Safety Section

This section will provide information that applies to the safe operation of most motorgliders, rather than type-specific advice. Most articles will begin life as an ASA newsletter article, but here it can be more easily accessed and kept up-to-date than is possible using the newsletter and the archives. Significant changes to website articles will be announced in the newsletter and in the "News" section of the web site.

If you have suggestions for web site articles, or want to suggest additions or changes to current articles, please post a suggestion on the ASA newsgroup, or contact any of the ASA directors.

Operating a self-launching sailplane

A Guide to Self-Launching Sailplane Operation - 3rd Edition (56 pages) - by Eric Greenwell. Go to the description and download page.

Towing the Trailer Safely (originally ASA newsletter - March/April 2009)



The Warnings – Read this first!

Any combination of tow vehicle and trailer will be safe if you go slow enough. What people really mean when they say "it's unstable", is "it's unstable at the speeds I want to tow".

The problem is we don't have a good way of determining how safe (stable) the combination is at a given speed. By “good”, I mean a reliable, simple way to determine the safety margin for you driving your vehicle while towing your trailer. As you know, people sometimes do determine what is definitely too fast by crashing, or, if they are lucky, just scaring themselves silly. Vehicle engineers can make measurements, calculations, and tests that would determine the safety/speed tradeoffs, but we don't have access to that expertise.

What we have in this section is some generic advice and specific owner experiences. Because there are so many variables, you should not automatically assume that what works well/poorly for one person will work just as well/poorly for you. For example, two cars of the the same make, model, and year can come with different tires, wheels, and suspensions, depending on the exact “package” of options purchased with them. This can produce substantial differences in their towing stability.

Some rules to live by (this is not a complete set):
  • If the trailer is constantly wiggling, you may be going too fast. Slow down.
  • If you feel you might be going too fast, you are going too fast. Slow down.
  • If your wife or other people are too frightened to ride with you, you are going way too fast. Slow way down.

Improving towing stability

The simplest technique is “slow down”. The slower you go, the steadier the tow vehicle and trailer will be. It works.

Next, check your tire pressure in the tow vehicle and the trailer. Running the pressures 5 psi above normal might make a noticeable difference. Check the tires every day you travel by at least looking at the tires for one that looks softer than the others.

Ensure you have between 5% and 10% of the trailer weight on the tongue. Shift some of the items you carry (wing dollies, gas cans, tool boxes, etc.) to do this.

And now, the methods that aren't so easy. Some choices have to be made when you select the vehicle or trailer; some can be made to the one you already own.

Selecting a new tow vehicle

There are some design features that make for a better tow vehicle, in rough order of importance:
  1. The distance from rear axle to tow ball: shorter is better
  2. Wheel base: longer is better
  3. CG: lower is better (a mini-van versus a SUV, for example)
  4. Weight: heavier is generally better.
Some of the newest vehicles have active stability control that may improve towing stability, but I have no idea how much these systems can help us. We are eager to hear reports about these systems, so please report your experience with them to the group!

The last section (Vehicle Experiences) lists vehicles that other owners have used and how well they worked out for them.

Improving your current tow vehicle

Note: before changing tire types or sizes, check your manual (or with the manufacturer) carefully, as tire choice can affect the safety of some SUVs and other higher CG vehicles by increasing roll-over risk, and perhaps other problems.

The easiest change is better tires. A higher speed rating than the original tires will usually improve the stability, and the higher the better. The ride might not be as smooth.

Next easiest is a “wheel upgrade” to a bigger diameter, ; e.g., from a 15” to 16” (or even a 17”). You'll need new tires of the same outside diameter for the new wheels. That gives you a lower profile tire (sidewall height to tire width), which reduces the tread deflection under side loads (cornering or while “swaying”). The ride will definitely not be as smooth with these lower profile tires, except on good highways. Going to a higher speed rating than the original tires will help, too.

Make sure the new wheels and tires are compatible with the vehicle and won't cause suspension interference when turning or driving over bumps. The wheel/tire/car dealer should be able to tell you this. A “return if they don't fit” agreement is a good idea.

