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RV14 insufficient forward trim above 140KIAS

MalSmith

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Hello all,

Whilst flying my RV14 taildragger i am experiencing inadequate forward trim over 140KIAS, with full forward trim the aircraft will sit in a nose up position and i am unable to trim for level flight.

The revised trim actuator arm from Vans was installed at the time of build.

I have heard from another RV14 builder that he had the same issue of not enough forward trim. The builder custom made a new trim actuator arm that was 5-6mm longer than the revised arm supplied from Vans. This has fixed his issue and he now has trim throughout the speed range.

Has anybody else experienced the same issue? If so how did you rectify the problem?
Any comments welcome.

Thankyou Mal.
 
I've always had enough nose down trim in my tri gear 14. The revised arm came out before my first flight so I have always flown with the new one.

Even at max aft CG it has always been plenty at any speed.
 
Hello all,

Whilst flying my RV14 taildragger i am experiencing inadequate forward trim over 140KIAS, with full forward trim the aircraft will sit in a nose up position and i am unable to trim for level flight.

The revised trim actuator arm from Vans was installed at the time of build.

I have heard from another RV14 builder that he had the same issue of not enough forward trim. The builder custom made a new trim actuator arm that was 5-6mm longer than the revised arm supplied from Vans. This has fixed his issue and he now has trim throughout the speed range.

Has anybody else experienced the same issue? If so how did you rectify the problem?
Any comments welcome.

Thankyou Mal.

Additional info regarding airplane configuration (engine and propeller that is installed, any other deviations from a standard built to plans build, etc.) would be helpful.
 
This is the first I’ve heard of a revised trim arm and don’t see anything in the revisions. Was this a very early change? Information pointing to this would be appreciated.

Builders with empennage kits shipped prior to 10-Jul-14 were advised on 5-Nov-14 to contact Van's for a revised E-01401AB "Elevator Trim Pushrod Parts". The text of that notice was as follows:

"Van's Aircraft has determined that the existing Elevator Trim Pushrod has insufficient length for proper RV-14 elevator trim tab movement. For builders with empennage kits received earlier than July 10th, 2014, contact Van's and request a new E-01401AB Elevator Trim Pushrod. Fabricate and install the replacement Elevator Trim Pushrod per Pages 09-12 and 09-24 in the RV-14 fuselage plans pages.

Be advised that these Plans page updates have been posted to our website on 10-17-14. Please visit www.vansaircraft.com, click on Support, then Service Information and Revisions.
"

This is what the original pushrod would yield. This is explained in more detail here in this blog post.

Down+limit,+horn+contacts+skin.JPG


Here's a comparison of the pre 10-Jul-14 pushrod (top) with the post (bottom).

IMG_6365.JPG


As explained in this blog post, elevator trim travel is correct with the revised trim tab.

IMG_7352.JPG


IMG_7353.JPG


The original N214VA demonstrator, as of 7-Aug-14, did not use the same pushrod design. The picture below is from my visit to the home base on that day, outlined in further detail here.

20140807_142940%2Belevator%2Btrim%2Bpushrod.jpg
 
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We have built an RV14 Taildragger, stock lycoming io390 with scimitar hartzell 74" prop. VPX ECB and dual G3X displays, stock standard installation.

When testing the trim the aircraft had full fuel, both pilots weights were 91kg and 89kg respectively and there was nil baggage on board.

The link below has a detail of the revised trim actuator that was installed as specified by Vans.

Thankyou for taking the time to reply and for the information received to date.


https://photos.google.com/share/AF1...?key=dmR2RkJxOWhpUGdaczVCWXJmeXZGX3pRQnZVR0Fn
 
Hello all,

Whilst flying my RV14 taildragger i am experiencing inadequate forward trim over 140KIAS, with full forward trim the aircraft will sit in a nose up position and i am unable to trim for level flight.

The revised trim actuator arm from Vans was installed at the time of build.

I have heard from another RV14 builder that he had the same issue of not enough forward trim. The builder custom made a new trim actuator arm that was 5-6mm longer than the revised arm supplied from Vans. This has fixed his issue and he now has trim throughout the speed range.

Has anybody else experienced the same issue? If so how did you rectify the problem?
Any comments welcome.

Thankyou Mal.

Hmmmm. I haven?t seen this. I have flown the demo RV-14A at max gross weight, including max baggage, and I see the auto trim barely moves forward in cruise flight. I?m inclined to think ther may be something else going on with your airplane. Don?t hesitate to contact me and we can discuss.

Vic
 
Having a similar situation with insufficient nose down trim. Testing my CG limits during phase one. I believe I have the revised link, 4-14/32" hole center to center, since the kit is fairly new (Jan/2020). I have 8 degrees up (nose down), and 39 degrees down (nose up) well outside of Van's 11 and 35 min/max numbers. Anyone have a measurement of their link that I can compare? Thanks.
Juliette
 

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Basic question, does the elevator trim tab have the required up/down deflection as required in the plans?

Outside chance, but did someone added a shim under the Horizontal Stabilizer forward spar? This is not an unusual mod on older RVs to correct for too much Horizontal Stabilizer downward force.

Carl
 
IO-390 RV-14 flys with neutral trim in cruise. Neutral Trim puts the tab in line with the elevator. The neutral position is somewhere in the 35% of the trim range (don't quote me on this figure I am trying to recall off memory. This leaves 65% of available for trim up. I never need to go more than 30% trim down. Anything over 100 kts requires very very little trim change. Below that I need trim up.
 
