The theory of the fan wash from the bypass blanketing the hot exhaust gases is quite plausible.

On the other hand, the cold air would have a pretty low static pressure, particularly at altitude. I'm not really sure how much of a barrier it would be to IR.

The NTSB experiment appears to have been performed during climb-out where the air in much denser and more likely to absorb IR and lead to a lower signature at the engine.

A cold substance between an IR detector and a hot body isn't much of an impedance. Look at those new spy cameras the FBI and DEA use that can see people through walls!

Plausible it may be, but like others, I find it hard to believe.

Don't the military use cold air to hide/ reduce the IR signature on helos and fixed wing as a matter of basic design philosophy?

If it didn't work, I'm sure they wouldn't go through all that effort and expense for nothing.

Just my two cents worth guys.

Cheers all.