|Electrifly 2S 720mah LiPoly Battery|
|Physical Dimensions:||2.5" X 1.375" X .375"|
|Max Discharge:||5.8 amps (8C)|
|Available Online From:||Tower Hobbies|
|Coverite Microlite Covering|
|Amount of Material Per Roll:||14 sq.ft.|
|Working Temperature Range:||195 - 250 degrees|
|Weight:||0.60 oz/sq. yd.|
|Available Online from:||Tower Hobbies|
Have you ever had a plane that used to be a favorite, but just ended up sitting on the shelf? You've kind of stopped flying it, but can't seem to part with it because of fond memories? Well I had just such a plane. It was a "grenade launch" glider kitted by Joe Bridi called the Tercel.
I'm sure some will remember Mr. Bridi's kits as fondly as I do. I stumbled onto this kit about three years ago on eBay. I bought it and did an E-conversion to a motor glider with the day's best equipment. I covered it with LiteSpan and was very pleased with the results. At the time, three years ago, the model had what the local bunch considered very impressive performance and was a big hit.
I logged many enjoyable flights over a two year period with this little bird. However, as time progressed, along with technology and my flying skills, my little Tercel began to collect dust. The covering was in bad shape from hangar rash and a couple of minor crashes and I had other ships with better performance. I just wasn't motivated to do anything with it, but couldn't bare to part with it either. Then came a chance to review some covering and the new 2nd generation LiPoly's!
Before I began the project, a little thought was in order. At first I considered only recovering the wing and horizontal stabilizer since that was where the bulk of the covering resided. However, the more I thought about it, the more recovering the vertical seemed like a good idea. I had learned a lot about aerodynamics since I built this model and the vertical needed some structural changes. For one, since I had converted this glider from hand-launch to motor-glider, the subfin and rudder weren't really necessary and were just dead weight. I had also learned that the aerodynamic counter-balancing on the top of the rudder created more drag than it was worth.
With that decided, it was time to strip my old bird down. I took a couple of pictures before I actually started the strip down, and weighed everything so I could do a comparison later. The wing weighed 66 grams and the fuse without battery weighed in at 208 grams.
Removing LiteSpan turned out to be very easy. I turned my iron all the way up and started running it over the attached covering. This heated up the balsaloc and released the LiteSpan. It was a little tedious, but after about three hours my Tercel was in it's birthday suit again.
The next step was to rework the vertical stabilizer. I seperated the long top portion of the rudder and made it part of the fin. Then I removed the subfin and reworked the rudder to match. I also took the opportunity to perfect some repairs from the minor crashes while the covering was off. After some finish sanding, I once again weighed the stripped wing and fuse for comparison. The wing weighed 52 grams and the fuse with reworked vertical and no battery weighed 200 grams.
After reading the included directions, I set my iron to approximately 200 degrees for attaching the covering. The Microlite adhered to the balsa and hardwood surfaces very well. When a section was done, I used my heat gun to shrink the covering in the open bays. Once again the Microlite performed wonderfully and all my mistakes shrunk into oblivion. Microlite would make anyone look like an experienced finish modeler. This article wasn't intended as a tutorial on covering, so presented is simply a series of uncaptioned pictures documenting the recovering process.
I was very pleased with the finished product! I was also pleased with the weight. With all the rework complete, I reweighed the airframe. The wing once again weighed 66 grams and the fuse now weighed 2 grams less at 206 grams. The lost weight was at the very tip of the tail which was a great place to lose it. Obviously the Microlite had added absolutely no extra weight over the LiteSpan and now the Tercel looked GREAT!
