Monday, November 23, 2015

Engine Accessories

With the engine basically assembled, the next tasks involve the addition of systems like oil, ignition, fuel, and electrical.

Assembling the Oil Pump

Oil:  This was relatively easy. With the old duplex and scavenge oil pumps cleaned, inspected, and re-assembled with new seals, etc., it was just a matter of installing them on the back of the engine. The order that accessories are added is important since safetying the mounting nuts becomes difficult if some things are mounted before others. Jim’s experience with this engine was again invaluable in this regard.

Duplex oil pump—installed.
This shows the oil pump along side the step up drive for the generator. There was interference which had to be eliminated by grinding some of the step up drive pad by the upper left stud. Now they fit. I'm not sure why they didn't to begin with unless they were components on different series engines.

Ignition:  After a great deal of consideration, I’ve decided to utilize tank engine spark plugs which was a big decision since the fittings on the ignition wires are different. The determining factor was the expense. Modern spark plugs (which are really no better than the old tank plugs) are around $28 each, while tank plugs can be bought for around a dollar or so each. The fittings for the wire ends are also available for much less. With seven cylinders and fourteen wires/spark plugs, this is a significant savings. More on this to come.

Fuel:  The carburetor on my engine is a NAR 6G, which is designed for use with a pump and an input fuel pressure of around 3 psi. With the main fuel tank being the fuselage tank, which bottoms out very close to the same level as the carb, as fuel level decreases, the fuel pressure could possibly decrease to less than this using just gravity feed, which may not be enough to lift the float valve and allow fuel to flow into the carb bowl. A fuel pump would solve any gravity/pressure problems. My friend, Bill Hammond, agreed. Jim saw a Titan fuel pump on eBay for only about $80, so I bought it. It is an old pump, but a very robust design. It needed new rubber parts, so I ordered an overhaul kit and found a manual for sale in .pdf format. This will be installed as well. More later.

Electrical:  There will be an electrical system on this airplane. (My decision.) I could have gone with a non-electrical build and avoided the need for an ADS-B, transponder, etc., but I would have been very limited in where the airplane could be operated, plus it would need to be hand-propped on every start. I could have gone with just a battery and starter which would require frequent recharging, or the addition of a wind-driven generator (these are very low current). I decided to go with a full electrical system regardless of the aforementioned requirements. It really isn’t difficult to design and install, I’ve done it before. So, now the decision of whether to utilize a generator or alternator. The old generators are large, heavy, and don’t generate much electricity at low RPM. Alternators are great, but the only ones available for direct drive (from the accessory case) are very expensive. Very expensive! No real reason for this except that they have the magic STC attached. Here’s what I decided to do. The electrical system on this airplane will not be driving high-draw items. I only plan to have one radio, a transponder, and eventually, an ADS-B which will be required by 2020. I will also install a couple of 12vdc outlets for charging personal devices like a GPS, iPhone, iPad, etc. The engine starter will be the only heavy draw electrical device. Most, if not all of these items will be hidden from view in some manner. That will be covered much later.

The good part of licensing an airplane in the Experimental Category is the ability to practice innovative designs for various systems. This is where it will pay off. There are many small alternators on the market designed for old cars or possibly tractors or forklifts, etc. I don’t need more than 25 amps or so to keep the battery charged. I found a tractor alternator rated at 35 amps for $65! Much better than the $700 required for a B&C alternator or $1500 for another W670 capable device.

6-Spline Drive

First of all, I had to mount the “step-up” drive for a generator. This engine already had one, so I just cleaned it up, we pressed in a new sealed bearing, and mounted it on the accessory case.
Scavenging a Shaft From an Old Generator

6-Spline Shaft

 The drive lug on this is a 6-spline female which will require a 6-spline shaft from an old generator. David Harwell at the Barnstormer Workshop, sold me an old generator for $10. It was a non-operative unit, but it had a good shaft. Jim Friedline found an old mount that he had laying around that was probably for a hydraulic pump or something. This would provide the mount.

Now to fabricate a way to drive the little alternator using a direct drive. Problem is, it came with a pulley, which was removed immediately. Jim to the rescue again. He had a few small couplings that were probably designed to drive something on a car. He had planned to use one as a flap motor drive for his Cabin Waco, but he gave me one to couple the alternator's shaft to the 6-spline drive shaft.

Fitting the other half of the coupling to a pin in the 6-spline shaft

We first removed an old bearing from the 6-spline shaft and turned it down to a usable diameter on the lathe. This was very hard steel and was slow going.

Next, we turned down an old bolt to insert into and weld to the shaft, but the difference in hardness made it difficult to get sufficient penetration with a weld, so I drilled a hole through the shaft and rod and inserted a roll pin. This was used to attach half of the coupling to the pin, as well.

 I took the alternator apart and removed the front fan since it will be turning opposite of it’s designed direction. (An alternator will generate current in either direction) A blast tube will provide cooling air. I then chucked the alternator shaft into my lathe and turned it down to 7/16”. This way I could use a 7/16 drill bit to open the hole in the other coupling. This coupling half was placed on the alternator shaft and secured with a roll pin as before.

Fitting the coupling to the turned down alternator shaft.

There is a small four-legged hard rubber insert that lies between the two coupling halves that serves to allow a non-perfect mating of the two shafts.

 Here are the couplings installed showing the rubber insert.

I modified the mount that Jim gave me by cutting the sides off which allows it to fit between the duplex oil pump and the fuel pump. Next, I found a sealed bearing to fit into the race to hold the shaft. The alternator fits on this mount by utilizing the holes for joining the two alternator halves and bolted on with four long AN3 bolts. I had to add four aluminum tubes cut to a length that would allow for the correct spacing to yield a smooth rotation without binding. Once put together the alternator turns very well and the 6-splined shaft fits perfectly into the drive.

Modifying the mount.

Milling a space for the front of the alternator.

 This whole device is very compact, light weight, and will be much more efficient than an old generator. It was a good bit of work to fabricate all this, but it was actually fun and is much cheaper than a “store-bought” option.

It fits!