What's new
Van's Air Force

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

Manual trim cable installation

LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
Pg 8-17 says "pry up the rubber button with a small screwdriver." Has anyone been able to actually do this? I'm digging and digging and can't get the darned thing off. Maybe I should just cut it with a box cutter and be done with it?

Also is the hole that should be drilled in the bracket fore of the fuel valve 7/16"?
 
Bob Collins said:
Pg 8-17 says "pry up the rubber button with a small screwdriver." Has anyone been able to actually do this? I'm digging and digging and can't get the darned thing off. Maybe I should just cut it with a box cutter and be done with it?

Also is the hole that should be drilled in the bracket fore of the fuel valve 7/16"?
Click to expand...


Mine didn't pop out. Just cut it out. I found a nice black plastic cap at Home Depot that fit in the top really nice.
 
replacement cap for manual trim

I found a crome button (for lack of better term) at Home Depot or Lowes.
Don't remember which now.
 
Stupid question time for me. I have my best luck at HOme Depot when I'm just browsing and find stuff. I never find it if I head right for where I think it will be. In what department can one find the beer can cap substitute?

Also, one other question: has anyone who has BOTH the Airflow pump and manual trim had any problem with that big 180-degree fuel line that goes from the filter underneath the bracket that holds the pump/filter interfering with the route of the cable?
 
Everything imagineable is in the way of the trim cable when using the AFP pump. The tubing from the tank also interferes with the cable as the hole in the F704 bulkhead is blocked.

I finally decided to route the trim cable through the RIGHT side of the tunnel as this is more open (at least in mine) around the plumbing area. The only problem I had doing this is the cable will not clear the F706 vertical rib flange cleanly. I will fasten an Adel clamp to the rib to keep the cable from chafing. The placement of the holes in the bulkhead were obviously not well thought out for IO engines with manual trim. :mad:

Maybe we are the only two in the world with IO engines and manual trim, I don't know.

The cable does not easily go through the snap bushings either. I read somewhere recently that you can get bushings with a slightly larger ID but can't remember where. I just reamed them out a little.

Larry
 
Bob Collins said:
Stupid question time for me. I have my best luck at HOme Depot when I'm just browsing and find stuff. I never find it if I head right for where I think it will be. In what department can one find the beer can cap substitute?
Click to expand...


On the hardware isle where the nuts, bolts and screws are at. Look in the sliding drawers that have the more oddball types of hardware in them. I found both a plastic black plug and a chrome metal one. I am not sure yet which I like better.


By the way, I know several guys flying with the vernier type button still installed. Having seen how sensitive the manual trim is (at speed anyway) I would definitely disable the vernier type button on the manual trim.
 
lrfrey said:
Everything imagineable is in the way of the trim cable when using the AFP pump. The tubing from the tank also interferes with the cable as the hole in the F704 bulkhead is blocked.
Maybe we are the only two in the world with IO engines and manual trim, I don't know.
Click to expand...
Heh heh. I actually pulled the fuel tank line out and redid it because I had it dropping slightly after the rib cover, just enough so it blocked the F-704 bulkhead, but there's no way I'm redoing that fuel pump line so Maybe I'll do down the right side too...doesn't seem to be much in the way obstruction. of course I've already cut the hole in the cover. Sigh.

I played around last weekend with the snap bushings. I think I'll be able to get the thing routed through them OK, if I put them on the cable first and then insert them into the bulkhead. That's the way it seemed to me anyway. I found it only slighly more difficult than getting the rudder cable through those bushings. We'll see. Thanks for the advice.
 
Curious

OK... I'm curious. Does removing the button affect how it functions?? In my -9A, I have not removed the push-button and I'm inclined not to because of the sensitivity of the trim. If someone's knee bumped the trim knob you could get a little surprise.

Am I missing something?
 
Yes, removing the button does affect the way it operates. With the button still enabled you could push it in and change the trim very rapidily. Disabling the center button only leaves turning it for adjusting the trim.

If fast enough, you could cause high G-loading possibly overstressing the aircraft. Not sure about the 9 manual but the -8 recommends it be disabled.
 
You have to remove the rubber covering t get to the "plunger" (basically just a 4 or 5" metal rod) that makes the Vernier aspect of the cable work. Disabling the function is just a matter of pulling out the rod and tossing it in the Homer bucket. Then, you're left with this hole there so the purpose of the button is cosmetic; to cover up the hole.

I read the Van's instructions and sat on my own "thinking bench" (a bench on my lawn where I do most of my "what do I want to do now" thinking) and decided to heed Van's warning. If you're not going to use the Vernier function of the cable, there's really no sense having the Vernier function. And Van's clearly recommends that the Vernier function be disabled.

