How many letters does the top answer for “the flow of air that is driven backwards by an aircraft propeller” have?

The most common answer is airstream (9 letters).

Crossword clue: the flow of air that is driven backwards by an aircraft propeller

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

airstream 9 letters wn-def

the flow of air that is driven backwards by an aircraft propeller

slipstream 10 letters wn-def

the flow of air that is driven backwards by an aircraft propeller