Why does my C172 POH use "mph"??

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tobnpr

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tobnpr
I obtained a new (for real), original POH for the 172M that I've just started flying.
I'm so used to using knots, and every reference to speed is in mph.

Airspeed is so critical I don't want any confusion and doing conversions in my head while I'm flying and want to maintain consistency here. Shouldn't I go through this POH and mark everything up in knots? I thought knots was universal in marine and aviation...
 
tobnpr said:
Airspeed is so critical I don't want any confusion and doing conversions in my head while I'm flying and want to maintain consistency here.
Click to expand...

My suggestion would be to not do the conversion. It's just a number, learn the speeds for this aircraft using the unit of measure that the airspeed indicator is marked in.

Do you convert the temperatures from C to F? This is the same thing.
 
Most older planes used mph. What's on the airspeed indicator?
 
You can add Kts to the poh if you want, but unless your plane is so old that they hadn’t starting painting operating ranges & speeds on the airspeed indicator along with the numerical speed, you’ll still have MPH values marked on the dial for flap range, VNE, etc.

You’re impulse to avoid mixing scales is particularly important when studying for written exams, since the “correct” answer for the mixed conversion is usually a distractor answer on the test.

But personally, since my plane is marked in mph too, I do all my cross country planning in Kts & nautical miles & convert the airspeed from knots to mph for in the cockpit use. That way, if I glance at the many placards on the plane, I’m not having to make the conversion on the fly.

Speed is just a crutch for learners. As a practical matter, particularly in a 172, the sound & feel of the plane and the RPM become the key indicators of your speed. You’ll get there eventually. Until you do, learn the speeds.
 
Airspeed indicator shows both knots and mph, just like the one I fly in the X-Plane sim.

i can use either- but as i said, my thinking was to e consistent as a beginner. In a few more.flights I'll probably want to fly their Cherokee, which is most probably knots. Instinctively, i know I'm better off keeping it consistent at least for now. I may be overthinking it, but needing to remember mph for the Cessna, and knots for the Cherokee (and probably every other plane I might fly in the future) sems counterintuitive.

Respectfully, I think some of you need to think back to your first time ever in the cockpit...
I fully expect to.get the "feel" for flying the aircraft-hopefully sooner rather than later- but I ain't there yet.
 
tobnpr said:
Why does my C172 POH use "mph"??
Click to expand...

‘Cause the sales and marketing boys thought bigger, faster numbers would sell more planes. Especially if your competition still had knots in their brochure.
 
We had to memorize speeds in kts and Mach in the S3. Problem was that ASI didn’t have mach…
 
tobnpr said:
Airspeed indicator shows both knots and mph, just like the one I fly in the X-Plane sim.

i can use either- but as i said, my thinking was to e consistent as a beginner. In a few more.flights I'll probably want to fly their Cherokee, which is most probably knots. Instinctively, i know I'm better off keeping it consistent at least for now. I may be overthinking it, but needing to remember mph for the Cessna, and knots for the Cherokee (and probably every other plane I might fly in the future) sems counterintuitive.

Respectfully, I think some of you need to think back to your first time ever in the cockpit...
I fully expect to.get the "feel" for flying the aircraft-hopefully sooner rather than later- but I ain't there yet.
Click to expand...
The cherokee and the Skyhawk will fly at similar, but different speeds. It really doesn't matter if one is in knots and one on mph, in fact it might be better to keep you from confusing them.

Every plane you fly, you should brief yourself on the important speeds, particularly best glide. I make custom checklists with all speeds listed so it's right in front of me. Even a pair of 172's can have different speeds depending on vintage and modifications.

I did all my training in knots, then bought a plane marked in mph. It felt weird at first, but before long you realize it's just a number on a dial and it doesn't matter that much what the unit is if you have the right number. The only thing that is a little bit of a pain is figuring TAS in knots to compare to the ground speed reported by the gps to figure winds aloft.
 
Both pa32 and pa28's in my hangar are in mph...
 
tobnpr said:
Airspeed indicator shows both knots and mph, just like the one I fly in the X-Plane sim.

i can use either- but as i said, my thinking was to e consistent as a beginner. In a few more.flights I'll probably want to fly their Cherokee, which is most probably knots. Instinctively, i know I'm better off keeping it consistent at least for now. I may be overthinking it, but needing to remember mph for the Cessna, and knots for the Cherokee (and probably every other plane I might fly in the future) sems counterintuitive.

Respectfully, I think some of you need to think back to your first time ever in the cockpit...
I fully expect to.get the "feel" for flying the aircraft-hopefully sooner rather than later- but I ain't there yet.
Click to expand...

