Why do twin piston aircraft not have a barber pole?
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Why do twin piston aircraft not have a barber pole?
Here’s a question:
Why do twin piston aircraft that have service ceilings of 30000ft and VNEs the exceed 230kts IAS not have a barber pole showing MMO on their ASI? They don’t even have an MMO published in their aircraft handbook. (shouldn’t it be 0.48 mach?)
Are they not subject to Mmo restrictions like a turboprop that has similar service ceiling and Vne?
Why do twin piston aircraft that have service ceilings of 30000ft and VNEs the exceed 230kts IAS not have a barber pole showing MMO on their ASI? They don’t even have an MMO published in their aircraft handbook. (shouldn’t it be 0.48 mach?)
Are they not subject to Mmo restrictions like a turboprop that has similar service ceiling and Vne?
Re: Why do twin piston aircraft not have a barber pole?
Maybe they don't have enough power to go that fast?
Re: Why do twin piston aircraft not have a barber pole?
What twin piston can reach 30 000'?
Liberalism itself as a religion where its tenets cannot be proven, but provides a sense of moral rectitude at no real cost.
Re: Why do twin piston aircraft not have a barber pole?
Aerostar 601B for one....
Re: Why do twin piston aircraft not have a barber pole?
https://www.globalair.com/aircraft-for- ... specid=589
https://www.globalair.com/aircraft-for- ... specid=287
601B and P shows at 25 000'.
Do you have a reference for 30 000'?
Liberalism itself as a religion where its tenets cannot be proven, but provides a sense of moral rectitude at no real cost.
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Re: Why do twin piston aircraft not have a barber pole?
A Cessna 414 and Cessna 340 have a service ceiling of Fl300.
But even for twins that have FL250 as their ceiling, wouldn’t their MMO be around 190kts ias? I just find it odd that piston twins make no reference to Mmo. I’m sure you can easily exceed 190kts IAS if you pushed the nose over in a descent from 250, similar to how you would with a pc12 or king air.
But even for twins that have FL250 as their ceiling, wouldn’t their MMO be around 190kts ias? I just find it odd that piston twins make no reference to Mmo. I’m sure you can easily exceed 190kts IAS if you pushed the nose over in a descent from 250, similar to how you would with a pc12 or king air.
Re: Why do twin piston aircraft not have a barber pole?
A Cessna 414 at FL300 has a VNE of 235 KIAS, which is a true airspeed of 371 kts, which is about mach 0.7 at that altitude. Seems to me there is just no danger of getting close to any mach 1 speeds at VNE.Dronepiper wrote: ↑Sat Mar 27, 2021 11:15 pm A Cessna 414 and Cessna 340 have a service ceiling of Fl300.
But even for twins that have FL250 as their ceiling, wouldn’t their MMO be around 190kts ias? I just find it odd that piston twins make no reference to Mmo. I’m sure you can easily exceed 190kts IAS if you pushed the nose over in a descent from 250, similar to how you would with a pc12 or king air.
As an AvCanada discussion grows longer:
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Re: Why do twin piston aircraft not have a barber pole?
That's an informative anecdote but it still doesn't seem to explain the "why." (Or maybe it is that simple, I don't know.) The aircraft I fly will theoretically never reach even close to barber pole in level flight at normal cruising altitudes in the fight levels. But it still has one. There's still the possibility of cruising much lower, in which case it may need to be powered back to stay within barber pole. And there's that pesky descent thing.
I'm not at all familiar with high performance piston twins, and was unaware they do not have a barber pole, but it's an interesting question.
I'm not at all familiar with high performance piston twins, and was unaware they do not have a barber pole, but it's an interesting question.
Re: Why do twin piston aircraft not have a barber pole?
It might be anecdotal, but it seems to make sense. If your Vmo is always higher than your Vne, why would you need to define it as a limitation?shimmydampner wrote: ↑Sun Mar 28, 2021 9:18 am That's an informative anecdote but it still doesn't seem to explain the "why." (Or maybe it is that simple, I don't know.) The aircraft I fly will theoretically never reach even close to barber pole in level flight at normal cruising altitudes in the fight levels. But it still has one. There's still the possibility of cruising much lower, in which case it may need to be powered back to stay within barber pole. And there's that pesky descent thing.
I'm not at all familiar with high performance piston twins, and was unaware they do not have a barber pole, but it's an interesting question.
What's the VNE/VMO of your airplane? And the MMO?
Definitely an interesting question

Since Cessna's were mentioned. If we look at their basic slow(est) jet, the Citation series, then the Vmo is around mach 0.7. At FL250, that's 290kts calibrated. Which piston twin has a Vne that exceeds 290 kts?
Last edited by digits_ on Sun Mar 28, 2021 9:47 am, edited 1 time in total.
