REFLECTOR: Unexpected door opening

Sun Jun 7 11:05:34 CDT 2009

Hi Scott Baker,

I agree that the possibility of all 4 areas failing of the fiber-glassed in tubes is unlikely (things do change when one or more of the latches are not enguaged), However almost the entire outboard load is taken up by a small round section of the tube pushing on the interior of the fuselage.  The attached "Door Latch Socket picture" shows my stainless steel T shaped answer that has a large flat section to spread the load over a larger section of the fuselage and to prevent the rolling tendency of the round tube.  If you look closely you will see that the top side holes are slightly tapered to allow easier pin entry into the close fitting hole.

Jim

James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying

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From:reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Scott Baker
Sent: Monday, July 20, 2009 7:00 PM
To: Jim Agnew ; Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Unexpected door opening

I think the liklihood of four (4) areas of failed fiberglass in the receiver areas is slim to none.
Not engaging the pins into the receiver - likely if the door handle is not rotated to its fully closed position.  Definately a possibility if there is no micro switch and warning light to tell the pilot that the pins are not fully engaged.
Good point on the possible problem of using wooden dowels as a "pin extension".  If the dowels were to become stuck in the tube and remain in contact with the micro switch, it would cause a false "door locked" indication (absence of a door ajar warning); however I would hope that we would recognize this situation following start and taxi (meaning we want to verify the door ajar warning should be ON with the door open).
SB
----- Original Message ----- 
From:Jim Agnew 
To:Velocity Aircraft Owners and Builders list 
Sent:Friday, June 05, 2009 5:39 PM
Subject:Re: REFLECTOR: Unexpected door opening

Al,

There are several failure modes for the door latches.  First the tubes that accept the latch pins could fail I.E., part from the fiberglass.  Second the latch pins may not be deep enough into the tubes so the stress is on the flat portion and not the tapered part that will try to push itself out. Third the latch pin can unscrew from the push rod (I know one of mine did even with locktite on the threads, I now use RED Locktite on them).  

I have auto locking so closing the latches automatically locks them and you must pull up on the door lock before you can move the handle.

As far as the door warning switches go I only have one in the forward center pin location with a nylon mushroom button that activates a roller micro switch.  I know a lot are in the bottom tubes with wood rods that can swell from water and in the perfect place to collect dirt that can jam them.  

Just food for thought.

JIm

James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying

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From:Al Gietzen <ALVentures at cox.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Friday, June 5, 2009 1:48:33 PM
Subject: Re: REFLECTOR: Unexpected door opening
And for those who at the end of your personal deliberations who would still opt for the gull wing, would something as simple as a deadbolt (weighing only a few ounces) serve as a fail-safe back-up to the traditional lock assembly?  Thanks for your thoughts.
 Robin 
Robin;

My thought is that we essentially have 4 ‘deadbolts’ in the current configuration.  We simply need a ‘dead sure’ way of knowing they are in place.

My further observation is (added to by my experience flying home with a temporary door) that net outward forces on the door in flight are relatively small – at least compared to the strength of the four latches. I think there is likely some negative (outward) pressure over much of the door, likely stronger toward the front edge, and some positive (inward) pressure in the area of the strake extension, and its junction. 

I have no idea if there are forces due to small distortion of the fuselage during flight that may work to move the latch pins out of the tubes, but it is not impossible.

FWIW,

Al

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James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying
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