Parts departing aircraft

[Bino]

...
the fake red needle is TAS, the actual needle is IAS.. IAS is what the airplane is experiencing.
...

You have that backwards. 

"TAS is the true speed an aircraft moves through an air mass."  (see http://tailspinstales.blogspot.com/2009/11/vne-ias-tas-and-bvds.html)

Which is why Vne (expressed as IAS) goes down as altitude increases.

[kvuo75]

You have that backwards.  

"TAS is the true speed an aircraft moves through an air mass."  (see http://tailspinstales.blogspot.com/2009/11/vne-ias-tas-and-bvds.html)

Which is why Vne (expressed as IAS) goes down as altitude increases.

I'm not backwards.

I had never heard of Vne going down as alt increased until you posted that. I knew of mach limits (Mmo) which would essentially behave that way.

Is this only common in gliders?

IAS is really all we need to be concerned with in game.


I'm pretty sure thats why every aircraft has an IAS gauge, and the V speeds are reference to IAS, not TAS.

[Bino]

I'm not backwards.

I had never heard of Vne going down as alt increased until you posted that. I knew of mach limits (Mmo) which would essentially behave that way.

Is this only common in gliders?

IAS is really all we need to be concerned with in game.

I'm pretty sure thats why every aircraft has an IAS gauge, and the V speeds are reference to IAS, not TAS.

Sorry, I really don't mean to be rude. But for Vne, you do, in fact, have it backwards:  TAS is relevant, not IAS.  And this applies to all aircraft, powered or not.

Have a look at this PDF from over on the Van's Aircraft site:  http://www.vansaircraft.com/pdf/hp_limts.pdf

"...the airspeed indicator is The Gauge That Lies.  Despite it name, an airspeed indicator does not measure speed.  It measures "q" - dynamic pressure caused by packing air molecules into a tube.  Now, several limiting speeds like stall speed (bottom of the green and white arcs), gust loads (top of the green arc), and maneuvering speed (blue line) are also functions of "q", so they may be read directly off the dial... This logic is NOT true for the very important red line at the top of the yellow arc."

On page 3 of that PDF is a short description of accidentally exceeding Vne in a "very stock 150 hp RV-4" by a gent who writes that he has 1400+ hours in his RV-4 and 3000+ hours in F-16 and other aircraft.

[colmbo]

You have that backwards.  

"TAS is the true speed an aircraft moves through an air mass."  (see http://tailspinstales.blogspot.com/2009/11/vne-ias-tas-and-bvds.html)

Which is why Vne (expressed as IAS) goes down as altitude increases.

Huh?  Vne is IAS and does not change.  IAS is what the airplane "feels".  TAS is IAS corrected for altitude and temperature.

**Edited

Just read the PDF you linked.  First time in 40 years of flying I've heard that.  Interesting, but I'm wondering if there may be some apples/oranges comparisons going on?

[earl1937]

Huh?  Vne is IAS and does not change.  IAS is what the airplane "feels".  TAS is IAS corrected for altitude and temperature.

**Edited

Just read the PDF you linked.  First time in 40 years of flying I've heard that.  Interesting, but I'm wondering if there may be some apples/oranges comparisons going on?

You sir, are CORRECT! TAS is only computed for navigational purposes, i e, to aid in computing ground speed. All forces which act on an aircraft are introduced by airflow passing over the airframe, hence the V speeds are all base on Indicated Air Speed. Example, a VR speed of 90 knots at sea level, barometic pressure 29.92, out side air tempurture 59 degress, with zero wind velocity and zero runway gradiant produces a 7,000 foot roll down the runway. Take the same example and put it at Stapleton Airport in Denver, Col, with same conditions will produce a roll down the runway of say, 8400 feet, but the VR speed will still reflect the same IAS. At Denver, the density altitude will produce the extra runway distance required to reach VR, but again, the VR speed IAS will be same as at sea level. Denver, of course is 5,280 feet above sea level.

[earl1937]

You have that backwards.  

"TAS is the true speed an aircraft moves through an air mass."  (see http://tailspinstales.blogspot.com/2009/11/vne-ias-tas-and-bvds.html)

Which is why Vne (expressed as IAS) goes down as altitude increases.

Don't mean to argue with you sir, but true air speed is useful only in computing aircraft ground speed. Yes, it is a reflection of the aircraft moving through the air mass at altitude because of the less dense air in which it is moving. But, the VNE published for any aircraft is the same at sea level as it is at 30 or 40,000 feet. The difference again is the density altitude at the higher altitude's, but the Vne, IAS speed,  would still be the same. No Pilots Operating Handbook that I have ever studied for certification process in that aircraft, has ever listed Vne of one value at sea level and another at some other altitude. The RED line as indicated on a airspeed indicator does not move as the aircraft gains or loses altitude. Does that answer your question?

