Red Cube Install - A new look at an old challenge

[wirejock]

Thanks Tom. Please update after Airventure.

[Mark33]

My question is a little bit off subject because the main discussion is concerning the red-cube. Also, I?m a high pressure/electronic fuel injection guy, so the potential issues such as vapor lock and hard starts that can occur with with a standard manual fuel injection installation such as this really don?t apply to me. However, I?m curious to know why people don?t install a small 1/8? fuel return line ?T?d? in right at the spider divider. It seems to me that if a small fuel return line was incorporated into the plumbing and controlled via an on/off solenoid, that all of the hot fuel and vapors could be purged out of the system which would eliminate vapor lock and hot starts. My buddy installed a purge/return line such as this with his Ellison T.B. equipped -7. He was having terrible issues with vapor lock, but once he incorporated this little purge/return line, all of his vapor lock issues went away.

[jabarr]

Maybe slightly off topic but in the OPs picture there is that plastic cap that is addressed in SB 18-05-21?. https://www.vansaircraft.com/service...s/sb-18-05-21/
I realize this is a build in progress but obviously others have neglected to properly terminate that fitting.

[TS Flightlines]

Jon, Chris just hasnt plugged it off yet---he knows about it.

Mark---AFP did have a purge valve for the FM200 servo. Don redesigned it so the purge wasnt necessary.
I cant speak for everyone, but I think a hard hot start on a FI engine is somewhat common, versus a carbed install, since the carb is up draft.
Downdraft carbs have a similar hot start issue---remember the hot running engines we had in the 60s and 70s with headers> the old Rochester Quadrajets were notorious for hot start---even some Holleys were.
Mark I assume you have a EFii or SDS injection, you have a full return fuel system and when the pump is running you (supposedly) have cool fuel that flows through the entire system and back to the tanks---just like your car. Mechanical Injection isnt like that.

Tom

[Mark33]

Hey Tom. Yes, I have continuous, cool, high pressure fuel flowing through my entire fuel system, so V.L. or hot starts are never a problem. I understand that that carbureted and or mechanical F.I. systems and plumbing are completely different from my setup. However, I?ve seen so many people struggle with V.L. and hot starts with mechanical systems that I was just curious as to why more people don?t incorporate some kind of a little ?controllable? return/purge line into the plumbing so that they could just ?sweep? the hot fuel and vapors out of the lines?? When I saw the results my buddy had when he incorporated this simple ?controllable? fuel return/purge/sweep line into his plumbing, I was sold on his results and was/am convinced that this was/is the ?fix? for V.L. and hot start issues.

[rvbuilder2002]

Originally Posted by TS Flightlines

I know of several OE install on certified planes where its mounted on top of the engine, with 2 hoses, so if its good enough for a certifed install, why not an experimental?

One reason I can think of is that it is very rare for any certified aircraft to be a tightly cowled as an RV (though maybe the examples you are thinking of are.... can you mention specifics?). With small inlet and outlet openings (compared to most certified aircraft anyway), RV,s don't naturally cool via chimney effect when parked. Opening the oil door helps a lot but that does not directly cool the plenum area above the engine.

The OP put his idea out here and many people have offered their opinions. If he chooses not to heed any of the advice or comments, that is his choice. With you now offering defense of his plan, it somewhat appears that it was your design idea. If not, then it doesn't seem necessary.

One suggestion that I hope will be taken very seriously is the installation of a hard line between the flow transducer and the rear baffle. This section of baffling is exposed to a lot of vibration because of the mass of the oil cooler and the influence of the baffle seals on the non-moving interior surface of the top cowl. I have a serious concern with this. The excess hose causing a hard starting issue will simply be an annoyance and can be corrected with a future change, but a brake in the hard line could be very serious or worse.

[TS Flightlines]

Scott---Chris came up with several ideas, and after doing some mock ups, we built the hoses and tubes for him for his application. The baffles are going to be reinforced, 1 due to the oil cooler, 2 for the bulkhead fitting/stainless tube install. We really tried to do a hose from the bulkhead fitting to the transducer, but the overall length was too short, too much offset, making a hose application not practical, with out a big loop. His servo to bulkhead fitting hose is long enough to reach the transducer, if necessary.

Tom

[rvbuilder2002]

Originally Posted by TS Flightlines

Scott---Chris came up with several ideas, and after doing some mock ups, we built the hoses and tubes for him for his application. The baffles are going to be reinforced, 1 due to the oil cooler, 2 for the bulkhead fitting/stainless tube install. We really tried to do a hose from the bulkhead fitting to the transducer, but the overall length was too short, too much offset, making a hose application not practical, with out a big loop. His servo to bulkhead fitting hose is long enough to reach the transducer, if necessary.

Tom

Then may I suggest that a hose be used for the entire circuit from the throttle body to the flow transducer and seal it with a grommet where it passes through the baffle.

I have seen dozens of different ideas implemented, in attempts to re-enforce that corner of the rear baffle and they all failed. The left rear corner is the least supported (because of how it has to jog around the #4 cyl head), but is the most vulnerable because of the mass of the oil cooler and hoses. This is evidence enough that there is a lot of vibration induced on this area of the baffling. Putting a hard line between the solidly mounted transducer and the baffle (which has tons of in service evidence to be always influenced by some level of vibration) is not a good idea.

I don't post very often regarding something I see as a potentially serious safety issue, but this is definitely one. I hope the OP will consider changing at least this one aspect of his design.

[TS Flightlines]

Scott, the baffle reinforcement does bring up a very valid point. We never really know how much is enough. So after thinking about this, I altered the inlet line and fitting arrangement to use a hose with enough flexibility that will solve that issue.

Tom

[CJ in EP]

Thanks to everyone for the thoughtful discussion!

Let me first tell everyone the most disappointing part of my Van?s -9A build. After considerable research on the three most likely engine sources, I decided that the best path to a trouble free engine install (admittedly my weakest skillset in the build) had to be buying a factory Lycoming through Van?s, as well as the Van?s finish kit. Honestly, I have a hard time believing that Van?s has any idea if the oil and fuel hoses, and control cables they sell with the kit have any possibility of fitting. One of the two oil hoses had no possibility of fitting (well documented elsewhere on VAF where the fitting will physically interfere with the oil filter), the throttle and mixture cables were both well short of reaching their positions, and as demonstrated, the fuel system is proving to be a bit of a challenge.

It also doesn?t help that my divider seems to have been mounted in an usual orientation by the factory, making one of Tom?s best solutions difficult without redoing the injector lines, which I?d prefer to avoid.

For the record, for whoever was asking, this is my design, Tom and I talked through its weaknesses, and I decided to start here. I?m the one who stepped in it.

So in summary, my engine install has been a total PITA, and my new look at an old challenge pretty much sucks. Bummer. However, I got exactly what I was hoping for by posting in this forum, and I?m genuinely grateful for the good feedback! My system will only get better from here, and Tom has already shipped a new flex hose prototype to replace the the hard line.

As uncomfortable as public scrutiny may be, I?ll keep this thread going with the hopes of coming up with a really good solution, and hopefully making it easier for the next builder. And BTW, Ed in Zimbabwe, your comment that the only place for these is in close formation with the aircraft made me laugh, thanks for keeping it light!