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0.0 Fuel pressure while on cross country

Hi Steve:

As the operator of an S-LSA RV-12 used in a flight school in SE Wisconsin I would dearly love to have lifetime fuel hoses and an oil thermostat - our winters are long and cold.

Since you and I are in the same locale Steve I wonder if Van's would allow you to install those items on our aircraft, periodically inspect them and send the data you collect to the factory so blanket S-LSA approval can be given?

Just a thought. I think I'll call Gus this coming week and ask him about this idea.

John,

If Van's is onboard with your request, we would be more than happy to work with you on this project.

Steve
 
Sold- NO LONGER AVAILABLE

I have a customer who purchased the RV-12 Conductive Teflon Fuel Retrofit kit He never installed it as he purchased an RV-9 and sold the RV-12 about 2 weeks ago.

Since it is unused, but still "technically" 3 and a half months old, I won't sell it as new.

It still comes with a 10 year warranty from the date of purchase for whomever would like it.

$450 including shipping ($164.95 discount off list.)

First person to email me at [email protected] gets it!

Thx and have fun building!

Steve

Sold- NO LONGER AVAILABLE......
 
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To add some clarity....

There are now 563 (that are known about) RV-12's competed and flown.

I realize there are some that have had low fuel pressure indications but it appears to still be a small percentage of the total fleet.

I don't have an answer for those that are having low pressure indications but work is still being done to try and find an answer.

Tom has previously promoted that none of the RV-12's that have incorporated his aftermarket hose kit have had low fuel pressure indications. Perhaps if someone that does have low pressure indications was interested in changing out their hoses, we could find out if his hose set does make a difference and possibly have some additional info that could be used to solve it.

Scott,

At the time you suggested this, plans were already in the works to seek out volunteers to do a fuel system comparison.

We are going to be sending an email over to Rian this afternoon detailing some of the discoveries that we made, and then will be releasing the data on VAF after that.

Steve and Tom

Aircraft Specialty/TS Flightlines
 
Scott,

At the time you suggested this, plans were already in the works to seek out volunteers to do a fuel system comparison.

We are going to be sending an email over to Rian this afternoon detailing some of the discoveries that we made, and then will be releasing the data on VAF after that.

Steve and Tom

Aircraft Specialty/TS Flightlines

I can tell you that my fuel pressure has been giving me fits from going to 2.0 upon decent....and until recently, lower than 2.0 @ wot during climb out and cruise. Steve sent me their kit; and the fuel pressure has been rock solid...never less than 4.4, normally 5.4. I’m a very happy camper.

Edit: I should mention that a ball of what looked like shaving of the internal lining of the fuel hose from the mechanical fuel pump to the fuel distribution block assembly was found (my uneducated assumption is this came from the assembly of the fuel hose because there is no way the **** would have made it through the gasolator or filter on the front side of the mechanical pump)....Steve, any word on your thought of the material composition. I’d like to render a report to Van’s & Rotax.
 
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I can tell you that my fuel pressure has been giving me fits from going to 2.0 upon decent....and until recently, lower than 2.0 @ wot during climb out and cruise. Steve sent me their kit; and the fuel pressure has been rock solid...never less than 4.4, normally 5.4. I’m a very happy camper.

Edit: I should mention that a ball of what looked like shaving of the internal lining of the fuel hose from the mechanical fuel pump to the fuel distribution block assembly was found (my uneducated assumption is this came from the assembly of the fuel hose because there is no way the **** would have made it through the gasolator or filter on the front side of the mechanical pump)....Steve, any word on your thought of the material composition. I’d like to render a report to Van’s & Rotax.

Ric,

Glad you are happy with your fuel hose package.

I took a picture of the debris that you sent to us from inside the fuel system. It is enroute to Tom at the moment. He is going to take a good look at it as well as do a full hose dissection to see what he can find.

Rotax%20Debris.jpg


Here is the original picture showing the debris clustered together.

Rotax%20Debris Original.jpg


We will definitely keep you updated on what we uncover.

Have a great weekend,
Steve
 
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Some more information after several months of testing

Over the past 2-3 months, Tom and I worked with three RV-12 owners who had been experiencing intermittently low fuel pressures. We replaced those fuel systems with our Conductive Teflon retrofit kit.

