TAS Calc Help.

SixPapaCharlie

SixPapaCharlie

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So in another thread I got some feedback suggesting I calc TAS in my plane. I went up today to practice flying in clouds and decided to get some numbers for calcs.
I can't figure out how to do it using my POH.

2 things going on below

1. Need TAS calc
2. Alt static port giving different readings (not just briefly)

1st. Help me calc TAS (feel free to give me crap about being a PPL and not knowing how to do this. I should fire my former CFI and I am not fit to fly)


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~2450 RPM
Alt: 5500 MSL
Alt. Setting 30.42
IAS: 90 kts

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Other thing I notice is when I go to alt static source, my IAS jumps and stays consistently.
We just had the pitot static system checked so I figure there are no blockages but getting different reading.

Same RPM and Alt but IAS now showing 102

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Thanks in advance!
 

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FWIW, I haven't had a single reason to convert to TAS as of yet, but I also don't own my own plane. I know, this post doesn't help u any, sorry.
 
It looks like 6PC has a TAS indicator - set the pressure altitude on the OAT and read the TAS directly...
 
No math required
 

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Your TAS indicator on your plane is indicating correctly. You need to reference your book to see what a normal TAS is at that altitude. I seriously doubt at that altitude, temp and rpm that you'd only get around 100 KTAS. I'd say the picture of the 113 KTAS is the correct number.
 
eman1200 said:
FWIW, I haven't had a single reason to convert to TAS as of yet, but I also don't own my own plane. I know, this post doesn't help u any, sorry.
Click to expand...

What does not owning your own airplane have to do with needing to know how to determine true airspeed?

:dunno:

Mike
 
SixPapaCharlie said:
Page 86 and 87
http://www.davinciflightschool.com/wp-content/uploads/Tb9pim.pdf

It shows pressure alt in 2000, 4000, 6000
Shouldn't that be density altitude?

I wish my POH had the cessna style charts that were all over the written exam.
Click to expand...

No PA is correct. That's why you put PA outside of the OAT on your ASI. That's basically determining DA (minus humidity). Now that I look at your flight manual, your 90 KIAS and 100 KTAS appears to be accurate. I thought TB-9s were faster than that.
 
Velocity173 said:
No PA is correct. That's why you put PA outside of the OAT on your ASI. That's basically determining DA (minus humidity). Now that I look at your flight manual, your 90 KIAS and 100 KTAS appears to be accurate. I thought TB-9s were faster than that.
Click to expand...

Nah, they are slow.
Thats how they get you to but TB 10s and 20s
 
SixPapaCharlie said:
Nah, they are slow.
Thats how they get you to but TB 10s and 20s
Click to expand...

OK. I used to have an AA-5 Traveler. She did about 115 KTAS. I just figured you were around that speed. I imagine interior dimensions are larger on the TB-9 though.
 
MikeELP said:
What does not owning your own airplane have to do with needing to know how to determine true airspeed?

:dunno:

Mike
Click to expand...

I didn't say anything about "not needing to know how to convert", I said I haven't had any use for calculating/using TAS. I rent different planes that are all in the 100kias range and so far my trips have been under 200nm. Whenever I take these trips, I plan using projected ground speed, and monitor ground speed in flight. I have never found a use for TAS as of yet. I would think if I owned and was going on longer trips, flying higher, this information would be helpful.
 
Nobody mentioned your Alternate Static Port giving different readings. This is normal. The ambient air pressure in the cockpit is not equal to the static pressure outside, and this difference shows on your ASI. In an emergency situation when you need to use the alternate static port, close in this case is good enough....
 
eman1200 said:
I didn't say anything about "not needing to know how to convert", I said I haven't had any use for calculating/using TAS. I rent different planes that are all in the 100kias range and so far my trips have been under 200nm. Whenever I take these trips, I plan using projected ground speed, and monitor ground speed in flight. I have never found a use for TAS as of yet. I would think if I owned and was going on longer trips, flying higher, this information would be helpful.
Click to expand...

I believe you, but find that odd.

Both learning to do a navigation log and later teaching it, TAS was paramount. Or at least the foundation for every wind triangle and GS calculation.

In flight, one of the first things on leveling off in cruise would be to confirm TAS was about correct. If not, think flaps or cowl flaps or something amiss.

And, as you said, flying above 10,000' there's a much larger discrepancy between IAS and TAS.

Anyway, modern avionics makes obtaining TAS straightforward, as does the TAS airspeed indicator. Garmin portables have an E6B page that will compute it as well. And of course there's the trusty "real" E6B - if you remember those!

Mine gets shown on my Dynon once I input OAT and altimeter setting, and that becomes my primary source for "how fast I'm going", though of course ATC is only interested in indicated airspeed if they ask for or assign and airspeed.

You've shown its not 100% necessary, I guess, but I still hold its an important and fundamental thing to know - unless you're just puddle jumping down low!
 
