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Written by Chris Mulcahy
RC Helicopters
Column
As seen in the October 2017 issue of
Model Aviation.


I love 3-D helicopters. I really do. I can’t imagine my life without them. They require such a challenging skillset, both in the flying and building aspects.

Building a scale helicopter is something that I’ve always been interested in, but I have never settled on exactly what to build. If you feel as though your choices are limited, there is another possibility: scratch-building your own.

It’s not as impossible as you might think. With some guidance from modelers who have built them before, you could be on your way.

I spent a few days with my friend, Darrell Sprayberry, who helped clue me in on exactly what it takes to scratch-build your own helicopter. Darrell is no stranger to building scale helicopters, and his name is not unfamiliar among scale heli enthusiasts. He is well known in those circles for his incredible scale helicopter models. He has shaped fiberglass fuselages for many years and won countless awards, and is an all-around good guy.

I won’t be able to explain everything I learned from the weekend that I spent with him, but I will be able to break down the process a little to give you an idea of what is involved.


Choosing a Subject

Before you even look at a piece of fiberglass cloth, it’s all about gathering as much reference material as you can for your intended model. If this is your first attempt, make things a little easier on yourself by choosing a helicopter that has simple mechanics. For instance, avoid angled tail rotors, Fenestrons (fantails), or anything else complex.




This is a nosecone mold for a 1/6-scale UH-1D Iroquois Huey. The part is waiting to be popped out of the mold.


Something with a straight-back tail, such as an MD 500, could be a good starter model. Plastic model kits make great reference material, as do detailed books by Squadron Signal publications about your particular model.

You can gather the best material by visiting local museums or taking a road trip to one. Check out local airports to see what they have. If you are lucky enough to find your subject in the form of a full-scale helicopter, strike up a conversation with its owner and ask if you can take photos of the aircraft. The more photographs you can take, the better off you will be.


What Size?

This is entirely up to you, but remember that there are certain things you might not be able to build by yourself, such as rotor blades. Choose your power system and decide which blades you will use. There are blades out there up to and exceeding 1,000mm, which would give you an impressively sized scale model.


Making the Master Pattern

You will need a good three-view drawing of your subject. Remember the plastic model kits that I mentioned earlier? They often have excellent three-view drawings in the instruction manuals. After you’ve calculated the size of your fuselage, you can have those views blown up to the scale that you want. The side and top views will be your templates for cutting the master pattern.

The master pattern can be made out of foam. Darrell prefers the type of foam that is commonly used for floating docks because it is dense but easy to cut and sand.




With one half of the mold removed, the author carefully pries the part out of the second half.


When you have your block of foam and the side and top views are mounted to a hard board, use a hot wire to cut the side and top elevations out of your chunk of foam. You will end up with what Darrell describes as a “Lego” helicopter.

From here, you need to continue to cut and round off the edges until you get the final shape you are looking for. When Darrell is happy with the master pattern, he lays a couple of fiberglass layers around the whole thing and begins the process of priming and sealing the pattern. The goal is to get the primer as smooth as possible. The more time you spend at this stage, the better it will look later.

Darrell also measures and scribes in the panel lines and adds the rivets with a syringe and white glue. While doing this, he thinks about how many parts the mold will be. You will probably always mold the tail separately from the fuselage. When you have the pattern as perfect as it can be, it’s time to move on to the mold.


Making the Mold

Use your pattern to make a mold. This is usually done in two halves. Build a wooden “dam” around where the seam will be to mask off at least half of the model. Spray mold release and lay down multiple layers of fiberglass, covering the entire exposed half of the pattern.

When this has cured, the whole thing is flipped over, the wooden dam is removed to expose the uncovered side of the pattern, and more fiberglass is laid down on the second half. Make sure mold release is sprayed onto the newly formed flange from the first fiberglass lay-up. You can then pop them apart when they done.

If you’ve thought ahead, you have left areas such as the nosecone and tailboom former open so that you can lay up the fiberglass when the mold is done. After both sides have cured, drill holes around the flange so bolts can be used to hold the two halves together. Pop the two halves off. Don’t worry if you damage the pattern. You’ll be able to make more!




Here, the author pops the tail out of the mold that goes with the nosecone. The rest of the helicopter is in the background, to his left, on a rack.



Molding Your Fuselage

Now that you have your mold, it’s time to make a part! Prepare the mold with mold release and start adding layers of fiberglass cloth—squeezing out any excess resin. When you are satisfied, let the part finish curing. Perhaps one of the most satisfying portions of this process is popping the parts out of their mold, or, as Darrell calls it, “birthing” the parts. This is where you will see all of your hard work pay off.

Now that you have your fiberglass shell, you can trim it, build some wood formers for it, and start figuring out your mechanics. You can build Frankenstein mechanics from parts donated from various kits or you can elect to scratch-build your own.


Conclusion

This is an incredibly condensed CliffNotes version of the whole process, but it should be enough to give you an idea of what is involved and if it is something that you think you would like to do! It can be a very satisfying process, and in the end, you will have a wholly unique aircraft!

Chris Mulcahy
cspaced@gmail.com


Sources:

International Radio Controlled Helicopter
Association (IRCHA)
www.ircha.org

Squadron Signal publications
(877) 414-0434
www.squadron.com

Darrell Sprayberry’s Competition Site
www.uniqueaircraft.com






1 comments

Would the AS3X type receivers used for quads work to make a collective pitch four rotor heli stable? I've seen on youtube, but it was scratch made, and would like to build for myself...!

It would be a real monster, if I used 2000mm CP roters x 4!!! I wouldn't know how to figure what motor & Batt (if one is made large enough?) or Engine size to use for such a monster, Anyone have a clue???

Kind Regards, & May Our Lord and God Bless you all!

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