Shaft Extensions

[Zuriel Armstrong]

For those of you that build some of the classic airplanes, many of them show the use of a shaft extension.  Are these necessary for the particular design or not.  I have some of the Fox extensions but have never used them.  It appears the spinners will need different hardware to make everything work.

Any help or advise appreciated.  I plan to build a Neptune and am trying to get my "Ducks" in a row.

Thanks,
Zuriel

[Randy Powell]

Shaft extensions are a pain because you have to drill out the prop to accommodate the screw. The reason for using them has been that it pushes the engine back and you can have a cooler looking cowl. Arguments that it pushes the engine back and so, reduces nose weight are bogus. The additional weight of the shaft extension overcomes any benefit for the engine being mounted closer to the CG. Also, remember that this in effect makes the crankshaft quit a bit longer, pushing the prop farther from the crank counter weight and piston. Balance problems are magnified.

I've used the periodically, but for the obvious reason. Makes for a cool looking cowl.

One note: Richard Oliver came up with a slick solution that actually serves the purpose of pushing the engine back and so offsetting some of the engine weight with a further aft CG. RO-Jet engines have and screw in prop shaft separate from the crank. He offers and longer screw and and sort of thrust washer that is about 3/4" long and serves as a shaft extension. And it doesn't weigh much more than the original thrust washer. So you get the benefits of a shaft extension without the draw backs.

[Bill Little]

For those of you that build some of the classic airplanes, many of them show the use of a shaft extension.  Are these necessary for the particular design or not.  I have some of the Fox extensions but have never used them.  It appears the spinners will need different hardware to make everything work.

Any help or advise appreciated.  I plan to build a Neptune and am trying to get my "Ducks" in a row.

Thanks,
Zuriel

Hi Z-Man,

Randy has a lot of good points, so i am going with a different course!

The Neptune, Atom, Argus, Ares, etc., etc., used the Fox 35 which is notoriously "short" in the frint end.  If you plan on using a Fox on your Neptune, you will need an extension to make it look anything close to the original.

If, however you use an engine like the Aero Tiger 36 or similar, you will not need an extension!  The distance to the drive washer from the C/L of the cylinder is about the same length as a Fox w/extension.

If you use the Fox extension, you need a Fox spinner or Tru Turn with the screw in the cone tip.  If you want to use an Aero or Froom/Veco spinner, you need a Veco extension.

[Randy Powell]

Bill,

I've used Fox extensions with a Veco/Randy Smith type spinner. But you do need to drill out the end of the of the bolt and tap it for a 1/4, what is it, 28? Can't remember. But not a big deal. On the other hand, if you have a veco extension handy...

I made an extension for the Saito 56. It's a lot more complicated than it looks. The bolt I spun up had to tapped 7mm with the front section 1/4-28 for the spinner. Fun stuff and hard to get balanced so the engine did'nt go wack in.

[Bill Little]

Bill,

I've used Fox extensions with a Veco/Randy Smith type spinner. But you do need to drill out the end of the of the bolt and tap it for a 1/4, what is it, 28? Can't remember. But not a big deal. On the other hand, if you have a veco extension handy...

I made an extension for the Saito 56. It's a lot more complicated than it looks. The bolt I spun up had to tapped 7mm with the front section 1/4-28 for the spinner. Fun stuff and hard to get balanced so the engine did'nt go wack in.

Hi Randy,

I don't have a lathe, but I got a bunch of new Veco extensions. 

All are planned for. 

It wouldn't be too bad to drill and tap the Fox for 1/4-28.  But I'm lazy!

[Chris McMillin]

Zuriel,
I have a Veco extension and union nut I can spare. Send me a note.
Chris...