Aug 15, 2009, 02:05 AM
Alam
RENO
Joined Aug 2007
525 Posts
New Product
True Air Speed Meter

I am starting new project that will measure the

1) GPS ground speed
2) Air speed
3) True Air speed
4) Log the GPS ground speed, Air speed and True speed.
5) Data will be available through USB and serial port.

For now I am using my old board, you can buy that board from

http://thesiliconhorizon.com/store/a...02dp-p-87.html

Fakhre Alam

# Files

 Aug 15, 2009, 02:30 PM Alam RENO Joined Aug 2007 525 Posts Hi Guys Give me any input, let me know any thing need to add, any input will be good and appreciated. Fakhre Aalm
 Aug 15, 2009, 08:57 PM R/C Electro-Gadgeteer N.E. USA Joined Oct 2003 815 Posts Got to ask... What's the difference between airspeed and true airspeed?
 Aug 15, 2009, 09:31 PM Registered User Tacoma WA Joined Feb 2008 561 Posts I think he may mean airspeed and speed over the ground. Will differ in winds.
Aug 15, 2009, 09:43 PM
Alam
RENO
Joined Aug 2007
525 Posts
Quote:
 Originally Posted by Tomapowa Got to ask... What's the difference between airspeed and true airspeed?
Its kind of use in real aircraft.

1) The true air speed of the aircraft is equal to the speed of the aircraft relative to the earth surface (by GPS or some other means).
2) Air speed is the speed (air mass flow under need/over wings) of an air measure by pitot tube.

One use for keep plane float and the other one use to measure how much distance plane is traveling. In some cases ground speed can be zero but you have +ve air speed.

I am also a life time student learning from your questions. Please correct me if I need correction.

Fakhre Alam
 Aug 16, 2009, 01:09 AM Registered User Sweden (Åkersberga) Joined Nov 2004 777 Posts I'm extremely interested. A question to start with, Will the board your are referend to in the first entry be able to host all three: 1) GPS ground speed 2) Air speed 3) True Air speed Or do I need three boards for that? To where are the data going to be logged, will it be a separate logger? I have a Eagle Tree logger, could that be used to log the data? Thanks! /Håkan
Aug 16, 2009, 02:43 AM
Alam
RENO
Joined Aug 2007
525 Posts
Quote:
 Originally Posted by hakank I'm extremely interested. A question to start with, Will the board your are referend to in the first entry be able to host all three: 1) GPS ground speed 2) Air speed 3) True Air speed Or do I need three boards for that? To where are the data going to be logged, will it be a separate logger? I have a Eagle Tree logger, could that be used to log the data? Thanks! /Håkan
1) I designed air speed board just for my use, for now I will use that one.
2) For GPS, LS20031 is good option, just hook-up with PIC32. PIC32 board will have EEPROM to store all GPS parameters and temperature, current, voltage and RPM sensor interface.
3) OSD board I did year back, for now I will use that one, just connect it to PIC32 using SPI port.
4) Data upload and download and config can be done by PC using serial port or USB, I am learning USB interface, can be done easily on serial then USB for now but USB will be for final product.
5) For prototype we can stack all three board and do testing then for final it will be two PCBS.
6) I did not have enough info about eagle tree data logger, if some can give me some insides it can be use. Not sure eagle tree will give their trade secret.
7) Ground speed can be done by on board GPS.
8) Air speed can be done by A or D pressure sensor using pitot tube.

Thanks.
Fakhre Alam
Aug 16, 2009, 02:49 AM
Alam
RENO
Joined Aug 2007
525 Posts
Quote:
 Originally Posted by Ron W3FJW I think he may mean airspeed and speed over the ground. Will differ in winds.
U are right if your head wind is hitting you with 50 MPH and your plane engine is giving 50 MPH thrust you ground speed will be 0, means your are floating in air but kind of stand still w.r.t ground. That's a funny situation.

Fakhre Alam
 Aug 16, 2009, 03:22 AM Registered User Staffs, UK Joined Nov 2003 12,506 Posts But you're still talking about three different speeds. I understand ground speed and air speed but what's "true" air speed if it's different from both of those ? Steve
 Aug 16, 2009, 04:03 AM Registered User Tacoma WA Joined Feb 2008 561 Posts TAS if I can remember back to my flying days a lifetime ago is the proper term for speed over the ground.
Aug 16, 2009, 04:27 AM
Alam
RENO
Joined Aug 2007
525 Posts
Quote:
 Originally Posted by Ron W3FJW TAS if I can remember back to my flying days a lifetime ago is the proper term for speed over the ground.

You can say like that, its just a wording. The true airspeed of the aircraft is equal to the speed of the aircraft relative to the earth's surface (ground).

Fakhre Alam
Aug 16, 2009, 05:46 AM
Registered User
United States, CO, Denver
Joined Sep 2005
298 Posts
Quote:
 Originally Posted by Tomapowa Got to ask... What's the difference between airspeed and true airspeed?
This is actually a question on the private pilot exam. The answer that is expected is :

"True airspeed is calibrated airspeed corrected for non-standard temperature and pressure."

Airspeed indicators work via differential pressure from the ram air pressure of the pitot tube and static pressure. Since the air density will vary with altitude and temperature then the ram air pressure will vary with these changes.

Calibrated airspeed is simply indicated airspeed corrected for any installation errors in the system.

So at sea level on a standard temperature day of 59 degrees F and standard pressure of 29.92 with an airspeed indicator that has no errors..... indicated airspeed would equal true airspeed. As we go up in altitude then indicated airspeed will go down as true airspeed increases.

If he truly intends to do the calculations to show us true airspeed it would be cool to see the true airspeed when DSing your glider on top of your favorite mountain slope, otherwise indicated airspeed is likely close enough.

Mike
 Aug 16, 2009, 07:28 AM Dave the Rave Joined Jun 2007 937 Posts Exactly right. The term "airspeed" always refers the the movement of the aircraft through the air, and as Mike has said, there is sometimes a difference between indicated and true airspeed. Calculating true airspeed was probably much more important some years ago than it is now, because it often affected navigation, back before the days of GPS. The correct term with which to refer to the movement of an aircraft relative to the earth is "ground speed". Fly at 150 knots IAS into a 30 knot head wind, and your ground speed will be 120 knots. It's much the same as the differences in altitude readings. "True" altitude is measured above sea level, but what's most important to a pilot is his altitude AGL, or above ground level. The altimeter is adjusted for the ASL altitude of the airport, so the altimeter can indicate to the pilot his altitude AGL. (It needs to be >0)
 Aug 16, 2009, 08:11 AM Registered User Staffs, UK Joined Nov 2003 12,506 Posts But the person doing the measuring thinks "true airspeed" means speed over the ground (or what most of us call ground speed)...this is not even close to being the same thing as airspeed corrected for specific temperature and pressure. So my question is still what is the "true airpeed" that Fakhre Alam is intending to measure and how is he measuring it. Steve
 Aug 16, 2009, 08:29 AM "MAYONNAISE" Le Treport, France Joined Jun 2004 1,504 Posts Hi, It might be an airspeed that is much much much more precise than the one given by competition ... DO NOT ask how much !!! Seriously, that will need, temp ( static ... ! ) , Hygrometry and abs pressure, may be a gas analyzer too ( for real true air density ) ... if my Thermodynamics lessons were right ... of course. Alain