Sopwith Camel - Cox & Manzano Laser Works

Melanie gave me a Peter Rake-designed Sopwith Camel from Manzano Laser Works short kit for Christmas 2008. The entire building process has been documented here. The laser cut parts are very nice, as can be seen in these photos.

See the silkspan and dope covering tutorial video (April 2010).
Updated December 4, 2009  (click here)
Updated November 5, 2009  (click here)
Updated October 12, 2009  (click here)

There are a couple places you can go to read construction articles on the Sopwith Camel, but they are for radio control. My Camel was originally going to be built for control line, so I figured it would be worth including some additional information here. I have since decided to use a 3-channel R/C setup. I planned at first to use the recommended Graupner GR170323 motor/gearbox combination, but have since settled on an E-flite Park 370 brushless outrunner motor to get the extra power. Either a 2-cell, 1500 mAh LiPo or a 3-cell, 1300 mAh LiPo battery will be used. Using an APC 10x4.7 e-propeller and the 3-cell LiPo, the thrust ration on a full charge well exceeds 1:1.

The instructions and plans are very sparse, and leave a lot to the imagination regarding the actual construction, so there are photos here that you will not find elsewhere. A lot of balsa sheeting, wire bending and soldering, and balsa carving and sanding is required. While there are people out there gifted with an ability to figure it all out even the first time around, many will appreciate some help. Hopefully, this content will take the edge off the difficulty in getting through the process. The old says goes that a picture is worth a thousand words, and for model building that is definitely true. Here are a few thousand extra words.

See a video of Clive Gamble's FF Sopwith Camel in flight. Its distinguishing feature is a very short distance between the prop hook and the motor peg (~4.5").

New photos will be added as building progresses.

The photo below shows the bellcrank mounted in the fuselage. I plan to attach the wings permanently, so the bellcrank faces upward for access through the cockpit for maintenance. Lead-out lines are coiled for now. You can also see how the landing gear wire is laced and epoxied to the plywood mounts. After the bottom balsa sheet is on, filler will cover the wire. There is another shot of the bellcrank, only this time from the top. You can also see where the the cabane struts are laced and epoxied to the formers.



I have found that it is easier to get the balsa sheeting right for compound surfaces by first making paper templates. The ones shown below were taped tightly to the frame, then a pencil was used to trace the edges. I cut the templates with scissors, then used them to draw the outline on the balsa sheeting. Cut them just slightly oversize, then sand to fit. For installation, I glued the straight, flat edge toward the rear of the fuselage, then wetted the top surface with water and used masking tape to pull the sheeting tightly to the formers and fuselage. After it dried, I lifted the sheeting enough to apply glue, then taped everything back in place and let the glue set. The process was repeated for most of the curved sheeting pieces, including the front fuselage top pieces (I did it in three separate pieces).
 
Here is the completed side sheeting, the rear top sheeting, and the front top sheeting. The rear top sheeting (over the cockpit area) was first cut a little oversize, then one edge was glued to the fuselage side. The top of the sheeting was wetted, and then masking tape held the sheeting to the formers while it dried. I then sanded the loose side to make it mate with the other fuselage side. I personally do not like having to use a lot of filler for sanding later, so I put a little extra effort into getting a good fit. In order to provide a good gluing surface for the front fuselage top sheeting, I cut an 1/8" wide strip of 1/16" thick balsa that matches the curve of the rear cockpit former. Otherwise, you would need to have the sheeting join within the width of a single piece of 1/16" balsa former.


Instructions for building the cowl are equally ambiguous. Nothing indicates that the thin strip of plywood that gets wrapped around the perimeter of the cowl should not go all the way around, but it does not. The first step is to cut 1/8" balsa stick separators that set the proper distance between the plywood cowl rings. I used five separator pieces. Be sure to get everything square. Next, wet the outside surface of the thin plywood and wrap it around the rings. I used clamps to hold it in place. Once dry, remove the plywood, apply glue, and clamp it in place until the glue sets. Sand both side flush once dry. Finally, the 1/8" balsa half-circles (8 of them) are glued to one face of the cowl ring. I shifted each set of halves by 90° in order to keep all the joints from being in the same location.



