VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   Glass Cockpit (https://vansairforce.net/community/forumdisplay.php?f=35)
-   -   MPH vs Kts (https://vansairforce.net/community/showthread.php?t=145521)

Robert Anglin 01-10-2017 07:19 AM

Metric
 
Quote:

Originally Posted by RV7A Flyer (Post 1140700)
I hope they're faster than that :)

Quickie on-line conversion tool says 170 kts = 525859 furlongs/fortnight! Impress your friends: "This plane goes over half a million furlongs per fortnight! And it only weighs about 35 slugs!"

You know we are supposed to use metric if we can according to Jimmy Carter.
mm. per second would be about as good as you could want to state.

rzbill 01-10-2017 09:52 AM

884,800,000,000,000,000,000 Angstroms per Aeon????

dave4754 01-10-2017 10:07 AM

MPH or Knots
 
Here in Canada where I trained in 1981 it was done in MPH for me and I have always had an ASI that indicated MPH and knots were in small letters.

I have noticed the switch in the newer model planes I rent especially the ASI and struggle sometime with the :"conversion". Similar to our late PM sending us into "metric" chaos this does make for some trouble sometimes in the pattern; "have i trimmed for 70 MPH or have i trimmed for 70 knots?"

That is where the fun of this issue ENDS! I hate that momentary confusion on final and twinge of non confidence. So I fly er by the feel and use the ASI as a guide the way we were meant to.

I always just add 10 to the new plane ASI(knots) and hope it is "close enough".

Great thread here! Us old guys always need training eh?

sblack 01-10-2017 11:10 AM

At my Engineering school the problems on assignments and exams mixed up the units. The questions defined the desired units for the answer and you had to convert. Distance could be feet, meters, inches etc. Temps could be C or F, speeds in mph, kph or knots, and the worst, mass, could be kg or slugs. Slugs were my arch nemesis. Try to explain to a layperson why you buy hamburger at the grocery store in units of force (lbs) in America and units of mass (kg) in Canada. Try to explain that a model airplane servo torque rating in g/cm (not even g-cm) is wrong.

Interestingly, after that space probe slammed into Mars a bunch of years back, NASA has gone all metric to avoid a similar screw up. But at the aircraft company where I work, which is in Canada, which is officially metric, we work in imperial units. We will kick out the afm in metric for European customers if they ask for it.

The problem with establishing standards is that it requires humans to agree on something. Humans don't like agreeing on stuff in my experience and I think this thread illustrates that very well :D

Now about that primer....

az_gila 01-10-2017 11:16 AM

Quote:

Originally Posted by sblack (Post 1140790)
At my Engineering school the problems on assignments and exams mixed up the units. The questions defined the desired units for the answer and you had to convert. Distance could be feet, meters, inches etc. Temps could be C or F, speeds in mph, kph or knots, and the worst, mass, could be kg or slugs. Slugs were my arch nemesis. Try to explain to a layperson why you buy hamburger at the grocery store in units of force (lbs) in America and units of mass (kg) in Canada. Try to explain that a model airplane servo torque rating in g/cm (not even g-cm) is wrong.

Interestingly, after that space probe slammed into Mars a bunch of years back, NASA has gone all metric to avoid a similar screw up. But at the aircraft company where I work, which is in Canada, which is officially metric, we work in imperial units. We will kick out the afm in metric for European customers if they ask for it.

The problem with establishing standards is that it requires humans to agree on something. Humans don't like agreeing on stuff in my experience and I think this thread illustrates that very well :D

Now about that primer....

The colonies may have trouble, but I'm always amused at the UK's conversions.

All there are now used (EU based) to buying stuff in kilos and feeling C temperatures, but they still drive in miles and mph, buy petrol in litres but still use MPG for fuel economy...:)

RV7A Flyer 01-10-2017 01:09 PM

Quote:

Originally Posted by sblack (Post 1140790)
Interestingly, after that space probe slammed into Mars a bunch of years back, NASA has gone all metric to avoid a similar screw up.

I think you mean the one that *missed* Mars, Mars Climate Orbiter.

NASA had been specifying SI units for many years prior to that, but the lower-level software was incorrectly coded (did not adhere to interface spec for SI units, and not caught during V&V).

