Safety Comes First - 2009/08
Dave Gee | [email protected]
Cutting-edge information about hand launching a pusher-propeller model
I love to hand-launch a model. It gives me a closer connection with flight to physically send an airplane soaring into the sky. Conventional tractor-type aircraft with the propeller in front (the way nature intended) respond nicely to hand launching, as long as you give them the proper flying speed.
Since this is the safety column, you know this discussion will veer into launching some not-so-easy types of models. A new trendy thing these days is to fly RC electric-powered jets with either a pusher propeller or one mounted in the middle of the model. They fly well and are convincing in flight, but getting them into the air without bloodshed can be tough.
A standard 1930s overhand-launch technique will bring fingers and propeller together in an unpleasant way. Some builders add a special strake on the airplane’s belly as a holding fixture. Others launch their jets from the top, holding the fuselage and giving an underhand fling, hoping they can pull their hands back quickly enough to avoid the propeller tips. Yikes!
One creative strategy is to use a helper who holds the wingtips and pushes the airplane away with both hands. This leaves the spinning propeller closely centered to the launcher’s chest, but at least all 10 digits are clear.
I do not claim to have the answer to this situation, but too many pilots have shown me their scarred hands. We have to give this some thought.
In the early days of marginally powered electric models, it was common to use a bungee launch. This added another exciting element to the mix: the stored energy of a giant slingshot.
For better or worse, at least we have more motor power these days. This high power-to-weight ratio is the very thing that allows such creative new airframe designs, which bring new problems to solve.
The picture of pilots mass-launching their RC Combat F-22 jets shows a variety of techniques. Nobody got nicked, so apparently each launch style can be used safely. Please contact me with your wisdom, ideas, and opinions about hand-launching these finger-biting little models. If there is a better way, we all want to know about it. I have more to write about that jet mass launch later.
One way to escape the pusher-prop, finger-fillet situation is to do away with the propeller entirely and use those great new Rapier rocket motors. These are the next generation of Jetex-type power plants but are much more reliable than Jetex.
Free-flight (FF) pilots can enjoy the sight of their models zooming into the sky with a faint smoke trail and the distinctive sound of a tiny reaction motor. Launching them can be slightly less romantic. Again, a standard overhand toss is not recommended because the pilot gets a face full of hot exhaust.
I managed to complicate things by building a dual-powered Ercoupe with a rubber motor for the propeller and a Rapier underneath. Yes, there really was a full-scale prototype; it was used to develop the system. My model flies sweetly but requires more than two hands for motor ignition and launch. I found that I could get away with a hand launch if I tossed the airplane across my body to my left instead of overhanding it straight away from my face. That way I end up standing next to the flight path instead of directly behind the model. This works only for small, lightweight models, but it does the trick for me.
My friend Ted Davis built a sleek profile HA-200 jet trainer for Rapier power. Look at the picture of this airplane climbing out and get a load of the exhaust trail centered on Ted’s face. If you look carefully, you can see that he is wearing his Zurich sunglasses. These provide wrap-around coverage from glare and dust and are rated for impact protection. Although these sunglasses are not recommended for direct exposure to rocket exhaust, they provide excellent eye protection at the field or anywhere. I use them, and there are none better. Zurich gets an enthusiastic plug here only because its products and service are so good.
Hand-launching Rapier motors — a cautionary tale
Where was I? Oh yeah — Ted Davis was hand-launching a Rapier-powered model and got a face full of smoke. There is more to that story.
Ted and I were using motors from the same package, but his were getting "burn-throughs," where exhaust came through the side of the motor casing. Mine were running fine. He got a little tired of seeing his flights end literally in a smoking hole in the ground.
We finally determined that, although the older batch of motors was somewhat prone to burning through the side of the casing, our lighting technique had a lot to do with it. We were both using a standard electronic lighter, but I was carefully inserting mine dead center into the rocket nozzle, while Ted went in from an angle and lit his motor off center. We confirmed this by doing an autopsy on a burned-through motor.
Shorty's Basement now carries an upgraded motor style that seems to have cured this problem. The company's website is in the Sources list.
Small RC turbines and rule changes
I've seen pictures and video of some new, extra-small RC turbine engines being flown in Europe. These little power plants are often mounted on the tail of a small delta-wing model, which is hand-launched and belly-landed on grass. The current AMA guidelines for turbine-powered models do not allow for this type of model because of requirements for rudder control and landing-gear steering and braking.
There is talk of altering these rules to allow the smaller jets, but one serious issue is how to hand-launch the things without receiving a facial barbecue. Apparently it can be done, since the pilots in the videos still have eyebrows.
Another issue involves landing these little jets with no undercarriage. A grassy field is one thing, but what about landing on winter snow? The jets might skid a long way while they are essentially out of control.
Much smarter people than I are working on this matter. If there are any changes, this magazine and the AMA website will have the news first.
F-22 mass-launch and Knight Fighter Combat rules
Here's the information about the F-22 mass-launch photograph. These little airplanes are the ones I mentioned last month, redesigned by Ron Knight for his Knight Fighter RC Combat event.
This is possibly the safest Combat event ever. I watched these pilots fly and fight until their batteries wore down, with only the slightest midair damage during the match. The other picture shows the Combat zone with five airplanes visible and no casualties yet.
It seems that these foam jets turn on a dime and accelerate quickly on their electric propeller power, so it is hard to bring two of them together, even deliberately. They are easily repaired, but may never need it. As of press time, the following are the latest rules for Knight Fighter Combat:
- The event is for 30-inch-long F-22 (Knight Fighter) aircraft.
- 6 mm or thinner Depron foam must be used, except for one carbon-fiber wing spar.
- Except for the spar, no glue is used—only tape.
- Only a GWS 5030 propeller is permitted.
- The aircraft's maximum weight is 8 ounces.
Charging batteries from a running car — safety concerns
After the exciting but uneventful first match using these rules, I strolled around the flying field and noticed some battery packs charging from a car battery.
The unusual thing was that the car engine was running at the time, with the hood up and nobody at the wheel. It was parked in the lot at a busy RC field, and nothing bad occurred. What do you think about this?
I was trained to avoid a situation such as this for several good reasons. I've heard about cars going for a drive on their own when left running and unattended. I once saw a driver's-side door sheared off by a post when an unoccupied vehicle cruised by in reverse. When we have to "static run" truck engines at my company, we use extra-large wheel chocks and all other possible precautions.
I think that charging an RC power pack is a small drain on a normal car battery compared to starting the car engine, and running the engine is unnecessary, but I might be wrong. If you know more about this than I do, please hook me up with the electrifying truth and I'll share it with the world.
Sources
- Dave Gee
Box 7081 Van Nuys, CA 91409
- Academy of Model Aeronautics — National Model Aircraft Safety Code
www.modelaircraft.org/files/105.pdf
- Zurich Sunglasses
(800) 533-5665 www.zurichsunglasses.com
- Shorty's Basement
(740) 225-8671 www.shortysbasement.com
Transcribed from original scans by AI. Minor OCR errors may remain.
