Wooden prop placement when parked.

[Frank Giger]

I had heard somewhere along the line that when parked, a wooden prop should be placed horizontal to the ground; I vaguely remember it had something to do with moisture.

The Champ I fly has a wooden prop, and as I did the post flight I turned it (after triple checking the mags!) to be that way and got a lot of looks like I had a third eye in the middle of my forehead.

Is this one of those Old Pilot Tales, or was I correct?

[petehall]

This is a good habit to get into. It most likely doesn't do much for a short duration, but, if the prop is left near vertical for months at a time, mosture could settle in the low end cause an out of balance. Pete

[David Darnell]

Well , Sensenich Doc # W69EK7-CF Rev F says
"Place the propeller in a horizontal position when parked. This will keep the moisture in both blades evenly distributed."

AC 20-37E says-
"Leave two-bladed metal propellers in the one o’clock position to minimize bird droppings and water being retained in the spinner. Wood propellers should be stored horizontal to prevent moisture accumulation in one blade, which would cause unbalance."

Might be a old pilots tale, but looks like its a "official" old pilots tale.

[rosiejerryrosie]

One other point I've been taught - when moving the prop to position it horizontally, turn it backwards (counter to its normal rotation) to further minimize the possibility of an unintended start. (I wish my engine started that easily :)

[aandpmechanic]

Wood props should be left in the horizontal position when parked so that moisture won't settle in one blade. actually, it would nice if we could get enough rain for any moisture to settle anywhere!

[Tom Downey]

Every one realizes that the holes in the end of each blade is for allowing water to escape, few realize that they work in reverse also. put the blades horizontally when parked for a day or more.

OK we know water makes a wooden prop un-balanced, what do we do about that? You know it has sat 2 weeks vertical in the rain. Oh My Goodness What now?

[Mike Busch]

...when moving the prop to position it horizontally, turn it backwards (counter to its normal rotation) to further minimize the possibility of an unintended start.
This has some validity on engines that use impulse coupling magnetos, not on engines that use shower-of-sparks (retard breaker) magnetos.

The downside is that if the engine has a dry vacuum pump installed, rotating the prop backwards can theoretically hasten vacuum pump failure (although in my experience the risk is low).

My rule is never to rotate the prop unless the ignition keys are in your pocket or clearly visible on the glareshield. (Works for most singles that have a key-operated mag switch, doesn't work for twins that use toggle switches.)

[Tom Downey]

When a vac pump is operating, the angle that the carbon vanes are set into the rotor and centrifugal forces causes the vanes to make a better contact with the walls of the pump. when a vac pump is rotated backwards at the speeds we turn the prop, there is no centrifugal force, so friction on the walls of the pump cause the vanes to be pushed back into the slot they ride in, and away from the pump walls.

If a pump fails when turned backwards, the vanes were so short they cocked in the slot they ride in. IOWs it was worn out to start with.

114411451146

[rosiejerryrosie]

My rule is never to rotate the prop unless the ignition keys are in your pocket or clearly visible on the glareshield. (Works for most singles that have a key-operated mag switch, doesn't work for twins that use toggle switches.)

And that's not 'fail safe' either. I've had an engine start with the keys in my pocket. (The mechanic improperly installed the "P" lead.) And one could break or come loose also. Best bet is to treat all props as "live" just as we treat all guns as loaded.

[Mike Busch]

Tom, those lovely photos look like a Sigma-Tek metal-hub vacuum pump which uses non-canted vanes and is bidirectional. Most pumps (Airborne, Rapco, Tempest) use a graphite hub with canted vanes and are designed to turn in only one direction (e.g., 211CCW or 212CW). I've actually never seen a Sigma-Tek pump disassembled before, that metal hub and big ball bearing are impressive. No wonder they cost more. --Mike

[Tom Downey]

Tom, those lovely photos look like a Sigma-Tek metal-hub vacuum pump which uses non-canted vanes and is bidirectional. Most pumps (Airborne, Rapco, Tempest) use a graphite hub with canted vanes and are designed to turn in only one direction (e.g., 211CCW or 212CW). I've actually never seen a Sigma-Tek pump disassembled before, that metal hub and big ball bearing are impressive. No wonder they cost more. --Mike

No Mike, it's a regular old Pesco wet pump. you can buy them off E-bay for 40 bucks they are used on a lot of old aircraft. Any dry pump that uses the vane style pump uses centrifugal forces to hold the vanes to the pump walls, that force is not present while rotating by hand. Any pump that uses a canted vane when rotated in reverse, actually will push the vanes away from the walls as it is turned. They will only pump in one direction that is why the model says CCW or CW.

