Roger Lee Posted March 30, 2016 Report Share Posted March 30, 2016 At what rpm does the starter spin at? At what approximate rpm does the ignition modules switch from starting ??? degrees BTDC to ??? degrees ATDC. (3 answers here) What is the degree setting for start up with the soft start module with a new style flywheel? Hard extra credit question. What happens to owners that don't use cool outside air for the engine intake and only use air filters mounted on the carbs inside the cowl using hot engine air which is like running carb heat 100% of the time and using 100LL all the time? Link to comment Share on other sites More sharing options...
cdarza Posted March 30, 2016 Report Share Posted March 30, 2016 Extra Credit Q: That's an easy one which involves simple mathematics. Current bank balance less cheque issued = new bank balance (with a "ouch") Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 30, 2016 Report Share Posted March 30, 2016 Hard extra credit question. What happens to owners that don't use cool outside air for the engine intake and only use air filters mounted on the carbs inside the cowl using hot engine air which is like running carb heat 100% of the time and using 100LL all the time? Other than the obvious engine power loss, I have not heard of long term problems with this. This is how the RV-12 is set up. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 30, 2016 Report Share Posted March 30, 2016 My Sky Arrow takes a middle ground. It uses a an oiled foam filter attached to the airbox - think K&N. Though it draws air from inside the cowling, it's at the very front of the cowling, so the air reaching it is essentially at the outside air temp. Seems to work well enough. Link to comment Share on other sites More sharing options...
IrishAl Posted March 30, 2016 Report Share Posted March 30, 2016 Hard extra credit question. What happens to owners that don't use cool outside air for the engine intake and only use air filters mounted on the carbs inside the cowl using hot engine air which is like running carb heat 100% of the time and using 100LL all the time? They never get carb icing. Their engines run rich..........but why should this setup be like using 100LL all the time? Link to comment Share on other sites More sharing options...
Roger Lee Posted March 30, 2016 Author Report Share Posted March 30, 2016 I need some numbers. It isn't like running with 100LL. The question is when using this type setup with 100LL all the time, what happens? Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 30, 2016 Report Share Posted March 30, 2016 I need some numbers. It isn't like running with 100LL. The question is when using this type setup with 100LL all the time, what happens? It's running rich, so increased lead deposits. Link to comment Share on other sites More sharing options...
Tom Baker Posted March 30, 2016 Report Share Posted March 30, 2016 I need some numbers. It isn't like running with 100LL. The question is when using this type setup with 100LL all the time, what happens? That may have been what you wanted to ask, but that is not how your original question is worded. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 30, 2016 Author Report Share Posted March 30, 2016 "It's running rich, so increased lead deposits." Bingo! Nice one Andy. Give that man a Lollipop. I'll buy lunch next time we meet. Running with the air filters in the engine compartment and only using the hot air inside the cowl is the exact same as running your carb heat all the time and this makes the engine run rich. If you use 100LL all the time it will cause much larger lead deposits. It will clog the starter sprag clutch and it will need to be replaced. Parts alone are around $450 plus pulling the engine and the whole back end of the engine down. The gearbox overload clutch will gum and it will need to be removed, disassembled and cleaned. This usually happens around the 800 hr.+/- mark. Running like this isn't a big issue if using 91 Oct., but you are still running rich which gets worse as altitude increases. Most MFG's use this alternate air source setup due to lack or space in the engine compartment and or cost. What they don't know is the long term affect because these guys never go to class or listen to Rotax. I know this from a little inside info. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 30, 2016 Report Share Posted March 30, 2016 That's pretty cool info. The decreased high altitude performance never even occurred to me, but makes sense. Thanks! Link to comment Share on other sites More sharing options...
DHeal Posted March 30, 2016 Report Share Posted March 30, 2016 Is it possible to lean the 912 ULS somewhat to account for this configuration? I have an RV-12 ELSA and burn Autgas 91 (with @ 8% ethanol) @ 90% of the time. Link to comment Share on other sites More sharing options...
