As the picture above shows, the ailerons on the King Air 200- and 300-series models include a pronounced lump on their trailing edges. The official name for the lump is “Trailing Edge Bulge” but, to me, they are simply “lumps.” The ailerons on other King Air models don’t have the lump. Presenting the reason why the 200- and 300-series have it and the other models do not is the purpose of this month’s article.
The straight 65-90 King Air, as well as the A90 models, have ailerons that are hinged at their leading edges. Beginning with the B90 model in 1968, a wingtip extension was added. This longer wing needed more aileron authority and Beech addressed this need by building an aileron with more chord. Also, the hinge point was relocated. Instead of the hinge being fully forward at the leading edge, it was now moved back slightly. To be more accurate, the hinge actually stayed in the same place but the aileron’s extra chord was installed in front of the hinge. With this design, as the trailing edge of the aileron goes down, the leading edge goes up. This type of control service is referred to as being “balanced” and less force is required to rotate the control wheel.
The balanced ailerons that first appeared on the B90 made a huge improvement in roll authority and overall aircraft handling. Although the models 90 and A90 handled well, they feel “truck-like” when compared to the B90 and later King Air models. It feels like the newer airplanes have power steering and the handling qualities went from “OK” to “Wow!” The 100-series and F90-series reverted to the shorter wingtip extension and therefore have the same wingspan as the 90 and A90. However, the balanced aileron was now installed and the handling quality remained excellent.
Have you learned yet that the wing on a Bonanza and on a King Air not only have the same NACA Airfoil shape but they are the exact same size?! For as long as most of us have been pilots Beech has used two different wingtip extensions. This is the piece that is outboard of the aileron, outboard of the main and rear wing spars. The shorter one is what’s found on almost all Bonanza models, except the B36TC. That particular Bonanza model, as well as all of the Baron series, use the longer extension so as to reduce wing loading. Go to a crowded hangar with a tape measure. Isn’t it mind-blowing that the Baron’s wingtip is the identical size to most King Air wingtips? Now, of course, the fuel tanks, spar strength and attach fittings vary but the wing on the King Air outboard of the nacelle and the entire wing on a Bonanza are indeed the same size, give or take whether they have the shorter or longer wingtip extension.
When the model 200 prototype (serial number BB-1) made its first flight in October 1972, it had the longest wing yet found on a King Air. The wing’s center section – the part that goes through the fuselage and contains the main landing gear wheel wells and the engine mounts – was widened by 50 inches, 25 inches per side. The larger three-blade propeller that the 200 used to absorb its additional power would have hit the nose of the fuselage if the center section were not widened. For the purpose of making the cabin quieter – by moving the prop tips further away – the center section was widened more than the minimum distance required to fit the propeller. The wing outboard of the center section, as you have now read, was the “standard” Beech design with the longer tip and the balanced ailerons.
During the flight test program, it was discovered that the roll control was a tad weak; the longer wing was a little too much for the ailerons to properly control. The designers came up with a clever and effective solution: a portion of the wingtip extension’s trailing edge was cut away and a new, longer aileron was installed. Although all previous ailerons had two hinge points, a third hinge point was added on this new aileron with its longer span.
Well, the test pilots discovered a “good news, bad news” situation. The good news was that the airplane now had excellent aileron authority. The bad news was that the aileron lost much of its natural centering tendency. When the pilot took his hands off the control wheel with the ailerons well-deflected, the wheel did not automatically center as much as they desired. Back to the drafting boards the engineers went.
Being the first instructor at the factory on the 200 model, I was privileged to get to know a few people on the design team including the chief project engineer, Leroy Clay. Leroy walked me around BB-1 as it neared the end of the experimental flight test role, to show the changes that were made and which I may want to explain to our students. That’s when I first saw and heard about the lump.
Mr. Clay used the comparison of the lump being like the feathers on the tail end of an arrow, always helping to streamline the projectile and keep the pointy end forward. With the lump, the ailerons exhibited the proper amount of centering tendency. Here’s a chuckle for you: Leroy went on to say that adding the lump to the trailing edge of the existing aileron was a “temporary fix” but that a totally new aileron would be designed and available soon. Well, let’s see … 1972 to 2022 – 50 years and we’re still waiting for that new aileron. The latest models, the 260s and 360s coming off the Wichita production line still have the lumps. But, wow, do they handle nicely!
Now let’s talk about the rudder on the T-tailed King Airs. I have never experienced this phenomenon personally in all of the model 200 flying and instructing that I have done. But the T-tail’s rudder is susceptible to “rudder lock.” When Beech was conducting the severe yaw tests required for FAA certification, they found that a certain configuration of power, rudder displacement and horribly uncoordinated flight would result in the rudder remaining fully deflected after the rudder pedals were released. All it took was a minor push on the “back” pedal to return to normal, so this was never viewed as being unsafe, but merely a slight handling anomaly. It also played a minor role in autopilot/yaw damper certification.
When the model 300 was being developed, and with the rudder lock phenomenon well known, Beech decided to “fix” it. How? By adding another centering lump, this time on the trailing edge of a portion of the rudder. This was/is also supplied on all B300s, known as the 350- and 360-series.
Now when you get the rare question about the lumps on the ailerons and rudder, you will have the correct answer to give. I know that you will continue to enjoy the fine handling qualities of these lumpy King Airs!