Engine in reverse

Now that I got most problems figured out with my new aircraft/engine combo there remains one nagging problem which I tried to adress earlier but has not been solved satisfactorily. One out of five times approximately the engine reverses when started manualy. It is a little better now then in the beginning because I start to 'know' the engine better, lowered the compression to prevent pre-ignition, installed a new longreach glowplug so there no longer is a 'puddle' in the combustion chamber where raw fuel can accumulate, less choking (2 flips). Still, it is not to the standard of reliability I strive for, at contests I don't want to loose the easy points for not starting within 1 minute. Backflicking does not help and I could revert to using an electric starter but want to prevent that if possible.
As you may remember I am using a Stalker .46SE mounted inverted. My previous Stalker (.40SE) has never had this problem so I was quite surprised with this reversing tendency which already showed up during running-in. Also it sounds surprisingly healthy when running backwards. Revs are down offcourse but it is not very noticable by the sound and I have to positively check if it is running in the right direction (yes, I have already been standing in the middle ready to release my stooge when I noticed the smoke blowing in the wrong direction). Things could be improved when I start with the aircraft inverted but then it becomes a hassle to install it in the stooge and even then it will reverse 1 out of 10 times.
The only remaining remedy I can think of is using a heavier APC prop iso the lightweight wooden prop to improve flywheel effect but then I am at the end of my wits. Is this a timing problem? What am I overlooking?


[photo not recovered: 32922.jpg]

Rgds, Bram

Attachment #1, (jpg file)

A lot of my R/C engines would start in reverse. I just let it run and bump the spinner with my closed fist, thumb and fore finger end, like you would to stop the engine. Only bump it to slow it not stop it. 99% of the time the engine will reverse itself and run forward. The one minute rule just says running, forward or backward don't matter.

Starting backwards seems to be associated with rich (or flooded) engines, with higher compression and with timing. No surprise there. What is surprising from your description is that it appears to run steady enough and strong enough for you to get all the way out to the handle. From what I have seen, most engines won't run anywhere near normal rpm when going backwards. Perhaps that suggests a parts or assembly problem? Can you compare the crank and port timing to your other engine, which has no "el reverso" problem? Is it better or worse when hot? When upright or inverted? Are you running no-nitro fuel?

When I (finally!) finish a new plane, it is always an experiment to see how best to start it. One of the more interesting was an old ST.35C. A ton of compression, and flipping it thru was exciting. It has a violent "bump," but even with an APC 9x6, not enough inertia to make it easy. Backflipping not much of an improvement. The secret was to put it up against compression going backwards and practically just touching the prop backwards gave instant starts. Much, much easier on the hand and safer.

Good luck, keep trying, and let us know what you find.

Dave Hull
LA_Flyer

As Dave said, with RC engines it's almost always a case of too much prime (flooded) and likely exacerbated by having the throttle at or near idle. You've partially remedied it by cutting back on how much you've been priming so it could still be a slight overprime. Some engines are very susceptible to the prime, my Irvine 40RE will just about take my finger off with half a drop too much prime .

But kicking back and running in reverse is caused by an ignition that's too far advanced which overcomes any inertia you give to the prop by flicking. The kickback gives enough inertia in the opposite direction to make the engine want to keep running that way. If flooding isn't the problem (which gives a short period of over compression) then it could be too much nitro or driving the plug to too high a temperature with the battery. Either of these (or a combination) will advance the ignition. I note you're using a long reach plug so fuel won't get into the coil and put out the fire but I'm assuming you mean an extended nose 4 stroke plug. These are normally a hot plug which is fine but I'd check to see how hot it glows out of the engine. I use a glow driver power panel and always check for the setting that gives a brightish orange glow before fitting a plug. The setting needed can vary hugely between brands of plugs.