Larger Elevator Trim Tab

[andoman]

No doubt about it: my HR2 with -4 tail feathers needs more elevator trim tab.
This cat has been skinned before. See this short thread:

Great Ideas...

My buddy Slim (a real craftsman) has these great ideas for Rockets but would work on any RV. First is a very simple rudder trim device made with a bungee. The other is a larger elevator trim tab for Rockets, really helps at low speed. Enjoy! Smokey HR2 Rudder Trim Big Trim

vansairforce.net

Unfortunately, the pix in the tread no longer post.
Anyone have any details on the trim tab mod referred to?
I‘m about to make a new tab with about 20% more chord, but I’d like to go down a road successfully traveled instead of throwing my TLAR ideas into the air. ;-)

Dan

 

[rv8ch]

...
I‘m about to make a new tab with about 20% more chord, but I’d like to go down a road successfully traveled instead of throwing my TLAR ideas into the air. ;-)

Dan

Wise. I'm sure you know about this crash which resulted from the failure of a trim tab.

The Galloping Ghost (aircraft) - Wikipedia

en.wikipedia.org

While I doubt an RV or a Rocket would be as difficult to control without the trim tab, I'm sure you can think of scenarios where a failure would result in a very bad day.

 

[PCHunt]

Just curious what the issue is? Not enough nose up trim available during landing? Or something else.......

 

[131RB]

I to am curious what your issue is. I have a standard RV4 tail on my rocket and have plenty of trim. Is your trim manual or electric and if electric there are at least 3 different Ray Allen trim servo's with different throws. Any chance you just don't have enough throw?

 

[andoman]

I have the longest travel RA servo.
Wing and stab incidences are correct
-With a 165 lb pax and 90 lbs of baggage I run out of nose down trim in cruise.
-Solo with 1/2 fuel and no baggage, I’m short of nose up trim unless I land no flap.
I can bias the tab’s travel to cover a CG with 40 lbs of ballast in the baggage compartment, but that isn’t optimum.
I need a larger tab and it appears other Harmons have had the same issue.

 

[Ralph Inkster]

I wonder if your trim tab was built with the longer(manual) tab lever. Electric trim tabs should have a shorter lever, giving the servo more ‘sweep’.
Maybe someone can measure their tab skin to link distance to test if this theory might be the issue.

 

[andoman]

Excellent suggestion, Ralph. I will check the plans and measure.
I’m still hoping for more info on the larger tab mentioned in Smoky’’s 2009 thread.

 

[131RB]

I think Ralph is probably correct. Without measuring I can’t tell you what my exact throws are on my tab but I would guess at least 45deg. My tab is standard size for an RV4. I have never run out of trim in any load configuration.

 

[andoman]

EDIT: The -7 and -8 actuator to horn attach point for electric trim is indeed closer to the hinge point. It’s obvious that my trim tab was set up originally as a -4 with manual trim. I shall copy the -7 trim tab horn for electric trim and I think my problem will be solved.
Thanks for the input.
I really do wish someone would chime in ref the larger rocket trim tab. It is a curiosity.