Thursday, May 10, 2018

Flight Controls

Once the stringers were fabricated, they had to be removed while I made flight control cables. Actually, the only cables made today were the elevator control cables, but access to the inside of the fuselage frame required removing some recently fabricated items.
On the Travel Air, the elevator control cables are made in pairs. From the book “Travel Air–Wings Over the Prairie,” by Ed Phillips, the idea for this redundancy came from Walter Beech, who insisted on dual elevator control cables in the event of cable failure. Lloyd Stearman agreed. He had most likely witnessed a cable failure at some time and was determined that such would not affect the ability to control the airplane, after all, this was 1925 and the state of the art for aircraft materials and design was in it’s infancy. So two cables are attached to the stick above and below the hinge point, running aft to the elevator control horn.
Making four cables for elevator control was not a problem, but routing them to the control horn revealed obstructions in the form of the extra tubing welded into the fuselage frame not present on the original.

Using string for a guide, I had to devise a pulley arrangement that would provide clearance from frame parts throughout the full throw of the stick, not only fore and aft, but side to side as well.

















The first bracket was made from 4130 steel plate 1/8” thick drilled to accommodate two 3” pulleys, but they proved to be too small for the amount of cable deflection required. Typical of my work—too much trial and error. The larger 5” pulleys did the trick. The smaller pulleys will be used for rudder cables. Of course, this necessitated making a new bracket as well.










The pulleys are held in place by a piece of spruce with two 3/4"x3/4", .063" extruded angles held in place with four tubing clamps. The chromoly pulley bracket is attached by four 3/16" AN bolts and lock nuts. There is a spacer between the two pulleys to provide the proper alignment of the cables.


The cable used for the controls is 1/8” diameter 7x19 wire rope. This is comprised of seven strands of 19 strand rope all woven spirally. It is fairly flexible and 1/8” cable has a tensile strength of about 2000 lbs. I am fortunate that when a neighbor moved, he left me a box of cable of this type with right-hand thread studs swaged to one end.

Swaging is a process that uses a specialized tool to compress a steel end of some sort (stud, eye, or fork) onto the cable. So much pressure is generated by the tool that the end is actually extruded into the cable slightly, making for a very strong attachment, equaling or exceeding the cable strength. Each of the cables that had the 1/4” threaded studs swaged to the end were long enough to use for the elevator cables. I only had to attach an eye on the other end at the correct length.






I used the “Nico-Press” system for these ends. This requires a much simpler tool. The cable is run through a copper sleeve, wrapped around a thimble and routed back through the sleeve.






The Nico-Press tool is then used to compress the copper into the cable just like the swaging process does with stainless steel, but requiring far less squeezing force. Three compressions are required to complete the joint. A go-no go gauge is used to check that the sleeve was sufficiently compressed to make the joint meet specifications.
The loose end of the cable is then trimmed. Later, the whole joint will wrapped with rib-lacing cord to look period correct.
Once all four cables were made, the swaged ends with the stud, turn buckle, and fork were attached to the stick and the Nico-Pressed ends were attached to the control horn at the elevator.
  

 
The cables were the correct length, but some adjustments must be made to center the stick with the elevator flush with the horizontal stabilizer. I just wasn't getting full up elevator with the stick back as far as it would go, so the only way to correct that (can't make the cables longer) would be to re-make the little steel tangs on the stick. With these tangs a little longer, I should be able to adjust the elevator travel with no problem.
The only issue left to correct is the area where the cables criss-cross. Some rubbing is evident, and intolerable. More head-scratching.

Thursday, April 12, 2018

Restarting the Travel Air Project

Well, it's now spring of 2018 and the new shop/brewery/observatory is finally finished. Travel Air work began again in earnest a couple of months ago, but inertia has kept me from updating the blog. Now all two of you can start reading again.
Actually, it's just finished to the point that I can start working on projects again. I guess the work will never be done. In fact, I've stopped working on the wood parts being fabricated for the fuselage until the dust collection system could be completed. No more messy wood shop. Well, maybe.

