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Test Data!!!- Anatomy of a fuel pump, part 3-

I have recently purchased the RV7A from Frank Hinde who used electric fuel pumps in the wing roots and no mechanical fuel pump. He built dual electrical systems (single battery) with 2 alternators. On my flight back from AZ, the right fuel pump failed on climb out from Levingston, TX. I was able to make it home to KNEW on the other tank with anxious thoughts. My suggestion is to allow access to either tank with both fuel pumps. My plane was set up with the fuel selector valve only serving as an on off switch and not right or left tank.

This is specifically why we don't recommend a pump for each tank or submerged pumps. If it fails, you can't access fuel in that tank.
 
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The OEM Mazda FPR is a good choice. Very reliable. I've seen a number of problems with cheap aftermarket FPRs and feel they are a poor choice for aircraft. It's a critical component when running EFI, not a place to save a few bucks.
 
Mazda

Finn, looks like you've had multiple Mazda powered RVs. How has your experience with these been? Fuel burn vs. TAS, problems, engine life etc? Interested to know.
 
Probably not the best thread to post this reply, but here goes ...

The Mazda rotary is all I know. Know nothing about Lycomings.

Fuel burn a non-issue (cost) if compare 10% 87 Mogas to Avgas or even 89 or 91 Mogas. The 13B and 13B Renesis can easily be leaned without any problem.

Not sure why asking about TAS.

First two engines on the RV-3A were junk yard. First failed with slow coolant leak (o-ring groove in steel end-housings). Had 575 hours on the RV-3A till I totaled it trying to land at night, engine running fine all the way into the trees.

The RV-3B I bought already flying. Has been trouble free with 520 hours on the Hobbs. Typically cruise at 160 mph burning 7-8 GPH depending on altitude.

The RV-4 with the Renesis 13B now has 50 hours on the Hobbs plus 20 or more hours ground runs before I hooked up the Hobbs.

The basic engine is rarely a problem (unless overheated or otherwise abused or damaged -- and will continue to run even if overheated but may not start again). Turbocharging it does open it up to possible detonation and I would not consider doing that.

My trouble area with the RV-4 has been cooling. Being cheap (and going for minimum weight) I got too small radiators and have been trying to tweak airflow to get sufficient cooling to run continuously at full power on 85F+ days. I can easily climb to pattern altitude without overheating, but have to pull back on power to stay below my 220F coolant red line on hot days. In retrospect 10 to 20% bigger radiators (with maybe a couple of pounds weight penalty) and controlling excess airflow with exit flaps would have been the much easier way to go.

In general, I'll consider these the main problems:
1) Correctly sized, designed and implemented cooling (water and oil).
2) Taming exhaust noise. (I'm currently using stock RX-8 exhaust manifold, 180 degree bend into straight pipe. Heavier than just simple pipes but seems to tame the noise. The 13B Renesis is not as noisy as the 13B.)

So far the stock new 13B Renesis in the RV-4 has never quit on me.

Please feel free to ask any specific questions and maybe suggest a better thread to post this.

Finn
 
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I have recently purchased the RV7A from Frank Hinde who used electric fuel pumps in the wing roots and no mechanical fuel pump. He built dual electrical systems (single battery) with 2 alternators. On my flight back from AZ, the right fuel pump failed on climb out from Levingston, TX. I was able to make it home to KNEW on the other tank with anxious thoughts. My suggestion is to allow access to either tank with both fuel pumps. My plane was set up with the fuel selector valve only serving as an on off switch and not right or left tank. I made it home and disassembled the system, purchased Vans plans and rebuilt the fuel system according to Vans original design. Installing the mechanical fuel pump was not the easiest part of the project. I am not against electric fuel pumps as an option, I have just experienced an issue with a flaw in the design of mine and wanted to share that with you. Great test information and good luck.

I've flown two different types with pumps in the wings near/in the tanks. However there were TWO pumps for each tank for a total of 4 pumps. They also happened to be twins, and left tank fed via dual pumps to the left engine. Same on the right side. Seems unnecessarily complex for a piston single.
 
