So headed to KOSH shortly and was wondering how the best way to tie down a tail wheel aircraft.
Should I tie it facing into the prevailing wind direction and tie the elevator for full nose down? Should I tie it tail first and angle the elevators down? My thinking is nose into the wind and set the elevators to lower the nose(reduce angle of attack) into a storm and leaving the tail ropes a little loose to allow the tail to rise.
Having gone through the tornado in SNF in 2011 and the storm at the beginning of OSH last year, I saw a lot of tie down failures, albeit, not much would have survived the tornado in Lakeland.
Anybody have any tips?
Pete

tie it down not for the current winds, but for the worst winds which will be generally from storms coming from the west. But you may not have much choice depending on where you park. Install gust locks with elevator at a neutral position. use good quality anchors not the dog spiral stake. Flyties or claw work well. keep knots snug and tend the plane during the storm. Make sure all the planes around you are tied down well too - because it's their plane that will give you the worst day ever.

Do not leave the tail line loose...all lines need to be snug. Once the airplane starts bouncing around in the tie down it's all over. The shock load is going to pull your ground anchors out, guaranteed. Shock load will compromise your ground anchors a lot faster than a high angle of attack and resulting lift.

I'd double up or triple up whatever ground anchor system you're using. Most ground anchors just don't hold that well.

I think we had a similar discussion awhile back and using a trucker's hitch knot was considered a good choice for securing your lines.

http://www.animatedknots.com/truckers/#ScrollPoint

That knot or rolling hitch around the center line also seem to work well.

http://www.animatedknots.com/rollinghit ... crollPoint

As hammer said keeping tension on the lines prevents the shock loads. If the wing or tail gets some momentum you are into the old velocity x mass formula which can produce big loads on your tiedowns and aircraft.

I have always used the TAUTLINE hitch: You can tighten OR loosen it WITHOUT having to untie it.
Never had one slip in 60 years.

Chris C

OK but nose TO or AWAY from the storm?

pouellette wrote:OK but nose TO or AWAY from the storm?

I'd say nose to the wind if you have a choice....that's what the airplane wants. Though it seems like with summer thunderstorms the wind direction is less than predictable.

One thought on gust locks and being human: I won't attach them externally to ailerons, elevator or rudder surfaces. I secure those from the pilots seat so they have to be removed before I can physically fly the plane. Came to that logic after landing with a gust lock still attached to a flap. Had I left it on the aileron instead, I might not be here today.

I think Pops and Shortfielder may have a story to tell, too...

Some folks will pooh poo internal control locks saying it is too hard on control cables. I call BS on that!

I know very little of an S7, but I know for certain that a big wheeled cub parked tailed to a giant wind is a sure way to collapse the rear struts. Once the first rear strut fails the aircraft will most often beat itself into a complete loss. It is not uncommon to see cubs that park outside in high wind areas have 2x4 doublers on the struts when parked unattended. When I kept my cub outside at our work strip I kept one tiedown on the cabane, so I could turn loose of the wing and tail and pivot it into the wind if it switched up by more than 90 degrees.

Take care, Rob

Hey Mike, Amen to the human things, we do both inside and out on the work planes, and I have seen more than one comeback with a lock left somewhere. Have also seen more than one Pratt started with a prop lock still on

You really don't have too much of a choice on which way the airplane points at OSH, unless you raise a hubbub if they want to point the tail to the west. That's the normal direction from which the storms come, but once they're on top of you, the wind blows different directions.

Having seen airplanes which weren't snugged at all 3 points get severely damaged in a gusty wind, I agree that all lines should be tight. Personally, I like some forward stick (down elevator), whether a tail dragger or a trike, rather than exactly neutral--and definitely not aft stick.

I do use exterior gust locks, but I remove them as part of an extended walk-around pre-flight. I first walk around, removing the gust locks as I get to them, and then do a normal walk around pre-flight, just in case I miss any on the first pass--although that hasn't happened yet. Both my IA and a good friend who is an IA in Idaho have told me that repeated winds beating against the control surfaces will eventually do damage to the control cables, if only the interior gust lock is installed. How long is eventually? Who knows?

