Bearhawk Five Plans #5053

[Redneckmech]

Center ribs are now primed and have stiffeners riveted on! All .024 ribs used AD3-3.5 rivets, I used AD3-4 for .032 ribs and AD3-5 for the root ribs. Pretty much all of them about a 1/2 size above what I had originally calculated.
I also upgraded rivet guns. I had been using a surplus IR AVC12 gun which did not have good trigger control and had a great deal of leakage. I found a NOS Chicago Pneumatic 4444-RUSAB (3X) on EBay for a good deal. With the new gun I was able to regulate the trigger down to a single hit. This made a world of difference.. I liked it enough I found a CP 4444 RURAB (2X) gun that was missing a spool valve and repaired it. The 2X has quickly become my favorite gun for the 3/32 rivets when adjusted down to 25-30PSI and I can have an entire stiffener riveted on in the time it took me to squeeze one-two rivets with a squeezer.


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The next step to do was one that I have been putting off: drilling the balance tube hole in the Aileron nose ribs.

I first tried a Forstner bit as I had one on hand and I had seen another builder use with good luck. Well... My luck was not as good.

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I ended up drilling the remainder with a dull Harbor Freight step drill bit.

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I think my next step once i get the Aileron and Flap ribs primed is to start cutting spar blanks and figure out how I am going to bend them....

[SpruceForest]

Too late for you this time around, but a jig which clamps the aileron nose rib web-down, a 1/4" pre-drilled center hole, and a bimetal or carbide hole saw with the center drill replaced with a bit of 1/4" drill rod works well in the drill press for those minimum-clearance aileron balance weight holes .

[Redneckmech]

I am at the point in the project where bending the spars is quickly going to be a gating option and I still have not been able to make a decision on how I am going to do it. So far, I have been unable to locate a usable 10' brake within a 100 mile radius, the only one I have found is not in a condition that would produce a scratch free spar and I like doing all work myself anyhow so I am currently leaning towards building a brake out of some scrap I beam that I have laying around or possibly investing in the material to build a good quality brake.

Does anyone know if the Mac's Machine brake plans are still available? The links I have tried no longer work and I have been unable to locate them. It looks like a well built brake that could be increased to the needed length with only minor changes.

Has anyone tried priming one side of an aluminum sheet to protect it prior to bending spars? The aluminum sheet I have for the spars only has plastic on one side of it and I am weighing my options between priming it or using adhesive floor protector to protect it from scratches during bending.

Thanks,

Bill

[jaredyates]

There is another thread going on now, in addition to a few others in the archive, that address brake building. They all follow a similar arc of "how hard can it be" with a few replies to the contrary, to "well that didn't work" to "why is this so hard", then after many iterations and much work, maybe to "I finally got it to work" but not always. The forces involved are very high and if you've seen a 10' brake big enough to do the job, you know it's a seriously heavy machine. Something more on the scope of a truck than a workbench.

Can you make little shoes for the brake out of soft aluminum flashing?.it comes in a long skinny piece and is easy to find locally. Bob mentions this in one of the early Beartrscks for both scratch protection and also radius modification.

[Redneckmech]

Unfortunately, the brake that I located is well past being in adequate shape for a shoe to help it. It is a large finger brake that someone must have bent much thicker material than it's capacity at some point in its past. Several of the fingers are bent over 1/8" and I don't think they could be shimmed back into alignment.

I just got another lead on a shop semi-locally that may have a brake so will be checking with them today. Alternately, kilohotel had his spars bent at a shop in Post Falls, it is about 120 miles away from me so may be worth the drive...

[Redneckmech]

For anyone that is looking for protective film for their aluminum I was able to locate it online and US made! The same brand is also available on Amazon.

https://tapemanblue.com/products/aluminum-protection-film?variant=39324522119248

[Bcone1381]

Your local fabrication shop may not have a 10' brake, but I bet he knows his competitors and may tell you who does. Some jobs just need a professional touch.

[Redneckmech]

That is the problem with not being near a major population center, I have gotten several references but all were to shops that are in Spokane Wa, which is a solid 120 miles away from where I live. I now have a line on a shop in Clarkston Wa, which is only about 40 miles away. Going to give them a call today and hope they have the capability and willingness to bend them.

[Redneckmech]

Has anyone else run into an issue on plans page 7 where the actual measurement differs from the call-out? I was copying the sketch with a light-box and engineering paper and noticed that it doesn't quite match up. The Main Spar Inner plate measures 5-7/8" where the call-out is 5-3/4" and the Splice Plate measures 5-13/16" instead of 5-3/4".
Is this just my set of plans or is is a known issue? If it is a known issue has everyone has just been trimming their plates to the call-out?

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[Redneckmech]

Spar webs are bent!!!

Plenty of learning happened of which first and foremost, do not assume that a regularly used brake is actually in adjustment. I was able to find a small local shop that had a brake in good shape, When I inquired about having my spar webs bent, the owner responded " I don't want to bend those for you, but if you want to use the brake you are welcome to try!"

Well, I tried...

several times...

I was able to successfully get test pieces bent left right and center that were perfect matches but when I bent full length pieces (read: spars) they ended up narrower in the center than on the outside edges. After getting frustrated, stepping back, and researching potential issues, I was able to determine that the truss rods were FAR out of adjustment. I spoke with the owner and reported my hunch, he was willing to let me make any needed adjustments to the brake. I was able to find a document from a brake manufacturer that gave very limited information on adjusting a leaf brake essentially stating that it was shipped from the manufacturer set for maximum capacity with the leaf flush on the outside edges and 1/32" low in the center of the leaf. The listed caveat was that if bending material thinner than maximum capacity the leaf may need to be adjusted "closer to flush". I spoke with several fabricators and A&Ps and was told that the only real way to know was trial and error... Although I felt that I already had my share of error, I am also too dumb and too stubborn to give up, so I spent two days and several additional test pieces until I finally had a satisfactory result.

I spent all of last Saturday bending spars and trailing edges and am happy to report that my maximum width variance was less than 1/32" with most being less than 1/64" with no vertical bowing.

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[sjt]

a.jpg There is a line on your mylar sheet that has the marking CL. For the patrol that line is perpendicular to the spar lines. You need to block up the rear spar so that the CL line is parallel with table. Or you could use squares to make the spar lines perpendicular to table. Either way you need to find out what size wood block has to be placed under rear spar so that it is spaced up correctly.


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I liked assembling on a table. On you plans you need to figure out how high the rear spar needs to be spaced up off of the table.

On the patrol I found it should be about 1.34 inches.

[Redneckmech]

Good info! Thank you for sharing!

[sjt]

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When you get to the step after that -and you suspend a line thru the attach hole- it will not line up. It is not suppose to in the short web direction. The plumb bob is for lining up in the long web direction.


I kinda wished I had put some tiny tooling holes in center ribs along that CL line. Doing so would serve no purpose other then allowing you to use a second plumb bob and realize that it could not have been anything other then that.

I advocate for delaying the cutting of the center ribs to accommodate the spar capstrips to the very last step.