Legal Eagle XL in Pennsylvania

[Kamcoman77]

Not shown in your last photo is the K-block the aileron cove cover attaches to. Of course, you could use two of your 1/4" K-block gussets in place of the K-blocks.

[Pilotarix]

Good picture, thanks.
Obviously, an excellent idea to use two K-blocks to have more surface area to glue the cove cover on.

Today, I had just some time cleaning the shop and arranging the ribs on the mock-up spar.
Now I have to do the ribs 7, 12, and 13. But before that, I need to make a hinge pin to perfectly line up all the hinge holes.

[Pilotarix]

Hi all,

I am in the process of making ribs 7, 12, and 13, which causes more brain twist than likely necessary.
Because I cannot fit the plywood covers in my jig and the space inside the rib around the hinge hole should be filled anyhow, I made some kind of a hinge hole locating block. Then I made a Delrin hinge hole locating pin. With the hinge hole positioned, I can later attach whatever piece of plywood right and left to the rib and have the hinge hole always perfectly located.
The hinge block between ribs 12 and 13 will be glued onto the hinge hole locating block. That assembly should be strong enough.
Now I can finish these last ribs and get the jig of my workbench. That will free up space to start with other stuff.

[Pilotarix]

One question to the control surface hinges.

I am going to make the aluminum version, not because they are better,  just because I can.

However, there is one thing I am not sure about. In the Facebook group, somebody mentioned increasing the distance of the steel tubes before welding by about 1/16 inch makes things easier. See screenshot.  But that also causes the gap between the control surface the stabilizer to widen.
Any thoughts about that?
I did the first version of the aluminum hinges with increased space between the holes. With that, the gap between the tubes already looks like a lot.

[Kamcoman77]

At our speeds I don't think a little more gap is going to matter. Unless you use a gap seal, I'll bet about the same amount of crossflow exists in a 1/2" gap and a 3/4" gap. I don't know if an excess gap would contribute to flutter, but maybe there is an article about this somewhere on the Internet.

[Pilotarix]

Cross flwo and flutter is both not really great. I may change the hinges back to the original form.



I am still in business, work is just very intense these days, thanks to COVID, and there is not much time left in the day for progress on the eagle project.

Still working on the last wing ribs, had to make some new gussets and pieces since I broke two ribs while getting them out of the jig.

I think my hinge hole location block works like expected, no gussets behind the rear spar on these ribs, they get covered with 0.08 mm ply on one side and 0.25" ply on the other. That should give plenty of stability.

On a very positive note, my spar wood arrived this week, way way earlier than expected. So I can continue working on the wings.

Not so positive... when I made a list for my aluminum supplier, I copied the information out of the plans. That may have been a big mistake. Now I am the proud owner of aluminum tubing 1.25" in diameter for a lot of money that I probably not going to use. I am open to suggestions on what else I can do with that. Maybe a roll cage for my sprinter van ...    

[Chuck in Indiana]

Now I am the proud owner of aluminum tubing 1.25" in diameter for a lot of money that I probably not going to use.

Uhh, while much of the materials and hardware list is suspect.. 1 1/4" diameter is correct for the spar aluminum.

[Kamcoman77]

I thought they were for the struts?

[Chuck in Indiana]

I thought they were for the struts?

Duh. Think one thing, type another.

[Pilotarix]

... while much of the materials and hardware list is suspect.. ...

Unfortunately 

I thought they were for the struts?

That is what I thought as well.

However, under "Struts," it's mentioned that extrusions from Carlson Aero were used, obviously not the stuff listed in the material list under Aluminium.
Has anybody used round tubing for the struts? Sometimes hard to see in pictures or videos, but I think I have seen mostly oval-shaped extrusion rather than round tubes.
I checked the Carlson Aero website, looks like these tubes are roughly 8$ per foot if I understand their pricing correctly. The transport costs will be very high though.

[Tom XL-7]

many fly with round struts they are less expensive but more importantly much lighter. the Carlson or rounds still require jury struts.
if you a concerned about the drag round things have been faired since the beginning of aviation

[Pilotarix]

many fly with round struts they are less expensive but more importantly much lighter. the Carlson or rounds still require jury struts.
if you a concerned about the drag round things have been faired since the beginning of aviation

Thanks for your input, those are important points to think about.

I am not really concerned about drag, not at 60mph, and I am thinking about using the Hirth F23 engine, which has 50 hp.

That is the tubing I got from my metal supplier.

1.25" OD x 0.058" Wall x 1.134" ID Aluminum Round Tube 6061-T6
weight per foot 0.26 lb.


This is from the Carlson website, assuming that their small struts will do it. They compare them to:

Stronger than but compared to 1.275 Dia x .065 wall 6061T6 tubing

ULTIMATE = 18,012 PSI
YIELD = 15,947 PSI
SHEAR = 11,637 PSI
AREA = .431 SQ IN
CIRCUMFERENCE = 5.625
WEIGHT = 0.517 #/FT
126 ” LG – $71.00 / LENGTH

As one can see, there is a significant weight difference. Round 0.26 lb and oval-shaped extrusion 0.517 lb /FT.
If all these numbers are correct, struts from round aluminum tubing could save about 3-4 lb, which seems to be a lot.

It also brings up the question of why the designer has chosen extruded oval-shaped struts for his airplane? Sticking to lightweight construction would have called for round struts, but only if they are not markedly inferior in strength compared to the extruded oval struts.

Anyhow, lots of time for more research until I have to make a final decision about the struts.

[Kamcoman77]

Round struts are plenty strong. Putt Putt (high time LE) used round struts with a thin aluminum fairing. I don't think there were any issues. He even left the jury struts off at times. I plan to use round struts to save weight & money.

[Pilotarix]

Thanks!

Since my last posting, I went into the garage and looked at the tubing. Pretty substantial stuff. I am going to stick with it as well.

Today I finished sanding all the ribs. No more making ribs... if I don't break any 

Here are a couple of pictures showing rib number 7 with all that will be attached to it. Not shown is the hinge block.

My laser is too small to make the whole piece so I made two pieces from it. Should not be a problem since it will be glued to the "hinge hole locating block".

[Chuck in Indiana]

I am going to stick with it as well.

Attaboy. The round tubing is plenty strong. I would think the lack of streamlining will show up mostly on landing. I'm at least planning on carrying some power all the way to touchdown until I get some experience with it. As Keith said, it would be easy enough to fair it if necessary.