Robster,
Do what you like with the OCI, surprises eventually can happen, some like to have a safety factor or buffer against oil degradation and associated wear. But it all comes down to how lucky you are with your gamble.
Originally Posted By: Robster
For those interested. . .up to now (according to the on-board computer) I've averaged 46 MPG over this OCI so far. If that average stays about the same for the rest of the OCI, that equates to about 108 hrs. of engine operation over 5000 miles. Most of the operation is at about a 2500 RPM average (5100 RPM redline). From this info I can approximate average engine output at about 49%.
So we have 49% average power output over 108 hrs. of operation--it doesn't seem like this engine is working very hard most of the time.
Very good observation. It's not.
The dominant factor in the power-load curve vs speed (or rpm if you will) for a typical rolling vehicle is approximated with the aerodynamic drag function,
P = unitless coefficient of drag * air density * sihuoette area * Relative Air Velocity^3
Of course there are other power parasites such as some bearing drag, tire flexing & heating, brake drag, from climbing inclines, driveline inneficiencies, etc. But for the most part those which are external influences are typically around 3 - 5% of the total required for a steady-state speed.
The Velocity^3 component means that doubling your speed requires 8 times as much hp.
Imply the opposite, that you are operating your motorcycle at 50% of your maximum speed (50% of max rpm), presumably in high gear, the Velocity factor makes the aero drag power 1/8th of the steady-state power at redline.
Land based vehicles are mostly relaxing at very low percentages of their total available power output. The exceptions are hard acceleration and high speeds on autobahns especially into a headwind.
At level flight and constant speed, the power propelling an airborne vehicle is entirely used to overcome aerodynamic drag. I think plane designers intend for the wings to approach high speed lift characteristics and your cruising speed is a relatively high percentage of that. So if wide open on your Skyhawk gets 125 knots at 180 horsepower, doing some Sunday afternoon sightseeing at 110 knots only takes 68% of that, or 122 horsepower. You probably need flaps to go much under 80, and even just above that point, the plane probably has a noticeably higher level of instability than at cruising and WOT speeds. And those engines are set up like stationary diesels that run compressors and pumps. Very high torque, relatively low rpm to avoid high levels of wear.
I often wonder how automotive oil with moderate levels of zinc doesn't cause even more misfiring/ detonation/ pinging when there are valve and combustion chamber deposits. Does aircraft oil also take out the other additive metals like moly, magnesium, calcium, sodium, potassium, titanium, and possibly others?
