Reading over some back posts, and thinking about engines, I've got a couple
new questions...
Pierre's Rebel with XP-360 has a CG of ~13, empty wt of 1060.
Ken's Rebel with Sub EJ22 (and dual electrics, etc) has a CG of ~9, and that
is with firewall moved back. Empty 1040.
Is Pierre's firewall moved back?
I had always guessed that a Subaru would tuck pretty close to the firewall
and present less of a concern for forward CG than Lycomings (unless the
redrive negates this?). How have other Subaru Rebels come out for CG, and
any with original firewall position?
Thanks,
-Ben/ 496R
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CG of Subaru Rebel ?
-
Ken
CG of Subaru Rebel ?
Ben
I think Pierre's firewall is not moved back.
I don't know about installations with nose mounted rads, but yes the
soob engine block (with psru) balance point is aft of a Lyc. My engine
could actually be moved aft a few inches, however I put a vacuum pump
behind the port camshaft which takes up a fair space. With my short psru
(Marcotte 200) the prop is actually in the same position as a Lyc. Now
that there are reasonably affordable electronic instrument options, if
starting again I'd forget about the vacuum pump, move the engine aft a
few inches, probably go with the longer 300 model psru, and seriously
consider not moving the firewall.
When actually doing the calculations it becomes apparent how
dramatically the battery position affects the cg. A 300 lb engine moved
3" is only 900 inch-lbs. A 20 lb battery moved aft 100" is 2000
inch-lbs. plus a strong mount, contactor(s), and cables.
In my case the realistic operational empty cg is more aft of the empty
number because it would include 12 lb of fuel in the header tank which
is 65" aft of the door post. That's another 780 inch-lbs. or 3/4 in. of
cg change at 1040 lb weight. Moving 20+ lb of battery back could move
the empty cg back another 2 inches! That would cause gross weight aft cg
problems for me but you can probably see my point.
Once again my fuel weight is less than for a Lyc. so my high empty
weight does not bother me. I was confident enough of that to only put in
5 wing bays total of fuel tank. 8+ gallons per bay is 50 lbs per bay.
Another factor was that with an electrically dependant engine and two
hot battery buses (fuse blocks) to feed it, I had a strong preferrence
to keep the batteries and all those components close together on the aft
side of the firewall.
Ken
bransom@dcsol.com wrote:
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I think Pierre's firewall is not moved back.
I don't know about installations with nose mounted rads, but yes the
soob engine block (with psru) balance point is aft of a Lyc. My engine
could actually be moved aft a few inches, however I put a vacuum pump
behind the port camshaft which takes up a fair space. With my short psru
(Marcotte 200) the prop is actually in the same position as a Lyc. Now
that there are reasonably affordable electronic instrument options, if
starting again I'd forget about the vacuum pump, move the engine aft a
few inches, probably go with the longer 300 model psru, and seriously
consider not moving the firewall.
When actually doing the calculations it becomes apparent how
dramatically the battery position affects the cg. A 300 lb engine moved
3" is only 900 inch-lbs. A 20 lb battery moved aft 100" is 2000
inch-lbs. plus a strong mount, contactor(s), and cables.
In my case the realistic operational empty cg is more aft of the empty
number because it would include 12 lb of fuel in the header tank which
is 65" aft of the door post. That's another 780 inch-lbs. or 3/4 in. of
cg change at 1040 lb weight. Moving 20+ lb of battery back could move
the empty cg back another 2 inches! That would cause gross weight aft cg
problems for me but you can probably see my point.
Once again my fuel weight is less than for a Lyc. so my high empty
weight does not bother me. I was confident enough of that to only put in
5 wing bays total of fuel tank. 8+ gallons per bay is 50 lbs per bay.
Another factor was that with an electrically dependant engine and two
hot battery buses (fuse blocks) to feed it, I had a strong preferrence
to keep the batteries and all those components close together on the aft
side of the firewall.
Ken
bransom@dcsol.com wrote:
Reading over some back posts, and thinking about engines, I've got a couple
new questions...
Pierre's Rebel with XP-360 has a CG of ~13, empty wt of 1060.
Ken's Rebel with Sub EJ22 (and dual electrics, etc) has a CG of ~9, and that
is with firewall moved back. Empty 1040.
