Wayco's RW Mongoose 54 build

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I got an email this morning from a member here following my thread. I prefer to have questions posted up on my thread, but any method you use to ask questions will get a response. I'm all about sharing info., and since I'm not competing for altitude records or have a secret formula for making my rockets better/faster/prettier than others, and no interest in that aspect of the hobby, all my stuff is laid out in my build threads. Unfortunately, I'm a victim of age and other factors that cause me to leave out stuff that I assume everybody knows or just forget to add. This is the case with my post regarding motor retention. I didn't mention the tool that I use to countersink the holes in the fincan that the 6-32 flat head screws go into:
https://www.amazon.com/gp/product/B00004T7OQ/?tag=skimlinks_replacement-20

There is a "touch" you have to learn using this tool, and the more you work with it, the better (more flush) the screw will fit. I will go into more detail when I get back to countersinking and drilling holes in carbon fiber. It's one of my least favorite jobs, so be patient. I will also go over how to align the holes when installing a motor. It's not that complicated, and I have a special tool made from PVC pipe that makes the whole process pretty easy.

So here is some Wayco philosophy that will help you understand my goals regarding rockets in general. Like I said in a previous post, I'm a rocketman, some of the science I don't understand. My primary objective with my rockets is to have a successful flight and safe recovery. I build durable rockets that I can fly over and over without having to fix stuff. If something does break, I figure out a way to keep that from happening again. I'm a backyard mechanic kinda guy, not an engineer. Math is not one of my strong points. I fly a lot of rockets, so if I don't get something right, it will become apparent in short order. Here is an example of that:
My first "real" MD rocket was a Blackhawk 54, I mentioned it in my first post of this thread. I made a couple of mistakes, mainly due to my "build fever" attitude that comes over me from time to time. I didn't move the fins forward one caliper, and assumed that redundant altimeters wouldn't fit in a 6" 54mm avbay. On "Silver Streak's" third flight, the ematch failed to ignite at apogee and the rocket returned ballistically to 700 ft. where the main deployed. It stripped the fabric off the shroud lines and the shock cord tore a 6" zipper in the payload tube. It must have landed pretty flat, because two of the fins were broken off on landing. I was lucky to find it, having lost sight well before it reached the 14,700 ft. altitude it went to. The Eggfinder GPS failed on landing when the GPS module broke off the board. I did get some packets back, and that got me in the general area. After an prolonged search, I found it laying beside the road, about a half mile from the launch.
I decided that since two of the fins were already off, I would remove the last fin and re-attach them in the proper place. That's when I found out that Rocketpoxy is really good at attaching fins. I finally got the fin off by cutting slots into the fillets and smacking the fin with a hammer. I rebuilt the rocket with the fins 1 caliper forward and managed to stuff another altimeter in the avbay. Next flight was on an L935 Imax to 23, 230 ft. Good flight, good recovery with a new Eggfinder in the nosecone.
Today I ran my first set of fillets on the fins. First, I took a short piece of 1" PVC and ran it back and forth along the joint of the fin and the fincan. The is gives me a mark to apply tape:
004%203.jpg


Next I mix up a batch of Rocketpoxy and start my timer. I'm weighing this batch in a little fruit cup, 24 grams and about 10 drops of black tint. Mix it up for a couple of minutes and it looks like this:
005%202_1.jpg


As you can see, all kinds of bubbles in it! This used to drive me crazy, but now I have a trick from another crazy guy who builds lots of rockets. Crazy Jim told me to spread it out on a smooth surface really thin, and all the bubbles go away:
006%202_1.jpg


Now we're gonna leave it set for about 20 minutes. Meanwhile I will tape up the area and sand it with 220 grit sandpaper, wipe it off with acetone and it's ready for the epoxy:
009%203.jpg


Scrape up a good batch of black goop and lay it carefully into the valley. It should be pretty thick at this point:
014%202.jpg


Since I can't run out fillets and take pictures at the same time, I will just describe the next step. Dip your tool in alcohol and give it a quick shake. All you guys with dirty minds can take that sentence and run with it, but for the rest of us, we're moving on to the next step. Keep the tool at a constant angle and run it the full length of the fillet. If you got the right amount of epoxy in there, it will leave a line of extra epoxy along the edge of the tape. I pull this off with a handy little tool I found at Hobby Lobby in the painters dept. It has a curved tip that allows you to lift off the extra and you can use it on the second fillet:
017.jpg


