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  #31  
Old 03-15-2005, 09:12 PM
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Girrrls,

I've been reading with relish, your chapters on your fuel system and retracts. Please finish your chapters on the strakes.

Have you estimated the fuel capacity of the sump tank yet? Do you have a source for the flow sensors yet? Is the output a frequency?

I like sensors, and a lot of them. I will be using an automotive controller with my own strategy. I'll have lots of inputs and outputs available.

I don't like the idea of a transfer pump. I'd rather draw from both tanks at the same time, into the sump. But, if you are going to have the transfer pump, I'd put a monitor on the output driver or a flow meter on the line to verify it's properly working.

We (actually dust, Dave, and Thane) put 1.5 gallon fuel blisters on the two planes here. I'll do the same and empty them into the sump. The question is; is it gravity feed, or will the fuel pump will also draw, or suck fuel out of the blisters and thus the main tanks? If the return is pumped back into the sump, it may be a moot issue, but returning fuel to the sump may introduce air into the sump, which I don't want.
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  #32  
Old 03-15-2005, 09:44 PM
Brian Gamm Brian Gamm is offline
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What is the downside of draining the strakes into a header and having a on/off valve before the fuel pumps? Fuel management = on or off.

Brian
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  #33  
Old 03-16-2005, 04:03 AM
HM Andersen HM Andersen is offline
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Cozy girrrls fuel setup looks nice to me.But I do not understand the purpose of the transferpump. You have enough information on the fuelmanagement issue to leave out the transfer pump and just make a simple connection from strake sump to strake sump.This should be with a pipedimension not to big in order to avoid to much fueltransition during uncoordinated turnes.
To keep the fuel level equal in the tanks, the vents could be connected to make sure that there will be no diff.pressure
The left strake being primary due to left patterns!!!!!
Dont the BMA autopilot make coordinated turns.
HM
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  #34  
Old 03-16-2005, 08:06 AM
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Quote:
What is the downside of draining the strakes into a header and having a on/off valve before the fuel pumps?
One down side to this system is "single point of failure". Once the fuel flow goes through one pipe after the fuel valve you have one system that HAS to work. Any problem with that system - contamination, blockage, leak etc. and you have no fuel to the engine. Fuel injection introduces the need for returned fuel. If you send it to the header tank then there's a potential for build-up of air in the header as Paul Conner discovered. Venting of the header becomes critical and it must be in a cool place. Ideally the pumps need to be somewhere cool and low too.

My system has it's drawbacks too, but I plan to keep it because of the pump / filter / fuel line redundancy. I may add a transfer capability from left to right. The advantage of the transfer pump is the ability to ensure that there is no inaccessible fuel. There's a discussion on this in Marc's list right now. Some say that a few gallons can be thrown forward away from the main tank sump during descent. I believe it's possible to suffer fuel starvation with a total of 4 or 5 gallons on board if you're nose is down in a long descent.

With a transfer capability you can pump the last 5 gallons of fuel from one tank into the other during cruise (level). Knowing what you have where is a nice feeling.
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  #35  
Old 03-16-2005, 10:00 AM
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Quote:
Originally Posted by John Slade
The advantage of the transfer pump is the ability to ensure that there is no inaccessible fuel. There's a discussion on this in Marc's list right now. Some say that a few gallons can be thrown forward away from the main tank sump during descent. I believe it's possible to suffer fuel starvation with a total of 4 or 5 gallons on board if you're nose is down in a long descent.
My buddy the airplane accident investigator, 7000 hour ga pilot learned and used a simple fuel management system on long cross countries.

Emptied the low tank until the engine shut off and restarted on the tank that now had ALL of his fuel.

I also don't like the clog issue, there have been a few reports over the years of tanks being clogged at the screen door screen that is floxed in the bottom of each tank, before the sump. these clogs typically occur in the first period of flight testing from crapola that breaks off from the corners inside the tanks.

For that reason, we changed the shape of the sump so that we could insert 3/8 inch x 3 inch finger strainers.

after the first 10 or so hours of flight and at the annual, they will be pulled and cleaned. Tweek
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  #36  
Old 03-16-2005, 10:12 AM
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Quote:
Emptied the low tank until the engine shut off and restarted on the tank that now had ALL of his fuel.
You can't be serious! Maybe you misunderstood him. Are you sure an airplane accident investigator and a 7000 hour ga pilot is recommending SHUTTING DOWN THE ENGINE on every cross country. If so, I don't see that as good advice.
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  #37  
Old 03-16-2005, 10:19 AM
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Quote:
Originally Posted by Dust
am i reading this right - fuel has to be pumped to the other tank to be used? if so - you WILL forget the pump on and pump overboard.
No, you are reading that wrong, or only looking at the pretty pictures and not reading the text, I suspect you used to read a lot of girly magazines
The only way you can have continuous pump flow would be if you were to hold the button down.
Quote:
Originally Posted by Dust
The fuel returns have to be to the top of a tank - the one pumping from, with no back pressure, has been know to stop flow. just looked at the flow further- the return line goes into the sump - back pressure - not good
The return line does go to the top of a tank, the main sump tank. This is where the fuel is being pulled from in the first place. Capacity estimated at 4.5 gallons. Agreed there may be some back pressure of the gravity feed strakes above it.
[quote=Dust]
What is the ball valve for?[quote=Dust]
It is a service shut off.
Quote:
Originally Posted by Dust
how big are the lines from the tank to the tank, tank to sump return line to sump
all lines are 3/8"
Quote:
Originally Posted by Dust
I don't think you want to here more from me
Only if you don't know what you are talking about. So far all valid questions I think.
Here is the issue with returning fuel to the strake (when you have a main sump), if you are down to your last 5-10 gallons of fuel the EFI pumps can pump it into the strake and deplete the sump very quickly if you were in a descending attitude.
We put a 3/8" return line into the right strake in case we thought of a different way to do this.
...Chrissi
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  #38  
Old 03-16-2005, 10:38 AM
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first of all, no, not on every cross country, only on very, very, long ones.

