Hayhoe

Preliminary vehicle safety report

Students from PS 1003, Practical Mechanics and Carpentry, and one instructor ran the twice-yearly Vehicle Safety Day on Thursday November 15th between 8.00 and noon at the workshop in the Unity House garage. The timing was changed because of likely inclement weather.

We went overtime because of high demand. Around 30 vehicles were examined. Our air compressor gave up the ghost early on in the process, delaying the process because tires had to be pumped up with a small back-up compressor. Apologies for the slow service.

A further session is scheduled for November 16th, 12.30pm - 4.00pm, if weather permits.

If you planned to get your vehicle checked and were not able to because of the change of time or some other reason, email mwomersley@unity.edu and ask for an appointment. The plan is to go ahead with more inspections tomorrow unless a snow day is called.

Most safety checks were routine. The following specific problems were noted and are reported here so other vehicle owners can learn from them. If you can't afford a brand new car, but want to get around reliably, you need to begin building some knowledge about automotive technology, even if it's just knowing when to take it to a shop! Students that want to learn more about mechanics and vehicle maintenance can now sign up to take PS 1003, Practical Mechanics and Carpentry, every second fall.

1. Nearly all vehicles were low on tire pressure by two or three pounds per square inch. This was likely due to the cold weather this morning. Tires pumped up to 35 PSI in August at 70 F would read only 32 or 33 PSI by November at 15F. Considering that it's quite likely to warm up again before January, if only to 40 F not 70 F, and that there is snow coming tomorrow, it's probably better not to pump these tires up right away. Slightly low tire pressure improves traction in snow. Tires that had greater disparity between the measured pressure and the manufacturer's recommended pressure (which is nearly always to be found on a sticker on the driver's side door jamb) were pumped up. Once the cold weather really sets in, tire pressures should be adjusted to the manufacturer's recommended pressure.
2. Several vehicles had the check-engine light on and so reported  "trouble codes", which were "pulled" and recorded for the owners to seek further help. Some trouble codes can be more or less safely ignored, but not all or even most. Even if you choose to ignore one, it's best to check it periodically to make sure a second code has not been triggered.
3. The "Maintenance Required" light is not the same as the "Check Engine" light. Maintenance Required lights come on when scheduled servicing is due. They can be turned off after the servicing is complete. Read the vehicle manual to find out what needs to be serviced at each stage.
4. One fuel-injected vehicle had an intermittently flashing "Check Engine" light. The codes were pulled, reporting "misfire number 4 cylinder." This can be either an ignition- or a fuel-injection related misfire. A test drive proved that the light began flashing when accelerating uphill under load. This is likely, but not certainly, diagnostic of a fuel-injection related misfire. The best thing to do is switch out the number four cylinder fuel injector for a new or rebuilt one. If the misfire goes away, the problem is then diagnosed 100%. This student, who was out of time to get the repair done before leaving for home, can probably make it home in this car, considering the problem is intermittent and only occurs when the engine is under load. Most likely it would run just fine on the freeway at 65mph. But it's best to plan to drive in daylight, just in case. This was the advice the student was given.
5. One vehicle was examined for damage to the rear undercarriage following an accident (driving into a ditch). Nothing was found. Most likely this car, a particularly sturdy make and model, is fine. Take things slow after any accident affecting the wheels, undercarriage, and drive train, especially when accelerating on the highway for the first time after a ditching like this. Any vibration or strange noise is a sign that there is more damage than you think. In these circumstances, if you're worried about drive-ability after an accident, you should get the frame dimensions and alignment checked at a proper alignment or body shop.
6. A different vehicle presented with uneven tire wear and obvious over-camber of the front wheels. Camber is the angle the wheel makes with the ground, and, under neutral vehicle load, it should be slightly less than vertical, i.e., the bottom of each wheel should be further outboard than the top, but this ought not be noticeable with the naked eye. Camber angle is usually less than one degree. The driver reported difficulty wearing out new tires too fast, and with getting proper service from tire shops. Some tire and car repair shops may not have the equipment or expertise to do this work right. This car needs a proper alignment by a well-trained alignment specialist, and may need special "camber bolts" to adjust the camber, which is otherwise set at the factory and not adjustable. An inspection should first determine whether or not all the undercarriage components are working properly, undamaged, and properly connected. 
7. One vehicle had much greater tire pressure than needed in the front tires,over 50 PSI. This is very dangerous. Tires that are over-inflated bounce much like an over-inflated basketball, and can bounce you right off the road on corners or bumps. This likely happened because the tire pressure had been pumped up without a gauge, or with a badly working one, after the tire pressure light came on. The tire pressure light then came on and stayed on because of over-filled tires, but the driver assumed they were under-filled, and may even have added yet more air. It's best to "splurge" for a proper tire gauge. It's $2.99 from the hardware store. Three bucks, versus your life. What a bargain!
8. One vehicle was missing more than two quarts of oil. Considering that in this case the the oil hadn't been checked since August, it may not be a great problem, but the driver needs to know. In a case like this it's best to start checking the oil every time you fill the gas tank, and make a record, if only a mental note, of the oil consumption, at least until you have it figured out. If a normal sized car engine begins to burn more than a quart in 500 or so miles, it's time to consider an engine rebuild, replacement engine, or getting a different car. Always check the oil and other engine fluids before a long trip. This student, who was planning a particularly long drive, can also probably make it home in this car, but needs to check the oil at the first gas fill-up and each one thereafter. Again, it's best to plan to drive in daylight, just in case. This was the advice the student was given.
9. One vehicle had a loose tailpipe. This was wired in place temporarily with the proverbial "baling wire".  The owner had plans to get a proper repair once home. Another had a loose battery connection tightened. We can usually help with this kind of ad-hoc repair during Vehicle Safety Day.

