[bkthomps]

97 gallons?? details?

 

[David-aviator]

OK - can you tell us exactly what your operating technique is on these flights that produce this close approximation, startup to shutdown? I'm just trying to pin down the differences between what people are seeing, and figure out what is different and where the error might be. If you get this result with the boost pump off and operating on the engine driven pump, then your first statement that this scenario produces a lower-than-true flow indication cannot be correct.

First off, Kahuna's flow sensor was installed before the mechanical pump, on the suction side (if I understand the situation correctly). My sensor is on the pressure side of the mechanical pump about 8" ahead of the FM200 controller inlet. It is never subjected to sucked fuel anomalies.

The electric pump is ON for start, for take off and landing. It usually is turned OFF at about 1000' AGL climbing. It is turned ON when switching tanks.

There is a fuel pressure drop from about 27 psi to 22 psi when the pump is turned OFF but there is no change in fuel flow. That is so because there is always a head of pressure on the sensor from the electric pump or the mechanical pump or both. Kahuna's sensor did not have a head of pressure on it when the electric pump was OFF.

None of this is an absolute exact science. I had a sensor in the Cozy that never had a head of pressure on it and it too was very accurate. But it was a gravity flow system. I do believe a high pressure fuel injection system with the mechanical pump sucking and pushing fuel is not the best environment for the flow sensor especially on the suction side. Some may work, others won't. For sure Don is on the right track installing the sensor in the line between the controller and flow divider as the pressure is relatively steady and low. I did not install it there because I did not have the 1/4" hose fittings but did have two AN6 hoses just the right size coming from the mechanical pump.

 

[airguy]

First off, Kahuna's flow sensor was installed before the mechanical pump, on the suction side (if I understand the situation correctly). My sensor is on the pressure side of the mechanical pump about 8" ahead of the FM200 controller inlet. It is never subjected to sucked fuel anomalies.

The electric pump is ON for start, for take off and landing. It usually is turned OFF at about 1000' AGL climbing. It is turned ON when switching tanks.

There is a fuel pressure drop from about 27 psi to 22 psi when the pump is turned OFF but there is no change in fuel flow. That is so because there is always a head of pressure on the sensor from the electric pump or the mechanical pump or both. Kahuna's sensor did not have a head of pressure on it when the electric pump was OFF.

None of this is an absolute exact science. I had a sensor in the Cozy that never had a head of pressure on it and it too was very accurate. But it was a gravity flow system. I do believe a high pressure fuel injection system with the mechanical pump sucking and pushing fuel is not the best environment for the flow sensor especially on the suction side. Some may work, others won't. For sure Don is on the right track installing the sensor in the line between the controller and flow divider as the pressure is relatively steady and low. I did not install it there because I did not have the 1/4" hose fittings but did have two AN6 hoses just the right size coming from the mechanical pump.

Yes, that makes a lot more sense now, thanks for the clarification.

 

[mcencula]

Matt Draille at Matronics sells one. The Pulsation Damper (PD) is a stainless steel sphere with a fitting on one side that connects to a 'T' AN fitting and is placed in-line with the fuel flow either just before or right after the fuel flow transducer. The PD acts like a common 'air shock absorber' isolater in a typical sink facet. The air is compressed inside of the sphere in time with the pulses in the fuel line caused by the boost pump and/or the mechanical fuel pump. This extremely simple device is incredible effective at reducing the fuel flow reading fluctuations common in turbine transducer-based electronic instrument installations. Below is a paraphrased testimonial from a customer on the use of the PD in his 0360 power RV-8 installation.

Bob or Matt,

Does the pulsation damper have a bladder to prevent the air from escaping the damper and entering the fuel line (say, for example, when flying inverted)?

 

[rvmills]

From Kahuna's OP, I interpreted it that when the boost pump was turned on, and FF went up, innacuracies were generated in the fuel burn and fuel remaining calculations that were significant enough for him to not use his boost pump at times when he otherwise would. Am I reading that right Mike?

