Lets talk elevator trim

[TJay 1041]

I was thinking about extending my elevator today but can't decide what to do for trim. I am stuck between trim tab with a servo in the elevator or the much simpler aerotrim that connects to the control stick. What Is the reason some put it in the elevator and some just use bungees, they are both doing the same thing.

[1avidflyer 1983]

I think if it was me, I would go with the spring hooked to the trim lever like some one posted a few days ago.  As simple as anything and pretty near fool proof.   I had the electric trim on the yellow Avid in my avatar, and on the second day I flew it,  the pin fell out on the rod connection to the trim tab.  Happened just as I was lifting off the ground, and at first I wasn't sure what was going on, and ended up having to go around the pattern with the trim tab flopping up and down.  Don't know what happened, I had things apart when I went over the plane before I flew it for the first time, and the day before it came undone  I had flown the plane about 30 miles home from an airport where I did the first flights on the plane.   I can say this, the joystick will really flop around when the trim tab is unhooked.  I probably never got above 60 MPH on the flight, cause I throtteled back as much as I dared and did a tight pattern to get back on the ground.  Would have been worse at 80 or 90 I'm sure.  My guess is I some how didn't get the cotter pin put back in, not sure how I would have missed it in a couple of preflights, but don't have a good reason why it could have fell out either.  Now you know why I used the term fool proof.   I must say, I usually don't use the trim much anyway, usually just to take the pressure off the stick in level flight.   Jim Chuk

[LSaupe 123]

I added three inches to the cord and also used the HIghwing LLC trim kit.  Went together real well.

 

 

 

 

[tcj 150]

You don't need elevator trim on an early kitfox.  Rig the horizontal stab so it flys level with just you and a light fuel load in the plane.  Anything else you put in the plane will move the CG rearward then you trim the nose down with the flaperons.  The plane was designed to trim with the flaperons.  You will never need nose up trim.  For landing approaches the stick force is very light to hold a slow approach speed and you can feel whats going on so know if you're getting near a stall.

Edited 22 Mar 2015 by tcj

[akflyer 1427]

My avid has always needed almost full up trim to fly level unless I load it with an aft CG (around 18" I can fly with no trim needed)  The flaperons will do some trimming, but then the roll forces get a tad heavier.  I like to play with the flaperons and watch the AI.  Its pretty easy to find the sweet stop of the flaperons as the airspeed increases and the stick forces are lighter when they are set in the optimum position.  Yes I could fly my plane without the elevator trim, no I don't want to fly my plane without elevator trim.

 

On my buddies Kf II we just put a fixed tab on the elevator and set it.  For some reason, the stick forces on the KF are lighter than the Avid and it takes a much smaller tab to trim it.

 

[C5Engineer 1170]

With one that attaches to the linkage you are deflecting the entire elevator which induces a lot of drag. A tab is a much smaller surface. Being able to trim at your fingertips with your hand on the throttle sure is nice! I vote for an electric tab. Is the horizontal adjustable on the early foxes?

[EDMO 1078]

With one that attaches to the linkage you are deflecting the entire elevator which induces a lot of drag. A tab is a much smaller surface. Being able to trim at your fingertips with your hand on the throttle sure is nice! I vote for an electric tab. Is the horizontal adjustable on the early foxes?

Joey,

The Kitfox 1 and 2 that I owned - the HS was not hardly or easily adjustable - I think the Kitfox 4 may have had 3 different positions - The Kitfox 5 had a large servo unit (I have a new one) to electricly adjust the HS.

I plan my flying trim tab to be a manual control, and the flap trim tab to be an automatic manual control connected to the flap control.

I have the Kitfox 5 servo, and 2 (one untested) trim tab servos for sale.

EDMO

Edited 22 Mar 2015 by Ed In Missouri

[akflyer 1427]

Joey, on the earlier kit foxes, there were a couple holes in the forward mount tab on the horizontal stab.  You could move the leading edge up and down.  Some guys added a third hole for use on floats.  I tried that on mine but we dont have a wide enough slot that our horizontal goes through to move the leading edge up or down.  I would love to lower my leading edge about a 1/4" and not have to carry so much uptrim on the tab, especially when on floats, but I would have to do a lot of rework in order to make that happen.  I just need to make a larger elevator and larger tab like yours is.

