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Capacitance fuel gauges - - - and stalls

 
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briana(at)xtra.co.nz
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PostPosted: Tue Mar 08, 2011 3:04 am    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
Went flying today. First time in about 4 weeks. Little bit rusty so did a few circuits to get my brain into gear, then a trip around the local area, down the beach, climbed up to 4000ft to practice a few steep turns and stalls etc.

I knew before heading out that one fuel gauge was stuck on full, so I dipped the tanks to check on the fuel load 18L in one tank and 28 in the other. On startup I noticed that actually both gauges were reading full. I've had this problem intermittently for a long time, but frequently the gauges seem to clear themselves after the taxi out or after flying for a bit.

After flying for about 40 minutes the gauges were still on full so I decided to do a few unbalanced turns, a few slide-slips and a deal of yawing with rudder only to slosh the fuel about in an effort to clear the pickups. Nothing worked. I resigned myself to having to pull the wings and take out the capacitance pickups to investigate.

I carried on up to 4000ft for some stalls. I just do some for fun occasionally, to make sure my feet push the rudder in the right direction mainly, and to see if I can minimise any height loss. Got a bit carried away experimenting and managed to drop the left wing for the first time ever. Normally, without fail, it is the right wing that drops. Recoveries were all fine. Tried some accelerated stalls in each direction - - hold a steady bank angle, power back, stick back as speed decays rapidly to maintain altitude, very tight turns - - and see what happens. I've done these before holding 30 deg bank, and every time the right wing drops, so while turning left the plane rolls out level. While turning right the right wing drops further, suddenly to 60deg. This time while turning left I had perhaps 40 deg of bank, and a small amount of power. Speed decaying rapidly, ASI passing through 40 knots, and suddenly the left wing dropped further. Surprised me, but thankfully my feet reacted correctly and the rudder instantly stopped the yaw.

An aside - - - last time I went flying I experimented with the "impossible turn" that has been written about recently in the EAA magazine. Interesting result. The Pulsar has an amazing glide ratio, something like 13 or 14 to 1. I found that I could simulate an engine failure on takeoff, allow a few seconds to recognise it and stabilise the speed at 70 knots, then execute a 180 deg turn and do it with less than 300ft loss of height. Having tried a few times I am confident that provided I was at or above 500ft I could make the "impossible turn" in my Pulsar and get back on the airfield. I hope I never have to try.

So, while contemplating pulling the wings I flew back to the local airfield. Glanced at the fuel gauge and Eureka ! they were both reading normally.

I wonder what causes the problem. The capacitance pickups have a very small hole in the outer tube at the bottom bend just inside the tank end plates to allow the fuel level in the tube to follow the tank level. I wonder if this gets blocked. I think it doesn't help having fuel sitting there motionless for 4 weeks or more. I've never found any contaminants in the fuel or the tanks or filter, and never any water. Maybe it is the additives in the Mogas. Who knows. Anyhow, the solution, for the moment, seems to be to give the plane a good workout, and get that fuel really sloshing around, by doing some fully developed stalls. Helps get the pilot up to speed too.

Brian

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rickyd54(at)gmail.com
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PostPosted: Tue Mar 08, 2011 5:13 am    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
Brian,
Have you checked for loose ground connection? I think the gauges read full when there is a broken/faulty ground.

On Mar 8, 2011, at 4:58 AM, Brian Anderson <briana(at)xtra.co.nz> wrote:

Quote:


Went flying today. First time in about 4 weeks. Little bit rusty so did a few circuits to get my brain into gear, then a trip around the local area, down the beach, climbed up to 4000ft to practice a few steep turns and stalls etc.

I knew before heading out that one fuel gauge was stuck on full, so I dipped the tanks to check on the fuel load 18L in one tank and 28 in the other. On startup I noticed that actually both gauges were reading full. I've had this problem intermittently for a long time, but frequently the gauges seem to clear themselves after the taxi out or after flying for a bit.

After flying for about 40 minutes the gauges were still on full so I decided to do a few unbalanced turns, a few slide-slips and a deal of yawing with rudder only to slosh the fuel about in an effort to clear the pickups. Nothing worked. I resigned myself to having to pull the wings and take out the capacitance pickups to investigate.

I carried on up to 4000ft for some stalls. I just do some for fun occasionally, to make sure my feet push the rudder in the right direction mainly, and to see if I can minimise any height loss. Got a bit carried away experimenting and managed to drop the left wing for the first time ever. Normally, without fail, it is the right wing that drops. Recoveries were all fine. Tried some accelerated stalls in each direction - - hold a steady bank angle, power back, stick back as speed decays rapidly to maintain altitude, very tight turns - - and see what happens. I've done these before holding 30 deg bank, and every time the right wing drops, so while turning left the plane rolls out level. While turning right the right wing drops further, suddenly to 60deg. This time while turning left I had perhaps 40 deg of bank, and a small amount of power. Speed decaying rapidly, ASI passing through 40 knots, and suddenly the left wing dropped further. Surprised me, but thankfully my feet reac!
ted correctly and the rudder instantly stopped the yaw.

