BillL
Well Known Member
The topic of "derating" an IO360 by dropping the "rated" RPM from 2700 down to 2400 came up in another thread.
Here are some comments about it:
Lets make some base assumptions and then address what happens as the RPM drops on this engine.
Given:
1. IO360 - no compression ratio change, same cooling system as standard Vans, 100LL, no ignition timing change for the RPM change.
2. A prop with no speed operating limitations for this engine. ref:Hartzell Composite
That should do it.
Now, let's break down the factors what will change and affect the life.
1. inertial forces - including piston weight, conn rod, and lack of counterweights on the crank to balance piston/rod weights.
2. Heat flux - BTU per unit area per time
3. Friction - ring/bore, bearings, air pumping losses.
4. Cylinder pressure due to firing.
I will post some comments on each of these, give me a little time to properly construct them.
Here are some comments about it:
David, are you sure we disagree?
The engine wear of a 2700RPPM engine operated at that RPM is no more than 2400 RPM provided the oil is OK.
The forces on the crank of a 360/2400 are greater than those at 2700 in a 320 at the same HP. Do the physics/maths.
The majority of its life it will be at a cruise RPM anyway so much the same number. If there was any wear difference, it would be negated by the above.
I think you actually agree.![]()
I wouldn't worry about de-rating the 360. The lycoming family is already de-rated. Think about how much HP you got from a 350 CI Chevy with no emission constraints! Heck, I have a 383 CI Ford that puts out over 500HP. The aviation engine philosophy is to use large, de-rated engines to improve reliability. My BMW 5 series rarely has cruise RPM's above 2300 and it has 120K miles and doesn't burn a drop of oil.
The only issues is heat. You don't want to run it so low that that CHT's fall out of the normal range. I don't think that would be the case. Lots of the RV's out there with 360's are cruising at 2400 RPM with no issue. The fact that they take off with 2700 is doing nothing to enhance their longevity.
Larry
The fact that they take off with 2700 is doing nothing to enhance their longevity.
Larry[/Quote...
Can you explain why this is true? Can you show the data or provide the math and physics that prove this particular crankshaft's frequency is happier at 2100 rpm than it is at 2700 rpm with no mention of what propeller its swinging, its inertia , the compression ratio, it's timing and the resultant power pulses.
Lets make some base assumptions and then address what happens as the RPM drops on this engine.
Given:
1. IO360 - no compression ratio change, same cooling system as standard Vans, 100LL, no ignition timing change for the RPM change.
2. A prop with no speed operating limitations for this engine. ref:Hartzell Composite
That should do it.
Now, let's break down the factors what will change and affect the life.
1. inertial forces - including piston weight, conn rod, and lack of counterweights on the crank to balance piston/rod weights.
2. Heat flux - BTU per unit area per time
3. Friction - ring/bore, bearings, air pumping losses.
4. Cylinder pressure due to firing.
I will post some comments on each of these, give me a little time to properly construct them.