I get a lot of questions about just how hard my airplanes are to build. Many think they must be hard to build because of the dihedral and swept forward hinge line. Molded parts and realistic appearance are also daunting. Some builders think they are can build them with only plans and parts. They are both missing some very important points. I'll try to offer fair judgments and details as to why these judgments are accurate. Follow along, the changes in aerodynamics and structures are cumulative.
[photo not recovered: 425eaf3337c1376e.jpg]MUSTANG II
The Mustang II was published in June 1969 American Aircraft Modeler. It was a slight upgrade of the airplane I flew at 1968 NATs. It had a dramatic appearance for 1968 and flew reasonably well. Being an early design, in was of relatively conventional structure. It had dihedral, but a straight trailing edge. It was a basic, simple airplane. Anyone could build one from plans. Why wasn't it more popular with builders? Dihedral, mostly, I think, and it didn't look much like an airplane that would do a decent pattern. I used it to qualify at my first NATs. Many builders are afraid of dihedral’s effects on flying characteristics. Some don't want to try building wings with dihedral, thinking them difficult to build accurately. As for the aerodynamics, there have been enough successful competition airplanes to demonstrate dihedral, properly used, has no ill effect on an airplane’s ability to fly a competitive pattern. It’s simply a matter of putting the leadouts in the proper location, the Vertical CG. Most low wing stunt ships would profit from a bit of dihedral, particularly the popular profile warbirds with low wings. As for difficulty in construction, there isn't any greater difficulty if the tube type jig is used. I used my tube type jig to build both straight wings, for Mustunts, and dihedraled wings. The only difference in building a dihedral wing is the jig tube holes go through the top of the center section ribs and through the bottom of the tip ribs. Actual construction of both is identical. I published the first tube type wing jigs in that Mustang article. I didn't like the only available jig at the time, the Ajusto Jig. I didn't think that Ajusto's 1/4" rods offered enough support to ribs. Also, I could buy aluminum tubes cheaply through Braniff’s company stock room. Many builders think jig tubes are superior for wing building, but, simple as tube type jigs are, their use has also improved over the years.
[photo not recovered: 425eaf7b384c345e.jpg] OK, Building wings with dihedral presents no problems with structure, but what about the flap horns? At first, I used double flap horns as being a compromise solution knowing that there would be some asymmetry at maximum control deflections. This solution would minimize friction in the control system. Later, I found that long flap horns could be "bowed" around the wing center section trailing edge. I was amazed to find that four low friction bearings could exert enough force on the wing trailing edge that the structure would have to be temporarily braced to keep the ribs from pulling loose. The temporary bracing could be removed when some of the sheeting was in place. There is very little difference in the friction of "loaded" bearings as opposed to unloaded straight horn bearings. The difference can't be felt in flight, and my flaps hang from their own weight like anyone else's. The trick here is not to bend the flap horn, just "bow" it. Flap horns "bent" to the shape of the wing trailing edge will have some "spring" in them, and will tend to move toward and remain in some position. I install "bowed" horns by sanding a bit of curve into the wing trailing edge to eliminate the sharp angle where the wing panels meet. Next, two bearings on one side of the horn are laced to the trailing edge with many wraps of thread. Then the other end of the horn is pulled into position with a little force and secured with wraps of thread. Once installed and lubricated, there is little difference in friction of the "bowed" and straight 3/32” horns. Sometimes, it is possible with dihedral or swept forward trailing edges to simply glue the horns into the flaps as though the dihedral or sweep doesn’t exist. I got away with this gluing 1/8” horn wires into the BBQB Bearcat flaps. When I tried this on the Millennium II flaps, they were “springy” on “down”. I fixed this by adding “lucky boxes” in the flaps to obtain smooth operation in full flap deflections up and down. My new Sanggletooth II has 3/32” “bowed“ flap horns.
The Mustang II had conventional fuselage construction with sheet sides and hollowed top and bottom blocks. This airplane is easy to build, but better alternatives exist.
BEARCAT II
The Bearcat II was published in the March 1970 issue of American Aircraft Modeler. The wing construction was identical to the Mustang II with dihedral, straight trailing edge and dual flap horns. The fuselage was conventional with sheet sides and hollowed blocks on the top and bottom. This article introduced the reversed bellcrank and sliding block adjustable leadouts. This airplane was easily to build, managed a second at the NATs, but better alternatives exist.
