# Flight Club - Ultralight Build Log

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##### Well-Known Member
Do you have a photo/drawing/link of these extrusions? I wasn't able to find them on Airdrome's website...

Thanks for all the great feedback and discussion, everyone!
Do you have a photo/drawing/link of these extrusions? I wasn't able to find them on Airdrome's website...

Thanks for all the great feedback and discussion, everyone!

#### jedi

##### Well-Known Member
I do not see how this is an extrusion. It does not look like the excess is milled off and the match parts could not be zig zag cut easily.

Could the actual hinge part be shortened to just the large cross section area and three identical components fastened to the structure for each hinge?

#### Victor Bravo

##### Well-Known Member
Could the actual hinge part be shortened to just the large cross section area and three identical components fastened to the structure for each hinge?
Yes this is also what I had assumed too. One inch slices of the extrusion, three pinned together at a time.

##### Well-Known Member
It is an extrusion and my quick sketch may not be accurate. Robert mills them to fit as shown. If you can get him to sell you a length of extrusion you can make it as you see fit.

##### Well-Known Member
I found a good picture of the hinges.

##### Well-Known Member
Yes this is also what I had assumed too. One inch slices of the extrusion, three pinned together at a time.
You don't need an extrusion to do this. Just cut them to shape from a 1" aluminum plate.

#### jedi

##### Well-Known Member
It looks as though you could just mill the nub off of the extrusion. It would not hurt if the cut went into the hole for the tube support.

#### Dana

##### Super Moderator
Staff member
It's hard to tell from the picture, but I'd guess the relief cuts go straight across rather than being curved to match the sleeve OD. Pretty common way to make things: Take an extrusion, chop it to length, and do some simple secondary operations.

#### Hot Wings

##### Grumpy Cynic
HBA Supporter
Log Member
It's hard to tell from the picture, but I'd guess the relief cuts go straight across
Zoom in on "right click-view image" (CTRL/+)

It is a straight cut.

#### Victor Bravo

##### Well-Known Member
Using a band saw, belt sander, 1/8" drill, and three or four feet of Baslee's extruded hinge material, I don't think you can get it any easier, safer, and faster than this. No milling, no welding, no precision machining, Two or three pop rivets for each hinge. Line it all up with one long rod at the same time, drill, cleco, and pop rivet.

#### BBerson

##### Well-Known Member
HBA Supporter
Don't always need three hinge blocks if mounted firm. Just two on the Grob.

#### Victor Bravo

##### Well-Known Member
Don't always need three hinge blocks if mounted firm. Just two on the Grob.
Yes, I agree three hinge blocks is arguable one way or another. The two-element glider hinges are a lot more securely mounted (glassed in) in the European composite aircraft, so the hinge pins are loaded in pure shear. I'm guessing that a riveted hinge in thin wall aluminum tube would be a little more prone to the rivets working a little, and off-axis loads windingup in the system. Maybe getting the pin loaded in double-shear is a worthwhile goal on Ollie's project, or maybe it's overkill. Somebody would have to examine all the loads on the fasteners and whether it's prone to the rivets working loose in the tubes, etc. to be sure.

#### proppastie

##### Well-Known Member
Log Member
might want to take a ride to where they fly or have an untra lite with similar structure of your wing rear spar and aileron.....take some pictures....If you know the aircraft you are close to in terms of structure, they will have a website.....You could ask if there any builder/owners near you that you could look at one....Might express an interest in building one and want to talk to someone that has one.......

Your idea of the eye bolts should work......The piano hinge should work and I believe is the easiest.

If the hinge is in shear there is a shear value to the rivets, With the cross section area of the element you are looking you can determine the shear and yield strength of that piece of metal in question. You also have to look at the bearing yield of the tube wall.....It can get tedious so that ride to the airport or a faithful copy might be easier.

Edit:.....I looked at what you have ....and with over kill on number of rivets (looks like you can get 8 or 10 on each half) that hinge should work. please load test and check for looseness before every flight

minimum rivet pitch is 3D (3 diameter)

Last edited:

#### Ollie Krause

I just called Robert from Airdrome and offered to sell us some extruded hinges for $18/piece +$14 S&H. I didn't get to talk to him for very long but he seemed like a really nice guy and I think $18 is a fair price (We'll be using 4 hinges total). While I really like his hinges, I don't like that the repeatability of our design is now dependent on a single source. We'll use the Airdrome hinges for the first version of our airplane but we'll also look into the welded option discussed above as an alternative method. #### proppastie ##### Well-Known Member Log Member he seemed like a really nice guy see if you can get the tube sizes for the various locations to compare with your tube sizes....I assume he has different sizes but I do not know. #### Ollie Krause ##### Well-Known Member see if you can get the tube sizes for the various locations to compare with your tube sizes....I assume he has different sizes but I do not know. He only mentioned one size that he said slides over a 1" tube. I'd be concerned that larger sizes would weigh too much to be practical for aileron or other large hinges. #### Victor Bravo ##### Well-Known Member Don't worry at all right now about repeatability. A single source is just fine for what you are doing at this stage. When you are pursuing your postdoctoral degree in manufacturing design, then worry about this kind of stuff. When that happens Addicted2Climbing will give you his source for custom made hinge extrusions #### proppastie ##### Well-Known Member Log Member He only mentioned one size that he said slides over a 1" tube. I'd be concerned that larger sizes would weigh too much to be practical for aileron or other large hinges. A schedule of tubes used would be useful,...if he slides one over the other for strength and that is the only two sizes for his aircraft that certainly is interesting, unless he is talking about the hinges, in which case yes the hinge slides over a 1" tube. #### Rudy Lee ##### Member Hi all, As we move into our phase of revisions, one big step that we need to do is stress test our ribs. We want to know exactly how much they can hold so that we know how many we need. Our ribs will consist of 1" thick house insulation surrounded by 3/32" birch plywood epoxied on. We can pick up the foam insulation and epoxy locally, but we had a very hard time sourcing our plywood. We have a few options, which I would love to get some opinions on. Option 1: Buy the aircraft-grade plywood from AircraftSpruce but we have to pay around$200 for freight shipping, which is fine for the shipment of all of our materials, but it's kind of a waste just for a bit of plywood. We aren't nearly ready to order all our materials yet, so we would be spending the shipping fee just for the wood. We are willing to do this if need be, but we'd rather find another solution.

Option 2: Use some other form of plywood that has similar specs to AircraftSpruce's, however, this would likely take the form of thicker plywood, which might totally change how our ribs behave, although we're not certain on this, any thoughts? Accurate data is super important, as we will be using these numbers to figure out how many ribs we will need and to start our truss analysis on the frame. Even small inaccuracies could lead to us adding an extra rib which would mean several pounds of unnecessary weight.

Option 3: Thanks to Dana, we have a great rib test comparison, attached below, that we used to determine which type of rib construction we will be using. Is there any way we can use these numbers to somehow estimate what the whole rib can hold (these only test the trailing edge)? We assume the breaking behavior will be totally different on a full rib, but we're not certain. Lastly, does anyone else have any other ideas for how we might be able to get our hands on aircraft grade plywood for testing?

Thank you all and have a good one.

#### BJC

##### Well-Known Member
HBA Supporter
Where are you?

How much do you need?

When do you need it?

BJC

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