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cjaviator(at)gmail.com
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 Posted: Mon May 17, 2010 2:39 am Post subject: CJ-6 Fuel Feed |
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Hi all. I have been meaning to post this for a few weeks now...
You may recall a posting approx a month ago about a Nanchang being flown out
of a 'bush strip' in New Zealand. Well, that was us.
Trying to cut a long story short...
The pilot took off believing he had (at)10 litres in the LH tank and (at) 45
litres in the RH tank for a planned 15 minute flight. After climbing to (at)
4000 ft he carried out 2-3 basic aerobatic manoeuvres and then began a
prolonged descending RH turn. Approx 12 minutes into the flight the engine
surged and soon after quit. The wobble pump would not restore fuel pressure
and a FLWOP was commenced. He did a very good job and the only damage was
bent leading edges on the lower gear doors.
*Right from the get-go, lets forget about the wisdom of taking off in that
fuel state as the pilot believed he was OK to fly with the fuel he had.*
After being called to the scene I dipped the tanks and found (at) 15 litres in
the LH tank and (at) 20 litres in the RH tank. It had taken 2 hours to get to
the aircraft and the fuel had cross fed to a more even level than was most
probably landed with. I tried to start the aircraft as it was, but was
unable to. A further 20 litres of fuel was added to each tank and the engine
was started and ran perfectly.
After some more rudimentary checks the aircraft was pronounced fit for
flight back to the home field with the gear down.
On getting her home we drained the tanks and blew out all the vent lines and
removed the collector tank to check the flapper valves. The only hint of a
defect we could find was that the vent line outlet was not entirely alligned
with the airflow.
(One unrelated defect we inadvertantly found was corrosion in the bottom of
the collector tank. This was in the rear one of the two pressed channels
that the retaining strap sits between - I have now found this in two
machines)
We went on to drain the fuel system and calibrate our dipstick and the
gauges. The gauges and low level lights were incredibly accurate but we
found our dipstick to be over-reading by approx 5 litres.
As nothing could be found the aircraft was released to service for a check
flight over the field. I got airborne with 25 litres per side and climbed to
3500 ft where I initiated a figure 8 track. Initially fuel feed looked even
but after 5 minutes it was obvious that the LH tank was feeding faster (as
it has always done). After (at)20 minutes the LH low level light came on and I
hoped that the RH one would follow shortly. After another 10 minutes it had
not come on and the gauges were indicating 2 litres in the LH tank and 12 in
the RH tank. At this time I commenced LH orbit and after another 5 minutes
nothing seemed to have changed but the fuel pressure began fluctuating so I
levelled the wings, the pressure came back and I landed.
On draining the tanks I had 2 litres in the LH, 12 litres in the RH and 5
litres in the collector tank.
So all in all, nothing terribly conclusive. I believe that had I been in
straight and level flight I would have been able to get more out of the RH
tank. With regard to the first incident I believe that the ultimate cause
was the prolonged descending turn with the 'empty' tank on the high side.
Unless perfectly in balance the fuel in both tanks would tend to run forward
and away from the outlet point, particularly on the LH tank which was
probably down to 2 or 3 litres. Thus the collector tank would not be
replenished and after approx 4 mins fuel pressure would begin to fluctuate
(I say 4 mins because the tank has an 8 litre capacity and the pick
up for it's outlet is dead in the middle of the tank and fuel consumption is
60 litres per hour for the standard CJ-6
I was able to produce similar results on the second flight except for the
fact that I flew level orbits with the fuller tank on the high side.
Correct me if I am wrong, but I believe that fuel feed problems,
particularly in tight turns was why PA-18A Super Cubs have a header tank for
each wing tank???)
Like Walt said in his eariler post, I think the uneven lengths of the vent
lines from the tank to common T point contributes to the problem with the
shorter LH vent line giving perhaps a greater head of pressure to the LH
tank (or something like that). It would be interesting to seperate the two
vent lines and give the RH tank it's own anti siphon line... i.e create a
self contained mirror image for each tanks vent system
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ldakos(at)bigpond.net.au
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| Posted: Mon May 17, 2010 4:23 am Post subject: CJ-6 Fuel Feed |
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G'Day All
My Cj has 3 hacksaw cuts across the seat of flap valves it came from china like that and most of the time it feeds ok I have never had a low level warning as yet. This subject was well discussed some years ago without any firm result if I remember correctly .
I think replumbing through a fuel valve so left or right only could be selected would be a way to get rid of the problem.
