The one aspect of "inches of development" calculations is that it needs the wheel diameter (or gear inches) first. So in my mind gear inches comes first and thus is easier to calculate. I have read of "development" as what the ratio makes the wheel seem like (as in being gear inches). But I good with agreeing to consider it only as the distance traveled in one wheel rotation. It's just a label that serves to allow discussion. Andy

I never made the switch from English units to metric in my days working in naval architecture. Yes, metric is cleaner, simpler, easier but I had the key numbers memorized or knew right where to get them - and - little mistakes could well be fatal, both to the vessel and everybody on board. I now use and do math with both but if it's important enough, I do it in English or convert the results because I am so familiar with it and I am radically more likely to see mistakes. Bikes I do both. I draw them in English (usually). Measure in both but tape measures are English. On my frame drawing, dimensions display in both.

I wish I started on metric but that switch came way too late for me to relearn without real risk.

Did it go WHOOOSH?

Or closer to earth the Gimli glider.

For those who don't recognize the reference, a short write-up on the incident can be found here.

Bad math - specifically, using the wrong conversion factor to convert from fuel volume to fuel mass - indeed appears to have been the proximate cause.

Read the link. The part I liked was that it was a Boeing 767. Ran out of fuel at 41,000 and the pilot landed it at an airport he could reach. And landed it almost entirely successfully. Photo showed the plane tipped forward and to the left like he collapsed a landing gear or two, but no one got hurt, the plane suffered only minor damage and went back into service. That sounds to me like a plane that is fundamentally a good flying plane. The kind of plane I like to occupy as a passenger.

The part I thought was absolutely asinine highly ironic regarding the incident was the fact that the Captain and Flight Officer were (1) initially disciplined after the incident, then (2) received an award for Outstanding Airmanship for bringing the plane down safely about 2 years later.

And yeah: the 767 is a damn good airframe.

I guess successfully saving the airplane you caused to run out of fuel is ironic.

The Air Force first disciplined and then awarded a women in the Gulf War that successfully landed her shot up A-10 with no hydraulics. Good piloting, but it violated the flight manual for the aircraft.

More than one set of hands in the Gimli Glider fiasco. The First Officer actually did the required fuel calculation. The Captain verified the math using a slide rule, but not the conversion factor. Maintenance techs who were to help didn't even complete the calculation. This also happened when Canada was converting from English units to metric for flight operations. Plus, new aircraft (in service with Air Canada <4 months), and an unreliable master minimum equipment list (MMEL) with both missing and/or unreliable procedures - to the point that maintenance crew sign-off took precedence over the MMEL.

At a minimum, two complete and independent calculations/verifications should have been required for fuel calculations IMO under these conditions. As I read it, that wasn't required at the time.

Yeah, Captain is ultimately responsible. But this fiasco was eminently foreseeable given the circumstances, and IMO allowances should have been made for forseeable human error in this case.

I'm not sure why the conversion factor is such a sticking point. A ship tried to refuel my helo in kg once, and we did the math. No different than gallons to pounds. Part of the job of not getting yourself killed.

I think (actually I know) that anyone who knows what ratio means knows.

Like that pilot who landed a Boeing 7-something on the service road along a Florida Everglades levy when his fuel gauges said he couldn't reach Miami. Rules say ditch the plane at sea. Total loss to the plane and probably a few lost passengers. Instead he landed the plane perfectly on the little used but Army Corp of Engineers quality dead straight dirt road like he knew as a kid growing up in the area. No one got hurt, plane was completely unscathed and flew out with fanfare a year or two later after they paved enough road for it to take off.

Pilot was threatened with loss of license for not following the rules and directly dis-obeying orders to take the plane to sea. Eventually reason prevailed and he was credited with some excellent flying.

If anyone wants to read about what goes on inside a commercial plane's cockpit, read "Fate is the Hunter". Granted, this only covers up to the late '60s aircraft but it is written by one of the early commercial pilots who flew everything from small twin engined postal planes to the biggest prop airliners. And what he saw! (And what his fellow airmen saw and did not live to tell. Book starts with a list of 400 pilots who didn't make it.)

The dynamics of a working flight crew are covered well in that book. The mistakes, the avalanching of bad events, the sometimes "where did that come from" pure intuition needed to make the right call (and sometimes pure, blind luck). Sounds like this fuel mis-calculation qualifies as the next chapter.

Yeah... it's a pretty simple concept - the ratio of wheel revolutions to crank revolutions. 1 is real small, 4 is real big. Street fixed gears are generally about 2.6. As long as we're all talking about normal sized wheels that works great.

Gear Inches is a little harder to wrap your head around. And outside of comparing bikes with different sized wheels, it offers no advantages to the plain old front-teeth/back-teeth ratio. Still worth knowing because it's still used and discussed frequently... seperates the newbs from the cognoscenti.

Gain ratio and development are concepts that nobody needs to learn... but still kind of fun for data junkies.

Sure, ratios are easier, unless you learned gear inches many decades ago and have used those values ever since. Even if I switch to ratios, I'll still have to convert that to the (approximately) equivalent gear inch value in my head for it to make sense to me.

As I probably said earlier in this thread, I imagine that most people who grew up with Fahrenheit (like me), unless they've had to learn to think in Celsius numbers for some reason, have to calculate a clumsy Fahrenheit approximation when confronted with Celsius values. ("Celsius is easy! Just think of the percentage between freezing and boiling!")

You don't need to wrap your head around any of these. They are just numbers that are comparable to each other. I might be more comfortable thinking about miles, but I honestly can't even really picture what a mile feels like.

Treat all these scales as arbitrary. The only reason to choose gear inches is because they are the most common arbitrary scale.

There are two scales with non-arbitrary reasons to exist. Development for the (arbitrary) gear limitation for junior riders and ratios for fix gear riders. Integer ratios can be bad. The max pedal load hits the same point on the chain each chain revolution. (Not an issue for most of us weaklings.)

That said, I don't use either of those scales. Started racing 4 years post junior and am not strong enough to ride 42-14 with any kind of regularity. (Did watch a junior flunk his development years ago and have to go find another wheel to start his race.)