FastEddieB Posted February 24, 2013 Report Share Posted February 24, 2013 Now I know this goes against many pilots' training but fundamentally: leaning does not cause detonation. I think this is overstated, because... ...leaning most definitely CAN and DOES cause detonation. Maybe what you're saying is that excessive leaning does not cause detonation, and that is true - beyond a certain point LOP you're pretty safe from detonation. But detonation is definitely a concern if you lean from a ROP setting into a "leaner but not lean enough" area. Rather than restate what's been said better, one can go to the links I posted earlier in this thread that describe that exactly. As far as absolute EGT values, that was never a concern when all we had was this: You never had any idea what your absolute EGT was - you just found peak and leaned or enrichened from there. Roger is right in that the smallest variation in probes or probe placements can cause a difference in the absolute number you see on the EGT display for any given cylinder. It really, in general, makes no difference - EGT is not a limiting factor where there's some max value - it can only get SO hot with a "perfect" fuel/air ratio and will fall off on either side of it. Anyway, I don't know if I linked to this before, but its well worth taking some time to read: http://www.warmkesse...ng/td/jd/43.jsp Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2013 Report Share Posted February 24, 2013 Hi Kurt, Here is a prime example of gauge and engine inaccuracies. Fred's EGT temps at the stock #3 position is 1324 to 1367F and mine at approximately the same settings are 1440 to 1480F. Even if you do no short term damage it could easily be a long term damage. There is a reason Rotax does not recommend the #1 position. The temps are guides and not absolutes. I'm all for research and experimentation as anyone around me will tell you, but not when the risk out weigh any returns. As we said in the Fire Department: We risk a little to save a little and only risk a lot to save a lot. The gains have to out weigh the risk. Your losses here could be very substantial with very little gain. As friends it's not my intension to give you a hard time, I just don't want to see you having any costly problems. Link to comment Share on other sites More sharing options...
chanik Posted February 24, 2013 Author Report Share Posted February 24, 2013 Anyway, I don't know if I linked to this before, but its well worth taking some time to read: http://www.warmkesse...ng/td/jd/43.jsp I totally don't mind the critique. It's a main reason I post here. It's a good article but it sort of emphasizes my point. Leaning, specifically to 50 ROP, can yeild higher CHTs and that contributes to detonation. But it is both a secondary and indirect effect. In other words, if the CHTs stay down, only those other factors cause detonation. He makes a few other points most people don't know, paraphrasing G. Braly: Notwithstanding bad gas or ignition system problems, it is virtually impossible to induce detonation in a non-turbo engine at any throttle or mixture setting. Also, while he only touches on it, preignition is different (but more dangerous) and the risk there for a ROTAX would be mostly lead deposits on plugs which build up at low CHTs and rich mixtures. We did check the EGT probes last time. They are correct but closer than ROTAX recommends, probably on everyone's CTSW. More like 60mm from the flange. I used to be 1280 to 1300 on #3, not far from Fred. Curious that yours are so relatively high, Roger Link to comment Share on other sites More sharing options...
chanik Posted February 24, 2013 Author Report Share Posted February 24, 2013 Sadly, the 912i won't fit in the existing cowl. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2013 Report Share Posted February 24, 2013 Hi Kurt, The 1440-1480F EGT's are the norm for the 912 if the probes are at the right distance and accurate. Being in the 1300's is actually too low and the 1200's even worse. The points you talk about in the article is another reason not to be near the ragged edge. A big change in OAT, poor fuel, ignition issue, carb slide not freely moving, small air leak in a carb flange or air intake, lower fuel octane from normal. MY point is you will be so close to the ragged edge that any little influence out of your immediate control will cause a serious problem and you won't know what it was that caused the problem and it will be all over before you see it in the cockpit. I have been flying 2 strokes and the 4 strokes since 1980 and have seen hundreds of seizures and damaged engines. If I have to pick a side to fall on being a little too lean or a little too rich, the rich is far more forgiving and will usually save your engine where the leaner side trashes it. We're plying with too much money here and or other peoples lives when they fly with us. The old 2 stroke I could fix for a couple hundred dollars is gone. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 24, 2013 Report Share Posted February 24, 2013 Kurt and Roger, If you want to save gas when crossing the sierra or when cruising at 10,000' you would need to change the main jet. The needle / needle jet is controlling a fuel circuit that is not being used at high throttle settings. If you adjust the needle you change everything from idle to 3/4 throttle only. Think about it, 3/4 throttle @ 10,000' and you are at 49hp. At that altitude you want 69hp and that takes WOT and WOT means the main jet is controlling the mixture, right? If all the CV altitude compensating carb does (to adjust mixture) is affect the needle differently at different altitudes/air pressures then it is only coming into play on partial throttle descents, pattern work or slow and low. To climb and cruise leaner I would need a leaner main jet a condition that could be abused. I also have high oil temps when oat is > 70F so I would hesitate to lean my main jet. The way I see it is that I don't waist a lot of fuel, I use most of it for fuel and the rest for cooling, economy is still pretty good. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 24, 2013 Report Share Posted February 24, 2013 Hi Ed, That's right. I agree. Link to comment Share on other sites More sharing options...
