Shinn Brake Spring Tool

Seems like nobody likes to install new springs on the Shinn brakes.  It can be done (sometimes) with a screwdriver using the pry and pop method.  But after one frustrating day spent struggling with my springs (4 of them, 2 on each side), I decided to take the time to may a spring stretcher tool.

I used a gas welder, a hack saw and a die grinder to make the tool.  It's constructed of scrap steel tube.  Photo 1. 

The stationary part of the tool is 2inches of 1/2" tube with a 1/4-20 nut welded to one end.  Also on the nut end of the tube a 3/4 inch by 1/2 inch piece of steel flat is welded on with a slot hack sawed in it to fit the loop end of the spring (the "fork").  (Photo 2)  A 1/4-20 bolt is screwed into the nut on the end of the stationary tube and provides the force to stretch the spring.

The movable part of the tool is a 2 inch length of 3/8" tube that fits nicely inside the 1/2" stationary tube.  One end of the tube is welded closed so the bolt can push it.  And the other end has a 1/2 by 3/8 flat welded on with a "spur" that can grip the hook end of the spring.  (Photo 3)  The movable part also has a 1/8" peg that rides inside a 1/8" slot in the stationary part.  The slot/peg is to keep the movable part of the tool from rotating when the tool is under tension.  (See "IF I make another"  below)

The spring tool is easy to use.  Install the spring loop end onto the brake, Push the fork end of the tool down over the loop to lock the tool in place, Engage the spur in the hook end of the spring and, Crank the bolt actuator until the tool expands the spring as much as you need.   Great for an old geezer like me because everthing happens in slow motion and I can even expand a spring and pause, go get a coffee or something, then come back later and finish the job.  Wonderful!

IF I make another tool.   If I made another tool I would eliminate the peg/slot setup and just have the 1/2 by 3/4 flat ride in the slot.  In other words, make the stationary tube a little longer with a longer slot and no peg.  I'd also put a big handle on the bolt, that little wing nut thing really hurts the fingers!

 

 

Ethanol Fuel Test

If you run auto fuel in your aircraft engine it's best to avoid the kind of auto fuel that contains ethanol.  Sometimes you cannot be sure if the fuel you're using has ethanol or not.  This test is an admittedly unscientific version of the ethanol test on the EAA website.

I use a pint size Mason jar for the test with about a inch of water.  Photo 1 shows the jar with water and a black strip of tape marking the water level.  I colored the water with a little grape juice for the photographs.

Next add 2 or 3 inches of the fuel to the jar.  Put the lid on the jar and shake it for a minute or so to mix the water and the fuel.  Photo 2.  The water will dissolve any ethanol in the fuel sample.

Finally, let the jar sit for several minutes.  The water/ethanol will settle to the bottom of the jar and the gas will rise to the top.  Note in Photo 3 that the "water" level is now nearly to the top of the tape.  The increased volume of water is due to the dissolved ethanol.  If there is no ethanol in the fuel sample, the water level will not rise.

Most folks only care if ethanol is present or not, but (Photo 4) you can calculate the approximate percent of ethanol in the fuel as follows: (1) measure from the tape mark to the new water level, in this example the water level went up 7/16 inch (.437") and (2) measure from the tape mark to the top of the gas, in our example it's about 2 1/4 inch (2.250")  then (3) divide the ethanol amount (.437) by the total fuel added (2.250) and we get  0.19 or 19% ethanol.

How accurate is this test?  Well, the pump where I got my fuel sample was labeled 15%  ethanol (and I measured 19%).  I've also tested several samples labeled "pure gas, no ethanol" and only one of them showed a slight indication of ethanol (the water level on that one sample rose about 1/8 inch, suggesting about 5% ethanol).  So I'm thinking this test is plus or minus 5% accurate...or maybe the fuel compounders have a 5% tolerance!

Imperial Fuel Valves

There are better, more modern valves than the old Imperials, but the new valves are expensive and they're not ORIGINAL so let's take a few minutes to fix up our old fuel valves.  There are three major problems with the Imperial valves: (1) they can "sieze" or lock up so you cannot turn the fuel on OR off  (2) they can leak in the Off position so that fuel runs through when you don't want it, resulting in a dripping carb or overflowing main tank and (3) most annoying of all is a leak around the stem which results in fuel dripping INSIDE the cockpit!

It doesn't take long to spruce up this old girls...take them apart by removing the handle and unscrewing the top, pull out the stem and spring.  There's a half round washer that will tip up when you pull on the stem.  It has a tab on the back side so you have to pull the tab out of its notch to get the washer free.  Clean everything using a toothbrush and MEK

Next you'll "lap" the stem into the tapered body of the valve.  There are special lapping compounds available, but most folks use toothpaste (a nice smelling mild abrasive).  Coat the stem with toothpaste (Photo 2) and then put it back into the valve body.  Use the handle to turn the stem back and forth in the body as if you're turning the valve on and off.  Do that a hundred times or more and the toothpaste will start to wear the stem and body so that they match perfectly.  Remove the stem and you can tell the lapping is working because the toothpaste has turned black.  Wash off the toothpaste to check lapping progress.  You're done lapping when the stem and body look nice and shiney.  Photo 3 shows a comparison of before and after lapping the stem.

Finally, re-assemble the valve using a new seal and fuel lube grease.  Newer (!?) Imperial valves use O-ring seals, just put a new one on.  But the older valves used leather seals which are no longer available.  I haven't tried this but people tell me you can use waxed dental floss or teflon string wrapped around the stem to replace the leather seals.

Engine primer

Not much to overhauling the engine primer, but you'll need to have on hand two O-rings of the correct size (Kohler takes a -12 O-ring) and a very small amount of fuel lube grease (EZ Turn).

