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Argument for good tie-downs

flyboy1963

flyboy1963

Well Known Member
Sorry if there's an existing thread on this....
Interesting that on some days, there are no posts to 'Safety'. What does that say?

....anyway, this video of some guys Pipersport or similar bird, B]blowing away[/B] in a 40 knot wind or whatever, just makes you cringe.

http://www.youtube.com/watch?feature=player_embedded&v=O-wjtP90d_g

...so, yes, it should have been tied down, obviously. More interesting, following a recent thread on control locks, is the practice of tieing the stick full back, because it's handy or whatever. You can see in the video, it definitely can contribute to the wing achieving the necessary angle of attack for max lift-off! Even if it were a TAIL-wind, it would be more likely to lift the tail, and possibly flip the bird.
I'll vote for parking with nose down elevator, or neutral at the least!
( also keeps water - snowmelt from running into the hinges etc.)
 
I sure would like to ask the Cecil B. Demille wanna' be's why they could not have forgone the video, and done something to secure the plane??
 
Mark,

I thought that was some sort of security camera footage, but certainly agree with you if it was being live shot at the time!

greg
 
Blowing Away?????????

That thing flew away! :eek: Holly-molly I didn't expect that to happen.:(
 
Greg Arehart said:
Mark,

I thought that was some sort of security camera footage, but certainly agree with you if it was being live shot at the time!

greg
Click to expand...

I did not think so since the plane was centered in the shot. However, the fact that the camera did not follow the plane probably indicates that I am in error.
I guess that I am still living in the past century, where a camera was usually attached to a human!

Anyway, as the OP stated a good case for always tying down!
 
End result??

So how far did it go? I am guessing the "landing" was ugly......

DETAILS????
 
Pretty stable flight it took.

Imagining the loads on the wings and tie down points with that kind of wind though.... How do you know when the wing has been over-stressed (but not broken) from loading and restraint?
 
DCat22 said:
Pretty stable flight it took.

Imagining the loads on the wings and tie down points with that kind of wind though.... How do you know when the wing has been over-stressed (but not broken) from loading and restraint?
Click to expand...

if it's above manuevering speed?
 
Very little load on the tiedowns when the wind is at liftoff

bkthomps said:
if it's above manuevering speed?
Click to expand...

At the point this plane lifted off, there wouldn't have been more than a few pounds load on the tiedowns. Lift is just sufficient to overcome gravity. As the plane rotated to a higher angle of attack, the lift would have increased somewhat, but certainly not enough to cause any damage. That's suggested by the rate of climb we see in the film. You're probably correct in that no damage would occur unless wind speed were some percentage or multiple above maneuvering-depending on how design limits were established. Probably looking at a tornado/hurricane/typhoon. I'm sure an aeronautical engineer could offer a better explanation.
Terry
 
engineering theories?

I think overstress indicators would be.......... the tie-down rings at the end of the rope....and no plane in sight!

but, really, was it a jet run-up that caused this? Man I feel for the guy, but I can't see insurance doing much for him, unless negligence of the jet could be shown?
 
VTOL?

You're all assuming that it was the wind that did this. Perhaps Piper is working on a VTOL aircraft and this is (was) the prototype.

The vertical takeoff was excellent ... not so sure about the landing, though. :D
 
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The more I look at that video the more that looks like a model airplane. Something just doesn't look right as it lifts off.
 
Bruce said:
I thought it was Andrew at LOE.

Wrong plane though.
Click to expand...

Close enough though...same stall speed and all. The little 12 had about all the wind she wanted there...the video certainly reminded me of LOE, watching the nose bounce up and down. Pretty scary stuff.

I am always torn as to whether or not down elevator is the way to go in a big wind? I have certainly been in some winds where I elected to taxi with at least neutral to slightly down elevator. LOE was certainly one of those. With any forward speed at all, the nose was pretty much trying to come up. Hmmmmmmm...
 
terrykohler said:
At the point this plane lifted off, there wouldn't have been more than a few pounds load on the tie-downs.
Click to expand...
Only if it is a model. If the airplane had been tied down, the load on the tie-downs will a little greater than the weight of the airplane.

bkthomps is correct that the airplane shouldn't be damaged if the wind is below maneuvering speed unless the tie-down mounting is poorly designed . . . or Airbus designed the tail, er wing.
 
