The following information is out of the Standard Aircraft Workers' Manual, tenth pocket edition by Fletcher Aircraft.
Air pressure must be carefully controlled regardless of the type of riveter used. Approximate air pressure required for the various size rivets are indicated:
|
RIVET DIAMETER |
AIR PRESSURE LBS./SQ. IN. |
|
3/32 |
25-35 |
|
1/8 |
35-45 |
|
5/32 |
55-65 |
|
3/16 |
85-90 |
|
1/4 & 5/16 |
90- |
BRAKE FIRES
From the musclebiplane.com website
My search for information on wheelpant fires was prompted by a friend who's Extra 300 burned. Apparently he had a fuel drain that exited on the wheel pant, which somehow caught fire. This interesting story was sent to me.
I had a brake fire on an RV-8A last weekend. Tidy combination of operator error and design issues, much of which is specific to the 8A and/or castering nosewheel, steer-with-the-brakes airplanes in general. However, research did turn up a few items perhaps everyone should know.
The fire started after an overheated caliper leaked fluid on a hot disk. The fluid flashed and lit the resin in the fiberglass wheel pant, as well as the tire sidewall. The brake worked fine, with only slightly higher pedal pressure required even when on fire.
I've posted a photo to the vault (yep, a bystander had a digital camera). In the photo, I'm holding pedal pressure while shutting down for the fire crew. Note the fire on the ground under the pant, believed to be fluid and dripping resin. I don't recall any additional pedal travel.
When something like this happens I get curious. Why did the seal leak at some temperature well below a failure temperature for the rest of the brake? And why did the fluid catch fire?
Fast forward: It turns out the Cleveland piston seal for the little 30-9 caliper is an ordinary MS28775-218 nitrile o-ring. Nitrile's temperature rating is - 65F to +275 F. We found the seal to be brittle and flaking when we dismantled the caliper. A caliper seal with a 275 F temp limit is below automotive standards, but that's another story.
As for fluid, Cleveland's tech manual specifies either Mil-H-5606 or Mil-H-83282 as acceptable. Both are listed in AC-43 and the A&P texts. Turns out that Mil-H-83282 was created because the military was tired of setting it's airplanes on fire. Mil-H-5606 is the standard red hydraulic fluid sold by Spruce, Wicks, Chief, etc. It is a petroleum base, and turns out to have a very low flash point. The Mil-H-83282 is also red, and compatible with 5606 fluid as well as seals created for 5606. However, it is a synthetic, with much higher flash and burn points, and is self-extinguishing when removed from the ignition source.
You can download complete specs for Aeroshell Fluid 41 (Mil-H-5606) and Aeroshell Fluid 31 (Mil-H-83282) at: http://193.113.209.166/aeroshell/aeroshellhydraulicfluids.pdf
Note the flash points of the two fluids. Aeroshell 41 is 104 C, which is only 219 F. Aeroshell 31 is 237 C, or 458 F.
A flash point of 219 F means that when a Cleveland caliper seal fails at something above 275, the fluid is already hot enough to light when it hits a hot disk and vaporizes inside the pant. Makes for an interesting combination.
Live and learn. I always assumed standard "mil-spec red brake fluid" was something special, and I doubt I was alone in this assumption. It's not. It's just another one of those "always done it that way" things prevalent with light airplanes. Note that the Shell literature declines to even refer to it as brake fluid.
Spruce, etc, doesn't sell Mil-H-83282 fluid, but they should. I've already ordered a gallon of Fluid 31 from the local Shell distributor. Since the old and new fluids are compatible, switching is as easy as draining the old, flush with new, refill, and bleed.
Let's be careful out there.
A coworker has asked me to gather any information on wheel pant fires for his friend who's Extra burned. Apparently he had a fuel drain that exited on the wheel pant, which somehow caught fire. He is having trouble with his insurance company and wants to have some other cases of such an event to help his case. Seems like I remember this happening to someone a few years ago. Any information is appreciated!
FIBERGLASS GAS TANKS
Chapter member Bill Unternaehrer provided this interesting story. A friend of his had just started flight testing his Subaru powered Kitfox when he noticed that the fuel in the tanks had turned a nasty brackish color. After draining out the fuel and replacing it with a fresh load he noticed the same thing happen to the new fuel in a week or so. After draining the tanks he discovered that the fuel had stained the inside of the gas tanks in each wing. Getting on the phone to the Skystar factory that builds the Kitfox, he learned that the Kitfox fiberglass gas tanks are not compatible with automobile gasoline. They recommended only using avgas. The builder had chosen to put the Subaru engine in the plane to have the ability to use auto gas and now has to run avgas with an additive in order to keep the gas tanks from being eaten away.
