Seems like it's been a while now. What gives?

Why Zane....trying to place an order???

You can get to some of the info through http://www.justkitplanes.com Not sure what gives with the company site, I can't get it either.

Speaking of the Highlander, I wonder if someone who has built one would chime in here and talk to me about if they are actually pop - riveting the strut fittings to the spar as depicted in one of the build pics and what are the rivets they are using.

From justkitplanes.com build pics:



gb

Gb, from the look of those pics, I'd say yes. However it looks like the fitting is a machined fork welded to a tubular sleeve over the spar itself, and pop riveted to secure it, with a multitude of rivets as we can see. Seems to me to be fairly bomber. The collective shear strength of all those rivets is prob pretty high.

But I haven't actually built one. Yet.

I watched the operation being done on the highlander that BCP member rfinkle now owns. It is a tubular sleeve and fitting as mentioned. The holes get drilled and deburred, the fitting test-fit several times, and then it is put on with filled epoxy AND the Avex blind rivets.

The general rule is that you need 5 Avex rivets to give you the same strength as 3 AN solid rivets (according to Heintz).

In THEORY and on PAPER, the epoxy should be a strong enough bond with no rivets, and the rivets are strong enough with no epoxy. So the combination of both yields a very overkill structure and they compliment each other. The epoxy keeps the parts from movement relative to each other (shear) that would eventually weaken the rivet holes. The rivets keep the parts from peeling apart, which would eventually break the epoxy bond. It is apparently a good mutually beneficial use of materials.

What's the verdict on the wood ribs?

Is it cause for concern that all those holes are perforating the spar at the very point of highest stress?

The verdict: they really are made out if wood.

So you could build a bridge out of them. They also float, and weigh as much as a duck, ergo the plane is actually a witch.

Sorry, couldn't resist. Not sure how many will get that.

Just pray they aren't patented and someone extracts a license fee out of you.

Oregon180 wrote:Is it cause for concern that all those holes are perforating the spar at the very point of highest stress?

No.. This same construction method is used on the Avids and Kitfox line, and there has never been an inflight structural failure of the wing. We have beat the ever loving crap out of them and they soak it up and keep right on flying. No issue with the wood ribs either. The Avids just used SS pop rivets at all the attach points for the drag tubes and the strut fittings. When I rebuilt the plane I have do to a lil incident the previous owner had, I replaced all of the flaperon hanger rib tails, and checked all fittings. 12 or 13 yrs of flying had not loosened a single rivet or popped a single glue joint, and the plane had been on its back TWICE!

gbflyer wrote:You can get to some of the info through http://www.justkitplanes.com Not sure what gives with the company site, I can't get it either.

Speaking of the Highlander, I wonder if someone who has built one would chime in here and talk to me about if they are actually pop - riveting the strut fittings to the spar as depicted in one of the build pics and what are the rivets they are using.

From justkitplanes.com build pics:



gb

They are Stainless Steel Rivets ('Rivets - lift strut attach bracket to wing spar - 1/8in x 1/2in stainless) Part # SSD48SSBS. I'm pretty sure there are 20 of them on each bracket. I'll count tonight and correct this post if I'm wrong.

Rich

Rich

If you look at the bracket, there are 17 showing on one side of it, with 5 or 6 more down the center, then another 17 on the other side. I am guessing closer to 40 per bracket.

Zane wrote:What's the verdict on the wood ribs?

No biggie, they're pretty thick Birch plywood, maybe 3/8" or more. They're a little more work than aluminum ribs because you have to go and hand-varnish them with epoxy, but if designed properly they are plenty strong. Sawn plywood ribs are not quite as light as built-up ribs made out of a dozen pieces of 1/4" square Spruce. But they are easier to make and when designed properly they are very strong. They are also likely more resistant to damage from handling/hangar rash as well, because of the plywood's bending resistance. As mentioned, thousands of KF/Avid airplanes flying around.

Warning: Slightly off-topic but still relevant to this subject IMHO

The one and only weak spot, in my opinion as a semi-educated, non-engineer sideline observer, is that aluminum does not like to be glued. No matter how well you clean it, a microscopic layer of oxide forms within seconds, and you are actually trying to glue to that oxide layer. I was informed (by a scientific chemist type person who knows far more than I) that you will get about 20% bond strength that way, meaning 20% of the strength of the base metal.

Now if you design for that by shaping the ribs with rounded cutouts that wrap halfway around the alum. tube, and/or putting the glue joints under loads that are more favorable (i. e. not "peeling loads") it is relatively safe. This wing design has the tube spars being "pulled" together by the fabric and any compression struts or diagonals, pulling the spars into the rounded rib cutouts. This helps greatly. But you still have the possibility lurking that the oxidation layer can start to creep under the epoxy over time and weaken it. So you need to inspect for this type of de-bonding at annual and you need to strip and recover at some interval even if the fabric is good.

There are two main factors to remember IMHO when bonding aluminum:

1) Big Aerospace does it all the time, with honeycomb and structural bonding and plenty of glued aluminum joints, even on small airplanes like the Grumman's AA-1 and AA-5. But they have special facilities and methods not available to homebuilders.
2) Homebuilders have a poor record of being able to accomplish bonded aluminum safely, we've lost a few Monnett Monerai and Moni aircraft, and Schreder HP series gliders... because you cannot reliably create the environment for bonding in your garage.