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Having a similar situation with insufficient nose down trim. Testing my CG limits during phase one. I believe I have the revised link, 4-14/32" hole center to center, since the kit is fairly new (Jan/2020). I have 8 degrees up (nose down), and 39 degrees down (nose up) well outside of Van's 11 and 35 min/max numbers. Anyone have a measurement of their link that I can compare? Thanks.
Juliette

I have 8.5deg up (nose down) trim. In flight, the trim indicator looks like it is pegged at the full nose-down indicator as well; however, both the autopilot and manual trim can go past this position indication to provide ample nose-down trim even at max speed in all CG and weight/load configurations.

I first contacted Ray Allen, since I thought it was an issue with the position sensor built into the servo - it wasn't (and it turns out that when the sensor is maxed out, there is at least 10% additional servo arm travel past this point). I then communicated with Van's support several times, and the consensus was that the indication is of no matter as long as there is adequate trim - even though I only measure 8.5deg nose-down trim. I calibrated the G3X correctly, and I have the revised push arm linkage.

The options from Van's were to either leave it alone since it wasn't an issue in flight, or to use the Ray Allen adjustable rod arm. If I decided to do the latter, then the threaded rod arm would need to be bent, much like what "E"'s picture (above) shows with the prototype RV-14A. I purchased the adjustable arm and was going to implement that solution ... until I read an article in Kitplanes magazine about an airplane (not an RV) that had used the same bent threaded arm, which eventually failed at the bend point in flight. Nope! I'll just live with the wonky indication on my G3X.

-Alex
 
This is my experience…

IO-390 RV-14 flys with neutral trim in cruise. Neutral Trim puts the tab in line with the elevator. The neutral position is somewhere in the 35% of the trim range (don't quote me on this figure I am trying to recall off memory. This leaves 65% of available for trim up. I never need to go more than 30% trim down. Anything over 100 kts requires very very little trim change. Below that I need trim up.

Trim tab neutral in cruise in my RV-14, flying 3+ years now, stock 390, 72” Hartzell BA aluminum prop, regardless of loading. I use a lot of up elevator trim when flaps are deployed to achieve and maintain approach airspeed, but have plenty of trim available to do so. I agree with Vic, something else seems to be going on. My kit was 140329, shipped August, 2016.
 
Having a similar situation with insufficient nose down trim. Testing my CG limits during phase one. I believe I have the revised link, 4-14/32" hole center to center, since the kit is fairly new (Jan/2020). I have 8 degrees up (nose down), and 39 degrees down (nose up) well outside of Van's 11 and 35 min/max numbers. Anyone have a measurement of their link that I can compare? Thanks.
Juliette

Old version is 4-15/64” centre to centre.
 
Thanks everyone for your help. I decided to make a new link from the oil door scrap (same thickness). Extended the length by approximately the diameter of the pin (.125) in order to change the trim tab from 8 degrees up to twelve. The indicator on the G3X is still near the top of the nose down scale, but at least I'm feeling more confident in continuing my aft CG testing.
Juliette
 

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Thanks everyone for your help. I decided to make a new link from the oil door scrap (same thickness). Extended the length by approximately the diameter of the pin (.125) in order to change the trim tab from 8 degrees up to twelve. The indicator on the G3X is still near the top of the nose down scale, but at least I'm feeling more confident in continuing my aft CG testing.
Juliette

I like this solution; thanks for posting. Let us know how the testing goes, please.

_Alex
 
Sorry for the long delay in responding.... having too much fun flying now that phase one is complete. The longer link is working out great so far (75hrs); can fly full aft cg with a little trim to spare.
Juliette
 
Sorry for the long delay in responding.... having too much fun flying now that phase one is complete. The longer link is working out great so far (75hrs); can fly full aft cg with a little trim to spare.
Juliette

Great to know; thanks for the update! I talked with Van's support (actually they contacted me directly, due to this and another post), and they suggested that I fabricate a new linkage similar to yours.

My plane is still in the paint shop, but once I retrieve her, I'll be fabricating a new one like yours.

_Alex
 
Im still curious about the outlying question; why would full trim be needed for cruise flight? That amount of trim deflection has to slow things down.
Rigging problem? An extended pushrod seems to be avoid the larger issue.
 
Im still curious about the outlying question; why would full trim be needed for cruise flight? That amount of trim deflection has to slow things down.
Rigging problem? An extended pushrod seems to be avoid the larger issue.

At least for mine, I still have nose-down trim available - it just registers full deflection on the G3X because the position sensor doesn't detect the last ~10% of travel (according to the manufacturer, and confirmed by me on the ground).

That said, Van's still isn't sure why some of us are having this problem ... at least when I last talked with them. The support tech stated that they have had a number of -14(A) planes with a similar issue, with no known rigging issues. I know that I went back-and-forth with them showing various pictures of potentially affected parts, I took measurements, etc. - nothing pointed to anything that either Van's or I could notice.

I'll note that there were known issues of the pushrod being too short for the original -14(A) kits, since those older rods didn't provide enough nose-down trim. That issue was corrected using a longer pushrod in later kits. The fact that some of us have to add another ~1/8" to the pushrod might simply be an extension of the original problem that was previously addressed by Van's.

_Alex
 
A photo of the trim tab in the limiting “I don’t have enough nose down trim” position would answer many questions.

For properly rigged RVs and with W&B in a neutral zone, the trim tab should be close to neutral (as in the in trail position) in cruise.

Carl
 
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