Ballast.
Yeah, the ballast is in the thing, and the thing moves forward or back on the track. Let me see what they say on the Air Swimmers site … okay, they’re calling it a pod. The pod holds the batteries and also the putty that provides extra weight as necessary.
I got one for my son for his b-day last week. Had his sister play the jaws theme on her ipad while I flew it in over his head.
It’s sturdy enough, and the cat runs away, so she’s not a danger!
Damn you **Man in Black ** for resurrecting all things blimp!! :::shakes fist:::
And thanks to Moonlitherial, I’ve ruined my eye make-up - once again. Scylla’s ‘The Horror of Blimps,’ tale of terror should come with health warnings.
The cats are up on the sofa staring at the crazy woman who is still wheezing with hysterics while strange black streaks run down her face. 
And yes, I wanna air swimmer. Bad.
Good gad, a drunken air shark!
Seen the film , I want one now!
From the site -
Rats.
One of the guys at work brought one in, and at 5:00 am started flying it through the cube farm. Really good movement. I just got one to send to my nephew for Christmas and Mr. singular said in a small voice “you could get one for me, too”. Done and done, my love.