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My idea is to have a motor system that can be interchangeable in at least two diameters, such as 29/38mm, for a minimum diameter airframe as in the sustainer, which has a diameter of 2.152" id.  This would allow a model rocketeer a chance to go from a novice  to a NAR or Tripoli level three certification using one rocket, if there is the desire too, thereby saving time, money and effort.

This concept also allows the rocketeer to advance at his or her own rate of progress, in such areas as reaching higher altitudes and longer duration flights, going from simple recovery systems to the more complex, as in duel  recovery deployments - see CPR3000 - and installing flight gathering data systems - see Electronics.

 Update Oct. 16 2000 After purchasing more items, such as the PML extended Kwik switch 2000 kit, and  seeing how the kit goes together,  I feel confident that I can achieve the  interchangeable  motor mounts  for the sustainer. It will require the purchase of some Polypenco Nylon 101, to make various parts at a local machine shop. First is the  Mother tube screw mount, taking the standard   PML mount and removing the outside shoulder, so that it fits inside the 2.152" airframe tube. 

Next is modifying the boattail that came with the Mini BBX kit. For this step, I bore the 29mm step out to 42.5mm. This allows the 38mm motor mount tube (MMT) to slide through the boattail. A spacer ring will be made to take up the distance between the OD (Outside Diameter) of the inside of the boattail and the ID (Inside Diameter) of the 29 mm MMT. 

The Mother tube screw mount will be placed 19.2 " inside  from the bottom of the sustainer airframe. This will leave 11mm of the 29/38mm Motor Mount Tubes sticking out of the airframe. That distance will be taken up by the boattail and spacer ring so that the end of the MMT will be flush with what was the step inside the boattail, as required in the original PML plans.  

Update Oct. 18 2000 I have chosen to use rail lugs instead of regular tubular  launch lugs, because of the quantity of induced drag launch lugs create versus a rail lug. Also they are removable when flying the whole rocket together vs. flying only the sustainer. I have mounted them at both ends of the sustainer fin can, the rear one being  up 4.125" from the bottom & the top one 2.625" from the top of the fin can section, using 6-32 modified T-nuts, epoxying them in place. 

Update Oct. 28 2000  I have received my parts back from the machine shop and everything fits great. I have epoxied in place the 38mm screw mount adapter into the sustainer fin can.  Now I have a sustainer that can handle motors from an I 200 29mm through a  J570 38mm. Also I have modified the way the fins (G10 fiberglass .063" thick) are mounted to the sustainer fin can. In the PML design the fins mounted through the airframe to the 29mm MMT, which is stronger. I have mounted the fins to be flush with the inside diameter of the airframe. I will be using fiberglass milled fibers mixed with epoxy and making  fin fillets to stiffen the fins and to cut down on what could  possibly be fin flutter at high speed (near mach - the speed of sound). By mounting the fins this way,  I can fit a 54mm K 700 RMS motor into the airframe as well as the 29mm & 38mm motors.   Also completed is the sustainer fin can coupler to the mid section. It has been epoxied in place on the sustainer fin can with two inches exposed for the mid section to align on. Four  7mm vent holes were drilled  90 degrees apart from each other to allow the ejection charge gases from the motor to separate the fin can from the mid section, when not using electronics for recovery deployment. The mid section also contains the lower half of the CPR 3000 coupler, the G-wiz flight computer, one of the two CPR ejection charge canisters, and Sonic locator, while deploying either a streamer or parachute depending on the configuration of the rocket.     

Update Nov. 10  2000  I have drilled two 5mm holes 180 degrees apart in both extended motor mount tubes aft center rings to facilitate  installing and removing the 29 & 38 mmt. from the airframe using a spanner wrench type device. 

This page was last updated on 11/22/00.

If you have any Questions or Comments please E-mail me at Airdale@icehouse.net