With all my recent testing on cordage, I got curious about how much load my wooden stake ground anchors will hold.

The system I use is pretty simple. Two or three wooden stakes driven in line and connected with pre-tensioned lines.





Obviously there are going to be huge discrepancies in the holding power of any ground anchor. Soil consistency, stake strength, disruption to both soil and the stake when it’s being driven in, etc.. But a HUGE variation in strength comes with the geometry of the system, which the pilot has some say over. If the pull angle is too steep, the stakes come out of the ground before they snap. If the angle is too shallow, system is less effective at keeping the airplane securely on the ground.

I started with three stakes on the smaller side of what I’d like to use. The front stake was the largest, but it all split when I drove it into the ground. I loaded the system until the front stake broke.





1,300 lbs.


So I used a larger stake, but it wasn’t quite as long. I also used only two stakes rather than three. There was a noticeable difference using only two stakes.



1,200 lbs and a lot of movement as the stakes pulled out.


Back to three stakes, with a moderately large front stake. Once again the front stake broke before it pulled free, but I've had it happen the other way, too.



This one did the best...1,550 lbs before it broke, with very little movement beforehand.


This is all antidotal. I’m quite sure if I continued driving sets of stakes in my yard I’d get different results based on nothing more than how many rocks the stake had to push out of the way on its trip into the earth. Go to a different area with different soil, and the results will be different. But it gives a general idea of what’s possible.

I've got some other ideas for stick-based ground anchors which should yield higher strengths, but they will also take longer to construct. I'll try them out when I've got more time.

Hammer, for comparison to your multiple stake approach, can you run another test where you dig a "T" slot and bury one stake as a deadman aligned with the head of the T and the load aligned straight from the tiedown to the deadman along the stem of the T. Maybe three tests at 6, 12, and 18 inch burial depth so we could see the relationship between resistance to soil cover. As you mention, resistance would vary with soil type, but with the deadman if you knew you were in a weak soil you would just bury it deeper. In practice this would mean that you would need a trenching tool in your field kit instead of a heavy hammer (or axe) and the deadman would be expendable unless you went to the effort to dig it up before departure. We use a similar approach for anchors in snow in Alaska and the resistance mobilized can be pretty substantial.

Just found this on Google. Food for thought.

Literature I have read...

No directly aviation but, interesting. John Long is a well respected climber and writer. From what I know he has no idea how to fly. Regardless, the practice of anchoring is a relentless pursuit.

Climbing Anchors:

http://www.amazon.com/Climbing-Anchors-How-Climb-Series/dp/0762782072

https://en.m.wikipedia.org/wiki/John_Long_(climber)

Thanks for starting the thread.

Yes, good thread, thanks for starting it.

I watched this Avweb video recently on the topic of tie down's.

Aviation Consumer Tiedown Shootout
https://www.youtube.com/watch?v=UIuYK_eEQ9c

My takeaway was there are several excellent designs, that all claim to be the best, and each is "best", in a different kind of soil.

I am wondering if I might end up buying more than one type, and taking whatever is best for the soil conditions I expect to encounter.

-Jim

what about 3 stakes driven in a triangle the a direct pull in the center of them vertically. Something you would place directly under your tie down.

M3X wrote:Yes, good thread, thanks for starting it.

I watched this Avweb video recently on the topic of tie down's.

Aviation Consumer Tiedown Shootout
https://www.youtube.com/watch?v=UIuYK_eEQ9c

My takeaway was there are several excellent designs, that all claim to be the best, and each is "best", in a different kind of soil.

I am wondering if I might end up buying more than one type, and taking whatever is best for the soil conditions I expect to encounter.

-Jim

Good video...thanks for sharing. But there is one fantastic flaw in the testing he does. The pull on the Abe's anchors is about 90 degrees to the ground, which is the strongest orientation for a ground anchor. Had the Abe's been tested at 45 degrees like the rest, I believe it would have failed at a much lower rate.

I do like the Abe's design, but the test wasn't apples to apples because of the different angles.

The problem I have with all of these systems is A: they don't really work that well most of the time, and B: they're heavy...or at least too heavy for me to haul into the backcountry. Are they better than nothing? Sure...but almost strong enough doesn't save your plane. I guess 350 lbs of resistance is a hell of a lot better than none, but I sure wouldn't sleep well if that's all that was holding my airplane down. I can pile up 350 lbs of rocks pretty fast, and all I have to cary with me is a rope.

Duckbill anchors work better than any of the airplane specific anchors, but they're expensive, unretrievable for all practical purposes, and you still have to cary a heavy steel bar to plant them.

Bottom line is all of the "portable" anchors leave something to be desired.

cstolaircraft wrote:what about 3 stakes driven in a triangle the a direct pull in the center of them vertically. Something you would place directly under your tie down.

