I was wondering similarly: what's so different about ramming in dog barf and pouring in epoxy that one should be allowed under the safety code and the other not?
Quite a bit technically. In the first case you are simple installing a thermal protection system to prevent hot gases from damaging your rocket, and the seconds you are permanently modifying the motor.
As for Estes giving permission, don't hold your breath. I come from the engineering profession, and I don't believe any company would say that's OK without going through a whole new qualification test program; they'd never accept the liability. I also don't believe the certifying agencies would accept such an OK without the testing even if Estes did say it; they'd never accept the liability either. Estes would probably be happy to do the certification IF they could be convinced that doing so would increase sales by enough to justify the cost. But really, who among us can honestly say "I'd buy a dozen more D12-0 engines if only I could fly them at sanctioned events after plugging them with epoxy?" And say it again about E9-0s and E12-0s and C6-0s, etc.? Because each one is a separate certification program..
Except that Estes already makes and sells plugged motors, currently in 13 mm and 24 mm diameters. All they have to do is to set up their production Mabels to shoot a shot of clay over the end of the booster propellant grain to make a cap. We have probably certified all of their motors as plugged motor over the past half century, but not all the motors they certified are in current production. If we haven't certified a plugged version of a currently certified motor, all Estes has to do is to send us 3 motors and they'll get certified within a month.
The person legally responsible for a rocket flight is the person whose name is on the flight card. Their signature on the flight card legally means that the have determined that their rocket is safe to fly. Most motor manufacturers warrantee their products to meet the performance specifications as labeled on their motors for a certain time period provided they are stored properly, not modified, and used according to the manufacturer's instruction sheet. And Estes is top notch on honoring warrantee claims on the engines, but Estes or any other manufacturer has no control of their product and its use after it leaves their shipping dock.....
The only thing a certifying authority is legally responsible for is to measure and verify that the lot of motors sent to them by the manufacturer for certification were properly labeled, performed according to their label specifications, and were operated safely when the manufacturer's instruction sheet is followed.
I'm not knocking Estes, this is just the expected and reasonable behavior of for-profit companies.
Estes and the other motor manufacturers are in business to make a profit. While they may certify many variants of their motors, it does not guarantee that they will manufacture them. And they will and do discontinue production of motor variants that do not sell well.
I think the better chance would be to make a case to the NAR safety committee (or whatever is the official name of the appropriate body) to have the safety code amended or clarified such that pouring in an epoxy plug is not considered modifying the engine.
It really does not matter what NAR S&T thinks. We are required by NAR to test and certify motors under NFPA 1125, and our procedures are 100% compliant. The unabridged NAR Model Rocket Safety Code is a superset of NFPA 1122 and the unabridged NAR High Power Safety Code is a superset of NFPA 1127, so to eliminate certain items from our safety code requires a change in the NFPA code.
What is currently allowed under NFPA 1125 is for the manufacturer to amend their instructions that would give permission for the user to put a cap over the end of the propellant grain. If Estes wants to grant that permission, the procedure would either be automatically accepted by NAR and TRA because it comes from the manufacturer, or if either certifying authority felt the change would be dangerous, the original certifying authority could decertify the motor for safety. That wouldn't happen unless the manufacturer didn't require the owner of the motor to indicate on the motor label that the motor was plugged permanently.
Making a
unapproved change to a motor decertifies the motor because the motor will not perform according to the label printed on the motor casing. If you put a permanent epoxy cap on a motor labeled as a booster, forget about it, and then give it to someone who uses it as a booster motor, the motor will not behave like a booster motor and the rocket will crash. That's not Estes fault but they most likely would be blamed for it because the motor did not perform as labeled.
If on the other hand, you filled in the back end of the motor with dog barf to prevent hot gas from scorching your rocket, you did not permanently modify the motor because if you remove the dog barf, the motor will perform as labeled. If you give the motor to someone else, they will clearly see the forward end of the motor is filled with dog bark, so if they want to use it as a booster they can easily remove the dog barf.
Bob
