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  #11  
Old 10-21-2013, 01:51 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
Default

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.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #12  
Old 10-21-2013, 02:03 PM
Fred.Stucklen's Avatar
Fred.Stucklen Fred.Stucklen is offline
 
Join Date: Oct 2006
Location: Brooksville, FL
Posts: 356
Default 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...)

Quote:
Originally Posted by jjconstant View Post
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.
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Fred Stucklen
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RV-7A N924RV Flying (1825 Hrs & counting)
RV-6A N926RV 875 Hrs (Sold)
RV-6A N925RV 2008 Hrs (Sold)
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  #13  
Old 10-21-2013, 02:21 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default All of my tanks are totally independent

Quote:
Originally Posted by jjconstant View Post
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

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

Last edited by Bob Axsom : 10-21-2013 at 02:36 PM.
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  #14  
Old 10-21-2013, 03:12 PM
Tony Spicer Tony Spicer is offline
 
Join Date: Dec 2005
Location: Wilmington, NC
Posts: 517
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Quote:
Originally Posted by Fred.Stucklen View Post

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
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  #15  
Old 10-21-2013, 04:46 PM
131RB 131RB is offline
 
Join Date: May 2009
Location: Colorado
Posts: 302
Default

Quote:
Originally Posted by jjconstant View Post
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

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
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  #16  
Old 10-21-2013, 05:12 PM
Fred.Stucklen's Avatar
Fred.Stucklen Fred.Stucklen is offline
 
Join Date: Oct 2006
Location: Brooksville, FL
Posts: 356
Default 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....

Quote:
Originally Posted by Tony Spicer View Post
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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Fred Stucklen
wstucklen1@cox.net
RV-7A N924RV Flying (1825 Hrs & counting)
RV-6A N926RV 875 Hrs (Sold)
RV-6A N925RV 2008 Hrs (Sold)

Last edited by Fred.Stucklen : 10-21-2013 at 05:15 PM.
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  #17  
Old 10-22-2013, 01:00 AM
Barry's Avatar
Barry Barry is offline
 
Join Date: Jan 2005
Posts: 112
Default Tip Tanks

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
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  #18  
Old 11-14-2013, 12:42 PM
gjslutz gjslutz is offline
 
Join Date: Dec 2011
Location: Beach City, Ohio
Posts: 32
Default 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.
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  #19  
Old 12-30-2013, 04:03 PM
Bluebeard Bluebeard is offline
 
Join Date: Mar 2005
Posts: 60
Default

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.
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  #20  
Old 12-30-2013, 04:58 PM
Geeman Geeman is offline
 
Join Date: Apr 2010
Location: Novato, CA KDVO
Posts: 377
Default I would buy some too.

Johanson style tip tanks.
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