Building the SR Batteries 1/4 Scale Fokker Eindecker E1

I spent the first evening flipping through the 100+ page instruction manual and reviewing the plans.  The second evening was spent doing the same thing but in greater detail.

The third and fourth evenings were spent sanding all the balsa wood and lite-ply sheets on both faces as well as all the strip stock on all sides.  There are a lot of sheets so this is no small task.  Wear a mask and work outside if you can.

I took special care with the longeron and bracing stock so that it would have a finished appearance with soft corners instead of looking rough sawn.

There are a lot of parts that must be laminated together.  I suggest that you positively identify these pieces and get all the laminating out of the way so that when you get started building you don’t have to stop to fiddle around.  If you don't want to do all the laminating then at least do it in batches.  Construction will proceed much more smoothly if the parts are ready when you need them.

• Eindecker Photo Gallery

Adhesives used for construction

Thin CA or epoxy was used for wood to carbon fiber bonds.  Carpenter’s glue or 30-minute epoxy was used for wood-to-wood joints.  The instructions do not specifically state what adhesive to use for laminating, but I suggest using a good 30-minute epoxy or laminating epoxy.  Apply sparingly to both pieces and use a squeegee to take up excess.  Clamp firmly or place parts under a lot of weight.  Wipe up excess ooze.

Some of the laminated parts can be glued together insitu, but I chose to laminate items such as the aileron leading edges as separate components using straightedges to assure accuracy.  I wiped excess wet glue from notches where parts will be glued later and then used alcohol on a paper towel to get the joints really clean so a good bond could be established.

Also see

• Adhesives used for Model Building

Wing panels

Wing panel construction consists of balsa and lite-ply ribs with 2 carbon fiber tube spars and a carbon fiber tube leading edge.  The trailing edge is laminated from one wide and one narrow 1/8” thick balsa strip.

I began by removing all the wing pieces from the balsa and lite-ply sheets.  The laser cutting was good for the most part but the lite-ply and harder balsa sheets contained several parts that were not cut all the way through.

I cut these parts loose and removed all laser ticks (the areas not cut by laser to prevent parts from falling out of the sheet).  I then moved on to dry assembly.  Parts fit and match to the plans is excellent.

I attempted to use the alignment devices included in the kit but didn’t find them to be of use because they are very flexible.  Instead I aligned everything over the plans.  Each panel required a few hours for basic framing.

I glued the 3-lamination root rib to the spars using slow-setting epoxy.  When the wing is rigged there is a lot of force on this rib.  All remaining ribs were glued to the spars using thin CA.

I elected not to incorporate the wash-out called for in the instructions.  My only reservation being that parts may have been designed taking the wash-out into consideration.  Fortunately no problems were encountered.

I don't like fishing servo leads through holes in wing ribs so I built in 1/2" rocket tubes to allow the leads to feed through easily.  The longest tubes I could find were too short so I used packing tape to join two tubes into a longer one.  The tubes were glued in place with a small bead of Weldbond at each rib.

Note that the hole I fed the tube through (5/8") is larger than the tube (1/2").  The rocket tubes are not structural members so they don't need a lot of glue to secure them.

I replaced the laminated lite-ply flying/landing wire anchor blocks with maple blocks.  I would like to see the kit updated to include hardwood blocks that tie the flying wires to the landing wires.  I consider separate blocks to be a poor practice.

The block could be fabricated to extend from the top to the bottom of the wing and be drilled to slide over the spar.  This arrangement would be multitudes stronger in exchange for a few grams of weight increase.

The ailerons are simple and quick building.  The leading edge of the ailerons taper at the tip when viewed from the front.  I sanded one aileron and then matched the other to it.  Then I sanded the aileron bays to match the ailerons.

I used large cotter-pinned hinges from Dubro to attach the ailerons.  The leading edges of the ailerons have a single bevel and are hinged at the top.  I made a simple jig to cut hinge slots using a Dubro hinge slotting fork.  See the Photo Gallery for more details.

Take your time sanding the wing tips.  They can look really nice with effort.  If you just round them over then you won't get the right look.

Fuselage

The fuselage is a cavern built primarily from lite ply and spruce (which looked and performed more like basswood than spruce).  The firewall is laminated from two pieces of lite-ply and one of birch.

I replaced the firewall with one made from 2 laminations of 3/16” aircraft plywood.  There are very few firewalls I would even consider using lite ply for and this wasn't one of them.

There is a lite-ply doubler glued inside the lite-ply fuselage sides to reinforce the wing mounting area.  The rest of the construction is typical gusset-reinforced truss construction having spruce longerons and cross-braces.

The instructions call for pulling the tail together using a lite ply former to align it.  In theory this should work fine, but in practice a small misalignment in the former between the two sides will result in a warped fuselage.

I joined the fuselage as suggested using rubber bands without glue and found that it can flex back and forth considerably.

