Building the Los Alamos Aeromodelers Geotextile Runway -

...a mini-HOWTO, with updates following ~2 1/2 years of use.

Document version 1.3, October 12, 2009
Author R. Gritzo, gritzo at jericho data dot com
Website at http://www.laaeromodelers.org

Arial view of the new runway, S. Egdorf photo

Introduction

The Los Alamos Aeromodelers, located in Northern New Mexico, USA, has had a number of flying sites over the years. By far the best was the San Juan Airport paved runway in Espanola. It was a full-scale airport, but with such light traffic that we were able to use it most of the time. When the landowner wanted to improve the runway, we relocated onto another part of the airport. The landowner is the San Juan Pueblo, also known as the Ohkay Owinge, and over the years they have been gracious to let us use the land for a nominal annual fee.

For the past few years we have been using a dirt runway, but we have been actively wanting to improve the site. Our flying site committee looked into a number of options, including paving the runway. Due to the geography around here, there were no sites within Los Alamos County, and nobody in our county wanted to fund the development of a runway on non-county land. We looked into paving costs, but with estimated ranging upwards of $40,000 they were out of reach for our club.

Noticing that several other clubs have been looking into the geotextile (a.k.a 'petromat') type of field, we decided that that approach was the only viable option for us. We began collecting a $100 annual site usage fee a few years ago, and in the fall of 2006 the Club voted to proceed with the geotextile type runway. Total budget allocated was around $4000. We began preparing for the construction in earnest in the spring of 2007, and rolled the runway out in a single day on June 2, 2007. At the end of this document is an update on how the field is holding up as of October 2009.

The Field Layout

The original dirt runway was 50' wide by 500' long, oriented almost due east-west. There is a slight slope to the west. There is a 50' wide pit and parking area to the south of the runway. We elected to put the mat down on the runway, two on-ramps, and a 30' deep section of the pit area.

We used the mat material that is 15' wide and 300 feet long (see the Materials Section below) oriented as three long strips. We allowed for an overlap of 1 foot on each of the strips, so the final runway was 43' x 500'. The outer two strips have the end seam at 60% of the field length (nominally 300'), but the middle strip's end seam is cut short at 200' from the east end. In this manner the seams are staggered. The middle strip overlaps on top of each outer strip to facilitate drainage. Note that the edges of the material as it comes on the rolls are folded over about an inch and glued or melted to keep the material from unraveling. While the main fabric did not seem to have a preferred side to leave up, we elected to ensure that we put the folded edge down against the dirt. A photo later in the document shows a detailed view of this.

The pit area was to be comprised of two strips of 15' material, 50' long, making a 30'x 50' pit area. In the end we used a roll of 17.5' wide mat for the pit area, so now the pit area is 35' x 50'. Two on-ramps were added to connect the pit area to the runway.

The runway and pit area needed slightly more than 6 rolls of material, so we planned on buying 7 to have some left over for repairs, last minute additions, etc.

Late in the planning stages we decided to add a control line circle. This circle would be a strip of mat going around in a ring, and would provide a nice smooth surface for stunt and racing control line planes. The circle area was cleared as part of the preparatory dirt-work. The control line circle would be made up of the same mat material, folded at 24 places around the circle to make 24 trapezoidal segments which approximate an annulus. We elected to NOT cut the material, but instead fold it over itself in the direction of normal flight (counter-clockwise here in the US) to minimize the fold's effects on the plane. The addition of the control line field meant that we needed an 8th roll of material. Since our main order had already been placed, we needed to just use whatever the distributor had on hand, which was how we wound up with a 17.5' wide by 260' roll.

Materials Used

Geotextile Mat

We spent some time researching this, and in the end went somewhat with a guess based on the recommendations of the material distributors. Most of the geotextiles are not designed to stay out in the open all their life, and suffer from UV degradation to some extent. We hoped that we could get at least 5 years out of it, and should that be the case we would re-evaluate it's use at that time.

