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"Jump Dog" Canopy Jettison

vlittle

Well Known Member
Jump Dog

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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.

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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.

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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).

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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.

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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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Very clever Vern. Do you know if you can slide the canopy back in flight? In my 6 the slipstream prevents it from sliding back.
 
This is not the point of my thread. My objective is to make it possible, not guarantee the outcome. Hence my caveat at the end of the post. If this thread devolves into a long running debate, I will have failed at my objective of just 'showing how I did it' and providing some technical info for others to build on, if they choose.

I have found that Safety issues on VAF are often met with scorn and condescending opinions and I don't want to go there. A good example is the SWZL-1A stick shaker that I developed. Folks on VAF in general pooh-poohed it, but the FAA part 23/ASTM F44 Spin Avoidance committee has purchased one for demonstration of haptic feedback in General Aviation and my other company is providing a haptic/control loading flight simulator yoke to the same committee for the same purpose.

So..... I make no claims.
 
Vern,

How much room do you have on the outside edge of the track. I'm thinking of a pivoting rail cap that could also act as a ramp.

Paige
 
I suspect you would need the adrenaline present in the situation to get the canopy back far enough to engage the ramp.
 
On the -6a, if you unlatch your canopy it will open about 1.5-inches by itself.
So, IMO, I think this idea would work without issue. But not willing to try unless absolutely necessary.
 
Vern,

How much room do you have on the outside edge of the track. I'm thinking of a pivoting rail cap that could also act as a ramp.

Paige

Edit, see installation pic:

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The challenge is providing a mechanically robust ramp configuration. As Rob mentioned, in an emergency there will be a lot of adrenaline and it's possible to apply large forces to the ramp. They way I designed it, it keys into the channel and is held by the pin that goes through the track and the fuselage top deck.

I had looked at a few self-contained mechanical geegaws, but in the end I thought that for the serious acro days when a parachute is required, it is a minor inconvenience to 'arm' the Jump Dog before flight.
 
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Here are the pics of the Jump Dog installed in the Rocket. The first pic shows how the canopy truck rolls up the Dog when the system is armed. Due to variations in construction, the opening in the left and right tracks are different, so I had to measure carefully to ensure symmetrical operation.

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This pic shows the sliding collar in normal (disarmed) position. Friction is adjusted using tension on the two #6 screws that attach the collar. I used nylon washers as bearing surfaces between the slider rail and collar and the collar and attachment nut, but there is room here for some more innovation.

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Final install shows the new stainless steel leash between the release pin and the Dog. Colour coded heat shrink identifies which side the Dog lies.

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Finally, when the Dog is resting, I leash it to the seat-back frame. The holes in the Dog can be used to clip it almost anywhere convenient. I may even drill a hole somewhere just to stow it, or keep it in one of my storage compartments (the Doghouse?).

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Finally... I just have to say it... in Dog we Trust!
 
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