[Bino]

Don't mean to argue with you sir, but true air speed is useful only in computing aircraft ground speed. Yes, it is a reflection of the aircraft moving through the air mass at altitude because of the less dense air in which it is moving. But, the VNE published for any aircraft is the same at sea level as it is at 30 or 40,000 feet. The difference again is the density altitude at the higher altitude's, but the Vne, IAS speed,  would still be the same. No Pilots Operating Handbook that I have ever studied for certification process in that aircraft, has ever listed Vne of one value at sea level and another at some other altitude. The RED line as indicated on a airspeed indicator does not move as the aircraft gains or loses altitude. Does that answer your question?

Please read the sidebar on page 3 of this PDF from the Van's Aircraft site:

http://www.vansaircraft.com/pdf/hp_limts.pdf

"...
I know that the RV-4 has a Vne for a reason and now I understand why that limit changes with altitude.
..."

[bustr]

Can civilian light aircraft exceed Vne in level flight at 10k?

A freind of the family owned a Piper PA-24-250. In the 80's he made a hole in a corn feild in Kansas. The radar record showed him level at 10k then porpoising up to 12k then down to 7k and so forth before he went into the corn feild.

The FAA report concluded the stabilator balance weight tube had iced up locking him out of control. But, in 1976 an airworthiness directive had come out concerning longitudinal porpoising to the follow:
----------------
 To prevent possible hazards in flight associated with cracks occurring in the corners of the balance weight cutout of the stabilator balance weight tube assembly, accomplish the following within the next one hundred hours in service from the effective date of this AD unless previously accomplished.
----------------
The family freind had just purcahsed the plane and being quite wealthy and a collector of planes often didnt RTFM. Just hopped in and flew. My father was kept on retainer as his cheif pilot and the gentelman was known to joke with my father that it was my father's job to read the manuals for him. His PA-24-250 never had the service direcitve performed it came out in the investigation becasue the previous owner rairly flew it and kept it in a hanger on his property. The family freind needed to be in L.A. and took off from the previous owners home strip after the money changed hands heading west to his appointment without speaking to my father or his own mechanic.

A few years earlier he did the same thing with a PT19 on take off but, only plowed up a cornfeild with the underside of the aircraft. No one understood why he suddenly bought a corn farm for cash, had all the corn plowed under, and a large temporary barn constructed in the middle of the cornfeild with a new road plowed along side of it untill the FAA wanted to know where he landed the plane right after takeoff. Lots of money can fix some mistakes.

The FAA credited the PA-24-250's porpoising to a known issue with ice build up in the balance weight tube after passing up through 7k. After reading the linked articles and looking at the videos concerning flutter in this post.

Is it possible he exceeded Vne and the assembly failed rather than ice build up in the tube?

[kvuo75]

First time in 40 years of flying I've heard that. 

good, I'm glad I'm not completely insane

[colmbo]

Please read the sidebar on page 3 of this PDF from the Van's Aircraft site:

http://www.vansaircraft.com/pdf/hp_limts.pdf

"...
I know that the RV-4 has a Vne for a reason and now I understand why that limit changes with altitude.
..."

The F-16 pilot didn't have it right....he too confused IAS with TAS regarding Vne.

The PDF addresses flutter problems in the RV aircraft and perhaps in an RV you do need to adjust Vne depending on altitude to compensate for poor flutter prevention in the design.  That doesn't mean it applies to all aircraft.  The FAA certainly doesn't think so.

Doesn't Hitech have an RV?  maybe he can address this?

[shdo]

Bino,

Look at the diagram on page 4 of the PDF you posted.  The first thing to notice is that the horizontal axis is labeled "INDICATED AIRSPEED - V (mph)".  The second thing to notice is the vertical line at the right edge of the white area labeled "NEVER EXCEED SPEED". 

From the diagram you can see that Vne is a constant Indicated Airspeed (IAS).  It does not change with airspeed.

shdo

[Bino]

If it were true that Vne did not change with altitude, then this P-47 training film would not list different "safe diving speeds" (at about 8:15) which vary with altitude:

http://www.youtube.com/watch?v=db0mEXgySeU

So it seems to me that the Republic Aircraft engineers knew about this back in the Forties.

However, in looking around the i-net, I see that there is some debate on ATP forums about whether Vne is related to TAS or IAS, or even that using TAS is merely an approximation. 

[colmbo]

If it were true that Vne did not change with altitude, then this P-47 training film would not list different "safe diving speeds" (at about 8:15) which vary with altitude:

http://www.youtube.com/watch?v=db0mEXgySeU

So it seems to me that the Republic Aircraft engineers knew about this back in the Forties.

However, in looking around the i-net, I see that there is some debate on ATP forums about whether Vne is related to TAS or IAS, or even that using TAS is merely an approximation. 

The safe diving speeds have to do with not exceeding the limiting Mach number.