chanik Posted February 24, 2013 Author Report Share Posted February 24, 2013 I think it is the other way around, at least that was the consensus when I discussed this with Jeremy. At higher elevation the mid-range circuit dominates because there isn't enough differential pressure to move the jet needle up out of the way. Below 5K and at full throlle, the main jet dominates the fuel supply. I can confirm that at high throttle, low altitude I see little fuel flow difference regardless of needle position. I fly at 5,000RPM because I like round numbers, I suppose. So to recap, I still don't believe based on the technical data from ROTAX and elsewhere that I am risking detonation moving the midrange leaner, notwhithstanding the many old wives tales that leaning = detonation risk. If I do have detonation or preignition due to bad gas or a broken plug, say, the odds that I would prevent either with the tiny amount of extra cooling and slightly compromised combustion due to extra ROP is very slight. Extra fuel does very little to mitigate the real causes of detonation and preignition. What to watch for in any case is rapidly climbing CHT and unexpected roughness. Full thottle or idle and reduced climb are the best responses if you suspect anything. If one carb springs a leak, then that one will get much leaner but those two cylinders will tend to run much cooler. The engine will be quite rough, but that isn't detonation, it is imbalanced power. Richer jet position isn't going to help you there either. How far are your EGTs from the flange, Roger? Link to comment Share on other sites More sharing options...
Jim Meade Posted February 25, 2013 Report Share Posted February 25, 2013 I noted a few numbers today. I have one strip of tape over the radiator. I have not measured my EGT's location for distance. I'll try to remember to do that. My sensors were pretty stable, except that #1 CHT was fluctuating again for some reason. I did not note OAT, but will estimate it at about 0°C or less. Stock carb settings. 3660' 5210 rpm 117 kias oil temp 220°F EGT L1357 R1381 CHT L214 R213 Link to comment Share on other sites More sharing options...
Jim Meade Posted February 25, 2013 Report Share Posted February 25, 2013 Sadly, the 912i won't fit in the existing cowl. It just strikes me - does the 912i bolt up to the CTSW? In other words, is all that is stopping an engine switch the cost of a new cowl? Link to comment Share on other sites More sharing options...
chanik Posted February 25, 2013 Author Report Share Posted February 25, 2013 For you and I and E-LSAs, yes. A powerplant change is a major mod so need to fly a new Phase 1, but since this is just a 912 varient, it would likely be just a cursory, 5hr Phase 1. For S-LSA, you would need an LOA from FD. Good luck with that. It is a complete firewall forward rebuild and some extra panel inputs for the EMS, fuel pumps, backup alternator, etc. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 25, 2013 Report Share Posted February 25, 2013 Hi Kurt, The EGT probe is 100mm or 3.94" from the flange. Too cold EGT's means you probably aren't developing as much power as you could be. Link to comment Share on other sites More sharing options...