I have RV buds that describe exactly what Kahuna stated originally...fuel flow/ totalizer fuel burn is incorrectly high with boost pump on.

David's scenario above describes the opposite...innacurate readings with the pump off. So I'm still a bit mysitified as to what causes this...I re-read Don's posts and see why fuel pressure goes up, but not why fuel flow goes up, as Kahuna and others have seen. Interesting (and frustrating) phenomenon.

Seems best success is with the transducer in the metered line between the servo and the spider, but sounds like just after the fuel selector has worked with little issue. Interesting discussion of failure modes in a push vs. suck system too.

Mike, I know its a thread-drift threat, but any links to how you put your ER fuel tank system together? Thanks!

Cheers,
Bob

 

[Danny King]

Sorry for the blurry image. The fitting is a custom fitting that was welded up. Works perfectly. The transducer is in a nice cool place, with no mickey mouse fittings or firesleeve wrap required.

RocketBob,

I addressed this with my first post, then deleted it after seeing the small brace I had missed when I first glance at your picture, but I'm still uncomfortable with your initialization. A failure of your welded fitting would be disastrous! It would mean an engine failure and a possible fire feed with 100LL. There will be a lot of cyclic stress from engine vibration on that fitting, and I'm afraid that your brace will not dampen it all out. The strength of the fitting is an unknown! Please build a mounting bracket to install the transducer on, similar to the guy that installed it on the spider bracket.

There was a RV-10 that made a forced landing from IFR conditions when a hard line he made mounting the transducer between cylinder 1 and 3 failed. He came out of the clouds and was above a grass airstrip. His guardian angel was working overtime. The bath of 100LL the engine got did not catch fire. If your initialization fails, you might not be as lucky.

This is just my opinion, but after days of thinking about it, I can't get this feeling of dread out of my mind.

 

[longranger]

...For those cases where the flow meter reads high, or incorrectly when the boost pump is turned on and does not return to a lower flow, I would suspect that there is some kind of EMI or error in the instrumentation due to current load. I am no authority on electronics so do not assume this statement is correct; It’s only a theory. ...
Don

I don't really consider myself an expert either but being an instrumentation engineer Don's EMI (electro-magnetic interference) theory was the first thing that occurred to me. Turbine flow meter instrumentation basically just counts electronic pulses. As long as the fuel is in a liquid state, each pulse received indicates some fixed volume of fuel passing through the meter. It's not hard to imagine that through improper/inadequate grounding or shielding, turning on a pump adds pulses of sufficient level to trigger the counting circuit, especially if the meter and pump both happen to be on the same side of the firewall. It would have been interesting to put an O-scope on the output of Kahuna's flow meter in it's old location and read it with and without the boost pump running. In the new location, the baffling could be providing just enough shielding to clean up the meter's output signal.

 

[Bavafa]

For whatever it is worth

I have posted this before, but I thought it maybe worth providing the data once again as more hours has been accumulating (over 300 hours now)

My Red cube has been installed in the tunnel between the electric fuel pump and mechanical and the accuracy has been amazingly on target each time. I make a practice of always checking the fuel added compare to the fuel totelizer. I get inaccuracy of 0.2-0.3 of a gallon in 30 gallon fuel burn. This ratio is consistent at any level, if I add 10g or 30g. The fuel totelizer is hardly ever solidly stay on a given fuel burn and usually varies within a 10th of a gallon (8.2-8.3) but at the end it has always shown accurate fuel usage. This is using in conjunction with GRT system.

At some point I explored the idea of moving it to FFW and can not find a good enough place that satisfies my safety concern and since I have not observed any issue, I have kept it in the same place.

 

[Kahuna]

From Kahuna's OP, I interpreted it that when the boost pump was turned on, and FF went up, innacuracies were generated in the fuel burn and fuel remaining calculations that were significant enough for him to not use his boost pump at times when he otherwise would. Am I reading that right Mike?

Yes.

And since you beat me up about it. Some of the tank discussion here in another thread.

 

[rvmills]

Yes.

And since you beat me up about it. Some of the tank discussion here in another thread.

