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  #31  
Old 07-03-2013, 08:50 PM
Mich48041 Mich48041 is online now
 
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Location: Riley TWP MI
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Quote:
OK - the question is -- will the 2.7 psi from the elec boost pump run the engine normally with an INOP engine driven pump???
NO !
I have no personal experience, but have read reports from others who experienced partial power loss on takeoff. Very unnerving! The Dynon EMS indicated low fuel pressure and high fuel flow. The bad mechanical pump either leaks fuel or ingests air or both. The pilots were able to keep flying at reduced power and returned for landing. Replacing the engine driven fuel pump fixed the problem. Theoretically the electric pump alone should be able to supply the engine with ample fuel. And I think it would if the mechanical pump was bypassed. If the aircraft had two electric pumps and no engine driven pump, there would be less chance of fuel leaking inside of the cowl or sucking air into the fuel lines. But then what happens in the event of an electrical failure?
Joe Gores
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  #32  
Old 07-03-2013, 09:11 PM
Mark Henderson Mark Henderson is offline
 
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Location: Napa, Calif
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Default Is Alcohol a surprise to Rotax

In everything I have seen on the 912 Rotax recommends auto fuel, even with etoh. In fact, our service requirements are cut by 50% if we use 100 LL. So can someone tell me why they use hoses that need to be replaced at 5 years with autofuel?. I am sure that there are a number of us on this forum that drive a car or truck that is way more than 5 years old. I have not replaced the hoses on my 7 year old Nissan truck, nor have I had to clean the carb bowls. My 16 year old Nissaan Frontier is still on the road, and agin, on the same hoses. So tell me why on my $25,000 "modern" 912 do I need to do this at 5 years. Yeah, There is the old argument that a failure in the air is more significant etc. Ok, with all the cars on the road, how many do you see broken down on the side of the road each year?
I agree with earlier comment about the lawyers siping their coffee and expounding ways to sell more parts for Rotax. If the hoses on the 912 are so poor that they only last 5 years, why are they using them? None of the auto makers have this requirement, and they sell a lot more cars. Sure, they don't worry about inflight failures. But what do do think Consumer Reports, The car magazines, let alone the Feds would say if cars were dropping like flies along the road due to failure of the fuel hoses at 5 years?
Either the 5 year replacement schedule is way too conservative, or Rotax is ripping us off. I for one will monitor my engine, but I am not replacing good parts based upon an arbitrary schedule. As the NTSB and AOPA have noted, post maintenece is one of the most dangerous periods of flight. I am not going to cut into hose and replace parts with low service time due to flipping the pages on a calender.
This is my 2 cents, and as others have said, your mileage may vary. Flying is expensive enough without replacing perfectly good parts.
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  #33  
Old 07-03-2013, 09:20 PM
RFSchaller RFSchaller is offline
 
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The Pap's include a fuel flow test. If the electric fuel pump passes you WILL be able to run the engine on the electric pump. That's why you do the test.
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  #34  
Old 07-03-2013, 09:42 PM
NASA515 NASA515 is offline
 
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"I agree with earlier comment about the lawyers siping their coffee and expounding ways to sell more parts for Rotax. If the hoses on the 912 are so poor that they only last 5 years, why are they using them? "

Here's a discussion on the 5 year question - I posted on it the same way I did on here. Like you, I distrust everything about this requirement. Plus - I'm told Rotax has actually run their engines satisfactorily with 20% (or even 25%) ethanol, with no problems. The U.S. seems to be moving towards 15% ethanol - a decision just in the past week - and maybe 20% is not far behind.

http://www.rotax-owner.com/rotax-blo...er-replacement

I personally feel there is a cred (credibility) problem - on the one hand, you have Rotax saying 5 years and "yer out!", and on the other hand, they spec'd, purchased, installed, and then got A.D.'d over fuel hoses that were not compatible with gasoline (nothing said about ethanol.)

Actually, altho this thread has drifted into the ethanol arena, I don't believe the Rotax 5 year requirement has been described as an ethanol problem. Rather, it may be due to - say - high ozone levels in the atmosphere - like in S. California - and aircraft that have their fuel hoses exposed to sunlight (like in say, a Trike, etc.)

Then, of course, Vans has muddied the waters with their own ethanol Service Bulletin - which doesn't say much, but seems to be 100% CYA.

Bob Bogash
N737G
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  #35  
Old 07-04-2013, 06:57 AM
TS Flightlines TS Flightlines is offline
 
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Bob and all--
I feel the 5 year replacement on the Rotax hoses is like the old AC20-7N, which stated hose pressure tests every 100 hours, and replacement at 5 years. Now, I dont know about you guys, and some of our A&P and I&A guys can tell us (me)---who was REALLY pulling hoses at 100 hours and pressure testing them? I've done some 303 hose for some people that had 15-20 year old date codes. ( I saved one that I did in 2006 that had a date code of 1966, and was still flying).