Lou
On 17/05/2010 8:37 PM, Jay McIntyre wrote: [quote] Hi all. I have been meaning to post this for a few weeks now...
You may recall a posting approx a month ago about a Nanchang being flown out of a 'bush strip' in New Zealand. Well, that was us.
Trying to cut a long story short...
The pilot took off believing he had (at)10 litres in the LH tank and (at) 45 litres in the RH tank for a planned 15 minute flight. After climbing to (at) 4000 ft he carried out 2-3 basic aerobatic manoeuvres and then began a prolonged descending RH turn. Approx 12 minutes into the flight the engine surged and soon after quit. The wobble pump would not restore fuel pressure and a FLWOP was commenced. He did a very good job and the only damage was bent leading edges on the lower gear doors.
Right from the get-go, lets forget about the wisdom of taking off in that fuel state as the pilot believed he was OK to fly with the fuel he had.
After being called to the scene I dipped the tanks and found (at) 15 litres in the LH tank and (at) 20 litres in the RH tank. It had taken 2 hours to get to the aircraft and the fuel had cross fed to a more even level than was most probably landed with. I tried to start the aircraft as it was, but was unable to. A further 20 litres of fuel was added to each tank and the engine was started and ran perfectly.
After some more rudimentary checks the aircraft was pronounced fit for flight back to the home field with the gear down.
On getting her home we drained the tanks and blew out all the vent lines and removed the collector tank to check the flapper valves. The only hint of a defect we could find was that the vent line outlet was not entirely alligned with the airflow.
(One unrelated defect we inadvertantly found was corrosion in the bottom of the collector tank. This was in the rear one of the two pressed channels that the retaining strap sits between - I have now found this in two machines)
We went on to drain the fuel system and calibrate our dipstick and the gauges. The gauges and low level lights were incredibly accurate but we found our dipstick to be over-reading by approx 5 litres.
As nothing could be found the aircraft was released to service for a check flight over the field. I got airborne with 25 litres per side and climbed to 3500 ft where I initiated a figure 8 track. Initially fuel feed looked even but after 5 minutes it was obvious that the LH tank was feeding faster (as it has always done). After (at)20 minutes the LH low level light came on and I hoped that the RH one would follow shortly. After another 10 minutes it had not come on and the gauges were indicating 2 litres in the LH tank and 12 in the RH tank. At this time I commenced LH orbit and after another 5 minutes nothing seemed to have changed but the fuel pressure began fluctuating so I levelled the wings, the pressure came back and I landed.
On draining the tanks I had 2 litres in the LH, 12 litres in the RH and 5 litres in the collector tank.
So all in all, nothing terribly conclusive. I believe that had I been in straight and level flight I would have been able to get more out of the RH tank. With regard to the first incident I believe that the ultimate cause was the prolonged descending turn with the 'empty' tank on the high side. Unless perfectly in balance the fuel in both tanks would tend to run forward and away from the outlet point, particularly on the LH tank which was probably down to 2 or 3 litres. Thus the collector tank would not be replenished and after approx 4 mins fuel pressure would begin to fluctuate (I say 4 mins because the tank has an 8 litre capacity and the pick up for it's outlet is dead in the middle of the tank and fuel consumption is 60 litres per hour for the standard CJ-6
I was able to produce similar results on the second flight except for the fact that I flew level orbits with the fuller tank on the high side.
Correct me if I am wrong, but I believe that fuel feed problems, particularly in tight turns was why PA-18A Super Cubs have a header tank for each wing tank???)
Like Walt said in his eariler post, I think the uneven lengths of the vent lines from the tank to common T point contributes to the problem with the shorter LH vent line giving perhaps a greater head of pressure to the LH tank (or something like that). It would be interesting to seperate the two vent lines and give the RH tank it's own anti siphon line... i.e create a self contained mirror image for each tanks vent system
.
As an aside, prior to this incident we had already purchased extended range bladders and will be looking to install these shortly using taps in the vent lines to control the uneven fuel flow.
Regards, Jay
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dsavarese0812(at)bellsout
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| Posted: Mon May 17, 2010 5:02 am Post subject: CJ-6 Fuel Feed |
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A suggestion is to also think vent lines first as contributing to the problem versus fuel flow obstruction out of the tanks. If the tanks don't vent properly, then all the fuel output from the tanks will stop. My experience has been if I fixed the venting problem, the fuel feeding problem went away. If you find fuel in the vent lines, it will stop the tank from feeding.