Well, a lot less scientific than the testing above, but I have some data that may be of interest. I was experiencing intermittent loss of fuel pressure in a Hirth F23 EFI powered (45HP high torque model) Moni. Pressure would drop from 42 to 2 psi. I had experienced this one time before over 50hrs (pressure came back on line pretty quickly that time).

But, I just redesigned the exhaust system and the fuel pump moved from a tunnel with ambient temps to the hot side of the firewall. Also, the plane had been in storage for 5 years, so I completely went though everything, replacing a lot. In the first couple of hours of test flying (over a 9k foot quiet airport) I experienced the loss of fuel pressure several more times as I went though Extensive troubleshooting. (note, the Moni is a "motorglider", and I've got almost 10k feet on an almost dead quiet airport).

After far too much time and money, not surprisingly, a simple answer- Too much restriction on the inlet side of the pump. The gerotor pump can't seem to tolerate much at all. The pump was cavitating/vapor locking. I had put that low on the troubleshooting list as this pump can supposedly lift 500mm, and I was level with the bottom of the tank.

I have an Andair duplex fuel selector, and used a fair amount of forged elbows and Parker hose as there just no space for traditional bent aluminum lines.

The Pierburg pump (100 lph rating) flows multiples more that the 25lph peak my engine needs. I couldn't find a decent quality smaller pump (which is maybe why Hirth uses it). 7.21287.53.0 PIERBURG)
https://www.kmotorshop.com/document/tecdoc/5/PI-0034_e_1599590.PDF

I didn't like the idea of pumpling 4x my peak flow, so I found a quality looking down convertor. Walbro says their gerotor pumps run fine down to 9v, so I plan on running at 9.5v (it runs smoothly well below 8v). Flow is about 80 lph at 9.5v, vs about 110 lph at 13.5v. I spoke with the mfg of the down converter in Utah, and they said it's designed to their specs (made in China), and they sell a lot to a couple of major manufactures. Very nice looking, vs the junk I found on Amazon.
https://www.powerstream.com/dcp.htm#2237

Most interesting of all (to me) is that the current draw of the pump dropped 50% once I eliminated the large (pump inlet side) restriction(and cavitation). The cavitation must be terribly inefficient. (I need to measure the flow again with no cavitation).

(note- gauge tee'd into the inlet side of the pump- misplaced my nice digital manometer, so blew the dust off of this gauge)
 

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Cavitation on a gerotor pump is damaging so if it's done that a lot I wouldn't be using it.

Cavitation is best avoided by flooding the inlet, avoiding any drilled 90 deg fittings before the inlet (use mandrel bent types) and using a low restriction filter. You must have unrestricted fuel tank vents as well.

Winter blend Mogas gas on a hot summer day at high altitude is asking for a forced landing.
 
If using PWM to the motor is an issue then one would have to use a linear regulator instead. That basically equates to the same effect that simply lowering the voltage to the pump would have.

What Mark Hubelbank did with the fuel pump drive on the Honda L15 engine was insert a resistor in line with the pump motor to limit fuel flow and current consumption to a value perhaps 25% over what was needed at WOT. The backup fuel pump was run at full voltage if it was ever needed. The current limiting resistor extended the time the engine could run on battery power if the charging system failed and it would also help extend the life of the fuel pump itself because it was less stressed.
 
It's maybe not a bad idea to measure pump inlet pressure/vacuum (in addition to flow testing) if you deviate from the plans.(no plans, or other installations for guidance, so I was on my own).
Mine flow tested above specs.

My nephew works in power systems and he nixed the resistor idea as too inefficient.
I have a two way switch for the fuel pump that bypasses the down converter in case it fails.

(Ross, thanks for the input. As mentioned the plane was in storage for five years. Not surprisingly, old pump was locked up tight. It’s a new pump with only about two hours on it, so hopefully it’s fine.)
 
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