The mat material we chose was the CONTECH brand C-300 woven geotextile. It is primarily used as underlayment below an aggregate roadbed, to minimize the siltation of the aggregate, but still permit water to run down through it. There are several manufacturers of similar materials, and a few links are provided below (opening in a new window)

Manufacturer	Link	Comment
CONTECH CPI	CONTECH Geotextiles (Woven and Non-woven)	We used the C-300 mat from this Manufacturer
Carthage Mills	Slit Geotextiles	The FX-66 is supposed to be the equivalent to the material we used.
Roadrainiage.com	List of Geotextiles	Long list of geotextile materials, specs, and manufacturers contact info. Kind of technical (wish I had paid attention in that civil engineering class!).

Stakes

Most folks are using some form of stake, nail, or staple to hold the stuff down to the ground. This is a different deal than would normally be done with the matting, since normally the aggregate or topcover would hold it down. Since it is our topcover, we need to hold it down somehow. We chose to do what most are doing, and that is putting a fastener in every foot or so along each edge, including the seams. For us we calculated we needed about 2500 fasteners for the R/C facilities, and another 1000 or so for the control line circle.

We looked into nails, U-shaped lawn staples, and spikes. Most of the options were way too expensive. We decided that we needed to go on the order of a foot deep into the ground with each nail, and 100d nails were not cheap. It looked like we were going to spend alot of money on fasteners, until one of our guys came up with an idea. He noticed that the local builders supply carried rolls of 9 gauge galvanized wire, used mostly for chain link fence tensioning wire. 9 gauge wire is stiff enough that in pieces a foot or so long it can be pounded into even compacted dirt. We were able to pick up 170 foot rolls for less than $20.00 per roll, and were able to do even better in 1000' rolls.

We wound up buying the rolls of wire, cutting them to 14 inch lengths, straightening the lengths out with a bit of hammer action, then bending a J hook in one end. The J-hook had a 2" short segment, a 1" long head, and the remaining 11" length. This made a nice galvanized stake to hold the material down, and cost us less than a dime a piece. It was alot of work to make the staples, but by dividing the task up among a half-dozen or so guys, it was not too bad. We discovered that a landing gear wire bender is the ideal tool for making the staples.

The week prior to the rollout one brave soul cut out all the wire to length, and we distributed it to folks to bend the J hook in. On the day we rolled out the mat, we ran out of staples and wound up going to the local Lowes and buying 4 more rolls of material and hacked out a bunch more nails for the control line circle in a just-in-time fashion.

A close-up of one of the stakes.

Glue

We agreed to glue the seams together, in addition to stapling them down. We spent alot of time fretting over what to use, since we wanted it to not stay sticky, but not dissolve the polypropylene mat either. We settled on BlackJack brand number 55 Emulsion Roof Coating, which we found at our local Lowes. We purchased it in 5-gallon buckets, and used 2 buckets to do the seams, including gluing down the folds in the control line circle. When it dries, it dries to a non-tacky rubbery consistency, and did not attack the poly mat.

A close-up of the glue we used.

Tools

We used the following hand tools and materials:

Inverted sprayable fluorescent marker paint (1/2 dozen cans), plus 2 cans of white marker paint.
Rubber or wood mallets to drive the stakes
A 100d nail to pre-punch through really hard dirt
A large roofers brush or roller to brush out the glue
Rakes to smooth the dirt
Hammer, Bolt Cutter, and Landing gear bender to make the staples
Box cutter or sharp shears to cut the mat
Safety glasses, leather gloves, knee pads, and sunscreen

The Construction Process

Field preparation

Aerial view of the dirt runway, S. Egdorf photo

An aerial view of the dirt runway before mat layout

The field preparation started with an already existing dirt runway, that had been crowned, rolled, and packed. Over the years it had gotten really dry and loose in a few areas, and there were some weeds growing up in the middle. Final preparation consisted of the following:

Re-blade the runway and re-establish the crown and drainage down the sides,
Fill in one or two low areas where water had been accumulating and establish better drainage in that area,
Scrape off all the weeds,
We tried to roll and pack the field, but it was too dry to do without water,
Rake the worst of the ridges and bumps out of the field right before laying out the mat.

Finishing up the dirtwork, including the control line field.

