MadCow Bomarc

[troj]

Friday, I came home from work to a nice little box sitting on the front porch. Said box contained a MadCow Bomarc kit, something I've been interested in since it was first released.

Yesterday, I poked around at the parts, and started scanning the instructions.

One thing that I noticed immediately is that the coupler is tight. Very, very, very tight. For construction, this is awesome, as it will result in a nice, solid joint. It will, however, also make it "entertaining" to assemble with a bit of glue on it! I normally use wood glue for rockets in this range, but I don't think I will on the coupler, as there's no way I'll get it all the way in before the glue grabs, with as tight as it is!

The balsa cones for the inlets are also very snug in their tubes -- no wood glue there, either.

-Kevin

 

[troj]

First up is the motor mount, one of the more exciting parts of any build.

I'm not fond of friction fit for motor retention, so I plan on installing some inserts into the rear centering ring, to allow better retention. Because the rings are thin plywood (more than sufficient for the rocket), and I'm not using T-nuts, I wanted something a bit more substantial to put the inserts into. So, I cut and glued small blocks to the back of the ring, where I plan to install the inserts.

I've also got the forward ring on the motor mount. Not too exciting looking, just yet.

-Kevin

 

[troj]

For those of you who've seen it, Don Magness (Squirrel Works) and I had a bit of fun going back and forth about his suggested weight for when assembling wings for his Dogfight kit. Don suggests condiment packets, and was even kind enough to send me a generous selection to choose from.

Well, for the Bomarc, condiment packets aren't gonna cut it, unless you happen to have a case or two of them handy.

So, for assembling the wing, along with its top balsa surface, I pulled out something convenient -- 12 packs of Coke!

The main wing on the kit comes as two pieces of laser-cut plywood which are first edge-joined. Then, four strips of 1/8" thick balsa are cut to go over the top of the wing. These are edge-joined to each other, as well as glued to the top of the plywood surface. To keep them from warping, moving, and doing other obnoxious things, a bit of weight is in order. Thus, the cases of Coke.

It's an exciting picture, almost up there with Art's unboxing photos!

-Kevin

 

[sodmeister]

Hmmm...for a second there ,I thought you were going to enjoy a few rum n` cokes before starting the Bomarc project.

I am planning on buying that kit ,so I`ll be watching your build.

Paul

 

[troj]

Hmmm...for a second there ,I thought you were going to enjoy a few rum n` cokes before starting the Bomarc project.

Vodka & OJ would be more my style, but rum & Coke isn't bad, either....

I am planning on buying that kit ,so I`ll be watching your build.

So far, I'm liking what I'm seeing of the way it goes together.

-Kevin

 

[troj]

More work on the most exciting part of the kit -- the motor mount!

Once it's epoxied in place, I like to put a thin layer of lightly thickened epoxy over the rear ring, to make sure it's solid, as well as make sure the motor retention inserts stay in place.

The motor mount was previously installed with epoxy thickened with a little bit of chopped fiberglass, to keep it from running past where it belongs. In this case, I've thickened the epoxy with microballoons (the epoxy smooths out more than with chopped fiberglass) just enough to get it to the consistency of thick syrup. It runs, but slowly. The goal is to cause it to fill any small gaps without all running down where it doesn't below.

One thing about applying thickened epoxy -- it doesn't penetrate as well. So, before I apply it, I brush a thin layer of unthickened epoxy onto the parts. I then thicken the epoxy and apply it where desired.

-Kevin

 

[troj]

Now on to more exciting parts!

The forward end of the engine nacelles is made from two balsa parts. The machining on these is very well done, and the results will be great! The little cone is glued into the middle of the main piece; in this case, I used Titebond II, which is more than strong enough.

Being a balsa part, however, it will be susceptible to dings and dents very easily. That's easily fixed by applying a thin layer of epoxy, and letting it soak in. The blue tape is around the shoulders to keep epoxy off, as that's a bonding surface I'll be using later.

-Kevin

 

[troj]

...and now back to the main wing. It's been sitting under 36 cans of Coke since yesterday -- it needs to sit there until fully dried, or it will warp, due to the moisture in the glue.

What I did was let the glue sit for an hour yesterday, then I pulled off the top layer of waxed paper, and replaced the Coke. This was done to help let moisture out. At that point, if left alone, it had a definite warp.

This morning, I pulled off the bottom layer of waxed paper and reapplied the Coke. Only the forward tip is wanting to warp now, so the glue is drying nicely.

I did grap a quick picture before I put the weight back in place. The yellow you see is the glue on the excess balsa. After it's fully dried, the extra balsa gets trimmed away.