Cary

Almost any airplane is built to withstand at least 90 MPH (cruise speed) head-on. At high flight speeds if you pull back on the stick too hard and raise the angle of attack too much, you can overstress the airplane. Same on the ground; if you force the airplane to be at a high angle of attack and the wind gets strong enough, you overstress the airframe just like as if it was abused in flight. So the trick becomes finding a way to have the airplane in the best configuration and angle in a windstorm that does not create all those over-stresses in the first place.

Although I am absolutely certain that the physics and overall concepts mentioned above are valid, in fairness I do not have years and years of experience tying down airplanes in a windstorm. So what I am about to say is theoretical. That said, see if it makes sense in your mind.

I believe that the most effective method of preventing damage to a tailwheel airplane in a wind event is to reduce the angle of attack to zero. Whether the wind is coming from the front of the airplane or the back, having the wing chord parallel to the wind dramatically reduces the loads that the wind can put on the airframe. One poster has mentioned that wind coming from the rear can collapse the wing struts, even though you might think that this is a "safe" configuration (because the wind is pushing the wing down instead of lifting it off the tiedown).

However, it has also been mentioned that leaving the tail ropes loose (to allow the airplane to level itself automatically) presents other problems.

So one potential solution is to have the aircraft's tail supported in a level attitude by some sort of sawhorse, stand, tripod, crate, etc. This would allow the tail to be "tied down securely" and still put the airplane at an angle that would not dangerously load the structure.

For a light aircraft (Cub, Taylorcraft, RANS) it seems possible to me that a reasonably lightweight folding tripod or 3 sided pyramid can be constructed that supports the tailwheel tire or fork. Supporting the tail this way will REQUIRE two additional ropes and anchors on the left and right side of the tailwheel, to prevent the airplane from yawing or rotating off the tripod. Also there will need to be the one "standard" tail tie down that pulls the tail downwards downwards to the ground (and onto the tripod).

With all sincere respects to Blackrock, I have to cast my vote for the external gust locks. Preventing damage to the control system should also be a very high priority. If forgetting these gust locks is a risk or problem you are concerned with, then have a fixed, permanent rope that connects the gust locks to the tiedown ropes, so you cannot move the aircraft without having removed the gust locks.

Effective, big-wind-proof gust locks are cheap and easy to make. The old reliable "plywood oval" is 100% effective, prevents ANY loads from being put on the control system, and is cheap to make. They can store flat against each other, and the weight conscious folks can make them out of carbon or aluminum instead of plywood. These type of gust locks are actually shown in the Cessna operator's manual if you look for them.

The simplest solution to the OP's question:

Buy three Duckbill model 88 ground anchors with the driving rod, sledge hammer, a set of cable cutters, a garden trowel, and 40 feet of 7mm kernmantle nylon rope. At Oshkosh park the airplane wherever they instruct you to, drive in the duckbills to the full 42" and tie the airplane off good and snug on all three points. Make sure you position the tie downs so they pull against each other...in other words, once the airplane is tied down you can't roll it backwards or forwards and loosen the lines. That set up provides approximately 3000 pounds of holding force per anchor, which should be a bit more than adequate if you tied the knots correctly. Chalk the tires. Secure the control surfaces. Keep the doors and windows closed. Stake down your tent and secure the lawn chairs and other items so they don't fly into your airplane when the wind hits. Photograph everything in tip-top shape in case you have to file an insurance claim and this is as secure as you're going to get.

When it's time to leave, dig down six or eight inches around each duckbill anchor and cut the cable off so it doesn't get wrapped up in a mower blade and the cut ends don't impale some barefooted pedestrian. Consider the $50 in lost duckbills a tie down fee.

A quick note on liability: I don't know what the norm is for insurance claims, but I know of at least one case where an uninsured airplane broke free from inadequate tie downs and struck a neighboring airplane. The uninsured owner claimed it was an "act of god" and therefore not his fault. He got sued and lost, and had to pay damages for his neighbors airplane out of pocket. Oh, and his airplane was totaled. Good things happening to good people, but that's a different story.