Runway Rollout

Once we got the field preparation done, we actually rolled out the runway in a single day, using about 20 people. Bear in mind that the runway runs east-west, and we use three strips of material; a north strip, south strip, and center strip. We worked from east to west. We layed it out using the following steps:

Look at the edge of the material. Some rolls of matting were rolled up with the folded edge outside, and some with the edge on the inside. If the folded edge was on the outside, we could roll the material out as we went. If the edge was on the inside, we had to fully unroll the material and flip it over. Doing so required a person every 20 feet or so, so it takes 10 to 15 guys to flip a roll over.

A close-up of the material, including the edge. Note the folded edge. The side closest to the camera in the photo is the top side as we laid the material out.

When we drove the stakes in, we did so about an inch in from the edge, and lined the head of the stake up with the long edge of the material. We drove the stakes in until the heads just pushed down slightly below grade level. It is best if you start the stakes by pushing them in half-way or so by hand, then driving them the rest of the way with a rubber or wooden mallet. (October 2009 - See the October 2009 update at the end of the document about a mis-stake ( :} ) we made on the staking.)

One of the youngsters is starting a stake. Note the other stakes on the ground in front of him.

We set out all 300' of the the north strip, and got it nice and straight. We staked down the north edge of this strip about every 10 feet or so just to hold it in place.

The first section being laid out, north strip, east end.

We set out the south strip in the same manner as the north strip above. We left 13 feet between the two strips, and staked down the south edge of the south strip every 10 feet or so.
We picked out a roll that would allow us to roll it out as we went to use as the center roll. We rolled out about 10 feet and staked it down even with the east end of the runway, overlapping the north and south strips by a foot each. We brushed out a strip of glue about 6" wide on the north and south strips where the center strip overlapped, and rolled out the center strip over the glue.
We staked the center strip down (including the underlying north or south strip) as we went along, every 10 feet or so.
We stopped the first center strip at the 200 foot point and cut it so we could stagger the end seams. At this point we had essentially a 43' wide by 200' long runway with longer outer sides, and limited stakes in the edges.
We patted ourselves on the back for a nice job done so far, and sent teams of people back along each edge to fill in the remaining stakes. We made sure that there was a stakes in each edge or seam about every foot.

Filling in the remaining stakes every foot or so along the seams.

We then unrolled a few yards of a third roll (which we will use all 300' of) as the start of the remainder of the center strip from the 200' point to the west end, and joined it at it's east end with the west end of the center strip laid down before. We rolled this section out to about the end of the north and south strips already down.

The center section being joined, east end is done, west end being started.

We then took two new rolls of material, unrolled a few feet of each, and made the end seams on the north and south strips. We rolled each edge over 6" or so, overlapped the material, lined it up, glued it, and staked it. We unrolled the north and south strips towards the west end the same way as we had done before, staking every 10' or so on the north edge of the north strip, and the south edge of the south strip. We stopped and cut the material at the 200' point from the east end seam, giving us a total of 500' of runway with two 100' long remnants to use on the pit area and control line circle.
We then rolled out the rest of the second center section towards the west end, gluing and staking every 10' or so as before. At this point we had 3 100' pieces left over for use in the pits and control line circle.
We then went back on the west half of the runway and filled in the remaining stakes.
We layed out the pit area and the on-ramps using the same techniques for the edges, gluing, and stakes the edges.

500 feet looks like a long ways from here (the east end of the runway).

Done! We stood back in amazement and looked at what we had done. We started about 7:00am, and at this point it was about 11:00am.
We then put two big X's on the ends of the runway so that smaller fullscale and ultralights don't try and use the runway.

The view down the runway from the east end.

Control Line Circle

Since we had all the guys there, we decided to push on and get the control line circle done. As mentioned elsewhere we planned to approximate a circle with 24 trapezoidal elements, with the outer edge of each element 18 1/2 feet long. Here are the steps we used to do that part:

Identify the center of the area where the pilots box was going to be, and drive a stake down there.
Using a long tape, mark with spray paint a 58' inner circle to guide the mat placement, and then mark a 73 foot radius circle.
Start at some point on the circle and stake the end of a roll down. We actually started with some remnants from the RC runway so that the rolls were easier to handle.

The start of the control line circle. Note the inner paint mark and the outer drag mark.

