Lazerworks Slim Jim .20 Group Build
 

My local club, the Wichita Falls Remote Control Club (WFRCC) is taking on a group build. We just took delivery of 14 Lazer-works Slim Jim 20's, (Lazer-works.com). Our club has several experienced builders and a number of people who are interested but who never made the leap into building. We want to provide a successful build experience for those members while still providing something that will be interesting to fly. The Slim Jim falls into the "good first aerobatic airplane" class. One goal is to be able to have a mass fly of Slim Jims at our October fun fly with one completed model as a prize in the pilot raffle. While I will be doing a build thread of my own Slim Jim, the idea is that other club members can post their own progress and use this thread as a visual reference. The photo below is a Slim Jim .40. They can be had in .20, .40, and .60 size.

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The Lazerworks Slim Jim is sold as a short kit. The wood pack is pretty inclusive requiring only a couple of sheets of balsa, some triangle stock and straight stock for spars. the landing gear is an off the shelf item from Sig. One neat feature of this kit can be seen in the background. the kit comes with a laser cut spar web. It fits between the upper and lower spars and accurately locates the ribs.

Handing out plans and kits on a windy day.
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The first step in building this model is building up the fuselage floor out of 3/32 balsa. While most of this plane will be built with thin and medium CA This is one part that is better with regular wood glue as it sands more easily. This technique can be used to edge glue any size of sheet balsa. Just tape the edges together then open the joint and fill with glue. Wipe off the excess and weight it down so that it will dry flat.

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Here is the bottom of the fuselage. You may have to look closely to see it but there is a straight line down the middle of the sheet. This is a datum line that all of the formers line up on and which helps with building a straight fuselage. The dimension that is written on the sheet indicates that it is just wider than the fuselage. Once the fuselage sides are attached, it will be trimmed to fit.
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This is one of the fuselage sides. There is a left hand and a right hand side with the etch line, that I have marked "do not cut" facing the inside of the fuselage. The dotted lines are the approximate positions of the formers.
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Here is the 1/32 ply fuselage doubler ready to be offered up to the fuselage side

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Here is the fuselage doubler after being tacked to the side of the fuselage. The instructions indicate that it can be first tacked in place with slow CA. I would suggest that you get it positioned quickly as even slow CA doesn't give you a lot of working time. The main purpose of the slow glue is to hold the doubler in place while you use the lightening holes as access to wick drops of thin CA between the plywood and the balsa fuselage side. The notch on the long flat side of the fuselage is for the landing gear plate. This notch is present on both the fuselage side and the doubler. It is best not to get too much glue in any of the rectangular slots as various formers and plates will be glued into them later.
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Here are the fuselage sides, bottom and some of the formers all together. You can see the centerline on the fuselage floor and on the firewall, formers and landing gear plate. Note: Some kits identify the firewall as F1. In this kit the firewall is labeled as simply the firewall with the formers proceeding a F1 through F4
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The bottom photo shows the landing gear plate and F1 in place but not yet glued.
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Once the doublers have dried then the F1 and F2 formers can be added. they shouls be square to both sides. Any suitably right angled object can be used for a square. I've been carting that aluminum block around for 30 years.
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The rail between the F1 and F2 is 1/4 x 1/8 hardwood. Along with helping to stiffen the fuselage sides it will be used to mount servos.
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Bob Redmond sent in some photos of his build along with some comments. The first picture shows shows the balsa stripper he used to make up the stick wood for this project. The next shows him cutting the ribs free from the sheets. The ribs didn’t want to leave the sheet gracefully, so that was his solution. Saves breaking ribs as you try to “pop” them out. It has been identified that slot for the rib next to the wing tip is missing from the shear web. The third and forth pictures show the shear web and missing slot. This is the first batch of kits so we will let Eddie know so that future cuttings can be corrected. One nice thing about cut as you buy is that corrections/ improvements can quickly be incorporated. The bottom two pictures show the framed up wing with bottom TE sheeting drying. The TE method is not clearly explained. The best way to approach it is to extend the TE sheeting ¼” beyond the rib. After the top TE sheeting and the remainder of the wing (sans Bottom TE sheeting and TE), Flip the wing over and glue a piece of 3/16” x ¼” to the TE of the ribs and the top sheeting. Then, carve and sand the 3/16” x ¼” TE to follow rib taper. Finally glue the bottom sheeting on, weighting it against a flat surface as shown in the pictures. Bob used scarf joints on all the TE pieces as he didn’t have any 48” 1/16 sheet. The TE piece was similarly made up. The sheeting joints were toward the tips (used 36” sheets), and the joint was reinforced with a cross grained piece of 1/16” sheet. Bob will get a picture of the scarf joint and add it shortly.
This model is most easily built with 48 inch stock but often 36 inch is more readily available. If you aren't familiar with using a scarf joint to lengthen wood stock, just ask and we can throw up some info on how to make this joint .

Another WFRCC member, Greg Skinner is also getting started with his.
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Gluing the fuselage sides together. If the formers are square to one side of the fuselage then the other side should be also when the formers are in the notches but it is best to check all the way around. Keeping the bottom of both sides flat on the building table helps to assure that they are parallel and no twists creep in.https://cimg6.ibsrv.net/gimg/www.rcu...a3d53ad2bd.jpg
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Once the front two formers are installed you can install the landing gear plate. There are notches in the fuselage sides for fitting this plate. You were careful about lining up the balsa fuselage sides with the ply doublers weren't you? Note the etched line on the gear plate. It goes on the inside and should align fore and aft. This will be important shortly. It shows up later but there is also a ply doubler that reinforces the front wing mount.

