Volume vs. Depth of Black Ariel Oil Tanks

[cmfalco]

Since I needed the information myself as I complete the shakedown runs on my rebuilt 1928 Ariel in preparation for the Cannonball cross-U.S. ride, I calculated the "calibration" of a dipstick for the oil tank. I had not seen this information anywhere else so it might be of interest to a few other owners of Black Ariels.

I took a photograph of the tank from a distance to minimize perspective effects, pulled it into Photoshop, and traced its outline. The tank is 5" deep at the base of the filler neck so I deployed my indispensable Gerber Variable Scale to draw lines corresponding to every 1". I then deployed my indispensable Zero Setting Compensating Planimeter to measure the areas corresponding to oil filling the tank to those depths.

The front half of the tank has a nearly constant width of 10"~10.5" and the rear half tapers to 7" wide as well as decreases in height. Because of this I broke the drawing into front and rear halves and measured the areas of each depth separately. Since volume is area x width I scaled the rear areas linearly between 100% (when full) and 70% (when nearing empty), summed with the matching front areas to get the corrected total volume at each depth, and normalized to the total volume of the tank. Of course, the very front of the tank curves inward, but that affects all the front areas approximately equally so the overall effect on the calculated volumes will be relatively small.

As can be seen from the final results, the decrease in width of the tank at the rear is roughly compensated for by the increase in length of the tank. As a result, to a pretty good approximation each 1" of oil above the bottom of the tank adds another ~20% of content. For example, if you have, say, 2-1/2" of oil you have ~50% of your oil remaining (2.5" x 20%/" = 50%). Although the 20% per inch factor somewhat underestimates the amount of oil remaining (e.g. at 2.5" it's more like 54%), I would prefer to err in thinking I have too little oil remaining rather than too much.

[dave.owen]

An observation, the oil tank on my 27 is not full length of the petrol tank. I'm sure this is true for the 28.
Dave

[cmfalco]

An observation, the oil tank on my 27 is not full length of the petrol tank.

Ah, a very silly error on my part. The fact the fuel capacity is in gallons and the oil capacity in pints should have alerted me. I just now checked and a ruler hits a bulkhead about 5" back from the filler cap, i.e. in the front portion of the tank, before it starts tapering inward and downward. That makes the volume correspond even better to the "rule" of 20%/inch. Thanks for catching my mistake.

Perhaps a saving grace is my calculation does (approximately) apply to the fuel. For the same reason that the increase in length roughly compensates for the decrease in width, the height of the fuel above the bottom of the tank is roughly linear in the remaining volume. For example, if the fuel is halfway to the top, roughly half the fuel remains.

[markus.nikot]

My 28B sucks around 6l per 100km, maximum distance until I have to fill up is 130km. Tank volume is approx. 8,5l.
Sorry for the continental numbers.

You need a lot of filling stations for the cannonball distance.

Markus

[cmfalco]

You need a lot of filling stations for the cannonball distance.

Thanks for the information in your post. They've advised us there will be at least two days with more than 100 miles between stations so I have a supplemental 1 gal. tank to strap to the package tray. I've only managed 30 miles on it so far since completing the rebuild, and it will be nearly 110 oF (43 C) the next four days, so I'm spending time getting items crossed off my to-do list rather than riding. Anyway, I don't yet have gasoline consumption figures for my bike so I don't know yet if the 1 gal. tank will be sufficient for those long days.

Temperatures are supposed to be reasonable again by this coming weekend so I plan a ~90 mile trip to the top of the neighboring 8200 ft. mountain. If I make it there and back I should have my first measurement of its range.

[dave.owen]

My 27, model C will do 100-110 miles on a full tank of fuel.
Dave

[Steven.Carter]

My 27, model C will do 100-110 miles on a full tank of fuel.
Dave

Mine can do 25 miles on a pack of 8aa batteries

[cmfalco]

My 27, model C will do 100-110 miles on a full tank of fuel.

That's very helpful information. Thanks. Assuming the capacity I found is correct (2.4 U.S. gallons), that's ~42-46 mpg. Taking the lower figure, and assuming I get the same mileage as you, with the spare tank I'll have a range of ~140 miles, which is more than necessary.

[Richard Kal]

I anticipate having my 27 Model A running by Christmas; good riding weather - middle of summer in Western Australia.
"My 28B sucks around 6l per 100km"

Does this mean that riding a total loss Black Ariel is a messy affair? 6 litres / 100 km expelled from engine........

Better keep a rag in the tool box....!

Richard

[dave.owen]

Richard, this is fuel not oil consumption.
Dave