Pending new revised Sky Arrow POH, revised Operating Limitations and SB

[Jim Hardin]

As the Doctor says

[MrMorden]

Using indicated or true?

All the V speeds are based upon indicated. That's the only information readily available to the pilot in flight.

Also my understanding is that indicated speeds are a more direct measure of what air pressure in actually on the airframe (e.g. loads) than TAS.

[MrMorden]

I wonder what the reasoning is for different Vne for the Part 23 and ASTM versions of the airplane? If they are built the same, it seems they should have the same speeds. Now if one is built with AN hardware and the other with Harbor Freight nuts and bolts...

[ShawnM]

Now if one is built with AN hardware and the other with Harbor Freight nuts and bolts...

Are you suggesting I shouldn't be using Harbor Freight nuts and bolts?

[CharlieTango]

Using indicated or true?

All the V speeds are based upon indicated. That's the only information readily available to the pilot in flight.

Also my understanding is that indicated speeds are a more direct measure of what air pressure in actually on the airframe (e.g. loads) than TAS.

We encounter this in the Europa, Descending from 16,000' we easily exceed Vne at TAS. I'm told flutter don't care about IAS its about TAS so we slow below Vne indicated.

[CharlieTango]

https://www.flyingmag.com/technique/pro ... ling-lucky



In certified, manufactured airplanes that are not very old and have not been modified or repaired, you are safe at redline speed in smooth air at any altitude below the service ceiling. In uncertified airplanes, more caution is in order; you should shy away from redline speed at high altitude, especially in types of which there have not been many examples flying for many years, and you should not exceed the redline speed at any altitude. That's why it's called the "never-exceed speed." After all, which part of "never" is hard to understand?

[MrMorden]

All the V speeds are based upon indicated. That's the only information readily available to the pilot in flight.

Also my understanding is that indicated speeds are a more direct measure of what air pressure in actually on the airframe (e.g. loads) than TAS.

We encounter this in the Europa, Descending from 16,000' we easily exceed Vne at TAS. I'm told flutter don't care about IAS its about TAS so we slow below Vne indicated.

My CT has a Vne of 145KIAS. It’s easy to exceed 145kt in a descent in TAS yet still be under 145kt IAS. I have assumed this is safe. If I get close to Vne IAS the airplane lets me know with lots of wind noise, and seems not to like that much. I get no such indicators when exceeding Vne TAS, it stays smooth.

I was given to understand V speeds are in IAS because they better represent the actual pressures, and thus loads, on the airframe. After all, the TAS at higher altitudes could be high, which represents the total speed through the airmass, but IAS might be lower, and indicates the actual drag pressure exerted on the airframe.

Am I incorrect there?

[Warmi]

There is an interesting section in the Pipistrel virus sw manual discussing the very topic of vne and tas vs ias.
http://www.flypipistrel.com/manuals/Vir ... 600-R5.pdf

Check out the “How fast is too fast” chapter.

[drseti]

Am I incorrect there?

I can see no flaw in your reasoning.

[CharlieTango]

Also my understanding is that indicated speeds are a more direct measure of what air pressure in actually on the airframe (e.g. loads) than TAS.

We encounter this in the Europa, Descending from 16,000' we easily exceed Vne at TAS. I'm told flutter don't care about IAS its about TAS so we slow below Vne indicated.

My CT has a Vne of 145KIAS. It’s easy to exceed 145kt in a descent in TAS yet still be under 145kt IAS. I have assumed this is safe. If I get close to Vne IAS the airplane lets me know with lots of wind noise, and seems not to like that much. I get no such indicators when exceeding Vne TAS, it stays smooth.

I was given to understand V speeds are in IAS because they better represent the actual pressures, and thus loads, on the airframe. After all, the TAS at higher altitudes could be high, which represents the total speed through the airmass, but IAS might be lower, and indicates the actual drag pressure exerted on the airframe.

Am I incorrect there?

Yes you are, sorry Andy. Flutter is one of 2 things in aviation that happen suddenly with no buildup. There is no warning hence we need a Vne to provide a speed with a safe margin. Many designs base there Vne on flutter but LSA are not subject to conclusive testing so even additional margin is needed.

[CharlieTango]

Am I incorrect there?

I can see no flaw in your reasoning.

Flutter is about harmonics not pressure building on the airframe. Vne at IAS in Part 23 certified aircraft does not provide adequate margin for flutter at all altitudes.


http://www.australianflying.com.au/news ... -explained

https://www.flyingmag.com/technique/pro ... ling-lucky

https://mooneyspace.com/topic/11013-vne ... d-flutter/

http://www.atpforum.eu/forum/technical- ... ion-of-tas

[MrMorden]

We encounter this in the Europa, Descending from 16,000' we easily exceed Vne at TAS. I'm told flutter don't care about IAS its about TAS so we slow below Vne indicated.

My CT has a Vne of 145KIAS. It’s easy to exceed 145kt in a descent in TAS yet still be under 145kt IAS. I have assumed this is safe. If I get close to Vne IAS the airplane lets me know with lots of wind noise, and seems not to like that much. I get no such indicators when exceeding Vne TAS, it stays smooth.

