Bell 430 down N3 Colenso KZN

[jimdavis]

Guys, that's exactly what I am saying: VNE is a function of TAS - NOT IAS as Cage contended. So the pilot needs a chart to tell him what indicated airspeed he must use in order to get that FIXED TAS value. And no it is not semantics - it's aerodynamics.

In the above chart this is quite clear VNE is a fixed figure of 140 knots TRUE Airspeed. I don't know why there are minor tweaks at extreme temperatures.

On a fixed wing aircraft the limiting factor is flutter

On a chopper the limiting factor, according to you guys, is roll - which is quite understandable.

jim

[cage]

- NOT IAS as Cage contended.

We were talking at crossed purposes, I did not contend VNE is determined by IAS.
From a eyeballs and planning perspective we are working with IAS and never give TAS another thought.
Obviously from an aerodynamics perspective it is all based on TAS.

In reality, and most conditions at altitude, we will start running out of power at the corners of the envelope.
The aircraft does let you know it is becoming unhappy, the vibrations in the disc let you know you are moving out of the comfortable zone.

[jimdavis]

- NOT IAS as Cage contended.

We were talking at crossed purposes, I did not contend VNE is determined by IAS.
From a eyeballs and planning perspective we are working with IAS and never give TAS another thought.
Obviously from an aerodynamics perspective it is all based on TAS.

Ha ha, Cage I think we are still at crossed purposes.

1. Surely for flight planning you work on TAS. No?

2. For most aerodynamic purposes one works on IAS. The aircraft feels what the pitot head feels. For instance a fixed wing aircraft always stalls at the same IAS regardless of density altitude.

So, on a fixed wing the IAS of flutter varies with DA, but the IAS of a stall does not. That's why I asked whether it was the same on a chopper (although for a different reason).

jim

[cage]

- NOT IAS as Cage contended.

We were talking at crossed purposes, I did not contend VNE is determined by IAS.
From a eyeballs and planning perspective we are working with IAS and never give TAS another thought.
Obviously from an aerodynamics perspective it is all based on TAS.

Ha ha, Cage I think we are still at crossed purposes.

1. Surely for flight planning you work on TAS. No?

2. For most aerodynamic purposes one works on IAS. The aircraft feels what the pitot head feels. For instance a fixed wing aircraft always stalls at the same IAS regardless of density altitude.

So, on a fixed wing the IAS of flutter varies with DA, but the IAS of a stall does not. That's why I asked whether it was the same on a chopper (although for a different reason).

jim

Obviously, we are indirectly, but being dumb chopper pilots from our perspective it is only IAS. There are no TAS charts in the manual.
Its much like we don’t care about density altitude. You won’t find a helo guy with a DA calculator.
It is already integrated into all our charts and tools, the envelope just gets smaller as temp and pressure alt increases.

[henkhugo]

https://www.timeslive.co.za/news/south- ... obe-finds/

[Arch]

We were talking at crossed purposes, I did not contend VNE is determined by IAS.
From a eyeballs and planning perspective we are working with IAS and never give TAS another thought.
Obviously from an aerodynamics perspective it is all based on TAS.

Ha ha, Cage I think we are still at crossed purposes.

1. Surely for flight planning you work on TAS. No?

2. For most aerodynamic purposes one works on IAS. The aircraft feels what the pitot head feels. For instance a fixed wing aircraft always stalls at the same IAS regardless of density altitude.

So, on a fixed wing the IAS of flutter varies with DA, but the IAS of a stall does not. That's why I asked whether it was the same on a chopper (although for a different reason).

jim

Obviously, we are indirectly, but being dumb chopper pilots from our perspective it is only IAS. There are no TAS charts in the manual.
Its much like we don’t care about density altitude. You won’t find a helo guy with a DA calculator.
It is already integrated into all our charts and tools, the envelope just gets smaller as temp and pressure alt increases.