However, there's something you CAN do easily to solve this problem if you are building with bonding to aluminum, which is why I am ranting about it here on a Highlander thread. There are certain types of conversion coating (Alodine type wash coatings) that make the surface of aluminum into something that DOES like to be glued. These conversion coatings actually change the chemistry of aluminum in the outer surface layer. It was reported that after the conversion you will get 80% bond strength, which is as good or better than a riveted joint.

So one fact is that there are thousands of KF/Avid airplanes flying safely without the conversion coatings, but IMHO they need to be inspected for creeping bond failures on a regular basis, the same way as you inspect for dry rot and worn rivets and rusted steel tubes. And the other fact is IMHO that if you are building an airplane with glued aluminum, doing the conversion coating before bonding is a very cheap and simple method of getting far better strength and reducing the likelihood of bond failures. You also get permanent corrosion proofing as a side benefit.

The site is back up now..............

EZFlap wrote:

Zane wrote:What's the verdict on the wood ribs?

No biggie, they're pretty thick Birch plywood, maybe 3/8" or more. They're a little more work than aluminum ribs because you have to go and hand-varnish them with epoxy, but if designed properly they are plenty strong. Sawn plywood ribs are not quite as light as built-up ribs made out of a dozen pieces of 1/4" square Spruce. But they are easier to make and when designed properly they are very strong. They are also likely more resistant to damage from handling/hangar rash as well, because of the plywood's bending resistance. As mentioned, thousands of KF/Avid airplanes flying around.

Warning: Slightly off-topic but still relevant to this subject IMHO

The one and only weak spot, in my opinion as a semi-educated, non-engineer sideline observer, is that aluminum does not like to be glued. No matter how well you clean it, a microscopic layer of oxide forms within seconds, and you are actually trying to glue to that oxide layer. I was informed (by a scientific chemist type person who knows far more than I) that you will get about 20% bond strength that way, meaning 20% of the strength of the base metal.

Now if you design for that by shaping the ribs with rounded cutouts that wrap halfway around the alum. tube, and/or putting the glue joints under loads that are more favorable (i. e. not "peeling loads") it is relatively safe. This wing design has the tube spars being "pulled" together by the fabric and any compression struts or diagonals, pulling the spars into the rounded rib cutouts. This helps greatly. But you still have the possibility lurking that the oxidation layer can start to creep under the epoxy over time and weaken it. So you need to inspect for this type of de-bonding at annual and you need to strip and recover at some interval even if the fabric is good.

There are two main factors to remember IMHO when bonding aluminum:

1) Big Aerospace does it all the time, with honeycomb and structural bonding and plenty of glued aluminum joints, even on small airplanes like the Grumman's AA-1 and AA-5. But they have special facilities and methods not available to homebuilders.
2) Homebuilders have a poor record of being able to accomplish bonded aluminum safely, we've lost a few Monnett Monerai and Moni aircraft, and Schreder HP series gliders... because you cannot reliably create the environment for bonding in your garage.

However, there's something you CAN do easily to solve this problem if you are building with bonding to aluminum, which is why I am ranting about it here on a Highlander thread. There are certain types of conversion coating (Alodine type wash coatings) that make the surface of aluminum into something that DOES like to be glued. These conversion coatings actually change the chemistry of aluminum in the outer surface layer. It was reported that after the conversion you will get 80% bond strength, which is as good or better than a riveted joint.

So one fact is that there are thousands of KF/Avid airplanes flying safely without the conversion coatings, but IMHO they need to be inspected for creeping bond failures on a regular basis, the same way as you inspect for dry rot and worn rivets and rusted steel tubes. And the other fact is IMHO that if you are building an airplane with glued aluminum, doing the conversion coating before bonding is a very cheap and simple method of getting far better strength and reducing the likelihood of bond failures. You also get permanent corrosion proofing as a side benefit.

Not picking at this kit one bit, or the builder. I think it's a real neat airplane. However....

Agree with you 100% with regards to gluing and painting aluminum, I was surprised there was no conversion coating (aka acid - etch, alodine) under that fitting and I'm glad someone else noted that. Might be overkill in this case, but that's my middle name. I've goofed around with aluminum off-shore boats quite a bit and nothing sticks to it worth a damn without the above steps. I wonder what alloy that spar tube is.

gb

I'm obviusly biased on this since the pics listed below are of my plane, that I built. I'm no expert on anything but I feel completely and totally comfortable in my plane with my wife or daughter with me. All kits use different materials and techniques but I chose this airplane after seeing one in person and taking note of its structural superiority to many I had looked at.

The first pic is the strut attach bracket which is 1/4" 2024 aluminum, the holes in the green colored bracket were enlarged to 3/16ths and fastened with AN3 nuts and bolts. The holes on the aluminum spar are for 1/8th" solid rivets which hold the .040" backing plate in position. The end of the strut has a machined 2024 fitting with 3 AN5 bolts to attach it to the strut, the strut gets attached to the bracket shown here with another AN5 bolt: http://webhosting.web.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://www.donsbushcaddy.com/sitebuildercontent/sitebuilderpictures/WingsRightRearSpar005.jpg&target=_self

The second pic is the wing structure. Front and rear spars are .040" C channel aluminum. There are trailing edge ribs, center ribs and leading edge ribs. There are 3 stringers on top and bottom of the wing and it is covered in .025" aluminum skin. These are all fastened with Avex blind rivets. The structure speaks for itself:http://webhosting.web.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://www.donsbushcaddy.com/sitebuildercontent/sitebuilderpictures/LeftWingStringers002.jpg&target=_self

Just my $.02. Don...