CT_MATT Posted March 30, 2016 Report Share Posted March 30, 2016 Roger, Do you have any pictures of pistons in various states (normal, "leaded" , other) that you could share? It would be interesting to see some of the differences in the running conditions... Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 30, 2016 Report Share Posted March 30, 2016 Is it possible to lean the 912 ULS somewhat to account for this configuration? I have an RV-12 ELSA and burn Autgas 91 (with @ 8% ethanol) @ 90% of the time. I think other than at idle (which is set with the idle mixture screw) the mixture is set by the needle jets. You'd have to get custom jets to make a change, and then you might go lean and detonate at low altitudes if you ever went there. There is a manual "HACMan" unit to make changes, but many have said the danger of using them is not worth it. Somebody correct me on this if I'm misunderstanding. Link to comment Share on other sites More sharing options...
FastEddieB Posted March 30, 2016 Report Share Posted March 30, 2016 There's also a clip on the metering pin where it meets the slide, with 4 (I think) notches. I think lowering the pin makes the entire midrange leaner, raising it makes it richer. When the slide is all the way up, the needle is out of the picture and the main jet determines the mixture. I think. Let me find a good summary to link to. Here: http://avsport.org/acft/Rotax/bing64.pdf Link to comment Share on other sites More sharing options...
Anticept Posted March 30, 2016 Report Share Posted March 30, 2016 Eddie got that right. Related: at high elevations, people benefit from raising the clip to needle position 2 (up from 3), but as a result they cannot fly to lower elevations. In his link, on the last page, the needle is #4, and the clip is #14. #15 is a tiny o-ring that dampens vibrations, it snugs up against the clip. There are other ways of changing the mixture too, but disclaimer: none of this is endorsed by rotax and I'm not responsible for your experimentation!!! Adjusting float level: this has a light to moderate effect on mixture across throttle ranges. This is because it requires more vacuum to draw fuel on lower float levels, and less vacuum on high levels. Changing the idle jet adjusts mixture in low throttle. Changing the needle jet adjusts mixture in the midrange RPM. Changing the main jet adjusts mixture in high throttle. Link to comment Share on other sites More sharing options...
Jacques Posted March 30, 2016 Report Share Posted March 30, 2016 Roger, Do you have any pictures of pistons in various states (normal, "leaded" , other) that you could share? It would be interesting to see some of the differences in the running conditions... CT_Matt look at the pictures on page # 5 of the attached document = = = = = = = = running with air filters breathing warm (cowling) air makes the engine running too rich for the carburators calibration coming from the factory [ main jets ] so installing smaller # main jets would correct that . but best is having the engine breathing cold (ram)air. I remember a customer who had the airbox on his ULS but the single filter on the airbox was still ''under the cowlling''.. I had him relocated the filter and installing a Naca scoop...so it was now breathing outside air...result: .the engine gained 300 rpm...so we had to get more pitch on the prop to have the same 'wanted ' 5600~ rpm WOT 912 maintenance article Conair.pdf Link to comment Share on other sites More sharing options...
FlyingMonkey Posted March 30, 2016 Report Share Posted March 30, 2016 Corey, with the needle set to position 2, what is the altitude to start worrying? Link to comment Share on other sites More sharing options...
CT_MATT Posted March 30, 2016 Report Share Posted March 30, 2016 Thanks Jacques! That is helpful but I am hoping to see some actual pictures of pistons since you can see them without taking the engine apart (through the spark plug holes). This would be more of a sanity check to ensure the engine is "healthy" and doesn't exhibit an unusual amount of buildup that might require a tear down for further inspection. Any easy to do anytime you change plugs. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 30, 2016 Report Share Posted March 30, 2016 Eddie got that right. Related: at high elevations, people benefit from raising the clip to needle position 2 (up from 3), but as a result they cannot fly to lower elevations. Corey, There is nothing to prevent you from flying to Death Valley at the leaner needle setting. If you are worried about detonation you can climb at WOT and bypass the extra leaning. Link to comment Share on other sites More sharing options...