When you have the second fillet filled up, take your PVC pipe, dip it in alcohol and run that fillet out. You can go back over these fillets and add more epoxy, clear extra off using whatever tools you find that work for you. Each time you run out a fillet, be sure to dip your tool in alcohol and flick off any extra before running them. As soon as you have an acceptable fillet, take the tape off. I do this while the epoxy is still runny, so the edges have time to settle down. Touch up with a q-tip and alcohol and you should come out with something like this:
022.jpg


I'm hoping to get all these fillets done tomorrow, and I will cover countersinking holes and how to get the motor retainer lined up in the tube.
If you have a question, don't keep it to yourself. There are probably others thinking the same, and you can get your answers faster by posting up.
 
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Wayne,,
I get the felling everyone knows the answer to this question but me...
Why do you put the aft end of the fins 1 airframe diameter caliber forward of the aft end of the rocket ??
I have seen this before on other minimum D rockets...
You're moving the center of pressure forward....
There goes my guess that it'll increase stability...lol...

Thank you for going to all of the trouble of the build thread Wayne...
It's very interesting to read and see how others accomplish what has to be done on a build...
And it is most definitely not easy to do,, much extra time and effort goes into a thread like this...

Teddy
 
onebadhawk said:
Wayne,,
I get the felling everyone knows the answer to this question but me...
Why do you put the aft end of the fins 1 airframe diameter caliber forward of the aft end of the rocket ??
I have seen this before on other minimum D rockets...
You're moving the center of pressure forward....
There goes my guess that it'll increase stability...lol...

Thank you for going to all of the trouble of the build thread Wayne...
It's very interesting to read and see how others accomplish what has to be done on a build...
And it is most definitely not easy to do,, much extra time and effort goes into a thread like this...

Teddy
Click to expand...

It's rocket science Ted, and you know what I say about that. Something to do with linear air flow off the back of the fins, supposed to reduce drag similar to a boat tail or tapered aft closure. :confused2:
 
You've mentioned PEM nuts in a number of builds and I was wondering if you could show in detail, video may help me visualize, (or direct me) to a build where you do how they get mounted and where you source them from? Thanks for the awesome detail learning lots seeing these builds.
 
alex_car763 said:
You've mentioned PEM nuts in a number of builds and I was wondering if you could show in detail, video may help me visualize, (or direct me) to a build where you do how they get mounted and where you source them from? Thanks for the awesome detail learning lots seeing these builds.
Click to expand...

One source of Pem nuts is Missileworks.
 
MW has three different sizes. Curious to what size is most popular for rockets of say 54mm or 38mm MD size?
 
McMaster Carr has many types of counter sink bits. The site explains how to pick the correct one for your application:

https://www.mcmaster.com/#countersinks/=103mnjl

Missile Works does have PEM nuts, I use them to mount my RRC3's. However, I don't think that the tops of those Pems will be very flush with the retainer piece. I was also going to ask Wayco which PEM nuts he uses and where he gets them. McMaster Carr has all kind of PEM nuts, but again, I'm not quite sure what Wayco is using. Wayco has a bit of PEM sticking out that he puts epoxy on. Some of the Pems would barely get through regular walled FG tubing.
 
4kids49 said:
McMaster Carr has many types of counter sink bits. The site explains how to pick the correct one for your application:

https://www.mcmaster.com/#countersinks/=103mnjl

Missile Works does have PEM nuts, I use them to mount my RRC3's. However, I don't think that the tops of those Pems will be very flush with the retainer piece. I was also going to ask Wayco which PEM nuts he uses and where he gets them. McMaster Carr has all kind of PEM nuts, but again, I'm not quite sure what Wayco is using. Wayco has a bit of PEM sticking out that he puts epoxy on. Some of the Pems would barely get through regular walled FG tubing.
Click to expand...

That is called the shank height, here is a copy and paste from DizWolf's Tomach, it's not a toomach, build thread. BTW I use the same method Wayco uses to glue them in, which is to use a screw with a nut on it and washer to sit against the outside of the airframe then crank it down so it pulls right in until it sets up. I also use the same countersink bit, as a matter of fact Wayco is the one who pointed me in the right direction on that tool. Believe me the right bit makes a big difference in the outcome, as does the technique but I will let Wayco show us his technique.