Below is a link to a pdf document detailing our findings.

http://aircraftspecialty.com/PDF Documents/Rotax Fuel Pressure.pdf

We sent this information over to Vans earlier in the day.

As always, we want to thank everyone who helped us out with this project. We wouldn't be able to do nearly as much testing without the incredible support of the Vans community.

Have a great weekend.

Steve and Tom
Aircraft Specialty/TS Flightlines
 
Ric,

Glad you are happy with your fuel hose package.

I took a picture of the debris that you sent to us from inside the fuel system. It is enroute to Tom at the moment. He is going to take a good look at it as well as do a full hose dissection to see what he can find.

Rotax%20Debris.jpg


We will definitely keep you updated on what we uncover.

Have a great weekend,
Steve

Steve,
Post the original picture if you would that I sent you. The pic above has the crud scattered out.
 
I was one of the recent beta testers for the Aircraft Specialty fuel hose kit. Prior to the installation of the new hoses and hardware, I had been having issues with sporadic low fuel pressure indications since I have been flying the aircraft. I have a relatively recent -12 kit, so the stock fuel hoses were the newer Teflon variety. Unlike the poster above, despite repeated inspections, I never found a reason for the pressure fluctuations. It has now been a bit over two months and 21 hours since I replaced the hoses and fittings with the Aircraft Specialty kit. I have had no further fuel pressure indication problems. I would feel better if I really understood why the change resolved problem. Perhaps the dissection of the old hoses will give us a clue.
Alex
 
Over the past 2-3 months, Tom and I worked with three RV-12 owners who had been experiencing intermittently low fuel pressures. We replaced those fuel systems with our Conductive Teflon retrofit kit.

Below is a link to a pdf document detailing our findings.

http://aircraftspecialty.com/PDF Documents/Rotax Fuel Pressure.pdf

We sent this information over to Vans earlier in the day.

As always, we want to thank everyone who helped us out with this project. We wouldn't be able to do nearly as much testing without the incredible support of the Vans community.

Have a great weekend.

Steve and Tom
Aircraft Specialty/TS Flightlines

We also tested the Aircraft Specialty Hoses, upgrading from the original Van's supplied hoses. We were at our 5 year replacement for rubber anyway. Over the last 5 years, we also noticed sporadic unexplained drops in fuel pressure. Over the last year, the fuel psi drops became more frequent, and usually in cruise flight. Fuel levels varied, as did altitude. PSI would drop to 2.5 and below. I want say that the engine never stumbled, ran rough, or acted funny in any way. This purely seemed to be some sort of indication issue. The fuel pressure sensor was also the original VDO (larger gray) style sender.

Testing the hoses, I have put 10+ hours on them and the fuel psi stays in the normal operating range for all phases of flight. Usually 5.0-5.5 in cruise now. We also left the original VDO fuel pressure sensor in place as well. Only changed the hoses. The old hoses are enroute back to steve for a look.

Also, we have kept up with the recommended 200 hour carb overhauls, and have never had any noticeable fuel overflow in the drip trays or debris in the carb bowls (to my knowledge this far).

Thanks to Steve for allowing us to help him out, and find some answers going forward.
 
I was one of the recent beta testers for the Aircraft Specialty fuel hose kit. Prior to the installation of the new hoses and hardware, I had been having issues with sporadic low fuel pressure indications since I have been flying the aircraft. I have a relatively recent -12 kit, so the stock fuel hoses were the newer Teflon variety. Unlike the poster above, despite repeated inspections, I never found a reason for the pressure fluctuations. It has now been a bit over two months and 21 hours since I replaced the hoses and fittings with the Aircraft Specialty kit. I have had no further fuel pressure indication problems. I would feel better if I really understood why the change resolved problem. Perhaps the dissection of the old hoses will give us a clue.
Alex

Alex,

At this point in time, all we can say is that an analysis of the stock Vans/Rotax fuel system has revealed several differences in both fuel and return line fuel distribution from the Aircraft Specialty/TS Flightlines retrofit.

The documented case of debris in the fuel lines does NOT appear to be an issue with your lines.

