Semroc Nike Tomahawk

[Bruiser]

I've started a new build. This is going to be my first foray into gap staging but I've gotten a lot of advise from fellow members and I think it's going to be so cool.


As designed this is a single stage rocket so of course I won't be building it as instructed. This is probably no surprised to you all who have followed my other build threads

The plan for the Tomahawk sustainer is to build it pretty much as designed with just few changes. First change will be to use the 18mm motor mount that came with the kit. Second change is to have the rocket "break" where the motor meets the payload section instead of just having the nose cone pop off. Last thing (I think) is to make the fins ttw and paper them.

The design of the booster is still a work in progress so while I think about that, let's get started building the Tomahawk

So here is the motor mount. I've used some cardboard to fab up the centering rings. I have also designed it so the motor will stick out the back of the mount 1 inch so it will slide into the booster


To make the fins ttw, I notched out the basswood and glued in another piece that will nestle between the centering rings of the motor mount.


To make sure the basswood is up to the performance of the D12 booster, I used Avery labels to paper the fins Using Neil's technique.


I've filled the body tube seams with cwf and sanded them smooth. I sprayed on the first coat of filler primer this morning. Next task will be to sand it down nice and smooth and get a picture

-Bob

 

[Scott_650]

I didn’t realize that there the Semroc version was that much bigger than the Estes version. Nifty!

I assume you’re using the 18mm motor in the Apache sustainer and a 24mm motor in the Nike booster? Do you need an extended motor mount tube in the booster to get the second stage to light? All my two-stagers have been direct staging types.

 

[Bruiser]

Hey Scott, I think you have it figured out. The sustainer will be a 18mm motor and the booster a 24mm. I was thinking about an 18mm in the booster too but some people who know more than I said I would need the 24mm for this size rocket to get enough rail speed for it to be stable.

There will be a tube going up the middle of the booster to the sustainer. The 1 inch of motor that is sticking out of the sustainer will slide into the top of the "inner" booster tube. All, or some of that "inner" tube will have to slide out of the back of the booster to deploy the chute or streamer so the booster will not turn into a lawn dart. I've attached an article about a similar rocket.

So today I primered the body tube to make sure I filled in all the spirals with the cwf. Then I wet sanded the primer and I tried sanding all the primer off the last three inches so I would get a good glue joint on the fins. Well, I got the cardboard wet and made a mess but I stopped before it got too bad. I went to the other end and cut my slots on the primered tube then I used a razor blade to scrap the primer off the body tube immediately around the fin slots. Next I dry sanded the same area and it is all ready for the fins now.


After the area I got wet dried, I applied several coats of primer and it looks like it will sand out nicely.

I've also sprayed the first coat of primer on the fins. Once dry enough, I will sand them and decide if they need another coat of primer before I attach them or if they are good to go as is.

I am a little unsure of the motor mount as designed by Semroc. There is no engine block per se. THe only thing that stops the engine from moving forward is the little tab of the engine hook. I think I am going to sacrifice an old 18mm motor to make an engine block. It's much easier to put one in now before the mount is glued in.

Thanks,
-Bob

 

[Scott_650]

Groovy. The article from Apogee made it look pretty straightforward. Kind of glad I haven’t built my Estes Nike Apache since this is really tempting. Thanks!

 

[GlenP]

...need the 24mm for this size rocket...

It might possibly be light enough for an 18mm booster if you used a 13mm sustainer, but maybe cutting it close though. I did an 18mm to 13mm gap-stage conversion of an Excalibur, but that is a little shorter and lighter rocket and I think smaller dia (lower drag) than this one.

 

[Ez2cDave]

The Nike-Tomahawk is a long-time favorite of mine . . .

Dave F.

 

[Ez2cDave]

A couple of pics . . .

Dave F.

 

[Bruiser]

I started working on the exhaust baffle today. I thought a Semroc #8 tube might be too small but then I found one on the Apogee site for a BT-20 so I went for it.

