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Plumbing in some extra fuel capacity

 
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ogdenk



Joined: 05 Feb 2007
Posts: 40
Location: Syracuse, NY

PostPosted: Mon Mar 04, 2019 2:05 pm    Post subject: Plumbing in some extra fuel capacity Reply with quote

All,
I would like to build in some fuel plumbing to allow for optional extra capacity, perhaps using tanks like these:
https://www.turtlepac.com/products/collapsible-aircraft-ferry-tanks/
A 25 or 33 gallon tank would add significant range for the occasional long distance flight or allow for improved range at high speed cruise.
I am trying to not design in a weak point in my fuel system though, as it is so critical and there have been some accidents related to fuel system issues.
One idea is to add a 'T' AN fitting to the fuel line under the copilot seat, that would then have an aluminum line run along the right side of the cockpit to the right rear seat, and would normally hide under the side cover next to that seat. I would put a shutoff valve there that would normally be closed, and on the other side of the valve put an appropriate fitting that could attach to the ferry tank that could be strapped to the seat. To use, take the side cover off, connect the ferry tank, bleed the air out of the system, then during flight fuel could be pumped into the right tank while running the engine on the left tank (or maybe the right tank, might not matter). When the ferry tank is nearly empty, shut off the pump and close the valve.
One concern is that the extension plumbing would have air in it until it is used, and air bubbles could conceivably find their way into the main line. The extension line could be filled with fuel too, but that would sit there stagnant for possibly long periods of time (is that an issue?). I had also considered adding a check valve to prevent fuel from flowing from the main tank side back into the extension plumbing (in case of a leak in the extension), but that would be generally uphill so gravity would be on your side there.
Another possibility is to plumb directly to the tank, but the tank is finished and I'm not sure I'd like to poke any more holes in it, which would probably leave some aluminum bits inside to boot. I can't just plumb into the vent line since there is no way to let the displaced air out of the tank when pumping in fuel through that line.
I don't want to start a debate about the RV-10 range etc, just want to hear thoughts on what's likely to work without adding too much extra complexity and risk.
Thanks for your thoughts!
Kent Ogden
#40710


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carl.froehlich(at)verizon
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PostPosted: Mon Mar 04, 2019 2:49 pm    Post subject: Plumbing in some extra fuel capacity Reply with quote

