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701 Elevator Cable Balancing

 
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beachyjeff(at)juno.com
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PostPosted: Sat Jan 12, 2008 10:44 am    Post subject: 701 Elevator Cable Balancing Reply with quote

I am currently flying my Phase 1 test hours. One thing I noticed is a
tendency for the stick to move to the left. I don't think this is a heavy
left wing, but rather the elevator cable tension caused by the elevator
bellcrank being off-center. This is a common issue with the 701 and has
been discussed in the archives. I have installed the bungee as instructed
and it helps, but the control stick still favors moving to the left side.
In searching the archives, I found one builder who installed a nylon
fairlead on the back bottom of the baggage compartment for the upper
cable (that is, the upper cable at the aileron bellcrank 7C1-1. This
cable goes to the bottom of the elevator) to run through. In
experimenting, this solution does a better job at evening the control
stick balance between left and right. For any of you that have installed
such a fairlead, is this a good solution? Have you had any issues with
the side pull on the aileron bellcrank that such a fairlead would
produce? How long does the nylon fairlead last before wearing through?
Have you had any problems with using such a fairlead? Any things to look
out for?

My issue with the bungee is that, to completely balance the stick, my
upper cable (at the bellcrank) is pulled so far to the starboard side
that it hits the flaperon control threaded rod. Also, my lower cable just
brushes the 7F6-1 bottom channel. I can add a piece of nylon on top of
the bottom channel but I would prefer that the cable doesn't rub it at
all. I have also considered remaking the aileron bellcrank with a
slightly raised lower hole, but this will affect the elevator travel.

If others have different solutions (in lieu of the bungee), I would be
interested in reading and seeing those solutions. Thanks!

Jeff Beachy
CH701, Phase 1 Testing


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jpspencer(at)cableone.net
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PostPosted: Sat Jan 12, 2008 3:46 pm    Post subject: 701 Elevator Cable Balancing Reply with quote

Instead of the bungee(which I think is to keep the cables from rubbing together??) I slipped a long length of vinyl tubing over one of the cables and then just let them rub. I will inspect that cable for corrosion under the tubing annually but don't really expect to find any. I also put a rub guard on the lower crossmember you mention. I am running my down cable as loose as I can stand it to avoid binding with right aileron application, particularly with flaps extended.

Joe
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beachyjeff(at)juno.com
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PostPosted: Sat Jan 19, 2008 4:37 pm    Post subject: 701 Elevator Cable Balancing Reply with quote

Last week I reported the tendency of my control stick to pull to the left during my initial flights. I am pleased to report that I have solved the issue using only the recommended bungee. I kept experimenting with different elevator cable tension until I had the cables tensioned as tightly as possible without causing any binding on full right stick deflection. At this point the cables are loose, far too slack to be acceptable. Next, I added a bungee, trying different lengths and different vertical L-angle locations to find the one that would tighten both cables to acceptable levels at full right and full left deflections. The bungee tightens the cables nicely, but it also adds tension to the cables when using left stick deflection. This balances the stick forces, since the cables naturally tighten with right stick deflection and are tightened by the bungee with left stick deflection.

I added the bungee on the right side of the fuselage to the short L-angle which goes from the back of the baggage compartment down to the bottom of the fuselage. It attaches to the uppermost elevator cable (which travels back to the bottom elevator horn attachment. No bungee on the lower elevator cable that travels back to the upper elevator horn attachment. I also had to enlarge the U-shaped cutout on the L-angle just in front of the lower elevator horn attachment since the bungee pulled the down elevator cable more to the right, enough so that it scraped the L-angle on the side. It took two days of working at it, but I am very pleased with the control stick forces and balance I now have.

Thanks to all who responded with suggestions.

Jeff Beachy
N701N, Flying Phase One Hours




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