The yellow arc

[mandm]

I know that the yellow arc is for smooth air but what about when you run into occasional bumps or rough air. Is there a time frame (5 seconds, 15 seconds, 30 sec, 1 min?) of rough air that you would accept before lowering your airspeed or would you immediately reduce throttle?

Also, what about the descent, if you plan a slow descent (let’s say a couple hundred few per minute) controlled by the trim would you still keep your speed up provided it doesn’t approach the red arc or is this a no go?

 

[MauleSkinner]

I quit considering the yellow arc to be operational when I started flying turbines. The yellow arc goes away, and red line/ Vmo is at the top of the green arc.

 

[rhkennerly]

Depends on how suicidal you are. In truth, you’ll likely pitch for ride. If stuff levitates in the cockpit, it’s time to slow down.

 

[Tantalum]

The wing, at least in 'slow piston planes' doesn't know how fast it's going, what it knows is how many Gs are pushing on it. Your maneuvering speed will stall the wing before you break it, but as you go faster you may not hit that critical AoA before the wing breaks, the yellow arc is a buffer for that.

As long as you're not pulling any kind of Gs (either through maneuvering or turbulence) the yellow is okay, assuming of course you are under Vne.

Vne has other factors that went into it to determine, flutter, dives during testing, etc.

 

[Salty]

I quit considering the yellow arc to be operational when I started flying turbines. The yellow arc goes away, and red line/ Vmo is at the top of the green arc.

In my c model Mooney I learned to fly nearly all the time in the yellow arc. That’s one reason I tend to hop up above the cloud layer whenever possible.

 

[nauga]

I know that the yellow arc is for smooth air but what about when you run into occasional bumps or rough air. Is there a time frame (5 seconds, 15 seconds, 30 sec, 1 min?) of rough air that you would accept before lowering your airspeed or would you immediately reduce throttle?

The bottom of the yellow arc is Vno, the max speed at which a 50 ft/sec vertical gust will not exceed the g-limits of the airplane. As such, my willingness to cruise in the yellow is based on turbulence intensity more than frequency.

Vno is typically higher than maneuver speed, so being below the yellow arc is no assurance that aggressive maneuvering will cause a stall before an overstress. It's purely a function of response to a spec vertical gust.

Nauga,
who can hear the oilcanning

 

[455 Bravo Uniform]

How many of us have been cruising along, smooth air, then out of nowhere, BAM! some turbulence. Not flip you over or knock you senseless, but enough to get your attention, looking for whose wake turbulence you just smelled? Now what would have happened if you were flying above Vno (in the yellow)?

I’m not suggesting that one should fly so fearful of the yellow, but I can’t see when I’m going to cross a ditch or speed bump in the sky. Maybe one bump won’t kill ya or hurt the plane. Or maybe it will? I only know what the aviation training books say, I’m no aviation engineer.

I’ll keep in the green, especially since my plane can’t hit yellow except pointed down.

 

[midwestpa24]

The bottom of the yellow arc is Vno, the max speed at which a 50 ft/sec vertical gust will not exceed the g-limits of the airplane. As such, my willingness to cruise in the yellow is based on turbulence intensity more than frequency.

Vno is typically higher than maneuver speed, so being below the yellow arc is no assurance that aggressive maneuvering will cause a stall before an overstress. It's purely a function of response to a spec vertical gust.

Nauga,
who can hear the oilcanning

Ding ding ding! Nauga has the correct answer. The yellow arc has nothing to do with maneuvering speed.

There are some aircraft that actually cruise in the yellow arc. Once you get into turbines the yellow arc disappears altogether and all you have is the red barber pole.

 

[MauleSkinner]

Once you get into turbines the yellow arc disappears altogether and all you have is the red barber pole.

Just to make an apples-to-apples comparison, a quick search for v-speeds shows a piston engine A-36 has a Vno of 167, with the yellow arc extending up to a Vne of 205. The turbine conversion has a Vmo of 171 (no yellow arc).

 

[dmspilot]

Ding ding ding! Nauga has the correct answer. The yellow arc has nothing to do with maneuvering speed.

There are some aircraft that actually cruise in the yellow arc. Once you get into turbines the yellow arc disappears altogether and all you have is the red barber pole.

