REFLECTOR: RS-10B1 problems

Brian Michalk michalk at awpi.com
Thu Oct 4 12:49:32 CDT 2012


Andrew, there are several reasons for the choices I made.  I wish I were 
a better researcher to document the choices I made, but I'll try to 
remember my best.

First, I believe my incident was caused by a fuel problem.  Either too 
much of it, or not enough of it.  And since I don't know with 100% 
certainty, I went in trying to find some potential root causes.  I 
believe I've detailed my inspection before where I measured the amount 
of fuel in various fuel lines, tested the pressures and flow rates, and 
found the mechanics to be functional.  I did find that there were three 
potential causes of the failure.  1) insufficient venting, 2) vapor 
lock, and 3) excessively rich fuel calibration.

After examining all of the evidence, the most likely cause was #3, an 
over-rich situation.  I decided this was the culprit because of wet 
spark plugs and sooty (smelled of gasoline)  buildup in the exhaust.  
However, I also decided to address the other possible failure modes.

#1
It turns out, that after I made my modifications to the venting system, 
what I came up with as a solution is nearly identical to the current 
builders manual.  The vent manifold used to go down to the vent on the 
belly of the plane.  I modified it to go up the firewall, and overhead a 
few feet before turning back to be vented.

#3
I'm going out of order to address your question last. Essentially, all 
of my initial testing was done up to 2250 RPM.  I did more extensive 
testing this time with a reconfigured prop that allowed me to more 
accurately map out the fuel table.

#2
For my inspection tests, I noticed some foam in the sump tank. Now I 
don't think this was the cause on the first flight because of the short 
times involved, but again, I had not run the engine and fuel flows that 
high in testing before the incident.  My fuel system is very much like 
that in an automobile.  I'm running 45PSI rail pressure with electronic 
injectors.  With no restrictions to the system, I am flowing 120 gallons 
per hour of fuel back to the sump.  I came up with the idea of a simple 
foam separator which I described in the previous email.  I had 
considered other options as well such as a T into each tank outlet as 
you suggest.  I decided to not go that route because it seems that 
people have a difficult time with balanced tanks, and I simply did not 
have enough data or experience that this would not cause a problem.  If 
someone is using this method, I would really like to hear about it.  
Another solution would be to drill new holes into each tank, and return 
the fuel there.  It's almost identical to Teeing into the outlet, except 
that there's a lot more mass and area to dissipate heat and foam.  It 
still has the downside of potentially unbalanced tanks, and I really 
don't want to implement a fuel selection valve, which would really be 
the correct approach.  With the fuel selection valve, a tank would feed 
the sump, and fuel return would be directed to the feeding tank.

I am using a Waterman Racing Sprint car fuel pump (smallest one 
available), a Bosch electric pump for backup, and an Aeromotive fuel 
pressure regulator.  The pumps are in parallel, feeding to the FPR.


On 10/02/2012 07:37 PM, Andrew Ellzey wrote:
> Brian,
> I have thought a lot about what you wrote, and I wanted to ask, why 
> didn't you choose to T the return line, and plum these two lines, 1ea 
> into each tank? I would think that if you kept the two new lines the 
> same length, that the return volume to each tank should be very close 
> to the same, helping to stop a fuel imbalance. As far as heating your 
> fuel, again this would give a far greater volume to dissipate the 
> heat. The same goes with any vapor or bubbles returned to both tanks. 
> I don't really understand why there would be any vapors returned to 
> the tanks, can you explain what you were seeing. Our two fuel servo 
> systems may be different, I don't know what your system is. I will do 
> a test using my fuel pump to analyze what my return fuel looks like as 
> soon as I get time.
> My RS-10B1 fuel servo valve output line uses # 4 AN fittings, which 
> then goes to the input of my T fitting, which is installed on the top 
> of my distribution valve. The inside diameter of the T fitting, 
> is .167 inches. My # 72 bleed (.025 inches), is 6.68 times smaller 
> than the original line and fittings feeding the T'd fitting, which now 
> has the output with the # 72 bleed installed. I have then install 
> approximately 36 inches of #4 braided stainless steel Teflon line and 
> #4 AN fittings to get me through the firewall. I was going to plum it 
> into my sump tank, but now I may T my line coming through the fire 
> wall and plum a single 1/4" line to each fuel cell, since there may 
> be, like you are saying a vapor or bubbling of the fuel.
> If my gage was correct, I was seeing 55PSI at this same T fitting 
> before I installed the # 72 bleed. I haven't done the calculations as 
> to what volume of fuel will be returning to the tank. My operators 
> manual for my engine says that the fuel consumption for its rated 
> power at take off, is 24.6 gal per hour. 75% should get me in the 16.5 
> gal per hour range.
> Andy Ellzey
>
>     *From:* Brian Michalk <michalk at awpi.com>
>     *To:* Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>     *Sent:* Monday, October 1, 2012 9:57 PM
>     *Subject:* Re: REFLECTOR: RS-10B1 problems
>     How much fuel returns to the sump? Also, how much fuel is too much
>     to attempt to return to the sump?  At some point the vapor amount
>     will be too much as well as heating for the sump to handle. I ask,
>     because I was using my sump for fuel return.  I did max fuel
>     return tests and decided to add an additional one gallon
>     liquid/vapor separator tank above the sump. It's plumbed with fuel
>     exit on the left that tees into a sump inlet.  The opposite side
>     is (foamy) return from the fuel pressure regulator.  It is vented
>     to a fuel tank vent. It fits in the main spar, so it's at the same
>     height as the tanks.  With testing max bypass flow, it accumulates
>     vapor till about half vapor, and does not fill up completely with
>     vapor.  My hope is that with the electric pump off, it will be
>     able to separate vapor indefinitely. The reason why I did this, is
>     because one of the failure scenarios for my incident was fuel
>     starvation due to vapor lock.  I do not think this was the cause,
>     but it's hopefully more safety.  Oh, and it gives me one more
>     gallon of useful fuel. On 10/01/2012 09:21 PM, Andrew Ellzey wrote:
>>     John, Just wanted to thank you for getting me the contact
>>     information for Don Rrivera at Airflow Performance, Don told me
>>     that I needed to install a .025 inch, #72 bleed in the T fitting
>>     on the top side of my distributor valve. Then install a new
>>     return line to my sump tank. I made the modification on Saturday,
>>     and my engine ran like a champ. Thanks again for your help, Andy
>>     Ellzey By the way, I replaced all of the aluminum fittings with
>>     steel, for everyone that e-mailed me about their concerns.
>>
>>     *From: * John Tvedte mailto:johnt at comp-sol.com;
>>     *To: * ajlz72756 at yahoo.com <mailto:ajlz72756 at yahoo.com>
>>     mailto:ajlz72756 at yahoo.com;
>>     *Subject: * RS-10B1 problems
>>     *Sent: * Thu, Sep 27, 2012 3:05:12 PM
>>     *Andy,*
>>     **
>>     *I would contact Don @ Airflow Performance -- see website, and
>>     contact info below.  Don worked at Bendix under Elmer Haasse, the
>>     inventor of the RS and RSA Fuel injection systems.*
>>     **
>>     *I would plan on replacing those aluminum fittings with steel. 
>>     Just too many fuel problems / fires caused by fatigue.  They are
>>     likely AN4, which is really small -- steel fittings won't add
>>     much weight.  I'm talking specifically about the ones on the fuel
>>     spider that you have hoses connected.*
>>     **
>>     Don Rivera don at airflowperformance.com
>>     (864)576-4512
>>     http://www.airflowperformance.com/html/site_html.html
>>     *Be safe,*
>>     *John*
>>
>>
>>
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