Snowblower Snowblower improvements
- Thread starter jaybirdt
- Start date
MadDog
Platinum Member
pks: I don't mean this in an abrasive way, but your analysis aroused my curiosity and I did some figuring. My calculations differ from yours, as do my empirical results.
I have a Puma-64. It has a 20" diameter impeller, rotating at 540rpm at full pto speed. This produces a tip speed of 2827 ft'/min, assuming my 22pto horsepower are sufficient to keep the impeller running under load with no appreciable slowdown. Why am I able to throw snow 50' or more despite not having the 4500 fpm that you posit?
Here, I think, is how. 2827 fpm tip speed translates to about 47' per second. The impeller is accelerating snow thrown from the end of the impeller to about that velocity (and snow not quite at the end to something less).
To attempt to be more precise, the velocity of the impeller arm 4" in from its end is 2262 fpm or 37' per second. Centrifugal force will tend to throw the snow out towards the tip of the impellers, but even disregarding this, the average velocity of snow coming off the final 4" of the impeller arm is still about 42' per second.
Assuming no wind, that my deflector is sending the snow up and out at about a 45 degree angle, and no loss of velocity due to air friction, the upward and outward vectors are each 29.7 feet, i.e., the snow will travel upward 29.7 feet while going out 29.7 feet during the first second of flight. (the upward and outward vectors are the legs of a right triangle with 45 degree angles, so their lengths are each the square root of 1/2 the square of the hypoteneuse of 42')
Since the acceleration force of gravity is 32' /sec/sec. (i.e. the downward velocity from gravity reaches 32'/sec at the end of the first second) the snow will continue to fly upward and outward for well more than a second before it starts to fall. (For most of the first second, gravity is reducing the upward flight of the snow by considerably less than 32'/sec.) It will then take well more than another second before it hits the ground, assuming that it takes about as long for the snow to return to the ground as it spent rising. Friction with the air will slow both the rise of the snow, its fall and its outward progress from the snowblower, assuming that these come close to cancelling eachother out, the snow should be airborn for at least 2 1/2 seconds during which (except for air friction slowing its progress away from the chute) it should travel some 59.4 feet or possibly more. ...all this with tip velocity of (only) 2827 fpm.
I realize, of course, that these are only approximations, because they do not take account of the actual effect of air friction, wind and perhaps other factors. I am no engineer or physicist. But the point is still clear; I don't think that you need to have anything like 4500 fpm tip velocity in order to throw snow MUCH farther than 20'. My Puma does not and it is certainly capable of throwing most snow between 50' and 100' depending on wind and snow conditions.
Needless to say, if there is an error in my reasoning, I would be most interested. BTW, it's lots of fun doing something wholly different from my usual thought processes. /forums/images/graemlins/grin.gif
I have a Puma-64. It has a 20" diameter impeller, rotating at 540rpm at full pto speed. This produces a tip speed of 2827 ft'/min, assuming my 22pto horsepower are sufficient to keep the impeller running under load with no appreciable slowdown. Why am I able to throw snow 50' or more despite not having the 4500 fpm that you posit?
Here, I think, is how. 2827 fpm tip speed translates to about 47' per second. The impeller is accelerating snow thrown from the end of the impeller to about that velocity (and snow not quite at the end to something less).
To attempt to be more precise, the velocity of the impeller arm 4" in from its end is 2262 fpm or 37' per second. Centrifugal force will tend to throw the snow out towards the tip of the impellers, but even disregarding this, the average velocity of snow coming off the final 4" of the impeller arm is still about 42' per second.
Assuming no wind, that my deflector is sending the snow up and out at about a 45 degree angle, and no loss of velocity due to air friction, the upward and outward vectors are each 29.7 feet, i.e., the snow will travel upward 29.7 feet while going out 29.7 feet during the first second of flight. (the upward and outward vectors are the legs of a right triangle with 45 degree angles, so their lengths are each the square root of 1/2 the square of the hypoteneuse of 42')
Since the acceleration force of gravity is 32' /sec/sec. (i.e. the downward velocity from gravity reaches 32'/sec at the end of the first second) the snow will continue to fly upward and outward for well more than a second before it starts to fall. (For most of the first second, gravity is reducing the upward flight of the snow by considerably less than 32'/sec.) It will then take well more than another second before it hits the ground, assuming that it takes about as long for the snow to return to the ground as it spent rising. Friction with the air will slow both the rise of the snow, its fall and its outward progress from the snowblower, assuming that these come close to cancelling eachother out, the snow should be airborn for at least 2 1/2 seconds during which (except for air friction slowing its progress away from the chute) it should travel some 59.4 feet or possibly more. ...all this with tip velocity of (only) 2827 fpm.
I realize, of course, that these are only approximations, because they do not take account of the actual effect of air friction, wind and perhaps other factors. I am no engineer or physicist. But the point is still clear; I don't think that you need to have anything like 4500 fpm tip velocity in order to throw snow MUCH farther than 20'. My Puma does not and it is certainly capable of throwing most snow between 50' and 100' depending on wind and snow conditions.