As an AvCanada discussion grows longer:
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
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Re: Why do twin piston aircraft not have a barber pole?
From FAR 23.1303
As per para one the barber pole is only required in turbine powered aircraft or,
per para 2, any aircraft capable of greater than Mach .8, which applies to no piston twin I am aware of.
If there is a piston twin that can do Mach .8, I want one !
(e) A speed warning device for—
(1) Turbine engine powered airplanes; and
(2) Other airplanes for whichVmo/MmoandVd/Mdare established under §§23.335(b)(4) and 23.1505(c) ifVmo/Mmois greater than 0.8Vd/Md.
The speed warning device must give effective aural warning (differing distinctively from aural warnings used for other purposes) to the pilots whenever the speed exceedsVmoplus 6 knots orMmo+0.01. The upper limit of the production tolerance for the warning device may not exceed the prescribed warning speed. The lower limit of the warning device must be set to minimize nuisance warning;
As per para one the barber pole is only required in turbine powered aircraft or,
per para 2, any aircraft capable of greater than Mach .8, which applies to no piston twin I am aware of.
If there is a piston twin that can do Mach .8, I want one !
Re: Why do twin piston aircraft not have a barber pole?
Well... there is this one. http://www.aviation-history.com/lockheed/p38.html
But it may be difficult and expensive to find one.
But it may be difficult and expensive to find one.
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Re: Why do twin piston aircraft not have a barber pole?
Then why do PC12s or king airs have a barber pole?!? When I used to fly a pc12 we used to ride barberpole down from the flight levels, and this was way less than Vmo.
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Re: Why do twin piston aircraft not have a barber pole?
Because as I posted above FAR 23.1303 requires itDronepiper wrote: ↑Sun Mar 28, 2021 11:03 am Then why do PC12s or king airs have a barber pole?!? When I used to fly a pc12 we used to ride barberpole down from the flight levels, and this was way less than Vmo.
(e) A speed warning device for—
(1) Turbine engine powered airplanes; and
(2) Other airplanes for whichVmo/MmoandVd/Mdare established under §§23.335(b)(4) and 23.1505(c) ifVmo/Mmois greater than 0.8Vd/Md.
The speed warning device must give effective aural warning (differing distinctively from aural warnings used for other purposes) to the pilots whenever the speed exceedsVmoplus 6 knots orMmo+0.01. The upper limit of the production tolerance for the warning device may not exceed the prescribed warning speed. The lower limit of the warning device must be set to minimize nuisance warning;
Re: Why do twin piston aircraft not have a barber pole?
Metro 2’s don’t even have a barber pole. They do have a VMO limit but you have to do math and reduce your Vne by something like 5kts for every 1000’ over 17000 or something like that.
Re: Why do twin piston aircraft not have a barber pole?
Doesn't that FAR just require a speed warning device? Wouldn't an overspeed indicator based on Vne not satisfy this requirement as well?Big Pistons Forever wrote: ↑Sun Mar 28, 2021 11:08 amBecause as I posted above FAR 23.1303 requires itDronepiper wrote: ↑Sun Mar 28, 2021 11:03 am Then why do PC12s or king airs have a barber pole?!? When I used to fly a pc12 we used to ride barberpole down from the flight levels, and this was way less than Vmo.
(e) A speed warning device for—
(1) Turbine engine powered airplanes; and
(2) Other airplanes for whichVmo/MmoandVd/Mdare established under §§23.335(b)(4) and 23.1505(c) ifVmo/Mmois greater than 0.8Vd/Md.
The speed warning device must give effective aural warning (differing distinctively from aural warnings used for other purposes) to the pilots whenever the speed exceedsVmoplus 6 knots orMmo+0.01. The upper limit of the production tolerance for the warning device may not exceed the prescribed warning speed. The lower limit of the warning device must be set to minimize nuisance warning;
As an AvCanada discussion grows longer:
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
-the probability of 'entitlement' being mentioned, approaches 1
-one will be accused of using bad airmanship
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Re: Why do twin piston aircraft not have a barber pole?
Just saying “because the rules require it” isn’t exactly helpful lol.
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Re: Why do twin piston aircraft not have a barber pole?
The first Merlins were actually twin Beech wings grafted onto a new fuselage and certified under CAR 3. I believe the SW2 were mega grandfathered from the original frankenstine certification which probably did not require a lot of the things more modern designs do. I believe Swerigen was finally forced to recertify the design and hence the SW3 designation. The SW3 has a totally new and different certification and thus had to meet more modern requirements
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Re: Why do twin piston aircraft not have a barber pole?
"Well... there is this one. http://www.aviation-history.com/lockheed/p38.html
But it may be difficult and expensive to find one."