I can address stresses, at least from personal experience. About 20 years ago, I owned a Phantom ultralight that survived a tornado that ripped out a row of hangars at OVO. Mine was tied down in the end space, and the only plane to escape with only very minor damage. After the twister went through, it was setting there, all alone on its pad, hangar gone, with six twisted wrecks in a line beside it. Under it was the end hangar wall. That had slid under it while the UL was "airborne" by about a foot or less. The ropes were stretched to the point of being less than 3/8" in diameter (they were 1/2" before) and stiff, until you twisted them and they resumed their previous diameter. Many hours of inspection and two hour's work and I was flying again. NO stresses detected on the airframe. BTW, I still tie down in the hangar, and always will.

Bob
 
Re stress, if it had been tied down it would not have rotated and would not have produced anywhere near the lift necessary for liftoff let alone stress.

At liftoff I doubt it had more than a few hundred lbs excess lift over weight.

2 cents

.?????
 
flyboy1963 said:
More interesting, following a recent thread on control locks, is the practice of tieing the stick full back, because it's handy or whatever. You can see in the video, it definitely can contribute to the wing achieving the necessary angle of attack for max lift-off! Even if it were a TAIL-wind, it would be more likely to lift the tail, and possibly flip the bird.
I'll vote for parking with nose down elevator, or neutral at the least!
( also keeps water - snowmelt from running into the hinges etc.)
Click to expand...


Well, in the case of a tricycle gear, this is correct. belting the stick back helps to rotate the wings to higher angle of attack.

But, on a tailwheel airplane, it would make no difference. The wing is already at a high angle of attack, and the tail loads can not change the wing angle. Only lifting the mains off the ground could increase the load further. SO - I still think it is OK to belt the stick back on taildraggers.

Also, Seems to me that belting the stick back rotates the elevator hinge openings down so they are not open to the environment from above, and also creates a natural way for any rain that gets in the elevator nose to drain out.
 
Terry is correct

What Terry said is correct. At the point where the wing lift is just enough to offset the weight of the airplane, there would be no force in the tie-downs, except for whatever pre-load was in them with the wheels on the ground.
The wing lift would have to equal the airplane weight plus the tie-down pre-load before the wheels would come off the ground.

The stresses in the wings would be less than those from 1-g flight, since they would be producing somewhat more lift as 1-g flight (weight + tie-down pre-load), but have some of the load reacted through the tie-downs, which cancels a LOT of bending moment.

Unlikely you could ever overstress wings while tied down. Lets say the wind was strong enough to produce 6 g's of lift. But 5 g's worth of that force would be canceled by the tiedowns. The tie-downs are outboard of the effective center of lift (something like 45% semispan) so they would actually produce the equivalent root moment of a negative-g condition. For my 24' span RV-8, they are at 52% span. A quick moment balance says it would take 48 g's of wing lift to cause -3 g's of net moment on the wing root from the combination of wing lift and tie-down downforce.


terrykohler said:
At the point this plane lifted off, there wouldn't have been more than a few pounds load on the tiedowns. Lift is just sufficient to overcome gravity. As the plane rotated to a higher angle of attack, the lift would have increased somewhat, but certainly not enough to cause any damage. That's suggested by the rate of climb we see in the film. You're probably correct in that no damage would occur unless wind speed were some percentage or multiple above maneuvering-depending on how design limits were established. Probably looking at a tornado/hurricane/typhoon. I'm sure an aeronautical engineer could offer a better explanation.
Terry
Click to expand...
 
You guys concluding that there is very little load in the tie downs are assuming a perfectly stiff airplane. Wings are quite flexible, so the much of the weight is still being supported by the gear.

I still don't think there are many cases where the load is high enough that the structure will be damaged.
 
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