172 Approach Speed

Gray Ghost said:
I am a student pilot, so please excuse my ignorance.

The Airplane Flying Handbook repeatedly says that you should fly final approach at 1.3 x Vs0. Vs0 in the 172R I am mostly flying is 33 kts. 1.3 times that is 43 kts. Nobody flies the approach that slowly in the 172, and I have been instructed to fly it at 65 kts, which works well.

Can someone explain the discrepancy to me? Does the 1.3 x Vs0 formula just not apply to a 172?

Thanks in advance.
Click to expand...

What is your stall speed?

Take a photo of your airspeed indicator and look at the green and white arcs too (confirm they are correct, mine are not :confused:)

The most likely way you’ll end up in a fatal accident is a stall on landing or take-off. Sorry it has to be said, you have to realize the importance of stall speed.

Stay well above the stall speed, do not let your stall horn start blaring on approach or take off, know what to do to increase airspeed immediately if needed. Wings level! Bank angles increase your stall speed dramatically. That’s why instructors will give you a higher approach speed and tell you to not bank that much at lower altitudes.
 
dmspilot said:
Please follow along. The sources clearly disprove Clips's argument that 1.3 x Vso is "higher than usual".

Also, he literally said "Cessna is recommending approach speed greater than 1.3 Vso". It is not greater than 1.3 Vso on account of a 1-knot rounding error, which was my original point.

When I pointed this out, he exercised the fallacy known as "moving the goalposts". Oh, he didn't mean 1.3, he meant 1.2. Whatever.
Click to expand...
True…I quoted more of his post than you responded to. Consider my response to be ignoring the “Vref+1” goalpost that you ignored in your post that I quoted.
 
mandm said:
Stay well above the stall speed, do not let your stall horn start blaring on approach or take off, know what to do to increase airspeed immediately if needed. Wings level! Bank angles increase your stall speed dramatically. That’s why instructors will give you a higher approach speed and tell you to not bank that much at lower altitudes.
Click to expand...

Along with this good advice I would add to maintain coordination through your turns.
 
midlifeflyer said:
These are from the link you posted. The 1.3 formula applies just fine.


View attachment 105043

View attachment 105044
Click to expand...

I agree with Salty! I didn't know it was this hard to learn. :)

When we had a C-172, it was an older model without the chart you attached I usually was at about 60 knots indicated over the threshold. Flying at 33 kts indicated times 1.3 as the chart says, or 33X1.3=43 kts indicated (give or take) seems to me way too slow. I guess I am missing something, but it seems to me most of you are using the calibrated airspeed X 1.3 to come up with the recommeded airspeed, but the pilot will be looking at the indicated airspeed on the ASI unless I am missing something. No wonder Gray Ghost is confused! I am too. :)
 
somorris said:
I guess I am missing something, but it seems to me most of you are using the calibrated airspeed X 1.3 to come up with the recommeded airspeed, but the pilot will be looking at the indicated airspeed on the ASI unless I am missing something.
Click to expand...
You’re missing the conversion back to indicated airspeed after making the 1.3 calculation.
 
dmspilot said:
Please follow along. The sources clearly disprove Clips's argument that 1.3 x Vso is "higher than usual".

Also, he literally said "Cessna is recommending approach speed greater than 1.3 Vso". It is not greater than 1.3 Vso on account of a 1-knot rounding error, which was my original point.

When I pointed this out, he exercised the fallacy known as "moving the goalposts". Oh, he didn't mean 1.3, he meant 1.2. Whatever.
Click to expand...


Stall speeds and final approach speeds are generally published for the airplane at or near maximum gross weight. Unless you are doing mid air refueling in the pattern, we rarely land an airplane when it’s that heavy, because presumably we have been flying around for a while, burning avgas at the rate of six pounds per gallon per hour. In training, we are also taking off below gross. The airplane’s stall speed increases with an increase in weight and the actual Vso at the moment of landing is lower than what’s listed in the POH.

Assuming 61 published speed and shaving 5 knots to ~1.2 of the published stall speed still has you about 1.3 of the real stall speed and is within the -5/+10 allowed in the ACS.
 
