Workshop

Jerry Bates Hellcat F6U - 5

This is a build of a 50cc version of the famous Grummen plane from WWII

9/5 working on the fuse, the wing mounts and he air system

Prep and setup for the build

This is a plane for John McGowen and he has waited quite a while on my list to get this plane done. As I begin the build he has not yet decided how scale this plane will be and that is fine since those decisions will be made as I begin to frame it up.

The plans for this kit have many pages and I studied the planes and made a list of materials. This is a short kit and I gathered all the wood and sorted the laser cut parts into bags according to what they will build.

All other things like glue were checked to be sure I had proper quantities. The wood list will be put in the final book with the plane and on the customer invoice

Decisions on the general features of the plane will need to be made:

ENGINE -- It will be a DLE 55 gas motor with electronic Ignition

RADIO EQUIPMENT -- Futaba 9C will limit us to 9 channels

SERVOS -- Others have flown this plane with 100 oz/in servos and that is a minimum for us. The elevator will be done with one servo.

LIGHTS -- Nav lights with a switch on the plane -- landing lights with the retracts down

BATTERIES -- Two for the main power and one for Ignition. All 6volt. Mains at 2700 ma and the engine at 1500ma

AIR SYSTEMS - Retracts for the main and tail wheel and air for the canopy

Stab and elevator Construct

The stab construction began by laying out the plans and getting all the wood and parts together. The stab has a symmetrical air foil and it is built by making the top half over the plans as shown below

The parts were glued up per the plan including the wing tips.

As you can see below the top half is build and planked and then the bottom half is built over the top. Also notice there is a shroud designed in that overhangs the trailing edge of the stab and covers part of the gap with the elevators.

After the top half was constructed, the trailing edge had to be cut flush with the aft end of the ribs. (See the drawing above) so I used a flat gouge to make the cuts. This can also be done with a mini plane or sandpaper. I use the gouge because it is really fast and accurate. The trailing edge must be flush.

Below you can see I checked the cut with a straight edge to be sure it is flush as I was ready to plank over the ribs and trailing edge.

Next I cut 1/16 inch soft balsa from some 6" wide stock and fit it to the leading edge with the shroud cut for the trailing edge. When the fit was good I glued it in place with CA on the structure and yellow glue on the leading edge joint. I then checked each rib.

Below you can see that the leading edge for the bottom is in place and I glued up all the rest of the parts.Once all the parts were in place, the stab bottom was ready.

Below you can see the ribs have been glued top to bottom and the one leading edge is in place.

The joint at the leading edge was reversed to provide better strength.

The rest of the bottom half was glued up and the trailing edge was trimmed as before. Once that was done, the bottom was planked with 1/16" balsa as before.

I rough shaped the stab and sanded it to be sure all imperfections were addressed. I left the edges square as I find I do beter if I put the final shape on laer in the build to prevent damage.

The stab was then set aside to be put on the fuse at a later time

The elevators were next to be done. The elevators are constructed in halves much like the stab. See the drawing above for details. I first glued in the leading edges for both the left and right sides and then added the ribs.

I cut the ribs to rough shape

I then turned both elevators over and placed them over the plans. The Elevator control horn was made up so that the servo could be located in the fuse and there will be a push rod down the center of the fuse that will activate the motion. The shot below shows the control horn and rod being glued in place with the elevators in the inverted position

Next, the structure was glued in place on the bottom of the elevators and the ribs trimmed to rough shape. you can see the result below.

The hinges were located and drilled on both the leading edge of the elevator and the trailing edge of the stab. Because of the design of the elevators, the hinges operate in slits in the leading edge. I roughed in the slits and tested the hinges.

Before the elevators were completed, I refined the slits and tested the throw I could get.

The trim tabs are metal on the full scale so I planked the trim tabs and final shaped the surfaces.

Construction of the fuse

The firewall was completed as shown in the section on mounting the engine and then I prepared the motor box sides and top. I used servo screws to position the firewall and the motor box sides.

The joints with the firewall were frozen with thin CA and the hardwood triangle stock was glued in the corners of the joints. Since I know the owner of the plane, I am adding extra reinforcements on the motor box and some other places.

Next I set up the top view of the plans and put the motor box over them. I use blocks to hold the sides on the plans and prevent movement. There are lots of different ways to do this, but it must be stationary and square to the board. I use Luan doors for boards. The cost about $25 at the H depot and they last for several planes and then they make fine shelves for the upper part of the workshop. They are flat as long as your bench is correct and you can sand off all the gunk that accumulates.

