SR3500 TIP TANK RETROFIT (PROPOSED)

Warren T. Montgomery · Post by **Warren T. Montgomery** » Fri Feb 17, 2012 9:21 pm

I propose to do the following mods and am in the process of seeking MAMs
comments.
I would certainly like the extra 40 gals of fuel when flying in the
remote north.

MAM is now offering 120gal tanks using the first six bays but a retrofit
would be difficult as the spar wasn't prosealed and it requires a plate
next to the strut attachment to allow dry access. I think the following
should work and welcome comments. I have my wing already opened up for
the 3500 mods so a little extra work wouldn't be too bad at this stage.

SUBJECT: SR3500 TIP TANK RETROFIT (PROPOSED)

See attached schematic.

Location: 2nd and 3rd tip bays between stn 14 and stn 16.
This will allow installation of fiberglass tip and area to install
strobe system in last bay.

1. Remove leading edge extension
2. Remove and cutback top wing skin to outside edge (tip side) of 4th
end rib (stn 14).
Allow overlap sufficient for extra row of rivets. Wing skin will be
between Stn 14, W-173 rib and tank skin to allow easier sealing of
stringers from inside before tank skin installed.
3. Cut access hole in bottom wing skin between stn 13 and 14. (fuel tank
typical) This will allow access to fuel line fitting.
4. Leave end rib stn 17 in place.
5. Replace Stn 14/16 ribs with W-173
6. Replace Stn 15 rib with W-516
7. Replace main spar extension rivets with tank rivets from stn 14 to
stn 16.
Install plates with pro-seal over main spar lightening holes at stn 14
and stn 16
8. Replace rear spar rivets with tank rivets from stn 14 to stn 16.
9. Using drill attached to long tube drill appropriate hole through all
ribs so as to exit aft of main tank outlet between rear spar just aft of
last stringer. Pre-drilling Stn 14/15/16 will aid in guiding. Where
access available have a helper ensure proper drill location at rib
stations. Mark and use short drill where possible.
10. Install W-160 flange on stn 14 and Stn 16. (Stn 16 will be plugged
but will allow straight insertion of fuel tubing from tip through wing
if replacement required)
11. Install Nylon gussets in all assessable carry through ribs stn 7-13
12. Drill out two W-159 flanges to OD of Alum Fuel tubing.
13. Install W-159 Flanges on Stn 6 and Stn 1
Alum fuel tubing will be pro-sealed to these flanges mounted on main
tank ribs and tip fuel will be routed through main tank. Ensure Alum
fuel tubing extends 1" beyond stn 1 flange so as to allow rubber tubing
to be clamped over.
14. Install top tank skin from stn 14 to stn 17; use existing holes in
stringers, spars and stn 14 and stn 17 rib. Drill additional rivet holes
between existing holes along rib flanges at stn 14. (Caution do not
drill between flange and stringers) Drill stn 15, 16 flange with same
spacing as stn 14. Add an extra row of holes along wing skin overlap
with same spacing. Tank skin will be over wing skin and under leading
edge skin.
15. Remove and cutback bottom wing skin to outside edge (tip side) of
4th end rib (stn 14).
Allow overlap sufficient for extra row of rivets. Wing skin will be
between Stn 14, W-173 rib and tank skin to allow easier sealing of
stringers before tank skin installed.
16. Install bottom tank skin from stn 14 to stn 17; use existing holes
in stringers, spars and stn 14 and stn 17 rib. Drill additional rivet
holes between existing holes along rib flanges at 14. (Caution do not
drill between flange and stringers) Drill stn 15, 16 flange with same
spacing as stn 14. Add an extra row of holes along wing skin overlap
with same spacing. Tank skin will be over wing skin and under leading
edge skin.
17. Fabricate access holes on bottom tank skin
18. Fabricate flanges to go around top and bottom stringers where they
pass through stn 14 rib.
19. Install flush fuel cap in top skin outer fuel bay. Tip tanks will be
individually vented through inverted 'J' pipe in cap.
20. Install fuel probe in stn 16 rib.
21. Debur all holes, pro-seal and rivet ribs, bottom skin, flanges and
leading edge skin clecoing main skin to stn 14 rib.
22. Install top skin with leading edge on top and tank access covers to
bottom tank skin.
23. Insert Alum fuel tube through wing. Insert screen filter in stn 14,
W-160 and join to alum tubing with nylon nipple and rubber fuel hose
with clamps. Ensure alum tubing well pro-sealed at stn 6 and stn 1 W-159
flanges. Alum tube will protrude 1" at root to allow attachment of
rubber tubing. Insert plug in stn 16 flange.
24. Pressure test.