Thanks for doing that...sorry to pester...will post there on tanks. Will take a pic of my FF transducer bracket (between fairing mod sanding sessions) and post it tonight.

Cheers,
Bob

 

[Finley Atherton]

As I understand it, if you have an installation where the FF displayed (but not actual FF) increases with the boost pump on then I suspect the indicated FF in the cruise may be inaccurate (under-reading) to some extent.

Most people adjust the k factor so the total indicated fuel used equals the actual fuel used over a number of tank fills. This means the resulting k factor value takes into account the higher/lower pulsations depending on the boost pump operation. As I see it, this averaging of the k factor would give rise to inaccuracies in the immediate FF reading (g/hr) shown by the gauge in cruise with the boost pump off.

I want accurate real time FF readings in the cruise so rather than adjusting the k factor against total fuel used over a number of tank fills, I have adjusted my k factor by draining then filling a tank with a known quantity, flying at constant throttle/mixture/prop settings with the boost pump off for a set time on that tank then draining what's left and comparing actual FF to the indicated FF.

Can't say for sure if this method of k factor calibration is significantly more accurate. i suspect the standard method of adjusting the k factor over a number of tank fills would be good enough.

Fin
9A

 

[Kahuna]

Im so confused by this in so many ways I hardly know where to begin.

So in the end, you settle with wrong readings cause you fly one profile?

If you accidently leave your pump on then you now have bad #'s?
If you need to run your pump for some good reason (hot climb, low level flight or what ever), you disregard the values cause you have calibrated for one flight profile type?

 

[rvmills]

Fin,

I'd have to agree that your method is a little confusing...may give you accurate FF in a steady state cruise...perhaps great for use in setting your cruise power setting. However, my desire is accuracy in all flight regimes (and boost pump on or off), so as to have accurate totalizer readouts of EFB (burned) and EFR (remaining) at any point in the flight. That's the only true cross-check to our fuel guages.

The mystery of how a boost pump causes high FF readouts (which mess with the totalizer) but no actual fuel flow increase still evades me, given there's no bypass in the system (AFAIK), so I'm no help to explain it to my friends that have the issue Kahuna brought up. Guess if they are injected, I'll pass Don's advice to mount the transducer between the servo and the spider, or direct them to this thread for alternatives.

Here's that pic of how my plane's builder mounted the VM-1000 FF transducer. 12 year old install between #1 and #3 that's been very steady and accurate, FWIW. Boy, I need to do a little clean-up!

Cheers,
Bob

 

[nomocom]

Microcavitation

.......putting the fuel flow transducer after the electric pump gives bad data with the electric pump on. Flow increases +2gph with the pump on. No change in any other engine parameter except fuel pressure of course.
........
The engine is not getting any richer. Im not burning any more fuel. There is no place for the fuel to go after the sensor except to the engine in my installs. SO why on earth does it go up when the pressure increases and no more fuel is going by?

I'm not suggesting the electric pumps are cavitating in the normal use of the word- as in the destructive and noisy phenomenon. However, the symtoms you describe suggest to me (someone with a bit of pump and meter experience) transient vapor bubbles. I've seen a similar situation before, but in a more controlled setting. We had a 3 inch Liquid Controls positive displacement meter overstating flow several percent, when normally they are accurate to 00.03%. We were comparing the meter against calibrated tanks both upstream and downstream of the meter. In this situation, the culprit appeared to be paper filter elements upstream a few feet of the meter. We took the filters out of the filter housing, retested, and the meter and calibrated tanks agreed. Put the filters back in..... over statement of flow. It was repeatable and the error seemed to hinge on whether or not the liquid just prior to measuring had gone through a tight paper filter.

I'm not suggesting the injected RV flow anomoly is due to filters, but I did share the anecdote to illustrate that upstream disturbances are capable of causing an upset of the normal liquid vapor equilibrium. Specifically, some energy goes into exciting a bit of the liquid enough that it flashes, and you get temporary vapor, and thats how you get the increased volume. Well, this isn't equilibrium conditions, so the vapor does recondense, but it takes a bit of time for that to occur, meanwhile the increased volume gets tallied.