But what I can tell you from my automotive experience is that ethanol will eventually attack the neoprene/nitril liner of a rubber hose, like those on your Rotax, and begin to form some work harden cracks. Under flexing, these cracks begin to open up, and the hose begins to seep. Granted---your plane doesnt put anywhere near the amount of hours on it that your car or truck does. Late model vehicles have a teflon, or thermoplastic hose/liner combination, that isnt affected by the ethanol additives.

Rotax, and others are being safe by recommending the hose change. Just like the old 20-7N. Rubber hose is easy to install, way less expensive than teflon hose and crimped fittings. In some cases, it may be better and less expensive to just replace the hoses every 5 years. ( I dont know what the cost is of the Rotax hose replacements). But---IMHO--teflon will out service any rubber hose out there. Yes--it is overkill on a very low pressure system, but it is the best for this application.
Tom
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Last edited by TS Flightlines : 07-04-2013 at 07:21 AM.
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  #36  
Old 07-04-2013, 09:20 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Tom,
What would you consider the safe useful life delta between plain rubber hose and Teflon lined hose? Twice the service life (10 years)?
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  #37  
Old 07-04-2013, 12:55 PM
TS Flightlines TS Flightlines is offline
 
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Tough question, since teflon has virtually an unlimited service life. As long as it isnt abused, abrased, or subjected to alot of heat, it generally will outlast the airframe. Rubber hose, neoprene, nitril, or those rubber based liner really should be changed out on a regular interval. Lets face it---5 years of flight time is pretty good.
One point that I will make is that teflon hose, although is pretty forgiving to abuse, it doenst like to be straighten out after being in its 'installed configuration'. Its like 303 hose in that respect. Ever seen a piece of 303 that has been on a plane for a long time---such as an oil hose? Try to straighten it out and listen. Sounds like a bowl of Rice Krispies. Teflon doesnt snap and krackle like that, but remember the liner is thin, so if you try to straighten it out, you can fracture the liner. So---if you do take one off and plan to reuse it, take care to leave it as it is.

I'd have to say that teflon should outlast a rubber hose by 5 times---so maybe 25 years? Ive seen some teflon assemblies on military aircraft with mid 60's date codes that were still flying. Great testimate to teflon---
Tom
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Joint Venture with Aircraft Specialty
Teflon Hose Assemblies for Experimentals
Proud Vendor for RV1, Donator to VAF
RV7 Tail Kit Completed, Fuse started-Pay as I go Plan
Ridgeland, SC
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  #38  
Old 07-05-2013, 10:27 AM
dick seiders dick seiders is offline
 
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This has turned out to be an interesting thread in spite of the drift to hoses and ethanol. but that's ok as we are all learning something. Getting back to the question of the fuel pump SB I believe the electric pump would keep us in the air altho at much lower power settings. Even Joe Gores kind of came to that conclusion considering the referred to takeoff power losses that managed to fly to landing. I don't believe the elec pp would satisfy full power requirements, but don't know, and hope to never find out during takeoff. To those I confused with my psi numbers sorry as I mis-spoke (Wash. DC speak for making wrong statement). My 1.2 lbs was accurate, but my 3.8 was a fuel cons. readout while taxi-ing. My normal flying psi is about 5.7 psi. I just returned from field after conducting another elec. pp. test, and the readout was 1.3 then gained to 1.5, and fell back to 1.2 as the system filled and started using the return line. Bob was right on the PAP flow test and my results were 115 sec. for one gallon. Seems to me that would be ample as it exceeds any hourly requirement that I am aware of. At any rate it raises my confidence regarding fact the elec. pp. will keep us flying well above stall speed should the mech. pump fail. Of course if the diaphragm breaks and the fuel starts coming out the weep holes other unpleasentries may occur.
Dick Seiders 120093
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  #39  
Old 07-05-2013, 12:35 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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As designed, the electric pump will run the engine just fine up to rated power. The problem comes from the variability of failure modes of the engine driven pump. If the engine driven pump fails in a way that causes a heavy loss of fuel, at a higher rate than what the electric pump can over come, it is possible that only partial throttle could be used.

The majority of the engine driven pump failures that I am aware of, has been a failure mode where the pilot was unaware of the failure, other than an increase in fuel flow and/or a decrease in fuel pressure, but the engine still running normally.
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Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #40  
Old 07-05-2013, 02:04 PM
dick seiders dick seiders is offline
 
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Thanks for the input, Scott. Your pump failure comment brings to mind that a favorable point for the new pump is the dump tube keeping fuel out of the engine area in event of failure. While the possible loss of fuel is still (or could be) a factor in adjusting throttle to keep flying the dump overboard feature makes the c/o to the new pump a bit more attractive.
Dick Seiders 120093
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