Full RPM or high idle? Bush hogging fuel efficiency

[DarkBlack]

AH-HA.. I asked you a straight out question and you are deflecting it..

I know my tractor is going to use more fuel per hour running at 2100rpm under mowing conditions.. vs no load. thus load DOES factor in on fuel usage.

now.. man up and answer my question.

you called me a liar right? or you didn't read my post? ( or didn't understand it? )

it's one of the 3.

don't deflect. be a man. and answer... liar? didn't read?, didn't understand?

which one?

You're not even in the ball game.
Man, you need to lay off the sauce.

 

[Soundguy]

i see.. not man enough to answer. I figured as much.

No problem.. takes all kinds I guess.

sauce? I don't drink.. .. however you might want to lay off on whatever keeps you from manning up and answering a straight question.. eh?

liar? not read? not understand? ( not man enough to answer yet? )

i love threads like this where the spineless ones get rooted out.

 

[Soundguy]

i hope this lack of a reply means user darkblack has put me on ignore... vs just calling me a liar.

I think I'll preemptively do the same.. threads getting cluttered....

 

[Redneck in training]

This thread is about doing the same job at high or low engine rpm.
You won't confuse me by changing the subject to seem like we are talking about different mower sizes and types. maybe that confuses you?

This thread is about if it makes sense to mow at lower rpm.
My conclusion is that it will not lower fuel consumption or affect wear on the equipment significant way. And I still maintain that power produced by the engine is EQUAL to power required to perform the task. I also maintain that, for all practical purposes, energy (fuel consumption) is proportional to mass of grass mowed.
It will lower noise if that is the issue.

 

[jejeosborne]

http://www.tractorbynet.com/forums/...22-full-rpm-high-idle-bush-5.html#post2980849

post 42.. when I said, after mowing in those harsh conditions and said I'd be dirty.. you asked why.. then made a comment about your brain helping you out. That sounds to me like you were implying my brain was not helping me out by some how magically dodging debris i had NO WAY to dodge whilst mowing in those rough conditions.

as to wear? another poster summed it up well. no need for me to revisit that.. nor to post my opinion again.

I'm not inot babying a tool. i don't choke up on hammers, nor run mowers at low rpm.. I've found higher the blade tip speed.. the better the suction and cut. thus 'I' mow that way. again.. as said.. I don't give a oot what anyone else does to their equipment.

Actually I called you a possible dust addict which you interpreted as moron.

I see you have come full circle with the hammer example which you first used to belittle and the OP with. At least you didn't rudely use the word "geesh" at the end this time. Although, we differ with this example too. Yesterday I was installing aluminum fascia using aluminum nails and "choked" up on my hammer. Another example of a light load situation.

It appears as if you did give a "oot" what anyone else does to their equipment.

i am continually amazed at the people afraid to run their tractor at it's rated work rpm?

it's a tool!! use it.

when a wear item wears.. replace it.

if a durable part breaks.. fix it.

keep on going.

this weekend I was out hogging 8 ac of 7' to 8' ragweed, dog fennel and something that looked like goldenrod at the back of my pasture along a causeway strip. stuff was so tall I couldn't see anything but the treeline in the distance to judge my position.. was on my old clapped out 1955 ford 950 trike running at 7/8 throttle the entire time... only stopped when i ran out of gas and the rain set in sideways ( both at about the same time )...

use that tractor.. it's what it was meant for!! you don't swing a framing hammer softer to 'save' it do you?

sheesh

I am just glad to see you are now stirring up DarkBlack so you are on a roll. When will your goal be met? OP, me, now DarkBlack who will be next? I will try to answer your question you had for him though. I do believe your experiment could have netted the same fuel consumption. Your experiment though is completely flawed because you are using two different tractors with differing technologies and efficiencies. There are a lot more parasitic losses in larger HP tractors and rotary cutters. Imagine driving a car on the same 100 mile course. First trip you drive 30 MPH and the second trip you drive 60 MPH. You lead me to believe both trips would use the same amount of fuel just because they accomplished the same task. Nothing is free.
Another example, run both trips at 60 MPH but one at 2000 rpms and the second trip at 8000 rpms. Again, the 8000 rpm trip you would use more fuel due mostly to parasitic losses in the engine. Imagine all the accessories like the power steering pump, alternator, water pump, etc you are spinning at the higher rpms. That 6000 rpm difference would make EACH piston travel 4000 feet further each minute or 240,000 feet (45.5 miles) in one hour given a 4" stroke.

