Tailwheel castor angle

[Jbird 15]

Hi all I'm in the process of makeing a tailwheel spring for my mk4 . I have done some research and their seems to be some differing theory's .do I need positive or negative castor ? Does the axel lean forward or backwards ? Thanks

[Av8r3400 1179]

With the weight on it, the kingpin of the tailwheel should be perpendicular to the ground.

Leaning the kingpin forward will cause shimmy, leaning it back will cause it to be unstable making straight travel difficult.

[akflyer 1427]

Leaning it forward (the top of the king pin in relation to the bottom) will also cause it to steer straight on the ground as it will have to "lift" the tail to turn the wheel.  I always start the summer out with mine angles slightly back, then after a few gravel bar landings it seems to be angled forward.  It sucks, but I get tired of pulling the tail springs off to re-arch them.  Maybe next time I will have a spring shop do it and re-temper them so hopefully they will hold shape a bit longer.

 

[EDMO 1078]

My landing gear book says top of pivot about 5 degrees forward with a load on it - leaning backward is dynamically unstable, to use other words for what Leni said.   Tailwheels can be downright fussy, and sometimes more tweaking is needed to stop shimmy.
EdMO

Edited 14 Jan 2015 by Ed In Missouri

[Jbird 15]

Thanks this helps a lot Jbird

[EDMO 1078]

Tailwheels came along before concrete was invented for airstrips and cow pastures - They can be a PIA on pavement! The original Wright Flyer was a nose-dragger, well - a nose-skidder!

EDMO

Edited 14 Jan 2015 by Ed In Missouri

[Guest]

The larger tire you run the more tendency to shimmy. The only way to kill shimmy is with resistive damping. Changing castor angle will only move the shimmy around with respect to speed, surface, weight and tire pressure. May or may not be important in your case but I tried for a long time to eliminate shimmy with castor angle based upon what I read, and from actual experience, ONLY resistive damping will eliminate shimmy!

 

I know that does not answer the original question, but it turned out to be the biggest problem I faced with a large tire on the back!

[EDMO 1078]

Chris has the sure cure for tailwheel problems - Put the wheel on the FRONT!

That also lets you haul your boat under the bird!

EDMO

Edited 14 Jan 2015 by Ed In Missouri

[akflyer 1427]

Putting the little wheel in front does not cure the problem.. How damn many cessnas have you flown that you had to get the nose wheel off the pavement ASAP and hold it off as long as possible or it would shimmy on ya.  The little wheel in front is a cop out for my feet don't work very good

 

[EDMO 1078]

Putting the little wheel in front does not cure the problem.. How damn many cessnas have you flown that you had to get the nose wheel off the pavement ASAP and hold it off as long as possible or it would shimmy on ya.  The little wheel in front is a cop out for my feet don't work very good

 

You got to balance that nosewheel! That was probably a balance problem or a bad shimmy dampener. I try to have the nose off as soon as throttle is pushed....Just like getting the tail up asap.

EDMO

Edited 14 Jan 2015 by Ed In Missouri

[Guest]

Just to be clear...I love all airplanes whether the little wheel is in the back or front and I have both.....neither of which is flying right now, but I am working on that!

[EDMO 1078]

Just to be clear...I love all airplanes whether the little wheel is in the back or front and I have both.....neither of which is flying right now, but I am working on that!

Me too Chris - I have probably more time in the antique taildraggers, but prefer the nose gear - My Ercoupe could be flown without having usable legs, as a friend of mine used to do, but I prefer a plane with all the separate controls, like flaps and ailerons and rudders - Everything is a compromise, but if it gets off of the ground and lands safely, then it is good IMO.

  I just like to stir up some conversations  and comparisons when I can.

EDMO

Edited 15 Jan 2015 by Ed In Missouri

[akflyer 1427]

And for the record, I was just poking fun at Ed and his quest to turn all planes into mind numbing wheel barrows..

 

[EDMO 1078]

And for the record, I was just poking fun at Ed and his quest to turn all planes into mind numbing wheel barrows..

 

And, Leni has to put "Water Wings" on his bird because the tailwheel spring gets all bent! 

All in fun!

I wish I could fly from water, but I have a panic attack every time I have to fly across a river or lake - not because I drowned once trying to learn to swim, and never learned;  but the thought of being bitten by all the things hiding in the water terrifies me - like Big sharks, Big gators, Big snapping turtles and Big snakes - Leni don't have the last three in Alaska.

EDMO

Edited 15 Jan 2015 by Ed In Missouri

[saskavid 47]

i'll add these thoughts. for optimum steering ease and responseiveness the pivot bolt should in theory be at the same angle as the rudder hinges. Not always pracital and with a short coulped aircraft with tall legs the handleing can get a bit more than squirrley. I did fly my matco tw equipped avid like that for a period of time got along with it but always had to be very attentive of directional control tapping one brake or the other. Could spin it on a dime good brakes or pissy brakes didn't matter. Pivot bolt vertical to the ground and brakes up to snuff so u can unlock the tail wheel on demand is best option in my opinion.