Heavy Elevator, maybe install a spring ????

[rogerh12]

Howdy all;

With the controls in my Model 4, I noticed the elevator moves down when I let go of the stick from a neutral position. Also, it’s a lot easier to move the stick forward than back, so I am thinking this will make my controls kinda uneven in flight. Though I am still building, I don’t see elevator balancing in the plans (my zentih had a balanced elevator) and thought maybe I could install a spring to counter some of the elevator dipping force, or something like that (or maybe that's a bad idea).

Has anyone tried this, or have any other ideas?

Am I missing something in the plans?

Thanks

Roger

[War Eagle]

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.

I looked for pictures but couldn't find any at first look.

Contact the factory and they can help you out quickly.

[t j]

Roger, I wouldn't be adding stuff that is not in the plans or didn't come with the Kit. A model 4 built by the book does not need any springs on the elevator.

After it flys you will know more about if it needs some help on the elevator. If it does it is because of a foreward CG, not the weight of the elevator.

Each day you work on the plane try to save an ounce, not add ounces.;)

[jtpitkin06]

Roger,


The Kitfox elevator will align itself with the stab when the slipstream blows on it… just like it does for Citabrias, Super Cubs, and MD-80s.



Stick to the plans!



You’re not missing anything. Thousands of Kitfox IV’s fly very nicely without any modifications.




John Pitkin
Greenville, TX

[akflyer]

Have you ever flown a KF? I would look someone up and take a ride in a KF IV before you start modding it out and adding a pound here and there. Strip it down and keep it light. The controls are very light and well balanced in the air...

[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:eek: than the original problem.

I haven't flown every:o 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,..

[rogerh12]

Skypirate:
The plane is being built with serviceability in mind, after having issues with some older planes and finding out parts of the plane can’t be accessed for maintained or even inspections without cutting cloth or drilling out some rivets (my floor boards are now made of metal and segmented to be removable in the future, if needed). Adding a spring to the horizontal elevator later, if needed, should be no problem as I will have good access in the tail cone with extra inspection plates (or behind/ under the seat).

I also have removable counterweights mounted in the tail. I had special mountings welded in as far back as I could get it in the tail cone for the lead weights (also, if needed), so I should be able to compensate for the heavier VW engine, one way or another (horizontal stabilizer rigging, electric trim tab, counter weights or elevator spring,,, or maybe a little of all 4 !!!!! ). The custom VW engine mount should compensate for the heavier VW engine, however, I just don’t want to build myself into a corner, so to speak. Anyway, the extra time it takes to improve the plane is kinda fun, so why not do it.
Also, regarding a previous posting about reducing the risk of a stall & spin on my plane, I am installing mountings in the fuse tail cone for a lower shark fin that can be installed and removed as well (located on the far aft fuse) which should increase directional stability and also provide surface area below the horizontal stabilizer to help counter spin rotation. Being removable, I can make several sizes and try them out (start small, and work my way up I guess). This is not done on Kitfox's as they are tail draggers and would quicky bend anything hanging down in that area, but I can do this as my plane is already a nose gear model 4 and I don’t have to worry too much about bending the thing as my tail skid should not touch the ground anyway (I hope) and will help to protect the fin if it does.
Roger

[SkyPirate]

Roger,..dont "over" build it,
have you done any preliminary weight calculations to figure out how much your plane will weigh when it's done? all the little add ons add up.
I'll stick to you aught to do one Mod at a time,. starting with the motor,...if there is a problem ,..and you've done all of these mods ,..prior to it's first flight,..you wont know where to begin to correct any "bad habits" the plane might have.

[SkySteve]

Roger,
Here may be an option. I have been considering adding it to my plane for cruise trim.
http://www.aeroconversions.com/products/trim/

[Slyfox]

when I first bought my airplane it had the standard elevator. Yes more pressure needed for landing. When flaps were on it was harder to pull back for flair to land. I redid my rear elevator and put in the electric trim. Now me be spoiled:D absolutely love it, like power steering.

[Slyfox]

Now, also I want to point out that having the stick fall down when on the ground means nothing. once the air goes over the elevator it will come up on it's own. If this is what your concerned about, don't. It will act as normall as any other elevator in an airplane. Yup you have different airspeeds that will affect the stick pressure. best to put in electric trim and be happy afterward. I am. In fact if your kit is around mine, mid 90's than the best thing you can do is cut that stupid stop in the back of the tail and put a stop on the floor to copilot stick. What this does is allow the stick to flop full forward. Now you can get in and out with the greatest of ease. After I did this to mine it was like what stick when I got in and out. I'm a small guy and can't emagine a bigger guy trying to get in without this mod. I flown my fox over 1000hrs with it like this.

[Slyfox]

also want to point out that there is or was a kit to install the trim in the elevator, a little cutting and welding, an electric motor and all was done.

[dholly]

In fact if your kit is around mine, mid 90's than the best thing you can do is cut that stupid stop in the back of the tail and put a stop on the floor to copilot stick.
Ok I'll bite, got pics?

[szicree]

Skypirate:
Also, regarding a previous posting about reducing the risk of a stall & spin on my plane, I am installing mountings in the fuse tail cone for a lower shark fin that can be installed and removed as well (located on the far aft fuse) which should increase directional stability and also provide surface area below the horizontal stabilizer to help counter spin rotation. Being removable, I can make several sizes and try them out (start small, and work my way up I guess).

Have you thought about why no major manufacturer installs these fins? Are you assuming that with over a hundred years of development no aircraft designer has thought of it? I would suggest that there are compelling reasons why you don't see these on aircraft. You would do well to investigate this before spending the time, money, and perhaps exposing yourself to physical risk.

[rogerh12]

Steve;

Not sure of what you mean about nobody using it? It's on the new Cessna Skycatcher 162.


http://www.cessna.com/MungoBlobs/83/260/sin_catcher_ext23_view,0.jpg

[Slyfox]

Ok I'll bite, got pics?

I'll take some pics the next time I'm at the airport.

[szicree]

Steve;

Not sure of what you mean about nobody using it? It's on the new Cessna Skycatcher 162.

Fair enough, but do you know why they have that goofy looking fin on there? It's my understanding that they lost two different prototypes after they entered unrecoverable spins. It's important to remember that these accidents occurred during testing while the plane was being intentionally mishandled. My point was that any single change you make to the airframe is going to have effects beyond the desired one. When the plane is falling (in a spin) the vertical tail is partially blanked by the fuse and h-stab, thus reducing the effectiveness of the rudder. However, the Kitfox has huge flat fuselage sides. Adding a little ventral fin is going to add next to nothing and may produce unforeseen side effects. While I may have been a bit bold when I said nobody uses them, the fact remains that they are rare on small, slow, draggy aircraft like ours. If spins could be prevented by rivetting a little fin on the bottom of the tail, then we'd all have em by now.

[SkyPirate]

I have seen the ventral fin used on a champ that was on floats,..it was installed so the pilot did not have to continuously apply excessive rudder pressure even in cruise,..yes the plane flew straighter with less rudder pressure at cruise,..but it took more rudder at slower speeds to counter the ventral,..so ,..what happens in a cross wind landing where the plane is rated for lets say a 20 knot crosswind in stock configuration,..now add more vertical surface(ventral fin) with the same rudder area,..whats going to happen? I have a pretty good idea of what will happen even if it is a tricycle gear set up,
Roger ,..whats going to happen if you have to make a STOL take off with a ventral fin? and the fin pushed the lower longerons of the tail section up because it hit the ground? if it gets bent up..it could change the AOA of the leading edge of the horizontal stabilizer,.it doesnt take much of angle change in the horizontal stabilizer to get allot of change in flight.
Gonna stick to my guns with the "one mod at a time" until you know the characteristics of the plane in flight,..I'll add if it's a proven mod like a trim tab ,.go for it.

Chase

[rogerh12]

Steve & Chase
Yes, the little fins are small, but the key is they are in the right place, and that makes all the difference.
During a stall, for the plane to spin it has to also whip the tail around laterally. The small fin located below the horizontal tail helps to counter this initial lateral tail whip, at least that’s my understanding of it. Also, having the fin below the horizontal stabilizer allows it to avoid being blanketed by the main wing, which occurs with some high wing planes in a “deep stall”, that’s why trainers are usually built with rudders that extend below the horizontal stabilizer. Fin location in the far aft tail cone maximizes it’s effectiveness as well, from a “leverage” aspect.
Having said all that, a fin in this lower area can be damaged more easily than one above the fuse, that’s why it’s not too popular on aircraft, though on the kitfox in Tri-gear configuration, the tail skid would hit the ground first in a STOL takeoff, thus protecting it ( Please note: one can fly the kitfox in normal takeoff mode as well, STOL takeoffs are not required !!!!!!). Around here (Kansas), we have lots of ground, so I don’t’ do STOL, just regular performance take offs or short field landings at a mild angle of attack (my flight instructor would actually get mad at me if I did a STOL type landing, as he said it was hard on the plane !!!) . But in the Sky catchers case, the lower fin was a necessity as they could not sell the plane without one after the two crashes of the during testing ( though it’s primary purposed is not to get the plane out of a spin, but to keep it from entering one, even during crossed control stalls).
Roger

