Safety Comes First
Dave Gee | [email protected]
Don't mess with perfection
Mike Powell and I had an email exchange with a few holes in it. Mike mentioned an incident where a propeller hub was hand-drilled with the wrong bolt pattern (maybe more than once), filled with epoxy, and redrilled to correctly fit the engine.
As you might guess, since you're reading about it in the safety column, the propeller failed and shards flew everywhere. I didn't bother to track down this story for verification, since I know it has happened to others throughout the years. There may be a proper and safe way to redrill a propeller hub, but that isn't it.
Some modelers think nothing of drilling or altering a propeller hub, but they wouldn't just cut away part of the landing gear or wing mount or rotor shaft, which are usually under less stress than the propeller.
I'm no engineer, but I know it is a bad idea to weaken or alter such a critical airframe component. Someone likely did stress calculations on that hub and I'm not going to cut a bunch of material away and then see if it is still strong enough! And despite my legendary cheapness, I think that a new propeller is a bargain compared to the risk of using one that has been damaged or compromised.
Mike said the lesson is to never attempt to repair a propeller, and to use a drill press and drill guide when making holes in a propeller hub. The electric-power pilots used to be more casual about this than the "gassies," but the current power of some electric systems is just amazing. Shortcuts should not be used when it comes to propellers.
I'm always glad to get emails from readers. Some have great topic ideas, others have scary near-miss stories, and a few take me to task for goofing up.
My son, Jeff, was the first of many to send me an Internet link to some video footage of an amazing test flight. The "e-volo" vehicle is similar to those multirotored RC model helicopters, with electric motors on the ends of crossed booms. Such a configuration is unstable except for a computer that keeps everything right side up.
Models of this type have been on the market for years, but Thomas Senkel, the constructor and test pilot of the machine, thought bigger was better. He made a large, cross-boom rig and put four big motor–propeller assemblies on each arm. The rig is essentially 16 large, powerful model-airplane electric-powered propeller assemblies on booms.
The landing gear is a giant, inflated rubber ball strapped underneath the rig. If you're more than 40 years old, you'll recognize it as a Hoppity Hop bouncing toy. Younger folks call it a Pilates exercise ball. Either way, it's a clever way to absorb landing forces. The video shows this big contraption taking off, hovering, and landing under radio control. Pretty cool! Then, it gets interesting, because a man climbs into a chair on the center of the machine, and someone hands him the transmitter! The rotors start whirling and once again, the entire thing rises into the air, with a human pilot sitting amidst all of the spinning propeller blades, flying himself by radio control. Talk about First Person View! People sent me the link because of the apparent danger to the pilot. He sits in the same rotational plane as all those blades. Onboard computers maintain flight stability, since no human pilot could possibly keep such a machine on an even keel. This is certainly not the first aircraft to depend on computers for safe flight, but the concept is still a bit hard to accept for some of us old Free Flighters who are accustomed to models with built-in stability.
I'm not sure if this all really relates to aeromodeling, but I do think the pilot had nerves of steel to fly that rig. It certainly looked risky to be surrounded by so many whirling propellers. One false move or computer glitch and he would experience a real Ginsu (knife) moment.
Of course, since this story doesn't really involve modeling, a responsible columnist would never take up valuable space in the magazine to discuss it. Oops.
Some subjects don't really belong here, but there are gray areas. Readers sometimes email me about problems they have with hobby products, and they want me to put pressure on manufacturers to resolve things in their favor. The matter is often pitched as a safety issue that affects everyone, but more often it is a business dispute.
In nearly every case, the manufacturer is eager to quickly solve any problems with the product. By the time I hear about an issue, it usually has been corrected.
Warning everyone about a problem that was resolved long ago does no good, and the out-of-date information would be in print for years.
Although it disappoints those readers, it's not my job to get embroiled in consumer disputes. I'm just a safety advocate. The fact is that our models are inherently dangerous. Most have a spinning airscrew on the nose, and only our care and vigilance keep us safe. An incident rarely can be blamed on equipment failure; accidents are nearly always caused by pilot error. That's a reason for staying vigilant as we have fun with our aircraft.
Remember a few paragraphs ago when I ranted about altering model airframe components? There's a time and place for everything, because I have a story about doing something similar.
I work with an active student model airplane club at Luther Burbank Middle School in Burbank, California. The club is full of inquisitive, sharp kids. Local adult modelers mentor the school-age members and provide them with a program of lectures, building sessions, and flying meets.
It's a big advantage to learn how and why a model flies as you progress from simple gliders to complex models of all types. Too many adults miss out on these basics when entering the sport. Sometimes they pay a price by crashing models that cannot be repaired. Don't underestimate the value of understanding the construction and operation of your machine!
The best evidence of this is those popular videos showing RC airplanes crashing, one after another, with musical accompaniment. A large percentage of the models seem to be out of balance, mainly tail-heavy.
After a few months of meetings, any kid in the model airplane club can identify that problem and ask why the pilot in the video didn't balance the aircraft before test-flying it. Of course, being young, they also enjoy seeing the crashes.
They love to construct their own models and fly them in the schoolyard and in the gym. As the middle school kids progress each year, they consistently ask to "build something." This warms my heart, since it seems to be a vanishing part of aeromodeling. I am sad to see such an enjoyable segment of the hobby disappear among model airplane enthusiasts.
As the school year progresses—and there have been lessons on aerodynamics and flight-trimming models—the students build more complex airplanes. After the basics are mastered, we schedule a session of Monster Hangar, one of their favorite activities. The adult mentors bring bags of salvaged and new balsa glider parts for the youngsters to combine and modify into whatever flying machines they can imagine.
Kids can be open-minded about aircraft design. Any configuration seems worth a try, and they want to know why something will or won't fly. My crew wanted to make "something like the Wright brothers' plane," despite the fact that this configuration is fragile, hard to launch, and fairly unstable in flight. They wanted to know what angles and sizes were best for the control surfaces, and then away they went!
The designers and builders work in teams, with adult supervision of the CA glue and tools. Too many children have never built anything with their hands, and this is a golden opportunity to help them develop some skill by letting them measure, cut, and sand the balsa parts. They are attentive and use great care with hobby tools.
These little gliders became important to them and were heavily decorated with felt-tip pens and signed by all who helped. No multimillion-dollar airliner prototype ever got a more serious rollout than these oddball gliders, with each team admiring and worrying about the creations of rival crews.
Finally, it was time to test-fly the weird flying machines to determine a winner. The photos show the results of this session, with beaming kids, strange models, and a triumphant test flight of the "Wrong Stuff" glider, as it was named by the builders.
Sources
- e-volo Electric Helicopter: [email protected]
- Website: www.e-volo.com/home.html
Transcribed from original scans by AI. Minor OCR errors may remain.