This hypothesis would be suited to a bench trial. Operating the flow meter at various distances (retention time) away from the electric pump, you would test the hypothesis that the farther the flow meter is from the pump, the more time the microbubbles have to condense. Maybe the pump manufacturers have already done this testing and have data, but without very specific test data to suggest otherwise, this is where I'd put my money.

Mike, the microcavitation would be worth exploring more especially if you saw more error when the fuel was warm versus cold, or if you saw more error when say running winter blend car gas versus avgas. I understand you've moved you flow meter so you can't really test this, and I don't know if you run autogas or not, but maybe you have some data logged from both a winter and hot summer day where the airplane sat on the ramp and the fuel ended up very warm.

The EMI hypothesis is interesting as well. I hope somebody has the time and inclination to do a bit of testing and reporting.

 

[Brantel]

To me it is simple to see why this happens. Each pulse the pump makes expands and contracts the hoses in the system a small amount. These sensors count the pulses created by movement of the vane inside past a sensor. As far as I know all the current sensors will count in both directions and they move with very little flow. If the pulses of the pump and the resultant expansion and contraction causes the vane inside the sensor to rock back and forth, you will get extra counts even though there was no actual increase in mass flow thru the entire system.

Those that have an increase in fuel flow readings only when the boost pump is on could test for this by plugging the fuel line right before the servo or carb and turn on the boost pump and see what their fuel flow reading is. With the plug in there, there is no actual "flow thru the system" but there very well might be a fuel flow indication due to the effects the pulsing and expanding/contracting of the volume of the system would have on the transducer.

 

[nomocom]

cavitation

In any fluid system, good design takes careful analysis to ensure that local cavitation does not occur.

When I read the thread earlier, I missed it, but Terry had already mentioned cavitation back on post 35. As I mentioned a post or two back, I've seen something as minor as a filter induce microcavitation- bubbles so small you likely woundn't even see them- but they are there briefly (long enough to futz up your totalizer) before the liquid goes back to equilibrium. Pumps are even more frequent offenders than filters. Not saying that is what it is, but it's pretty likely given the symtoms.

Brantel, on your post, I'm not sure I follow. Are you suggesting at a flow rate of 10 gpm plus a hour, there are flow reversals? I've seen mag flow meters "count" on a deadheaded line when the system had quite a bit of vibration. Maybe a turbine meter would as well, but not sure how that translates to the symtoms that Kahuna has described (scenario one).

 

[Brantel]

Brantel, on your post, I'm not sure I follow. Are you suggesting at a flow rate of 10 gpm plus a hour, there are flow reversals? I've seen mag flow meters "count" on a deadheaded line when the system had quite a bit of vibration. Maybe a turbine meter would as well, but not sure how that translates to the symtoms that Kahuna has described (scenario one).

Thats exactly what I am saying... It is clear that the impeller in the transducer is producing extra counts when the boost pump is on. The only way it can do that (since we know it is not real mass fuel flow) is to be oscillating back and forth and one reason it could do that is the reverse flow caused by the collapse of the volume in the lines/system when the pump pulse is over or at its low point.

 

[nomocom]

extra counts

Thats exactly what I am saying... It is clear that the impeller in the transducer is producing extra counts when the boost pump is on. The only way it can do that (since we know it is not real mass fuel flow) is to be oscillating back and forth and one reason it could do that is the reverse flow caused by the collapse of the volume in the lines/system when the pump pulse is over or at its low point.

We can agree there are extra counts, the meter is overstating, but I don't follow you on how you can say there is only one way it can happen. This is a long thread, and several methods have been proposed. I have read the description that you've offered on flow reversal, but I don't see how a hypothesis equates to there only being one possible answer, especially when there hasn't been testing to weed out the various hypothesis.

My two cents.

