Howdy, all…
My Facebook feed is mostly pictures of cats and models, links to music videos, and history tidbits. A few months ago, I noted the celebration of the first flight of the Cessna Citation. In my narrative, I said “Cessna’s first jet flies”, and was taken to task by someone who corrected me—Cessna’s first jet was their Model 318, aka the XT-37 trainer.
The Cessna T-37, designed as an economical basic jet trainer for the U.S. Air Force, featured side-by-side seating for the instructor pilot and student and was powered by a pair of Teledyne-Continental Aviation and Engineering (CAE) J69-T-9 or (T-37B) -25 single-spool centrifugal flow turbojet engines (license-built copies of the French Turbomeca Marboré). Between the engine design and the inlet design, the airplane had a rather recognizable sound. Because of the bulbous canopy and the high-pitched engine sounds, it was alternately called “Tweety Bird” (usually shortened to “Tweet”), “Screamin’ Mimi”, “Kerosene Converter” (it converted JP4, aka Jet fuel—which is basically highly refined kerosene—to noise), and “6,000-Pound Flying Dog Whistle”.
Scanning the feed a day or so ago, I noted that it was the anniversary of the mighty Cessna Tweet’s first flight, which reminded me of something I experienced in my early days as a spark chaser. Let’s get in the Wayback Machine and travel to 1989…or maybe it was 1990…
We got a phone call from the owner of a 1947 Beechcraft “Bonanza” (aka the “Fork-Tailed Doctor Killer”). The gentleman told us he was having some problems with his COM radio, and asked us if we had time that day to take a look at it. We told him to bring it on, and after he arrived we started to debrief him as to the nature of the problem. He was an older man, jolly and friendly—he reminded me a lot of Burl Ives as Santa Claus riding a Norelco razor head as it slid down a snow-covered hill.
He said his transmitter was noisy—according to him, the actual symptom varied from “hash” (a low rush of static) to a low whistle any time he keyed the microphone. Some further prodding yielded more of the story—it was a new radio, recently installed by a shop that had a monthly two-page center spread advertisement in “Trade-A-Plane” and “Aero Trader”. These guys were sort of the “Crazy Eddie” of the avionics world, promising to turn lead to gold in an hour at a discount price. He told us that they did the job while he waited, which raised all sorts of alarms—on an airplane that old, there were a lot of tripwires that could delay completion of even a simple job. Anyway, he filled out a Work Order and we got to work.
When this airplane was built, it was built with no radios—that’s simply how they did it back then. As time wore on, and more air traffic filled the skies, the need for radio communications arose. Then came a need for some sort of aerial navigation system, then a secondary radar (aka an ATC Transponder), and pretty soon, avionics became a thing. This airplane previously had an older NAV/COM and transponder installed (probably sometime in the late 1960’s), and they were both recently replaced with new radios, as noted above. The transponder was working fine, the customer said, as was the NAV. Only the COM transmitter was giving him problems. Or so he said…
A quick visual inspection of the airplane indicated that the antennas were older types. They weren’t the best antennas to use with a modern (well, “modern” for the late 1980’s) radio, but a quick consultation with the installation manuals and a quick phone call to the radio manufacturer in Fort Washington, Pennsylvania (you old time airplane guys know what that means!) allowed that yes, they could be used—they weren’t optimal, but they were allowable. We checked them for good ground plane and electrical bonding, and they looked as good as 20-something year old antennas could.
The airplane had only a COM and a NAV for audio sources. The microphone wires were connected directly to the microphone jack, and the NAV and COM headphone audio—did I mention that this airplane didn’t have a cockpit speaker?—was controlled through an unlabeled toggle switch. In the UP position, the COM audio went to the headphones, DOWN and the NAV audio was heard. Not ideal, but workable. We made a label for the switch functions, stuck it on the instrument panel, and continued.