Is Pierre's firewall moved back?
I had always guessed that a Subaru would tuck pretty close to the firewall
and present less of a concern for forward CG than Lycomings (unless the
redrive negates this?). How have other Subaru Rebels come out for CG, and
any with original firewall position?
Thanks,
-Ben/ 496R
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-----------------------------------------------------------------
-
bransom
CG of Subaru Rebel ?
Ken,
Sounds very well thought out. I wasn't sure you really had 2 complete
electrical sources (including 2 batteries) ... yes, that accounts for a lot
of the weight up front. I guess with the header tank your "empty" cg is
closer to 10". Was there anything specific about your decision to keep the
batteries at the firewall, or just general concern having all that current
running a long distance if they were moved aft? My question is pointed to
the alternative of avoiding moving the firewall by putting the batteries in
back.
BTW, are you using a stock Subaru fuel pump (or 2) in your header tank?
Thanks again,
-Ben
On 12/30/2005 7:22 AM, klehman@albedo.net wrote to rebel-builders:
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Sounds very well thought out. I wasn't sure you really had 2 complete
electrical sources (including 2 batteries) ... yes, that accounts for a lot
of the weight up front. I guess with the header tank your "empty" cg is
closer to 10". Was there anything specific about your decision to keep the
batteries at the firewall, or just general concern having all that current
running a long distance if they were moved aft? My question is pointed to
the alternative of avoiding moving the firewall by putting the batteries in
back.
BTW, are you using a stock Subaru fuel pump (or 2) in your header tank?
Thanks again,
-Ben
On 12/30/2005 7:22 AM, klehman@albedo.net wrote to rebel-builders:
coupleBen
I think Pierre's firewall is not moved back.
I don't know about installations with nose mounted rads, but yes the
soob engine block (with psru) balance point is aft of a Lyc. My engine
could actually be moved aft a few inches, however I put a vacuum pump
behind the port camshaft which takes up a fair space. With my short psru
(Marcotte 200) the prop is actually in the same position as a Lyc. Now
that there are reasonably affordable electronic instrument options, if
starting again I'd forget about the vacuum pump, move the engine aft a
few inches, probably go with the longer 300 model psru, and seriously
consider not moving the firewall.
When actually doing the calculations it becomes apparent how
dramatically the battery position affects the cg. A 300 lb engine moved
3" is only 900 inch-lbs. A 20 lb battery moved aft 100" is 2000
inch-lbs. plus a strong mount, contactor(s), and cables.
In my case the realistic operational empty cg is more aft of the empty
number because it would include 12 lb of fuel in the header tank which
is 65" aft of the door post. That's another 780 inch-lbs. or 3/4 in. of
cg change at 1040 lb weight. Moving 20+ lb of battery back could move
the empty cg back another 2 inches! That would cause gross weight aft cg
problems for me but you can probably see my point.
Once again my fuel weight is less than for a Lyc. so my high empty
weight does not bother me. I was confident enough of that to only put in
5 wing bays total of fuel tank. 8+ gallons per bay is 50 lbs per bay.
Another factor was that with an electrically dependant engine and two
hot battery buses (fuse blocks) to feed it, I had a strong preferrence
to keep the batteries and all those components close together on the aft
side of the firewall.
Ken
bransom@dcsol.com wrote:
Reading over some back posts, and thinking about engines, I've got a
thatnew questions...
Pierre's Rebel with XP-360 has a CG of ~13, empty wt of 1060.
Ken's Rebel with Sub EJ22 (and dual electrics, etc) has a CG of ~9, and
is with firewall moved back. Empty 1040.
Is Pierre's firewall moved back?
I had always guessed that a Subaru would tuck pretty close to the firewall
and present less of a concern for forward CG than Lycomings (unless the
redrive negates this?). How have other Subaru Rebels come out for CG, and
any with original firewall position?
Thanks,
-Ben/ 496R
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-----------------------------------------------------------------
-
Ken
CG of Subaru Rebel ?
