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Posted: 10/17/2022 8:47:33 PM EDT
It is just about dark here right now. There was a Cessna 172, I think (it is damn near dark) at about 500 feet and was moving slowly. Thing about it was, it sounded like the pilot was slowly but methodically throttling the engine down even slower as he cruised on out of sight.
The best estimate about how fast he was going looked like below 60mph at sunset no wind. So, how slow is to slow at low altitude before old girl starts to tip forward. Could this have been a student who was going to put the aircraft down for a night time landing? The aircraft may have even been below 50mph I'm really not sure. So, as a rule and under these conditions, does the airplane look like it's going faster, slower, or can you judge pretty accurately from where you are versus it's true speed in flight?. What about watching one at ten thousand? Thanks. Go!!  |
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Posted: 10/17/2022 8:51:04 PM EDT
[#1]
It probably sounded like it was slowing down as it got further away due to Doppler effect.
It was going faster than 50-60 unless it was on final coming in to land. |
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Posted: 10/17/2022 8:53:19 PM EDT
[#2]
Define airspeed..
Indicated, true, calibrated, groundspeed....pretty broad question. Entirely different answers to each. Eg: in the flight levels, 280 indicated, 480 true, 550 ground. |
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Posted: 10/17/2022 8:53:37 PM EDT
[#3]
Just because the wind is light on the ground does not mean it is not blowing up higher. I have encountered 40mph winds at 2000' when it was almost calm on the ground.
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Posted: 10/17/2022 8:55:21 PM EDT
[#4]
With enough of a headwind you can be stopped in relation to the ground but have a 60kt indicated airspeed.
If it was a tailwind you'd have a 60 knots indicated but moving 120 knots in relation to a ground observer. |
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Posted: 10/17/2022 8:57:28 PM EDT
[#5]
that first post thing, most likely doppler effect
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Posted: 10/17/2022 8:57:38 PM EDT
[#6]
Quote HistoryQuoted: Just because the wind is light on the ground does not mean it is not blowing up higher. I have encountered 40mph winds at 2000' when it was almost calm on the ground. We did have a cool front roll in last night. The aircraft was not flying with the wind if there was some. Deadly silent on the ground as well. |
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Posted: 10/17/2022 8:58:50 PM EDT
[#7]
Were you on a treadmill, OP?
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Posted: 10/17/2022 8:59:52 PM EDT
[#8]
Quote HistoryQuoted: Were you on a treadmill, OP? On the rower at dark out front bro. Bringing the wife's plants in. |
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Posted: 10/17/2022 9:00:19 PM EDT
[#9]
 LA Speed Check Story by SR-71 Blackbird Pilot Major Brian Shul USAF (Ret.) - A Pilot's Story |
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Posted: 10/17/2022 9:06:37 PM EDT
[#10]
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Posted: 10/17/2022 9:08:17 PM EDT
[#11]
It probably wasn't a 172, more like a 182 with a variable/constant speed prop.
Once takeoff has been achieved with the prop set at fine pitch, the pilot pulls the pitch lever back to a coarser pitch obtain a higher airspeed where speed and optimum power can be balanced. Fine pitch gives you maximum takeoff power, coarse gives you speed and optimum efficiency. You just have to know the proper procedure to adjust it. It's like taking off with a lower gear (Like 4 Low) and switching to a higher gear (4 Hi) . ETA, to clarify, just because you heard a noticeable RPM drop does not mean the speed of the aircraft dropped. |
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Posted: 10/17/2022 9:08:34 PM EDT
[#12]
Quote HistoryQuoted: Indicated, true, calibrated, groundspeed....pretty broad question. Entirely different answers to each. ICE-T Indicated Calibrated Equivalent True |
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Posted: 10/17/2022 9:11:49 PM EDT
[#13]
In a Cessna 172 (or 182) 60 is about when I'm starting to flare for the landing.
