Propellers are DANGEROUS

[flyme273]

same problem with my Rallye, only practical way to ground handle is to push-pull the prop. Slats are too weak to push and no Cessna type struts. Tow-bar is only good for steering not push-pull.

For cold start, I turn the prop to reduce starter load. Should I do this?

if I understand the position correctly, even with the battery disconnected (e.g. for maintenance), the prop would still start?

[tacpot]

flyme237: Can you explain why the 'towbar' is not suitable for towing the aircraft? Could it be made more suitable via a modification?

For cold starts I'm not sure that turning the prop will reduce starter load appreciably, unless we're talking about a radial or inverted engine where hydraulic lock will overcome the starters efforts, and possibly damage the engine. It's probably not worth doing on a flat four/six cylinder engine.


On engines where magnetos provide the sole source of the spark, the battery is not part of the ignition system, so providing there is fuel in the supply to the engine, the engine would still run for long enough to do you a serious injury.

take care

tp

[Lister Noble]

I fly a hand start L4 Cub,and the only way to start is to swing the prop.
Chocks in place first.
First 6 blades pulled through to prime engine. with mags off .
Mag one on,swing to start.
Walk round and get in,run up and power checks etc.
Set engine to tick-over,get out and remove chocks,get back in and you are ready to fly.
No other way unless there are other bods about.

The big rule
Always treat prop as live.
Have massive respect for prop.
Walk forwards away from prop and out towards wing tip.
I am happier if others are around ,but that is not always the case.
Lister

[Zulu Alpha]

If the solid state ignition is switched on it should still not fire as the system will not produce a spark below 300 rpm.

This does sound a slightly dangerous piece of advice.
I am sure that electronic ignition will fire below this speed, probably with a retarded spark to assist starting.
I certainly know that mine does. And its doubly dangerous as electronic ignitions produce a much bigger spark than magnetos at very low rpm, hence even more chance of firing.
I have even had my electronic ignition 'kick' the prop when turning the ignition switch from off through, left, right to both. I put it down to the sensor being aligned with the magnet in the pickup. Switching it on and off in quick succesion replicated the engine turning and initiated a spark, hence the kick.
So even a completely stationary prop can kick.!

[flyme273]

tp

tow-bar on Rallye fits in the port side of the tyre spindle only, there is no corresponding starbd fitting e.g. unlike a Cessna. Provided there is no load it can be rotated to steer the nose-wheel. Any force and it keeps falling out. When one's-self is ground handling it can be quite a hand full, one hand holding the tow-bar the other pulling-pushing on the prop.

Cold starts, my intention is to pass over compression, then the starter has a half turn to spin up before being loaded. The 220 hp Franklin six has a significant compression and the starter will often not start to turn or labour heavily against initial compression.

Thanks for confirming battery information.

Have also used a Rotax, where rotation is required to clear sump oil. Would prefer a safer procedure.

Following this thread I shall take extra care. The Cessna 150 incident and loss of watch incident above really catches the attention - too close for comfort. Remember the one in USA where a Piper Cub owner was single-handed and was swinging the prop without anyone inside. It started flew itself for 5 miles and landed itself undamaged. The owner was lucky on two counts, firstly getting out of the way of the forward charging propeller and second to avoid a wreck.

[Windy Militant]

There is a reason to pull on the prop. Those of us who fly behind wooden propellers need to check that variations in temperature and humidity haven't caused the bolts to loosen.
The sage advice passed onto me by various venerable aviators, and it must be reasonably good advice as all of them still had a complete set of peripheral digits.
1) Chocks in, Brakes On or better still tied down.
2) Stay well clear of the prop arc unless you have a specific reason to be there: IE Inspecting it or starting it.
3) Never turn a prop unless you're actually starting the engine.
4) When inspecting the prop, check mags off, throttle shut, Mixture lean and fuel off.
5) If for any reason you do need to turn a prop, follow starting drill so if it does kick you can get clear.
5) Never stand in line with the plane of rotation just in case something lets go.

As for electronic ignition not sparking below 300 rpm I seem to remember an article in Popular flying where a Rotax engine started after having a water dispersant aerosol sprayed into it to inhibit it for storage. It didn't even have carburetters if memory serves, but it still ran for long enough to scare the daylights out of the poor bloke!

[Gertrude the Wombat]

Please, please, please - think about the inherent danger and brief your pax accordingly.

I always specifically tell my pax not to pose for photos near the prop. The universal reaction I get is "what do you think we are, stupid?" and I have a hard time persuading them that some people really do do this.

[SkyHawk-N]

I have a Horizon P-1000 digital tach., one of it's many useful features is it's ability to warn of a "hot-mag" situation. Consider one if you ever need a new tach.

