skydeuce

My Feedback: (30)

I have a fiberglass fuselage for a P-51B and foam core wings that I got at a swap meet. I also have acquired the plans for the aircraft as it was designed to be a scratch-built job. What is the best technique for installing a wooden support structure inside the fuselage to add flying strength and rigidity. I want to keep it light, but I need provisions to mount a firewall fairly securely, and I'm assuming I will need a way to transfer the stresses from the engine and wing saddle throughout the aircraft. Has anyone done this before? Here is what I was thinking:

Using the plans, cut formers for various necessary fuselage stations, ie firewall, wing saddle, radio gear mounts, and tailwheel mounts and epoxy them in, then join them all with either a plywood or spruce longeron.

MarkNovack

My Feedback: (3)

Greetings from SHAPE Belgium.

In regards to the fuselage, you should not have to lay any longerons down the sides. When the firewall, gear plates, and wing mounting blocks are installed your fuselage will have the required stiffness. A little carbon fiber matt applied to wiggly spots will stiffen any areas up nicely if necessary. On airplanes with cavernous wing saddle areas, a former in front of and just the the rear of the saddle can be installed. The fiberglass "skin" is what ties in the formers giving stiffness to the entire assembly. You want to fit your formers loosely as to not give any bulges to the fuselage. Let the epoxy and microballoon create the final clearencing between formers and fuselage. I recommend using R&G 24 hour resin and hardner ("L" is the reference for this) with thixoptropic addative and microballoon mixed to a mayonnaise consistency. It is the best epoxy I know of for this application and made in Germany so it should be easy to get for you.

Mark

skydeuce

My Feedback: (30)

Thanks Mark,

I think we're both on the same track. Having never doe this before, I was leaning toward over-engineering this project. The fuse is pretty flimsy right now, but it doesn't have anything inside of it and should stiffen up once I start adding structure.

Now if I could just stop procrastinating and start building....

slipkid

My Feedback: (4)

Hi,
I would suggest that instead of expoy, you use an adhesive called PFM. If you have any pattern guys in your club, they can tell you all about it. THe best thing about this adhesive is that it is extremely strong but remains slightly pliable. Expoy dries rock hard and does not give on things like "firm" landings. I use PFM on my fiberglass fuse and especially on firewall and gear mounts, even on an all wood frame. There is a downside of using this adhesive - It does not have long shelf life - you need to buy a tube and use it, it is also a bit pricy, but nomore so than CA. It also has an interesting characteristic I have never really sen in other adhesives in that it skins very quickly, then cures overnight. THe outer most layer will appear to cure quickly ( 20-40 seconds). I find this quite useful as it acts as a good tack. ALso, PFM also has a distinct odor that the better half may complain about. The good points of this stuff far outweigh the bad points though. Regardsless of how much lumber you decide to put in your fiberglass fuse, use PFM to glue it in