measuring /logging air speed ?

[wrongway]

Has anyone put an airspeed sensor on their vehicle?

I thought it would be a great way to understand actual performance since ground speed is affected by head/tailwinds.
Air speed( and air pressure/drag)  should be consistent in anycase , except maybe a crosswind.

I am looking for a logger that will do airspeed, gps , and wheel speed.

Any ideas?

Roy

 

[bbarn]

Air speed is relative, cross-wind, tail-wind and head-wind will all effect the readings. If the vehicle is traveling at 100mph (ground speed) in still calm air, the AS indicator will read 100. if there is a 10 MPH headwind and the vehicle is traveling at the same ground speed as before, the air speed will indicate 110. For a 10 mph tail wind, it will read 90. Cross winds (component) will change the reading based on the angle of incidence relative to the pitot tube.

Then there is temperature, density and altitude that have to be factored in to give you a corrected air speed. It's not hard, pilots do it all the time. Indicated airspeed and ground speed are never accurately correlated when flying, airspeed merely indicates the speed at which the air is moving over the vehicle, not the true vehicle speed (ground speed).

[wrongway]

I agree, ,,,

that is why I am interested in logging air speed on my car and bike.... with the same setup , I should always get a fairly consistent airspeed. that way I wont be chasing imaginary gremlins at the track due to variations in ground speed.

so back to the original question ,,, what can I use to measure/record airspeed .... gps and wheel speed would also be nice to figure out head ot tail winds.

Roy

[Stainless1]

Airspeed is usually acquired via a Pitot Tube, and the impact pressure is converted to airspeed in the indicator electronically or mechanically.  Modern airplanes feed a transducer than gives a computer a signal relative to voltage developed by the transducer by the impact pressure.  Temperature and static pressure are mixed in there to give them True Airspeed.  You could feed any extremely sensitive pressure transducer and record that voltage with almost any data recorder.  I think you will not get the consistent data that you desire from this... headwinds and tailwinds will affect your data.

[petercalaguiro]

That fellow from Quebec with the hemi in the white/red Studebaker has an airspeed indicator in his car. He was at Maxton last summer and Bonneville also. Keith knows his name.
Good luck.
Peter

[wrongway]

  I think you will not get the consistent data that you desire from this... headwinds and tailwinds will affect your data.

I dont understand your statement.

If the vehicles speed is limited by the amount of aero drag applied and horsepower available, and that drag is created by the speed of the air seen by the car , why wouldn't air speed be the same on EVERY run if the same HP is available?

and if that is true , why wouldnt HP changes be easier to see using air speed? since ground speed is affected by head/tail winds?

Roy

[Stainless1]

Roy, the more I think about it, you are right, impact pressure will remain the same.... provided you put barometric pressure into the equation.  The speed through the traps may change, and I guess if you precisely shift at the exact same points, or aero drag is your only limiting factor, then your data may help you figure out if you changed HP, but that is a lot going on in a mile... a 3/4 second shift instead of a 1/2 will change your speed at the traps, and the IAS.... So what are you planning to correlate your data to?  it is an interesting idea.

[wrongway]

both the bike and the car reach terminal speed well before the traps, so I dont think i will have other elements affecting the run.

Air speed should be an easy way to measure improvements in HP or aero package , assuming that I only change 1 thing at a time

Roy

[bbarn]

I think the biggest issue in not getting consistent data is the wind. The speed and direction of the wind will be different on every run, a 10mph headwind will give a different reading than a 10mph cross-wind (each degree change in the angle of incidence will affect the readings). Depending on the angle of incidence to the pitot tube, you will likely have a wide range of readings along the track and between different "identical" runs. Along the entire run, the air may also change direction and velocity relative to the vehicle, each of these changes will affect the readings of the air speed indicator.

One thing you will have to do if you want more accurate data is to collect wind speed and direction before each run. You will need to factor these two variables into your readings as corrections.

btw, it's not a bad idea, but it wont be a plug and play setup. You will need to determine where you are going to record your atmospheric corrections (wind speed and direction) and where you are going to capture your AS at. The best place to capture your atmospheric data is the same place you record your IAS, with those two pieces of data, you will have a more accurate measurement.

[Seldom Seen Slim]

So I've gotta ask -- why do airplanes even have airspeed indicators -- if there are so many variables?  There's no way to get accurate readings of all of the variables when you're XX,000 feet above the ground, so what good is the reading?  For fuel consumption determination, probably, but what else?

[Stainless1]

Jon, think stall, take off and landing speeds... those are at IAS numbers determined by weight.... Kind of important in the whole flying thing

[bbarn]

Also think about the wings staying attached, it's sort of an important part of the theory of flying. Depending on the type of flying conditions (bumpy, gusty, rough), you use different indicated speeds. If you are pushing the aircraft to it's max speed, it is the maximum speed (with a safety margin) that the aircraft can structurally withstand (Vne), if the weather is rough, your max indicated speed + the abrupt changes in direction can easily compromise the structural integrity of the aircraft.

[Gwillard]

So I've gotta ask -- why do airplanes even have airspeed indicators -- if there are so many variables?  There's no way to get accurate readings of all of the variables when you're XX,000 feet above the ground, so what good is the reading?  For fuel consumption determination, probably, but what else?

Because it is the airspeed that determines the performance characteristics of the aircraft, not groundspeed. Critical airspeeds such as "never exceed" and stall speed have nothing to do with ground speed and everything to do with the speed of the air over the wings and tail.

[A2WindTunnel]

When track testing it there are many variables to keep track of that will affect the results of your test.  The one thing you cannot control is Mother Nature.  Temperature, barometric pressure, and wind conditions are constantly changing during the day.  As you guys know, the wind will never be a constant speed or direction.  You must log your input readings as a function of position on the track and your readings must correspond with each other, in order for you to match wind speed, angle, ground speed as they are happening on the track.  Along with a pitot tube you can use a device to measure wind angle.  It is a wedge shape probe that sees pressure on both sides and you can calibrate it to yaw angle so you can plot it to see what the wind angle is on a particular run at any location/time on the track.  Simple to machine, and I will see if I can get an image up once I'm back at the office next week.

[A2WindTunnel]

Here is a sample track test at Charlotte Speedway where we logged wind speed vs road speed as a function of position on the track for a bicycle.  Note that this was a very calm day with ideal conditions for track testing.