Here's the inner section


Here's the tube


I've coated them both with epoxy and they are off drying now.

I also have my fins glued on using the template from https://www.payloadbay.com/page-Tools.html


Got my fillets started


Starting to look like a rocket

-Bob

 

[Rex R]

put a pair of vent holes(1/4") in your booster motor tube just below where your sustainer motor ends, to vent the cold air at booster burnout.
Rex

 

[Bruiser]

That would be the easy way but I'm not sure if I want to ruin the scale lines. I want to duct the gases out the bottom but I'm having a little trouble figuring out how to keep the gases from melting the chute.

TO keep the gases from melting the parachute in the sustainer, I've finished the baffle. It just needs to be installed now.


I need to glue on the launch lugs as well. I want to be able to launch it independent of the Nike booster.

So a little more gluing and it's off to the paint shop.


-Bob

 

[Ez2cDave]

That would be the easy way but I'm not sure if I want to ruin the scale lines. I want to duct the gases out the bottom but I'm having a little trouble figuring out how to keep the gases from melting the chute.

TO keep the gases from melting the parachute in the sustainer, I've finished the baffle. It just needs to be installed now.

I need to glue on the launch lugs as well. I want to be able to launch it independent of the Nike booster.

So a little more gluing and it's off to the paint shop.
View attachment 372817

-Bob

Bob,

The Coupler on your Payload Section looks a little short. I always do 1 caliber on mine.

Dave F.

 

[GlenP]

.. I want to duct the gases out the bottom but I'm having a little trouble figuring out how to keep the gases from melting the chute...

In the Apogee article, it appears that he is using a heat-resistant mylar streamer on the rear-eject booster. If a streamer is not going to be sufficient for your booster, maybe you can make a parachute from mylar.

Do you have enough space to fit a BT-5 tube in between the booster centering rings for a hot-air vent duct to keep the gases away from your chute?

 

[Bruiser]

It looked a little short to me too but it is what Semroc provided with the kit and I figured they know what they are doing

It was a little loose in the tube but a wrap of blue tape has it fitting just right.

-Bob

 

[Bruiser]

The main body is a BT60 and the 24mm mount is a BT 50. I could possibly fit a T2 tube between them

What I have been contemplating is having the rear engine mount/fin can assembly pop off the back of the main tube. I want to stuff the chute in the main body between the body tube and the motor mount/ejection tube but the space is appr .3 inches, not too much. A streamer may be a better idea but I've never used one. Do they slow it down much? I don't want it slamming into the ground after I've put all this work into it. The launch area here is desert dirt so besides being hard will scratch the heck out of a nice paint job.

-Bob

 

[Bruiser]

I've attempted to draw a diagram of what I am thinking of. You can see how the rear of the booster has the fins, the fin can and the motor mount assembly.

The forward part of the booster has the body tube, the transition and the gas tube assembly. The transition is hollowed out to support that end of the gas tube and there is a centering ring to support the other end of the gas tube.

To assembly the two parts you would slide the gas tube into the engine block .25 inch then the body tube will engage and slide over the coupler.

Somehow the fin can assembly and the main body would be connected together via the recovery system shock cord. Haven't quite worked that out yet but I am thinking a Estes style tri fold on the main body and Kevlar tied off around the motor mount. The parachute (or streamer) would have to fit between the body tube and the gas tube.



I also need to vent the hot gases from the booster engine. Without a vent, the initial charge of gases will separate the rocket before the sustainer engine has a chance to ignite. I need two holes in the gas tube just after the transition. I will also need two holes in the body tube or I will need to provide a route for the gases to exit the rear of the rocket. That would mean holes in the centering ring on the gas tube and holes in the centering rings of the motor mount. Venting the gases out the rear means the recovery system would be exposed to the hot gases. The only thing I can think of is to build in a duct down on side of the rocket to confine the gases away from the recovery system. Still thinking this over. Oh, and when I draw it up in Open Rocket I get less than one caliber of stability..

