Things you always wanted to know the answer to [Vol. 3]
Discussion
Fane said:
scarble said:
I can't help but wonder at your logic?
My non-scientific brain assumes that more revolutions of the wheels = more fuel used. On the other hand, I assume that there would be a trade off in terms of aerodynamic efficiency - the slower you go, the less you have to punch a hole in the air.There is a balance point between high gears covering more ground for each revolution, and high speeds incurreing more aerodynamic drag.
The optimum point is usually around 30-40mph in top gear, AAUI.
illmonkey said:
TheEnd said:
blade runner said:
Hope it's not been done before, but when out running on pavements, cycle paths etc. I keep coming across these small metal dome head bolts and flat washers sunk into the tarmac/concrete. Always a bolt and a washer together, usually slightly rusty but worn smooth. Thought maybe they were just a UK thing, but was recently running on holiday in Florida and saw a load of them there as well. Doesn't seem to be any logical spacing between them (sometimes they are miles apart, other times one a few metres from the other) so my first thought (mile/km markers) doesn't seem to stack up. Any ideas?
Survey marker bolts.http://www.sccssurvey.co.uk/10zs-centre-marker-wit...
They usually come with a little dimple in the top to stick a survey pole, and that can then be used for repeated measurement.
A surveyor will then use these nails (2 or more) and values to triangulate a location from where they can continue surveying or marking out
You will find that the nails will usually go mostly in a loop and they are always in sight of each other.
Hope this helps
Fane said:
Would a car doing 3,000 rpm in 3rd gear use more fuel than a car doing 3,000 rpm in 4th gear over a set distance of, say, a mile?
My Speed Awareness Course provider reckoned it would use less, I think it would be more, due to the gearing, but I'm no engineer or mathematician.
I'd guess so, and it is a guess.My Speed Awareness Course provider reckoned it would use less, I think it would be more, due to the gearing, but I'm no engineer or mathematician.
Obviously in 4th gear it's going to be traveling faster so it will cover the mile in less time - engines aren't 100% efficient so the longer they run the more they waste - BUT as speed goes up, so does air resistance so there's a 'sweet spot' for efficiency.
In the back of my mind 56mph is about the more efficient constant speed - it's certainly the speed most big commercial stuff is restricted to, even though legally they can do 60mph and it was always the speed they tested fuel efficiency in car mags way-back-when before combined EU rates and stuff.
4th at 3krpm would be closer to 56Mph than 3rd in most cars.
Yep.
For example, you could start off with a total station measuring to a couple of known points.
A total station measures angles up and down, in 360 deg rotation, and also distance.
If can sort itself out from one point, but two will help for less fancy versions.
By doing that, you can drop your Total Station anywhere, measure off a known point to fix its location in 3D space, and then use it to mark any other locations.
Say for example you are setting out the footings for a house.
You can put your total station anywhere that has line of sight to where the footings would be, and the datum point which would be the survey nail.
Use the datum to figure out where the TS is, and then input the co-ords for the footings and it'll be able to point you to them and mark them up.
Now lets say a few weeks later down the line, some walls go up, a site cabin in put in the way etc, you can shift that Total station to any other point as long as it can see everything.
Sometimes if things are planned well, there might be a datum point sat on an area out of the way, and you can set the total station up directly ontop of it (they have sighting targets that look directly down too) but that might not always be possible.
For example, you could start off with a total station measuring to a couple of known points.
A total station measures angles up and down, in 360 deg rotation, and also distance.
If can sort itself out from one point, but two will help for less fancy versions.
By doing that, you can drop your Total Station anywhere, measure off a known point to fix its location in 3D space, and then use it to mark any other locations.
Say for example you are setting out the footings for a house.
You can put your total station anywhere that has line of sight to where the footings would be, and the datum point which would be the survey nail.
Use the datum to figure out where the TS is, and then input the co-ords for the footings and it'll be able to point you to them and mark them up.
Now lets say a few weeks later down the line, some walls go up, a site cabin in put in the way etc, you can shift that Total station to any other point as long as it can see everything.
Sometimes if things are planned well, there might be a datum point sat on an area out of the way, and you can set the total station up directly ontop of it (they have sighting targets that look directly down too) but that might not always be possible.
Issi said:
Every now and then you'll see a photo in a local paper of an abandoned horse/pony in a terrible condition,i.e starved, but it appears that it's standing in a field full of grass.
Is it the 'wrong' type of grass, do modern horses need supplements?
Yes, like humans have evolved over time to require a unique combination of McD's/BK and several litres of WKD without fail every weekend followed by caffeine and berocca during the week - "modern" horses die without a strict multi-vitamin regime marketed under the brand "Well-nag".Is it the 'wrong' type of grass, do modern horses need supplements?
No.
