Wings #5

Aileron cable pulley

Starting to get more of the preliminary work done to start on the aileron for this wing.  The aileron cable pulley bracket was completed and installed.  The cable exits the wing about mid-chord on the bottom of the lower wings, and top of the upper wings.










The aileron hinge brackets were also completed.  Here's how they were made:  Started with a shaped blank of .100" 4130 attached to the forming block.  The part is then bent into a U-channel, which requires heating to prevent cracking.  It was then drilled, painted and attached.  Three eye-bolts thru each aileron spar serve as the hinge.  It is attached to the brackets with a clevis pin.

Blank attached to forming block

Heated and formed into a U-channel

Finished parts on right after drilled.  The four flat pieces

are the backers that go on the other side of the spar.  The

parts on the left are originals with one flattened to use

as a pattern.

Finished hinge installed

Finished backer installed

With this done, I'm ready to start making aileron components.  Continuing some work on the OX-5 as well.  Overhauling the water pump at present.  here's a pic of the pump disassembled.

Wings #4

Over the weekend, I got the plywood sheeting on the wing walk area.  Used 3/16" mahogany ply.   My friend Mark came over, and I talked him into varnishing it!

Original aileron spar mounted on wing

I also started working on the aileron installation.  One of the first things to do was figure out the aileron cable pulley bracket.  I temporarily mounted the original aileron spar to see where the cable needs to run and started laying out a bracket.  I got most of it fabricated (I'll put pictures in the next post).










Besides that, it was time to get the mighty Funk out.  We had decent weather Friday night, so Cindy and I went out for a nice 1 1/2 hour flight - very good for the soul!

Hope everyone has a blessed and happy Easter!

Zenith Duplex Carburetor

Dyke's Aircraft Engine instructor

I mentioned in one of my previous posts that I was working on the Zenith carburetor installed on the OX-5.  I finally completed the overhaul, and thought a more detailed post may be in order as information on this carburetor is a little difficult to find.  Old car and airplane people will be familiar with Dyke's Automobile and Gasoline Engine Encyclopedia and Dyke's Aircraft Engine Instructor.  Both are great resources for these carburetors as well as other antique engines and accessories.  I have the 1928 edition of the Aircraft Engine Instructor and find it very valuable and helpful.

Zenith History
The history of the Zenith carb is interesting.  It was invented by a French scientist, M. Baverey in 1906 and eventually were manufactured by the Zenith Carburetor Co. of Detroit, MI.  The company still exists today, but is now in Bristol, VA and make carbs for numerous manufacturers.  Baverey's claim to fame was that he overcame a problem with a simple jet in a carb - the ratio of airflow to fuel thru a carb is not linear, i.e. the faster the airflow, the richer the mixture gets.  This would obviously cause problems as the engine's RPM increases.  Baverey came up with a compensating jet which causes the mixture to become leaner as the RPM or airflow through the carb increases.  He then combined the standard jet with the compensating jet into a compound nozzle.  When properly sized to the engine, the combined effect of the increased flow of the main jet and decreased  flow of the compensating jet produces a proper air/fuel mixture over all RPM.

The compound nozzles are the 2 brass tubes in the
upper right hand corner of the picture

OX-5 Installation
The O6DS was designed for 8 and 12 cylinder engines - both automobile and aircraft.  It is a 2-barrel carb that is actually 2 single carb's combined together with one float chamber.  Because there are very few adjustments to the carb, each one has to be properly "sized" to the engine it will be operated on.  This sizing refers to the jets, venturi, etc.  The Curtiss OX-5 installation requires:

• 22 mm venturi (old manuals call these chokes)
• 120 main jet
• 100 compensating jet
• 70 idling tube

It's interesting to note the sizing here.  As I mentioned, the carburetor was invented in France, so all the specs are metric units.  The jets are in 1/100's of a mm and even some of the internal components have metric threads.  (I was told in grade school in the 1960's that in a few years the entire U.S. would switch to the metric system - what happened!!)

The only adjustment once properly set up are the 2 slow speed (idling) screws.  These control the amount of air and ultimately the amount of suction in the idling tube causing more or less flow of fuel in the carb during low RPM settings.

Slow speed screws

Overhaul

The overhaul is pretty easy.  The carb is about as basic and one can get.  There aren't even any gaskets inside!  The only part that can be a little tricky is the float setting which I'll talk about below.  I posted some photos previously of the initial condition of the carb - here's more.

It goes without question, the first thing to do is clean everything.  I'm a big fan of blasting things like this with walnut shells in my blast cabinet.  Cleans good without damaging the castings.  You just have to be careful to remove all residue.

I then made sure all the components, jets, etc. were correct for the OX-5.  They were as expected, as this is the original carb that came off the OX-5 from the LP-3.  It's then a matter of reassembly and setting the float level.

