Strange metal hoses on Savannah S

Sean Griffin wrote:

Ref corrugated metal hoses

Questions:

Are these hoses used throughout the fuel, oil & coolant reticulation systems?

What is their construction eg metal, "rubber" lined?

Do they conform with Rotax commendations?

Do you need to comply with the Rotax recommendation on 5 year replacement?

Availability? 

Are they limited to a few aircraft types eg Savannah?

What advantages/disadvantages do they confer?

Hello Sean,

These hoses are installed throughout the airframe and engine compartment, for fuel, and cooling system.( Oil lines were changed last year due to a too small diameter opening) 

Construction material is stainless rippled line, not rubber lining at all.

They do NOT conform with Rotax commendations. (that's why I will replace them) as customer wants to comply with the Rotax 5 year recommendation. 

After my inquiry I received a message from the Savannah US distributor and he confirmed that these hoses are per ICP factory specs..

I have not seen them elsewhere and if you read previous posts there are Savannah owners which have had no problems with them.

I have never seen them in my whole career but this is also the first Savannah I am maintaining.

Advantages/disadvantages... based on several replies they seem to work but in my opinion they are unsafe for fuel transport in the engine area. 

I get that they work (despite my misgivings) but what advantage do they have over the more common & easily found  "rubber" hose?

Sean Griffin wrote:

I get that they work (despite my misgivings) but what advantage do they have over the more common & easily found  "rubber" hose?

I would say you do not have to replace them every 5 years especially in the wings which saves a lot of time and effort, check out the link on the first page where a builder is installing them in the wing area.

My biggest issue is that it is untested and not aviation standard material. (already mentioned by Roger Lee)

I have two issues with the flex hose. First it allows debris to build up n each protruding ripple especially in bends.

A worse issue is flow friction loss. As a retired firefighter we had to learn the physics of fluids flowing through hose and pipes. To keep it simple, as a fluid flows through a hose or pipe it contacts the inner structure walls  of the hose or pipe. This action causes friction and reduces the flow and pressure and gets worse the longer the hose or pipe. The longer the hose or pipe the flow and pressure is reduced. This friction loss is far less in smooth bore hose than a flex hose with the ripples. The rippling cause a great more loss of flow vs smooth bore. For an example if you put  a 12” piece of hose on you water faucet and measured the quantity and pressure it is greater than at the end of a 100’ hose or a 200’ hose or pipe. Firefighters and engineers have calculations they use to increase the pressure and flow at the pump to get the desired flow and pressure at the end of the hose and the calculation is based on hose length and size.

Other physics to consider; when you double the inside diameter of a hose or pipe you can quadruple your flow. 
As an example if you go from a 1/4” hose to a 1/2” hose you can quadruple your flow. If you went from a 1/4” hose to just a 3/8” hose you could double the flow. There are a couple variables here, but this is the basis.

These are all things to consider in design setups or when you think you know more than all of Rotax’s testing with fluid flows and engine demands on the engine. Yes aircraft Mfg’s get this wrong at times too when changing what Rotax regular specs are.

Thank you very much Roger for the very clear explanation.