly through the muffler pressure tap when throttled down.

Last edited by Glowgeek; 09-22-2022 at 03:39 AM.
Old 09-22-2022, 04:32 AM
  #863  
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Originally Posted by Cat 1 View Post
I've typed long winded explanations out twice and lost them as I clicked the wrong button - long day!!! John - I didn't mean to suggest that you implied a megaphone would work - that's something that lived in my head and it was because I often confuse theory from different processes - Usually incorrectly I think I get it now but will read up on the anti-rev theory a bit more... Bert and Lonnies comments show that Increased tap pressure is possible without serious power losses...

SOOOO.... Since we have an electronic needle valve how about electronic tank pressure control - I can here the groans now BUT... I did a little mock up of the "method" and I think it would work in a relatively simple form. The test pressurizes a 4oz tank using a tiny air pump that runs on 5-6v with a low amp draw . Im using a needle valve to create a Bleed (for testing) but that would be covered by a fixed orifice. As the test shows its easy to achieve a very linear and repeatable tank pressure based on voltage and good response. My thought would be to use an simple MPU (Arduino) to measure engine RPM from the ignition and set a tank pressure (as pump voltage) on a simple curve - the tank pressure would follow RPM and should mimic muffler pressure - except its tuneable and could be adjusted to help out as the engine unloads in the air.

positives would be no crap trap and tune-ability - you know the negatives

video just finished processing - here it is.. gauge is in mmHG - 50=1PSI

https://www.youtube.com/watch?v=wi09xpu9jBk
Oh I've lost posts that way, and in the process of the turmoil caused by hitting the wrong button, lost my train of thought.

The reversion chamber maintains exhaust gas velocity through the trap chamber... the pressure pulses coming off the end pipe inside the chamber is what is trapped, and then dissipated back out the outlet... there should be sufficient pressure in the reversion chamber to tap for tank pressure... and then adjust the pressure tap orifice size to get the tank pressure to follow exhaust pressure.

The electronic tank pressure sounds like a viable idea... the only issue would be the lag in response with throttle changes... the air pump could run continuously pressurizing a small reserve air tank, and then use the arduino and another solenoid air control valve to bleed the reserve air pressure into the fuel tank, using your fuel mix curve as a reference to control tank pressure.
Old 09-22-2022, 05:27 AM
  #864  
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Originally Posted by Glowgeek View Post
Very cool Chris.

How is the pressure bleeding off so quickly? Carb fully open?

As it is, when the tank is at full pressure (wot) the tank pressure bleeds off fairly quickly through the muffler pressure tap when throttled down.
the pressure is bleeding off through the "metering orfice" (needle valve) and its air only - part of the tank pressure system. I think it decays quick enough not to cause issues...
Originally Posted by John_M_ View Post
The electronic tank pressure sounds like a viable idea... the only issue would be the lag in response with throttle changes... the air pump could run continuously pressurizing a small reserve air tank, and then use the arduino and another solenoid air control valve to bleed the reserve air pressure into the fuel tank, using your fuel mix curve as a reference to control tank pressure.
The system as shown John is capable of pressurizing the tank quite quickly (and depressurizing also) . In my estimation it is capable of "moving" fast enough as to not cause issues - I have watched tank pressure on a muffler tap install and it moves much slower than this is capable of..watch at the 45-55 second mark of the video and you can see the response - this is into an empty 4oz tank

If I can dig up a small brushed speed control out of my parts bins I will test it "on the stand" just using a receiver output to drive speed and see how it works...

Last edited by Cat 1; 09-22-2022 at 05:31 AM.
Old 09-22-2022, 06:31 AM
  #865  
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Originally Posted by Cat 1 View Post
I've typed long winded explanations out twice and lost them as I clicked the wrong button - long day!!! John - I didn't mean to suggest that you implied a megaphone would work - that's something that lived in my head and it was because I often confuse theory from different processes - Usually incorrectly I think I get it now but will read up on the anti-rev theory a bit more... Bert and Lonnies comments show that Increased tap pressure is possible without serious power losses...