What we do know is that our fuel system has not had any documented fuel pressure issues in the RV-12 or the multitude of other aircraft types that we build this configuration for.

Steve
 
Below is a link to a pdf document detailing our findings.

http://aircraftspecialty.com/PDF Documents/Rotax Fuel Pressure.pdf

I read this report and to me it sounds more like an infomercial where a guy cuts his boat in half and then tapes it back together with his wonder product and it doesn?t leak water. Not a whole lot of empirical data conveyed or hard engineering conclusions in this report.

I understand the necessity to change-out rubber hoses as they age. Replace with new rubber hoses and wait for timeout again or replace with Teflon hose and forego future maintenance required. I can?t imagine Banjo fittings being a culprit of low fuel pressure. I?m sure Rotax did a full design analysis and testing.

Don?t get me wrong; I?ll replace my hoses most likely with Teflon, as this is a superior material. I have no qualms with the original Vans/Rotax fuel system, which has served me flawlessly for 300 flying hours.
 
Ric--
from the pics, it looks like liner debris. I havent received the hoses from Steve yet--they are inroute-- so I'd like to withhold our findings until we can take a look. But that much debris and the shape its in certainly looks like its from the extrusion process, more specifically from the screw mandrel that forms the hose bore.

Should be interesting!
Tom
 
I read this report and to me it sounds more like an infomercial where a guy cuts his boat in half and then tapes it back together with his wonder product and it doesn’t leak water. Not a whole lot of empirical data conveyed or hard engineering conclusions in this report.

I understand the necessity to change-out rubber hoses as they age. Replace with new rubber hoses and wait for timeout again or replace with Teflon hose and forego future maintenance required. I can’t imagine Banjo fittings being a culprit of low fuel pressure. I’m sure Rotax did a full design analysis and testing.

Don’t get me wrong; I’ll replace my hoses most likely with Teflon, as this is a superior material. I have no qualms with the original Vans/Rotax fuel system, which has served me flawlessly for 300 flying hours.

Jim,

Good morning.

There are three primary differences in the fuel systems. One is Banjo versus flare fittings. The second is a different fuel distribution block. The third is a different return line setup, including a different restrictor and restrictor location. ALL three of these design aspects were considered and done in a methodical manner based on customer feedback and testing.

The hoses in the stock fuel system are OEM Rotax with the exception of the VA-216 which is NOT a standard Rotax hose. As we stated in the PDF, we have sent some more information on the VA-216 to Vans. We have also dissected several of the Rotax hoses and have identified differences that exist in terms of bore size, type of fitting, and aspects that may impact flow.

To reiterate.... There is no reason to swap out a fuel system that is performing flawlessly.

Our testers were having erratic low fuel pressure indications. In order to eliminate the potential of a faulty sensor, we asked them to ONLY replace the fuel system to get accurate results. The fuel system replacement appears to have eliminated their low fuel pressure issues. We have their data downloads that were emailed to us. However, it really isn't all that exciting. Basically it shows that the fuel system operating at a stable, consistent pressure whereas before it was not.

All of our testers have posted on this thread confirming that in their specific cases, our system has had a positive result regarding their prior low fuel pressure indications.

Have a great weekend and feel free to call if you have any additional questions.
Steve

P.S. I would seriously question the judgement/mental stability of anyone that cut their boat in half and then used "wonder tape" to stick it back together. However, taking action to repair a boat that doesn't appear to be functioning properly is an entirely different case.
 
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Jim and others,
no infomercial intended -again-. Some of the Rotax owners were having fuel pressure issues with the OE system. All of the original users including the RV12 owners were affected by the Rotax 5 year replacement of the rubber products.
Early on, we were contacted about making teflon assemblies to do away with the rubber hoses. We did that. At the same time, Rotax and their distributors did not want to sell the banjos, or they were expensive. So, we set out to make an alternative to the stock package.
So it met the original intentions of a teflon hose package---which ROTAX has now done and Vans has done with their return hose. Just so happens that SOME Rotax owners, and not necessarily just RV12 owners, but other models with the 912ULS engine were experiencing low pressures (yes actually measured) after Rotax switched to teflon. Didnt seem to be any reports that I know of, of any with the rubber hose, although some rubber liner debris was reported in various installs, thus the 5 year replacement SB and the Rotax switch to teflon.
Thats why we did it.
A byproduct of the way we did our package was owners that have our system were not reporting the low pressures that other stock Rotax users were having. YES---we got very curious as to why this was occurring or more correctly wasnt occurring. NOW that we have the original hoses off 2 different RV12's inroute we will be able to analyze and see whats causing it.