You are indeed overthinking it. Use the values in the POH, they are the ones depicted on the ASI. The units (knots, mph, kph, meters/sec, whatever) don't matter. If the airplane stalls at 45, or climbs at 85, or has a flap speed at 115, it doesn't matter what units those numbers are in - just that you look at the ASI and see those numbers.

The truly ONLY place it matters is in cruise speed (TAS) calculations. But really, you're flying a simple airplane - you pretty much just have to remember "my cruise speed is 120 ktas" or whatever. That's the only knots value that matters to you.
 
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Jim K said:
The only thing that is a little bit of a pain is figuring TAS in knots to compare to the ground speed reported by the gps to figure winds aloft.
Click to expand...

Not for me anymore...Screenshot_20221018-214108.png
 
ElPaso Pilot said:
‘Cause the sales and marketing boys thought bigger, faster numbers would sell more planes. Especially if your competition still had knots in their brochure.
Click to expand...

Has nothing to do with sales and marketing.

Most vintage airplanes (both military and civil) from the 60s and earlier have airspeed indicators in MPH.
 
Jim K said:
Yep... got the gad13 to go with my new g5; looking forward to not having to do all that guessing any more.

Edit: looks like all those are in mph?
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First flight back everything was in mph. Used to those numbers for approach speeds. Will probably it after I learn the system. Was nice having the wind data there. Information overload
 
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I remember when my flying club sold our 1969 172 and bought a "Modern" 1976 172 and it had the fancy airspeed indicator in KIAS.
 
tobnpr said:
I obtained a new (for real), original POH for the 172M that I've just started flying.
I'm so used to using knots, and every reference to speed is in mph.

Airspeed is so critical I don't want any confusion and doing conversions in my head while I'm flying and want to maintain consistency here. Shouldn't I go through this POH and mark everything up in knots? I thought knots was universal in marine and aviation...
Click to expand...
Should you change the numbers in the POH? Probably not. Unless a new Knot Airspeed Indicator has been put in the plane. Why change the numbers in the book and then have to mentally convert back when you get in the plane and fly it.
 
Tools said:
We had to memorize speeds in kts and Mach in the S3. Problem was that ASI didn’t have mach…
Click to expand...
Probably because the Hoover wasn’t macho enough to mach. Lol, ha ha. Curious though. Did you ever get Mach speed assignments from ATC?
 
Ouch… be nice…. And, sadly, no. No Mach assignments.

So there I was… taking off out of midland I think in the old hoove. Wolf 703 your cleared for takeoff. Roger…

Shortly after liftoff tower enthusiastically called again… Wolf 703 you’re cleared for an unlimited climb!

Tower 703, uh, this IS our unlimited climb… sorry!!
 
Racerx said:
First flight back everything was in mph. Used to those numbers for approach speeds. Will probably it after I learn the system. Was nice having the wind data there. Information overload
Click to expand...
Technically, the stc says you must use the units used in your poh.
 
tobnpr said:
I obtained a new (for real), original POH for the 172M that I've just started flying.
I'm so used to using knots, and every reference to speed is in mph.

Airspeed is so critical I don't want any confusion and doing conversions in my head while I'm flying and want to maintain consistency here. Shouldn't I go through this POH and mark everything up in knots? I thought knots was universal in marine and aviation...
Click to expand...
What does your airspeed indicator show? If it shows only mph, I'd use mph. If it has been updated and only shows knots, I'd write my checklists to reflect that. If it shows both, I'd write my checklists to show whichever is easiest for me.

Your POH? I'd leave the original intact. Do whatever you feel with a copy.
 
Fearless Tower said:
Has nothing to do with sales and marketing.

Most vintage airplanes (both military and civil) from the 60s and earlier have airspeed indicators in MPH.
Click to expand...

The why do kit builders put their numbers in mph today?

it IS marketing. An airplane with a top speed of 218 (mph) is much sexier than an airplane that only goes 189 (kts)

upload_2022-10-19_6-47-24.png
 
tobnpr said:
I'll probably want to fly their Cherokee, which is most probably knots.
Click to expand...

Wrong. The Cherokees also did the MPH thing for a while, so, like the 172, it will depend on the year.

As another freebie, depending on the year of the Cherokee, you may even have the trim above you, in the headliner! Once you get used to it, it can be pretty cool.

tobnpr said:
Instinctively, i know I'm better off keeping it consistent at least for now. I may be overthinking it, but needing to remember mph for the Cessna, and knots for the Cherokee (and probably every other plane I might fly in the future) sems counterintuitive.
Click to expand...

If MPH and KTS are causing you this much grief, you're going to love different configurations of cockpits.