My understanding is the P-38 compressibility issues around M.68. IIRC the Bf109 was able to get to about M.75 or M.78 in a dive. The Spitfire was very slightly lower than the Bf109.
But it may be difficult and expensive to find one."
My understanding is the P-38 compressibility issues around M.68. IIRC the Bf109 was able to get to about M.75 or M.78 in a dive. The Spitfire was very slightly lower than the Bf109.
Re: Why do twin piston aircraft not have a barber pole?
Indeed, but he did say "Twin." 

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Re: Why do twin piston aircraft not have a barber pole?
The reference mentioned the P-38 had compressibility issues at about M.80. In fact it was a problem at about M.68. For comparison, some other contemporary fighters could reach higher mach numbers before encountering the same problem.
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Re: Why do twin piston aircraft not have a barber pole?
You’ll find that a lot of regulations and standards are written based on risk assessment and done so to simplify who they are applicable to.
The number of light piston twins that could inadvertently exceed critical Mach vs the number of turbine aircraft that can do the same are negligible. The risk to the general population from a light twin exceeding Mcrit is even more negligible.
There aren’t that many piston twins to begin with. There aren’t many that are pressurized and have the performance necessary. Most don’t go above 250 because that’s their certified ceiling based on the pressurization system. And the ones that can are rarely flown that high anyways. And then that pilot has to deliberately fly a profile that will take it through critical Mach. 20 degrees nose down on a cold day before the critical Mach exceeds Vne as he descends.
Light piston twins not requiring a barber pole is the same reason they don’t need a CVR/FDR, or TCAS or EGPWS. They could definitely benefit from all of those and some owners have elements of all of those with new avionics and video recordings. But the risk of them not having those simply isn’t as high.
The number of light piston twins that could inadvertently exceed critical Mach vs the number of turbine aircraft that can do the same are negligible. The risk to the general population from a light twin exceeding Mcrit is even more negligible.
There aren’t that many piston twins to begin with. There aren’t many that are pressurized and have the performance necessary. Most don’t go above 250 because that’s their certified ceiling based on the pressurization system. And the ones that can are rarely flown that high anyways. And then that pilot has to deliberately fly a profile that will take it through critical Mach. 20 degrees nose down on a cold day before the critical Mach exceeds Vne as he descends.
Light piston twins not requiring a barber pole is the same reason they don’t need a CVR/FDR, or TCAS or EGPWS. They could definitely benefit from all of those and some owners have elements of all of those with new avionics and video recordings. But the risk of them not having those simply isn’t as high.
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Re: Why do twin piston aircraft not have a barber pole?
I think the reason some planes don't have a "barber pole" is economic and regulatory. There must be other reasons besides critical mach number that an aeroplane has diminishing indicated VMO with increasing altitude. Even the extremely humble DHC-6 has placarded maximum speeds which diminish incrementally with altitude. That placard, effectively, takes the place of a "barber pole" in this simple aircraft. But the reason it's there is the same reason more sophisticated planes have a barber pole. I refuse to believe there is any part of the airflow anywhere on the brick-like DHC-6 that is anywhere close to the speed of sound at any altitude: yet, for some reason, the maximum indicated speed you are allowed to fly in a descent is a lower value starting at about 6,000 feet than it is closer to sea level.
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Re: Why do twin piston aircraft not have a barber pole?
There's limiting factors other than critical mach number. As it's been said, Mcrit isn't really a factor at M0.7 and below. Aerodynamic flutter is a combination of TAS and IAS, and is roughly mid-way between the two. Are manufacturers required to flight test aircraft at all corners of the envelope? Presumably, a test pilot went up to FL250, FL300 or whatever and rode the limit all the way down. Well actually, I assume they rode Vd, the design dive speed, which is 110% of Vne. If the airplane wasn't able to meet that, they'd be forced to lower Vne. One way to do this is decrease Vne at altitude only. The typical "above 13000', reduce Vne by 3kts per 1000'" would do that. Barber pole is merely a needle on the ASI that shows that graphically. Saves the pilots from doing the math in their head.
Re: Why do twin piston aircraft not have a barber pole?
On the 1900 Vmo is there to prevent the tips of the props going too fast. With the exception the the lightning i can't think of a piston twin with props near the size of a 1900. That system is stupid anyway-using altitude as an analogue for temperature and no consideration for actual RPM. I'm pretty sure you could go Vne In the low to mid 20s with the props at 1400 and not have any issues with the props, but I'm not gonna find out. That horn is loud!
Re: Why do twin piston aircraft not have a barber pole?
possibly we should consider the "KISS" philosophy
Black air has no lift - extra fuel has no weight
http://www.blackair.ca
http://www.blackair.ca