I was given to understand V speeds are in IAS because they better represent the actual pressures, and thus loads, on the airframe. After all, the TAS at higher altitudes could be high, which represents the total speed through the airmass, but IAS might be lower, and indicates the actual drag pressure exerted on the airframe.

Am I incorrect there?

Yes you are, sorry Andy. Flutter is one of 2 things in aviation that happen suddenly with no buildup. There is no warning hence we need a Vne to provide a speed with a safe margin. Many designs base there Vne on flutter but LSA are not subject to conclusive testing so even additional margin is needed.

Well, I have experienced tail flutter in my CT. It does come on quickly, but not instantly. I had time to slow down. BTW this happened at WELL below Vne, and was due to a manufacturing issue in a few CTs and has been corrected.

If the manufacturer gives Vne in IAS, then in my opinion it is incumbent on the manufacturer to be damn sure that the IAS will be below the Vne in TAS for any altitude at which the airplane could be expected to operate.

The Pipestrel manual cited above is a curious artifact. They give the Vne in IAS, then later in the book mention almost in passing that above 13,100ft the Vne number switches over to TAS. Presumably this occurs because at that altitude the correct factor between the two numbers reaches a point where TAS Vne can be reached before Vne in IAS. IMO, this needs to be in bold print next to the Vne number, not buried in the back of the book.

The airplane does not care how fast it’s going, only what the pressures are against the various control surfaces and structures. For example, let’s assume that you could get my CT to 250,000ft, still flying. To keep flying, the airplane would have to be going VERY fast. But the air up that high is so thin, it would exert almost no pressure against the airframe. So even though TAS might be very high, the actual stress on the airframe (including surfaces prone to flutter) would be no higher than in denser air at far lower speeds. (TAS).

As another example, if my airplane was flung through deep space at 10,000 mph, would it ever experience flutter? Of course not, as there is no air pressures against them to cause them to move at all. So as we go deeper into the atmosphere, forces increase at similar TAS. At sea level TAS and IAS are similar, then diverge as we go higher and the discrepency between an airplane’s speed through the airmass and the density of that airmass cause different readings. IAS is a measure of air pressure (or air density at a given speed), and to me seems a more reliable measure of the forces that might threaten an aircraft. Apparent the FAA agrees, as they specify Vne be expressed in IAS for certified aircraft.

I am willing to be proven wrong on any of the above.

[MrMorden]

Am I incorrect there?

I can see no flaw in your reasoning.

Flutter is about harmonics not pressure building on the airframe. Vne at IAS in Part 23 certified aircraft does not provide adequate margin for flutter at all altitudes.


http://www.australianflying.com.au/news ... -explained

https://www.flyingmag.com/technique/pro ... ling-lucky

https://mooneyspace.com/topic/11013-vne ... d-flutter/

http://www.atpforum.eu/forum/technical- ... ion-of-tas

Those articles imdicate that TAS makes more sense at high altitudes, which agrees with Pipestrel. So it might make a difference to you, at your 14,0000ft+ cruise level at the upper limits in descent. To me as a flatlander sport pilot, I think I am safe at 10,000 and below level using IAS exclusively. In fact I know I am — I did a descent on Tuesday from 6500ft under power and hit 154KTAS and 122KIAS with no issue at all.

[CharlieTango]

I can see no flaw in your reasoning.

Flutter is about harmonics not pressure building on the airframe. Vne at IAS in Part 23 certified aircraft does not provide adequate margin for flutter at all altitudes.


http://www.australianflying.com.au/news ... -explained

https://www.flyingmag.com/technique/pro ... ling-lucky

https://mooneyspace.com/topic/11013-vne ... d-flutter/

http://www.atpforum.eu/forum/technical- ... ion-of-tas

Those articles imdicate that TAS makes more sense at high altitudes, which agrees with Pipestrel. So it might make a difference to you, at your 14,0000ft+ cruise level at the upper limits in descent. To me as a flatlander sport pilot, I think I am safe at 10,000 and below level using IAS exclusively. In fact I know I am — I did a descent on Tuesday from 6500ft under power and hit 154KTAS and 122KIAS with no issue at all.

TAS is a major consideration in Vne. Only planes we can't afford have the design and testing to provide a well defined envelope. That would be Vne at IAS up to service ceiling. For most of us we don't have as well a defined limit.

You are picking a number that is lower than IAS to service ceiling but higher than never exceeding at TAS. A feel good fudge with a round number I would call it.

[FastEddieB]

Andy,

If there is a flaw in your reasoning, I think it’s covered in that first link to that Australian site.

In part...

“4. Air density
Thick, dense air damps oscillations and delays the onset of flutter. It’s like oil in the shock-absorbers of your car. Obviously you have direct control over the density of the air in which you fly. High altitudes and hot temps mean less damping and a greater chance of flutter.”

Since you used the reducto ad absurdum of outer space, try the other direction - if you submerged your plane and tried to push it through water, I think you’d see the damping effect of the thicker medium, which would make flutter very unlikely.

Right?