If you still aren't happy with the tow vehicle, it might be possible to improve it with better shocks, bigger sway bars, or wider wheels. Because it's hard to predict the effects of these changes or to test their benefit easily, you are on your own.

Selecting a more stable trailer

Getting two axles instead of one will give a much more stable trailer. The biggest reason not to get the two axles is the extra difficulty of moving the loaded trailer around by hand. An empty two axle trailer is generally manageable by one person on level ground, but with the glider in it, you'll likely need help or a vehicle to do more than rolling it back and forth with small changes in direction. If you need to turn it 180 degrees in a small area, as I do, you're going to need some more muscle, either on you or in the form of a helpful neighbor!

While the comments above may reflect the majority opinion, not everyone agrees the two axle trailer is that much trouble. Here are some opinions on single versus dual axles:

John Murray (USA Schleicher dealer), Aug. 2007:

John used to agree with Uli [Kremer] at the factory that a single axle is fine, but then “sort of changed my thinking as the ship's value has climbed so much. You have $200K in the box and no one denies that the two axle system is more stable and definitely better in a blow out. I have moved softly to the tandem axle column even though Uli at AS and Alfred [Spindleberger] at Cobra prefer single axles. To me, $200K is a lot of money! You can quote me.”

Russ Owens, Aug. 2007:

“I carefully researched the possibility of ordering a double axle trailer to replace the single axle trailer that I destroyed in the towing accident. Several major factors came into play in deciding against ordering a double axle trailer. All the experienced people I consulted seemed to agree that a double axle trailer is much more difficult or impossible to maneuver when disconnected from the tow vehicle. Since I must maneuver the loaded trailer manually to park it at the side of my house, that was a major factor in my decision to go with a replacement single axle trailer.”

Mitch Polinsky, March 2009:

“I have a two axle Cobra trailer and am very happy with it; not as hard to move around as some suggested, and very stable.”

Improving your current trailer

Remember, these are suggestions, not guarantees! While others have had success with these changes, it's not possible to know in advance how well they will work for you. It is even possible a change will worsen your situation, so please be cautious when towing the trailer after any changes.

Do it with tires and wheels..

The easiest change is better tires. A higher speed rating than the original tires will usually improve the stability, and the higher the better.

Next easiest is wheels with a larger diameter, e.g., going from 14” to 15” or 16”, or from 15” to 16” or 17”). That allows using a tire with lower profile (sidewall height to tire width), which reduces the tread deflection under side loads (cornering or “swaying”). It's important the wheels have the correct “offset” (the position of the hub to the rim), so the wheel bearings are loaded properly and the tire doesn't rub on the trailer or fender. If you are feeling sporty, you could get some fancy aluminum wheels.
 
17" wheel with low profile tire on an ASW 27 Cobra trailer

Get tires of the same outside diameter as the original tires, otherwise the surge brakes will not operate properly. Might as well go to a higher speed rating – it helps, and it's usually a cheap upgrade.

Tire choices

Commonly available tire types are P (passenger car), LT (light truck) and ST (special trailer). While each tire series shares basic construction methods, the details vary meaningfully among the three.

There are other differences:
  1. P tires use a load rating system that is different from ST and LT tires; generally, you have to discount their rating 10% to get the equivalent ST or LT rating.
  2. ST tires speed rating is 65 mph. The speed rating increases to 75 mph IF you increase the tire pressure to 10 psi above the pressure required for your load at 65 mph. These are not the tires for folks that like to drive 80 mph across the Nevada highways in 100 deg F temperatures.
  3. ST tires come in both bias-belted and radial construction. The only advantage to a bias-belted trailer tire is it's cheaper.
  4. LT tires are a bit "stiffer" than either P or ST tires, and are available in speed ratings to at least 118 mph.
Suggestions:
  1. P tires might work fine, but I don't know what speed and load ratings would ensure this. If I decided to use P tires, I'd use them at the pressure that gave a load rating of ~40% more load rating than the load they has to carry. I'd choose a speed rating at least 20 mph higher than the speed rating on my tow vehicles tires.
  2. If you like the way the trailer tows, staying with the same make and model of tire means no surprises. The same type and size tire from an equally trusted manufacturer is probably good, too.
  3. If you like to tow faster than 70, don't use ST tires; instead, get an LT tire rated at least 20 mph more than your intended tow speed.
This web page has more information on trailer tire safety, written by Tom Wilson for Trailer Life magazine in 2002: https://www.subaru.com/my-subaru/tire-safety.html

Do it with a better hitch connection...