I suggest that you join the fuselage sides over a centerline and take careful measurements to ensure it is straight before gluing it together.  The instructions make no mention of this and imply that simply aligning the sides to the tail formers will ensure the fuselage is straight.  It might be "straight enough" but it probably won't be straight if you do it that way.

The instructions indicate that the cross-bracing should be temporarily left out of one bay to simplify the pull-pull cable installation.  I don't install cables until the model is covered and painted so I ignored this instruction.

I fed the cable through the exits into the fuselage after the finish was complete.  The cable likes to get between the cross-bracing and covering but it wasn't a problem because I was paying attention to what I was doing.

I was careful when feeding the cables rather than just dropping them in so they didn't do something stupid like puncture the covering.  I don't think it took more than a minute to feed each cable.

The cowl is a massive aluminum tub that is pre-cut but slightly oversize.  I wrapped a piece of card stock around it to mark the existing edge and transfer it so that it could be cut to the correct dimension.  I used a heavy duty Robart cut-off wheel followed by a belt sander to trim the cowl.

I scrubbed the cowl with #0000 steel wool and warm, soapy water to remove the patina in preparation for using a brush covered with steel wool in my drill.  Doing the swirly-thing gets tedious because there is a lot to do.  I did it at various stages of construction instead of sitting down and spending hours doing it all at once.  I had to change the steel wool about every 10 minutes.

I read a tip on a forum that mentioned cutting disks from a 3M Scotch Brite pad and using double stick tape to adhere them to disk sander for a moto tool works very well.

Upper Deck

The upper deck is made from a lite-ply base having several lite-ply formers that lock into notches in the base.  I suggest that you face the instrument panel with a thin veneer to improve its appearance.  As designed there are pieces that notch into the panel that will be visible and unattractive.

I used 1/64” plywood for this and to wrap around the inside of the cockpit to give it a more finished appearance than the stock kit.

Spruce stringers tie the formers together.  The deck is skinned using a joined balsa skin.

There are two 1/4” square spruce sticks inside the hatch that prevent the triangular trapeze from spreading and breaking free.  Per the instructions, these are added after the hatch is skinned but I suggest you add them prior to the skin.  Cut them as per the instructions.  The upper, outside of the edge of the sticks should align with the edge of the former so that they will touch the skin but not interfere with it.

Another stick is glued to the bottom of the hatch to prevent it from sliding rearward.  My suggestion is that you finish the hatch and the back of the firewall prior to adding this stick so that you do not need to account for the thickness of the finish.

Wrap some waxed paper over the top of the fuselage former that the stick rests against.  Put the hatch in place and screw it down.  Now glue the stick to the bottom of the hatch.  I used three #2 wood screws to hold the stick while the glue dried and then left them there as reinforcement.

Although the instructions show the trapeze assembly being added prior to finishing the hatch, the finish will be much more difficult to apply if you do that.  The holes were drilled per the plan and came out dead on which was a pleasant surprise.  After drilling the holes and verifying the alignment of the trapeze I removed it so the finish could be applied.

I fiberglassed the upper deck using my standard technique and 3/4 ounce cloth.  After a light sanding I brushed on a second coat of resin.

The hatch has a lot of work done on it.  Mine got dinged a few times as I was working on the flying wire mounts and gun.  In retrospect, I wish I'd used 2 ounce cloth instead of the lighter cloth.

When the resin was fully cured I sanded the hatch to a smooth finish and applied the aluminum tape per the plan.  After swirly-thinging the deck, I permanently glued the trapeze in place using epoxy reinforced with milled (chopped) fiberglass.

The forward braces were soldered in place and then glued using more chopped fiberglass and resin.

The only thing keeping the deck from sliding back and forth are two small lite-ply rails glued to its bottom.  The only thing holding the wings on are the flying and landing wires.  The landing wires attach to the trapeze.  Obviously the upper deck is a very important component.

Do make sure that the rails fit properly inside the fuselage.  If they are too tight then sand the rails or the fuselage longerons until a no play fit is achieved.  If the fit is too loose then shim the rails or fuselage longerons.  Use thin plywood or hardwood for the shims.  Do not use balsa.

We doweled the hatch to the firewall for added strength.  I used (2) 3/16" dowels glued into the forward lite ply former in the hatch.  I then reinforced the dowels behind the former using epoxy and chopped fiberglass.

Landing Gear

The landing gear is shock absorbing, scale in appearance and appears very durable.  Although there are many pieces, it looks more complex than it actually is.  I hope you enjoy soldering though.  There are 20+ solder joints in the gear and many of them are wire-wrapped.  I used regular rosin-core solder throughout.

Don't cook the solder joints or you will change the temper of the music wire and significantly weaken the gear.

I suggest that you use a small torch (carefully) or a heavy-duty soldering iron.  The type iron used for electronics work probably can get the job done, but takes a very long time to heat the large joints to the point that the solder will flow properly.