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Personally.... GS is more important then IAS. CAS or TAS..... I want to know how long till the waypoint or destination.... and fuel needed to get there..:yes:
 
N801BH said:
Personally.... GS is more important then IAS. CAS or TAS..... I want to know how long till the waypoint or destination.... and fuel needed to get there..:yes:
Click to expand...

No argument there. But how do you accurately determine your ground speed unless you know your true airspeed?

:confused:

Mike
 
MikeELP said:
You're right, Eddie. :D

My bad....I guess the question I should have asked was "how do you PLAN your groundspeed?"


Mike
Click to expand...

Flight planning is almost the only reason for knowing TAS. Everything in flight is based on ground speed unless you feel the need to calculate actual winds aloft.

If you want to have an accurate flight planning speed, you need to compare actual TAS with what the book predicts, so you'll have an idea how to apply the book numbers to subsequent flights.
 
I still like the idea of computing TAS one way or another when setting up for cruise.

1) It tells you if your performance charts were accurate.

2) It can be the first indication of something subtly wrong with the engine or airframe.

Anyway, my students had to do it. Can't say how many still do. But in both my Cirrus before and my Sky Arrow now I have easy access to a TAS display, and in cruise it's what I watch - along with groundspeed, of course.
 
Your E6B has a true airspeed function on it:
http://www.banyanpilotshop.net/products/JS514105.jpg

"Set air temperature over pressure altitude. Read TAS over CAS and density altitude in window."

Your fancy airspeed indicator has the same thing in it.

You only need the POH to go from IAS to CAS.

However it is not uncommon for the calibration of the airspeed indicator to be several knots off especially in cruise at higher altitudes. If you want an accurate reading, use the 3-way GPS method: http://www.csgnetwork.com/tasgpscalc.html
 
You definitely do need to know your TAS for every flight, or you'd be missing information that could prove vital. There could be an engine issue where the power output is sub-normal, and if there is no associated roughness or temperature deviations, you might not realize it. There could be an aerodynamic issue, e.g cowl flaps not properly closed, gear not properly retracted, or some other unexpected drag (or loss of drag if something fell off) that you'd really want to know about. So unless you know your TAS and compare it to the expected value, you'd be blind to the above. Ground speed is nice, but it's not good enough, since the wind is not accurately known.
Since TAS is easy to determine, it is incumbent to find and verify it once you settle into cruise flight. It is a very basic and useful "bottom line" health check of your machine.
 
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I can't believe you put your PoA screen name on your panel. That's just wierd.

:)
 
I use TAS on every XC flight. If I'm not getting my normal numbers, then I know something is amiss or different.
 
At 5500 msl, TAS = IAS + 11% = 90 + 9.9 = 100 knots.

Or set the IAS wheel on your Airspeed indicator. Note that using Alt Static that airspeed will read different due to different pressure.
 
Your TAS was 104.

Covert your indicated alt to PA. Use PA in the TAS calc.

You do realize that you can calculate in on your airspeed indicator, right?
 
Cpt_Kirk said:
You do realize that you can calculate in on your airspeed indicator, right?
Click to expand...

I know it can do that but I never sat down and figured out how to use it.
It is not intuitive. It is probably in a book and I do not read while I fly :)
 
RotorDude said:
You definitely do need to know your TAS for every flight, or you'd be missing information that could prove vital. There could be an engine issue where the power output is sub-normal, and if there is no associated roughness or temperature deviations, you might not realize it. There could be an aerodynamic issue, e.g cowl flaps not properly closed, gear not properly retracted, or some other unexpected drag (or loss of drag if something fell off) that you'd really want to know about. So unless you know your TAS and compare it to the expected value, you'd be blind to the above. Ground speed is nice, but it's not good enough, since the wind is not accurately known.
Since TAS is easy to determine, it is incumbent to find and verify it once you settle into cruise flight. It is a very basic and useful "bottom line" health check of your machine.
Click to expand...

But wouldn't indicated airspeed show a discrepancy in those cases as well?

The C-172C I often fly indicates ~110 mph at normal cruise setting under 3000 feet msl. If there's a power or aerodynamic issue it would indicate slower. No need to calculate TAS to see there's an issue, correct? What am I missing?

(I can calculate TAS on my E6B and my iPad just for the record.)

John


Sent from my iPad using Tapatalk HD
 
Often traveling, I fly at a variety of altitudes, mostly 7500-10,000 but sometimes 4000 or 11,000. With different power settings to stay around 70% power! IAS varies right along with TAS. But I can do 2% per 1000' in my head and compare against the chart. That way I know that everything is hunky dory.

Groundspeed is what gets me to my destination, and determines fuel requirements for the trip, though.
 
Clark1961 said:
It looks like 6PC has a TAS indicator - set the pressure altitude on the OAT and read the TAS directly...
Click to expand...
This post seems to have fallen on deaf ears...
Bryan, just turn the knob to get TAS! :D

BTW, where is the alternate static source knob? I wonder if the PC plane have it and the ER ones don't?
 