AEROQUIP FLEXIBLE LINES
Last month I was giving a ride in my J-3 Cub to a friend visiting from snowy Michigan. It was a nice sunset flight followed by a couple of touch and goes. On final approach he said that there was oil coming from under the instrument panel. Back at the hangar we discovered one of the Aeroquip hoses had cracked. This was a professionally built, pressure tested, and certified hose that had been subjected to a maximum of 60 psi for 205 hours time in service. After hearing stories of ADs against these types of hoses I removed it and took it back to the manufacturer, Varga Enterprises. They said this type of hose had no life limit and had no ADs on it. They recommend that after five years they be inspected yearly and replaced at engine overhaul or on condition. Always check for AD notes on any type of hoses you might have on your aircraft, even if it is experimental. The ADs might not come up under a normal AD search and have to be looked for separately. Last summer I had an Aeroquip 303 high-pressure fuel line fail on an Aero Commander 500B I was flying, and now a line failed in the Cub. You can be assured that I will give all flexible lines a good inspection and replace any at the first sign of leakage.
Oil leaks?
Try this. This piece of advice comes from Terry Emig, who hopes to save someone else all the grief he experienced recently with an oil leak in his Stearman: "After nearly 200 hours of trouble-free operation on my recently-overhauled Continental W-670 engine, I began to see more and more oil in the bottom of the cowling and running down the front of the engine from the crankshaft seal. After everyone I asked came up with a different opinion about the source and cause of the leaks, I decided to call Aero Engines in Los Angeles because they had done the overhaul.
The first question they asked was whether the breather tube going from the engine down the Landing Gear Leg was clear. I was not sure. They explained that if the breather tube became plugged, the nose case could be partially pressurized and that would cause oil to leak from around the crankshaft and all over the front of the airplane. They recommended that I remove the clamps that hold the flexible hose to the rigid aluminum tube on the back of the engine and pull the tube out of the hose. Next, use the blow gun from the air compressor to CAREFULLY blow out the line. I set the pressure regulator to 20 psi and let her rip. Wow, you could not imagine how much goop came out of that breather tube. What a mess it made on the hangar floor. That stopped the oil leaks instantly. I wished that I had called them sooner and saved all those hours of cleaning oil off the airplane after each flight. The only thing I could add would be to place a larger bucket under the tube to you don’t have to clean that mess off the hangar floor. Fly safe!" -Terry
Fly Frequently to Avoid Problems
Todd Clamp, A&P Mechanic
The biggest impediment to trouble free operation of your airplane is inactivity. Your aircraft needs to be flown and flown regularly. If it is not flown regularly, minor maintenance items go unchecked because of lack of regular preflight inspections. Airplanes especially fabric covered ones, deteriorate whether they are in the air or on the ground.
Engines also die a slow death if they are not exercised. Dry engine seals produce leaks and moisture builds up inside the engine, leading to corrosion. At the same time electrical contacts corrode and electrical problems can be a nightmare!
The best antidote to all is to fly frequently and not just around the pattern. You need to get the oil hot enough to boil off the accumulated moisture in the oil. 180 degrees is the ideal oil temperature year round.
Another problem is that you pilot skills will also deteriorate with inactivity and this is the worst situation you can inflict on your airplane. It deserves to be flown properly and with a degree of competence. Take care of your ship and it will take care of you.
RECOMMENDATIONS TO CONSIDER BEFORE STARTING A PROJECT
BY JACK HAKES, TECHNICAL COUNSELOR, EAA CHAPTER 49 (LANCASTER, CA)
I highly recommend that anyone starting a homebuilt aircraft project do the following:
1.
Purchase and study some basic books that will answer most of the questions
regarding standard aircraft practices, techniques and procedures used in
the construction of an experimental airplane. The following is a
list of these books. Federal Aviation Regulations for Mechanics - AC 43.13-1A
& -2. This covers acceptable methods, techniques and practices for
aircraft inspection and repair. Standard Aviation Maintenance Handbook,
is another great guideline book, published by IAP
Tony
Bingelis' series of books: "Sportplane Builder", "Firewall Forward", "Sportplane
Construction",
and his latest "Tony Bingelis Engines.” All of these books are available
through OSHKOSH EAA AVIATION CENTER. It is very difficult to construct
an airplane without this series of books by Tony unless you've built a
half dozen airplanes before.