Anticept Posted March 30, 2016 Report Share Posted March 30, 2016 Corey, with the needle set to position 2, what is the altitude to start worrying? This is one of those unknowns. It changes from engine to engine. The rotax class I took said around 6-7,000. Corey, There is nothing to prevent you from flying to Death Valley at the leaner needle setting. If you are worried about detonation you can climb at WOT and bypass the extra leaning. This is true, but try landing like that! Link to comment Share on other sites More sharing options...
Roger Lee Posted March 30, 2016 Author Report Share Posted March 30, 2016 At what rpm does the starter spin at? 6000+ At what approximate rpm does the ignition modules switch from starting ??? degrees BTDC to ??? degrees ATDC. (3 answers here) 850 rpm from 4 BTDC to 26 BTDC What is the degree setting for start up with the soft start module with a new style flywheel? 3 ATDC if you also have the new style flywheel Link to comment Share on other sites More sharing options...
Doug Hereford Posted March 31, 2016 Report Share Posted March 31, 2016 I have the answer to all of these...........refer to the applicable mfg. tech pubs... Every aircraft can have different specs. I have a fun question........Who has given numerous replys of misinformation and passed them off as fact? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted March 31, 2016 Report Share Posted March 31, 2016 This is one of those unknowns. It changes from engine to engine. The rotax class I took said around 6-7,000. This is true, but try landing like that! There's a CT around here based near sea-level but crosses the Sierra at 14,000' and he uses the leaner needle setting. Landing is done with a retarded throttle and not under load. Seems to work fine. Personally I don't see the point unless you want to fly at high altitude and low power settings. It would make more sense to me to use a leaner main jet. Link to comment Share on other sites More sharing options...
Anticept Posted March 31, 2016 Report Share Posted March 31, 2016 There's a CT around here based near sea-level but crosses the Sierra at 14,000' and he uses the leaner needle setting. Landing is done with a retarded throttle and not under load. Seems to work fine. Personally I don't see the point unless you want to fly at high altitude and low power settings. It would make more sense to me to use a leaner main jet. There's a point where the manifold air pressure is so low, that WOT doesn't open the slide all the way, and thus does not ever go full rich. The slide is actuated by vacuum above the piston and piston diaphragm, and the higher the Delta P to atmospheric pressure below the diaphragm, the more the slide opens. There is absolutely no mechanical linkage between the throttle arm and the slide. I have been interested in figuring out a way to observe the slide operation on a bench. I might try a powerful vacuum cleaner and put a gauge and a bypass gate on it... I DO have a spare carb here in front of me! Anyways, as for our sea-level friend: as long as his systems function correctly, this isn't a problem. But, when I set things, I'm always thinking of "what if some deity hates me?" EDIT: By vacuum, I am referring to vacuum created above the piston and diaphragm, NOT engine vacuum! Added red text to indicate clarification. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 31, 2016 Author Report Share Posted March 31, 2016 Hi Corey, "The slide is actuated by vacuum" This isn't quite right. We just got through going over this in 8 days of class. It is actuated by pressure differential. As air passes through the carb it creates a venturi which cause a pressure drop. The piston (slide if you want to call it that) has two holes (#19) in it that go up through and into the carb dome (#23). The carb has a large air hole on the air filter side of the throat at the top (#2). This atmospheric pressure enters a chamber there (#1). The atmospheric pressure is higher than the lower air pressure in the domb. This lifts the piston up against the spring force pushing it down. So what lifts the piston is pressure differential under the diaphragm verse what's on top. The low pressure is in space 23 and the atmospheric pressure is in space 1. The holes in the piston are 19 that go up into the dome. 2 is where the atmospheric pressure enters out by the air filter. Link to comment Share on other sites More sharing options...
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