Barber Pole Question...Pilatus as an example

[deafsound]

This could pertain to other aircraft, like King Air, or TBMs, but here's the question:

Why does an aircraft like the Pilatus, which has a Vmo of 236 and a Mmo of 0.48 need a barber pole, if at these speeds there[FONT=&quot]’[/FONT]s no chance of a transonic shock wave forming on the wing? Is there a legal reason the barber pole exists in this aircraft, or is it something else? Do all aircraft with a Vmo instead of a Vne necessitate the inclusion of a barber pole?

 

[gismo]

This could pertain to other aircraft, like King Air, or TBMs, but here's the question:

Why does an aircraft like the Pilatus, which has a Vmo of 236 and a Mmo of 0.48 need a barber pole, if at these speeds there[FONT=&quot]’[/FONT]s no chance of a transonic shock wave forming on the wing? Is there a legal reason the barber pole exists in this aircraft, or is it something else? Do all aircraft with a Vmo instead of a Vne necessitate the inclusion of a barber pole?

Flutter potential is related to TAS not IAS so an airspeed limit that varies with altitude is needed for a high flyer. Some airplanes like the P-Baron have a scheduled reduction in Vne with altitude instead, but I suspect that current certification requirements specify the barber pole.

 

[poadeleted20]

Without having done the research, I'll bet it's a certification requirement for its type.

 

[deafsound]

Without having done the research, I'll bet it's a certification requirement for its type.

Would you mind doing a little research on this? This is a question that is driving me and my very intelligent CFII mad. Any help would be appreciated. Thanks.

EDIT:
Would you guys mind explaining this so that a PPL would understand? It would be helpful to us hopeful future turbine guys.

Thanks

 

[etsisk]

What's a barber pole? Ok, I know what a barber pole is, but what's an AIRPLANE barber pole?

 

[gprellwitz]

What's a barber pole? Ok, I know what a barber pole is, but what's an AIRPLANE barber pole?

I don't know, but somehow Clinton sitting on the ramp getting a haircut, while funny, probably isn't the answer!

 

[Richard]

/SNIP/

... what's an AIRPLANE barber pole?

Some may say it's a limitation but in actuality it is a goal.

 

[TMetzinger]

For the first half - What is a Barber Pole?:
Rather than have an IAS indicator for low-altitude flight, with a corresponding max indicated airspeed, and then a seperate mach meter for high altitude flight, an alternative single instrument is the "maximum allowable airspeed indicator." It has a movable pointer that indicates the never-exceed speed, which changes with altitude to avoid the onset of transonic shock waves on the wing. The pointer is usually red-and-white striped, and thus known as a "barber pole". As the aircraft climbs to high altitude, such that MMO rather than VMO becomes the limiting speed, the barber pole moves to lower IAS values.

On the other half of the question - My guess is that since the airplane is certified with a Vmo and Mmo, regardless of whether transonic shock waves may actually form, those limit speeds need to be indicated to the pilot, and it's just easier to do that with a single instrument than with a separate IAS and Mach Meter.

 

[Lance F]

I can say that on the Learjet 24/25/35 there is no barber pole. For the 35 e.g. Vmo below 14,000' is 305 kts IAS and above 14,000' it's 359 KTAS. Mmo is 0.83. You can see these three speeds as red lines on the ASI in the middle of this picture. Above those speeds one gets a very loud alarm horn . V speeds and M speeds are on the same ASI as inner and outer scales.

 

[Everskyward]

I can say that on the Learjet 24/25/35 there is no barber pole. For the 35 e.g. Vmo below 14,000' is 305 kts IAS and above 14,000' it's 359 KTAS. Mmo is 0.83. You can see these three speeds as red lines on the ASI in the middle of this picture. Above those speeds one gets a very loud alarm horn . V speeds and M speeds are on the same ASI as inner and outer scales.

