Main Boom & Axle


MAIN BOOM

May 8, 2014
I'm super bummed!

The 2.5" x 065 tube from Alcoa has a bumpy surface finish instead of smooth. So, after Scotch Brighting one of the two tubes to remove oxide, handling marks, and the laser-etched manufacturing info (lot #, size, mill, etc.), I applied a few dabs of Mother's and rubbed it in. Tube turned black, so I know it was "working," BUT, after removing the black haze with a clean towel, the tube did not become a mirror-like shine. Instead, it remained a few shades darker than the untreated surface because the polish remained in the micro valleys of the bumpy texture. I sprayed Simple Green cleaner and BAM! the polish just washes right away, leaving the tube identical to the untreated portion.

No chrome-like finish for my main boom. >:-[

The other 1" and 1.5" tubes have a smooth, flat finish that should mirror up.

May 9, 2014
Close up of the fine, bumpy texture on just the two tubes for my main boom.

I tried wet sanding a 8" section with 150 grit paper. Barely made a dent.

So, I guess I'm stuck with this permanent "satin" finish.
Tools and pieces required for splicing 2.5" OD x 065 tubes together (an 8 foot and a 7 foot) to make the Weedhopper's 15-foot main boom (some call it a keel).

Get the Splice Template PDF here.
  1. A 12" long 2" ID schedule 40 pipe (6061 T6 of course) lathed down by 5/1000ths of an inch. Note: the one shown was salvaged from my damaged boom that was ever so slightly bent, thus why it is already drilled.
  2. A 50-count box of 3/16" x 1/4" grip aluminum pop rivets.
  3. Pop rivet tool.
  4. 3/16" drill bit and drill (a set punch or sharp awl is very handy for making a little dent in the tube in order to get the drill bit tip to stay put when starting the initial rotation).
  5. Two print outs of my splice template cut, trimmed, and taped to the end of the tubes.

The internal splice sleeve is inserted 6" in to the end of one tube, then the other tube is carefully slipped over the remaining 6" of the splice.

Since this is the same template I used to drill and splice the previous boom, it was just a matter of aligning the existing holes in the splice sleeve with the paper template to guarantee that drilling the dots on the paper and through the tubes would be exactly where the existing holes were.

After drilling, removal of template, and deburring.

I only riveted one end so that I can pull the tubes apart in order to drill the holes in the boom for the frame tubes and structures. Not enough room in the shop for maneuvering a 15-foot tube on a small drill press.

Ain't she purtty!?


May 12, 2014

The next 9 images show how I cut the rounded notch at the back end of the boom for holding the trailing edge (TE) tube of the vertical stabilizer.

The end of the boom has a 2" long piece of 2" schedule 40 pipe (left over from the boom splice and motor mount sleeves). This material is around 1/4" thick.

  1. Using a 1" diameter spacer, place its forward edge 1 1/2" in from the end and mark its outline with a ball-point pen.
  2. Using a straight edge, mark the straight sides of the notch tangent to the 1" circle.

  1. With a 3/32" bit, perforate along the inside edge of the curve.

  1. At around 200 RPM, CAREFULLY drill at an angle through the "walls" of the perforations. Once through, slowly tilt the drill up towards vertical and you should end up with a nice, albeit rough, slot with very little material left in the slot. No need to remove it all.

  1. Use a hacksaw to cut the straight edges a smidge on the inside of the line. Also, with the tube clamped vertically top to bottom, cut with the blade positioned vertically as well, not angled toward the center of the tube as if cutting a pie wedge.

  1. Remove the cut out piece. The thin amount of material left between the perforations in step 4 will easily break.

  1. Using a 1/2" radius file, remove the remaining material until the sides are smooth and vertically parallel. Use a 1" OD tube as guide to find high spots and file them down until the tube snuggly fits the notch's curve.
Like so.

The 3/16" pop rivet holds the sleeve in place.

The 1/4" vertical hole going through the sleeve is for one of the vertical stabilizer's 5 1/2" long attachment bolts that will pass through the top v. stab. spreader bar, a nylon saddle spacer, the boom, another saddle spacer, and the bottom v. stab. spreader bar.

