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Model Forum / Radio Controlled / Air Models / January 20084 stroke cuts at end of outside loop
I have a 120 4 stroke mounted inverted in a Cyclone 3D Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise runs fine. Doesn't cut with any other aerobatic manoeuvres I've checked the plumbing, clunk & tank. All seems OK What could be the problem ? Thanks Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted that runs fine with the model upright (engine inverted) but then when you flip 'er over it cuts out. Hum, could it be that it's set up too lean but runs fine an upright model/inverted and the inverted engine is compensating for a too lean needle setting. I'd set the needle with the model inverted so that it's 300 rpm or so less than full bore and see what that does. Then it may be a little rich flying upright and then just right at the top of that loop. Prolly can't have it perfect in both attitudes without a pump. > I have a 120 4 stroke mounted inverted in a Cyclone 3D > Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise [quoted text clipped - 6 lines] > > Thanks  SignaturePosted via a free Usenet account from http://www.teranews.com > Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted > that runs fine with the model upright (engine inverted) but then when [quoted text clipped - 16 lines] >> >> Thanks are you sure the clunk is far enough away from the tank end? Yeah, the clunk does not touch the rear of the tank in any orientation. > are you sure the clunk is far enough away from the tank end? > Yeah, the clunk does not touch the rear of the tank in any orientation. > >> are you sure the clunk is far enough away from the tank end? even under -G and suction from the motor ,it has to be fuel lines or tank I would think It will fly OK inverted, its just the outside loop that causes the trouble. Might get a perry pump for it, and also the fuel lines could be shortened, they are needlessly too long. > Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted > that runs fine with the model upright (engine inverted) but then when you [quoted text clipped - 5 lines] > at the top of that loop. Prolly can't have it perfect in both attitudes > without a pump. >Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted >that runs fine with the model upright (engine inverted) but then when [quoted text clipped - 5 lines] >just right at the top of that loop. Prolly can't have it perfect in both >attitudes without a pump. http://www.caliburn.nl/topposting >> I have a 120 4 stroke mounted inverted in a Cyclone 3D >> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise [quoted text clipped - 6 lines] >> >> Thanks Barry ===== Home page http://members.iinet.net.au/~barry.og Bottom end mixture set too lean.The engine will always go slightly lean when the nose is pitched down in a bunt (outside loop).If you were to keep the throttle half open when executing this manouver I bet it keeps running ok.If you richen the main mixture any amount to compensate for this you will lose too much power in level flight.Richening the bottom end mixture should cure the problem but make sure all fuel lines are ok and pressure test the tank.A fuel pump is not neccesary unless the tank is a long way from the engine. >I have a 120 4 stroke mounted inverted in a Cyclone 3D > Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise [quoted text clipped - 6 lines] > > Thanks > Bottom end mixture set too lean.The engine will always go slightly lean when > the nose is pitched down in a bunt (outside loop).If you were to keep the [quoted text clipped - 13 lines] >> >> Thanks bottom end to lean? I would have thought you are going to be at somewhere near full throttle at the end of a bunt >> Bottom end mixture set too lean.The engine will always go slightly >> lean when the nose is pitched down in a bunt (outside loop).If you [quoted text clipped - 7 lines] > bottom end to lean? I would have thought you are going to be at > somewhere near full throttle at the end of a bunt Doesn't it depend which way you do the bunt ? If you start low then roll to inverted and bunt from there then you will finish at low throttle. If you start high and bunt from upright level flight then of course you do end up at full power. Maybe the OP can tell us which way he does his bunts ? SignatureBoo from the top, flying level, push the nose down.........plane is inverted at lowest point engine doesnt want to get up to full power on the climb out, cuts at the top. >>> Bottom end mixture set too lean.The engine will always go slightly lean >>> when the nose is pitched down in a bunt (outside loop).If you were to [quoted text clipped - 14 lines] > > Maybe the OP can tell us which way he does his bunts ? >>>> Bottom end mixture set