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RV-3B Electric Trim question

Basco

Member
Anybody install the Ray Allen trim servo in the elevator? Vans sent me the plans for the kit, so I fabricated my own parts I installed it (already had servo). I notices the plans were for the RV-4, and just assumed there were no RV-3 plans because it was designed with manual trim. Now I'm wondering if it was a mistake installing the trim motor in the unbalanced elevator. (flutter from added weight) Looking at vans website they sell electric trim for all aircraft except the -3. Build support never mentioned anything about not installing electric trim in the elevator, and they sent me the plans. Any experience out there on this?
 
Ben, welcome to VAF!

Sorry, but I don't know anything about electric trim on the -3B. I'm using manual myself. My only suggestion is to get it as forward as you can manage it.

Good luck with the project... and please keep us informed as to how you're coming with it. My blog is the only RV-3B so far in the "My RV Build Project" section so there's plenty of room for yours.

Dave
 
I installed electric trim in my 3B, but did not install the trim motor in the elevator. I installed the servo motor under the vertical stab and connected it to the trim tab with a short flex cable. The 3 elevator is so small that I was reluctant to even try to fit the servo in it. Also the extra mass is a concern in an unbalanced elevator.
 
I installed electric trim in my 3B, but did not install the trim motor in the elevator. I installed the servo motor under the vertical stab and connected it to the trim tab with a short flex cable. The 3 elevator is so small that I was reluctant to even try to fit the servo in it. Also the extra mass is a concern in an unbalanced elevator.

This is how we did ours as well - shamelessly copied from Randy Lervold’s web site.... has worked very well for almost 800 hours now.
 
Yes

Yes, I've installed the trim servo in both my RV-3 and RV-3B in the elevator.
Moved it from my totalled RV-3 to the RV-3B when the manual trim cable broke at the horz stab torque tube on the RV-3B.

Also I kept the hardware real light. No forks, threaded steel rod and nuts. Just a bent 1/8" rod with washers and safety pins. No access panel. If I'd ever have to service the servo, I'll have to drill out the rudder skins rivets enough to get to it (just like I did when installing it in the RV-3B).

Mounted servo as close to forward spar as possible (hole through spar for the servo "screw").

Flew it in the RV-3 for 575+ hours without any problems.

But then I rarely, if ever, fly near top speed, although I obviously tested it in Phase 1 for the RV-3.

Finn
 
Thanks everyone, This -3B is a whole new building experience! I built an -8 years back and currently have a -3a with some friends while I build the -3B. The lack of accurate info on the -3B from Vans is interesting (and sometimes frustrating). I started this project 6 weeks ago, and just finished the tail last night. Hopefully this won’t be too heavy in the tail, or I may move the servo under the VS and run a short cable. I’ll try to post a couple pics
 
I’m obviously new to posting but I’ll try a pic
 

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Now I'm starting to get nervious

FinnFlyer,

Looking at the elevator trim arrangement on my RV-3 it appears that if the trim cable breaks the spring will drive the trim tab to full down trim or further.

Were you in flight when the cable failed? If so, were you able to overcome it with reasonable stick force?

Guys, what am I missing here?
 

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Rv3B trim

I built my 3B with a manual trim and glad I did. It is very easy to change trim quickly in flight. I take off with full forward trim to get the tail up then full back trim when the numbers are good . You can unload elevator stick pressure instantly.

Steve Lenne

Rv3B built and loving it.
 
I built my 3B with a manual trim and glad I did. It is very easy to change trim quickly in flight. I take off with full forward trim to get the tail up then full back trim when the numbers are good . You can unload elevator stick pressure instantly.

Steve Lenne

Rv3B built and loving it.

Manual trim works great. If you plan to fly any formation, it sucks. Easiest way to make the swap is to replace trim lever with trim servo and put a rocker switch on the stick.

Tony Spicer
 
FinnFlyer,

Looking at the elevator trim arrangement on my RV-3 it appears that if the trim cable breaks the spring will drive the trim tab to full down trim or further.

Were you in flight when the cable failed? If so, were you able to overcome it with reasonable stick force?

Guys, what am I missing here?

Mine did not have a spring. Fortunately I discovered it on preflight. Of course it could have happened during the previous flight; I just didn't notice anything unusual. In my case the danger would have been a flutter issue.

I did not want to take any chances, so locked it in place close to neutral and flew it the 120 miles home. Of course required more than normal stick forces, mostly at landing, but easily doable. At cruise it was just a question of picking
a speed that required least forces.

Finn
 
Early RV-3 manual trim design

Thanks Finn for shedding some light on my trim design. From your '3B as built not having a spring like in my '3 (a mid to late 70's kit) and from what little I can find in my preview plans, and '3 service bulletins, my trim control design has been updated or may even be the builder's own design.

Is there anyone who may have seen a trim control like the one in my RV-3? It has one cable in tension pulling against the spring to set the tab angle. My '3B preview plans refers to a F-341 trim cable assembly, but no mention of a spring.