Clip4 said:
Stall speeds and final approach speeds are generally published for the airplane at or near maximum gross weight. Unless you are doing mid air refueling in the pattern, we rarely land an airplane when it’s that heavy, because presumably we have been flying around for a while, burning avgas at the rate of six pounds per gallon per hour. In training, we are also taking off below gross. The airplane’s stall speed increases with an increase in weight and the actual Vso at the moment of landing is lower than what’s listed in the POH.

Assuming 61 published speed and shaving 5 knots to ~1.2 of the published stall speed still has you about 1.3 of the real stall speed and is within the -5/+10 allowed in the ACS.
Click to expand...

Your assertion was that Cessna recommends an abnormally high airspeed "because it's a high wing" and also that the normal short field approach speed is 1.2 x Vso, and have yet cite anything to back up either argument. Your condescending lecture on the relationship of weight and stall speed has nothing to do with either.
 
The book numbers are good ball park. And, sitting down to figure out IAS vs. CAS is nice on the ground. But, with aging Cessnas with various quality in rigging and maintenance, I like to take a 'new to me' airplane out and see what it stalls at in the landing configuration, then compute my touch-down speed from that.

I've been "that guy" in the C-172, skipping down the full length of a 2,700' runway, praying the airplane would come to a stop before the fence. And, as a result, I like to touch down as slow as safely practical. And, a lot of the time that speed has nothing to do with how fast I'm going on the downwind.
 
wilkersk said:
The book numbers are good ball park.
Click to expand...

And that's really all they are. Show me an airplane that has an airspeed indicator accurate +/- 1 knot. Show me a pilot that can consistently fly an airspeed +/- 1 knot. Throw in variables such as aircraft weight, rigging, load factor, etc.

That is why the true answer for any airplane is that it will stall at any speed. Arguing whether an airplane will stall at 46 or 47 knots is ludicrous. "About 45-50" is close enough for me.
 
Wow, it took 15 posts before it was simply stated that IAS vs. CAS x 1.3 is the answer to the OP's question. No wonder flying is so hard.
 
RoscoeT said:
Wow, it took 15 posts before it was simply stated that IAS vs. CAS x 1.3 is the answer to the OP's question. No wonder flying is so hard.
Click to expand...
It’s even harder if you can’t count…I see Post #12 giving that answer. ;)
 
Good Morning Gray Ghost. Your post has generated a lot of off-the-point discussion, so let me answer your question succinctly. Yes, your POH correctly lists VSO at 33 KIAS. Indicated airspeed is what you should note for that number. That speed is the lower limit of your airspeed indicator white arc. If you examine the Stall Speed Chart in section 5 you will see that 33 KIAS (indicated) is 46 KCAS (calibrated): an error of 13 knots! That is not unusual for many airplanes at slow speeds. Therefore: 46 KCAS x 1.3 = 60 KCAS which is exactly at the low range of recommended approach speeds in the normal section of the POH for full flaps. Yes, you could then convert 60 KCAS to 59 KIAS with the Airspeed Correction Chart (only a 1 knot error at that speed). The "1.3 rule" is a rule-of-thumb (a guess!) used when manufacturer data is not provided.

Use the POH recommendations. You will hear pilots say they use different speeds. Those speeds may very well work better for them for some common reasons: flying at lighter weights, inaccurate airspeed indicators, leaks in the pitot-static system, flying in a persistent local windshear. As you progress in your learning, you should learn how to lower your target approach speed at lower weights to prevent ballooning and oscillations during the landing flare.

(PS - I am a CFI with over 100 types of aircraft flown)
 
wilkersk said:
I've been "that guy" in the C-172, skipping down the full length of a 2,700' runway, praying the airplane would come to a stop before the fence. And, as a result, I like to touch down as slow as safely practical. And, a lot of the time that speed has nothing to do with how fast I'm going on the downwind.
Click to expand...

The techniques taught by the old guys have largely been lost. I used to see a lot of airplanes get to two feet above the runway, still doing approach speed (or worse) before flaring. That meant ballooning, or floating, or touching down too fast, which means too flat (if one knows anything about the relationship between airspeed and AoA) and maybe porpoising and breaking something.

