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RV-14 forward trim in cruise- poll question

If your -14 needs full (or near) forward trim in cruise flight, is your plane a

  • Slow Build

    Votes: 2 100.0%
  • Quick build

    Votes: 0 0.0%

  • Total voters
    2
  • Poll closed .

BruceW

Well Known Member
Exploring a theory on why some RV-14s need full (or near) forward trim in cruise mode, and some do not.
(I am convinced it is a rigging issue, but NOT going there with this post.)

Of the -14s with lots of forward trim in cruise flight, is yours . . .
- slow build, or
- quick build ??



Thanks.
 
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Howz this . . . .

"Lots of" = Near or full forward (down) trim, where the trim tab is greatly extended from the neutral position.
 
I can't say the actual position of the trim tab since I have not measure it but based on my trim indicator, I have about 60% more travel if that is a linear deflection. But I know that my leading edge of the elevator is about 3/16" up from neutral position @180 knots or even faster. You maybe able to see it better if you click on the image and zoom in.
It is SB.
 

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I can't say the actual position of the trim tab since I have not measure it but based on my trim indicator, I have about 60% more travel if that is a linear deflection. But I know that my leading edge of the elevator is about 3/16" up from neutral position @180 knots or even faster. You maybe able to see it better if you click on the image and zoom in.
It is SB.

Most pitch trim installs are not linear. Most pitch trim indicators do not have neutral in the middle of the scale. The current RV displays neutral at the bottom 1/4 of the scale. Put some temporary marks on your trim indicator to indicate when the trim tab is really neutral.

Your in cruise elevator tailing edge down is typical for most. A while back there was a feed from Van’s that this is normal - and desirable. Don’t know. My simplistic view is it shows a HS that is putting in too much downward force. On my first RV I addressed this by adding a shim under the HS forward spar. It got the elevators better in trail for cruise, but used up all my nose up pitch trim for landing. The second RV I did the same but saw no improvement (as in drag reduction) so I pulled the shim out. On the current RV-8 I just accepted it.

Carl
 
Most pitch trim indicators do not have neutral in the middle of the scale. The current RV displays neutral at the bottom 1/4 of the scale. Put some temporary marks on your trim indicator to indicate when the trim tab is really neutral.
Carl

I do have marker for my neutral position and my 60% estimate was based on the run time of the trim. It is not hard to make additional markers or better yet, measure the deflection of the trim tab in terms of degrees.
 
RV-14 trim

I fly 14s and 10s a fair amount and when I do checkouts on either I emphasize that the 14 is a trimming needed machine and the ten even more so. With the huge range of speed and load it is needed. While checking folks out I usually verbalize “trim, trim, trim” all during the flights
 
Agreed. This will take some getting used to.
Flying my 'pitch sensitive' RV-7, I never re-trim and just put a little back pressure for landing speeds.

I fly 14s and 10s a fair amount and when I do checkouts on either I emphasize that the 14 is a trimming needed machine and the ten even more so. With the huge range of speed and load it is needed. While checking folks out I usually verbalize “trim, trim, trim” all during the flights

What of others that have posted about full forward trim???
 
Agreed. This will take some getting used to.
Flying my 'pitch sensitive' RV-7, I never re-trim and just put a little back pressure for landing speeds.

This is possible for an RV-7 that is mostly flown at a more aft C.G. position but if that is not the case then it is also possible that it has other issues (because it is not a normal thing for an RV-7 otherwise). Such as incorrectly shaped elevator trailing edges.
 
I'm not responding to the poll at this time, because I have not done the fiberglass gear fairings (legs, wheel pants, or intersections). I'm also still tweaking my full flaps setting, as a compromise between having full flaps available and not having the VP-X call a flaps fault when I go to full flaps and the PH Aviation actuator stops moving before the flaps are measured at the position number I want. But in ~120 hours of flying, I will say the following about trim in my taildragger RV-14:

Just like the RV-14 taildragger factory demonstrator that I got transition training in, there is a big pitch trim change between half and full flaps, to maintain speed. I have also noticed

The last bit of flaps movement appears to be the greatest rate of pitch trim change. I have noticed that my trim position at touchdown is noticeably backed off with the flaps set to stop a little short of full down, compared with where it was when the flaps were going to full down travel.

The trim is quite a ways forward in cruise, but not to the end of travel.

If I notice big changes when I do the fiberglass work, I'll try to remember to report back here. But those are my observations in RV-14 trim behavior so far.
 
So I measured my nose down trim and @182 knots my trim tab is about 4 degree from neutral which is about one third of overall nose down travel. A full nose down travel is about 13 degree from the neutral position.
 
This is possible for an RV-7 that is mostly flown at a more aft C.G. position but if that is not the case then it is also possible that it has other issues (because it is not a normal thing for an RV-7 otherwise). Such as incorrectly shaped elevator trailing edges.

+1

When I did my IFR training, the pitch sensitivity of the 6 was a bit problematic for holding 100" altitude on the gauges as a novice. It took some time to make the elevator skins perfectly flat, by manipulating the TE radius. Reduced pitch sensitivity by a good amount. Still very light and a joy to fly, just not overly sensitive. I recommend everyone reviews Section 5 and follows the guidance for radiused TE's.