Interesting timing, I just discussed this with another RV-10 builder earlier today. Some thoughts:
- There are commercial wingtip tanks that add 15 gallons or so of fuel, but I ruled this option out as it added a lot of complexity, weight and has a huge price tag. Add to that the obvious “Van’s did not consider this in the wing design” aspect.
- My neighbor at Dogwood is the guy that flew his specialty build Lancair IV over both the North and South Poles. He had a total of seven fuel tanks added to the plane (380 or so gallons). Five of the tanks he custom made using carbon fiber board to fit all the contours of the plane, the aft large one strong enough to support the one large and one small badder tanks like that you reference. He had a very straightforward approach to fuel plumbing to mitigate risk of something going wrong - yielding a forced landing in the Arctic or Antarctic. He had a single, simple 90 degree isolation valve for each tank going to a Facet pump. The transferred fuel only goes to the 10 gallon header tank that has a clear sight glass for fuel level. He transferred fuel every hour or so like Limburg did in the Sprit of St. Louis.
Stealing from the above and ruling out the header tank or extra wing tanks leads to a 20+ gallon ferry tank that gets mounted in place of one or both rear seats. The ferry tank being one of many composite racing tank options (I would not consider the badder tank for this application). I have this set up for my new RV-8 project, the tank being fed into a T on the right tank fuel line before it goes to the fuel valve. The T will be normally capped when not being used for this connection. Ferry tank vent will go to the wing root area or aft to exit the bottom of the fuselage. Operation will be to burn 20 or so gallons out of the right tank, fly on the left tank, open the ferry tank isolation valve and turn on the Facet pump (with check valve) to transfer fuel to the right tank. My Lancair buddy tells me the change in noise from the Facet pump when the ferry tank is dry is obvious - but you will also get the right tank fuel sender increasing as a positive indication.
My thinking is that 99+% of the time having more than the five hours of gas will not be needed, so the ferry tank will spend most of it’s life on the shelf in the hangar. Make it easy to get in and out of the plane.
If you want to get fancy you can build a couple of tanks out of carbon that exactly fits the rear seat floor area, moving the ferry tank weigh a little more forward toward the center of gravity.
No other changes to the standard fuel system other than this T is done. While I did build the right tank with an extra fuel fitting for this purpose I decided a T on the inside of the fuselage line was more practical.
For the RV-10 you lose one or both back seats depending on ferry tank size, but the added weight of the fuel translates to not carrying four people.
Carl
On Mar 4, 2019, at 4:03 PM, Kent Ogden <ogdenk(at)upstate.edu (ogdenk(at)upstate.edu)> wrote:
Quote:
All,
I would like to build in some fuel plumbing to allow for optional extra capacity, perhaps using tanks like these:
https://www.turtlepac.com/products/collapsible-aircraft-ferry-tanks/
A 25 or 33 gallon tank would add significant range for the occasional long distance flight or allow for improved range at high speed cruise.
I am trying to not design in a weak point in my fuel system though, as it is so critical and there have been some accidents related to fuel system issues.
One idea is to add a 'T' AN fitting to the fuel line under the copilot seat, that would then have an aluminum line run along the right side of the cockpit to the right rear seat, and would normally hide under the side cover next to that seat. I would put a shutoff valve there that would normally be closed, and on the other side of the valve put an appropriate fitting that could attach to the ferry tank that could be strapped to the seat. To use, take the side cover off, connect the ferry tank, bleed the air out of the system, then during flight fuel could be pumped into the right tank while running the engine on the left tank (or maybe the right tank, might not matter). When the ferry tank is nearly empty, shut off the pump and close the valve.
One concern is that the extension plumbing would have air in it until it is used, and air bubbles could conceivably find their way into the main line. The extension line could be filled with fuel too, but that would sit there stagnant for possibly long periods of time (is that an issue?). I had also considered adding a check valve to prevent fuel from flowing from the main tank side back into the extension plumbing (in case of a leak in the extension), but that would be generally uphill so gravity would be on your side there.
Another possibility is to plumb directly to the tank, but the tank is finished and I'm not sure I'd like to poke any more holes in it, which would probably leave some aluminum bits inside to boot. I can't just plumb into the vent line since there is no way to let the displaced air out of the tank when pumping in fuel through that line.
I don't want to start a debate about the RV-10 range etc, just want to hear thoughts on what's likely to work without adding too much extra complexity and risk.
Thanks for your thoughts!
Kent Ogden
#40710





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Kellym



Joined: 10 Jan 2006
Posts: 1583
Location: Sun Lakes AZ

PostPosted: Mon Mar 04, 2019 6:29 pm    Post subject: Plumbing in some extra fuel capacity Reply with quote

A few thoughts as to extra tankage. Traditional methods have been to
either add to the wing capacity, or put an additional tank in the
baggage compartment. One advantage of the baggage compartment is that
the weight can be determined with great accuracy, and it is a safer,
easier place to add the fuel. I know that for most loading up to 150 lbs
works for c.g. Apparently Vans later clarified that the limit was
supposed to be 100 lbs. Easy enough to do a tank for 100 lbs...allow
5-10 lbs for the tankage, with 90 lbs or 15 gal fuel. 20 gal baggage
compartment tanks are very common in other aircraft and allow adjusting
fuel for rearmost allowable cg for max speed. Much more than 20 gal is
going to suggest need for baffling and puncture resistance, as well as
cg issues. It may be possible to do a 15 gal in baggage and 15 gal in
rear seat area, if you want to be assured 6 hr plus minimal reserves.

