vlittle
Well Known Member
Jump Dog
In order to have the aerobatic limitation removed from my Harmon Rocket, the regulations require the ability to open or jettison the canopy in flight. After much pondering, I decided to make a 3" slot in the top of my slider rails, about 2 inches aft of the closed position of the roller truck.
This slot would allow the canopy to be slid aft, then up. At this point, the slipstream would take over and the canopy should rapidly exit, allowing for rapid egress in the event of an emergency.
In order to prevent inadvertent canopy removal during gusty ground operations, I fabricated a sliding collar with 0.063 Aluminum that traps the roller truck unless the collar is slid all the way back.
It is normally held closed by the friction of the collar slider mechanism, which is adjusted by the tension of two #6 screws and nylon washers used as bearing surfaces (not visible).
But wait, there's more! I CNC cut plastic inserts that slide into the canopy track and are retained with quick release pins. These inserts, which I call "Jump Dogs" are the key to reliable canopy extraction.
Before take-off, the system is armed by sliding the collar back, inserting the Jump Dogs in the track and inserting the pin. After takeoff, if bail out is required, the only action required is to unlock the canopy and pull back which should eject the canopy. This is a natural motion and does not require the removal of pins, or actuation of a separate jettison mechanism.
After landing, the Jump Dogs are removed and stowed in a convenient location and the collar is slid forward, allowing normal canopy operation. In an unexpected ground emergency, this system does not interfere with canopy removal in either configuration.
It is still possible to jettison the canopy without the Jump Dogs in place, but this requires sliding the collars back, pulling the canopy back and pushing up at the right position. Someone smarter than me will have to design an automatic system. Seems to me that if you were not planning acro, you would not be wearing a chute, so this is academic anyway.
The original Jump Dogs were prototyped using wooden wedges that work just fine, but I have access to a CNC machine that made quick work of cutting the black dogs (cue Zeppelin music). Now I just have to lose a few pounds to fit the parachute limitation.
I posted this as a "how I did this" and not a recommendation or claim of superiority over any other method. The photos are of a prototype I developed using leftover slider track material. The final installation is slightly different and I will post pictures later.
In order to have the aerobatic limitation removed from my Harmon Rocket, the regulations require the ability to open or jettison the canopy in flight. After much pondering, I decided to make a 3" slot in the top of my slider rails, about 2 inches aft of the closed position of the roller truck.
This slot would allow the canopy to be slid aft, then up. At this point, the slipstream would take over and the canopy should rapidly exit, allowing for rapid egress in the event of an emergency.
In order to prevent inadvertent canopy removal during gusty ground operations, I fabricated a sliding collar with 0.063 Aluminum that traps the roller truck unless the collar is slid all the way back.
It is normally held closed by the friction of the collar slider mechanism, which is adjusted by the tension of two #6 screws and nylon washers used as bearing surfaces (not visible).
But wait, there's more! I CNC cut plastic inserts that slide into the canopy track and are retained with quick release pins. These inserts, which I call "Jump Dogs" are the key to reliable canopy extraction.
Before take-off, the system is armed by sliding the collar back, inserting the Jump Dogs in the track and inserting the pin. After takeoff, if bail out is required, the only action required is to unlock the canopy and pull back which should eject the canopy. This is a natural motion and does not require the removal of pins, or actuation of a separate jettison mechanism.
After landing, the Jump Dogs are removed and stowed in a convenient location and the collar is slid forward, allowing normal canopy operation. In an unexpected ground emergency, this system does not interfere with canopy removal in either configuration.
It is still possible to jettison the canopy without the Jump Dogs in place, but this requires sliding the collars back, pulling the canopy back and pushing up at the right position. Someone smarter than me will have to design an automatic system. Seems to me that if you were not planning acro, you would not be wearing a chute, so this is academic anyway.
The original Jump Dogs were prototyped using wooden wedges that work just fine, but I have access to a CNC machine that made quick work of cutting the black dogs (cue Zeppelin music). Now I just have to lose a few pounds to fit the parachute limitation.
I posted this as a "how I did this" and not a recommendation or claim of superiority over any other method. The photos are of a prototype I developed using leftover slider track material. The final installation is slightly different and I will post pictures later.
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