The only “sway dampener” I know that is directly compatible with our Cobra trailers is the Alko AKS Stabiliser series, similar to the AKS1300 shown in the picture. Check with the Cobra factory before ordering one so you get the correct model number. It works by clamping onto the towball, using friction to dampen swaying. It replaces the standard coupling on the trailer tongue, and you have to use the correct 50 mm ball and mount with it. The ball can not just be bolted on, as it might work loose.

They cost several hundred dollars and might have to be ordered from England or Europe. The two pilots I know that have used them on their DG 800's say they work very well. See Jim Herd's article in Aug. 2001 Soaring magazine, or Gary Evans' article in the Aug. 2003 ASA newsletter (available online from the ASA web site).


Weight distributing hitches compensate for high tongue loads (relative to your tow vehicle). There are several styles, but only a few that might work with our “pole” (single tube) trailer tongue AND with our surge brakes. I don't know anyone using one on a Cobra trailer, or if they are even available. Start by asking Cobra, then go from there, and please report any that you find.

Do it with axle relocation...

Moving the axle aft can markedly improve the trailer stability. For our 34 foot (10.3 meter) long trailers, a reasonable amount would be about 10” (25 cm). This will increase the tongue weight about 100 pounds (45 kg), so your tow vehicle and hitch must be able to handle the increased load.

Several things must be changed to accomplish the axle relocation:
  1. New bolt locations for the axle mounts and the shock absorbers.
  2. The axle mount to tongue mount straps should (probably) be lengthened.
  3. The brake actuation rod must be lengthened.
I know people that did this to Cobra trailers with good results, but no one that's tried it on an ASH 26 E trailer.

Do it by retrofitting dual axles...

I have no idea how practical this is, but it should be a lot cheaper than buying a new trailer!

Other Safety Issues and Mitigation

There are other issues besides stability.

The tongue can crack and break off

Whether you are using chains or not, I think every tongue should be inspected for cracks at least every year. The most likely place these begin is at a weld on the tongue, e.g., where the parking brake bracket is welded to the tongue. I inspect the tongue at least once a year.

The trailer can disconnect while traveling

The trailer can disconnect because the coupler wasn't properly connected in the first place, the tow ball comes loose, the hitch mounting fails, or the tongue breaks.

If you use safety chains between the tow vehicle and the trailer (standard operation in the USA), the chains should be very strong. The trailer can whip violently if it becomes disconnected from the tow vehicle, so I use two chains with links of 5/16" (8 mm) thickness.

Trailers, including older Cobra trailers, have had tongues crack (like mine) and even break off. Safety chains between the tow vehicle and the tongue don't keep the trailer connected when this happens, so some pilots continue the chains back to the trailer body, and also make a sturdy connection there.

The tires can lose air pressure and fail

Most of my towing is with a motorhome. It's size and weight almost completely mask what the trailer is doing. Over the 140,000 miles of the towing the trailer, I've had only one complete tire failure, but I've found two tires with large bulges in the tread, and one where an edge of the tread had the steel belt exposed. After the complete failure (blowout) at night on a lonely road in Nevada without cell phone coverage, I decided I needed to know what the trailer tires were doing way back there.

The solution was a Tire Pressure Monitoring System (TPMS) that uses sensors mounted on the two trailer wheels and the six motorhome wheels, and these send the pressure readings by RF signal to a dash mounted display. The display allows reading the pressure in each tire while traveling, plus it automatically warns me if the pressure in any tire drops by 12%. The pressure reading enables detection of a slow leak before the pressure gets to the warning stage; the warning gets my attention if a more rapid loss occurs.

