Letters to the Editor
Battery Evaluator
I tried to make a battery evaluator as per Frank Kelly's article in the June 1984 issue. So far it has cost about $20 in parts and 20 hours. I'm ready to give up. After assembling the components and plugging in my receiver battery (four-cell Futaba 500 mAh) for a final test, it took about 1 hr. 40 min. to get 4.0 V on my voltmeter. Neither the LED nor my alarm have turned on. Can you use any of my parts?
It seems the receiver battery will continue to drain if left unattended. If I'd known this, I would not have started the project.
What I needed was a shutoff of the discharge cycle that was automatic at about 4.4 V and would stop the clock. I'm beginning to think I should buy something from the ads in the magazine—that seems cheap by comparison. What do I do with all this stuff? Any suggestions?
How about a circuit that shuts off the 1.5 V battery power on any clock? I only found two Copals with the shorting pad. My Timex doesn't have one. Copals cost about $2.49 around here.
I was using a 1.5 V battery instead of a clock, and also tried a 9 V. How about a circuit that runs off the receiver battery? Help!
Jonathan Rabe Santa Barbara, CA
Response from the designer/author, Frank Kelly:
Sorry Jonathan had a problem with my circuit. It kept me entertained for a few days until I got it to do everything I wanted it to, but there's nothing critical about it.
The circuit has positive feedback for a crisp latching action. It was designed around the clock I happened to have, and we still use that alarm clock. We live in the Australian outback now, and it doesn't require 110 V, 60 Hz power and isn't susceptible to blackouts. I tried to keep the circuit simple and inexpensive, so I left out battery disconnection at end of discharge, which would require a relay. I just figured I'd set it down next to the TV and let it go.
I have sketched a modification that will solve Jonathan's problems (except miswiring). It requires a micro-mini 5 V relay, available from Tandy (Radio Shack) for about $2.99. It's about 3/8 in. square by 1/2 in. long, so it ought to fit somewhere. You'll have to disconnect the negative end of the 1.5 V battery from the clock circuit and run it through the normally-closed contacts on the relay. You can either cut the copper trace on the PC board or stick a solderable metal contact to the existing battery-holder contact with double-back tape.
With the relay you won't have to worry about the inhibit pad that your clock seems to lack. The relay will also disconnect your test battery at end of discharge. Everything else will work as advertised. You can test the circuit by simply disconnecting the battery under test; the circuit will sense a voltage below the trip point and will sound the alarm.
If you have a voltmeter and a pot of about 100 ohms, place the pot between the battery under test and the circuit input. Start at zero ohms and increase the resistance while monitoring the voltage across the 43-ohm resistor until the circuit trips at about 1.1 V. If it doesn't, something's wrong. Monitor Pin 1 of the IC and short Pin 3 to ground. The meter should read high (7–8 V). Then short Pin 3 to +9 V (through a 1 kΩ resistor). The meter should go low (a volt or so). Similarly, Pin 7 should be doing the opposite. The alarm should energize when the alarm pad is shorted to ground (the alarm must be set).
Frank Kelly Alice Springs, N.T., Australia
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Looking for PA-48 Builders
The project manager for the PA-48 Enforcer project at Piper Aircraft in Lakeland, FL, informed me that modelers in the Tampa area have built several nice flying models based on three-views and dimensions from Piper. I have enclosed a small drawing that you may wish to print.
I'm writing because I would like to establish contact with these modelers in Tampa to see if any model plans, photos, flight info, etc., are available.
The PA-48 is a highly modified offshoot of the P-51 Mustang, and it would make an excellent Sport Scale subject with fine aerobatic capabilities if properly built.
Keep up the good work with your fine magazine.
Dave Trabert 65 Cynthia Dr. Richboro, PA 18954
Dave's full address is provided so that direct contact can be made. We agree the lines and proportions of the Enforcer look great for modeling.
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Fabric-Winged Corsair
In reference to the caption for the picture of the Chance-Vought F4U-1 Corsair on page 48 of the June issue of Model Aviation: none of the many Corsairs on which I worked during the '40s had fabric-covered wings, whether built by Chance-Vought or under license. If by "prototype" you mean the very first one built while the Corsair was still in the design stage, then maybe (and a big maybe at that) it had fabric-covered wings. Many WWII aircraft had fabric-covered control surfaces even though the rest of the plane was metal-skinned. Perhaps this is what the caption-writer meant.
