REFLECTOR: Unexpected door opening

Stockman, Bill bill.stockman at daytonaero.com
Tue Jun 2 15:05:04 CDT 2009


MTCW

Some of you may not remember, but what got us down this road was that
early builders spent a lot of time finessing their gull wing door
mechanisms so they smoothly operated and opened easily.   Bad news since
that unwanted friction kept the doors closed, now they might potentially
vibrate the latch open or the latch could be bumped or caught on a coat
sleeve and opened.    The lock pin was designed to require two hands so
you can not accidently open it or a passenger can not grab the handle in
a panic and open the door.  

I've never seen Al's new passenger latch with a button, but I hope they
can't easily do it with one hand.   I fly a lot of young eagles and
other first time flyers and the nervous ones instinctively grab for the
door handle with the slightest bump.  

Off the subject, you have to watch some of the mentally challenged
pilots we take up in our planes (which sometime is us).   While most
will politely sit and admire your plane, others will just grab stuff or
twist knobs without even asking.   Even one of our own Velocity pilots
got confused one day on a flight and mistakenly pulled the fuel cutoff
T-handle mistaking it for the heater shutoff T-handle--guess what, it
worked and the engine quit.  Thus, the tried and true simple door latch
with the lift-pin has proven to be idiot proof as long as you actually
latch the door.

I totally agree with you guys that you shouldn't strengthen the hinges
since it probably better in cruise to lose the door and regain flight
control than to save the door and lose the plane.

One of the early builders used a variant of the strap on the handle
idea--they attached a small strap to the fuselage below the door opening
and then attached it to the bottom of the door.   This was to keep the
door from opening in flight if it became unlatched.



Bill Stockman, Senior Associate
Dayton Aerospace
 
(937) 369-4799 cell
(937) 426-4300 work
bill.stockman at daytonaero.com

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brian Michalk
Sent: Tuesday, June 02, 2009 3:28 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Unexpected door opening

Al,

Excellent post.

I never did like the passenger latching mechanism, and now that the 
plane is out for a while, I might change it. Could you send some 
pictures of your push button design?

Al Gietzen wrote:
>
> Here are my replies and further thoughts on the door issue.
>
> Certainly, with the front hinging, Rodney has addressed the root cause

> of the dangers of our standard door design. It is a design that would 
> likely never make it in the world of certified airplanes. However; I 
> think the existing door, and door frame configuration does not lend 
> itself well to front hinging; and is a major rework. The existing 
> latch design is plenty robust; it just needs to be insured of being 
> fully latched when the plane is in flight.
>
> Dennis: I would not recommend beefing up the hinges or hinge mounts. I

> suspect that I would have been in a lot more trouble had the door not 
> departed the airplane. Of course, departing the plane could result in 
> prop damage, which could also be very bad. So the bottom line is that 
> this door design *_must not_* open in-flight.
>
> Larry: Your safety latch is eloquent in its simplicity; and very 
> easily verified visually. (I'll admit it doesn't appeal to my sense of

> sophisticationJ; but I'll never argue form over function)
>
> I did not install the automatic lock assembly provided by the factory 
> for design reasons as well the necessity of needing two hands to open 
> the door (at least that's how I saw it). On the passenger side I made 
> my own design of an automatic lock which requires pushing a button 
> just behind the handle to release it and allow the handle to be pulled

> back. I didn't do that on the pilot side because of the need to unlock

> from the outside - instead I added a second spring to the over-center 
> linkage to provide more force holding the latches in place. For the 
> first 50 hours or so of flight I monitored the handle to insure there 
> was no sign of movement during a flight. There never was; so I gave it

> no further thought.
>
> My opinion is that it is very unlikely that any of these door opening 
> incidents occurred as a result of a failure of a fully latched 
> closure. Even a simple warning light on the panel that the pins are 
> not fully inserted would be an effective deterrent. In 20/20 
> hindsight, I reflect upon the time and effort I put into design of the

> electrical system, and engine systems, to eliminate potential 
> single-point failures; but didn't consider sufficiently the need for a

> warning if the doors were not fully latched. The checklist, and a 
> glance at the handle isn't enough.
>
> Al
>
>
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