Rubber for aircraft fuel cells

[berkshire]

For years the preferred rubber for aircraft fuel cells/ bladders, has been nitrile or Buna N . This has worked well with most Avgas including 100 octane low lead.
Now the Feds are working on getting the lead out, switching to several proposed fuels: 93 octane unleaded with more aromatic components, and or Isopropanol. there is also a possibility that they may allow Ethanol which is currently banned in most aircraft fuel systems. Some fuel cell manufacturers are switching to PUR which does not seem to play well with Ethanol . I know plastic tanks can be made from HDPE , but in this case I am looking for flexible fuel tanks.
The catch 22 seems to be that materials that play well with Avgas do not play well with unleaded or Ethanol containing fuels, and materials that work with unleaded and Ethanol, do not work as well with Avgas

Does anybody have any opinions, ideas or links to research papers on this subject?
B.E.

You are judged not by what you know, but by what you can do.

 

[MikeHalloran]

I think the Feds are running a huge, impromptu, uncontrolled, material compatibility experiment.
... and they are not paying for the test articles; we are.

I am not pleased that they are extending the experiment to vehicles that fall out of the sky when the engine dies.



Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

Look into polysulfide rubbers. I do not have any personal experience with them but they seem to be the preferred rubber or sealant for military aircraft.

 

[berkshire]

Polysulfides are used in fuel tank sloshing compounds, and the problem extends even there, there are two types, one for fuels with no alcohol, and the other for alcohol bearing fuels. You cannot mix them up.
B.E.

You are judged not by what you know, but by what you can do.

 

[TugboatEng]

NBR/PVC blends are used by the automotive industry for their high resistance to oxygenated fuels.