Stiffening the Imitation

[Kevin Wright]

Hi,
I'm building my first Fancher Imitation and have read that it's important to stiffen the rear
of the profile fuse with glass or carbon fibre veil.

I'm planning to use carbon fibre tube layed in two half-round channels routed into the balsa
halves - see attached photo.

Before I epoxy the two halves together, I'd be interested in hearing from modellers who have built
an Imitation  - what they think of my solution and how they solved the stiffening problem.
Regards,
Kevin

[john e. holliday]

Not having the kit, I have a question.  Is the fuselage sides 1/4 or 1/2 sheet?   If laminating 1/4 sheets use the original Gorilla Glue.   Some say it is messy, but I used it on the Primary Force fuselage which was two 1/4 inch sheets.   Made for a very stiff fuselage.   

[Allan Perret]

You dont get the biggest bang for your buck (weight of added material) if you add stiffing elements inside (middle) of a structure. 
You would do better to add carbon tow to the outside surface of the fuse in a long X pattern (from above wing TE to below stab and vice versa, on both sides.

[Randy Powell]

When I  built my Ringmaster Deluxe, I used an interior frame in a geodetic pattern and ran tow along the supports then sheeted it with balsa. Very stiff indeed.

[Derek Barry]

Not having the kit, I have a question.  Is the fuselage sides 1/4 or 1/2 sheet?   If laminating 1/4 sheets use the original Gorilla Glue.   Some say it is messy, but I used it on the Primary Force fuselage which was two 1/4 inch sheets.   Made for a very stiff fuselage.   

Doc is correct. Two pieces of 1/4 inch glued together is very strong especially if you put carbon fiber or glass cloth between them.

Derek

[Dick Pacini]

Kevin, is your Imitation a kit from Ultra Hobby Products?  They haven't been made for a few years, but I was fortunate enough to buy the last one they had in stock.  I haven't built it yet.

[Kevin Wright]

Dick,
Kit? People build from kits?

No, This is a scratch build from the plans. The fuse is two 6.5 mm (1/4 inch) sheets.

Regards,
Kevin

[Kim Mortimore]

Kevin,
My Imitation has a very floppy tail due to fuselage flexibility.  Your idea is brilliant.  It looks like you haven't made the wing cutout yet, and the forward tube will extend forward past the trailing edge of the wing?--where profiles are also weak and tend to break.  CF tubes give tremendous bang for the buck in terms of weight/stiffness.

Another help with profiles (which also improves appearance and reduces weight a little), is rather than just rounding the edges and leaving flat fuselage sides, if you sand even a relatively small amount of curvature from top to bottom on both sides, the stiffness provided by your covering material and paint (assuming it's not an iron-on film) is enhanced by "eggshell" or monocoque effect, just as a flat piece of cardboard is easier to twist than one which has a slight bow in it.

My Imitation is the best plane I've flown (LA46 with 12.25 x 3.75" APC prop).  What engine are you planning on using?  Keep us posted on your progress.  Best of luck.

[Kevin Wright]

Kim,
Thanks for your input - very useful suggestion regarding the slight curvature. I'll use your idea along with carbon fibre tape
as suggested previously - running from above the wing cutout to below the stab and from below the wing cutout
to above the stab.

I have three engines I can use in the Excitation;

OS 46LA (like yours)
Enya 45 CX
Merco 49 Series 1

The beauty of the Excitation of course is that with it's interchangeable front end I could fly with all three in one day!

I'll keep folks posted as I progress.
Regards,
Kevin

[Lauri Malila]

 Hi.

 As Allan said earlier, it would be much more efficient to have the carbon reinforcements near the surface of fuselage, not in the centerline. That way you'd be fine with about 1/4 of carbon you´re using now (and less glue). My choice would be about 1/64x1/4" flat carbon strips, thinned down towards the tail. It would also be easier to make.
 Ideally, the best thing would be to have vertical grain balsa between the carbon strips but I wouldn't do such an overkill, it's still just a profile model.

 Lauri

[Walter Hicks]

This is a actually an Imitation. I used .02 Carbon fiber tissue on the fuse and covered that with silkspan as a filler.

It did help a lot. Imitations have been flying for years with the twisting fuse. There are at least 5 flying in the group I

fly with. It is obviously better to stiffen the fuse. The originals were powered by St .46. Most now are using PA

65 one has PA 61. Mine has a Double Star .54.( the plane pictured above.) These are excellent flying airplanes.

The front end is bulletproof, and with the Carbon fiber covering the fuse it really stiffens it up. Most weigh in between

55-65 oz depending on the power plant. The plane pictured has a foam wing and is scratch built with stab/elevator, rudder flap modifications to make it look like a Chipmunk. The plane is 10 years old and still flies very well.

[Steve Helmick]

Carbon mat actually comes in .2 oz/sq. yard, .3 oz/sq. yard, and .5 oz/sq. yard. Walter slipped a decimal there, FYI. Don't go crazy looking for .02 oz/sq. yard (or sq. meter) stuff!  Steve