SOOOO.... Since we have an electronic needle valve how about electronic tank pressure control - I can here the groans now BUT... I did a little mock up of the "method" and I think it would work in a relatively simple form. The test pressurizes a 4oz tank using a tiny air pump that runs on 5-6v with a low amp draw . Im using a needle valve to create a Bleed (for testing) but that would be covered by a fixed orifice. As the test shows its easy to achieve a very linear and repeatable tank pressure based on voltage and good response. My thought would be to use an simple MPU (Arduino) to measure engine RPM from the ignition and set a tank pressure (as pump voltage) on a simple curve - the tank pressure would follow RPM and should mimic muffler pressure - except its tuneable and could be adjusted to help out as the engine unloads in the air.

positives would be no crap trap and tune-ability - you know the negatives

video just finished processing - here it is.. gauge is in mmHG - 50=1PSI

https://www.youtube.com/watch?v=wi09xpu9jBk
It MIGHT work, but a "tuned" tankpressure would need two parameters as imput, throttle position and RPM. And I think the first is easy, but the 2nd might show a very non-linear curve. Technically I do not see issues creating something like that, but determining those two curves... THAT might prove to require countless hours on a testbed with a variable load (for example a controllable pitch propeller) in order to simulate the unloading in the air.

I don't think the ratio between efforts and gains justifies this. I mean: setting a fuel curve is hard enough as it is for some, and all that effort just to get rid of the craptrap...

Then another thing: you do not NEED to make a separate tank pressure system. You can also "simply" add an RPM feedback on the fuel metering. But again, same problem: HOW to determine the required curves.

Mind you, when a random car or bike engine is developed from new, hundreds of testbench hours are spent to get the EFI mapping right for all conceivable running conditions.
IF we want an electronically controlled varable tank pressure (or an RPM dependant electronic fuel supply), then THAT is the direction we are going, but contrary to cars and bikes, where the manufacturer does this once then churns out hundreds of thousands of units, for us modellers we are going to do this each and every single time we commission an new plane.

So I think this is not a viable way. But that is just my opinion, and I know Chris is way more resourceful than I am...
Old 09-22-2022, 11:16 AM
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Originally Posted by Cat 1 View Post
the pressure is bleeding off through the "metering orfice" (needle valve) and its air only - part of the tank pressure system. I think it decays quick enough not to cause issues...


The system as shown John is capable of pressurizing the tank quite quickly (and depressurizing also) . In my estimation it is capable of "moving" fast enough as to not cause issues - I have watched tank pressure on a muffler tap install and it moves much slower than this is capable of..watch at the 45-55 second mark of the video and you can see the response - this is into an empty 4oz tank

If I can dig up a small brushed speed control out of my parts bins I will test it "on the stand" just using a receiver output to drive speed and see how it works...
Oh, some other metering orifice, other than the carb. OK

I have a small tablet screen and can't see much detail in vids.

Last edited by Glowgeek; 09-22-2022 at 11:19 AM.
Old 09-22-2022, 03:12 PM
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Originally Posted by Cat 1 View Post
the pressure is bleeding off through the "metering orfice" (needle valve) and its air only - part of the tank pressure system. I think it decays quick enough not to cause issues...


The system as shown John is capable of pressurizing the tank quite quickly (and depressurizing also) . In my estimation it is capable of "moving" fast enough as to not cause issues - I have watched tank pressure on a muffler tap install and it moves much slower than this is capable of..watch at the 45-55 second mark of the video and you can see the response - this is into an empty 4oz tank

If I can dig up a small brushed speed control out of my parts bins I will test it "on the stand" just using a receiver output to drive speed and see how it works...
Well you could do the same with managing crankcase pressure and do away with the electric air pump and support system for that... and regarding the sluggish response from the muffler pressure, some of that can be dealt with by opening up the orifice in the pressure tap... You were going to also try the clone of the cline demand regulator... that would be interesting to see how that works out with the electronic mixture control... I run one on the boxer running CDi / glow fuel, and it works as intended, primarily used to stop the wing tanks from siphoning, but it also stops the fuel from entering the venturi under tank pressure.

