Forrest..... Strut Question Tf#733

[1938BF50]

Forrest,

Can you PLEASE look at the old strut drawing(s) and tell me what the thickness, material, major and minor axis dims are for the earliest "B" models? If you read my testing post you will see that my original 1938 strut is .038 thick full length.

Can you tell me if the drawing has a REV history regarding material thickness. This will be a very pertinent issue where NDT is concerned. I would like to run strength calcs based on what my plane(20407) was certificated with.

Thank you,

[Forrest Barber]

Re: Forrest..... Strut Question Tf#733

That is all on the A-A815 drawing. there are three alternates mentioned.
changes are by E.O. and redrawn when necessary.

Front strut Kawneer Streamline , section #1728 - .049 #1025 steel
note: Optional section #1668- .035 #1025 steel

then "G" added Alternates on 9-17-45 by E.O. ( Engineering Order)

wall maj minor equiv. round

1st Alt .042 3.035 1.286 2.25
2nd .049 3.035 1.286 2.25
3rd .049 2.866 1.214 2.125

THEN Feris added others as material became scare, I may post them later in the week. She went as low as 1010 , YES 1010 steel. These various changes played havoc with the rear strut welding jigs for proper alignment.

[VictorBravo]

Re: Forrest..... Strut Question Tf#733

I would like to run strength calcs based on what my plane(20407) was certificated with.

Mike one thing I forgot to ask you... it might be interesting and useful if you can calculate the amount of load that the aircraft's geometry can put on the struts. At 6G and 1100 pounds gross, what would the approx. tensile loads be on the front and rear struts?

Obviously you could then just compare that load to the loads that a new/old/undamaged/corroded/cracked strut can withstand, and have a very useful picture of where we stand in terms of "strength reserve" when we are talking about strut corrosion reducing the wall thickness.

If other engineers on the Forum already have some idea of this now would be the time to make it known.

Forrest thanks for looking the strut dimension info up. Does any info exist on what Kawneer Streamline number 1728 or 1668 is, compared to whatever is available today?

[Forrest Barber]

Re: Forrest..... Strut Question Tf#733

yes all that is availalbe, but we have to use what is available today. The strut strength is good up to a point, I was present for the destruct testing on the F-21 and know what breaks first... All this is being shared with the FAA engineer. Right now I am more concerned with the A-A11 area and the loads we can put on that area with a corrosion factor. IT is not much folks at the higher gross weights. More as I get it.

[Guest]

Re: Forrest..... Strut Question Tf#733

yes all that is availalbe, but we have to use what is available today. The strut strength is good up to a point, I was present for the destruct testing on the F-21 and know what breaks first... All this is being shared with the FAA engineer. Right now I am more concerned with the A-A11 area and the loads we can put on that area with a corrosion factor. IT is not much folks at the higher gross weights. More as I get it.

Tell us, what breaks first?

[1938BF50]

Re: Forrest..... Strut Question Tf#733

Worst case.....

Using .035 wall, 2 1/4" dia equivalent, 1025 tubing and in using a tensile strength of 60K(60-103K listed), I get 14,585 lbs per front stut. I don't know what the design distribution is between front and rear struts. I thought that I read 2/3 front to 1/3 rear at one point years ago. Does anyone know?

At any rate ONE front strut of the smallest/lightest configuration listed has a safety factor of 13X at a gross of 1100lbs in straight tension!

I need to calculate vector and distribution on the "as installed" condition to get final results. I will estimate this based on line drawings when I get the chance.

[1938BF50]

Re: Forrest..... Strut Question Tf#733

For what it's worth....

My simplified calculations show that if my.038" thick front lift strut(one side) carried 1/2 of my 1100# gross it would be in tension at 1468 lbs. or a factor of 2.7 times 1/2 the gross weight.

In the example of my 1938 Taylorcraft with it's 1100lb gross, each front lift strut in theoretical perfect condition has a safety factor of almost exactly 10X, which in reading, I believe was the accepted practice in aircraft design in the earlier days. This totally ignores the contribution of the aft lift strut which will add considerably to the overall safely factor.