The barber pole (VMO/MMO) is analogous to the bottom of the yellow arc, not the top (ref. old 14 CFR 23.1505). It should not be a common practice to cruise beyond the maximum structural cruising speed.

 

[Bill]

my willingness to cruise in the yellow is based on turbulence intensity more than frequency.

That's a good call. My Mooney cruises at 155, which is comfortably in the green (yellow starts at 176), but in smooth air I leave cruise power set on the initial descent, which results in a speed of about 185kts at 500fpm down. That's nicely in the yellow (redline is 198), and I just monitor for turb. Light turb or bobbling doesn't bother me, it's the sharp thumps that do. At the first sharp thump, power comes off and we slow down and get back into the green.

Once I was in the yellow and it was perfectly smooth, and then the sharp thumps came in rapid succession. Power to idle, gentle pitch up, and I converted speed into altitude, using speed to climb about 1000ft, both getting me above the thumps and dumping speed. Once speed was down near Va I began the descent again, and good thing. The whole ride down that day, including the pattern, was a paint mixer.

 

[Jim K]

In my c model Mooney I learned to fly nearly all the time in the yellow arc. That’s one reason I tend to hop up above the cloud layer whenever possible.

The lance is the same way. If I stayed out of the yellow I'd cruise at 55% power, so I look for the smooth air, which is usually just above the cloud layer. Another reason the instrument rating is so useful, and why I usually file if I'm going more than about 30min away.

To answer your question, Nauga nailed it. It's more about the intensity than the frequency. You'll know it when you feel it. Imagine setting a glass of water on the floor.... will it spill? If not you're probably fine.

Jim,
Who's not an aeronautical engineer, and sometimes has nightmares about the wing falling off his piper.

 

[steingar]

Descent is always problematic for me, Mooney will go down or slow down, but it won't do both. I'm always in the yellow in descent, often in cruise too. I actually don't worry about it that much, Mooneys are stout. I do my best to keep the speed down.

 

[Clip4]

I know that the yellow arc is for smooth air but what about when you run into occasional bumps or rough air. Is there a time frame (5 seconds, 15 seconds, 30 sec, 1 min?) of rough air that you would accept before lowering your airspeed or would you immediately reduce throttle?

Also, what about the descent, if you plan a slow descent (let’s say a couple hundred few per minute) controlled by the trim would you still keep your speed up provided it doesn’t approach the red arc or is this a no go?

If you are descending in the yellow and experience turbulence, you should immediately reduce throttle and increase pitch to slow to Vno.

 

[nauga]

I'm always in the yellow in descent, often in cruise too. I actually don't worry about it that much, Mooneys are stout.

That's not how Vno works. The yellow arc is defined as the speed where a 50 ft/sec vertical gust will cause the airplane to exceed that 'stoutness'. Your airplane is probably a CAR 3 cert basis but I don't believe that makes a difference in this case.
Maybe yours has a lot of extra structural margin built in but that's uncommon when designers are chasing performance.

Nauga,
and his gust load alleviation system

 

[Mtns2Skies]

The wing, at least in 'slow piston planes' doesn't know how fast it's going, what it knows is how many Gs are pushing on it. Your maneuvering speed will stall the wing before you break it, but as you go faster you may not hit that critical AoA before the wing breaks, the yellow arc is a buffer for that.

That would only be for a failure in the "Z" direction. The wing absolutely knows how fast it's going for failure along the longitudinal axis.

 

[Tantalum]

How many of us have been cruising along, smooth air, then out of nowhere, BAM! some turbulence.

This has never happened to me, at least never out of nowhere and no real 'BAM!' - my big jolts were always flying near mountains or I had some other clue I might get jolted, winds aloft, clouds, PIREPs, usually you will have some clue that things are about to get rough

That would only be for a failure in the "Z" direction. The wing absolutely knows how fast it's going for failure along the longitudinal axis.