-Bob

 

[Bruiser]

. Ok, I re-read everything I could find and I have come up with something new; something innovative!

Here are the two assemblies separated. There is the outer body and transition assembly and the inner tube with fin can/motor mount assembly. There are two 1/8th by 1/2 inch keyways glued to the inside of the outer body tube. Centering number 2 has corresponding notches in it so you slide the assy into the outer tube until you hit the keyways then you turn it to line up the keyways. Once pass the keyway, you turn it again and finish inserting the inner assembly. This will eliminate the need for any kind of shock cord between the inner and outer assemblies. The only thing I can think of that might be an issue is the force of the inner assembly being pushed back might be to strong for the keyway to stay anchored.



It would look like this when deployed. You can see where centering 1 has bottomed out against the keyways. You can also see the open area where the chute would go.


What say you? Anyone think of any potential issues? I also see that I could run "vent tubes" thru the centering rings to duct the gases out the rear while keeping the heat away from the parachute.

-Bob

 

[Bruiser]

Back to the sustainer. I have the ejection baffle in. The only thing left is the recovery system and I think I am going to keep that simple on the sustainer. The kit came with some 1/8" elastic so I think I will use that and mount it inside the body tube using the Estes tri-fold paper method. The chute will be the one that came in the kit. I think you can make it different sizes when you assemble it. I am thinking 9 inches. How do you know what size for a "standard" rate of descent? Anyway, I will wait to glue that in until the paint and finishing is done.

I need to figure out how much more detailing. The only decals that came with the kit are two "UNITED STATES" for the sides and a "semroc" decal. Nothing for the 88 screw heads in the payload section. I wonder if I should just paint them on. They would be about 1/16th in diameter so I'd have to find something small to make little dots with. What color do you suppose they would be? Silver/metal color or do you think they would be the color of the area they are used on?

I also need to decide if I am going to try to make the fin hubs. They are very small, but noticeable. I did do the fin can so I will probably see if they are "do-able" for me. Fine details are getting harder with my eyesight the way it is and my hands just aren't as flexible as they once were.



-Bob

 

[Bruiser]

So I've had a couple of epiphanies. I realized this morning that mylar is what some party balloons are made of and I think I can get them at Wally World. So that helps with my concern about melting the booster shot.

I just had the other epiphany a moment ago. I realized that I make openings for the cold air to come out of the booster gas tube where the transition is inletted for the bolts that hold it to the booster. That would keep the hot gases from the chute altogether.



-Bob

 

[Ez2cDave]

I need to figure out how much more detailing. The only decals that came with the kit are two "UNITED STATES" for the sides and a "semroc" decal. Nothing for the 88 screw heads in the payload section. I wonder if I should just paint them on. They would be about 1/16th in diameter so I'd have to find something small to make little dots with. What color do you suppose they would be? Silver/metal color or do you think they would be the color of the area they are used on?

I also need to decide if I am going to try to make the fin hubs. They are very small, but noticeable. I did do the fin can so I will probably see if they are "do-able" for me. Fine details are getting harder with my eyesight the way it is and my hands just aren't as flexible as they once were.

View attachment 373199

-Bob

A few images . . .

Dave F.

 

[Bruiser]

I have started working on the fins for the booster. In all my years (almost one now) I have never seen this type of fin construction . It is a lot like building and r/c airplane wing though.

First you cut out the skin from the cardboard


Then you build the structure out of the laser cut ply


You scribe the bend lines on the cardboard with a ball point pen and pre-bend them to the desired angle then you glue one side of the skin to the frame


Then you apply glue to the frame and fold over the skin and wha-la, you have a fin


That last fold is critical because if you fold it over and it's not even you'll end up with a wavy trailing edge. I had one do that so I had to cut the skin apart on that area and try again.

