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Tip Tanks

workerbee77

I'm New Here
Hi guys,

I'm new to this forum (although I've been on and off with a build of my RV7A for 7 years now!). I was hoping someone might be able to shed some light on tip tanks and whether they can feed the engine directly (everything I see online speaks of transferring from the tip tank to the main tank).

I understand that a tip tanks may not have a fuel gauge, sump and pickup as standard but has anyone got experience in plumbing the tip tanks such that they feed the engine directly though the tank selector valve?

I've bought a nice Andair valve selector with separate inlet ports for two tip tanks but realise now that if I can't get a tank to feed directly to the engine, then I've got the wrong valve.

Any help would be much appreciated.

Regards,

Rowan
 
I believe Mr. Axsom has tip tanks plumbed like that; his are also removable for racing, IIRC.

If you're going to feed directly off your aux tanks, I think you'll want to make sure you have a sump and some kind of fuel level sender.

On my 7, I'm closing out my outboard leading edge and using a setup very similar to Pat Tuckey's outboard tanks, since I was still at a stage I could do it that way. The fuel transfers automatically (with a pump for insurance). The setup also ensures the outboards are dry before emptying the main tanks, without having to possibly run the engine till it stutters.
 
This can be accomplished many different ways. I believe in keeping it simple. My rocket has tip tanks. I chose to route the fuel directly to the selector valve rather than through the main tanks. The reason is simply to be able to burn the fuel out of the tips first with less chance of having to land with fuel in the tips. I have sumps on each tip. Each tip is plumbed into a T fitting then to a filter then on to the 3rd port on the standard vans fuel selector. Its all fed by gravity. I use my fuel flow computer as my fuel indicator and ususally run both down to about a gallon on each side prior to switching to mains. I always launch on the mains and never switch to tips until I am at a safe altitude.
Ryan
 
The fuel system is as you make it.

As stated I have tip tanks which I remove for racing even though the original concept was driven by the Aircraft Spruce race distance for the 1996 "Great Cross Country Flying Race" from Denver to Oshkosh. Jeanine and I flew in that race and I liked the long cross country race idea but they seldom come up.

All four tanks are plumbed directly to their own fuel filter in a center console. The out put from each of the four filters is routed to a port on one of two Vans standard fuel valves.

1 - There is a "Tip" valve for the tips that is physically restricted by the console design to two positions with 90 degrees of rotation - one port/position for each tip tank - the valve mounting rotated 45 degrees to the left to narrow the console width. A new flat was added to the shaft so the 45 degree left position selects the left tip and the 45 degree right position selects the right tip. The output of that valve goes to an input port on the second valve.

2 - The other "Main" valve has 4 ports and corresponding positions. It is also rotated 45 degrees left to minimize the lateral confinement envelope. Originally built it square but it was so wide that it was uncomfortable for the crew's legs. All four ports are selectable and here again the shaft had a new flat added so the crew selectable positions are 0, 90, 270 and 180 (0 being straigth ahead toward the nose of the airplane on the centerline) even though the corresponding selected port positions are 315, 45, 225 and 135 degrees respectively. The output from the Tip valve goes into the 315 port and fuel flow from the currently selected tip tank is enabled when the valve selector is pointed at 0 degrees and coincidently directly toward the Tip valve that is mounted in front of it on the console. When the selector points to 90 degrees the right main tank is selected, 270 degrees selects the left main tank and 180 degrees points toward the rear of the plane selecting a plugged port the and is the all fuel "Off" position. The output of the main Fuel Valve goes to the aux. pump in the console and the output of that pump goes directly to the engine driven pump with a "T" off in the console to the primer solenoid.​

I have two dual EI fuel gauges located side by side in the instrument panel and there are fuel quantity senders in each of the four tanks. They are completely independent of the plumbing for fuel flow. I should add that the outboard side of the left gauge contains the series level/warning lights for the left tip and the inboard side of the same gauge contains the ones for the left main tank and the same visually intuitive logic is applied to the right fuel quantity gauge for the tanks on the right wing.

I recently installed an EI fuel flow gauge (what a precious thing this turned out to be) where the "Red Cube" transducer is mounted on a firewall bracket. The output from the engine driven fuel pump goes into the "IN" port of the transducer and the "Out" port of the transducer is connected to the carburetor input.

So you see you can develop your own configuration. I think it should be simple, reliable and operationally intuitive.