The 1 package from Ric's install may have 2 issues, with 1 being very obvious--the debris as pictured earlier in this thread. The other may be like the other ones.

NOW--i'll say again. NOT every RV12 or Rotax 912ULS has a low fuel pressure issue. But it is documented on various forums pertaining to the Rotax engine. Some, like yours operate just fine, no runs, drips or errors. BUT others, with seemingly the same exact equipment, engine, avionics, same part of the country, different parts, different altitudes, even different countries around the world, have experienced this anomaly. Rules out pilot error, fuel blends, climate, avionics. So the thing thats left is the fuel system at the engine. OH---and Rotax put out an SB to replace the fuel pump several years ago with an updated version to try to eliminate the pressure issues. They had some that had issues, so the new version with its threaded fittings was supposed to fix the problem. Seems it may have on some but not on others. Thats why we started investigating what the issues were.

I suppose Steve and I could have just kept our mouths shut and let things continue rolling. WE really wanted to know, so there would be no 'infomercials'. Tell you my feeling----what IF there was a solution with our package and we kept it to ourselves. Suppose we knew about it and didnt tout its advantages. Suppose someone 'could' have used it, and didnt because they didnt know ----and they had a real pressure loss and the plane went down. How do you think we we would feel about that?

So--for the time being, thats the last I'll say on this subject. The hoses in question from Ric and another owner are inroute to use for inspection. Part of that inspection may be using the flow bench of a well known accessory supplier of fuel systems---although we havent talked about it.
Nevertheless---when we are done we'll let you all know what we find, and if any of you engineers want to join in ----come on down.

Tom

p/s---apologize for this getting out of hand. Tom
 
Jim-
"I understand the necessity to change-out rubber hoses as they age. Replace with new rubber hoses and wait for timeout again or replace with Teflon hose and forego future maintenance required."

New rubber hoses are not used by Rotax---they are all teflon now. So is this issue going to become apparent on your plane with the Rotax hoses? I dont know, maybe , maybe not.
So if you want rubber hoses, and change them every 5 years as per your above post, you'll have to secure the hose and make them yourself. YES, teflon is the way to go, especially for the liner degredation issue.

Tom
 
Just received word from Tom that **** found in “new Rotax Teflon fuel lines that caused low fuel pressure and wot rough running engine was in fact material from manufacturing process (nothing foreign brought in with fuel).

By the way....these lines were flow tested by me during pre-initial first flight and none of the material made it through the banjo fittings into the carbs.

Sugggest anyone having low fuel pressure problems check their fuel lines from mechanical fuel pump to carbs (this stuff dosen’t Easily blow out of the affected hoses).

Edit: my fuel pressure is rock steady @ 5.4 psi since change out to new fuel line set up from Tom& Steve..
 
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Ric,

Tom and I are working jointly on what we found. We are also now engaging in another round of testing with another rv-12 owner who contacted us with low fuel pressure issues. After dissecting your lines we were able to confirm the differences between the stock fuel system and our retrofit kit. The results matched the dissection of a fuel system I did several weeks ago on another rv-12. (Without the debris issues)

We are working hard to narrow down which of the 4 main specific differences/combination of differences between the packages is causing the different fuel pressure results with our system versus the oem hoses.

Steve
 
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Just to clarify--

"Just received word from Tom that **** found in ?new Rotax Teflon fuel lines that caused low fuel pressure and wot rough running engine was in fact material from manufacturing process (nothing foreign brought in with fuel)."

YES the debris was liner material that was present after the hose manufacturing process, NOT the assembly process of installing the fittings. Yes the debris COULD have contributed to some low pressure issues in Ric's case, but not everyone has that debris issue. In Fact, this is the first one I've heard of with that particular brand of hose. When I'm DONE, I'll present all the facts as I see them.

