Cessna 172, double ignition failure on departure. Freeway was the only available concrete, but had to move to the center lane to miss the clapped-out Datsun wagon with six kids on board chugging up the hill in the right lane. Bridge abutment in the center divider took off 8 feet of the left wing, airplane rolled counterclockwise over the center divider and came to rest upside down in the fast lane of the opposite side of the freeway. Four walked away without a scratch, except my watch band got a nasty ding in it from the door handle.
Ah, yes! At Motorola we called it greased pig snot ;-)
...Jim Thompson
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| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I used wax for potting electrometers. We got sub fA performance at room temperature. It beat out everything else we tried including that clear snot that thy use for automotive electronics.
This was twenty years ago and it was a special blend for sealing junctions in underground telephone cables. So I was told.
The product name is DILWAX #35 It was quite soft and very sticky.
We potted the entire electrometer front end which put the end to the humidity caused surface leakage and it also eliminated parasitic ion chamber effects. The instrument was used to measure Tritium in air in presence of gamma radiation.
Sigh. In the Air Force all we had was "[Granny's] Goose Grease", some Dow Corning silicone grease in a tube ... OK, found it: "DC-4". And, since it was so long ago, RTV was just "RTV", since it had just been recently discovered. ;-)
A manager I once worked for had a cam shaft come unglued (head cracked releasing the rocker) in his 172 and had to do an emergency landing. He got lucky and was able to trade the last bit of his KE for enough altitude to clear a tree-row and put it on an uncontolled runway. He did the right thing and put a note on the windshield and walked to civilization. ;-) As he pointed out later, missing once cylinder (of four) doesn't drop the HP by 25%; more like 75%.
Yes, a lot of undersea stuff works because of a joints made with "monkey shift" wrapped in electrical tape. Its sort of the duct-tape and WD40 of the marine world.
I didn't say "both magnetos", I said "double ignition". We found out the following morning the forensics of the failure. Briefly, unleaded avgas was phased out and we were forced to burn a fuel that had four times the amount of lead that the engine was happy with. This caused lead deposits on the plugs that we cleaned every 25 to 50 hours. We had 15 hours on these plugs when the accident happened.
Top magneto (the one that fires the top plugs) had a thermal failure of the magneto coil. Engine gets hot, magneto opens up, no top plugs. That's why we have dual ignition. However, flame front starts at bottom plugs and instead of burning to the center of the piston and meeting the flame front from the top plugs, the flame front burned all the way to the top plugs. That is where the flame front burns out and is at maximum temperature. Max temperature melts the lead in the top plugs and on the way to the exhaust valve the lead goes by the bottom plugs and gives them a quadruple dose of lead. A few seconds of this and the bottom plugs are lead-fouled and fail.
Double ignition failure.
NTSB doesn't really get excited about figuring out what went wrong unless there are fatalities.
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner
The "unleaded" was 80/87 octane "red gas" with a maximum lead content of 0.5 ml/gallon of tetraethyl lead. Back in those days you also had "green gas" that was 100/130 octane with a maximum of 4 ml/gallon of lead. Newer aircraft with compression ratios more than 8.5:1 needed the 100 octane fuel and the cost to refine and distribute two octanes of fuel became prohibitive. THe compromise was on a low-lead version of 100/130 called "100LL" or "blue gas" that contained no more than 2 ml/gallon of lead and was approved for all engines requiring 100 octane fuel or less including the old low compression engines that burned 80.
The problem is that the combustion temperature of the low compression engines is insufficient to activate the bromide lead scavengers of 100LL and so the lead plated out on whatever surface it pleased including valves and valve seats, plugs, and the like. After a while somebody came up with a chemical (tricresyl phosphate - TCP) that purported to scavenge the lead out of low compression engines, but it was a witch to mix (it really didn't like being mixed with gasoline) and nasty to keep in the airplane. And it really didn't work all that well ... you still had lead, but a little less of it in the combustion chamber after a few hours.
The problem went away for a while when a couple of businesses got official FAA permission (STC -- supplemental type certificates) for specific engine/airframe combinations to burn 87+ octane unleaded car gas. That particular airplane had the STC, but for liability reasons airports were reluctant to pump car gas into airplanes. At home I have a 55 gallon tank on a trailer and used to use car gas on a regular basis. THe problem was that this airplane was on the road for a couple of weeks prior to the incident and I had to use whatever gas was available at the destination airport(s).
I said "used to". The great state of Californicate for whatever reason mandated 6% ethanol in all grades of car gas a couple of years ago. Ethanol is absolutely forbidden by the STC for use in aircraft ... the rubber bladder fuel tanks and seals in the carburetor are eaten alive by ethanol. Therefore, we either go over to Nevada every time we need a fillup OR we go back to using 100LL. It sucks.
Oh, it is really interesting. Without so much as a maintenance logbook to look at, the NTSB "found" that the root cause of this accident was "improper maintenance". Since I've got a Sammy Unkle Airplane Tinker's license, I know what the maintenance records for these magnetos was and I know what service interval on the spark plugs was. The coil break was way down deep in the innards of the coil where you would have had to unwind the whole coil to find the break. That's not a normal service procedure, nor are 15 hour plugs part of the routine. However, bitching about the findings would have done no good OR a trip to Washington to fight it, neither of which is particularly appealing.
That looks like a typical mandate by the 'higher ups' w/o thoroughly investigating the consequences. Reminds me of the MTBE disaster. I remember that we had 80/87 fuel in Cameron Park. At a meeting at our airport a year ago or so they decided to abandon it and AFAIK sold the last few thousand gallons to another FBO.
Probably the only way out would be to have an engine that doesn't drink ordinary gas, like one of those new Diesels (Turbomeca?) if there is one STC'ed for the 172. But that retrofit would probably cost more than a few hundred trips to Nevada.
That's like fighting a speeding ticket. Tried it, on the only one that I ever got in CA. The vehicle could have never reached 85mph with the load I had. The calibration cert on the cruiser was wrong and I had secured proof of that (meaning it was out of cal even though the officer said otherwise...) and so on. Judge hesitated for quite some time and then sided with CHP, the usual I guess.
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