Consoleopen_zpse6baee0a.jpg


consoleclosed_zps1e5115fd.jpg


Bob Axsom
 
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Just for clarity...I have tip tanks that are gravity fed into the main tanks. There is no way NOT to burn the fuel out of the tips first. It flows from the tip through a check valve to the main tanks, then to the standard set up with a regular left/right/off andair valve. This was the Jon Johanssen set up.
 
Not exactly the same thing

Just for clarity...I have tip tanks that are gravity fed into the main tanks. There is no way NOT to burn the fuel out of the tips first. It flows from the tip through a check valve to the main tanks, then to the standard set up with a regular left/right/off andair valve. This was the Jon Johanssen set up.

The tips may empty first but unless the fuel goes directly from them to the engine it burns first only in concept.

Bob Axsom
 
fair enough

You're absolutely right Bob. I was coming from the perspective of Ryan's desire to empty the tips first, which I share:

... The reason is simply to be able to burn the fuel out of the tips first with less chance of having to land with fuel in the tips...
Ryan

You don't need a different valve and fuel feed system to accomplish emtying the tips first. The gravity feed system, feeding into the mains accomplishes this.
 
You don't need a different valve and fuel feed system to accomplish emtying the tips first. The gravity feed system, feeding into the mains accomplishes this.[/QUOTE]

Like I said, there are many different ways to do it. How you do it is up to you but to be clear there is no extra fuel feed system. Only 1 valve for the entire system. The fuel going from the tips to the mains is dependent on where the fuel is brought into the mains and when there is room for it feed in if it's a gravity system.
Ryan
 
An advantage of both Ryan's and Bob's systems over mine has to do with filling all tanks. On mine I only put fuel in the tips just before takeoff, othewise if everything is full and it starts to get warm ouside, the combination of heat expansion plus the increased head pressure of the tips over the mains and the fact that the end of the fuel vent in the main tanks is covered by fuel will drive the fuel up and over the riser in the main fuel vents. Fuel will start puking out at a prodigious rate and there's really no good way to stop it:eek:

If I understand both Bob's and Ryan's installations, venting fuel on the ground with full tips and heating in the sun should not be a problem.

Is that correct guys?
 
I didn't put tip tanks on mine, but I made the outboard leading edges into another set of tanks, with the same potential problem for venting. The way I solved it was to have one vent at each wingtip, and it provides flow-through venting for the main tank by going through the outboard. No way to vent fuel overboard that way unless both tanks are completely full and you add sunshine. Each wing is a separate setup - left vent handles both left tanks, right to right.
 
Tip Tanks with a check Valve

So I have to ask, does the main tank have it's own vent (maybe the original vent?)? Does the tip tank have its own vent?

If the main tank isn't vented, what happens to the excess pressure in the main tank when you leave the plane out in the sun?

If both the tip tank and main tanks are vented seperately, how do you balance the vent air pressures while in flight? If the tip tank vent pressure is higher, the tip tanks will drain into the main tank, overflowing out the main tank vent. If the tip tank vent pressure is lower, the tip tank will never flow into the main tank.

I experimented with Jon Johanssen's set up setup, and found the above results to be valid. I ended up taking the check valve out from between the tip tank and main tank, and capping off the main tank vent. The tips will always flow into the mains, and only the tip tank is vented. (The tip tanks hold 9.5 gals for a total of 60 gals of fuel in the RV-7A...)

Just for clarity...I have tip tanks that are gravity fed into the main tanks. There is no way NOT to burn the fuel out of the tips first. It flows from the tip through a check valve to the main tanks, then to the standard set up with a regular left/right/off andair valve. This was the Jon Johanssen set up.
 
All of my tanks are totally independent

An advantage of both Ryan's and Bob's systems over mine has to do with filling all tanks. On mine I only put fuel in the tips just before takeoff, othewise if everything is full and it starts to get warm ouside, the combination of heat expansion plus the increased head pressure of the tips over the mains and the fact that the end of the fuel vent in the main tanks is covered by fuel will drive the fuel up and over the riser in the main fuel vents. Fuel will start puking out at a prodigious rate and there's really no good way to stop it:eek:

If I understand both Bob's and Ryan's installations, venting fuel on the ground with full tips and heating in the sun should not be a problem.

Is that correct guys?