And not that people don't manage it, but you'd have to work hard to stall and crash one - they give you all kinds of warning, and when it finally happens, it's gentle. |
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Posted: 10/17/2022 9:18:34 PM EDT
[#14]
Quote HistoryQuoted: With enough of a headwind you can be stopped in relation to the ground but have a 60kt indicated airspeed. If it was a tailwind you'd have a 60 knots indicated but moving 120 knots in relation to a ground observer. You can actually float a 172 backwards in relation to the ground with enough of a headwind. I forget what the stall speed is but it's pretty low, like 40 knots I think. |
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Posted: 10/17/2022 9:19:16 PM EDT
[#15]
Quote HistoryQuoted: You can actually float a 172 backwards in relation to the ground with enough of a headwind. I forget what the stall speed is but it's pretty low, like 40 knots I think. Quote HistoryQuoted: Quoted: With enough of a headwind you can be stopped in relation to the ground but have a 60kt indicated airspeed. If it was a tailwind you'd have a 60 knots indicated but moving 120 knots in relation to a ground observer. You can actually float a 172 backwards in relation to the ground with enough of a headwind. I forget what the stall speed is but it's pretty low, like 40 knots I think. I do that with RC planes a lot, it's a hoot 
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Posted: 10/17/2022 9:28:48 PM EDT
[#16]
Quote HistoryQuoted: ICE-T Indicated Calibrated Equivalent True lol.. thanks for the reminder. Had to look up the equation for Equivalent A/S, have not seen that in a long time. Stuff I forgot over the years... Although, the only number that really matters is ground speed as in " are we there yet? " Anything over 600 knots is acceptable... Duke |
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Posted: 10/17/2022 9:30:52 PM EDT
[#17]
Laden or unladen?
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Posted: 10/17/2022 9:35:38 PM EDT
[#18]
Quote HistoryQuoted: Laden or unladen? Spit or swallow ? |
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Posted: 10/17/2022 9:44:26 PM EDT
[#19]
Quote HistoryQuoted: You can actually float a 172 backwards in relation to the ground with enough of a headwind. I forget what the stall speed is but it's pretty low, like 40 knots I think. We’d fly backwards in the J3 working a fire in heavy wind. |
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Posted: 10/17/2022 9:45:40 PM EDT
[#20]
Quote HistoryQuoted: Spit or swallow ? Quote HistoryQuoted: Quoted: Laden or unladen? Spit or swallow ?  Attached File |
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Posted: 10/17/2022 9:45:45 PM EDT
[#21]
Could just be a pilot practicing slow flight.
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Posted: 10/17/2022 10:34:24 PM EDT
[#22]
Slow flight training? Too low though.
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Posted: 10/17/2022 10:42:34 PM EDT
[#23]
A C172 will comfortably fly at 40mph or so. Stall is 36, IIRC. I would have to pull my POH.
I have landed and pulled off the taxi way in less than 100 feet of ground roll. |
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Posted: 10/17/2022 10:45:59 PM EDT
[#24]
European or African?
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Posted: 10/17/2022 10:47:11 PM EDT
[#25]
No wind.
At ground level. |
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Posted: 10/17/2022 10:51:18 PM EDT
[#26]
Quote HistoryQuoted: Slow flight training? Too low though. This is what I initially thought as well. He could have been even lower than that maybe 400 and some change. |
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Posted: 10/18/2022 6:32:53 AM EDT
[#27]
The stall speed for a 172S is 48 knots, approximately 55 mph.
I think the November version is very close to that, possibly one or two knots slower. Estimating an aircraft's speed from the ground is deceptive. I'm sure he was going faster than what it seemed. |
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Posted: 10/18/2022 7:05:52 AM EDT
[#28]
Quote HistoryQuoted: The stall speed for a 172S is 48 knots, approximately 55 mph. I think the November version is very close to that, possibly one or two knots slower. Estimating an aircraft's speed from the ground is deceptive.[color=#0000ff] I'm sure he was going faster than what it seemed. I used to live on flight path of WPAFB when they were still flying C-5's there. Those things looked like they were going to fall out of the sky sometimes. |
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Posted: 10/18/2022 7:18:06 AM EDT
[#29]
I have flown Cessnas and Pipers BACKWARDS with enough winds aloft.