The motor box top was glued in place being sure to keep everything square and the down thrust in the firewall. Servo screws were used to hold everything tight to the firewall.

The formers were then glued to the motor box and then re glued for strength.

next, I set the assembly on the building table.

below you can see the next step. I drew the center line of the fuse on the board and then drew the location of each of the formers. This allowed me to place each former and set it square to the board. The stringers are what hold the rear part of the fuse so I put them in place and added each former in turn.

After some time and a great deal of checking with squares, the fuse is taking shape. I cut off the formers so they would sit flat on the board to square the formers. The part of the formers I cut off will be added after the top of the fuse is done.

The structure was then re glued to be sure all the joints were correct and glued up as they should have been.

Next, I build the frames for the air container and glued them to the formers. CA will not do a good job on the air tank, so I used some glue that will hold it better. It was wise to get the air tank in at this stage as it was easier to get the structure in place.

The front end also got stringers and the first several also got some triangle balsa supports that are not shown below.

Next I began the work on the stab saddle and the support for the tail assembly. This plane builds better if the entire top of the fuse is completed while it is still flat on the board. The stab saddle is key to the structure and the first fit of the stab showed plus 1.1 degrees of incidence. I measured the stab relative to the building board as that is the datum for the plane.

There was a lot of fitting to be done in order to get the stab straight and level with the correct incidence. I got it fitted but did not want to glue it in as yet. The linkage that will operate the elevator must be cleared from the fuse structure and the rudder fit before the glue up is done.

The stab was final shaped and sanded before mounting. I then set it up and cut the fiberglass cloth to fit.

I used Zpoxy resin to wet the surface and then stretched the cloth over the wet surface. I worked all the bubbles and imperfections out of the surface and allowed it to set up.

Once it was dry, I trimmed the cloth and did the bottom side. The resin needs overnight to set up before sanding and priming. I decided to do this before mounting to the fuse because it would be a lot easier than working with the finished airplane.

While the stab was drying, I framed up the vertical fin over the plans much like the stab was built.

Above you can see the first side framed and planked. The ribs and leading edge were then added to the upward side and the strobe light for the top of the rudder was installed. Once the shape was correct, I planked the second side of the fin and shaped it .

Below you can see the fin with the filler on it

You can see the strobe light that will be at the top of the fin. The lenses for all the lights arrived today so I can be sure they will fit on the plane.

Below you can see the rudder framed and hinged to the fin. It needs to be finish sanded and shaped. The fin will then be glassed and the elevator and rudder will be covered with paintable fabric.

The glassing operation turned out just fine and the stab looks like we hoped it would. In the past I had problems glassing balsa and the problem was using too much resin and working the surface too much/. The hot plan is to wet the surface and then apply the cloth. I pull the cloth flat and as soon as it is flat, I leave it alone. I find the top coat of resin or primer should be put on later after the first coat sets up.

The resin will take overnight to be sandable and then you can do what you want with it. I added no more weight than the monokote would have done.

I then sanded the stab and applied a coat of primer to see what the surface will look like.

I sanded the elevators and checked them for final shape. I then used Solartex natural covering and covered the bottom of the elevators

I finished the covering with the top of the elevators and then assembled them to the stab to check fit and finish.

In the shot above you can see the primed stab and the covered elevators. They came out very nice and the next steps were to fill the imperfections and apply a second coat of primer.

The elevator hinges were then glued in place and the control horn was checked to be aligned for the control rod to be added later.

The fin was sanded and glassed just as before and then it was put in place on the plane. The backbone was then glued on and the turtle deck began to take shape.

Next was the beginning of the planking operation and the skin for one side was put on and allowed to dry. I use CA on the interior joints because it holds well and is fast. I use yellow (yella) glue for the joints that show because it can be sanded better than CA. Lots of pins and tape hold the soaked wood to the formers.

The lower area will be planked after the bottom of the fuse is constructed.

How about this, John??? looking like a hellcat now!!

Above you see the fuse after it was removed from the board and rough shaped. I checked it for straight and everything looks good.

Next I constructed a rack for the fuse that will allow it to be worked on without damage. This will become the rack the plane is stored in and the method of assembly at the field. The saddle was lined with foam and the plane test fit.

