Limitations on Tractor/Combine Design 4

[gontek]

I have never had any experience with farming or tractor design per se, but I was trying to figure out what limitations are placed on design of Farming machinery, and why not go way bigger. With farms becoming corporate, are we looking at farming machines going the way of mining/quarry machines and becoming superhuge? I figure size limitation probably has to do with the requirement of being able to drive down a narrow dirt road with overhead wires, is there a standard weight limitation or other limitations to sizing a new tractor or combine design?

I am wondering it an aircraft could be designed to do some serious farming. I am thinking about a low speed flyer, with about 4 engines, and multi-tailboom design. It would be heavy and have a ton of drag, but you could have an enormous wing with controlled attachments for doing the cutting/tilling/ whathaveyou. Nothing like it has been done before to my knowledge, but I would compare it to a slow B-52 with no wing sweep, narrower & shorter fuselages, and huge tires. I honestly don't know enough about the ag market to find out if it would be cost effieient do design a fleet of these beasts, but I think it would be a cool option to go bigger.

Thoughts? Comments? It is a totally crazy and impractical idea? Assinine to even pursue marketability?

If anyone could provide some resources online I might not be aware of, or some good specific references to get an idea of the mechanical terminology, mechanical systems and design parameters of tractor/combine/ farming machinery, that would be helpful, especially dealing with price/cost parameters associated with tractor design. ($/acre, section; $/hr; $/year, lifecycle, etc)

 

[Slowzuki]

Re the flying tractor, not gonna happen right now. The drawbar pull required for almost all ground engaging equipment would stall the plane like you wouldn't believe. Also the speeds at which this stuff can maintain proper ground engagement is pretty low which is why you see bigger and bigger equipment, not faster and faster tractors.

Planes are used in modern farming for liquid application of fertilziers, pesticides etc. This is a reasonable use because reduced soil compaction increases production.

I could envision a ground effect vehicle such as a hovercraft doing mowing or something to reduce compaction but it would only work in very flat areas.

 

[gontek]

Thanks for the reply. I was thinking the attachments would retract into the fuselage/tailbooms for flying, then upon landing, the equipment would unfold, and the engines would transfer power to the ground wheels and pto, and you would have a tractor with about 80% the width of the winspan. I agree, bigger not faster, while in tractor mode. The faster comes when moving from field to field. Then Retract farm equipment into fuselage, transfer to prop or fan, Takeoff and land in the next big field.

A flying tractor would be a very expensive program, but it seems like tractors are getting more expensive, farms are getting larger, and particularly I want to project a crossover point where tractors can't get any bigger. I am looking for a resource for economic data for tractors re costing and price for a program of a certain number of tractors. Maybe ag industry doesn't work that way, I don't know.

I have some other projects going on, so I haven't had any time to work on developing this other than thinking it out in my spare time. I know it could designed, I just don't know if it would be worth it, and that really depends on size and cost, which are directly related.

 

[drkillroy]

Your idea does address another issue farmers experience. Transportation of equipment to and from the fields. The equipment has to fold up, sometimes several times, to become compact enough to transport on to roads to get to the field. Some equipment is transported sideways until ready for use. Weight is another problem. A small 10 foot header is just over 1000 pounds. A 20 foot header requires so much extra reinforcement and larger material handleing capability that the header becomes 3 to 4 times the weight. A header placed 10 feet ahead of the front axle will place far more weight on that axle. Only a small percentage of the perimiter of the wheel is in contact with the ground, 2 wheels 2 to 3 feet wide, causes a lot of soil compaction. As Slowzuki mentioned, very large equipment requires very flat fields. A header 150 feet wide must flex to follow the conture of the ground. Otherwise too much of the crop in low spots will be missed and dirt and stones will be picked up from the high spots.

 

[dwt]

Another reason for the larger equipment is a combining of tasks. Harvesting use to involve cutting the grain stalks, tying them into bundles, then hauling the bundles to the threshing machine where the grain was separated from the straw. The modern combine "combines" all these processes including accumulating the grain in hopper tanks which are bigger then the granaries on the farm I grew up on.
Same thing with seeding, zero till or minimum till combines cultivating, seeding and fertilizing into one process. The amount of grain & fertilizer being hauled around is a major reason why such large tractors are required.