The next step in the restoration process was a battery makeover. Originally, when I first built the Tercel, I had used a 7 cell 270mah 2/3AA Nicad. This pack weighed approximately 2.75 ounces, making the all up flying weight 12.5 ounces. I felt this was pretty good since Mr. Bridi the designer listed the weight as a pure glider at 11.5 ounces. Of course that was with the clunky radio gear of the 80's. Still, being only 1 ounce heavier with an added motor, gearbox, ESC, and motor battery was quite good in my opinion. With the Nicad battery at that weight, I was getting 3-4 trips to altitude and the Tercel thermaled very nicely. The climb was spirited, but I knew I could do better with more voltage. My power system which consisted of a 280BB 6V motor geared 5:1 wasn't even getting warm after several ascents. The 2/3AA Nicads just couldn't hold their voltage and I was only getting about 4 amps through the motor. I didn't try any other batteries at that time though, because keeping the all up weight as light as possible was my main objective.
Finally I did decide to try a new power source last year. Lithium Polymers were starting to become mainstream and name brand commercial chargers also became available. I purchased a Great Planes Triton charger and a first generation Etec 2S 1200 mah pack with the intention of using the Tercel as a testbed. The original Etecs weighed in at 1.8 ounces, which lowered the all up weight nearly an ounce. That was an 8% overall reduction -- that's significant! The original Etecs were 5C cells so they were supposedly good for 6 amps. Unfortunately the 280BB was a little too much for these first generation cells and they dropped their voltage nearly as quickly as the small Nicads. I didn't notice any difference in the climb, but duration was another matter. The ounce less weight noticably increased the dead air glide ratio. The 1200 mah capacity meant that on one charge I could fly till I was tired of flying and the charger could stay home!
With all this past data in mind, I set up to test the new second generation LiPoly's I had for review. I specifically chose the Electrifly 720mah 2S pack because this would lower the all up weight even more! After the recover and rework, switching to these cells would take the weight down to just under 11 ounces. That would be a 14% reduction from the original weight and half an ounce under what Mr. Bridi listed the plane at as a pure glider! It all depended on whether these new cells could handle it.
At full throttle static my wattmeter showed 6.6 amps at better than 50 watts! These new little cells were definitely holding up. The current was a little more than 8C, but I knew that it would be less in the air. Further more, I use this system to do burst runs to altitude that only last around a minute. Then the motor would be shut down for gliding. Taking these facts into consideration, I felt the 720mah 2S pack to be a great choice. It was time to show off my new covering job and do a test flight!
At the new lighter weight, increased voltage, and higher watts per pound, the Tercel climbed noticably faster. It was clear that the Electrifly 2nd generation cells held their voltage better than the original Etec pack I had been using. This was in spite of the fact that the Electrifly battery was smaller, significantly lighter, and had a slightly lower rating. The extra voltage and lighter weight allowed shorter motor runs to gain the same altitude. This fact allowed just as many trips to altitude even though the Electrifly battery is rated at less capacity than the first generation Etec 1200's. It was still a "leave the charger at home" plane!
But the real reward for me were the great looks and the lighter weight. The Tercel seemed to float like smoke at it's new weight. This was what really put it back in my first string line up. Of course the lighter weight put the Tercel in the "light wind only" catagory, but that was OK, I've got other planes for windy days. It was like getting a new plane for only a few hours work, and a sweet looking one at that!
Coverite Microlite is now definitely my first choice for small models. Microlite is just as light as LiteSpan and doesn't require using messy adhesives, the adhesive being part of the covering itself. It stretches and shrinks exceptionally well and will make even the beginner look good at covering. Last but not least, Microlite looks great! I'd use it even if it wasn't so easy to work with.
The new second generation Lithium Polymer batteries are a revolution for E-flyers! The Electrifly brand of these type cells make truly outrageous performance possible in small planes and rival glow power in larger planes. What a great time to be an electric modeler! The built-in overcharge protection circuit along with the Triton charger makes this type of power source as safe as using Nicad and Nimh cells in my opinion. Be sure and watch for my upcoming review that focuses on three different sizes of Electrifly LiPoly cells in 4 different test bed planes.
|Dec 05, 2004, 07:54 PM|
Long Beach Municipal, California, United States
Joined Feb 2003
Got one of the Bridi Tercels still in box waiting paitently for me to build. Your article has inspired me to put it next in the que after the other three projects on the table.
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