[Captain Sacto]

Hi folks!

I'm prepping the tiedown bar for the wing spars on my 7A, and I have a question for the resident experts.

It seems to me that I can save some weight by removing some material from the bar, much of the squarish bit from the top down to a half inch from where the bolt threads start. (Pls see photo insert. I'd slice along the solid blue line.)

I can't see this as being a major stress issue, because the force will always be pulling downward, from the bold threads. However, I'm just guessing, and before I start slicing, I thought I'd run it by y'all.

Thanks in advance! -- Tom in Sacramento

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[L.Adamson]

Box structures provide a lot of additional strength. Besides pulling straight down, you could get a lot of loads to the sides, due to wind. IMO, you'd be reducing the effectivness. But I'm not an engineer...........I just deal with sheetmetal boxes all the time.

L.Adamson --- RV6A

 

[Danny7]

I don't know what else that part ties into atm, haven't got time right now to dig out my plans. but you will be removing the meat of most of the T section, the remaining portion will be significantly less stiff in a different manner than stock. I seem to remember this part being tied into some other parts of the structure, this will affect how it supports those parts. It is a very little weight you are removing (much of it is already hollow), is the weight difference going to matter?

 

[larrynew]

Aileron Bellcrank

It also supports the aileron bellcrank on the other side of the main spar web.

 

[bruceh]

Don't forget that these can also be used as jacking points.

 

[DarylT]

Tie Down Points

Especially with these.

 

[civengpe]

Also remember that tie downs don't come straight down from the rings. They tend to form a 45 deg or so angle from the ring to the tie down itself. This induces a lot of lateral loading on the ring.

If we use the 45 deg as an example and you have 400 pounds of lift on your one wing from wind the lateral and vertical loading are both 282 pounds. This lateral loading induces a moment at the ring and wants to try to twist the support structure that you are going to cut.

If the angle is greater than 45deg the lateral loading goes up.

 

[Captain Sacto]

Thanks all!

I'm always amazed, but not surprised, by the aero-acumen and helpfulness on this forum.

I'll leave it as is (for all the good reasons stated above.)

Thanks muchly!

 

[civengpe]

Sorry. I fat fingered the calculations above.

The vertical and lateral loads would both be 400# each. The total tension of the tie down would be 565#