-Kevin

 

[barstoolmike]

Kevin,

I had the same problems with my Bomarc. I sanded the coupler & nose cones to the nacelles to fit better. I also put T-nuts in the lower centering ring for retention. I like your idea about cases of soda. I used a piece of plywood & everything I could find in my shop for weight. I enjoyed building the kit.

Mike

 

[Stymye]

to help solve your worry about the wood glue grabbing , If you put a ring of glue deep enough into the >tube< rather than the part ,
put the glue ring deep enough to start the cone,or coupler..

than push it in .. it's done with little chance to grab and seize .

I always do it that way,, no problems (so far)

epoxy is not my crutch...lol

 

[troj]

Aaaaaarrrrrrrgggggghhhhhhhhhhh!!!!!!

I pulled out the Bomarc to do some more work, and made a discovery -- the main wing warped! :y:

I suspect the glue took more than the 24 hours I had weight on it before it dried, and warped as it finished doing so.

It's fixable, but it won't be "fun".

-Kevin

 

[troj]

The conduit down the top of the rocket is made from multiple pieces of balsa. The first step is to glue two pieces of 1/4" x 1/2" balsa together, and to the top of the wings. Because pieces like this warp a bit in storage/shipping/etc, I didn't want to fiddle with gluing them together and gluing them in place, at the same time. Instead, I just wanted to get the two strips together and straight.

So, I used a piece of aluminum angle I have as a guide, and glued them together inside the angle. A piece of tape was using to hold them down on one end, and weight on the other. I used 3 staples across the two pieces to hold them together while the glue dried. The end result is a nice 1/4" x 1" strip that's very straight.

-Kevin

 

[troj]

Progress is now on hold for a few days; I got in contact with Mike, and I'm ordering replacement wing parts from him.

This time, I'm going to use epoxy instead of Titebond II (which I suspect is at least partially responsible for the warping), and will keep it clamped longer than I did the first time. That should prevent a repeat of the problem.

-Kevin

 

[Pem Tech]

The conduit down the top of the rocket is made from multiple pieces of balsa. The first step is to glue two pieces of 1/4" x 1/2" balsa together, and to the top of the wings. Because pieces like this warp a bit in storage/shipping/etc, I didn't want to fiddle with gluing them together and gluing them in place, at the same time. Instead, I just wanted to get the two strips together and straight.

So, I used a piece of aluminum angle I have as a guide, and glued them together inside the angle. A piece of tape was using to hold them down on one end, and weight on the other. I used 3 staples across the two pieces to hold them together while the glue dried. The end result is a nice 1/4" x 1" strip that's very straight.

-Kevin

Hmmmmmmmmmm
Very good idea...

 

[OverLord]

Great job! I love this kit!

Mike

 

[troj]

Back to progress! The replacement wing pieces arrived Thursday, but it wasn't until today that I had a chance to pick up some new balsa. I ordered the wing from Mad Cow, but didn't see any point in having them ship me balsa, when I can find it locally. Mike got the wing bits right out; FedEx just takes a few days to get here from California....

Anywho, since the first one warped during the gluing process, I'm changing a couple things.

First, rather than a single layer of 1/8" balsa, I've put down two layers of 1/16". The first rings lengthwise, and the second runs sideways. Basically, I'm creating balsa plywood, with the thought being that if the balsa decides to try to warp, the two layers of balsa will pull against each other, helping to keep it flat.

In addition, I think my original problem came from removing the weight too soon -- I'm thinking the glue took 36 - 48 hours to dry fully. So, tomorrow (after sitting for about 24 hours) I'll remove the top layer of waxed paper, to allow more moisture out, but I'll put the weight back on, and let it sit for another 24 hours.

I've got some pictures; will post them later.

-Kevin

 

[Luv2launch]

Why didn't you just spray the wing down with some water from a misting bottle and put the weight back onto it until it dried?When I got my estes Executioner the fins were warped and that fixed it up with no problems.

 

[troj]

Why didn't you just spray the wing down with some water from a misting bottle and put the weight back onto it until it dried?When I got my estes Executioner the fins were warped and that fixed it up with no problems.

I considered that, but with it being a layup of plywood & balsa, I wasn't confident it wouldn't later warp again.

Now that I have a replacement in the works, I'm going to do some fiddling with the original, and see if fiberglass on the underside won't hold it flat.

-Kevin

 

[Luv2launch]

Most of the time if you spray on the water on the opposite side of the direction it warped its enough to pull it back into shape but you need to go sparingly on the water to make it work.

 

[troj]

Pictures! We have pictures!

First shows the initial layer of 1/16" balsa, running lengthwise. Second shows second layer, going sideways. Third is a closeup of the edge.

-Kevin

 

[troj]

A bit more progress today. I have the wing fully trimmed, and have made more progress on assembly!