Stretch out about 20 feet of material striking a tangent to the circle. Mark and hold the 18 1/2' point, and holding that point move the roll and that marked point inward towards the pilot box until the outer edge of the material is even with the 73' circle.
There will be a ginourmous fold of material near the first edge. That is ok. Tuck it under itself such that a plane landing in the normal counter-clockwise direction will roll over the fold pressing it down, not lifting it up. This means that the inner part of the fold is actually pushed in in the opposite direction from the normal flight direction.

A close up of a control line circle section joint.

Stake down the 18 1/2 foot point on the outer edge, stake down the inner edge at the corresponding point, and stake down the fold in a spot or two.
Repeat for the next segment. Repeat for a total of 24 segments. Use the material left over from the RC runway, and part of another full roll of material. You will need 458 feet of material to go the full circle.
We wound up closing the circle with the last segment just over 15' long. Less than a 1% error on this is darn good!

The control line circle closed up.

Go back and put glue in the folds, and put stakes in the inner and outer edges and along the fold every foot or so.
Layout and stake down a pilots box, and if you have enough material you may want to layout a 15' wide by 70' long control line pit area.
Stand back and congratulate yourself on a great job. Your new field is done!

Here are a few Do's and Don'ts that we learned (updated October 2009)

First the Do's

Do get the field prep done ahead of time - preferably by a professional or with large equipment. At least get the runway graded and a crown put in, as well as getting any severe low areas filled in so water does not collect under the mat. If you live in an area that actually gets rain (unlike New Mexico!) you probably need to pay attention to the drainage. We chose to remove all the vegetation before we put the mat down.
Have a "job boss", someone in charge on the day you do the work. In our case we had several key players prior to the day that made all the arrangements, handled the logistics, etc., but on the day of the job we all pretty much got in line behind a single job boss. You really need one guy calling the shots, and everyone agreeing that he makes the final decisions, so that everyone is working in a coordinated manner to the same end. Be sure and pick this person carefully!
Plan through and have all your materials ready before the day. Have extra on materials on hand, and know where you can get more if you need them during the job.
Pick a day when the winds are light. More than about 5 to 7 mph and the stuff will be too hard to handle. Make a visit to the site and plan the sequence of events before you start, including painting guide lines where the seams go.
Do have plenty of folks on hand. We had about 20 show up. Much less than that and it would have been a multiple day deal.
Angle the stakes over the seams so that you don't have ridges curl up after the material shrinks.
Arrange for lunch (we grilled hotdogs), munchies, and plenty of drinks (mostly cold water). You want folks to be able to stay focused on the project, since it is a pretty big effort, and not lose people to run into town for lunch, etc.
Stay well hydrated. I was bringing the teams water every 30 to 45 minutes. At least in the New Mexico summer sun, that was probably marginal. Keep people well hydrated and watch for overexertion.
Do bring and wear protective gear. Safety / sunglasses, leather gloves, kneepads, and sunscreen are a must.
Do mark some X's on the end of the runway so that fullscale and ultralights will know to stay off.
Do bring an airplane! Once we were done we realized nobody brought a plane to try out the field with!
Train club folks on how to make repairs and put together a repair 'kit'. Make sure that folks take the responsibility to repair any cuts or prop-strikes reasonably soon.
Do keep after the weeds on the edges of the material. Don't let them get too high or they are hard to deal with.

And now the Don'ts

Don't fuss too much over the smoothness of the dirt. Rolling and packing it are nice, but not necessary. Just smooth out the large tire-tracks and large clumps, the mat will hide a number of smaller imperfections. Plus, you can always roll the field later if need be. Be sure and don't crown the field too much.
Don't lay out much more than you can stake down right away, unless you know the winds are calm.
Don't pre-stretch the material as you lay it out. Just get the major wrinkles (more than an inch to inch-an-a-half or so tall) out, and get it straight. The sun will do the rest of the shrinking!
Don't let people over-extend themselves and get hurt. The rolls of material weigh ~300 pounds each, so it takes a minimum of 4 guys to move one.
Don't be too precise about the staple spacing. We tacked some parts down with stakes a couple of feet apart, and they seem to be ok. Precision is not really the game here, just getting it held down plenty well.
Don't forget to keep some material, glue, and stakes on hand to make repairs. After the material has been down for a while you may need a re-staking and patching party a couple of times a year.
Although it is not a problem to let cuts sit in the fabric, you probably don't want to let a damaged section (like from a prop strike) sit around too long without getting fixed.
Don't let anyone get too worked up about a prop strike or accidental cut in the mat. It is like a door ding on a new car - it is bound to happen. Best to just get it fixed, and move on!