[SkyPirate]

I notice that in your photo Roger,..cessna also extented the rudder,.so is this your plan also?
As for STOL performance,..or wether not to do a STOL take off or landing,..sometimes it's unavoidable,..I've done a dead stick landing where the skid on the tail struck the ground,..I had no choice ,..landing in a grass patch in the woods less then 150 foot long, of course that is a worse case situation,.and protecting the plane is on the agenda but not the highest on that list ,..but I was lucky ,..didnt hurt the airframe but the piston that got burnt was a goner.

Sorry ,..but I'm still sticking to my guns about the mods

[jtpitkin06]

“Also, having the fin below the horizontal stabilizer allows it to avoid being blanketed by the main wing, which occurs with some high wing planes in a “deep stall…”,

Not true. Deep stall is an aerodynamic condition that applies to swept wing aircraft where the center of lift moves forward in the stall and the aircraft pitches up to a point where the elevator has insufficient force to lower the angle of attack.


“…that’s why trainers are usually built with rudders that extend below the horizontal stabilizer.”

Rudder location has nothing to do with “deep stall” or recovery.

[SkyPirate]

I've been trying to think of any plane that doesnt have the rudder extend below the horizontal stabilizer ,.and the only planes I can think of are the A-35's which actually dont have either a vertical or horizontal stab,..it's a "V" tail,..there might be a glider or another fixed wing plane where the rudder doesn't extend below the horizontal stab ,...but off the top of my head I cant think of one

( im thinking prop driven)

[jtpitkin06]

Well,... you can start with my Cessna Cardinal RG, then check out the Grumman American series (Tiger, Yankee). Look at the Beech Musketeer, and of course the Piper Cherokee series and the Comanche for starters.

JP

[szicree]

This is an issue on T-tail aircraft. On a kitfox there is no way that airflow across the horizontal tail would be obstructed by the main wing during a stall. In fact, the kitfox tail is lower than the wing in level flight and is more so in a stalled condition.

[SkyPirate]

OK you got me JP ,..although almost all of them have the flying tail or actually no elevator/ horizontal stab seperation the whole surface moves :)

i was thinking apples to apples

[jtpitkin06]

OK... How about a Mooney M20, Beech Debonaire, DHC-2 Beaver, Cessna 180, 185, 310R, or 208 Caravan? They all have stabs and elevators and the rudder does not extend below the stab.

Is them apples?

JP

[HighWing]

Interesting subject. Actually I think Roger has thought this through a bit more than we may think at first glance. Previous discussion groups have mentioned numerous times what some call the dumbell affect. This occures when weight is added to the tail to balance heavier than designed engines. Essentially, the weight at the end of a stick has much more angular momentum than the same stick without the weight. Start it swinging and it becomes more difficult to stop = uncontrolled spin. I just remembered - while sitting at a table at the facrory fly-in the topic of spins, spin training and Kitfox spins came up. Those who have done them in the Kitfox say it is relatively difficult to initiate a spin and easy to exit.

The point most detractors have been trying to make is that there are consequences to almost every addition we make to the original design. Granted some can be good - elevator trim, likely the Laker Leading edge, Fairings, these sorts of things. Others, not so good. The way I see it, heavy engine needs weight in the tail. Weight in the tail needs something additional to mitigate the undesirable spin characteristics. What we will most certainly get is a heavy airplane. In my opinion close to the empty weight of some of the lightest 7s or more. Is that good? In my opinion, for a Model IV - No!

