I bought a Madcow 54mm FW nosecone and darn it, it didn't fit in the LOC 54mm tubing I have. I don't want to sand fiberglass, so naturally, I decided to buy all the matching Madcow FW tubing and some G10 fins and make it a minimum diameter! I think I have an idea of how I'm going to do the build in general, except motor retention and motor accommodation. I want this rocket to work with any 29, 38, or 54mm motor, from a 1 grain 29 to a 6XL grain 54. Maybe it's wishful thinking, but I think it's possible. I think the right way to do this is to add mounts for machined brass on the nosecone, but I'd be interested to hear better ways. The second question is on motor retention. I'm thinking I can just put a standard Aeropack 54mm retainer on the back end and be done with it. This way, I wouldn't have to use one of the less accommodating minimum diameter retainers that are out there. It would also enable me to use the included motor ejection charges as redundancy, which I believe most minimum diameter retainers don't allow. More importantly, though, it would allow me to use Aeropack's motor adapters to fit the smaller diameters. The only downside I can see is a little more drag. I am interested in any thoughts you guys have.
Minimum Diameter Rocket Build - Motor Questions
- Thread starter moormanj
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Install the Aero-Pac Min dia. motor retainer for the 6GXL. Them have some tailcone adapters made for the 29 and 38mm motor flanges. The forward end is sized to slip inside the 54mm airframe. The aft end gives positive retention of the motor, with enough of the flange sticking out from the piece to allow untwisting the motor to remove it. Threaded forward closures are used on the motors, with threaded adapter rods to connect with the Aero-Pac retainer up front. I have this exact setup, except no need for the 29mm motors, only 38 and 54.
The adapter rods for smaller motors also allow for weights to be installed to adjust for, and minimize over-stability.
This setup allows for the 54mm motors to use a tailcone, and the others, also.
A machinist can make this part pretty easily. I made mine, turned from aluminum.
The adapter rods for smaller motors also allow for weights to be installed to adjust for, and minimize over-stability.
This setup allows for the 54mm motors to use a tailcone, and the others, also.
A machinist can make this part pretty easily. I made mine, turned from aluminum.
Nytrunner
Pop lugs, not drugs
Check out slimline retainers by Giant leap. They are much slimmer and won't disturb the air as much as aeropack retainers (and I believe the adapters still work in them)
I have used both and like both solutions above.
The GLR Slimline has a very nice low profile and IMO is one of the nicest aesthetically looking retainers. I use them in 29, 38, and 54 mm configurations, although I have never used them with adapters. I recall a thread a while back where someone brought up a concern about damaging this style retainer on landing, and not being able to unscrew it. While I have never experienced this, I can envision it happening, but I don't think that this scenario is limited just to this design.
The Aeropack MD retainer is what I have used exclusively on my 38, 54 and 75mm MD rockets, but I use a removable method to install it. If you decide to use this retainer, I can provide some details as to how I do it. The downside to this is if you are attempting to use the range of motors that you say, then it will require a variety of extension rods, and I am not sure that this solution would be appropriate for the lower-powered motors.
For that matter, I don't know how realistic it is to expect the range you are targeting. I believe that most of the 54 and 38 reloads will be attainable; however, the 29mm motors in the mid and low end may be a stretch.
The GLR Slimline has a very nice low profile and IMO is one of the nicest aesthetically looking retainers. I use them in 29, 38, and 54 mm configurations, although I have never used them with adapters. I recall a thread a while back where someone brought up a concern about damaging this style retainer on landing, and not being able to unscrew it. While I have never experienced this, I can envision it happening, but I don't think that this scenario is limited just to this design.
The Aeropack MD retainer is what I have used exclusively on my 38, 54 and 75mm MD rockets, but I use a removable method to install it. If you decide to use this retainer, I can provide some details as to how I do it. The downside to this is if you are attempting to use the range of motors that you say, then it will require a variety of extension rods, and I am not sure that this solution would be appropriate for the lower-powered motors.
For that matter, I don't know how realistic it is to expect the range you are targeting. I believe that most of the 54 and 38 reloads will be attainable; however, the 29mm motors in the mid and low end may be a stretch.
I have built and flown many MD rockets, from 38mm to 98mm. All but one have flown only on motors that match the airframe. For the one outlier I used a slimline retainer (with the snap ring) and feathered the airframe into the larger diameter of the adapter using fairing epoxy. I use the slimline motor adapters to fly smaller motors.
I don't like the hassle of the adapter rods for the Aeropack MD retainer. Just seems like a lot of extra effort.
I also think it's a bit ambitious to want to use any 29mm motor. 38mm and 54mm seems a much more reasonable goal. With a 29mm motor or a small 38mm motor it's going to be very over-stable if it will also fly on 54mm 6XL motors. And if you are having to adjust nose weight for every flight that seems like a pain. But that's based on my experience of building MD rockets for a very narrow range of motors rather than for general purpose flying.
Tony
I don't like the hassle of the adapter rods for the Aeropack MD retainer. Just seems like a lot of extra effort.
I also think it's a bit ambitious to want to use any 29mm motor. 38mm and 54mm seems a much more reasonable goal. With a 29mm motor or a small 38mm motor it's going to be very over-stable if it will also fly on 54mm 6XL motors. And if you are having to adjust nose weight for every flight that seems like a pain. But that's based on my experience of building MD rockets for a very narrow range of motors rather than for general purpose flying.
Tony
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I don't think it's possible to have a 54mm min diameter that will fly on 29mm 1-grain motors and 54mm 6XL motors. My cardboard 54mm that's about the total length of the 6xl case is heavy enough that it would barely fly on an F59. Maybe if you have a stash of F120 VMaxes hanging around, but even that is unlikely.
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Your higher initial thrust F's and many G's should work, but I'd be very surprised if you could cut enough weight for any 1G except maybe the vmax 120, if you can find any.
I'd target the CTI f79 for the bottom end.
Here's two stories that let you know it's totally doable:
https://publicmissiles.com/UltimateIo.htm
https://www.rocketryforum.com/threads/bluefin-tuba-3.67358/page-2#post-739851
EDIT: tailcones, retainers, adapters will all weigh too much for the lowest end. If I ever did this I planned on just a lowpower spool taped on and taped in.
I'd target the CTI f79 for the bottom end.
Here's two stories that let you know it's totally doable:
https://publicmissiles.com/UltimateIo.htm
https://www.rocketryforum.com/threads/bluefin-tuba-3.67358/page-2#post-739851
EDIT: tailcones, retainers, adapters will all weigh too much for the lowest end. If I ever did this I planned on just a lowpower spool taped on and taped in.