Tom
 
I read this report and to me it sounds more like an infomercial where a guy cuts his boat in half and then tapes it back together with his wonder product and it doesn?t leak water. Not a whole lot of empirical data conveyed or hard engineering conclusions in this report.

Tom and Steve,
I sure wouldn?t want you guys to think this quote is widely believed! For those of us who built our airplanes and benefited from your various kits such as the stainless brake lines, oil pressure relocation kit, oil thermostat and the modifications being discussed in this thread, we are well aware of the good, honest work y?all do. We are also aware of what a pleasure it is to deal with both of you.
Furthermore, if either of you fellers develop some miracle tape, send me some with an invoice. I am sure it will be good stuff. Thanks for doing what y?all do.
 
What I should point out is that all the debris on Rics plane was in the adapter on the outlet side of the fuel pump. I had run the fuel flow test in the Vans manual (which is at the gascoloator) and then because of the issues Ric and Mark were experiencing ran it again at points up the fuel system, seeing a noticeable degradation in fuel flow after the pump. How the debris got there and got compacted in the adapter I have no clue (when they took the pump apart it looked brand new).

So I would suggest that on condition inspect people remove the adapters and inspect.

I don't have the TS flightlines on my plane, but it looks from the instructions that the adapters are replaced by that solution.
 
Julian----I was told the pump was clean, with no traces, so I was concentrated on the discharge hose. Did find that anomaly with the liner, that isnt present anywhere else. Did section a piece out of the -6 supply hose and the anomaly isnt there. Clean as a whistle, as you would expect a teflon hose running fuel through it would be.

Agreed---inspection is a good course of action, and even flushing the hoses. But if there wasnt any debris in the gascolator, or the supply hose, then it got there some how, and the size of the debris is much larger than would have passed through the gascolator screen.

Tom
 
What I should point out is that all the debris on Rics plane was in the adapter on the outlet side of the fuel pump. I had run the fuel flow test in the Vans manual (which is at the gascoloator) and then because of the issues Ric and Mark were experiencing ran it again at points up the fuel system, seeing a noticeable degradation in fuel flow after the pump. How the debris got there and got compacted in the adapter I have no clue (when they took the pump apart it looked brand new).

So I would suggest that on condition inspect people remove the adapters and inspect.

I don't have the TS flightlines on my plane, but it looks from the instructions that the adapters are replaced by that solution.

Azjulian....the material did not come through the pump. It was moving around in the fuel line between the banjo fitting that attaches to the fuel block assy and the outlet fitting of the fuel pump. The material being debris from the Teflon hose liner left there following manufacture of the hose. And it had been previously flow tested with okay results. Did I look down the bore of the hose...no; I guess my mistake. As it was part if the equipment received from Rotax I assumed it was okay.
 
Wherever it came from it?s scary. I blew out out my fuel lines with air and a flush cloth over then end when I installed them. I never got anything on the cloth. That amount of debris is just bizarre!
 
TS FLIGHTLINES keep up the good work! Thanks for dedicating time and money to figuring out our problem. We also have a low fuel pressure readings from time to time. I've ruled out the sending unit but that's as far as I've made it. Our problem is hit or miss as of now making it hard to duplicate.
 
Chuck---thats one of the strange things about this whole deal. Some Rotax 912's have it, some dont. It doesnt seem to be geographical, altitude, RPM, fuel blend, or any other obviously related items. Some with the old rubber hoses were fine, some werent. Some with the Rotax version teflon were fine, others werent. WE did take Scott's advice and ask for testers that were having pressure issues to contact us, AND several have. Interesting results.
We are still gathering data--because all of you want to know. We're down to the last 5 testers that are helping us (Aircraft Specialty and TS FLightlines) gather this data. Weather, schedules, and gee sometimes life happens that throws a kink in plans, so its taken longer than we wanted, but its been methodical.
Oh and this isnt just US based planes, we have an Australian based 12 that is also involved, as well as a European owner.