Thanks to all the students who assisted with this activity, as well as the Student Affairs and Maintenance Departments.

Drive safely, please,

Mick Womersley

Professor of Human Ecology

Head Grease Monkey

Tilt-up wind turbine/anemometer tower problem, redux

Today we calculated the actual vs. theoretical load on the tilt-up tower with the intention of checking the engineering safety margin, but ran into difficulties with the winch and made other errors. In particular, our load cell was reading incorrectly. Here is a partial fix:

What you know:

1. The tower is made of three 30-foot sections, each weighing 253 pounds
2. The gin pole when first manufactured weighed 369 pounds and was 18 feet long
3. Now it is 13 feet long
4. Payload (anemometry equipment) is less than 50 pounds
5. We will use pounds-feet, not Newton-meters, because the tower (a Bergey Excel 10kW model) was originally engineered using US "customary units"
6. This is normal. Much American engineering still uses these units

How to do the calculation:

1. Imagine the tower as a rigid lever with a 90 degree angle, like a crow-bar
2. Calculate the turning moment when the tower is horizontal:

• The center of gravity of a uniform shape tower 30 feet long is at 15 feet
• The weight of the tower is 3 x 253 pounds per section + 50 pounds payload = 809 pounds
• The turning moment is 809 pounds at 15 feet = 809 pounds x 15 feet = 12,135 pounds-feet

3. Calculate the gin pole turning moment:

• The weight of the gin pole is 13/18ths of 369 pounds = 266 pounds
• The center of gravity is 7.5 feet
• The turning moment = 266 pounds x 7.5 feet = 1,995 pounds-feet
• This bears only when the gin pole begins to angle away from the vertical
• This is why manual effort is required to tilt the tower in the first place, and to slow the final movement back to the vertical (so the rear anchor doesn't receive a shock load)

4. Calculate the winch force needed when the gin pole is vertical:

• The force that must be opposed by the winch when the tower is horizontal and the gin pole vertical is 12,135 pounds feet (minimum) 
• The gin pole lever arm is 13 feet
• 12,135 pounds feet divided by 13 feet is 934 pounds

5. Calculate the force based on the angled pull of the winch to the winch anchor:

• The winch doesn't pull perpendicularly to the gin pole. Instead it pulls at an angle down to the gin pole anchor
• The gin pole is 13 feet long. This length is represented in both the opposite and adjacent, so the starting angle of the pull is 45 degrees
• 934 pounds divided by cosine of 45 degrees = 934 pounds/0.70 = 1,334 pounds
• This means that all items in the system are within a safety margin of 100% or X2. The weakest links in the system are the smallest shackles at 4,000 pound rating. Since this was the main point of the exercise, we're good.

6. Compare to actual load as reported by the load cell.

• The actual reported by the load cell, once we solved the difficulty with the winch, was 1,100kg, which is 2,425 pounds, way too much, so something is either wrong with our theoretical load, or with our load cell
• The best explanation is load cell mis-calibration. We had experimented using humans of known weight (the only experimental "masses" large enough that we had), and discovered the load cell was over-reading significantly. Earlier too, I had weighed the spare tower section with the load cell at 340 kg, way too much
• The manufacturer's reported actual weight at 253 pounds is equivalent of 114 kg, so 114kg/340kg provides a possible correction factor of 0.34
• 2,425 pounds x 0.34 is 824 pounds, which is much closer to our actual result
• This isn't very satisfactory, but the best we can do until we get the load cell re-calibrated

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