We checked the airplane’s battery—a low battery level can cause some problems, even though modern radios were more tolerant of low voltage conditions. The battery checked out, so we did some radio checks sitting on the ramp apron outside the hangar. Calling the shop wasn’t bad, but a call to Ft. Lauderdale Ground resulted in a reply of “garbled”. So, the problem varied with distance. We decided to do some checks with the engine running. Again, calling a hundred yards to the hangar was okay, but a call to Ground resulted in another “garbled” reply. We varied the engine RPMs to see if the problem varied with power (indicating a possible generator/alternator issue), but it remained more or less consistent—the transmission was low level audio surrounded by hash. Every now and then we’d note a low-level whine, too, but the hash was the main issue.
We also noted that the NAV indicator needle tended to “windshield wiper” at times, and the NAV audio had some noise in it, too. These signs—the weak audio, the weak transmitter at distance, and the erratic navigation needle swings--pointed to bad shielding on the antenna cables and signal wires, and possibly defective antennas and antenna cables.
We taxied back to the hangar and removed the radio for a bench check—as my boss hammered into my young head many times, “You have to know what you know”. In other words, we weren’t to assume just because it was a new radio that the radio wasn’t at fault. We handed the radio off to our bench guy, and he ran it through a functional check. Everything looked good.
With the radio out, we examined the installation. The hole in the panel had been enlarged with what appeared to be a chain saw. The radio mounting rack (“can”) wasn’t very secure, and the forward end wasn’t supported. We removed the can to get to the wiring. The wiring—well, let’s say the wiring wasn’t tidy (“mouse nest” more aptly describes what we found). The wires were stretched tightly behind the instrument panel, and the bundle—if you could call it that—was poorly tied and secured.
Audio lines are shielded wires—the conductors that carry the signals are surrounded by a metallic braid. This braid acts as a sort of antenna that receives potential noise to keep it off of the signal lines. The braid would be connected to an airframe ground at one end to shunt the noise to ground (these days, the shield is grounded at all ends, because radio technology has changed and requires stricter High Intensity Radiated Fields, or HIRF, protection). The antenna feeds are coaxial cables--in this time period, it was RG-58A/U 50-ohm impedance cable with a single braid (more modern radios have low-loss cables with multiple braids and foil shields, again to combat HIRF). We reasoned that the old cables were probably re-used with the old antennas, because aging cables could have multiple problems, from corrosion to deteriorating shield and/or dielectric insulator.
The audio wiring in this installation may as well have had no shielding at all. The audio pairs from the COM and NAV to the switch were unshielded twisted pairs. The one audio wire that was shielded was the twisted triple conductor for the microphone audio. The installer didn’t do a good job in terminating the shield—through chance or by sheer luck, he managed to get a few strands of one end of the shield tied to the radio’s power ground. The audio selector switch was a low-quality switch of the type you might find at Radio Shack (or, as it was also known, “Tandy Avionics”). The wires were also too short, and it was under tension as routed. The first thing we thought was that we might as well have the whole mess removed and replaced with a proper harness and new antennas, but that would take quite a while to accomplish. We showed the customer what we found, and explained just how poor this job was, and that it really needed to be re-accomplished from the beginning. He wasn’t going for it. His jolly nature was beginning to recede…
We were told to do what we could with what was there. After untying the harness (such as it was), we found places where we could get a bit of slack in the harness. The unshielded audio wires were replaced with properly shielded wires. We extended the power and ground wires to further alleviate the banjo string tension of the harness. Finally, we inspected the wires to the NAV indicator, and they looked acceptable. Our senior installer had a look and gave his seal of approval.
After the wiring was addressed, we looked at the antenna cables. As we feared, the cables were in bad shape. The connectors were poorly installed (and these were new connectors installed on the old cables), so they were removed. We noted some green corrosion between the braid and the dielectric, the jacket was hard and brittle, and the dielectric was crumbling, so we got approval to run a new antenna cables. We reasoned that while we had everything open, now was the time to make it right.
We finished our work and called for an inspection. The shop inspector gave us a thumbs-up, and we closed up the work areas and taxied out for a final check. The radio checked out good on the ground, all that was needed was an in-flight check. We told the customer that he really needed to get those antennas replaced. He said he would do that when he got to his home airport, he paid the bill (grousing about every last nickel we charged him, too!), and prepared to leave. His jolliness had by now turned to grumpiness.