 

[JoeBuyer]

I pretty much run the engines so that I have 540 RPM all the time if I am using the PTO as everything is designed for that RPM. I change the ground speed (gear) of the tractor if I am unsure of the loading rather than increase or decrease the RPMs. Having said that there are times (rare) where I drop the RPM such as near a road, near neighbor's buildings or if I am kicking up too much dust at 540, etc. I would think total fuel use for the job would be close to the same but I can't say I have checked it.

 

[Redneck in training]

Your example is about the car is flawed due to aerodynamic drag difference at 30 and 60 mph. Aerodynamic drag increases with square of speed while rolling drag increases linearly. Therefore doubling the speed of the car will require eight times as much power. The same apply to tractors but since the speed they are moving is slow we don't need to take aerodynamic drag into account. Download engine charts from the Internet and look at the power and/or fuel consumption versus rpm. It clearly shows that the fuel consumption is lowest at about maximum torque. That is also usually the PTO speed.
You can mow grass at lower rpm but it will not save fuel and will not make much difference to wear of the tractor.

 

[jejeosborne]

Your example is about the car is flawed due to aerodynamic drag difference at 30 and 60 mph. Aerodynamic drag increases with square of speed while rolling drag increases linearly. Therefore doubling the speed of the car will require eight times as much power. The same apply to tractors but since the speed they are moving is slow we don't need to take aerodynamic drag into account. Download engine charts from the Internet and look at the power and/or fuel consumption versus rpm. It clearly shows that the fuel consumption is lowest at about maximum torque. That is also usually the PTO speed.
You can mow grass at lower rpm but it will not save fuel and will not make much difference to wear of the tractor.

My example is not flawed. I agree with your numbers. I understand the reason for the additional fuel consumption, I am a pilot and an airframe and power plant licensed mechanic and have studied aerodynamics.

The point I was trying to convey was that fuel consumption is not fixed to complete a given task. A tractor example using the same ground speed would include more wheel slip with a larger implement, more gearbox parasitic drag using a larger implement, etc. Using the SAME tractor to pull a larger implement to get the job done quicker can cost more in fuel.

The possible improvements in a larger implements is less overlaps on your passes are required. Today's modern tractors display ground speed and wheel slip so the operator can make adjustments to hit a predetermined sweet spot for fuel consumption.

The thread title is based on engine rpm though so back to that example. The charts are basically showing how to complete the most work using the least fuel. To accomplish this, large loads have to be put on the engine. I agree that when mowing thick brush, the opportunity is there to gain from these charts. But if the engine load opportunity is not there, such as in light to no brush similar to what I have in my forest, these charts are not helpful due to the parasitic drag being a higher percentage of the total engine load. Try this experiment: run your rotary cutter in your driveway using the sweet spot rpm your chart suggests with the emergency brake on and see how long a tank of fuel last. Are you telling me it will last longer than a rpm setting just above idle?

 

[PapaPerk]

Wow... this thread is out of control. :number1::rotfl:

When approaching a question like the OP has asked.... you must eliminate variables. The question is... Full RPM or high idle? Bush Hogging Efficiency.

Let's make some constraints and constants. 40 hp tractor, 6' bush hog, 5 mph travel speed, grass height = 12"
Variables. Throttle setting,

If we mow grass at 540 PTO speed we will burn more fuel per hour than at 400 PTO speed. Rotating machinery at a higher RPM takes more fuel. Period.

Now will cut be as good? Who knows?! It depends on the output the operator is observing from the seat. We cannot determine this answer. Only operator can.

 

[Oaktree]

Not to add another curve to this thread, but what about those of us who have 2 speed PTO's (my Kioti is 540/1000). Does using the 1000 rpm setting at a lower engine speed help or hurt wear/fuel economy?

Likewise, does it damage an implement to run it at a higher PTO speed? Dealer told me it shouldn't, and so far he seems to have been right, but I'm concerned about long-term.