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New RV-3 Owner (Fuel System Question)

jim miller

Well Known Member
I just closed the deal on a very nice RV3 less engine which has flown 200hrs
over 3-4 years. As stated in a previous post I will be using my 0235 C-1
engine and want to get some advice on a slightly unusal fuel system.
I can easily have the acessory case machined for mechanical pump if
necessary.My plane has two wing tanks and a custom made fiberglass
fuselage tank that holds 10 gal. It's lower edge or "bottom" is even with
or slightly above the bottom of the instrument panel and I think testing
will confirm adequate gravity flow. I used to own a ercoupe which has a
mechanical pump but it only fills the gravity flow fuselage tank from the
two wing tanks. Would it not work to use the wing tanks on my RV3 to
fill the 10 gal fuselage tank. Fuel would be fed into the fuselage tank thru
a standpipe fitting where the transfer pump would not have to push against
fuel already in the tank.

Thanks
Jim Miller
 
I also have a three with no engine driven fuel pump provision. My plan is to have a standard electrical system with two electric fuel pumps and a back-up battery. I no longer see a value in a engine driven fuel pump and it's location problem. Electronic ignition requires a back-up battery so the only thing you are adding is another electronic fuel pump $42.00. for that price, you could have three.

Picture how clean the back of the motor would be without the mags, vac pump, prop governor and the fuel pump. One line going from the firewall to the carb. CLEAN!!
 
I also have a three with no engine driven fuel pump provision. My plan is to have a standard electrical system with two electric fuel pumps and a back-up battery. I no longer see a value in a engine driven fuel pump and it's location problem. Electronic ignition requires a back-up battery so the only thing you are adding is another electronic fuel pump $42.00. for that price, you could have three.

Picture how clean the back of the motor would be without the mags, vac pump, prop governor and the fuel pump. One line going from the firewall to the carb. CLEAN!!


Gasman
I want to talk further with you about your plans. It would be great if I can
avoid the mechanical pump. Ten gallons is 1 1/2 hr for a 0235 and if I had
one facet pump pumping from each wing tank at the flip of a switch I
could about every hour refill the 10 gal tank. What kind of electronic
ignition are you planning on using?

Jim Miller
 
Jim, With wing tanks, the 10 gallon tank is not needed and that space is better used for other things. I would make the fuel system simple. Simple to build and simple to operate.

All RV's (almost all) use the Facet fuel pump as a back-up to the engine driven one. My plan is to use two Facet pumps in line. It would go like this..... Fuel select valve, inline quality fuel filter, Facet fuel pump, Facet fuel pump then fuel line to carb.

One fuel pump would run the full time the motor is running. It could be controlled by a vacuum switch. The other pump would be operated just like any other aircraft with a back-up pump. This is STANDARD. You just switch tanks every hour. If you forget to fill the header tank, the engine will die. With no fuel pump mounted in the hot area of the engine, and no Gascolator mounted on the hot firewall, your carb will get cool fuel direct from the cabin area.

I would run a backup battery that would operate the fuel pump and the LIGHTSPEED ignition for at least one hour.
 
Gasman
That is certianly something to consider. Is there no problem pushing
fuel thru the un-engergized pump?
Two Oddessy batteries weight about same as aircraft battery and will fit
into as small a space.

Jim
 
This is someone with little real RV experience however I would do whatever you can to avoid having a tank in the fuselage. From a safety standpoint I really like having all the fuel out in the wings.

George
 
Gasman
That is certainly something to consider. Is there no problem pushing
fuel through the un-energized pump?
Two Odyssey batteries weight about same as aircraft battery and will fit
into as small a space.

Jim


Most all stock carb RV's pull the fuel through the Van's Facet fuel pump. Test it, but it should be no problem.

Your back up battery only needs to be about 1/2 the size/weight of the 680. And they are getting smaller.
 
The 3 / O-235 I owned had wing tanks and 2 electrical fuel pumps in series ( one ahead of the other) and 2 batteries. No mechanical pump.

I agree with the other poster, with the fuel burn of the 235 you do not need the header tank. I assume it was so the pilot could run empty wing tanks and use the header tank when doing acro?
 
Thanks all for the advice. I think I will go with the two fuel pumps and remove the header tank. Its good to know that I can operate without a
engine driven pump.
 
Changing out the accessory case on your O-235 to one with a mechanical fuel pump is easy to do.

Heck, if I could do it, anyone can.

You will need the appropriate accessory case, a timing gear w/ the cam lobe (75072), and the fuel pump plunger (61544).

Call Wentworth for the parts.

Here are some tips on how to make the change.
 
Changing out the accessory case on your O-235 to one with a mechanical fuel pump is easy to do.

You will need the appropriate accessory case..............$$$
A timing gear w/ the cam lobe (75072)......................$$$
The fuel pump plunger (61544)..................................$$$
A fuel pump, hose to and from, and fittings.................$$$

Or you can spend less than $100 using electronic that would do the same thing at the same time be less weight, less complex, one less thing to work around on the back of the motor and one less heat sink for the fuel.
 
I often tell people not to mess with the fuel system. There are thousands of RV's flying with the "stock" system, stick with something tried and true. Besides, some day you might want to sell your plane and installing other than a "stock" fuel system might impact your ability to sell it.