My (limited) understanding is that should you pass Vne your biggest risk (assuming 1G smooth flight) is flutter, though I see your point

sometimes has nightmares about the wing falling off his piper

..speaking of, I love Pipers but always felt the PA-28 attach points looked 'underwhelming' .. they had one in pieces at the airport I learned to fly at and it was impressive how 'thin' that tab on the bottom is. Certainly seemed different than the 210 I saw with it's wings off and the Aerostar that had the panels open and its huge wing attach bolts. But I trust the engineers know what they're doing. It's entirely more likely I'll die flying because of something stupid I did than the wing snapping off

 

[steingar]

That's not how Vno works. The yellow arc is defined as the speed where a 50 ft/sec vertical gust will cause the airplane to exceed that 'stoutness'. Your airplane is probably a CAR 3 cert basis but I don't believe that makes a difference in this case.
Maybe yours has a lot of extra structural margin built in but that's uncommon when designers are chasing performance.

Nauga,
and his gust load alleviation system

More modern Mooneys moved up all the speeds, but they're largely built the same way as mine. I think it's just paperwork. Later engineers learned just how strong their airplane was.

 

[EdFred]

Descent is always problematic for me, Mooney will go down or slow down, but it won't do both. I'm always in the yellow in descent, often in cruise too. I actually don't worry about it that much, Mooneys are stout. I do my best to keep the speed down.

Slips man, slips. Can come down fast vertically and slow horizontally (relatively speaking). Stalls and spins are also an option.

 

[Tantalum]

Mooneys have had inflight breakups, and while those seem to have occurred outside typical operating envelope I'd say it's foolhardy to ignore Vno and what engineers at the time published. 'My stout plane can handle it' might work until some day it doesn't. Remember fatigue is accumulative and it's not just wing spars.. as I understand it most breakups happen near the tail, for Mooney, and other planes. The yellow arc should be understood, and respected.

 

[Bill]

Slips man, slips. Can come down fast vertically and slow horizontally (relatively speaking). Stalls and spins are also an option.

Even though the plane is slick, put the gear and flaps out, pull it to idle, pitch for 60-65kts, and it will come down pretty fast. I've experimented by flying pattern altitude until rolling out of the base/final turn and it still makes the runway easily.

 

[mandm]

How many of us have been cruising along, smooth air, then out of nowhere, BAM! some turbulence. Not flip you over or knock you senseless, but enough to get your attention, looking for whose wake turbulence you just smelled? Now what would have happened if you were flying above Vno (in the yellow)?

I’m not suggesting that one should fly so fearful of the yellow, but I can’t see when I’m going to cross a ditch or speed bump in the sky. Maybe one bump won’t kill ya or hurt the plane. Or maybe it will? I only know what the aviation training books say, I’m no aviation engineer.

I’ll keep in the green, especially since my plane can’t hit yellow except pointed down.

This is my thinking about the occasional bump in the sky. And I spent time getting the trim setting, power setting, RPM setting and mixture just perfect. A sudden bump and I should reduce throttle? Or can it handle like 5-10 seconds, then evaluate if it’s a sudden burst or the current condition that is likely to be ongoing (then reduce throttle). I don’t want to over stress the plane, I read the POH and didn’t see any mention with regards to this.

 

[MauleSkinner]

This is my thinking about the occasional bump in the sky. And I spent time getting the trim setting, power setting, RPM setting and mixture just perfect. A sudden bump and I should reduce throttle? Or can it handle like 5-10 seconds, then evaluate if it’s a sudden burst or the current condition that is likely to be ongoing (then reduce throttle). I don’t want to over stress the plane, I read the POH and didn’t see any mention with regards to this.

Obviously the first sudden bump wasn’t a vertical gust in excess of 50 ft/sec because t didn’t bend or break the airplane. And as long as none of the other ones are less than 50 ft/sec, it can handle 5-10 seconds of it (or more). Problem is, it’s pretty tough to evaluate bumps you haven’t hit yet.

It’s not mentioned in the POH because Vno has a standard definition. The POH just tells you what that speed is for your airplane.

 

[mandm]

Obviously the first sudden bump wasn’t a vertical gust in excess of 50 ft/sec, and as long as none of the other ones are, it can handle 5-10 seconds of it (or more). Problem is, it’s pretty tough to evaluate bumps you haven’t hit yet.

It’s not mentioned in the POH because Vno has a standard definition. The POH just tells you what that speed is for your airplane.

