Hi Everyone. Recently, while watching a bunch of Twin otter videos online, I keep hearing this recurring sound, like a whine, and it has been bugging me ever since to figure out what it is. The link for the video is here, and the sounds are at :08, :13, and :16 seconds. It's been in a number of other Twin Otter videos like shutdowns and startups and takeoffs, and I can't find any info on it anywhere! I was just hoping a Twin Otter expert or somebody familiar with it's systems would know what causes the sound. Thanks everyone!

Not a twotter expert at all, but since the whines occur just when turning onto the runway, I expect the pilot is setting take-off flaps. As the whines are three short bursts rather than a single longer burst, it would seem the flaps are not electric but rather hydraulic. And since the hydraulic actuators are not heard, I would guess the whine is the sound of the turboprop accessory drive engaging the hydraulic pump 3 times during flap extension to maintain hydraulic pressure. The part that doesn't fit in the above is the twotter is too small an aircraf to require hydraulic actuators for the flaps: Electrical would be simpler. A third alternative is the flaps indeed are electric but not detented and for some unknown reason rather than holding the flap switch down for a single flap movement, the co-pilot sets the flaps in 3 separate increments.So this is just a guess...OK, too curious so I cheated and googled a video of a

, so evidntly the flaps indeed are hydraulic and the first interpretations stands.Cheers,- jahman.

Not a twotter expert at all, but since the whines occur just when turning onto the runway, I expect the pilot is setting take-off flaps. As the whines are three short bursts rather than a single longer burst, it would seem the flaps are not electric but rather hydraulic. And since the hydraulic actuators are not heard, I would guess the whine is the sound of the turboprop accessory drive engaging the hydraulic pump 3 times during flap extension to maintain hydraulic pressure. The part that doesn't fit in the above is the twotter is too small an aircraf to require hydraulic actuators for the flaps: Electrical would be simpler. A third alternative is the flaps indeed are electric but not detented and for some unknown reason rather than holding the flap switch down for a single flap movement, the co-pilot sets the flaps in 3 separate increments.So this is just a guess...OK, too curious so I cheated and googled a video of a

, so evidntly the flaps indeed are hydraulic and the first interpretations stands.Cheers,- jahman.

thanks for the reply, I really appreciate it! Mystery FINALLY solved, lol.