### How to adjust Air Speed ratio ?

HI, all

i want to change the air speed ratio for an airplane that have a cruise vel of 21 m/s but i have no idea how to do it .

There is a formula to calculate this value  ?

Ciao

Alex

#### Replies

• anks guys for the expalnation.

So if i undestand correctly i have to found a way to mesurate the exact airspeed of the airplane to found the exact value of this ratio for a data Velocity Vx .

a possibility is to calculate the Airspees by tree pitot tube  and the use " a Media Pesata" (sorry i don't  hot to translate in english is possibile as "weighted average" )  ?

I ask myself  if the phone board  in this case can help to solve this problems .

Ciao

Alex.

• Developer

Alex,

I don't think Martint answered your question.  The differential pressure to airspeed formula we use in the code is inexact.  The default value of the airspeed ratio was picked to give fairly accurate readings in the typical user flight speed range - 12-15 m/s.  If you are flying faster you can adjust the airspeed ratio so that the measured airspeed is more accurate at higher speed.

The method you use to determine if your airspeed measurement is OK, high or low is up to you.   The method by which you change the airspeed ratio is to simply change the parameter value using APMPlanner or another GCS.

Keep in mind that for 99% of applications, you would probably like the airspeed to be most accurate at the low end of the range, near stall speed.  Error at higher speeds usually does not cause problems.

• Distributor

Hi Alex,

You will need to set the airspeed to on in the code:

*EXPLAINED*
//                               A airspeed sensor helps the APM to calculate the airspeed more accurately and
//                               therefor helps for better wind handeling and airspeed calculation.

//                           *INSTRUCTIONS*
//                               Because a airspeed sensor is a additional add on you need to tell the APM that it has a airspeed sensor
//                               If you have a airspeed sensor and you have installed it excately like in the link provided above then follow these instructions.
//                               Simply change the statement from "#define AIRSPEED_SENSOR     DISABLED" to "#define AIRSPEED_SENSOR     ENABLED"

//                           *AVAILABLE OPPTIONS*
//                              #define AIRSPEED_SENSOR     DISABLED
//                              #define AIRSPEED_SENSOR     ENABLED
//              *****************
//              *SELECTED OPPTION*

#define AIRSPEED_SENSOR     ENABLED

You can then adjust the airspeed in the code with this:

// AIRSPEED_CRUISE                          OPTIONAL
//
// The speed in metres per second to maintain during cruise.  The default
// is 10m/s, which is a conservative value suitable for relatively small,
// light aircraft.
//
//#define AIRSPEED_CRUISE     12

I hope this helps.

Regards

Martin.

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