I still have two more to go. Just needed to let my fingers dry a little so I could peel off the glue

I am contemplating cutting a slot in the root rob with my dremel tool to make these fins ttw. Remember, original design was a single stage powered by a "C" motor and now it is a two stage with a "D" in the booster so I am not sure if butt gluing the fins on the booster will hold up.

I am also working on the screws on the sustainer payload and fin can area. No pic of those until they are painted though. Once the white glue dries, it gets so clear you can't see it. Sorry

-Bob

 

[Ez2cDave]

I have started working on the fins for the booster. In all my years (almost one now) I have never seen this type of fin construction. It is a lot like building and r/c airplane wing though.

-Bob

Bob,

That is called "built-up fin construction" . . . I like to substitute thin plastic sheet or 1/64" plywood for the "paper".

Dave F.

 

[Bruiser]

To tell you the truth, I kinda like it. Brings me back to my aircraft modelling days. I think I will experiment with it again using some 1/64th ply. Just need to get some of that. No where local to source it so I'll have to order it in.

I drew the round covers on the payload area last night. But the Sharpie kinda dragged when I moved the guide after doing a spot so I thought I could just touch it up. I sprayed a little paint in a cup and attempted to brush it on. I basically softened the paint under it and any brush stroke pulled the paint off down to the primer. The more I tried to work with it, the worse it got so I put it up for the night.

This morning I took it to the sink and lightly wet sanded the area and once dried I sprayed it again and walked away. It looks like it will be alright but I haven't looked at it since it's had a chance to really flash off.

This is Rustoleum Universal Mettallic. I've used it (Copper Rose) on my Nike 10 Degree Heat Test rocket (aka Nike Heat) with problem, actually on the plastic nose cone. This time though, the paint (Champagne Mist) was still a little tacky yesterday when I tried to draw on the spots. Lesson learned: wait until the paint is totally dry before going to the next step. Sometimes it takes longer than what is printed on the can.

-Bob

 

[Bruiser]

Been up to the painting. It's a part that I both love and hate. I love it because when the paint is on you can really see the progress. I hate it because something always happens that causes you to take steps backwards like in the last post above.

Last I posted about the fin can I was working on the screws. I was also trying to decide if I was going to try to add in the spindles or not. I decided that if I was going to do the screws, I would have to do the spindles as well. Here is how they came out.



Now some of you that are familiar with the Nike Tomahawk are probably calling foul ball! But I'm not modelling that Nike Tomahawk. With a lot of help from Ez2cDave, I am modelling one of three that were launched in Antarctica in the early eighties. Here is the pic I am working from.



I also painted the nose cone twice. I had sealed it with thin CA, then I sanded, then I primered, then I sanded and primered again before I painted. I still had some grain showing thru after the first coat of white. I should have gone over it with more primer but I didn't think of that and shot it with the gloss white. This time the paint gods smiled upon me and it came out great!



Ok, so what about the area between the fin can and the nose cone? Well the payload area is still in the shop. The re-spray came out good and I drew the black covers back on. Next I clear coated it then I painted on the silver bands. I need to paint the phenolic area next but I don't have any red or brown paint. I am planning a trip to Hobby Lobby tomorrow.

Work on the sustainer is just about done

-Bob

 

[Bruiser]

Yesterday was a busy day. I worked on the motor mount and fin can assembly.

Here is the motor mount with the aft centering ring installed



Here is the fin can with the forward motor mount centering ring and the coupler for rear ejection installed


I also worked on the fins. I have been concerned about them not being ttw with the "D" engine. Yesterday I butted them up to the body tube and was surprised by how much they wiggled left and right. That settled it and I decided to make them ttw.

I took my Dremel tool (one of the best tools ever) and cut a slot into the root rib and about 3/8 inch deep into the spar

Next I glued in a piece of 1/16th basswood and trimmed it to the correct depth. Well, at least I thought I did, but maybe not. Up until last night I was going to glue the fins right to the fin can. Last night I realized I still need to wrap the body tube to actually "create" the fin can so hopefully that won't throw it off too much. It's only one thickness of paper


Thanks for reading,
-Bob

 

[Bruiser]

It's time to put the two parts together now.