MUSTANG III
The Classic Mustang III was a 1969 design. It featured a much improved wing with an improved airfoil and swept forward wing trailing edge to trade wing area for flap area for increased lift without changing the apparent outline of the wing. The fuselage construction was conventional. The wing construction featured the "bowed" flap horn. When the Flap horn is "bowed" to accommodate dihedral, it will also accommodate trailing edge sweep with no difference in friction or change in installation. A bow in the horn is a bow in the horn, whether from dihedral or trailing edge sweep. No plans were published until 30 years later when I made a drawing intended to update the magazine plans. Now, this drawing for the Mustang III is available from PAMPA. These plans are actually updates for the magazine plans and, as such, are poor stand alone construction drawings. Still, the airplane is classic legal, attractive, and a good flying airplane. Bill Rutherford used his Mustang III to place third at the NATs. Mustang III wing kits are available from tanks-hangar.com. Mustang III canopys are available from
[email protected].
[photo not recovered: 425eafab38c03f4d.jpg]BEARCAT III
The classic Bearcat III was also a 1969 design. It featured light weight construction with a molded balsa fuselage and an improved wing similar to the Mustang III. It had dihedral, swept forward trailing edge, improved airfoil and the now familiar "bowed" flap horn. It was also an update of a published airplane, the Bearcat II. As I built, parts were traced onto the plans update. As a result, the Bearcat III drawings available from PAMPA are helpful but not truly construction drawings either. With some demand for laser cut parts, I had Kyle put the Bearcat III wing into his computer. Later, in response to request, Kyle copied the Bearcat III drawings and incorporated BBQB longerons, engine installation and jig building of the fuselage. He also molds full length fuselage shells from my molds and sells them. This isn't a completely successful package as there are conflicts between the assembly of the Bearcat III and BBQB. Still, with a bit of determination, and thoughtful resolution of apparent conflicts, the lightweight Bearcat III can be duplicated. Fuselage parts fit. It’s just a little difficult to decide what to do with them. For now the construction is a bit of a mixed bag but the airplane flies well. Keith trostle just won Classic at VSC flying a Bearcat. Maybe I can get together with Kyle and fix the fuselage. If we update the Bearcat III, it will then include eight segment shells. With eight segment shells, the airplane will build much like the BBQB. BBQB videos would then be a big help in building the Bearcat III. These segmented shells will cost more due to the extra labor, but they'll be worth it. Canopys are available from
[email protected].
[photo not recovered: 425eafda3d724dd7.jpg]MUSTANG V, VI, VII (Snaggletooth)
The molded Mustangs were a no holds bared attempt to build a World Championship airplane. It was a near miss. Snaggletooth only managed a second place in the World Championship, but it did win the 1977 NATs and Walker Trophy. Molded Mustangs featured many changes from the airplanes which preceded it. In general, they had; molded fuselages, built up control surfaces with a spruce I-beam stab spars, Dihedral, swept forward wing trailing edges, a still further improved airfoil, internal mufflers, stab incidence, "canted" tanks, “canted engines”, "reverse asymmetry" and shock gears. Does this make it nearly impossible to duplicate? Not really, Last year I updated the Snaggletooth design with laser cutting, provisions for larger engines, removable tank, and mold forms for easier mold construction. I drew new plans, revised and updated the structure, made building/assembly videos and worked with Kyle to get parts into the computer for laser cutting. There was a lot of effort expended to make Snaggletooth easily buildable. John Hill built nine of these Mustangs before laser cutting. Now he is working on a new Mustang utilizing both laser cut parts and modifications from years of building these airplanes.