I've considered that, but without even trying it I see problems. Unless you can pull on all three anchors equally, one will come up, then the next, then the next. You won't get 3X the hold. A constrictor knot should pull the three stakes together so you're pulling them as a unit, but stakes disrupt the soil significantly when you drive them in, especially if there are any rocks mixed in. Driving stakes in close proximity to each other weakens the soil that they pull against, and stakes wander as you pound them. Getting three stakes in a tripod that touch each other would be unlikely in most soil types.

The three-in-a-row system I use (also a standby of traveling circuses) spreads the "dirt damage" out. Because each stake is tied under tension to the stake behind it, it acts mostly like a single unit. Not perfect, but the design makes up for some of the shortcomings of soil.

I still don't have a real good idea of how much anchoring is enough. I just know that more is better.

cstolaircraft wrote:what about 3 stakes driven in a triangle the a direct pull in the center of them vertically. Something you would place directly under your tie down.

That's essentially "The Claw". FWIW, I've had my "The Claw" for about 9 years, originally purchased for the turf at OSH. But it's worked fine at every other soil condition I've encountered since then, mostly hard packed natural soil, although I've never had it in just hard sand--my guess is that it wouldn't work very well there. The strongest winds have been at OSH this year, at about 56 knots "official"--who knows the actual gusts--and none loosened.

On the wooden stakes issue, their sideways load capacity would be much less than an equivalent steel spike or angle iron. I'm no engineer so I don't know the terminology, but wood's strength is much greater lengthwise than sideways. Granted that steel is heavier, but not so much as to make wood better.

Cary

Cary wrote:
On the wooden stakes issue, their sideways load capacity would be much less than an equivalent steel spike or angle iron. I'm no engineer so I don't know the terminology, but wood's strength is much greater lengthwise than sideways. Granted that steel is heavier, but not so much as to make wood better.

Cary

You're absolutely correct. Steel would be a better choice, at least for the first anchor stake, but even two steel stakes are too heavy for me the majority of the time. Also, while angle iron is better, a (relatively) small diameter steel rod will pull through the soil easier than a fatter wooden stake.

Maybe one day I'll score some heavy-gauge angled titanium stock... Until then I'll probably be cutting stakes after landing.

I'm sort of surprised they didn't test the claw. I bought a set, tried them a few times, and eventually decided they weren't worth the weight. I think it's a clever design, but I just don't trust it enough to haul it around. That's a gut feeling on my part...I've never tested it. Also, given my horsepower and where I like to play, I'm a real weight weenie...much more so than a lot of flyers.

I've got a couple more wooden stake based designs I'll test when I get back from my next trip.

Hammer wrote:


Maybe one day I'll score some heavy-gauge angled titanium stock... Until then I'll probably be cutting stakes after landing.

I'm sort of surprised they didn't test the claw. I bought a set, tried them a few times, and eventually decided they weren't worth the weight. I think it's a clever design, but I just don't trust it enough to haul it around. That's a gut feeling on my part...I've never tested it. Also, given my horsepower and where I like to play, I'm a real weight weenie...much more so than a lot of flyers.

I've got a couple more wooden stake based designs I'll test when I get back from my next trip.

I've always thought the Claw with titanium spikes would be a good ground anchor. I think Abe tested the Claw and others at Johnson Creek a few years back. Those results should be posted on here somewhere.

Anyone have a source for titanium rod/spikes? Those wood anchors look intriguing for use in soft ground.

I ran across an older test by someone else at Avweb. In it they test the claw and some others:
https://www.youtube.com/watch?v=Loq1olceSIE

This second video reinforces for me the idea no single design is best in all soil types.

If I could get my hands on Titanium spikes I would also be very interested. Most of these multi spike designs would suddenly get light enough one could build some sort of master kit with the benefits of all, for hardly more than the weight of one type.

I am also extremely weight sensitive. The clever tie Down system Hammer has developed will add to this recipe very well. I have learned from a lifetime of backpacking the truth in the cliche "watch the ounces and the pounds will take care of themselves".

I ordered a claw for my trip from Alaska but it didn't come in time. My backup plan was to bury stakes I'd cut similar to snow toggles. Luckily I didn't have to do that.

Other than the extra work to dig and bury, would that have been a good field-expedient method? I carry a small hatchet and E-tool when I fly.

blackrock wrote:Anyone have a source for titanium rod/spikes? Those wood anchors look intriguing for use in soft ground.

http://www.onlinemetals.com/merchant.cf ... p_cat=1353

Bring your wallet...

CamTom12 wrote:I ordered a claw for my trip from Alaska but it didn't come in time. My backup plan was to bury stakes I'd cut similar to snow toggles. Luckily I didn't have to do that.

Other than the extra work to dig and bury, would that have been a good field-expedient method? I carry a small hatchet and E-tool when I fly.

