Landracing Forum
East Coast Timing Association => ECTA General Chat => Topic started by: wrongway on February 03, 2010, 07:24:52 PM
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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
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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).
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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
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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.
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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
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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
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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.
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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
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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.
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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?
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Jon, think stall, take off and landing speeds... those are at IAS numbers determined by weight.... Kind of important in the whole flying thing
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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.
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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.
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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.
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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.
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We use a airspeed ind. on the Turbinator streamliner.
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here is the first test , logging gps speed and air speed. This was on the car going down the interstate last wednesday when the wind was gusting to 30 mph.
(http://www.zzrbikes.com/albums/WrongWay/airspeed.jpg)
Roy
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Roy - I assume the Series 1 is the GPS and series 2 is from airspeed?
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yes ....series 1 is gps speed
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here is the first test , logging gps speed and air speed. This was on the car going down the interstate last wednesday when the wind was gusting to 30 mph.
(http://www.zzrbikes.com/albums/WrongWay/airspeed.jpg)
Roy
What are you using to measure air speed? What voltage range?
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i am using a homemade setup , logging thru the USB onto my laptop. The airspeed sensor doesn't have an analog output, but this setup allows me to log GPS coordinates and speed also. hoping to have a standalone setup done by the april race.
that is why I was asking what others were using ,,, so I would not have to build something. But I didn't get any real info from anyone.
Roy
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You might look into air speed sensors readily available for sailboat racing. These are pretty sophisticated devices able to deal with wind direction, wind speed, vehicle speed, barometric pressure, etc. There might be an issue with the speed differential between a sailboat and an LSR but possibly worth a look.
robin
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Also check White Industries in Kansas. They are a bone yard/salvage shop for aircraft. You may be able to get a good deal on a serviceable but not airworthy unit.
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I know (now) that they do make electonic aircraft speed sensor ... wonder if one of those will work?
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and while researching this, I found this sensor.
http://www.eagletreesystems.com/Standalone/standalone.htm (http://www.eagletreesystems.com/Standalone/standalone.htm)
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Dwyer Industries sells small pitot static tubes; run the two output lines into a sensitive differential pressure sensor; its output will then be proportional to the airspeed. Remember that it is nonlinear, though!
Regards, Neil Tucson, AZ
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Remember that the Pitot tube must be in a location unaffected or the least affected by the streamlines. Here are some pictures of a Cup car instrumented with a Pitot and Yaw probe to give you an idea of location. The yaw comes from the wedge shape with a left and right channel. As air comes to the front of your vehicle it will slow down in the front and the point at which the air will “stop” is the stagnation point (in blue CFD picture). You DO NOT want to put a pitot tube in that location, but rather in free stream as far away from the surface of the car as you can get away with. The Cup car in the 2 lower pictures has it located about 16-in away from the top of the roof. In the CFD below you can see that to be totally unaffected by the streamlines you would have to have the Pitot tube very far away.
(http://www.exa.com/images/azeal_streamlines.jpg)
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As air comes to the front of your vehicle
I always thought your car comes to the air!
kent
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Not in a wind tunnel Kent. :evil: :evil: :-D
Pete
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I always thought your car comes to the air!
kent
haha! Thanks for keeping me honest Kent. After 6 years in the wind tunnel I guess I view it different than most. Same concept as I stated before but as the car goes through the air..
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Just wondering. When I was shooting long range (1000 yds) slowly rolling the focus back with a 60x power spotting scope, you could see the heat waves moving in different directions. Does the wind direction vary across a particularly long distance - like Bonneville. I'm sure this is not significant at a short course like we have at Maxton, but could this be a factor on a longer course?
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Yes, the wind at Bonneville cad blow in different directions along the long course.
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As a great example -- during the Top Speed Shootout Mike Cook will request wind readings from the various course watchers as a vehicle is being final-readied for a run. We'll hear speeds from the zero, the three, the tower, the lights (about the 5 1/2) and at least one more, maybe at the 7 or 8.
They are NEVER all the same -- in either velocity or direction. The direction might be most of the 360 degrees of a circle, in fact.
Therefore, especially if you're running a fast vehicle - it's wise to ask for a wind reading form the starter before making a run at any event. Informed might just be safer.
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I always thought your car comes to the air!
kent
haha! Thanks for keeping me honest Kent. After 6 years in the wind tunnel I guess I view it different than most. Same concept as I stated before but as the car goes through the air..
I believe that is called a Galilean Transformation"
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Hey now Eric--watch the sex talk, this is a kid friendly web site.
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Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post Don't drink and post :-D
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:cheers:
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I've been enjoying this thread. Nothing to add - just tryin' to wrap my little thinker around it. I don't have to worry about any of this for THOUSANDS of dollars. Hopefully someday - like right after I win the lotto.
Dan
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I've been enjoying this thread. Nothing to add - just tryin' to wrap my little thinker around it. I don't have to worry about any of this for THOUSANDS of dollars. Hopefully someday - like right after I win the lotto.
Dan
Dan did you say Lotto ?
After my most recent Studebaker build that was just completed fully today..... I go by the " Notso" theory,, and just hope for the Lotto..
Building an LSR Car is easy --- "NotSo"
Set a Budget and Stick with it ---- "NotSo"
Set a Timeline and finsh as expected --- "NotSo"
I am sure there are many more "NotSo's" these are my most recent 3 ....
Charles
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Living life to the fullest ----"Notso" but we try
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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.
I think this is the only way that any beneficial info can be collected. Simple airspeed is worthless, as several have explained, to due changing wind speeds, direction, etc. Even with measuring the wind angle, wind speed is needed.Will this do that?
This is a great thread, but I'm wondering what is to be gained here? Track conditions will always be different, and winds unpredictable. If it's the effect of wind on the car and speed, wouldn't wind tunnel testing be more benificial.
I'm new, and certainly not trying to be disrespectful, but simply asking for educational purposes.