Lets put a little reality into the range needs. You can do 170-175 kts
on 13 gph at any altitude that you can achieve that fuel flow while
LOP..generally it will be below 8500 and higher than normal cruise rpm.
You can do 160-165 on about 11 gph LOP, and 150-155 on 10 gph.
Take the later, which will get you 5 hours with one hour reserve, while
going 750 nm, on stock fuel. Go fast mode gets you 4 hrs with 8 gal
reserve..bare minimum in my book. That gets you 680 nm. An extra 15 gal
would get you 850 nm with 10 gal reserve, in 5 hours.
Now if you want to go a bit faster, you can operate ROP with about 1.5
gph more fuel flow, and may close to 180 kts. You would need the extra
15 gal tank to go 4 hours with 15 gal reserve, giving you a 720 nm range.
Oh, I would suggest you need relief tube or equivalent to consistently
go 4-5 hours non-stop without having issues with dehydration.
In summary, you can easily get 750 nm range with stock tanks by slowing
down a little. Sticking to LOP and adding 15 gal tank will get you up
to about 850 nm range without slowing noticeably, or over 950 by slowing
to 150kts. That would require sitting for 6.5 hours without relief.
You can do two comfortable legs of 3 to 3.5 hours at 160 for reasonable
speed and economy to cover 1000nm. With 30 min for refuel, relief,
snacks, that is 7 hours, vs 6.5 to do it non-stop with additional tank.
Not arguing that one answer is better for one method over the other,
just trying to quantify the alternatives. I think going beyond 6.5 hours
at one sitting is moving into the territory of long range ferry flights
that use special gear and techniques, where water leaves no options.

What ever you do, you want to consider failure analysis for your
plumbing. If the plan is to pump all the aux fuel into one tank, your
fuel selector becomes critical, with 60% or more of your fuel being
dependent on being able to switch to that tank. Which side of the plane
do you want that extra 100-200 lbs of fuel, for lateral trim?
What if transfer pump fails? You probably recall the Cirrus that had to
ditch about 100nm from Hawaii, because something in the transfer process
failed and wasn't detected until beyond turn back distance.
Going above a wide spread fog layer might as well be the same as over ocean.
Sure, I would like an extra 15 to 20 gal capacity, but I haven't found
not having it to be particularly limiting.

On 3/4/2019 3:48 PM, Carl Froehlich wrote:
Quote:
Interesting timing, I just discussed this with another RV-10 builder
earlier today.  Some thoughts:

Quote:
My thinking is that 99+% of the time having more than the five hours of
gas will not be needed, so the ferry tank will spend most of it’s life
on the shelf in the hangar.  Make it easy to get in and out of the plane.

For the RV-10 you lose one or both back seats depending on ferry tank
size, but the added weight of the fuel translates to not carrying four
people.

Carl

On Mar 4, 2019, at 4:03 PM, Kent Ogden <ogdenk(at)upstate.edu
<mailto:ogdenk(at)upstate.edu>> wrote:


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d.j.goneflyin(at)earthlin
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PostPosted: Tue Mar 05, 2019 8:40 am    Post subject: Plumbing in some extra fuel capacity Reply with quote

How about having your injectors matched flowed to save around 2 gallons per hour. Your temp will go down and your range will go up. You will not change your load capacity.

Sent from my iPad

Quote:
On Mar 4, 2019, at 9:27 PM, Kelly McMullen <kellym(at)aviating.com> wrote:



A few thoughts as to extra tankage. Traditional methods have been to either add to the wing capacity, or put an additional tank in the baggage compartment. One advantage of the baggage compartment is that the weight can be determined with great accuracy, and it is a safer, easier place to add the fuel. I know that for most loading up to 150 lbs works for c.g. Apparently Vans later clarified that the limit was supposed to be 100 lbs. Easy enough to do a tank for 100 lbs...allow 5-10 lbs for the tankage, with 90 lbs or 15 gal fuel. 20 gal baggage compartment tanks are very common in other aircraft and allow adjusting fuel for rearmost allowable cg for max speed. Much more than 20 gal is going to suggest need for baffling and puncture resistance, as well as cg issues. It may be possible to do a 15 gal in baggage and 15 gal in rear seat area, if you want to be assured 6 hr plus minimal reserves.

