One of my current projects is to figure-out a way to get one my older and heavier model rockets to “fly better.”
The rocket in question is an Estes Photon Disruptor, which I built a few years back per the original kit instructions to fly on 18mm black powder Estes motors, and then finished meticulously. Unfortunately, after finishing, the model turned-out heavy…Much heavier than the weight advertised on the kit packaging. Simulations after the build predicted that the model could only be flown on only a few of the highest impulse, shortest delay black powder (BP) motors in the Estes line without risking a crash. Flights with the rocket have confirmed the sim’s predictions…To date, I’ve only been able to fly it successfully on an Estes C6-3…And all of those flights have been very low, slow, arcing flights. This rocket also has a tendency to weathercock, resulting in even lower flights featuring “exciting” last-minute deployments. At the recent CMASS/RIMRA joint launch in June, I made the mistake of trying to fly this marginally powered, heavy rocket on a Quest C6-3 on a windy day. Despite what the simulations said, the flight didn’t go well, and the rocket weather-cocked, arced-over, and crashed before deployment. (Kenn: You were right to warn me about the overhyped / underpowered Quest C6 motors…I should have listened to you, despite what my simulation with the NAR-tested thrust curves said…D’oh!) The rocket suffered heavy damage to the nosecone and upper body tube, but I was able to successfully repair it. And after making a few mods to take some weight out (truncated the nosecone shoulder a bit, swapped-out the heavy ¼” elastic shock cord with 90# Kevlar cord) the rocket is ready to fly again.
Poking-around on TRF and the web, I was surprised to learn of the existence of 18mm Aerotech AP motors which would fit my Photon Distruptor. Looking at the manufacturer data sheets and thrust curves on the NAR website, and running some quick sims, it seems that these AP motors would give this rocket a better kick off the pad, and result in higher altitude flights (vs. Estes C6-3 motors). I’m looking at the Aerotech Single Use D10-3W and D21-4T as good candidates for this rocket. I was also surprised to learn of the existence of Reloadable Motor System (RMS 18/20) motors which might also work…D13-4W and D24-4T among them.
But before I take the plunge to try to fly my newly rebuilt Photon Disruptor on 18mm Aerotech motors, I wanted to ask-around a bit from folks like you who might have some experience with these motors.
Questions which come to mind include:
> Are the thrust curves published on the NAR website for these motors representative of current production stock? Looks like these motors were last tested back in the 1990’s. Wondering if the thrust curves have changed since then. And is the initial thrust build-up with these motors really as quick as the curves suggest, or do they take awhile to come up to full thrust?
> Data on the NAR test sheets indicates longer than advertised delay times…I’ve heard this is typical of Aerotech motors. Is the situation still like this?
> Anyone know if the 18/20 casing and 18mm RMS reloads are still in production? he Single Use (SU) D10 & D21 motors seem to be readily available from several sources online. But the RMS D13 & D24 motors seem to be harder to get. I’d probably go with the SU motors, but trying to decide if I’d find enough places to use a RMS 18/20 casing to pay for the upfront investment.
> Do the 18mm SU casings fit well in motor mounts and motor hooks originally built for 18mm BP motors? (Almost, but not quite?)
> Any comments on reliability (or Unreliability) of these 18mm Aerotech AP motors would also be appreciated.
I see there are also Aerotech SU & RMS AP motors in the 24mm size range as substitutes for C11 and D12 BP motors.
> Any differences in reliability when you go 1 size-up?
Dan Tyszka
CMASS Member; NAR #95916