Obstacle Takeoffs in Bonanzas and Barons
By Hank Canterbury
Should I use Vx or Vy? How about adding partial flaps? Although your Pilot’s Operating Handbook [POH] may not have a table for using flaps, it is permissible to use them if you desire. Please be sure to read the “Cautions” section below before you decide to climb out at Vx.
In the previous article, I discussed what to expect on takeoff by using “half” – or “approach” – flaps. We saw that if you had the flaps down, you should rotate about 6 knots sooner than without flaps. If you did so, you would likely see a decrease in roll of about 15-20%.
But what if there is a nearby obstacle beyond the end of the runway? Should you climb at Vx, the airspeed that theoretically gives you the most altitude gain for distance from start of climb? Or would Vy, the best rate of climb work better? How far beyond liftoff or start of roll can the obstacle be – and how high – before you should use Vx? Let’s see if we can get a better understanding of the choice.
Our performance charts give us some guidance by looking at the distance necessary after liftoff to climb to just 50 feet AGL. You may be surprised how much distance this requires. For example, here is a comparison of the two configurations in a climb to 50 feet.
The airspeed used for no flaps is higher than when using flaps. Note that in both cases, despite using two different climb speeds, an additional 1100 feet of distance is still required to reach 50 feet. Conclusion: the shorter total distance reaching that altitude is achieved by the shorter roll, not so much by the speed used in the initial climb. Before leaving this point, it should be noted that if the climb segment is longer because the obstacle is farther away, using Vy — best rate — will provide superior performance. Sustained climb rate at Vx is not as great as it is using Vy.
In his book “Flying the Beech Bonanza,” John Eckalbar compared two takeoff profiles, both using Vx airspeed after takeoff, but one with flaps at 20 degrees and the other flaps up. The result of his analysis was that if an obstacle is close to your takeoff point, then Vx may be appropriate in some circumstances. In John’s examples, both profiles cross the same altitude (320 feet) at about 3400 feet from start of roll.
I wrote an article several years ago comparing two aircraft under identical conditions except using different airspeeds – one using Vx airspeed and 20 degrees of flaps and the other using Vy airspeed with no flaps – seeking which procedure would be optimum. The conclusion was that using Vx provided only a small advantage if the obstacle was closer than 3,400 feet from start. Data above support the finding that the roll distance appears to account for the shorter distance to 50 feet.
If using a sustained longer climb segment is needed, the profiles reverse positions passing through 320 feet at about 3,400 feet after start of roll (Eckalbar). So, the deduction from the examples is that if the obstacle is at a greater distance, the superior Vy climb rate over more time / distance would likely be the best choice. On the other hand, using Vx would make a small difference only if the obstacle is higher than 50 feet and closer than about seven tenths of a mile from start of roll. Before you decide, see the “Cautions” section below.
Notice that in both cases 50 feet of altitude was attained at about a half-mile from start of roll. The Vx profile reached 50 feet in just a bit less distance due to a shorter roll and earlier start of climb, but the distance is small and may not be worth the added risk. Please note: these example distances are likely the most optimistic and attained by perfect execution. Your results may vary. Also keep in mind that these numbers are sensitive to density altitude and gross weight. If higher values exist, performance outcomes will be less by considerable amounts.
Technique
The procedure taught by Bonanza Pilot Training (BPT) is to use flaps for a “contaminated” runway, meaning rough, snow, debris or anything other than a smooth runway. The procedure follows closely the Airman Certification Standards [ACS] guidelines for a “Short Field Takeoff and Maximum Performance Climb” after liftoff.
For the second part — “Maximum Performance Climb After Liftoff”— if you decide to use the early climb procedure, we recommend that the plane be rotated to a pitch attitude that provides Vx for your current weight. This will be approximately 12-13 degrees.
Recall when using flaps, you must rotate sooner or you gain nothing. Leave the gear and flaps down and hold Vx until you are above the obstacle (or 50 feet above takeoff surface per ACS), simulating a real obstacle that’s close to beginning of roll. Upon reaching your target altitude, lower the pitch and begin to accelerate to Vy (best rate approximately 10 degrees pitch attitude).
While holding that attitude, retract the gear first. Then, when you have a minimum of 85 mph or 80 knots, raise the flaps. Raising them sooner will result in decreasing climb rate to near zero or even a sink, depending on density altitude, weight and whatever excess power is available for climb.
Once Vy is attained (110 mph/96 kts), hold that speed as you climb to pattern attitude or above before reducing power to cruise climb. Modern engines are certified for maximum continuous power: full throttle and maximum rpm. Some turbo installations may require a reduction of power after a period of time: see your POH.
CAUTIONS:
Before using Vx for your climb at reduced airspeed and steeper pitch angle than what you normally do, consider that it places you is a very precarious flight condition should this be a “bad hair day,” and your engine suddenly quits. Example: An A36 near full gross weight has a power off stall speed of 64 kts with flaps up or 55 kts with flaps full down. Vx with flaps is 77 kts at pitch attitude of 12+ degrees. A total power loss at this steeper climb angle, lower airspeed, and very low altitude requires that you decrease the pitch immediately to prevent a stall. Even so, a very significant sink rate develops.
Additionally, the “startle factor” delay of 3-5 seconds before you react will result in even greater loss of airspeed / energy. Below about 300 feet agl, the abrupt and very high sink rate cannot be arrested before reaching Mother Earth. During any climb immediately after takeoff — when the engine goes on vacation — do quickly get the nose down below the horizon or your airspeed will disappear from sight. An old fighter pilot friend I knew who told stories about dog fighting using lots of Gs and steadily losing energy, would say, “There I was with nothing showing on the airspeed indicator but the maker’s name.”
At this critically low altitude, you’re not trying to gain best glide speed; rather, you’re trying to preserve what you have. You won’t have time to ponder the situation before taking precise actions. Your response must be immediate and without hesitation to maintain some control (i.e., no stall). Nevertheless, you are going to impact the ground at a very high descent rate and probably won’t be able to use this plane again that day.
As I have attempted to point out, the marginal gain in performance may not be worth the considerably increased risk at low altitude during the initial climb segment. Other choices could reduce your risk such as lower gross weight, delaying departure until cooler temperatures, selecting another runway or even evaluating performance using a downwind departure without an obstacle.
Only regular practice of situations like this – with more altitude for safety – can improve your performance, making response automatic, should it ever become necessary.
As always, I am interested in hearing your thoughts.
Until next time: Fly Often – Train Regularly!
Hank Canterbury,
ATP, CFII, SEL and MEI