The private pilot departed with two passengers for a personal, local flight in a Wheeler Express amateur-built airplane. Air traffic control data indicate that, after departing the airport, the airplane climbed and performed several maneuvers.
A review of onboard flight data revealed that the airplane then maneuvered into a nose-high attitude while in a steep, right turn. As the airspeed decelerated below stall speed and the turn steepened, the airplane pitched nose down and entered a prolonged, right-turning spin until hitting the ground near in Holland, Minn. All three souls aboard were killed.
Examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
Previous flight testing of a Wheeler Express kit airplane similar to the accident airplane revealed that it had poor yaw stability at low airspeed due to the aerodynamic design of the tail section. The testing also revealed that, during post-stall and high-yaw maneuvering, the horizontal tail and elevators appeared to have an inadequate effect.
Following bankruptcy of the original kit manufacturer, a variant of the Wheeler Express kit airplane was developed using the same wing and fuselage as the accident model, but with a larger tail that had 40% more wetted area to provide additional yaw stability at low airspeed.
Probable cause: The pilot’s failure to maintain adequate airspeed during a high-pitch, steep right turn, which resulted in the exceedance of the airplane’s critical angle-of-attack and a subsequent aerodynamic stall, loss of control, and impact with terrain. Contributing to the accident was the airplane’s design, which resulted in poor yaw stability at low airspeed.
NTSB Identification: CEN15FA321
This July 2015 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
I have 1100 hours on my Wheeler Express and if you try a steep turn at low speed what do you expect. Most if not all of these accidents were the lack of proficiency of the pilots involved!!
Lou Lacy
Express Owner
You need not be an owner to understand the concept of steep turn at low speed at low agl.
This is all that matters:
A review of onboard flight data revealed that the airplane then maneuvered into a nose-high attitude while in a steep, right turn. As the airspeed decelerated below stall speed and the turn steepened, the airplane pitched nose down and entered a prolonged, right-turning spin until hitting the ground near in Holland, Minn. All three souls aboard were killed.
Hello Louie
We finissez construction ô four Wheeler express CT we are Proceed test flight shortly what advice can y ou give us for assess correctly the plane
Tkank for share your great expérience
Jacques Faure / Jacques Larouche
Pilots from Québec Canada ??
Was there any flight test data related to spins even though the category may have prohibited intentional spins? Yaw Stability is a misnomer. The correct term is “Directional Stability.” One wonders if this pilot had ever seen a spin (absolutely essential for any private pilot) or was familiar with the “standard” recovery technique applicable to the vast majority of GA airplanes, i.e. neutral or nose down pitch and neutral roll control with full opposite rudder to the direction of the spin (always indicated correctly by turn needle or turn coordinator regardless if upright or inverted). Depending on the altitude at which the spin was entered the weak directional control could still have been enough to stop the rotation and recover from the dive.
Take a look at the NTSB Docket for this accident. In addition to the CAFE Report authored by two test pilots who flew the prototype, the Docket includes both ATC and onboard data about the flight, including very specific information about the last three minutes. The aircraft appears to have entered the uncommanded spin at over 5,000′, and was in the final maneuver for “a prolonged period”. I didn’t see any information in the Docket about the pilot’s experience or quals. Among the facts presented in the Docket is a history of the early models of this aircraft of having insufficient tail authority to reliably escape a spin. The CAFE report mentions that the fuselage shape did not contribute to directional stability (i.e. ‘yaw stability’). Evidently later models of the kit had significantly larger rudders and therefore greater control authority at the margins of the envelope. One might argue that loading the aircraft with three persons and then performing maneuvers close to the envelope edge might be a poor idea. This is a very interesting accident report and Docket.
Not mentioned in the article, but three passengers and unknown baggage, what was the CG? In a stall, the pitch attitude should have reduced the AOA and recovery from the spin and stall should have been possible.
Depending on aircraft configuration and design, a stall could blank air flow over the rudder and elevator.
Your final sentence notes the potential for the tail to authority to be affected by blanked air flow. That’s one of the design flaws discussed by the NTSB in their final report, and by documents in the docket. Another is the pronounced tendency for the aircraft to experience uncommanded yaw at high AOA in some configurations. The NTSB Docket includes an a performance report published by the CAFE Board that discuses these and other “problem areas” identified in flight testing. The test pilot also recommeded addtional flight testing.