MadCow 2.6" Jayhawk build log

[K3LAG]

Now that the work bench is cleaned off after the 5 month semi-truck build it's time for something a bit more straight forward.

I will be building a 2.6" MadCow Jayhawk. Nothing spectacular or out of the ordinary planned for this build.

The work bench is clean, let's go...



Hmm. I should probably close the bathroom door when I take pictures next time.

Parts inventory: Everything is here. The laser cutting all looks good. The included dowel for the canards is supposed to be 1/8" but my kit included a 1/4" dowel for some reason. No big deal, I have plenty of dowel stock around. The boat tail is really soft light balsa and is fairly rough. It's going to need some clean up, filling and sanding.



The main fins are slightly warped. With the aft end of them held to the bench the forward tips are about 1/2" off the bench. I need to decide whether to try to flatten them now or just do it when I glue them on. They flex back to flat pretty easy so I'm leaning toward just tacking them down straight when I put them on then glue the entire edge.



The only planned modifications from the kit/directions I'm planning at this point are:
1. Rail buttons instead of the lugs. Probably mini buttons
2. StickerShock23 vinyl instead of the included decals.

I'll probably change the assembly slightly. The instructions have you glue the boat tail and centering ring onto the motor tube than glue the whole think into the rocket but I think I'll wait and glue the boat tail on later so I can do internal fillets.

I'm glad I got this kit as part of a 30% off sale. I think I'd be disappointed if I paid full price for it. It's not bad at all it just feels like there isn't much to it for the price.

 

[NOLA_BAR]

Nice workbench! Love the wood top.

 

[K3LAG]

Nice workbench! Love the wood top.

Thanks. The slab is from a tree we had taken down behind our church. We got about 6 decent sized slabs out of the trunk. I flattened the slab myself using a big frame built from MDF and a big router. The slab was a bit flexible along its width so I embedded 3 steel bars in it from the bottom. The frame is from Uplift Desk.

 

[K3LAG]

I little minor progress. I prefer to get all of the parts in the condition I want before I start assembling. The first two things to tackle are the boat tail and warped fins.

I sanded the boat tail to clean it up and put a coat of Varathane sanding sealer on it. Once dried I gave it a light sanding and a 2nd coat of sealer. It's looking much better.



Next I have begun trying to get the warp out of the fins. I thought about skinning them with paper or glass or various other things but then though about the fact that the CP on the Jay Hawk is fairly forward so I don't really want to add much weight to back half of the rocket if I can avoid it. So, for the first attempt I've restrained the aft end of the fins and put some weight on the forward end to flex them back the other direction. I'll see if that does any good. If not, I'll do the same but with some water or windex. I'm going to try to get them straight without adding weight.



I truly think they are flexible enough that I could just straiten them as I put them on but I'd rather get them straight first if possible.

 

[K3LAG]

Just using weight to try to coerce the fins back flat wasn't working so I decided to get them fairly wet and see what would happen. I ran water on both side of them at the sink for a few minutes and a miracle occurred. They actually straitened out right there as I was holding them. So, I put them under some weight overnight and when I checked them this morning they look great!

 

[K3LAG]

Since I am picky about things that are supposed to be square actually being square, or very close to it, I decided to mount the fin tips to the fins before the fins are attached to the rocket. I also quickly 3d printed a 3/8" thick ring to hold the centering ring square on the motor mount. All are tacked up with a few spots of CA in this picture and they will get epoxied a bit later.



1-2-3 blocks are a great way to make things square.

 

[K3LAG]

A bit more accomplished in the last day or so. I filled and sanded the tube spiral joints. I was out of my usual fillers I normally use so I grabbed some Bond Spot and Glazing Putty. I really like it so far.

The fins are temporarily fit to test the fit of the jigs/stands that will hold them straight when they are installed. The fin to tip joints have also been epoxied. I didn't think to make the 3d printed stands tall enough to account for the tips so the 1-2-3 blocks come to the rescue again.




The boat tail fit was a little loose on the motor tube so I temporarily wrapped a bit of tape around the tube to so it fit tight enough that I could slide the tube and centering ring into place with the boat tail yet still pull the boat tail back off after the epoxy on the centering ring is cured. There isn't a picture of this but that assembly is installed and I'm waiting for the epoxy to cure. The only suitable epoxy I have on hand is West System 105 so I have to wait quite a while. 30 minute would have been fine for this project but I didn't have it on hand or a convenient place to pick some up. All HD and Lowes has is 5 or 6 minute and I'm not a big fan of those.