But not just those two, these two parts too This high tech alignment device was special made for this rocket.


I did not primer the fins before I put them on this time. I decided to try gluing, filleting and then primering on this build. Well, jut on the booster because I did the sustainer my usual way

I hope to get all four fins on today. I like to let each sit for 20 minutes or so before I move them. Five minute epoxy doesn't always set in five minutes. Better safe then sorry.

-Bob

 

[Bruiser]

Sustainer is painted. I only need to find some mylar for the chute.



Back to work on the booster. The transition is resisting and I am trying to figure out how to align the alignment pins inside the body tube. I also need to make my centering rings tonight.

-Bob

 

[Ez2cDave]

Bob,

Looking GOOD !

Post up some pics of the problem with the transition and the alignment pins.

Dave F.

 

[Bruiser]

I have been working on my booster today. First task was to glue in the lugs that will align the inner part of the booster to the outer body of the booster. The lugs are inserted 5 inches into the ST-16 body tube so I need to come up with someway to glue them in and they needed to be perfectly aligned.

I epoxied in the first lug yesterday. I carefully measured the depth and tried to get it as straight down the body tube as possible



Next I need to make my centering rings as they would also be the guides for gluing in the other two lugs. I stacked two pieces of 1/8 inch aircraft grade ply and tacked them with c/a before I started to make them. Then I drilled the hole with a step bit and used a sanding wheel to shape the outside. Next I used my dremel to cut in the notches and squared them up with the hobby knife.



Next I glued the centering ring to the inner tube to act as a guide for the placement of the remaining two lugs.



Then I inserted the tool in the outer body tube



Next I tack glued a lug to the end of a slick



I applied epoxy to the bottom on the lug and inserted down the body tube and into the cut outs in the centering rings. I broke the stick away and used a depth gauge I had made from another piece of balsa and let it sit for a few minutes, until the epoxy got tacky then I removed the alignment tool. Once the second lug had set up I did the process over for the third lug and now I have all three lugs at a uniform depth and in great alignment



Here I have glued the centering rings to the gas tube. The notches are spaced 180 degrees from each other so that the inner assy will only slide back 5 inches.



This next pic is with the inner gas tube connected to the fin/can assy




This next pic is the inner and outer tubes in flight position. The inner tube needs to be trimmed to length but that has to wait until I get the transition. It will go thru the transition and be flush with the top of it. The transition will actually be attached to the outer body tube. You can't see it but the lower centering ring is now keeping the inner and outer tubes in alignment, not allowing the inner to spin inside the outer



This is what it will look like when the sustainer motor blows the inner tube back, allowing the chute to deploy. The top centering ring limits the travel. Once trimmed you won't see the gas tube sticking out like it is now.




Oh, BTW, I got the fin can primered too

Have a great weekend. I hope to make some headway on the transition.

-Bob

 

[Bruiser]

Well I took a little break from the Nike Tomahawk. I haven't been feeling to well. Crone's disease is like that. Sometimes you're good and sometimes you're not. I think I was getting a little burnt out on the engineering of the booster stage and worrying that it just wasn't going to work as advertised...

Anyway, I was feeling a little better the last few days and I tried to touch up the area around the Thikol logo that I messed up when try to touch up the logo. I ended up just spraying a light coat of color over the logo, writing the logo on again and then clear coating the area.

I also put together the recovery system. I used the trifold method to retain a piece of Kevlar cord to the inside of the body tube. Then I tied the Kevlar to the 1/8 flat elastic (not rubber band) that came with the kit. I attached the parachute with a swivel about 12 inches from there and attached the nose assy to the other end. It is ready to launch now, sustainer only.



I don't think I am quite ready to tackle the booster quite yet. I am thinking of starting on something different like an Interceptor. I should build something simple like a Gooney Bertha, lol!

Anyways, thanks again for reading,
-Bob