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RE: Engine running Backwards? - 2/9/2008 9:23 PM   
Wild Foamy



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Status: offline 		agreeing with the comments about flipping the prop with the glow circuit active.

its common sense, once the ignition circuit is live the engine has the potential to start, so to have a prop in your hand whilst cranking it over isnt the best idea

you wouldnt hold the blade of a blender whilst you turned it on at the wall would you?

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RE: Engine running Backwards? - 2/9/2008 11:05 PM   
B.L.E.



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Status: offline 		When my engines start backwards, I slowly close the throttle trim, as the engine idles slower and slower, it sometimes will suddenly reverse. This will be accompanied by a sudden jump in idle rpm because the intake timing is correct for forward rotation and incorrect for reverse rotation.

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RE: Engine running Backwards? - 2/10/2008 5:40 AM   
HighPlains


 

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Status: offline 		I'm guessing due to some of the comments on this thread, that some of you really don't understand how a 2-cycle engine works. In particular, comments about what going to happen when you hook up the glow plug. As I posted earlier:
quote:

When the engine has the exhaust open, it can not kick regardless of the mixture with the glow plug driver on the engine

That means that there is no way the engine will jump, bump, move, or start just because you hooked up the battery, regardless of the amount of fuel present. You may have a small fire going on inside the exhaust and muffler, but that is all. Before mufflers were common, you often caught the grass and model on fire from excess fuel, and since it was mostly alcohol your first indication of the fire would be the covering burning away or the grass burning under the exhaust. (Methanol burns without visible flame).

Now there are several conditions that can cause serious problems. It is sometimes possible to fill the engine crankcase with fuel, due to tank position, engine installation, or careless handling (carrying the model around nose low with a full tank is a no-no). What happens when the starter is applied is hydraulic lock, which can bend the rod inside the engine and/or spin the prop and spinner off and throw them some distance depending on how hot a starter set-up you are using. Many of our props are rather sharp and it’s a bit like closing your eyes and throwing a knife over your shoulder. So before you grab the starter, pull the engine through a couple of turns and stop with the exhaust port open.

Now with a primed engine, it is quite possible to have too much fuel present in the cylinder. So when the starter is applied instead of turning the engine over smoothly, the mixture fires too soon and kicks back against the momentum of the starter/prop/spinner. Impulse is one of the more interesting functions in engineering and mathematics. So the shock wave from the cylinder is enough to cause the prop nut to spin right off the threads, and again an uncontrolled sharp object can go flying though the air. Fortunately, the most common result is having to disconnect the battery and go get a screwdriver and prop wrench.

But none of these problems need trouble you if you just learn to firmly grab hold of the prop and pull it though compression until the hard bumps are gone. As long as the engine is not left in compression, it will just sit there and wait for you to start with your starter. When you go start it, it will never throw or loosen the prop again.

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RE: Engine running Backwards? - 2/10/2008 6:28 AM   
[AKA]StraferX



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Status: offline 		HighPlains, I have read all the post and have a couple questions. First I understand your method but might be something best taught to a beginner and not to just practice on your own until one sees how it is properly done. Perhaps a video would be great. My question is a beginner question, About how many revolutions should it take before the hard bumps are gone and also can this step be achieved with-out the glow igniter attached?

I would be interested in trying this. I was taught to start with my finger and on my Evolution .46 this is no prob. Its prime 3 to 4 pumps then a finger pop forward or backward on the prop and off it goes. Now on my new JBA .56 this is a diffrent beast. I tried the same steps but primed 6 pumps for a richer start, did the finger pop and snap. It started so quick I about dropped a, well lets say it was fast. It sort of startled me that it was that much more powerfull than the .46 so I went to the electric starter. This motor sure is touchy/aggressive and would much rather use a smarter approach. I don't really like the way the electric starter seem to slam start the motor.

