Standard Turn Rate indication isn't

[Jeff_R]

The cyan triangles on the attitude indicator, as I understand, indicate a standard rate turn, which is a two-minute turn. I have twice tested this out and when I fly at this bank angle, I find a 360 degree turn takes 1:40, not 2:00. The way I performed the test was to enter the bank and get stabilized, then then note the time when passing through 360 degree mag heading and then noting the time delta after completing a 360 turn, with the aircraft banked throughout. I have performed the test several times and carefully maintain bank angle and altitude.

Am I misreading or otherwise misunderstanding the indicator?

 

[dynonsupport]

You aren't mis-interpreting how this should work.

These angles are based on TAS, so first things first, is your TAS accurate?

Beyond that, this is just physics. Here is an excellent description of the math needed to do this:
http://www.luizmonteiro.com/Article_Bank_Angle_for_Std_Rate_03.aspx

At 100 knots the bank is 15.4 degrees, at 200 knots it's 28.8, and at 300 knots it's 39.5 degrees.

I just tried this on a SkyView with these TAS settings, and the angles match exactly. It worked with the system in MPH or Knots. So SkyView's software appears to be faithfully running the equation correctly.

Finally, were you well coordinated when doing this?

 

[TRCsmith]

Just though I'd take a look at the web site:

"http://www.luizmonteiro.com/Article_Bank_Angle_for_Std_Rate_03.aspx"

I was there for about 4 seconds and I thought my head was about explode! so got out there just in time.  :-X
Caution: if you go there have the mouse ready to go back out of the page.... It was like being in alien world...

 

[trevpond]

http://www.luizmonteiro.com/Article_Bank_Angle_for_Std_Rate_03.aspx

Bet you didn't know you knew all that! Ain't we pilots amazing!!

Regards

Trevor ;D ;D

 

[GHDZ]

You aren't mis-interpreting how this should work.

These angles are based on TAS, so first things first, is your TAS accurate?

Probably not because TAS is based on CAS not IAS. That is why airplanes have IAS to CAS charts. Skyview has no IAS to CAS correction factor capability. So when IAS does not equal CAS, TAS will be off and everything based on an accurate TAS will also be off. There are few aircraft, experimental or certified, where IAS is exactly the same as CAS across the entire flight envelope.

Unless the Skyview owners has done an IAS to CAS flight check, which is not required, they won't know the data displayed numbers are not accurate. Hopefully the information will be close, but still not accurate.

 

[dynonsupport]

IAS and CAS are generally very close unless you are flying at high angles of attack, which I assume is not being done here. One or two knots of error is not going to be detectable.

 

[GHDZ]

IAS and CAS are generally very close unless you are flying at high angles of attack, which I assume is not being done here. One or two knots of error is not going to be detectable.

On some airframes I have seen differences of up to 10kts at certain speeds in the envelope and are significant in TAS calculations. This is more prevalent when an aircraft has a large angle of attack/speed envelope, fast cruise with a slow stall. A lot of "high performance" experimental airplanes have such an envelope.

 

[dynonsupport]

Isn't that what I just said? CAS is often off at high angles of attack, but not by much at cruise. If you have a CAS that is 10 knots off at cruise, your pitot or static is in the wrong place.

So, unless this poster was trying his turns at low speed, it is unlikely that his IAS to CAS error is the issue here. Also note that he made the turns too fast, not too slow, so he was over-banked, which comes from a TAS that is too high, not too low. High IAS is almost always due to bad static, which should be fixed, not covered over with a CAS table that will do nothing to fix your altitude error.

 

[paul330]

Bank angle for a rate 1 turn = first 2 digits of your TAS plus 7 - more or less.  Let's not get too worked up about this - how accurately can you maintain the angle of bank?   :