[rosti]

And what about those of us who don't fly 50's technology and have modern dry sump engines like a Rotax with the dipstick in the tank? You have to turn the prop. to pump the oil into the reservoir to get a reading! There's electronic ignition, choke and of course a master switch so it's really quite safe...

[davidatter708]

Do you think it wrong then If your instrustor send you out to do a preflight and start up and they will join you when they hear you radio check or after 5 mins or so. Beacuise for 90% of my training my instrutor did exactly that and on first solo hopped out whilst engine was running.
David

[SNS3Guppy]

First of all Guppy this is not a forum for AG pilots but PRIVATE FLYING.

To start, I know this isn't a forum for ag pilots. You might benifit from experience that goes beyond your own, however. You seem to be offended by experience which may go beyond your own. You may not have ever flown an airplane such as a J-3 cub, for example, which lacks a starter. You may never have flown it by yourself to a location where there are no tie downs, or understand that you can't be in the cockpit during the starting process. You ma not know that one uses a piece of rope to tie down the tail, then handprops the engine and allows it to warm at a low power setting while untying the tail and entering the airplane...by yourself, with no one in the cockpit.

You may have never operated airplanes in cold settings or round engine airplanes (which private pilots fly, incidentally), where the aircraft is required to warm up for an extended period of time. Allowing the airplane to lope and warm up (generally with the oil cooler blocked by a cover) while attending to ground duties, especially if you're the only one there, is standard practice, and no, it's not lazy. A good practice, if one must get out of the aircraft with an engine running, is to chock the airplane or otherwise secure it.

Having flown frequent flights to remote areas to pick up persons or cargo, and having experienced airplanes that wouldn't start, I learned long ago that sometimes keeping the engine running is far more adviseable. In the case of some airplanes, it's necessary. On some older airplanes, standard practice has been to place the engine on the left magneto and let it lope while gaurding the propeller area and arranging cargo and passengers. This can be particularly true in a very cold environment. Perhaps you don't do it at your local flying club with lineboys, a hard surface runway, and all the support you need. You need not dismiss out of hand experienced input, however.

Yes, I'm an ATP, but I also hold private privileges and have a lot of years of flying privately, and instructing private pilots. No, I'm not a lazy instructor. I am an experienced one.

Don't make the assumption that an engine won't fire at low RPM. Residual energy in an ignitio coil may still cause a spark even if the magneto (or other ignition source) isn't properly grounded. Hot engines can fire by themselves, albeit rarely. An engine sitting with one cylinder at the top of the compression stroke can kick, and one should keep in mind that the propeller direction may also reverse, kicking forward or back. Merely getting smacked on the head by the propeller can do enough damage to seriously hurt (or even kill) you. If the propeller kicks back the other way (such as hand propping with your fingers curled around the propeller), it can toss you.

Last winter I was in Riyadh, doing some work on a Cheyenne. This has a turbine PT6 engine rather than a piston engine, which is why I'm still here to tell you about what happened. The airplane had an instrument problem, and I was working in front of the propeller, and moving back and forth past the propeller. It's a free turbine engine, meaning the propeller is driven by nothing more than exhaust gasses; nothing mechanical turns the propeller, from the engine gas generator. You can grab the propeller and move it all day long, no worries. I heard the turbine begin to wind up and saw a pilot had climbed into the cockpit and for some unearthly reason, elected to start an engine with two of us working in the prop arc. Fortunately for us, the turbine gives time to get out of the way, and initially, at least, the propeller moves very slowly.

I mention this to point out another way the prop can move; you might not be in the cockpit, but someone else could be, and they could move it.

I flew a large four engine radial powered bomber for several years. Standard entry was up the side of the airplane on a ladder built into the fuselage, right in front of the #2 propeller. The prop had a 12' arc, and was large. I always felt a strong sense of caution when climbing into the airplane in front of that turning propeller. Yes, there are certainly times when working around the propeller when it's turning is necessary and proper, but care must be taken. When working on a piston engine (I'm also an aircraft mechanic), sometimes one is required to stand directly behind the prop while inspecting for leaks, etc

When turning a propeller by hand, many myths exist. Some basic rules of thumb should be followed.

Your vacum pump, if engine driven, is either a wet pump or a dry pump. If you have a dry pump, chances are it's a carbon vane pump, which are notoriously weak. The pump is designed to turn in one direction because that's how it pumps air (or draws air, depending on it's useage as a vacum pump or air pump for boots)...not because it will shatter and fail if the engine is pulled backward. The carbon vanes internally slide in and out of a shaft in which they are loosely mounted. They do this in order to form a loose seal with the chamber walls of the pump, internally. In order for them to slide more easily, they are angled in their mounting to enable function...turning them backward doesn't cause them to break, as the vanes are free to slide in and out of the slots in which they ride. If you already have debris in the pump (it's i the process of failing), or it's cold and there's condensation and ice in the pump then turning it backward can cause a vane to break...but turning it forward will do the same thing, and after that breakage will continue by virtue of the broken vane parts alone.