Below is the inside of the fuse and you can see the flat cuts in the formers that will have the bottom half glued in place and additional stringers. the rest of the fuse will then be planked and sanded just as the top was.

Before the final construction, there are some equipment issues that needed to be resolved while the fuse is open. John will order the tail wheel and the servos for the elevator and rudder need to be set up.

I test fit the wing on the fuse and you get an idea of the size of the bird and the layout.

below you see the wing configuration and the motor box. The motor has been mounted so that is not an issue.

The elevator servo was put in place and the control rod was made and adjusted to fit to the elevator control horn. Below you see full up elevator with the servo hooked up and working

The shot below shows full down elevator and this will be more than the spec calls for.

The wooden control rod will bend under stress so I added a support that will also be a brace for the width of the fuse.

next was the tiller control horn for the rudder. I made it from brass rod and I soldered a control horn to the end of the shaft for the pull pull system to attach.

You can see the tiller in place in the rudder and it will be glued and banded in lace for final assembly.

below you can see the elevator control horn, the rudder control hour and the wire for the aft light in the far end of the fuse,

I have to pause on the back of the plane while I wait for the tail wheel assembly

Moved to the wing saddle and began with the former at the leading edge of the wing. It was designed with a notch in it that was not correct so I filed the area in and glued the former in place.

Next I constructed the wing saddle from some 1/32 ply and some supporting wood.

With the saddle in place, I checked the wing alignment and pinned the leading edge in place with 1/4 inch dowels. They will be glued in the wing later on, I just wanted to get them in position now.

On the trailing edge I added blocks that will be spacers for the wing bolts and then fitted the wing saddle to the top of the wing.

I found I do not have a bolt long enough to mount the wing so I went to the air system. I ran the tubing and valves to the system and pumped to 100 lbs. With adjustments, the retracts came to life and all was just fine. The big landing gears move as planned and I cycled the gears 18 times on one load of air. The tail wheel will use some air so that number will be reduced later.

Above you can see the retracts down and locked and the fuse has the firewall doubler in place. This will form the mounting ring for the cowl.

Next I made the drawing of the retract doors. This will be used later after the planking is in place.

Above you can see the wing mounting plate with the holes and the blind nuts in place. I took care to be sure the bolts were square to the plate so they would thread in easily.

The wing was then mounted to the fuse for the first time and all looked very good. Below you can see the plane up on its feet for the first time and it looks ready to fly.

Another view of the plane shows the ailerons and the planking on the trailing edge of the wing that will form the fuse fillet later on. The wing can now be finished as I am sure things are straight and true.

Engine Position and Mounting

The engine is a DLE 55 cc engine and it is in hand and ready to go. The engine designed for the plane is an OS 550 and several things were noted about the engines

The DLE is longer from the mount to the back of the prop I changed the plans to allow for this difference. I marked the motor box sides back 1/2" from the plan position as shown below.

The dle is a rear carb motor and it likes having some room behind the carb. After I marked the mount location from the plans I cut a hole in the firewall and made a plug to fit over the hole.

The plug is made by using two hole saws in come 3/4" ply and then gluing 1/16 balsa over the one end. The plug is shown above.

I mounted the motor to the firewall to ensure it will fit properly.

Next I ran the final check of the motor position be propping the engine over the plans with the firewall in position. I checked that the front of the motor will be in position properly by using a square as shown below. This step is unnecessary, I set it up for illustration of how the motor will fit in the cowl

I checked to be sure the muffler would work with the cowl and it looked good.

Below you see a shot of the rear plug in position.

I then used a square to see if the head of the engine will clear the lower cowl intake. The square indicates it will have to be cut out just ahead of the lower scoop. I will try to avoid this problem and therefore stopped work to research solutions.

below is the cowl with the lower scoop.

Research on the solutions did not yield any good answer to the cowl question and the motor would like the additional air flow from the cut out of the front. I will go ahead and figure to09 cut out the cowl enough to clear the head and give the good air flow.

The plane was designed for a glow motor that weighs 3.4 lbs with the mount and the muffler. The DLE is 3.5 with the muffler and 3.6 counting the ignition module. This tells us that the plane will be close on weight and balance. With this info I will put the servos inside the fuse and not back in the tail to avoid a tail heavy problem at the end of the build.

The gas engines use less gas than glow so the tank will not be any problem at all. I will mount the ignition on the side of the motor box and that should resolve any other problems with the engine install.

