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08-29-2018, 11:03 AM
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Join Date: Nov 2010
Location: ____
Posts: 829
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[quote=BMC_Dave;1284442]Huh, that's interesting thanks for the link!
Here is a much deeper look at the history and some of the early research and aviation user data.
https://youtu.be/1PA70pN6zPM?t=4m8s
A bit long but a lot of good information.
Last edited by F1R : 08-29-2018 at 11:06 AM.
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08-30-2018, 01:36 PM
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Join Date: Jul 2018
Location: WNC
Posts: 246
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Quote:
Originally Posted by rv6ejguy
If an in tank pump fails, you can't access the fuel in that tank. The current pump life is excellent and vapor lock hasn't been an issue if proper location and plumbing practices are followed.
We strongly recommend that people use what's been proven over a half million flight hours with regards to the EFI fuel system if you don't want surprises or to be on a test program to validate a new design.
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You could use a venturi-style cross-draw setup in the event of a pump failure in one wing. This setup has been standard practice in automotive applications that have the fuel tank straddle the driveshaft hump for some 20 years now.
It would make plumbing slightly more difficult and it would be a lot harder to change a pump in the event of a failure but no more difficult than a bad fuel sending unit.
And yeah I get the "don't rock the boat" comment. I was just curious if anyone had tried dual in-tank pumps in an aircraft before.
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08-30-2018, 01:57 PM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
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Quote:
Originally Posted by jacoby
And yeah I get the "don't rock the boat" comment. I was just curious if anyone had tried dual in-tank pumps in an aircraft before.
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Why? It's not needed. Dual parallel pumps and a simple duplex valve accomplish the same thing with less complexity and cost, and preserve the redundancy of dual pumps.
__________________
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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08-30-2018, 04:27 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by jacoby
You could use a venturi-style cross-draw setup in the event of a pump failure in one wing. This setup has been standard practice in automotive applications that have the fuel tank straddle the driveshaft hump for some 20 years now.
It would make plumbing slightly more difficult and it would be a lot harder to change a pump in the event of a failure but no more difficult than a bad fuel sending unit.
And yeah I get the "don't rock the boat" comment. I was just curious if anyone had tried dual in-tank pumps in an aircraft before.
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I'm not understanding what you're describing here. If you have one pump in each tank and the pump fails, you can't get at the rest of the fuel in that tank.
In aviation, once we have demonstrated the reliability of a layout or system, we repeat that without deviation to get the same results over and over.
If you want to put pumps in the tanks, you could. I've just outlined the main reason it's not done. We have a proven, very reliable layout now with few drawbacks. I'm not sure why it would be a good idea to change that. What would be the advantage over the existing layout?
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08-30-2018, 07:49 PM
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Join Date: Jul 2018
Location: WNC
Posts: 246
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Quote:
Originally Posted by rv6ejguy
I'm not understanding what you're describing here. If you have one pump in each tank and the pump fails, you can't get at the rest of the fuel in that tank.
In aviation, once we have demonstrated the reliability of a layout or system, we repeat that without deviation to get the same results over and over.
If you want to put pumps in the tanks, you could. I've just outlined the main reason it's not done. We have a proven, very reliable layout now with few drawbacks. I'm not sure why it would be a good idea to change that. What would be the advantage over the existing layout?
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You use the velocity of the fuel to create suction to basically create four pumps out of two. In an EFI setup you would put it on the return line since you don't want any air in the event of the other side running out of fuel. When both pumps are running they're cross feeding at the "same" rate (you would probably size the restrictor to be slightly larger on one side so you don't feed fuel out the vent when running on both). If one were to die the other would pick up the slack and cross feed the dead side into the active side.
And I understand the current setup is quite reliable. I am not at all questioning that. However in-tank pumps live a happier/cooler/quieter life and you don't have to worry about vapor pressure at all and the packaging is a bit simpler since most of the bulk lives in the tank. It's more of a question of "has it been done" and "why not if not?".
Here is a random image I found that describes the setup. Just imagine each side of the saddle is a wing:

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08-30-2018, 08:05 PM
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Join Date: Dec 2011
Location: Alpharetta, Ga
Posts: 212
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Motive Flow
Same as motive flow? Motive flow is used in fuel tanks of most biz jets I'm familiar with.
Here's a basic description I found.
https://aviation.stackexchange.com/q...raulic-systems
Last edited by Mudfly : 08-30-2018 at 08:08 PM.
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08-30-2018, 08:21 PM
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Join Date: Jul 2018
Location: WNC
Posts: 246
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Quote:
Originally Posted by Mudfly
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Yes. You'd use the motive flow to move fuel from the dead tank to the active tank in the event of a pump failure. In a dual-pump situation both pumps would be moving fuel equally and would cancel each other out (or you would have pressure valves that prevent the cross-flow in equilibrium).
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08-31-2018, 04:54 AM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by jacoby
Yes. You'd use the motive flow to move fuel from the dead tank to the active tank in the event of a pump failure. In a dual-pump situation both pumps would be moving fuel equally and would cancel each other out (or you would have pressure valves that prevent the cross-flow in equilibrium).
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I'm familiar with the widespread use of jet pumps in jet aircraft. With the present system, we usually run on one pump at a time and there are less components and plumbing so less weight and complexity.
This being experimental aviation, nothing is stopping you from implementing your ideas on your aircraft if you see some advantages there.
I just don't see any advantages with this layout.
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08-31-2018, 05:50 AM
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Join Date: Jan 2005
Location: NC25
Posts: 3,507
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SHELL?S FUEL UNDER STUDY
Most recent AOPA article on 100LL replacement. EAA had a similar article.
__________________
Gary A. Sobek
NC25 RV-6 Flying
3,400+ hours
Where is N157GS
Building RV-8 S/N: 80012
To most people, the sky is the limit.
To those who love aviation, the sky is home.
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08-31-2018, 06:26 AM
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Join Date: Dec 2011
Location: Alpharetta, Ga
Posts: 212
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Quote:
Originally Posted by RV10inOz
Do not stress.
The PAFI process was fatally flawed right from the beginning. Recently proven.
There is a certification project almost complete and has taken time due funding and apathy of the market to get behind it, but is literally "months" or "weeks" from a major milestone.
G100UL is the likely fuel you will have when the time comes. So relax. Build on.
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Quote:
Originally Posted by RV6_flyer
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Thanks Gary. Interesting info. Sounds like discussion @ 5 min mark on
AOPA video https://www.aopa.org/news-and-media/...n=180830epilot could be related to what RV10inOz brought up in his post.
Last edited by Mudfly : 08-31-2018 at 06:34 AM.
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