One little pet wish of mine: I'm sure more builders would put pilots in their planes, as was done with this F4U. Whoever saw an otherwise complete and beautiful P-6E land sans pilot, as the one on page 49 of the same issue is doing?
The bit about altitude affecting models is very interesting. A few months ago I visited the flying field of Club Aeromodelismo de Jalisco, AMA y FAI, in Guadalajara, Mexico. The altitude is about 1,550 meters (5,100 ft. or so), but there certainly was no lack of zip to the flying. The members fly everything from powered sailplanes to Pattern. The field is somewhat inconvenient to get to, but well worth the effort—beautiful setup with paved taxi strips and runway, shaded work areas, flush toilets, etc. And the club members! I have never met a nicer, friendlier, more varied-in-interests bunch of RC fliers in my 50 years of modeling. You may contact Jose Barrios at his business address for more information:
Jose Barrios Morelos 487 Guadalajara, Jalisco, Mexico
Ed Lowe Holdingford, MN
Response from Bob Wischer:
Upon checking my drawings and data on the Vought F4U-1, I find that the wings were indeed fabric-covered on the outer panels from the main spar rearward to the trailing edge. The ailerons were also fabric-covered, as were the outer flaps, rudder, and elevators. Dale Arvin was proud of the fabric detail on the model.
The other comment concerned the Curtiss Hawk P6-E flown by George Rose in several World Championships. The model does have a pilot in the cockpit; in the magazine photo the top of the pilot's head is just beneath the landing wire. George would have lost flight points if the dummy pilot was not used during flight. A pilot isn't required when the airplane is static-judged but is mandatory in flight.
Actually, a pilot occupies the cockpit of all full-sized planes only during flight, which is a very small percentage of an airplane's life. When a pilot is seen in the cockpit while the model stands on the ground, it can give the impression that it is a toy. In models where pilots are permanent because the radio equipment occupies the fuselage space, I feel this detracts from the model's appearance while on the ground.
Drawings of the Vought F4U-1 were published in Model Airplane News, June 1972, and in American Aircraft Modeller, October 1968. There are also numerous books available on the F4U series, such as Aircraft in Profile and Squadron Signal In Action. See page 5 in your June issue for the Zenith Aviation Books ad.
Bob Wischer Delafield, WI
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Dope Blushing
This is in reference to the letter from Craig McGuern in the June 1984 issue of Model Aviation—and your reply. Craig spent a paragraph on respraying a doped surface with thinner when the dope had blushed. Your reply was to wait for lower humidity. In some locations, one might have to wait for months! I have lots of experience with humidity here on the Gulf Coast, 45 miles west of Galveston.
How humid is it? It's so humid that the mosquitoes are born equipped with tiny Mae West life jackets. Would you believe a tiny pair of Eo floats? Or, just ask anyone who attended a Lake Charles Nats.
We have had to find a way to dope in humidity—or give up and use only plastic films. There's a simple solution. Both dope suppliers and acrylic lacquer suppliers provide an equivalent retarder for their products. It reduces the cooling of the paint film due to thinner evaporation so that the film never cools below the dew point, and no dew forms on the surface. Use of regular thinner as an after-spray can cool the surface below the dew point, giving a blush.
I suspect most retarders are compounds such as ethylene glycol monoethyl ether acetate (Dow Chemical's Dowanol EAA). They are added to the dope as part of thinning to proper consistency. Start at 1 oz. per quart, increasing the amount if blushing still takes place. As more retarder is added, drying time increases somewhat, so you have to wait a little longer before sanding and recoating. Check with your dope supplier or local automotive paint store for a can of the retarder. It can be used as an after-spray as Mr. Mecum suggested, and it works fine.
P.S. Speaking of painting, did you hear of the chemistry professor whose quiz asked for the name of the element whose symbol is Ru? One student gave the answer, "Rustoleum."
Bob Lane Lake Jackson, TX
Transcribed from original scans by AI. Minor OCR errors may remain.
