Aviation-TAS(true airspeed) question

Posted on 2013-06-19
Last Modified: 2013-06-20

I hope that someone can help with the following question. I read the following sentence in an aviation book but need a further explanation why this is:

"In comparison to the true airspeed in still air conditions, the TAS for the best range in a strong tailwind will be slightly lower"

My initial thought was if the wind is behind you would your TAS not be greater? Your groundspeed would be higher as you would have the TAS + windspeed.


Question by:ross13
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
LVL 83

Assisted Solution

by:Dave Baldwin
Dave Baldwin earned 84 total points
ID: 39258656
The statement says 'best range'.  Maybe that's the key.
LVL 37

Assisted Solution

TommySzalapski earned 166 total points
ID: 39259349
"true air speed" is the speed of the craft relative to the air around it. So if you have a tailwind, the wind is moving with you relative to the ground, so your speed relative to the air is going to be slower.

Yes, your ground speed would be TAS + wind speed. So your ground speed would be higher than in still air.
LVL 37

Assisted Solution

TommySzalapski earned 166 total points
ID: 39259395
Also, you are reading an aviation book not a physics textbook so the tailwind most likely isn't pushing you perfectly straight. It would generally be at some angle, so you wouldn't get the full thrust of the wind in the forward direction.

Technically, velocity relative to the ground will be a vector sum of the true air velocity and the wind velocity. Only if the tailwind is 0 degrees relative to the airplane's flight path will a simple TAS + wind speed really work.
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

LVL 27

Assisted Solution

aburr earned 83 total points
ID: 39260271
As baldwin says
the TAS for the best range in a strong tailwind will be slightly lower"
is the key.
"My initial thought was if the wind is behind you would your TAS not be greater?"

Not TAS but ground speed
LVL 27

Assisted Solution

d-glitch earned 83 total points
ID: 39260965
The design of an airplane will be optimized for a particular set of conditions:  load, range, air speed, rate of climb, altitude, ...

There will certainly be a speed that optimizes range (miles per tank of fuel).
If you idle on the runway, you can use up all your fuel in several hours and go nowhere.
Or you can run at full throttle and waste fuel due to nonlinear air resistance.

But if you don't know the function of range to TAS for still air in some detail, I don't see how you can make a such a general statement.

They are making claims about the derivative of a function without knowing anything about the function.  I actually believe they are mistaken.  I would expect fuel consumption and time aloft (and hence range) to depend only on TAS.
LVL 32

Accepted Solution

aleghart earned 84 total points
ID: 39261474
They're not discussing the effect of the wind on your IAS or TAS.  It's how you fly to best effect.

In a headwind, you fly faster to reduce the amount of time the headwind negatively affects your range.

In a tailwind, you fly slower to increase the amount of time the tailwind positively affects your range.

There are rules of thumb saying 1/2 headwind speed added to your V(br) in your POH, adjusted for weight.  And 1/4 tailwind speed subtracted from your V(br).

Somebody did calculation here, showing that rule was close for certain speed ranges.

Author Closing Comment

ID: 39261715
Thanks for the help.

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Where is the math error. 13 74
Graph Function 6 116
Best Graph 2 65
can any US household electrical device/equipment be made to work in asia.. 9 61
We are taking giant steps in technological advances in the field of wireless telephony. At just 10 years since the advent of smartphones, it is crucial to examine the benefits and disadvantages that have been report to us.
This article provides a brief introduction to tissue engineering, the process by which organs can be grown artificially. It covers the problems with organ transplants, the tissue engineering process, and the current successes and problems of the tec…
This is a video describing the growing solar energy use in Utah. This is a topic that greatly interests me and so I decided to produce a video about it.
Although Jacob Bernoulli (1654-1705) has been credited as the creator of "Binomial Distribution Table", Gottfried Leibniz (1646-1716) did his dissertation on the subject in 1666; Leibniz you may recall is the co-inventor of "Calculus" and beat Isaac…

738 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question