Tom
 
In response to requests from many RV-12 owners to publish more data regarding what we have uncovered throughout our multiple fuel system dissections, we are releasing a follow up report to our original report issued in January.

This one is much more detailed with pictures of what we have found.

www.aircraftspecialty.com/PDF Documents/Rotax Fuel Pressure2.pdf

As always, Tom and I want to thank ALL of you for the help we have received throughout this process.

Have a great weekend, and happy flying/building

Steve and Tom
 
Did you do a fuel flow analysis with 0.021 Vs. 0.014 restrictive orifice at the low ~ 5 psig fuel pump delivery pressure? At such a low pressure the flow difference may be significant.

Vans may specify a larger orifice for more return fuel flow to the tank for a specific reason and that might be to prevent vapor lock on engines that are heat-soaked. The 912 installation in the RV-12 is tightly cowled with minimal air flow during ground operations. Perhaps Vans wanted additional cool fuel flow to prevent fuel from vaporing in the carburetor float bowls.

I suspect a higher fuel flow back to the tank would be beneficial when re-starting a hot engine that has sat for some period of time where the fuel in the carb bowls, if not beginning to vaporize, would surely be heated above ambient temp. Having an abundance of cool fuel in the fuel delivery rail located on the top side of the hot engine sounds like a good idea.
 
Did you do a fuel flow analysis with 0.021 Vs. 0.014 restrictive orifice at the low ~ 5 psig fuel pump delivery pressure? At such a low pressure the flow difference may be significant.

Vans may specify a larger orifice for more return fuel flow to the tank for a specific reason and that might be to prevent vapor lock on engines that are heat-soaked. The 912 installation in the RV-12 is tightly cowled with minimal air flow during ground operations. Perhaps Vans wanted additional cool fuel flow to prevent fuel from vaporing in the carburetor float bowls.

I suspect a higher fuel flow back to the tank would be beneficial when re-starting a hot engine that has sat for some period of time where the fuel in the carb bowls, if not beginning to vaporize, would surely be heated above ambient temp. Having an abundance of cool fuel in the fuel delivery rail located on the top side of the hot engine sounds like a good idea.

Jim,

In short.... yes. We know what the fuel flow differences are. If we wanted to utilize a larger return orifice it would be very easy to swap out the restrictor for a larger diameter one.

However, our system utilizes the size specified in the Rotax manual. (within .001”) Our system is NOT the one having fuel pressure issues and is not having ANY issues with the starting of a hot engine. So, there is no reason for us to go against what the manual specifies.

Personally, I think that there are much more intriguing elements to this document than the restrictor orifice size.

Steve

P.S. As Tom mentions below, and has been documented previously......the Stock OEM Rotax fitting is sized differently than what they specify in their own manual. A #75 drill bit would easily enlarge our orifice out to the actual size of the Rotax OE fittings. However, doing so would enlarge the orifice size beyond what Rotax specifies in their manual. Based on real world testing in customer aircraft, it certainly does not appear that there is ANY meaningful difference in operation or performance between the .015 and .021 restrictor sizes.
 
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Jim---the Vans restrictor is a .021 orifice. Its a STOCK Rotax fitting, as compared to a OE Rotax fitting---yes the WHOLE banjo fitting that I purchased from a Rotax parts distributor in Florida---dont know If I can mention the name here---but they are prominent. I also purchased the restrictor separately. Compared ALL of them. They are the same. Vans doesnt specifiy a larger restrictor.
3 different return hoses were checked, and all 3 had the same restrictor. MY conclusion, was that the restrictor size was the same as the OE Rotax----since I also had theirs to compare.

AND--what I really wanted to do was do a test on an ENTIRE fuel system, as installed in a RV12. Yep, tank, boost pump, lines, gascolator, engine, etc. THAT way you have all the components, not just the hoses off the engine. Utilizing just those hoses would mean some creative adapter fittings to connect sensors, and may or may NOT be entirely accurate. Steve and I had discussed contracting with a well known fuel systems manufacturer to utilize their flow bench, but after some of the results we decided that wasnt necessary. BUT, certainly if someone wants to donate their plane for that its would be great. Dont know how we'd get the plane into their flow bench room, even with the wings off. Thus the multiple testers in different parts of the country, and several overseas in an unofficial capacity.

