Bob is sure RIGHT, that stuff he named works and I have used it A LOT.
BUT one word of Caution ! These chemicals are highly dangerous acids and the vapor from them can kill you, so ONLY use in VERY well ventilated places! If You can smell it while you use it its allready potentially dangerous. Its great working stuff, but do use caution and wash it off the plane etc with LOTS and LOTS of warm water !!!
Do not try these in a basement or closed garage....
And the stuff has limited shelf-life, use it after you buy it and do not leave it sit for month and years, it looses its "bite" and all effectiveness.... I had to "do" all of my Do27, gezz it was nasty work....
AND make sure You NEVER ever use Steel brushes or steel wool on your sheetmetal....also there are steel brushes 4 sale that are brass-coated and look like good brass-brushes, do not fall for That trap, its way bad.
also, but off topic here: