54mm MAC Performance Radial Flyer

[RickB]

I took advantage of MAC Performance's Black Friday sale and purchased a single deploy 54mm Zodiac kit, though I immediately emailed Mike and asked him if he could turn it into a Radial Flyer (which isn't yet an option in 54).  He willingly obliged, and shipped what really amounts to the first 54mm sized Radial Flyer.  I started building after the new year settled down.  I haven't bothered posting a thread about it on TRF, but I figured I'd share here.  At this point, most of the construction is finished and I'm playing catch up in my writing.  The rocket should be with me at the April launch, though it might not be painted yet due to weather.

My first steps were to create a Rocksim file for the model.  I downloaded MAC's 3" Radial Flyer file and scaled it down, then started sorting it out match what I wanted.  Once I had the kit in hand, I measured all the parts length/diameter.  Then I put everything individually on the scale in our metallurgy lab at work.  So, I have component mass to the 1/1000th of a gram.  The measurements all go back into Rocksim to improve the over accuracy.

[RickB]

OK, first things first.  What I really liked about the Radial Flyer is as much as how its presented on MAC's site as much as how its designed.  What I mean is, I like the clean proportions and somewhat forward set fins, but that combined with the shown color scheme and the use of a boat tail motor retainer really all come together to make a very aesthetically-pleasing form.  Of course, in the 54mm size and with a 29mm mount, there's no off the shelf boat tail retainer available.  So, I designed a little boat tail to have 3D printed.  I made it so that the actual motor retainer (from Aero Pack) is partially recessed into the tail.  In the end, about half of the length of the screw-on ring is exposed, so it looks cleaner than if the whole retainer was aft of the boat tail, but there's still enough sticking out to grab a hold of.  At least that's the intent.  I designed the part using the CAD system I use at work (on my lunch break, really!), then exported to an .STL file.  Since I don't yet have access to a 3D printer, I uploaded it to Shapeways.com and had them print it.  It was a little pricey, but not more than an actual boat tail retainer would've been.  I look it as an experiment, and if it works, the cost is justified.  Anyway, here's the boat tail:


You can see the bore that the retainer sits in.  It nicely clears the Aeropack ring, but not the plastic Estes ring, as that latter's ribbed OD is too big.  On the inside, you can see that I (tried to) design it so that it would balance mass and robustness.  The part is 1/8" thick throughout, except the tapered end which becomes solid past the bottom of the counterbore.  It attaches to the body tube as well as the motor tube, acting as a thrust ring, and is ribbed internally for strength.  I didn't do any FEA on it, but I wanted to make sure it wouldn't readily break if it hit the ground first.  Once I got the actual part, I had to do a bit of sanding to make it fit, even though I sized the features after measuring the actual tubing in the kit.  I guess the print tolerances aren't as close as I imagined.  Anyway, the tail dry fit onto the tubing:

[RickB]

Two things might be apparent in the last photo above. 1) the boat tail shoulder extends into the fin slots, and 2) I've also marked an extension on the slots.  The extension is, in part, because of the boat tail, but also because this started as essentially a Zodiac kit with different fins, the slots were cut proportionally farther aft than they at least appear to be in the Radial Flyer photos on the MAC Performance site.  So, I made an adjustment. 

The fin slots were marked for a 1" extension:


I then drilled the new endpoint of the slots, and used a hacksaw blade to cut the lines.  They aren't perfect, but they sufficient.


Fins dry fit in, showing the slot gap that will have to be filled later:

[RickB]

Next up, when I purchased the kit, I also bought Mike's nose bay kit for 54mm cones.  I figure any rocket that has the potential for 2000+ feet ought to have a tracker regardless of deployment system.  So, best to be prepared for eventually getting one.  This also meant I wouldn't have to add any ballast to the cone.  So, cut off the end of the shoulder as neatly as I could with a razor saw. 


The internal diameter wasn't perfectly round, as the wall thickness increases around the mold parting line.  So, a bit of filing was needed to clean it up.  I also sanded the ID of the forward centering ring so that I had a good slip fit between it and the bay tube.  If the fit had been at all tight, it would be difficult to insert if the ring wasn't perfectly square when installed.  I think the toughest part was reaching up into the shoulder to (attempt to) sand the surface that the ring would be bonded to.  My fingers were barely long enough.  Anyway, with that, the ring was epoxied into the cone and set aside.


Next was epoxying the aft closure ring to the bay tube:


With that, both parts were set aside overnight for curing. 

[RickB]

OK, with the epoxy on the bay tube and for the centering ring dry, I could insert the bay into the cone.  Dry fitting was important here, as aft closure ring needed a lot of sanding/filing to get it to slide into the end of the nose cone.  Once I got it to slip in reasonably well, I mixed up more epoxy and installed it.  Having the end cap with eyebolt in it made it easy to hang onto. 



With that set aside, I also worked on assembling the motor mount.  Nothing really noteworthy here; the parts had MAC's usually near-perfect fit and I used the same BSI 30-minute epoxy as throughout. 