too lean.The engine will always go slightly lean >>>> when the nose is pitched down in a bunt (outside loop).If you were to [quoted text clipped - 17 lines] > engine doesnt want to get up to full power on the climb out, cuts at the > top. Maybe the fuel tank's too high in the fuselage or there's a lean spot in middle of the throttle range ? SignatureBoo >>> Bottom end mixture set too lean.The engine will always go slightly >>> lean when the nose is pitched down in a bunt (outside loop).If you [quoted text clipped - 14 lines] > > Maybe the OP can tell us which way he does his bunts ? I always thought a loop started from inverted was called an inverted loop rather than a bunt > I have a 120 4 stroke mounted inverted Is it a Laser or a Weston engine where the carb is directly behind the top of the cylinder head ? If so then you may need to take special action to ensure the tank mean level is centered on the carb. Usually, engines have the carb mounted nearer to the crank axis and if a plane has been designed with this in mind then the tank position may be wrong. As an aside, does anyone know why these two engfines have that peculier layout ? Quite apart from the tank position issue there is the problem of ensuring enough room for the engine to breathe between it and the firewall. SignatureBoo >> I have a 120 4 stroke mounted inverted > [quoted text clipped - 8 lines] > ensuring enough room for the engine to breathe between it and the > firewall. @Boo: Putting the carb directly behind the jug shortens the intake manifold and helps prevent carburetor icing. Used to run into that with one of the first Saito 80's. @ Fred: Richen up the low end 1/16 of a turn. | @Boo: Putting the carb directly behind the jug shortens the intake | manifold and helps prevent carburetor icing. Is that really a significant concern in model airplane engines -- carburetor icing? SignatureDoug McLaren, dougmc@frenzied.us `It takes only one drink to get me drunk. The trouble is, I can't remember if it's the thirteenth or the fourteenth.' -George Burns Thanks for all your comments. Dug out the instructions and the factory default position for the low end idle is: Unscrew (ccw, richen) low idle until it stops, then screw back in 6 turns. Mine seem to be screwed in a LOT more than that, which could account for the lean setting. Got the tank back in, the plane is ready to fly with the cowl off for easy needle access. > | @Boo: Putting the carb directly behind the jug shortens the intake > | manifold and helps prevent carburetor icing. > > Is that really a significant concern in model airplane engines -- > carburetor icing? Only if you do touch and goes in cool humid weather and the engine design cools the manifold..that was how I discovered it. It really used to suck to make this beautiful approach and touch only to have the full throttle engine die just as you rotated during the go around part. I learned how to make excellent emergency landings under varying poor conditions of speed and altitude because of that. Each and every time I would get to the model the manifold would be dripping condensation. That was a clue. Later models of the Saito 80 had the updraft tube moved slightly closer to the jug which keeps it warmer. I suspect that engine tuning might be a factor, but I never did any serious research into that as a solution as other easy to implement tricks presented themselves. > | @Boo: Putting the carb directly behind the jug shortens the intake > | manifold and helps prevent carburetor icing. > > Is that really a significant concern in model airplane engines -- > carburetor icing? When I used to run a Saito 91 years ago it would get condensation on the intake. I never saw any ice on the outside, and it never seemed to affect the performance. > When I used to run a Saito 91 years ago Strewth, how old are you? SignatureDave (Sgt. Pepper) Epsom, England My photo galleries at http://www.pbase.com/davecq "I will not tolerate intolerance ... Doh!!" >> When I used to run a Saito 91 years ago > > Strewth, how old are you? what a difference a "," makes When I used to run a Saito 91, years ago still I cant mock Im one of the worst offenders >>> When I used to run a Saito 91 years ago >> [quoted text clipped - 3 lines] > > still I cant mock Im one of the worst offenders :o) All just a harmless chuckle. SignatureDave (Sgt. Pepper) Epsom, England My photo galleries at http://www.pbase.com/davecq "I will not tolerate intolerance ... Doh!!" >>>> When I used to run a Saito 91 years ago >>> [quoted text clipped - 5 lines] > > :o) All just a harmless chuckle. "What cahhenl are you on? I am on 40" "Oh, I am on 40, too" "Oh that's OK then!" CRASH! "You said you were on 42...!" >>> When I used to run a Saito 91 years ago >> [quoted text clipped - 3 lines] > > still I cant mock Im one of the worst offenders That was pretty funny. I didn't notice the ambiguity until you guys pointed it out. I used to run the Saito 91 on a Big John Biplane, about ten years ago. The only reason I mentioned that it was years ago is because I didn't think I would be able to answer a bunch of detailed questions. On Jan 25, 11:46�pm, "Doug McLaren" <dougmc +usenet-20080...