Ironflight 01-10-2017 03:32 PM

Quote:

Originally Posted by RV7A Flyer (Post 1140825)
I think you mean the one that *missed* Mars, Mars Climate Orbiter.

NASA had been specifying SI units for many years prior to that, but the lower-level software was incorrectly coded (did not adhere to interface spec for SI units, and not caught during V&V).

Which units you used at NASA depended on which program you were working. The ISS actually has used both. Shuttle was built all imperial, but we used a lot of metric once we started working with the Russians. The truth was - we had to be able to work in both, and regularly convert.

When doing maneuvers, I mostly wanted to make sure I wasn't off by a factor of three (meters per second versus feet per second). And we changed from fps on orbit to knots on the way downhill.....:rolleyes:

RV7A Flyer 01-10-2017 08:13 PM

Quote:

Originally Posted by Ironflight (Post 1140871)
Which units you used at NASA depended on which program you were working. The ISS actually has used both. Shuttle was built all imperial, but we used a lot of metric once we started working with the Russians. The truth was - we had to be able to work in both, and regularly convert.

When doing maneuvers, I mostly wanted to make sure I wasn't off by a factor of three (meters per second versus feet per second). And we changed from fps on orbit to knots on the way downhill.....:rolleyes:

Yeah, Paul, in truth...even though the policy has been metric for a while, a lot of mechanical stuff on our flight vehicles has been and still is imperial. Old habits die hard. But for MCO, the specs on the s/w were clear...SI units. It just was coded wrong and never caught. :(

dutchroll 01-11-2017 02:27 AM

Quote:

Originally Posted by sblack (Post 1140790)
The problem with establishing standards is that it requires humans to agree on something. Humans don't like agreeing on stuff in my experience and I think this thread illustrates that very well :D

I think it's more that people don't like change. Especially major change. It's big and scary and too hard. Even if it makes more sense in the longer term.

I like knowing everything is a factor of 10 and that prefixing it with "milli_ centi_ kilo_ etc" all means something consistent. It's consistent with the entire decimal numbering system. Dividing something up into quarters, eighths, sixty-fourths to get smaller but multiplying by 12, then 3, then 1760 to get bigger.......who the heck thought that system up? :)

But, as I said earlier, ya gotta be at least bilingual to get by these days! :D

jay bell 01-11-2017 09:41 PM

Quote:

Originally Posted by N941WR (Post 1140148)
If you have an EFIS, it should be easy to swap between the two with a few button pushes.

I flew off my test hours in MPH because I was comfortable with them after 20 years of renting and owning small Cessnas and Pipers, and because my transition trainer (Old Blue) used MPH. I switched the Dynon to KTS after I started flying around our countries and talking to ATC a lot. It took a few circuits to get used to the "new" approach speed, but I never considered changing back.

When I want to impress my non-pilot Canadian friends, I tell them cruise speed is 280 klicks, with top speed of 340 ;)
Jay

BillL 01-12-2017 06:48 AM

Quote:

Originally Posted by dutchroll (Post 1140983)
I think it's more that people don't like change. Especially major change. It's big and scary and too hard. Even if it makes more sense in the longer term.
. . .
But, as I said earlier, ya gotta be at least bilingual to get by these days! :D

Mental change is not so bad, if it is consistent. One this the other that, partial - just a lot of confusion. It's all theory and equal except for the standards, testing, materials, availability of ready replacements, machine tool set ups, forging dies, and lots of other capital machinery.

Dealing with a ba$tard units GM (and others) car that mixed imperial and metric fasteners hoses etc was a nightmare after Carter (along with the other nightmares).

Or getting fuel across borders - Boeing 767 glider

Me - I am going all knots.

Jimzim 01-22-2017 09:43 AM

Ya, I use both now, knots and mph. One thing though, as to the mph of the past, I remember my primary instructor (Luscombe, 1970) would ask me for current ground speed. I would time our progress over the section lines in the Colorado plains and solve with my trusty E6B. The section lines remain statute miles, so far as I can tell! It was fun, too.

David Paule 01-22-2017 04:13 PM

The folds in my Sectional charts were 40 statute miles apart, too.

Dave


All times are GMT -6. The time now is 04:24 AM.