Build the Holeshot
A CL Stunt Model Inspired by Bob Hunt
By Frederico Cesquim [email protected] Photos by the author
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01. The Holeshot Master and the aircraft that originated the design, Bob Hunt´s profile Hole Shot.
The story of the Master version of the original profile Hole Shot model can be traced back to 1984, when, as a young modeler flipping through a Flying Models magazine at a bookstore, I noticed a great how-to article about making and installing wheel pants for Control Line (CL) Aerobatics (Stunt) models.
Back then, in Brazil, we only had one magazine devoted to model airplanes, which hardly ever had any technical articles and was mostly advertisements. Short on money, I read the article at the shop. Looking closely at the pictures, what caught my attention was the neat and clean workbench, flawless woodwork, and skills of the author, Bob Hunt!
Years later, I was given a bunch of back issues of Flying Models, and Bob’s work was throughout the magazines.
02. The wing is clear, red MonoKote, and the fuselage is covered with silkspan and auto lacquer paint. The color design is handmasked and painted over the fuselage and MonoKote and then finally clearcoated.
My admiration for his craftsmanship, the selfless sharing of his knowledge, and his achievements as a competitor and classy designer, was such that I elected him as my role model in this hobby.
Fast-forwarding to 2018, I became distressed with the lack of interest of Brazilians in building and flying models, preferring instead to spend hours on WhatsApp CL groups talking about the past and losing connection with what our hobby is all about—the workbench and flying field.
I proposed a challenge to build a specific model within a six-month period. The model chosen was Bob’s Hole Shot because it is relatively easy to cut and build, and it is also inexpensive to build because it uses very little balsa wood. It can be powered by a wide range of .25 to .35 engines. (A common engine in Brazil is the locally produced CB-25; nearly all CL fliers have at least one laying around in the workshop.)
The Hole Shot also flies well, looks elegant, and, to top it all off (indeed my first reason for choosing it), it would be the perfect homage to Bob, who is one of the nicest gentlemen around and a great inspiration in this hobby as a supporter, designer, builder, and pilot.
03. The wheel pants can be carved from wood or made from fiberglass. The author opted for the latter. Wire covers that are made from 1/64-inch plywood and balsa are expoxied to the wheel pants and wheel fairings with super fill, resulting in a lightweight, strong unit.
04. You can achieve a perfectly sanded airfoil protecting the fragile ribs with masking tape and sanding with large blocks sliding over the tape.
Because Brazil is such a huge country and the goal was to see people doing real-life modeling, we designed rules for the Holeshot Challenge that required only building pictures and a flight video to enable people from across the country to take part in the program. A team of judges would choose the best effort.
The challenge went well, and roughly 15 modelers submitted their models. When told about the event, Bob was kind enough to send one of his great DVDs to be awarded to the winner, who also received a nice commemorative trophy.
Unfortunately, I missed participating in the challenge because life changed my plans, but after a fouryear hiatus and several other projects passing across my workbench, it was finally time to finish my model.
I already had a profile electric-powered Holeshot that helped me to learn the full "round" pattern within a year with no incidents. Because I was never a fan of profile models, I decided that such a fine-looking and nice-flying airplane would look even better with a full-body, built-up fuselage.
I traced some reference points over the original plans and chose a new O.S. Max .35 FP for power. I have always loved I-beam classic models but had never built one before, so I figured, "Why not give it a try?" This wing turned out to be easy and fast to build. The rudder owes the ribbed look to Bene Rodrigues’ Cheyenne 2000 peculiar tail design. I ended up changing a few other things, such as increasing the rib airfoil, rounding the wingtips and stabilizer tips, adding flaps, and adding 10% more area to the wing and stabilizer.
When the airplane was finished, I sent the pictures to Bob, along with my thoughts of the flight. He was impressed with the results and encouraged me to draw plans and prepare an article.
I felt honored and asked my good friend, Luis Strufaldi, to draw the plans. I only had the cutting jig for the ribs, a few reference sketches, and the airplane. We took measures from the prototype, and Luis began to draw.
We had to refer to the building pictures to remember what was done and the dimensions of the materials used. Luis is a craftsman and has a great understanding of the building process, so he kept sending me revisions and we made corrections here and there. In the end, he showed up with a beautiful set of plans and made the electric-powered version as well.
After I exchanged a few emails with Bob, he kindly sent me his autograph so that I could add extra class to the airplane. The opportunity to connect with Bob was awesome, and he was always supportive and gave me good advice on designing, building, and flying.
05. An O.S. Max .35 FP powerplant is a lightweight, friendly, dependable engine with plenty of power for this lightweight model.
06. The landing gear cover doubles as a hatch and fixture for the wires. It is better to have the landing gear apart for finishing and painting.
Building
First, cut all of the parts so that you have them ready when building and to avoid a messy workbench. Use lightweight balsa, but select good medium/hard balsa for the ribs and the I-beam spar. I started with the tail and notched the spar for the 1/8-inch balsa ribs to have a secure unit. Sand the surfaces flat, round off the perimeter, and make a V shape on the stabilizer’s leading edge (LE).
Laminate the I-beam spar plywood reinforcement with epoxy then add the top spars with aliphatic glue. (CA is too fast for this and you need to check for straightness.) Use a metal ruler to keep it straight. I like to draw a centerline on nearly every piece to keep an eye on the proper alignment of all of the parts.
Laminate the plywood doublers on the fuselage with a thin layer of epoxy, and then glue formers F1 and F2 to one of the fuselage sides with epoxy, taking extra care to square them up. This is the main component for making a straight fuselage. My tip with epoxy is, "A little bit goes a long way!"
