Type

Reverse Causality (RC) was named for the reason I built it; to fly some E9-8 motors I had bought at a clearance sale for $3.00 a pack. Not really wanting an E motor two stage rocket (I like to get at least two or three flights per rocket before losing them), I scrounged around the parts bin and found two lengths of BT-55 tubing that might be used in a high performance single stager. A session with Rocksim showed that an 8 second delay was fine and that RC should also fly well on 24mm C and D motors. Just in case, the tail section of RC was designed to accept a gap staged booster.

Still experimenting with different ideas, RC turned out to be a 3 fiberglassed TTMM finned, baffled piston recovery design. She's 36" long and about 4 calibers overstable with the E motors (I definitely want her to turn into a breeze).

Construction

	The motor mount is a 10" length of BT-50 with a thrust ring to accomodate 95mm motors and an Estes engine hook for positive retention. The section of the MMT tube ahead of the forward centering ring is plugged with epoxy/tissue and several rows of 1/8" holes are drilled in the MMT tube walls to allow ejection gasses to vent into the BT-55 airframe. The inside of the MMT and the airframe along the vent holes was coated with epoxy to increase resistance to the ejection gasses. (Click on image for full size picture. Use "BACK" button to return.)
	The swept trapezoidal fins are glassed 1/8" balsa and have notches in the leading and trailing root edges which mate with the MMT centering rings (CR). The fins are epoxied to the MMT tube and CRs. The aft CR is recessed into the fin can section about 1" to allow a booster coupler to be mated for a two stage flight. The MMT slides into the slotted airframe and the CR and fins are epoxied and filleted. Cut engine casing provides an adapter for C/D motor flights. A baffled tube coupler attaches the 12" fin can section to the forward 18" airframe. (Click on image for full size picture. Use "BACK" button to return.)
	The piston (a BT-55 coupler with a 1/8" ply bulkhead) is attached to 30" of sewing elastic shock cord epoxied to a short coupler in the 18" airframe section. The recovery side of the piston is attached to three feet of 3/8" elastic shock cord, a 14" mylar chute, and a NC from an old Estes CC Express. (Click on image for full size picture. Use "BACK" button to return.)

Baffle system

Because of a construction error the night before a launch, I was forced to use standard 3/8" sewing elastic (shock cord) for the motor-side piston retaining strap. That sounds like sheer stupidity since elastic shock cords are routinely burned through by ejection charges. Not in this model.

After four flights, the motor-side retaining strap is still white and there is almost no ejection residue or color within the forward 18" airframe section. With a strong light, I can just detect a black discoloration on the aft coupler bulkhead when viewed from the front. A moist paper towel wipe of the inside of the forward airframe showed almost no ejection deposits.

From the aft end, the inside of the MMT tube baffle is completely blackened and contains a lot of visible, solid deposits. It will have to be cleaned at intervals. The airframe between the MMT tube and coupler bulkheads is not visible.

I am very surprised that the baffle system works as well as it does. Not only is the particulate matter stopped, the temperature of the ejection gasses seem to have little effect on the "flimsy" elastic piston strap. And there is no metal or other filter material in this system; just a bunch of small holes and two balsa bulkheads. It may be a little early, but I am sold on this technique already. No wadding required. No heat damage to recovery devices. Quick prep and turn-around. The only downside will be the cleaning of the baffle tube and the unknown state of the airframe between the MMT and coupler.