Source: 2021 Q2 Beartracks Jared Yates
Last quarter we included a few responses from Bearhawk operators about how they prefer to manage their engines in cruise, and what speed they use on final approach. Here are a few more responses. Bobby Stokes in Arizona has flown around 320 hours in 3 years, and while his mission is varied, most flights seem to involve going places. He aims for 70 knots on final, slowing over the fence depending on the runway length. With 31” tires he gets 115 knots TAS at 8.5 gph, which is a loss of 10 knots compared to the 8.50 tires.
Dave Roberts in Montana has flown 930 hours since 2007. While he does takes some cross country trips, his primary mission is agricultural. He uses different speeds on final approach depending on the engine usage. At idle thrust, his target is 52 knots which leaves some margin for higher density altitude, but not below 46 knots. With a little power, he’ll use 42-43 knots, and notes, “Probably one of the most important things is to be aware of sinking. Not a problem to correct, just be aware. Especially at higher density altitude.” In cruise, he uses 1970 rpm and 22” MAP. That yields 112-109 knots at 9.5 to 10 gph. He says, “This is with a low compression 540. I’m in the process of putting 8.5 compression pistons in it now. It will go faster, but with the Bushwheels it really likes fuel when trying to push it over 113 knots.” At 2450 and 24.5 inches, he gets 130 knots at 15gph. At 2140rpm and 23.7 inches, 120 knots at 13.2 gph.
I’ve converted everyone’s answers to knots and gallons per hour to try and make it a little easier to compare, and also made some charts. Keep in mind that these data points are coming from a wide variety of engine sizes, a wide variety of tire sizes, and a wide variety of missions. Yet, there is certainly some centering. Take these values not as “the best the plane can do”, but rather as the “happy place” where operators have found good harmony and economy.
I think it’s noteworthy that none of these points is outside the realm of what an O-360 could do. We don’t seem to be selecting our engine displacement for cruise, but rather for the takeoff roll and the climb rate. I’m sure there are exceptions to this idea, and I’d love to follow up on this topic again with twice as many responses. The O-360 is the engine that the Bearhawk was designed around, which also speaks to Bob’s excellence in selecting that engine for the airframe, when it comes to cruise, drag, and economy. As we would expect, the data points do show a slight trend moving to the right as they move up, which relates increased speed to increased fuel burn. The noise in that sample comes from factors like tire size differences, and collection accuracy.
B. H. Carson (which I highly doubt is an abbreviation for “Bearhawk Carson”) has written about economy in our type of airplanes. Increasing speed above best glide speed leads to an increase in waste, but his point was that there is a method of operation which represents the least wasteful way of wasting fuel. Vastly over-simplifying his work, we can get to that point by multiplying best glide speed by 1.316. Without considering wind and speaking in round numbers, I found in our airplane that the Carson speed at 1700 pounds gross weight was 80 knots, and at 2500 pounds, 97 knots. If you are flying without somewhere to be, those are handy numbers to keep in the back of your mind as you decide how to manage the engine.
As for final approach speeds, my favorite answers were that we are looking outside of the airplane to decide how to fly it, at least from the fence inbound. Energy management on final is crucial to keeping enough energy to flare, but not excess energy that we must lose in a float. Experienced Bearhawk pilots aren’t staring at the airspeed indicator, but that doesn’t mean they haven’t mastered energy management. We are setting up a good pattern and stable approach at a good speed, and validating our visual cues with either indicated airspeed or AOA. For the last few seconds, it’s a matter of managing the elevator to execute the best kind of landing for the runway surface.
The chart below to the left shows the distribution of speeds, with the average being around 56 knots. It’s worth noting that the curve is pretty wide and flat, meaning there’s a fairly wide range of speeds for the paltry sample size that we have. The chart below and to the right shows the fuel burn vs cruise speeds.