 

[1avidflyer 1983]

Hey Joey, I'm not arguing with you or anything, but am pondering this in my mind...  I wonder if there is a difference in drag.  You wouldn't need to lift the elevator much to change the flight attitude, compared to how much the tab has to move to do the same thing.  Not arguing, just wondering.   As far as it goes, on the Avid rebuild I'm doing, I did buy a new trim cable instead of just going with the spring, but if the elevator didn't have the trim tab built into it, I'm thinking I wouldn't  add it for myself.  If I ever get back to finishing the Kitfox 4,  that comes into play, because it didn't have a trim tab, and I covered the elevator already.  Guess that one will get the spring.    Jim Chuk

[C5Engineer 1170]

Just going off stuff I've read Jim no experience or facts to back it up. Most planes including jets have a moveable stab. I used a bungee cord on my stick for 5 years hahaha. I imagine the drag is negligible at 80 mph. I just love how instant the response is on my Ray Allen set up. It just requires tiny blips on the rocker switch. Don't know how I flew it so long without trim especially on those 10 Hobbs hr days to Idaho. Between the trim, Hacman, and prop Ive got a high performance complex going on ))

[EDMO 1078]

Why not just eliminate the elevator and trim tab altogether, and make a "Flying Tail" just using the stabilizer, with electric trim on it? This has been done before.

EDMO

[TJay 1041]

Now were talking ED, Just when you thought you were done with your build, ha time to start over.

[EDMO 1078]

Now were talking ED, Just when you thought you were done with your build, ha time to start over.

I WILL leave that to the younger designers/builders - mine is already welded.

EDMO

[TJay 1041]

Yeah I think I have decided to just start out with a spring aero trim for now since I have it, its light weight, less corners to fabric, way less time spent welding, and 1 less hinge to oil and check on preflight, It might not be as fast but hey at 70 mph it will be ok. And if I don't like it, ill have something to do next winter, thanks for all the info guys.

[allonsye 85]

Why not just eliminate the elevator and trim tab altogether, and make a "Flying Tail" just using the stabilizer, with electric trim on it? This has been done before.

EDMO

Capitol idea. Wasn't this typical in the earlier Pipers?  The horiz stab was adjusted via a jackscrew.

 

I'm soon to fly my "C" for the first time. It does not have horiz trim tab. Presumably the previous owner/builder used the flaperons for trim. Is there anything wrong with this method?

[Luked 71]

A whole bunch of Kitfoxes use this method. You could  find one of them to look at. Your HS braces will need to change though to allow rotation of the HS.

[tcj 150]

Capitol idea. Wasn't this typical in the earlier Pipers?  The horiz stab was adjusted via a jackscrew.

 

I'm soon to fly my "C" for the first time. It does not have horiz trim tab. Presumably the previous owner/builder used the flaperons for trim. Is there anything wrong with this method?

 

I use flaperons for trim and it works beautifully.  Like I said in my post above, you need to rig the horizontal stabilizer so the plane flies hands off with just you and and a light fuel load on board.  This will move your CG to the most forward for any loading scenario.  This allows you to rig the horizontal stab so it flys hands off at this forward CG location.

 

You then do not ever need nose up trim because anything else loaded in the plane moves the CG back and pitches the nose up.  The nut on the flap handle needs to be tight enough that the flap handle stays where it is put and does not need a notch system installed to hold it in place.  You need just a little bit... I need to pull the flap handle up about 1/2 inch to trim the nose down when I have a heavier load on board.  I do not notice any decrease in airspeed.

 

The flaperons must be rigged correctly too.  When the flap handle is pulled up it causes the nose to pitch down.  If flaperons are rigged so the nose pitches up when the handle is full down they are not in the "Sweet spot" as some call it.

 

Mine is a kitfox model 4 and I think the first model to have 3 different holes for the bolt on the front mount of the horizontal stab.  Evidently an Avid doesn't have room to do that so you probably can't make it so.

 

There are all manner of trim systems to attach to the elevator.  I prefer my airplane to be basic and simple and would use the spring or bungee on the control system if I needed one.

 

This is not intended to disagree with any other good advice from other Avid/Foxers.  Good luck, hope you are flying soon.

[FoxDB 17]

Tjay,

I added an electric trim tab to my Tailwind for 1 reason. Jesus bolt if it fails with an electric trim tab you have a chance to survive. That said I have an aero trim system on my Kitfox 1. It uses springs and was easy to install and the only mod was a place to mount the control knob and a tab for the spring on the control.

Dave

[EDMO 1078]

Capitol idea. Wasn't this typical in the earlier Pipers?  The horiz stab was adjusted via a jackscrew.

 

I'm soon to fly my "C" for the first time. It does not have horiz trim tab. Presumably the previous owner/builder used the flaperons for trim. Is there anything wrong with this method?

Early Pipers used the Stabilizer Jackscrew in addition to using an elevator.

Piper Cherokee, Cessna Cardinal, and some others, Zenith, used the flying stabilizer too.

Flaperons will give you nose down - You have to supply nose up with stick pressure or trim tab.

When you lower the flaperons your up stick pressure will have to increase.

EDMO

Edited 23 Mar 2015 by Ed In Missouri

[akflyer 1427]

Early Pipers used the Stabilizer Jackscrew in addition to using an elevator.

Piper Cherokee, Cessna Cardinal, and some others, Zenith, used the flying stabilizer too.

Flaperons will give you nose down - You have to supply nose up with stick pressure or trim tab.

When you lower the flaperons your up stick pressure will have to increase.

EDMO

Not quite accurate.. its a long accepted practice to use flaperons for trimming (but I dont like it due to increased stick forces in the roll axis).  To get nose up trim, you set the flaperons so with the flap handle pushed fully forwards, the flaperons will "reflex" like maule flaps and the trailing edge of the flaperon will be higher then normal.  This will pitch the nose up.  I am pretty sure the bulletin on this says set them for max 5° up deflection.  I found that using the flaperons to trim the nose up not only gave me heavier stick forces (not much but enough that I didnt have the super light stick that I am used to in the Avids or KF) it also slowed me down a few MPH on bot the ASI and GPS speeds.  Having a way to trim the elevator be it the aero trim system that will just put some force on the push tube, the Ray allen electric trim tab, or a manual trim tab, is the best solution.

 

For me, electric versus manual comes down to personal preference.  Kind of like do I have to have an IFA prop to fly an Avid or KF.. The simple answer is no, of course not.  The long answer is, yes it will make your plane perform better, it will make your engine much happier and you will have another switch in the cockpit to play with   The down side is it will lighten you wallet as well.

 

[EDMO 1078]

Not quite accurate.. its a long accepted practice to use flaperons for trimming (but I dont like it due to increased stick forces in the roll axis).  To get nose up trim, you set the flaperons so with the flap handle pushed fully forwards, the flaperons will "reflex" like maule flaps and the trailing edge of the flaperon will be higher then normal.  This will pitch the nose up.  I am pretty sure the bulletin on this says set them for max 5° up deflection.  I found that using the flaperons to trim the nose up not only gave me heavier stick forces (not much but enough that I didnt have the super light stick that I am used to in the Avids or KF) it also slowed me down a few MPH on bot the ASI and GPS speeds.  Having a way to trim the elevator be it the aero trim system that will just put some force on the push tube, the Ray allen electric trim tab, or a manual trim tab, is the best solution.

 

For me, electric versus manual comes down to personal preference.  Kind of like do I have to have an IFA prop to fly an Avid or KF.. The simple answer is no, of course not.  The long answer is, yes it will make your plane perform better, it will make your engine much happier and you will have another switch in the cockpit to play with   The down side is it will lighten you wallet as well.

 

You are right Leni - I only flew the early Kitfox and they didn't do the "upwards" flaperon at that time - this came with the later instructions - mine only went down from neutral.

EDMO

Edited 24 Mar 2015 by Ed In Missouri

[KFfan 151]

'Simple' trim tab setup on a KF1

 

[EDMO 1078]

Kool idea - but they should cut that eye-poker wire in the rear, and bend the end of it.

EDMO

[Av8r3400 1178]

He did a very good job using the cable for pull only.  The spring counteracts the cable's pull.

 

Dave did a similar system on his Sputzee.  He used two cables pulling opposite one another.

[SuberAvid 617]

I love the minimalist aproach to outfitting these birds but I have to admit that having the electric trim and the ivo prop with the Ray Allen stick grip and all the switches on the grip is sure nice.  You get so you tweak the switches almost subconciously; just little bumps here and there to get it to hands off flight and rpm.  It is sort of like the difference in driving a 1970 all manual pickup vs a newer one with power everything.  Each one has its own charm.