chanik Posted February 25, 2013 Author Report Share Posted February 25, 2013 Absolutely right, which is why I'm adjusting the clip. Your engine seems to run EGTs much higher than others. My EGTs, on #3, were a bit lower than the other 2, Fred and Jim, but only 40F or so. It's a mystery why you run SO much leaner. But your numbers are more in line with proper leaning and the expected ROTAX guidelines. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 25, 2013 Report Share Posted February 25, 2013 ..I think it is the other way around, at least that was the consensus when I discussed this with Jeremy. At higher elevation the mid-range circuit dominates because there isn't enough differential pressure to move the jet needle up out of the way... concensus can be a very poor basis, think global warming! At higher elevation the mid-range circuit dominates means 'little to nothing' in climb and cruise because there isn't enough differential pressure to move the jet needle up out of the way the throttle position determines that the main jet controls the mixture from 75-100% throttle where the needle controls from 15-75%. Once the throttle is open past about 3/4 the needle is pulled high enough out of the needle jet that the size of the main jet begins to control fuel flow. We keep looking for an effective altitude that the partially compensating Bings can work to, but it is not an altitude or pressure that determines the range. The altitude compensation works in a 15% to 75% throttle range, and throttle ranges only correspond roughly to altitude. If you climbed to altitude but limited throttle to 65% your richness is determined by the needle clip, if you climb WOT the richness is determined by the main jet. Unless you are willing to fly with less than all available power when available power is reduced below 70% and you are willing to retard your throttle below 75% throttle your richness is controlled by the main jet at altitude and there is no compensation. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 25, 2013 Report Share Posted February 25, 2013 Most of the owners I know fly up in this area at the #3 clip position IF they have everything else set up right. The big factor seems to be probe location, many are way off, gauge accuracy, plug gaps too wide or too narrow, different MFG gauges in the cockpit, air box and filter setups are different, different air filters (paper verses K&N type), carb heat leaks, poor carb sync, WOT prop settings,. Unless you remove all these variables and make sure they are correct and how each one interacts you will be using skewed numbers. Rotax and considers EGT's within 30F of each other are the same. My EGT's are usually 0-30F from each other and my CHT's are usually 0-8 of each other and the EGT's are controlled by my throttle setting. Mid-range (4600-4900) runs hotter than higher rpms (5000-5300). This is normal and the way Rotax has the system set up. Link to comment Share on other sites More sharing options...
FastEddieB Posted February 25, 2013 Report Share Posted February 25, 2013 I have not checked this out for accuracy, but it looks like its worth checking out... http://www.omnilex.com/public/bmw78/cvcarb.pdf edited to add: I think this one is better: http://avsport.org/docs/bing64.pdf Link to comment Share on other sites More sharing options...
Roger Lee Posted February 25, 2013 Report Share Posted February 25, 2013 Hi Eddie, The second one is better and right on. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 25, 2013 Report Share Posted February 25, 2013 "The needle-jet system operates at part-load and part throttle. The tapered needle exposes an increasingly larger annular area as the slide rises. Eventually the area is larger than the main jet itself (at the bottom) and the main jet then controls mixture." The transition from needle-jet to main jet happens at 75% throttle. Lets envision a typical flight for me and compare how the Bing64 compensates to how I would compensate flying my Skyhawk with a 180hp Lycoming. CT Depart MMH (7,100) and climb to 11,500 - WOT - mixture determined by main jet - no altitude compensation. Cruise 11,500 - WOT for ~65% power - mixture determined by main jet - no altitude compensation. Descent - ~65% throttle - mixture determined by needle set up - mixture finally leans 1 1/2 hours into my 2 hour flight. Mixture richens as I descend setting me up to save 1 gallon of fuel on an otherwise 11 gallon flight. I am set up for a go-around on arrival but only because all bing 64 departures are controlled by main jet. Skyhawk Lyc IO-360 Depart MMH (7,100) and climb to 11,500 - WOT - mixture set at runup for best power (rich of max RPM). - Fuel saved from leaning Cruise 11,500 - WOT for ~65% power - mixture set at 11,500 or prior to run lean of peak - Fuel saved from leaning Descent - reduce throttle to achieve 500'/min @ comfortable speed - mixture adjustments as egt changes - fuel saved from leaning - mixture set to full rich for go-around prior to landing. Conclusion. The bings don't lean for take-off but the Rotax does not seem to need it. Most altitude related crashes that I see are related to a failure to lean for best power prior to take off. The rotax always seems willing to climb with the stock main jet. The bings do not lean for climb and cruise, helps with cooling at the expense of fuel. The bings do lean for descent which saves fuel and avoids loaded plugs The bings protect against a failure to richen as you descend resulting in poor go-around performance or engine damage. The bing 64's altitude compensation is quite limited and cannot save you fuel in cruise unless you can cruise at altitude and at less than 75% throttle. Moving the needle clip to a leaner condition will cause leaner descents but will not do anything when throttle is near or at full open. Link to comment Share on other sites More sharing options...