First, unscrew the locknut and pull the plunger out of the barrell (Photo 1).  Remove the old O-rings from the plunger...they may just fall off if they're more than 15 years old.  Examine the inside of the barrell for any dirt, crud, or scratches.

Apply a light coat of special grease to the new O-rings and to the end of the plunger (Photo 2)  Roll one O-ring into the first groove, the roll the second O-ring over the first and into the second groove.

Finally, grease the plunger and barrell good and reassemble.  (Photo 4) Test the unit.  If there's any problems, remove the check valve springs and balls (under the two screw covers on the end of the primer) and clean and lube them.

Fuel system test rig

Easy to make (and cheap) test rig for fuel systems.  Use it to test valves, fuel line connections, gascolator, carburetor float level, etc.  Consists of:

(Photo 1)  1 1/4 to 3/4 reducer coupling...makes the reservoir for the test fuel.  Wrap a piece of safety wire around it so you can hang it up.  Needs at least 19 inch "head" above the item being leak tested.

3/4 to 3/8 bushing to step down to the hose barb

3/8 pipe to 3/8 hose barb

4 feet or so of 3/8 inside diameter vinyl hose

(Photo 2), two more 3/8 pipe to 3/8 hose barbs

3/8 ball type valve, and

another 2 feet or so of that 3/8 ID hose

and a few hose clamps, total cost about $10

To use your tester hang it at least 19" above your work bench and attach the loose end to the valve or whatever you're testing.  Fill the reservoir with fuel or even with water (I use E85 because of its low density and distinctive fruity smell).  Open the hosevalve and wait...if no leaks appear, wait overnight then give it the smell test (if using water place a piece of paper under your test item and see if its damp in the morning).  Of course if you use fuel to test your fuel system components, you should test outdoors and away from any ignition source!

Rivet tools

There's not all that much sheet metal work involved in restoring a classic airplane, but there is always some minor repair work that needs to be done, so you need basic rivet tools.

A modest rivet gun (a TP83) is shown in Photo 1.  In addition to the rivet gun you need rivet sets.  I have three: a 1/8" set, a 3/32" set and a flush set.  The flush set needs a different type of retainer, so you need two retainers: a beehive retainer and a quick change type. 

Of course you need a bucking bar.  There are dozens of different styles and you can even make your own.  But I have only ever needed one, a #647.  The 647 seems about the right size for general use and the small end will even buck the hard-to-get-at rivets on Taylorcraft wing ribs.

Photo 2 shows some nice to have (some would say required) items for riveting.  The air drill is one of my favorite tools, I got it for $10 on eBay.  It's old and its castings are worn smooth from years of use, but it still works great and I love the high pitched whine it makes. 

Next to the drill is a rivet cutter.  With one of these you can buy a batch of long rivets and cut them to length as needed.

Also handy is an assortment of cleco fasteners.  I have 8 each of 1/8" and 3/32" clecos.  Some folks who build aluminum planes buy hundreds of clecos and wish they had more, but I've never needed more than 8.  You'll need a cheap cleco pliers to install and remove the clecos.

Finally in the photo is a little bottle of Marvel Mystery Air Tool Oil.  I put 3 or 4 drops of oil in the air inlet of my air drill and rivet gun every time before I use them.

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Fiberglass Layup

All the materials and tools needed for a fiberglass layup are readily available at your friendly local WalMart.  Get:

      1. Fiberglass resin and fiberglass cloth and a can of car wax in the automotive department

      2. A couple of 2 inch chip brushes and a quart of acetone in the paint department

First, give the mold a couple coats of wax.  Car wax is not the very best mold release available, but it works fine and it's cheap.  Photo 1

Next, rough cut two pieces of glass cloth at least 1/2 inch larger all around than necessary to fill the mold cavity.  Use cheap sissors to cut the cloth.  Mix about 1/8 of a quart of resin with about 1/8 of the small tube of catalyst that comes with the resin.  While it's not necessay to be terribly accurate in your mixing ratio, it's a good idea to use a ruler and felt tip marker to number depth marks on the side of the resin can and the catalyst tube.  I found that roughly 1 inch out of the resin can needed about 1/4 inch out of the catalyst for a nice mix.  Photo 2.

Once the resin is mixed you have only 10 or 15 minutes (depending on temperature) to finish the layup, so from this point move quickly and smoothly.  Coat the inside of the mold cavity and about 1/2 inch around the outside with a thick layer of resin.  Some people just pour in some resin and then smear it around with the brush.  Photo 3.

Then stuff the first piece of pre-cut glass cloth into the wet mold.  Use the brush to push the cloth down into the resin, brush on more resin to completely wet out the cloth.  Areas that are not wet out will appear white.  Photo 4.

Put the second piece of glass cloth into the mold and wet it out like you did the first piece.  Then, using the brush in a stabbing, stippling motion to poke the resin into the cloth weave.  The idea is to get all the air bubbles out of cloth and get the cloth down snug against the mold surface.  Air bubbles will appear lighter than the rest of the layup.  Pay special attention to cornors and curved areas.  Photo 5. Keep working the layup until the resin starts to set up.  When the resin starts to set it will first get a jelly like texture, stop stippling at that point and throw away the brush. If you got any resin on your hands, a little acetone will clean it off. 

Let the layup cure for several hours or overnight, then use a putty knife to pry around the outside of the molding until the part pops loose from the mold.  Photo 6.

A bandsaw works great to trim the excess glass from the outside of the part.  Some folks use old tin snips or even sissors.  Photo 7.  Finally, finish with sandpaper, clean the surface with acetone and paint.

Link to Yoke Centerpiece,  Fiberglass Mold

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