Fuselage tubing size - shoulder harness analysis

[TimHicks]

Re: Fuselage tubing size - shoulder harness analysis

I really would like to hear from Carrieve about her test of the Shoulder harness attach.
Her accident surely put greater loads than a ground-loop.
Her harnesses were wrapped around the fuselage tube by the aileron cables.
What was the result? Did the steel tube fail? Did it bend?

[Hank Jarrett]

Re: Fuselage tubing size - shoulder harness analysis

The cold will slow the cure of the JB-Weld. Doubt it will stop it from kicking off before it gets to the "exit" though!

Hank

[Peterroy]

Re: Fuselage tubing size - shoulder harness analysis

I've been out with Skip. If the JB-Weld and beer is ice cold and has a good head on it, he might try it!

Peter

[Hank Jarrett]

Re: Fuselage tubing size - shoulder harness analysis

Don't blame me! It was Skips idea.

Hank

[dalijohn]

Re: Fuselage tubing size - shoulder harness analysis

Hank!! What would possibly make you want to try that concoction?

[Hank Jarrett]

Re: Fuselage tubing size - shoulder harness analysis

Don't mix the JB-Weld and Beer. Tried it, tastes terrible and REALLY blocks you up!
Hank

[skip]

Re: Fuselage tubing size - shoulder harness analysis

Hey Skip,

...

Well the airplane was outside of the hangar so I look a chance and used ultrasonic thickness machine anyhow.

First I calibrated it on the .250" standard that came with it. Then I measured a new unused piece of 7/8" x .049" from the shop. It measured .046". I am not sure why. But I re-calibrated on the known sample tube to .049". Then I measured my rear cross tube. The aft headliner is out but the forward headliner extends about 8" behind the tube so you have to reach up and past the end of it. Then you have to feel with your fingers and place the transducer. It not really very difficult. I did it 3 times each with new couplant. The readings were in the .036" to .038" range. Each reading was taken when the machine indicated that the transducer was coupled. I suspect the fact the I had to feel what I was doing rather than see and that the tube is painted with 3 coats of paint probably account for the variation. Wicks lists 7/8" tube in .028", .035", .049". I suspect that mine is .035".

Dave

p.s. hopefully the audience can tell where fiction ended and reality started in this post

Dave,

Thanks Loads!! That is wonderfully helpful!

I remember when the infamous strut AD came out. I dug up our really good old propeller wizard who was certified doing ultrasound inspections for propellers and took him some new sample streamlined 4130 pieces to get his machine calibrated. I remember being impressed at both how good he had to get consistant readings and how flakey the technique could be in the presence of things like paint or crud. Given that data point, I'm really impressed with your data range. You must be good!

I am a little surprised at the .035 instead of .049, but then I know C.G Taylor was really good doing the calculations. Given the geometry of the struts and the fues I can accept that he probably put less force through the rear spar than one might think. Also, that he probably used the little 6" diagonals on that tube to increase the buckling resistance and allow for the .035 which saves a bit of weight and money. He was good at that. My engineer friend and I did the calulations based on .058 tube hoping... but I had really expected .049. We will look more closely at the numbers for an .035 tube.

And by the way, it is a really good feeling to be on an internet forum where one can make comments about grinding welds and gluing with JB-weld without some jerk busting in with a flame thrower screaming about too few smiley faces. I really like you guys!

Dave, I owe you a tube of JB-Weld and a beer next time we run into each other!

[Hank Jarrett]

Re: Fuselage tubing size - shoulder harness analysis

Fiction?!?!?!?

Hank

Re: Fuselage tubing size - shoulder harness analysis

Dave,

Thanks for the followup. Yup, I had seen your hookup in that thread and it is a good one. It also closely matches one method diagrammed in AC 43.13-2A, Acceptable Methods for Aircraft Alterations (not to be confused with 43.13b Acceptable Methods for Inspection and Repair).
Chapter 9 is all about shoulder harness installations and is a good read for anyone wanting to play in this area. Figure 9.16 on page 75 shows a swaged cable loop around tubes much like yours.

I have looked at using a 5/32 swaged cable around the tubes like you did to re-enforce the fitting on the rear spar carry-through tube as described above. It is really a fairly neat solution as it adds plenty of strength in the horizontal plane. The cable does not need to be taught, e.g. with a turnbuckle or anything. I looked at a swaged loop with an AN-111 and an AN-4 bolt to a dual .063 bracked welded to the back of the split-tube fitting. As the tube fails forward, it takes up a minimal bit of slack and doesn't fail any more!

The big problem is that It is really hard to get back to that next station crawling back behind the seat to install a loop of cable. So I prefer trying to trade a little more weight and complexity for not having to crawl back into the fuselage. If I were doing this on an uncovered fuselage, that would be a really good way to do it. But I'm trying to come up with a retrofit that can work on a completed covered airframe. Thus I'm trying to add more split fittings along the spar tube with the dual .090 flanges to add the strength. Talk about my laziness and lack of flexability leading to engineering design tradeoffs... :-)

I'll appreciate it if you manage to get out and find the wall thickness of that 7/8" tube. Just remember that when you hacksaw through the tube so that you can measure it for me, do a good butt-weld and then grind it down nice and clean so the inspector doesn't ever know...

Hey Skip,

I went to fly today so it was a good time to get an answer to your question. Yes I had planned to cut the cross tube right in the middle. That is where the stringers hold the fabric the farthest away from the tube so I could have room to patch it back up.

My plan was JB Weld tough so as to avoid welding and heat on the fabric. I have heard so many good things about JB Weld. I figured that I could just make golf ball size glob of it and then stick each end of the cut tube into it and smooth the outside then paint to match the rest of the cross tube.

