Pneumatic based door retention sytem

[bagarre]

I dare not call it a Door Steward. That name is already taken.

DoorStrut.JPG

The Door Steward requires an STC because it modifies the airframe with a bunch of holes for rivets.
This system requires NO drilling nor changes to the airframe of any kind.
Instead, it uses 3M VHB tape. 3M states that VHB has better holding strength than mechanical fasteners. (Let's hope so )
My initial testing of VHB is very promising. A 1" square piece applied to two pieces of steel is impossible to pull apart. I was finally able to wrench it apart with a crowbar and vice While wrecking the steel. That's more than enough adhesion to hold a door open. The adhesive remains flexible

Most of the parts are off the shelf.
2 standard 15" 10 pound gas struts (The lightest strut made)
2 right angle brackets with 10mm ball mounts (Will mount to the door)
2 10mm threaded ball mounts
2 Home made brackets out of .050 4130 steel for the door posts.
The final solution will have metal strut fittings instead of the photographed nylon ones to comply with burn tests.

Ignore the acorn nuts, they were all I had in the garage for the mock-up. The installation will have more appropriate fasteners.

If all goes well, it will work. Since there is no airframe modification, it's a log book entry.

Total cost: $45.00 including a whole roll of VHB tape. More to come!

DoorStrut2.JPG

[Bruce Fenstermacher]

So how would one remove VHB tape if one wanted to?

Great project I'll be coping.

Obviously metal will meet a the most stringent burn test. But have you looked at what burn test is required of a CAR 3 aircraft. Bet the plastic will pass.

Also drilling holes or not is not what is the difference between a minor or major alteration. I think depending on where the holes are drill this is could be a minor alteration. The fact Door Stewart is an STC'd product as no bearing on whether it would have to be STC'd. Lots of STCs are issued simply to because doing business with an STC is absolute but a product without may always draw questions.

[bagarre]

I figured there would be a solid argument for airframe modification because the holes are drilled in the lower portion of the door frame.

Also, I already ordered the metal fittings. I'll be sure to burn test them to be sure

Removing VHB tape requires quite a bit of elbow grease but is not impossible and leaves behind no traces. You could use a razor blade with a lot of patience but a piece of very fine music wire and a little oil will cut thru it. Kinda like cutting out a windshield. I dont know if MEK will soften it.

VHB is such an impressive bonding tape, people may consider it an unfair loophole.
In the experimental realm, you could skin a wing with the stuff.

[FredMa]

I don't know if I would get my hopes up. A sustained force from the struts over a long period of time might pull the Flexible adhesive apart even if a short term much stronger force doesn't, like in your test. You may come back to your aircraft the next day to find your struts dangleing.

[bagarre]

That is a possibility and I even thought about performing a 10 pound hanging test on the bond.
But, this stuff is used to suspend panels from buildings. That's a pretty decent test in itself.

This is a good point tho. I think I'll hang a barbell on a piece of the tape over the holidays while I visit family.

*Edit* The tape does require 20 minutes for a 50% strength bond and over a day for 90%. So, it would be a good idea to let the pieces set in place for a few days before attaching the gas strut. I just joined two pieced of aluminum with the tape and will hang a weigh on it tomorrow.

[GAHorn]

Epoxy would likely work well, also.

How 'bout a list of parts (SKU numbers, brand names, models, etc..) and places to purchase, and an ARTICLE FOR "THE 170 NEWS"?

[bagarre]

How 'bout a list of parts (SKU numbers, brand names, models, etc..) and places to purchase, and an ARTICLE FOR "THE 170 NEWS"?

Exactly what I was thinking.

[bagarre]

The saga continues.

I thought I'd run a small test using the same surface area as would be used in the set up.
After 20 hours of set up, we should be at about 80% strength. Again, There is no way Im going to pull or twist this apart.
For the sustained load test, I thought a 20 pound pull would work. The strut is only 10 pounds.

I'll check it again after Thanks Giving.

In the mean time, I'll get all the part numbers together.

Cheers!

vhb_hang.JPG

vhb_side.JPG

[Bruce Fenstermacher]

This is really cool David. I can not wait to install them on my 170 which has no door stops. I wonder if Leroy has any of those gas cylinders in his pile? (But of course they'd be flat. )

[bagarre]

Pull test failed.

20# load on 1.25 sq inch surface of tape failed at 24 hours.
The failure was 100% to one side of the tape and remained fully adhered to the other.
This was 4941 VHB tape and is supposed to have an 85 psi strength and is intended for painted surfaces.
That makes me think poor surface prep. It was bare aluminum wiped down with alcohol.

Down but not out.

Need to read up more on VHB tapes and what's the most appropriate for our condition.

**EDIT**
The one side of the aluminum seemed to have some type of a film over it.The other was an old piece that has been worked, sanded, filed...
I decided to acid etch and alodine both pieces and tr-try the test. The initial adhesion of the tape seems to be WAY more significant on initial contact. (anecdotal)
So, the pieces are joined once again and will be hung 24 hours from now.

Evidently, surface preparation is incredibly important.

[wingnut]

We used a similar 3M product, maybe the same stuff, to bond lighting protection panels to the wings of Saab 340's. Surface prep is important. We used the tape to attach a large sheet aluminum shark fin to the cabin top of 1973 Olds Delta 98 that we left at N. Kentucky/Cincinati Int airport, because we did so much work up there at the time. The fin was about 4 ft long, and 3 ft tall. The base flange was only 2 inches wide, by 4 feet long, and all that was used to attach it was that 3M tape. We drove that car for 3 years with that fin on top.

[Bill Hart]

Was the shark fin for going to Jimmy Buffett concerts?

[hilltop170]

Yeah Del, just what was that fin for? It had to have some significance.

My nephew, the A-10 pilot, was handed-down a "beater car" in Korea when he was stationed over there that had two trash cans bolted to the trunk. Imagination can run wild sometimes.

[wingnut]

I was just fun. The owner of the company was saving money by buying the old car, in lieu of renting. We had a 4-6 man crew there for 3 years. Everybody that lived and worked up there had fun with us hillbillies. They called us Del Bob, Joe Bob, Rick Bob, Rob Bob, and so on. For some reason they laughed at our "new" ride, and it somehow got the name "Land Shark". That's another story. One day we decided to make the car fit the name. Rick Bob, was the artist who used electricians tape to make the evil eyes, and teeth on the front fenders. I think Keith Bob made the tail fin, and I made the cabin top fin. We didn't want to permanently alter the car by drilling holes, so we proof tested the tape.
We made the news, and were often mentioned by the traffic helicopter. There was a dive where we got discounts on catfish dinners, and pitchers of beer just for parking out front. They said it attracted business. The local mechanics soon became envious Somewhere I have pictures. Maybe I can scan and post. Good times in that old car. I drove it from Mena to the Cincinnati airport. It had the 455 rocket and expected serious fuel burn. To my surprise the car got 20mpg. Motor blew between the Oldenberg Brewery and the colossal flea market south of Ft Mitchell. We coasted in to Denny's and left it

[Brad Brady]

That's funny, Del. The best I had was an old 70 LTD, I used as a work car....It was dubbed the four toned, for door, Ford...Every door was from another car....and another color than the base color of the car. I can't remember what happened to It.