Summary

The work week after we laid the runway down was one of bizarre weather here. We had a series of weather extremes, including a few really hot days and a series of severe storms, including a tornado warning (very rare for this part of the state). At least one major thunderstorm dropped a torrent of rain, and we had wind gusts over 55 MPH. We were all worried that the runway would be damaged, so one of our guys went out to check on it that Friday afternoon. He called to report that not only had the runway survived, but in fact the rain had cleaned all the dirt footprints off the mat and it looked great. Not a bit of damage.

One unexpected bonus was related to the firmness of the dirt. Recall that we could not roll pack the field due to it's extreme dryness. One of the guys claimed that it was like trying to roll talcum powder. Turns out that the combination of the rain, heat from the sun baking the mat, and keeping the wind off of the soil turned the ground under the mat very solid, kind of like baked adobe! We were quite shocked to walk across the runway after the first week and find the ground underneath as firm as if we had rolled and packed it first.

It has only been a couple of weeks, and so far no problems. Pilots report that it is easy to oversteer on ground handling compared to the dirt, but other than that it does not seem much different - except that the planes are much cleaner! We have heard reports that other clubs have had their fields down for 5+ years, but it will be interesting to see how the New Mexico weather treats this material. We are hoping for 5 years of life out of it, but we will see!

We hope this HOWTO has been a help. Feel free to contact either myself at the email address at the top of the document, or contact Ray Martinez via email at jetray47@yahoo.com. Also please see the photo gallery at the club website, http://www.laaeromodelers.org/gallery/sj_petro/index.html

Postscript

We were surprised at how much this mat shrinks in the sun. After a couple of weeks, there is evidence that it is curling up at the edges some, mostly due to shrinking. We plan on going back and re-gluing the edge seams where the center rolls overlap the edge rolls. The glue dries to a rubbery compound so this should work fine to hold the seams down.

Over the Father's day weekend we had a combined fly-in and club meeting on Saturday morning. We got some good real-world experience with the mat. I over-rotated my control line smoothie on take off and drug the prop on the mat. No real damage, just some scrape marks. Later in the day, however, a gust of wind came up and lifted the tail on a 0.90 powered plane enough that the prop dug into the mat and killed the engine.

The resulting damage was surprisingly minor, with a 1/2 dozen or so scrape marks and two small (less than 1" long) cuts in the mat. We repaired the cut by simply painting a layer of glue over the area. About 5 minutes later the glue had dried and left a rubbery patch where we made the repair. We have discussed clipping out some new material and laying it underneath the cut area if needed, but so far the only damaged spot has been easily repaired with just a thick layer of glue. We do have all the material on hand at the site, however, so that folks can fix up any minor boo-boos right away.

Update, October 2009

So, it has been almost 2 1/2 years since we rolled this field out, and folks who read this on the web are beginning to ask how it has been holding up. I am happy to report that even after more than 2 "New Mexico Years" later the runway is holding up amazingly well. There is no indication that the material is degrading or getting brittle in the sun. One of the concerns we had was that tears and damage to the fabric would propagate and get worse. This was an unfounded concern. Prop cuts, tears from animals and even sections chopped up by over-zealous lawn mowers have not progressed any worse than the original damage, even after more than a year untreated.

Main Runway, October 2009, looking to the East.

Main Runway, October 2009, looking to the West.

To be honest, the material has held up so well that we have gotten very lazy in maintaining it. We only patch the really bad cuts, and then only once a year or so. The photo below shows an area on the main runway that was patched some number of months ago. The patch was over a section with a long rip in the fabric. The patch was applied with some of the roofing glue discussed earlier. Many (in fact most) of the occasional prop cuts and places where something nosed in and punctured a hole in the material go un-patched for months, with no indication of the rips or tears progressing. In the photo below, note the motorcycle track on the right. Even with vehicles driving on the fabric we have had no problems with them causing damage.