The thing I've been anxious to install is the set of stringers down the fuselage. Two on each side and two on the bottom. These just form the shape of the fuselage for the fabric to follow. They are non-structural, but hold the taut fabric in it's shape for the life of the fabric, so the stress on the little wood parts is considerable considering the pressure on them is constant. I've seen one project that had little tabs welded to the fuselage tubing which held the stringers very firmly. My fuselage has already been blasted and primed, so I'm not too keen on messing up the very expensive Poly Fiber Epoxy Primer to install that type of "stringer mounts." A friend's T/A had little half-round plywood plates notched to receive the stringers which were then tied to the fuselage tubing with rib lacing cord. I wanted something more substantial without adding a lot of weight. Making these little plates was pretty easy. There are pictures in an earlier post showing the procedure.
What I came up with was just a home-made u-bolt, cut and bent from long #8 threaded rods. A small piece of rubber tubing was slipped over the middle before bending to protect the tubing after tightening. Each one was hand bent around a piece of 1" steel tubing as a form. Holes drilled in the plates receive the ends and metal stop nuts hold them firmly to the tubing.


I like the way they turned out. I just have to be careful when tightening the nuts since the only resistance is the (relatively) thin wood. Too tight and I'm sure it would break in half, or at least crack.

















They are left loose while lining up the stringer slots, then carefully tightened. The fuselage has a natural curve (of course) and the upper and lower tubing converge toward the tail. Had to take all this into account while running the stringer "line" in order to assure a smooth, appealing surface to the fabric. Any mis-alignment,  or bumps on any of these stringers will result in an ugly protrusion. It should not look it has warts.

Another obstacle to progress has been the absence of wing bracing wires for the upper wings. The lower wings had a full set along with end forks and jam nuts.
These are the internal bracing wires that criss-cross in several "bays" within the wing. The actual name of these wires are drag and anti-drag wires. They prevent the wing from bending aft or forward during flight. Piano wire or braided cable is often used as are threaded rods. Mine will have rods. On the Travel Air drawings, wires are specified with rods as an option. Required tensile strength: 2100 lbs. with 10-32 threaded ends. Even 1/8" piano wire probably has tensile strength above 6000 lbs.
Now the big problem. There is only one manufacturer of flying and bracing wires left in the world: Bruntons of Scotland. And they are pricey! And I mean VERY pricey. The way Bruntons makes their rods is very cool. Steel rod, even cheap mild steel has tensile strength far in excess of anything required for this purpose. The weak part of a rod/wire in tension is the ends. On a rod there must be a threaded portion to accept a fork end that is held by a clevis pin. The threads are the weakest link. So Bruntons manufactures their rods with larger ends than the middle. Also, all threads are rolled, not cut. Cut threads result in a smaller diameter thread compared to rolled, and the cuts through the natural grain of the steel tend to weaken the rod compared to rolled threads. So all bracing and flying "wires" utilize rolled threads.
Here is a picture of an old MacWhyte rod along side (above) mine. As you can see, the middle of the rod is smaller than the end and there is a square section to hold a wrench for tightening. The lower rod is what I had made. It is a stainless steel rod with rolled right hand threads on one end and left hand threads on the other. A quote from Bruntons' supplier in the U.S. was $270 per rod. I need 16!! Yep, that's over $4000 for bracing wires. No way. I found a business in Wisconsin that rolls threads on various type rods and they quoted me a price for 16 rods of $388. SOLD!!!

 The only drawback is that the entire rod is approx. 3/16", so they will be slightly heavier than the smaller Bruntons rods. Both use stainless steel, which has slightly less tensile strength than carbon steel, but the resulting tensile strength is so far in excess of what is required, it is of no consequence. Now a builder of a standard certificate airplane would be stuck with finding originals or the hyper-expensive Bruntons rods. Experimental category is great sometimes.


Now the wings are braced and ready to be trammed.

Thursday, August 31, 2017

New Shop

Well, it's been a long year. Once the engine was finished, it was time to upgrade my hangar and build on a new shop with enough room to restore old cars, build more planes, brew beer, and have a permanent mount for my telescope. The excavation began in May of 2016 with the expectation that all would be finished by my planned retirement date of March 2017. It didn't happen. As usual, the building project droned along for over a year. But now it's finished. There's the new shop with a garage door, a car lift, an upper building (a quonset) and an observatory. The upper building is used as a brewery and "sky lounge" for get-togethers. The old shop is now a wood shop and a paint booth.


Soon, the Travel Air will be back on the front burner. I'm retired and the space in one corner of the hangar is just for the T/A project. Work will resume soon...

I hope.


Monday, May 2, 2016

Finishing the Engine

Last of the engine work



The engine was essentially complete last November, but individual accessories and the ignition system needed to be completed. This along with my work schedule plus planning for retirement left little time for serious work. But we got some done anyway.




Since then, the starter was sent away for overhaul, the ignition wires were made up and installed, the timing of the magnetos was set, and the pressure output of the fuel pump was set.






