Clinching the Engineering Cliche!

I think you should meet kay williams. You could have some really interesting rousing relevant _inane conversations.

Always the attacking forward Lyn Lynch -I think that eggs hatched!

What?

When I was recovering from a broken hip and hand and pelvis after a bad landing on a concrete slap, I wrote some really strange stuff, that I've yet to delete from my website, simply because it is so strange, as if someone else wrote it that maybe someday somebody else will be able to tell me what it was I was talking about.

In fact I have written things that were totally incomprehensible, even to me.

Anyway so what the hell are you talking about?

Is it a rocket propelled car with a lawnmower on the front that floats on cut grass?

Possibly you ought to take up Painting, as there is a market for surrealistic painting of mechanized monsters.

Personally I think a good car has good ground clearance, and admire the Citroen for its ability to change that according to road conditions.

Thanks Transcendian,

I thought maybe it was just me.

Were you in a plane, or free falling, when you had the bad landing?

Lucky you, you have another attacking forward! (Is this a basketball site?)

Long story for your flame thrower fueled by grass!

I am travelling, sitting in an airport lounge and very tired. Please could you repeat this in English or tell me what you are taking so that I can get onto the same "planet"?

The words are quite big so I assume this is not a "language" problem.

"Your tired" is a horrible way to invalidate someone but "simple comprehension" is a fair request! Hopefully your more bright eyed the next time you see this.

In points;

Engineering perpetuates the same routine assumptions? Agree or not?

An example case; cars are designed to assume optimizations in "zero drag".

But cars can be viewed as a wing forcing the car down (the fulcrum shape)

Which is the real working factor?

But designers know more about the many car movements; do they hide the other design features in "ad slogan rhetoric" or does engineering by convention ignore the aviation knowledge?

Finally; is this example case creating a historical background that will allow a future designers a view of typical human short sightedness.

A historical view normally states; if only you knew the people working on the required technology somewhere else; then your current work would have been inspired!

I kinda get the drift about the cars. (pun intended) But maybe we can ask him for his blueprints on his design and get an idea about the lawnmower, rocket thingy?

He's probably back down off that trip he was on. He won't remember anything.

If the last part about using an air cutter left the greatest impression, then anybody stating incomprehension as the total mandate is lying. (plus I reached my target audience of 2%; goodnight lady!)

Hi.

Actually, I'm affraid that the concept of inverted wing for increasing the car downforce has been abandoned sometime ago. Mainly, because no one can assure the optimum angle of attack of the car in respect to the observed air stream. As an example, there are several videos in the internet showing car races in the early 80's when cars just lift from the track after some ondulation or vacuum from the car in front of it.

A more modern approach is to use low drag designs as you mentioned to increase efficiency. Racing cars - note formula 1 ones - currently have raised noses to increase body design for aerodynamics. Then, while everything else goes fine, hyperlifting devices - airfoils - movable and/or adjustable, and more prone to control. And, of course, much better eficiency, with engineered profiles that do result in higher downforces with lower drags.

After all, what was the question?

BTW, a flying grass cutter, like a hovercraft or something like this, would be great... just a though that have just arisen...

Regards.

"After all, what was the question?". Do you really want to know?

The last part you mentioned was the question; the optimizations of downwards forces are a huge key; perhaps the real working theory! I would suppose it's almost an inverted style of aviation and along with other engineering advancements it would be part of dimensional analysis.

Does the rhetoric of zero drag overtake the real working analysis; and possibly detrimentally because it holds back on designs overcoming the air resistance by propelling around it?

(Cutting the air to the other dimensions of the movement plane seems like a more sound theory to me personally, because you can ultimately speed it up and look for "faster than fuel" regenerative moments (what is normally rhetorically recorded as looking for average efficiency!)

Thankyou so much for the fantastic comprehension capabilities shown as a sentient human when answering intuitively amongst a comment melee! :)

"BTW, a flying grass cutter, like a hovercraft or something like this, would be great..."

You mean like this: http://en.wikipedia.org/wiki/Flymo ?

That's just for an air cushion with coincidental ease in glide not exactly a "forward air cut that pressurizes an accelerated glide cushion whilst maintaining a pathwayway traction capability despite the vehicle size and momentum within a varied system of forces caused by environmental change, desired guidance along pathway and choice of velocity (or feel desired by the occupants)".

Is it just me or would an air cushion just push the grass flat to the ground and prevent it from being cut by the blade? And if I'm not mistaken, conventional lawnmowers blade design actually pulls the grass for an even cut....

Much depends upon how airflow is controlled within the housing; in theory you might be able to pull air up & in near blade tips and force it down & out centrally, but that's tough to imagine. I do know that the Flymo actually worked, so they must have done something right . . .

I'd still like to see the airflow diagram that would permit this on a mower...unless they spent (and charge) a huge sum of money on this....

Well, I haven't seen a good clear airflow diagram, but Husqvarna ("Flymo" is their brand) is still making them after 40+ years, and their website shows sixteen different hovering lawnmower models (http://www.flymo.com/node3126.aspx). One source refers to "fans above the cutting blades" as providing the hover cushion air. The thumbnails for specific models, such as http://www.flymo.com/node2415.aspx?nid=48822, do appear to show a fan above the blades, with air inlets high up on the housing. In the FAQs, there is a reference to tilting the mower in order to start air circulation under the housing, which suggests that there is more to the flow pattern than the thumbnails show (and there are circulation illustrations only for some of the smallest machines in the range). It is possible that they treat the full pattern of airflow as a trade secret . . . They claim to have become the leading lawnmower brand in the UK in 1969, and to have sold a million units there in 2000 [but that likely includes many other products, with the hover mower only a fraction of that volume].

Ron

Have had different Flymos over the last 30 years. Useful on banks etc as no "directional" wheels. The old ones did not have grass catchers and worked well. The ones with grass catchers suffer some handling problems as the weight is added. I think it also disturbed the airflow from the lift fan.

The fan is indeed above the blades. The main reason for tilting the mower on start up and stopping is so as not to cut a perfect little circle of very short grass before the mower "takes off" and rises slightly off the ground.

It makes more sense now that I've seen the pics. Much smaller cutting area than my 22" Craftman but I guess the cut-in-any-direction must make it somewhat faster (than an equivalent width wheeled mower).

Learn something new everyday...... Thanks Ron.

True, but the standard mower is a swinging fan, I guess the speed limits the actual forces to not much downward despite the huge gust in the chamber; if anything, all create a venturi effect to aid operation.

"Low to the ground cars cause flying downwards by extending the path of air over the vehicle and shortening the path of pressure under the vehicle."

"extending the path of air over the vehicle and shortening the path of [air] under the vehicle." is precisely the traditional explanation for why an airfoil has lift: longer path = higher velocity; higher velocity = lower pressure (Bernoulli/Venturi).

There are lots of other factors, but the shape you seem to be describing should make the car lift, not hold down,

Your right if you read my words as a forward convex bubble such as a standard wing but I was considering the raked form of a sports car having two elements

convex nose and concave sweep but like bhrescobar said it's just about optimizing the downward forces,

"And, of course, much better eficiency, with engineered profiles that do result in higher downforces with lower drags."

And the reason I think it works as a reverse wing (not to confused with an upside down wing) is that also less air pressure is available under the vehicle. That makes it the opposite of flying into a lift but I think your bang on with your summary of a flying bubble car being a good airfoil shape.

http://www.maddernracing.com/images/headlines/wing.jpg this is concave raked wing.