Safety Comes First!

SAFETY COMES FIRST!

If you are a sailplane or HLG enthusiast, this month's column on safety may not be of value to you. The subject of our discussion is the hazard of that rotating component on the majority of powered model aircraft—the propeller.

I doubt there are any readers who regularly fly engine-powered models who haven't at some time or another come in contact with a rotating prop. Most often this happens when we are adjusting a needle valve which, since the majority of models use a tractor propeller set-up rather than a pusher, is behind the prop. Contact with the rear surface of a prop blade usually results in minimal or no damage to the human digit. The shape of the blade merely knocks one's fingers or hand out of the way. There are exceptions to this general case, as we will see. However, injuries to the fingers or hand that require some form of medical treatment are most often the result of contact with the propeller blades from the front or the leading edge. In such a case the prop blade shape tends to drag the contacting member further into the arc, resulting in motor stoppage, blade breakage, or even finger breakage. Serious lacerations or even amputations have resulted.

We know of no positive solution to contact with propellers. Electric starters are now commonplace in a lot of modelers' field boxes and go a long way to reducing finger injuries during the engine starting operation. As for needle-valve tweakers, all we can say is: be careful. Since the most popular engine induction is via a front rotary valve, the carburetor and its attendant mixture control, the needle valve, is very close to the propeller arc. A flexible shaft on the needle valve that can be angled rearward goes a long way in making adjustments to the mixture safer.

Blade fracture and high tip speeds

The real hazard with propellers, and to some extent spinners, is the fracture of a blade during engine operation. In last month's column we briefly mentioned an incident in which the fracture of a blade on a carbon fiber/resin propeller cost a French modeler his life when it pierced the aorta. It was speculated that over-tightening the prop retaining nut may have produced stresses that, combined with stresses due to blade flexing, precipitated this disaster.

Another account of propeller blade failure is very graphically reported in the July 1979 newsletter of the Ames Sundusters. We think the following account is well worth repeating.

Propellers—now there is a subject that need not be RC or CL oriented. We all fly powered models (at least part-time) and so we all use props. At least I haven't seen any ducted fans yet. Due to several factors inherent to the operation of propellers—high speeds involved and the vulnerable position occupied by the prop—combined with possible carelessness or inexperience, propellers can become the most dangerous part of the model.

Consider for a moment the speeds involved. Tip speeds may come as a shock. Let's run our TD .049 at 15,000 rpm with a 6-3 prop. Sounds pretty tame, right? The tips of that prop are whirling along at a sedate 270 mph! How about that sport .40 with a 10-inch prop? Let's say 11,000 rpm (another tame engine). These tips do considerably better than the TD—almost 360 mph!

All this means we are dealing with potentially lethal initial velocities. If a blade separates, someone could be hurt very badly. So keep spectators out of the arc of your prop! I know they often like to hang over your shoulder while you adjust the engine, but politely move them back. And keep yourself out of the line of fire, too! That includes the front of the plane. Just keep all living things behind the running engine.

I'll give you my dum-dum experience now. You know how the prop instructions say to boil nylon props? Do it! I had a .29 on which I was adjusting the carburetor. I was running an old nylon prop that I got from a box of junk. I knew it was old because that brand no longer looks the way this prop looked. Anyway, while tweaking the needle valve, I got the very tip of one finger into the prop. The blade let go in an instant and hit me squarely between the eyes. I was not hurt, partly because I was wearing sunglasses, and partly because the engine was not at full throttle. Now this prop looked brand new, but had dried out. Three dumb tricks will almost always add up to an accident. Keep your face away from the prop, don't stick your fingers in it, and boil it if it is nylon. In fact, the manufacturers put out very good little instruction sheets—read and heed for SAFETY FIRST!

Props are a prime cause of accidents—some of them quite serious. If you aren't aware of all the "beware" tips in this month's article, may we suggest you mend your ways—right now! — John Preston

So there you have it: one modeler's experience with a propeller that might easily have resulted in a very serious injury. There is, however, another side of the coin. I was browsing through a file at AMA HQ recently in search of material for this column when I came across a copy of a letter that a modeler had sent to a spinner manufacturer. This manufacturer includes with each of his spinner units some instructions and precautions. While most of us readily recognize the hazards associated with whirling props, perhaps we are less aware of the fact that spinners have been known to fly apart, too. The following 10 items are printed on a sheet which accompanies every spinner this manufacturer ships. They are well worth reading and heeding.

1. Always make a round or curved cut-out for the propeller opening. Do not leave a sharp corner.
2. Most spinners come off because the propeller is loose. Do not use a 4-way glow plug wrench to tighten the propeller—use at least a 6-inch wrench. Make sure that the propeller is tight every time you start the engine. Do not use soft wood propellers as the wood crushes and becomes loose.
3. Do not lean over, or reach over, the propeller-spinner combination. Get behind the airplane to adjust the engine while it is running.
4. Wear safety glasses when near a running engine.
5. Do not run a plastic spinner over 12,000 rpm.
6. Do not run a metal spinner over 18,000 rpm.
7. When tightening the spinner onto the backplate with the center screw, be sure the spinner is centered properly in the backplate groove, and do not over-tighten. Do not turn the center screw more than 1/4 turn after it becomes snug. Any plastic part can be broken with a big screwdriver.
8. Do not run a plastic spinner at temperatures below +36°F (+1°C).
9. Always check a spinner for cracks before using. Do not use a spinner with any size crack.
10. A little care and common sense will cure a lot of problems. Always balance the propeller and spinner. Almost all radio failures are caused by vibration. A little care and your equipment will last a lot longer.