The turbulence I’m talking about is getting gusted around (more left to right and unstable and yes your drink would spill if on any surface) due to lake effect, yes I guess I should have been aware of this approaching a huge lake. But it’s not the loss of gravity feeling that I’ve felt previously in another airplane at slower green arc speeds.

I’m also thinking the yellow arc on the airspeed indicator and Vno-Vne numbers in the POH are not matching up. I’ll need to look into this more to fully understand. According to the POH, I never exceeded the Vno but I was in the yellow arc as I recall.

 

[MauleSkinner]

I’m also thinking the yellow arc on the airspeed indicator and Vno-Vne numbers in the POH are not matching up. I’ll need to look into this more to fully understand. According to the POH, I never exceeded the Vno but I was in the yellow arc as I recall.

Depending upon the age of your airplane, the markings on the indicator could be in CAS instead of IAS.

 

[mandm]

Depending upon the age of your airplane, the markings on the indicator could be in CAS instead of IAS.

Sounds like you have the right idea. See POH speeds and Airspeed indicator images below. The yellow arc on the Airspeed indicator is 140-170mph whereas the POH Vno is 170mph and Vne is 214mph. The white arc however goes up to 115mph but the POH says 125mph. Gear extension of 125 & 150mph in POH and placards are the same.

 

[geezer]

The item being missed here is wake turbulence from a heavy plane that is no longer in sight.

I have experience this twice, once in each front seat. Both times, seat belt firmly secured. Both times all on bo0ard literally hit the overhead, hard.

The incidents lasted less than one second.

If we had been up in the yellow arc, the structural strength might have been terminally tested. Or not.
At 10,000 feet in a Piper Cherokee, if the test was a failure, the opportunity to regret the extra airspeed would have been uncomfortably long.

Others above have hinted at this in saying that you cannot see the bumps ahead, as you would in a car, but they can be quite violent.

Flying, the best lessons are from someone else's adventures

 

[Tantalum]

The item being missed here is wake turbulence from a heavy plane that is no longer in sight.

I have experience this twice, once in each front seat. Both times, seat belt firmly secured. Both times all on bo0ard literally hit the overhead, hard.

The incidents lasted less than one second.

If we had been up in the yellow arc, the structural strength might have been terminally tested. Or not.
At 10,000 feet in a Piper Cherokee, if the test was a failure, the opportunity to regret the extra airspeed would have been uncomfortably long.

Others above have hinted at this in saying that you cannot see the bumps ahead, as you would in a car, but they can be quite violent.

Flying, the best lessons are from someone else's adventures

Were you cruising along VFR not talking to anyone or were you on FF, or better yet, IFR? Curious if you were getting traffic or wake advisories

 

[nauga]

My (limited) understanding is that should you pass Vne your biggest risk (assuming 1G smooth flight) is flutter, though I see your point

Maybe, maybe not. Most airplanes I have enough detail on to know are limited by flutter margin, but not all. The limiting factor is something you should know if you ever consider exceeding Vne. For my airplane it's flutter, and has been tested flutter-free.

Nauga,
and a facefull of windscreen

 

[N1120A]

Mooneys have had inflight breakups..

I'm pretty sure the only ones have been mid airs or flying into massive thunderstorms.

 

[MauleSkinner]

Sounds like you have the right idea. See POH speeds and Airspeed indicator images below. The yellow arc on the Airspeed indicator is 140-170mph whereas the POH Vno is 170mph and Vne is 214mph. The white arc however goes up to 115mph but the POH says 125mph. Gear extension of 125 & 150mph in POH and placards are the same.

View attachment 103652
View attachment 103651

No, there’s something else wrong there. There’s not going to be 34 mph difference between CAS and IAS.

 

[mandm]

No, there’s something else wrong there. There’s not going to be 34 mph difference between CAS and IAS.

So my question is whether 140mph or 170mph is the Vno for light turbulence conditions. The plane flies easily at 160mph.

 

[MauleSkinner]

So my question is whether 140mph or 170mph is the Vno for light turbulence conditions. The plane flies easily at 160mph.

