I received the following question and thought the answer would be of interest to King Air magazine readers.
I was wondering if you could elucidate a bit upon the thinking behind Beech going to a T-tail on the King Air 200. If I remember correctly, the 100 series had a conventional tail. So what were Beech’s reasons for going to the T-tail on the BE200? What are the advantages and disadvantages of the T-tail?
I am glad this question was asked because not many pilots know the reason for the T-tail design.
The 100-series tail was the same tail first used on the Beech 99, the 15-seat, unpressurized, commuter airliner. When the cabin was stretched as much as it was—making a turbine-powered Queen Air into a 99—the prototype flew with much the same tail as on the 90 series, using fixed horizontal stabilizers and elevators with trim tabs. Alas, they could not achieve a long enough center of gravity (CG) range to suit the longer airplane with that system. So, the Beech engineers went back to the drawing boards to come up with a solution.
In the resulting design, the elevators have no trim tabs and, instead, the whole horizontal stabilizer pivots near the rear and an electrically-driven jackscrew moves the leading edge up and down. It is like a Piper Cub or Cessna 180, but without any manual system, only an electric Main and Standby system, with a clutch arrangement to allow either to work should the other jam.
When you next see a 100, A100 or B100 on a ramp, notice the huge span of the stabilizer—it is one massive tail! In fact, do you realize that the top of the 100’s vertical stabilizer is a few inches higher than the top of a 200-, 300- or F90-series T-tail? Surprising but true.
Next came the 200, which had the same fuselage/cabin as the 100 but with 850 shp per side (versus 680 shp for the 100/A100) and the centerline of the engine moved 25 inches outboard. The appropriate propeller to handle the higher horsepower had enough additional diameter to hit the fuselage if the existing 90/100 center section was used and the tip clearance with the ground was too small. So, if Beech had to move the engine both outward and upward, the decision was made to really move it out—much more than the minimum requirement—to give extra clearance between the prop arc and the fuselage, making the cabin quieter.
They designed a new engine mount that holds the engine at four instead of three locations, lifts it 4 inches higher and has a new, more efficient ram air recovery design. The larger center section would provide more fuel capacity there to satisfy the bigger, thirstier PT6s used on the 200. Hmm, 170 more shp sitting 25 inches further outboard. Keeping Vmca down was going to be a challenge!
So off to the drawing boards and wind tunnel they go, experimenting with different tail configurations to find the one that would keep Vmca down where they wanted it. The conventional 100 tail wouldn’t hack it, and it was found that at the high angles-of-attack (AOA) associated with Vmca, the position of the horizontal tail was blocking much of the airflow up to the bottom portion of the rudder.
At that time, Beech had an agreement with Hawker that involved flying “green” airplanes from England to Wichita (with a portable avionics package, but no paint, options or interior) and Beech had the exclusive rights to finish them and handle all sales and marketing in North America. Based on their Hawker familiarity, they considered a cruciform tail, in which the horizontal stabilizer is about halfway up the vertical stabilizer. The only T-tailed civilian airplanes at that time were the Boeing 727 and the Learjet (long before the Learjet was “tamed” with Delta Fins and wing improvements), and both had horrible stall characteristics. It was with reluctance that Beech considered the T-tail, fearing that the dreaded deep stall would follow.
Nevertheless, the computer/slide rule studies, as well as the wind tunnel tests, showed that the T-tail was best in maximizing rudder force. Not only did the new position of the horizontal surface not block the airflow to the rudder at high AOAs, but it also provided an endplate effect that captured the air and prevented it from spilling off the top of the rudder, thereby making the rudder even more effective. In one sentence, the T-tail design was chosen because it maximized rudder effectiveness and kept Vmca at a reasonable value.
