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Old 08-31-2018, 11:34 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
Join Date: Jul 2009
Location: Mojave
Posts: 4,297

What's the PN of the hose stock (Aeroquip 303, etc) that you use?

How many examples of your direct mount injectors are flying, and what's the approximate cum hours?
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
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Old 08-31-2018, 01:54 PM
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DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 8,533

Makes for an interesting comparison.

The EFII injector mount starts with a length of ordinary aluminum tubing. The ID is threaded at both ends, probably with an NPT pipe tap. Then a section is cut from the side to clear the injector's electrical connector.

The engine end of the tube can be screwed on a welded bung, as in this photo...

....or on a machined adapter for the 1/8" NPT primer port. Apparently the material is 6061.

A fuel feed fitting is screwed into the outboard end of the tube. As you see above, it can be a tee, or something similar to an AN914.

The inboard injector o-ring seals against the inner bore of the welded bung or port adapter. The outboard o-ring seals against the ID of the screwed-in fitting.

Given the cutaway section, the outboard end of the aluminum tube cannot support the screwed-in fitting without spreading and splitting. So, EFII installs an Oetiker clamp as a hoop reinforcement. The Oetiker is a spring clamp normally used to squeeze elastomer hoses. It is intended to be crimped into place with a jaw tool to a specified crimp force (see the Oetiker catalog for details), compressing the elastomer hose, then springing back to a final diametrical dimension. Here, because it's crimped on a metal tube, there can be no significant compression, meaning springback doesn't allow the finished diameter to provide any significant clamp force. Thus the thread interface between the tube and the feed fitting is loose enough to wiggle and shake; it cannot be tightened. The fitting floats in the end of the tube, and depends on the injector's o-ring to absorb the relative motion.

Robert, is the above description correct, and those two broken mounts you mentioned....where did they break?
Dan Horton
Barrett IO-390

Last edited by DanH : 09-07-2018 at 09:59 PM.
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Old 09-03-2018, 09:20 AM
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DanH DanH is offline
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Location: 08A
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Originally Posted by Toobuilder View Post
...Engineering practices specifically caution that hose assemblies need to have some slack in them so they don't become a "structural element" between two assemblies - In this case the hose is certainly a tension element, and thanks to the adel, it's a fairly effective compression element as well. When the heads move apart due to thermal or operating stresses, the hose is not going to stretch. The reaction is going to be bending through the 1/8NPT nipple.
Originally Posted by rcpaisley View Post
The teflon hoses linking cylinders are not stiff hoses. Hard line is a "stiff hose".
We have had no issues what-so-ever with properly supported installs. The referenced injector failure was after many years of operation with an inadequately supported install.
"Support your fuel rails and anything else bolted to your engine -properly" is the lesson here. Robert
Both arguments have merit, although the parties are not talking about the same loads. Mike is discussing tension/compression due to fore and aft movement of the heads. Robert's adel clamp addition is an attempt to provide support in response to a vertical movement of the heads, the effect of torque reaction (block shake counter to prop rotation), or piston side loads within the cylinders.

The modulus of elasticity for teflon is only 0.5 Gpa, roughly 140x less stiff than alumimum, and fore/aft cylinder displacement would be very small. Given those factors I would tend to ignore the tension/compression concern.

However, Robert can't have to both ways. If we buy into the argument that the teflon hose is not stiff (and the above modulus says it's not), then the adel clamp cannot support the injector bodies. At best, the adel can only support some percentage of the hose mass. It's an improvement, but the feed fittings are still free to vibrate in the threads of the aluminum tube injector mount, and the injector mount itself is still cantilevered from an 1/8" NPT aluminum nipple.

Previously I asked Robert to confirm where the injector mounts had broken, and here's why. Although the cut-thread NPT nipple is being fingered as a potential failure point, I suspect the broken mounts pre-dated those nipples, and being installed on welded steel bungs, had to have been failures of the aluminum tube body.
Dan Horton
Barrett IO-390

Last edited by DanH : 09-07-2018 at 10:00 PM.
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Old 09-17-2018, 04:48 PM
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rv6ejguy rv6ejguy is offline
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,158
Default Safety Issue

Two of the Reno RV racers installed SDS top injector mounts on short notice after a failure of one of the mounts being discussed here which resulted in a fuel fire (it was fortunately put out quickly on the ground).

We`re pleased to report that both planes were quickly re-tuned with the SDS hardware and injectors and made the races this year.

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 432.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016

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Old 09-18-2018, 06:22 AM
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jeffkersey jeffkersey is offline
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Location: Cottontown, TN
Posts: 205
Default Great articles!

Originally Posted by DanH View Post
My FM200 is closed loop. I have a large meat servo with its own CPU (apparently running DOS) monitoring exhaust temperature, with additional aural and tactile inputs.

Seriously, both Bendix style constant flow injection and the current electronic offerings are open loop, and there is no reason for any significant quantity of "wasted fuel" with either kind.

As Ross said, the typical constant flow system with .028" restrictors doesn't meter as well as an EFI system at low flow rates. At idle, the constant flow delivery is more dribble than squirt. Atomization is less than ideal, so vaporization is poor, thus cycle to cycle variation tends to be worse. In cruise, fuel divider accuracy drops off below roughly 6 GPH. That's not a big deal for most of us, as we tend to cruise above that, even LOP. Smaller engines can substitute .022" restrictors for an improvement. The EFI will generally deliver a smaller GAMI spread at very small fuel flows, as Dave Anders has demonstrated.

Dave, you should find all the basics in these two articles:

I enjoyed both articles. It helped fill in a lot of blanks in my ignorance about fuel injection. I will try to make it to one of the AFP classes.

Thanks for all you do,

Jeff Kersey
RV7A Purchased Flying
Dues paid
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