 

[Brantel]

I stated that "the only way" to get extra counts is for the impeller to be oscillating. There are many things that have been offered up as reasons why it could be oscillating and I offered up my idea, notice I say "one reason it could"...Don from AFP has already confirmed that there is a volume change in the "System" with pulses from the pump. I would say that he has confirmed this with testing.

I do not buy the theory on electromagnetic interference causing the extra counts due to many reasons too broad to discuss here.

Just my opinion and it ain't worth much...

 

[nomocom]

oscillation and expansion

I stated that "the only way" to get extra counts is for the impeller to be oscillating. There are many things that have been offered up as reasons why it could be oscillating and I offered up my idea, notice I say "one reason it could"...Don from AFP has already confirmed that there is a volume change in the "System" with pulses from the pump. I would say that he has confirmed this with testing.

I do not buy the theory on electromagnetic interference causing the extra counts due to many reasons too broad to discuss here.

Just my opinion and it ain't worth much...

Brantell
Appreciate you input on this....
Oscillation- as in speeding up and slowing down, I get a fair bit of that with spam can FP-5 and the EI cube. The EI on the Cessna wanders from 6.5 gpm to 7.5 gpm over the period of 30 seconds. I haven't done anything about it, at refuel time, I'm within a 1/2 gallon or less. Not what Kahuna is describing, however the idea of exteme oscillation- full reversals, that does seem like it needs explored.

Positive displacement pumps do allow a bit of backflow as the outlet valve (ball or swing) moves back against its seat when the diaphram is repositioning for another stroke. This back flow would have to propogate clear over to the flow meter, the turbine stops, reverses briefly, then forward again and counts some of the liquid twice, maybe even three times. Pump manufacturers? I've read you lurk and maybe even post once in a while Any test data on backflow? If I recall correctly, the tech term is "slippage". PD pumps in their spec sheets will often list a slippage that goes along with the liquid, flow rate, viscosity, lift....etc.

However, there certainly are other ways to get extra counts without oscillation. T Kahuna described a displayed 2 gallon a minute increase without an EGT change. Fair enough.. you don't buy the EMI, but hypothetically, interference could cause some extra counts getting back to the computer without any flow meter oscillation. Cavitation could cause over reporting as well without oscillation. The vapor takes up much more volume than the same mass of liquid, so the volume really could be 12 gpm, rather than 10, its just that it still only has the energy of the 10 gpm liquid.

As far as the fuel system that expands so to speak....as Don described it well... but isn't it an explanation for scenario two, the transient increase? The fuel system expands- maybe an increase for a few seconds, but ultimately goes back to what it was moments before, no?

Need to go do some work..

 

[rv7charlie]

I get the same symptom on the el cheapo Lowrance marine totalizer in my carb'd O-320. I doubt that the 3psi Facet can push hard enough to swell stainless braided lines (though a Walbro positive displacement pump might).

However, air is pretty easy to compress. If there's air trapped in the system anywhere after, or especially if there's some on both sides of the sensor, it's easy to see the turbine oscillating with pressure pulses. Mine definitely has air trapped between the Facet & the engine pump.

I wonder if the presence/absence of air might explain why some see the problem & others don't.

Charlie

 

[Ted Johns]

Quadrature output needed

Gotta agree with Brantel here. Regardless of whether you have a carb or injectors, the pump(s) will put out more than the engine can use. That is a design requirement. Given this fact, unless you have a bypass regulator, and thus a flow meter on the return line that subtracts from the supply line, the fuel flow will be stopping on regular intervals. This is going to cause standing wave pressure pulses in the fuel delivery system, which will certainly cause the simple flow detector some grief. The output on the "Red Cube" flow detector is a rotational counter, without any mention of hysteresis.

In my brief searching I failed to find a cheap fuel flow sensor with a quadrature output, which has the potential to solve this problem. And of course the EFIS would need to provide a quadrature interface for same.

It might be possible for the EFIS interface to implement a gated counter window to block some of the spurious oscillation from being counted. Any EFIS insiders care to comment?

 

[rocketbob]

Caveat: don't expect the fitting between the flow divider and the sensor to be able to support the sensor on your vibrating Lycosaur (especially if it is aluminum) - add a support for the sensor.

