Nose Tank support rods

[8708]

Can anyone tell me the diameter of the support rods that pass through the nose tank? My project is missing them.
Thanks!
Jay

[mulwyk]

Re: Nose Tank support rods

Jay:
They are 1/4 inch rods. And 1/4"ID rubber fuel line hose from NAPA happens to fit perfectly around the rods and inside the tank through holes.

[8708]

Re: Nose Tank support rods

Thanks Bob!
I knew someone would know the answer.
Does the rubber tubing cover the whole length of the rod or just at the ends where the rod enters the tank?
Jay

[Ragwing nut]

Re: Nose Tank support rods

THere is a steel bushing the rubber goes over and slide on the rod. It only goes at the openings and about 2 inches long

Mike

[astjp2]

Re: Nose Tank support rods

The rods have rolled threads like the flying wires on the tail, do not get some steel rod and cut some thread on it, if you ball it up, the tank could come loose and you would have a potential for a nasty fire...Tim

[Hank Jarrett]

Re: Nose Tank support rods

I thought the threads were rolled too (on the tail AND the tank rods) but they aren't. I'm an engineer and they SHOULD be in my opinion but they are cut. Cutting is much cheaper and Taylorcraft just used bigger wire to make up for the strength loss. I check mine pretty close in the thread base and run out for damage. I really like rolled thread better and pay close attention to any corrosion in the thread area.
Hank

[astjp2]

Re: Nose Tank support rods

I could be wrong but I remember seeing a spec for one a few years back and they were rolled on the spec. Brunton is one of the only companies where you can get them rolled. I think that Steen aero lab is thier dist. I had forgot about Steen till just now...its amazing what happens to the brain when you get older....

[Hank Jarrett]

Re: Nose Tank support rods

That was what I thought too, till Forrest told me they were cut. I checked both my planes and they were all cut threads. The tank rods don't bother me as much as the tail wires but the wires are HUGE for the loads.
Hank

[Guest]

Re: Nose Tank support rods

I doubt that cut or rolled makes much diff on these rods.

I am not aware that they carry much load.

They need only be tightened enough to put them in slight tension, no pre-load required, no cyclic loading.

If they were to be replaced by tubing the tubes would be more or less neutral, no preload other than built in stresss.

Also I wonder about their actual structural value. They form a cross and two of the ends (at the panel) do not terminate in such a way that other members pick up their tension like a truss would. They stiffen up the little square box that surrounds the tank, not much structural value there that I can see. Makes me wonder if their only purpose is to hold the tank.

On second thought it does form a stiffened structure, I think I am all wet above.

[lfries]

Re: Nose Tank support rods

This was a very timely thrread for me. In the process of replacing the
fuselage/engine mount bolts we found that the rod going from the pilot side to the passenger side was not in the bushing near the firewall. I believe the
tank was installed in 88 during the rebuild. We were able to get the rod out
and re-installed correctly. All four of the old engine mount bolts were bent.
We don't know if there is a correlation. Not to get an argument started but a
prev. post says look at the spec sheet. My mechanic, who is very knowledgable in regards to aircraft of our era, claims that they are rolled and that they are a part of the structure integrity. Obviously my Taylorcraft flew for most of 19 years without the benefit of "one". My rods must be rolled as he wouldn't have fixed it if they were cut.

[Hank Jarrett]

