Hartstoc
Well Known Member
I’ve just launched into an aerobatic training program in my tilt-up RV-7A. After shelling out big bucks for the required parachutes, I began to wonder if the gas springs on my tilt-up could thwart or complicate an actual attempted bailout following a structural failure or mid-air collision. The thought of the potential injuries that could result from a flailing canopy still attached by gas springs to an aircraft tumbling out of control is disconcerting. I started a thread on this subject a while back, and a link to that is at the bottom of this post.
There are only three conditions during which the gas springs and their retainers are not subject to about 20# of compressive force: when the open canopy is struck by a gust of wind from behind, when the hapless pilot backs the airplane with open canopy into a partially closed hangar door, and when the canopy is jettisoned during flight.
Considering this, I elected to modify the excessively-sturdy 5/16” diameter anchoring bolts to include the breakaway feature described below. The trick was to keep them strong enough withstand the ocassional gust of wind from behind, but weaken them enough to break when subjected to an in-flight canopy jettison event. Photos with descripive captions of the modification I decided upon can be found here (9/23 edit: after the “ruthlessly helpful” suggestions and admonitions Appearing later in this thread, I concluded that I also needed to cut slots allowing the canopy hinges to depart directly upward during canopy jettison ;-). Photos and captions of this process have been added here as well.
https://public.fotki.com/Hartstoc/canopy-release/?view=roll#1
Yes- this IS a purely intuitive modification that probably should be subjected to some calibrated destructive bench-testing to make sure it will behave as desired. Sometimes it just makes sense to trust ones intuition, so I’ll leave the bench-testing to others. Fortunately, the consequences of a fatigue failure of one of these bolts would not amount to more than an inconvenience, and I’ll report back if that ever happens. So far it is working fine. I hope we all have adopted the policy of never walking away from an RV with an open tilt-up. I’m especially attentive to that now!
Buy the way, I did try out the idea of simply removing the gas springs for aerobatics, but the challenge of getting in and out of the plane with a parachute strapped on your back while managing the unsupported canopy led me to promply discard this option.
Here is the link to my earlier thread on the topic. It also poses the question of whether it makes sense to just leave those expensive parachutes in the hangar when not doing aerobatics:
http://www.vansairforce.com/community/showthread.php?t=162107&highlight=Canopy+jettison
There are only three conditions during which the gas springs and their retainers are not subject to about 20# of compressive force: when the open canopy is struck by a gust of wind from behind, when the hapless pilot backs the airplane with open canopy into a partially closed hangar door, and when the canopy is jettisoned during flight.
Considering this, I elected to modify the excessively-sturdy 5/16” diameter anchoring bolts to include the breakaway feature described below. The trick was to keep them strong enough withstand the ocassional gust of wind from behind, but weaken them enough to break when subjected to an in-flight canopy jettison event. Photos with descripive captions of the modification I decided upon can be found here (9/23 edit: after the “ruthlessly helpful” suggestions and admonitions Appearing later in this thread, I concluded that I also needed to cut slots allowing the canopy hinges to depart directly upward during canopy jettison ;-). Photos and captions of this process have been added here as well.
https://public.fotki.com/Hartstoc/canopy-release/?view=roll#1
Yes- this IS a purely intuitive modification that probably should be subjected to some calibrated destructive bench-testing to make sure it will behave as desired. Sometimes it just makes sense to trust ones intuition, so I’ll leave the bench-testing to others. Fortunately, the consequences of a fatigue failure of one of these bolts would not amount to more than an inconvenience, and I’ll report back if that ever happens. So far it is working fine. I hope we all have adopted the policy of never walking away from an RV with an open tilt-up. I’m especially attentive to that now!
Buy the way, I did try out the idea of simply removing the gas springs for aerobatics, but the challenge of getting in and out of the plane with a parachute strapped on your back while managing the unsupported canopy led me to promply discard this option.
Here is the link to my earlier thread on the topic. It also poses the question of whether it makes sense to just leave those expensive parachutes in the hangar when not doing aerobatics:
http://www.vansairforce.com/community/showthread.php?t=162107&highlight=Canopy+jettison
Last edited: