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  #1  
Old 10-03-2019, 03:21 PM
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Art_N412SB Art_N412SB is offline
 
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Default Why is VNE TAS in the RV-12

I have looked at a few Type Certificate Data Sheets. Velocity Never Exceed (VNE) is usually listed as an Indicated or Calibrated Airspeed. Why is the Van's RV-12 VNE listed as a True Airspeed?
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  #2  
Old 10-03-2019, 03:38 PM
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To ensure that the airplane has proper flutter margins at higher altitudes.

Awhile back Van's redefined all of the Vne's for their various models from IAS to TAS for that reason. See this Van's document for more info on why:

https://www.vansaircraft.com/faq/hor...epower-engine/

Unfortunately, with the exception of the RV-12 (via POH) and the RV-14/A (via Service Letter), Van's has neglected to publish a Service Letter denoting this important safety-of-flight information change for all their other models.

In fact, Van's still has this erroneous document on their website showing Vne in terms of IAS for their other models:

https://www.vansaircraft.com/faq/air...ings-by-model/

Some sailplanes and high perfomance singles (and others) have their Vne's published as TAS; or IAS up to a certain altitude and TAS above that altitude, or just a decrease in IAS above that altitude. (I'm excluding airplanes where compressibility (Mach effects) becomes a limiting factor.)
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Last edited by RV8JD : 10-03-2019 at 06:01 PM.
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  #3  
Old 10-03-2019, 04:17 PM
bobnoffs bobnoffs is offline
 
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so far this as clear as mud to me. every ias equates to a tas. does the tas number that vans lists now equate to the old ias?
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  #4  
Old 10-03-2019, 04:23 PM
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Quote:
Originally Posted by bobnoffs View Post
so far this as clear as mud to me. every ias equates to a tas. does the tas number that vans lists now equate to the old ias?
As far as I know for the older models, Van's just took the old Vne number in terms of IAS and said they are now TAS.

For example, the old Vne for the RV-7/-8/-10 was 230 MPH IAS/200 KIAS. Now it is 230 MPH TAS/200 KTAS.

Here are tables:



There is still a lot of confusion out there and that's why Van's needs to clarify this critical safety-of-flight information by publishing a Service Letter for the older models stating exactly what they want for Vne's.

But for the RV-12/iS it is all spelled out in the POH, and for the RV-14/A it's in the Service Letter.
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Last edited by RV8JD : 10-03-2019 at 04:49 PM.
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  #5  
Old 10-03-2019, 04:41 PM
Desert Rat Desert Rat is offline
 
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Quote:
Originally Posted by bobnoffs View Post
so far this as clear as mud to me. every ias equates to a tas. does the tas number that vans lists now equate to the old ias?
IAS and TAS don't have a constant a=b relationship. Basically, the higher you go the further they are apart, due to less dense air having fewer molecules of "stuff" going into the pitot tube at a given true airspeed.
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  #6  
Old 10-03-2019, 04:48 PM
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I refer the OP to a post I made a short while ago.

During flight testing, I took our 12 to 15,000'.

At that altitude, the speed scales referenced to TAS, the Vne was lower etc. As I started to descend, the Vne gradually increased back to normal.

Think that this is a combination of Vans and the Dynon Wizards

I was most impressed............

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  #7  
Old 10-03-2019, 04:54 PM
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RV8JD RV8JD is offline
 
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Being able to input Vne in terms of TAS in most modern EFIS' is very helpful. On the Dynon Skyview with a USB drive connected, pressing the 2nd and 7th button simultaneously will give you a nice screen capture. It's great for taking data.

Not an RV-12:

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(Pic 1),(Pic 2)
- Out with the Old, In with the New
(Pic)
RV-8, 1938 Tach Hours (Pic 1),(Pic 2) - Sold

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Rolladen-Schneider LS1-f - No longer owned

Last edited by RV8JD : 10-03-2019 at 05:06 PM.
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  #8  
Old 10-03-2019, 05:16 PM
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Man, you guys are flying high. But you don't need to be very high to see a significant drop in the Vne number.

The POH Vne for the -12 is 136KTAS. Yeah, I know, she's a slow bird compared to the other RV's.


Here at only 2600 feet the Dynon has dynamically changed the bottom of the red zone to 131KIAS. The red line marker at 136K is the Vne TAS at sea level on a standard day (when IAS equals TAS).
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  #9  
Old 10-03-2019, 08:14 PM
NinerBikes NinerBikes is offline
 
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Quote:
Originally Posted by Tony_T View Post
Man, you guys are flying high. But you don't need to be very high to see a significant drop in the Vne number.

The POH Vne for the -12 is 136KTAS. Yeah, I know, she's a slow bird compared to the other RV's.


Here at only 2600 feet the Dynon has dynamically changed the bottom of the red zone to 131KIAS. The red line marker at 136K is the Vne TAS at sea level on a standard day (when IAS equals TAS).
Tony, is this pic on a Skyview D1000 Touch or a HDX model?
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  #10  
Old 10-03-2019, 11:04 PM
rongawer rongawer is offline
 
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Just in keep in mind that Vne for the RV12 is 136 KIAS below 16,000' and 136 KTAS 16,000 and above.

I don't know how many folks are flying their -12's above 16,000, but I'd guess for the vast majority, 136 KIAS is the Vne to be concerned with.
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