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First, the ignition wires:  Each wire is a different length, and the length varies by a significant amount.

The trick is to go “by the book” plus a couple of inches to insure enough wire to strip and cap at the mag end, and enough to install a spark plug coupling at the other. This also assumes enough slack to route each wire around the rear of the engine. But ignition wire is not cheap, even in bulk, so avoiding waste is also a consideration. The spark plug ends have these nifty little 90º guides which alleviate stress on the wire.

The spark plug fittings must be matched to the type spark plugs in use. I decided to go with the surplus “tank” plugs which are available in abundance vs. the modern aircraft plugs which run about $27 each. I heard about a retired Delta pilot who wished to sell his supply of tank plugs, so I gave him a call. He just wanted to get rid of them for what he paid…50¢ each!! So, I now have a lifetime supply of new (surplus) plugs for less than the cost of one AC or Champion plug. According to Jim, they are just as good. I’m happy with that.
The wire we used is shielded, which means there is a braided steel layer around the central conductor, separated by insulation. There is a layer of rubber on the outside which is blue. They really stand out. The braided layer is stripped back enough to allow only the insulated conductor to run from the wire guide to the mag block or the spark plug.


Spark plug end:  The ends of the wires have the shielding stripped back a certain amount and a “cigarette” attached to the end. These cigarettes are just a hollow cylinder made of non-conductive plastic, with a metallic hole in one end and a spring attached to that end. The conductor is inserted through this metal hole and soldered in place. The spring provides a cushion for the conductor to make contact with the center of the spark plug, and the cap is screwed onto threads on the end of the plug. The end where the wire enters the guide has a screw-down clamp that traps the braiding. These were not such a good fit, so Jim machined a whole set of custom wire clamps on his lathe while I was on a trip. Bless his heart! They work perfectly, of course. After leaving the spark plug, the wires are routed through a tube that keeps them all together as they travel around the engine toward the magneto. After careful consideration, I decided that the guide tube would probably interfere with my planned cowl arrangement, so I removed them and took the tube off the engine. I’ll use spiral wrap, or some other product to bundle the wires and keep them a little lower so as to clear any future fabrications.







 The magneto end:  On top of each mag there is normally a hard rubber block with seven holes through which the ignition wires enter the mag  block. On these mags, we used an aluminum cap with a small section cut from the bottom which bolts to the main section trapping the shielding thus grounding it to the mag case.


The ignition block within the mag accepts each wire into a hole where the conductor is captured and the circuit is completed. This is done via a copper cap crimped to the end of the wire. the cap end is inserted into a hole for that cylinder and held in place by a pointed-tip screw that pierces the copper cap completing the circuit. Each wire has to have the shielding stripped from a precise point allowing just enough wire to enter the mag block at it’s location because once the cap (with all the wires in place) is attached to the top of the mag there is no room for movement of the wires. It is a very tight fit. Jim actually has a rubber cap with the proper lengths of wire sticking out to use as a guide.























All Done!

Setting the magneto timing is very straight forward, much like any other airplane engine. The difference here is that one mag is set to 29º before top dead center (BTDC) and the other is set to 31º BTDC. Of course, Jim Friedline has all the tools and accouterments necessary to do the job.


It was just a matter of finding TDC for the number one cylinder and backing off to the proper setting using a gauge installed on the crankshaft. The magneto is then rotated to the “firing position” and the hold-down nut tightened. This procedure actually involves some back-and-forth adjustments from the crankshaft to the magneto. A red light on the timing box (attached to the mag) illuminates when the mag is in firing position. Of course, there will always be a bit of backlash that must be dealt with, but by working “forward and back” that is averaged out.


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Also, during this period since the last update, I was able to acquire a tachometer and send the old instruments off for overhaul. This tachometer is very special for this reason: when I acquired this project, a friend of mine (Van Thurston) gave me a tach face that has the Travel Air logo on it.


This was one of a group that he had silk-screened years ago. It was perfect! What was needed was a tach to put it in. This face is for a Jos. Jones tach and I wasn’t sure I’d be able to find one.


Enter Brian Karli, who built the Jenny that resides at Candler Field Museum. He had one and sold it to me for what he had in it! To say I was thrilled would be an understatement. This panel will be great, with period gauges and materials. I can’t wait to get to that part of the project. This is one thing that really stands out on an airplane like this. Keystone Instruments in Lock Haven, Pennsylvania will do the work.


"Height"  Isn't That Cool?















They also have my mag switch, altimeter (Zenith non-sensitive), and bulb-faced compass. Actually, I have two of these compasses; one of which is only good for parts.