In most soil, I don't think the buried picket would be a great system. In soil that will have some hold, it's a lot of effort to dig a trench (rocks, roots, sod, shallow graves), and in doing so you've disturbed the integrity of the soil. Once one side of your buried picket starts coming up, the whole thing is going to pull out with little effort. I'd be more inclined to bury a rock than a picket if that was my only choice, but digging holes isn't my idea of a good time and I'd try something else first.

The system is used in snow because there's often little other choice. In soil you'd be better off just driving the stake into the ground and tying off to it, in my opinion.

By the way, a 3-pound boys axe weighs little more than a hatchet but you can do real work with one, and they're much safer to use because of the longer handle and two-hand grip. E-tools are handy, especially after morning coffee. The lightest and strongest one I've found is made by Glock. It's a beautiful piece of engineering, but still a piss-poor tool for digging any sort of real hole.

So I tried another version I've been curious about. It held pretty well, though I used short stakes and that was a mistake. I need to try it again with longer stakes. I should also try it with a load strap anchored to each end and a pulley equalizing the load between the anchor and airplane. That might be the ticket.




The load strap was directly under the winch and at the balance point of the anchor log, but once one side started to go that was all she wrote.


Not a bad showing though...1,500 lbs from forest gathered materials and a bit of rope.


It looks like a lot of work, but it wasn't too bad. The skinny stakes pound in easily, and tying them together was a couple minutes at the most. Assuming there is an abundance of good stake wood close at hand, a person skilled with an axe and hand saw could make one in fifteen minutes without rushing.

And by the way, I'm not disrespecting the claw or any of the other pre-fab tie downs. They're one of the few options for parking on "lawns" such as you might find at Osh or Sun n Fun, as I don't think the groundskeepers would look favorably on large stakes being driven into their grass, then cut flush on leaving (often you cannot get them out). They're also better than nothing if circumstances make those your two options. I just don't think they are ideal for the backcountry, both because of weight and holding ability. Since weight and holding ability are two of my fetishes, that opinion is probably of limited value to other pilots.

blackrock wrote:
Anyone have a source for titanium rod/spikes? Those wood anchors look intriguing for use in soft ground.

Hammer wrote:

http://www.onlinemetals.com/merchant.cf ... p_cat=1353

Bring your wallet...

Not really all that bad. This is closer to the size we would be looking at for Claw Spikes, but we would want 9 of them for about $100 in total.

http://www.onlinemetals.com/merchant.cfm?pid=6784&step=4&showunits=inches&id=185&top_cat=1353

Grade 2 is pretty soft. grade 5 is the good stuff.

tailwind5sw wrote:Grade 2 is pretty soft. grade 5 is the good stuff.

Good to know so thanks for that. Any idea where to find it for less $'s wife balked on $100 for for 9 nails. Smart lady!

I'd stick with steel. Land scape spikes or rebar spikes with rings welded on. 2024t3511 or 7075t7351 would be OK but still won't take the hammering well as steel

EBay for those interested 170690597798

Good idea re 7075. Really don't use them but a few times a year so aluminum would be ok. Those steel spikes are awfully heavy to pack around all the time. I also carry duck-bill style anchors. Maybe, I should just carry those alone instead of both those and the Claw.

Anyone find any duck bill results?

blackrock wrote:Anyone find any duck bill results?

Duckbill #68 in "average" soil is rated to 1,100 lbs (485 kg) by the manufacture with a 30" drive depth.

They make one smaller and a few bigger, but this is about as big as you'd want to drive, and plenty strong. They are a great design and the anchors themselves are really light, but they have some issues for any sort of regular use. I use an ax to drive wooden stakes, but would never use it to hammer on a steel driving rod, so either find a rafting ax with a hardened poll (rare) if you want a multi-use tool, or lug a hammer around which is of little value for anything else. Driving a duckbill thirty inches with a rock is probably possible, but not feasible.

You also have to cary around the steel drive rod, which is a couple pounds. I guess you could substitute a titanium one, but $$$. And, at $6 a piece, the anchors make for a pretty steep backcountry ramp fee. On top of that, if the field gets mowed (and many of them do, even if it's with a horse-drawn rig like at Fish Lake), leaving those loops of cable sticking out of the ground is very irresponsible. Digging thirty inches to retrieve them is impractical and you can't drive them deeper once they set, so I guess now there's a set of cable cutters in the tool box, too. That'll discourage people from going barefoot...

tailwind5sw wrote:Grade 2 is pretty soft. grade 5 is the good stuff.

Can you explain a little more what that means? Soft as in easily deformed, or easily bent, or poor edge holding, or...? Soft compared to what...I mean is it really too soft for this application? Would it bend under force in the claw, or deform from the hammering? Most of my experience is with titanium tent stakes which are astoundingly strong, but I don't know what grade they are. Does titanium get brittle the way steel does as it gets harder?

Steel might be the perfect material from a structural point of view, and certainly from a price point of view it superb, but it's simply too heavy for me.