Replacing Tail Wheel

[skippydiesel]

I am contemplating changing my API 4" tail wheel, to an API 6".

 

The reason for the possible change, is that my bird lives on a grass airfield. The 4" tail wheel does not like ground ops after rain (diggs in). The 6" wheel will reduce the ground pressure/unit area (improve "flotation")  ie  be less likly to penetrate the surface & reduce rolling resistance, in all circumstances.

 

Depending on single fork or two fork configuration, the weight difference (from the 4") will be 0.06 kg & 0.15 kg .

 

My Sonex Legacy is a tad "nose heavy" in Cruise , some up up elevator trim /stick back is applied, when no weight in (rear) baggage area. I would expect that a slightly heavier tail wheel, may reduce the need (to some degree?  for aft trim.

 

I know I should do the proper W&B calculations but just wondering what you think (possibly from experience) what the subjective effect (if any) will be, with the 6 " tail wheel weight increases , so far back on the airframe & of course a smidgeon more drag? 

 

PS - I think it likly that I could replace the API solid tyre/wheel, with a Peter Anson pneumatic, for reduced weight & even better "flotation' which may negate the weight increase 😈

Edited 15 hours ago by skippydiesel

[facthunter]

You should be able to calculate the New C of G position and New AUW from the existing W& B docs. The Safest thing is to do a reweigh and Balance. AS troubling as it is. Tailwheels can easily develop "shimmy" If the castor angle or damping is wrong. That will rapidly Ruin the tyre on sealed runways, unless you taxi tail up, risking a ground loop. Nev

[Blueadventures]

I'd do a w&b, do the cofg calcs for loads and compare with its most recent and original weighing report, 5 kg / percentage max will determine next steps.

[rodgerc]

I replaced the Sonex wheel with the Vans RV (solid) wheel and a bracket that was supplied by Kip Laurie (see photo) at the time.
During building I had ditched the Sonex push-rod for an aluminium version with a couple of rod ends.

The wheel and bracket swap had  negligible impact on weight and moment. 
Peter Anson’s bracket has been subject to FEA and validated in application. 

[skippydiesel]

Thanks Rodgerc,

 

My Sonex has a custom tail wheel "head" ie the API  swiveling fork fits into it.

 

The head is delivering the correct caster angle.  This means that I am stuck with the API forks, the only alternative being replacing the whole" kit & caboodle" - expensive & unnecessary, as its only the tail wheel diameter that concerns me.

 

Just done a  rough estimate of 4'-6' weight - Seems likly that the an Anson wheel, mated to the API 6" fork, would  be lighter than the current 4" API solid wheel/fork assembly.

😈