Re: Nose Tank support rods

You will NEVER have a problem using a rolled thread in place of a cut one (except in the check book). Rolled threads actually yield the metal so that the grain flows into the threads for significantly higher strength and resistance to fatigue and cracks in the base of the thread. Cut threads actually cut through the grain and create huge numbers of potential crack origins. In modern aircraft design you almost never see cut threads called out in the load bearing primary structural design. In the 30's, 40s and 50s they did it a little differently. There are a LOAD of hardware store and car parts on my 41 in non-structural areas that are original parts. They compensated for the lower reliability and strength by making things like the tank rods much bigger. If your plane has cut threads the rods are probably original and you just need to inspect them for cracks in the thread base carefully before re-use. If you have rolled threads someone found a place to roll them and has replaced the original rods. That is fine but I have inspected MANY rods (I worked in NDT for many years and I know how to etch and inspect, but the quick way is to measure the diameter of the thread and shaft. A rolled thread will be larger in the major diameter of the thread than the shaft) and I can tell you, Forrest is right, there are a bunch of them with cut threads. Rolled is stronger (and costs more), cut is original.
Your IA is being safe and replacing with rolled is better, but the rest of us DO NOT need to go out and replace ours if they are in good shape.
By the way, your bent engine mount bolts "could" have been related to the non-functioning tank mount rod. I haven't done an analysis but that rod IS NOT just there to hold the tank, it resists the fuselage frame twisting under thrust loads. Yours was only resisting in one direction.
Hank

[lfries]

Re: Nose Tank support rods

Thanks for your reply

[Guest]

Re: Nose Tank support rods

You will NEVER have a problem using a rolled thread in place of a cut one (except in the check book). Rolled threads actually yield the metal so that the grain flows into the threads for significantly higher strength and resistance to fatigue and cracks in the base of the thread. Cut threads actually cut through the grain and create huge numbers of potential crack origins. In modern aircraft design you almost never see cut threads called out in the load bearing primary structural design. In the 30's, 40s and 50s they did it a little differently. There are a LOAD of hardware store and car parts on my 41 in non-structural areas that are original parts. They compensated for the lower reliability and strength by making things like the tank rods much bigger. If your plane has cut threads the rods are probably original and you just need to inspect them for cracks in the thread base carefully before re-use. If you have rolled threads someone found a place to roll them and has replaced the original rods. That is fine but I have inspected MANY rods (I worked in NDT for many years and I know how to etch and inspect, but the quick way is to measure the diameter of the thread and shaft. A rolled thread will be larger in the major diameter of the thread than the shaft) and I can tell you, Forrest is right, there are a bunch of them with cut threads. Rolled is stronger (and costs more), cut is original.
Your IA is being safe and replacing with rolled is better, but the rest of us DO NOT need to go out and replace ours if they are in good shape.
By the way, your bent engine mount bolts "could" have been related to the non-functioning tank mount rod. I haven't done an analysis but that rod IS NOT just there to hold the tank, it resists the fuselage frame twisting under thrust loads. Yours was only resisting in one direction.
Hank

Hi Hank, I would love to learn from from you analysis. Any chance you could scan it and send by email?

Thanks, Dave.

[Hank Jarrett]

Re: Nose Tank support rods

I have all of the fuselage tube drawings for one of the Taylorcraft fuselages (need to check on which version I have) and have always wanted to do a full analysis, but never have. It is NOT a simple process and since loads data is almost impossible to get, doing one from just the drawings would take a lot of time.
I can point you towards some great sources to learn stress analysis if you want. About the best I have found is "Stress Without Tears" which is a reprint of a series from KitPlanes. It is far and away better than any book I used getting my degree and if you go through it (you only need algebra) you will have a good basic understanding of how to calculate aircraft stress and strength distribution. The University texts are great, but none of us really need all the theory. We just need to know what we fixed isn't going to break.
Get a copy of "Stress Without Tears" and I will drag some books off the shelf to get you some more titles that will teach you a lot. The Bruhn aircraft design book is great too, but look for an OLD one. It has been reprinted since before WW-II and the old ones still have good stuff on things like fabric, wood and tubes. The newer ones are pretty much all stressed Aluminum skin stuff.
Hank

[Guest]

Re: Nose Tank support rods

Hank, thanks, I was thinking that you had an analysis of the tank support that you had done and could scan in and send and I could read rather than do any actual work But I see that I do need new reading glasses because you said that you had not done that. Sorry.

I have some engineering texts on aircraft and materials but the Bruhn book sounds interesting and I don't have. May look for that.

Thanks, Dave.