Why a TPMS for the motorhome? Can't I feel when a tire is going soft? No, not if it's a rear tire, because it has dual wheels on that axle, and one flat tire out the four on the axle doesn't seem to affect the handling at all. Of course, it does overload the tire next to the flat one, since it now has to carry the full load for that side. Since I'd had four flats on the motorhome over the years without ever knowing it until I stopped for some other reason, I decided the motorhome needed the TPMS, also.

There are several types of systems. I use the PressurePro system, which mounts a small sensor on each valve stem. It's easy to do, and the cost is reasonable (about $600 for the display and the 8 sensors  in 2007). A similar system is the TST system sold by Camping World and others. It's cheaper at $300 for six sensors (just right for a car and trailer), and the display is easier to mount. I use one on my Camry, and it seems to work fine.

Other types mount inside the wheel like the new cars, but require dismounting the tires to do it. Prices have come down since I bought my system.
 
If you don't have a TPMS, you should check your tires for correct pressure every day before you travel, at least visually, but prererably with a tire gage.

Vehicle Experiences


These are reports by owners. Again, remember there are many variables in the towing safety equation, so you should not assume that what works well for one person will work just as well for you. Not only may other drivers drive differently than you, but even two cars of the same make, model, and year can come with different tires, wheels, and suspensions, depending on the exact “package” of options purchased with them. This can produce substantial differences in their towing stability.

If you'd like to add your vehicle to the "Vehicle Experiences" list, post the information on the ASA newsgroup or send me (Eric Greenwell) an email. Here's what we need:
  1. the make and model of your tow vehicle
  2. your name
  3. Your glider and type of trailer
  4. the year and options of the tow vehicle, like bigger engine, "towing package", tires that aren't standard; basically, any changes to the vehicle that might affect it's towing ability.
  5. how well it towed, what speeds you towed at, how much you've towed with it, and if there were any changes to your trailer that might affect how stable it is.
Remember, we're interested in any experiences, good or bad.

BMW X5 SAV

1) Andrew Wood
2) BMW X5 4.4liter 2002 4-wheel drive SUV, completely standard.
3) Ventus 2cxM 18m 4-piece wings in 2003 standard glass-top Cobra trailer
4) My impressions: I've towed this combination about 6000 miles now. This combination tows extremely well. Completely stable up to the highest speed I've used (70mph). The car has so much power that performance is good even with the trailer on. Good rear view: can see back over the trailer top in the rear-view mirror and around the sides with the wing mirrors. Can nap in the back of the SUV at rest stops. Good storage area in the front of the trailer. Over long cruises 19-20 mpg (1 or 2 mpg less than without the trailer). Cobra factory lighting plug did not initially work properly with US standard trailer socket supplied by BMW, required rewiring.

Dodge Grand Caravan (mini-van)

  1. Eric Greenwell
    1. 1989, 150 hp V6, with towing package
    2. ASH 26 E in a single axle Cobra trailer
    3. I haven't towed the 26 E very much with the Caravan. It did an excellent job with my 1700 pound trailer for the ASW 20. Towing the 26 E seems stable enough up to 70 mph, but normally I tow at 60-65 because it's old and the power isn't what it used to be. My trailer has the 1000 kg axle (newer ones have the 1300 kg axle) with Michelin LT185R14/C, speed rating R.

Ford F-150 Pickup Truck

  1. Mitch Polinsky
    1. 2010, 5.0L V8
    2. ASH 26 E in a double axle Cobra trailer
    3. I now use an F-150 pickup truck (crew cab, 6.5 foot bed) as my tow vehicle and as a platform for my pop-up camper that I live in when I go on soaring trips. The camper weighs about 1,050 pounds dry and about 1,200 pounds when I leave on a trip. The F-150 does a great job dealing both with the weight of the camper and pulling the trailer. The whole package is very stable on the highway and I have no sway issues going 75-80 mph. I'm sure this is due in some part to my having a dual axle trailer. My only complaint is that I wish I had more power when climbing hills. Ford came out with a bigger 6.2L V8 engine for the F-150 for 2011 and I would recommend that if one is also carrying a camper in addition to towing. For towing alone, the next engine down the line, a 5.0L V8, would be fine.

