joepilotmooney Posted February 10 Report Share Posted February 10 Wondering about whether its best to delay engaging starter until about 5-6 seconds after turning off the boost pump, or if it's best to engage starter immediately after turning off the pump. Kinda silly question maybe, but I've always wondered and recall hearing there is a preferred procedure. Referencing here the IO 360 motor found on 78 M20J models, and a cold start, with ambient air temp around 32-60 F. Also, I typically engage boost pump for about 6 seconds prio to start. Appreciate any ideas as to how and why on this... Quote Link to comment Share on other sites More sharing options...
Shadrach Posted February 10 Report Share Posted February 10 The boost pump is used to prime the engine. I don’t think there is much of an operational difference. The intake has been charged with fuel. 6 seconds later, it’s still charged with fuel. 1 Quote Link to comment Share on other sites More sharing options...
Joshua Blackh4t Posted February 10 Report Share Posted February 10 9 minutes ago, Shadrach said: The boost pump is used to prime the engine. I don’t think there is much of an operational difference. The intake has been charged with fuel. 6 seconds later, it’s still charged with fuel. Except in very hot conditions where the engine bay temp is hot enough to vapourise the fuel straight away and it gets flooded in a few seconds. Or I think thats what happened to me. I try to crank directly after priming now. 1 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted February 10 Report Share Posted February 10 7 minutes ago, Joshua Blackh4t said: Except in very hot conditions where the engine bay temp is hot enough to vapourise the fuel straight away and it gets flooded in a few seconds. Or I think thats what happened to me. I try to crank directly after priming now. Don’t prime a hot IO360. Quote Link to comment Share on other sites More sharing options...
Joshua Blackh4t Posted February 10 Report Share Posted February 10 Just now, Shadrach said: Don’t prime a hot IO360. I mean a 'cold' engine one 45 C day. Quote Link to comment Share on other sites More sharing options...
Mooneymite Posted February 10 Report Share Posted February 10 Simple rule of thumb: O-360: Turn key, go fly. IO-360: Carefully read POH and 4000+ pages on Mooneyspace about starting procedures. Analyze, implement and discard. Go to bar, come out the next day and do the cold start procedure. 6 7 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted February 10 Report Share Posted February 10 I never start with the boost pump on and I never prime the engine. If it is cold, just set the throttle, mixture rich and crank it. If you don’t see fuel pressure after a few seconds, turn on the boost pump, but it is rarely needed. If it is hot (within 2 hours of running) set the throttle, mixture at cutoff, crank till it fires, then advance the mixture. Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted February 11 Report Share Posted February 11 I never start with the boost pump on and I never prime the engine. If it is cold, just set the throttle, mixture rich and crank it. If you don’t see fuel pressure after a few seconds, turn on the boost pump, but it is rarely needed.Why not save a few seconds and use the boost pump to pressurize the fuel lines? 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted February 11 Report Share Posted February 11 7 minutes ago, ArtVandelay said: Why not save a few seconds and use the boost pump to pressurize the fuel lines? I’ve rarely found it necessary. The engine usually starts in less than 5 seconds. The only time I do is if the plane has been sitting for a long time (months) or I have opened the fuel system. The fuel pressure gauge will tell the tale. Fuel injected Lycomings are usually hard to start because they are flooded. The injection system does a great job of supplying the correct amount of fuel. If you pump fuel into the engine before it is turning, it will have too much. This isn’t true of Continentals. They never seem to have enough fuel. 1 Quote Link to comment Share on other sites More sharing options...
PeteMc Posted February 11 Report Share Posted February 11 1 hour ago, N201MKTurbo said: I never start with the boost pump on and I never prime the engine. Doesn't that lead to a LOT of cranking? Not that I've flow a huge number of different aircraft models, but I've never seen one that did have some sort of priming or charging the fuel lines in various conditions. Not for every start, but a lot of various conditions. And you're saying you never do it. Quote Link to comment Share on other sites More sharing options...