Main Runway Patch, October 2009, Patch in place for several months.

We have also not had problems with things growing up through the fabric. Not sure if the hot sun on the black mat has sterilized the soil underneath, or what, but the only weed issues we have had have been at the edges (see the photo below). We either mow the weeds down, taking care not to get the mower blades low enough to grab the fabric, or we pull the weeds out, or use some weed killer. Occasionally we use a drag to drag the dirt and knock down the weeds. Driving an SUV on the material (if done gently) is no problem, and even the occasional contact between the drag and the fabric is no problem. The weeds in the photo below were removed the day of the photo.

October 2009, control line circle with border weeds

Control circle, example of weeds growing at the edge. Weeds were pulled and removed later that day.

There are two things that we have had to do. First, we have had to keep up with some of the stakes. The ones around the edges occasionally got loose, especially the first year or so as the material was still shrinking. About a year or so ago we had to have a re-staking party, where we went around and pulled out stakes that had gotten lose or bent over from the fabric stretching, and re-set them at an angle. Lately we have not had a problem unless someone has done something to pull the stake up. Wind and other forces (ATV's, cars, motorcycles, etc) have not torn up any sections of the fabric.

We did learn a lesson about the staking. As described in the article above, we initially put the stakes parallel to the seam or edge, and recessed in about an inch or so. This is fine for the outer edges, but when applied in this manner on the inner edges it allows the seams to curl up as the material shrinks. This creates some annoying ridges. Later we went back and angled the stakes over the seam, as shown in the photo below. This works much better, and is the technique that should be used on all the seams.

October 2009, showing a revised stake pattern along a seam

Revised stake pattern crossing the seam at an angle to reduce the curl at the seam.

The second thing we had to do was to roll the ground. A series of 'washboards' had developed in the soil under the fabric. In the middle of the runway (on the crown) these were so bad that it was getting hard to take off. We stewed over it for a number of months, wishing that we had taken the time to roll and pack the ground firmer before putting the fabric down, and concerned that rolling it now would be harmful to the fabric and not address the problem. In the end, we decided to purchase a 24" x 48" steel drum lawn roller (the kind you fill with water) and roll it behind one of the guy's ATV. It worked very well, smoothing out the washboards and doing no harm to the fabric. It was good to know that we could go back after the fact and do whatever smoothing was needed anytime we wanted to.

The club had estimated that the fabric would last 5 years. We charged our field use assesment such that we would recover the cost of the fabric (expecting to not have to do the dirt work again if the fabric needed replacement) in 3 years or so. As it stands now, the club cut the field use assesment in half for 2009, since at this point the fabric looks like it will last at least 5 years and we have more than half the amount needed to replace it in our club account at present.

Our landlord has recently informed us that we will likely need to move to another location on their property. We are quite happy that we did not make anything permanent, and other than the amount of work to pull up stakes, we think that we could move pretty easily, probably in a couple of weekends if need be.

Overall, we are quite pleased with our efforts, and would recommend this approach to anyone who is in similar circumstances. We know of several clubs here in New Mexico that are getting ready to do the same thing, and would love to hear from folks in other parts of the country who have done this and how it has worked for them. I plan to post another update in another couple of years.

Acknowledgments

Thanks to the Ohkay Owinge Pueblo and the Tsay Corporation for the lease of the site.
Thanks to all the club members that supported the effort with their dues and assessment fees, and by helping either before or on the day of the rollout.
And finally I wish to extend special thanks to three individuals without whom this would not have happened (in alphabetical order) -
- Juan Baldonado
- Art Lavy
- Ray Martinez
  - Thanks for all you guys have done over the years!

Revision History

Version 1.0, 6/10/2007, Original Version released for comment
Version 1.1, 6/13/2007, Minor revisions to sequence of rolls, and finish up for posting.
Version 1.2, 6/18/2007, Added snapshot of stake, writeup of prop cut repair.
Version 1.3, 10/14/2009, Added update ~ 2 1/2 "New Mexico Years" later.