Most common damage to carbon vane pumps is caused by the use of teflon tape on the inlet and outlet fittings, or use of pipe thread compound...which enters the pump. It's also caused by those replacing the pump, but not the filters and not thoroughly cleaning the system by blowing it out. Vacum pumps fail regularly, and should never be counted on past about 500-600 hours. I've seen them fail in 5-10 hours in service. Owners or mechanics cleaning engines who allow moisture or solvents into the pump are also responsible for premature failures.

As for counsel regarding never turning a propeller unless you're starting it, the advices too broad. After shutdown, a wooden propeller, for example, should be placed parallel to the ground. This is done to prevent imbalance and moisture buildup in the lower blade...a concern with the wooden propeller. Metal propellers should often be placed like this too, to prevent passing aircraft from striking a blade that might be sticking up. Three bladed props should be placed in the Y position, with two blades up, to reduce the vertical distance extended upward by the propeller for the same reasons...to reduce the chances of a passing aircraft encurring a wingtip strike. This also has the added benifit of avoiding tripping people who might strike their legs when the blades stick down by the knee caps. You'd be surprised how often this happens. In some cases turning the prop so a blade points down (metal props only) to allow the spinner to drain is appropriate.

Turning a propeller by hand may be done as part of the preflight for several reasons, including listening to the engine, as well as clearing potential hydraulic lock (radial engines). It may be turned through when finding the impulse coupling to hand prop, or simply to place a blade in the proper position for hand propping, or finding the top of a compression stroke. It may also be moved to place the blade in a position for starting if one must start and has a weak battery...giving the engine the greatest chance to fire. Many reasons to move the propeller when not actually starting or using the starter are valid. You should never do so, however, without having been properly trained, being fully alert, and leaving yourself an escape.

Many years ago when I was a teenager, I was working at the airport on a Sunday afternoon. A local private pilot entered the building, looking like he'd been in a gang fight. His clothes were shredded, he was cut and bruised and beaten up, and had blood all over his body. I asked him how he was. He said he was surprisingly well, and that he had just been struck by his own airplane. He had incorrectly set the throttle at half before hand propping, hadn't chocked, and tied down (inexplicably) the left wing only. The engine fired, the airplane ran over him, and was destroyed when it made an arc to the left and struck a nearby fuel truck (puncturing the truck in the process).

Hand propping and handling the propeller is safe if done responsibly. It's potentially very painful if not.

As for pulling or pushing on the propeller; one is best advised not to do so, but if you must push near the engine, you're better off doing do on the propeller as close to the shank (hub) as possible, rather than on the cowl. Use caution, obviously, and don't reach through the prop arc to push on the cowl or other parts of the airplane if at all it can be helped.

If you are going to move the propeller, don't wrap your fingers around it. Place your palm on the blade back (the part facing the front of the airplane...the blace face is what you see from the cockpit). If pulling the propeller through in the direction of rotation (typically clockwise as seen from the cockpit, but varies depending on what and where you fly), you can use your fingers slightly but they should be kept mostly straight and not curled around the propeller. Don't stand far enough away you have to lean toward the prop; your center of gravity will take you into the propeller if you slip. Don't stand so close it strikes you.

My preferred method when pulling a prop through is to stand about 1/2 to 2/3 radius (two thirds of the way out from the hub, on the blade), or a little farther. I use flat hands on the prop, and will put my right leg forward into the prop arc (prop not moving). When I pull downward, I ensure I don't bend at the waist, and at the same time I swing my leg to the rear keepng my back straight. As I do, I step backward, so that the momentum of that backward kick carries my body away from the propeller. (should go without saying that you ensure nobody else is behind you first, and that your starting area is clear). If the propeller fires, I'm already moving away from the propeller and to one side...to my right, and I can continue to take steps backward should the airplane move. (Remember, it's chocked, tied, and if a parking brake is available, brakes set). If the propeller doesn't fire, then I move up and start again.

As far as pulling the propeller through to "limber up" the engine as some instructors teach, you're not really accomplishing much. You're not going to be circulating oil (especially in cold weather), and any residual oil on the cylinder walls and bearing surfaces is going to be disturbed so that the engine experiences higher wear on startup. No need for that. Preheat the engine thoroughly; this will do more for protecting the engine on startup during cold weather than any perceived benifits of pulling the prop through. Remember that vacum pump with condensation inside, too...pulling it through in either direction can result in broken vanes.