Sounds like you need to get with your mechanic and figure out whether you’ve got the wrong airspeed indicator or the wrong POH…or aren’t looking at the appropriate supplement.

 

[geezer]

"Were you cruising along VFR not talking to anyone or were you on FF, or better yet, IFR? Curious if you were getting traffic or wake advisories"

First time was VFR under a thin layer, near a major airport. Our track was perpendicular to the arrival path of the airliners. In 1970, vortices were poorly understood, and avoidance was random.

The second was much later, IFR flight plan in VFR conditions. There was no warning from ATC. No aircraft were in sight when we were hit, and we only hit one of the pair. We may have been driven down enough to miss the other side of the path, or the other one may have descended at a different rate. That was in the Cherokee.

I have observed the phenomena as the vortices arrive at water level off the south end of DCA, and left and right swirls are often quite different. They often suck water several feet into the air from one, and not the other. They can lay a sailboat well over on her side. Sails have been torn. The official position of DCA on this subject is that sailboats should avoid an obviously dangerous part of the river.

 

[Tantalum]

or flying into massive thunderstorms

in some cases, others it was LOC IMC.. but my point is that if someone gets used to thinking the 'yellow is okay, this plane is stronger than the engineers knew' on nothing other than just a gut feeling, then it may goad someone into pressing on, pushing the plane harder than they ought to..


I have nothing against the yellow arc, planes are for going fast and I love making up lost time on a smooth descent well into the yellow. But, I wouldn't fly my plane assuming it's stronger than what the manufacturer's own engineers published

 

[N1120A]

in some cases, others it was LOC IMC.. but my point is that if someone gets used to thinking the 'yellow is okay, this plane is stronger than the engineers knew' on nothing other than just a gut feeling, then it may goad someone into pressing on, pushing the plane harder than they ought to..


I have nothing against the yellow arc, planes are for going fast and I love making up lost time on a smooth descent well into the yellow. But, I wouldn't fly my plane assuming it's stronger than what the manufacturer's own engineers published

The Aerostar apparently has a true Vne of like 450 KIAS, but they set it up with a yellow arc much lower than that. Some of those settings are liability based. I also keep out of the yellow most of the time, but I also know that there are plenty of airplane/engine combos that cruise in the yellow when flown by the POH (IO550 and TN straight tail Bonanzas come to mind.

 

[Tantalum]

Maybe, maybe not. Most airplanes I have enough detail on to know are limited by flutter margin, but not all. The limiting factor is something you should know if you ever consider exceeding Vne. For my airplane it's flutter, and has been tested flutter-free.

Nauga,
and a facefull of windscreen

Thanks for the insight. These are the considerations that make me less interested in building some day.. even if you're going with an establish kit (Vans, Velocity, Sonex, etc.) I'd imagine you want (need?) to validate certain parameters during the initial testing phase..

 

[Tantalum]

Aerostar

You had me at Aerostar. Although Ted Smith originally built that as a jet, so it may not be a fair example

PS - if you Flightaware the Aerostar jet's tail number (N31TT) it still occasionally flies, not often, most recently Sep of last year.. originally they had dreams of certifying it..

 

[dmspilot]

Sounds like you have the right idea. See POH speeds and Airspeed indicator images below. The yellow arc on the Airspeed indicator is 140-170mph whereas the POH Vno is 170mph and Vne is 214mph. The white arc however goes up to 115mph but the POH says 125mph. Gear extension of 125 & 150mph in POH and placards are the same.

View attachment 103652
View attachment 103651

That is not the correct airspeed indicator for a PA28R-180. I used to fly one, even did my commercial checkride in one. I would have been ecstatic if I could get into the yellow arc in level flight. Sometimes it took a descent just to get to VA.

 

[dmspilot]

Sounds like you have the right idea. See POH speeds and Airspeed indicator images below. The yellow arc on the Airspeed indicator is 140-170mph whereas the POH Vno is 170mph and Vne is 214mph. The white arc however goes up to 115mph but the POH says 125mph. Gear extension of 125 & 150mph in POH and placards are the same.

Your airspeed indicator is meant for a PA28-180, no "R" (Cherokee 180/Challenger/Archer) rather than a PA28R-180 Arrow. Someone made a big oops.