I thought the original question was about what limits a helicopter's speed, not how that speed is measured. The airfoil doesn't give a hoot for IAS or TAS, it simply stalls at a point, as any airfoil does somewhere between 14 and 16⁰ AOA, and the roll is resultant, not causal, and there are warnings long before a roll would occur. But maybe plank drivers will never get it. There seems to be a tendency to nitpick language use rather than try to understand the concept. How's that for a stick in the wasp nest .

I'm not aware of a single incident where someone I know had rolled a machine by flying too fast. Semantics

[cage]

I'm not aware of a single incident where someone I know had rolled a machine by flying too fast. Semantics

I can only recall a couple of occasions that were reported with the MD500 that were being put through their paces for a services evaluation.
At high speed, after starting a tight turn the aircraft had an un-commanded roll. One was fatal IIRC.
Will have to go dig to find those docs.

[jimdavis]

There seems to be a tendency to nitpick language use rather than try to understand the concept. How's that for a stick in the wasp nest .

Come on Arch - in order to properly understand a concept one has to understand its components. If understanding the difference between IAS and TAS is nitpicking then I am indeed a nitpicker

But I thought the idea here was to play the ball not the man.

jim.

[Peregrine]

I'm not aware of a single incident where someone I know had rolled a machine by flying too fast. Semantics

I can only recall a couple of occasions that were reported with the MD500 that were being put through their paces for a services evaluation.
At high speed, after starting a tight turn the aircraft had an un-commanded roll. One was fatal IIRC.
Will have to go dig to find those docs.

Modern machines should not have a tendency to roll at Vne. Older machines (such as the S55) were prone to attempting to roll upside down. Vne is generally relevant for wings-level flight, and many helicopter FMs limit roll angles at higher speeds because of increased loads and reducing lateral cyclic margins. In the case of the MD500 I suspect that a high speed turn in the critical direction, particularly if there is a degree of skid present, could have led to a an uncontrollable roll. It will be interesting to see what you dig out Cage.

[cage]

In the case of the MD500 I suspect that a high speed turn in the critical direction, particularly if there is a degree of skid present, could have led to a an uncontrollable roll.

From what I recall, you pretty much nailed it.

[Arch]

In the case of the MD500 I suspect that a high speed turn in the critical direction, particularly if there is a degree of skid present, could have led to a an uncontrollable roll.

From what I recall, you pretty much nailed it.

The 105 was prone to a right roll in a high speed turn with not enough left cyclic to roll out. The fix was to smash the left pedal in, or not get into the situation to start with, but it didn't have anything to do with vne. Siggy Hoffman killed himself like that.

[rb]

I asked further up but was lost in the IAS TAS debate .. did this machine have FD and AP

[Arch]

Prelim has some details

[cage]

I asked further up but was lost in the IAS TAS debate .. did this machine have FD and AP

It should by default as they can be flown single pilot IF, not that they were used for that purpose.
No idea if it was operational, it wouldn't be required for VFR.

[rb]

Prelim has some details

Seems to only reference standard navigational and communication as per Type Cert requirements unless I missed it. They talk of FDR but not Flight Director and what seems to be would be a 3-Axis AP which cage you can use under VFR if you need workload absorbed unless I am mistaken. And if it was possibly under AP control what happens if you hit bad turbulence - has been mentioned above by another pilot in a small machine that the air was stable in that area around that time, but out of interest as I believe the system controls the machine in series, and doesnt move the pilot controls accordingly ..like a vehicle speed control.. what would happen if it let go. It apparently makes what long term changes to control position anonly over time due to fuel burn etc so that it hands it back to you close to where you would have it (assumption).

Google c/o "Paul J. Magno" Today’s helicopter autopilots can be three-axis or four-axis systems. A three-axis system provides pitch, roll and yaw axis stabilization around the pilot’s desired attitude and heading reference. In a four-axis system there is also a collective axis, where the autopilot provides collective (i.e., power) control. These systems are considered to be limited authority systems in that for short-term external disturbances, the cyclic control does not change position. For long-term disturbances (i.e., change in CG or fuel burn), the cyclic control is allowed to move to a new position that extends the authority of the autopilot.