2. Contact one of the Tech. Counselors and have him visit your project as soon as possible upon starting construction. Often you can get good advice on what not to do before getting yourself backed into a corner and then have to restart. We are here to help improve the aircraft and are not policing the builder.
Quite often the inexperienced builder is quite willing to accept advice and help; however, I also find that the same individual becomes an expert in his own mind once he starts building, and the first thing you know he is giving advice and not all of it is good. It is good to get into a type group club or to look up other builders that have been down the same road that you are taking and ask them for advice and constructive inspections.
NOTE:
To get a discount for "AVEMCO' Insurance: Upon receiving the annual questionnaire
on hours flown, etc. In the past year, make sure that you send a notation
that you are an EAA member with your local chapter number and your national
EAA number. This can save you some of those $$ to spend on your plane.
Probably everyone who has worked with fiberglass already knows this, but it was a revelation to me. How do you force the fiberglass to form itself to the tunnel and to the curved opening in the cowling? What I needed was some way to apply an even force to the entire surface of the fiberglass. A short trip to the local drugstore provided a supply of party balloons. The balloon designed to look like a torso was ideal. With the small area in the tunnel area and the two larger volumes on the outside of the tunnel, the balloon applied and almost perfect pressure to the fiberglass. The resin didn’t stick to the rubber balloon, so, after curing, the balloon was easily removed. The inside of the tunnel was smooth and the edge of the fiberglass was smoothly bonded to the canopy. With a little sanding, the job was done and done well.
When calculating fuel a good rule of thumb to use regarding fuel burn is that the hourly fuel burn, in pounds, is a reasonable and repeatable measure for power settings. It is also a good measurement of engine efficiency. Most old technology engines, which include our aircraft engines burn about .44 to .45 pounds of fuel per hour per horsepower. Since 75% cruise fuel consumption figures are commonly known you can check the numbers for the plane you fly below.
Cub: 75%x65hp=49hp x.45=22lbs/6ppg=3.7gph
C150: 75%x100hp=75hp x.45=34lbs/6ppg=5.6gph
C172: 75%x150hp=113hpx.45=51lbs/6ppg=8.4gph
RV6: 75%x180hp=135hpx.45=61lbs/6ppg=10.1gph
C180: 75%x230hp=173hpx.45gph=76lbs/6ppg=13gph
Glassair III: 75%x285hp=214hpx.45pph=96lbs/6ppg=16gph
Beech 18/AT-11 (per side): 75%x450hp=338hpx.45pph=152lbs/6pg=25gph
Boeing B-29 (1 of 4 engines): 75%x220hp=1650hp x .45pph=743lbs/6ppg= 124 gallons per hour per engine x 4 engines=496 gallons per hour x $1.95= $967/hour cost!
It seems based on my observations that the bigger engines are slightly more fuel efficient and are closer to the .44 pounds per horsepower number. So if you are burning 9 gallons per hour in your Cessna 180 or your P-51 you are producing 120 horsepower, for a 52% power setting in your Cessna, or 10% in your Mustang. It seems logical that you can burn more fuel, as waste or for cooling, but it would seem that you can’t burn much less and have reasonable engine life. The engine efficiency rule is of course invalid for our friend Mike Evans. He has installed a $5.99 atomic fuel atomizer from J.C. Whitney and has been able to decrease fuel consumption by 20% by aligning the fuel’s oxygen molecules before they go into the carburetor!
Teledyne Continental has just released another mandatory service bulletin for crankshaft propeller flanges. The inspection covers 360, 470,520, and 550 series engines that were manufactured from April 1, 1998 through March 31, 2000. Also if you had a new crankshaft installed at overhaul (or repair) that was manufactured during those dates you will be effected. If you think you maybe effected by this service bulletin call TCM at 1-888-2007565 or 334-438-3411 extension 5100. The local FAA FSDO has provided our chapter with a comprehensive manual with all the serial numbers in that will be available at our meetings.
Fire Extinguisher Warning !!
From Jim Gray
Avoid using Class A-B-C Fire Extinguishers on aircraft if possible. This type of extinguisher poses a severe aircraft maintenance hazard because monammonium phosphate is highly corrosive to aluminum. If used to put out a carburetor or electrical fire for example, the resulting damage could easily exceed that of the fire itself! The chemical can easily migrate into cracks and crevices and cannot be adequately rinsed. This could lead to severe corrosion or even structural failure. Threfore, be sure in your hangar or onboard your aircraft a B-C (Halon) Dry Chemical type. Always get proper training on how best to use your portable extinguisher, if you need assistance contact your local fire department.