Recently several clients admitted that they had been flying with peeling slosh in their fuel tanks. This is a truly alarming situation which calls for great caution on the part of aviators and requires immediate inspection of all fuel tanks.
In my experience, properly applied sloshing compound sticks very well to the insides of an aluminum tank. The problems arises mostly with adhesion to very smooth surfaces. If you have scuffed up the entire inside surfaces of your tank with a Scotch Brite pad or used it only in cracks or on top of rivet heads, you very likely have no worries. The sloshing compound simply needs something to physically adhere to. The areas where it seems to be having trouble sticking are typically the smooth underside of the skins and rear baffle.
When it does come off, you will start to see small white particles in your quick drain and in your gascolator. If nothing is done about it, the slosh will start to peel in larger and larger pieces. Please see the picture for an example. The tank shown has had the rear baffle drilled out and bent back so that the peeling slosh is visible. I have seen sheets of it inside tanks as large as a business card waving around in the fuel like sea kelp. A piece the size of a corn flake is large enough to wrap over the fuel pick up and starve your engine. I hate to imagine that on climb out.
Ok so you have slosh inside your tanks…what do you want to do about it? Well you have several options.:
If you are fairly confident that your slosh is applied properly then by all means keep flying. My suggestion is to be extremely vigilant in monitoring its condition. Watch for particles during your fuel inspection at each pre-flight (gascolator and water check). Periodically use a flashlight to look for loose material inside the tank through the fill up. No smoking please! Also it is very important to remove the tank and inspection plate to check your fuel pick up, make this at the very least a part of your annual inspection. Small flakes of slosh can slowly build up in the slots cut into the pick up. If you have gone this far, the screened fuel pick up that Vans sells in the catalog are a bargain. You get a much larger open area to draw fuel through and a pre-filter to catch small particles. All at a price that makes it hardly worth building yourself. I encourage all of my clients to use these.
Removing the sloshing compound can be accomplished. I have done this on several occasions, but I don’t care to do it again. It is a nasty process, which requires you to wear a good respirator in a well ventilated area and several layers of alcohol resistant gloves. I use Nitrile exam gloves available at most local pharmacies, these are usually blue or green. Do NOT use standard “turn your head and cough” white latex gloves. MEK (methyl ethel keytone) will melt latex immediately, the Nitrile gloves will hold for a few minutes. You will have to cut a large hand hole into the rear baffle centered in each bay, and build a cover plate to reseal them when finished. The slosh can be dissolved using an MEK soaked rag. Wipe it over a small area of slosh, give it a few seconds to soften, then scrub it with a Scotch Brite. I have considered just dumping a gallon of MEK in a tank and shaking it around for a while, but to be honest I don’t know how it will affect the Pro Seal. I consider this too large a risk. After about two days of this, you should have the tank pretty well cleaned out. The areas where the slosh does not release will be in the cracks and over the rivet heads. At this point you can seal any residual particles in these areas with a thin layer of Pro Seal. Use Pro Seal and closed head pop rivets (AD 41H) to reseal the rear baffle with your cover plates. Pressure check with balloons and soapy water, and you are done. Your wrists will be cut and sore and you will have an imprint of a respirator mask on your face, but you wont have to rebuild your tanks, and you wont have to repaint. (unless you melted your paint with the MEK)
The last option and by far the safest, is to replace your fuel tanks with new ones. Those of you willing to take on the task are encouraged to do so. For the balance of the group, give me a call or check out my new website www.evansaviationproducts.com
I can build you brand new slosh free tanks at a price that may surprise you. What you will receive are pressure checked tanks with ¼” oversized trailing edges on the top and bottom and none of the tank attach points drilled. This will allow you to fit the tank, trim off the extra material and match drill all of the attach points to your existing wing. For those of you who are lucky enough to have bought your wing kits after Vans started pre-punching the ribs, I can use the pre-punched, standard sized skins. (no trimming) These are provided for the RV7, RV9, and the newer RV8. The RV4, RV6 and early RV8 do not apply here.
Whichever decision you make, I am always available for advice. Feel free to call or email. The last bit of preachy wisdom I have on the subject is this. We all take enough risks with things we do without knowing about them. If you know that you have loose slosh in your tanks, do something about it!
Be safe, and happy flying.