 

[sbi]

Hahaha Slowzuki is right, a 747 which is the largest flying plane at present uses 4 large jet engines that each produce 45,000 Lbs of thrust each ( push) at 180K lb is not that much when you takl about a large 4x4 tractor or one of the track monted one which can pull twice that amont!

not to mention you need to move air over the wings to produce lift,
You need to study real time equipment not theroy!

SBI
Central Ne.,USA

 

[gontek]

that's cool, I expected that kind of reaction when I made this post. What you say sbi sounds about correct. Also a 747 has way different operating envelopes than my flying tractor.

The John Deere 9620 has about 500 HP and weighs about 40,000 lbs. So you are saying a large tractor roughly of that size and power cal pull about 360,000 lbs? Good to know

The same powerful turbine engines in a 747 can also be used to turn a driveshaft or an axle. Aren't these are the same types of turbines that turn an electric power generator producing up to 480MW? There are several vehicle/motorbikes that use a turbines as a powerplant. The nice thing is that with a turbine engine you can realize about 99% of the ideal Brayton cycle efficiency.

However, I was kind of leaning toward a diesel motor with electric transmission - as used in train locomotives. The diesel motor would also be able to turn a prop I think - however I haven't got that far yet.

sbi, your post gives me an idea - a Convair XB-36 Bomber used caterpillar style track landing gear - I'll work that in and it is a useful thought. Also your link to

http://tractortestlab.unl.edu/

on another post will probably be useful.

I think as long as there are naysayers, I will keep thinking about this and continue on my preliminary design. Nothing has been done like this before so it is hard to compare to existing vehicles, tractors or aircraft, and it is why I find it an interesting puzzle to work on in my spare time. Thanks

 

[gontek]

hell, I didn't know what a drawbar was when I first posted here. That helps a lot.

 

[griffengm]

Gontek,
The turbine-in-a-tractor bit is relatively commonplace among the tractor pulling crowd.
What you propose has a mix of variables that interact so highly that almost inevitably the decision is made to favor one area over another.
Aircraft as spray equipment only became feasible when chemicals were concentrated enough to allow enough acres to be covered. Still today, the plane spends more than maybe half of its fuel on turning and reloading.
Let's say your machine has a ground speed (yes I realize it is flying but the effective speed is gs)of 60 mph and a tool width of 20 feet. For easy calcs, the field is one mile long. Each pass covers 2.42 acres. @60mph, 100 bushel/a yield, 56 #/bu this means that the equiptment increases its gross weight by 13,500#/min. Add to this fact that the "combine" portion must process this at the same speed. This rate equates to harvest speeds in the neighborhood of 145 a/hr. There may be farmers willing to pay for that kind of speed but remember that you will be lucky to get half of that, more likely 30%.
Have at it!

Griffy

 

[ornerynorsk]

I don't think an XB36 had tracked landing gear. My father was in AF at the time of their deployment and subsequent crashes and various other problems at Ellsworth AFB. I have seen many photos of this magnificent aircraft, and I believe they had "truck" style landing gear, as do all large aircraft.

 

[gontek]

I think maybe I am not being clear enough - in tractor mode we are a ground vehicle with power going to the wheels on the ground and PTO equipment. Speed is like that of a regular tractor, maybe 15-20 mph. Advantage being size over speed.

In transfer from completed field to next field to be completed we fly. Advantage is speed of transportation between fields, and once again, reduction of effective size limitations due to enviornment variables such as GVW limitations, overhead power lines, and narrow unpaved roads.

Reagarding the B-36, the XB designation usually means eXperimental aircraft, and the experiment in this case wat to develop and proof the concept of track landing gear for heavy aircraft. Here are some cool pictures:

http://www.wpafb.af.mil/museum/research/bombers/xb36-13.jpg

http://www.wpafb.af.mil/museum/research/bombers/xb36-15.jpg

http://www.wpafb.af.mil/museum/research/bombers/b3-69.htm

I remember learning about this in aero design class, and sure enough it is an option especially useful for a heavy vehicle operating in dirt.

I started with configuration layout yesterday to get a picture. I have some ideas, but I need more information still.

Is aluminum used ever or fairly often in tractor structures? I would imagine a lot of the parts are steel or cast iron.

