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  #31  
Old 10-01-2017, 04:21 PM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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Quote:
Could being cowless and direct wind pressure and turning prop wind pressure impact fuel pressure?
Yes, the fuel pressure sensor compares atmospheric pressure to fuel pressure. If the air pressure at the sensor changes, then the displayed fuel pressure will change too, even though the fuel pressure remains constant. Who knows how much the air pressure actually changes with cowl removed?
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  #32  
Old 10-01-2017, 05:48 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by Rrhsch View Post
The fuel sensor was replaced and all is well. I never intended to start a war of sorts. This is definitely not in the same league an tail wheele or primer wars.

I now show a 0.5 PSI increase in fuel pressure. I like to know that everything is working within normal ranges. The one minuet warning before the engine quits is one more minuet I have to react to a potential issue. Just my view.

Now back to thread drift.
What?
You didn't have to replace all of your FWF fuel hose system with an after market kit to have normal fuel pressure readings?
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  #33  
Old 10-01-2017, 07:28 PM
Aircraft Specialty Aircraft Specialty is offline
 
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Originally Posted by rvbuilder2002 View Post
What?
You didn't have to replace all of your FWF fuel hose system with an after market kit to have normal fuel pressure readings?
Of course not. Why would anyone replace an entire fuel system due to an erratic sensor? That would make no sense. There are a lot of reasons to utilize the aftermarket fuel hose kit, but an erratic sensor is definitely not one of them.

Keep in mind the history of the development of the aftermarket kit. It started shortly after Vans issued service bulletin 13-3-21 in March of 2013.

"Rotax has recommended a 5 year replacement schedule for rubber hoses and fittings in their engine."

After reading that, Tom and I were wondering why ANY aircraft should be utilizing rubber hoses in any portion of their fuel system. We also were wondering why RV-12 owners should be paying more for a rubber hose setup than a much higher quality conductive Teflon setup would cost.

We set out to offer RV-12 owners a better option. Originally, we utilized the same banjo fitting and fuel block design to keep the system exactly the same. The difference was that we utilized conductive Teflon hose assemblies with no life limit and a resistance to damage from any fuel additives.

After building several systems like that, we realized that if anyone ever suffered hose damage (physical damage to a hose from not being secured properly, etc...), they would not be able to field replace the hoses. We decided to source adapters to change the entire fuel system over to aviation standard type hoses. Now, all hoses utilize 37 degree flare fittings so any mechanic can make a up a field replacement hose quickly and get a customer on their way. No longer would a rotax owner need to order a specially sourced hose to repair an issue. This is especially true in the case of the restricted return hose.

So, you are 100% correct that ordering a different fuel system to fix an erratic sensor makes no sense. Potential reasons to replace the fuel system include:

1. Our package is lighter weight than the stock hose setup. (with early rubber hoses....I am not sure of the weight of the current setup being sent)
2. All hoses are field replaceable in the event of any physical damage.
3. No life limit on ANY of the fuel system components
4. 10 year warranty on all components.
5. Less expensive than Rotax provided Teflon
6. Every hose is pressure tested prior to shipment.
7. All stainless steel fittings on hose ends.
8. Just as a random side benefit...no known reports of low fuel pressure for undetermined reasons.

With that said, if someone's current fuel hose system is working great, there is no reason to replace it. But, if/when it requires replacement, all options should be considered.

Since you are actively monitoring this thread, here are a few questions...

1. Are all rv-12 hoses currently being shipped made of conductive Teflon, or just the carb hoses?
2. Are all fittings currently stainless? Or are they a combination of CR Steel and Brass?
3. What is the current replacement schedule for firewall forward hoses? Are they all on a 10 year replacement schedule?
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Last edited by Aircraft Specialty : 10-01-2017 at 07:35 PM.
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  #34  
Old 10-01-2017, 11:06 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by TS Flightlines View Post
Rich---I put it on the cross for photo purposes.
Tom

BTW---Steve and others did most of the beta work on this package. We knew the guidelines we wanted, and then had to design a package to integrate it all together. Teflon hose, AN hardware, etc.
We havent heard from anyone with this package having a pressure issue. Alot of them flying worldwide, not only on RV12's but others with the 912 Rotax.

Tom
Quote:
Originally Posted by Aircraft Specialty View Post
Of course not. Why would anyone replace an entire fuel system due to an erratic sensor?
Steve,
Tom was the one that originally inserted an infomercial promoting the idea that users of your hose kit haven't had any low fuel pressure indications....
In this thread about an instance that clearly looks like a sensor problem.
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  #35  
Old 10-02-2017, 07:25 AM
TS Flightlines TS Flightlines is offline
 
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Scott---no infomercial here. No Alex Trebek, no buxom blonde in stillettos, no toll free phone number, no add a second order for free, just pay the shipping and handling. Quite the contrary. NOT selling anything. In fact, we've helped alot of RV builders WITHOUT selling them anything.

As far as the Rotax fuel pressure issue, it does NOT have anything to do with Vans hoses, or our hoses. YES, most of the low pressure warning issues ARE instrument related. (We actually advise owners to check the pressure with a known good mechanical gauge to verify the results.) Some were from an actually failing mechanical fuel pump. Rotax, put out the SB on the 5 year hose replacement, we didnt. We just make them from teflon. YES the carb hoses from Rotax are Stratoflex 101 teflon. BUT the other hoses WERE SAE 100R30 rubber at the time we were working on this kit. The effects of an ethanol additive fuel on the rubber hose is well known--gee thats why most all the automotive companies have gone to teflon, thermoplastic, and nylon hose in their systems instead of using rubber hose. Begs to ask why Vans didnt use it, but thats not for me to say.

Minor history lesson here--Page 46-08 of the 11/10 powerplant install instructions of the RV12. I'm sure its been updated now, but thats what we were working with back then. Step 1, RTV seal the end of the rubber hose, the firesleeve, and the band area at the banjo fitting. Well gee, we KNOW of builders that were PULLING the firesleeve and the HOSE off the banjo barbs (pretty easy with Oetiker clamps), and actually pulling the end part of the hose liner with the barbs.) They replaced the Oetiker clamps with screw clamps and finished the install. The question arose was Why Vans didnt do all that before hand? They were supplying the hoses. No telling how many early 12 builders just forced the hose back on the barbs and left it at that. Yeah, 2.4 to 5 lbs isnt much pressure, but you would think your planes fuel system would be slightly more substantial than your Briggs & Stratton mower. THATS where all of this started, NOT fixing a low fuel pressure WARNING issue. It was about using a teflon hose for the other hoses in the system to MATCH what ROTAX had put on the carbs.

WE checked with several Rotax service centers and Rotax engineers that told us the 912 would run at full power at the reported low pressure of 2.2 psi. YEP it will, but certainly most guys would appreciate more fuel pressure than that. So I assume thats why Vans designed the system to run the boost pump all the time, to maintain the constant flow and elevated pressure to the system. Yes, some builders have put their pumps on switches, and have been spanked because of it. I'm thinking that its because Vans wants the pumps on to make sure there isnt a fuel starvation issue, JUST IN CASE there actually was an issue. BUT, if the Rotax runs at 2.2 psi, then why run the boost pump all the time?

Steve and I didnt take on this project on our own. In fact we were asked to do it by some RV12 builders. They didnt want a rubber hose fuel system. The originals we built did use banjo fittings. We still do some like that. It wasnt to FIX a low pressure 'issue', it was to provide a hose that didnt need to be changed every 5 years.

OH--IF its just a sender issue thats creating this illusion of a real pressure loss, then why not solve that problem? Oh gee, every time someone goes out and gets a warning of low pressure lets throw another sender on the plane. It might be fun to find out how many guys have had to put multiple senders on their planes. Is it an interface issue with the sender and the EFIS? Is it a plumbing issue for the sender? Can it be duplicated so the root cause can be established?

I'm all for getting to the bottom of the cause for this. Instrumentation or real pressure loss. Either way, its a problem. The solution isnt in an infomercial.

