I'm not sure if this is common knowledge but I was curious does it matter the location of the prop when engine is under compression? Should the prop be vertical or horizontal? I figured vertical so its easier to turn over but thats just my reasoning for it.

I like mine at about 1 oclock, but I've seen others that like theirs at 3 oclock or even 11. I think it's whatever you're comfortable with.

I like mine at 1 o'clock tooo since i hand start with my right hand.. i know a couple that like 11 because they use their left hands

1:00 for me as well for ease of starting with my right hand. Helps get your hand out of the prop after flipping it.

yes 1 o'clock for me as well

I prefer 8 o'clock to 2 o'clock, but I flip with left hand, also. Sometimes right, but not much.
What I personally think is more important is to develop and practice a propping routine that has about as much "pull" as there is "flip", meaning I try to angle my body so the propping hand is moving in an arc OUT of the prop rotation to the front. Safe is good.

I WAS TAUGHT THAT WHEN YOU HAVE AN ENGIN WITH A MAGNITO, YOU SHOULD SET THE PROP AT ABOUT 1:00 OCLOCK OR JUST AT THE POINT WHERE YOU FEEL THE TENSION. THIS IS SUPPOSE TO SET THE SPARK TO FIRE AT THE RIGHT TIME AND MAKE STARTING EASYER AND CAUSE THE PROP TO STOP IN A POSITION THAT WONT LEAVE IT HANGING DOWN TO BREAK IF THE MOTOR IS STOPPED.  WORKS VERY WELL FOR ME. GUESS THERE IS MORE THAN ONE WAY TO SKIN A CAT.

the best way to start a engine with a magnito is to set the start of the compression stroke (prop) at 12:00. then start your flip at 3:00. if u try to flip a magnito right on compression you will just keep getting a pop. if u do as above u get full spark then bang!!!

As implied above, you want the prop positioned so you have maximum speed for the flywheel magnet as it passes the coil. That will give the best chance of starting.

For engines where magneto's etc aren't an issue (glow, electronic ignitions etc) my limited testing [testing the engines I have - mix of glow and some gas] placing the prop in-line with the piston/rod at TDC yields maximum revs. I'm sure some will dispute this but it works for me. My theorizing is that a single cylinder engine will never have a perfect balance. Adding a prop gives another plane of imbalance to the engine. It's better to have all those imbalances line up on a common plane or...theoretically...you now have two imbalances which could lead to vibration/harmonics that detract from engine performance.

I see variances of 300rpm on most glow engines depending on whether the prop is aligned with TDC or not. Always the TDC comes out with the higher peak RPM.

All of my gassers have had EI and I always have my prop set at 11:00. I can get my right hand out of the way a lot sooner since I don't use a glove. I always pull down and out.

I like your mention of pull down and out. Too many people throw the prop and immediately pull their hand back in preparation for another attempt......which is asking for trouble if the engine pops just when the pilot decides that last throw didn't work. Goodbye fingers and/or hand.

Swing your hand and arm through and past the prop arc. Don't pull it back until the engine stops turning and, then only whilst keeping yourself clear of the prop.

Just take a look at some hand starts in the video section.....it makes me cringe watching some pilots.....and gassers with EI are probably the most dangerous to play with.

I'm not saying don't hand start, just avoid it where possible and use electric starters. Hand starts need to be treated with the utmost of caution.

Early in my glow days I learnt the hard 'rapped knuckles' way to WAIT before positioning my hand for that next flip. Also a throw back from those days is positioning my prop at 1.00 o'clock to get my fingers up, over and out of the props arch the soonest.

Karol

For glow two strokes *IF* I hand start them I always use two fingers on the face of a prop blade, right down near the hub. I still get plenty of power to flip the prop and know my fingers will be well out of the way by the next rotation. If the engine should kick back or some other unknown, only the broadest and flattest part of the prop can strike my fingers.....which is a lot better than a sharp edge or tip.

Except for deadsticks on the runway, electric starters are used wherever possible which makes the whole prop positioning issue irrelevant for starting.

Sorry mate, you've lost me. Statically and dymamically a balanced prop is a balanced prop and can be considered a disc as far as the dynamic forces go. There is no resulting "imbalance" in any plane in a balanced prop that can be used to offset the reciprocating imbalances in the engine. You need to look elsewhere for the reason for your 300 rpm increase.

michael.

I see your point but the prop is imparting a centrifugal force on the crank in one particular plane (along the prop centerline). Hence, I'd expect a minor but theoretically measurable sinusoidal load on the crank.

A single cylinder engine is inherently imbalanced due to the reciprocating and rotating forces. Placing the prop in-line with this imbalance, which I assume peaks around TDC/BDC, puts both the prop and engines forces on the same plane. Positioning the prop otherwise *may* (note I'm speculating) cause an additional imbalance which could magnify at various rpm ranges. By aligning the prop/crank you may minimize any effect the prop forces generate.

Yes, it's only a theory and perhaps a flawed one. However, I can't deny the empirical evidence that aligning the prop to TDC/BDC has yielded 300rpm improvements on every single cylinder I've tried.

Happy to hear anyone elses thoughts on this and/or an independent test to verify my findings.

Good on you Raven for applying the scientific method to test your theory, even if it is just a mind experiment. Do us a favour next time though, and write down what you observe. That way, we can see if for a significantly large number of engines, that placing the prop in line with TDC agrees with your hypothesis. Going off memory is not the best way of doing it, and I doubt you'll find anyone else to carry out this work but you. I'd say go for it and report back here with what you find.

I'd like to try and help you get a grasp of this though, even it it's just so that I can prove to myself that five years of Uni was not a waste of time, (including the time spent on an undergrad thesis on dynamic engine balancing) so here goes:

You are right, there are many vibrations in any reciprocating engine that are for practical reasons, impossible to balance out, and a two cycle single is one of the hardest of all. The fact that the prop does not have it's mass evenly distributed in a disc about it's point of rotation though is not one of them. Yes it's mass is mostly distributed along a line which intersects the prop point of rotation and the prop's own center of mass, but each blade is balanced statically, dynamically and aerodynamically (mostly) by the other, and therefore exerts no "sinusoidal" load on the crank. There is no force going into the hub from the prop that changes as the prop rotates. The same is true regardless of how many blades the prop has. Think of a multi bladed fan as in a turbine engine. Does this fan exhibit a vibration equal to the frequency of the blades passing some arbitrary point, purely due to the spinning mass?

m.

I'm cheap so in my glow days I set my props to horizontal when the engine comes up on compression so in the event of a dead stick no broken prop. I learned to flip the the prop to start the engine with that position. Now with gassers there a lot less dead sticks, but I still do the horizontal prop thing.