There is no barber pole per se, but the inner scale (knots) and the outer scale (mach) rotate relative to each other so that at lower altitudes Vmo is limiting and at higher altutudes Mmo is limiting. The concept of "maximum allowable airspeed" is the same, the display is just a little different.

In the example in your picture, you are at FL270 and you would reach .83 mach before you reached 359 KIAS so Mmo is limiting at that altitude.

 

[TMetzinger]

Lance, it looks to me like somehow the needle will shift from indicating IAS to Mach at some point - is that automagic or do you have to change it? Or (as Mari said), does the outer scale automagically rotate to reflect the relationship between IAS and Mach as altitude changes?

 

[Lance F]

The knot scale is fixed. The M scale (outer scale between approx. 5 and 11 o'clock positions) rotates with altitude as Mari described. But no red and white stripes .

 

[RotorAndWing]

Lance, it looks to me like somehow the needle will shift from indicating IAS to Mach at some point - is that automagic or do you have to change it? Or (as Mari said), does the outer scale automagically rotate to reflect the relationship between IAS and Mach as altitude changes?

It's a function of the air data computer, so no input from the pilot.

 

[TMetzinger]

It's a function of the air data computer, so no input from the pilot.

Ah - so what is that knob/button on the ASI for?

 

[Everskyward]

Ah - so what is that knob/button on the ASI for?

That moves the little triangular pointer which is currently on about 128 KIAS. You use it as a reference for V1 (takeoff), Vref (landing) or actually whatever you want.

 

[TMetzinger]

D'Oh! I've been spending too much time on glass.

 

[Everskyward]

D'Oh! I've been spending too much time on glass.

I have been too, recently, but looking at the Lear panel that Lance posted makes me nostalgic...

Speaking of the panel, why are the nose and right main gear unlock light illuminated? Microswitch problem?

 

[Let'sgoflying!]

Speaking of the panel, why are the nose and right main gear unlock light illuminated? Microswitch problem?

Probably just parallax...we know that ball is really on dead center!

Above those speeds one gets a very loud alarm horn .

I fly with a guy who uses the bp as a goal, not a limitation! I call him the "Pole-Rider"!

 

[Ted]

I have been too, recently, but looking at the Lear panel that Lance posted makes me nostalgic...

That panel looks cool! I want a VSI that does 6000 FPM and an ASI that goes up to 600 kts (or even that 359 kts number)!

Then I want a plane that can do that.

 

[Lance F]

Speaking of the panel, why are the nose and right main gear unlock light illuminated? Microswitch problem?

I knew, just knew, you'd pick up on that . Yes, stuck microswitches. Of course, they've been fixed, but this was the first flight of the plane after sitting too long. Inactivity is BAD for airplanes.

And Ted, I have seen 6,000 fpm up and down on the VSI. However this plane will only do 600 kts once and fortunately we have not experienced that yet. I've also attached the other half of the panel (Note the 1900 pph total fuel flow = 270 gph. Ouch!). Other than the 530W, this is old, old stuff. Someday maybe I'll get to fly glass.

 

[Teller1900]

Some may say it's a limitation but in actuality it is a goal.

Barber Pole's the Goal!

Our Vmo is 248kts from the surface to 13,000, then it goes down above 13k. In the photo below we're level at 16 and the air data computer has calculated the Vmo to be 240kts and moved the barber pole down. We have no input over it, it's just PFM. Anything above the barber pole and it gets loud in the cockpit (think stall horn, but 20X louder and 200X more obnoxious). And in case you're wondering, the 1900 can do better than 180kts, but we were speed restricted for crossing traffic.

 

[TMetzinger]

What's with the red froot loop on the comm panel?

 

[Teller1900]

What's with the red froot loop on the comm panel?

The AM crew messing with us. The guy I was flying with likes Fruit Loops, so that was their gift to him.