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The old inertia wheel starter I bought from Jim Friedline needed to be taken apart, at very least for an inspection. I soon realized this was beyond my capabilities, so I went searching for an overhaul shop. Needless to say, there aren’t a plethora of facilities out there doing this sort of thing. I was told of a shop in Kentucky that does good work and was able to overhaul this starter. I spoke with them on the phone and boxed up the heavy beast for shipping. It is heavy! After it arrived, I got a phone call telling me they couldn’t do that model because they didn’t have the proper manuals. Great. They did recommend a shop in Tulsa, and they were kind enough to send it back. I never even removed it from the shipping box, just sent it along to them.






When the starter came back from overhaul, I set it into place on the back of the engine to check clearances. This starter is an inertia wheel type with an accelerating motor built onto the back. These starters are period correct for this vintage airplane, give or take a few years. They also sound very cool starting. You first engage the motor which spins up the inertia wheel, then engage the wheel to the starter lug in the accessory case via an electric solenoid turning the engine. A simple inertia starter has a lug into which a handle is set and using muscle power, you spin the inertia wheel up by hand until it reaches the proper speed. This is done by ear. Then you pull a handle that engages the wheel to the engine. The motorized starter also has this hand crank lug as a backup in case of a dead battery or a bad motor. Most Stearmans have this handle lug on the left side of the fuselage, but mine will have to be on the right side due to clearance issues between the magnetos and the solenoid. An extension is required from the starter to the lug on the outside of the fuselage. Luckily, I have one in a box. It’s old and dirty, but it will work.

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The fuel pump I bought from eBay and overhauled, is a very robust unit capable of quite a high output. But for this installation, I had to make sure it would not put out more than about 3 psi. This is the maximum pressure for this carburetor, since that is the pressure at which the fuel would overpower the float mechanism (which shuts off the flow of fuel into the carb bowl) and lift the shutoff valve from it’s seat, thus overfilling the bowl. There will be plenty of fuel sucked into this engine—I don’t need it being dumped overboard.

So we set up a pressure gauge and some tubing, along with a drill adapter to spin the pump. This pump is adjustable via a spring loaded screw that puts pressure on a bypass valve within the pump. When I began to spin the pump, it was putting out around 5-6 psi at the low end. I finally figured out that the spring under the adjusting screw was too strong and was putting too much force on the bypass valve, not allowing enough fuel to circulate around the pump vanes. I replaced this spring with another one I had in a “bag-o’-springs” bought years ago, but seldom used. Success. The pressure is now adjustable down to around 1.5 psi. I set it at 2 psi. This should be enough to supply fuel in any attitude. Now the pump can be installed and safetied.

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This next step in the engine saga will be to remove it from Jim’s fixture and relocate it to my hangar. I sure would like to test run the engine before installing on the airplane, but this will require some engineering that I don’t have time for presently. We shall see.

When the day arrived to transport my engine home, Jim and I stood looking at the thing and realized there were just a couple of minor things left to accomplish. The tubing that connects the lower cylinder’s valve housings had to be installed and a few nuts had to be tightened with pal-nuts securing them. There always seems to be one more item. I had brought my trailer to Jim’s shop a few days prior, but a few of those “last” items set us back. On top of that, I had to leave for a trip (gotta pay for it all).

Now, with no more to do, the head scratching began over how best to get the 500 lb. beast out of his shop and onto my trailer, which was situated in the main hangar. Luckily, Jim has a chain hoist mounted on a rail with a handy little door that opens into the hangar.


















Unfortunately, the little door is just that…too little to move the engine through lifted horizontally. It had to be lifted vertically to fit through the door, then swung horizontally again to set on the mount. This is the same mount on which the engine was removed from it’s last airplane. I just made a dolly, of sorts, from some scrap 2x6s with casters to make moving it around easier.



















This whole process took the better part of an afternoon, but we eventually got the beast on the mount and lifted onto my trailer. The moving procedure was nerve-wracking to say the least, since any mistakes, bumps, or drops would render the last year’s work useless. Dropping a newly overhauled 1942 engine would have wrought wailing and gnashing of teeth.
























The drive home was no less stressful, with the engine securely strapped to a trailer, but very top-heavy. Upon arrival at my hangar, I secured the engine from a chain wrapped around the front-end loader of my tractor, lifted it a few inches and drove it slowly into the hangar. Once it was sitting safe and secure on my hangar floor, I finally breathed a sigh of relief and had a beer. Or two.