Larry
 
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I recommend everyone reviews Section 5 and follows the guidance for radiused TE's.

Larry

Hi Larry, Bob From 153.

Always good advice from you as usual. However, in this case the 14's have a unique trailing edge on the the elevator and trim tab that is unlikely to be the cause of the OP's issue. Take a look at a 14 elevator TE the next time you get a chance and you will raise your eyebrows and say "that's different"
 
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We chronically run out of down trim in cruise on our RV-14A (quick build) and are contemplating replacing the E-01401 Trim Pushrod with the longer Ray Allen RC8-7 Clevis/Pushrod Kit (which came with the actuator). This would require enlarging the E-01402 Trim Cover Plate/E-01410 Trim Access Reinforcement Doubler/Horizontal Stailizer Skin (and possibly the E-01411 Reinforcement Doubler Brace) to accommodate the large forks attached to the Pushrod. Anybody done this and, if so, with what result?
 
We chronically run out of down trim in cruise on our RV-14A (quick build) and are contemplating replacing the E-01401 Trim Pushrod with the longer Ray Allen RC8-7 Clevis/Pushrod Kit (which came with the actuator). This would require enlarging the E-01402 Trim Cover Plate/E-01410 Trim Access Reinforcement Doubler/Horizontal Stailizer Skin (and possibly the E-01411 Reinforcement Doubler Brace) to accommodate the large forks attached to the Pushrod. Anybody done this and, if so, with what result?

I talked with Van's about that option; it can be done and requires a bend in the threaded rod to match the bend in the original pushrod. I bought the kit to do it from Ray Allen ... but, I didn't install. I read an article (by Paul Dye, I believe) where this threaded pushrod snapped in half and he had to land with elevator trim flapping around. That was a slower plane, so it was doable. RVs would be more problematic. The bend Van's recommended would further weaken the pushrod. I elected to keep the original pushrod.

When you say you are running out of trim, is that just on the indicator? Or, are you pushing the trim forward and get no further down-trim response? For me, it is an indicator only - the G3X reads full down trim, but I actually have plenty of trim left. I contacted Ray Allen and they said there is around 10% more servo movement than the position sensor indicates.

_Alex
 
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RV 14 Fwd Trim in Cruise Poll

RV 14 Tailwheel. Just my experience.
I was very surprised how benign the aircraft flew from first flight. No adjustment or further set up required. A/C flew straight and true out of the box. Much time and effort was spent on pre flight set up of all controls as per the Vans and Garmin instructions. (G3x 3 axis Servos).
Elevator trim - speed dependant in cruise, but normal just forward of neutral ( again time and effort spent on determining set up of the neutral trim position )
There is no configuration or speed at which the aircraft is not fully trim-able; Note in test phase did not trim to Vs1g or VNe.
Trim on Approach with 15 or full flap normal with ample range remaining. Approach speed range dependant on configuration\Weight currently 60 -80 kts,
although not a précis or actual AoA, calibrated AoA now used utilising Garmin GI.
Stop trimming at 5kts prior to Vat. (Again set up critical prior to use of AoA) Biggest pitch trim change is from a full flap TOGA - GA manoeuvre, however, Again easily manageable with ample trim range available.
Hope this may be of use. Test phase now complete. RV 14 U.K. LAA build.
 
Trim position

What MIGHT help this discussion is documenting actual trim position at the 2 extremes and other important reference points. I am going a little from memory so if anyone has the exact data please correct. To begin with probably the most reliable methods and consistent with Vans terminology is measuring elevator trim position is degrees from neutral. Vans states this is - 11 degrees to + 35 degrees I believe. If this is backwards, we all understand the issue. Initially mine was 9 degrees to 39 degrees. This looked off and I increased the rod length to give 12 to 37 degrees. (I was not sure if I had the newer version of the rod or not just seemed incorrect) I know not very data driven. After over 300 hours have gathered some data and take-off is in the +11 degree range and landing (full flaps) in the +16 degree range. I say range as I use the trim indicator and pictures to estimate actual position once on the ground. In cruise at 175 knots TAS and 10,000 ft. it's -1 to -2 degrees elevator trim. The Garmin auto trim is used and seems to work well and certainly better than my manual trimming. It seems -11 degrees should be plenty of actual trim needed. I am not sure if readers are just assuming the airframe should have equal amounts of +/- trim and thus brings out comments around not enough down trim available vs needed. I had QB wings and fuselage. CG slightly aft most of the time but in acro specs.
 
On my RV14 I set the elevator trim to neutral for takeoff. I observe the auto-trim adjustments don't move far from there in level flight at altitude. Of course the trim starts to move around with flaps.

I had previously adjusted my trim speeds to slower values than the Vans starting points ; there is another thread on that.
 
Trim indication

Anyone have a picture of their trim calibration? Neutral seems out of whack to me and my indicator reflects this.

Thanks!
 

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