VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV General Discussion/News
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 01-08-2020, 02:09 PM
mtnflyr mtnflyr is offline
 
Join Date: Mar 2019
Location: Boulder, Colorado
Posts: 1
Default How to fix RV-6A that needs large changes in elevator trim

I bought a 6A some time ago and need some help understanding what changes I can make to it to reduce the need for large changes in elevator trim.

On final, I can't trim out the stick force with full nose-up trim. It's manageable, but I like to trim to a stable hands-off state and I can't do that today.

For takeoff, flaps up, the airplane rotates nicely with a fair amount of nose-up trim, and I have to trim aggressively down as the airplane accelerates. This isn't a huge deal for a normal takeoff but makes the airplane a handful on a go-around.

The trim movements I need to go from 80 mph to 120 mph are significant - much more than I'd like to have to do.

What should I check? CG comes to mind - I'm guessing that the airplane has a CG that is further forward than optimum. Would forward CG cause the need to trim more than a properly balanced aircraft? I don't want to start messing with stuff without understanding the aerodynamics causing the behavior I'm seeing.

The set up: Lycoming O-360 with a Hartzell constant speed prop. Battery on the aft side of the firewall.

Last edited by mtnflyr : 01-08-2020 at 02:11 PM. Reason: clarification
Reply With Quote
  #2  
Old 01-08-2020, 02:39 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
Join Date: Jan 2005
Posts: 3,616
Default

From your post, it sounds like you are a new (non-builder) owner. If so, hope the following helps:
1. Get a set of plans/drawings from Van's that will describe/show how the trim system works and is adjusted. All RV owners, builder or not, should have these plans and drawings. You will need them for basic maintenance and troubleshooting (and just to understand your plane) in the future. Can be found here:
https://shop.vansaircraft.com/cgi-bi...oduct=fd_plans

2. Assuming manual trim on a 6, you adjust the trim back where the trim cable comes out of the bottom of the elevator. There is a double set of nuts on the trim cable that can adjust travel both up and down where it connects to a bracket on the inspection cover plate. Generally speaking, a neutral trim tab should occur when the trim knob in the cockpit has roughly half of its turnability in each direction, but the actually amount of needed travel up and down in degrees is probably listed in the 6's manual and/or drawings. From your description it sounds like you need to make this adjustment.

Good luck.
__________________
Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto

Donation reminder: Jan. 2021

Last edited by alpinelakespilot2000 : 01-08-2020 at 02:47 PM.
Reply With Quote
  #3  
Old 01-08-2020, 02:41 PM
D Weisgerber's Avatar
D Weisgerber D Weisgerber is offline
 
Join Date: Sep 2019
Location: Ionia Michigan
Posts: 93
Default

The first thing I would do is a weight and balance. You might want to check the angle of incidence of the horizontal stabilizer also.
__________________
RV6 N7219d
IO-320-B1A
Sam James cowl
first flight May 2, 1997
RV8 #83830 tail done
Wing and fuselage kits ordered
Reply With Quote
  #4  
Old 01-08-2020, 03:20 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,145
Default

Quote:
Originally Posted by D Weisgerber View Post
The first thing I would do is a weight and balance. You might want to check the angle of incidence of the horizontal stabilizer also.
Plus one for these two items to check. RVs require a fair amount of pitch trim when flaps are used but if they are rigged correctly or there isn't a big issue with CG, all well within trim range. My RV7A needed trim but even with nearly full weight in the baggage, we never ran out of trim.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
Reply With Quote
  #5  
Old 01-08-2020, 03:33 PM
merlin3 merlin3 is offline
 
Join Date: Jul 2014
Location: ohio
Posts: 157
Default

I only trim based on different loads. I can takeoff, trim and never touch the trim again for rest of the flight. Something has to be majorly wrong.
__________________
Justin
Rv-6, o360, whirlwind cs prop, old paint and panel
Rv-4,o-320,prince prop, mgl avionics screens - sold
Reply With Quote
  #6  
Old 01-08-2020, 04:35 PM
RVDan RVDan is online now
 
Join Date: Jun 2012
Location: Frederick, MD
Posts: 748
Default

Quote:
Originally Posted by D Weisgerber View Post
The first thing I would do is a weight and balance. You might want to check the angle of incidence of the horizontal stabilizer also.
I second this. Even if the trim was misrigged, it should be much more sensitive. But I’d start with the basics, weight and balance. An aft CG will require excessive elevator, thus excessive trim. W&B is a place many home builders come up short.

If loaded CG is within limits, the next problem area could be horizontal angle of incidence. Need the plans set for that.
Good luck.
__________________
Dan Morris
Frederick, MD
PA28-140
Hph 304CZ
RV6 built and sold
N199EC RV6A flying
Learn the facts. "Democracy dies in darkness"
Reply With Quote
  #7  
Old 01-08-2020, 04:46 PM
DeeCee 57's Avatar
DeeCee 57 DeeCee 57 is offline
 
Join Date: Sep 2018
Location: Zürich W, Switzerland, Europe, Earth, Milky Way, known Universe...
Posts: 252
Default

yep, all good answers above.

Talking incidence, also check the wings incidence, then the HS incidence. The relation between those 2 is important.
__________________
Life's short... Enjoy!

DC aka Dan

http://www.aerofun.ch

RV-6 #25685, slider, O-360-A3A (carb/dual Lightspeed II), MTV-12-B, HB-YLL owner & lover
RV-4 #2062 HB-YVZ airframe builder
Reply With Quote
  #8  
Old 01-08-2020, 04:49 PM
Kyle Boatright Kyle Boatright is online now
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,007
Default

Quote:
Originally Posted by merlin3 View Post
I only trim based on different loads. I can takeoff, trim and never touch the trim again for rest of the flight. Something has to be majorly wrong.
That isn't my experience. Solo, my airplane requires full nose up trim to hold 75 knots with the flaps all the way down and power at idle. Effectively, this is my landing configuration. With a farther aft CG, the need for full up trim goes away. At the same (solo) CG and weight, trim is roughly neutral during full power takeoff and climb (assuming no flaps).
__________________
Kyle Boatright
Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10

Last edited by Kyle Boatright : 01-08-2020 at 05:01 PM.
Reply With Quote
  #9  
Old 01-08-2020, 04:49 PM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,007
Default hmmm...

Quote:
Originally Posted by merlin3 View Post
I only trim based on different loads. I can takeoff, trim and never touch the trim again for rest of the flight. Something has to be majorly wrong.
So you are saying that you do not trim for different speeds? Highly unlikely...
__________________
Bob
Aerospace Engineer '88

RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...

Dues+ Paid 2019,...Thanks DR+
Reply With Quote
  #10  
Old 01-08-2020, 05:03 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,346
Default

Quote:
Originally Posted by rocketman1988 View Post
So you are saying that you do not trim for different speeds? Highly unlikely...
Unless his c.g. is very far aft. At the true neutral point, there would be no change in elevator position with speed. And if the horizontal tail incidence was chosen just right, there would be no change in hinge moment either.

For the OP, assuming your trim system is mechanically adjusted so that you are actually getting full tab deflection, then your observations strongly suggest you are very nose heavy.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 600
also LS-6-15/18 sailplane
VAF donation Jan 2020
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:34 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.