Curtiss Jenny Restoration

Welcome! We hope you enjoy following the restoration process of a 1918 Curtiss JN4D Jenny. Once completed, the aeroplane will be flown and displayed at the Candler Field Museum in Williamson GA (30 miles south of Atlanta). You can contact me below by clicking on "VIEW MY PROFILE"

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Location: Peachtree City, Georgia, United States

Monday, May 06, 2013

Prop Hub saga

OK...I was waiting to post this information until we figured out a solution. Here goes:

It all started when we decided to install the propeller.  Hey, we had a really nice hub and a really nice prop so everything should have fit just right.  Right?  Not really.

We noticed that the propeller was too thin!  The front of the propeller should have been resting on the thick boss on the front of the hub, but it didn't. 

That meant that the front plate would only contact the boss with less than a sixteenth of an inch!  All the stress of the spinning propeller would be transferred to the bolts rather than this plate. 

Something was terribly wrong. Was the prop made wrong?  Did we have the wrong hub?

We measured the hub...

And measured the prop noting a half inch discrepancy. 

The wrong prop?....Chad Willie had built the prop a few years ago.  He had made a Hisso prop for Denny Trone and I wanted the same one.  So I was confidant he knew what he was doing.

The wrong hub?...  Throughout this restoration, our E-2 version of the Hisso has been much different from the more common A, E and I Hissos.  This hub came with the engine, so it must have been the right one. Our only option was to add a half inch wooden spacer behind the propeller.  I didn't want to do that.

Sometimes you have to walk away from a project and think about it.  I went to work for a few days and had time to digest the problem.  I remembered seeing a Hisso prop hub drawing that John Gaertner had sent me.  It was for a Hisso Model E. I dug it up and took a look.  The hub was different!

I came to the conclusion that the higher horsepower E-2 must have used a thicker propeller and needed a bigger hub.  Rats! The thought of buying another prop didn't thrill me.

So, I wondered if the E hub would fit the E-2 engine?

I had bought a spare Hisso hub a few months ago, but I never had a chance to pick it up.  Now I needed it!  If it was one of those more common Hisso E hubs, I'd be in business.

When I got there, the owner said "You are in luck. This is one of those rare big Hisso hubs."
Oh, no!  I already had a big Hisso hub.

When I got it home, we decided to take it apart.  The first hub went together like this.

I figured the second one would come apart the same.  No...the threads were the opposite direction. And they took some steel rod and made a spacer.  Interesting...

But we still had a problem.  Luckily, fellow Jenny restorer Kevin Connor heard about it and sent me his Hisso E hub to try.

It fit perfectly!  Great! 

Here you can see the hub differences. Hisso E above.  Hisso E-2 below.

 The prop fit the hub exactly.

So did the front plate.

The "small" hub actually moves the propeller forward. 

Now we know the "small hub" fits our engine.  I must give this hub back to Kevin so now I'm looking for one of our own.  At least the problem is solved!  The big hubs are fine as long as you order the big prop.  Anyone need a big hub?

Thanks, Kevin.

We are on track for having the Jenny on display at the museum next month.  Here is a poster for the event.

More soon.  Enjoy



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