Below are a couple photos of the wings being rigged on the Sopwith Camel.


This is the Sopwith Came on the workbench during the wing rigging procedure. Per the instructions, the top wing was attached first, since the dihedral of the bottom wing is set by the length of the wing struts. Note that while I originally planned to make the Sopwith Camel a control line model, I have decided instead to do 3-channel radio control using rudder and no ailerons. Therefore, I have configured about twice the normal dihedral in the bottom wing; the top wing is still flat. That's not too much of a deviation from scale, so only the true Camel fan will suspect anything is amiss. The first step is to fix the fuselage in position and hold it there rigidly. I used large T-pins crossed across the landing gear wire to stake the model to the building board. A prop was placed under the rear fuselage to make the fuselage bottom where the lower wings attach level with the board.

Next, the top wing was attached by sliding the cabane wires into the plywood saddles. It took a while, but I kept measuring, removing the wing to bend the wires, and re-installing the top wing to get everything exactly aligned (equal distance from wingtips to rear of fuselage, wings level with building board). Once satisfied, I removed the wing, sanded and cleaned the music wire cabane struts with alcohol, then squirted thick CA into the plywood saddles and re-mounted the wing. Finally, re-check alignment and let the glue set. On my Camel, I used a small jeweler's file to file a couple small grooves in each of the strut wires where they are captured inside the plywood saddles just as an extra gripping point.


Here is a close-up that shows how the cabane struts are attached to the top wing using 1/8" aircraft plywood that has a groove filed in the middle to accept the music wire. Make the slot is a snug fit that the wires can be slid in and out of during adjustment.


Aligning the bottom wings: Use a large square or triangle contacting the trailing edge of the top wing to mark the location of the top wing on the building board - one mark very near the fuselage and then another out near the tip. Apply masking tape and mark the tape (keeps the board clean). Then, using the 1/8" dowel stubs in the bottom wing root rib, slide it into place against the fuselage. Use the square or triangle right next the fuselage to mark the location of the bottom edge trailing edge on the building board. Do both left and right wing halves and verify that the distance from the top wing mark to the bottom wing mark is the same on both sides (or within a small fraction).  Remove the bottom wings and place a piece of masking tape on the board out near the tip where the top wing mark is located. Place a mark on that tape the same distance as the ones near the fuselage. Do the same for both sides. Now, reattach the bottom wing halves and use the square or triangle to align the trailing edges. Prop the wingtips up using the rear wing strut as a gauge. Measure to make certain that both halves are at the same dihedral angle. Re-verify the trailing edge alignment, then flow some CA glue into the wing mount areas at the fuselage interface. Leave the fuselage attached to the building board while fitting the outer wing struts. Be sure to sand to shape and verify that the angle of attach (incidence angle) of all wings are correct before gluing the struts.




November 5, 2009 Update

Well, it is November 5, 2009, and my Sopwith Camel is just about ready for covering. Although I was going to do a silkspan and dope job when the Camel was going to be configured for control line flight, I am now planning to use Monokote - olive drab everywhere except on the bottoms of the wings and rudder. The photos below show details of the open framework, radio and battery installation, motor, wheels, wing strut attachment points, elevator and rudder hinged surfaces, etc. As mentioned earlier, the plans and instructions are very sparse so I was sure to take lots of photos along the way for the benefits of others.

November 22, 2009 Update

Covering with Monokote has begun. Yellow is used on the bottoms of the wings, and olive drab is used everywhere else except on the rudder (which is bleu, blanc, et rouge). Decorations (roundels, etc.) will be added after the first few flights. That's one of the many benefits of electric flight - test flights can be made without fear of rendering the finish unable to accept paint or iron-on covering because of oily exhaust residue.

For the lower wings, a 1/4" wide strip of olive drab Monokote was attached at the junction between the wing and fuselage in order to accommodate a not-so-perfect joint later. A paper template was made for the top of the lower wing halves to get the contour of the fuselage interface right without having to trim the Monokote at the fuselage during the ironing process. Likewise, a paper template was used to cut the contour of the top of the wing halves into the fuselage side covering prior to ironing. It worked out very well.


