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Wendell , I really don't know how much heat the fuel picks
up. Depends on a number of factors.
However, a low pressure (4-6 psi) boost pump, increases
the pressure in the header tank and suppresses (in my case) any tendency of the
fuel to percolate. I used the one Van recommends for the RV series - a
facet fuel pump with 37 deg fitting (vice the 45 for auto
installations). They are used on a number of different
aircraft. Here is some more information about the pump, I would recommend
the model 40106 which has up to 6 psi
output.
Before going further, I think its safe to say, that having a
system that has the high pressure EFI pump in the fuel tank and that
returns the heated fuel back to a main tank which acts as a heat sink
is probably the safest approach from a heated fuel stand point. I
personally did not want to run more fuel lines (particularly high pressure ones)
through the cockpit area. If you switch tanks then that would necessitate
switching both main line and return line to get the fuel back to the correct
tank. Also the ideal of a replacing a pump inside the tank (if needed) did
not appeal.
Tracy Crook uses a system whereby he feeds the engine from one
wing tank only and simply transfers fuel from the second wing tank into the feed
tank (one big header tank {:>)). Works fine as attested to by his 17
years of rotary flying.
There are other good, reliable and safe approaches, just need
to think them all through regarding fuel flow, leaks, vapor lock,
etc.
Having said that, here is my system:
I have two high pressure fuel pumps each with its own feed
from the bottom of my tiny header tank (important that the header tank be air
tight and as low in the system as you can get it and feed to pumps be as short
as possible), each pump has its own high pressure (Stock GM EFI filter with
saganaw fittings and O ring) after the filters the line from each is "Y" into a
single line to feed first the primary injector and then the secondary before
returning to a pressure regulator the output of which dumped back into the
header tank. Each pump has its own power feed and switch.
I use An-6 stainless steel braided lines for all fuel lines
and the 4 injectors feed in series off of it - no problems with adequate fuel
flow (at least up to 200HP).
The boost pump is hooked into the line between the wing tank
feed and the header tank. I take off and land with both EFI pumps and the
boost pump on. My standard practice.
That's about it. Yes, copying a successful system is a
proven way - but, as I tell folks, unless you have an exact duplicate in all
details - you have a different system and it may respond differently than the
one you copied.
Ed
----- Original Message -----
Sent: Monday, August 27, 2007 12:46
AM
Subject: [FlyRotary] Re: need help
Ed,
Thanks for the reply, now I believe I'll go with a smaller
header tank and make it aluminum or maybe go with fiberglass and use a
cooler on the return line, save a few pounds in the process. Just how much
heat is picked up in the fuel on the return? The Mazda fuel pump
assembly has the return going in a few inches from the pick-up for the pump
and I suppose there are no fuel heat related problems on the
car.
You talk about a boost pump. What type and how is it
plumbed in to the fuel system? (Maybe you get the idea I like to copy from
successful people?)
Wendell
Fuel system design is certainly a critical area and a lot
of thought needs to be given it.
I went against the concept of large header tanks and have
one that holds approx 32 oz or one pint. I have it mounted on
the engine side of FW (would change that) and at the lowest point.
After my pressure regulator, my return fuel dumps into this tiny header
tank.
Many of today's EFI automobiles now use a "returnless"
fuel system by controlling the fuel pressure as needed to prevent vapor
lock. I view my tiny header as sort of an in-between a header than and
no header tank {:>).
I do have blast tubes of cooling air going to it and I did
have fuel percolation on the ground before putting the tubes in.
However, the boost pump (6 psi) immediately squished any that
occurred. Having been flying with it in the sunny South for almost 10
years.
My rational was that IF your larger header tanks does get
filled with hot fuel, its going to take a long time to burn that hot fuel
off and get new cooler fuel. My pint gets replenished at flight power
settings so quickly that heat is not an issue. A long idle on a hot
day could cause some percolation, but since I always take off with boost
pump on, its never been an issue.
Be oh-so-careful in design of your fuel system - needless
to say, but will anyhow.
Ed
----- Original Message -----
Sent: Saturday, August 25, 2007 9:59
PM
Subject: [FlyRotary] Re: need
help
Thanks Ed and
Charlie,
You both got the same answer, I
think the 1.8 gal. estimate came from my first mock-up and it was 14 in.
instead of 15. In some of my calculations I did get 2.0 +something
as an answer. Now how much sump tank volume is really needed?
I think Perry Mick uses one slightly over a gallon. If one gallon is
sufficient, then I can save 6 pounds of usually unused fuel.
I regret hearing about George
Graham, I was hoping to meet him, he sent a drawing of his cooling set-up
and was always ready to help.
Wendell
You can look at your tank as composed of two boxes
(actually one and 1/2 boxes). 1st box is 3.75" x 6" x 15" =
337.5 cubic inches.
A second box is 3.75 " x (11-6)" x 15" = 281.25 Cubic
inches but you really only have 1/2 of this box, so triangular
section volume = 1/2 (rectangular section) volume =
281.25 * 1/2 = 140.625 cubic inches
So total volume = volume of 1st box (337.5 )+ 1/2
volume of second box (140.625) = 478.125 cubic inches or 2.07 US
Gallons
Ed
----- Original Message -----
Sent: Saturday, August 25, 2007
1:19 PM
Subject: [FlyRotary] Re: need
help
Thanks for the responses to my requests.
I wasn't to go John Slade's route and try to put in an air
conditioner and the lines need to take 250 to 300 psi. The
larger return line should only see about 175 psi on a hot tarmac
(engine off) and the feed line will see up to 275 psi (assuming a
inefficient condenser) on a hot day.
Finding a place for the condenser is the main problem as I
see it.
I'll look up Mazdatrix for the exhaust studs. I hoped
someone knew the exact size so they could be purchased
locally.
Here is a math problem for you brain types (all rotary head
but me) -how much fuel will a tank hold that is 3.75 in. tall, 15
in. long, 11 in.deep on the bottom, top is 6 in. deep then slopes to
zero at the front? I think it is about 1.8 gal.
___6in._
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11in.
Wendell
In a message dated 8/23/2007 8:29:10 PM Pacific Standard Time,
jwvoto@itlnet.net
writes:
Hey guys,
I still need help in obtaining the nuts for the exhaust studs
on the 13b. Also, does anyone have working phi ratings for 3003-0
aluminum tubing. Can it withstand 250psi
Wendell
What wall thickness Wendell? .010 thick NO! 1 inch (wall) yes.
Give us an idea of what you are using it for.
Bill Jepson
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