Smoketoomuch:
Yes, the balloon would be just as useful as a pendulum.
Caution: In aircraft not certified for inverted flight, special certification is required to conduct IFR operations using helium filled balloons in place of faulty pendulums in the instrumentation!
compressor stall:
Very interesting issue. However, the first question to be raised should be "how far could a swallow carry a coconut?" (*)
I guess you're familiar with the rest?
"Would that be an african or a european swallow?"
"I don't know.... YAAAAAAGH!"
Gotta love british humour. If you lot in the UK just get the food and the weather sorted out, I'm moving!
Cheers,
/ft
(*) Or was it "how many coconuts..."?