Car Roof Mounting an anomometer

[Stuart Robinson]

I need to come up with a suggestion on how to do this. Recently I have used a small mag mount Instep anomometer but it did not perform well at all. I have a number of Davis Vantage pro Anomometers assembles and i would like to mount one to the roof of a car but I have a few problems with this.

The mag mount must survive 125 mph!

It will be fitted to a hire car (no holes drilled)

I must be able to take it with me on a plane - both size and weight are an issue here!

Any suggestions ?

 

[Michael Carlson]

Hey Stuart,

Go check out Chris Collura's web site, he has an awesome mesonet that can be flown where ever. It is also a magnet mount station.

http://www.sky-chaser.com/wxlab4.htm

 

[Dan Robinson]

I made a quick and easy rig out of 1 3/4" PVC pipe, then used pieces of foam pipe insulation to protect the car's finish. I used wire ties to secure the rig to the luggage rails. The pipe is easy to cut to fit whatever design you want, and it is easy to mount things to it. I did not even use bonding agent on the pipe joints, as the elbows and tees fit tightly enough that they won't come apart when mounted on the car. This means the whole thing can be disassembled and even packed into a suitcase if needed. Total cost was less than $20, and I've traveled tens of thousands of miles with it with no issues.

 

[Skip Talbot]

Dan, that is a really nice setup. I love the fact that you can easily just pull the PVC pipes off, and the simple/cost effective mounting using the luggage rack. Do you have any more close-up shots, detail pictures, a list of the instruments you are using, or a page on how you setup your weather station? I was using a window mount inspeed anemometer, but deploying it was problematic, and I accidentally severed the cable in the door last year.

 

[Stuart Robinson]

Look good Dan - but what if the hire car has just a flat roof with no rails to attach it to?

BTW I dont want the whole assembly - I just want the Anomometer (Davis)

 

[Brett Adair]

Might have to ask Chris how much he would charge to build me one of those!

 

[John Diel]

What about a magnet mounted tripod type system? This would consist of the main brace (a single pole) tall enough to get the cups out of the Bernoulli Effect (Do a search on that for more information, it's been discussed quite thoroughly) and two rear bracing poles.

Each contact point would be a triplet of rare earth magnets as strong as you could afford.

What I don't know is how it would fair against 100+ mph wind speeds. The hgher you place the cups, the more force will be exerted against the entire system. 3 point bracing would be the easiest to build and carry. 4 or 5 point bracing would be better, but you get into weight when figuring the magnets for the attatchment.

You could simply carry the whole thing in a fishing rod container (6 or 7 foot) and have the whole thing attached in a matter of minutes. I would use aluminum tubing, about 1/2 inch.

 

[Dan Robinson]

Here are a few shots of my quick-and-dirty setup. This is a wireless Oregon Scientific station. The ends of the long-way span are fastened to my roof rack with wire ties.

This is all very lightweight. The nice thing about PVC is that you can design whatever configuration you like, as big, little, simple or complex as you need. I guess it is possible that you could mount a setup like this with cargo straps wrapped through the passenger doors.

Of course, I have to add the standard disclaimer about the accuracy issues of a rig like this. You won't be collecting data for NOAA research with this. However, the anemometer does better than you'd expect for not being out of the vehicle slipstream. The wind vane is calibrated so north is to the front of the car, which allows for wind speed and direction estimation when in motion. The hygrometer and thermometer are useful for showing boundary crossings. The rain gauge is of course useless unless you are measuring rainfall rates while sitting still.

Chris might have better experiences than me, but magnets can scratch the finish on a car pretty easily. Especially if they are the high-strength variety holding on a large instrument rig. If they must withstand high winds, then they also must have a strong high-friction grip on the roof surface. Even the slightest shift while installing or removing the rig might scratch the paint. Those strong magnets have a tendency to 'slam' hard down on the roof no matter how slowly you lower the rig into place, and it is very hard to remove them without any of the magnets sliding laterally in the process.

 

[Greg Stumpf]

BTW I dont want the whole assembly - I just want the Anomometer (Davis)

Stuart,

This is not intended to ruffle your feathers, but if you can afford at the drop of a hat, to travel to Taiwan to intercept tropical cyclones, why not use R. M. Young wind equipment, which is far superior than Davis?

 

[Stuart Robinson]

No offence taken at all Gregg – actually you may be surprised to know that overall the Taiwan flight cost LESS than my Wilma intercept in Florida back in 2005 ($1060 Taiwan Vs $1300 Florida) That aside I can assure you that I am a normal wage earning guy like most folks here on Storm Track - I save my money up hard over the winter to chase in the spring / summer. Sadly I am no millionaire

Back to the Anemometer mounts …

RM Young is indeed great equipment – but I have two spare complete Davis systems at home that are doing nothing…
I like Dan’s idea of the through the door ratchet straps – But this may let in too much water – perhaps if they go UNDER the door seals it may work…
Also the use of PVC tubing may be the way to go but I would rather go aluminium for the strength.
Mag mounts are fine but they weigh a ton and remember that I want to get this in under my allowance for the aircraft.
Perhaps a blend of a single mag mount with a single strap may work…

 

[Stuart Robinson]

To add to this - given that the car is not the best place to mount an anomometer anyway (I.E not 10 meter high mount) would RM young give better readings that the davis- cup vane Vs propeller ??

 

[Stuart Robinson]

One last thought... How does an aircraft messure head / tail wind - ! think that they use Ultra Sonic Anommeters - can any one expand??

They dont have a cup anommeter spining mounted 10 foot away from the plane.

 

[John Diel]

Most aircraft use ground based observations and observations aloft from the same things we use to make our forecasts in calculating head/tail winds. The more sophisticated aircraft will use GPS for ground speed. True air speed is measured via a pitot tube which also allows the altitude measurements.

Some airports are starting to use the "Ultrasonic" measuring equipment. Many Emergency Departments are starting to go with these as well for their compactness. Depending on the model (i.e. price) the accuracy differs as well and the data logging systems, sampling rates, etc.

Some of these units are quite sohisticated in their own right, being integrated with GPS, software that will calculate your ground speed, wind speed, and direction to give you a better, more accurate wind measurements.

Take a look at the old Mobile Mesonets from various projects in the past. Most of those weren't 10 M from the ground. It just isn't feasable from a mobile platform (at least most mobile platforms). Getting the anemometer high enough to get out of the vehicles bernoulli effect will do wonders for your observations.

I might add, that there are several makers of various "gutterless mount" luggage racks and bicycle carriers that may be adapted to mount your anemometer. Magnets are the fastest and easiest, but their holding strength can be suspect.

 

[Stuart Robinson]

In the end I elected to go with mag mounts!

I found a company in the UK that produces Rare earth magnets that weigh just 250g each but provide 22 Kgs of shear pull - they are also coated with a plastic cover to prevent scraches to cars and come with a 6mm thread to allow conection to what ever. This way I can attach a frame to a car and still take the whole assembly with me on a plane.

Cost for the magnets was just $12 each.