Bowl cover, float, seat and needle valve down center

Setting the float level can be a little tricky.  The level is set by measuring the height of the fuel in the float bowl, not the level of the float.  The specific height for this carb on the OX-5 is 1 9/64" from the top of the bowl casting.  The problem is, and you'll see in this picture, is the needle valve is attached to the float bowl cover.  So, you cannot remove the cover without draining fuel from the bowl.  I had to come up with an adapter to leave the needle valve and float bowl cover in place, and still be able to measure the level.

The top of the blue line is 1 9/64" (the correct level)
from the top of the bowl casting.

Here is what I came up with:  an adapter that attaches to the bottom of the seat, which is the fuel inlet, and a second one that is used to measure the level.  This second adapter is threaded into one of the compensating jet plugs and has a clear tube that runs up along side the bowl.  The level of fuel in this tube is the same as the level of fuel in the bowl.









I then made an apparatus to create a head of fuel pressure and flow fuel into the carb to ultimately see where the level is in the bowl.








The float level is changed easily, but not in a very conventional manner.  A brass collar that is soldered on the needle valve is moved to change the level.  Moving the collar towards the pointed end of the needle valve raises the level.  Away from the pointed end lowers the level.  It's important the level is correct.  Too high, and fuel will continually leak through the compound nozzles and run rich.  Too low, and the proper amount of fuel will not flow out the nozzles and the mixture will be lean.

Collar on needle valve

It took 3 tries to get the level right and I also drained and refilled the bowl several times to make sure it was repeatable.  Everything came out good!

It was then time to fully assemble and button everything up.  I installed new hardware, and in the end, she looks new!  The corks in the picture below plug up an altitude valve which came this way from the factory.  The altitude valve acts like a mixture control to lean the mixture at higher altitudes.  When open, a vacuum is applied to the float bowl and restricts the fuel flowing through the jets.  This will lean the mixture.  Aircraft not equipped with a mixture control, which the LP-3 does not have, will have these plugged.  Plus, according to Dyke's Aircraft Engine Instructor, the valve is not even used until high altitudes, above 10,000 feet are reached!  This totally goes against my normal mode of flying - low and slow!

Probably way more than anyone would be interested in knowing about a carburetor.  I find them fun to work on though.  Just another comment, I'm not an expert or guru on these.  Most all of the info here is from one of Dyke's books.  I just spewed it out in a way that made sense to me, and hopefully will to anyone reading this.

Wings #3

A little more progress this past week.  The brace wires and fittings were painted and reinstalled.  Bay #1 (root end) was trammed.   The cap strips need to be attached to the ribs before I can tram the rest of the wing - they tend to bow when I start tensioning the wires.  The wing walk structure was completed except for the plywood sheeting, and I got the nose ribs and trailing edge ribs installed.

Here's some misc. pics of the progress.

Wing walk structure

Nose ribs

Trailing edge ribs

I'll soon start on the aileron also.  I would like to have each wing completely done before I move on to the next.  This aircraft does have 4 ailerons, but the structure is basic and not too complicated.  I do have a couple of complete ailerons to use as patterns, but like the rest of the wing parts, there is nothing usable.  Hinges, brackets, wood parts, etc. will all have to be made.

Some of the original ailerons, complete with 86 year old
Grade A cotton!

I still have a lot to do on the wing first:  plywood on wing walk, install trailing edge and leading edge, make the last set of ribs that go towards the tip where the spars taper down to the wing tip bow, and make the wing tip bow.  I'm really starting to wish this was a monoplane!

Wings #2

I've been trying to add new posts to this blog once a week, but really didn't accomplish much last week to make it worthwhile.  This first wing is taking extra long since I have to figure out everything as I go.  Sometimes it's one step forward, two steps back!  As an example, the fittings I made sometime back that attach to the drag/anti-drag wires had to be modified.  The fittings were made from .100" 4130,  the correct thickness for the original fork on the turnbuckle end.  New, modern turnbuckle forks have a larger opening, so I had to weld a .050" shim to these fittings.

Original fork on left, new on right with shim
added to fitting.

Besides that little setback, I got 2 coats of traditional spar varnish on the spars and main ribs - will do the nose ribs and trailing edge ribs after they are installed.  I wanted the interior part varnished first before the brace wires and fittings were installed.  The N-strut fittings were also completed.

Varnished wing panel with fittings installed

N-strut (interplane) fittings

I completed the structure for the wing walk area as well with exception of the plywood sheeting on top.  I'll attach it after the nose and trailing edge ribs are installed and the wing in trammed.  Fittings were painted and attached, and I was finally able to fit, make and install the drag/anti-drag wires.

Wing walk structure and brace wires

Other Misc. detail shots....

N-strut fitting

Wing attach fitting

Other wing attach fitting

Brace wire attachment

My wife, Cindy relaxing in our hangar apartment
while I'm slaving away

What's next?  I removed all the brace wires for paint.  Will reinstall them and start adding nose and trailing edge ribs.