 

[Ted]

And Ted, I have seen 6,000 fpm up and down on the VSI. However this plane will only do 600 kts once and fortunately we have not experienced that yet. I've also attached the other half of the panel (Note the 1900 pph total fuel flow = 270 gph. Ouch!). Other than the 530W, this is old, old stuff. Someday maybe I'll get to fly glass.

Alright, I give up, where's the fuel flow? I just don't see it. I know, bad pilot.

And yes, I know the 600 kts is a once-in-an-airframe experience, but hey I'd be happy with a piddly 200 kts! At least, until I got used to it.

 

[tonycondon]

i couldnt find it either ted...

 

[Dave Krall CFII]

Barber Pole's the Goal!

Our Vmo is 248kts from the surface to 13,000, then it goes down above 13k. In the photo below we're level at 16 and the air data computer has calculated the Vmo to be 240kts and moved the barber pole down. We have no input over it, it's just PFM. Anything above the barber pole and it gets loud in the cockpit (think stall horn, but 20X louder and 200X more obnoxious). And in case you're wondering, the 1900 can do better than 180kts, but we were speed restricted for crossing traffic.

That obnoxious sound you describe reminds me of hearing it for a good 20 minutes while a PAX on a 1900 flying quite fast into Reno.

I almost went to the cockpit to ask WT_? but instead asked the pilots while deplaning. They said they didn't know what the noise was. Some other source you can think of?

 

[Teller1900]

Alright, I give up, where's the fuel flow? I just don't see it. I know, bad pilot.

I'd bet it's down below the ITT gauge.

 

[Teller1900]

That obnoxious sound you describe reminds me of hearing it for a good 20 minutes while a PAX on a 1900 flying quite fast into Reno.

I almost went to the cockpit to ask WT_? but instead asked the pilots while deplaning. They said they didn't know what the noise was. Some other source you can think of?

Ha. Umm. Hmm. There's only a couple audibles in the 1900, and they should know them quite well. The stall horn (a loud version of any other stall horn), the gear horn (slightly deeper tone than the stall horn, goes beep-beep-beep at about 2-3 cycles/sec), the overspeed horn (high pitch beeping, very high cycle rate, and very loud), and the altitude alerter -APA (single beep, fairly low pitch). Otherwise, all the other audibles use plain english (TCAS and EGPWS). I honestly can't think of anything else that would make a noise even slightly similar, unless the older models had different orals. The ONLY guess I could make is that, when the APAs start to get old they kind of make funny noises, but it shouldn't be sustained unless the thing is totally f-ed. What carrier were you on?

 

[tonycondon]

perhaps they didnt think you were a pilot and would believe a lame excuse?

 

[Lance F]

i couldnt find it either ted...

Sorry, it's not obvious. (I couldn't figure out a 421 panel I am sure.) It's a round indicator just above the top right of the 530. It has two pointers, one for each engine, and is calibrated at pph x 1,000. The pointers are about on top of each other at 0.9. Therefore 900 pph/engine or 1,800 pph total FF.

 

[tonycondon]

oh duh, i wasnt in multi mode. i was looking for a single indicator pointing to 1800. doh!

 

[Dave Krall CFII]

Ha. Umm. Hmm. There's only a couple audibles in the 1900, and they should know them quite well. The stall horn (a loud version of any other stall horn), the gear horn (slightly deeper tone than the stall horn, goes beep-beep-beep at about 2-3 cycles/sec), the overspeed horn (high pitch beeping, very high cycle rate, and very loud), and the altitude alerter -APA (single beep, fairly low pitch). Otherwise, all the other audibles use plain english (TCAS and EGPWS). I honestly can't think of anything else that would make a noise even slightly similar, unless the older models had different orals. The ONLY guess I could make is that, when the APAs start to get old they kind of make funny noises, but it shouldn't be sustained unless the thing is totally f-ed. What carrier were you on?

I'll try to remember the carrier but can't right now. It sounded most like the overspeed horn that you describe above. It started when they leveled off and I could just feel the plane was really booking, as the 1900 certainly can. It was then absolutly continuous (and this was in the cabin!) until slowing down for the landing.

