Traron Squadron

[This article first appeared in The Roar of the Harvard, December 2007 issue; newsletter of the Canadian Harvard Aircraft Association and is reprinted with their permission. I have added a few comments. – Skipper Hyle]

The radial 1340 cubic inch displacement engine, known as the Wasp, proved the motto correct. First built for the US Navy in 1926, it was perfected in time for mass production during the Second World War and Korean War. The fact that the same engine, albeit many overhauls later, is still power Harvards [it’s a CHAA article] and agricultural aircraft in the new millennium is a testimonial to its reliability.

If you can reduce wear, hopefully the engine will not sting you before major overhaul. The secret is proper lubrication.

Due to its radial nine cylinders arrangement, the bottom cylinders end up inverted. In time, while sitting, engine oil will seep past the piston rings and into the cylinder head. This preserves the cylinder, but will bend a connecting rod or blow a jug upon compression during start. Pulling the prop through by hand in the direction of rotation prior to start squeezes this preservative into the exhaust where it will be consumed by flame upon combustion on start. If it doesn’t want to move – don’t force it. Your mechanical advantage acting through the prop blade can do internal damage. Instead, pull a spark plug to create a drain hole. Exercise extreme caution as the simple act of turning the propeller will start the engine if conditions are right. I am speaking from experience here!

[I don’t’ want to open the debate on pulling through, the Pratt Manual has their recommendations, based on the type of starter you have. They built it, they wrote it. Two other things here: if you are of the pulling through type, watch your help – untrained, well-meaning help with full force at the end of a blade have quite the advantage mechanically and doesn’t take much to bend the rod. She may not let go then, but she will one day of her choosing. Pulling a plug is how I got my first T6 ride about 25 years ago. Another helper, as I pulled the plug on the ODS’s C60 and was reaching for a trash can, moved the prop and I wore about a quart of oil. By way of apology, I got an hour of dual in his T6.]

The top cylinders will be drained of oil and will be next to last to be lubricated until warm splashed crankcase oil hits them after start. (The top cylinder valve train is last to receive oil pressure as it is the highest point from the oil pump.) If you pull the dipstick out on a cold morning and the goo attached to it looks like soft taffy – how much splash lubrication do you think is going to take place? One word – preheat.

Once the engine fires to life, the oil pump does its thing. Keep the idle as low as possible as the oil pressure builds on the gauge. Do not starve the engine of lubrication by pushing the prop into fine pitch before the oil pressure has registered. Two revolutions of the prop fires every cylinder once (a complete 4 stroke cycle consisting of intake/compression/power/exhaust) so at 600 RPM a piston travels the length of the tapered barrel 20 times per second. With each internal combustion the cylinder warms and the taper or “choke” is eliminated which stops the expansion/contraction of the rings in the piston grooves. Remember; they too are splash lubricated. The same fins on the back of the piston that keep it cool by transferring heat to the oil, help to rapidly warm the oil on the start.

[The first engine my grandfather worked on was a Wright J-5 attached to a Pitcairn PA-5 Mailwing. He instilled in me not jamming a throttle anywhere, especially when the engine was cold. And it was always a pet peeve with my students (before the USAF I was a CFII for three years) who managed to start the engine at 1500 RPM. If you need to warm up, inform the flight lead and start early if required.]

The 10:1 gear driven supercharger is lubed by engine oil as well. At 600 RPM it is turning 6000 RPM in cold oil. If its bearings don’t receive proper lube, the resultant wobble from poor bearing will destroy the intake seal resulting in huge oil consumption, that is if you can keep the plugs firing. If any metal is made, it’s just a matter of time…

Starting with the throttle more than cracked defeats it’s butterfly choke like the effect on the carburetor for a cold start and results in a gasp of air rushing into the manifold leaning the resultant mixture every time it tries to pick up on start. Cough, gasp, silence. Backfire – bang, silence. Gasp, cough, whir, snort, chug, bang, run or quit – it’s truly an ugly event and that’s just on the outside! With the throttle closed you are on the carb’s idle circuit which is exactly what you are trying to accomplish – an idle.

If the throttle is pumped rapidly, the acceleration pump comes into play squirting raw gas into the carb for instant power. While this is a great thing in an unexpected Go Around, one does not quite want nor need 600 horsepower suddenly on start. When the engine gasps, the fuel will fall out the bottom of the updraft two barrel carb due to gravity and the resultant over leaned mixture backfire out the intake will ignite it with spectacular results. Keep on cranking with the starter if the engine has quit. Caught with an unwound inertia starter? How fast are you at ground evacuations? Quickly now – what’s the number for 911? What’s your 911 address?

[This sounds silly, but I’ve started on many ramps I had no idea where they were. If anything bad had gone wrong and I was the only cell phone around – where was I going to tell them to come put out the fire?]

Throttle changes should always be slow as this not only allows the dynamic counterweights on the crankshaft to not hit their stops, but it also gives you more time to compensate aerodynamically. Even if you make a mistake, it will be a slow mistake allowing you ample time for correction. Slower throttle movements also result in less thermodynamic stress on the air cooled cylinders. Do you know how many times those jugs have been overhauled? You don’t want to be responsible for an unscheduled one now do you?

[Back to that jamming the throttle thing… “Take care of your engine and she’ll take care of you.” – Eddie Rickenbacker, Commander 94^th Aero Pursuit Squadron, 1918. If you can’t believe a Congressional Medal of Honor winner, who can you believe?]

Over priming results in a flooded start, with the associated dangers of fire, and the engine chugging, burbling, and coughing but slowing cleaning itself out to a smooth idle. Under priming results in a short run then sudden silence when that prime has been exhausted. Severe under priming results in no result, i.e. not even a lone cough. Knowing the right amount of prime for the engine temperature and following procedure is what it’s all about on a normal start. After that you’re going flying. What a reward for a job well done.

[The engine is probably the most expensive piece of the airplane. A couple of years ago I put a new one on mine and it was over $40,000 – I’m sure the price has not gone down. Hopefully this article will provide some thoughts on taking care of the one you own or fly.]