 

[K3LAG]

Test fitting parts is wise. I realized this morning that my brilliant idea of leaving the boat tail off to do internal fillets won't work. Since the fins angle inwards to attach to the boat tail you have to put the boat tail on before the fins. Doh!

I'm glad it dawned on me before I put the fins on.

 

[Back_at_it]

Great build. I've been wanting to build another one of these for years. I had the Estes Pro Series version back in the day but I challenged the rocket gods and tried to fly it on a day with 5-7mph winds and it didn't end well. I was frustrated and never rebuilt it.

 

[K3LAG]

This mornings update:

The motor mount and boat tail are now epoxied into place.

The seams on the nose cone have been filled and holes drilled for the dowels for the canards. Also filled the joints on the face of the fin tips.



I'll epoxy the fins on this afternoon.

 

[K3LAG]

Fins are epoxied on. Since there is no access into the motor mount area at this point I took a couple steps to attaching them. First I painted a thin layer of neat epoxy on the fin tabs so that the epoxy could penetrate the wood well. Then I mixed some 404 high density filler into the remaining epoxy until it was peanut butter thick. I then injected that with a syringe through the fin slots to build up a ridge of epoxy for each fin and inserted the fins into the thickened epoxy. Then I placed the whole thing on the 3d printed stands to keep it all flat.




You may notice the word ‘top’ on the body tube. The fin slots were very slightly out of line so it was important to orient it correctly on the stands or the fins would have drooped slightly.

 

[K3LAG]

Friday evening update...

I put a couple of light coats of primer on the nose cone. I'll give it a day or so then lightly sand and put another coat on.



I also did the fin fillets. I used West Systems 105 with 407 micro-balloons filler. I love how easily the 407 sands. Sanding will happen tomorrow after it cures then I'll put a couple coats of Varathane sanding sealer on it.



I also played with my new toy/tool a bit. Time to start making fins for clones and upscales. That is 1/4" baltic birch plywood.

 

[K3LAG]

All of the serious sanding is finished and all that's really left is paint prep. I put a heavy coat of sanding sealer on the fins and I will head down for an additional light layer later tonight. Will do light sanding tomorrow and maybe apply one more coat of sealer.

I still need to put the canards on the nose cone but I want to give the nose cone one more light sanding after the latest coat of primer before I put them on.

My orange paint showed up from SprayGunner.

 

[K3LAG]

A bit more progress this afternoon.

I put the first coats of primer on the rocket. I will wait until tomorrow to sand the whole thing down again with 400 and put another coat on. I really need to clean out my spray booth.



The 2nd coat of primer on the nose looks excellent.



I put some painters tape and wax paper on the nose to protect the nose cone while I attach the canards. I plan not to attach the canards to the nose cone at all. Not that this is a scale model or anything but real canards wouldn't be attached to the nose or have filets anyway. However, the main reason I'm doing it is so that I can more easily tape off the canards and surrounding areas when I paint the black part of the nose later on. The fact that I think it will look good with the really thin gap there is just a bonus. The canards are tacked in place with a couple a drops of CA to hold them in alignment and I'll follow up with a bit of epoxy to attach them later and then a bit more epoxy with micro-balloons to fill the gaps between the dowels and canards. It will take a couple days to get all that done due to curing time even though they are pretty small jobs.

 

[K3LAG]

The final primer is on the main rocket and the canards are attached, filled and sanded. The canards are also primed but no picture of that at the moment.




I'll let the primer cure for a few days to a week before I put the color on. It shouldn't be necessary with the paint I'm using but I'd rather be safe than sorry. There probably won't be another update until orange goes on.

 

[Hobie1dog]

Excellent build and thanks for the explanations.

 

[K3LAG]

I lied. Two more pictures before it sits for a few days before orange paint.

I peeled the tape off around the canards and cleaned them up a little and I'm really happy with how the gaps between the canards and nose cone came out. It looks really good. It was a little bit of a pain in the neck to execute but I think it was worth it. Three is a light behind the canards that is showing through the cracks. Here is also a picture of the whole thing primed as it sits for a few days.

 

[Pepe Le Pew]

K3, that build looks awesome!

 

[ljwilley]

Looking amazing! Can't wait to see it fly!

 

[K3LAG]

Well, it's not ready to fly but it has been a bit over a week since the primer was done and it's orange now so time for an update.

Time to paint the orange. Everything is together and the booth is on.



Createx Autoborne Sealer process orange mixed with 10% 4011 reducer.


Temperature and Humidity good to go.


