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Mixing different aviation units

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Why to manufacturers still use the stupid marketing stunt trying to cheat with mph and sm instead of kt and NM as it should be for aviation?

I thought this went out in the 1960ties. Usually if MPH are used, it means the planes have inferior performance and need to beef up their leaflet with this stunt or they address themselfs to inept buyers which think “car” rather than “plane”.

Why not use km/h and km? They give even more impressive figures……. Goes into the same cathegory as using “overhead to empty” range figures, which I always thought should be put away in a class action suit, as they will cause people to run out of fuel.

Well, they are not impressing a great lot of people who can see through this petty scam.

LSZH, Switzerland

Mooney_Driver wrote:

Why to manufacturers still use the stupid marketing stunt trying to cheat with mph and sm instead of kt and NM as it should be for aviation?

Maybe because 90% of RVs are sold in the US, and they prefer mph there? I wild guess from my side The plane I did most of my PPL training on had mph instead of knots. Gliders use km/h and meters. Besides, knots are nautical miles.

Cobalt wrote:

Nobody would even try to ask “why is Mercedes even building the SL, when you can buy a BMW M4 convertible for half the price? The BMW has two more seats, too!”

I think this is different. BMW and Mercedes do sell lots of cars. lots and lots. The Panthera is not even available, and never will be by the looks of it. As an experimental, I don’t see what it has to offer over the RV-10. Where do the the extra 3-400k come from?

LeSving wrote:

Maybe because 90% of RVs are sold in the US, and they prefer mph there? I wild guess from my side The plane I did most of my PPL training on had mph instead of knots. Gliders use km/h and meters. Besides, knots are nautical miles.

Bölkow had an innovative solution to the issue, as shown below. In the plane in which it was installed, you keep the needle more or less straight up on approach, cruise should be horizontal or higher, don’t let the needle go beyond vertically down. You can tell ATC you’re cruising level at 3 o’clock

All FAA certified light aircraft were built using statute mph until the 1970s. My observation on US homebuilts is that some builders choose knots as the main calibration on the ASI, and some choose statute mph. Of the roughly 30 to 40 vehicles I’ve owned, all but one have indicated speed in statute mph.

Last Edited by Silvaire at 01 Dec 16:21

LeSving wrote:

Maybe because 90% of RVs are sold in the US, and they prefer mph there? I wild guess from my side

Originally it was perfectly clear why they would do it. Cars to this day have mph and so they wanted to have a direct comparison. It also helps that a plane will have a higher figure in mph and range in sm rather than kt and NM where the marketing figure is about 15% less. In other words, 115 mph sounds better than 100 kt, even though it is identical. Same thing with range, 1150 sm looks better than 1000 NM.

This went out in the 1990ties though when KT and NM became standard in the US (and elsewhere), even Mooney and other speed focussed makers changed to KT. The first Acclaim Ultra was registered N242KT (still is, now flying in Switzerland) which would be 279 MPH. It appears that eventually the marketing folks realized that pilot-buyers are not as easily fooled and maybe some complained about having to do the conversions when they got the brochures. So much more annyoning that RV apparently is still betting on this old horse and have not “gotten the memo”

Anyway, what are the two figures next to speed and range? Real and marketing wet dream?

The data are not shabby, 165kt @ 75% and 147 kt @ 55% with corresponding ranges of 700-800 NM (unless they have been calculated 8000 ft overhead to tanks dry as some salesmen have done in the 1970ties….) Roughly what a Mooney 201 or an SR20 will do, so a nice plane for America and Scandinavia.

LSZH, Switzerland

Mooney_Driver wrote:

So much more annyoning that RV apparently is still betting on this old horse and have not “gotten the memo”

Van’s in general and Van Grunsven himself can be accused for many things, but hype marketing is definitely not one of those. Their kits sell by word of mouth exclusively. Their web site and info about the planes haven’t changed in at least one decade, probably closer to two. Americans will use mph if for no other reason than mph is “American”, while knots and km/h are foreign “Euro stuff”. IMO that is a better explanation. With Vans, it’s more old habit I think.

Capitaine wrote:

the instructor said that it was easier in the certification process to convert from km/h to mph than km/h to kt.

That is just a legend. You can use whatever you like, basically. Just make it consistent (i.e. don’t give operating speeds in kph, performance in mph and install an ASI with kts). You may use furlongs/fortnight if you please.

mh
Inside the sky.
EDXE, EDXF, Germany

mh wrote:

You may use furlongs/fortnight if you please.

Still you need to supplement conversion tables in the POH?

EGSX, United Kingdom

Ibra wrote:

Still you need to supplement conversion tables in the POH?

Not by CS-23, unless you find that this is part of “Further information necessary to comply with the relevant operating rules.” (CS-23.1581). CS-23 just specifies that the units given in the manual are the same as the units marked in the aircraft / on the instruments.

Of course furlongs/fortnight would be a little impractical to use and for sales reasons alone you’d use at least one more conventional unit.

GAMA POH-specs define speeds in kts, but this is just one way to comply with CS-23.

Last Edited by mh at 04 Dec 13:11
mh
Inside the sky.
EDXE, EDXF, Germany

LeSving wrote:

Americans will use mph if for no other reason than mph is “American”, while knots and km/h are foreign “Euro stuff”. IMO that is a better explanation. With Vans, it’s more old habit I think.

I don’t think it’s anything to do with the geographic or political origin of nautical miles. It’s just that nautical miles and knots add no value to light aircraft operations and many planes, every other US vehicle, every map, road sign, discussion and so on is conducted in stature miles, not nautical miles.

Last Edited by Silvaire at 04 Dec 16:09

Silvaire wrote:

every other US vehicle, every map

Other than larger aircraft. It seems to make more sense to have light aircraft relate to larger aircraft than to cars. Especially when ATC is common, no?

Every map with a latitude scale ends up having a NM scale (1 minute of latitude → 1 nm) so probably every map also ends up having a scale in nm.

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