I used 6-32 .25" Stainless flat head screws that use a T10 drive https://www.fastenal.com/products?r=~|categoryl1:%22600000%20Fasteners%22|~ %20~|categoryl2:%22600051%20Screws%22|~%20~|catego ryl3:%22600059%20Machine%20Screws%22|~%20~|sattr02 :^5pound6-32$|~%20~|sattr03:^%22Stainless%20Steel%22$|~%20~| sattr04:^Flat$|~%20~|sattr06:^T10$|~%20~|attrlengt h:310|~

For the nuts don't forget to rough up the inside of the tube before you epoxy them in. I use the following 6-32-0 stainless steel self clinching nuts.

https://www.fastenal.com/products/details/0127446?term=self+clinching+nuts&r=~|categoryl1:%2 2600000%20Fasteners%22|~%20~|categoryl2:%22600191% 20Riveting%209and%20Self-Clinching%20Products%22|~%20~|categoryl3:%22602450 %20Self-Clinching%20Nuts%22|~%20~|sattr01:^%22Stainless%20 Steel%22$|~%20~|attrdiameter:107820|~%20~|sattr02: ^%22Self-Clinching%20Nut%22$|~

You want to make sure that the shank height is low, which is what the "-0" represents...in this case that translates to .03" This is the bit of the nut that sticks up past the knurled shoulder and fits into the hole you drill. By keeping it low you will ensure that when you tighten the screw it will have a longer distance to travel before bottoming out. Otherwise your screw may not fasten all the way down.

I use a 2-56 self clinching nut, for my shear pins but it has a longer shank "-1 or -2, can't recall" basically so it's just about flush between the coupler and airframe...right where it would shear. I personally like the ability to screw my shear pins in and so far the argument that you can screw them down too tight has not proven to be a concern. This is simply because if you try to screw those nylon shear pins down with too much force, the head just pops off. This was the argument that was presented to me when I proposed it in a previous thread. I understand the logic, as it is intuitive, however in practice it has not proven to be a concern in my application.
 
alex_car763 said:
You've mentioned PEM nuts in a number of builds and I was wondering if you could show in detail, video may help me visualize, (or direct me) to a build where you do how they get mounted and where you source them from? Thanks for the awesome detail learning lots seeing these builds.
Click to expand...

I copied this picture from my first post on this thread:
009_1.jpg


As described previously, you hold the screw from turning and tighten the nut, that pulls the pem nut into the hole. The serrated edges you see on the pem nut hold it in place, but does not go all the way through the fiberglass.
I get my pem nuts from Missleworks, the 6-32 size is used for this application, but I use the 4-40 size on avbay sleds and the 8-32 size on bigger rockets.
Thanks to all who posted about this, Do you guys ever sleep?
 
Wayco said:
I copied this picture from my first post on this thread:
009_1.jpg


As described previously, you hold the screw from turning and tighten the nut, that pulls the pem nut into the hole. The serrated edges you see on the pem nut hold it in place, but does not go all the way through the fiberglass.
I get my pem nuts from Missleworks, the 6-32 size is used for this application, but I use the 4-40 size on avbay sleds and the 8-32 size on bigger rockets.
Thanks to all who posted about this, Do you guys ever sleep?
Click to expand...

But then the other poster mentioned adding epoxy? Do you do so? I ask because I always have these things popping out of fiberglass airframes (like one third of the time). So much so that I've just gone back to using inverted t-nuts with epoxy (as I'm having to use epoxy anyway to keep them in place and they are much cheaper than PEM nuts).
 
Last edited:
dixontj93060 said:
But then the other poster mentioned adding epoxy? Do you do so? I ask because I always have these things popping out of fiberglass airframes (like one third of the time). So much so that I've just gone back to using inverted t-nuts with epoxy (as I'm having to use epoxy anyway to keep them in place and they are much cheaper than PEM nuts).
Click to expand...

Yes, I use epoxy to hold them in place:
011_1.jpg


This was also explained in my first post on this thread. I guess we have a different perspective on what "much cheaper" means...
I need some more coffee before I post in the morning.
 
Wayco said:
I guess we have a different perspective on what "much cheaper" means...
Click to expand...