Air pressure set to 14 PSI and paint on the gun. I sure love my Iwata LPH-80. It atomizes at 14 PSI, and only needs 2.1 CFM of air. I have a full size compressor now in my shop but back when I lived in a townhouse I could run this thing off a pancake compressor no sweat. I have the 124G version with the 1.2mm needle and E4 air cap. There are versions available with needles from .4 to 1.2mm and with two different air caps. I use the E4 air cap which requires a little more air than the E2 but it has a wider fan which is nice for larger projects.



The paint is on. The test splotches on the back wall are to ensure I have the gun setup the way I want. Since this rocket isn't too large I actually narrowed the fan a bit and dialed the paint quantity back a little. Still wet in this picture.


Dry. I'll let it sit for a few days before I tape off the nose area for black paint. I have a few other, non rocketry projects, to work on in the mean time. I have to laser cut and glue together 30 little gift boxes for the attendees for my nieces wedding shower. The createx paints dry to a really smooth finish. The sealers, in particular, are designed to be painted directly over as desired. Using a sealer that is about the same color allows you to use a lot fewer coats of the more expensive metallic, pearl or other coats that go over top of it. It's also great for flourescent colors. The pigments used in fluorescent paints usually aren't UV stable. So, by putting them over a color keyed sealer they don't appear to loose as much of their color when they fade. In this case, the sealer is the final color which works great. Since it dries so smooth I won't need to put a clear coat on before the vinyl graphics go on. It will get cleared after the vinyl graphics are on.

 

[CrownUK]

Great job so far will be so good you won’t want to fly it.
Here is mine I made mine 5 years ago and haven’t flown yet , put so much into getting a perfect finish , don’t want to crash it

 

[ljwilley]

What would this hobby look like if people didn't take risks? I say fly it!

 

[AfterBurners]

What would this hobby look like if people didn't take risks? I say fly it!

get a JLCR and have it deploy at 1000' under a big chute it lands really soft.

 

[K3LAG]

I finally got back to the Jay Hawk today. I got the nose painted.

 

[K3LAG]

Decals are on. Normally I'm very happy with stuff from StickerShock23 but in this case Marks's vinyl decals have some issues. They are a bit too big which makes the rocket look kind of cartoony. And the decals with the 'DANGER...." words were upside down so I had to do some surgery on them. It looks fine but it's not going to win any scale contests that's for sure. I'll get some clear on it in the next few days, do the final install of the rail buttons and parachute, weight it for balance and some nose weight and call it done.

 

[ljwilley]

Nice job!

 

[K3LAG]

Finished!

A few comments on the last few steps.

1. I used the glidden matte clear spray available at Home Depot to clear coat it. It was the first time I've used that clear. It dries very fast. They say it is lacquer but the smell is slightly different than most lacquers I'm used to. It worked well though.

2. For adjusting the CG the MadCow provided RockSim file says to add 3 oz to the nose cone. Since epoxy won't stick to that nose cone well they describe a process of putting the weight mixed with epoxy toward the bottom of the nose and using a screw to hold it in place. I prefer the have the weight as close to the tip as possible so I did it a bit different.

a. I have weights I use to simulate the weights of various motors. They are 3D printed shells with screw on caps that I can put steel shot in to make them weigh whatever I want. In this case I filled my 29mm shell with the correct amount of weight for the heaviest 29/40-120 motor then balanced the rocket with the CG 19" from the nose as recommended. It took nearly 4 oz of weight rather than the recommended 3 oz. The picture shows my 29, 38 and 54mm weight shells. The caps are the right size that a standard retainer can be used to hold them in place.



b. After I determined the desired weight and poured it in the nose I filled the rest of the nose with PML variable density foam that I happened to have on hand. I used the maximum drops of water allowed to get the minimum density. It took less than 1/2 oz of foam to fill the nose cone. I had mixed an ounce because mixing much less than that would be difficult and I knew there would be some left in the funnel and cup. This is the first time I've tried this method to hold weight in a nose cone and it seems to have worked well.

Here's the final picture:



My next build is a scratch built 3x Estes Black Hole Probe. I've already begun making parts for it and will start a build thread soon.

 

[Bruiser]

Came out very nice. I'd be afraid to send it

-Bob

 

[Daddyisabar]

I flown mine many times. It likes a lot of moderate power like a G53 Black Jack. Too punchy of a motor will bring out the bad characteristics of all Jayhawks. Typical damage after many flights landing on the hard Prairie to the fin edges/nose cone and cracked body tube fiilets, paper is only so strong. A little thin CA and stronger than new.

 

[cat5752]

You did a great job on it. I am about halfway through the decals after today. I used a combination of Estes Pro Series and the ones that came with the MadCow. I added some scale details to it and a electrical conduit underneath Good luck flying it.