Double tail spring

[Bandit 286]

Akflyer

Got my F7a's and the double tailspring yesterday. I see the new spring is a little thicker than my old one. Why couldn't I just use it as a single spring. If I use it as a double it adds more weight and seems like it would be to stiff for my Bandit. I am assuming after I drill the hole for the second bolt I need to grind the head of the bolt down to fit between the longerons. It looks like a real tight fit. I am hoping I can get the bolt in without cutting a hole in my fabric. I think I will cut the spring down some to shorten it up so I get a little more angle to my airplane on the ground.

Bandit

[akflyer 1427]

I am going to cut mine down, and I did have to grind the head of the bolt to get it to fit in between just like you are thinking.

What is your CG at?  I have 51# on my tail weight and I want to add some more to slide the CG back to at least 18"  I talked to dean and he said it will make a whole new bird out of it.

[Bandit 286]

So you have 51# extra weight in your tail, and you would like to add more? I think my CG is at around 15.45". Dean said it will make a new airplane out of it if you move your Cg back? What does it do. Maybe I should add both tail springs if that would help? How much tail spring are you going to cut off? Could you get the second bolt in without cutting the fabric? I think I can with a bit of swearing. I also have a dumb question.When I install my F7a's I need around -6, does that mean it is -6 with the leading edge of the flaperon up and trailing edge down?

[akflyer 1427]

NONONONONONONO on the weight and balance, the total weight on my tailwheel is 51#.  I want more.  by moving the CG back, you are spose to get better short field, better climb, lighter stick force, more elevator authority in the flare etc.  Dean said they tested it back to 21 or 22" but he advised not to stall it without flaps on if you go back that far.  He said that at 18 or 19 you wont have any issues other than better flight performance.

I installed the bolts and tac welded the heads in when I covered mine.  I can give them a good whack with a hammer and they will pop right out.  I also put an inspection plate back there in case I do need to get to them to remove the tail wheel for when I go on floats.  It would only take an hour or two to put inspections rings back there so you can cut the fabric out then you wont have to worry about it ever again.

I have not come up with a measurement yet, but an going to shorten it as much as I can, and still clear the rudder on a good bounce.  With both springs there is not much give in it so I dont think you need more than an inch of two of clearance.  I am willing to trade off clearance for as much AOA as I can get.  As it is now, the tail wheel always touches before the mains, and I should be able to drag it in at 35 instead of 40 if I can get the AOA.  Take off is the same.  I could get off WAY faster if I had more AOA on the wing.

For the flaperons. -6 is the leading edge of the flap DOWN and trailing edge UP.  I think you will find that you will end up with them about -2 or -3 if you trim it out for level flight, then land without touching the flap handle and measure it.  Atleast mine is at -2.5 for level flight.  By reflexing them the full -6, you will get alot more stick force on your roll inputs.

[Bandit 286]

Checked my weight and balance, I to am at 50# on the tail. With my cg at 15.45. I am going to cut my spring as short as I can to. Thanks for your help.

Some times I need a little direction. I did put a inspection hole by the front bolt. I think I can get two fingers behind that diagonal tube to get the back bolt in. Try to get everything done this week.

[Av8r3400 1179]

Feel free to smack me down if this is too outside the box, but:

Why is there so much trouble breaking these tailwheel springs??  Leni-- you admit to only 51# of dead weight, so maybe a max 250# of landing impact weight?

Sounds to me like this is an extremely poor engineered spring.  I would say replacing this with something a little better quality (like a POS, chinese trailer spring segment) would gain much more durability!  (These are experimental planes, right?)  Even if it is heavier, rear CG does not seem to be an issue!!

Sorry, I have to call  on this problem!

[84KF 4]

Ya'all talking tail weight when in a level attitude (as shown on the W&B form), or in a three-point attitude?

I don't have my W&B here, but I'll bet I'm somewhere near 45-50 when level but set it on the ground I get 100+ lbs on the scale.

I won't guess as to what the force will be when landing " forcibly".

Personally, I'd rather have a good strong multi-spring set (stiff) as compared to one that has to/will flex excessively.

[akflyer 1427]

Feel free to smack me down if this is too outside the box, but:

Why is there so much trouble breaking these tailwheel springs??  Leni-- you admit to only 51# of dead weight, so maybe a max 250# of landing impact weight?

Sounds to me like this is an extremely poor engineered spring.  I would say replacing this with something a little better quality (like a POS, chinese trailer spring segment) would gain much more durability!  (These are experimental planes, right?)  Even if it is heavier, rear CG does not seem to be an issue!!

Sorry, I have to call  on this problem!

The stock spring is a single leaf spring.. It was probably OK when the model A came out at 440#... now that the planes are 580#+  the spring WILL break.  Hell I was flying Gregs model A and it looks ;like it is gonna break just sitting on the trailer.  Most planes have multiple leaf springs so why would the Avid or kitfox be different?  You need weight in the tail, you know the single leaf is gonna break, it dont take a rocket scientist to figure out the easiest way to get weight as far back as possible and cure the breaking spring at the same time.

If on the remote chance you break the 2 leaf spring, you still have a tail skid that will keep the rudder from getting ground off..

[Bandit 286]

You have to also remember if you are folding the wings and transporting your plane, that will add a considerable amount of weight on to your tail. It puts

lots of stress on that single small spring. I cut 2" off of my tail wheel spring today and installed it. Thought I could get the back bolt on without cutting a hole in my fabric, after a 1/2 hr of swearing I had to get out the razor blade and go to work. With just a bit  more filing of the bolt head the bolt fell right in. So now I get to patch some fabric. I had my inspection cover placed so I could get at the front bolt. Not knowing they would come out with a double bolt spring. When I cut the short spring I cut it straight off. When I got it from Airdale it was rounded on the end. Would a straight cut put more stress on the main spring or wouldn't this matter. I see the Kitfox top spring is rounded also.

[akflyer 1427]

I would round it... a straight cut is just seting you up for a stress riser and a good place for it to break.  I will come in with mine on a 45 so it disrtibutes the load.  I also fly off big rocks and beat the shit out of the plane... If you are flying off grass or nice gravel it probably wont make that much difference.

[Av8r3400 1179]

[Engineer Hat = ON]

When ever you have a sharp edge or corner in a heat treated or hardened piece of material - like a spring leaf - it is very important to radius all edges to prevent stress risers from becoming cracks.  Filing a radius on the cut that you made on the spring is good, but then polishing that filed radius very smooth to the touch with emery cloth similar will be better still.  I've seen file marks cause cracks at times.

This is also important on any drilled (or punched) holes in these leaves (yes you can drill through a hardened spring leaf) are chamfered and polished, too.

A coat of paint to protect from corrosion is a good bet, too.

[Engineer Hat = OFF]