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Posted: 10/18/2022 7:26:17 AM EDT
[#30]
Those guys in Alaska with the big balloon tires take off and land in like 10' because of the headwind. Pretty cool to watch,
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Posted: 10/18/2022 7:47:10 AM EDT
[#31]
53 knots (61 mph) is the level flight, flaps up stall speed of the Cessna 172.
If the pilot is flying to the wind the ground speed will be lower. Flying into a 40 mile per hour wind the guy would fly by as slow as 21 miles per hour. |
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Posted: 10/18/2022 3:26:17 PM EDT
[#32]
Reminder: There's no such thing as "stall speed".
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Posted: 10/18/2022 3:32:01 PM EDT
[#33]
Quote HistoryQuoted: Reminder: There's no such thing as "stall speed". Thank you.. that’s a critical concept that needs to be understood. Fortunately, there are air data computers that figure that out for you and set the floors/cues so no guesswork is required. AOA ( alpha) gentlemen, is all that matters. Duke |
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Posted: 10/18/2022 3:35:50 PM EDT
[#34]
Quote HistoryQuoted: Reminder: There's no such thing as "stall speed". I know where you’re going here, but most airplane POH’s list VS, VS1, and VSO so it’s not like it’s just some made up idea… |
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Posted: 10/18/2022 3:43:02 PM EDT
[#35]
Quote HistoryQuoted: 53 knots (61 mph) is the level flight, flaps up stall speed of the Cessna 172. If the pilot is flying to the wind the ground speed will be lower. Flying into a 40 mile per hour wind the guy would fly by as slow as 21 miles per hour. He or she looked to be doing about 48-53 knots as far as I could tell. |
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Posted: 10/18/2022 4:05:40 PM EDT
[#36]
Quote HistoryQuoted: Thank you.. that’s a critical concept that needs to be understood. Fortunately, there are air data computers that figure that out for you and set the floors/cues so no guesswork is required. AOA ( alpha) gentlemen, is all that matters. Duke Quote HistoryQuoted: Quoted: Reminder: There's no such thing as "stall speed". Thank you.. that’s a critical concept that needs to be understood. Fortunately, there are air data computers that figure that out for you and set the floors/cues so no guesswork is required. AOA ( alpha) gentlemen, is all that matters. Duke I am an aviation novice (newly certificate private pilot), so please excuse my ignorance. As I understand it: 1) Most if not all airplanes have published stall speeds. There is usually Vs0, which is stall speed in landing configuration (i.e. full flaps) and Vs1, which is stall speed in clean configuration. These assume level flight. IIRC the Vs0 for a 172 is 38 knots indicated. 2) It is possible to stall an aircraft at any speed. The variables are angle of attack (AOA) and angle of bank. You could be flying at a level attitude, but if you bank into a steep enough turn, you would produce an accelerated stall. Similarly, you could be flying wings level, but whatever your speed, if you pitch up enough (at least in normal airplanes) you will eventually exceed the critical angle of attack and stall. Am I mistaken? |
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Posted: 10/18/2022 4:10:31 PM EDT
[#37]
Quote HistoryQuoted: Thank you.. that’s a critical concept that needs to be understood. Fortunately, there are air data computers that figure that out for you and set the floors/cues so no guesswork is required. AOA ( alpha) gentlemen, is all that matters. Duke The subject is a 172 not a modern business or military jet, and I’d venture to say that very few of the former have AOA indicators. While technically correct, in a typical GA airplane IAS is about the only way to tell if you’re approaching a stall, not counting the buffeting that occurs prior. Yes it’s affected by weight, load factor, weather conditions etc but most 172s also don’t have air data computers. |
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Posted: 10/18/2022 4:13:29 PM EDT
[#38]
Quote HistoryQuoted: Just because the wind is light on the ground does not mean it is not blowing up higher. I have encountered 40mph winds at 2000' when it was almost calm on the ground. |
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Posted: 10/18/2022 4:18:02 PM EDT
[#39]
Slow flight is a part of pilot training. You throttle back to approach speed and increase angle of attack to maintain lift until near stall speed.