I think that making it into a ball and then sticking the tube end into it is best. That is because it would fill the inside of the tube with JB Weld adding support and preventing collapse at the tube end. This could prevent a buckling failure (especially since it is at the middle). The smoothing and painting would make it not show so much to future buyers and inspectors.

I ran into a problem though. The local hardware store had no JB Weld for me. There is a guy in town restoring a Stearman. Its a big plane with two wings so I think he must be using up the local supply.

I could have waited until they get their order in on Tuesday. Rather than make you wait for that I decided to use my ultrasonic thickness machine. At first I was concerned that introduction of the high frequency sound into the tube would harden it resulting in fatigue cracks later on. Also was not sure if the high freq. sound could cause the greasy couplant to start on fire.

Well the airplane was outside of the hangar so I look a chance and used ultrasonic thickness machine anyhow.

First I calibrated it on the .250" standard that came with it. Then I measured a new unused piece of 7/8" x .049" from the shop. It measured .046". I am not sure why. But I re-calibrated on the known sample tube to .049". Then I measured my rear cross tube. The aft headliner is out but the forward headliner extends about 8" behind the tube so you have to reach up and past the end of it. Then you have to feel with your fingers and place the transducer. It not really very difficult. I did it 3 times each with new couplant. The readings were in the .036" to .038" range. Each reading was taken when the machine indicated that the transducer was coupled. I suspect the fact the I had to feel what I was doing rather than see and that the tube is painted with 3 coats of paint probably account for the variation. Wicks lists 7/8" tube in .028", .035", .049". I suspect that mine is .035".

Dave

p.s. hopefully the audience can tell where fiction ended and reality started in this post

[M Towsley]

Re: Fuselage tubing size - shoulder harness analysis

Thanks guys.

[skip]

Re: Fuselage tubing size - shoulder harness analysis

Hi Skip,

Not trying to push you into anything but want to be sure that you are aware of a no weld solution using a cable loop.

Check out my post on page 2 of this=> http://vb.taylorcraft.org/showthread...lder-harnesses.

I will be at the airfield Thursday and can measure tube thickness that you are looking for.

Dave

Dave,

Thanks for the followup. Yup, I had seen your hookup in that thread and it is a good one. It also closely matches one method diagrammed in AC 43.13-2A, Acceptable Methods for Aircraft Alterations (not to be confused with 43.13b Acceptable Methods for Inspection and Repair).
Chapter 9 is all about shoulder harness installations and is a good read for anyone wanting to play in this area. Figure 9.16 on page 75 shows a swaged cable loop around tubes much like yours.

I have looked at using a 5/32 swaged cable around the tubes like you did to re-enforce the fitting on the rear spar carry-through tube as described above. It is really a fairly neat solution as it adds plenty of strength in the horizontal plane. The cable does not need to be taught, e.g. with a turnbuckle or anything. I looked at a swaged loop with an AN-111 and an AN-4 bolt to a dual .063 bracked welded to the back of the split-tube fitting. As the tube fails forward, it takes up a minimal bit of slack and doesn't fail any more!

The big problem is that It is really hard to get back to that next station crawling back behind the seat to install a loop of cable. So I prefer trying to trade a little more weight and complexity for not having to crawl back into the fuselage. If I were doing this on an uncovered fuselage, that would be a really good way to do it. But I'm trying to come up with a retrofit that can work on a completed covered airframe. Thus I'm trying to add more split fittings along the spar tube with the dual .090 flanges to add the strength. Talk about my laziness and lack of flexability leading to engineering design tradeoffs... :-)

I'll appreciate it if you manage to get out and find the wall thickness of that 7/8" tube. Just remember that when you hacksaw through the tube so that you can measure it for me, do a good butt-weld and then grind it down nice and clean so the inspector doesn't ever know...

[Bravo 6]

Re: Fuselage tubing size - shoulder harness analysis

Marty,

I just bought the same belt sets from Wag Aero that Skip listed.

Re: Fuselage tubing size - shoulder harness analysis

Hi Skip,

Not trying to push you into anything but want to be sure that you are aware of a no weld solution using a cable loop.

Check out my post on page 2 of this=> http://vb.taylorcraft.org/showthread...lder-harnesses.

I will be at the airfield Thursday and can measure tube thickness that you are looking for.

Dave

[Hank Jarrett]

Re: Fuselage tubing size - shoulder harness analysis

Before you approach the FAA let's do some Peer Review of the analysis. I really need to find my crash data since it has the latest numbers from actual GA aircraft we drop tested at the Impact Dynamics Facility. at NASA Langley Research Center. I am sure the real crash loads would be better than the FAA "Best Guess" of 60/40.

If you DO get out this way, you need to visit the Military Aviation Museum in Virginia Beach VA. It has the largest privately owned FLYING collection of aircraft from WW-I and WW-II in the world. No Taylorcrafts yet, but I am working on it. ;-)

Hank

[skip]

Re: Fuselage tubing size - shoulder harness analysis

What belts/shoulder harnesses did you guys obtain? Thanks.

I have the Aero Fabricators harness sold by Wag Aero and in their catalog (page 52). My installed-in-1991 seat belts are also FAA/PMA Aero Fabricators belts and so the harness matches. Wag's part number is H-702-xxx with xxx for the color. H-701 is the seat belt part number and H-858 is the seat/shoulder combination. The good part is that they are FAA/PMA tagged so they meet one part of the requirement for installation by an A&P as a minor modification as stated in ACE-00-23-561-01.
Funny thing is that Aircraft Spruce resells them and sometimes has a bit better price.