All Tristars had provisions for a trailing cone. It was used on the first production acceptance flights to calibrate the airspeed system.
A conduit from the aft pressure bulkhead in the cabin up inside the leading edge of the to the rear of the fin tip let us install one any time it was needed.
We used two types. The Douglas cone system used a 1/2" nylon tube, which was keep in a water tank when not used to keep the nylon flexible. The sensor was an aluminum pipe with a calibrated series of ports machined into the tube side. Generally it was 150 feet behind the plane in flight.
The Boeing system used a larger diameter nylon tube with a 1/8" steel cable running all the way thru it, from a location at the cabin end to the cone itself. Both types of systems had the cone about 15' behind the sensor.
We would deploy the cone after takeoff, but before the plane got to cruise speed. Once it was out, it remained out until the plane slowed for landing. On the few times a cruise speed retrieval was attempted, it was found to be impossible to pull it in!
The trailing cone system was developed as the earlier system using a streamlined lead block for weight was found to be unacceptable when doing manuvers such as stalls. It would frequently fly -around- the airplane, or thru it!
The nylon tube and f.g. cone was less capable of damaging the airplane.
I spent many hours watching these things... we frequently had a window with an extension outside the skin of the plane with a mirror so we could see what was going on behind the plane.
During two types of tests, the cone system could be expected to be damaged/destroyed/lost. Stalls. all by themselves weren't bad, but if the pilot hit the rudders... a giant wave from the fin tip vortex would travel down the hose, and usually snap the cone off.
Vmca tests, minimum speed for control in the air, were generally done low over the ocean, abt 1500', with one engine dead. Not idling, it was turned OFF!! not running! The pilot would then see if he could get the plane to fly as slowly as theory predicted! Knowing it required something on the order of 5,000 feet to recover from a symmetrical stall... I always wondered about these test conditions.
With the constant rudder required to maintain heading, the cone would be beat to death. THe cable in the Boeing system wouldn't let anything fly away, but we'd always bring back a useless mess of snapped snarled tubing from these tests.
The Boeing system had another "feature".. during electrical activity lightning could enter the cabin down the cable to the tie-off point!
Sometimes the steel cable would vaporize, and the whole thing depart out the fin!
We scattered them all over So. Cal and the ocean.
Despite a reward notice on the cone itself, we never got one back.
First picture... The Tristar is close to the stall break point, the cone has dropped behind the airplane, with the hose showing no tension on the hose..
2nd picture... the wave from a rudder pulse going down the hose... a real "E-ticket" ride coming! The cone will be VIOLENTLY jerked to the right...
3rd picture... a couple of waves in the hose due to rudder pulses..
4th picture.. when it's being used properly