No biggie. Practicing stalls and recovery procedures also. |
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Posted: 10/18/2022 4:40:53 PM EDT
[#40]
Quote HistoryQuoted: The subject is a 172 not a modern business or military jet, and I’d venture to say that very few of the former have AOA indicators. While technically correct, in a typical GA airplane IAS is about the only way to tell if you’re approaching a stall, not counting the buffeting that occurs prior. Yes it’s affected by weight, load factor, weather conditions etc but most 172s also don’t have air data computers. Quote HistoryQuoted: Quoted: Thank you.. that’s a critical concept that needs to be understood. Fortunately, there are air data computers that figure that out for you and set the floors/cues so no guesswork is required. AOA ( alpha) gentlemen, is all that matters. Duke The subject is a 172 not a modern business or military jet, and I’d venture to say that very few of the former have AOA indicators. While technically correct, in a typical GA airplane IAS is about the only way to tell if you’re approaching a stall, not counting the buffeting that occurs prior. Yes it’s affected by weight, load factor, weather conditions etc but most 172s also don’t have air data computers. Well, that and the damn kazoo that starts squaking at you. 
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Posted: 10/18/2022 4:47:02 PM EDT
[#41]
I knew geeky enough dudes who would try to calculate the boundary layer thickness while in a spin versus executing PARE.
I figure asking “what is stall speed for XYZ aircraft?” is a lot like asking “What is the boiling point of water?” It’s kind of a trick question. Yes, given certain parameters, water does boil at 212*F. However, you can “boil” water at room pressure (if you get the pressure low enough). |
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Posted: 10/18/2022 4:51:38 PM EDT
[#42]
Man, where is the “ackshually” meme when we need it?
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Posted: 10/18/2022 4:54:27 PM EDT
[#43]
Quote HistoryQuoted: I am an aviation novice (newly certificate private pilot), so please excuse my ignorance. As I understand it: 1) Most if not all airplanes have published stall speeds. There is usually Vs0, which is stall speed in landing configuration (i.e. full flaps) and Vs1, which is stall speed in clean configuration. These assume level flight. IIRC the Vs0 for a 172 is 38 knots indicated. 2) It is possible to stall an aircraft at any speed. The variables are angle of attack (AOA) and angle of bank. You could be flying at a level attitude, but if you bank into a steep enough turn, you would produce an accelerated stall. Similarly, you could be flying wings level, but whatever your speed, if you pitch up enough (at least in normal airplanes) you will eventually exceed the critical angle of attack and stall. Am I mistaken? You are not mistaken.To your points.. 1. “Stall” speeds, if published , would be weight/configuration dependent but are ultimately driven by AOA considerations. Published speeds for small aircraft are a necessary number when you do not have an air data system available to provide dynamic (real time) calculations and a moving cue. Put another way, because your pitch control is likely not being commanded by a flight director, you need a baseline. 2. Critical angle of attack is a stand alone number, largely based off airfoil design. Other factors, bank-weight-configuration etc. will contribute to how quickly you approach that angle but when you reach it, flow will separate and lift will be lost. A practical example: For many years, the teaching was to minimize altitude loss during stall recovery. Obviously no one wants to impact terrain. Current doctrine is to decrease angle of attack, and accept the altitude loss. Synopsis: Break the critical angle. Roll wings level. Power as required. Trim as necessary. Duke |
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Posted: 10/18/2022 5:00:13 PM EDT
[#44]
