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Fuel flow transducer mounting question

lostpilot28

Well Known Member
I've spent a lot of hours reading the various threads on mounting a fuel flow transducer. I plan on buying the Floscan (flowscan?) unit and my initial idea was to buy an extra 6-inch piece of fuel line and mount the transducer between the carb and the mechanical pump. I've seen another installation where the flow sensor just hangs there (wrapped with firesleeve and aluminum heat shield wrap) and it appears to provide great results.

I'm planning on doing the same thing, and want to make sure just letting it hang wouldn't be a problem. I only ask because many of the threads I've read have the sensor mounted to a plate somewhere. Does anyone see a problem with doing this?

One last bonus question - how critical is it to add a fuel filter upstream of the sensor? I have the gascolator (mounted on the firewall) between the boost pump and mechanical pump...is this good enough, or do I need to add another filter?
 
Fuel Flow

In general, it's a good idea to add a filter between something that might create debris if it came apart and the point of final use. However, a filter will always call a pressure drop. If your flow transducer doesn't have anything in the fuel stream, you don't gain anything by adding a filter. However, turbine flow meters (if that's what you're using) are often a little twitchy. I would imagine there are some old military specifications that might be some help to you.
 
Thanks, Jay. I think the manufacturer recommends a filter...I just want to know if the firewall mounted gascolator is sufficient.

My biggest question is about the transducer not being mounted to anything. I'm sure someone has an opinion about that...

;)
 
My concern is whether doing it your way could lead to a fatigue in the fuel line. I don't know if that is a valid concern but it needs to be considered. The fact that someone else did it that way does not make it a sound method. Perhaps theirs has not had time to fail.
 
Mine has been mounted like that for almost six hundred hours and six years of flying. I have the unit wrapped in fire sleeve with a dab of high temp RTV between the fire sleeve and the oil sump. No problems so far and none expected. Over the years I have mounted them in all sorts of locations and they seem to work well in every installation.
 
Electronics International has some excellent info in their manual on installing the FF xdr, starts on page 26...

Link to MVP-50 install manual

As long as your gascolator has some kind of filter or screen in it you'll be ok with it as the "pre-filter".
 
Mine has been mounted like that for almost six hundred hours and six years of flying. I have the unit wrapped in fire sleeve with a dab of high temp RTV between the fire sleeve and the oil sump. No problems so far and none expected. Over the years I have mounted them in all sorts of locations and they seem to work well in every installation.

Thanks, Tom. You wouldn't happen to have a picture of your installation, would you?
 
What do you guys think of making your own fuel lines? I made 2 of them before when running from the fuel tanks to the selector valve...the hose and fittings are from Pegasus Racing. They don't leak, which I'm guessing is the important part!

I could build the same thing for my FWF section from the mechanical fuel pump to the carb. Being that it's low pressure, I think this would be OK. Again, what do you guys think? :D
 
Update

OK, this is prompting me to wonder how you guys did this. I've built two sections of fuel line, one is about 9 inches long & the other is about 5 inches long (including the fittings).

My questions are:
1. In looking at the aircraft standards handbook, I couldn't see any reason to worry about making a short run of fuel line, such as my 5 incher.

2. There is NOT a lot of room in that area to run fuel line - see the pictures below. Is there any concern with the way I'm doing this?

3. The very front section of fuel line (to the carb) actually touches the engine mount (middle picture), which I'm not happy about. So did the old hose, although I don't see any wear on the hose or mount. I don't think running the hose on the OUTSIDE of the mount is a good idea because it's too close the exhaust. What do you guys think?

4. I bought AN6 straight fittings for the flow meter, but they force the hose to bend pretty sharply by the firewall, so I put in that aluminum 45 degree fitting to see if it would make it better - and it does. I will use Steel if I go this route...any reason I shouldn't use a 45 degree fitting?

As always, much thanks to all of you guys...you're much smarter than I am!





 
FFTX

Sonny,
I have seen a few FF transducers forward of the firewall however I am not a fan. The only FWF installation I have seen that I thought was marginally ok was when it was mounted to the firewall. Your installation concerns me. It is going to shake and vibrate in my opinion way to much, too much risk. My recommendation is that if you put it FWF put it on the firewall.

Do you plan on leaving the fire sleeve as installed? The ends need to be coated on the inside with high temp silicone or they will just become a wick for fuel. They also need the metal strapping on each end.

Fuel lines touching anything is never a good idea. I would use a simple tie wrap standoff for the forward line.
 
Hi Pat, thanks for the reply.