Lets put a little reality into the range needs. You can do 170-175 kts on 13 gph at any altitude that you can achieve that fuel flow while LOP..generally it will be below 8500 and higher than normal cruise rpm.
You can do 160-165 on about 11 gph LOP, and 150-155 on 10 gph.
Take the later, which will get you 5 hours with one hour reserve, while going 750 nm, on stock fuel. Go fast mode gets you 4 hrs with 8 gal reserve..bare minimum in my book. That gets you 680 nm. An extra 15 gal would get you 850 nm with 10 gal reserve, in 5 hours.
Now if you want to go a bit faster, you can operate ROP with about 1.5 gph more fuel flow, and may close to 180 kts. You would need the extra 15 gal tank to go 4 hours with 15 gal reserve, giving you a 720 nm range.
Oh, I would suggest you need relief tube or equivalent to consistently go 4-5 hours non-stop without having issues with dehydration.
In summary, you can easily get 750 nm range with stock tanks by slowing down a little. Sticking to LOP and adding 15 gal tank will get you up to about 850 nm range without slowing noticeably, or over 950 by slowing to 150kts. That would require sitting for 6.5 hours without relief.
You can do two comfortable legs of 3 to 3.5 hours at 160 for reasonable speed and economy to cover 1000nm. With 30 min for refuel, relief, snacks, that is 7 hours, vs 6.5 to do it non-stop with additional tank.
Not arguing that one answer is better for one method over the other, just trying to quantify the alternatives. I think going beyond 6.5 hours at one sitting is moving into the territory of long range ferry flights that use special gear and techniques, where water leaves no options.

What ever you do, you want to consider failure analysis for your plumbing. If the plan is to pump all the aux fuel into one tank, your fuel selector becomes critical, with 60% or more of your fuel being dependent on being able to switch to that tank. Which side of the plane do you want that extra 100-200 lbs of fuel, for lateral trim?
What if transfer pump fails? You probably recall the Cirrus that had to ditch about 100nm from Hawaii, because something in the transfer process failed and wasn't detected until beyond turn back distance.
Going above a wide spread fog layer might as well be the same as over ocean.
Sure, I would like an extra 15 to 20 gal capacity, but I haven't found not having it to be particularly limiting.

> On 3/4/2019 3:48 PM, Carl Froehlich wrote:
> Interesting timing, I just discussed this with another RV-10 builder earlier today. Some thoughts:

> My thinking is that 99+% of the time having more than the five hours of gas will not be needed, so the ferry tank will spend most of it’s life on the shelf in the hangar. Make it easy to get in and out of the plane.
>
> For the RV-10 you lose one or both back seats depending on ferry tank size, but the added weight of the fuel translates to not carrying four people.
> Carl
> On Mar 4, 2019, at 4:03 PM, Kent Ogden <ogdenk(at)upstate.edu <mailto:ogdenk(at)upstate.edu>> wrote:





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Kellym



Joined: 10 Jan 2006
Posts: 1583
Location: Sun Lakes AZ

PostPosted: Tue Mar 05, 2019 1:22 pm    Post subject: Plumbing in some extra fuel capacity Reply with quote

You don't want to flow match the injectors per se. You want the
cylinders to all peak at nearly the same mixture. Similar but not the
same. You still won't save any fuel unless you operate LOP, which above
altitude where you can achieve desired power, will cost you a little
speed. It is also the lean of peak operation that lets the cylinders run
cooler. Matching mixture is what lets you run LOP.

On 3/5/2019 9:38 AM, David Jones wrote:
Quote:


How about having your injectors matched flowed to save around 2 gallons per hour. Your temp will go down and your range will go up. You will not change your load capacity.

Sent from my iPad



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A&P/IA, EAA Tech Counselor # 5286
KCHD
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