Roger, for the sake of those who will most certainly come later, please post some actual performance figures. The ealrier thread titled something like VW power Performance Data Available !!!!!L Is a bit disappointing because it is a report of only one of many many VW powered airplanes - not very scientific. We need at least one more - For the next guy to evaluate engine options he will need things like things like Empty weight, Weight and ballance data, Fuel consumption, Stall speed, cruise at various power settings - both AIS and GPS (compensated). Take off distance, measured climb - saying it climbs better than my kid's Radio Flyer doesn't quite cut it.
Lowell
Model IV-1200 900 hrs.
Model IV-1200 Nearing Completion

[SkyPirate]

dems apples :) ..bows to the airplane god chanting I'm not worthy ,..I'm not worthy but they still aint LSA's lol

[SkyPirate]

JP ,..my problem was I wasnt thinking to clear ,.after being up for going on 24 hours when I posted that ,.I wasnt too clear in my presentation ,..thinking? ,..but not discribing to the letter what I was thinking ,.Vicodyn does that to you :) but I'll be off that crap soon I hope seems my "elevator" had too much weight in it and the doc's removed some of it between L2 thru L5,..I had the same problem though ,..I'd go into a spin and the ground would fall up and hit me ,..luckily it was only 6 foot away lol

[SkyPirate]

OK as for all the mods,..I'l be one of the first in the "guilty " line for trying new concepts,.. I have a yard full of evidence to prove that,..from motors that dont use any source of burnable fuel ,. to boats with built in trailers.
But in each step of any "improvement" I brought what ever it was I was working on to a "Known" stage first ,..then went from there in little steps , that is my main concern,..especially in an aircraft, add a life into the picture ,..relying on those "new concepts" ,..as someone had put it in an earlier post ,..your now a "test pilot" I can relate to that as well,..building my own design aircraft,..but I'm still bringing that plane to a known standard first ,..as I mentioned in a earlier post ,..you need a ground "Zero" which equals to a "known" status in the concept.
When I built my race car ,..even though I scratch built,I didnt buy a chassis to start with..I knew that my end result in the build had to be as close to 51% front weight to 49% rear weight and 51% left weight to 49% right weight ,..that was my starting ground before tweaking(circle track car) sure ,.if I didnt stick to the formula ,..it would still go around the track,..but chances of me hitting the wall at 150 mph greatly increased if I didnt start at that ground "Zero"
I'm not dissin you Roger for thinking,..I'm just saying slow down the process,..I do the same thing all the time ,.I'll have 100 plus avenues to take on paper concerning a a hundred mods,..but I stick to one mod at a time when it comes to applying them.

Chase

I'll add this too Roger from experience ,.if your plan( or even if it's not and you have to anyways) in the future is to sell your plane,..or anything that was a proven design that has been modified ,..it greatly narrows the list of people that would buy it,..

[rogerh12]

This is an issue on T-tail aircraft. On a kitfox there is no way that airflow across the horizontal tail would be obstructed by the main wing during a stall. In fact, the kitfox tail is lower than the wing in level flight and is more so in a stalled condition.

Sorry guys, quite right, I got it bass-acward. Low wings can block the tail in a deep stall, not high wings.

[rogerh12]

I'm just saying slow down the process,..I do the same thing all the time ,.I'll have 100 plus avenues to take on paper concerning a a hundred mods,..but I stick to one mod at a time when it comes to applying them.

Hey chase, when it comes to working on planes, I really only work one of three ways:

Slow
Slower
Even Slower !!!!!

I never seem to get any work done fast, I just make sure it's done right (until I discover I did it wrong). I think all my mods are reversible to one extent or another, but things have to be modified when you stray from the Rotax/Taildragger mold and incorporating design features from other successful planes is one way to do it (both kitfox and others).

I know there are a lot of other guys out there wanting to build a kitfox with a low cost VW, or some other engine, I know because they keep emailing me or call me to learn more about and I am doing and how. I am trying to find other flying Kitfox –VW combo for raw data, but don’t have a lot of time to do it outside of this limited forum, but I will keep looking. I do know, the kitfox-4-1200 with it’s generous wing area is a better platform for a VW engine, better than my zenith 601 with it’s short wings (but even so, it still had acceptable climb performance on all but the hotest Kansas days).

Roger

[SkyPirate]

Roger,..we are building a 601 at TBN ,we got the parts for the AD on the carry thru last fall..although we haven't worked on it in quite some time ,.we are considering the 0-200,..but ,.if I get my plane I'm building here at home done first ,.we might use that same power plant on it ,..a 2008 Ford Focus motor 2.0 rated 140 hp,.. so I understand your quest .

I'm just saying one mod at a time ,..get it flying first with the
VW ,.. rack up some time on it,..then do a mod,..fly it some more ,.I'm sure you'll know right off if the mod was for the good or bad,..but you will know it was the last mod applied ,..there wont be any guessing ,..was it the added vertical surface or ?? or changing the CG? or ??
if i am repeating myself,..sorry ..just cant stress it enough

Chase