The Fastenal 6-32 PEM nuts referenced by the other poster are $0.42 a piece but you can get the same thing at McMaster-Carr, 25 pcs @ $8.25 (33 cents ea.) or zinc-plated 50 pcs @ $9.79 (19.6 cents ea.). Comparatively t-nuts are 100 pcs @ 8.59 (8.6 cents ea.)--less than half the cost of zinc-plated and 1/4 the cost of stainless PEM nuts.
 
dixontj93060 said:
The Fastenal 6-32 PEM nuts referenced by the other poster are $0.42 a piece but you can get the same thing at McMaster-Carr, 25 pcs @ $8.25 (33 cents ea.) or zinc-plated 50 pcs @ $9.79 (19.6 cents ea.). Comparatively t-nuts are 100 pcs @ 8.59 (8.6 cents ea.)--less than half the cost of zinc-plated and 1/4 the cost of stainless PEM nuts.
Click to expand...

So is one any better than the other, PEM vs. T-nuts?
 
timbucktoo said:
So is one any better than the other, PEM vs. T-nuts?
Click to expand...

PEM nuts are potentially better as they mechanically bind to the material. But in practice, they don't. At least in fiberglass and carbon fiber they pop out (maybe they work better in their intended application, metals, but I don't know as I haven't studied it). So the fallback is using epoxy to keep them secure, in which case a PEM nut or a t-nut are about the same.
 
timbucktoo said:
So is one any better than the other, PEM vs. T-nuts?
Click to expand...

dixontj93060 said:
PEM nuts are potentially better as they mechanically bind to the material. But in practice, they don't. At least in fiberglass and carbon fiber they pop out (maybe they work better in their intended application, metals, but I don't know as I haven't studied it). So the fallback is using epoxy to keep them secure, in which case a PEM nut or a t-nut are about the same.
Click to expand...

This is obviously an interesting subject to some here, so I'm gonna jump back in and add my "perspective" on this. Both the T-nut and PEM nut do the same job, add durable threads to hold stuff together. The "stuff" in this case is carbon fiber, and it's part of a kit that most of us got on sale for $189.99. Smokin' deal when you consider it's listed on RW's site right now for $379.99. So, keeping things in perspective, you could say that we already saved ourselves $190. I checked on Missleworks site, and the PEM nuts I'm using on this kit sell for $2 for ten. I will use nine of those on this build. As much as I respect and admire what Tim (dixontj) brings to this forum, I just can't get excited about saving a buck on fasteners. Me, I'm gonna take that $190 and spend it on an L935 Imax, just to see how high I can get this rocket to fly to.
Honestly, I'm not trying to discount the input others add to my threads, it's all good to me. We're here to share ideas, and I'm all for that.
Now I'm gonna go run out another set of fillets.... I want to get started on my avbay this weekend, and I'm probably gonna use some more PEM nuts there too.
 
timbucktoo said:
So is one any better than the other, PEM vs. T-nuts?
Click to expand...

Technically speaking you are referring to a self-clinching nut. PEM is a brand name, PEM Engineering. It's like calling all snowmobiles a Ski-doo. T-nuts are completely different. I use T-nuts in ply bulkheads, but self-clinching nuts in composites.

As far as a PEM self-clinching nut being better at bonding than another manufacturer, that is a matter of opinion. I would argue that in this application there is no appreciable difference. The differences are typically in the size, shank height and the material as well as hardness...so you can get different grades of stainless or zinc. Again for our application my only concern is the size and shank for practical reasons, and I prefer the stainless to mitigate oxidation.

Last week a swapped three self-clinching nuts out of a nosecone for ones with a shorter shank, and I can tell you it took quite a bit of force and effort to get them out. I use Aeropoxy structural adhesive ES6209 to bond mine in.

As far as the link I provided, this is where I sourced them, which is convenient for me. However as others pointed out you may be able to source them for less. My intention was to simply provide a link for information purposes and not necessarily a source as I am located in Canada.

This is the shoulder of a nosecone, removed and looking from the top. It is removable, which is what the 3 self-clinching nuts on the side are for and you can see I used two self-clinching nuts in the bottom ring which secures the aft bulkhead. The bulkhead is installed with a Kevlar loop as an attachment point in lieu of a u- or eye bolt.

