Edward,
Looking forward to seeing this - what is your web page address please?
Dave Simpson
----- Original Message -----
From: Edward Gladstone <Ted_Gladstone@compuserve.com>
Subject: Door Strut - - The Solution ??
>
>
> >>
> >>Daydreaming some more.....
>
> >Modifying my original suggestion, more effective than a "ramp bracket"
> would
> >be a pivoting, slightly over-center lever with a small bucket-like end to
> >capture the end of the gas strut and unload the door as it's closed. This
> >would get rid of any friction of sliding up the 'ramp bracket' when
> closing
> >the door, and would actually pull the top corner of the door inwards
> >slightly when fully closed (due to being over-center). The lever would
> need
> >to be lightly spring loaded to position it outwards to receive the end of
> >the gas strut when the door is open.
> >
> >I could sketch it out if need be to explain a little more clearly.
> >
> >Cheers,
> >Pete A239
> >>
>
>
> We will be shortly approaching the time to fit our gas strut and have been
> watching the comments re this with interest. We thought the above an
> excellent idea and it was our favourite until we studied the geometry of
> the door hinge & strut pivots. It would appear to us that the direct
> line of force exerted by the strut when the door is closed is almost
> exactly through the hinge pin and, although there is a slight twisting
> moment on the door frame due to the length of the lug the strut is
attached
> to on the door, there is almost no vertical bending component on the door
> which would tend to lift the rear as has been reported. When the door is
> held in the open opsition, however, there is an enormous force bending
the
> door frame. Even although the strut has reached the end of its travel it
> is still supporting the door on a very small moment arm. One only has
to
> pop the end of the strut off its ball joint at the door end and try to
> support the door in the open position by pushing on the exposed ball with
> your thumb to appreciate the force involved. By alternately holding the
> door up with your left hand on the door handle and pushing on the pin with
> your left thumb you can see the bend occurring in the door. From this we
> are suggesting that the bend is being induced only when the door is in the
> open position and, as it gradually takes up this set, it becomes more and
> more visible when the door is closed.
>
> We have now given this problem some thought and our solution (which is
only
> in the mockup phase at the moment made out of 2 lengths of scrap 1" X
3/4"
> aluminium angle ) is to use a simple folding lever strut, as has already
> been suggested, but to incorporate the gas strut within it. The gas
> strut is pivoted on the lower pivot point of the folding lever on the
> fuselage and the other end of the gas strut is pivoted about 1 1/2 " from
> the folding point of the levers and on the top lever. The top lever is
> then pivoted on the door about 1/3 way round its curve.
>
> This method gives the following advantages:-
>
> 1. The lever pivot points are a reasonable distance from the door hinge
> line and therefore only exert a low force to hold the door open.
> 2. The line of force exerted by the lever is almost in the same plain
> as the door centre of gravity.
> 3. The gas strut is totally contained within the folding levers and
> exerts NO FORCE IN ANY DIRECTION on the door or fuselage when the door is
> in the closed position.
> 4. The gas strut offers the maximum lifting force when the levers are at
> right angles to one another and this occurs when the door is about half
way
> up.
> 5. The force produced by the levers lifting the door gradually
decreases
> from the half way point upwards just as the force required to lift the
> door decreases as it approaches the fully open position.
> 6. The levers are designed to reach their fully open position at 150
> degrees and are held in this position by the force in the gas strut,
> therefore there is no necessity to unlatch the levers to close the door
nor
> is there any possibility of a gust of wind causing the door to crash down
> as would be happen with a simple, over centre, lever strut.. All that is
> required is to reach up and pull down the door.
> 7. The damping action built into the gas strut slows the opening of the
> door and, as it is expanding twice as fast as the door is opening, its
> effect is even more evident.
> 8. As the force produced by the strut reduces to zero as the door is
> closed there are none of the distorting forces which prevent the rear of
> the door from seating properly with the possibility of the rear shoot
bolt
> not engaging. (this has resulted in the door being sucked off in flight
> on at least two occasions - - one of which I videoed)
>
> With the desire to utilize the existing gas strut the resulting lever
> mechanism is rather large and it is a tight squeeze in the recess in the
> door aperture but it looks as if it could be made to fit. The ideal
> solution would be to scrap the existing gas struts and purchase the next
> smaller size. This would allow greater leeway in positioning the pivot
> points to produce the greatest mechanical advantage and possibly allow
some
> of the gas to be released from the strut by means of the Schroeder valve
in
> its base to fine tune the balance for the door.
>
> We will shortly be putting some pictures of the mockup strut on our web
> page.
>
> Anything we have overlooked ?
>
> A Guid New Year to One & All
>
> from
>
> Ted & Justin
> G-ZTED
>
>
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