What does it mean that an airplane "trues out"?

LongRoadBob

LongRoadBob

Cleared for Takeoff
Joined
Feb 26, 2016
Messages
1,393
Location
Oslo, Norway
Display Name
Display name:
Jacker
In the section on calculating TAS from IAS (CAS) and how TAS increases over CAS as you climb, the book mentions the rough rule-of-thumb of 2% per 1000 ft. for mentally calculating and "for when experienced pilots talk about the speeds at which their aeroplanes (it's Uk English) "true out""

But they never explain a word about what "true out" means.

I know this place is crawling with experienced pilots, so...
 
Fearless Tower said:
I’ve always understood the term ‘trues out’ to mean the true airspeed a particular airplane gets in cruise (vs factory published/advertised speeds)
Click to expand...

Nailed it! I've noticed that the aircraft I fly never "true out" as fast as those airplanes that other pilots own/fly. I must not know how to properly get them on "the step".
 
Last edited:
Fearless Tower said:
I’ve always understood the term ‘trues out’ to mean the true airspeed a particular airplane gets in cruise (vs factory published/advertised speeds)
Click to expand...

Thanks. Maybe a dumb follow up question but then again, it's me...student. Your answer implies a single cruise speed, so just guessing, I'm thinking it is the best speed, TAS (so it is consistent no matter the altitude up to the service ceiling?) that gives best fuel consumption per distance?

The reason I am a little confused is that in the performance charts I see often different cruise speeds, with different power settings (from memory which can be wrong, like 55 %65% 70% ) which made me think there are different cruise speeds. Also that if consumption is the biggest issue, slower flight is more economical, but not very convenient? Am I way off here?
 
LongRoadBob said:
Thanks. Maybe a dumb follow up question but then again, it's me...student. Your answer implies a single cruise speed, so just guessing, I'm thinking it is the best speed, TAS (so it is consistent no matter the altitude up to the service ceiling?) that gives best fuel consumption per distance?

The reason I am a little confused is that in the performance charts I see often different cruise speeds, with different power settings (from memory which can be wrong, like 55 %65% 70% ) which made me think there are different cruise speeds. Also that if consumption is the biggest issue, slower flight is more economical, but not very convenient? Am I way off here?
Click to expand...
Besides all the various other falsifications involved ;) most pilots only tell you what their airplane "trues out" when it's the fastest. That doesn't mean a single cruise speed is available, just that it's the only one they tell you about.

Slower than max cruise will give better fuel economy, but most pilots find that to be too slow for their preference.
 
Really, true out means a plane, unlike a woman say, will not be unfaithful, and usually never let you down. BUT, like a woman (no disrespect ladies & 'Dog), they can be demanding AND expensive.
 
LongRoadBob said:
Thanks. Maybe a dumb follow up question but then again, it's me...student. Your answer implies a single cruise speed, so just guessing, I'm thinking it is the best speed, TAS (so it is consistent no matter the altitude up to the service ceiling?) that gives best fuel consumption per distance?
Click to expand...

Typically would be at the highest power setting recommended by the manufacturer for cruise flight (usually 75% hp) because pilots don't usually go around telling people their plane is slower than it could be otherwise. It's not consistent with altitude so it would be at whatever altitude the pilot usually flies at.
 
Thanks everyone. Still not sure why the words "true out", though at least I got the meaning.
 
The term “trues out” is used to describe the max cruise speed of the aircraft when the owner of said aircraft is lying to his friends about how fast his spam can really goes.


Sent from my iPhone using Tapatalk Pro
 
LongRoadBob said:
Thanks everyone. Still not sure why the words "true out", though at least I got the meaning.
Click to expand...
The "true" is just from "true" airspeed. Not any more complicated than that.

Actually, my definition is a little different than the others, although most similar to @Fearless Tower's.

You mentioned there are multiple power configurations which result in different performance. In complex aircraft, there are also different MP/RPM combinations which will result in similar performance.

To me, "trues out" refers to the true airspeed one gets in the sweet spot - the combination of power settings and altitude which provides the best mix of low vibration, efficiency, and performance at cruise.

Of course, with so many different definitions, I’ve adopted a CFI friend's own term for this: Vh, or "happy speed."
 
true airspeed.....temperature and pressure affect density altitude...the reason for the change.
 
It’s basically aviation speak way of saying what speed does it max out at

For instance in a car one would inquire about top speed “what does it max out at?”

In aviation since we care mainly about TAS in terms of cruise performance since we can’t control wind the term most use is “true out” the max speed at which your plane will cruise true airspeed wise
 
LongRoadBob said:
Thanks. Maybe a dumb follow up question but then again, it's me...student. Your answer implies a single cruise speed, so just guessing, I'm thinking it is the best speed, TAS (so it is consistent no matter the altitude up to the service ceiling?)
Click to expand...

