Grumman F8F Bearcat. Click photo
for enlarged view.
are to glue on the canopy and install the elevator pushrod, then test fly. All up weight came in at 2 lbs, 14 ounces - Ouch! But no
real attempts were made to build it light. Will have a test report next week on my first SSC Warbird.
high initially and the stab has since been reduced from 23 inches span to 19 inches.
The airplane flies very very well. It is fast, turns tight and will be very competitive. It launches well. If there is a good headwind I launch it with an underhand toss
into the wind. It climbs effortlessly and will climb vertically for about 150 feet before running out of steam. Continuous loops are effortless and inverted flight
requires a slight pressure on the stick to get it set at the right pitch but once done it holds the line well. Four point rolls require elevator correction but look so
cool!
I am very pleased with the Bearcat and number two is already on the workbench. The second one will have one inch of dihedral in each wing panel and be lighter
by about six ounces. I also intend to use bi-directional tape to hinge the aileron and navy blue polyester fabric for the finish (thank you Ron Caravona) which will
eliminate the need to paint the plane.
The full scale Grumman F8F-2 Bearcat has always been a favorite of mine. I first saw one fly at the AMA Nationals in
1964, at the Dallas Naval Air Station.
Bill Fornoff had an airshow Bearcat painted in copper and black. In those days the Nats events were spread all over
the Naval Station and you had to walk between the venues. I was returning from visiting the free flight area when a very
powerful prop fighter can roaring past me about 20 feet off the deck and then pulled straight up into a vertical climb that
seemingly never ended.
Back across the runway it came a second time doing an 8 point roll before it swung around and set up for a landing
approach. As long as I live I will never lose the memory of that powerful fighter roaring past me on that hot summer
evening in Texas.
The F8F-2 Bearcat has almost none of the characteristics we require in an RC Combat Figher. It has short wings, a
portly fuse, and is very small compared to other fighters. For all its drawbacks it has one thing going for it that makes
up for those deficiencies and that is how incredibly cool it looks!
In RCCA Scale 2105 or 2610 the rules state that the fighter must be 1/12th the scale of the full size plane. The Bearcat
would only have a 35" wing in 1/12th scale and would have very high wing loading. The rules for 2105 and 2610 are
very strict. The rules of SSC on the other hand have no "scale" rules, as the class was intended for Open designs.
That is until someone came along (like Lee Liddle) and decided to build "real" looking airplanes to fly in SSC. The only
rules he had to follow were the Five Commandments so he could take liberties with designs for SSC which allow
designers to create planes that loosely resemble their full scale counterparts and are recognizable as a WWII fighters.
Instead of "scale" these planes are more appropriately called "warbirds".
Design Parameters
Actually I arrived at the Bearcat after considering then discarding a number of other fighters. Initially I had considered
the ME163 rocket interceptor but finally realized that the high degree of wing sweep led to more problems than could
be easily overcome. Next I looked long and hard at the Hawker Tempest II, but never could figure out how to duplicate
the semi elliptical wing planform in foam.
The conclusions I had come to for a SSC Warbird were that it would have to have a relatively low wing taper, and a
round fuselage. The low taper ratio does two things: first it allows one to cram more area into the span and second a
gentle taper is better than a radical one when it comes to low speed performance. The round fuse is simple to make
with a foam bow than one that has profile changes or external protrusions like radiators or air inlets.
The experience we have gained with Open SSC planes has proven that at the speeds we fly a wing with 500 or more
inches of area is necessary for good performance. With this in mind the SSC Bearcat wing was drawn up to have 54"
span, a root chord of 11" and a tip of 8" for a total wing area of 513 square inches. If the plane when finished weights 2-
3/4 lbs the wing loading would be 12.35 ounces per square foot, which is within the range. Twelve ounces per square
foot seems best. The remaining airframe proportions were laid out once the wing size was determined.
Construction Sequence:
The 3 View drawing shown above was "stretched" horizontally in PowerPoint to lengthen the fuse without making it
taller. This stretching allowed the basic shape to be modified slightly but still be recognizable. The fuselage side view
was then printed out on 8-1/2" X 11" paper and the scaling process began.