Questions:
1. Is this the best location, 2nd and 3rd outer bays?
Other options are last two or all three.
2. Is this an acceptable way to route the fuel?
3. Does the plumbing solution sound feasible?
4. Will gravity feed work from the tips
5. Is the current rivet spacing acceptable with 1/8" rivets?
Should I add an extra rivet between existing ones along the rib flanges
and main spar.
6. Thickness of tank skins .032 or .040?

--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

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Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Fri Feb 17, 2012 9:21 pm

Warren, have added my two cents (that may be worth only one or less!) in
amongst your text!

Wayne

----- Original Message -----
From: "Warren T. Montgomery" <monty@emirates.net.ae>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, October 28, 2001 5:16 PM
Subject: SR3500 TIP TANK RETROFIT (PROPOSED)

I propose to do the following mods and am in the process of seeking MAMs
comments.

WILL NOT COMMENT ON STRUCTURAL THOUGHTS ON THIS AND WILL LEAVE THAT TOTALLY
TO A MURPHY OKAY!

I would certainly like the extra 40 gals of fuel when flying in the
remote north.

YOUR RIGHT, THAT EXTRA 2 OR 3 HOURS OF FUEL MIGHT MAKE THE DIFFERENCE
BETWEEN A WARM FLIGHT AND A COLD WALK HOME!

Questions:
1. Is this the best location, 2nd and 3rd outer bays? I WOULD THINK SO,

IF MAM APPROVES IT STRUCTURALLY

Other options are last two or all three.
2. Is this an acceptable way to route the fuel?

KISS - KEEP IT SIMPLE STUPID AND THAT SEEMS TO BE IT

3. Does the plumbing solution sound feasible?

YOU WILL NEED TO MAKE SURE THAT YOUR MAIN TANKS CAPS ARE ABSOLUTELY
LEAK/VENT PROOF AND GET RID OF ANY VENT TUBES ON THEM OR THE CABIN ROOF,
USING YOUR TIP TANK VENT TUBES AS YOUR ONLY VENTING ON EACH WINGS FUEL
SYSTEM!

4. Will gravity feed work from the tips

YES, BUT IN ABSOLUTELY LEVEL FLIGHT ONLY. WITH ONLY ONE DEGREE OF WING
DIHEDRAL IT WON'T DO LIKE A ZLIN (with it's very heavy diheadral angle)AND
KEEP THE MAIN TANK FULL UNTIL THE TIP TANK IS EMPTY. YOU ARE ALWAYS GOING TO
HAVE FUEL IN ALL THE TANKS, WHETHER YOU WANT TOO OR NOT (until the mains are
down very low anyhow).

5. Is the current rivet spacing acceptable with 1/8" rivets?

DON'T SEE WHY NOT AS THE ORIGINAL REBEL TANKS HAD HALF THE RIVETS (DOUBLE
THE SPACING) AS THE CURRENT MANUAL SHOWS AND MINE DON'T LEAK, BUT OF COURSE
THERE ARE ONLY HALF THE HOLES TO DO SO (and that"s a good thing IMHO!

Should I add an extra rivet between existing ones along the rib flanges
and main spar.
6. Thickness of tank skins .032 or .040?

AS YOU KNOW MAM USED .040 IN THE EXISTING TANKS. WOULD SUGGEST THIS WOULD BE
THE SAFE THICKNESS TO USE AGAIN

THE BIGGEST CONCERN FOR ME IS THAT IF YOU END UP WITH ONE TIP TANK FULL AND
THE OTHER EMPTY FOR SOME REASON YOU ARE ASKING FOR A REAL YAW PROBLEM (OR
WORSE IF YOU SPIN IT) WITH 120 POUNDS OF FUEL IN ONE TIP AND NONE IN THE
OTHER!!

--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

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Mike Davis · Post by **Mike Davis** » Fri Feb 17, 2012 9:21 pm

Warren, we have a builder here in Fairbanks who has done what you are
talking about here. I'm not sure whether Murphy approved of it all or not,
but the first thing I recall is that he had the tank skin extended much
further because it's thicker, 32 instead of 20 I believe. By putting the
bays out toward the tips he didn't have to worry about interfering with the
aileron push rod or the strut attachments. Mike Kimball and I have both
hinted at this builders participation (lack of) in this forum, but he says
he doesn't like to use the computer... only does at work because he has to.
Mike sees him much more often than I, perhaps he could ask him for (or
already knows) more details.