Slide your fuel tank into position and add the engine mounts, checking to be sure that the engine fits properly between them. When you’re satisfied, epoxy the mounts in place. Glue the other side of the fuselage in place, checking squareness all around. Lay the fuselage upside down on the bench and add the remaining formers.
Hang the nose of the fuselage off of the workbench so that it sits flush. I like to lay down a long strip of masking tape on the bench and draw a centerline on the tape. I also draw a centerline on the formers, and then tack-glue them to the masking tape, making certain to align the center of the formers to the centerline on the tape.
Next, bring the fuselage sides in to meet the formers, checking squareness with right angles. Fill the horizontal gap of the engine bearers with 1/2-inch crossgrain balsa to reduce vibration.
Laminate the balsa and plywood nose rings, cut the outside fuselage side to accommodate the engine, and then bolt it in place and glue the nose unit to the fuselage sides. Remove the engine, tack-glue the bottom and top blocks in place, roughly shape them to the radius shown on the plans, and then sand everything close to the final shape.
Pop the blocks from the fuselage and hollow them as much as possible. You will need to add balsa triangle stock inside of the nose area to enable you to properly round off the fuselage.
With the fuselage upside down on the bench, slide the control horn, LE, trailing edge (TE), 1/16-inch rib support, and I-beam into place. Fit the wingtip ribs supports using the masking tape method (make sure of the top/bottom side direction). Check that the alignment of the I-beam with the fuselage and wingtip supports to be parallel to the bench and perpendicular to the fuselage centerline. When satisfied, glue them in and add supports on the LE and TE at half span.
07. The wing is finished and only the LEs and TEs need sanding. Don´t forget the 1/16-inch support spar to prevent damage to the fragile I-beam ribs and to round off the end of the sub ribs.
08. The bare bones of the model are ready for finishing. Despite its fragile nature, the wing turned out very strong after covering.
Now comes the fast and fun part. Laminate the 1/4-inch balsa root ribs, sand them so that the surface is even, and glue them in place. Add the ribs and half ribs using the jig for spacing (note that there is a left and right side).
Next, glue the stabilizer to the fuselage using the bench as an alignment surface. Turn the fuselage upside down and add the remaining ribs, making sure that the tip alignment jigs are correctly seated to avoid wing warps. Install the leadouts to the bellcrank, drill a hole in the I-beam, and slide the 1/8-inch music wire bellcrank mount wire into place.
I epoxied the bellcrank mount wire onto the plywood/balsa sandwich. My choice was a Sig 4-inch inverted bellcrank with heavy-duty, braided cable leadout wire.
Connect the horn to the bellcrank using 2:56 Du-Bro ball links. Make up a pushrod using a carbon-fiber tube and threaded inserts that will accept ball links. Add the tail gear wire support and main landing gear plywood sandwich.
Now is a good time to sand the LE and TE to shape. Be extra careful to keep a straight and regular radius on the LE.
Glue in the wingtip weight box, adjustable leadout guide system, and the wingtips, then perform a general wing sanding with a long T-bar. Sand a small radius at the aft end of the half ribs to avoid stress points on the covering.
Glue on the hollowed top and bottom blocks, assemble the rudder (the wood grain is parallel to the LE), add the half ribs, and sand them according to the plans top view. Note that there should be a slight offset sanding on the inside surface. Add the hinge pockets and sand everything a final time.
Bend the landing gear, and if you opt for the wheel pants, you can either make them from wood or fiberglass (my option). The wires have been covered with a 1/32-inch plywood and balsa sandwich, which is then sanded to an airfoil shape and blended to the wheel pants. I made them permanently attached to the gear wire.
Notice that the wires exit the fuselage at mirror points, so you might have to check the wheel’s alignment and bend the wires accordingly. Luis created a great method of using a slightly twisted mount so that both wheels are parallel. Study the plans closely and this will become obvious.
Finishing
My finishing method of preference is MonoKote covering for the wing and tail. I chose the translucent option to show the beauty of the I-beam construction. I then doped the fuselage, covered it with medium-grade silkspan, and sprayed it with two-part automotive primer.
I hardly used any putty; the primer was enough to fill imperfections. I lightly sanded the MonoKote with 1,200-grit sandpaper, and then I painted the fuselage and trim overlapping the MonoKote using polyester for metallic and auto lacquer for solid colors.
Ink lines are one of my trademarks, so I drew them in gray and finished the entire airplane with an automotive two-part clear coat. Next, I polished the airplane and glued in the hinges. It’s the last thing I do to avoid paint buildup on hinges and to have a better finish on the mating surfaces.
Flying
I was slightly anxious because of the unusual four years of building time, and I was a bit unsure of my design skills. The final ready-to-fly weight is 1,060 grams, or 37.3 ounces. The balance point was spot on for the engine I chose.
As soon as the airplane lifted fron the ground, my concerns proved unfounded. The model flew straight with no hunting tendency and it had smooth responses.
The first flight was too fast for aerobatics, but it was a great sight in the air and a heck of a glider when the engine quit. I switched to a 10 × 4 propeller and the speed was tamed down to a comfortable lap time.
I was really surprised by how well the airplane behaved, and I started training to learn square maneuvers of the pattern. Don’t let the constant chord (non-tapered) wing fool you; it flies great! I believe that a strong .25 engine can do the trick, but a .30 would be a perfect match.
So, here’s my gratitude and respect for such an outstanding design from a legendary modeler. Thank you, Bob! The model airplane community owes a lot to your designs, ideas, innovation, and support. Thanks to Luis Strufaldi for the plans and for his patience with my endless changes.
I hope to see a few Holeshot Masters around. I am currently building an electric-powered version!
SOURCES:
Model Aviation
2 comments
Holeshot Master
RC version?
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