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From: Vermont
The Bernoulli principle is spot on.
Hole size doesn't necessarily matter as much as the free cross sectional area of the screen. More material = greater pressure drop across from inlet to outlet. My hunch is the smaller screen has the most free cross sectional area, hence more "felt" air flow.
Hole size doesn't necessarily matter as much as the free cross sectional area of the screen. More material = greater pressure drop across from inlet to outlet. My hunch is the smaller screen has the most free cross sectional area, hence more "felt" air flow.
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Now that I've wasted the money on screens, I have proven to myself that no matter which one I tried, they all blocked a significant enough amount of air to make a difference. From my experiments I think this would be especially true when moving at the slower speeds that I travel on my gravel road. At this point, I'm going without the protection screen and see how it goes? Thanks for all of the great insight and replies!
Last edited by Rickr01; Apr 9, 2013 at 02:45 PM.
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Rick,
I started writing before your last post, and my points have been captured by others, but Ill go ahead and hit reply anyway.
If you look back at the McMaster Carr website, at the part numbers you ordered, in the description you will see "% of open area" whichever one has the highest percentage of open area will generally flow the most air. Oil to air heat exchangers are heavily constuced and very rugged compared to common aluminum/copper/plastic automotive water to air type heat exchangers. I understand your concern for protecting your heat exchanger while stillp roviding "adequate" airflow. My guess is if you hit something, or something hits you hard enough to breech the heat exchanger, you are going to have much bigger problems than an oil leak. In the unfortunate event you do encounter a damaged and/or leaking heat exchanger, you can pull one of the adapter hoses off, then pull the other one from the heat exchanger and rout it back in to the adapter, simply looping it back to the adapter temporarily and tahing the core out of the circuit until you can get it fixed. I dont mean to trivialize your project, but I think you may be too concerned over a potential problem that is very unlikely to ever occur. If your road is that hard on your oil cooler what is it doing to the rest of your bike? Im far from an engineer but here is the direction I would go: you have a very specific section of gravel road between you and the hardball that is your primary concern, what is the fastest you travel on that road, then at your fastest travel speed what is the smallest rock that could actually damage your heat exchanger, that is what size opening mesh I would be looking at to build a guard with. You will first have to accept that you cant have everything in one package, so either compromise on the protection or the airflow. Contrary to conventional wisdom, I have consistently observed that you really dont need that much airflow for the heat exchanger to do its job, under the best conditions traveling at highway speed with the cover removed, the heat exchanger is not getting unrestricted air at the same velocity you are traveling.The front end, forks, wheel, tire, fender, brakes, all push the air out away from a straight line path to the oil cooler, and the vacuum created in the little pocket between the front end and the chassis, all restrict the air flowing across the heat exchanger, but it still works.
I started writing before your last post, and my points have been captured by others, but Ill go ahead and hit reply anyway.
If you look back at the McMaster Carr website, at the part numbers you ordered, in the description you will see "% of open area" whichever one has the highest percentage of open area will generally flow the most air. Oil to air heat exchangers are heavily constuced and very rugged compared to common aluminum/copper/plastic automotive water to air type heat exchangers. I understand your concern for protecting your heat exchanger while stillp roviding "adequate" airflow. My guess is if you hit something, or something hits you hard enough to breech the heat exchanger, you are going to have much bigger problems than an oil leak. In the unfortunate event you do encounter a damaged and/or leaking heat exchanger, you can pull one of the adapter hoses off, then pull the other one from the heat exchanger and rout it back in to the adapter, simply looping it back to the adapter temporarily and tahing the core out of the circuit until you can get it fixed. I dont mean to trivialize your project, but I think you may be too concerned over a potential problem that is very unlikely to ever occur. If your road is that hard on your oil cooler what is it doing to the rest of your bike? Im far from an engineer but here is the direction I would go: you have a very specific section of gravel road between you and the hardball that is your primary concern, what is the fastest you travel on that road, then at your fastest travel speed what is the smallest rock that could actually damage your heat exchanger, that is what size opening mesh I would be looking at to build a guard with. You will first have to accept that you cant have everything in one package, so either compromise on the protection or the airflow. Contrary to conventional wisdom, I have consistently observed that you really dont need that much airflow for the heat exchanger to do its job, under the best conditions traveling at highway speed with the cover removed, the heat exchanger is not getting unrestricted air at the same velocity you are traveling.The front end, forks, wheel, tire, fender, brakes, all push the air out away from a straight line path to the oil cooler, and the vacuum created in the little pocket between the front end and the chassis, all restrict the air flowing across the heat exchanger, but it still works.
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Rickr01, I have a gravel driveway to my shop that is 6/10 mile long. I run over the crushed limestone about 40 MPH all the time and have never created a problem with the oil cooler. In the spring thaw I do find limestone mud in the cooler so am mindful of washing out often. I would say that I am most likely a more aggressive gravel rider than most and other than the mud in the fins I have had no issues. I have more problems getting small gravels in my rear rotor than issues with the oil cooler.
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Hey Thanks for the insight Jason and Scrmnvtwins. I don't travel very fast down the gravel road at all, which is one of the biggest reasons I purchased your fan in the first place Jason. Since I'm not moving fast in order to try and protect my bike from stone damage, its not getting a lot of fast moving air to cool it down. I purchased the fans initially just to help with the slow ride cooling. This was before I realized all the additional benefits of having a head cooling fan. I have a friend who has a 103 in his bike and his came with a cooler from the factory. He also lives on a similar gravel road and his oil cooler fins are all bent up from where gravel and stone has beat against it. In fact when we make the first stop of the day after meeting up in the mornings, the first thing he usually does is get on all fours with his jack knife and pick pebble out of his oil cooler fins. He has never had a leak because of it, but his cooler sure looks like crap! That's what has prompted me to look at protection. As I mentioned though, I think I'm just going to give it a try as is. I do have to say that I was surprised that the much larger open holes in the heavier screen did some serious enough blocking of air that I really noticed it, where as the small thin more tightly placed together holes had MUCH less impact contrary to what I think many believe? As you mentioned in your last email Jason, I went back and looked at the free area listed in the McMaster Carr specs and the smaller lighter screen which flowed the most air, said it had a 70+% free area. Total surprise that I'm still not sure I completely understand? I'm just slow I guess? Anyway, Thanks guys!
Last edited by Rickr01; Apr 9, 2013 at 03:36 PM.
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