1/2 Sport Scale ALCM AGM 86-A

[sambatterman]

I'm beginning the chronicle of a project for creating a 1/2 scale Boeing Air Launch Cruise Missile (ALCM). This will be the AGM 86-A variant - the initial prototype that flew in the late 1970s. You'll find the preamble to this project over at this thread (Cruise Missiles and non-traditional airframes). The real model is viewable at the Smithsonian Udvar-Hazy complex in Washington, DC. The original was approximately 14' long, so this will be a model that is 1/2 scale - 7' long. For the scale people here, this is SPORT - not a perfect scale model. Getting this to fly is the goal as well as getting a good fuselage design that is durable for flight. I have not found any large ALCM models - with the notable exception of the rocket glider that Frank Burke (burkefj) has built. I'm expecting this model to weigh in between 50 and 70 lbs. and fly on an "L" motor. It will include the option for the wings on or off. As with the 1/5 Nike Hercules build, I did this year, this will be a heavy picture thread as I get through the design and build and finish of the model.



Come along for the ride. This should be an interesting build.

 

[sambatterman]

High Level Design

The overall dimensions of the ALCM are 14', 9" by a wingspan of 9' 6" - so the half scale version is about 7', 5" and a wingspan of about 5'.

There are two basic ways (okay, there are probably more, but two for me), to build this fuselage. One, is build a plug and do a fiberglass shell - super lightweight and lots of room inside, but on the con side - everything internal is completely custom - bulkheads, center rings for motor mounts, etc. - still probably the lightest approach. The other way is a bulkhead/foam approach - similar in some ways to what I did with the Nike Hercules sustainer, but in a more profound way. Either approach requires custom bulkheads (that fuselage demands it). The plug and shell approach is going to demand a perfect plug to get the sides perfect - so you have to model the bulk of the fuselage either way. Because of this, I have decided on a bulkhead and foam approach, with a carbon fiber and fiber glass covering - a bit heavier, but I can control a lot more about the profile of the thing. This approach also allows me to use off the shelf stuff for MMT (75mm), center rings (birch), motor retention (Aeropack) and recovery (various).

The bulkheads have to be perfectly identical for this to work out. Because of this, I am CNC'ing all the fuselage bulkheads. I will use my personal CNC (Shark HD500) for some prototype work but will likely use a fulfillment shop like SendCutSend for the final parts. The fins will also be CNC'd. I'm still studying the wings, but thinking they have to be 3/8" Carbon Fiber that's CNC'd. Very little hand cutting on this model or the shape warps.

The spine of the rocket will be a 6" Blue Tube that I will section into about 3' pieces to allow for modeling of the aft and mid-portion of the fuselage, using a coupler that will glue the two parts together. The key to this project will be absolutely identical bulkheads that are lightweight, aligned perfectly and not too far apart to keep the continuous surface from breaking down. It's looking like I will have a bulkhead every 6" of so with foam sandwiched between.

It's impossible to model this fuselage with something like OpenRocket, but I can do some approximation to work the wings, 3 fins and bulkhead weights in to get an idea of what it will weigh and where the CP and CG will be. Additionally, as I mentioned previously, the wing unit will be removable to fly with or without them. The wings are a huge drag factor - losing almost 450 feet in altitude when they are attached. Let's face it, there's a lot of drag with the entire fuselage - the air inlet the polygonal fuselage, the change up of the fuselage after the inlet, etc.



This isn't the end-all-be-all design, so don't get overly excited. It's a placeholder to understand some basic dynamics of the model.

 

[sambatterman]

Reference Material

A head on view. The distinctive "duckbill" nose. An unusual shape for a missile, let alone a rocket. The nose cone will easily be the most difficult part of the job.



The BAV view shows the complication and asymmetry of the nosecone. The fins (rudder and elevons) are 115 degrees apart from the rudder - increasing the asymmetry of the entire design.


Side on view of the prototype at Udvar-Hazy - note the height difference of the section immediately aft of the air scoop. You can also see with the help of the light on the aft portion of the fuselage the blending with the thrust plate at the back of the vehicle.