Dennis
[quote] ---
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gill.g(at)gpimail.com
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| Posted: Mon May 17, 2010 8:41 am Post subject: CJ-6 Fuel Feed |
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Jay,
Make sure you look at the vent mods required for the bladders, as the
concept is different than the standard CJ venting system.
Gill
From: owner-yak-list-server(at)matronics.com
[mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Jay McIntyre
Sent: Monday, May 17, 2010 3:38 AM
To: yak list
Subject: CJ-6 Fuel Feed
Hi all. I have been meaning to post this for a few weeks now...
You may recall a posting approx a month ago about a Nanchang being flown out
of a 'bush strip' in New Zealand. Well, that was us.
Trying to cut a long story short...
The pilot took off believing he had (at)10 litres in the LH tank and (at) 45
litres in the RH tank for a planned 15 minute flight. After climbing to (at)
4000 ft he carried out 2-3 basic aerobatic manoeuvres and then began a
prolonged descending RH turn. Approx 12 minutes into the flight the engine
surged and soon after quit. The wobble pump would not restore fuel pressure
and a FLWOP was commenced. He did a very good job and the only damage was
bent leading edges on the lower gear doors.
Right from the get-go, lets forget about the wisdom of taking off in that
fuel state as the pilot believed he was OK to fly with the fuel he had.
After being called to the scene I dipped the tanks and found (at) 15 litres in
the LH tank and (at) 20 litres in the RH tank. It had taken 2 hours to get to
the aircraft and the fuel had cross fed to a more even level than was most
probably landed with. I tried to start the aircraft as it was, but was
unable to. A further 20 litres of fuel was added to each tank and the engine
was started and ran perfectly.
After some more rudimentary checks the aircraft was pronounced fit for
flight back to the home field with the gear down.
On getting her home we drained the tanks and blew out all the vent lines and
removed the collector tank to check the flapper valves. The only hint of a
defect we could find was that the vent line outlet was not entirely alligned
with the airflow.
(One unrelated defect we inadvertantly found was corrosion in the bottom of
the collector tank. This was in the rear one of the two pressed channels
that the retaining strap sits between - I have now found this in two
machines)
We went on to drain the fuel system and calibrate our dipstick and the
gauges. The gauges and low level lights were incredibly accurate but we
found our dipstick to be over-reading by approx 5 litres.
As nothing could be found the aircraft was released to service for a check
flight over the field. I got airborne with 25 litres per side and climbed to
3500 ft where I initiated a figure 8 track. Initially fuel feed looked even
but after 5 minutes it was obvious that the LH tank was feeding faster (as
it has always done). After (at)20 minutes the LH low level light came on and I
hoped that the RH one would follow shortly. After another 10 minutes it had
not come on and the gauges were indicating 2 litres in the LH tank and 12 in
the RH tank. At this time I commenced LH orbit and after another 5 minutes
nothing seemed to have changed but the fuel pressure began fluctuating so I
levelled the wings, the pressure came back and I landed.
On draining the tanks I had 2 litres in the LH, 12 litres in the RH and 5
litres in the collector tank.
So all in all, nothing terribly conclusive. I believe that had I been in
straight and level flight I would have been able to get more out of the RH
tank. With regard to the first incident I believe that the ultimate cause
was the prolonged descending turn with the 'empty' tank on the high side.
Unless perfectly in balance the fuel in both tanks would tend to run forward
and away from the outlet point, particularly on the LH tank which was
probably down to 2 or 3 litres. Thus the collector tank would not be
replenished and after approx 4 mins fuel pressure would begin to fluctuate
(I say 4 mins because the tank has an 8 litre capacity and the pick up for
it's outlet is dead in the middle of the tank and fuel consumption is 60
litres per hour for the standard CJ-6
I was able to produce similar results on the second flight except for the
fact that I flew level orbits with the fuller tank on the high side.
Correct me if I am wrong, but I believe that fuel feed problems,
particularly in tight turns was why PA-18A Super Cubs have a header tank for
each wing tank???)
Like Walt said in his eariler post, I think the uneven lengths of the vent
lines from the tank to common T point contributes to the problem with the
shorter LH vent line giving perhaps a greater head of pressure to the LH
tank (or something like that). It would be interesting to seperate the two
vent lines and give the RH tank it's own anti siphon line... i.e create a
self contained mirror image for each tanks vent system
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http://www.matronics.com/Navigator?Yak-List |
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