IAS to TAS ?

[vector at work]

Hi
Anyone know how to convert IAS to TAS at altitudes 5k 10k 15k and 20k?
Thimb rule would be something like 3mph/1000ft, but I'm sure there's more accurate method.

Thanks!

[butch2k]

The most simplified formula i know :
TAS = IAS+((IAS/50)*(ALT/1000ft))

[ 11-23-2001: Message edited by: butch2k ]

[Hammerhead]

Just three curious questions:-
One:-
The indicated airspeed is the airspeed that the aircraft would have at sea-level, right?

Two:-
Did WWII aircraft have some kind of basic linkage between the altimeter and the speedometer? If not then how come AcesHi has two indicators, for TAS and IAS?
(Is that a unreal thing?)

Three:- Which indication is what?

[J_A_B]

"how come AcesHi has two indicators"

To make your life easier.


J_A_B

[Vector]

Originally posted by Hammerhead:
The indicated airspeed is the airspeed that the aircraft would have at sea-level, right?

IAS is speed that's measured by aircraft equipment. Air density decreases as you go higher and thus measured speed is less than TAS (this is due the instruments). So, TAS is speed that aircraft would have at sea level.

EDIT: TAS is speed that aircraft has if measured from sea level.Should aircraft be in sea level, speed would drop due the air density. OMG! Someone please explain this!
 


-vector

--------------------
     
    414 RCAF THE BLACK KNIGHTS
"Totis Viribus-With All Our Might"

[ 11-25-2001: Message edited by: vector ]

[Seeker]

"Just three curious questions:-
One:-
The indicated airspeed is the airspeed that the aircraft would have at sea-level, right?


The indicated airspeed is the airspeed the aircraft "feels". Imagine that you've your hand sticking out the window of your car at 30 mph, and you can feel 10 lbs of force.

Now drive on top of a mountain where the air is thinner, you're doing the same speed, but you feel less force (say 5 lbs) because there's not as much air pushing back on your hand.

This is why we fly to IAS. We don't care how fast we're flying over the ground, we care about how close to the stall speed we are, and what that means is how much air speed the A/C "feels".


Two:-
Did WWII aircraft have some kind of basic linkage between the altimeter and the speedometer?

No, they didn't. When flying, the only time true speed is of importance is for navigation, which isn't a factor in AH. Navigators would compute true speed by simple arithmetic and timing.

If not then how come AcesHi has two indicators, for TAS and IAS?
(Is that a unreal thing?)

It's unreal.

Three:- Which indication is what? "

The needle is IAS and the one you fly to, the red tick is TAS and can be ignored.

[Nomde]

The TAS will always be more than ur IAS.

[Shire_PLH]

Originally posted by Nomde:
The TAS will always be more than ur IAS.

unless you're on the ground  

[Nashwan]

The TAS will always be more than ur IAS.

I don't know about the other planes, but in a Spit IX at high speeds at very low level, the ASI shows higher IAS than TAS, by a few mph.

[Nomde]

Have a look at this PDF file :

PDF File explaining IAS, CAS, EAS, TAS.

[Blue Mako]

TAS and IAS are related to the dynamic air pressure the aircraft is subjected to.  Pressure is related to density so as density reduces with altitude, the dynamic pressure the aircraft "sees" for a given speed is reduced.

Thus the easiest way to explain TAS is that this is the speed the instrument would display (as IAS) if your aircraft was at sea level travelling at the same speed over the ground.

The dynamic pressure is given by the equation below.

DP = 1/2 x (air density) x velocity^2

The airspeed indicator is calibrated such that it indicates the pressure with the IAS needle, just that the scale is marked in airspeed values.

To convert the IAS to TAS, the dynamic pressure at altitude is related back to sea level density such that:

TAS = IAS x (air density at sea level)/(air density at altitude)

Hope this helps  

[Hammerhead]

DUH!  
I must have been sleepy when I posted that.
Thanks for all the replies guyz!
(Sounded just like my aerodynamics class   )

[ 11-26-2001: Message edited by: Hammerhead ]

[SpinDoc1]

How do you know when WEP will run out? And also, what does the beacon light mean? Thanks.

SpinDoc

[Seeker]

WEP is related to engine temp, when the needle's in the red, no more WEP, when the engine cools off, you get WEP back.

No, this isn't "real", but that's how it is.

The beacon light is an indication of your connection quality, it should be out. If it's green, your connection is less than optimal, if it's yellow it's borderline, you may well be warpy and you can expect to be disco'd at any time. Re-log.

[Glasses]

TAS is the relative speed at which the aircraft is moving through an air mass. Meaning it's how fast  you're going through an air mass  registered as airspeed and corrected for temperature and altitude changes(Density Altitude= Pressure altitude corrected non standard temperature and non standard barometric pressure ). Meaning that Tas is affected by the OAT which relates to your Groundspeed and also what is the local airflow of the mass traveling across your aircraft which will explain why you might have 500 IAS and 600 TAS. IN the RL Airspeed indicators have a moveable card which you can set accordingly to the OAT and it will give you the TAS for the Temp and altitude at which you're at.