A rare look at the side panel removed - a flat surface - in the age of stealth in the 1970s, polygonal, faceted panels were the way to the future.



A good view of the duck bill again.



Imagining the thrust line of the vehicle - again, the nose will be complicated. Also notice the backmost bulkhead - especially at the bottom elevons. This complex shape blends into a nearly flat side panel that goes all the way to the rudder spine.

 

[sambatterman]

Looking back Twenty Years

As I stated earlier, I've been waiting twenty years to build this model. When I started in High Power back in the early 2000s, I was enamored with non-traditional rockets - Jayhawks, Bomarcs and especially cruise missiles like the Tacit Rainbow (AGM-136) and JASSM (AGM-158).

After getting my level two using a Polecat Aerospace Bullpup, I set my mind to building one of these non-traditional airframes.

I built a full scale JASSM, that never flew - for a lot of reasons - and I still have it in my basement. Here's a picture of it in all its glory. A single rudder (fin) and an underslung set of wings makes for a wild CP/CG dance. The nosecone is quite heavy with nearly fifteen pounds of shot. It weighed in around 65 pounds and was based on the construction technique I outlined above - bulkheads and foam around a central tube. This tube was a 7.5" diameter body tube, and the nose cone was custom built. It has a bit of the duckbill feel to it that the ALCM has.

A few challenges that I'm hoping to remedy on this model that I learned the hard way. The bulkheads can be thin and closer together and since I know more about where I'm going, I can reduce weight by eliminating space in the bulkhead that's not needed. The closer the ribs/bulkheads are, the less apt for the foam to sag between the bulkheads which creates a monster challenge for finishing the shell with straight panel lines. I'm thinking the bulkheads will be 3/8" birch and about 6" from one another. I'll include the design for the bulkheads in the next thread.

 

[sambatterman]

Measuring Distances - Determining Scale

The ALCM does not have an abundance of scale drawings available - or if there are scale drawings, I could not locate them easily. Instead, I decided to use more of a photogrammetry approach. I chose a side view of the ALCM on display at Udvar-Hazy and determined scale from the photograph.
Knowing the real model is 14'9" long, you can measure the distance tip to tail to take in pixels and do the scale calculation. In the image I used, 1" = 10.75 pixels. From this simple measurement you can begin to approximate where different features of the model will be.

You can see in the model below that the MMT - a 75mm tube will end just beyond where the air scoop is. It also gives you an idea of how much space I have for recovery. I'm thinking right now that the nose cone will separate around the 18" from the nose mark, just in front of the "USAF" decal.

The three fins are 10 1/4" and 4 1/2" on the tip root. Over the long weekend I will post what the bulkheads will look like. This is starting to get fun.

The Center of Gravity and Center of Pressure are shown here as well in green. Center of Pressure is right in front of the air scoop and the Center of Gravity is sitting roughly 18 3/4" forward. This may need to change, but at least we see it visualized and realized in this photo.

 

[sambatterman]

Prototype Work

Okay, so I put my CNC to work and cranked out a rudder (fin) and two types of bulkheads. I wanted to check fit and proportion before I sent it all off to SendCutSend. Here's the rudder between two bulkhead types - in reality, the rudder and lower fins are sandwiched between two of the 12" tall bulkheads. The smaller one is what moves on the fuselage ahead of the air scoop - shown here as a 3D printed part (before sanding). I put the motor mount tube (MMT) next to the assembly with a small mark, showing where it will end inside the fuselage - just a few inches in front of the air scoop.



Here's a shot of the thrust plate. Notice how strange the fuselage really is when compared to a 6" body tube.


Here's a shot showing the rudder sandwiched between the thrust plate and the next bulkhead and the air scoop in the distance.






Roughest part of the prototype - the lower fins. I'm still working on this - it's quite a tricky angle (115 degrees and not exact with the body tube.
The fins and rudder are a fit proportionally along with the bulkheads and the air scoop. I'm ready for the next stage: Ordering the parts from SendCutSend.

 

[sambatterman]

Beginning work on the aft portion of the fuselage.