Ben
The batteries are dinky 9AH things so both together weigh about the same
as one 17AH class battery like an Odyssey. Both alternators also only
added up to 10 or so pounds so also not too bad. Rear batteries have
some minor electrical issues like a little more noise in the system and
add a couple of lbs of wire but as long as they are well secured they
generally don't bother me, especially with a Lyc where most everything
can be shut off with the battery master. In my case a lot of the wiring
is off the hot battery buses for the engine for a total of 12 fuses. I
figure even if I roll this thing into a ball most of the wiring is well
protected with almost everything close together on the back of the
firewall. Upon further consideration though I think I would be
comfortabe with rear batteries and ANL fuses or CB's at the battery and
running 8 awg wires up to fuse blocks on the firewall. And of course a
contactor and perhaps 2 awg up for the starter and everything else.
Yup stock submersed pumps in the header tank. A float switch illuminates
a big flashing red and green LED if the header isn't full but that will
still leave a gallon or so useable. Since I never expect to see that
light it does seem to me that I'm probably comparable to a 10" cg. The
header tank doubles as the required gascolator but it was too much
trouble to build and mount in a crash surviveable manner so I'd just use
external aftermarket pumps if I did it again.
Ken
bransom@dcsol.com wrote:
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The batteries are dinky 9AH things so both together weigh about the same
as one 17AH class battery like an Odyssey. Both alternators also only
added up to 10 or so pounds so also not too bad. Rear batteries have
some minor electrical issues like a little more noise in the system and
add a couple of lbs of wire but as long as they are well secured they
generally don't bother me, especially with a Lyc where most everything
can be shut off with the battery master. In my case a lot of the wiring
is off the hot battery buses for the engine for a total of 12 fuses. I
figure even if I roll this thing into a ball most of the wiring is well
protected with almost everything close together on the back of the
firewall. Upon further consideration though I think I would be
comfortabe with rear batteries and ANL fuses or CB's at the battery and
running 8 awg wires up to fuse blocks on the firewall. And of course a
contactor and perhaps 2 awg up for the starter and everything else.
Yup stock submersed pumps in the header tank. A float switch illuminates
a big flashing red and green LED if the header isn't full but that will
still leave a gallon or so useable. Since I never expect to see that
light it does seem to me that I'm probably comparable to a 10" cg. The
header tank doubles as the required gascolator but it was too much
trouble to build and mount in a crash surviveable manner so I'd just use
external aftermarket pumps if I did it again.
Ken
bransom@dcsol.com wrote:
Ken,
Sounds very well thought out. I wasn't sure you really had 2 complete
electrical sources (including 2 batteries) ... yes, that accounts for a lot
of the weight up front. I guess with the header tank your "empty" cg is
closer to 10". Was there anything specific about your decision to keep the
batteries at the firewall, or just general concern having all that current
running a long distance if they were moved aft? My question is pointed to
the alternative of avoiding moving the firewall by putting the batteries in
back.
BTW, are you using a stock Subaru fuel pump (or 2) in your header tank?
Thanks again,
-Ben
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-
Bob Patterson
CG of Subaru Rebel ?
Hi Ben !
Been away a couple of days ....
Unfortunately, Pierre's firewall WAS moved back - he bought a
partly built project, and the move was done even before final engine
choice ... :-( He does have a huge Odyssey battery right at
the end of the floor, AND a huge hydraulic pump for the floats
& skis, also at the rear ... probably well over 50 lb. back there !
And a light ( 9 lb. !) Prince prop up front. Not moving the
firewall gives you a full range of future engine choices, as well as
a better seating position, better visibility, and makes the panel
setup a lot easier for full-length avionics !
Most Rebels with EJ-22's have NOT had the firewall moved - and
the C of G's are usually in the 10.5 - 12 range -- mostly dependent
on battery position. Good to save securing the battery until you
can do a trial weight & balance, then just move it to the best spot !
Empty weights are usually in the 960 - 1060 range, when finished
and painted (The Sub & re-drive, with rad & coolant, is usually
only about 30 lb. or so more than a Lyc.) Of course, ALL of these
Rebels had the bungee gear, some with the die spring mod..
Most also had 3 blade or 4 blade Warp Drive props - the 4 blades
had a LOT of drag on approach - made for a steep approach, and
the engine windmilling up to 2500+ rpm !!