It's had to imagine they would have voluntarily flown with that noise for 20 minutes, even if premeditated.

 

[Ted]

oh duh, i wasnt in multi mode. i was looking for a single indicator pointing to 1800. doh!

Yeah, I was too! I found it now, though. It's not obvious looking at a picture where I can't read everything the gauges say.

And dang, that's a whole lotta fuel.

 

[Teller1900]

Yeah, I was too! I found it now, though. It's not obvious looking at a picture where I can't read everything the gauges say.

And dang, that's a whole lotta fuel.

That's pretty good economy! That's about equal to or even slightly less than what we burn in cruise in the Q! Of course they're a bit higher than we usually are, but also quite a bit faster!

 

[Ted]

That's pretty good economy! That's about equal to or even slightly less than what we burn in cruise in the Q! Of course they're a bit higher than we usually are, but also quite a bit faster!

Aren't they also smaller than you? I just look at it as a whole lotta fuel because that's still roughly 8-9 times the fuel burn of my biggest engine at full power, full rich. So, maybe 4 times what the biggest twin with my biggest engine burns on takeoff... and that's in cruise!

Obviously, I live in a different world. But it's ok, they like me here.

 

[Geico266]

I don't know, but somehow Clinton sitting on the ramp getting a haircut, while funny, probably isn't the answer!

I like this answer best!

 

[Lance F]

Of course they're a bit higher than we usually are, but also quite a bit faster!

Altitude is everything, isn't it. At FL430 or 450 we're about 1200 pph with a loss of only about 5 ktas. IOW 50% more fuel burn at FL270 with 1-2% loss in airspeed. If you're slugging around in the teens on shorter legs, I am sure you're glad you're not paying for the gas!

 

[Teller1900]

Aren't they also smaller than you? I just look at it as a whole lotta fuel because that's still roughly 8-9 times the fuel burn of my biggest engine at full power, full rich. So, maybe 4 times what the biggest twin with my biggest engine burns on takeoff... and that's in cruise!

You're absolutely right, and that's the joy of Jet-A...all the numbers are much bigger. There's a reason we measure our gas in thousands of pounds.

Obviously, I live in a different world. But it's ok, they like me here.

At least someone somewhere likes you.

 

[Teller1900]

Altitude is everything, isn't it. At FL430 or 450 we're about 1200 pph with a loss of only about 5 ktas. IOW 50% more fuel burn at FL270 with 1-2% loss in airspeed. If you're slugging around in the teens on shorter legs, I am sure you're glad you're not paying for the gas!

Those are pretty incredible numbers, actually! Fortunately with the TP we're a little more consistant across our altitude range, but there is a marked difference between our 900-1100pph at FL250 (our service ceiling because we opted for the cheap O2 system) and our short legs at 9-11k and 1400+pph. Especially when you consider the speed differences (290kts above fl180 vs 245 at <8k). It's amazing how much these turbines love the cold thin air! I can't imagine the kind of acceleration and climb you're gonna be getting in the winter months!

Please just don't use the hand mike while taxiing like the Lear driver no one could understand at EWR today!

 

[Everskyward]

Those are pretty incredible numbers, actually! Fortunately with the TP we're a little more consistant across our altitude range, but there is a marked difference between our 900-1100pph at FL250 (our service ceiling because we opted for the cheap O2 system) and our short legs at 9-11k and 1400+pph. Especially when you consider the speed differences (290kts above fl180 vs 245 at <8k). It's amazing how much these turbines love the cold thin air! I can't imagine the kind of acceleration and climb you're gonna be getting in the winter months!

Since we are comparing barber pole pictures, here is a (really crappy) one of the panel in the Sovereign that I took today. Vmo in this airplane is 305 KIAS and Mmo is .80 mach. Our fuel flow isn't bad either, about 1600 pph at FL410, for an airplane that is quite a bit bigger than a Lear 35.