I've never had a sigma-tek pump apart either. I've only dealt with 1, it was on warrantee so I could not play with it.

[Bill Berson]

My aircraft is parked outside. The wood prop has a light breathable cover when at the airport.
In the winter, I remove the prop and now the prop is in my unheated garage with humidity 80-90%.

I wonder if the prop should be stored in the warm house with drier air for the winter, or should it stay in the higher outside humidity all year?

[Tom Downey]

My aircraft is parked outside. The wood prop has a light breathable cover when at the airport.
In the winter, I remove the prop and now the prop is in my unheated garage with humidity 80-90%.

I wonder if the prop should be stored in the warm house with drier air for the winter, or should it stay in the higher outside humidity all year?

The water content of wood isn' t the real issue as to much of an unbalanced the blades are. I normally store a wooden prop on a shelf with the prop lying flat.

In either case simply run the prop at a low RPM the excess water will leave, it really isn't that big of a deal.

[IDAH]

There is one exception to the horizontal rule, and that is with a De havilland Gypsy Major engine (and may be other Gypsy series) and that is because with the prop horizontal oil ways are in such a position in the engine that the oil will drain from the crankshaft leaving the journals dry for re start. Of course that would matter only if left for long periods, or the prop could be put on in a different position, except that you could not prop it easily to start it.

[Richard Warner]

I might also add, Mike, check to see if the mag switch actually cuts off the mags at every shutdown if you normally stop your engine with a mixture control. Might just save your life.

[George Clymer]

Since most of the maintenance prop and vacuum pump points thusfar have been debated and/or amount to chickenshit, permit me the following REASON to turn ALL non-hangered two blade props horizontal whren parked: collisions. Anyone busy in the biz a coupla decades knows about and may even have seen or heard the impact of wingtip againt vertical prop blade. Oh sure... they were SUPPOSED to stay on the centerline but if it is their (and now your) unlucky day and they didn't, leaving the prop horizontal will be the difference between a ten grand (or more if spar bent) repair for them and a new prop for you vs having a wingtip harmlessly (or with only a paint scrape) breeze over the top of a cowling as the pilot stabs rudder. This could even be true for low wing in some combinations but certainly can avoid high wing/prop impact. And if someone is too stupid or careless to stay out of the prop arc when turning it horizontal, I say let Darwin do his important evolutionary work unimpeded.

[Frank Giger]

Thanks, all!

Fortunately the Champ's engine is shut off by using the mag switch, so it's a positive check that the mags aren't doing what they're not supposed to do when the switch is off! I always do a double check before moving the prop and treat it as if it is live.

On propping backwards, a caution on some Rotax engines - the manual says not to do that; don't know why for sure, but I heard it has something to do with the oil pump.

Never thought about the aircraft being struck on the ramp by another plane! That would be really nasty if the prop gets whacked, as one then has to treat it like any other prop strike and have the crankshaft looked at - or at least I would. But I'm kind of a chicken when it comes to the Big Fan and the things that make it go 'round and 'round.

[Bill Berson]

With my G109, I normally shut down my engine in flight at about 3000 feet AGL.
Then I get the prop positioned horizontally with a few blips on the starter switch. The reason I want the prop horizontal is because a horizontal prop is much less likely to be damaged in the case of a tip-up on the nose from heavy braking or an unintentional groundloop or excursion into the soft grass.

Experienced airplane pilots can do this as well, in the case of a stuck retractable landing gear (stuck in the up position), it saves the prop and engine if stopped horizontally.

p.s. the G109 is a motorglider (engine off landings are preferred)

[Eric Brown]

It has been said; if you don't position a wood prop horizontally, all of the pitch will run out of it.

[FlyingRon]

No matter how many times I've checked things, I always move that prop as if it will fire when I do so.
You can turn it backwards but if it kicks forward on the compression it still could fire the mag.

I'm amazed how long my plane will run after starting it with the mixture pulled out.

[Bill Greenwood]

Bill Berson, Just remember whether you are flying a G109 or a 109G before you shut off the engine!

And to be serious for just a moment, if it was vital to postion wooden prop blades horizontal re water content,then what about 3, 4 , or 5 blade wooden props, they can't have all blades horizontal at the same time?

[Frank Giger]

My understanding is that for four-bladed props they're to be placed in a "plus sign" configuration, and for three blades with one pointing straight up.

Most four bladed wooden props are so big that I don't think water weight is much of an issue in balance.