Georgie Boy Maverick (motorhome)

  1. Eric Greenwell
    1. 1998 Class C motorhome, 23 foot length, 176” wheel base, dual wheel rear axle, 11000 pounds typical traveling weight, V10 with 225 hp.
    2. ASH 26 E in a single axle Cobra trailer
    3. The combination is very stable, even at 90 mph while passing other vehicles, or in strong winds. The motorhome doesn't even know the trailer is back there, except it's a bit harder to go up hills. 10 mpg while towing at 60 mph – buying gas isn't for sissies!

GMC Yukon

  1. Russ Owens
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. I have had good success with the Yukon, a gas guzzler

Honda Pilot

  1. Bill Gawthrop
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. I sometime tow my 26E with my Honda Pilot. It does pretty well below 70 mph, but with occasional oscillations. These don't bother me very much but my wife will not drive it towing the 26E.

Honda Ridgeline Pickup

  1. Mitch Polinsky
    1. 2007
    2. ASH 26 E in a double axle Cobra trailer
    3. When I went looking for a tow vehicle two years ago I thought the 4Runner would be a good choice, but didn't like the way it drove like a truck. I think the Honda Ridgeline is a terrific vehicle for pulling the 26E trailer. My only complaint, and it is relatively minor, is that I can't maintain 60-70 mph going up steep grades. Drops down to 50-55 mph. Other than that, it's terrific. However, I can't assess how much of the stability is due to the Ridgeline and how much is due to the fact that I've got a two-axle trailer. I am very happy with my two axle Cobra trailer. It's not as hard to move around as some suggested, and it's very stable.
  1. Jon Fitch
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. My Honda Ridgeline does a pretty good job of towing the ASH26. It is basically the same vehicle as the Pilot, though I think the Pilot has a shorter wheelbase which would not help. If you are towing over the Sierra, I think you would find it a bit underpowered - it will climb the hills but has to work to do it.

Jeep Grand Cherokee

  1. Val Dean
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. I just returned from a 1000 mile trip (Denver to Pinedale, WY) pulling a single axle Cobra trailer with a Jeep Grand Cherokee. I was able to maintain 70 - 75 MPH without much ass wagging. I did note that pulling up hill or level was better than downhill where the ass wagging sometimes required slowing to 65 mph.
  2. Mike Parker
    1. Years unknown - V6, 4WD with automatic, V8, 4WD with automatic, both had the factory "towing package" option.
    2. ASH 26 E in a single axle Cobra trailer
    3. No problems, both great tow vehicles, normally tow at up to 70 mph on good roads. I have needed 4 wheel drive to pull a glider (not mine) out of a field exactly once. So it may not be worth the extra cost and reduced gas mileage.

Lexus 430 hybrid SUV

  1. Mike Parker
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. No problems. Surprisingly, tows fine uphill in the mountains (I thought it would be underpowered). Great mileage. I am a little more careful on winding downhill roads than I was in the Grand Cherokee because the Lexus feels lighter (and probably is). Because it feels lighter, I worry about what would happen if I had a panic stop, and drive accordingly. It is a great tow vehicle overall, however, and I feel comfortable at 70 mph on good roads.

Subaru Forester

  1. Jim Dingess
    1. 2002 with the 2.5 liter engine.
    2. ASH 26 E in a single axle Cobra trailer
    3. The little 4 cylinder engine pulls almost as good as my V8 pickup, and only slows down on the very steepest hills. The trailer wiggles at and above 70 mph if not careful with steering, but is fine in all but the worst winds. When it gets very windy I just slow down, this doesn't happen very often. 65 mph is very comfortable and is the speed I usually drive, a little slower in California to avoid a ticket. I get from 22 to 24 mpg on the highway while towing.