This weekend I'm working on getting the bulkheads aligned and the rudder and fins sandwiched correctly between the back two bulkheads. I will also be modifying the thrust plate bulkhead to provide the distinctive curve that allows the fins to fold flat against the fuselage in the real thing. Sorry, for this model, the fins will be fixed. This single change will create a lot of work for blending the body from flat polygonal panels to more curved shape at the extreme aft end. The bulkheads were cut and shipped from SendCutSend in literally 36 hours - I can't wait to show that to you this weekend. What a savings in time and materials - not to mention great precision.

I did make the decision to break the fuselage into three parts - and the aft portion will be broken at the blue line shown in the image below. This is only for construction and to have the ability to work with each section instead of moving the whole beast back and forth during sanding and finishing.

 

[sambatterman]

Aft dry fit

Yay! SendCutSend arrived today - ordered on Monday and here before noon on Saturday. Not bad. Here's how the parts arrived - sealed and organized:

I also included the center rings for the motor mount, the thrust plate from Mile High Rocketry and the Aerotech Retainer. The 3D printed air scoop is also making a cameo.



I took the bulkheads out of the shrink wrap and test fitted them. Notice on the bottom right the rear-most bulkhead has a different profile than the rest - this is just like the real thing. These curves allow the fins to fold up against the fuselage, so it can fit on a rotary launcher (typically on a B-52). My fins won't fold of course, but the blending of this shape with the other polygonal bulkheads should pose quite a challenge.



No glue yet, but here's a quick dry fit - the thrust bulkhead, rudder and three extended bulkheads roughly positioned correctly and the air scoop in roughly the right place. It's going to be super critical to align and square these things up and I'm working on a jig for that. In the meantime, I used a piece of 2" PVC to help me align them quickly.



This is going to be a fun project.

 

[sambatterman]

Ready to glue

I finished the dry fit and the alignment of the aft portion bulkheads and beveled the rudder. Everything is ready to be glued down. Normally I would throw caution to the wind and glue it all down, but I'm going to take it slow this week gluing each bulkhead down and reinforcing everything. I'll post a final picture at the end of the week.

 

[Hobie1dog]

Talk about a challenging advanced rocket builds. This will end up being one of the more complex ones ever featured on here.

 

[sambatterman]

The Stack

This week I took my time and glued the bulkheads in alignment to two lines on the body tube. You can see the step platform about halfway up that will hold the air scoop. The angle of the air scoop is actually more gradual than you think. It's only about 1 3/4" above the high spine that sandwiches the rudder. Additionally, I measured the rear fuselage with the mid-section (not shown here) and it's over 7' long - won't fit in my Jeep Compass. So, I'm going to allow the fuselage to be assembled at the field, essentially separated at the middle. This will allow access to the recovery hard point, the tether and altimeters under an aluminum cowling. This particular feature is going to take a lot of thought.

 

[sambatterman]

Support for the Air Scoop

So, the air scoop is glued on top of the platform I built above bulkhead "E" to hoist it 1 3/4" above the "spine" of bulkheads "B", "C" and "D."
I used JB Weld to allow it to kinda "squish" into the foam and it gave me some time to get it positioned just right. It's in a bit of a "nose-down" attitude to get the right curve of the scoop that will start at bulkhead "C." I built a bridge from "B" to "C" to support the spine that will go into a crazy bend to form the top of the scoop. Without the bridge the scoop would sag there.

This entire structure is super light - weighing about 5 pounds (without the motor mount and hard point for recovery, which will add another 5 pounds). BTW, notice the folded-up fin near the rudder. It's not functional, but it shows the thrust bulkhead cut allows for the fold-up like the real thing. Cool, right?



Here's a view of what the fin will "kinda" look like when glued in. The angle isn't correct yet and there will be a lot of reinforcement. Speaking of reinforcement, you'll notice the rudder/fin has a layer of fiberglass across the fin root. Before it's filled with foam and closed off it will be reinforced yet again with Carbon Fiber.

 

[sambatterman]

Reinforced fins and foaming the bulkheads

The fins are now epoxied and reinforced big time with two layers of carbon fiber.