I've flown a few Sub Rebels, and even the stock EJ-22 works
very nicely - about 1,100 fpm climb, 105 - 110 mph cruise, on
about 5 - 6 gph mogas. The 180+ hp. modified ones are even more
exciting ! :-) And they're all SMOOOOOooooth ! ;-)
I do like the Marcotte redrive - compact & sturdy ! Most of
the early conversions used the Ross redrive - long, and some
gear problems - no longer available anyway ...
One had the stock Sub fuel pumps mounted in the bottom of
the wing tanks, on removeable plates - worked great ! The
return line came up to the roof, with a valve to direct return
flow to left or right tank, to aid in load balancing. Ideally,
the return line is not at the top of the tank, so the fuel
doesn't fall, picking up air & static .... One nice thing
about this is there were no fuel valves needed - just turn on
the pump on the tank you wanted to feed from ! ;-)
(Actually, it's still a good idea to install the valves -
for maintenance, etc. - also in the return line - just in case... )
Small valves at the bottom of the sight guages are also a
good idea - makes changing the tubes very fast & easy, and
adds a bit of safety.... (The 1/4" ones from the Renegage
work nicely ..)
The Murphy Rotax 912 cowling, with mods for easy opening,
worked very well, as the radiator mounting position was already
proven .... and it didn't look bad either !
.......bobp
-------------------------------orig.-------------------------
On Friday 30 December 2005 01:34 am, bransom@dcsol.com wrote:
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Been away a couple of days ....
Unfortunately, Pierre's firewall WAS moved back - he bought a
partly built project, and the move was done even before final engine
choice ... :-( He does have a huge Odyssey battery right at
the end of the floor, AND a huge hydraulic pump for the floats
& skis, also at the rear ... probably well over 50 lb. back there !
And a light ( 9 lb. !) Prince prop up front. Not moving the
firewall gives you a full range of future engine choices, as well as
a better seating position, better visibility, and makes the panel
setup a lot easier for full-length avionics !
Most Rebels with EJ-22's have NOT had the firewall moved - and
the C of G's are usually in the 10.5 - 12 range -- mostly dependent
on battery position. Good to save securing the battery until you
can do a trial weight & balance, then just move it to the best spot !
Empty weights are usually in the 960 - 1060 range, when finished
and painted (The Sub & re-drive, with rad & coolant, is usually
only about 30 lb. or so more than a Lyc.) Of course, ALL of these
Rebels had the bungee gear, some with the die spring mod..
Most also had 3 blade or 4 blade Warp Drive props - the 4 blades
had a LOT of drag on approach - made for a steep approach, and
the engine windmilling up to 2500+ rpm !!
I've flown a few Sub Rebels, and even the stock EJ-22 works
very nicely - about 1,100 fpm climb, 105 - 110 mph cruise, on
about 5 - 6 gph mogas. The 180+ hp. modified ones are even more
exciting ! :-) And they're all SMOOOOOooooth ! ;-)
I do like the Marcotte redrive - compact & sturdy ! Most of
the early conversions used the Ross redrive - long, and some
gear problems - no longer available anyway ...
One had the stock Sub fuel pumps mounted in the bottom of
the wing tanks, on removeable plates - worked great ! The
return line came up to the roof, with a valve to direct return
flow to left or right tank, to aid in load balancing. Ideally,
the return line is not at the top of the tank, so the fuel
doesn't fall, picking up air & static .... One nice thing
about this is there were no fuel valves needed - just turn on
the pump on the tank you wanted to feed from ! ;-)
(Actually, it's still a good idea to install the valves -
for maintenance, etc. - also in the return line - just in case... )
Small valves at the bottom of the sight guages are also a
good idea - makes changing the tubes very fast & easy, and
adds a bit of safety.... (The 1/4" ones from the Renegage
work nicely ..)
The Murphy Rotax 912 cowling, with mods for easy opening,
worked very well, as the radiator mounting position was already
proven .... and it didn't look bad either !
.......bobp
-------------------------------orig.-------------------------
On Friday 30 December 2005 01:34 am, bransom@dcsol.com wrote:
coupleReading over some back posts, and thinking about engines, I've got a
thatnew questions...
Pierre's Rebel with XP-360 has a CG of ~13, empty wt of 1060.