The first photo shows the wing from a bit of a head-on angle, to show the plies. This one is nice and flat.

Second shows the wing and stabilizer glued to the first two pieces that form the conduit. The conduit that runs across the top is built up from multiple pieces of balsa, and this is the beginning.

Third picture shows the conduit with additional pieces added. There are two pieces between the wing and the stabilizer, and two additional on the front.

The final picture shows my "poor man's clamp" to help hold the balsa in place, while the glue dries -- staples! I held the strips in place, then pushed regular staples down in, to hold everything in place while things dry. I'll pull them tomorrow, and the holes will get filled at the same time as the grain on the balsa.

-Kevin

 

[sodmeister]

My goodness.....I can see how my "furniture" making skills will come handy when I start my Bomarc! Never realized there was so much lumber in that kit ,and the many steps to forming the wings.......suppose I should stock up on a fresh jug of carpenters glue before I attempt my kit.

Looking good

Paul

 

[troj]

My goodness.....I can see how my "furniture" making skills will come handy when I start my Bomarc! Never realized there was so much lumber in that kit ,and the many steps to forming the wings.......suppose I should stock up on a fresh jug of carpenters glue before I attempt my kit.

Oh, but I'm not done -- there are more pieces of wood to use when building the conduit. Just a couple more, then some sanding.

It's really a pretty innovative way he's done it, I think.

-Kevin

 

[Pantherjon]

Coming along nicely Kevin! That looks to be a true 'builders' kit! Maybe once I get my few pennies in tax refund money I will get one..Not sure when it would be built...Eventually?:roll:

 

[troj]

Holy cow! I didn't realize it had been so long since I posted anything about this...

Lots of sanding in the past week. Lots and lots of sanding.

The supports for the motors are each made by layering 1/4" of balsa on either side of a piece of plywood, then sanding it to shape.

To keep things from sliding around, I put the balsa strips on one at a time, which meant lots of glue, clamp and wait....

Once they're done, they get sanded to shape, which is anything but a fast process, then glued on.

In these pictures, I have both already glued on, and fillets drying. Side view and top view, to show the profile of one of them.

-Kevin

 

[cjp]

More work on the most exciting part of the kit -- the motor mount!

Once it's epoxied in place, I like to put a thin layer of lightly thickened epoxy over the rear ring, to make sure it's solid, as well as make sure the motor retention inserts stay in place.

The motor mount was previously installed with epoxy thickened with a little bit of chopped fiberglass, to keep it from running past where it belongs. In this case, I've thickened the epoxy with microballoons (the epoxy smooths out more than with chopped fiberglass) just enough to get it to the consistency of thick syrup. It runs, but slowly. The goal is to cause it to fill any small gaps without all running down where it doesn't below.

One thing about applying thickened epoxy -- it doesn't penetrate as well. So, before I apply it, I brush a thin layer of unthickened epoxy onto the parts. I then thicken the epoxy and apply it where desired.

-Kevin

Whats the reason for using microballons in epoxy?Don't mean to steal the thread.Sorry.

 

[Pantherjon]

Whats the reason for using microballons in epoxy?Don't mean to steal the thread.Sorry.

It adds a bit of structural strength..Also, used as a thickening agent so fillets are easier to form and shape, and sand too, I suppose..

 

[dixontj93060]

Actually, I don't believe microballoons add any strength (they are lightweight and fragile--mostly air), they do thicken though and make the resultant epoxy easier to sand. For strength and thickening it is better to use milled fiberglass when mixing.

It adds a bit of structural strength..Also, used as a thickening agent so fillets are easier to form and shape, and sand too, I suppose..

 

[troj]

Whats the reason for using microballons in epoxy?Don't mean to steal the thread.Sorry.

In case there was a small hole somewhere. That way, when I stood it on end to let the epoxy level itself, it didn't all run down through a hole and end up pooled on the next ring down.

-Kevin

 

[troj]

Actually, I don't believe microballoons add any strength (they are lightweight and fragile--mostly air), they do thicken though and make the resultant epoxy easier to sand. For strength and thickening it is better to use milled fiberglass when mixing.

Correct.

Microballoons do reduce strength. Used in very small percentages, the effect is minimal. The amount I used will have an impact on the strength, but that's okay, because I had epoxy with fiberglass on the initial bond, for structure.

The bit where I used the microballoons is, as much as anything, aesthetics, to leave a smooth rear ring, and fill in any small gaps that may remain, as well as avoid leaving lumpy spots of fiberglass visible.

As a general rule, if the filler makes the epoxy easier to sand, it weakens the epoxy. If it makes it harder to sand (ie, fumed silica and chopped fiberglass), it has strengthened the epoxy.

-Kevin