Essentially that is correct. Each tank is completely independent including the tips with their pickup and vent ports at the wing tip which never vent fuel onto the ramp (there is a metal ball between spaced crimps in the vent line). The main tanks with the vent line that goes up to the near the upper fwd fuselage skin then back down to and out of the bottom fuselage skin as specified in the original design still vent fuel onto the ramp with full tanks sitting in the sunshine.

The one thing that got my attention several years ago on my third flight of the day without refueling was during a sustained high angle climb out while still on a tip tank that I had been using on in the previous flight. Even though there is a baffle in there if you tilt the plane up long enough with low fuel it will move to the rear of the tank and leave the pickup sucking air. I switched tanks and everything returned to normal. You should never experience the need for that operational workaround with your system - with flexibility comes operational responsibility.

I love the tip tanks (Bladder Buster Tanks by Farn Reed - no longer available) but can't afford the longer wing drag in short races or ones with no penalty fuel stops like the AirVenture Cup. When I remove the stock tips and tip tanks and instal my 3" racing tips the wing is 3 feet shorter. I recently added an EI fuel flow gauge and this allows me to manage fuel burn accurately real time which makes longer flights with the 38 gallons manageable.

Bob Axsom
 
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I experimented with Jon Johanssen's set up setup, and found the above results to be valid. I ended up taking the check valve out from between the tip tank and main tank, and capping off the main tank vent. The tips will always flow into the mains, and only the tip tank is vented. (The tip tanks hold 9.5 gals for a total of 60 gals of fuel in the RV-7A...)

My purchased RV-4 had Johanson tanks. After issues with reliable feed, I made contact with Fred. Ended up doing exactly what he did, except the plumbing was easier to just leave the check valve in place and remove the shuttle. Decided it would be smart to touch base with Jon, so I did:

"I thought long and hard before sending this email, as I know the last thing a designer wants to hear about is somebody messing with his design. Well, I messed with yours. Blocked off the vents in the inboard tanks and removed the shuttles from the check valves (that was easier than repiping). I've filled all four tanks at least six times and the outboards feed just fine. Thought I would touch base just in case I've overlooked something."

His response:

"No problems here, that will work. Make sure you stay well clear of icing conditions though."

Regards,
Jon Johanson

If the airplane was going to be in the sun for any length of time I stopped 1/2 gal short of the 7 gal capacity and never had an issue with puking fuel.

Tony
 
An advantage of both Ryan's and Bob's systems over mine has to do with filling all tanks. On mine I only put fuel in the tips just before takeoff, othewise if everything is full and it starts to get warm ouside, the combination of heat expansion plus the increased head pressure of the tips over the mains and the fact that the end of the fuel vent in the main tanks is covered by fuel will drive the fuel up and over the riser in the main fuel vents. Fuel will start puking out at a prodigious rate and there's really no good way to stop it:eek:

If I understand both Bob's and Ryan's installations, venting fuel on the ground with full tips and heating in the sun should not be a problem.

Is that correct guys?

For my system that is correct. My tips are vented separate of the mains.
I didn't do everything the way that Fred did but he was one of my major helps in getting this system put together.
Ryan
 
Tip Tanks Venting

On one of my RV's, I only had the tip tanks vented out at the tips. I did have an vent icing issue that didn't result in an engine outage (close, but no actual outage). What I decided to do was to put a "T" into the tip vent, and plumb in a vent check valve that took in air from inside the wing in the event of an actual vent blockage (but blocked any expanding fuel into the wing).

In my latest plane (an RV-7A) my tips are vented all the way back through the fuselage (behind the spare & using the original fuselage venting scheme) with the "T'ed" in check valve out at the tip (Flying IFR requires this redundency!). I've been in light icing conditions and never have had or seen any tank venting issues.

I can fill both mains and both tips (in that order) and, unless I overfill the tips, and leave the plane out in the hot sunlight, never see weeping tip tank vents....

My purchased RV-4 had Johanson tanks. After issues with reliable feed, I made contact with Fred. Ended up doing exactly what he did, except the plumbing was easier to just leave the check valve in place and remove the shuttle. Decided it would be smart to touch base with Jon, so I did:

"I thought long and hard before sending this email, as I know the last thing a designer wants to hear about is somebody messing with his design. Well, I messed with yours. Blocked off the vents in the inboard tanks and removed the shuttles from the check valves (that was easier than repiping). I've filled all four tanks at least six times and the outboards feed just fine. Thought I would touch base just in case I've overlooked something."

His response:

"No problems here, that will work. Make sure you stay well clear of icing conditions though."