“What does all this have to do with the T-37?” you’re asking.
I’m getting to that.
As our customer started up and taxied across the ramp, a T-37A was sitting at our FBO—we had the military fuel contract at Ft. Lauderdale, and this guy was on a cross country training flight and needed fuel. As we headed out to the ramp to watch our customer depart, we heard the Tweet fire up its engines—an event difficult to miss, since even a deaf man could hear the banshee-like wail of the J69s. As the Tweet pilot went through his preflight checks, the airplane sat there, whistling away.
We also watched as our customer taxied away from the hangar, rolled up directly alongside the jet, set his parking brake, and attempted to call the tower for his departure clearance. After a few minutes, the customer turned back to the hangar. We didn’t know what was going on, but we had an idea as to why. Our bench guy confirmed our thoughts. He had been monitoring the radio in the shop, and when the customer keyed his microphone, the only sound transmitted was the ear-piercing screech of two J69s at idle. The controllers in the tower never heard his voice, only the sound of the jets. Our bench guy came out of the shop and told us what was going on as the customer taxied up.
The customer shut the airplane down and climbed out—and boy, was he hot! “You have no clue what you’re doing! The problem is worse than it was before! I want my money back!” Frankly, I was worried that he would have a stroke or massive coronary right there on the ramp, he was shouting so loud.
The boss pointed to the diminutive jet trainer, by now taxiing out to the runway. The noise was still ear-splitting—even more so with the increased power settings needed for the airplane to taxi. “You were sitting right next to that when you tried to call the tower. Try again!” the boss shouted to him.
Red-faced, the customer got into his airplane, started up, and departed without further incident.
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I’m in the middle of a belated annual sports let-down. COVID-19, I don’t think I have to tell you, threw a large wrench into the sprockets of the major sports series. Since my annual yardstick tends to be measured by the various sporting events and seasons, this year a lot got bunched up in the past six weeks. So, instead of having a few months between events, they all came or are coming up in the space of about eight weeks. The Stanley Cup, the U.S. Open (tennis), the French Open, The Masters, Sebring, World Series, NBA Championships, they’ll all be back to back this year.
Also, several events I like to watch were cancelled: Wimbledon, the races at Watkins Glen and Pocono, some of the NHRA drag races…
After all this is over, I am hoping we can get a handle on COVID-19 and next year can reset to whatever the new normal will be.
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Other events effected by COVID-19, and I’ve mentioned this in passing, have been scale model shows. We were on the calendar for the Third Annual South Carolina Scale Model Mega Show in June. In April, we decided to postpone until August, and in July we finally pulled the plug. Most other local and regional shows were postponed or cancelled. The two big shows in the U.S., the IPMS/USA National Convention and the AMPS International convention were also cancelled, the latter after being initially moved from Harrisburg, PA to Danbury CT and postponed. Scale Modelworld in Telford as well as the Shizouka Hobby Show were also cancelled.
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So, with all this time on my hands, I should be a model building fool, right? Not so much. As noted previously, I have managed to winnow my long-term project drawers (some may call it a Shelf of Doom) to one—the Aeroclub 1/48th scale Gloster Gamecock. I also have embarked on a few 1/72nd scale F-4 projects. But what has really eaten into my time has been research and writing—I’ve been working on four articles in association with the Phantom projects, as well as trying to put something together for our club newsletter and this blog.
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Needless to say, my gripes are quite minor in comparison to folks who have been directly affected by this disease. In my own extended family, my cousin’s husband died in February from what was most likely COVID-19—remember, in February, 99.9% of Americans hadn’t even heard of COVID, so there is no 100% confirmation, but the symptoms he exhibited certainly sound familiar—high fever, cough, shortness of breath, and pneumonia-like symptoms.
Several other friends of mine have been infected, too, and are in various stages of recovery.
Bottom line: Wear a mask, maintain social distancing, and practice good hygiene. These are simple steps that, according to science, works. If we all do our part, we can put COVID out of business.
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