Ft Polymath

[oldham1]

Balloons lighter than air (9) a-r-s----

Catholic group of priests who took no vows (9). O-a-o-i-n

Relating to an individual (11) i-i-g-a-l-c

[Mamyalynne]

Aerostats

Oratorian

Idiographic

[Lie-in King]

4d Aerostats
21d Oratorian
28a Idiographic

Hi oldham - it's always nice to post the whole clue, so that people without the puzzle can more readily help you :-)

[oldham1]

Thanks to you both