# Civil Engr: Airplane tie-down hardpoint

1. Nov 4, 2008

### mshinavar

First off, I'm an aerospace engineer so please excuse the general incompetence in all civil and concrete matters

I would like to make a steel reinforced concrete anchor point to tie down an airplane. The force applied to the eye bolt tie down is 10,000 lbs at approximately a 30 degree angle. assume the concrete footing is cylindrical and the top of the concrete is level with the ground.

how would i go about calculating the required size/weight/etc... of the concrete footing to restrain this force? Is there an equation (or equations) for this? I assume there would be.

I guessed (remember, aerospace engr) that if each component of the force (x,y) was less than or equal to the weight of the concrete and the associated dirt pull out cone, I would be conservatively safe. Is there a dirt stickiness coefficient (the amount dirt tends to stick to itself)? the density of dirt (hard packed desert soil)?

It seems like these are all pretty elementary questions for anyone that has taken a class in foundations or the like, unfortunately that is not me. I've given it the good old google attempt...no dice.

any help would be greatly appreciated

2. Nov 4, 2008

### Danger

I expect that it would depend to a large extent upon the shape of the concrete. A fat plug would have different numbers than a tall column. You'll probably want to undercut it, so it will most likely be a conical or wedge shape. Sorry, but I can't help with numbers.

3. Nov 5, 2008

### FredGarvin

I came across a MIL spec for aircraft tie downs a while back. I will see if I can dig it up again.

4. Nov 5, 2008

### Mech_Engineer

All I could find were these two document numbers, but they aren't available online as far as I can tell:

MIL-T-21063A Tiedown, Aircraft Mooring, Type TD-1A
MIL-T-26908C Tie Down Kit, Aircraft Mooring, Arctic, Type MD&1

5. Nov 5, 2008

### FredGarvin

Take a look at ETL 1110-3-430 from the Corps of Engineers. It rates them at 15,520 Lbf at 19°.

6. Nov 5, 2008

### mshinavar

thanks for the help guys, ill look into those.

i figured as well that the shape would play a significant part. unfortunately it is cheaper to buy more cement than to pay people to dig a bigger hole. (without looking at the numbers, of course)