Ken's Rebel with Sub EJ22 (and dual electrics, etc) has a CG of ~9, and
is with firewall moved back. Empty 1040.
Is Pierre's firewall moved back?
I had always guessed that a Subaru would tuck pretty close to the firewall
and present less of a concern for forward CG than Lycomings (unless the
redrive negates this?). How have other Subaru Rebels come out for CG, and
any with original firewall position?
Thanks,
-Ben/ 496R
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-
Ken
CG of Subaru Rebel ?
That still requires active fuel management though which is still a
frequent cause of "incidents".
If you can find a place to put it, I really like the use of a header
tank with fuel returning to it. No management required and no concern
about injesting air when low on fuel!
I also like returnless EFI which has been on a number of cars such as
the Neon for about 10 years now. Such systems seem more common every
year and don't seem to have any hot start issues. Not sure but I think
the 40 ish psi rail pressure is enough to prevent fuel boiling when the
engine is shutdown.
Ken
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frequent cause of "incidents".
If you can find a place to put it, I really like the use of a header
tank with fuel returning to it. No management required and no concern
about injesting air when low on fuel!
I also like returnless EFI which has been on a number of cars such as
the Neon for about 10 years now. Such systems seem more common every
year and don't seem to have any hot start issues. Not sure but I think
the 40 ish psi rail pressure is enough to prevent fuel boiling when the
engine is shutdown.
Ken
One had the stock Sub fuel pumps mounted in the bottom of
the wing tanks, on removeable plates - worked great ! The
return line came up to the roof, with a valve to direct return
flow to left or right tank, to aid in load balancing. Ideally,
the return line is not at the top of the tank, so the fuel
doesn't fall, picking up air & static .... One nice thing
about this is there were no fuel valves needed - just turn on
the pump on the tank you wanted to feed from ! ;-)
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-
Bob Patterson
CG of Subaru Rebel ?
To each his own .... I've always disliked header tanks, ever
since I lost a good friend who was burned in a Super Cub crash
because the header tank split & sprayed gas all over him & the
burning engine ...
I know you did a lot of work to crash-proof yours, and I think
it's mounted in back, instead of on the firewall like the Cub,
but to me it's still extra work, & an added hazard, and besides,
I'm all in favour of "active fuel management" ;-) --- often
the lack of attention to the fuel status is what causes a lot
of silence, and an instant glider, at inconvenient times ! ;-) :-)
"Returnless EFI" - now THAT sounds like the ideal answer !!
It would be great if Subaru went that way !
......bobp
-------------------------------orig.-------------------------
On Saturday 31 December 2005 09:08 am, Ken wrote:
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since I lost a good friend who was burned in a Super Cub crash
because the header tank split & sprayed gas all over him & the
burning engine ...
I know you did a lot of work to crash-proof yours, and I think
it's mounted in back, instead of on the firewall like the Cub,
but to me it's still extra work, & an added hazard, and besides,
I'm all in favour of "active fuel management" ;-) --- often
the lack of attention to the fuel status is what causes a lot
of silence, and an instant glider, at inconvenient times ! ;-) :-)
"Returnless EFI" - now THAT sounds like the ideal answer !!
It would be great if Subaru went that way !
......bobp
-------------------------------orig.-------------------------
On Saturday 31 December 2005 09:08 am, Ken wrote:
That still requires active fuel management though which is still a
frequent cause of "incidents".
If you can find a place to put it, I really like the use of a header
tank with fuel returning to it. No management required and no concern
about injesting air when low on fuel!
I also like returnless EFI which has been on a number of cars such as
the Neon for about 10 years now. Such systems seem more common every
year and don't seem to have any hot start issues. Not sure but I think
the 40 ish psi rail pressure is enough to prevent fuel boiling when the
engine is shutdown.
Ken
One had the stock Sub fuel pumps mounted in the bottom of
the wing tanks, on removeable plates - worked great ! The
return line came up to the roof, with a valve to direct return
flow to left or right tank, to aid in load balancing. Ideally,
the return line is not at the top of the tank, so the fuel
doesn't fall, picking up air & static .... One nice thing
about this is there were no fuel valves needed - just turn on
the pump on the tank you wanted to feed from ! ;-)
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