Additionally a 3" long 3/16" bolt for the horizontal stabilizer's pivot hinges (one on either side of the boom) will pass horizontally through the center of the v. stab. TE tube.

In other words, the combination of these three anchoring devices (notch, 1./4" vertical bolt, and 3/16" horizontal bolt) will make for a very rigid tail group compared to the OEM method of using a 5/16" threaded rod that attached only to the bottom of the boom and required a set of brace tubes going from the bottom of the rod to the main axle. This redesign eliminates those two lower rear brace tubes.

The finished 1" OD rounded notches...

... that snuggly hold the TE tube of the vertical stabilizer frame.


May 13, 2014: Drilled the holes for the boom's fuselage and tail group, so now I can rivet the two sections together.

One 15 foot, 1.5" boom, ready for stuff.


May 29, 2014

Received in the mail today my custom selection of injection molded nylon 6/6 saddles from Scott McClure's WeedhopperUSA.com store. Here's how they look on the center fuselage brace.

I used two flat faced saddles for mounting my Tomar NEOBE 400-1228 dual-head strobe power supply to the boom. The aluminum project box is for neatness and a bit of RF (radio frequency) shielding.

NEOBE type strobe units were used by law enforcement before LED flashers became common. They fire at a constant 12 pulses per second, alternating 6 pulses between two strobe heads. The visual effect of the 20 watt xenon tube flashing 6 times in a half second is an apparent brighter, longer-lasting, near constant illumination. The tubes receive a lower voltage than single flash strobes, so the tubes last longer. The power supply itself produces a very audible ticking sound (12 ticks/second).

Sadly, I can't find anyone selling this particular power supply any more. I bought it as a package deal (supply, two 20-watt helix tubes, and two 15' shielded cables) from an online store that sold all sorts of emergency and law enforcement systems for $120 back in 2005 or so. Now all those sites are gone.

The brown wire wrapped around the ferrite clam-shell choke is the 12-volt power lead. The choke prevents RFI from getting into other devices, namely my radio and Magellan GPS, connected to the same power buss. Power and cables coming from the two strobe heads enter through the square opening.
Nose strut bracket with flat-faced nylon saddles. Nice, firm foundation. This bracket was scavenged from the four used on the wing LE and TE spars for attachment of compression / thrust-drag spars.

Notice I sanded and filed off the gold anodizing. Why? Simply aesthetic reasons. But due to it being so deeply applied (or maybe age) it was too hard to try and do the inside surfaces, so I gave up.



AXLE

May 4, 2014
1" x .120 chromoly steel axle tube (45" long) and 3/4" OD chromoly axle stud rods (8" long). This is 10 times stronger and a few pounds heavier than the OEM solid 1" 6061 T6 axle.

Ordinary 16" wheelbarrow wheels have been OEM since 1981 or so. But, instead of the OEM  3/16" thick plastic bushings for hub bearings, these have 3/4" bore ball bearings.
Dry fit of the main landing gear. Still have to drill all the various holes for attaching fuselage brackets, wing strut tangs, and control stick items.
Detail shot showing a 1" long piece of axle tubing to be used as the wheel's entrapment. The wing strut tangs and bolt will hold it in place.

May 11, 2014
How to add band brakes to a standard wheelbarrow wheel (4.80/4.00-8 tire).

Shown further below are go-kart type band brakes. I got a "kit" that contained the unmilled 4" diameter drum, a matching steel band lined with brake material, and a cable anchoring pin.
The 4" OD drum has a 2" ID hole surrounded by 8 bolt holes, one set of four being 5/16" dia. and the other four 3/8".

In order to get the drum perfectly centered on the wheel rim (which has a 3" wide centered hub that is  1 5/8" OD) I used 10 layers of cereal box cardboard cut into 1" wide strips and simply wrapped a strip around the hub, marked the overlap point, cut it there, and then taped the ends together. Rinse and repeat until the brake drum snuggly fits the stacked up layers of cardboard, as shown below.
Marking the 5/16" bolt hole pattern on the wheel with a pencil.
With holes marked, tap a set punch in the center of each circle.
A small drill press will not accommodate the 16" diameter of the tire, so I had to resort to drilling the holes with a hand drill.