View attachment 277381
 
Last edited:
Wayco said:
...If you got the right amount of epoxy in there, it will leave a line of extra epoxy along the edge of the tape. I pull this off with a handy little tool I found at Hobby Lobby in the painters dept. It has a curved tip that allows you to lift off the extra and you can use it on the second fillet:
Click to expand...
I like the curved tip tool. It sure beats the wooden stick I use. That line of extra epoxy is the bane of my external fillet existence. Ever notice how it seems to refill itself after you remove it? You would think the gap between the line and the fillet would keep that from happening, but epoxy wicks across the gap. I don't do your 20 minute set up, more like 10 minutes 'cause I am too slow getting the RocketPoxy into the fillet, so that might be part of the problem.
 
mpitfield said:
Technically speaking you are referring to a self-clinching nut. PEM is a brand name, PEM Engineering. It's like calling all snowmobiles a Ski-doo. T-nuts are completely different. I use T-nuts in ply bulkheads, but self-clinching nuts in composites.

As far as a PEM self-clinching nut being better at bonding than another manufacturer, that is a matter of opinion. I would argue that in this application there is no appreciable difference. The differences are typically in the size, shank height and the material as well as hardness...so you can get different grades of stainless or zinc. Again for our application my only concern is the size and shank for practical reasons, and I prefer the stainless to mitigate oxidation.

Last week a swapped three self-clinching nuts out of a nosecone for ones with a shorter shank, and I can tell you it took quite a bit of force and effort to get them out. I use Aeropoxy structural adhesive ES6209 to bond mine in.

As far as the link I provided, this is where I sourced them, which is convenient for me. However as others pointed out you may be able to source them for less. My intention was to simply provide a link for information purposes and not necessarily a source as I am located in Canada.

This is the shoulder of a nosecone, removed and looking from the top. It is removable, which is what the 3 self-clinching nuts on the side are for and you can see I used two self-clinching nuts in the bottom ring which secures the aft bulkhead. The bulkhead is installed with a Kevlar loop as an attachment point in lieu of a u- or eye bolt.
Click to expand...

Ok, so the three nuts are to attach the nosecone to the shoulder. Now the two in the base I take it is so the bulkhead is removable from the shoulder/coupler so you can replace the kevlar loop in the future? Are those plain nuts or Pem?

Kurt
 
WoShuGui said:
I like the curved tip tool. It sure beats the wooden stick I use. That line of extra epoxy is the bane of my external fillet existence. Ever notice how it seems to refill itself after you remove it? You would think the gap between the line and the fillet would keep that from happening, but epoxy wicks across the gap. I don't do your 20 minute set up, more like 10 minutes 'cause I am too slow getting the RocketPoxy into the fillet, so that might be part of the problem.
Click to expand...

I got a set of those tools at Hobby Lobby, they are used by painters to apply THICK paint.
 
ksaves2 said:
Ok, so the three nuts are to attach the nosecone to the shoulder. Now the two in the base I take it is so the bulkhead is removable from the shoulder/coupler so you can replace the kevlar loop in the future? Are those plain nuts or Pem?

Kurt
Click to expand...

First off I apologize and want to thank Wayco for allowing me the temp hijack...in my defense I figured it was topic related or at least conversation related. I will keep this to a minimum.

To answer Kurt's question, yes they are also PEM nuts, and your assumption is correct Kurt, I made it removable for servicing. One of the design goals when deciding on how to put the rocket together, was to make it as serviceable as possible. It is my 54mm MD carbon fiber Tomach, with the exception being the nosecone and nosecone coupler which is FW/FG.

Below is a pic of the complete assembly, minus the nosecone and coupler. The thin black ring is what I secure the self-clinching nuts to, and what you see in the pic in my previous post. The holes are the perfect size for a press fit but they are also epoxied in with ES6209. The two different diameter bulkheads fit together to make one bulkhead with a shoulder and the long board is the mounting sled for my TeleGPS on one side with a 2S LiPo and a Comspec AT-2b on the other side. The sled fits into the rounded groves in the bottom of the thin black ring, and is tight against the end of the aft bulkhead and nosecone, so it does not move.

What is not visible are three additional "PEM" nuts, located just below the ring which are 2-56, and what I screw my shear pins into. They also provide an additional anchoring point to prevent the bottom ring from pulling out. Although that was not their original intended use...just a happy benefit.



 
Thanks, I'm sure Wayne won't mind. Good information. I'm a simpleton and will likely epoxy the bulkhead, use an eyebolt and screw the nosecone on to the coupler with pem nuts on the interior so I can remove it.
Kurt
 

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