Tom
 
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A few additional thoughts to consider......

The Rotax 912ULS fuel system is operating at a maximum pressure of ~7.5 PSI.

A simple rubber (vacuum style) hose pushed onto a hose barb with a couple of ribs would probably take at least 3-4 times that pressure before it would blow off. In the process of doing my own research on orifice sizes I attempted to pull the hoses from the dual barbed banjo fitting on one of the early versions of the VA-216 hose assemblies and couldn't. I had to cut them off.
Spec #'s always sound good (especially when part of an advertisement or infomercial) but if they are 400 X higher than what is needed for a specific application, what is the point (advertising hype is the only thing I can think of)?
My point is that in an application like this, there is no need for a hose assembly rated at 3000 PSI.
There is mention of uncertainty of the quality of the fire sleeve. Does uncertainty mean it is not good? No, it just means Steve and Tom don't know, so because of that think theirs is better, because they do know its specs. Fair enough.

Orifice size-
Van's has never specified the use of a particular size for the orifice.
The VA-216 production drawing specs the use of the dual barb banjo fitting, Rotax part # 956602, as supplied by Rotax with the engines.
The orifice size is what ever Rotax installs before delivering the part.

I confirmed that as best as we can tell, the .020/.021 orifice diameter is what has been supplied in the standard factory parts from Rotax since Van's first began development of the RV-12 more than 10 years ago.

It is now easy to understand why the Aircraft Specialty / Flightlines hose kit would help increase the fuel pressure in any given condition..... reducing the orifice diam. by 25% will significantly reduce the return flow. It wouldn't surprise my if it reduced it by 50%.
This could raise the potential for problems caused by operating in hot conditions. Especially when using auto fuel.

I can not explain why Rotax's documentation specifies a different diam. orifice than what they actually supply on their engines, but I will be looking into it.
It could be a documentation typo, or they could have purposely changed it to a larger diam. and didn't update the documentation. I intend to try and find out and I will report here what I find.

If you operate your engine with auto fuel and you are using one of the aftermarket hose kits, I would recommend caution as we head towards spring (here in North America anyway), and near the transition period of warmer temps and the dangers associated with winter blend fuel use in warm temperatures.
A large purpose of the return flow (which with the .020 orifice is about 1.5 GPH) is to mitigate fuel system vaporization problems. A secondary reason is to provide a flow path to bleed off fuel pressure in situations where the pressure builds because fuel expansion because of rising engine compartment temps after shut down in hot conditions (a build in fuel pressure could overcome the float valves and flood the carburetors).
 
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Scott,

I can only assume that you didn't have time to read the document in its entirety as there are several items that need to be clarified.

1. First and foremost...... I am curious as to how you came so quickly to the conclusion that "It is now easy to understand why the Aircraft Specialty / Flightlines hose kit would help increase the fuel pressure in any given condition..... reducing the orifice diam. by 25% will significantly reduce the return flow. It wouldn't surprise my if it reduced it by 50%." -

As referenced in the document we published that was based on real world testing, we have a customer who has the new style VANS Stock Teflon fuel hose system. He is having low fuel pressure issues. We replaced ONLY the VA-216 hose assembly with a new VA-216 that we built with our external restrictor. It very minimally raised his fuel pressure and did NOT solve his problem. This is how we determined that the restrictor size and location does NOT appear to be the issue with those who are having low fuel pressure. In short, the smaller restrictor does NOT raise the fuel pressure appreciably. It is something else.

2. Our hose kit is not new and has been flying on a variety of aircraft worldwide for over 4 years in many different climates and different fuel blends with NO reported fuel pressure/vaporization issues. In addition, EVERY aircraft that was reporting fuel pressure issues with the stock kit that has made the replacement has had the fuel pressure issue appear to be rectified. In addition, those with our fuel system report more stable pressures than with the stock kit.

Months ago, you advocated testing our fuel system out on aircraft with low fuel pressure issues to see if they made a change. You stated that if there were positive results, that would be something to look into and perhaps be able to be used to solve the issues that some of your customers are having with their stock kits. Well, real world testing has shown that it makes a difference. If you are serious about trying to isolate the cause of the low fuel pressure issues that exist on some aircraft with the stock fuel system, it's in your hands now.