Thank you Forrest for supplying the needed sizes/thicknesses of the various tubings used on our fleet!

[Dano"T"]

Re: Forrest..... Strut Question Tf#733

I too am much more concerned with the attach fitting area.....I would fly with rusty struts knowing my fittings and fuselage were in good shape before I'd ever go with brand new sealed struts attached to a rusy, corroded fitting/fuselage. Sounds to me like it would be a safe bet that the strut (even corroded some) would have enough strength to allow it to pull the whole attach fitting cluster away from the airplane should that area show signs of excessive corrosion I'm certainly not saying its okay to fly with rust struts either....just making a point....don't just look at the struts and then go fly....even before anothe AD comes as rumored......look things over real good.

[1938BF50]

Re: Forrest..... Strut Question Tf#733

Using the same scenario with 2 1/4" equivalent daimeter 1025 tubing at .049" wall thickness we will see a safety factor of 12.7X per front strut at a gross loading of 1200 pounds.

[N96337]

Re: Forrest..... Strut Question Tf#733

The strut strength is good up to a point, I was present for the destruct testing on the F-21 and know what breaks first... .

If I'm not wrong, this is exactly what "Alwaysoar" was referring to in his post on the other thread..... it's the "bait" routine, that someone knows more, but wont say it.... It gets really old to me too.....if ya got information, share it... if not, don't get everyone wondering what else there is to know......
JH

[VictorBravo]

Re: Forrest..... Strut Question Tf#733

Using the same scenario with 2 1/4" equivalent daimeter 1025 tubing at .049" wall thickness we will see a safety factor of 12.7X per front strut at a gross loading of 1200 pounds.

Mike, my lack of brain power is becoming evident here... are you saying that a 1025 .049 wall strut will have a maximum loading (breaking strength) of 12.7 times the weight of the plane ... meaning it will take 12.7G's at 1200 lb. ? Or are you saying that it has a "safety factor" of 12.7 times what the plane was certified for (Utility category 4.4 G's) ?

Whenever you come up with a rough idea of how much force is actually applied to the struts (and thus the fuselage attach fitting) based on the geometry and force vectors of a 1200 pound Taylorcraft at 6G... I would very much like to see it. Thanks again for being part of this.

Bill

[Guest]

Re: Forrest..... Strut Question Tf#733

If I'm not wrong, this is exactly what "Alwaysoar" was referring to in his post on the other thread..... it's the "bait" routine, that someone knows more, but wont say it.... It gets really old to me too.....if ya got information, share it... if not, don't get everyone wondering what else there is to know......
JH

***************************

Amen

[tawadc95]

Re: Forrest..... Strut Question Tf#733

ya think J.H. !
What I like about the Cub Club is they are just into airplanes,not who knows the most. No rankings, just airport bums like I have grown up around at the duster strips where all you have to do to be a part is like to talk flying.

[hangarb7]

Re: Forrest..... Strut Question Tf#733

Any suggestions for examining that joint on the fuselage where everything comes together? I have always looked it over with a strong light and looked for cracks and bad welds (only looked once for the bad welds; they were done very well, actually).

Anyone have a guess as to what they will make us do on that joint if an AD comes out? I hate to spend the money for the sealed struts then find out that some alternative method is allowable on the old struts and/or some expensive repair is needed on that fuselage knuckle...

The sealed struts will really put me close to saying, "uncle." If I'm going to say it, I'd rather say it to the guy who is buying my plane rather than my wife after I pay a lot more money.

Jack D
N44057

[alwaysoar]

Re: Forrest..... Strut Question Tf#733

Well, Forrest knows what to look for at the strut fitting, but he won't tell. Some of the rest of you (bless your hearts) have have taken a stab at it so now I have a better idea. But Forrest has seen the actual pics of the failure, and outside of the NTSB probably knows the most about that failure. But he won't tell. He will say, "More coming," but more of the same nothingness doesn't really help, does it. How about it, Forrest? How would you inspect the strut fitting? Many thanks in advance!

Ed@BTV VT
TF 527