As for tie-down theory:

I agree that less angle of attack is better, but putting the tail up on a tripod or saw horse? No thanks!!!!!!

Something professionally engineered, tested, and fabricated for a specific airframe could certainly work, but lifting the tail up onto a improvised stand and tying it off to some ground stakes strikes me as infinitely more dangerous than just accepting the high angle of attack, regardless of wind speed or direction. I don't think you can adequately secure the tail to the stand or the stand to the ground, and when the tail comes off the stand or the stand breaks it could easily go through the tail feathers, AND the tail will no longer be secured.

For the bushwheel crowd a much simpler solution is the let most the air out of the tires. Ya...doesn't look cool, but it does reduce the angle of attack...

Another solution (probably not acceptable at Oshkosh) is to dig a couple holes for the main gear and push the tires in. This not only reduces the angle of attack without the complications and additional risks of lifting the tail, but it acts as super-chalks. Anyone trying this needs to ensure that a whole lot of manpower is available when it comes time to leave, as getting the airplane out of the holes is surprisingly difficult.

And at the end of the day, if you're dealing with wind strong enough to damage the airframe and you're not tied to permanent in-ground anchors, it's unlikely your airplane is going to stay put. It's certainly possible to rig field anchors that will hold the airplane in any amount of wind, and if I was going to be at Oshkosh for two weeks I suppose I'd take the time and expense to rig them, but it's not the norm. And even then your airplane is just going to act as a collection point for all the other airplanes, tents, chairs, kiosks, EzUp sun shades and small children that are tumbling across the field if the wind gets that strong.

As for gust locks...I secure my rudder and my elevator with the same external device. It ends up being full stick-forward...that's just how the device holds it, and it works fine.

I understand the inherent visibility difference of internal vs. external gust locks, but I don't subscribe to that line of thought. Like the admonishment about never turning the fuel selector to "Off" because you might forget to switch it "On" before take off, there's some logic in it, but not enough (to me) to warrant the procedure. "Controls free and correct" is a foolproof two-second part of the pre-takeoff check, just like "fuel on both".

If you chase down and eliminate every potential pitfall then you just have to quit flying. If not using external gust locks works for you then that's fine and I don't think it's wrong, but I don't feel they are inherently unsafe.

This thread is a good reminder that not every storm is survivable. Good review on techniques, Hammer's advice seems the most qualified in my opinion.

Wiki photo of trees in Wisconsin after a thunderstorm. Unbelievable winds...



In Oregon we had an entire forest sheared off a few years ago on the Coast. It was Biblical to say the least. I forgot to photograph the damage! Was in shock for a moment.

At OSH, it's unlikely that you'll get to choose which direction your airplane faces, and as others have noted, the wind often switches as a storm passes anyway.

One thing nobody has noted yet: Place your tiedowns (I use Fly Ties) DIRECTLY under the tiedown rings on your aircraft. Do NOT place them out to the sides, nor forward or aft of the tiedown rings.

If your tiedown rings are at the top of struts, as on highwing Pipers and cessnas, run that tiedown line through the tiedown ring, then around the top of the strut. That way, if the tiedown ring fails, the strut will still hold the line.

I've dug holes for tires to level the plane, but that's not an option at OSH.

In any case, my worst nightmare at OSH is not MY airplane, it's the ones around my airplane. All it takes is one plane getting loose and all hell can break loose, with lots of damage. Last year as that gust front came through, a J-3, tied with itty bitty crap poly rope and dog tiedowns came loose and banged up on its nose, then swung around and caught the aileron on a cessna nearby. I watched it happen....really lucky it wasn't much worse.

I've watched Piper aft struts fail, as Rob described. In one case, I stopped same by putting my back under the aft edge of the wing.....then what do you do? Fortunately, a town cop came along, and I told him to go roust the owner of the plane (who I knew) and tell him to get his ass to the airport.

Anyway, at OSH, tie things down as good as you can. Don't use the screw in "tiedowns" (dog tiedowns), use good stout lines, gust locks, and tend the plane if it blows.

