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  #1  
Old 04-16-2020, 03:57 PM
efitzgerald efitzgerald is offline
 
Join Date: Jul 2016
Location: Dryden, MI
Posts: 66
Default Rigid Fuel Lines

I am working on my firewall layout and started on the fuel lines. I am using a SDS fuel injection system with their case mounted fuel block. I had originally planned on using flex hose in fire sleeve from the firewall to the fuel block. I saw another members post with a similar install and he had used hard lines from the back of the engine near to the fuel block and it looked like a great idea.

In my picture the lines are aluminum for the purpose of mock-up only. I was going to have TS Flightlines make the stainless lines. The lines would be flared on each end with aluminum AN nuts. There would be a bracket bolted on top of the fuel pump block off plate to secure the end of the rigid line where the flexible hose connects to it with steel AN fittings. I planned 1 to 2 brackets bolted onto the engine to support the lines.

Is it a mistake to do it this way?

https://www.dropbox.com/s/xldzek2mrekb7s4/FL6.jpg?dl=0
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Dryden Mi

RV-7 Tipup; IO-375 EFII / SDS Fuel Injection
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  #2  
Old 04-16-2020, 05:23 PM
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rmartingt rmartingt is online now
 
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Location: Savannah, GA
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Hmm. Looks like I'm going to have to reevaluate my routing due to the engine mount. Nw I wish I hadn't just put the holes in my baffle...

Guess we'll see when I go to hang it in a little while.
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  #3  
Old 04-16-2020, 05:59 PM
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DanH DanH is offline
 
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Location: 08A
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Quote:
Originally Posted by efitzgerald View Post
I am using a SDS fuel injection system with their case mounted fuel block. I had originally planned on using flex hose in fire sleeve from the firewall to the fuel block. I saw another members post with a similar install and he had used hard lines from the back of the engine near to the fuel block and it looked like a great idea.
Why does it strike you as a good idea?

Seriously, every possible choice has some advantages, and some compromises.
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  #4  
Old 04-16-2020, 07:23 PM
efitzgerald efitzgerald is offline
 
Join Date: Jul 2016
Location: Dryden, MI
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- Dan

The engine has a lot of fluid connections behind the left side. The right side has the backup alternator in the way so it is not an option. I like that the metal tubing is smaller in diameter and can be routed precisely where it is wanted. The engine mount is also very close to the engine in this area, wouldn't chafing / rubbing be a problem with flexible hoses? To me is seems like the rigid tubing is less of a maintenance concern than 3 feet of flexible hose that is covered in fire sleeve. Aesthetically hard tubing looks better than hose to me as well.

This engine uses stainless tubing for the prop oil feed so it seemed like an acceptable option.

I made this post as I really don't know if the potential for failure is worth the advantages that I see. I am simply looking for information.

Thanks
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  #5  
Old 04-16-2020, 07:29 PM
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hgerhardt hgerhardt is offline
 
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Location: torrance, ca
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The way you have it looks like the hard lines on the rear of the engine would get in the way of maintenance, especially if you need to remove that ignition coil assy. You could use hard line up to the rear baffle and use bulkhead connectors there and hose running down the back of the engine. Or even better is making relatively short hoses from the bulkhead connectors to the firewall and use hard line up the firewall to the same height as the bulkhead connectors. Obviously need enough service loop in the hoses to accommodate the 'shake like a wet dog' that Lycs do on startup/shutdown.

BUT, you have a more serious problem: your lower Lord mounts are installed backwards.
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  #6  
Old 04-16-2020, 07:42 PM
efitzgerald efitzgerald is offline
 
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Location: Dryden, MI
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- hgerhardt

The upper and lower mounts are installed in opposite directions? The engine is only installed temporarily but thank you for pointing that out. Where are the engine mounts shown in Vans drawings?
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  #7  
Old 04-16-2020, 07:54 PM
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hgerhardt hgerhardt is offline
 
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Have a look at the -14 drawing here: https://www.vansaircraft.com/service...evisions/43-2/
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  #8  
Old 04-16-2020, 08:01 PM
efitzgerald efitzgerald is offline
 
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Location: Dryden, MI
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Thank you, Heinrich.

That is very useful information. It even explains why the Vans engine mount bolt kit includes 2 extra large washers.
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RV-7 Tipup; IO-375 EFII / SDS Fuel Injection
http://www.mykitlog.com/eric@marmo-n/
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  #9  
Old 04-16-2020, 08:42 PM
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DanH DanH is offline
 
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Make a list!

The key downside is probably vibratory fatigue, so even being stainless, it will need care in fixating it along its length. Take a look at the Adel clamp call out for the prop governor line. Got engine hard points available to mount the Adels?

Half the run will flex lines anyway (firewall to the stainless tube connection), so there is no actual maintenance advantage.

The bracket at the hose/tube junction will need to be pretty tough.

There are a few extra flare connections. Statistically, more connections mean more potential leaks.

You mentioned aluminum hardware on the ends. Why not steel? Stainless tube flares are not soft. Anybody have a torque chart for steel B-nuts on steel lines?

As I recall, certified engines were subject to an AD to replace prop line fittings with steel after some aluminum elbows cracked in service. Given the unknown vibratory behavior of a steel hard line, are you planning to replace the inlet and exit elbows on that fuel block?

Advantages? Small diameter so perhaps easier to squeeze through a tight spot.

Looks nice.

Anything else?
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  #10  
Old 04-16-2020, 08:48 PM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Location: Savannah, GA
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Hard fuel lines, firewall forward? Ask the man who?s had one fatigue crack in flight... like me.
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