The prototype 200, BB-1, first flew in October 1972 and onboard were a stick shaker/pusher and a rudder boost system. It also had no “bullet” on the T-tail and the ailerons and wing tips were identical to the B90/C90/E90. An airflow interference problem showed up at the vertical/horizontal tail junction and was solved with the bullet. Aileron effectiveness at slow speeds was found to be waning, and hence the wing tip was cut so that the aileron could extend to the very end of the wing. This involved a third hinge point as well as the infamous trailing edge lump. Why the lump? To provide more self-centering tendency when this bigger, balanced aileron was fully deflected.
With great trepidation, the stall tests were initiated. Fearing what might be found, the test airplane had the standard tail cone replaced with one that housed an explosively deployed drag chute. As the stall series progressed, moving from forward to aft CG, lead test pilot Bud Francis found that everything was quite conventional. Although the burble from the wing missed hitting the high horizontal tail such that there was very little pre-stall buffet—making the stall horn a requirement—every time the stall break occurred, the nose dropped at its own accord. But as the CG finally reached the aft limit, Bud related that not only did the nose not automatically drop at the stall break but it pitched up about 10 degrees higher! “Thank goodness for the chute!” he said silently.
But, voila! When he pushed the wheel forward, the nose came down and recovery was easy. This led to a statement made in the “Associated Conditions” portion of the Stall Speed chart that carries more significance than most readers realize. It goes something like this: “A normal stall recovery technique may be used. The best procedure is a brisk forward motion of the control wheel to a full nose down position. Recovery should be initiated when airspeed has increased approximately 20 knots above stall speed.” So the shaker and pusher went away, found not to be required.
It was thought that this new big rudder might well require more than 150 pounds—the FAA maximum allowable—to fully deflect, and hence the installation of the rudder boost system on the prototypes. The final tests showed the actual worst-case force to be 147 pounds, so the rudder boost also could be eliminated. However, it was retained as standard equipment since Beechcraft airplanes are supposed to be the “Cadillacs of the Air” and who wanted to apply that much force anyway? However, the MMEL (master minimum equipment list) allows operation without a rudder boost in the 200 series. (Not in the 300 series, where the maximum force can reach about 180 pounds.)
A few other benefits were found to follow the T-tail. First, there was much less pitch trim involved when the flap position was altered since the changed airflow from the wing mostly missed the tail. Second, the airplane was smoother in flight and during ground run-ups since the prop wash wasn’t hitting the tail. Lastly, and perhaps most beneficial, by moving the horizontal stabilizer up it was also being moved aft due to the sweep of the vertical tail, which led to a longer moment arm to the elevators. Now, with a much smaller horizontal surface than on the 100, they could revert to simple conventional trim tabs on the elevators and achieve a 4-inch greater CG range for the same cabin dimensions! Amazing!
That pitch up at the stall break is something I have never experienced since all flight training is usually with a fairly forward CG since we’re not carrying a lot of passengers during the training. It is exceedingly easy for that tail to create so much downforce even near stall that getting a secondary stall during recovery is quite common.
That explains the wording about
“…when 20 knots above…” in that Stall Chart paragraph I quoted earlier. When I received my first instruction in BB-1 from Bud, he had me trim for 1.3 times clean stall speed, then ease into a non-accelerated stall and note at what speed the break occurred (about 100 KIAS). Then, we dropped the nose to pick up speed until we hit 120, then 130, then 140, all the way up to 160. At each of those speeds, with only my little fingers wrapped around the control wheel as Bud instructed, we were able to easily induce stall rumble in all cases by pulling back aggressively! That airplane has some powerful elevators!
Beech was so enamored with the success of the 200’s T-tail that the initial thinking was, “Well, heck, let’s do this across the board!” They put a T-tail on an experimental flight test version of the A36 Bonanza and didn’t like it at all! It must have been a little like the short-lived T-tailed Piper Lance that not many pilots enjoyed. So with the exception of the long out-of-production F90, the only Beechcraft airplanes with T-tails are the direct descendants of the Super King Air 200.
Editor’s note: King Air first published this column in 2011.