Later in the build I will set up the throttle linkage and control arms.

Begin the Wing

First step was to get out the plans and study them again. The delay in the project meant I needed to get up to speed on the plan.

This is a big wing and it has lots of moving parts. I began with the center section and it is composed of ply ribs and dihedral braces. The structure was assembled without glue and checked out.

The shot above shows that I put blocks on the board to hold the center section in place and then I started gluing the joints with thin CA and checking the alignment of all the parts. The weak spot in the wing is the spot where the dihedral changes at the ribs that ser set at an angle.

The shot below shows that I continued the hard wood spars beyond the plan distances. The spar was supposed to stop at the rib to the right of the clamp and that would just not do the job at all. I continued the spar to the next rib and then I will restructure the joint to spread the load down the dihedral brace. These braces were laser cut from 1/8 ply and that is a bit thin to take the load of a hard landing. I will increase the strength of the wing outside the dihedral change.

The u shaped cutout to the right of the clamp is the bay for the retracts. My lan is to build the center section and then both wing extension and plank the top of the wing in total. Once the wing is roughed in and straight, I will turn it over and add all the mounts, servos, lights and hinges that will be needed to make it work.

The shot below shows the structure with the spars and the interior leading edge. This shot shows the section in the upright position ready for planking. I glued the planking on and then it got a first sanding.

Below, you can see the section after planking and it is inverted for the bottom construction. The first step was to cut out the ribs for the wheel wells. At the top of the shot you can see the right side with the ribs removed for the wheel.

Next I made 1/4" ply plates to hold the retracts. These plates are considerably larger than t he plans called for. This is the weak spot in the wing since the under side of the wing must be open for the retracts. The entire force has to be handled by the top of the wing and this is very dangerous. I started with the enlarged mounting plates and I positioned the retracts and checked the motion.

Under the enlarged plates I added structure that will allow the wing to survive a hit on the landing gears. You can see below that I have added reinforcements to the area under the plates and I positioned the plates so that the gear will fold all the way up and lock without contacting the under side of the wing planking.

After the structure was complete I mounted the landing gears to the plates with blind nuts and 6-32 bolts. I also routed the air lines that will drive the gears later on.

Next I framed a hole in the top planking that will allow the services from the fuse to be connected to the wing. You can see the two air line connectors in the hole.

The gear plates were then glued to the structure with Hysol glue that will give a good strong system in the center section.

With the landing gear in place, I then set the center section on the board with the left wing section flat on the plans and the center section inclined as shown on the plans. The spars and ribs were then glued in place.

Below you can see the wing section with the spars in place and the rear spars ready to be glued to the structure.

The shot below shows the spars in and next I put in 1/16" web supports to tie the upper and lower spars together. This little bit of wood will accomplish amazing things w2ith the strength of the wing.

Once the structure was done, the wing was planked on the top and removed from the board. I did not plank over the area of the flaps and the ailerons ad I will build them with the wing inverted and the bottom structure exposed.

Next I set the right wing panel on the board just as I did the left. It is essential that the wings be done flat and straight so a great deal of time was taken to be sure the thing was done exactly right. A warped wing makes the plane hard to fly.

Below you can see the wing after all the top planking was on it. The wing looks like is is all build but the entire under side and all the equipment has yet to be done. I am about 20% done with the wing rough construction.

This is another view of the wing and you can see the anti-hedral in the center section top surface and the dihedral in the tip sections. This is an unusual wing and it is a trial to build straight and get all the services in it properly. The list of things include

2 aileron servos with hatches and ailerons wired to the center section

2 flap servos with hatches and linkages wired to the center section

2 tip lights with wiring to the center section

2 air lines to the retracts and to the center section

The next task was to support the wing in the inverted position so the build could continue. The planking is contest quality and that means it is easily damaged so I did not sand it prior to inverting the wing. I then built a support that allowed the wing to be in a flat position and not warp or strain the structure. I began with a strong piece of 3/4 ply and checked it for straightness. I constructed a cradle for the center section and confirmed that the wing would fit as it should

I then hot glued foam to the cradle so that the wing would not be damaged as I work on it. The wing fit well, and the construction could continue.

Next I ran the wires for the running lights in the tips. These will plug in at the center section and the lights will be behind lenses that will be red and green. For now, I just wanted to get the wires routed to the tips.

