Turning the Prop

[StrateandLevel]

Daily, before flight, a Check A must be completed in order to validate the C of A. The Check A is listed in CAP411 the LAMS Schedule.
Item A1 states: If the aircraft has not been regularly used, ensure before resumption of flying that:

(a) Either (i) the engine has been turned weekly or fortnightly

or (ii) the manufacturer's recomendations have been complied with.

(b) Compression appears normal when the engine is turned by hand

[MLS-12D]

I always pull the prop. through on Harvards (the only radial-engined aircraft that I've had the privilege of flying, thus far), but I don't do it without personally treble-checking the mag switches; and even then, I try and keep as much of my body clear as I reasonably can.

A friend of mine refers to all propellors as "whirring blades of death", which is about right.

[ChrisVJ]

My plane has a Rotax 4 cyl, 4 stroke with a dry sump and the tank is foward and level with the engine. We turn the engine if not used for a few days because modern oils are such low viscosity that the oil siphons into the engine thru the oil pump in some (crank) positions if allowed to stand for a good few days.

The pressure generated in the crankcase, even with just turning over, is enough to push oil back into the tank. The tank level rises to normal. If you check the oil without doing this you can easily overfill.

[High Wing Drifter]

I neglected to mention that my engine is a Lycoming 320.

Wouldn't the first few turns under the starter motor have the same effect as initially turning it over by hand?

[ozplane]

Following StrateandLevel's post, does anybody know what the Lycoming/Conti manufacturer's recommendations on prop-turning actually are? I can't find any reference one way or another in my aircraft manuals.

[Circuit Basher]

The whole issue of turning props backwards was discussed in this thread around 6 weeks ago. The general consensus (from far better technical brains than me) was that for most modern engines, there will be no damage if the prop is turned backwards. There are, however, vaccuum pumps out there which will suffer from broken vanes if the prop is turned backwards and you need to refer to the POH for your aircraft to find whether there are any specific warnings about this.

Personally, I am in the "I don't turn the prop backwards unless I've got a damn good reason" brigade - saves remembering to check for each type I fly. This may be perpetuating an urban myth, but seems pointless to take the risk if it's not necessary.

[ozplane]

Thanks, Circuit Basher, for the reference to the previous thread. Missed that somehow. Obviously room for discussion.

[Davidt]

We all must have seen engineers limbering up the massive engines and props on vintage bomber types, Fortresses, Dakotas and the like by getting in there and actually walking the prop round. how many of those chappies got minced doing that?

[Flyin'Dutch']

Hi,

There are no vanes in a magneto (AFAIK) but there are in vacuum pumps and I have been led to believe they can fracture if you turn the prop the wrong way around.

More clever people can confirm this or not. Never felt the urge to try it but equally noticed that when an engine had run backwards (happened when it kicked back) the vacuum pump was not immediately 'kaput'

The turning back of the overprimed engine is indeed a good remedy but usually only applies to handswung engines, which most likely do not have a vacuum pump as ancillary. Just a thought.

For most engines with a starter the procedure for clearing an overrich/overprimed situation is to start it with the the throttle open and the mixture at ICO.

FD