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RE: Engine running Backwards? - 2/10/2008 7:28 AM   
hogflyer



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Status: offline 		I too learned to pull an engine through by grasping the prop with my hand waiting for the "bump" unless we primed directly into the open exhaust port like is common with the Cox engines. This is how it was done 35 years ago when electric starters where not prevalent (I still have the one I made from a 1958 Oldsmobile power seat motor), and while I feel comfortable doing it today I don't show my students how to do this (but I also teach them how to start the plane using a starting stand or tail restraint, not holding onto the fuselage with one hand and flipping the prop with the other). I also make sure the prop is well sanded so I don't cut my hand, have a very tight grasp on the prop and wont do this on anything larger than a .60.

For starting and running backwards, my Evolution .61 was doing this today and would actually start to accelerate over 1/3 throttle and keep running without reversing to the correct direction . Since this is a new engine (now has 10 flights on it) and with the temperature swings we are having right now I know the engine is a bit rich on both the high end and idle. It starts and runs the right way by flipping it backwards using a chicken stick while almost every forward flip caused it to run backwards . I have also found this particular engine requires about 13 choke flips with my finger over the carb after fuel starts to move through the fuel line to start when starting for the first flight of the day (probably flushing out the afterrun oil), and about 5 choke flips after its been run that day - guess just a quirk of this engine and it not being completely worn in yet.

Hogflyer

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RE: Engine running Backwards? - 2/10/2008 5:04 PM   
downunder



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Status: offline 		This "bump" felt by turning over the prop is just that, a bump. It's not a flesh tearing off-to-the-hospital KABOOM. Just hold the prop firmly and turn it into compression. It'll only happen if you've primed the engine and then got at least some of that prime up into the combustion chamber. If the crankcase is full of fuel but none up top then it won't go bump. This is the art of priming, finding out how little fuel can be drawn into the crankcase and then spread around inside the cylinder by a few quick flicks. Of course the priming and spreading is done first and then the plug heated. Usually an engine will only bump the first time because anything combustible gets burned but if you continue turning the prop fairly fast it might send a little more vapour up into the cylinder ready to bump again but you're better off just giving the prop a flick because the engine has told you it's ready to start. If you don't want to flick then one turn of the prop with an electric starter should have it running.

All of this is pretty much standard practise in CL stunt where one flick starts are the norm and most engines are at least a .60 size (and inverted as well).

You won't get the bump without the glow ignitor attached although I've heard stories (from reputable people) of glow engines firing with a cold plug. Never in my 50 years of turning/flicking over an engine have I ever felt even the slightest bump if the plug's not lit but it's something to keep in mind anyway.

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RE: Engine running Backwards? - 2/10/2008 8:33 PM   
WMB


 

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Status: offline 		Lots of good safety info here. One habit I've gotten into is find compression on the back stroke then turn spinner counter clockwise about 1/4 turn to get piston away from compression. Make sure transmitter and reciever are turned on and throttle turned down to idle, now attach glow power while keeping clear of prop.
I also now wear a glove on my right hand after getting wacked once and cut once last year. Seems like there is always something to learn or a procedure to improve upon.

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RE: Engine running Backwards? - 12/31/2012 5:16 PM   
HighPlains


 

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Status: offline 		I had forgotten how long ago we had this discussion. Still relevent information on how to start an engine.

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RE: Engine running Backwards? - 12/31/2012 9:32 PM   
Rodney



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Status: offline 		Twice in some 40+ years, I have had a glow engine start when I connected the glo plug battery. As a result, I ALWAYS hold on the prop very tightly when I attach the glow plug battery in case it wants to fire.

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RE: Engine running Backwards? - 1/1/2013 5:03 PM   
ramboy


 

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Status: offline 		My Tower .46 engine will almost always starts backwards when I use a chicken stick. I just let it run for 10-20 seconds and it quickly corrects itself.

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RE: Engine running Backwards? - 1/3/2013 9:20 PM   
Cruz6794


 

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Status: offline 		Yes do not worry about this I have had this happen to my rc cars. I believe it happens after the engine has been sitting for awhile.

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