A sniffle valve will help the hot-start problem too.

Carry on!
Mark

This is the Buster's setup and you can count on it being right! Look closely, there is a bracket going from one of the case bolts to the transducer...solid as a rock. You can grab the flowscan and rock the whole airplane with it...I've done it. Think he's got 800 hours on it now, no worries. The fitting is steel. The metered fuel line is not going to be moving/vibrating much anyway.

I would be interested in seeing someone measure the difference in fuel temperature of a firesleeved hose vs. unfiresleeved. Since this is in cool air its not going to need any insulating. Why aren't the fuel lines going to the cylinders firesleeved...? Because once the airplane sits for 5 minutes, regardless of firesleeve the fuel in the lines are going to boil.

 

[Brantel]

Like Don said though, you do have a pretty good area of expansion inside the mechanical pump as the diaphram can be pressed up against the spring....same effect.

I get the same symptom on the el cheapo Lowrance marine totalizer in my carb'd O-320. I doubt that the 3psi Facet can push hard enough to swell stainless braided lines (though a Walbro positive displacement pump might).

 

[F1Boss]

Huh?

Bob sez:
"Since this is in cool air its not going to need any insulating."

As my post mentioned, I was referring to a fuel stop situation...think Phoenix...in August. Bad juju - maybe the worst! If you think there is cool air on top of the engine during a fuel stop,....well....

In flight? Heck, there's plenty of cool air....who needs insulation?

That particular PHX experience plane had a single impulse mag, aft facing injector, no sniffle valve, no insulation on the sensor. The next ship had a Slick Start, an electronic ignition, and insulation, which sure made life (fuel stops) easier. I think the red paint on it now makes it easier yet!

And now, a few smart individuals are developing a stand alone electronic fuel injection system simply for starting! Maybe you could take your 'not going to need any insulation' argument to them, and save 'em a lot of money, time, and effort.

Or am I wrong about all this?

Carry on!
Mark

 

[rocketbob]

Since the R-value of firesleeve is going to be miniscule, its likely that after sitting for 15 minutes even if you had 2-3 layers of firesleeve not much is going to help once everything is heat soaked. The only way to go here is to put a purge valve on, purge the fuel and get the fan turning.

 

[N941WR]

Mark,

I'll take it to the next level.

While flight testing my carb'ed O-290, with the fuel flow meter located just above the Gascolater and no insulation on the U tube between the two, I had four engine stoppages during Phase 1 before I figured it out. (Slow learner here!) All four stoppages were the result of extended slow flight which heat soaked the fuel in that "U"; one after a long, low power letdown to downwind, one on short final after flying a LARGE pattern following a Cessna, one just after touchdown after flying a LARGE patern folowing a Cessna, and the final one after about five minutes of slow flight.

Normal operations and landings were fine but following a Cessna around the pattern on a tour of the county was an issue.

Once I put some fire sleeve on that "U", the problem went away, even on 100 degree days.

Although not a fuel injected system, I see no reason why some of you would be exempt from this issue.

 

[rocketbob]

Firesleeve is helpful if there's cool fuel running thru the lines. But once everything gets heat soaked, it does not provide much in the way of preventing vapor lock. My -6, since I run mogas, has everything firesleeved. But if I let it sit hot for 20 minutes I have difficulties starting.

 

[F1Boss]

YIKES

Hey Bill:

Glad you survived your instructional period! I've had symptoms of vapor in all the FI planes I have flown (climb-out, mostly) - the boost pump takes care of that quickly.

Dunno about Bob - maybe thermal characteristics are different in his world? His beer STAYS cold? Once he gets his plane flying, he may find himself in our world, where vapor locking and hot starting are genuine issues to be faced!

Ref: FAA TSO - C53a OR TSO - C75 requiring the sleeve withstand direct flame for 5 min with liquid flowing thru the line. I wouldn't call THAT miniscule protection.