@frenzied.us> wrote: > In article <13plbbeekr9q...@corp.supernews.com>, > [quoted text clipped - 8 lines] > `It takes only one drink to get me drunk. The trouble is, I can't > �remember if it's the thirteenth or the fourteenth.' -George Burns Carb icing does not happen often in model engines but you do need to be aware of it for it will drive you crazy some day. Two strokes do not seem to have it at all but four strokes do because the carb is mounted further from the engine on them. We had a fellow one day with a Saito 80 and he would take off and after about 2 minutes into the flight his engine would abruptly quit and would happen every time. By the condensation on the outside of the carb we expected carb ice. The day before and the day after, the engine ran fine. You can't see the ice in the carb because by the time you get to observe it, it will have melted. Carb ice is formed when the temperature in the venturi goes below 32F and moisture is condensed by the temperature dropping to the dew point of the air. This happens most between 40F and 70F because it is between these two extremes that the pressure drop in the venturi can cause the temperature to go below freezing and there is enough moisture to squeeze out of the air. In small man carrying planes a Lycoming engine is less prone to carb ice as the carb is mounted on the botton of the oil pan. Continentals on the other had have the carb mounted on a spider by two studs to the bottom of the engine. You had better keep the carb heat on it. > On Jan 25, 11:46�pm, "Doug McLaren" <dougmc > +usenet-20080...@frenzied.us> wrote: [quoted text clipped - 34 lines] > on the other had have the carb mounted on a spider by two studs to the > bottom of the engine. You had better keep the carb heat on it. As I have not seen this on a model just curious does ice form inside as well as outside? >> On Jan 25, 11:46�pm, "Doug McLaren" <dougmc >> +usenet-20080...@frenzied.us> wrote: [quoted text clipped - 31 lines] > As I have not seen this on a model just curious does ice form inside as > well as outside? Its only inside where it makes a difference. By restricting air flow, or fuel flow, or both. Good news. Went up the flying field today with my buddies. A few minutes fiddling with the low end needle (was too lean) and a small tweak of the main needle, the engine runs well. The throttle response is a bit non linear, but it can probably be improved by improving the throttle arm/push rod geometry and a throttle curve in the Tx. No icing or elephants were noticed in the carb ! YAY! mk > Good news. > [quoted text clipped - 6 lines] > > No icing or elephants were noticed in the carb ! > On Jan 25, 11:46�pm, "Doug McLaren" <dougmc > +usenet-20080...@frenzied.us> wrote: [quoted text clipped - 29 lines] > cause the temperature to go below freezing and there is enough > moisture to squeeze out of the air. The fact that you are also vaporising alcohol does not help either. A spray bar spraying alcohol is a fairly effective refrigerator. As anyone who has spilt fuel on their hands on a cool day knows. >>> I have a 120 4 stroke mounted inverted >> Is it a Laser or a Weston engine where the carb is directly behind the top [quoted text clipped - 10 lines] > @Boo: Putting the carb directly behind the jug shortens the intake manifold >and helps prevent carburetor icing. It also keeps the elephants away. That gets a *real* problem on outside loops. >Used to run into that with one of the > first Saito 80's. yup. Elephants LURVE them Saitos. Try richening your idle. > I have a 120 4 stroke mounted inverted in a Cyclone 3D > Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise [quoted text clipped - 6 lines] > > Thanks Fred -- It sounds like the tank might be mounted too high in relation to the carb CL. In this scenario, you would have to run the engine on the lean side to get normal ops; when you go inverted and put some negative G's on it, the engine would really go lean causing your sag. Cheers -- Lyman "On so-called global warming or climate change, let us not scare ourselves with catastrophic forecasts, or use them to defend and promote irrational interventions in human lives." >I have a 120 4 stroke mounted inverted in a Cyclone 3D > Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise [quoted text clipped - 3 lines] > What could be the problem ? > Thanks |
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