Manual Super Cub-Like Stab Trim?

[Spaghettiohead]

Heyy all,

I'm a big fan of manual trim, and decidedly not crazy about any of the electric trim options on LSA/Experimental aircraft out today. To keep the benefits of a trimmable stab, has anybody considered fitting a Super Cub system into a Kitfox? The jackscrew setup looks similar enough to the Model 7, just with a few cables and pulleys?

Andrew

[Av8r3400]

Weight and complexity are the enemies is LSA. The Piper pulley and crank jack screw system is much more complex and at least several pounds heavier than an electric jack screw or especially a servo driven tab.

[Dave S]

Andrew,

The early S-7s has a manual trimmable elevator. This system has the Horizontal Stabilizer held in a fixed position with a rod in place of the jackscrew; and, a trim tab on both sides of the elevator. The tabs are actuated with a push/pull cable connected to an adjustable friction lever on the console.

This system does not have the complexity and weight of the piper sysem; however, everything is a compromize; and, I believe Kitfox went back to the electrically operated jackscrew/trimmable stabilizer as the manual trim, since the manual tab system is a "servo tab" design (not to be confused with the antiservo design used on a stabilator such as the PA 28's) which blanks off a certain amount of elevator authority because as the elevator is raised to full up on landing, the trim tabs move the opposite direction due to the linkage.

Now, having said that, I do have an early S7 with the manual trim and configured as a trigear, not a tail wheel; and, the aircraft is just fine with the manual trim. I prefer manual to electrically operated trim & flaps as it reduces potential failure modes; and, I can go full up or down trim in a split second with the friction lever adjustment - (I never liked the endless cranking on the piper system) I suspect the same craft with a tailwheel (which most Kitfoxes are) benefit in landing performance from the electric jackscrew trim. The current electric trim also provides some in aerodynamic efficiency as it has no trim tab gaps.

Sincerely

[Spaghettiohead]

Thanks Dave and Av8r,

I certainly want the benefits of a trimmable stab as I plan to stay in a tailwheel, but I'm sure there is a happy way to marry that with a manual system...and it's important enough that I'd be willing to sacrifice a few pounds for the extra components. I still have plenty of time before I'd be ready to tackle a build though, so I'll do some more homework. Thanks!

[Esser]

In my opinion, I think you will just be adding more complexity and points of failure. No one here has had any problems with the electric trim. It doesn't get much simpler than an electric motor. I understand personal preference, I don't like electric flaps, but loads of planes have them with great success.

[jrevens]

... I suspect the same craft with a tailwheel (which most Kitfoxes are) benefit in landing performance from the electric jackscrew trim. The current electric trim also provides some in aerodynamic efficiency as it has no trim tab gaps.

I believe there is also definite increased aerodynamic efficiency potential in all flight conditions by having the ability to adjust the angle of incidence of the horizontal stabilizer, as opposed to an elevator with trim tabs, where you have surfaces angled in different, opposing directions, creating more parasitic drag.

[PapuaPilot]

Has anyone else had a problem with the electric trim?

A few weeks ago I had it stick in the nose up position while doing some maneuvers. It would only go nose up but not down. I flew it back and landed. Later that day I went to check it out and it worked normal. I checked the switch / wiring up front and couldn't find anything wrong.

I think it had one or tow more episodes since then where it didn't move nose down. Both of these times I blipped it the opposite direction and it worked fine.

I suspect the motor in the trim actuator, but haven't decided to pull it out yet. If I happens again I will need to address it, as it isn't very fun having lots of nose up trim and pushing on the stick till the landing.

[kitfox2009]

Hi Phil
About 5 years ago I had a similar problem. The builder installed a toggle switch as opposed to the rocker type and I believe (we had winter clothes on) one of us tripped the switch and the jackscrew went full stroke. Don`t remember if it was up or down. Anyway with slow flight and possibly some flap adjustment we got back to the airport.
The motor was toast so I replaced the assembly and installed the correct switch. Works great ever since, VERY sensitive though!
Cheers
Don

[kmach]

It sounds like the switch to me.
I have replaced and cleaned the switch internal contacts a time or two. Intermittent problems are followed eventually by one direction totally not working. If I recall correctly it was nose down that quit, flaps and speed to correct if required.

[DesertFox4]

Take a look at TCW's Safety-Trim offering. It will over ride a failed switching problem and allow you to recapture control of your trim system. Also run away trim problems are addressed. It can also allow you to slow down your trim motor speed above a user set airspeed for more precise trim adjustments at cruise speeds with the speed switch option. Pretty spiffy. I beleive John McBean said they offer a system specifically made up for our Kitfoxs available through Kitfox Aircraft.