<This> 172 has just an up-neutral-down flap switch! <That> 172 has a sliding switch with positions marked on the side!
<This> Cherokee has a starter button (put mag on left, then push starter)! <That> Cherokee has a normal switch where you turn the key to start!
<This> Airplane has the tach in front of me! <That> airplane has it to the far right!

tobnpr said:
Respectfully, I think some of you need to think back to your first time ever in the cockpit...
I fully expect to.get the "feel" for flying the aircraft-hopefully sooner rather than later- but I ain't there yet.
Click to expand...

Respectfully, I think you need to realize that the real world of aviation is not the same as X-Plane. In X-Plane you're flying reasonably modern versions of airplanes. In the real world, that is a rare thing, especially for renters. Older models have quirks and differences that you must be able to deal with, or else you will have a very hard time as a pilot. All of your effort spent thinking of "It <SHOULD> be like <THIS>" is wasted and pointless. Use your time to say "It IS like <THIS>, so I need to adapt by <doing this>" On behalf of reality I apologize for it not being as neat and clean as X-Plane, but I have faith that with a little effort you too can adapt to the reality.

I also apologize if this response is not of the kind, gentle, loving hand holding variety you seem to expect.
 
tobnpr said:
Airspeed indicator shows both knots and mph, just like the one I fly in the X-Plane sim.

i can use either- but as i said, my thinking was to e consistent as a beginner. In a few more.flights I'll probably want to fly their Cherokee, which is most probably knots. Instinctively, i know I'm better off keeping it consistent at least for now. I may be overthinking it, but needing to remember mph for the Cessna, and knots for the Cherokee (and probably every other plane I might fly in the future) sems counterintuitive.

Respectfully, I think some of you need to think back to your first time ever in the cockpit...
I fully expect to.get the "feel" for flying the aircraft-hopefully sooner rather than later- but I ain't there yet.
Click to expand...
If you were my student, you'd probably be getting the panel covered up treatment and learning to look outside and pick visual pitch references. Yes, speeds are important, but for consistent speeds, you'll need to learn consistent pitch inputs.

Yeah, you need to watch airspeed much more in the sim, but this actually shows something I believe to be true - excessive sim usage can actually make it harder for you to learn real airplane control in the first 5 hours.
 
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Fearless Tower said:
Has nothing to do with sales and marketing.

Most vintage airplanes (both military and civil) from the 60s and earlier have airspeed indicators in MPH.
Click to expand...

Military was using knots in the early 50s at least.

MPH DID persist in GA due to the bigger number. For an example look at the Mooney 201 and 231 (70s) and 252 (80s).
 
tobnpr said:
Airspeed indicator shows both knots and mph, just like the one I fly in the X-Plane sim.

i can use either- but as i said, my thinking was to e consistent as a beginner. In a few more.flights I'll probably want to fly their Cherokee, which is most probably knots. Instinctively, i know I'm better off keeping it consistent at least for now. I may be overthinking it, but needing to remember mph for the Cessna, and knots for the Cherokee (and probably every other plane I might fly in the future) sems counterintuitive.

Respectfully, I think some of you need to think back to your first time ever in the cockpit...
I fully expect to.get the "feel" for flying the aircraft-hopefully sooner rather than later- but I ain't there yet.
Click to expand...
Respectfully, stop playing x plane. And stop worrying about the instruments; they're not what makes the airplane fly.
 
Nothing wrong with playing x-plane as long as you realize it's limited usefulness. It's not the same, for sure.
 
furlongs / fortnight should give an even better speed reading.
 
There are MPH and knots 172Ms. Partway through the M model production Cessna switched to knots, and there are at least two different 172M POHs. From the C172 TCDS:

upload_2022-10-19_8-29-36.png

Note the two serial number ranges. More from the TCDS of the M:

upload_2022-10-19_8-37-52.png

POHs are specific:
upload_2022-10-19_8-36-22.png

That year is important.
 
Salty said:
Nothing wrong with playing x-plane as long as you realize it's limited usefulness. It's not the same, for sure.
Click to expand...

I knew this getting started, and first flight highlighted both the elements lacking (MOTION) but I also found the control inputs (e.g. resistance) from the Honeycomb Alpha yoke to be surprisingly realistic. No offense to anyone, everyone can have their opinions- but I do not regard X-Plane as a "game". My son is an AF pilot and he strongly encouraged me to set up a sim (and I'm going VR on his recommendation as well). Not close to being in the same league as a military sim (which I used on-base), but certainly valuable- at least to me.

Thanks to all for the input. I'll stick with committing the mph numbers to memory and have ordered a C172M kneeboard checklist.


Dan Thomas said:
That year is important.
Click to expand...

Yep- mine is 1975, all in statute.
 
tobnpr said:
No offense to anyone, everyone can have their opinions- but I do not regard X-Plane as a "game".
Click to expand...

Do you always choose the small things to argue about?

If so, you'll fit in fine here, just as soon as you stop try to not offend people.
 
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