What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Manual Pitch Trim Cable Bend Radius - How Tight?

J

jpharrell

Well Known Member
I have been checking out the manual pitch trim cable and the routing from the fuel valve cover plate through the main spar. That first bend where the cable turns almost 180 degrees and heads to the aft looks really tight on drawing 32A. :eek: When I laid the cable out on the work bench and tried to put a bend in it I could get to about a 3 inch radius without major strain on the cable but the drawing looks much tighter than that (maybe 1.5 inch radius). I'm afraid the cable will take a set and the smooth action of the vernier control will be compromised. My gut says to check this out before just forcing the cable into this tight of a radius.

Can someone who has installed the cable tell me if the bend radius shown on drawing 32A is an accurate depiction and if the vernier works smoothly with that tight of a radius? Any photos of the cable routing in this turnaround area would be great. This may be one of those cases where you can just trust the Vans drawings and go with it and it works fine but it looks risky to me.

I am installing manual pitch trim with fuel injection. I just recently came upon the note buried in the instructions to order the longer trim cable if you have a fuel injection boost pump. I still have the standard pitch trim cable that came with the fuselage kit and I have hesitated to exchange it because I am using an Andair boost pump. It is very compact compared to the Airflow Performance boost pump and it looks like I may be able to route the cable "normally" with the Andair pump and plumbing. If anyone has done this, or tried and failed, I would love to hear about it and see photos if possible.

Thanks in advance to those who can contribute to this discussion.

John Harrell
RV-7A
Emp done, wings done, building fuselage
http://www.johnsrv7a.wordpress.com
 
Last edited:
Trim cable bend

Yes, I also initially thought the bend was excessive. My trim tab screw control is attached to the standard Vans Fuel Selector Box with a carburated 0-360. To answer your question, I have not experienced any resistance in this bend. I did add some lubricant to the cable before installation. The radius will 'find itself' as it makes that bend. I gently moved the cable forward and aft 'till the radius found itself-if that makes any sense!

Jim 7A N891DD
99%+ complete.
Lock Haven, pa
 
Trim Cable Length?

Great pictures Mike. Did you use the stock trim cable or did you exchange it for a longer one with the AFP boost pump?

John
 
manual trim cable

Here is one option for using the longer cable. I am using the Andair fuel pump as well. I have the cable routing out the front of the 'dog house' over the fuel pump, then up to the fuel selector plate. I did bend the fuel selector plate a little more to the vertical to make the cable parallel the angle of the fuel pump cover. It doesn't interfere with the operation of the fuel selector. I still need to relieve the opening in the front of the dog house a bit just to prevent the cover cutting the cable housing.

IMG_1485.jpg


Here is a side shot showing the extra bend in the fuel selector plate and the cable routing parallel to the fuel pump cover.

IMG_1489.jpg


Inside the cover the cable will be secured to the wiring runs when everything gets wrapped up.

IMG_1478.jpg


Note: this is my first time inserting images. I hope they linked ok.
 
Manual Trim Cable with Andair Fuel Pump

Wow Jeremy, nice job with your setup and thanks for the excellent photos. My plan is very similar to what you have done except I hope to enclose the cable within a slightly larger pump cover. Based on Mike's routing it looks like I can do that with the standard trim cable but I'll have to keep the fuel selector plate at about 45 degrees resulting in a tighter bend than you have. I guess those are the choices.

Also, the new Andair fuel pump has an tiny integral controller so the external controller on the bracket beside the pump is no longer required. That means I can route the trim cable tucked in right next to the pump body which is a little more direct. I'll have to post photos when I get it all worked out.

John
 
What is the feeling on bend diameter of 8", radius 4", for an approximate 180 turn? This is for a retrofit of electric trim servo on the 'rear deck'.

Thanks,
GH
 
Cuz!

Must be a distant cousin!
"Jeremy Hull
Atlanta, GA
RV7
emp done, SB wings done, QB fuse underway"

...'cept you are obviously a faster builder than I am. Oh well, most folks are faster than me, it seems. :rolleyes:
 
I suspect my bend radius is very close to the 4" you ask about. I too was a little worried about it, but it works just fine .... no issues whatsoever.
 
You must log in or register to reply here.
Back
Top