|Flying the Sportster|
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In addition to the usual entertainment of pre-flighting a radial engine to check for hydraulic lock, with the Rearwin's Ken-Royce engine pre-flighting means making sure that the engine has adequate grease. Unlike more modern engines that have the top ends lubricated by pressurized oil from the engine sumps, the Ken-Royce 5F engine is a throwback to an earlier time in the late 20s where aviation engines had grease-lubricated top ends separate from the engine oil system.
The rocker arm boxes in the Ken-Royce have grease zerks and an open hole in the front in which to insert grease. Grease can and does leak out of the rocker box at many points. It is crucial to make sure that the rockers are freshly greased every 2 to 3 hours of flying time.
In addition to the zerks on each rocker box, you must squirt grease in through a hole in the front of each box, so that the grease goes into the valve springs. The Ken-Royce engines are unusual in that they use a volute, or conical shaped, valve spring. The spring must remain full of grease.
The grease to use seems to be a religious subject amongst antique owners. The original engine manual from the 1930's calls for "rocker arm grease", which was common then but unheard of now. I've heard suggestions for "cheap grease from the hardware store", Aeroshell 14 helicopter grease, and "expensive high temperature" grease. The original engine manual recommends Texaco Marfak #2 lithium-base grease, which you can still get if you know the right Texaco distributor.
Since the grease is the only lubricant for the rocker arm and valve stems, the grease theory I subscribe to (originally related to me by Al Ball) is that the proper grease will melt and get runny at the operating temperature of the cylinder heads (about 350 degrees F). As the grease gets runny it will slosh around in the box to lube the rocker arm pads and pushrod ends, and more importantly a little bit of runny grease will get pulled down the valve guide to lube the valve stem. This is why it is important to keep the inside of the valve springs full of grease on the Ken-Royce. If the grease is too thick and/or doesn't melt at operating temperature, then the valve stems won't get any lube and will quickly wear out. A "high temperature" grease suitable for an axle is great for axles but terrible when you actually want it to melt a little in an antique engine! Therefore I'm sticking with the low-tech Marfak.
When filling with gas, it is common with many antique engines to add "top lube", such as Marvel Mystery Oil, to the gasoline. This oil in the gas acts as extra lubricant for the valves, which is handy in an engine without pressure lubrication for the valves. The bad part is that adding oil to the gas reduces the effective octane rating of the fuel, but older engines like the Ken-Royce have such a low compression ratio it won't matter.
Beyond the engine, the preflight for the Rearwin is quite standard. You can't see the brakes, as they're inside the hub, but you can check on the brake actuating cables. The parking brake is actuated by a clever little locking-lever mechanism located just forward of the front stick.
The Rearwin has no electrical system, so you must flip start it. The key to starting the Ken-Royce is the Choke control. The procedure is to:
If the engine doesn't start, repeat these steps. Usually it starts right up. The key is having gas run out of the carburetor, otherwise you can flip the engine all day and get no results.
Currently it has a hard time idling slow when the engine is cold. This is something I will need to adjust.
During a runup all you need to check is mags and carb heat. There is no trim indicator, so I run the trim all the way forward and then crank back 8 turns (half way). A quick check of the altimeter setting, and verify that the fuel valve is selected for both tanks, and you're ready.
Taxi and Takeoff
The Rearwin taxies conventionally. My example has a steerable tailwheel, earlier model Sportsters came with a tail skid, but it is unlikely that any skids are still in use today. Forward visibility is poor, so S-turns on the taxiway are a requirement, however side visibility is good due to the narrowness of the fuselage. Heel brakes are needed to initiate sharp turns.
There are no bad characteristics on takeoff. The stick is a little heavy until speed is built up, then the tail comes off and the plane lifts off at about 40 to 45. Climb is flat, getting about 500 fpm at 60 mph indicated. I will have to explore the speed envelope further.
In the air, the Rearwin has lots of rudder authority, and flies fairly conventionally. The indicated cruise speed at 2100 RPM, near sea level, is about 97 mph.
As you fly along, streaks of grease start to appear on the windshield behind the top cylinder rocker boxes. There's not much you can do about this other than land and wipe it off.
The Rearwin is a low and slow kind of airplane. The window on the left hand side of the cockpit slides open from the front or back, affording a comfortable ride. If there is much of a headwind the cars will be passing you on the highway, so sit back and enjoy the ride!
The Sportster has no flaps and a big nose in the front, so it is a slip-on-final kind of plane. The approach is easy if the power cut is made adjacent to the numbers.
The roundout is standard but I don't have enough time in the aircraft to comment much further. Upon more experience I will add observations.
Touchdown is slow enough where braking isn't much of an issue, which is a good thing because the heel brake pedals are inconveniently located far away from the rudder pedals.
Since the engine often throws out grease blobs, a key part of the postflight ritual with the Rearwin is wiping down the aircraft to remove the grease blobs that are thrown out in the "grease radius" of the engine and prop wash area. The grease blobs end up in some unexpected places, including inside the cabin (having snuck under the wing root fairing).