PeteMc Posted February 11 Report Share Posted February 11 3 hours ago, joepilotmooney said: Wondering about whether its best to delay engaging starter until about 5-6 seconds after turning off the boost pump, or if it's best to engage starter immediately after turning off the pump. I was taught by my mechanic (not any of my CFIIs) that the reason you wait a bit it so let the wet fuel you pumped in vaporize a bit. You'll then get a much faster start. 3 Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted February 11 Report Share Posted February 11 27 minutes ago, PeteMc said: I was taught by my mechanic (not any of my CFIIs) that the reason you wait a bit it so let the wet fuel you pumped in vaporize a bit. You'll then get a much faster start. Yeah, if it’s cold and I’m going to prime, I’ll do it then wind my clock for ~15”. If the engine is hot, don’t prime. If you do prime, push the throttle and mixture all the way in so you actually get the fuel in there, then reset them to cutoff and ~1000rpm and then crank. 1 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted February 11 Report Share Posted February 11 13 minutes ago, PeteMc said: I was taught by my mechanic (not any of my CFIIs) that the reason you wait a bit it so let the wet fuel you pumped in vaporize a bit. You'll then get a much faster start. If you read any of the fuel system manuals (Bendix or Continental) they will state in on so many words that fuel is mixed with air (via bleed screen) in the nozzle to facilitate atomization. The mechanic who told you to wait for the fuel to vaporize probably heard it from someone else who probably heard it from someone else etc. In reality the fuel that is sprayed into the intake is atomized when it leaves the nozzle. Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted February 11 Report Share Posted February 11 4 minutes ago, Shadrach said: If you read any of the fuel system manuals (Bendix or Continental) they will state in on so many words that fuel is mixed with air (via bleed screen) in the nozzle to facilitate atomization. The mechanic who told you to wait for the fuel to vaporize probably heard it from someone else who probably heard it from someone else etc. In reality the fuel that is sprayed into the intake is atomized when it leaves the nozzle. I’m not convinced that “mixed” and “atomized” are necessarily the same things. I’m also not convinced that I’m right, but slightly longer priming and giving it a little longer on a cold day works better than a short prime and immediately cranking even though that’s ok on a hot day. Again, maybe it’s me, but it does seem to work… 3 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted February 11 Report Share Posted February 11 16 minutes ago, Ragsf15e said: I’m not convinced that “mixed” and “atomized” are necessarily the same things. I’m also not convinced that I’m right, but slightly longer priming and giving it a little longer on a cold day works better than a short prime and immediately cranking even though that’s ok on a hot day. Again, maybe it’s me, but it does seem to work… It semantics. The fuel and air are mixed in the nozzle which then atomizes in the ambient air when it discharges from the nozzle. I’m sure some of the fuel condenses on the cold intake in winter time. I prime a 40° engine a bit longe than a 90° engine, but not a lot longer. I’m not trying to be pedantic, I just think this is a “how many angels can dance on the head of a pin” type of analysis. 1 Quote Link to comment Share on other sites More sharing options...
PeteMc Posted February 11 Report Share Posted February 11 37 minutes ago, Shadrach said: If you read any of the fuel system manuals (Bendix or Continental) they will state in on so many words that fuel is mixed with air (via bleed screen) in the nozzle to facilitate atomization. I believe you're talking about a running engine where the cylinder also PULLS the fuel AND air in together. Not a stationary non running engine you're just pumping fuel into. Sure there is always some mixing/atomization when you shoot the fuel in. But I think there may be more wet fuel that just sprays in too. I'll defer to one of the real engine mavins here to weigh in, but my mechanic was pretty good. (Where's George Braly when you need him?! ) 2 Quote Link to comment Share on other sites More sharing options...
MikeOH Posted February 11 Report Share Posted February 11 Hmm, interesting discussion. I typically wait 10 to 15 seconds after prime before cranking; fires after a blade or two. If I crank immediately after prime, I have to crank for several seconds. Take that for what it's worth. 3 Quote Link to comment Share on other sites More sharing options...
