Letters To The Editor
Complex Areas: Another Way
Although Mark Fineman's method of calculating irregular surface areas is fine, those of us without the dollars required to purchase a computer need not despair. Thirties technology comes to the rescue. I claim no credit for this system; I've simply forgotten where I read it. Here's the low-tech way to figure areas of complex shapes:
- Take the cardboard back off a common 8-1/2 x 11 writing tablet.
- Carefully measure the total area of the cardboard (length times width).
- Carefully weigh the piece of cardboard.
- Carefully trace the irregular part onto the cardboard.
- Carefully cut out the irregular piece from the cardboard.
- Carefully weigh the irregular piece you have cut from the cardboard.
- Set up a ratio and solve for the unknown area. Since weight is proportional to area, use:
area_irregular = (weight_irregular / weight_original) × area_original
Example: weight original = 30 g area original = 93 sq. in. weight irregular = 13.3 g
area irregular = (13.3 / 30) × 93 = 41.2 sq. in.
That's all there's to it, folks. When reasonably done, the accuracy of this method far exceeds any practical need. On larger pieces it may well exceed the binary box (computer) in terms of outright accuracy. I would assume that the use of a calculator to multiply and divide in the above arithmetic should at least convert the whole procedure into "mid-tech." Have fun!
Doug Dahlke Oshkosh, WI
Rarely Seen
Enclosed you will find some photos of my latest project. I have seldom seen this particular plane published, so I thought I would give it a try. The model is a Cessna Skymaster 337 twin (without retracts) built from a Royal kit. It's my first scale attempt and took slightly under four years to complete. The plane was complicated to build, but it looks nice and flies very well.
The model spans 76 in., weighs 9 lb., and is powered by two K&B .45 Sportster engines. The finish is metallic green and white MonoKote and white Coverite spray epoxy. The young lady in the photo is my friend, Sharon Geigley.
Martin G. King Harrisonburg, VA
Radio Shack Ni-Cd D-Cells
I don't own a Radio Shack store, and I am aware that the ancient and honorable name of Radio Shack has been subverted to the merchandising of what, in some cases, is the garbage from the kilns of Bangkok. Nevertheless, it seems that Don Srull's oft-pondered attack on Radio Shack batteries ("Mini-Electrics," September 1988 issue) is contested by one of the most respected product testers in America—Consumer Reports.
In their November 1987 issue, Consumer Reports found just the opposite of what Srull said. They report that Radio Shack #23-140 D-cells are the only ones that were really D-cells. All the others except Radio Shack's were C-cells padded out to D-cell size. Yes, the Radio Shack D-cells cost more. No, I don't know myself if they are any better than the other kinds of true D-cells, and probably they are not any better.
Srull's other objection to D-cells as opposed to C-cells is well taken. The Radio Shack D-cells do weigh twice as much as the other fake D-cells, but they should actually give about 4.0 amp-hours. I'll admit I haven't actually tried them myself, but Consumer Reports usually is careful not to tout something on pure myth or hearsay.
Don't be too quick to knock Radio Shack. They carry some of the best switches I have found for low contact resistance for use as an arming switch in electrics. Try the #275-1545 or #275-1546. With both sides of the double-pole switch wired in parallel, there's hardly any resistance at all. I know this is not very important in the low-current mini FF jobs, but Srull and others may also be interested in larger RC electrics.
Writing magazine articles as Don Srull does on a semi-technical subject is a thankless task. There's always someone who will nit-pick on some minor point! I really did like the article, though. My first electric was a little Guillows Arrow converted to VL-70 power.
E. A. Westbrook Chelmsford, MA
Don Srull — Response
Thanks for your interest in the Mini-Electrics article. I'm baffled, however, how you could have interpreted anything I said in the article as a knock against Radio Shack. Most other people think I have a lot of Radio Shack stock!
If you take another look at the article, I recommended that Radio Shack C-cell Ni-Cds be used, along with their switches, plugs, jacks, resistors, lamps, timers, and wall charger. What I warned against was the so-called economy Ni-Cd cells that Radio Shack and others sell.
You may not have been aware that Radio Shack sells two different quality levels of Ni-Cds, and you have to be careful which ones you buy. In the Radio Shack catalog and on their store shelves, you will see that they carry less expensive, lower-capacity cells—a C-cell of only 1.1 Ah capacity as #23-124 and a low-capacity D-cell (also 1.1 Ah) as #23-123. Their higher-quality C-cells are #23-141 (which I recommended) and #23-140 for D-cells.
In that November 1987 Consumer Reports you will find that they tested both types of Radio Shack D-cells, and they reached the same conclusions as I did: the heavier, more expensive Ni-Cd cells are better for heavy-duty use. By the way, I did test all of the cells mentioned before I wrote about them in the article.
In any event I hope this clears up any possible misunderstanding that I was knocking all of Radio Shack's Ni-Cads. The message I was trying to get across is to stay clear of the cheap, lightweight, pseudo-cells of low capacity that are now being sold by many stores, including Radio Shack.
Don Srull McLean, VA
From Japan
Thought you'd be interested in these shots of our activities here in Japan. The Easy-Built FF Monocoupe makes consistent 40-sec. flights despite its lack of spiral stability. I made the rudder smaller rather than adding dihedral. A smaller prop finally did the trick.
The CL Mustang is from a Japanese KM kit—mostly hardwood and plywood covered with silkspan and doped. Engine is a PAW .19 DS4. Despite being somewhat overpowered, the Mustang is a real joy to fly.
In the Mustang picture note the can of Mr. Diesel fuel—the world's best, I think. Mr. Diesel (Ian McQueen) deserves a prize for his promotion of aeromodelling here.
Nathan Sturman Shibukawa City, Gunma-ken, Japan
All letters will be carefully considered; those of general interest will be used. Send to Model Aviation, 1810 Samuel Morse Dr., Reston, VA 22090.
Transcribed from original scans by AI. Minor OCR errors may remain.