Generally I consider trimming to be a task of small adjustments for which the Vernier function is not suited. Coupled with the control problems which may be associated with a rapid change in trim tab location, I decided -- not being an engineer -- that I would bow to the experts who designed the plane and take their advice.

The way my "thinking bench" session went, if there's a time I'd want a rapid adjustment in pitch, I'd use the control stick.

Of course, keep in mind the reason I put a manual trim in was because I was concerned about a runaway trim. So I'm a little more ...ummm... chicken about these things than a lot of people.
 
N523RV said:
OK... I'm curious. Does removing the button affect how it functions?? In my -9A, I have not removed the push-button and I'm inclined not to because of the sensitivity of the trim. If someone's knee bumped the trim knob you could get a little surprise.
Am I missing something?
Click to expand...
I think we're on the same wave length, just different peaks of it. Theoretically, yes, someone could bump the trim tab knob, but you can also adjust the friction on that sensitivity so a slight bump isn't going to change things. Plus they'd have to do more than just bump it, they'd have to roll across the top of it to turn it...and even then, that's not going to cause the same change in the cable that another scenario would. Let's say someone leaned over and used their hand to stabilize themselves by putting it on the top of the vernier knob....which then pushes the plunger, which then quickly changes the cable and puts full trim position in place?

Basically, the situation here is the Vernier function was never meant to be part of the design. It's just that 99% of the cable design make it functional for Van's purposes, and 1% did not. I think Van's is recommending that the 1% be eliminated. I don't think it's their view that there's really a proper role for a Vernier function in a trim cable.

That's the way I understand it, anyway, and I could most certainly be wrong.
 
Bob Collins said:
If you're not going to use the Vernier function of the cable, there's really no sense having the Vernier function. And Van's clearly recommends that the Vernier function be disabled.
Click to expand...

Maybe I'm missunderstanding you but the verneir function IS what you want. You are removing the push rod so that you can't override the vernier function.

N523RV said:
OK... I'm curious. Does removing the button affect how it functions?? In my -9A, I have not removed the push-button and I'm inclined not to because of the sensitivity of the trim. If someone's knee bumped the trim knob you could get a little surprise.

Am I missing something?
Click to expand...

If you take the push rod out you remove any chance of accidently making a rapid change in trim settings. Leaving it in increases the chance someone could accidently bump it and change the trim.
 
Bob Collins said:
I played around last weekend with the snap bushings. I think I'll be able to get the thing routed through them OK, if I put them on the cable first and then insert them into the bulkhead. That's the way it seemed to me anyway. I found it only slighly more difficult than getting the rudder cable through those bushings. We'll see. Thanks for the advice.
Click to expand...

Bob, I've got the AFP boost pump and manual trim as well (so has my friend). What we're getting concerned about is whether there is in fact enough trim cable length as supplied with the RV7(A) to follow the proper route all the way to the trim tab. Perhaps with the extra length of the boost pump cover there could be a problem. Perhaps the RV8(A) cable which is slightly longer might be the go. Does anybody have an answer to this.
 
Bob B... regarding cable length... yes it is definately a problem. In order to make the cable work you would have to come out the side of the pump cover somewhere. I did not like that option and sent the 7 cable back to VAN's and got the 8 cable (10" longer). This one is plenty long.

While on the topic of trim cables.... yesterday I ran mine back through the fuse, the HS and in to the Elevator.... well not quite! For some reason the hole in the rear HS spar is too small for the cable to go thru. Opening this hole (to 5/8 I believe) will mean the spar doublers will be drilled. I don't see a choice but it surprised me. Anyone else see this?

Larry
 
Muddy waters cleared...

Now I get it... removing the button completely eleminates the option doing large movements of the trim, forcing you to twist the knob to make any adjustments.

I'll take that into consideration.. I do have an unusual situation in that my wife flies from the right seat and cannot see the trim tab to set it neutral before T/O, so she pushes it in all the way and knows how many turns to do to get it neutral for her.

Thanks for clearing the muddy waters of my brain.
 
Great information! I guess this will work for us old RV6 guys who didn't get the FWF info?? (sorry to jump on your thread, but RV7s are cool too!))
Matthew: Suggestion for your wife's technique--on touch and gos I reset the trim using about two fingers measuring the exposed metal plunger under the trim knob for neutral trim (not exact, but pretty close). You get better at it with time. It might work for you guys. I'm right behind you at 60 hours so far.
 
Last edited:
lrfrey said:
Bob B... regarding cable length... yes it is definately a problem. In order to make the cable work you would have to come out the side of the pump cover somewhere. I did not like that option and sent the 7 cable back to VAN's and got the 8 cable (10" longer). This one is plenty long.
Larry
Click to expand...

Larry, is it possible that while the 7 trim cable is too short, the 8 cable might be too long. Have you fully installed the 8 cable....and where does the excess length go.
 
You must log in or register to reply here.
Back
Top