These are 1/8" pilot holes.

The drill doesn't have to be perfectly vertically "level" when drilling the top half of the wheel rim, but then you need to position the drill as vertically level as possible to drill the rest of the way through the bottom half of the wheel rim.

To do that, I used a dual bubble level app on my iPhone. I held the phone on a lip on the drill's battery and tilted the drill until the readings were as close to 0 and 90 degrees as possible. I then began drilling at very low speed until the bit was seated, then proceeded with firmer down pressure and at a faster speed.
Next, drill to final size using a 5/16" bit.
Five washers stacked on 1.5" long 5/16" grade 5 bolts to space the drum 1/4" away from the wheel rim.

It's tricky to balance the drum and four bolts on the tips of your fingers and thumb, but this way was easier to insert the lowest bolt into the lowest hole in the wheel as the two parts were tilted vertical.
Final inside assembly.
Final outside assembly.

No lock or bearing washers needed under the nylock nut. Only about one thread protrudes from the nut after torquing it down. Too much torque and the thin metal of the wheel rim will start to crush.

Since the wheel rim is convex, only a little bit of the nuts and washer stack touch the surface, so I'm not sure how this will behave under the force of braking.


June 30 - July 4: 2014:

Installation of the band brakes begins by locating and drilling a 3/8" hole for the brake band anchor bolt.Yes, every hole I drill gets deburred!

Laying out and cutting 3-1/4" x 1-3/4" x 1/8" aluminum reinforcement plates.

Outside view of installed reinforcement plates, one on either side of the C-channel multi-junction axle brackets, along with the 3/8" brake band anchor bolt, a cable seat L-bracket, spacers, and the 4" dia. brake band. The bolt has a 1/8" hole drilled thru its shank to allow the 3/32" cable to pass thru.

Inside view of the band brake installation without starboard wheel (left) and with port wheel (right).

Overall view of the completed control stick featuring a thumb-activated PTT (push-to-talk) switch on top of the rubber grip and an old-style Harley Davidson brake lever.

Close up details of the Harley brake lever. A 1/2" dia. x 2" long steel pin replaces the 1" OEM pin that was used for anchoring a single brake cable. As you can see, the 2" pin has 1/8" holes drilled at each end for anchoring each wheel's band brake cable. This Harley lever is the 5/16" cable seat version. The seat is just a 1/4" recess in the lever base. I drilled it all the way through and then cut 3/8-24 threads into it. A short 3/8-24 bolt and lock washer hold a 2" x 1/2" x 3/16" bar on which the two cable seats are mounted.

6 comments:

  1. How are the brakes holding up?

    I may do the same on my Hooiser Hopper

    ReplyDelete
  2. The fibrous brake band material lasts forever! So don't get the cheap rubber-based brake material bands from Northern Tool! Been there, done that. Lasted a few landings and they were toast. These band brakes have good stopping power when properly tensioned. They can hold the plane in place at near 4,500 rpm. At 6,100, the 503 will make the locked up tires and my ground-planted Flintstone foot brakes that are gripping the nose wheel between them, skid on pavement.

    ReplyDelete
    Replies
    1. I used your brake install pictures a LOT to build mine. Thanks for the guidance. I've got the drums, and bands installed. I drilled out the 7/8ths inch brake handle to 1". That was a challenge, but now it's installed below the rubber handle. I've ordered parts to install the cables. I also ordered 3/8ths bolts, I only had 5/16ths. If the 5/16 bolts break, I'll update them, or if I have spare time. Yours looks a lot neater than mine, but I think mine will work.

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    ReplyDelete

  4. It seems your brake band is on backwards. The movable end of the band MUST be pulled the same direction as the drum is turning! This allows the band to assist in the stopping effort by gripping the drum to help pull itself tighter. Band-wrap. A type of self energized braking. Greg Kess.

    ReplyDelete
  5. Nice, I'm using the same wheelbarrow wheels on my VJ-24w, at least until I can find some good spoked lighter wheels.

    CHOPPERGIRL
    choppergirl@air-war.org
    █♞█
    http://AIR-WAR.ORG

    ReplyDelete