engine ran backwards!

[Spanner]

Now I know a lot of you are going to say "impossible"(cue 10 posts all saying impossible ), but yesterday, somehow, my engine started but ran backwards. the 3 guys flying with me have never seen anything like it before, I've never seen an engine run backwards before, I know its theoretically possible but i never thought it could actually do it!

We initially thought the one way bearing was nadged on the main shaft as it was spinning like a demon but no rotation of the rotor. It sounded rough as hell too.

cut the fuel and restarted with no problems, flew the rest of the afternoon without a glitch!

Too hot a glowplug? too much compression, although it doesn't feel too much?

[wibplus]

Too hot a glowplug? too much compression, although it doesn't feel too much?

Nah !!
None of the above. It happens because of a "one off" pre-ignition which sends the piston down the chamber from exactly TDC (top dead centre). On extremely rare occassions, the crankshaft will move down the "wrong side" and will continue, then, to run the engine backwards.
The only disadvantage of the engine running backwards is that it will also drive the clutch backwards and therefore the clutch will never engage the drive train and therefore not drive the hub/blades.
Simply stop the engine and re-start. The chances of it happening twice are even more remote than it happening the first time.

[GravityKills]

Now I know a lot of you are going to say "impossible"...

but you need to start it backwards for inverted flight

It happens quite frequently when the ignition time is (too) early, as was already mentioned. I'll suspect this is more likely to occur in hot weather and high nitro content.
If you're using 30 % nitro and the engine doesn't behave, try 20 % for a change.

[spunkmyer]

I've seen it a few times on nitro engines, one time was on se titan... Its more common than you think..

[waveydavey]

Sometimes happens if your running rich on idle, we had a TT53 that would do it almost every time it was started. Cured by removing a head shim. A hotter plug would also help.

My SX would do it occasionally and most of the time by dropping to idle and then dropping the trim I could get it to fire down normally. Won't happen when the engine is running at full chat.

[chris jones2.4]

it happens continuesly on a 50 hyper for some reason, its when he engine fires right at the end of a stroke and pops into reverse, take the the trim down low and wait and it should run forwards again, never had it happen on my 91 though

[ddracer]

LOL Orange Colin once had 4 in a row, so he took the engine out thinking it was the clutch had gone. When he came back to the field red faced we leaned the bottom end out 1/8 of a turn and it never did it again.

[Mart61]

Happened to me once. My OS 50 started the normal way and, when flicking from TH after my walk to the field, the engine began to die on me but I caught it on the throttle just before it died.

Immediately I started to open the throttle several of the guys from the pits called out "It's running backwards!". And so it was...

[daren]

Won't happen when the engine is running at full chat.

Had a ys91 st fitted to a miniature aircraft tempest fai do it at full chat at the top of a stall turn, took the brain a while to figure out why the engine was reving it's nuts off and the blades were slowing down, a quick flick of throttle hold soon had it on the ground.
Restarted the motor and carried on flying.

[SRH990]

I also had it happen in mid-flight, this time a 50 Hyper in a Raptor. Also had the WTF!!! moment as the blades nearly stopped while the engine revved it's nads off, luckily got it down okay.

The Hyper is very prone to this, especially with a rich bottom end and a cold day.

[trillian]

This happened to me on Saturday and that was the first time (OS50 Hyper). I started it the same way I always do and I'm used to it firing up straight away. It seemed to idle a bit lower than normal and sounded maybe a bit quieter but I didn't think anything of it.

I set the heli down started to bring up the throttle and the blades aren't turning. My first thought was the clutch was broken or something, then I could see the gear turning backwards. So Killed the engine and went back and started it again and the difference in idle speed and sound was fairly obvious.

That was a very strange experience.

[pchristy]

It usually happens due to a rich mixture - flooding when starting. For it to happen in flight, the engine must be tuned to the n'th degree - not a recipe for long life!

Reed valve engines (small Cox engines and the like) will run equally well in either direction. Rotary valve engines may run in the wrong direction, but usually very inefficiently. Often they will simply stop when you open the throttle because the port timing is all wrong. Even if they do continue to run, they develop only a fraction of their normal power!

The reason they sometimes seem to "scream", is because there is no load on them - the auto unit disconnects the main rotors.

For it to happen during starting is not to unusual - especially if you've flooded it slightly. For it to happen in flight indicates too much nitro or too high compression ratio. Neither of these latter two is conducive to a long engine life!!!

[Spanner]

Hmm, I had just turned the low speed needle out a 1/4 turn to try and cure a snag, may have gone and 1/8th too far then and its running a little too rich at the bottom end.( was cutting out if I increased throttle too quickly)

Using 20% Optifuel.

[del19_82]

Yup seen this plenty of times now, Like most I normally kill the engine and restart it and it's generally fine after that!

[snowy]

i had this happen twice with Os55 in my raptor se worked out to be to rich bottom end!