yellow line

[01WJ]

Can anyone explain to me why piston powered airplanes have a yellow operating range on the airspeed indicator and turboprops do not? Also, why do turboprops have a different Vmo for different altitudes?

 

[svcta]

Vmo will decrease in terms of indicated airspeed as altitude increases(and true airspeed increases). This is the case for all aircraft capable of operating at higher altitudes(in the flight levels).

As far as the yellow line on the airspeed...I will assume that it is simply because the heavier, usually more sophisticated aircraft will have a limitation in airspeed regarding turbulence penetration. It is commited to memory and will likely change depending again on altitude.

 

[charter dog]

At speeds up to Vc, (or Vno, the top of the green arc and max structural cruising speed) part 23 requires that vertical gust factors of 50 fps must not cause the design load limit to be exceeded. From there to red line, (the yellow arc) the vertical gust factor slopes linearly down so as to provide for a vertical gust factor of 25 fps at Vd (maximum demonstrated dive speed) on normal, utility and acrobatic category airplanes.

So the top of the green arc and beginning of the yellow arc on the ASI define where gust factor protection of up to 50 fps begins to slope down to at least 25 fps at Vd, or about 115 percent of Vne. This is why operation within the yellow arc is recommended only in smooth air, and with the proviso that full or abrupt control movements not be made while operating within this airspeed range.

Hope that helps.

Best,

 

[svcta]

That was a good post regarding a yellow arc, but had nothing to do with the question asked.

Just to add.....full control movements should not be made above Va(design maneuvering speed), which will change with weight and is often(usually, I think) well below the beginning of the yellow arc(Vno). The "caution range" has nothing to do with Va.

 

[charter dog]

That was a good post regarding a yellow arc, but had nothing to do with the question asked.

Here's the question posed by 01WJ. I answered the first part of the question after you had offered an explanation of the second part of the question. I don't agree that my answer "had nothing to do with the question asked" as you put it. It appears that we just focused our efforts on different aspects of the same question.

Can anyone explain to me why piston powered airplanes have a yellow operating range on the airspeed indicator and turboprops do not?

Just to add.....full control movements should not be made above Va(design maneuvering speed), which will change with weight and is often(usually, I think) well below the beginning of the yellow arc(Vno). The "caution range" has nothing to do with Va.

You are correct that the "caution range" has nothing to do with design maneuvering speed. Also please note that I never said that it did. You are correct that the admonition regarding control movements is normally associated with Va, not Vno. My error for mentioning it. Perhaps I shouldn't have been awake so late! However, since Vno is typically well above Va in most light airplanes, it would be wise to heed the admonition regarding control movements even more so during operations above Vno.

Under part 23 rules, turbine powered airplanes and other airplanes for which Vmo/Mmo has been established in place of Vne do not have a yellow arc depicted on the ASI. Since under these rules, Vmo must occur at an airspeed which will provide for at least the same vertical gust factors as Vno, there is no "caution range" marked on the ASI. Vmo is the maximum indicated airspeed at which the airplane is certified to be flown, except for certification or certain training.

Compressibility effects must be accounted for when establishing the Vmo, so Vmo typically decreases beginning at some altitude (usually between ten and twenty thousand) and decreasing with higher altitudes until either Mmo or the maximum operating altitude is reached.

I hope this assists the original poster in some small way.

Best,

 

[01WJ]

so is that pretty much saying that in piston powered planes anything below yellow line 50 fps gusts must not cause the plane to exceed its design limitations and in the yellow arc 25 fps gusts must not exceed design limitations but in turbine powered aircraft there is no certification allowance for 25 fps gusts and only 50 fps ones so therefore Vmo is the maximum speed at which 50 fps gusts will not cause design load limitations to be exceeded?

 

[svcta]

Charter,

Sorry to sound like a wiener earlier. Here's a question(not rhetorical, I really wonder): Why, then, do some turbine a/c have a tubulence penetration limitation (IAS and/or Mach number) that is well under V/Mmo?