As for the cost of the accessory case, gear, plunger, and gasket kit. Check with either ECi for new parts or Wentworth for used ones. I was able to buy an O-320 accessory case for $100 and paid $80 for the gear and plunger. Of course, then I had to buy the fuel pump and a gasket kit.

Money wel spent, IMHO.
 
The 3 / O-235 I owned had wing tanks and 2 electrical fuel pumps in series ( one ahead of the other) and 2 batteries.


I like your and Gasman's two electric pump system. I am looking at using
two switches (ON-OFF-ON) so I can select Battery one or two and pump one
or two. How do you charge the backup battery in your systems?

Thanks
JM
 
Header Tank with 2 Fuel Transfer Pumps, 2 EFI Pumps - no engine driven pump

Folks,

I thought I provide some information about the fuel system we have on the Subaru driven Robin - just food for thought.

The plane:

v4x79s.jpg



The aircraft is fitted with two fuel tanks: a main tank underneath the rear bench and one header tank behind the rear bench. The main tank contains 110 litres (29 gals) of fuel, the header tank 28 litres (7.4 gals). As fuel is transferred by two fuel transfer pumps from the main tank to the header tank all fuel of the main tank is usable in level flight.

ibx6qx.jpg



The engine always runs off the header tank. Two manually operated low pressure fuel transfer pumps are used to transfer fuel from the Main Tank to the Header Tank via two filters. An overflow tube between the Header Tank and the Main Tank prevents fuel spilling. The overflow tube doubles as a vent line for the Header Tank. The Main Tank is vented to the outside by means of a vent tube behind the main landing gear but on the underside of the fuselage.

From the Header Tank fuel is gravity-fed (no vapour lock) into two high pressure Engine Fuel pumps (as well called Electric Fuel Injection or EFI pumps) which feed via two fuel filters (situated underneath the Header Tank aft the rear bench) fuel to the engine using a single fuel line at a 2 Bar pressure and pass by all six injectors via a common rail system. Via a pressure regulator, the excessive fuel is returned to the header fuel tank to be cycled through the system again.

Both automotive fuel (98 or more octane; Europe standard) and AVGAS may be used. In order to avoid the build-up of lead deposits, unleaded (automotive) fuel is preferred. All seals and fuel lines are suited for the use of automotive fuel. If using AVGAS ca. 0,5 once (30 ml) of Decalin RunUp should be used per 10 gals (ca. 38 ltrs) to avoid the build-up of lead deposits.

Use of the tank system

? Make sure that at least one Fuel Transfer Pump keeps the fuel level in the header tank at an appropriate level.
? Cycle the fuel transfer pumps (Fuel Transfer Pump A or Fuel Transfer Pump B) from time to time to check both are operational, check one fuel transfer pump is ON all the time.
? Two panel warning lights indicate fuel state and inform about the operation of the fuel transfer pumps
? Green light: the main tank contains ca. 18-20 litres of fuel only. If so switch OFF both Fuel Transfer Pumps after ca. 30-45 minutes depending on fuel consumption to prevent the Fuel Transfer Pumps running dry, be aware that than some 28 litres are left in header tank only.
? Red light: header tank is at a fuel level of 18-20 litres. The exact behaviour of this light is this: Flight testing with both transfer pumps OFF at 30 Ltrs. Fuel Flow per hour proved that this light starts flickering after ca. 8 minutes (so at ca. 23 Ltrs reserve) and becomes continuously lit after ca. 16 minutes (so at ca. 20 Ltrs reserve).
? If the main tank is empty or both Fuel Transfer Pumps do not transfer fuel to make the red light go off land within the next 30 minutes on an appropriate airfield or execute emergency landing if necessary if no appropriate airfield can be reached with the fuel remaining.
? If fuel is still in the main tank and ie. just the transfer pump selected failed or no transfer pump was ON it takes 6 minutes to fully refill the header tank at 30 Ltrs. Fuel Flow from 20 Ltrs. reserve remaining (the fuel transfer pump pumps ca. 8 Ltrs in 6 minutes or ca. 80 Ltrs. in one hour).

310+ hrs without a hick up and no vapour lock whe using Mogas.

Best, Heinz
P.S. I AM NOT TEACHING SOMETHING TO ANYONE AND I AM NOT SUGGESTING THIS WORKS IN OTHER APPLICATIONS TOO.
 
Heinz,

Very informative post. The main tank/header tank could be implimented in a 3 using the wing tanks and a fuselage tank. Two wing/main tanks would complicate the situation, a duplex fuel valve would probably be the way to go so if the header tank was full and overflowed, the fuel would return to the correct tank. The small and light facet cubes could be used for transfer.

I know there are at least two rv-3's with wing tanks and fuselage tanks (Vanguard's), though if you go with the idea of sizing the header tank to safely get on the ground, 5 or 10 gallon header tank would be adequate, no need for the original 24 gal fuselage tank. A small tank mounted high, and forward might even gravity just fine to a carb.

best regards
 
Do a search under my name..I have a combined 700 hours roughly on two airplanes with electric only fuel pumps.

My Zenair Zodiac was carbed and my current RV is fuel injected.

Frank
 
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