Rattletrap is the Beckfoot car of the Blacketts, described as a smallish, ancient motor-car with badly dinted (sic) mudguards and a luggage grid at the rear (PP1). Mrs Blackett turned the car round in a series of short dashes in the Tysons yard: Oh well, she said as she stalled the engine and got out and looked round the car: That front mudguard was dinted already several times. And that one at the back’s always unlucky. There’s no real harm done (PP17).
In The Picts and the Martyrs there is a picture of Rattletrap with the Great-Aunt sitting in the rear seat holding a parasol upright . Billy Lewthwaite drives her along the Lake road to Swainsons until he runs out of petrol (PM25). Rattletrap is crank-started: ... Billy, whirling the rusty crank, stirred old Rattletrap to life (PM25).
The car depicted (PM26) is clearly a Trojan (see photo on this page), although the Trojan has only two forward gears, raising an anomaly; at the end of Pigeon Post Captain Flint drives her up to the camp: Rattletrap, knowing her old master, started off as if she meant it. They swung through the gate and sharp right into the road. The gears changed, second … third. Captain Flint said Hold tight, Dick ... She won’t do forty except down-hill, but she's a bit of a broncho round corners.... (PP33).
The Turner/Blackett family don't appear to have a car before the events described in Pigeon Post; in Winter Holiday Molly Blackett uses a hire car to visit Holly Howe to discuss Nancy's mumps (WH9). Later, Captain Flint arrives at Beckfoot by hire car, which waits for him while he talks to Molly before setting off for the Fram.