[photo not recovered: 425ec0030e5d37ed.jpg]Ok, but how hard is it to build? Actually, it is very straight forward but involves making of molds and the use of many new and different building technologies. The molds are easy to make using mold forms included in the Snaggletooth kit. The plywood mold forms are visable in the photo above. They are simply filled with “drywall compound” (plaster) and shaped with a “Stanley Sureform” plane from Home Depot. Drywall compound cuts easier, and sands better than balsa. The fuselage is assembled in supplied jig pockets. Bulkheads are laminated balsa and plywood. The wing is assembled on a tube type jig and is straight forward except for the application of sheeting. The tail surfaces are airfoiled and built with spruce I-beam spars. The laser cut kit supplies most of the parts and is fairly complete down to the included gear doors. The construction is time consuming but easy enough if the Sanggletooth videos are used for reference. Without the videos, it would be difficult to even recognize the function of about a third of the parts. I think the videos are necessary to successfully build the airplane. I'm not nearly as interested in selling videos as in making sure that all of the necessary information necessary to build a competitive airplane is available. Perhaps several builders could pool their resources and share videos. Kyle sells the parts and offers molded leading edges. We had considered including foam leading edge molds with the laser cut parts, but decided it would be easier and cheaper to just offer the molded leading edges finished.
[email protected] sells canopys. Plans are only available with the videos. The plans can’t cover the many unusual details of the construction and would be considered incomplete without the videos.
[photo not recovered: 425eaffb3dc6a0cf.jpg]BBQB/BBFB BEARCAT
The big molded Bearcats are also reasonably easy to build, IF videos, laser cut parts, and molded parts are used. In fact, with all of the components above, the aircraft’s primary structure can be assembled in about 40 hours. With laser cut and molded parts, the fuselage and fuselage jigs can be assembled in about 9 hours. The wing construction is fairly conventional using molded leading edge, tube type jig, BBQB bellcrank mount, and sheeting of .077 balsa. The airfoiled tail surfaces are easily built taking only about 4 hours for the entire set. If your think the videos unnecessary, take a look at the accompanying photos.
[photo not recovered: 425eb02b3e5e45da.jpg]OK, with parts, both molded and laser cut, construction isn’t difficult but there is a lot of it. Regardless of how fast the basic structure goes together, it takes months of occasional building before a BBQB/BBFB is ready for paint. The BBFB refers to faster build and the availability of three engine mounting configurations. The Bearcat now can be built for a Saito .91, a Saito .72, or any of the larger PA and Ro-Jett engines from .61 to .76. The structure of the fuselage and the assembly of the fuselage to the wing has been updated, and videos, as appropriate, have been remade.
[photo not recovered: 425eb0483e97d1c7.jpg]The biggest fly in the ointment is the molded fuselage shells. The BBQB/BBFBs are designed to be assembled about the lower fuselage longerons. The lower fuselage longeron is located on the wing leading and trailing edge centerlines, the flap trailing edge and the length of the removable cowling. Upper and lower, forward and rear, molded shells join on those longerons. The shells are molded in four pieces, then precision cut into upper and lower pieces for a total of eight shell segments. The shell segments are first trimmed of excess balsa which overlapped the mold backing. This requires a simple cutting tool. Next, the molds, with the shells attached, must be mounted vertically and longitudinally adjusted for cuts which will separate upper and lower segments of the front and rear shells at the center of the lower longeron. The front and rear shells are separated with another cutting tool. Shell segments are cut to length, by the builder, using marks left on the inside of the shells by staples driven into “A” and “D” mold bulkheads. Cutting tools and alignment jigs are necessary to the process of cutting the shells. Some builders have made their own molds and the tools to cut the shells, but, again, it is easier, and in the long run, cheaper just to get the eight segment shells from Kyle.
Kyle sells the laser cut parts, molded leading edges, and eight segment shell parts. Canopys are available from
[email protected]. Plans and videos are available from me. The plans are incomplete as build alone construction drawings, and must be complemented by the videos. Building a BBQB isn't cheap, but then, If we are honest, no stunt ship is. Some builders consider the videos as optional, but they are really necessary to the construction of a competition quality airplane. Also, they offer 34 hours of video entertainment while you build. Again, construction videos could be shared by a number of builders. The construction isn’t difficult but it takes awhile. The result is an excellent competition airplane, stunning in its realistic appearance and performance.
Attachment
#1, (jpg file)
Attachment
#2, (jpg file)
Attachment
#3, (jpg file)
Attachment
#4, (jpg file)
Attachment
#5, (jpg file)
Attachment
#6, (jpg file)
Attachment
#7, (jpg file)
Attachment
#8, (jpg file)
