Fw 190D-13 "Yellow 10" construction page 2

The next step in the construction of the Dora is the scratchbuilding of the spinner and cowling. I started with the spinner as it was relatively simple to make a plug and mold it. I cut 2 matching spinner profiles out of 1/4 ply and cut them so that they fit together like an "X". The 4 spaces between the ply plates were then filled in with balsa and a 1/2" wooden dowel glued to the centerline. The dowel was then chucked in to the lathe and the whole spinner was spun at high speed as I shaped the balsa to match the ply plates. Once I had the plug shaped, I fiberglassed it with 2 layers of 5oz cloth and sanded it on the lathe to keep it perfectly balanced and centered.

Once the plug was sanded smooth, it was primered and wetsanded all the way to 1000grit. A parting board was made from ply, faced with mylar and positioned on the center of the plug which was waxed and coated with mold release. Thick resin was used for the corners and multiple layers of glass cloth were applied. Once cured, the parting board was removed and the other side was done in the same manner. This produced a 2 piece mold of the spinner. I used some black graphite powder in the resin as the dark color makes spotting air bubbles easier.

After the mold had cured for a week, I applied mold release to the inside and laid up a spinner from carbon fiber. I also machined  back plate from 1" aluminum plate. The spinner is held to the backplate with 10 countersunk allen head 6-32 screws. 2 other spinners were made in the same manner, one for a 3 bladed flying prop and another for static display.

Next it was time for the cowling. The cowl was made in a similar manner to the spinner but this time out of pink foam. I did the same ply cowl outline and filled in the open spaced with pink foam. It was spun on the drill press and shaped with various sanding tools to get the correct shape. A ply template was used to check the finished shape.

The cowl plug was then glassed, primered and wetsanded to 1000 grit before the same process as used on the spinner was started again.

Once the first side cured, the process was continued on the other half of the mold. Once cured, I laid up a cowling with fiberglass cloth and a layer of black gelcoat resin.  Basic cowling and spinner now complete.

Slots were then cut into the cowling with the intention of making the cowl flaps movable and servo operated. The individual cowl flap segments were cut free from the cowling and hinged with dubro flat hinges. A 1/8 ply ring was then epoxied to the inside of the cowling. A snake drive made from R/C boat flex drives was then positioned around the ply ring and held in place with nylon keepers. Small steel arms are brazed to the ring and actuate the flaps. When the ring is twisted or spun in its mounts, the arms move outward and open the cowl flaps.

I made a firewall from 2 layers of 1/4 ply and mounted the BME 110 twin with 2 deg of right thrust. A 1/8 ply baffle plate was then epoxied into the cowling. The baffle plate provides cooling air for the cylinder heads and gives a location for mouting the cowling to the firewall without interfering with the cowl flaps. Standoffs made from 1/2" aluminum rod solidly mount the cowling to the firewall. The bolts for the standoffs will be inside the spinner cone so they wont show in the planned radiator mock up.

The other wheel well was finished detailed with styrene plastic and both wells were painted RLM 02. I also took a minute to put the model together for a few inspirational or motivational pics.

2 futaba 9206 servos are mounted to the rear of the baffle plate and actuate the cowl flap drive ring. I also finished sheeting the wing bottom and leading edge.

Next the wing was mounted to the fuselage and the belly pan was fabricated from balsa ribs and sheeting.  Following this, the wing was glassed with 1.4 oz cloth and set aside to cure.  I also made some fiberglass panels to cover the exhaust area by glassing over monokote that was ironed down to the front fuselage area. Once cured, the glass was popped off and sanded to shape.

The stub was then cleaned on the wire wheel and 11 more were made just like it.

One of the things Ive always wanted to do is a live exhaust system. I started by hammer-forming some stainless exhaust elbows from K&S exhaust. Once shaped, I TIG welded several beads onto the end of the exhaust stub, then ground them down to get the flat flange shown. I then welded a bead running down the center of the exhaust stub just like the full size.

The exhaust areas were then removed from the fuselage and more stainless elbows were welded to the flange on the cylinder head and continue to a manifold inside the fuselage. I also cut the holes in the fiberglass covers to match the full size and shaped them to fit in the exhaust area.

The other side was finished in the same fashion. Small stainless tabs were welded onto the end of the manifolds and bolted to the wing saddle to support the rear end. I then sheeted the exhaust area with thin 1/32 ply. The individual exhaust stubs will be welded to the manifold 6 to a side and be fully functional.

The stubs were saddle cut and brazed onto the manifold. I tack welded all 6 into position and then brazed them all at once. I then sandblasted the entire assembly to remove the flux from the brazing process.

The rudder was constructed in the same fashion as the elevators and ailerons. 4 robart hinge points hold it in place. The Intake scoops were carved from balsa blocks. Plywood rings on the intake lip give some ding resistance. The scoops will be glassed seperately and attached later on.