ofergd,
Are you disregarding the relatively heavy ,unbalanced elevator, on the newer models especially, and the effect of gravity that pulls the elevator down, which must be overcome by aerodynamic forces, causing additional drag? Ideally, I would think that the spring could eliminate or diminish at least some of that additional drag. I think that the spring probably doesn't necessarily "pull the elevator up from it's trimmed position", but locates it in a more trimmed position to begin with. My understanding is that the spring should actually bring the elevator to the streamlined position on the ground, overcoming that "gravity droop", for lack of a better term. I'm certainly no aerodynamicist, and I'd welcome discussion of the "issue". Of course if you fly inverted it might not be so desirable.
The elevator is really quite "heavy" on the ground... it reminds me a little of a Skybolt I flew once. It took so much force to level the elevator when standing still without the engine running that I thought something was wrong. Of course I was used to flying many hours in my Thorp, which has a wonderfully light and balanced stabilator.
Last edited by jrevens; 11-12-2017 at 06:48 PM.
John Evens
Arvada, CO
Kitfox SS7 N27JE
EAA Lifetime
Chap. 43 honorary Lifetime
You are probably right. the weight of the elevator does increase drag.
But that is only the Shape Drag. For cruise speed you can win some speed with the spring system.
In slow flight, the main drag component is the induced drag. The induced drag does not change because it depends on the total drag that the horizontal stab and elevator create.
In my plane the problem is not having enough trim when the flaps are down. It's a short time in the overall flight so the effect will be minimal if not installing the kit.
I have a classic IV.
Thank you, John. BTW, installing the spring was no big deal... I made a hook out of a piece of piano wire and stretched it right on there. Don’t know why I thought it might be more difficult.
John Evens
Arvada, CO
Kitfox SS7 N27JE
EAA Lifetime
Chap. 43 honorary Lifetime
What model Kitfox were you flying when this happened?
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Help TKF. I had a little time today to take care of some odds and ends. I adjusted the trim actuator and followed the procedure for setting up the elevator push/pull tubes. Went ahead and bonded the trim position sensor bracket also. Hey so far so good.
I thought I would install the Trim Assist Kit but ran into a snag.
The bracket that was in the Trim Assist Kit looks nothing like what is pictured in the instructions. The half round part on the bracket that I have does not fit the curvature of the bellcrank and I see no way to attach the spring.
Did I get the wrong part in the kit? Am I missing something?
Wrong part. I had that one sent to me too
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Josh Esser
Flying SS7
Rotax 914iS
AirMaster Prop
Edmonton, AB, CWL3
Thank you Esser. That’s what I was thinking, glad someone could confirm. Looks like an email to KF is in order. Do you happen to know what that part is for?
I can't recall where you are at in your build but thought you could use the advice that John McBean gave me. Do all the flight control rigging without this connected. After rigging is complete throw the spring on. He says it just complicates the rigging process.
Eddie Forward
Flying
SS7, 912iS, Garmin G3X