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Now you can glue the firewall to the forward fuselage floor. The laser cut floor piece is used on both the nitro and electric version. The nitro version firewall is shown but the kit includes a laser cut firewall for mounting a brushless motor. The firewall and the floor are notched to fit together. Use a square to set the firewall angle at 0 degrees to the floor.
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Very nice thread and great club project; however, I could not find the 20 size on the website, only the 60 inch and 54 inch sizes. Thanks,
Jim

If you drop Ed a line at Lazer-works.com, he can help you out. Also since this is a Lazer-works original he can provide plans.

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Here are some more shots of the edge glued fuselage floor. The battery compartment floor (the part with 18 holes in it) has a center line scribed on it. When the fuselage floor is glued to the battery compartment floor you can then extend this line as a centerline for the entire aircraft. The formers F1 through F5 all have a centerline scribed on them. This assists with lining everything up for a straight fuselage. The sharp eyed among you may have noticed that this is a different firewall. This airplane can be built for either electric or fuel power and that is the electric motor firewall.

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Before joining the fuselage halves I really should have shown the rear fuselage doublers. These are two pieces of sheet that are mounted cross grain to reinforce the horizontal stabilizer and tail wheel locations. As seen in the bottom photo the fuselage bottom is trimmed to allow the tailwheel mount to glue to the bottom of the fuselage. The small former (F4) mounts between the fuselage halves just in front of the notch for the stabilizer. You can see the laser etched notch marking the centerline of F4 and the centerline on the fuselage floor.

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When gluing the fuselage sides to the bottom it is probably a good idea to use a little weight just to make certain that every thing lies flat while the glue dries.
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Just a picture of how the tailwheel mount goes on to the tail of the fuselage and buts up to the rear of the fuselage floor.
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The fuselage bottom is cut to be wider than the fuselage and then trimmed to size after the glue dries. While it is possible to cut the bottom freehand it is better to use a fresh blade and cut against a firm surface. In this case I'm using a wood plank that wont be harmed by a few Xacto scratches. Cutting this way is less likely to knock a divot out of the balsa. When the sides are trimmed you can sand the remaining ridge until it is even with the fuselage sides.

Here is another photo of the bottom going onto the fuselage. The bottom cross grain sheet and teh center line can be seen as can the etch line on F3 which has been extended in the photo. You can also see where I drilled the holes for the pushrods in F3. The position of the holes as shown in the photo works for mounting the pushrods without much bending but the position of the holes is not super critical as long as the rods don't get kinked. The less the rod bends, the less friction the servo will have to overcome. Running the pushrods through F3 also provides an anchor point and keeps the rods from flopping around. It's not too much problem on a model of this size but it can be an issue on larger models.
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Just some photos of the pushrod installation. I'm using the blue pushrods which are more rigid only because they were on hand. On a model of this size the red ( and more flexible) would work just fine and there will be some pictures of a fuselage with red pushrods soon. The blue pushrods are crossed because that is a way to get them through the fuselage without putting too much bend on them. Also note that the long push rod housing seen in the bottom photo will probably be trimmed when the servos are installed.
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It looks everyone is making some progress here Matt. I received my easy sport ARF last week and one the wing panels was damaged. I sent an email to Horizon and then I called Tower on Monday and had the new wing kit on friday. I cut the covering on the center back so I could wrap it with fiberglass or cloth to make it stronger. I was glue the wing together and I stuck my fingers through it! Ive mad a patch and now with it dries I will sand and fill then I will patch it with fiberglass and then wrap the wing and recover it!
Take Care
Michael Johnston

Setting things up for the engine installation. I'm just using a common 20-25 size engine mount and it is about as big as can be fitted to the airframe without modifications. This model seems to be at that size where electric or fuel power are equally practical. There are aspects of the engine installation that are driven by my engine choice. With the two .25 engines I have on hand, ASP and Thunder Tiger, the exhaust would exit directly onto the wings leading edge if the engine was mounted in an upright position. This also has the added benefit of locating the carburetor closer to the centerline of the fuel tank. Since this model will get a nice vibratey engine I installed some triangle stock to reinforce the firewall. the installation isn't very elegant but it is done that way to avoid gluing wood over the engine mount blind nuts.
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If you are going with fuel there is room for a four ounce tank. With .25 and smaller engines even 2 or 3 ounces would give adequate flying time. For size comparison here is a .25 ASP. It's a dual ball bearing motor and for its displacement is really pretty hefty.
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While there is access to the front wing mount it is a good time to shift to the wing. Some people prefer to start with the wing and I don't know of any reason why you couldn't. There was one problem with the first batch of wing spars. The cut file dropped one rib slot on either end of the spar web. The slot shows on the spar web diagram but didn't make it to the web. This problem has since been fixed but if you have spar web that is missing the slot it is an easy fix.
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As noted above this problem will be fixed in all future kits. I have scribbled on the plans to illustrate the problem area. The fix is simply marking the needed slot on the spar web and cutting a slot. It's nice if you have a zona saw or whatever but a razor blade will get the job done.
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Moving on, there is one rib to assemble at the beginning. The center rib is assembled from three pieces. Later in the building process it will be drilled for the wing dowel.
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The next step is to lay the lower spar on the plans with the web on top of it. Then the various ribs can be slipped into the slots in the spar web. The ribs and spar web are cut so that every thing locks together. Aside from assembling the center rib there is NO glue on the wing at this point
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