Dynamics of the Ram Air Canopy
If we achieve and cultivate a higher understanding of skydiving equipment, we will increase the. margin of safety in the sport.
The purpose of the following seminar is to examine and discuss the dynamic relationships of the ram air canopy in order to achieve a functional understanding of the modern parachute.
By "functional", I mean useful understanding that can help us in the real world.
By "dynamic", I mean the net result of two or more interactive variables, resulting in a phenomenon that would be otherwise unachievable but for the cooperative and complimentary forces joining to achieve a new level of possibility.
"Things derive their being and nature by mutual dependence and are nothing in themselves." Nagarjuna, Second century Buddhist philosopher
In order to fully understand the dynamics of the ram air parachute, one must consider all of the "players":
1) The parachute (the wing) Definitions of Orientation: (attitude)(axis of movement, relative to horizon)
a) Roll
b) Pitch
c) Yaw
2) The Pilot (Suspended Weight) ("G" Forces)
3) The Relative Wind Relationship of the Wing to the Wind ie., where you are Actually Going
One cannot understand flight in a comprehensive, synergistic manner without intimately lacing the actions of the wing to the air in which it is flying.
Angle of Incidence: Established by "Trim"
Airfoil Aspect Ratio Airspeed and "Glide Ratio effected by wing loading,
trim, airfoil, and aspect ratio, and planform.
Similar size canopies will fly at about the same speed
Depending on the design and wing loading, canopy may sink or glide flatter, decrease it's descent rate or increase it.
Braked Flight (dynamic characteristics):
Phase 1: Initial Input (pitching) Airspeed diminishes slowly
"G's" stay near One "G" Descent rate decreases, but does not reach zero Angle of attack is not changed significantly, therefore minimal dynamic forces are exhibited.
Phase ll: Canopy reaches level flight below half brakes, or not at all. Usually ends in a hard touchdown, with no time for choices prior to actual landing.
Phase 1: (initial Input) Airspeed diminishes somewhat
 |
 |
 |
 |
 |
"G's" increase above One "G" Descent rate reaches zero, level flight before reaching the half brake position.
The "Sweet Spot: The part of the toggle stroke at which the parachute transitions it's airspeed into lift, sufficient to stop descending. The Sweet spot is generally higher at higher airspeeds, and lower when flying at low airspeeds. {It is not a location; it is a phenomenon.}
Phase II: Once in level flight at a high airspeed, the pilot is afforded the opportunity to change direction, as well as choose foot placement. As airspeed diminishes, more and more angle of attack (i.e., pitch change) is necessary to maintain level flight. The absence of more brakes as speed diminishes yields increased descent rate and a premature landing. Discussion of "Foot Skiing": diminishes stall speed "Arrested Progression" Technique (pop up)
Phase 1: (initial Input) Airspeed diminishes abruptly "G"s increase sharply and dramatically. Canopy climbs for a short time
Phase ll: Airspeed approaches zero, risking a stall. Releasing the brakes slightly and slowly is the only hope, but the chance of a soft landing are very low unless canopy is flown at a very low wing loading. Re flare is not usually an option, as airspeed is already gone.
Asymmetric drag causes Roll axis change (bank) Roll creates Yaw "G" forces determine stability "G's" are dependant on angle of attack. Abrupt application of a single toggle often results in line twists. Likewise, abrupt reversal of the turn can an easily induce line twists. Pausing between turns will give the canopy a chance to "catch up" to coordinated flight and positive "G's", reducing the chances of line twists.
Low Speed, low line tension: Consider the possibility of line twists is quick turns. Maintain coordination to the relative wind. Turn slowly.
High Speed: Usually heavier toggle pressure and "G" forces, so risk of line twists is generally lower. Canopy is capable of level flight turns (no altitude loss), or even climbing turns. Many possibilities. (turn and flare, flare and turn...
Lower drag method of increasing Angle of Attack High risk of stall, as angle of attack is being changed without the need for pilot position change, Swinging the Pitch)This results in a higher risk of high speed stall. Pushing out vs. Pulling Down.
(works better with elliptical canopies) Pilot can accentuate or ameliorate the over steer tendency of the parachute lean into the turn to increase the over steer and recovery arc lean to the outside of the turn to decrease the over steer and dive tendency. Application during openings: Flying the canopy with weight shift prior to unstowing the toggles affords the pilot a chance to immediately steer the canopy following the opening. Over use of this technique too early in the opening can actually induce off heading openings and/or fine twists. Application for swooper's: If turn is too low: finish with weight shift.
Concept One: Airspeed creates internal pressure. Higher pressure in the canopy yields a more stable wing. Concept Two: High angle of attack flight increases "G" forces and line tension. Higher line tension increases stability.
Abruptly release control inputs in turbulence: (surge to line slack) Fly in deep brakes in turbulence. (not enough airspeed) Abruptly apply the front risers in turbulence. Continue a front riser turn if the front riser goes slack:
(apply brakes quickly) Fly behind large objects near the ground.
Maintain a high airspeed when flying in turbulence. Release control inputs smoothly and slowly, or positively maintain angle of attack through positive pitch input when reversing direction. Notice line tension and "G" loading, and be prepared to apply brakes when wing surges forward and decreases in angle of attack.
In the event of canopy collapse:
1) Aggressively maintain heading with opposite toggle input.
2) Pull or pump the toggle on the collapsed side to re inflate it, if it has not already inflated.
Quickens all canopy responses to input. Parachute performs more like an airplane.
More lift at the pilot's disposal.
More descent rate at the pilot's disposal
More "Response ability": The pilot has the ability to respond immediately with the appropriate control input.
When the pilot is over stimulated by the circumstances, he or she is less capable of performing complex tasks. If under stimulated, he or she is less capable due to lack of interest, and learns less from the experience.
Psychological Factors that may diminish pilot performance:
1 ) Wing loading too heavy for "Perceived Ability"
2) Canopy design too high performance for "Perceived Ability".
3) Too many new variables to process:
4) Skydive was too stimulating, and pilot is still recovering.
5) Flying technique is too aggressive for experience level.
6) Trying to execute a Preconceived Notion about how the landing will occur,
rather than responding to the sensory input regarding the Actual Situation.
Conditions Change. Response ability includes a malleable mind set, ready to
adapt to the changing environment. Response ability requires the pilot to
remain at the "Optimal Arousal level" at all times.
WNE: Wing Loading Never Exceed: Wing-Loading (Ibs/sq ft.) Number of Jumps
1.0 <100
1.1 100-199
1.2 200-299
1.3 300-399
1.4 400-499
1.5 500-599
1.6 600-699
1.7 700-799
1.8 800-899
1.9 900-999
2.0 1000+.
1) Pull Higher! 2000 feet is just not enough time to learn
2) look at your canopy! l'
3) Try new things.
4) "Call Your Pocket" (decide where you are going to land and how
prior to getting in the plane)
5) Fly Relative
If we do not expect to be able to learn how to freefall without a reference with which to fly relative, why do we attempt to do so with our canopy piloting skills?
Skydiving is the least dangerous thing we do at the drop zone. It is canopy flight that matters most. Just look at the statistics...
1) Basic Proximity and Stillness (all speeds)
2) Slot swapping
a. Over and under
b. Behind the back
c. Include formation heading changes
3) Catch me if you can
Stay Aware!
4) Swoop Practice
The best way to Learn: Teach!!