 

[gontek]

I think what will a big problem is the way larger tractors need the additional weight ballast to get the foothold necessary for wide tillage. Could be a killer I think. Thanks everybody for your comments and help.

 

[Slowzuki]

Gontek, I'm glad to see people thinking different too, it's hard as an engineer as we are usually trained to spot all the problems with an idea before money gets spent on it.

I fear with current technology the flying tractor would use too much fuel with turbine engines. With fuel prices how they are, profit margins are razor thin for farmers and they would have to have a really good reason to use more fuel to do something even if it saves some time.

 

[gontek]

It is starting to look like a flying landing gear. I got some information on combine attachments over the weekend when I visited my girlfriends farm and talked to some farmers. Sounds like aluminum is never used. If it was, and I am seriously thinking it is the only way to go, cutting surfaces would probably need to be replaced at least once a year.

I am thinking this aircraft is going to be a harvester or combine, not a tractor. I like the option of deisel, since most combines use diesel now anyway. It is really hard to size this thing though because of the problems noted with uneven fields and lack of data on flying harvesters.

I believe that when I get into it, there will be a breakpoint where a minimum size will be profitable in terms of harvesting seasons and and aircraft program lifetime. Of course it is a gamble still because of unstable gas prices, crop futures, and future technological developments in the industry. Hopefully that minumum size is less than a 747 in terms of winsgspan.

I like telling people about my idea for a flying tractor, They usually seem politely amused by it. I think I'll name the project "Locust" for now.

 

[Slowzuki]

I'm curious what you plan to do to address crop damage while landing it...

Steel is generally used in many ag applications for 3 reasons:

Weight isn't generally a problem and if it is a HSS gets close to the strenght to weight ratio of many materials.

Infinite fatigue life, aluminum has a finite fatigue life and farm equipment has to last a long time.

Easily Repaired with standard welders and techniques familar to farmers.

 

[gontek]

Thanks- my plan for crop damage on landing is basically to suffer the losses - but the max landing distance should be short, well under 1000 feet I think, to reduce these losses.

 

[cpretty]

Why not cheat, and go for a lighter than air aircraft. Essentially just use a large ballon to drop off and pickup an extremely large tractor. I would imagine the balloon would be enormous, but the amount of material required goes down in comparison to lift as you go larger, hence greater efficiency.

You would have issues with weather etc, but these would be similar problems with the flying tractor, as it would also be on the limit for flying.

 

[gontek]

Yeah, that balloon would be enormous, considering that the payload weight of your average hot air balloon is probably around 1000 lbs max.

I just started a new job, so I probably won't have as much time to sit around and think about these things anymore. At least I hope not, one of the reasons I changed jobs is because of lack of things to do to utilize my engineering mind, so I would sit around and think about flying tractors among other things. It still has some merit I think, and I will continue to learn about farm equiment and work it out.

I like balloons for certain things, I would like to see a comeback of zepplins and blimps for transportation, and they are coming back for unmanned remote sensing applications - but it is easy to underestimate the amount of lift you can get from a wing - and given the weight of the steel combine header alone, wings can do that better than balloons.

I think it could me done even more efficiently and synergetic from a from scratch combined design. It would also probably lead to new ideas regarding both aircraft operations on the ground and farming equipment even in the event of design failure - but it has a long way to go.

 

[Slowzuki]

Ballon is an interesting concept for spraying and fertilizer application...

 

[drkillroy]

Concerning tractor/ground mode going 15 to 20 mph is road speed. I bale at 3 MPH, plow at 4 to 5 MPH, and final fitting, conditions permitting, at up to a blazing 8 MPH. Knife sections are about 2.5 inches deep and must move the width of the knife section (about 3 inches) before changeing direction. That is for a typical sickle bar cutting head. Ground speed cannot exceed much over 2 inches per sickel bar stroke. A rotary style allows greater ground speed but I don't know how much dammage to the grain will result due to the more harsh cutting method. Usually a sickle bar will be driven from one side and extend the width of the header. Some have 2 knife bars that overlap in the center with special shaped knife sections for the overlap area only. I still say your biggest problem will be figuring the shape of some kind of articulating header with multiple cutter bars.
I like the ballone for some of these applications. How do you steer the balloon. Or just use to reduce soil compaction and working wetlands.
Drkillroy