I have 30 gallons per tank, will burn about 10 gph, so 1 hour per tank, twice, 4 hours, empty tank (5 hours) nose down restart engine - switch to tank that now has all fuel

I doubt i'll ever go that far, but if i do, that will be the procedure.
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  #39  
Old 03-16-2005, 12:34 PM
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Quote:
Here is the issue with returning fuel to the strake (when you have a main sump), if you are down to your last 5-10 gallons of fuel the EFI pumps can pump it into the strake and deplete the sump very quickly if you were in a descending attitude.
That is what I originally thought as well. But after Paul Conner was having trouble with his vapor lock in his sump tank during his first 40 hours, I thought that it would be better to run the return lines through the strakes to give the EFI return fuel a chance to cool off.

Paul vented his sump and made the EFI return to the strakes (IIRC) at the same time. I don't know if venting alone would have solved the problem.

Anyway. I don't see a problem with routing the EFI through the strakes to cool down and pointing the output into the strake mini-sump. Maybe the return could be routed through the tank for cooling and then back to the sump. I dunno. I just want to simplify fuel management... no transfer pumps, no tank selector valves... personal preference I guess.
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  #40  
Old 03-16-2005, 01:11 PM
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I like removable finger strainers at the sump for each tank, you have two pumps, but, only one transfer pump with complex controls.

I really do not like all the complexity of the fuel transfer system, i would put 1/2 inch or larger line to the sump from both tanks, insuring good gravity/suction flow

i have been told many many times that back pressure from the return line can stop fuel flow, i really think it must be returned to the top of the tank with little or no back pressure capable of occurring. I KNOW it doesn't make sense that the back pressure can make that big a difference, but it can.

now the next question is how to return the fuel whence it came?? Maybe MT system will work, i just don't trust it.

Pumping fuel around causes problems, someone here on this forum can verify that.
Back preasure on fuel injection causes problems
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  #41  
Old 03-16-2005, 02:32 PM
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Quote:
Originally Posted by Cozy Girrrl
Here is the issue with returning fuel to the strake (when you have a main sump), if you are down to your last 5-10 gallons of fuel the EFI pumps can pump it into the strake and deplete the sump very quickly if you were in a descending attitude.
...Chrissi
The reason my buddy runs the tanks out of fuel is that he has been to many, many, many accidents where there were multiple tanks with 3, 4, 5, gallons left in each tank and the plane crashed on final because of fuel starvation. - he takes the engines out of them, removes the bent up prop, checks for water with water finding paste then to a local A&P shop - adds fuel and whallah - they start

4 tanks, 3 with 3 gallons = 9 gallons, etc, etc. He has never had an engine fail to restart. These engines are dependable, no starter even needed to restart, just nose down for a moment to start er up again.
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dust

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  #42  
Old 03-16-2005, 09:23 PM
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Quote from web site

"In the AUTO position a comparator with hysteresis will monitor the right and left capacitive fuel probes. When the level in the right tank is below the level of the left tank it will transfer fuel from left to right. An annunciater light will indicate fuel transfers in process."

Fuel probs - capacitance - i think these work different on leaded and non leaded fuel - are you going to stick to one or the other?
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  #43  
Old 03-22-2005, 11:20 AM
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Quote:
Originally Posted by Dust
I guess the buble vent can stop fuel flow problems because of the venting? This pump back would probably be under a gallon per hour? - if so, just back to one tank should be fine - fuel injection pumps serious quanties back to the tanks

Yes, i have a double throw valve - where it comes from - it goes back to.

The is quite of bit of talk around the forum of using a t return system, interconnecting the tanks or just plane always pumping from a "supply" tank and moving fuel to it as needed from the other tank.

I am a PIA on this subject, but thought the rutan designed voyager and GLOBALFLYER were prime examples of what can go wrong - everything ended fine, as we all know, but, still the same.
According to this site:
http://www.yawpower.com/renespic.html
the Renesis standard fuel injection system is "return-less", and then these folks modify it for racing use.
But you probably know more about these things. I think I'll stick to my diesels.
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  #44  
Old 03-22-2005, 02:07 PM
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Most automotive have gone "return-less" pressure sensor regulates fuel pump to keep fuel pressure correct. I have looked at these fuel rails (see "show and tell") and one thing that they appear to do is drastically increase the size of the rail diameter.

Doing this, going return-less, is just the next level up on the electronic complexity schedule, aviation will probably see it in 20 or 25 years, would not want to move to quickly now would we
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  #45  
Old 09-02-2005, 06:36 AM
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Quote:
Originally Posted by Dust
For that reason, we changed the shape of the sump so that we could insert 3/8 inch x 3 inch finger strainers.

after the first 10 or so hours of flight and at the annual, they will be pulled and cleaned. Tweek
i got the 3 " ones from wall mart(all stainless), not good ? plz elaborate
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