An aside - - - last time I went flying I experimented with the "impossible turn" that has been written about recently in the EAA magazine. Interesting result. The Pulsar has an amazing glide ratio, something like 13 or 14 to 1. I found that I could simulate an engine failure on takeoff, allow a few seconds to recognise it and stabilise the speed at 70 knots, then execute a 180 deg turn and do it with less than 300ft loss of height. Having tried a few times I am confident that provided I was at or above 500ft I could make the "impossible turn" in my Pulsar and get back on the airfield. I hope I never have to try.

So, while contemplating pulling the wings I flew back to the local airfield. Glanced at the fuel gauge and Eureka ! they were both reading normally.

I wonder what causes the problem. The capacitance pickups have a very small hole in the outer tube at the bottom bend just inside the tank end plates to allow the fuel level in the tube to follow the tank level. I wonder if this gets blocked. I think it doesn't help having fuel sitting there motionless for 4 weeks or more. I've never found any contaminants in the fuel or the tanks or filter, and never any water. Maybe it is the additives in the Mogas. Who knows. Anyhow, the solution, for the moment, seems to be to give the plane a good workout, and get that fuel really sloshing around, by doing some fully developed stalls. Helps get the pilot up to speed too.

Brian










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rwilhelm(at)dc.rr.com
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PostPosted: Tue Mar 08, 2011 7:48 am    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
Brian,

I found the problem with mine was that the connection at the receptacle/
plug was not good after 10 years.

Ray Pulsar III/3300

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leubanks(at)sunflower.com
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PostPosted: Tue Mar 08, 2011 9:22 am    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
Brian
My Princeton sender says that the presence of water or alcohol will act like
a short between the brass inside tube and the aluminum outside tube. That
will cause the guage to show full or in my case it also could not be
calibrated.
Larry

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briana(at)xtra.co.nz
Guest
PostPosted: Tue Mar 08, 2011 12:40 pm    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
Mmmm. Could be that the connectors at the wing roots need a bit of a clean. They haven't been touched in years. The problem is intermittent, although worse than it has been in a while. I think I can get at the connectors from inside the fuselage without having to pull the wings.

Thanks for all the suggestions.
Brian

On 9/03/2011, at 2:11 AM, Rick Thomason wrote:
Quote:
--> Pulsar-List message posted by: Rick Thomason <rickyd54(at)gmail.com (rickyd54(at)gmail.com)>

Brian,
Have you checked for loose ground connection? I think the gauges read full when there is a broken/faulty ground.


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kulpa(at)att.net
Guest
PostPosted: Tue Mar 08, 2011 12:54 pm    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
If you're using standard Molex or similar connectors, try switching the contacts out with gold plating. You end up paying a small amount more for the gold plating but they will also not corrode.

Best Regards, Bill

Cell: 512-415-2991

Home: 512-261-6375

--- On Tue, 3/8/11, Brian Anderson <briana(at)xtra.co.nz> wrote:
Quote:

From: Brian Anderson <briana(at)xtra.co.nz>
Subject: Re: Capacitance fuel gauges - - - and stalls
To: pulsar-list(at)matronics.com
Date: Tuesday, March 8, 2011, 2:38 PM

Mmmm. Could be that the connectors at the wing roots need a bit of a clean. They haven't been touched in years. The problem is intermittent, although worse than it has been in a while. I think I can get at the connectors from inside the fuselage without having to pull the wings.

Thanks for all the suggestions.
Brian

On 9/03/2011, at 2:11 AM, Rick Thomason wrote:
Quote:
--> Pulsar-List message posted by: Rick Thomason <[url=/mc/compose?to=rickyd54(at)gmail.com]rickyd54(at)gmail.com[/url]>

Brian,
Have you checked for loose ground connection? I think the gauges read full when there is a broken/faulty ground.
http://www.matro====================


[quote][b]

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skipper144(at)juno.com
Guest
PostPosted: Tue Mar 08, 2011 1:50 pm    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
Bill
Do you have names and distributors
for connectors with gold contacts?
Thanks much,
Skip La Police
Pulsar III

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kulpa(at)att.net
Guest
PostPosted: Tue Mar 08, 2011 4:52 pm    Post subject: Capacitance fuel gauges - - - and stalls Reply with quote
I use Mouser, www.mouser.com as they are close and I can get parts overnight by ground. You can also find them at Digi-Key, Newark and Allied. Try Mouser first as they have the better search capability, find the part you want then order from your favorite supplier.

Best Regards, Bill

Cell: 512-415-2991

Home: 512-261-6375

--- On Tue, 3/8/11, Skip LaPolice <skipper144(at)juno.com> wrote:
Quote:

From: Skip LaPolice <skipper144(at)juno.com>
Subject: Re: Capacitance fuel gauges - - - and stalls
To: pulsar-list(at)matronics.com
Date: Tuesday, March 8, 2011, 3:47 PM

--> Pulsar-List message posted by: Skip LaPolice <[url=/mc/compose?to=skipper144(at)juno.com]skipper144(at)juno.com[/url]>

Bill
Do you have names and distributors
for connectors with gold contacts?
Thanks much,
Skip La Police
Pulsar IINavigator?Pulsar-List" target="_blank">http://www.matronics.com/Navigatorsp; - MATRONICS WEB FObsp; a href="http://www.matronics.com/contribution" target="_blank">http://w=======================


[quote][b]

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