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sdthatcher
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Joined: 13 Mar 2008 Posts: 91 Location: Port Saint Lucie
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Posted: Mon Nov 17, 2008 9:03 am Post subject: 9 Hour X-Country, engine purred, cables loosened! |
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Here is a rundown of my 9 hour x-country last month from Palm Beach Gardens, FL to Andrews, NC. It's only a 700 mile (statute) flight but I had headwinds and I kept the speed below 100 mph the entire trip. I put 40 pounds of baggage in the rear baggage area in order to help keep the nose up without using full trim during flight. And it worked beautifully. To alleviate my heavy left wing, I kept 12 gallons in the right wing, 30 lbs baggage in the right locker, and 6 gallons in the left wing. Now I could fly hands off most of the trip.
When I left Palm Beach Gardens, the aileron cables were tight although I didn't use a tensionometer to measure the tautness of the cables. My first stop was in Sebring for lunch. On takeoff, the left canopy lock unlatched. After Jay's experience, I throttled back and made a 500' pattern and retuned to land. Reseated the latch and again took off. Because of light turbulence (heavy in these LSA's), and strong headwinds with gusts, I decided to call it quits fairly early on Saturday afternoon and spend the night in Ocala, FL. I asked the FBO to tie down the aircraft and I headed to the Motel.
The next morning, I loaded the aircraft similar to above and noted that the tie downs were extremely tight. I would say at least 50-100 lbs of force were used to tie the wings down. At the time, I thought that was a good idea because of the gusty conditions but later wondered what affect the negative load had on the lower spar cap. A quick and dirty analysis indicated that the bending moments of 1100 ft-lbs (old school) would equate to a small 200 lb load at the center of the wing. That's about 0.25 g negative. Nothing to worry about. At least yet.
The next 6 hours were spent cruising around 4500 feet and landing at several locations for fuel. My first stop was at Tellfair-Wheeler in Georgia and to my surprise, they had no fuel and were completely unattended. So I made a short hop to Dublin and re-fueled there. Talked to a fellow who worked at the AMD factory and he mentioned I needed to look at the bearing covers on the wheels when I get a chance. He also spoke very favorably about the quality of workmanship and he really enjoyed the sound of that Corvair engine.
Next stop was to be Habersham at the foothills just south of Andrews, NC. But, while I was now at 6500 feet, it was very difficult to descend to land and make that long climb back up to altitude all over again so I decided to just continue over the mountains to Andrews.
It was about now that I noticed a slight difference in the feel of the ailerons. I could move the stick left and right about an inch without any movement of the ailerons themselves. As anyone knows when you fly over open water, the engine will invariably make small noises that you have never heard before just about the time you reach a point of no-return. And it is also true when flying over mountains, ailerons will start to buzz, cables feel like they are no longer attached and the engine starts making noises not heard before... you know the slight decrease in rpm that lasts about a thousandth of a second and causes your heart to momentarily stop.
30 minutes later I was pushing N601EL into my hangar in Andrews, NC. Other than directly over the mountains, she flew well and the engine ran exceptionally. My G-Meter showed that I had only experienced a 1.7 G positive and 0.4 G negative for the entire trip. But now I wanted to know what was going on with the cables. I pulled the seats out and ran my hand over the aileron cables and noticed they seemed much looser than when they were installed. Then I found the balance cable and it was limp... no tension at all.
I immediately ordered a Tensionometer from ACS and when I checked the cable tensions, here is what I discovered. Rudder Cable: 12-15 lbs. Aileron Cable: 10 lbs. Balance Cable: 0 (not measurable). Elevator cable: 10-12 lbs. Now what worried me was, "How does an aileron and balance cable become so loose in so short a time?" The only way I could think of was that the bellcrank moved or the wing geometry changed, both of which gave me a chill! But neither of these things occurred. I checked the fairleads and they were still in place. And all nicopress fittings were still attached and turnbuckes still safetied.
So I plan to re-tighten to the new specs of 40/30/22 +/- 5 (Elevator, Aileron, Rudder respectively) and recheck the lower spar cap and the rib attachment of the bellcrank. Anyone have any other ideas? From my experience though, check those cable tensions often because they seemingly loosen up without any reason! N601EL now has 25 hours of total time.
