Speed Nomenclature- M/S... why???

[vindibona1]

As an United Statesian, I have lived through the experiement where we were supposed to switch over to the metric system back in the 60's- but it never took. I've driven in Cananda, lived in and owned a car in Mexico so while my cognition of speed is naturally in miles per hour I can deal with Kilometers/hr. Knots is sort of based on miles per hour and a lot of aviation is done in nautical miles. But suddenly here I am in the drone world, and if I were to choose metric rather than Imperial for the units of measurement suddenly I'm faced with METERS PER SECOND (M/S).

WHY??? Isn't Km/hr good enought, or better yet more relatable for those who are metric-centric? We are, after all piloting a vehicle much like a car or airplane. I can understand using feet per second (or m/s) for ballistics where this nomenclature is more relatable.

So why M/S as opposed to Km/hr in the metric mode on DJI drones?
'Splain it to me Lucy.

 

[Kilrah]

Both m/s and km/h are available.

 

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[vindibona1]

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yeah... I understand how to change it. I'm trying to ascertain the usefulness. However if flying with a 3rd party program it often defaults to m/s rather than mph or kph which I find totally annoying as I usually don't notice the settings until up in the air (I hate layered/buried/hidden menus).

But again, what do people find more useful about meters/second? I dunno, one would think having more increments as you look at speed would be more helpful. As an example, 10 m/s= 22mph or 36kph. In terms of travel velocity it just feels (to me) like one has more control by the numbers with the longer scales of miles or kiloms.

Who here prefers M/S... and why?

 

[Yogi053]

Although my Mini 2 is set to imperial, I very rarely even look at the speed readings at all. The only time I even notice distance is after I land. All Ireally care about in watching the screen is being aware of any warnings flashing up in view. Stay safe!

 

[BigAl07]

I wonder if it has anything to do with weather/wind often going by m/s??

 

[Kilrah]

One annoying thing is that in metric you'd typically want to have horizontal speed in km/h and vertical speed in m/s, but you can only have both the same.

 

[zocalo]

The default to metric should be clear enough given the global market, but I think the use of m/s is probably a combination of it being commonly used for windspeed and user perception. It's a lot easier to be sure that you are on the right side of the vector calculation when your max speed in m/s exceeds that of the max wind speed, and even more so if it's for gusts.

I suspect many people also find it easier to conceptualise what m/s looks like in terms of ground speed rather than km/h; 1m (or a yard) is a distance you should be able to readily imagine with a sufficient level of working accuracy in terms of something familar on the ground near the aircraft; people, structures, trees, vehicles, etc. For instance, you might think of 10m/s as roughly a couple of car lengths every second, but good luck working out something similar for 36km/h on the fly. (It's the same velocity.)

 

[Rich QR]

I wonder if it has anything to do with weather/wind often going by m/s??

Could be. In the USA, I've only seen wind speed for aviation reported in knots (METAR, ATIS, control tower), but I understand that other countries use m/s or km/hr.

Climb/descent rates are always reported in (hundreds of) feet per minute, in my experience. Airspeed and groundspeed are reported in knots. Barometric pressure for purpose of altimeter setting is reported in inches of mercury.

What a cumbersome patchwork of units we have!

 

[sar104]

Metric is the SI unit of speed, which is one good reason to use it. More generally, if you want to do any calculations involving multiple variables then it is much simpler to work in SI units since the results will also be SI units. The nice people over in NASA understand that having learned the hard way.

In the case of the calculations that I do on flight data from a DAT or txt file, my first step is to convert everything to SI if it is not already in that form.

Could be. In the USA, I've only seen wind speed for aviation reported in knots (METAR, ATIS, control tower), but I understand that other countries use m/s or km/hr.

Climb/descent rates are always reported in (hundreds of) feet per minute, in my experience. Airspeed and groundspeed are reported in knots. Barometric pressure for purpose of altimeter setting is reported in inches of mercury.

What a cumbersome patchwork of units we have!

Exactly, and it then requires unmemorable conversion factors to perform useful calculations.

 

[Meta4]

But again, what do people find more useful about meters/second?
Who here prefers M/S... and why?

For the distances involved in drone flight heights and ranges, metres is the appropriate unit.
If you ever try to analyse any flight data and do a few calculations, you'd appreciate using m/s for speed.

 

[peterf]

I didn't really have an opinion on this going in, but as I used my drones to capture video it did prove to be very intuitive. When your mission area is, say, a 200m radius and 120m AGL (or really half that if you're not trying to do wide landscape shots) then "I climb one meter every second" seems like the right granularity and easy to conceptualize in relation to your surroundings. I'm trying to film stuff while not crashing into anything, so it's about positioning rather than travel.

If I was trying to get to a destination that's minutes away, as you would in a car, then kph would be more appropriate. In my case kph does help to internalize just how performant and potentially dangerous a drone can be, seeing that it can reach travel speeds akin to a car. So that's also relatable but in a different way.

 

[Dave Maine]

m/s, km/hr, and ft/s and mph all are the exact same measurement expressed in different units. There is no difference in accuracy. As SAR104 points out, it is far easier and less error prone to use a measurement system based on 10 rather than 12. Most all science work, and a lot of engineering gets done as base 10.

 

[waltermitty]

....NASA uses that unit for their telemetry annunciation for many of their remote flights. km for grander scale (Shuttle landing) vs m/s for finer increments e.g. Perseverance landing

 

[Rich QR]

it is far easier and less error prone to use a measurement system based on 10 rather than 12. Most all science work, and a lot of engineering gets done as base 10.

Except that seconds are not based on 10. The only natural units of time are the day and the year. The second is 1/86400 of a day, but even scientists find it easier to work in units of 1/86400 day than in centidays, millidays or microdays.

It's all in what you're used to.

 

[sar104]

Except that seconds are not based on 10. The only natural units of time are the day and the year. The second is 1/86400 of a day, but even scientists find it easier to work in units of 1/86400 day than in centidays, millidays or microdays.

It's all in what you're used to.

The factor of ten thing is a non-issue, since any unit can be used in that way provided that it is decoupled from the rest of its non-decimal system. You can use pounds but not ounces, for example, and instead go with µlbs, mlbs, klbs etc, as is done in the US for many engineering purposes.

And days and years are not natural units of time in any universal physical sense. In physics there is no unique natural unit, and so the second was adopted as one of the seven basic units from which all the other units are derived. What matters is that the overall system is unified, not that the units are somehow natural.

The result is that dimensionally SI is consistent and so, for example, whatever units you combine to calculate energy, you always get a result in joules.

 

[tommytavor]

I have to open another app to figure it out. 5m/s is 16 feet per second,I think.

 

[Dave Maine]

Feet/Sec would be the US measure.