Mike

----- Original Message -----
From: "Warren T. Montgomery" <monty@emirates.net.ae>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, October 28, 2001 1:16 PM
Subject: SR3500 TIP TANK RETROFIT (PROPOSED)

I propose to do the following mods and am in the process of seeking MAMs
comments.
I would certainly like the extra 40 gals of fuel when flying in the
remote north.

MAM is now offering 120gal tanks using the first six bays but a retrofit
would be difficult as the spar wasn't prosealed and it requires a plate
next to the strut attachment to allow dry access. I think the following
should work and welcome comments. I have my wing already opened up for
the 3500 mods so a little extra work wouldn't be too bad at this stage.

SUBJECT: SR3500 TIP TANK RETROFIT (PROPOSED)

See attached schematic.

Location: 2nd and 3rd tip bays between stn 14 and stn 16.
This will allow installation of fiberglass tip and area to install
strobe system in last bay.

1. Remove leading edge extension
2. Remove and cutback top wing skin to outside edge (tip side) of 4th
end rib (stn 14).
Allow overlap sufficient for extra row of rivets. Wing skin will be
between Stn 14, W-173 rib and tank skin to allow easier sealing of
stringers from inside before tank skin installed.
3. Cut access hole in bottom wing skin between stn 13 and 14. (fuel tank
typical) This will allow access to fuel line fitting.
4. Leave end rib stn 17 in place.
5. Replace Stn 14/16 ribs with W-173
6. Replace Stn 15 rib with W-516
7. Replace main spar extension rivets with tank rivets from stn 14 to
stn 16.
Install plates with pro-seal over main spar lightening holes at stn 14
and stn 16
8. Replace rear spar rivets with tank rivets from stn 14 to stn 16.
9. Using drill attached to long tube drill appropriate hole through all
ribs so as to exit aft of main tank outlet between rear spar just aft of
last stringer. Pre-drilling Stn 14/15/16 will aid in guiding. Where
access available have a helper ensure proper drill location at rib
stations. Mark and use short drill where possible.
10. Install W-160 flange on stn 14 and Stn 16. (Stn 16 will be plugged
but will allow straight insertion of fuel tubing from tip through wing
if replacement required)
11. Install Nylon gussets in all assessable carry through ribs stn 7-13
12. Drill out two W-159 flanges to OD of Alum Fuel tubing.
13. Install W-159 Flanges on Stn 6 and Stn 1
Alum fuel tubing will be pro-sealed to these flanges mounted on main
tank ribs and tip fuel will be routed through main tank. Ensure Alum
fuel tubing extends 1" beyond stn 1 flange so as to allow rubber tubing
to be clamped over.
14. Install top tank skin from stn 14 to stn 17; use existing holes in
stringers, spars and stn 14 and stn 17 rib. Drill additional rivet holes
between existing holes along rib flanges at stn 14. (Caution do not
drill between flange and stringers) Drill stn 15, 16 flange with same
spacing as stn 14. Add an extra row of holes along wing skin overlap
with same spacing. Tank skin will be over wing skin and under leading
edge skin.
15. Remove and cutback bottom wing skin to outside edge (tip side) of
4th end rib (stn 14).
Allow overlap sufficient for extra row of rivets. Wing skin will be
between Stn 14, W-173 rib and tank skin to allow easier sealing of
stringers before tank skin installed.
16. Install bottom tank skin from stn 14 to stn 17; use existing holes
in stringers, spars and stn 14 and stn 17 rib. Drill additional rivet
holes between existing holes along rib flanges at 14. (Caution do not
drill between flange and stringers) Drill stn 15, 16 flange with same
spacing as stn 14. Add an extra row of holes along wing skin overlap
with same spacing. Tank skin will be over wing skin and under leading
edge skin.
17. Fabricate access holes on bottom tank skin
18. Fabricate flanges to go around top and bottom stringers where they
pass through stn 14 rib.
19. Install flush fuel cap in top skin outer fuel bay. Tip tanks will be
individually vented through inverted 'J' pipe in cap.
20. Install fuel probe in stn 16 rib.
21. Debur all holes, pro-seal and rivet ribs, bottom skin, flanges and
leading edge skin clecoing main skin to stn 14 rib.
22. Install top skin with leading edge on top and tank access covers to
bottom tank skin.
23. Insert Alum fuel tube through wing. Insert screen filter in stn 14,
W-160 and join to alum tubing with nylon nipple and rubber fuel hose
with clamps. Ensure alum tubing well pro-sealed at stn 6 and stn 1 W-159
flanges. Alum tube will protrude 1" at root to allow attachment of
rubber tubing. Insert plug in stn 16 flange.
24. Pressure test.