The textbooks tell you to reduce the power and start raising the nose to kill of speed between 15 and 30 feet off the ground, continuing that process until the airplane reaches the surface nose-high and quite slow. Book values for landing distances are based on that, not on flaring at approach speed at two feet.

upload_2022-3-3_11-49-52.jpeg

Too many aren't doing any "round-out," the process shown above. They only flare at the last instant, at 1.3Vso, in ground effect where the stall is actually lower. No wonder they use up thousands of feet to stop a simple airplane.

wilkersk said:
The book numbers are good ball park. And, sitting down to figure out IAS vs. CAS is nice on the ground. But, with aging Cessnas with various quality in rigging and maintenance, I like to take a 'new to me' airplane out and see what it stalls at in the landing configuration, then compute my touch-down speed from that.
Click to expand...

That's informative as to where the thing can be expected to stall, and it would be 33 knots in the OP's airplane. But using that to multiply by 1.3 for approach would be foolish. The angle of the pitot tube against the airflow causes an artificially low reading, one that cannot be used for such calculations. In my old Auster, which stalled at around 38 MPH, I could get that ASI to go a bit negative in slow flight. That didn't mean that stall was below zero, or that I was doing zero MPH. It meant that the ASI was useless in that attitude.
 
Dan Thomas said:
Good argument for more and better training instead of more gizmos. Gizmos cannot replace knowledge. They can help, but only a bit, and they can offer a false sense of security.
Click to expand...

RV guys are huge into gizmos and AOA since military jets use them. Pilots of bush, acro, antique/classic types and pretty much everything else just learn to fly the airplane.
 
Dan Thomas said:
Good argument for more and better training instead of more gizmos. Gizmos cannot replace knowledge. They can help, but only a bit, and they can offer a false sense of security.
Click to expand...


That's why it's an argument, not a done deal.
 
Dan Thomas said:
That's informative as to where the thing can be expected to stall, and it would be 33 knots in the OP's airplane. But using that to multiply by 1.3 for approach would be foolish. The angle of the pitot tube against the airflow causes an artificially low reading, one that cannot be used for such calculations. In my old Auster, which stalled at around 38 MPH, I could get that ASI to go a bit negative in slow flight. That didn't mean that stall was below zero, or that I was doing zero MPH. It meant that the ASI was useless in that attitude.
Click to expand...

Fly the wing, not the ASI. That's pretty much true for everything. All the "numbers" are just gouge. What counts is what the airplane actually does. The best way to learn that is to go out and practice it. So, having an idea of where the airplane "can be expected to stall" sounds like a good idea to me. But, I would never, ever dare try and tell you how to fly an airplane. You do what you gotta do.
 
Dan Thomas said:
Good argument for more and better training instead of more gizmos. Gizmos cannot replace knowledge. They can help, but only a bit, and they can offer a false sense of security.
Click to expand...
I can’t imagine anyone who’s trying to tighten up the turn from base to final and is in danger of stalling trying to focus on AOA indicator to ensure they don’t stall.
 
Last edited:
MauleSkinner said:
I can’t imagine anyone who’s trying to tighten up the turn from base to final and is in danger of stalling trying to focus on AOA indicator to ensure they don’t stall.
Click to expand...
This is the problem. They're taught, or should be, about airspeed, load factor, bank angles, stall speed increases and accelerated stalls. When one learns to drive, he/she is taught how to modulate braking to avoid sliding (although ABS has dumbed down a lot of drivers) and how to recover from a skid. Why can't pilots get the picture on angle of attack, airspeed, and G-forces? An AoA indicator might be really neat but it cannot predict what the pilot is going to do in the next few seconds, stupid stuff like pulling up sharply after buzzing the runway or some friend's house. By the time the AoA shrieks or flashes, it's too late. Accelerated stalls like that don't give much time for any warning.
 