December 4, 2009 Update

My Camel is now fully covered, but without any trim markings other than the bleu, blanc, et rouge stripes on the rudder. An attempt to wrap the cowl in Monokote did not work out well enough to keep. Using lots of heat from the heat gun, I was able to successfully stretch the Monokote around the small radius to where there were no wrinkles anywhere, but it was so thin that it was translucent and you could see the wood underneath. So, I peeled off the Monokote and covered the cowl with medium grade Silkspan and dope. A few coats of clear were applied and sanded, then a couple coats of Testors silver dope finished it.

The front half of the dummy radial engine provided with the kit has been painted and installed in the cowl. The E-flite Park 380 brushless motor pokes out neatly through the crankcase area. As suggested in the instructions, the cowl will be held to the firewall with a couple small dabs of silicon cement.


Adjusting the incidence of the top and bottom wings took a fair amount of work, but was worth it to guarantee that no surprise rolling and/or stalling tendencies would be experienced! The first step was to block up the Camel on the lower wings near the fuselage, set to be parallel with the workbench surface. Then, measurements were made at the lower wingtips to get it level from side to side. The distance from the workbench to the trailing edge was measured near the fuselage, and that was used to adjust the angle of the wingtips. About 3/32" of washout (LE lower than TE) was set at the tips to help tame the stall behavior. Changes were made by twisting the wingtips while using a heat gun to re-shrink the Monokote to hold the shape. the fuselage needs to be held rigidly in place whilst twisting. The top wing was already set parallel to the bottom wing during the installation on the cabane struts, so only the top wingtip incidence needed to be checked. I used ruler measurements for that as well, and set the same amount of washout in the top wingtips. A final check was done using the Great Planes laser incidence meter, as shown in the photo below. It confirmed my measurement. I did not use the meter for initial adjustments because its weight was barely tolerated by the relatively flimsy wing structure. I was careful to configure the meter's distribution of weight to not cause the wingtip to tilt to the front of rear and thereby affect the readings.


To balance the Sopwith Camel, I taped a 1/4" round brass tube at the center of gravity point per the plans (2.25" back from the firewall). The tube was then set atop wooden block to get the wheels off the surface, then weight was added as necessary. Be sure to hold the airframe in a font-to-back level position before testing to see which way it is going to tilt, or you can get a false reading. I was a bit disappointed when it cam time to balance the Camel in that it required 3.5 ounces of dead weight in the front of the cowl. I hate that! Prior to adding the weight it was at a respectable 19.2 ounces; now it is sitting at 22.7 ounces - yuk. Well, it is better to be heavier than planned than to be tail heavy and destroy the craft.


 Here is the ready-to fly wing loading:

Wing Area:   2 x 36" x 5.75" = 414 in² = 2.88 ft²
Weight: 22.7 ounces

Wing Loading = 22.7 / 2.875 = 7.90 oz/in²

A lot of Park Flyers run in the 5 - 6 oz/ft² range, so she definitely will not fly like a Park Flyer, but then the Camel is not advertised as such. To the other extreme, the Great Planes electric Cub is rated at 16 - 17 oz/ft², so she should do much better than even a notoriously docile Cub. Now, I just need a good day...


Posted 8/30/2009

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Cox Sopwith Biplane

I finally hit on an eBay auction where the going price for a vintage Cox Sopwith Camel biplane was under $100. It did not come with the original box, but it appears to have never been flown nor even had the engine run. It's in perfect condition. Believe it or not, the Cox Sopwith Camel is regularly selling for more than $250. It's insane. I had the 3-model WWI set as a kid, that included this Sopwith Camel, the Fokker Dr.I (DR-1) Triplane, and the Fokker D.VII (D-VII, D-7) Biplane. A NIB version of that would probably sell for close to $1,000. The Camel seems to be the most valuable of the three. I've had the two Fokkers for a couple years. Now I finally have the set of all three!

    

Posted 2/11/2012