Questions:
1. Is this the best location, 2nd and 3rd outer bays?
Other options are last two or all three.
2. Is this an acceptable way to route the fuel?
3. Does the plumbing solution sound feasible?
4. Will gravity feed work from the tips
5. Is the current rivet spacing acceptable with 1/8" rivets?
Should I add an extra rivet between existing ones along the rib flanges
and main spar.
6. Thickness of tank skins .032 or .040?

--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

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Warren T. Montgomery · Post by **Warren T. Montgomery** » Fri Feb 17, 2012 9:21 pm

Thanks for your comments Wayne.

If the attachment I sent was view able, I actually plan to bypass the
main tank and have a separate feed for the outer tank although the line
will route through the main tank. The mains will be vented as per
original design. I'd only feed from the outers in cruise. Regarding fuel
imbalance, that's probably a good reason to limit to 20 gal per outer as
to 30 gal.

2. Is this an acceptable way to route the fuel?
KISS - KEEP IT SIMPLE STUPID AND THAT SEEMS TO BE IT
3. Does the plumbing solution sound feasible?
YOU WILL NEED TO MAKE SURE THAT YOUR MAIN TANKS CAPS ARE ABSOLUTELY
LEAK/VENT PROOF AND GET RID OF ANY VENT TUBES ON THEM OR THE CABIN ROOF,
USING YOUR TIP TANK VENT TUBES AS YOUR ONLY VENTING ON EACH WINGS FUEL
SYSTEM!

--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

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Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Fri Feb 17, 2012 9:21 pm

Missed that fuel line going through the entire tank and to it's own valve in
the cabin! That makes a lot more sense to be able to control the tip tanks
and that way they will not fill from the main in a wing down parking spot,
when you don't want any fuel in them!

Wayne

----- Original Message -----
From: "Warren T. Montgomery" <monty@emirates.net.ae>
To: <murphy-rebel@dcsol.com>
Sent: Monday, October 29, 2001 2:32 AM
Subject: Re: SR3500 TIP TANK RETROFIT (PROPOSED)

Thanks for your comments Wayne.

If the attachment I sent was view able, I actually plan to bypass the
main tank and have a separate feed for the outer tank although the line
will route through the main tank. The mains will be vented as per
original design. I'd only feed from the outers in cruise. Regarding fuel
imbalance, that's probably a good reason to limit to 20 gal per outer as
to 30 gal.

2. Is this an acceptable way to route the fuel?
KISS - KEEP IT SIMPLE STUPID AND THAT SEEMS TO BE IT
3. Does the plumbing solution sound feasible?
YOU WILL NEED TO MAKE SURE THAT YOUR MAIN TANKS CAPS ARE ABSOLUTELY
LEAK/VENT PROOF AND GET RID OF ANY VENT TUBES ON THEM OR THE CABIN ROOF,
USING YOUR TIP TANK VENT TUBES AS YOUR ONLY VENTING ON EACH WINGS FUEL
SYSTEM!
--
Warren T. Montgomery
<monty@emirates.net.ae>
Dubai, United Arab Emirates

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Al & Deb Paxhia · Post by **Al & Deb Paxhia** » Fri Feb 17, 2012 9:21 pm

Warren,
I like the idea of more fuel, but have trouble with any tank system
involving extra valves. When I fly the Beaver I spend more time managing
fuel than I would like. Tips have 21.5 gal each and sometimes they don't
drain evenly or I forget to select both after starting the transfer. Landing
with tip fuel is not recommended in the Beaver unless the water conditions
are smooth, heavy chop can damage the spar, don't know if your planning
floats. I've not had to land with a heavy wing, always able to transfer
prior to landing, but flying with a fuel imbalance and a load has not been
fun.
I would go after the next two bays. On the first Murphy SR they did not
proseal between the spars. I was told that the area was cleaned with scotch
brite and a fillet of proseal was applied between the skins and spar.
Keep us posted on how you go.
Al
SR#26
----- Original Message -----
From: "Warren T. Montgomery" <monty@emirates.net.ae>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, October 28, 2001 11:32 PM
Subject: Re: SR3500 TIP TANK RETROFIT (PROPOSED)

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