Preparatory Ground Instruction for Power-off Stalls with Power-off Recovery
- Preparatory Ground Instruction for Power-off Stalls with Power-off Recovery
In preparing this PGI, it is important to note that this is the first in a series of three PGIs on the stall sequence, beginning with basic stalls using power-off entry and power-off recovery, progressing through the intermediate stalls involving a power-off entry and power-on recovery, and ending with the advanced stalls requiring a power-on entry and power-on recovery. The words basic, intermediate, and advance, are used somewhat arbitrarily here, simply for the purpose of delineating the lesson plan structure pertaining to stalls in a Flight Instructor Manual. As experienced flight instructors know, there are actually a tremendous variety of both basic intermediate and advanced stalls. In accordance with the Flight Instructor Manual, basic power-off stalls with power-off recoveries are introduced in Lesson Plan #5, and this is the purpose of the present PGI on stalls. Intermediate stalls, with power off entries, and power on recoveries, are introduced in Lesson Plan #6, and advanced stalls, with the remaining variations in stall entry and recovery, or be reserved for Lesson Plan #22.
What is important from these discussions related to the sequence by which stalls are introduced is the fact that the present PGI is the first time the student is introduced to stalls, and your presentation must therefore cover the basics of stall symptoms, pilot management of the stall, and factors that affect stall recovery. Future PGI’s on the intermediate and advanced stalls did not repeat the fundamental information presented in this PGI, but need only review factors related to the intermediate or advanced all variation, as well as the associated changes in the how sequence. The discussions below, therefore, focus only on the student’s introduction to stalls, by way of a stall derived from a power-off entry and a power-off recovery.
The definition should be derived from the Flight Training Manual. Remember to use the student’s involvement in coming up with a definition of the stall as a means of assessing the level of understanding. Reference here should of course be to the critical angle of attack, and you should also provide some background information related to how the stall type examined today fits into the array of stall training the student will be introduced to during pilot training, progressing from basic stalls to more advanced stalls.
You should present the aim of this exercise in relation to effective recognition and recovery, with reference to minimum altitude loss. You could include learning the proper management of a stall conditions so as to avoid transition to a more complex upset condition, such as spin onset.
There are many ways to motivate a student for stall training. Perhaps the most effective and accurate line, however, is to point out that stalls, in and of themselves, are not difficult to recovery from—you simply decrease the angle of attack, and the wing is flying again. What is critical about learning about stalls is the fact that mismanagement of stall, or the failure to recognize the condition and apply proper management inputs, will allow the stall to develop into autorotation—a spin—and even the best of pilots require 700’ of altitude to recover from a full-rotation spin.
Three items are recommended here, the first related to the aerodynamics of stall onset and the the related symptoms apparent to the pilot, and the second related to the critical importance of keeping ailerons neutral in managing stall recovery. A final section should be a listing out of the factors that affect stall recovery.
For the aerodynamics of stall onset, layout on the whiteboard the diagram that appears in the Flight Training Manual should a cross-section of the wing through ever increasing angles of attack. As you work through the ever increasing angles of attack, point out the progressive movement of the separation or transition point separating laminar and turbulent flow, and point out the progressive movement of the Centre of Pressure. As relate to stall symptoms, the stall warning device of the aircraft will typically be triggered prior to buffeting. Have the student review with you the information in the Pilot Operating Handbook provided by the manufacturer related to the stall warning system. Buffeting is the second symptom, and this originates with turbulent flown striking the empennage, etc. The final symptom is the nose drop, and this is associated with the transition of the centre of pressure forward of the centre of gravity.
Critical information is provide next—the aircraft will stall in any attitude and at any airspeed, and all of these symptoms can be blurred to one sudden transition to the stall. The only time an aircraft will stall at the airspeed indicated on the airspeed indicator is when an aircraft’s speed is reduced in level flight—a slow and controlled event. Hazardous stalls occur unexpectedly, surprising the pilot.
Move onto the importance of keeping the ailerons neutral when a stalled condition is encountered. Draw two wing cross-sections on the board, the first representing the left wing, and the second being the right wing. The cross-section should be at the aileron area of the wing. Give both wings a 17° angle of attack (on the verge of the critical angle of attack), and show the ailerons in the neutral position. Now should the effects of roll inputs, whereby one aileron is defected upward, and the other deflected downward. Explain how one wing becomes more stalled, while the other is unstalled, and how this can lead to an autorotation condition. Include the fact that the downward wing will continue to move downward further as it becomes more progressively stalled with the progressive changes in the relative wind flow during its descent, and explain how the upward moving wing does the reverse. Explain that aileron discipline is critical in stall management and that they must be maintained in the neutral position from the point of recognition, to the point of recovery.
The final phase in the background knowledge section is a listing of the factors that affect stall recovery. These can be derived from the Flight Training Manual. Be sure you understand and can explain how each factor works. Each item should be paired with an explanation as to how stall speed is affected— i.e., how indicated stall speed is increased or decreased by the factor. This will be one of your early ventures into relatively complex aerodynamic theory of teaching, and it is important that you properly understand in detail the various factors that affect stalls and stall recovery. While you want to avoid going into these details during your actual PGI with the student, you must be prepared to answer questions that the student may present you. On your flight test, this part of your presentation provides an excellent opportunity for inspectors to probe your level of understanding.
The how section should begin, as always, with a review of any information and direction provided by the manufacturer for the exercise planned in the Pilot Operating Handbook. Once this is accomplished, you can begin with your standard flow for the power-off entry and the power-off recovery sequence. The items in the sequence should be numbered and clearly labeled, and as the items are placed on the whiteboard, you should dialogue on any background information related to the item or task which you feel is important for the student to be aware of. You may want to divide sure how sequence into three sections, the first being the setup, which includes the HASEL check, the second being the entry, and the third being the recovery.
Note that the stall recovery requires the aircraft being established in the power-off, maximum distance glide configuation.
It is worthwhile noting that it is really important for the instructor to emphasize how quickly and how far the nose of the aircraft should be pitch forward during the stall recovery. It goes without saying that the inputs must be smooth, and the goal is to produce a recovery with a minimum loss of altitude. The hands must be move slowly, the students elbow must be planted on the armrest so as to prevent aileron input, and the nose should be pushed forward only as is necessary to extinguish the stall symptoms. If the input is sudden, there is no time to reckon the stall symptoms, so this must be done slowly and thoughtfully.
sections, the first being the setup, which includes the HASEL check, the second being the entry, and the third being the recovery. There should be a reiteration here regarding the altitude requirements for entry, emphasizing that the height above ground must take into consideration the elevation of training. Security in the cockpit should also be reemphasized, especially as it relates to fire extinguisher security, seatbelt security, and rear seat security via the seatbelts being attached. The importance of keeping the ailerons neutral should also be reiterated, and you should emphasize that a wing drop typically invites an untrained pilot into using ailerons to maintain the wings level, and of course this simply aggravates the situation. Explain the effective use of rudder's in keeping the wings level in a stalled condition. Explain the actions that will be taken in the event of an inadvertent spin entry, and your communication here should relate to you taking control the aircraft to remedy the situation, and I think it would be a good idea for you to review the actions you will take and tell the student will learn how to do this at a later point in the training.