I bolted the landing gears in place and hooked up the ail lines. There will soon be a test of the system once I get wheels that will be right for the plane. Everything is looking good so I went on to the next things to put in the wing

The ailerons on the Hellcat were done two different ways depending on when the plane was built. The earlier ones had exposed hinges that protruded through the under side of the wing and the ailerons rotated around the lower hinge. This was good for the crew chief because the aileron could be removed very easily and the maintenance was simple. The drawback is that the downward motion of the aileron was like a flap and the upward motion was like an aileron. This produced aileron differential and the plane would yaw wildly when the ailerons were used to the right.

The later planes had ailerons with the hinge set up like I did on the elevators shown above. (way above in this file). They rotated around a hinge in the center of the leading edge of the aileron and that made the flight characteristics much better than the older models

For this plane, the centered ailerons are stronger and eliminate the fragile exposed hinges that can be damaged while handling the wing. The plane would fly better with the centered hinges and the appearance is not an issue since the hinges are on the bottom of the wing.

I, therefore, decided to go with the centered hinges and I began the construction with the hatch rails shown below. They are hard wood and the planking will cover 1/3 of the rails and the hatch will cover the rest.

The aileron hatches were cut from 3/32 bass sheets and the servos were mounted on the hatch. The servo arms will operate through the hatch and be connected to the aileron control horns.

below is the view of the servo mounted on the hatch and ready to be mounted in the frame.

The Build of the ailerons came next and it began with the plans covered with wax paper and a 1/2" leading edge tapered to fit the trailing edge of the wing.

The 3/32 sheet was glued to the leading edge and the ribs were set in place. The hinge blocks were glued in place and then a ply plate that would hold the control horn bolts was installed.

The design of the hinge is just like the elevator so I drilled for the hinges and then made the leading edge round so it could pivot correctly

The trailing edge of the wing got blocks for the hinges and holes were drilled.

The aileron was then installed and fitted to the wing so that it cleared the structure. The control horn was added and the aileron was put aside awaiting the shrouds on the wing that will cover the joint.

After the construction and fitting of the second aileron, it was time to begin the flaps. YOu can see above that the layout and rough build is the same as the ailerons

After shaping and fitting, the flap was on the wing and aligned to the location of the servo.

next I made the wiring for the ailerons. I do not like plugs inside the structure as it is asking for problems in the long run. I extended the wire to the two servos so they would reach the center of the wing and have room to plug into the fuse wiring. I soldered the joints and made a plug so that the left servo would plug into the line from the right side. This will allow the wire to be installed after the wing is painted and will only have one plug in the middle of the circuit. The two aileron servos will have only one plug to the receiver.

I built the hatches for the flaps and ordered a reverse for the circuit so that the flaps will work together. As with the ailerons, there will be just one line run to the radio as we have lots of things to make the receiver do.

The ailerons and flaps for the other side of the wing were then built. I went through the same process as the other side and hinged the surfaces to the wing.

Below you can see the bottom of the wing with the servos in place and the flaps and ailerons hinged to the wing. There is still a lot of wing building to do, but we are making progress.

The shot below is of the top of the wing and you can see the ailerons and the flaps in the up position. The trailing edge of the center section is to be done as well as the trailing edge of the wing tips outside the ailerons.

Next was the installation of the landing lights. There were two styles of landing lights used and we will be doing the later version which as the lights in the leading edge of the wing. I started by cutting down the diameter of the lights as shown below.

I then built a lithe compartment and painted it white to increase the brightness of the light later on.

You can see below that the light is mounted in the box and it will shine through a hole and lenses in the leading edge. The holes will be cut after the leading edge is in place.

Right next to the landing lights will be the guns. I started by mounting a block behind the 3/32 interior leading edge. The guns will screw into the block and that will allow them to be removed for transportation.

Next the leading edge was put on the interior leading edge. The plans call for joints at the change in dihedral and that is sure not a good idea for the structure. Instead, I did one joint in the center and used medium hard 1/2" leading edge stock cut from 4" wide sheets. One sheet did both sides and will greatly increase the strength of the wing at the joints and will be a strength member just ahead of the landing gear mounts. The shot below shows the process of gluing the leading edge in place.

I then cut the excess material away and the top of the leading edge was roughed in. You can now get a look at the shape of the wing and we will soon be able to plank the rest of the top and and add the tips. After all the mechanical issues are worked out, I will plank the bottom of the wing and we will be set to mate it to the fuse and the glass it.