And while all that epoxy was curing, I set about scuff sanding the fins so that epoxy and primer both would adhere...

[RickB]

Using sand paper on a stick, or more specifically a spare leg for the mid-power launch pads, I sanded the inside of the body tube to prep for installing the motor mount. 



I don't have any pictures specifically of the motor mount being installed, but you all know what that looks like, so we'll just assume that it was done.  Once the mount is in place, I could install the fins.  I used Dave's method of spreading epoxy over the slot and pushing the fin through.  This seems to do a decent job approximating internal fillets.  One side effect of the extended fin slots was that once the first one was in place, I could drop the other two fins in their slots, then push them forward into the fin jig, so the jig never had to pulled back during the process.



Then, I just turned it over every few minutes to attempt to even out any flow as the epoxy set.  You can sort of see the filletation:



Now that the fins are attached, the rear centering ring can be installed.  In this photo, the boat tail is re-dry-fitted. 



You can see that the cone shoulder and the centering ring block part of the slot, but there's a half inch or so between that will need plugging.  To do that, I placed pieces of masking tape to cover the inside of the open slot:



This should suffice to hold the epoxy filler while it sets, which will close the gap and get smoothed out on the outside.  Nextly, the tail cone itself has to be installed.  I haven't glued it in to this point yet, because although I intend for it to accomodate an Aero Pack 29mm retainer, I didn't have available on hand to actually measure.  I used the dimensions published on Apogee's website for it, with the hope that they were accurate.  By holding off on installing the part, I have the option of having a friend stick it on a lathe and open up the bore if needed...

[RickB]

I received the retainer yesterday, so I could finally dry-fit the tail cone and retainer onto the assembled structure last night.



As you can see, it does fit, no rework required.  In fact, its a fairly close fit.  The tail cone bore:



The threaded ring in place:



And the retainer cap on:



The fit together of all these bits is pretty ideal.  As mentioned above, the retainer cap is about half-recessed into the tail cone.  That allows enough to grip, but tucked in enough to smooth it out some and make it appear more integrated.  I also test fit it with a burn up single use motor to verify everything.  So, at this point, these parts can be attached.  Another aspect that can also be attached now are the rail buttons.  Normally, I'd drill for them now, but install after paint.  But in the spirit of a more integrated look, I drew up these surface-mount airfoil buttons (like I did with the tail cone) and had them 3D printed. 



I was test fitting them on a small section of 1010 rail in this pic.  The white ones have an mounting face curved for MAC's 54mm tube, whereas the green ones are for their 3" tube (and will later be mounted on my Scorpion).  I had to have them colored differently just to tell them apart.  It took a little bit of sanding over the tube to fine-tune their fit, but they otherwise look good.  They have a fairly large footprint to epoxy them on, like with an ACME guide.  But they have the streamlined shape of an airfoil button, but without the screw head sticking up.  Not only is the top portion airfoiled, but so is the center standoff.  If nothing else, that'll help align onto the rail when loading.  I'll see how well they work this season before trying to make more, but I've already got design variants for 54mm, 2.6", 3" and 4" tube sizes. 

[RickB]

The boat tail and retainer are now attached.  No new photo, but it looks pretty much like the last one posted.  I'm also now filling the rear portion of the slots with JB Weld, which seems like it'll be easier to shape once cured than the other epoxy.  Once that's done, I'll do the fillets.  The real reason for this update is to post images from Rocksim:

[RickB]

OK, next steps - the exposed slots were all filled with JB, then filed down to match the curvature of the tube.  One of them may require a little more fill to not have a low spot, but I'll address that later. 



With that done, I can now do the fin fillets with epoxy.



I found this time that using a metal bike tire lever with a wide spoon end does a nice job at forming the radius.  In the past, I've done it with my finger tip, so this was definitely neater.  Just have to remember to wipe the lever off immediately...

Now that all of this is done, I can do some prep sanding and prime it.  Oh, for a bit of warm weather... 

[RickB]

After a bit of sanding, I decided some spot filling was needed to make my fillets more consistent fin-to-fin, and also so I could shape the leading and trailing edge blends a little better.  In the past, I've used wood filler for some of this, but it isn't all that durable.  I'm not sure why it took my this long to try this, but this time I used JB Weld.  Since its tough but still sandable (and shape-able), it seems like an ideal filler.  Anyway:



After sanding that, I could shoot a primer coat on it, and then actually check how well things are blended.


I've found that this time of year, it helps a bit to park the rocket over a heat duct for a day once the paint is dry enough to (carefully) pick up.  That's not the end of this chapter, though.  I've since done a bit more spot filling on my fillets and reprimed.  So, right now, it looks just like the above picture, but its been through one more round of the same...

[RKeller]

Looks really nice! I need to get my Mac kit together!

[mike2wander]

Looks really nice! I need to get my Mac kit together!

Yes you do!