Finish mower blade

[nomad]

We all have seen/read on the web sources that finish mower and espcially its blade and deck design is a complex technique - meant/implied that air flow around the blade is very important. So, if it's really so, it must be designed by using some complex flow analysis.

Well, I finally found time to draw a simple rough solid drawing of that blade (see attachment) -

The size of this blade is about 1" x 22 " and it has a rotational speed of around 2750 Rpm. I did a simple rough magnitude analysis for the moment using this geometry at this speed, and it was enough for me to understand that air flow analysis of these blades of finish mowers have not been done yet. I have not seen any literature about this either. If I missed any, give us a link to such a source. So, if there is no detailed air flow analyse for these blades yet, then how come we are being told that the blades are being designed according to air flow around them? Somethings around there seem to be fishy.

 

[PineRidge]

When I am interested in purchasing any implement I normally first see what is available. I then talk to people that have either used or purchased that implement to see if they are happy with its performance. I am also concerned as to how well it will hold up under actual field use.

I leave the geometry and flow analysis to the engineers as I'm only interested in real field performance. I think the rest is all window dressing anyway.

 

[Villengineer]

</font><font color="blue" class="small">( I have not seen any literature about this either )</font>
Ever heard of proprietary information? Companies do not publish analysis or test data. Why give your design information to your competitors? Let them buy a unit and reverse engineer it if they want, but there is no way a company hands their design data out to the general public. Just because it's not published certainly doesn't mean it doesn't exist.
Published analysis data almost always comes from government and education based sources that are paid for by grants and such. I doubt that we'll be seeing any big push by these sources to spend $ on mower blades.
Based on the amount of time that companies spend on much simpler components, I guarantee that a lot more time is spent on the design of those blades than you think. All you should need for proof is that they are using more than just a flat piece of bar stock with an edge. Every bend and machined surface costs $ and they aren't adding those features for appearances. After all, I would guess that the majority of users never look at the blades until they have to service the underside of the deck the first time.

 

[nomad]

Finish mower blade has been in the field for decades. So, at least, older mower blade models are not a secret anymore and when a thing isn't secret anymore we would see many scientific research papers published by scholars. I am asking this; show a single air flow analyse around the mower blade. I am unable to find one yet. Yes, "MAJOR" finish mower manufacturers maybe doing such analysis, but MAYBE. You aren't sure, either. You can't be sure if they are already designing their blades using air flow analyse because, as you said, they don't publish anything about their researches. So, you and I know same things (nothing) about whether they do or not. My difference is I can understand (without seeing their research centers) if they are doing a flow analysis or not by using my own simple "flow magnitude" analyse. And, these existing mower blade geometries are telling me that they aren't doing any detailed air flow analyse when designing their blades. No MINOR finish mower or no dealer/distributor/farmer can disprove my these words - A major finish mower mfg will come here and tell us if they are really doing air flow analyse around their blades or not.

All these may not seem to be important for yoy. But, yes, these are important because we have been told how/why their blades&decks have so precious configurations in that the air flows through a sophisticated patterns. If majority of users aren't looking at the blades, then why are all so-called knowledgable seller people (like CCI) in the market who introduce themselves knowledgable experts often telling the users the blade designs are done according to the air flow around the blade in the deck? I guess there are lots of blows by people in the market, more than air blows by finish mowers.

 

[Villengineer]

</font><font color="blueclass=small">( So, at least, older mower blade models are not a secret anymore and when a thing isn't secret anymore we would see many scientific research papers published by scholars )</font>
Did you not read my previous post? Scholars don't publish that which they do not research. No one outside of the mower manufacturers care about the specifics of the flow around the blades. Not to mention that 99% of mower owners wouldn't understand the flow analysis anyway. For that matter, most engineers would only be able to muddle though it b/c we don't work with flows enough.
</font><font color="blueclass=small">( Finish mower blade has been in the field for decades )</font>
And if you look at a 10 yr old blade versus a new one, chances are the design changed. Perhaps you'd find that cheap mowers' blades looked like old "high-end" blades, but that happens in all segments of manufacturing. For that matter push mower blades have changed relatively dramatically over the last decade or so.
</font><font color="blueclass=small">( You can't be sure if they are already designing their blades using air flow analyse because, as you said, they don't publish anything about their researches. So, you and I know same things (nothing) about whether they do or not )</font>
No, I know from my experience being a design engineer for products that are actually manufactured and sold to customers that designs do not change just for the sake of changing them. Companies want to make $ and they do that by supplying products that meet their customers' needs and expectations better than their competition. It costs money to make changes that have no benefit, especially if they are a gimic b/c unhappy customers buy elsewhere. Additionally, I have yet to work at a company that neither instructed me to make design changes to "fool" the customer, nor that engineering lied to their superiors. Does it ever happen? maybe. In an entire industry? No way.
</font><font color="blueclass=small">( If majority of users aren't looking at the blades, then why are all so-called knowledgable seller people in the market who introduce themselves knowledgable experts often telling the users the blade designs are done according to the air flow around the blade in the deck? )</font>
It's their job. If you don't trust your dealer then buy somewhere else. There is very little incentive for agri manufacturers and dealers to lie to their customers. They are in a unique position that there is just enough competition to foster development and keep $ reasonable. The market is also such that the $ is in the repeat customer, so there is no logical reason to sell a product that doesn't do what you claim it does b/c you'll lose that customer.

 

[Egon]

Nomad:

could you post your flow magnitude program. It might be fun to play with.

Egon

 

[Junkman]

Nomad....... please show us how you arrive at the facts that you tout..... I look forward to seeing all your research.... Can you tell us what machinery you have been directly responsible for designing and manufacturing? Do you work for a manufacturing firm or are you a representative of one of them? Would like to know more about where you developed your expertise in the field of engineering....

 

[RalphVa]

It's not all in the blade. Gravely "bush hogs" can also be used as finish, mulching mowers. It's in the dome design of the housing, in their case. The blades are flat, very flat. Works a little better in finish mode if you use 2 flat blades crossed perpendicular. Better for hogging with 1 flat blade.

Does a beautiful job, and you won't have any trouble with your wife or kid wanting to do it unless they're both gorillas with long, strong arms.

Ralph

 

[chim]

Unless it's an optical illusion, it looks like your blade is lower in the center?

It's interesting that you ran calcs on the blade. If I understand your post, either all decks would need to be the same size/shape or blades would need to be designed for each different deck.

Ths past Fall I welded small "wings" to the upward-canted part of some RFM blades in an attempt to get more lift. It worked remarkably well and moved much more air. The extra lift resulted in the grass looking better (no long fuzzies where the tires pushed the damp grass down). It also made leaf cleanup a snap.

I bought a set of Gatorblades a couple years ago and was very underwhelmed with them. My simple experiment tells me the manufacturers could make more effective blades. This could be your chance at early retirement......................chim

 

[normde2001]

Nice "drawing", Nomad, is that India ink, or #2 pencil? /forums/images/graemlins/wink.gif