My trim works very smoothly with no binding, I'm just concerned with the trim tab pushing full down if the cable fails.
 

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I don’t mind manual elevator trim, except that 90 percent of my flying is in formation, and I would rather not have to take my hand off the throttle to change the trim. My -3 that I’m currently flying has manual trim, and my goal is to have all functions (trim, smoke, freq flip/flop, electric flaps) all on the stick in my -3B I’m building. At least that’s my plan... It looks like that spring weighs as much as a trim servo
 
Would you need a spring if you used a push-pull cable?

The spring appears to be used so that a tension-only cable can be used.

Also, Tony's suggestion, of the manual cable driven by the servo, is nothing more than the same idea of a push-pull cable and the servo, except that it lets you try manual and then retrofit electric. The manual trim cable, mine anyway, weighs a little over 900 grams or about 2 pounds.

Dave
 
Thanks David for confirming the current design is a push-pull cable, which leaves me wondering is my cable in tension design what Van used on his first RV-3's or is mine a one-off system?

The only service bulletin I found about the trim system concerned the trim cable anchor in Sept 2006. It would not apply to my design.
 
Old RV-3 plans

Looking at old drawing (Ser#488) "Rudder and Trim System" there indeed is a compression spring.

On later plans (ser# 11064) that detail has been removed and moved to a different drawing (#27). There is no spring. So was changed to a push-pull cable.

Same on drawing #27 on thumb USB drive with recent RV-3B plans from Vans.

So, yes, it was changed from spring and pull cable to a push-pull cable.

Finn
 
Thanks Finn for shedding some light on my trim design. From your '3B as built not having a spring like in my '3 (a mid to late 70's kit) and from what little I can find in my preview plans, and '3 service bulletins, my trim control design has been updated or may even be the builder's own design.

Is there anyone who may have seen a trim control like the one in my RV-3? It has one cable in tension pulling against the spring to set the tab angle. My '3B preview plans refers to a F-341 trim cable assembly, but no mention of a spring.

My trim works very smoothly with no binding, I'm just concerned with the trim tab pushing full down if the cable fails.

Mine is the same, with spring and cable in tension. My plane seems to have been made up of several leftovers, so I am not sure of the age of the kit. Given that the rivet lines on my fuselage seem to be of an outdated version as well (different rivet spacing, single rivet line from the wings trailing edge on up), I would not be surprised if the fuse is from a very old kit as well.

My plane is in pieces at the moment for a complete overhaul. Just shot a quick snap of the tail, which happens to be here in my living room ;-)

RV3trim.jpeg


And you're making a valid point. Maybe it would be a good idea to at least limit the possible travel of the tab, so that breakage of the cable will at least keep it in a flyable (albeit possibly annoying) position.
 
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Manual trim works great. If you plan to fly any formation, it sucks. Easiest way to make the swap is to replace trim lever with trim servo and put a rocker switch on the stick.

Tony Spicer

Why does it suck for formation flying?

About 30% of my flying is in formation (with my Jodel). It has manual trim, and that plane requires a lot more trimming than RVs do. Yet I've never thought of taking my hand off the throttle for a split second to re-trim as a problem, even in the tightest of formations.

Or am I missing something?
 
Why does it suck for formation flying?

About 30% of my flying is in formation (with my Jodel). It has manual trim, and that plane requires a lot more trimming than RVs do. Yet I've never thought of taking my hand off the throttle for a split second to re-trim as a problem, even in the tightest of formations.

Or am I missing something?


I'm guessing the Jodel requires a lot less trimming than the RV. 80 mph and one g in the Jodel vs a constantly changing 70-170 mph and 1-3g's in the RV.

Tony
 
I have the standard rv3 trim cable that came with my 3B kit available if someone could use it. Never installed, about 137 inches long. It’s just collecting dust so if you could use it, PM me a reasonable offer and you pay shipping from north Florida.
 
I'm guessing the Jodel requires a lot less trimming than the RV. 80 mph and one g in the Jodel vs a constantly changing 70-170 mph and 1-3g's in the RV.

Tony

Well, that is the whole thing. Mine has 170 hp and a constant speed prop on it, and my formation flying is with Stelio Frati and Sequoia Falco's. They tend to fly a lot faster than my Jodel really should be able to do. Speed range of the Jodel is 60 to 160 mph, and a LOT of trimming required between those extremes.

Noordzeekust800.jpg


I don't see manual trimming as problematic, although I must admit that I never have had the opportunity to experience electric trimming during formation flying...
 
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Well, that is the whole thing. Mine has 170 hp and a constant speed prop on it, and my formation flying is with Stelio Frati and Sequoia Falco's. They tend to fly a lot faster than my Jodel really should be able to do. Speed range of the Jodel is 60 to 160 mph, and a LOT of trimming required between those extremes.

Noordzeekust800.jpg


I don't see manual trimming as problematic, although I must admit that I never have had the opportunity to experience electric trimming during formation flying...

Sorry, my goof! Guess all Jodels aren't VW powered!

Tony
 
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