The skeleton of the air scoop is a 1/8” balsa strip. Took two days to make this bend. Gluing the base down and then the scoop with a clamp. Here’s the foam in progress…


From the front. It’s gonna take a while to carve this down…

 

[sambatterman]

Carving the Aft end foam

Okay, so phase 1 of cutting the foam down is done. It was a lot of work. I like to use a serrated steak knife and a long bread cutting knife. Like many of my tools, once I touch a rocket with a tool from our kitchen, my wife kindly donates it to my tool pile

Still filling in a few "ulcers" and voids in the foam - it's very forgiving and easy to patch. You might ask - after the foam what's next? Well, unlike the Nike Hercules where I used blue tube on top of the foam, these shapes are planar, so I can't use a tube. I'm planning on using 1/8" x 3" x 36" Balsa strips. This will give me the planar look I need and will be easy to finish with fiberglass or carbon fiber.

 

[sambatterman]

Starting the Panels

It's a rainy weekend in Pennsylvania - the remnants of Hurricane Ian that creamed Florida. Thoughts are with those folks down there.
After lots of carving on the foam I now have a nice foundation on which to lay down 1/8" x 3" X 36" balsa strips. This is a strange move on a high-powered rocket, but it's probably the best material for strength to lightness and then to have fiberglass laid on top of it.
Just a few points before we get into "balsa-land." ... The "E" bulkhead here will carry two MissleWorks RRC3 altimeters for firing a tether off the hard point, which will be in this neighborhood. This means a hatch or, more likely, a cowling will cover this spot - dual purpose as you will see in the next picture.


Bulkhead "F" and "G" contain the 6" diameter x 18" blue tube coupler for connecting the aft of the cruise missile to the middle portion of the fuselage. I reinforced both "G" and "H" - "H" being the first bulkhead of the middle fuselage component - with Carbon Fiber on the parts facing each other. Four 1/2" bolts will secure the bulkheads and the coupler will provide internal lateral strength. I will likely reinforce those areas between the couplers with fiberglass, just to make sure it doesn't stress out. This structure is very light right now - around 8 lbs. total.

 

[sambatterman]

Into “Balsa-land”

Got started with the balsa strips - it goes pretty fast and boy, does it reinforce how "planar" this rocket(missile) really is. The bottom panel by the lower fins will be done with 1/8" x 3" rubber - you can see a slice of it in the lower right by the plastic. Anyway, I used this on the Nike Hercules for the fin can and it was perfect for curved surfaces that need some tension. It follows curves really well and easily sands and feathers.

The air scoop will be very difficult to cover - probably the second most difficult feature outside of the duck bill nose cone.
Anyway, here's three photos for you...

 

[sambatterman]

Airscoop

Starting to work on the air scoop. I bent two pieces of balsa on the sides, to provide the support on the side of the scoop and then used about a dozen wet fiberglass strips to form the core.


After some sanding, I used SuperFill to begin filling in valleys and repairing "sanded off" mountains.


From the front, you can see I have a lot of sanding and finishing to do. Will complete it with a nice carbon fiber sheet.
I know it looks rough - have faith folks...

 

[Hobie1dog]

What a project, way too much for me to ever attempt.

 

[sambatterman]

Getting There

So, after many weeks, the air scoop is finally approaching what I was hoping for- still a lot to do, but the main form is there. The entire aft fuselage is now covered with Fiberglass, with the exception of the belly - that story will be told next week.



Still using SuperFill to fill imperfections and valleys - this is especially true on the tail fins where I used a rubber strip to perfectly match the fold curve on the thrust bulkhead. The rubber strip worked great, but I still have to blend that with the fuselage. I'm also working on the motor mount tube and the recovery hard point, which will be just a few inches forward of the air scoop.

 

[dbpeirce]

Wow…….

 

[sambatterman]

Almost there Airscoop & MMT

Okay - we are almost there - one more filling and sanding and then I will work on the Carbon Fiber - there are very specific features on the ALCM air scoop that Carbon Fiber will be perfect for... more detail on that over the weekend.



Remember how I used a 1/8" rubber sheet to match up the tight turns in the aft bulkhead (another distinct feature of the ALCM). Take a look at how the curve is matched and how the rubber sheet feathered into the balsa panels. The SuperFill helped to complete the blend. Just a little bit of filling to hid the gaps and cracks.