chanik Posted February 25, 2013 Author Report Share Posted February 25, 2013 Most of the owners I know fly up in this area at the #3 clip position IF they have everything else set up right. The big factor seems to be probe location, many are way off, gauge accuracy, plug gaps too wide or too narrow, different MFG gauges in the cockpit, air box and filter setups are different, different air filters (paper verses K&N type), carb heat leaks, poor carb sync, WOT prop settings,. Unless you remove all these variables and make sure they are correct and how each one interacts you will be using skewed numbers. Rotax and considers EGT's within 30F of each other are the same. My EGT's are usually 0-30F from each other and my CHT's are usually 0-8 of each other and the EGT's are controlled by my throttle setting. Mid-range (4600-4900) runs hotter than higher rpms (5000-5300). This is normal and the way Rotax has the system set up. I have about the same setup as you. Prop for 5750 WOT sea level per your guidance. EGT and CHT close to each other and measured with the Dynon. My probes are closer than yours so if anything, I'm even colder EGT than 1430. Which is the better air filter? K&N probably. On the air intake side that shouldn't make much difference to mixture. A restriction would just look like an altitude increase to the bings. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 25, 2013 Report Share Posted February 25, 2013 Hi Ed, Exactly. At high throttle settings and high altitude the main jet must be changed to compliment the needle. Doing so puts you in peril if you go from a high altitude and high normal cruise down to sea level and cold OAT's will figure into your already lean situation. Link to comment Share on other sites More sharing options...
chanik Posted February 26, 2013 Author Report Share Posted February 26, 2013 I'm not sure and can't seem to get consensus from the mechanics I've spoken with, but I think this video illustrates pretty well how a CV carb works (Bings are constant velocity). With the jet needle dropped down (#1 setting) you should need a higher throttle setting to lift the jet needle up high enough so that main needle jet is fully exposed. Similarly, at higher altitude, the jet needle assembly is sitting lower due to less vacuum pressure so you should need even higher throttle to pull the jet needle fully up. So the midrange throttle leaning should cover a range closer to full throttle than with #2 or #3 clip positions Link to comment Share on other sites More sharing options...
Roger Lee Posted February 26, 2013 Report Share Posted February 26, 2013 Hi Kurt, Cool little video. The problem isn't that you want to use the #1 position if you can have constant control over the other variables, it is all the these variables that you won't be able to control or even know when they are in the mix. Cars or other land based applications stay on the ground, but we have lots of altitude variance and atmospheric changes. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted February 26, 2013 Report Share Posted February 26, 2013 Kurt, The compromise that you seek would be a set up that leans to a much higher throttle setting, like 95% in stead of 75%. At altitude it would be nice to achieve leaning with a small throttle reduction so that we could either cruise or climb with compensation and yet always have the rich condition provided by the main jet available by advancing to WOT if and when needed. If you can't achieve the leaning you want by moving the needle then the next step would be to change the needle profile so that it doesn't go to relying on the main jet so quickly. As long as the throttle reduction to achieve leaning is too great you won't see any fuel savings above a certain altitude. Link to comment Share on other sites More sharing options...
chanik Posted February 27, 2013 Author Report Share Posted February 27, 2013 Sure, I just want to figure out how the carb really works. Like I said before, I am convinced by all the data that detonation is virtually impossible with any lean setting unless I was already close to the edge due to some major effect like bad gas or busted plug. But I think, the #1 needle position will let me have more leaning up to 90% throttle down low and probably at full throttle up high. When the air is so thin that the needle jet assembly is sitting as low as possible (i. e. above 7000'), then the #1 position should provide a lower threshold of leaning than #2 or #3. Not sure though. At 4000 ft, whcih is a common altitude for me, and #2 setting I definitely get lower fuel burn at 5,000RPM which is maybe 75% power. And fuel burn does indeed shoot up right along with lower EGTs at full throttle. I'll just have to do some more flight characterization with the #1 setting to get some empirical data. Link to comment Share on other sites More sharing options...
GlennM Posted February 27, 2013 Report Share Posted February 27, 2013 Read wikipedia for the SU carburetor, which is a constant velocity type like the Bing. It adjusts the airflow through the venturi to keep the same fuel mixture regardless of altitude or temperature. Here is a good write up on the operation of the Bing 64-3 carburetor: avsport.org/docs/bing64.pdf it mentions the operation of the jet needle adjustments. Link to comment Share on other sites More sharing options...
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