Kiddo's Driver said:
This post seems to have fallen on deaf ears...
Bryan, just turn the knob to get TAS! :D

BTW, where is the alternate static source knob? I wonder if the PC plane have it and the ER ones don't?
Click to expand...


I don't know how to turn it / how to use it.

So the alt static source is behind your keys.
It is a small knob just under the (on my plane) ignition

Pull it out when you need an extra speed boost!! :)

And if you just busted Bravo, push it back in real quick.
 
I'll look at mine later this week to see if I have the Alternate Static knob.

Ok, you line up the pressure altitude you are flying at with the outside air temperature. (Top of the AS indicator). The knob is on the bottom right of the airspeed indicator. Once that is done you see where the airspeed needle is pointing. Use the numbers in the window on the bottom of the AS indicator.

In your top photo +10 C is lined up with 5,500 feet. Your Air Speed needle is pointed at 90 IAS, but if you look in the window at the bottom the needle is pointed at 100 TAS.
 
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SixPapaCharlie said:
I know it can do that but I never sat down and figured out how to use it.
It is not intuitive. It is probably in a book and I do not read while I fly :)
Click to expand...

Your airspeed indicator has a built in true airspeed calculator.

Step by step how to get TAS in your plane while flying with no math.

1) set your altimeter to 29.92 as you are flying along straight and level. Read the indicated altitude. That is your Pressure Altitude (PA).

2) look at your thermometer and read the outside temperature.

3) on your airspeed indicator, there is a little ring on the outside of the airspeed indicator that you can rotate back and forth. (It looks like it is controlled by that little knob.) At the top of the air speed indicator you can line the temperature up with your pressure altitude. (Do this just like you would on your little E6B true airspeed calculator converter.)

4) read your True Air Speed by looking at where your airspeed needle is on the outside ring that moves (the smaller numbers that are black print on the white background) rather than the bigger numbers inside that remain stationary (the white numbers on the black background).

5) don't forget to return your altimeter setting back to the proper setting based on local conditions.
 
PPC1052 said:
Your airspeed indicator has a built in true airspeed calculator.

Step by step how to get TAS in your plane while flying with no math.

1) set your altimeter to 29.92 as you are flying along straight and level. Read the indicated altitude. That is your Pressure Altitude (PA).

2) look at your thermometer and read the outside temperature.

3) on your airspeed indicator, there is a little ring on the outside of the airspeed indicator that you can rotate back and forth. (It looks like it is controlled by that little knob.) At the top of the air speed indicator you can line the temperature up with your pressure altitude. (Do this just like you would on your little E6B true airspeed calculator converter.)

4) read your True Air Speed by looking at where your airspeed needle is on the outside ring that moves (the smaller numbers that are black print on the white background) rather than the bigger numbers inside that remain stationary (the white numbers on the black background).

5) don't forget to return your altimeter setting back to the proper setting based on local conditions.
Click to expand...

regardless of what 6PC types, he knows all that...note that the pictures show the correct TAS...he's just playing his usual games...
 
Clark1961 said:
regardless of what 6PC types, he knows all that...note that the pictures show the correct TAS...he's just playing his usual games...
Click to expand...


I wish it were true.

Really I know how to calc it on an E6B but I never understood that dial on the ASI

+30 -30 markings on either side were throwing me.
No clue what that was supposed to indicate to me.

Also didn't know I would need to set the alt to 29.92


For real, I have not calculated TAS since my written.

Maybe I am a crappy pilot but I care about Indicated Airspeed when taking off, in the pattern flying downwind and base at 80 and final at 70 and when practicing stalls.

When I am enroute, GS tends to be my focus.

Granted this is a slow plane. If you can go 200 kts you may have more choices of speeds to cruise at and want these calcs. I have not yet found a need. Jesse said I should figure it out as we are selling the plane and I might find that I am under selling it is I am listing typical indicated airspeed.
 
You're doing fine - we all have to learn sometime.

Me, I got to learn the TAS indicator twice since the first time I was taught wrong. Aren't CFI's wonderful.

Anyway, set pressure altitude (outer scale) over the OAT (lower scale -30 to 30) and read TAS under the indicator arm on the outer, moveable scale. Easy-peasy.

The first time I was taught the instructor had me use the difference between the standard temperature and the OAT on the temperature scale. Since the pressure altitude controls, the temperature error was usually not that significant and it took me a long time to fingure out. Since I have an Aspen it really didn't matter.

Anyway, you're doing great in using IAS in the pattern - that'll keep you out of a lot of trouble. It's really important when you fly to high elevation airports.
 
Not addressing any pilot in particular, but...

I would have my students sometimes arrive early so they could just sit in the plane for a while and look around.

The goal was to be able to explain what every switch, knob, placard, marking or display meant.

There's not much there that doesn't have some useful meaning or function.

Also a good springboard for discussion as I'd later point to things and ask about them.

For example...

What does "2 MIN" mean below?

Turn-Coordinator1.jpg


Similarly, what's that little rectangular cutout on the right?

Most of us should know, but students often do not. And everyone is ignorant - only about different things!
 
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