Heavy Elevator, maybe install a spring ????

[rogerh12]

Yes, I owned the model 2 for a while, but don't remember an issue with it as far as the elevator pitch force being uneven or anything like that, mostly I remember the adverse yaw (how could I forget it !!!).

My Aerospace engineer neighbor brought up the point about uneven control forces in pitch (as undesirable), he thought it note worth and suggest a spring, and so I figured I would check with the group. Though I must say, now that I think about it, a balanced elevator seems as good an idea as a balanced Aileron, but I guess it’s not a must-have in slower aircraft (though some people believe balanced aileron are not a must-have either).

John,; the MD-80s, was that a joke, right? I thought some other older production planes could fly this way just fine, but am not much of an expert on the older plane designs and have only flown one tail dragger (my model 2). Also, I want to build my kitfox “21st century style” with all the best mods, as long as I am taking the time to build it myself, but if thousands of flying kitfox don’t have an issue with the elevator, why should I?

However, looking at the past post, so now I am confused more than before:

War-Eagle stated: “I use the elevator assist spring on my series 7 and it seems to work fine. I used the kit offered but the Kitfox factory” . Since kifox is offering this as an option, I guess I am not the only one that has been thinking about it….. Is this a model 7 option only, or a Every-Model type option?

Roger

[akarmy]

I don't know if it's made for every model or not. John could answer that. I do however know what it's like to fly a series 7 both with the spring and without. I would say that without the spring it's a bit more pitch sensitive in flight (but not by much) Also without the spring it requires more trim adjustments at different speeds and flap positions. The spring was originally intended to add up elevator when pulling flaps as I understand it. With the spring in place the elevator stays centered on the ground, without the spring the elevator drops down and the stick is pinned forward when on the ground.

Right now I'm flying without the spring, but with the series 7 trim tabs. My winter project is to fill those in, go to the movable stab design and reinstall the spring. That's the base design for the current Super Sports.

[kitfox2009]

I have a Model 5 Vixen with the controllable stabilizer and have no issues with elevator control in flight. Of course the control stick is "heavy" when on the ground either stopped or taxiing. The natural weight of the elevator pushes the stick ahead.
I have a short "bungey cord" that I clip on the passenger stick and attach to the seat back when the a/c is parked in the hanger. This prevents the stick and PTT switches from ever hitting the lower part of the panel.
I gap sealed the elevators by using 3/4" foam pipe insulation cut to fit on each side of the control surfaces. These are held in place with tape and the two surfaces just "roll" as the elevator moves. Makes a very nice fit.
There are no issues "trimming out" stick pressures with or without flaps!
Cheers
Don

[catz631]

Roger,
My model 4 is just like yours. The elevator will balance out in flight just fine. The only thing I would concider at this point in your build is to install an elevator trim tab. That,in my estimation,you will need. I got tired of holding all the back pressure on approach to landing so I sent my elevator to Highwing LLC. Lowell installed the electric trim tab system. Actuation is by a "hat" switch on the stick. This,in addition to the "bush gear" is one of the best mods I have done to my plane.
Sure you can monkey with the flaps during cruise to get control pressures off but it sure is nice to flick a switch !
Dick
Fox 4,912
Milton,Fl

[jtpitkin06]

Roger,


Including the MD-80 was not a joke. The MD-80 elevators align themselves with the slipstream just like a Kitfox.



Here's the part you may not know...


The MD-80 elevators do not have a direct connection of cables or hydraulics for primary control. You fly the airplane with trim tabs. When you pull or push on the yoke, the cables only move a small control tab on each elevator. The slipstream flowing over the control tab is what moves the elevator.


Next time you see a MD-80 taxi out, watch the elevators. Left and right elevators are independent. In a tail wind you will often have one up and one down at the same time. When the aircraft aims into the wind everything lines up and the tabs become effective.



The ailerons are controlled with tabs the same way.


When taxiing an MD-80 in strong quartering tailwind conditions, the control tabs flop up and down so one pilot must hang onto the yoke to prevent bruised knees. Taxiing an MD-80 in gusty winds is a lot like taxiing a tail-dragger... Hang onto the Yoke!!!





John Pitkin

[Dave S]

Roger,

John has the issue covered well on the issue of the slipstream taking the pressure off the stick. 100% spot on. Elevators work pretty much like a wind sock.....they droop unless they have wind....

I would like to add a bit about the Spring assist kit which John Mc Bean provides.

I also have a series 7 - same deal as War eagle - and I got the spring assist and installed it following phase 1 testing. Works well and is a good enhancement for the plane.

My theory was fly it as designed - then consider enhancements only after getting acquainted with the handling characteristics to see if it is really needed and if it is even appropriate - and maybe a little of - I want to know how this things works first.

Kitfox models, while they have a lot in common - do have their individual uniquenesses; however, heavy controls in flight is not one of them - I love the light touch on the controls and freedom from mechanical drag and freedom from control slop so you can feel the air load rather than drag from assorted cables and pulleys.

The elevator is going to feel heavy when the plane is sitting in the hangar - mostly all airplanes are like that. That is not what the spring assist is for. What the spring deal is all about is providing TRIM ASSIST, not lightening the elevator feel when the plane is in the hangar.

I wouldn't make any assumptions that if it's good for a series 7 it is good for other models.

The way my KF 7 flew with flaps out at approach speed and full nose up trim required some backpressure to hold the attitude - in otherwords you could not completely trim out all of the backpressure.

The Trim Assist that John M sells is specifically designed to help trim out the backpressure (which is not in any way very much pressure in the firstplace) so you can arrive at a neutral stick pressure on approach WITH THIS PARTICULAR MODEL of kitfox.

It is not for alleviating the static elevator weight - it is for assisting the nose up trim on approach.

If a person makes design changes in controls before testing - the alteration/modification can mask basic handling characteristics and you can end up with something akin to the goofy obsessions we have in this country with medications - take a pill to fix everything - take a second pill to fix the side effects of the first, then a third to fix the side effects of the second ...till a person has a home pharmacy of 37 pills to fix one basic issue and the constellation of pills are worse than the original problem.

I haven't flown every kitfox model out there - a IV, a couple 5s and & a couple 7s and they all handle well easily enough as designed. Wouldn't be too concerned about modifications till some flight testing is done. There will likely be some fine tuning of the rigging after the first flight or two anyway.

Sincerely,
Dave S
KF7 Trigear
912ULS - Warp drive
W/Trim assist

[SkyPirate]

well put Dave and I agree totally,.build it to spec then after acumilating time in it, do a mod if it needs it ,..or if you want to try one ,..unless there is time on the aircraft or the pilot in type prior to flying the build ,..there is no "zero" ground to start from,..if the pilot has time in type and says OK,.I want my build to fly just like so n so's,..providing everything in his build is the same as the one he flew prior,.( same numbers WB,..same engine,..prop..etc) then I would consider it during the build prior to flying it.
Even though there is another fox flying a VW conversion from prior posts, and probably more kitfox's flying with VW conversions ,..as noted in prior posts ,there isnt much info on it ,..so that alone is one mod that I would want to work out before I applied another mod to the same plane.
I think I know what your thinking though Roger ,..the VW being heavier your wanting to apply some back pressure mechanically instead of balancing the plane? I'd opt to balance the plane,..