Honest Fins

Over 25 years ago I built an Estes Maxi Honest John. High power was beginning to really "take off" (pun intended), so I used my 29mm motor mount from an NCR Phantom 2600 (that met a less than glorious end) and uprated my HoJo. Unfortunately, I didn't "uprate" the most fragile part of the model...the vacuformed fins! The results were fairly predictable.

Now, over the years I have pondered about how to rebuild my injured model so that it can actually fly as intended. I have thought about solid carved bass wood (I'm not that good), thicker plastic (I never found what I was looking for), or built up fins using ply (I couldn't decide what thickness). Finally, this summer, I decided to go ahead and tackle the project. "Built up ply" won because it seemed to be the least crazy option. So I headed off to Hobby Town and plunked down some cash on a sheet of 1/16 inch ply. It was on.

I will now share exactly how I worked out these fins (mainly as I went along). To help with the descriptions, I have pictures of every step of the process! So hang on...here we go!

Fortunately, I had bits of the old thin plastic fins. These served as a template for the new fins. I used some card stock for the guide...

The traced fin...before being cut out.

...and after! The two sections were needed due to the fin's destinctive cross section.

Remember the 1/16 inch ply I was talking about? Here it is with the fins laid out. I was able to butt them up against each other and still use my Dremel cutting tool to cut them out because they are slightly oversized due to tracing them from the original.

16 pieces all ready to go! At this point they were fairly rough. I actually numbered each section so that each fin was "married." This meant I knew which parts went with each other so that slight differences could be accounted for.

The epoxy begins to fly! I put a 1/8 inch ply stick in between the two halves to get the cross section right...

...because I had an interesting idea on how to do the through the wall construction. First, I cut out the sections marked with a rectangle...

...then I cut out these interesting looking internal spars from 1/8 inch ply...

...thusly...

...and then epoxied them in like this. The spars not only hold the fins steady, but give them structural strength. 

The 1/8 inch sticks used to form the fin cross section while gluing them were therefore removed before the fins were glued to the model.

A little F&F to make things neater. At this point I could no longer read my 1,2,3,4 markings on the fins, so I lined them up in order. Each fin was specific to a position on the model.

A little epoxy on the spars and the fins are in place!

Next came the epoxy fillets. These are structural as well as for looks. The whole assembly is pretty darn strong...

When the fillets dried, I test fitted the body tube and nose cone. Not too bad, if I say so myself!

So there you go! The Maxi Honest John now has sturdy fins!

Now I need to complete the rest of the build. Don't worry, I'll share it right here!

Until next time, fly 'em fast and high!