With the exception of item 2, these instructions, if followed, should go a long way to preventing modelers from being struck by a fragment thrown from a rotating spinner or prop. In regard to the size wrenches that should be used to tighten a prop, much depends on the modeler's own strength. Some hairy-armed people I know could easily do damage to a prop or retaining nut if given a 6-inch wrench.

An irate modeler's letter

Now for the letter that was written to this spinner manufacturer by an irate modeler who, I'd bet, probably doesn't wear his seat belt when driving a car.

"What I want to know is who wrote the new instruction sheet that is laminated in with each of your spinners—an engineer or an attorney?

"I'll bet it was an attorney, and the same guy who advised [name of prop mfr.] to put some overly cautious advice in with their propellers. For example, both you and [prop mfr.] are now saying the pilot should get behind the plane to adjust the engine. Did you ever try that? You are more likely to stumble over your field box, or have a number of other difficulties as you move around while holding onto the plane, than just following the present practice of adjusting the engine from the front.

"The reason I am sensitive is sooner or later some insurance company is going to resist a claim, or offer a smaller amount, because the individual did not follow manufacturer's instructions. Then the individual's lawyer will be fighting both the insurance company and the manufacturer. Then there is your safety glass idea. None of them are corrected sufficiently for flying, so you are saying to put them on to start the engine, and then take them off before taking off. With all that handling they are bound to become fuel damaged or stepped on. Is the guy who wears glasses supposed to put safety goggles over his regular glasses, or invest in safety glasses just for flying? Have you enough accident reports to support this kind of a requirement?

"And since when are your plastic spinners not capable of going over 12,000 rpm? My Perry-potted Supertigre .60 does 12,900 and if I add a pipe it will go to 14,000. I must go to a metal spinner! Why? We've had no problem with your plastic one at these rpm. Even your metal you limit to 18,000. Are not the nylon and ducted fan units hitting 22,500?

"Your idea of not using a 4-way wrench is also over-cautious. Your darn aluminum nuts will strip their threads if you use too much force. And loosening is not a problem if a 4-way is turned down snugly with each change in humidity. You say tighten every time you fire up. Nobody does that.

"I am one modeler who does not like the way you are protecting your legal hide at the expense of the modeler. Offer more realistic instructions."

I've no doubt there will be readers who feel this letter-writer has a point. They, too, will probably ignore any safety precautions that are included with our modeling products. It's your hide that we are trying to protect. Unfortunately, when you have an accident, the chances are you will be seeking the help of others. Let's not spoil their pleasure because of our carelessness.

Reported injuries and recommended practices

As I write this second column on safety, we are still some two months away from the publication of the first column. Nevertheless, I'm already getting a lot of feedback on accidents that are happening to fellow modelers through the club newsletters that are mailed to AMA Headquarters. By far the most common reported incidents are those involving lacerations by propellers. For example:

"When the engine started, the rpm was much higher than expected. He was not able to hold the airplane and the prop struck him in the left arm above the elbow. The prop cut the brachial artery, the median nerve and the muscle, and nicked the bone before breaking."

This newsletter article goes on to say, "His arm is now in a cast to control movement until it heals. His thumb and first two fingers are numb and tingle and have limited mobility at the present." I think you would all agree that a small change in our past operating procedures might be well worthwhile to avoid this type of injury. In this particular case the engine was apparently inadvertently started at high throttle and the unexpected burst of power could not be handled by the victim. (Editor: We always start our engines at half-throttle—or less if they will start that way.)

Jerry Gotts' safety tips

To finish this month's sermon we have a tip that comes from Jerry Gotts, writing in the DCRC newsletter. Jerry is the club's safety director and happens to be one of the most safety-conscious modelers I know. Which just goes to show that none of us are immune from accidents. Jerry recently had to have many stitches to close lacerations in three fingers caused by contact with a black, glass-filled resin prop. These props are almost totally invisible on a running engine, so Jerry suggests that the prop tips be painted white for visibility. He also offers 10 other safety tips regarding propellers which we reproduce here for the benefit of all.

1. Tighten the prop nut at least at the beginning of each flying day.
2. Position the radio to the side and in front of the prop so you won't have to reach behind the prop to operate the radio. Be sure the radio is on and the throttle is closed before starting the engine.
3. Start the engine at low throttle—not wide open.
4. Keep your face away from the rotating plane of the prop.
5. Use a chicken stick or electric starter.
6. Take extreme caution with the glow plug wire and also in removing it from the engine.
7. Examine props often for cracks, chips, and balance.
8. Give that meat grinder a wide berth and the respect it commands.
9. Always keep uppermost in your conscious mind the special relationship of your hands and body to that spinning prop. Be aware of what your prop blast may be doing to others. Think about how the engine thrust might move or pivot the plane should it slip or get away from you.
10. Move slowly, deliberately, and think, think, think.

I would add one other item to Jerry's list: do your needle-valve tweaking and throttle twiddling from behind the prop.

Have a safe month.

John Preston 7012 Elvira Ct. Falls Church, VA 22042

Transcribed from original scans by AI. Minor OCR errors may remain.