Oh, and I'm finishing up the 75mm Motor Mount Tube (MMT). It has numerous center rings and 2 pieces of 1/4" all thread that run all the way to the top to a double ply disk that's reinforced with Carbon Fiber. That will be the hard point for the recovery gear. I got a little too happy with the West Systems and Colloidal Silica.

Why so built up? Everything is banking on that hard point, so I want a lot of strength and redundancy on those all threads. There will be a ton of epoxy in the 6" body tube to secure all these center rings, plus an ample amount of JB Weld at the rear to hold the aluminum thrust plate.

 

[sambatterman]

Mid fuselage work

This weekend I decided to put some work into the mid-fuselage. It's basically the main container for the recovery items and it's relatively straightforward - especially compared to the aft fuselage. I will slide onto the aft section (see next post) coupler and use 4 1/2" bolts and nuts to secure itself. The bolts also have the nice effect of insuring alignment of the two fuselage parts - key to pull off the planar look all the way to the nose cone.



Some reinforcement ribs between the bulkheads - almost ready to foam and more balsa strips.

 

[sambatterman]

Aft section is almost done

My workshop is toast and I need to take a few hours to clean it up, but the aft fuselage is almost there - still need work around the inlet and the neck supporting the inlet.

 

[sambatterman]

Foaming the mid fuselage

The 1/2” bolts were JB Welded to the bulkhead facing the aft fuselage bulkhead.


Here’s a test fitting with the aft fuselage…


Initial foaming of the bulkhead.

 

[sambatterman]

Mid fuselage and finishing the air scoop

So, after many days of cutting the foam down (not full time - lunch hours and after dinner), the mid-fuselage is looking good. I completed the foam by using a disc sander and smoothing the surface. Remember to use a dust mask or respirator for such as task. Also, I used a different kind of foam - this is essentially Styrofoam in a can - smaller cell foam and much easier to work with then the yellow stuff I used on the aft section. Highly recommend switching that up.

You can see the balsa panels that will be epoxied to the mid-fuselage sitting on the tabled labeled.



And here are those same panels now epoxied to the fuselage. T-pins to the rescue!



And the top panels with Superfill to fill the gaps. A bit of a gap at the top to fill still.
This whole assembly will be Fiber glassed this week.


Here's a view of the un-sanded panels and the connecting bolts (this part will face the aft fuselage; you can see in the background. The bolt holes are visible to the upper right.



I also worked on the air scoop - carbon fiber on the sides and Superfill to get that distinctive ALCM scoop look.
Lots of sanding still to come. Oh, and here's the bridge across to the mid fuselage: balsa panels and glassed for reinforcement.
There will be access panels on either side of the craft to work the recovery hard point and the tether for main chute deployment.

Getting there...

 

[sambatterman]

A quick assembly

 

[sambatterman]

Finishing the mid fuselage

After sanding the first layer of fiberglass, I’m now putting down the second, and final, layer of glass.



Single sheet covering top and sides.



Nice and transparent. Pretty happy with the finish.

 

[sambatterman]

Belly of the Beast

So, I worked on sheeting the underbelly of the aft section. The balsa panels work well here. I need to sand and blend these together - especially on the underside of the fins. Once it's sanded, I will do a coat of SuperFill. Sand again and then put carbon fiber and fiberglass on the bottom.

I have not talked a lot about the belly of this thing a lot, but there is a reinforcement on the center line for rail buttons (it's actually going to use Unistrut like the Nike Hercules).

I'm also working on the wing panel, which will sit from the exposed foam all the way to the connector bulkhead for the mid-fuselage (which I'm trying hard to complete this week).

 

[sambatterman]

Paint and Finish Poll

It's been rather quiet on this overall thread, and I thought I'd ask for some opinions to try to get some feedback.
The nosecone of the ALCM has three basic "looks" - what is your preference?

Please vote for your favorite way of completing the ALCM:

1) Nose with Center of Gravity Markings



2) Nose with Shark mouth and eyes



3) No Face - just white

 

[Jay Dub 4009]

SHARK MOUTH!