The only image I could find of a starved horse in a nice grassy field was a dead one that was dumped there.
If they had plenty of grass there are other health risks (laminitis) but they would be very unlikely to be skinny.
One shouldn't forget that a wider throttle opening will be needed to keep a car travelling at a certain speed in a higher gear, but frictional losses also need to be taken into consideration.
In general though, the slower the car goes the less fuel it will consume to cover any given distance, air resistance increases as the square of the speed, and is consequently a b
h when it comes to going quickly, and why enormous power is needed for very high speeds.
In general though, the slower the car goes the less fuel it will consume to cover any given distance, air resistance increases as the square of the speed, and is consequently a b
h when it comes to going quickly, and why enormous power is needed for very high speeds.
Fane said:
Would a car doing 3,000 rpm in 3rd gear use more fuel than a car doing 3,000 rpm in 4th gear over a set distance of, say, a mile?
My Speed Awareness Course provider reckoned it would use less, I think it would be more, due to the gearing, but I'm no engineer or mathematician.
The car doing 3000 rpm in 4th will be going faster than the one doing 3000 rpm in third, therefore require more power, therefore use more fuel.My Speed Awareness Course provider reckoned it would use less, I think it would be more, due to the gearing, but I'm no engineer or mathematician.
The interesting question is whether a car doing say 30MPH in 3rd uses more or less fuel than one doing 30MPH in 4th. At a first approximation the power required is the same. More realistically the other hand the lower gear/faster engine speed will mean greater losses due to inefficiency AOTBE, and engines are designed to be most efficient at certain revs. Usually fairly low revs. I suspect that for most cars 4th gear is fractionally more efficient than 3rd at 30, but 5th less efficient than 4th.
Dr Jekyll said:
The interesting question is whether a car doing say 30MPH in 3rd uses more or less fuel than one doing 30MPH in 4th. At a first approximation the power required is the same. More realistically the other hand the lower gear/faster engine speed will mean greater losses due to inefficiency AOTBE, and engines are designed to be most efficient at certain revs. Usually fairly low revs. I suspect that for most cars 4th gear is fractionally more efficient than 3rd at 30, but 5th less efficient than 4th.
I have a mpg gauge on my car and have spent a long time looking at it when stuck behind (about 6 cars behind) a slow moving vehicle, usually a wheezy old van or lorry, trying to optimize fuel usage when just cruising along (too slowly) on my daily commute. There is an optimum speed for each gear that maximizes fuel efficiency. Uncannily in these circumstances, the vehicle in front frequently chose a speed that was on the cusp of 3rd and 4th or 4th and 5th gears for optimization. Still, it kept me occupied.Dr Jekyll said:
The car doing 3000 rpm in 4th will be going faster than the one doing 3000 rpm in third, therefore require more power, therefore use more fuel.
The point about the question was that it will be using more fuel at any one instant, but for less time. I expect a mile in the highest gear possible at 3000 rpm uses the least fuel.On the fuel consumption theme, does a helicopter use more fuel traveling forward in level flight than when in the hover?
I assume that forward travel has drag and that the body provides negligible aerodynamic lift so I assume that the hover is more fuel efficient (in terms of gallons per hour rather than miles per gallon) as the lift requirement would be the same. However I couldn't work out if the forward motion somehow made the blades more efficient.
I assume that forward travel has drag and that the body provides negligible aerodynamic lift so I assume that the hover is more fuel efficient (in terms of gallons per hour rather than miles per gallon) as the lift requirement would be the same. However I couldn't work out if the forward motion somehow made the blades more efficient.
There is drag in the hover too.
This is quite a simple explanation:
http://www.copters.com/aero/drag.html
This is quite a simple explanation:
http://www.copters.com/aero/drag.html
deeen said:
The point about the question was that it will be using more fuel at any one instant, but for less time. I expect a mile in the highest gear possible at 3000 rpm uses the least fuel.
But power required increases by the square of the speed. So for example twice as fast means four times the power, therefore (efficiency differences aside) four times the fuel per minute, but half the minutes. I don't see how an engine can be more efficient at 3000 rpm in one gear than another.Ross1988 said:
The survey nails will be traversed in from a known point, a point with a easting northing and a height. These values can be 'projected' (using a total station, or similar survey equipment) or traversed in. This will give the nail a easting northing and a height, an so on for each subsequent nail.
A surveyor will then use these nails (2 or more) and values to triangulate a location from where they can continue surveying or marking out
You will find that the nails will usually go mostly in a loop and they are always in sight of each other.
Hope this helps
A surveyor will then use these nails (2 or more) and values to triangulate a location from where they can continue surveying or marking out
You will find that the nails will usually go mostly in a loop and they are always in sight of each other.
Hope this helps
So, fixed points, known quanity. Saves the hassle of calibrating every time.
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