Yes, there are many reasons when one might turn the propeller by hand, from a preflight inspection of the propeller and spinner to listening to the engine to verifying or alleviating hydraulic lock to finding the compression stroke, to setting the engine on the impulse coupling, and many more...but it must be done by someone who is trained, alert, and acting responsibly. Respect your propeller. Don't fear it. Get educated.

I'd like to touch on the notion of priming your engine by pulling it through. Don't do that. All you're going to do, assuming you do get fuel into the cylinders, is wash the lubrication from the cylinder walls, and you're putting yourself in a potentially bad situation. You wouln't want to handprop with more than the throttle open just a bit, and you wouldn't want to fill the cylinders with fuel before moving the propeller by hand, either. You have the equivilent of a wide open throttle then...the engine won't run that way for an extended time, but it only needs to wind up for a brief moment to seriously hurt or kill you. If you must pull the prop through when the engine has been flooded (and there are times when this may be necessary), do it against the direction of rotation, being careful not to grasp the blades or curl your fingers around them, and keep clear. Treat the engine as though it will fire each time you move it.

If you're doing like some and trying to "prime" using your accelerator pump (pumping the throttle)...don't do that. You're not accomplishing a thing other than posing a fire hazard. No matter what your instructor told you. I see this as a very common mistake, often made by the instructors themselves. It's okay to question what your instructor has taught; chances are that he or she was taught by another low time pilot, who was taught by another low time pilot, and you have there a heritage of inexperience and a litany of bad habits, each one doing it and not knowing why. Always look for better understanding and a better, safer way.

[davidatter708]

Guppy I follow my checklist and guess what it says pump the throttle

[stevef]

Vacuum pumps.

A and C & Guppy are right about the vacuum pumps. It doesn't matter at all which way you turn the engine by hand; you're not going to damage them. I have a letter from the Parker Hannefin (vacuum pump manufacturers) Service Department confirming this.

[stiknruda]

My "rant" was based at those who should know better, allowing the untrained/uneducated to handle their props - not the rest of us who regularly hand-swing, check for hydraulic loss or do a quick compression check assessment as we pull through.


It really was aimed at protecting the "innocent".

[eharding]

But an interesting exchange in any event.

In terms of pax briefing, my recurring nightmare is someone wandering off and walking into the prop of one of those Rotax machines you can hardly hear, especially if there is something else thundering away in the vicinity.

[Flying Binghi]

Beautifully written Guppy.

How true it is ..."a heritage of inexperience and a litany of bad habits, each one doing it and not knowing why."

[SNS3Guppy]

Guppy I follow my checklist and guess what it says pump the throttle

Perhaps you might be a little more specific as to the aircraft, checklist source, type of carburetion (surely you're not pumping the throttle in an injected engine), and if you have an updraft carburetor.

I've seen a lot of poorly written checklists that have incorrect information, or lack in presentation.

Do you understand what the accelerator pump is, how it works, and it's limitations?

Am I not understanding your penultimate paragraph? I hand-start my little Continental A-65. Are you saying that, following priming using the pump, I should not suck in?

If penultimate means the last paragraph, then it specifically referred to use of the accelerator pump. If you're referring to the second to last paragraph, I did discuss pulling the engine through after priming. Some feel this is an appropriate cold weather soloution, though it does remove lubrication on cylinder walls, increases the possibility of a stack or intake fire, and in the case of hand propping, can dramatically increase the impulse and RPM rise when the engine does fire.

If you're hand propping an airplane that has no other way to start, then yes, you may need to prime. You may, like some, prefer to start on the prime, then advance throttle. I always advocate caution in doing so, and discourage people who flood out the engine and then pull it into or through the engine by moving the prop. Depending on your priming system, you may not be pulling much in.

[BackPacker]

In terms of pax briefing, my recurring nightmare is someone wandering off and walking into the prop of one of those Rotax machines you can hardly hear, especially if there is something else thundering away in the vicinity.

My flight instructor told me this, and I always tell my passengers: "If you can't see the prop, it doesn't mean that the aircraft is U/S. It means it is turning."

[aviate1138]

Quote:
In terms of pax briefing, my recurring nightmare is someone wandering off and walking into the prop of one of those Rotax machines you can hardly hear, especially if there is something else thundering away in the vicinity.

From a Rotax 9 series engineering blog.


Warning! Never turn the prop backward
on a 9-series engine. Doing so will cause
the oil pump to work in reverse—draw-
ing oil out of the engine and filling the
oil passageways and hydraulic lifters
with air.

[Xoxon]

Guppy - thanks very much for taking the time to explaining that and giving me (and doubtless a few other people) the benefit of your experience. I really appreciate it.