The small print was measured at the wing root. In the case of my print it was 3.05 inches. The plane I was designing
would have an 11" root. So a scale multiplier of 3.6X was used to transfer all dimensions of the printed three view to a
full size cardboard template. On the three view print a center or thrust line was drawn in and the fuselage top and
bottom points were measured from this line. Stations were drawn along the fuselage center line and the points from
the small print were measured with a digital caliper, multiplied by 3.6 and then transferred again using the digital
caliper to the carboard template. Once the points were drawn in it was easy to "connect" the dots.
At this point I decided where to put the wing saddle and which point of the fuselage would be the high point. From this
I could mark off the wing saddle area on the fuse and cut it out of the template so that the wing cut out could later be
drawn on the foam blocks. My plan was to use my Feathercut Bow to completely cut out the fuselage and core the
inside of the foam so the fuselage would be hollow. To do this the fuselage would have to be made in four parts: a
right front, left front, right rear, and left rear. The location of the break between a front and rear fuselage shell would be
the high point of the fuselage, which ended up being over the wing saddle.
Three templates are used to cut out the fuselage: a front, middle (high point) and rear. The templates were made by
locating a set of F8F Bearcat cross section drawings then scaling them to match my fuse. The templates are one half
of the fuselage. Now it's time to transfer the carboard templates to the foam. Because the Bearcat is 4.25" at the cowl
and 5.25" high at the high point two blocks of 3" thick Dow Plazamate foam were used to make the fuselage. The one
template is now cut into a front and rear section (as shown in photo above) and four pieces of foam are marked out
and cut. The first step in cutting the blanks is to cut out the wing saddle. This is done on the band saw.
The hotwire is first used to cut the inside of each fuselage quarter then the outside is cut. The templates can be left in
place for both cuts. The middle template is used for the rear of the front fuselage blocks and the front of the back
fuselage blocks and insures a perfect fit of the parts.
Once the parts are cut each front is epoxied to the its corresponding rear section. They are placed flat on the building
board and the joint is held together as the epoxy cures with masking tape. Now you have a complete left and right
fuselage halves that can be glued together.
Once the fuselage is dry you will need to mark the location of your firewall on the foam. In the case of the Bearcat the
firewall is three inches back from the end of the fuse. Put the fuselage back into the foam cradles, mark your firewall
location and cut it off with the bandsaw. This front section of foam is later used as your cowl "plug". You can now trace
the firewall outline onto 1/4" lite ply and cut it out to shape. At this point I transfer the center lines, where the fuselage
halves join to the firewall then mark and drill the motor mount locations and open up the center of the firewall so that
the fuel lines may pass through it. Once this step is complete it can be epoxied to the fuselage and set aside to dry.
The wings follow conventional foam and glass rod construction. I did try a new covering material on them and was
very pleased with the results. When the local fabric store didn't have white rip stop nylon I began to look for an
alternative. On the sale tables they had white 100% polyester is a light weight weave. The fibers are not as tightly
woven as ripstop and therefore the Water based polyurethane flows through it easily. It is very strong but will rip quickly
when a tear is started. Application couldn't be easier - simply apply a coat of urethane onto the foam and then lay the
polyester on top of it. Use your brush to smooth it out and its stuck down for good. I had to pull some off the leading
edge overlap and found it was very well adhered.
The fuselage has two glass rods that run from the firewall to the end of the tail. They are placed in such a way that they
go right on the top of the wing saddle and form the supports at the rear of the fuselage for the stab to rest on. This
makes for a tremendously strong fuselage. The hold down dowels go above the glass rod so that the rubber bands
pull the dowel against the rod instead of against only the foam.
The photos shown above were taken the night of December 30th, exactly one week after construction was started. The
first day was spent designing the plane and making up the templates. A big thanks goes to Georgia Model Aviator
Club Member Mike Nemesh who used his CNC foam cutter to make the wing panels.
By the weekend of January 4th the final painting and detailing will be done and the SSC Warbird Bearcat will make its
maiden flights.
