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  #1  
Old 09-10-2018, 09:52 AM
Hartstoc's Avatar
Hartstoc Hartstoc is offline
 
Join Date: Aug 2017
Location: Sebastopol,CA
Posts: 141
Default Modification for assured tilt-up canopy jettison-

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/ca...e/?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/communit...anopy+jettison
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Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"

Last edited by Hartstoc : 09-23-2018 at 12:21 PM.
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  #2  
Old 09-10-2018, 11:42 AM
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Bill Boyd Bill Boyd is offline
 
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Default Re: walking away with canopy open

I do it all the time. There's a doo-hickey that attaches to the lift strut and snaps into position when the strut extends far enough. Once in position it prevents the canopy from closing until it's manually pulled out of the locked position.

Having mistakenly trusted a set of slowly failing lift struts before, I wouldn't be without it.

The only way an idiot like me can defeat this idiot-proof device is by not assuring the canopy has opened far enough for the lock to snap into position before letting go.

On the jettison subject, I'm assuming you've slotted the forward deck skin over the hinge arms so they can come clear when the jettison handle is pulled. I removed my jettison T-handle when I realized the canopy would never jettison from a closed position without these special rainwater ingress slots cut.
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  #3  
Old 09-10-2018, 11:54 AM
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Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by Hartstoc View Post
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.
The very early RV-6's used a prop rod instead of struts. You could remove the struts and resort to a prop rod.

Quote:
Originally Posted by Bill Boyd View Post
I do it all the time. There's a doo-hickey that attaches to the lift strut and snaps into position when the strut extends far enough. Once in position it prevents the canopy from closing until it's manually pulled out of the locked position.
A length of 3/8" fuel hose slit to allow it to be slipped over the strut rod accomplishes the same thing.

And yes, bad form to walk away from a non-secured tip-up canopy--only takes one strong gust of wind or an inattentive pilot to ruin your day.
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  #4  
Old 09-10-2018, 12:09 PM
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Mel Mel is online now
 
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Quote:
Originally Posted by Sam Buchanan View Post
The very early RV-6's used a prop rod instead of struts. You could remove the struts and resort to a prop rod.

And yes, bad form to walk away from a non-secured tip-up canopy--only takes one strong gust of wind or an inattentive pilot to ruin your day.
I recommend the original "Prop-Rod" solution. I never liked the struts.
And yes, you must have the slots cut above hinges. Cover the slots with 3-M tape and they will never be noticed.
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  #5  
Old 09-10-2018, 02:10 PM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by Mel View Post
I recommend the original "Prop-Rod" solution. I never liked the struts.
And yes, you must have the slots cut above hinges. Cover the slots with 3-M tape and they will never be noticed.
Thanks for the idea- If my breakaway bolts ever give me problems, Iíll resort to the prop-rod idea, but it is kind of nice having the gas struts. Working on the slots now. - Otis
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RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
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  #6  
Old 09-10-2018, 02:20 PM
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Piper J3 Piper J3 is offline
 
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I wonder if you could reduce diameter at the small end of the taper so the ball would pop off easier?
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  #7  
Old 09-10-2018, 08:37 PM
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G-force G-force is offline
 
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Quote:
Originally Posted by Piper J3 View Post
I wonder if you could reduce diameter at the small end of the taper so the ball would pop off easier?
-
Or machine some out of delrin. It might be easier to just chuck that up in a lathe and drill a hole through the center to weaken it. You would have to play around with the diameter.
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  #8  
Old 09-11-2018, 08:35 AM
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Here's a thought... If the struts are attached, and the canopy is trying to exit up and back, the struts should help raise the front of the canopy into the slipstream (and perhaps over your head) as it passes.

If I were really worried about them *not* letting go, when boarding for an aerobatic flight I would get in, then disconnect the fuselage end of the strut before closing the canopy. Then I could close the canopy and disconnect the upper end. Stow struts securely out of the way, and bob's your uncle.
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  #9  
Old 09-16-2018, 04:08 PM
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Quote:
Originally Posted by Piper J3 View Post
I wonder if you could reduce diameter at the small end of the taper so the ball would pop off easier?
-
I did consider this, but was concerned that flexing during normal operation could lead to random failures. The method I devised of weakening the bolt shafts is subject to very little flexing, if any, during normal ops because of the pre-stressed assembly and positive loading from the “strong” side from the gas springs. Also, the longer lever arm between the ball and weakened point on the bolt will amplify the shock load that will break to bolt.
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Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"

Last edited by Hartstoc : 09-23-2018 at 12:52 PM.
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  #10  
Old 09-16-2018, 05:30 PM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by Bill Boyd View Post

On the jettison subject, I'm assuming you've slotted the forward deck skin over the hinge arms so they can come clear when the jettison handle is pulled. I removed my jettison T-handle when I realized the canopy would never jettison from a closed position without these special rainwater ingress slots cut.
Iím still pondering this important comment, and I may yet cut these slots. For now, after studying the various posts on taking off with an unlatched canopy, or having a canopy inadvertantly unlatch in flight, I concluded that changing the bailout proceedure might make the slots unnecessary, especially if there are two people on board to help with canopy jettison.

If I did have the slots, my proceedure would be: 1- remove headsets. 2- check that center latch is engaged and leave it that way. 3- disengage primary latch. 4- pull jettison T- handle. This would hopefully make a pivot point put of the center latch, which would hopefully cause the canopy to do a clean back-flip as it departs.

In the absence of slots, my aerobatic instructor and I decided on this procedure instead: 1- remove headsets 2- disengage center latch. 3- disengage primary canopy latch while stabilizing canopy sides with the palms all free hands on board. The canopy should partially open and find an aerodynamic neutral point, but allow enough space for the it to slide aft and free the hinges when you: 4- pull the T-handle. For now, this is the proceedure that my instructor and I verbalize prior to boarding the aircraft before each flight. We also verbalize steps 5-7, 5- disengage seat belts. 6- Get your butt out of and away from the aircraft. 7- Visually identify the parachute D-handle, engage it with the thumbs of both hands if able, and push it briskly away from your chest with both hands. Having visualized your way through these proceedures just prior to each possible need to execute on them could save your life.

Of course, all bets are off if the aircraft is tumbling wildly out of control, which may be a fairly likely Scenario. In that case , there is just one item: Quickly find a way to jettison the canopy or open it sufficiently to fight your way out. You will at least have substantial motivation on your side! - Otis
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Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2018 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"
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