Ridged Fuel Lines

[lr172]

I was going to run a braided fuel line from the firewall to the fuel pump, but planned to run a stainless line from the pump to the carb. Both items are fixed to the engine, so figured there would be no issues with flexing. Also wouldn't need a fire sleeve.

However, I have not seen any lines set up on the pictures I have seen around here. Are there any problems with this approach?

Thanks,

Larry

[Toobuilder]

http://www.vansairforce.com/communit...d.php?t=108653

Fuel servo or carb... Same same

[TS Flightlines]

Actually no Larry---but use stainless instead of aluminum.
Tom

[Ironflight]

For anyone considering rigid fuel lines on their engine, I would sugest that you read this thread as part of your risk trade analysis:

http://www.vansairforce.com/communit...ad.php?t=57122

This is not a rejection of rigid lines - it is a suggestion to look at all aspects of a "minor" change to a critical engine part before making a decision. Nick shared his story a couple years back to make sure that people knew what happened in his case. I don't know if Lycoming uses rigid lines on any of their standard configurations - they very well might - but thre are a lot of flexible lines flying that work well.

We tend to think of the engine as one big monolithic chunk of metal, but I have seen slow motion films of engines on test stands that show quite a bit of flex between the parts - the cylinders can really wiggle around realtive to the case, for instance, and the case flexes.

Then again, the standard prop oil line is a rigid stainless tube - so that clearly is acceptable in that installation. And it probaby was the result of some engineering work to achieve that.

I'm not saying that rigid fuel lines are bad - I am saying that anyone contemplating a change to the "norm" should think about all of the aspects of the change, and that is true in any critical aircraft system or structure. Vibrational analysys is not simple, and can surprise you. For thsoe who have done the analysis and got the data to back up the design - great! But don't do it just becasue "That Looks About Right".

[aerhed]

Another consideration. You should be popping the line off the carb every year to check the screen. Would a hard line make that.....harder?

[BillL]

Originally Posted by Ironflight

For anyone considering rigid fuel lines on their engine, I would sugest that you read this thread as part of your risk trade analysis:

http://www.vansairforce.com/communit...ad.php?t=57122

This is not a rejection of rigid lines - it is a suggestion to look at all aspects of a "minor" change to a critical engine part before making a decision. Nick shared his story a couple years back to make sure that people knew what happened in his case. I don't know if Lycoming uses rigid lines on any of their standard configurations - they very well might - but thre are a lot of flexible lines flying that work well.

We tend to think of the engine as one big monolithic chunk of metal, but I have seen slow motion films of engines on test stands that show quite a bit of flex between the parts - the cylinders can really wiggle around realtive to the case, for instance, and the case flexes.

Then again, the standard prop oil line is a rigid stainless tube - so that clearly is acceptable in that installation. And it probaby was the result of some engineering work to achieve that.

I'm not saying that rigid fuel lines are bad - I am saying that anyone contemplating a change to the "norm" should think about all of the aspects of the change, and that is true in any critical aircraft system or structure. Vibrational analysys is not simple, and can surprise you. For those who have done the analysis and got the data to back up the design - great! But don't do it just becasue "That Looks About Right".

+1 - well stated.

[az_gila]

Originally Posted by Ironflight

...
Then again, the standard prop oil line is a rigid stainless tube - so that clearly is acceptable in that installation. And it probaby was the result of some engineering work to achieve that.
.....

Even that relatively simple line was the subject of a Lycoming AD in 1990 when the end fittings were changed from aluminum to steel.

http://rgl.faa.gov/Regulatory_and_Gu...C?OpenDocument

So even Lycoming can get it wrong initially even more reason to follow current certified practice.

[SHIPCHIEF]

Why Stainless Steel for hard lines? Carbon steel tube has some better mechanical properties, costs less and tends to seal more reliably at the flare?
Stainless isn't always better in every application, although it does look nice.

[Toobuilder]

Yes, rigid lines can fail, especially if done improperly. However, you are not going to tell me that a vibration analysis is required before making a hard line. There are very easily accessible standards for fabrication and application of hardlines and other general hardware like this. It is assumed that these resources are used if you are building an airplane in your garage. If you can't (or won't) follow these standards, THEN DONT BUILD AN AIRPLANE IN YOUR GARAGE!

I've been an aircraft mechanic since I was a teenager. I've maintained airplanes ranging from Cubs to SR-71's and I have seen more failures of hose than hard lines.

Bottom line: If you're going to do something on your airplane, learn the requirements, and execute the fabrication properly. This is a learning exercise, after all.

[TS Flightlines]

I want to clarify my post about using stainless rigid tube. Obviously a stainless braid teflon FIRESLEEVED hose is the best answer here. Larry's question was whether there was a problem with this approach. Technically, probably not, but I dont recall seeing any rigid tubing for this application. I'm guess the he wanted to use rigid tubing, and my comment about stainless was to keep him away from aluminum.
Lycoming did use rigid tube for governor lines in some applications, and they were of a similar distance, with I would guess, similar motion. So--I guess you could do it, and yep stainless tube looks good, but flex hose is the best bet. But---FIRESLEEVE the hose.
Tom