Then, enjoy the show.

MTV

mtv wrote:One thing nobody has noted yet: Place your tiedowns (I use Fly Ties) DIRECTLY under the tiedown rings on your aircraft. Do NOT place them out to the sides, nor forward or aft of the tiedown rings.

This depends on the quality of ground anchor you're using. One size need not fit all.

Snug Lines that wont break. Anchors that wont pull out. Use extras if need be. Nose into wind if possible. Dig holes for mains if you can. External gust locks. Make sure the neighbors plane is the same. Sleep easy. (I've had bent aileron push rods and a damaged rudder parked tail into wind in a storm with the internal control lock only . Couldn't fly it afterward.)

Battson wrote:

mtv wrote:One thing nobody has noted yet: Place your tiedowns (I use Fly Ties) DIRECTLY under the tiedown rings on your aircraft. Do NOT place them out to the sides, nor forward or aft of the tiedown rings.

This depends on the quality of ground anchor you're using. One size need not fit all.

Agreed. Some field tie downs like the Claw and Fly Ties are engineered to work best directly under the tie down ring like MTV says, which a lot of people don't seem to understand. But other systems, like duckbills or wooden stakes picketed together, will hold stronger if offset towards the wing tips. It just all depends on what rig you're using.

It's not a huge factor, but the more weight you have in the plane the more wind it will withstand. Fuel tanks as full as possible, and leave the ice chest inside the airplane with a sleeping bag over it...it's good ballast and the ice will last a lot longer than if it's sitting out in the sun. Might keep a few beers from disappearing as well...

Hammer wrote:

Battson wrote:

mtv wrote:One thing nobody has noted yet: Place your tiedowns (I use Fly Ties) DIRECTLY under the tiedown rings on your aircraft. Do NOT place them out to the sides, nor forward or aft of the tiedown rings.

This depends on the quality of ground anchor you're using. One size need not fit all.

Agreed. Some field tie downs like the Claw and Fly Ties are engineered to work best directly under the tie down ring like MTV says, which a lot of people don't seem to understand. But other systems, like duckbills or wooden stakes picketed together, will hold stronger if offset towards the wing tips. It just all depends on what rig you're using.

It's not a huge factor, but the more weight you have in the plane the more wind it will withstand. Fuel tanks as full as possible, and leave the ice chest inside the airplane with a sleeping bag over it...it's good ballast and the ice will last a lot longer than if it's sitting out in the sun. Might keep a few beers from disappearing as well...

A number of years ago, the Alaskan Aviation Safety Foundation sponsored a test of tiedowns. The tests were run with a strain gauge and cable. In every case I recall, the tiedowns held best with a straight vertical pull.

MTV

A number of years ago, the Alaskan Aviation Safety Foundation sponsored a test of tiedowns. The tests were run with a strain gauge and cable. In every case I recall, the tiedowns held best with a straight vertical pull.

MTV

Do you recall if they tested duckbills? Since they have to pull through more undisturbed soil (at an angle) I believe they should hold more in that configuration. Picketed wooden stakes will definitely hold better at an angle...I've done the tests with a load cell, and while I didn't pull straight up, the mechanics are pretty obvious. There's a post somewhere here on "field tie downs" with photos and numbers. All good information.

My view is that you aren't trying to deal with the 120 mph storm. You have very little ability to predict direction of the wind and the wing loads are way higher than you can design for especially when you consider the gust and variability components of a major storm. You will only get a choice of two directions at Oshkosh anyway since they park everybody in rows. Worry about the 70mph storms and that will be about all you can do. As far as leveling the aircraft, I completely disagree. Think maneuvering speed. You want the airfoil to stall to unload the wing which means high angle of attack. Tie the trail to the ground and with a TW aircraft, you'll be about right. I saw a 170 tired down broadside to the wind once with external gust locks and while the top of the rudder stayed straight, the slab side of the rudder bent over to the rudder stop. I haven't used external gust locks since. Some might be ok, but don't just put something on the balance horn.

Wayne