Electric Conversion: Part 2
Model Aviation regrets that space considerations forced a last-minute division of Bob Kopski's "Electric Conversion" into two parts. In what follows, Mr. Kopski concludes his discussion of how to electrify large noncompetition models. The text continues directly from the first segment, which can be found in the July 1991 issue of this magazine.
Seniorita modifications
Taking the Seniorita's heavier weight into consideration, I substituted a Sig 3/8-in. nose gear/mount that fits exactly like the kit-supplied 5/16-in. version. The main gear is stock, but I may decide to strengthen it. It tends to spread on landing, allowing the plane to bounce.
So far my Seniorita has flown without a windshield. I messed up the kit window plastic and was unable to get replacement material in time for the first flight. I did install side windows made of clear MonoKote. Actually, the combination of the gaping hole where the windshield should be and the opening in the firewall gives me supercooling of the motor battery.
Drag? Of course! But the Seniorita flies slowly, so it's of minimal concern. In fact, the cooling works so well that I think I'll leave the windshield off. Besides, that's exactly how I flew my cabin Playboy years ago — the yellow transparent one that's featured in the AMA film "Diamonds in the Sky." Check it out!
Weights and balance
For reference purposes, the Seniorita's completed wooden fuselage structure weighed 8 1/2 oz.; it's 10 1/2 oz. with the covering. The radio-equipped fuselage-and-tail assembly and landing gear weighs 27 oz., covered. The power system (motor, battery, wiring, prop, etc.) weighs four ounces.
By another rule of thumb, the power system in an electric should make up 40 to 60 percent of the finished model weight. In this case the power system is 52 percent of the final all-up flying weight of 84 oz. — right on! The wing loading is 14 oz./sq. ft.
Proper balance was attained with the battery packs in a forward location against the front former as shown. Had the plane been more tail-heavy (as it would have if I'd used the spruce longerons), I'd have reconfigured the packs into three rows of 5/4/5 to shift the battery weight forward. The only other option would have been to add nose weight — aagghh!
The remaining space in the battery compartment is filled with foam blocks. These keep the packs in place and force the incoming air through the cells.
Prop, wheels, and ground clearance
I've been flying with an 11x8 prop. I'd rather use a 12-in.-diameter one, but ground clearance would become marginal on a grass field. The nose wheel is two inches; the mains are 2 1/2 in. These items are by Sullivan Sky Lite.
Flight experience and performance
At this writing, the Seniorita has logged 43 flights in its first month. The first flight was in a mild snowstorm. Average cruising flight time in no-lift evening conditions is over nine minutes. That will improve noticeably when I replace the quite old, well-used temporary packs I stuck in the model just to get things going.
The electrified Seniorita handles very well on the ground and is smooth and positive on taxi, takeoff, and climbout. And — no surprise here — it doesn't blow a hole in the sky. I highly recommend use of a speed control — a high-rate one for best results — 'cause it adds so much to the fun of flyin'! Finally, the Seniorita handles wind surprisingly well.
This electric has proven its effectiveness as a trainer. So far, six field visitors who had never before flown have handled the Seniorita successfully. I've decided against trying to install a camera; no doubt I'll make some illumination pods (so-called illuminons) to strap to the wings for night flying this summer. I wouldn't even consider this plane were it not such a pussycat to fly. Next winter I'll look into the ski idea. Right now I'm looking for a small glider to tow.
Power-system recommendations
What power system to use with differently sized models that fit within the focus of this article — those with wing areas of about 700 to 1,300 sq. in. and wing loadings comparable to those described?
- The Astro geared 25 and 40 systems are both safe choices.
- Use the 25 for planes with wing areas at the lower end of the range, the 40 for larger planes.
- Examples: Powerhouse 84, Cavalier (from Model Aviation plans), Kadet Senior, and Senior Telemaster would be adequately powered with a 40, although I've seen some hotter ones with 60s.
- Use gears 25 and 40 — the larger, slower props are consistent with the relatively slow flight speeds intended. (Gears are not available for the 60.)
Conclusion
So choose an appealing model design, and go for it! Keep this article handy as you work, study the photos, and follow the rules of thumb. Fly quiet, long, and high! It won't be a Starship, but let's salute it anyway: "Live long and prosper!"
Transcribed from original scans by AI. Minor OCR errors may remain.