Once things are heat soaked, you are in trouble, but I am stating the obvious. Better get those clothespins out! (geez - dating myself there!) The purpose of the insulation is to slow, or prevent, the heat soaking, so you won't need the clothespins. Duh....stating the obvious again!

Carry on!
Mark

 

[rocketbob]

Yep beer is always cold. Maybe I should make some koozies out of firesleeve material?

Serioulsly though why wrap the hampster wheel but not the divider and the lines?

 

[Auburntsts]

Could be way offbase, but I was under the impression wrapping it in firesleeve was to protect the transducer itself because the housing is made out of aluminum and had nothing to do with trying to prevent vapor lock, although I suppose based upon the comments that could be a secondary benefit.

 

[F1Boss]

CAUTION: thread drift

Yep beer is always cold. Maybe I should make some koozies out of firesleeve material?

Serioulsly though why wrap the hampster wheel but not the divider and the lines?

Those would be some pricey koozies! But, they would be fire-resistant for 5 minutes if the can was full.

Divider:
You would need to insulate the divider from its bracket 1st, and then wrap it with a REAL FANCY (expensive) jacket, which I wouldn't think too many folks would buy. I will say that during the times I had trouble getting the 550 running, the divider was too hot to touch (it's right under the oil door on my installation - I can check it's temp). Dunno how it finally did start (and kept running - I used some of the Phoenix lesson), but I'll guess I just pumped a lot of $$$ onto the pavement to cool it enough. I have looked at shielding this part - it's not really practical, considering all the stuff attached to it that is not shielded - but I'm waiting for the iStart, which will probably be better/easier....I hope.

As for the lines, gravity empties 'em upon shutdown; no need for insulation: there is no fuel in 'em. Not sure, but I expect the divider dumps some of its contents out too? This draining is one of the the reasons for the sniffle valves....

Carry on!
Mark

 

[morristull]

Fuel flowmeter hose restrictions

I am about to install the flowmeter between the servo and the spider as recommended. I have cut the aeroquip 466-4 hoses to put extra fittings on for the flowmeter and noticed the end fittings of the aeroquip hoses have a significantly small hole, mine are only 0.125" which seems a massive restriction on the 3/16 hose. When you consider there are now 4 fittings with such restriction leading to the spider, I question whether this is safe practice after having spent considerable effort to have smooth flow of all the plumbing throughout the fuel plumbing. Such a small hole must have the potential for blockage or significant acceleration of the fuel into the flowmeter. Would this collection of restrictions fail to meet normal fuel flow requirements?
I researched the Aeroquip specifications which said the minimum internal diameter of the fittings should be 0.169" so the aeroquip fittings are not meeting the specification!
I am hence tempted to upgrade the hose to -5.

My other observations are the AN fittings that screw into the flowmeter do not bottom out leaving a 3/16 gap and resulting significant turbulence area immediatly before flowmeter so I will measure the gap accurately and fit an aluminium spacer at bottom of AN union in flowmeter to give best possible smooth flow into flowmeter. It would be better if the Red cube came with accurately machined fittings that provided no gaps and best chance of smooth flow into the flowmeter.

Do you gents think we should be concerned about these restrictions in the fuel feed hose and demanding larger fuel lines?
Regards Morris.

 

[Rupester]

My servo had a #4 hose fitting on the outlet, and the spider had a #4 hose fitting on the inlet. I just bought two #4 hoses of custom length and put the Red Cube between them. I'm still a few weeks from first engine start, but I'm not concerned about this arrangement. MANY others have the same arrangement and it works fine. FWIW.

 

[Stu McCurdy]

Fuel Flow Sensor

I have had a Flow Scan fuel flow sensor provided by Rocky Mountain Inst on my IO-360 in my RV-8 for 10 years. After a couple of initial K factor adjustments, my fuel to topoff has been within a 1/10 of a gallon or so of what my fuel totalizer said in the RMI Monitor. I placed the Flow Scan along the front side of the sump about 3 inches after a 90* fitting coming out of the rear of the FI servo before the fuel line goes up between #1 and #3 to the spider. Worked for me.