Subaru Outback

  1. Jim Staniforth
    1. 2000 with 2.5 liter engine
    2. ASH 26 E in a single axle Cobra trailer
    3. Out of the three vehicles I towed the Nimbus 3 with, the Subaru blew the doors off the Chevy Tahoe and Holden Commodore. " I always prefer the metal top Cobra trailer, for both
      towing stability and UV protection."

      (comment by Jim Dingess) Staniforth's Outback tows a little better than the Forester, I retrieved Staniforth (LS-6 at the time) from Eureka, Nevada with his car, it worked so well, I sold my big Chevy truck and replaced it with the Forester as it has a little more room than the outback. The big truck towed better but not enough to justify the extra fuel burn in my opinion.

Toyota 4Runner

  1. Jim Dingess
    1. year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. Towed from Williams to Boulder City, Nevada near Las Vegas through Tehachapi with the 4Runner, it did great. Speeds ranged from 55 to 75 mph. Mostly stayed at 65.
  2. Russ Owens
    1. 1998
    2. ASH 26 E in a single axle Cobra trailer
    3. I towed the ASH-26E with it for a while, and wasn't very happy about the odd dynamics of steering and fishtailing. I lost control at 70 mph of the combination (due to my error in steering) on the way from San Diego to Ely (aprox. 2003), rolling the 4Runner over and over (8 times?) destroying both the 4Runner and the Cobra trailer containing the 26E. My wife and I were extremely fortunate to survive the accident with only minor cuts and bruises. Rex Mayes expertly repaired the minor damage to the glider. I think the 4Runner was a bit light to be towing the big trailer, and as I mentioned, the suspension and steering dynamics of the combination never seemed right to me. It's pretty obvious (now) that I should have listened to myself and stopped towing when it just didn't feel right.
  3. Gary Evans
    1. Year unknown
    2. I tow with a Toyota 4-Runner which is a mid sized SUV. While it would appear to be a good choice for towing I found 60 to be the limit before sway would start. I believe the problem is that even though it has fairly heavy suspension you can still induce sideways movement by pushing with one finger on the rear of the vehicle. After trying every solution I could think of I finally changed the trailer connector to Al-Ko AKS 1300 Stabilizer, which works by pad pressure to the ball. Towing is now stable up to the max speed of the vehicle, which with a 6 cylinder engine and trailer in tow is 85. While pricey at $250 [2003 cost] for the connector and special ball coupler it is cheaper than unwrapping the car/trailer from a tree.
  4. Ed Salkeld
    1. 2003, V8, 2 wheel drive with factory towing package.
    2. I’ve towed about 10-12,000 miles with it.  Tows well up to 70 mph but the not very stable above that.

Toyota Sequoia

  1. Russ Owens
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. I have had good success with the Sequoia, a gas guzzler

Toyota Tacoma Pickup

  1. Hugh Milne
    1. 2001 - V6 with the TRD package including the supercharger and free-flow exhaust.
    2. ASH 26 E in a single axle Cobra trailer
    3. The supercharger increases output from about 180 to 245 bhpp, and means I can pull the 26 over the Sierra Nevada (up from sea level to over 8,000ft) without ever slowing down, and still get about17 mpg.. (Freeway driving at 55 with no trailer, I get 24 mpg.) It is not a perfect 26 tow vehicle, it is sensitive to weave if you are not precise with the steering wheel, but my wife is happy to tow at 75 when we go across the desert.

Toyota Tundra Pickup

  1. Tom Serkowski
    1. 2001 – V6 with manual transmission
    2. ASH 26 E in a single axle Cobra trailer
    3. I tow with a Toyota Tundra pickup and set the cruise control for 78 mph on the freeway ( if the speed limit is 75 :) and have no trouble. I do slow down a bit for strong cross winds, but have never had the feeling of imminent loss of control, it just becomes a lot of work dealing with side gusts.

VW Eurovan

  1. Jon Fitch
    1. Year unknown
    2. ASH 26 E in a single axle Cobra trailer
    3. My VW van was one of the better tow vehicles. 205 hp, very short coupling between the hitch and axle (like 20 inches or so) - it was quite stable. Much better than two medium sized SUVs we have owned.