Model Mystery Solved

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Well, it cost me over a month of not-so-patiently waiting, but now I can tell you that the little Ercoupe FLIES. Getting it to that point turned out not to be quite as easy as I expected when I posted my last entry on that model on March 10. It turns out that I have managed to outsmart myself once again, but as a result I have some interesting new stuff to share with you.

I have a problem that follows me wherever I go in the world of aeromodeling…I am not capable of leaving anything simple. In the case of my conversion of this little rubber powered, stick-and-tissue Ercoupe, that led me down the path of building up a more realistic cockpit enclosure, making a balsa cowl that looks like it’s made of sheet aluminum instead of tissue-over-stringers, figuring out how to get an opaque silver finish without adding too much weight, and so on. I managed to pull it all off…without adding enough extra weight to compromise relatively low speed flight…but in the process I ran straight into my old nemesis, the emotional loading. I liked the model too much to trust it to a questionable radio system. The little Cox “parkie” set-up would have controlled the model, but I was not satisfied with the degree of precision I could trust it to provide. Things like accurate servo centering count, sometimes.

The result was my decision to put a “real” radio in the Ercoupe, and of course I went straight to Airtronics (http://www.airtronics.net/), as I always do, for what I needed to do the job right.

Here’s what al the fuss is about…by the time I got the airplane to this stage I didn’t want to risk flying it with anything but a really good radio.

I have been using Airtronics' new 2.4 GHz systems ever since the first RDS8000 transmitters became available. I have been flying everything from tiny parkies to 1/4 scale airplanes with no sign, ever, of any problems. I bind a new receiver to the transmitter, set up my operating parameters, run a range check, and GO FLYING. Others have told me about various 2.4 GHZ issues with other radios, but they simply have not occurred with my Airtronics gear. This RX-600 is one of several new receivers just released. Airtronics offers one or two other models that are slightly smaller and/or lighter, but I chose the RX-600 to get full 6-channel capacity in order to be able to use a two channel differential aileron setup and to get maximum range capability. The RX-600 weighs only 0.27 ounces (with the case).

The RX-600 receiver is not only light, it's tiny. The inside of the Ercoupe fuselage at this point is less than 3" wide. I have the RX-600 mounted to a small piece of sticky Velcro. The 94802 Sub-Micro digital servo operates the elevator...it's attached using double-sided tape. There is no rudder servo...early Ercoupes didn't have working rudders.

Like all the other Airtronics 2.4 GHz receivers, the RX-600 uses a dual antenna set-up. There are two identical leads extending from the case; each of them consists of a co-ax extension about six inches long and a much shorter reception wire which is the actual "working" antenna. The right way to install them is to arrange the extension portions wherever you need to put them in order to locate the reception wires at a 90 degree angle to one another. Here's how I set up the little Ercoupe.

I used a pair of Airtronics 94802 Sub Micro Digital BB servos for the ailerons to take advantage of the two channel differential aileron capability of the RDS8000 transmitter. Aileron differential (more movement "up" than "down" ) is perhaps the best way to avoid adverse yaw (sloppy, uncoordinated turns) with many scale models. With the Ercoupe, which has NO rudders to coordinate, differential is vital and I din't even consider trying to use a mechanical gimmick on a single aileron channel to get it right.

It is my preference when building scale airplanes to use the best motors I can get my hands on. In most cases the choice is simple...I use AXI brushless motors from Hobby Lobby (http://www.hobby-lobby.com/). The best choice for this model was the llittle AXI 2204/54, which I am running on 3 LiPo cells. A useful feature of the 2204 series is the rubber mounted, knock-off propeller mounting feature intended for 3D flying. I don't need that feature for the kind of flying I do, and I wanted a scale-type prop attachment.

The answer was simple.. as with any AXI model, I was able to turn the motor end-for-end and use an off-the-shelf collet type prop driver asssembly. I could have mounted the motor directly to the rear face of the plywood box assembly, but the inside of the scale cowl was too narrow for that option to fit. Instead I made mounting stand-offs from ordinary hobby shop brass tubing, some short lengths of 2-56 threaded rod, and some 2-56 hex nuts.

Here's another look at the custom stand-off mount I made for the AXI motor. Have a look back at the first photo.. Everything you see here fits inside that scale cowl. Yes, it's tight...making stuff like that work is what MODEL BUILDING is all about. There is a Castle Creations Phoenix 10 ESC just inside the cowl, behind the motor, neatly hidden where you can

I used a Pwer Wing 600 mAh 3S LiPo pack from Hobby Lobby (http://www.hobby-lobby.com/100_900_mah_batteries_316_ctg.htm), which turned out to be more than sufficient to fly this airplane effortlessly. All the connectors extend from the rear end of the pack and ride in the open area just beneath the cowl. The pack rests loose in the combined motor mount/tray and is secured for flight by a short piece of tape (using Velcro under the pack would have caused it to protrude far enough to spoil the fit of the cowl. The piece of tan colored tape on the front of the pack serves as a pull tab for removal.

2 Comments

  1. That is a really neat model, I wish I had been there to see it fly. Any chance you’ll be bringing it out again? I’m gonna fly the C-3 all summer!

  2. This brought back memories. I used to fly an Ercoupe back in the mid-50s. Great job with the model and the associated article.

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