Quote HistoryQuoted: You are not mistaken.To your points.. 1. “Stall” speeds, if published , would be weight/configuration dependent but are ultimately driven by AOA considerations. Published speeds for small aircraft are a necessary number when you do not have an air data system available to provide dynamic (real time) calculations and a moving cue. Put another way, because your pitch control is likely not being commanded by a flight director, you need a baseline. 2. Critical angle of attack is a stand alone number, largely based off airfoil design. Other factors, bank-weight-configuration etc. will contribute to how quickly you approach that angle but when you reach it, flow will separate and lift will be lost. A practical example: For many years, the teaching was to minimize altitude loss during stall recovery. Obviously no one wants to impact terrain. Current doctrine is to decrease angle of attack, and accept the altitude loss. Synopsis: Break the critical angle. Roll wings level. Power as required. Trim as necessary. Duke Yep. The only way to recover from slow flight is to drop the nose and get proper airspeed back , not something I would attempt at 400 ft. You can firewall a 172 in slow flight but it won't change anything until you level the aircraft by dropping the nose. |
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Posted: 10/18/2022 5:09:47 PM EDT
[#45]
Quote HistoryQuoted: Well, that and the damn kazoo that starts squaking at you. Ag yes, of course. How could I forget  |
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Posted: 10/18/2022 6:14:58 PM EDT
[#46]
Quote HistoryQuoted: Man, where is the “ackshually” meme when we need it? Turns out, misunderstanding the concept of "stall speed" has killed a lot of people. |
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Posted: 10/18/2022 6:57:25 PM EDT
[#47]
Quote HistoryQuoted: Turns out, misunderstanding the concept of "stall speed" has killed a lot of people. Lol. You and the ackshually crew need to get on the horn with Cessna, Piper, and darned near everyone else who ever made airplanes and demand that they recall all of their POH’s with the term “Stall Speed” in them before even more lives are lost to their recklessness. You’d probably better get ahold of the FAA while your at it so they stop using it in their safety bulletins too: FAA V-speeds article |
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Posted: 10/18/2022 7:03:37 PM EDT
[#48]
It should also be factored the stall speed is for a max payload plane on a "standard" day.
It is also noteworthy slow flight in a 172 requires a significant amount of power |
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Posted: 10/18/2022 7:06:12 PM EDT
[#49]
Quote HistoryQuoted: Lol. You and the ackshually crew need to get on the horn with Cessna, Piper, and darned near everyone else who ever made airplanes and demand that they recall all of their POH’s with the term “Stall Speed” in them before even more lives are lost to their recklessness. You’d probably better get ahold of the FAA while your at it so they stop using it in their safety bulletins: FAA V-speeds article No matter what the FAA print (or requires aircraft manufacturers to print), the airplane remains an all-attitude vehicle. And, as such, there's no such thing as "stall speed". Failing to understand that you can exceed the critical AOA of the wing at any speed, or that you can still have plenty of lift and control of aircraft well below the straight-and-level-at-a-particular-weight-and-temperature "stall speed", is a very dangerous thing. You know that there is a whole segment of the professional aviation world that doesn't use "V speeds", right? Next time I get into an accelerated stall, I'll be sure to remind myself that "this isn't happening, I'm above the stall speed!" |
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Posted: 10/18/2022 7:52:29 PM EDT
[#50]
Quote HistoryQuoted: Lol. You and the ackshually crew need to get on the horn with Cessna, Piper, and darned near everyone else who ever made airplanes and demand that they recall all of their POH’s with the term “Stall Speed” in them before even more lives are lost to their recklessness. You’d probably better get ahold of the FAA while your at it so they stop using it in their safety bulletins: FAA V-speeds article It's a matter of perspective, ackshually. A fundamental understanding of aerodynamic theory is required of a competent pilot. This applies to everyone, irrespective of airframe. The POH for a given platform is largely written for the intended audience, ie; the level of detail in a 152/172 manual is markedly different than that of a NATOPS manual for a Hornet. The term "stall speed" is used as a generic term that is easily understood by the casual user or someone who may not be inclined to maintain peak proficiency or fly the aircraft to it's maximum potential. That does not excuse the user from having a clear understanding of how the vehicle works. As stated earlier, many people have lost their lives by having a cursory understanding of terminology and making assumptions that proved fatal. Duke |
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