PT20J Posted February 11 Report Share Posted February 11 Liquid gasoline will not burn. Only gasoline vapor burns. Gasoline will vaporize at any temperature above its flash point which is about -40 deg C, but the higher the temperature the faster the vaporization. Carburetors and fuel injection nozzles atomize the fuel (i.e., break the metered fuel stream into small droplets mixed with air) to facilitate vaporization but atomization and vaporization are not the same thing. So, given these facts, the colder it is (as long as it is above -40 deg C), the more beneficial it may be to wait a bit after priming before cranking because this gives the atomized fuel some time to absorb heat from the metal and vaporize leading to a faster start. But the benefit is probably small. The heat from compression during the compression stroke probably has a much bigger effect. 5 Quote Link to comment Share on other sites More sharing options...
PeteMc Posted February 11 Report Share Posted February 11 4 hours ago, PT20J said: But the benefit is probably small. The heat from compression during the compression stroke probably has a much bigger effect. So you're on the Prime and Crank team... No waiting? Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted February 11 Report Share Posted February 11 I would bet $1 that I can sit in your airplane and start it faster without priming. Of course it would be almost impossible to judge the contest because it is difficult to duplicate the exact same conditions without waiting a day or so between attempts. After 6 years of daily flying in the Rockies out of Denver (about 400 hrs/yr) and 20 years of commuting between Phoenix and Tucson (about 100 hours/yr) all in a Lycoming powered Mooney, I have had plenty of opportunities to try a lot of different starting methods in different weather situations. 3 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted February 11 Report Share Posted February 11 8 hours ago, N201MKTurbo said: I would bet $1 that I can sit in your airplane and start it faster without priming. Of course it would be almost impossible to judge the contest because it is difficult to duplicate the exact same conditions without waiting a day or so between attempts. After 6 years of daily flying in the Rockies out of Denver (about 400 hrs/yr) and 20 years of commuting between Phoenix and Tucson (about 100 hours/yr) all in a Lycoming powered Mooney, I have had plenty of opportunities to try a lot of different starting methods in different weather situations. I would bet your right about the time required, However, I would also bet that you are spinning your starter a lot more. Whether that makes a difference in it’s useful life is debatable. There is something gratifying about getting the prime just right and having it start in one blade like it’s rubber band powered. 2 Quote Link to comment Share on other sites More sharing options...
Fly Boomer Posted February 11 Report Share Posted February 11 4 minutes ago, Shadrach said: There is something gratifying about getting the prime just right and having it start in one blade like it’s it’s rubber band powered. I used to fascinate myself when starting the first car that was all mine. It only took 2- or 3-hundred milliseconds on the starter (I'm easily entertained). Quote Link to comment Share on other sites More sharing options...
Shadrach Posted February 11 Report Share Posted February 11 Just now, Fly Boomer said: I used to fascinate myself when starting the first car that was all mine. It only took 2- or 3-hundred milliseconds on the starter (I'm easily entertained). Me too apparently. However, when you think about all the things that are happening simultaneously to facilitate a perfect start to idle with no coughing or sputtering it is kind of fascinating. 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted February 11 Report Share Posted February 11 1 hour ago, Shadrach said: I would bet your right about the time required, However, I would also bet that you are spinning your starter a lot more. Whether that makes a difference in is useful life is debatable. There is something gratifying about getting the prime just right and having it start in one blade like it’s it’s rubber band powered. Ok, but that method requires absolute perfection. If you aren’t perfect, the second attempt may take considerably longer. My method is consistently successful. Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted February 11 Report Share Posted February 11 1 hour ago, Shadrach said: Me too apparently. However, when you think about all the things that are happening simultaneously to facilitate a perfect start to idle with no coughing or sputtering it is kind of fascinating. My wife’s Toyota does it effortlessly every time you come to a stop. 2 Quote Link to comment Share on other sites More sharing options...
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