A Part 91 operator in Texas offers a performance report since upgrading to MT-Propeller’s 7-blade Whisper Prop system.
In April, King Air magazine highlighted that MT-Propeller Entwicklung GmbH received supplemental type certificate approval for the 7-blade Whisper Prop system on King Air 300 series aircraft. The upgrade is distributed by BLR Aerospace LLC, and as the name implies, it is marketed as the quietest propeller option for this model of King Air.
As a reminder, the advantages advertised with the new propeller system include:
- General performance improvement (8% takeoff & climb)
- No propeller speed restrictions on ground while operating in low idle
- Lower ITTs at high altitude, allowing a top speed increase up to 6 KTAS or longer engine life
- Aesthetic ramp appeal
- Significant cabin noise and vibration reduction
- More ground clearance for less blade tip erosion and FODs due to a smaller diameter
- Nickel-cobalt leading-edge blade protection for superior resistance to erosion and damage
- No life limitation; they are repairable in case of FOD
A Part 91 operator based in Texas believes they are the first to install the upgrade, having had the propellers swapped on their King Air 350 in June. The company’s aviation department manager and chief pilot, who is a former American Airlines captain, advised that this is not the first King Air propeller upgrade the company has pursued.
“We previously operated a King Air E90, which had the 3-blade props and was the first airplane that the corporation ever had. While it was a nice airplane, it was loud and there was lots of vibration from the props,” he said. “Over a period of a couple of years, I told the boss [company’s CEO] that there was an option to make this a much more comfortable ride. There is a company out of Germany that makes composite, no vibration props with an interesting aerodynamic design. They’re very quiet and I think it would be worth our money if we are going to keep this airplane for a while.”
The board of directors OK’d the upgrade, understanding it would improve flights for the company’s pilots and personnel flying in the back. The operator reports a 7.5 to 8.5 decibel noise reduction, depending on where you are in the aircraft during cruise. The vibration was nearly eliminated.
A few years later, the E90 was replaced with a late-year, low-time King Air 350 that offered additional seating and increased performance. While this operator has requested to provide feedback anonymously to protect their corporate identity, they are excited to share with others what they’ve experienced with the 7-blade upgrade.
“Just like I had before, I told the CEO that we have a couple of options to make this a better airplane,” the chief pilot explained. “BLR Aerospace had the 5-blade propellers approved for the King Air 350, like they had for our last King Air. And they just came out – they’re brand spanking new – with a 7-blade model of the same prop. I think they are going to be even quieter than the 5-blade model in terms of noise reduction, and they’re claiming better acceleration and a better climb.”
While they’ve only had a few flights since upgrading to the 7-blade option, the operator said they are pleased so far.
“We picked up the airplane after the props were installed and did some testing of it before flying back home. The acceleration was noticeably greater than our old 4-blade props,” he said. “We got to V1 and I pulled the power back to idle, and the aerodynamic braking from the 7-blade props stopped the airplane – without using any brakes. So, we did that a couple of times and then we took off down the runway for a takeoff. It was like flying a jet instead of a turboprop. The initial climb was amazing.”
Since the new propellers were not used in the original FAA certification of the King Air 350, the performance improvement can’t be used for flight planning and the improvements are not quantified on any performance charts. But it does give this operator additional comfort knowing that the aircraft is more capable than they plan for in their missions.
“We measured the noise, and it was not as much of a difference as I expected it to be,” the pilot said. “It was about 2 to 2.5 decibels in the cockpit and immediately behind the cockpit, less than the 4-blade props. But the frequency of the noise was different, and we can converse in normal tones with our headsets off. I told my colleague that we are going to have to be careful because they are going to be able to hear what we say back in the cabin.”
Preliminary reports from passengers agree with the newfound quietness, as well as a reduction in overall airframe vibration. “Uncannily smooth” was how the flight has been described. The aviation department manager doesn’t explicitly state whether the approximately $250,000 upgrade has been worth it, as they are awaiting the final verdict from all team members. But the consensus is that the reduction in cabin noise and vibration will be appreciated by those in the cockpit and the cabin.
One downside to the new props is a possible reduction in cruise speed. This operator notes a minimal difference of 2 to 3 knots in their King Air 350. The reduction was as high as 5 to 7 knots from previous cruise speeds in the E90, though.
