REFLECTOR: Door strut review

Wed Oct 7 18:02:33 CDT 2009

Keep the doors closed as much as you can.  I have found that also helps, besides noticing that cooler temps make it easer to close.  Also look at all the rotating surfaces for clean off and as possible lube points.

Terry

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of nmflyer1 at aol.com
Sent: Tuesday, October 06, 2009 22:46
To: reflector at tvbf.org
Subject: Re: REFLECTOR: Door strut review

Dennis, 

Did you clean out the door pin tubes after you worked on your doors?  Mine had accumulated some crud & over spray in there and were not happy. So, I took a drill bit that was undersized for the door tubes (in the door & on the receiver). Then I took some 400 grit paper, taped it to the drill bit & wrapped it a turn or so around the bit (enough to cover the tape).  Then I just honed it out a little (cleaned it up mostly) with the sand paper on the drill. Once it comes back clean, you know you have the crud out,,,,, took a time or 2. Make sure you steel wool the pins themselves too. Amazing how much crud builds up on them over time. 

Then I used squeeze tube graphite on the pins.. Neater and worked great. 

Hope that helps. 

Kurt 

-----Original Message-----
From: Dennis Martin <dennis.doc at gmail.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Tue, Oct 6, 2009 8:27 pm
Subject: Re: REFLECTOR: Door strut review

My door pins are super tight - they were perfect and easy to move when I first fit them years ago. The handle requires a lot of force now to get the pins all the way in. Will this improve with time, or should I make some adjustments to the pins or the receiv er tubes? Grease helps a bit, but not enough. 

Doors fit great, but I did have to use heat on inside of doors to make them relax. Still required a bit of filling here and there. 

Thanks in advance,
Dennis

On Tue, Oct 6, 2009 at 8:08 PM, <nmflyer1 at aol.com> wrote:

Al, 

I too was not too keen on such beautiful aircraft having the aft potion of the doors bending under the load & heat. My approach was slightly different than yours: 

I purchased some gas springs that had half the force of the factory originals (mine are 30 pounds). Then I ended up working on the attach points to stiffen things up on the door, and find a place that would work for mounting the new springs. 

The spring source I used is : http://www.spdhardware.com/catalog/list.asp?id={A818FF64-E51A-422F-A59A-4E2E52A3BDA2 <http://www.spdhardware.com/catalog/list.asp?id=%7BA818FF64-E51A-422F-A59A-4E2E52A3BDA2> }   and the springs I used are the 5300-30's. 

I made a quick look over the site and didn't see a 23" extension spring. I am sure you measured attach point to attach point, but the closest they have is a 20" one on their website. 
You can always call them, but just=2 0make an inquirey and write down the part number if they have what you need. It is much cheaper to order off of the website. I think they have a minimum dollar amount on phone orders. 

The good news, My doors do not bend up at the back and they don't twist the door. The not so good news is that the door opens about 4" shorter height than the factory ones. Works for me since I'm short :) 

I also tried the "new method" while I was playing aroud and really did not like the front-door-twist, or the slamming at the lower end. Same results that you had. 

Kurt Winker

-----Original Message-----

From: Al Gietzen <ALVentures at cox.net>
To: reflector <reflector at tvbf.org>
Sent: Tue, Oct 6, 2009 7:30 pm
Subject: REFLECTOR: Door strut review

This is just a story about different door strut configurations and issues which may be of interest to builders who have not yet installed them, or those who may not like the way the door works.  I’ve now had experience with original version of the strut, my modified original version, and the new version.

First I’ll mention a couple of things I really like about the new door and hardware.  In fitting up the new door, I was pleasantly surprised and impressed that its shape matched up very nicely to the fuselage – much better than the original had.  Remember all that discussion years back about heating the doors to get them to fit right? And the over-center spring on the latch crank is much stiffer than the earlier version – good idea.

Those of you that built your plane some years ago with the elite doo rs know that there were some issues with the door struts.  They fastened to the door up at the back corner, tended to twist the door toward the back, and caused distortion so the top rear of the door tended to stick up above the fuselage surface. Disappointing after you had carefully fit the door.

My solution to that was to install a new hardpoint further forward in the doorframe; just in front of the rear hinge.  This took away the twisting force by putting the force between the hinges and perpendicular to the hinge line (See photo 1). Of course this didn’t eliminate the force tending to bend the door up in back. Noting that most of the bending was between the top frame and the hinge line, I reinforced that area with about 5 plies of BID, with a ply of fine BID over (photo 2).  This eliminated most of the problem, and with a little filler on the fuselage, all was copasetic. The behavior of the door was nice, and had a slight closing force near the end of travel.

After that someone came up with the idea of a longer strut, connected further down on the door, along with the claim tha t it eliminated the distortion of the door, worked better, etc; and the design was adopted by Velocity for subsequent kits. So naturally in replacing my door I chose the new approach so I wouldn’t have to install a new hardpoint and reinforce the hinge area – even though it wouldn’t match the other side.

After fitting up the new door and hinges to nicely fit the existing op ening; I installed the strut per the current instructions.  Yikes – the bottom front corner was now coming to close position almost ¼ - 3/8” too far forward.  And from about the 2’ open point it wants to SLAM shut.  If person had their fingers over the edge and wasn’t sure to restrain the door you could loose a finger. And now the downward force on the rear hinge, and the r esultant distortion, was about the same as in the original top corner approach – except downward instead of upward.

So a caution to those still building: install the strut BEFORE doing the final fitup of the door to the fuselage.

Had I reviewed the strut installation geometry, and the resultant force compone nts, before installing; I would have realized the likely result, and done as I did with the original.  With the current strut (photo 3, yes, I painted it the match the interior), the forward component of the force on the door during the stroke is nearly 30 lbs, pushing forward, which is why the door gets so twisted out of alignment toward the front.  The new geometry gives the strut much more mechanical advantage on the door, which could be a good thing for holding the door open, and allowing a lower strut force rating; except when the door is open a good percentage of the force is directed forwa rd instead of upward. That same advantage requires much more force to open or close the door, and makes it want to slam.  I’m sure one can get used to that; if that’s a characteristic you like.

The door frame is very rigid longitudinally, as down the sides of the door; but the force in the hinge area is transverse to the upper beam, and although there are some carbon plies in there, the distortion is basically between the upper beam and the hinge line.  So again I re inforced the hinge area as before; which solved most of the problem of the distortion of the hinge area.  Nonetheless, the 60 lb strut still has about 12-15 lb in excess of that needed for my door.

So the unshod is that I definitely prefer my original modified stru t and orientation.  Putting a new hardpoint into the upper door frame to install that strut is fairly easy – drill a couple of holes about ¾” dia just forward of where you want to mount the bracket, make a fairly still mix of epoxy and 50/50 mico and milled fiber and fill in the space behind where you want to mount the bracket. Light and strong.

The replacement for the original door is readily available from McMaster-Carr (part #9416K17, $12.85).

Before I consider a rework to my earlier version of strut; I’d like to try a 45-50 # strut in the new configuration.  So far I haven’t found any vendor for a strut with 23” extended length with the lesser rating – which may be why Velocity supplies the 60#.  Anyone know a source I should check? (e.i.; if you happened to be interested enough to read this farJ).

Al 

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-- 
All the best,
Dennis

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