Last edited by John_M_; 09-22-2022 at 06:55 PM. Reason: Humm interesting ! going to make copies
Old 09-22-2022, 04:22 PM
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Originally Posted by 1967brutus View Post
It MIGHT work, but a "tuned" tankpressure would need two parameters as imput, throttle position and RPM. And I think the first is easy, but the 2nd might show a very non-linear curve. Technically I do not see issues creating something like that, but determining those two curves... THAT might prove to require countless hours on a testbed with a variable load (for example a controllable pitch propeller) in order to simulate the unloading in the air.

I don't think the ratio between efforts and gains justifies this. I mean: setting a fuel curve is hard enough as it is for some, and all that effort just to get rid of the craptrap...

Then another thing: you do not NEED to make a separate tank pressure system. You can also "simply" add an RPM feedback on the fuel metering. But again, same problem: HOW to determine the required curves.

So I think this is not a viable way. But that is just my opinion, and I know Chris is way more resourceful than I am...
Here is what I'm thinking Bert... When we do a "conversion" now, we use muffler pressure and happily accept whatever it can give us with no tuning whatsoever - I don't think much tuning will have to go into making the system perfect as we can't really tune the curve on the muffler tap. It will give us that ability to "tune" the rpm response as the engine unloads as now we just accept what the exhaust system gives us - and in most cases we end up "setting rich" on the ground to compensate. I think I will have to try this just to see if its viable - my plan is to use a simple speed controlled unit on a radio curve to test initial viability in supplying pressure.

John - I haven't abandoned the Regulator yet and will probably revisit it soon also as I have already dumped 2 half tanks of fuel on the shop floor as a result of not paying attention attention to the laws of siphon.
Old 09-22-2022, 04:59 PM
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Originally Posted by Cat 1 View Post
Here is what I'm thinking Bert... When we do a "conversion" now, we use muffler pressure and happily accept whatever it can give us with no tuning whatsoever - I don't think much tuning will have to go into making the system perfect as we can't really tune the curve on the muffler tap. It will give us that ability to "tune" the rpm response as the engine unloads as now we just accept what the exhaust system gives us - and in most cases we end up "setting rich" on the ground to compensate. I think I will have to try this just to see if its viable - my plan is to use a simple speed controlled unit on a radio curve to test initial viability in supplying pressure.

John - I haven't abandoned the Regulator yet and will probably revisit it soon also as I have already dumped 2 half tanks of fuel on the shop floor as a result of not paying attention attention to the laws of siphon.
Kind of what I was thinking too. Tuning tank pressure doesn't have to be overly complicated. Maybe set the tank pressure to .25 psi at idle and 1 psi at peak rpm with a straight curve, then tune the needles and fuel curve as normal. To simulate unloading replace the prop with one with a lighter loading and adjust peak rpm with tank pressure. Might be a rough feasabilty test for bench testing.

After all, we're just looking for an adequate rise in tank pressure for the prop unloading 500-1500 rpm for most sport planes.
Old 09-22-2022, 07:17 PM
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You can simulate the rise and fall in tank pressure, to follow engine rpm, and mimic muffler pressure... but you can do what Cat's doing with the airpump, but using crankcase pressure and modulate that with another solenoid, using the same arduino used for the fuel mixture... similar to the OS EFi tank setup using a remote mixture needle to fine tune the bias pressure, and modulate the pressure in the tank with the solenoid valve... in both scenarios, you get rid of the crap trap, which I would be in favor of... you need to ovoid adding additional ancillary equipment, or its going to get overly complicated / complexed.... it will start to look like a distillery, if it doesn't already.
Old 09-23-2022, 02:19 AM
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Originally Posted by Cat 1 View Post
Here is what I'm thinking Bert... When we do a "conversion" now, we use muffler pressure and happily accept whatever it can give us with no tuning whatsoever - I don't think much tuning will have to go into making the system perfect as we can't really tune the curve on the muffler tap. It will give us that ability to "tune" the rpm response as the engine unloads as now we just accept what the exhaust system gives us - and in most cases we end up "setting rich" on the ground to compensate. I think I will have to try this just to see if its viable - my plan is to use a simple speed controlled unit on a radio curve to test initial viability in supplying pressure.
The thing is: That muffler pressure, whether it is tunable or not, it is a "natural relation" and we can tune the fuel supply for it without actually knowing what the relation between unloading and muffler pressure actually is. One thing is sure: that relation is NOT linear. Just because of the nature of things, it will be something with a square in it or something like that. But because it is a natural relation, it never can be too much or too little. All you need is "sufficient muffler pressure" and things will work out all by themselves.
That changes when you replace the muffler pressure for an artificial tank pressure. Now you need to recreate that relation between unloading and tankpressure, and you need to map that for all conceivable throttle positions and (un)loading conditions.