Tom


Tom
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  #36  
Old 10-02-2017, 06:15 PM
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Quote:
Originally Posted by TS Flightlines View Post
WE checked with several Rotax service centers and Rotax engineers that told us the 912 would run at full power at the reported low pressure of 2.2 psi. YEP it will, but certainly most guys would appreciate more fuel pressure than that. So I assume thats why Vans designed the system to run the boost pump all the time, to maintain the constant flow and elevated pressure to the system. Yes, some builders have put their pumps on switches, and have been spanked because of it. I'm thinking that its because Vans wants the pumps on to make sure there isnt a fuel starvation issue, JUST IN CASE there actually was an issue. BUT, if the Rotax runs at 2.2 psi, then why run the boost pump all the time?
The RV-12 has a tightly cowled engine and when you shut it down the heat is retained for a long period. The residual heat after engine shutdown can cause the fuel to boil off in the carburetor float bowls.

What you have to watch out for is restarting a warm engine that has been sitting for some time. In this case there is likelihood that fuel has vaporized from the float bowls and the carburetor bodies are still warm. That is why it is best practice to allow the electric fuel pump to operate for approx. 5 minutes to recirculate cool fuel through the upper distribution manifold and return to the fuel tank. If for no other reason this is why the electric fuel pump should be run in continuous mode. Why take the chance of switching the electric pump on/off and perhaps some day forgetting to turn it on. If Vans says it should always be powered, thatís plenty good enough for me.
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  #37  
Old 10-02-2017, 08:28 PM
AirHound AirHound is offline
 
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Originally Posted by Mich48041 View Post
Yes, the fuel pressure sensor compares atmospheric pressure to fuel pressure. If the air pressure at the sensor changes, then the displayed fuel pressure will change too, even though the fuel pressure remains constant. Who knows how much the air pressure actually changes with cowl removed?
Thanks Joe, had only half that picture.
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  #38  
Old 10-14-2017, 01:10 PM
todehnal todehnal is offline
 
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Originally Posted by rvbuilder2002 View Post
Roger,
The RV-12 Rotax power plant kit comes with a pre-made hose that already has the proper restrictor installed. The only potential problem is if someone installs the hose backwards with the restrictor path routed to the fuel pressure sensor instead of the return line. It is rather obvious when this happens because the fuel pressure will not get into the normal pressure range with just the electric pump operating on the ground.
I guess after reading this, I really need to investigate my restrictor installation. I typically allow the electric pump to run for a bit before starting, particularly after a breakfast or lunch stop. The idea is to circulate the warm fuel out of the engine compartment, and back into the tank, and thus reducing the chances of vapor lock. I never get all the way up to normal with only the electric pump running. Typical it settles at about 2.4 psi, whereas after starting the engine, it goes immediately up to 4.6 psi. If I am reading Scott's post correctly, my 2.4 psi with just the electric pump running is not satisfactory. It would be nice to hear what others are seeing with just the electric pump running.

Thanks.......Tom
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  #39  
Old 10-14-2017, 01:28 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by todehnal View Post
I guess after reading this, I really need to investigate my restrictor installation. I typically allow the electric pump to run for a bit before starting, particularly after a breakfast or lunch stop. The idea is to circulate the warm fuel out of the engine compartment, and back into the tank, and thus reducing the chances of vapor lock. I never get all the way up to normal with only the electric pump running. Typical it settles at about 2.4 psi, whereas after starting the engine, it goes immediately up to 4.6 psi. If I am reading Scott's post correctly, my 2.4 psi with just the electric pump running is not satisfactory. It would be nice to hear what others are seeing with just the electric pump running.

Thanks.......Tom
The electric pump by it self will not produce normal in flight pressure value that you get with the engine drive pump operating.
2.5 PSI is about right, and is more than enough to operate the engine at cruise power.
The design philosophy of the lower pressure pump is that with an in flight engine drive pump failure, the pressure will drop into the yellow range and que the pilot that something is not as it should be.
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RV-6A (aka "Junkyard Special ")
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  #40  
Old 10-14-2017, 01:47 PM
todehnal todehnal is offline
 
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Thanks Scott. That sure eliminates my worry. I was certain that I had installed the restrictor according to plans, and have never had a fuel pressure issue that I was aware of. I really appreciate you chiming in.........Tom
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