No, for any given power setting, TAS increases with altitude (see below for graphic representation).

The reason I am a little confused is that in the performance charts I see often different cruise speeds, with different power settings (from memory which can be wrong, like 55 %65% 70% ) which made me think there are different cruise speeds.
Click to expand...

Those are typical power settings, though 75% is more common than 70%:

Cruise%20Performance%20Chart%20(True%20Airspeed),%20Langley%20Flying%20School.gif


I think "true out" just implies a true airspeed after accelerating to cruise and stabilizing in level flight at a given altitude and power setting.
 
u got one of these in an plane u fly?

nfiXM.png
 
^^^ holy @#$% that's a large image, sorry
 
If I input OAT into my Dynon D10A, it outputs TAS and DA, which is largely all I use it for.

29035395685_a8ecb5fd88_c.jpg


One can wire in a temp probe, but I never found it worth the effort.
 
JustinD said:
It’s basically aviation speak way of saying what speed does it max out at

For instance in a car one would inquire about top speed “what does it max out at?”

In aviation since we care mainly about TAS in terms of cruise performance since we can’t control wind the term most use is “true out” the max speed at which your plane will cruise true airspeed wise
Click to expand...

Thanks, great answer! Got it!
 
FastEddieB said:
No, for any given power setting, TAS increases with altitude (see below for graphic representation).



Those are typical power settings, though 75% is more common than 70%:

Cruise%20Performance%20Chart%20(True%20Airspeed),%20Langley%20Flying%20School.gif


I think "true out" just implies a true airspeed after accelerating to cruise and stabilizing in level flight at a given altitude and power setting.
Click to expand...

Thanks, I knew that TAS increases with altitude, I thought IAS, but wrote TAS, and now not even sure what point I thought I was making. That IAS is consistent for Vspeeds, etc, where TAS increases. But your points were good and I get it, so thanks!
 
It's probably accurate that when people say a plane "trues out" they are talking about the maximum true airspeed they see.

Although, as eman1200 implied, you can calculate your TAS for any IAS with the "fancy" gauges or your E6B. (the cardboard and metal ones work equally well)
 
You can determine your TAS quite accurately. Turn into the wind until you get the slowest groundspeed (GPS speed). Fly for one minute and write that speed down. Now turn 180 degrees and fly for 1 minute and note that speed. Average the two. Unless the wind changes it is accurate to within 1 or 2 knots.

And no, flying at 4, 90 degree separated headings (E,W,N,S) and averaging does NOT provide a right answer.
 
coloradobluesky said:
You can determine your TAS quite accurately. Turn into the wind until you get the slowest groundspeed (GPS speed). Fly for one minute and write that speed down. Now turn 180 degrees and fly for 1 minute and note that speed. Average the two. Unless the wind changes it is accurate to within 1 or 2 knots.

And no, flying at 4, 90 degree separated headings (E,W,N,S) and averaging does NOT provide a right answer.
Click to expand...
Why not?
 
ktup-flyer said:
As said, throw in your OAT and altitude and you get your TAS. I think this is a more common style....it's what I have anyway.
View attachment 57982
Click to expand...

You madman! That’s way too fast. You’re going to kill someone speeding around like that! Slow down! ;)

d757a50bdfba2b62cf0ae2e3c6b98e08.jpg


(Photo taken at 10,200 in slow flight. I was being lazy and didn’t get it down to the peg.)
 
coloradobluesky said: ↑
You can determine your TAS quite accurately. Turn into the wind until you get the slowest groundspeed (GPS speed). Fly for one minute and write that speed down. Now turn 180 degrees and fly for 1 minute and note that speed. Average the two. Unless the wind changes it is accurate to within 1 or 2 knots.

And no, flying at 4, 90 degree separated headings (E,W,N,S) and averaging does NOT provide a right answer.
Salty said:
Why not?
Click to expand...

For the same reason that crosswind component is .7 at 45 degrees and not .5. The correct answer involves trigonometry (sines, cosines, tangents) and you cant just average the wind and angles arithmetically.
 
The actual speed the airplane flys,not the speed you boast about to your friends,which is always over published book speeds.
 
This post was removed, it was incorrect. coloradobluesky is correct.

Practically speaking however, if wind speed is < 20% of airspeed, it's going to be better than 99% accurate.

For example, TAS of 100, wind speed of 20, it's only off by 1 knot at most.
 
Last edited:
You must log in or register to reply here.
Back
Top