Simple TAS Question

[Olendirk]

Hi!

When I have headwind I need a higher TAS. Well what i dont understand: do I have to FLY a higher TAS or is the tas getting automatically higher when i have headwind?

Thanks!

OD

[Tinstaafl]

er....Don't understand your question. You need a higher TAS in order to achieve what, exactly? It's not clear from your question. Maximum range? A particular groundspeed?

You'll need to elaborate but here's my best guess:


A headwind doesn't change your TAS or IAS. It will affect your groundspeed though. You can choose to fly at a faster IAS which in turn will result in a faster TAS by using a higher power setting. You don't have to though. Usually you accept the reduced groundspeed.

If you're flying for max. range though, you'll need to increase the IAS (and therefore TAS) at which you fly. The reverse happens in a tailwind ie slow down a bit to maximise range.

The best way to think of it is with an example. If your a/c normally achieves max. range at 100kts, and you fly into a 100kt headwind, your range will be zero. You'll run out of fuel before travelling any distance. Increase speed to 120 kts & you'll travel further before the engine stops from lack of fuel.

Conversely in a tailwind it pays to reduce speed. The a/c will have a greater endurance (ie time in the air. The additional time in the air gives the a/c a longer free ride from tailwind. Think of a balloon getting blown along. The longer it stays airborne the further it will travel.

[Dick Whittingham]

Whoa there, boy. You don't need or get a higher TAS except under certain specific conditions. Condition one is that you intend to get max range, max ground miles per lb of fuel used.

This brings in condition 2, that you will start by flying at best range speed, getting best air miles per lb of fuel.

If you hit a head wind you will lose range. No way round that, but you can minimise the range lost by flying a little faster. This means that you will use more fuel, but only a little more, and that can be offset by getting to your destination a little quicker and getting down out of the headwind sooner.

Repeat. This does not give more range than in still air, just not so much range lost in a headwind as if you stuck to best range speed.

Contrarywise, in tailwind, slow down and stay up longer, and you will make the best use of the tailwind in gaining range.

These are marginal effects. It is not worth bothering unless your headwind is about half your TAS or your tailwind about one third your TAS.

Dick W