Engine running backwards?

[Rich 26]

Hey Guys

 

While running in my new engine today, after everybody buggered off and left me, I had a really weird thing happen.

My little engine spluttered a bit, as if it was going to cut out, then it came back to life again....

 

The weird part is, the propellor was going the wrong way round and it sounded a little different, but I didnt twig what was going on until the plane started moving backwards, and then the exhaust smoke started going towards the propellor!!

 

I didnt actually realise it was possible for this to happen at all, surely these little model engines only go 1 way round?

 

How the hell does this happen?

Has anybody had this happen mid-flight?

[Peter Royall 47]

They run backwards because the compression design is a compromise. The fuel detonation is at TDC, so it can easily run backwards, but no throttle up can be reached because of the porting.

Answer is, flick it firmly in the direction you want it to go.

 

Four- strokes can throw a propellor in flight if you run them too lean. Solution is to peak your throttle mixture when tuning, and then richen it up by a click or two. Also be aware that they have a nasty habit of throwing props at you on the ground as well, same reason. Cure; stand behind the motor when tuning, or expect a higher voice pitch before retuning home!!!

 

TTFn Oily

[Nutz 0]

Did you buy it form a short Irish bloke?

 

 

Pre-detonation will cause an engine to go backwards this happen normally from a rich or cold engine which is normally rich when you start a cold engine in the cold. I have seen it happen on helis before but it is so common on a plane you could say it is normal for this time of year, like Pete said just watch out in case it spits the prop off.

[Rich 26]

Thanks Peter

 

Is it dangerous or would it do any damage if it suddenly started running in reverse?

[Nutz 0]

Thanks Peter

 

Is it dangerous or would it do any damage if it suddenly started running in reverse?

 

Dangerous, small potential as it could throw the prop on reversal

 

Damage, not to the engine but if the prop was thrown it could do some damage to the prop or what the prop hit.

[Rich 26]

Hey Leon, hows things?

When you say "Throw the prop", do you actually mean throw it as in, launch it into mid-air, detached from the engine?

 

Well the prop carrys the momentum of the crank what normally and what happens (in slow motion) is the the engine pre detonates causing the engine reverses, this in turns loosens the prop nut, now depending how much thread is on the crank and how quickly it undo's will either mean a loose prop spinning on the crank or the prop detaching from the crank and airframe.