3. Regarding orifice size...... if Rotax decides to change the manual, and specifies a larger restrictor....it is VERY easy to drill our restrictor hole out to a larger diameter. If the information that has been published in the manual since we started building these kits is correct and Rotax decides to change their actual restrictor over to match what their manual shows, then that will be a more complicated process to fix the internal restrictor.

4. Firesleeve- Perhaps you can answer the question for us. Is the VA-216 utilizing AS1072 firesleeve? You are correct that we don't know if it is or not.

Here is an excerpt found online regarding that:

"SAE AS1072 Aviation Firesleeve. Our firesleeve meets the specifications of SAE AS1072E, allowing qualified hose assemblies to pass the fire resistance testing specification of AS1055D. It may be used for all fuel, oil, hydraulic, fire extinguisher and prop feathering lines."

5. You mention the 3,000 psi hoses and the fact that they are overkill. When we designed this kit, we were replacing a RUBBER fuel hose system. We saved over a pound of weight over the stock rubber system, put 3,000 psi hoses on it, had a much higher quality assembly and no 5 year replacement. In addition, the cost of our kit was very similar to stock rubber replacement hoses. That makes a lot of sense to me.

Now, the current RV-12 fuel system that Vans is using utilizes 101-4 hose (a 1,000 psi working rated pressure), and what appears to be an AFLEX hose assembly for the VA-216 hose (a 3,000 psi working rated pressure) There is no disputing that a TEFLON hose is much higher quality than the rubber hoses used originally. By nature Teflon braided hoses that are being used are going to be in a working rated pressure for these sizes of 1,000-3,000 psi. And you can make the statement that it is overkill, but the fact remains that Vans is doing the exact same thing. You are utilizing a multi thousand pound pressure hose on a 7.5 psi fuel system.

A few questions for you...

1. What are your honest thoughts on having a rubber hose with NO primary retention on the hose to hold the fitting in? I understand that you pulled on by hand and were unable to yank it out. There are specific proof tests for hydrostatic hose testing, and that is not one of them.

2. What are your thoughts on utilizing barbed fittings designed for rubber hoses in a Teflon hose assembly with a very thin wall versus a fitting with a smooth stem that is designed specifically for Teflon hoses? (As seen in the dissected va-216 hoses)

3. You state "In the process of doing my own research on orifice sizes I attempted to pull the hoses from the dual barbed banjo fitting on one of the early versions of the VA-216 hose assemblies and couldn't." - Why were you doing research on orifice sizes when Rotax has always provided the orifices?

4. Even though it is a minimal amount of fuel going through the return line, why is non conductive Teflon hose being utilized versus a conductive Teflon fuel line which is standard for aviation fuel and oil lines?

Scott,

This process has in NO way been intended to be an infomercial. Tom and I genuinely love doing this. We love designing products and working with testers to continuously improve them. We have personally spent thousands of dollars on this testing in order to get the information that people have asked us for.

Vans builds an incredible airplane. I love my RV-10. The RV-12 is an aircraft that has absolutely revolutionized the LSA market.

We offer options to those builders who want them. While we realize that a lot of customers want to build a completely stock airplane, others don't. We provide solutions for those that want to make changes that they feel improve their aircraft.

At the end of the day, this is about making a better product for everyone. You have said that work is ongoing at Vans to solve this fuel pressure issue. We didn't create an issue that didn't exist in order to try to sell something. We designed a product at the request of rv-12 owners, and a side effect happened to be that it appeared to rectify an ongoing problem.

You asked us to test our kit on aircraft with the low fuel pressure issue. Just because the results may not be what you expected doesn't mean that they should be dismissed or denied. As far as we are concerned, our testing is complete. We have a final version of our kit that works well and owners are very satisfied with. Should additional information come out in the future that warrants a change to the kit, we will do that.

Tom and I are open and available for discussion if you have any questions regarding our testing. If it can help Vans solve this elusive issue and also put it to bed, we are happy to be a part of the solution.

Happy Building and Flying
Tom and Steve
 
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