Regards,
Jon Johanson

If the airplane was going to be in the sun for any length of time I stopped 1/2 gal short of the 7 gal capacity and never had an issue with puking fuel.

Tony
 
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I installed the John Johansson tip tanks in 2002.
I did not like the idea of running the fuel from the tip tanks to the main tanks for two reasons. First as the tip tanks are higher than the main tanks if the main tanks filler cap O rings are not a perfect seal fuel will flow out over the wing. Secondly I did not like having two venting systems as if the main vent pressure is higher than the tip vent pressure all the fuel will not empty out of the tip tanks. I had previously met someone who had had this problem.
On my 6A the fuel lines of each tip tank are run directly to the fuselage then via an ON/OFF tap to at T fitting then to the third position on the standard Vans fuel selector valve. In this way it is possible to select each tip tank individually. I always use the main tanks for take off and landing. After take off switch to say right tip tank for 30 minutes then switch to left tip tank until it is empty and then back to empty the right tank.
I had read on this forum that with a low wing plane and tanks that it was impossible to use both tanks at the same time so as this is experimental aviation I decided to try it to see for myself. I have found that with my configuration I can switch both tanks on at the same time and the system works fine with both tanks completely emptying after nearly 2 hours. In this way the plane keeps well balanced about the roll axis and avoids switching tanks every half hour or hour. As I don?t have fuel gauges on the tip tank I note the time I switch and after nearly 2 hours listen out for a low pressure fuel alarm from my engine monitor. If I miss this alarm the Lycoming sends out an alarm asking for more fuel and telling me to switch to the main tanks.

Barry RV6A F-PRVM
 
Johanson tanks

I have the Johanson tip tanks on my RV4. I have the Andair 5 port valve. Each tank feeds the engine directly. Other than an plug in the vent on on one of the tips, not sure what got in that vent. They have worked well for about 10 years. Each hold 9 gallons. I only fill them for trips.

The quality was great and the added 18 gallons sure help with the range.
 
I suppose it is unlikely that I would find a spare set of Johanson tip tanks at this stage, for my RV6?

As an alternative if anyone knows of a potential constructor of a new set in accordance with the original format ....?

There does not seem to be anything suitable on the market, the tubular type are too small to be worth the effort.
 
I suppose it is unlikely that I would find a spare set of Johanson tip tanks at this stage, for my RV6?

As an alternative if anyone knows of a potential constructor of a new set in accordance with the original format ....?

There does not seem to be anything suitable on the market, the tubular type are too small to be worth the effort.

Johanson style tip tanks.

Why can't you add a couple of fiberglass ribs to your existing wing tips and close them off with fiberglass? Isn't that what Johanson did?
 
An alternative ..

I suppose it is unlikely that I would find a spare set of Johanson tip tanks at this stage, for my RV6?

As an alternative if anyone knows of a potential constructor of a new set in accordance with the original format ....?

There does not seem to be anything suitable on the market, the tubular type are too small to be worth the effort.

If you don't find what you are looking for for your RV6, this might be an option.

http://www.flickr.com/photos/7481868@N04/sets/72157638782147755/

Two 7.5 gallon (each) tanks that fit behind the seat of my RV6. I have two installed (one fuel and one smoke oil.) It works fine. I plan for only **7** gallons usable.

My only affiliation with these is that I provided Marvin "design assistance" on this version of the product.

See this thread ...

http://www.vansairforce.com/community/showthread.php?t=107699&highlight=fuel+aux+tank

James
 
If you don't find what you are looking for for your RV6, this might be an option.

http://www.flickr.com/photos/7481868@N04/sets/72157638782147755/

Two 7.5 gallon (each) tanks that fit behind the seat of my RV6. I have two installed (one fuel and one smoke oil.) It works fine. I plan for only **7** gallons usable.

My only affiliation with these is that I provided Marvin "design assistance" on this version of the product.

See this thread ...

http://www.vansairforce.com/community/showthread.php?t=107699&highlight=fuel+aux+tank

James
This looks like an easy way to add a few extra miles to your RV. No fuel pump needed and easy to plumb into your existing fuel system.

How did you get the fuel lines to your valve? Did you run them above the floor and spar or did you drill another hole and run the fuel lines through the spar?
 
Not a big fan of fuel right behind seat

I considered the tanks behind the seat but prefer to keep the fuel outside the fuselage. I know.....lots of planes have fuel in the fuselage, but not my first choice.
 
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