I have no idea how to get that mapping done for the average modeller.

It sure is an interesting idea, I just don't think it will be doable for Joe Average. But it sure will be educating.
The thing I would do first is take a normal set-up (muffler pressurized) with a U-tube for muffler pressure readings, and take those readings with a number of repeatable throttle positions and 3 or four different props (simulating unloading) to get an idea how unloading at partload and full throttle affects muffler pressure under the differing conditions.

Last edited by 1967brutus; 09-23-2022 at 02:30 AM.
Old 09-23-2022, 03:25 AM
  #872  
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I'm interested in how these gas conversions would work using only programmable tank pressure, no solenoid and no crap trap. I'll bet it would work, even if just ok. After all, there are quite a few people out there who are happy enough with running gas in their glow engines with no mods other than CDI. I would be happy doing that too, if not for the overly rich midrange.

But yes, as Chris stated there are other downfalls. Crap traps weigh less than air pumps and the extra battery mah to drive them.
Old 09-23-2022, 05:31 AM
  #873  
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Originally Posted by Glowgeek View Post
I'm interested in how these gas conversions would work using only programmable tank pressure, no solenoid and no crap trap. I'll bet it would work, even if just ok. After all, there are quite a few people out there who are happy enough with running gas in their glow engines with no mods other than CDI. I would be happy doing that too, if not for the overly rich midrange.

But yes, as Chris stated there are other downfalls. Crap traps weigh less than air pumps and the extra battery mah to drive them.
Bazinga.... there we go. Another thing to try. Good thinking Lonnie. It just might work well enough to make for a "simple" conversion setup. By running the top end and idle at a "higher than normal" tank pressure we could depress it to affect the mid range.

The air pump I'm proposing and testing right now is tiny and only draws about 140ma Im sure it could be "packaged" in a single unit about the same size as a regular servo and contain the board, pump and orifice - Just one line to the tank vent and one (or two) hook-ups to the electronics is all that would be required.

I think this is only going to get proven out by actual testing - so stay tuned.
Old 09-23-2022, 08:51 AM
  #874  
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Originally Posted by Cat 1 View Post
Bazinga.... there we go. Another thing to try. Good thinking Lonnie. It just might work well enough to make for a "simple" conversion setup. By running the top end and idle at a "higher than normal" tank pressure we could depress it to affect the mid range.

The air pump I'm proposing and testing right now is tiny and only draws about 140ma Im sure it could be "packaged" in a single unit about the same size as a regular servo and contain the board, pump and orifice - Just one line to the tank vent and one (or two) hook-ups to the electronics is all that would be required.

I think this is only going to get proven out by actual testing - so stay tuned.
In a static situation, I totally see this working. I just have no idea how to include the "unloading in flight" into the adjustments.
Old 09-23-2022, 11:42 AM
  #875  
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Originally Posted by Cat 1 View Post
Bazinga.... there we go. Another thing to try. Good thinking Lonnie. It just might work well enough to make for a "simple" conversion setup. By running the top end and idle at a "higher than normal" tank pressure we could depress it to affect the mid range.

The air pump I'm proposing and testing right now is tiny and only draws about 140ma Im sure it could be "packaged" in a single unit about the same size as a regular servo and contain the board, pump and orifice - Just one line to the tank vent and one (or two) hook-ups to the electronics is all that would be required.

I think this is only going to get proven out by actual testing - so stay tuned.
Here's another one I've been thinking on. Will the stihl solenoid control airflow? If it will then we could use checked crankcase pressure to the tank and control that pressure with the solenoid used as a programmable bleed off valve . No crap trap, no air pump, no additional battery mah. Hmmmmm

Last edited by Glowgeek; 09-23-2022 at 11:44 AM.

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