Pneumatic based door retention sytem

[Brad Brady]

On a serious note, would a good epoxy, and a single PK (to hold the epoxy in place while it cures) screw, on each end constitute an STC? All are minor.

[wingnut]

On a serious note, would a good epoxy, and a single PK (to hold the epoxy in place while it cures) screw, on each end constitute an STC? All are minor.

It could be argued either way. Answers will differ depending on who you ask. I would not have problem signing a log entry as a minor alteration.

[bagarre]

You wouldn't need the PK screw to hold it in place. If you don't hook up the strut until the epoxy is cured, you could hold it in place with duct tape.
but I'm not sure if epoxy would hold for very long. Or it would take quite a bit of surface area.

On the 3M VHB front, the 1.5" piece has been holding a 20 pound weight for two days now without deformation. Surface prep seems to be the key.

The struts I bought are suspect tho. They were supposed to be rated at 10 pounds (minimum possible with a gas strut) but they have 19 pounds of preload. I'm not sure if its a quality control issue or nor but that seems to be WAY too much for our little doors.

I'm looking into a set of dampers instead of struts. Same form factor but no preload. I don't need the door to automaticly pop open. I just want it to take some amount of force to move the door at some rate. That should prevent people from wanting to slam it shut or the wind taking it off the hinges.

[Brad Brady]

Well,that's the way i was thinking ,Del...... Dave, a PK is just a hardware piece......Has to help in the integrity of the item being held.....Just my thoughts..

[bagarre]

One of my goals is no new holes.

[Bruce Fenstermacher]

I think the right kind of structural epoxy would work since most cars today are held together with it. But the problem being disassembly once epoxied. I'm liking the 3M tape myself because it could be removed.

[bagarre]

Round two of testing. The 20 pound weight on 1.5 square inches of tape is still holding out in the garage.
This is a test using the actual brackets. Slightly different results.

(How many wives would let you do this on the kitchen table??)

Round2_1.JPG

The twisting moment of the strut causes a fair amount of deflection but it's not separating yet. The deflection occurred in the first 15 minutes of the load being applied and hasnt increased in the last 4 hours. I plan to leave it overnight.

Round2_2.JPG

It's worth mentioning that the strut being used has a 19 pound preload. WAY too much for our application.
I'm waiting to hear back from a few manufacturers about other options. For the experiment, these were an eBay purchase.

But still think this is a very viable solution.

[Bruce Fenstermacher]

David,

Flying my plane today I took note of a bolt with washer and nut that protruded out of structure in front of the door. A perfect place perhaps to attach a door strut bracket.

Looks like this bolt is number 96 Figure 21. It is a An-6-10A that holds the landing gear support bracket in. I'm thinking one might remove the washer and replace it with a bracket or replace the -10 with a -12 and put a bracket on it. Certainly a minor alteration

This would provide the place to mount the forward bracket with no modification.

Of course the other end goes to the door which is not as critical a structure and a few holes would be a minor alteration.

Just food for thought.

[GAHorn]

Round two of testing. The 20 pound weight on 1.5 square inches of tape is still holding out in the garage.
This is a test using the actual brackets. Slightly different results. ....

It might be good to test the strength of the tape in warmer weather.

I've been using some extraordinarily strong industrial velcro to mount my Garmin Aera 510 to the top of my instrument panel for a couple years now...with absolutely no problem...until I returned to the plane after the BBQ fly-in at Smithville a few months ago and found the unit dangling by it's cord. The sun's heat and greenhouse effect of a closed cabin softened the adhesive until it let go. I re-used the same tape, and with cooler wx and storing inside the hangar, the tape has held just fine. (I expect to remove the unit from it's mount when I park the airplane outside on future Texas summer days.)

[Bruce Fenstermacher]

I agree. A test in about 130 degree environment would be prudent.

[Brad Brady]

I like what I'm reading.... if nothing is held in place, with any type of structural clamp.....Where is a 337 or STC needed?

[GAHorn]

the common reason for STCs is to provide a basis of approval
for parts being sold as aircraft parts.
however one can manufacture parts for your own Pt 91 aircraft...
but you cannot offer them for sale to others as aircraft parts,
unless you have approval basis.
this is probably a minor alteration,
as long as you do not alter structure such as door postso, etc by drilling.
this may even qualify as preventive maintenance, since it is an interior trim item,
which would qualify it for owner pilot performance.
opinions may vary,

[bagarre]

To make and sell a part; wouldn't you need a PMA or some other approval under CFR 14 §21.9?
I thought the STC approves the design and implementation but you needed a PMA to make and sell any parts under that STC (XPMods for example).

Now, if someone has an STC they could sell the approved data in order to manufacture the parts and the Owner could produce the parts without PMA.

The 3M VHB experiment is turning out to be just that..an experiment.
The constant pressure of the gas strut WILL, over time, work the adhesive lose or at least allow the bracket to deflect until it interferes with operation.
I took a heat gun to it last night and the defection increased with the piece hot to the touch

The last idea would be to use a gas Damper strut rather than a spring strut. There woudl be no load on the brackets when closed. But you don't really get the benefit of the door being held open for you (it would slowly close). It may not be terrible. Those Dampers appear to cost $30 or so each. Plus socket, brackets and end fittings you're around $80.00 in materials and the inboard bracket needs custom made. That's still cheaper than the STC but you still have the VHB tape to contend with.

[GAHorn]

That is a more elaborate and more correct explanation. I was being contrary to my usual method and attempting brevity.
I was posting via smart phone.

[bagarre]

I only know that because I've been fervently researching Owner Made parts lately.