No, I'm not done installing this yet, and I do plan on coating the ends of the firesleeve, as well as binding the ends (probably with safety wire). There are a few other Fuel Flow meters in this location (specifically - not mounted to anything). The following link shows this configuration on page 10: http://www.jpinstruments.com/700-800_FF_install.PDF

I'm not so much concerned about the meter hanging there, as I am about the bends in the fuel line and also the point where the fuel line is touching the engine mount.

Least important (I think) is the 45-degree fitting, which I hope doesn't affect the accuracy of the meter.

Also, the final installation will have the FF meter wrapped in firesleeve, just like the documentation from JPI suggests. I'm also going to wrap the entire length from fuel pump to carb in heat reflective tape (summit racing stuff).
 
I'm going to expose myself to some commentary and I'm ok with it so here goes ...

I installed my transducer right to the elbow going into the carburator. My fuel line runs from the engine driven fuel pump, to the transducer, into the elbow and then right into the carburator. The transducer and wiring is all fire sleeved.

The install has been reviewed by a couple different knowledgable people and they did say, while it was ok, the Manufacturer's documentation did suggest having some amount of strait flow before and after the transducer. The manufacture clearly stated the transducer needed to be between the engine driven fuel pump and the carburator.

Since I was adding a FuelScan to an flying plane, my setup allowed the existing fuel line to be used and insured the transducer was well secured.
 
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OK, so I ran back out to the hangar and rerouted my fuel line, just because (for some reason) it hadn't donned on me that I could use a 45 degree fitting on the carb, which does 2 things: keeps the fuel line from touching the engine mount and allows the fittings into the transducer to be straight.

I found this old thread very helpful, especially post #12 from Don at Airflow: http://www.vansairforce.com/community/showthread.php?t=11698&highlight=fuel+flow+locatio n+carb&page=2

Here are a couple pictures of what I think will work pretty well. Feedback is always appreciated. :)

imag0060h.jpg
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You might consider replacing that blue aluminum 45-degree AN fitting with a steel one.

Not saying you can't use aluminum, but steel might be better for both vibration and fire reasons.
 
My red cube is in Vans recommended location in the bottom of the tunnel. Accurate to 1/2 gal at every fill up.
Hi Wayne-

To which RV model are you referring where Van's recommends bottom of the tunnel? Is this on a drawing somewhere? By "bottom of the tunnel" I assume you're referring to a location b/w the fuel selector and the firewall? If so, how is the transducer secured? Does it float or is it secured to the airframe somehow? (Just curious b/c I have mine here and I've been debating about how, and if, it should be secured to structure rather than just sandwiched in foam as I have it now.)
 
Hi Wayne-

To which RV model are you referring where Van's recommends bottom of the tunnel? Is this on a drawing somewhere? By "bottom of the tunnel" I assume you're referring to a location b/w the fuel selector and the firewall? If so, how is the transducer secured? Does it float or is it secured to the airframe somehow? (Just curious b/c I have mine here and I've been debating about how, and if, it should be secured to structure rather than just sandwiched in foam as I have it now.)

Bottom of the tunnel is the standard location on a RV-10. Many RV-10 builders are locating it FWF to reduce oscillation variations in the fuel flow readings. Some builders, like Wayne, report no problems in the standard location.

bob
 
Bottom of the tunnel is the standard location on a RV-10. Many RV-10 builders are locating it FWF to reduce oscillation variations in the fuel flow readings. Some builders, like Wayne, report no problems in the standard location.

bob
Thanks Bob. Is it attached to anything or does it float between two pieces of the aluminum fuel tube? (What I'm really interested in is whether it's fixed to the airframe or floats.) Thanks.
 
Thanks Bob. Is it attached to anything or does it float between two pieces of the aluminum fuel tube? (What I'm really interested in is whether it's fixed to the airframe or floats.) Thanks.

Per the RV-10 plans, there is a mount on the floor of the tunnel that the sensor is attached.

Those that attach FWF, at least the ones I've seen, also rigidly mount the sensor. Most use a piece of angled aluminum and mount to the engine. If you want to search, I know that Rob Hickman has posted a picture either on VAF or the AFS support site on where he located his.

bob
 
Per the RV-10 plans, there is a mount on the floor of the tunnel that the sensor is attached.

Those that attach FWF, at least the ones I've seen, also rigidly mount the sensor. Most use a piece of angled aluminum and mount to the engine. If you want to search, I know that Rob Hickman has posted a picture either on VAF or the AFS support site on where he located his.

bob
Thanks Bob. If anyone has a picture I'd love to see it.
 
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