True Airspeed Adjustment on Airspeed Indicator

kontiki

kontiki

Cleared for Takeoff
Joined
May 30, 2011
Messages
1,181
Display Name
Display name:
Kontiki
I've been going back and reviewing some of the material I didn't have time to focus on when I was prepping for my checkrides.

The 172S model I rent has a TAS adjustment on the airspeed indicator.

TAS.gif


The 172M does not.

According to the Info Manual, you use the knob to align press alt with OAT to read TAS on the gague.

None of my flight instructors mentioned it.

Anybody really ever use this?

Not too much unecessary gear on a small airplane, why is it there?

How do you get the most out of it.

Where should it be set if you aren't using it?

Thanks in advance,
 
Last edited:
If it's there I use it. I use it sometimes just for grins. Sometimes I use it to cross check my calculations. Or I might use it much like the stationary needle on a barometer...a reference to show a rising or falling pressure.

If you decide to not use it, simply ignore it. There's not really a place it should be set as a 'default' position.
 
I've used it on small airplanes. In fact that's the way I figured out TAS rather than getting out some other kind of calculator or E6B. It's right there so why not use it? When I wasn't using it I just ignored it.
 
I have never really used it because the one plane I flew most didnt have the option.
 
My instructors used to have us check the TAS periodically on XC flights to to see if we were getting the calculated performance that we had planned for and I guess just to see that we knew how to use them. Pretty easy when you have an OAT in front of you and an Xponder that displays pressure alt.

They were probably a lot more practical before everyone had GPS in their planes. Now that you can instantaneously check your groundspeed at any time, using TAS to verify performance is probably more work than it's worth.
 
OTLK VFR said:
My instructors used to have us check the TAS periodically on XC flights to to see if we were getting the calculated performance that we had planned for and I guess just to see that we knew how to use them. Pretty easy when you have an OAT in front of you and an Xponder that displays pressure alt.

They were probably a lot more practical before everyone had GPS in their planes. Now that you can instantaneously check your groundspeed at any time, using TAS to verify performance is probably more work than it's worth.
Click to expand...

OK, I'll bite. How does knowing your ground speed have any relation to performance?
 
OTLK VFR said:
My instructors used to have us check the TAS periodically on XC flights to to see if we were getting the calculated performance that we had planned for and I guess just to see that we knew how to use them. Pretty easy when you have an OAT in front of you and an Xponder that displays pressure alt.

They were probably a lot more practical before everyone had GPS in their planes. Now that you can instantaneously check your groundspeed at any time, using TAS to verify performance is probably more work than it's worth.
Click to expand...

kgruber said:
OK, I'll bite. How does knowing your ground speed have any relation to performance?
Click to expand...
He probably used the term "performance" with a different meaning than you took it. I'm guessing he meant if the groundspeed is slower then anticipated one might plan an earlier stop for fuel, for example.
 
Richard said:
If you decide to not use it, simply ignore it. There's not really a place it should be set as a 'default' position.
Click to expand...

My Cherokee has one. I use it all the time in cruise. My TAS in the -180 should br right at 140-145mph. It helps me make sure that the plane is performing as expected.
Keep in mind, out here, there is frequently a 30 to 40mph difference betweem IAS and TAS.

Before takeoff and landing phases, I reset the TAS indicator to match IAS. During takeoff and landing, I only care about IAS.
 
I use it, compare TAS to GS and a little mental math for winds aloft comparison to forecast, if my GPS is working, or ForeFlight on the iPad.

I also reset to IAS values for traffic pattern ops.
 
You must log in or register to reply here.
Back
Top