Frank,
My reply was not meant to be smart-ass. In my experience with a starter, how you hold it, apply it, and time it all reduce the normal bumpy-jumpy chatter that is common. If all of your setup is ideal, then the next thing to do is practice. You'll start to work on being steadier. Straighter. On when and how hard to bump it. And so on.
The only engine/starter combinations that never seem to chatter are sport 1/2As that are totally overpowered by a nice 1/2A-type starter. The ones I have seen/used had soft cones.
On the other hand, starting speed engines with high compression and small spinners is frequently a bumpy experience. It gets better when the crew has some practice. The last couple of speed contests, I was the volunteer "starter guy" if someone wanted help. I got to practice, and learned a few more things.
Perhaps some keys are:
--Strong, fresh battery
--Proper size cone that fits the spinner on the plane you are starting right then. Not one that fits most of your other planes.
--Clean cone with no internal cuts, tears, chunks missing or other unnamed damage
--A softer cone will usually give better traction, but poor technique will damage it much sooner
--Proper speed starter for type of engine. Just because a starter will do wonders on a racing 40 or stunt 60 doesn't mean it will do anything good to a 1/2A--except damage. This is more than just cone size
--Plane must have a suitable spinner. Big enough and tough enough to take the loads. No spinner? No usa da electric finger!
--Prop must not interfere with the cone. If you press the cone onto the spinner and it can contact the prop--including when the starter is not quite square to the whole deal--then it will never work well. Lumpa-bumpa-bump....
--If you see a lot of damage to the spinner, whether plastic or metal, then the setup or the technique is bad. Melted spinners are most likely from--
--The engine needs to be in good running condition. Using a starter to "fix" a messed up engine just leads to more stuff that needs fixing. If you can't just spin the starter and bump the spinner and get it to go, then it needs something else to be better prepared for starting. The determined "if only I could get it going so's I could tweak the carb" attitude leaves burn marks on spinners. And grooves. Which tears up cones, or vice versa. Kind of a chicken or the egg thing.
--Have someone hold the plane and brace it. The guy with the starter needs to use two hands to hold/guide the starter. This may mean one hand on the starter and one on the nose of the plane to make sure he can control the pressure being applied and get it straight. These are often held up off the ground for better bracing. The FF guys like starters on a fixed stand. Hold your own plane and shove the nose into the spinning starter. Foot pedals are de rigueur
--Adjust technique to match engine and plane. Sport and stunt engines seem pretty straightforward. Speed engines like to be bumped hard. Turn the prop back against compression and have the helper shove the plane into the starter, which is already running and braced firmly by the starter guy. I found the most awkward situation to be the larger 4-strokes. Never was comfortable turning the prop backwards to find compression. Sure, you can use a stick, but I always worried it would fire and grab/throw the stick on me. So I mostly stay away from 4-strokes. But electric starters are perfect for them. Anyone using a starter on 4-strokes would likely be able to help you.
Perhaps it would help to understand one of the things I think causes the starter cone to be "ejected" from the spinner. Imagine that the axis of the starter is slightly off in angle from the axis of the engine. Push the cone into contact slowly. It will first touch on one side--in one spot--on the spinner. There is a normal force (ie. a force from the rubber onto the spinner that is perpendicular to the surfaces in contact) and a friction force. The friction force is in the plane of the surfaces in contact. The engine comes up on compression and it takes torque to force it to go over. This has to come from the friction between one side of the starter cone, because it is the only place in contact. And the reaction forces back onto the starter that the person holding it will feel will not be centered on the axis of rotation of the starter or the engine. This means that while your brain, which is in charge of your technique, is expecting to handle an axial load (shoving it onto the spinner) and a centered twisting load (torque applied to the crank) it does not know what to do with an unexpected side load, jumpy force walking the cone back off the spinner and to the side. Now, you say that you are pushing hard enough that the cone is in contact all the way around? Maybe so, but if you are slightly crooked, the force on one side is absolutely larger than the force on the other, and when there isn't quite enough friction to turn the engine over easily, it does the same thing. So having all the parts trued up, clean, and holding the starter/plane absolutely straight and steady solves most of the problems. This is where the softer rubber helps. It deforms more at the loads we can apply and so it evens up the friction around the spinner.
So I'm back to my original comment: Practice. You'll see what you can do better with your technique, and you'll tweak the equipment as needed as a result.
The Divot
Disclaimer--I prefer to hand-prop sport, stunt and racing planes. I own one starter I've used mostly on speed planes. If I ran 4-strokes or pipe engines or larger than 40ish RC engines, I'd probably be using a starter for all of those. And, I don't use composite props on anything but the racing and speed planes. Except for the tame stunt engines, I use a glove.
Topic: How to prevent electric starter cone from chattering and bouncing? (Read 1622 times)