Bell Helicopter recently issued new information letters expressing concern about BLR Aerospace tailboom strakes. Bell issued a similar letter in 1995 when BLR obtained certification for use of tailboom strakes on Bell’s line of medium helicopters. The recent letters warn Bell 206 operators that “the monocoque tailboom structure of the 206A/B and 206L series helicopters was not engineered to accommodate the attachment of extraneous items like strakes, nor for the additional loads these strakes may impose on the structure.”
The FAA granted BLR a supplemental type certificate for dual tailboom strakes for the Bell 206 JetRanger on February 8 and amended it on June 30 to add the 206L LongRanger.
A Bell spokesman told AIN that while “Bell does not take exception to the FAA certification process,” the information letter “clarifies Bell’s position after numerous questions from our customer base. This in no way implies or says that the FAA processes are deficient.”
Nevertheless, Bell Information Letter 206-06-93 warns operators that “since the aircraft was not designed for such a use, operation with these strakes is outside the operational flight envelope tested for and developed by Bell. As a result, there is, at least in Bell’s opinion, a lack of fatigue data and maintenance or overhaul schedules for any mission other than that for which the aircraft was designed or delivered.
Operating the aircraft with these strakes in place could result in unknown and undefined maintenance and inspection requirement and, ultimately, render the procedures, retirement lives and so on contained in the Bell manuals inapplicable.”
Long-term Consequences Unknown
Installation of the strakes could also affect warranties, the Bell spokesman warned. “The installation of any product that is not approved by Bell can have the potential of invalidating the Bell warranty. Bell stands behind the genuine Bell parts but does not offer warranty on vendor- or STC-manufactured or -installed components.”
The information letters were not the result of specific problems with the BLR strakes, according to the spokesman, but Bell remains concerned that BLR would design and certify a performance-enhancing product without Bell’s blessing.
“Bell Helicopter is not aware of any problems with the 206-series helicopters,” the spokesman stated. “The vendor, BLR, on its own motives designed and received FAA certification on its STC without consultation with Bell Helicopter. We are not aware of the stimulus for that action. We understand that the STC has been in only limited service for approximately 18 months, which may or may not be sufficient to evaluate any long-term difficulties.”
BLR customers have not reported any problems in the past 18 months, explained Dave Marone, BLR director of sales and marketing. During the certification process, BLR performed a strain survey on the strake-equipped tailboom, which showed that “strain levels were less than or equal to those for the baseline aircraft,” Marone said.
The resulting data allowed BLR to STC the strake installation without requiring changes in tailboom or tailfin component inspection intervals or part life limits. “BLR customers,” he said, “do report improved handling qualities and increased tail-rotor authority, resulting in safer and more productive operations. BLR will continue its program of regularly monitoring the fleet of strake-equipped 206-series aircraft to respond proactively to any possible safety issues arising from the installation of BLR tailboom strakes.”
In 1993, NASA and the U.S. Army studied the effects of tailboom strakes in various configurations (NASA Technical Paper 3278, Flight Investigation of the Effect of Tailboom Strakes on Helicopter Directional Control). According to the study, the strakes help separate airflow over the tailboom, resulting in improved yaw control margins and thus reduced tail-rotor power requirements.
“At the most critical wind azimuth and airspeed in terms of tail-rotor power,” the study noted, “the strakes improved the pedal margin by 6 percent of total travel and
reduced tailrotor power required by 17 percent.” The ultimate benefit of this improved yaw control and reduction in tail-rotor power required is the ability to increase maximum weight and altitude capability.
JBI Helicopters, based in Pembroke, N.H., operates five 206 Jet-Rangers that have the BLR strakes installed. “I absolutely love the strakes,” said Ray Newcomb, president. “They give at least a 5- to 10-percent reduction in tail-rotor thrust requirements” and make the helicopter “a lot more stable in hover and out-of-ground-effect hover. It’s probably the single best product improvement aerodynamically to the 206 product line in years.”
Newcomb has seen the Bell information letter and understands why Bell issued it. “Bell still has product liability [issues] it has to be concerned with,” he said.
“I think Bell engineering..., it hasn’t reviewed it.” Because of the performance improvement and the reduction in power needed at the tail rotor, Newcomb feels sure that Bell will eventually consider installation of tailboom strakes. “It would solve lots of loss-of-tailrotor-effectiveness issues you have with any tail rotor,” Newcomb concluded.