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Ankle saver mod

D

danal

FRIEND
Sumter SC
Hey ya'll,
Anyone ever done the ankle saver mod? You know, the extra diagonal tube from the lower engine mount lugs up to the first cluster. I would like some thoughts as to how popular it is and if I should add it to this Spraker fuselage I have been working to sell. Also if anyone has done this what size tubing was used? Thanks, Dana
 
danal said:
Hey ya'll,
Anyone ever done the ankle saver mod? You know, the extra diagonal tube from the lower engine mount lugs up to the first cluster. I would like some thoughts as to how popular it is and if I should add it to this Spraker fuselage I have been working to sell. Also if anyone has done this what size tubing was used? Thanks, Dana
Click to expand...

use the search box, been discussed here before

only time it's gonna be useful is if you do something stupid like controlled flight into terrain... and then it's only sooo useful...
 
Stewart

Here is a link to a thread where it is discussed. In the one photo you can clearly see where the lower longhorn buckled and had clearly started the fold up process that traps the pilots feet and or crushes the ankles. In this case it did not totally fold and break anyones ankles but it was certainly on the way. The Mod adds about 15 oz for both tubes. Everyone has to decide on their own if they think it is worth it.

Bill
 
I think a lot of scenarios are statistically unimportant. In the past few years of my own observations two items stand head and shoulders above other Supercub safety concerns. If pilots want to improve self protection they should start at the top of the threat list.

Wear a helmet.

Improve the fuel system to prevent post-survivable impact fires.

The former is simple. The latter isn't. Both appear to be more important then an ankle tube. I don't have any criticism of adding the tube but guys should keep it in perspective. By the time that tube becomes important you have a good chance of being in bigger trouble from the bigger threats.
 
PA-22/20-160 said:
Has anyone ever figured out were the energy is going to be transferred too with this mod? Could you be making a failure of the fuselage worse in another spot, I'm not educated enough to know but not being STC'ed has an engineer ever looked at this?
Click to expand...

I think the same observation was made about the overhead X brace and transferring energy somewhere else. I think that experience will prove it out just like the X brace. Atlee was so convinced that it would save lives that he gave the STC out for free.
Every wreck/ impact has its own characteristics in energy dispersal. It would be very hard to evaluate without crash testing.

After first proposing this 12 years ago I was contacted by several people literally from around the world that wanted drawings or to just share experiences.

One individual had two friends die in two separate crashes because their legs were pinned in the cockpit and a fire broke out.
Another had his leg and hip shattered in his cub from a bad beech landing and he felt sure that something like this would have helped him. He installed it during the rebuild.

There is no way to ever tell its true effectiveness, and can only be evaluated similar to the overhead X brace. If the structure keeps together and not trap you then it was the right thing to have.

I have not heard from anyone who has actually "tested it".

I do feel that it is in the "direction of goodness" and install them every chance I get.
 
Not to hijack this thread, but you mentioned Atlee giving the X brace stc away. The cheapest I find this stc for now is $245. I have no problem spending that for a mod that is that important, but is it cheaper somewhere else?
 
When Attlee was alive he gave it away. Everything is now owned by Univair (to the best of my knowledge), which would explain the change.
 
Dave Calkins said:
I have always likes the mod

just wondered if it has been engineered through by a structures guy
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Dave: No formal engineering review has been done to my knowledge. I would like to see a review as well but don't have a resource for that. $$$
 
Atlee use to give it away but started charging for it long before Univair bought them if my memory serves me correctly.
 
Dave Calkins said:
I have always likes the mod

just wondered if it has been engineered through by a structures guy
Click to expand...

cubpilot2 said:
Dave: No formal engineering review has been done to my knowledge. I would like to see a review as well but don't have a resource for that. $$$
Click to expand...
Without putting a pencil to paper, by installing the new diagonal attaching it to the original in the center, you are effectively cutting the length of the original diagonal in half. This increases the column strength of the original tube by a factor of two thereby increasing the strength of the truss between the spars. An alternative method would be to replace the original diagonal with a tube of increased diameter and wall thickness. I like the cross tube method better because no matter which wing is hit one of the cross tubes will be in tension, which is a stronger option.
 
Pete. Thanks

now could you give an analysis of the extra crosstube to the firewall? Thanks:roll:
 
This increases the column strength of the original tube by a factor of two
Click to expand...
Actually by more than 2, for a "slender" column in pure compression. But there are a couple of primary "HOWEVERS" to go with that. Without doing any calculations, that tube may or may not be "slender". If it isn't, then the compressive strength is independent of length. If it is "slender", then buckling becomes the issue and the brace tube would only conteract buckling in the plane of the tubes, not cross-plane. Also, in a crash the imposed loads would most likely not be pure compression - bending would also most likely be introduced. I think the conclusion is that the cross brace will certainly increase strength, however how much is necessarily dependent on ill-defined circumstances.

The following links provide some basic info for pure compression
http://www.engineeringtoolbox.com/euler-column-formula-d_1813.html
https://www.quora.com/What-is-slender-column-and-short-column
 
I put it in when i had the chance. Im gonna roll the dice regarding load transfer vs leg entrapment should it ever be needed.

I dont know for sure but Im guessing Mr Piper didnt design the fuse structure with too much crash-worthyness in mind...
104_PANA-P1040568_P1040568.JPG105_PANA-P1050420_P1050420.jpg
 

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This mod was fitted to New Zealand Ag Cubs in the 50's and 60's. There was also a tube from the cluster at the top of the additional diagonal to the V-tube that runs across the windscreen.

Believe me, it was added because some very nasty crashes on ag work that caused major leg and abdominal injuries. While it would've been dreamt up by some practical LAME's after looking at wrecks, it went on to be reviewed and possibly analysed by some professional engineers in the then named NZ "Air Department", now CAA.

You can make of that what you wish, but that area on the Super Cub is very light; 1/2" and 5/8" tubes, yet everywhere else we see 3/4" and 7/8". For a 150 hp and greater Cub the weight involved is insignificant. The logic I follow, just says it's a good idea.

Andrew.
 
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