Elevator/stab trim

[jmodguy]

Thanks for the inputs. Guess I should be less vague about my intentions or why I'm asking about this.
I'm running a Lyclone and need a little more weight in the tail. I can put bigger batteries in the tail area and get my W/B correct without adding dead weight (Lead). To do this I need the area taken up by the HS trim servo. I guess my question is this; Is the elevator trim tab effective? I will be installing vortex generators across the windscreen to help control the air disturbed over the windscreen/H stab in high AoA situations.
Cheers!

[Dave S]

Hi Jeff,

That helps with understanding your original question.

Don't know if this may be helpful; however, of the KF builders I know of who did an S5 with a heavy engine, the battery was located approximately below where the fuselage handle is attached to the upper longeron - so it was ahead of where the jackscrew mechanism is located. I have not heard of anyone using a heavy engine with the manual trim tab system.

I am hesitant to speculate that my experience concerning elevator effectiveness with the manual trim (and a lighter Rotax) on a Trigear would translate to effectiveness of the manual trim system on an aircraft with a heavier engine in the tailwheel configuration.

[airlina]

Jeff I have the Series 5 with the Continental IO-240 engine (weighs at least 250 LBS) and the trimmable stab , which I believe is a necessity for the heavier engines. I don't think the trim tab option would have near enough controlability for your situation. The problem shows itself at approach speeds with full up trim . Early on that was a problem on my plane , where I would need aft stick pressure with full up trim coming down final. This was not an acceptable characteristic for me , so I went about the fix. First , like you said , get as much useable weight aft as you can. (I didn't want dead ballast weight, that to me is a sin) so in the empennage I have my battery (odyssey,) and my ELT behind the battery. Any item that could be mounted behind the seats practically , i did. This included a holley fuel pump , A/P servos , strobe box etc. Next is the trim assist kit-when Kitfox came out with this mod , I added it and it was a game changer. Last is gap seals on the stab the elevator. While it is hard to quantify the overall results , I did notice a difference especially in the flare with enhanced elevator authority . I also have a wiring diagram for a fast /slow trim speed switch for the trim , that I could send you if you go this route. I think Kitfox sells a speed controlled version of this as well. Bruce N199CL

[jmodguy]

Thanks all.
My batteries are currently just in front of the trim servo. I have dual Odyssey High performance batteries stacked back there due to the EFII system. I'm also in the "dead weight is a sin" camp. That's why I'm chasing this. Bought a couple slightly larger batteries that will fix the dead weight issue and they are slightly too large... So I was digging around back there (took the elev/stab out because I ordered the larger elevator) and thought "Hmmm If the servo was gone they would fit". If I can't fit them I will keep the batteries I have and add some lead shot or a dive weight. I'll stay with the servo as installed. Good to hear the elevator gap seal is somewhat effective. Never understood why the rudder was faired but the elevator was not.
I picked up the elevator spring kit when I was at S&R last April and it is installed. Took the spring out for now though.
Wish it would warm up - need to get back to the BossFox and get it finished.

[redbowen]

You can fit the battery just in front of the Trim actuator In the doodle 5-7. No need to convert to manual trim. As far as a heavy engine full up trim takeoff goes, I actually had a trim actuator failure on take off where it failed from takeoff position to full up trim. Let me tell you it is startling but completely controllable, in fact the airplane can be controlled in all trim positions it will just have heavy stick forces. I have attached the trim failure video, skip to 9:38 in the video.

[jmodguy]

Bryan,
How many hours on the trim jack screw at failure?

I was actually considering electric trim tab not manual.

[redbowen]

It had about 400 hours, but way over a thousand landings and it was 17 years old. No troubles with the replacement.

Bryan,
How many hours on the trim jack screw at failure?

I was actually considering electric trim tab not manual.

[airlina]

Also had mine fail last year , but it was the trim motor failure only , jackscrew was reusable. Luckily was on local flight , would have been a hassle if I was on the road. About 900 hours , 17 years, so no complaints. Bruce N199CL