All the pre-bent pieces fit well except the triangular piece in the first step.  It didn't match the piece it is wrapped and soldered to so I pulled out my wire bender.  I went back and forth bending and fitting until I was happy with the fit.

One thing that would be nice is for the manufacturer to specify how long to cut each piece of wrapping wire.  I had no idea so I took a wild guess and then added some to that.  Because of that several pieces were cut way over-length leaving excess that was too short for other pieces.  I ended up not having enough copper wire for the whole job.  Enough is supplied if you more accurately guess correct lengths than I did.

Running out of wire didn't cause any problems for me because I keep the stuff on hand.  You can get fine copper or brass wire at most hardware stores.

We put a lot of load on the landing gear when we were rigging the model.  We pushed down hard on both wing tips to bow the wings so we could attach the flying wires to the landing gear.  The gear can take a lot of force and spring back to its original position.  One solder joint broke where music wire goes into a brass tube.  I pulled out a small torch and silver soldered the joint using a very small bit of acid.

The Klass Kote paint did not burn off.  It did turn a little darker and shinier.  I like it better.  I think I just invented baked epoxy enamel paint.  OK, I didn't, but I'm thinking of torching the whole gear to see if it makes the paint harder.  If I'm wrong and the paint burns off then I get out the steel wool and repaint.

Mike made a nice tool to help assemble the model at the field.  It is very high-tech consisting of a cut-off 1/16" drill bit CA'd into a dowel.  It works great!

I wrote a very detailed article about painting the wheels so you can read about the wheels there.  When I began on this model there was a discussion about drilling big holes in the wheels to save weight.  I won't mention names, but it wasn't my idea.  I said, 'Let me paint the wheels and then see how much you still want to save that weight.'  The wheels made it to the end having only an axle hole.

I'm very happy with how the wheels came out.  Several people have told me that they aren't actually "scale" wheels.  Wheels used in WWI had spokes that overlap just like bicycles and motorcycles have today.  They were also dished meaning that the hub was off-center to the outside when viewing the aircraft from the front or back.  Ok, so the point is that these wheels are the same scale as the rest of the model.  Better than close enough for fun.

The tail skid is laminated from 3 pieces of spruce which are then sawed and sanded to final shape.  It's a focal point of the model and worth taking your time with.

I decided to make the skid from beech stock.  After final shaping, I fiberglassed it with a piece of 0.5 ounce cloth on each side.  I sanded the fiberglass after the resin cured and then sprayed two wet coats of satin clear Klass Kote.

The skid mounting requires some wire bending, but isn't too difficult.  If you don't like it and can't fix it, cut the wire using an emery wheel in a Dremel and try it again with a new piece of music wire.  Fit and adjust until you're happy.  This is the only portion of the kit where it isn't pretty much spoon fed.

Like the main gear, the tail skid is shock absorbing through the use of more elastic cord.  This model will be flown off grass so we didn't do anything special to save the bottom of the skid.  As it wears we plan to apply thin CA every so often until a hard, long-lasting surface is achieved.

Empennage

There is nothing difficult about building the tail although I don’t care for the design.  Every piece of the stabilizer and elevators is laminated with the exception of the carbon fiber tube outlines.  The lamination is mostly unnecessary.

I would like the outlines of all tail surfaces to be laminated around a form while having ribs and cross members that are closer to scale in thickness, number and spacing.

I used 1/8” Robart Hinge Points to attach the elevators.

The rudder consists of balsa framing built around the perimeter of both faces of  lite-ply core.  Note that the balsa pieces are not identical on both sides but some pieces look close to the same shape as others.  Pay special attention to part numbers and dry fit both faces at the same time to ensure you use the correct pieces together.

The rudder pivots around a built-in post — no hinges are necessary.  I elected to fill the area on both sides of the carbon fiber tube glued in the rudder with scrap balsa so that the tube would not be visible under the SolarTex covering.

The only thing preventing the rudder from flying free from the rest of the aircraft is the pushrod or pull-pull cables that attach it to the servo.  The instructions tell us not to worry about — it will be ok — really!  The rudder comes up every flight but only enough to be annoying.  There's no danger of it coming off as it would have to break both cables or the control horn.

The kit calls for plastic control horns which are really ugly.  I made control horns from plywood instead.  The elevator horns are made from 1/8" aircraft ply and the rudder horn is made from 3/16" aircraft ply.  The arms on all horns were sanded to an oval cross-section.

One last note:  Model Airplane News did a review of this kit.  At least one photo showed the rudder sticking up way too high above the fuselage.  I don't know if that happened in flight of if the builder installed it that way.  The tail post comes several inches over length for some reason.  If the builder didn't cut it that would explain why the rudder is where it ended up which is very wrong.  The plans clearly show the correct height to mount the rudder which is down near the fuselage.

• Eindecker Photo Gallery

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Copyright © 2005 Paul K. Johnson