Needless to say, if there is an error in my reasoning, I would be most interested. BTW, it's lots of fun doing something wholly different from my usual thought processes. /forums/images/graemlins/grin.gif
MadReferee
Elite Member, Rest in Peace
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</font><font color="blue" class="small">( it's lots of fun doing something wholly different from my usual thought processes )</font>
You're right. But you're starting to sound too much like an expert witness. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
You're right. But you're starting to sound too much like an expert witness. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
MadDog
Platinum Member
LOL. Nah, Mad, I'd never be that. BTW, you know the cynic's definition of an expert witness? "A guy with a PhD who for $1000/hr and a per diem, is willing to testify to whatever will win your case in language that no one can understand.
/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
Cord
Veteran Member
Sorry about the delay. I needed to get up to the shop with a digital camera and shoot some pics of my blower. I now have them uploaded to my gallery.
jim_wilson
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I actually talked with a service manager at Loftness before I bought the blower and he said that the basic snowblower unit is the same for the Jacobsen as a rear 3pt mount 540rpm PTO tractor unit. The blower as I got it had a conversion gearbox that was mounted up to the snowblower gearbox ( the gearbox that sends the power straight thru to the impeller and has a driveshaft coming out the side to drive the chain for the auger).
What I did was first weld up a 3pt mount to get the blower mounted on the tractor - then I got the correct PTO shaft from Loftness to hook the rear 540rpm PTO up to the gearbox. This PTO shaft fit right on like I would expect it without any mods.
If I take the auger and spin it around to count revolutions I get one full revolution of the impeller for every rev of the PTO shaft (1 to 1) and I get approximately 1/4 revolution of the auger for every revolution of the PTO shaft. It is my understanding from reading some other manufacturers sites that this is the correct ratio of impeller, auger and PTO shaft speed. I don't actually recall what the real PTO speed of the Jacobsen was - the number that it is in my head is 2000 or 2200 rpm which I remember thinking at the time was a pretty standard mid or front PTO speed.
I don't know exactly what the diameter of the impeller is without going back and measuring it - but I think it is closer to 20 inches than say 14. I will check that out tonite. The clearance from the impeller blades to the housing looks to be about 1/2 inch.
What I did was first weld up a 3pt mount to get the blower mounted on the tractor - then I got the correct PTO shaft from Loftness to hook the rear 540rpm PTO up to the gearbox. This PTO shaft fit right on like I would expect it without any mods.
If I take the auger and spin it around to count revolutions I get one full revolution of the impeller for every rev of the PTO shaft (1 to 1) and I get approximately 1/4 revolution of the auger for every revolution of the PTO shaft. It is my understanding from reading some other manufacturers sites that this is the correct ratio of impeller, auger and PTO shaft speed. I don't actually recall what the real PTO speed of the Jacobsen was - the number that it is in my head is 2000 or 2200 rpm which I remember thinking at the time was a pretty standard mid or front PTO speed.
I don't know exactly what the diameter of the impeller is without going back and measuring it - but I think it is closer to 20 inches than say 14. I will check that out tonite. The clearance from the impeller blades to the housing looks to be about 1/2 inch.
jim_wilson
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I measured the diameter of the impeller and housing on my blower last night - the impeller paddles are about 19 1/2" tip to tip - and the housing is about 20 1/2. So by MadDog's calculations I should have still gotten some decent performance out of the blower. I am still waiting for it to snow again around here. Now that I actually WANT it to snow it probably wont happen for weeks. /forums/images/graemlins/tongue.gif
MadDog
Platinum Member
I agree. The only thing that is troublesome is the 1" difference between the length of the impeller blades and the diameter of the drum housing. That leaves an average of 1/2" clearance between the impeller tip and the drum, which is awfully wide. The clearance on my PUma is about 1/16"
There is a link either earlier in this thread or in another recent snowblower thread to another thread which has a link to an after market kit for adding extensions to your impeller paddles. If your performance is unsatisfactory, that would probably help.
There is a link either earlier in this thread or in another recent snowblower thread to another thread which has a link to an after market kit for adding extensions to your impeller paddles. If your performance is unsatisfactory, that would probably help.
JoeL4330
Platinum Member
not an expert at this, and am not familiar with the extensions, but it seems to me that with a little cleaning of the tips w. sandpaper, and a little release agent on the drum, then some applied caulk ...acrylic or butyl, would give you minimal, flexible clearance ...if that is the goal ...maybe I will try it on mine, although I have close tolerances now
jim_wilson
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I have seen that kit - I may try using that or maybe just take the impeller off and weld some extensions onto the paddles. I really want to try the blower out in some more snow and see what it does. My only time really using it so far is when I made a couple of short passes over about 8" of snow (that was melted down from the original 16") - so the snow was relatively heavy. I figure if I get a lot of light snow and the blower still does not push that out a fair distance there really is a problem.