Dan Thomas said:
By the time the AoA shrieks or flashes, it's too late.
Click to expand...
Yup…If an AOA shrieking or flashing as a stall approached stopped stall accidents, there wouldn’t be any stall accidents in airplanes built after about the mid-1960s.
 
Dan Thomas said:
This is the problem. They're taught, or should be, about airspeed, load factor, bank angles, stall speed increases and accelerated stalls. When one learns to drive, he/she is taught how to modulate braking to avoid sliding (although ABS has dumbed down a lot of drivers) and how to recover from a skid. Why can't pilots get the picture on angle of attack, airspeed, and G-forces? An AoA indicator might be really neat but it cannot predict what the pilot is going to do in the next few seconds, stupid stuff like pulling up sharply after buzzing the runway or some friend's house. By the time the AoA shrieks or flashes, it's too late. Accelerated stalls like that don't give much time for any warning.
Click to expand...

Yes, unfortunately you can't fix stupid. If a pilot is jerking on the controls in the pattern, not much will prevent the inevitable result.
 
Isn't bottom of white arc Vso?
 

Attachments

  • Screenshot_20220309-001112_Drive.jpg
    Screenshot_20220309-001112_Drive.jpg
    103.4 KB · Views: 8
  • Screenshot_20220309-001155_Drive.jpg
    Screenshot_20220309-001155_Drive.jpg
    146 KB · Views: 6
Wow it all sounds so complicated. We are talking a 172 here. After my students get fairly consistent with their landings I cover the A/S indicator & we fly the pattern a bunch of times without A/S. Isn't everyone taught this? I realize I'm an old CFI with old ideas.
 
I mean… I haven’t flown a 172 in 30 years, but if I got in one today I’d fly a final around 65 kts. It doesn’t need to be that precise. You’re not flying the space shuttle.
 
Kritchlow said:
I mean… I haven’t flown a 172 in 30 years, but if I got in one today I’d fly a final around 65 kts. It doesn’t need to be that precise. You’re not flying the space shuttle.
Click to expand...

This. So this.
 
Kritchlow said:
I mean… I haven’t flown a 172 in 30 years, but if I got in one today I’d fly a final around 65 kts. It doesn’t need to be that precise. You’re not flying the space shuttle.
Click to expand...

So book knowledge is not important?
 
RoscoeT said:
If you flew a J-3 Cub, would you read the POH first?
Click to expand...

By "book knowledge" I am not (necessarily) referring to the POH.
 
Last edited:
mandm said:
Coordination via the ball? That’s one of my needs improvement points.
Click to expand...

I would say make that your very top priority. It’s a very simple thing yet kills us on a pretty regular basis. I’m not being a smart arse- go get that engrained into muscle memory. We all have certain things we’re not perfect at, and being cognizant of it give you a leg up on someone that can’t acknowledge they have a problem. All those base to final accidents are almost 100% preventable. Break the accident chain go nail your coordinated turns.
 
mandm said:
Coordination via the ball? That’s one of my needs improvement points.
Click to expand...

But you'll be better off if you learn to keep your eyes outside the cockpit and learn to fly coordinated without having to look at the ball. You can feel it easily. You just have to pay attention and build the muscle memory.
 
If you have a difficult time looking out the windshield AND controlling yaw..............install a yaw string like many sailplanes have.

yawstring_photo.jpg
 
kgruber said:
If you have a difficult time looking out the windshield AND controlling yaw..............install a yaw string like many sailplanes have.

yawstring_photo.jpg
Click to expand...
Not a very effective device when there is a giant coupled hundred horse power fan mounted 2 ft away. Much less of an issue on a glider.
 
RoscoeT said:
But you'll be better off if you learn to keep your eyes outside the cockpit and learn to fly coordinated without having to look at the ball. You can feel it easily. You just have to pay attention and build the muscle memory.
Click to expand...
I very good instructor I had used to say "you've got to feel it in your seat".
 
Last edited:
jesse said:
Not a very effective device when there is a giant coupled hundred horse power fan mounted 2 ft away. Much less of an issue on a glider.
Click to expand...
Yup. The blast off the prop is not straight. It spirals a bit.
 
You must log in or register to reply here.
Back
Top