Scott Thatcher, Palm Beach Gardens, FL
601XL with WW Corvair, Registered as E-LSA
N601EL, http://placestofly.com, http://eaa203.com,
http://mykitlog.com/sdthatcher
Webmaster: http://zenvair.com
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_________________ Scott Thatcher, Port Saint Lucie, FL
601XL with Corvair, Registered as E-LSA
N601EL, EAA203 140 hours and not flying currently. |
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larry(at)macsmachine.com Guest
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Posted: Mon Nov 17, 2008 9:41 am Post subject: 9 Hour X-Country, engine purred, cables loosened! |
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Scott,
I'd have recommended you go for 20/30/20 tension as you reference,
because the wing structure only has to give an extremely small amount to
give up tension. 6061 is
somewhat like bubble gum and a rib with channel reinforcement will
deflect and with additional tightening repeated, you will see more loose
cable. I don't think for a minute
that lack of tension could cause problems, but certainly over tightening
will eventually cause you grief. Look carefully at the skin where the
bellcrank is located and see if you find any indication of reading the
flange line. I've seen the rib pronounced at this location where cables
have been over tightened and for that reason I maintain the lesser
tensions without problems. Different wing on my HDS of course, but I
have the same concerns.
Larry McFarland 601HDS at www.macsmachine.com
Scott Thatcher wrote:
Quote: | So I plan to re-tighten to the new specs of 40/30/22 +/- 5 (Elevator,
Aileron, Rudder respectively) and recheck the lower spar cap and the
rib attachment of the bellcrank. Anyone have any other ideas? From
my experience though, check those cable tensions often because they
seemingly loosen up without any reason! N601EL now has 25 hours of
total time.
Scott Thatcher, Palm Beach Gardens, FL
601XL with WW Corvair, Registered as E-LSA
N601EL, http://placestofly.com, http://eaa203.com,
http://mykitlog.com/sdthatcher
Webmaster: http://zenvair.com
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japhillipsga(at)aol.com Guest
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Posted: Mon Nov 17, 2008 12:34 pm Post subject: 9 Hour X-Country, engine purred, cables loosened! |
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Scott, 1/8 cable will stretch. Also in the early flying time fittings, bellcranks and bolts will seat themselves and all this will create slack in the system. Ask me how I know. Further, I can't tell the difference between a cable at 20 and 30 pounds tension. Maybe others can, but I can't. So the tension meter gage is the real answer. Since I found my slack cables my new maintenance is check the cables with the meter with every tire air pressure check. Chances are your cables were below standard margin when you got started. Great story and best of luck, Bill of Georgia 601XL-3300 140 hrs
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Ron Lendon
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Joined: 10 Jan 2006 Posts: 685 Location: Clinton Twp., MI
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Posted: Mon Nov 17, 2008 6:20 pm Post subject: Re: 9 Hour X-Country, engine purred, cables loosened! |
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Scott,
Great report.
The only experience I have with keeping cables under consistent tension is my guitar strings. I have been restringing guitars for many years and what I do is bring them all in to tune then stretch them slightly by pulling them away from the finger board. Then I re-tune and for the most part they stay in tune. Experience has taught me that without the stretching step I chase the tune of the guitar for about a week before it settles in. I would imagine this also applies to cables but haven't found the documentation that states so.
YMMV
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_________________ Ron Lendon
WW Corvair with Roy's Garage 5th bearing
CH 601 XLB
N601LT - Flying
http://www.mykitlog.com/rlendon
Corvair Engine Prints:
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ashontz
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Joined: 27 Dec 2006 Posts: 723
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Posted: Sun Nov 23, 2008 5:41 am Post subject: Re: 9 Hour X-Country, engine purred, cables loosened! |
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Excellent example. Same here. You have to pull on them pretty good too. And without stretching them first they can become quite slack too.
Ron Lendon wrote: | Scott,
Great report.
The only experience I have with keeping cables under consistent tension is my guitar strings. I have been restringing guitars for many years and what I do is bring them all in to tune then stretch them slightly by pulling them away from the finger board. Then I re-tune and for the most part they stay in tune. Experience has taught me that without the stretching step I chase the tune of the guitar for about a week before it settles in. I would imagine this also applies to cables but haven't found the documentation that states so.
YMMV |
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